2010 - ATF Evaluation Study Final Report - LA Sewers
2010 - ATF Evaluation Study Final Report - LA Sewers
2010 - ATF Evaluation Study Final Report - LA Sewers
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Technical Memorandum - FINAL<br />
Team<br />
City of Los Angeles<br />
Department of Public Works<br />
Bureau of Sanitation<br />
Air Treatment Facility (<strong>ATF</strong>) Review <strong>Study</strong><br />
FINAL REPORT<br />
December <strong>2010</strong>
Technical Memorandum - FINAL<br />
Team<br />
City of Los Angeles<br />
Department of Public Works<br />
Bureau of Sanitation<br />
Air Treatment Facility (<strong>ATF</strong>) Review <strong>Study</strong><br />
FINAL REPORT<br />
EXECUTIVE SUMMARY<br />
November <strong>2010</strong>
Table of Contents<br />
Executive Summary ...................................................................................................................... 3<br />
1.0 Introduction ........................................................................................................................ 3<br />
2.0 Airflow Modeling <strong>Study</strong> ....................................................................................................... 5<br />
3.0 Sewer Siphon <strong>Study</strong> ........................................................................................................... 7<br />
4.0 Drop Structures <strong>Study</strong> ...................................................................................................... 12<br />
5.0 Total Non-Methane Hydrocarbon <strong>Study</strong> ........................................................................... 17<br />
6.0 <strong>ATF</strong> <strong>Study</strong> ........................................................................................................................ 22<br />
6.1 <strong>ATF</strong> Locations .............................................................................................................. 22<br />
6.2 Air Emissions Characteristics ....................................................................................... 22<br />
6.3 Air Emissions Control Technologies ............................................................................. 24<br />
7.0 Recommendations ........................................................................................................... 25<br />
7.1 <strong>ATF</strong> ............................................................................................................................... 25<br />
7.2 Drop Structure Modifications ........................................................................................ 25<br />
7.3 Flow Diversion .............................................................................................................. 26<br />
7.4 Technology ................................................................................................................... 26<br />
List of Figures<br />
Figure 1 - Base Map of <strong>LA</strong>BOS Collection System under <strong>Study</strong> .................................................. 4<br />
Figure 2 - Odor Areas of concern Location Map ........................................................................... 6<br />
Figure 3 - Detailed Sampling Location Map .................................................................................. 8<br />
Figure 4 - Baseline Air Pressure ................................................................................................... 9<br />
Figure 5 - Passive Air Duct Connection Data ............................................................................. 10<br />
Figure 6 - Combined NORS-NCOS Air Pressure with Fan Active .............................................. 11<br />
Figure 7 - Drop Structure Baseline Pressure .............................................................................. 13<br />
Figure 8 - Drop Structure Air Return Line Plugged Pressure ...................................................... 14<br />
Figure 9 - Drop Structure Pressure with Flow Management ....................................................... 15<br />
Figure 10 - Total NMHC VOC Sampling Result Summary.......................................................... 19<br />
Figure 11 – Hydrogen Sulfide Sampling Results Summary ........................................................ 20<br />
Figure 12 - Hydrogen Sulfide Emission Control Overview .......................................................... 21<br />
Figure 13 - Mission & Jesse Additional Air Pickup ...................................................................... 25<br />
Figure 14 - NEIS/ECIS Recommendation Summary .................................................................. 26<br />
List of Tables<br />
Table 1 - Mission & Jesse Interceptor Raw Emissions Characterization Results ....................... 23<br />
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EXECUTIVE SUMMARY<br />
The City of Los Angeles has a long history of implementing proactive and innovative steps to<br />
control odors from its interceptor collection system including using chemical addition to control<br />
odors with an extensive use of magnesium hydroxide and sodium hydroxide. Recently, the City<br />
has been working to improve odor control in several areas identified by local community groups.<br />
Air treatment facilities (<strong>ATF</strong>s) with known or predicted odor “areas of concern” were included in<br />
the 2004 Collection System Settlement Agreement (CSSA).<br />
Each technical memorandum and the Draft <strong>Final</strong> <strong>Report</strong> submitted during the course of this study<br />
were reviewed by the Independent Odor Expert. Comments generated by the Independent Odor<br />
Expert were incorporated into the <strong>Final</strong> <strong>Report</strong> and the technical memoranda it includes. The<br />
<strong>Final</strong> <strong>Report</strong> and its recommendations are consistent with the opinion of the Independent Odor<br />
Expert.<br />
The comments of the Independent Odor Expert are presented in Appendix A.<br />
1.0 INTRODUCTION<br />
The HDR Team conducted a study of the City’s wastewater collection system in order to evaluate<br />
the ability of proposed <strong>ATF</strong>s to provide satisfactory odor relief to the collection system.<br />
The study was performed between January 2008 and August <strong>2010</strong>. It included an analysis of the<br />
sewer system as a whole including both current conditions and planned modifications to the<br />
sewer system. It evaluated the effects that collection system structures such as drop structures and<br />
siphons have on the ventilation of sewer odors. Taking into account the pattern of sewer odor<br />
complaints and results of the drop structures and siphons field data collection, it assessed<br />
proposed facilities intended to mitigate sewer odor complaints. The study also analyzed total<br />
non-methane hydrocarbons associated with sewage and determined how to effectively remove<br />
them from the sewer system.<br />
The present document incorporates the results of the study and includes the five technical<br />
memoranda developed for the study:<br />
<br />
<br />
<br />
<br />
<br />
Airflow Modeling <strong>Study</strong><br />
Sewer Siphons <strong>Study</strong><br />
Drop Structures <strong>Study</strong><br />
Total NMHC <strong>Study</strong><br />
<strong>ATF</strong> <strong>Study</strong><br />
Figure 1 depicts the system under study.<br />
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Figure 1 - Base Map of <strong>LA</strong>BOS Collection System under <strong>Study</strong><br />
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2.0 AIRFLOW MODELING STUDY<br />
The Airflow Modeling Technical Memorandum provides documentation of the developed airflow<br />
model and presents the modeling results for the City’s current interceptor system configurations<br />
and the two planned wastewater flow diversion scenarios.<br />
The benefits of the airflow modeling study include supporting the findings in other studies and<br />
evaluating the impact of the identified future operational changes in terms of odor areas of<br />
concern. However, the airflow modeling results are not intended to be the sole material for the<br />
evaluations of the proposed <strong>ATF</strong>s and any recommendations for <strong>ATF</strong> installation.<br />
For the purposes of this study, an odor “area of concern” is defined as a location in the<br />
wastewater collection systems where airflow bottleneck occurs in the sewer pipe headspace. Past<br />
experience has shown that these locations are typically the primary cause of positive differential<br />
air pressure buildup in large diameter gravity pipe sewer systems. Positive differential air<br />
pressure buildup (difference in air pressure between inside and outside the sewer) can result in the<br />
release of odorous air to atmosphere, thereby resulting in odor complaints.<br />
The scope of the airflow modeling study is to identify locations with potential for odor emissions,<br />
referred to as “the odor areas of concern” under current conditions and examine the impact of the<br />
two planned wastewater flow diversion scenarios as follows:<br />
1. Flow diversion from NORS back to NOS<br />
2. Flow diversion of 30 cubic feet per second (cfs) from NOS to COS.<br />
In order to identify the odor “areas of concern”, a customized computer program called OPTools<br />
(Odor Predictive Tools) was developed as a part of this study. The program uses empirical<br />
surface drag equations to estimate air flow capacities in the sewer headspace, and calculates the<br />
difference in airflow capacities for consecutive sewer segments to identify locations with<br />
potential for positive air pressure buildup.<br />
The results of the airflow modeling are graphically represented in Figure 2 below.<br />
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Figure 2 - Odor Areas of Concern Location Map<br />
Based on the airflow modeling results, it was determined that:<br />
<br />
<br />
<br />
Under the current system configurations, nine areas of concern are predicted. These<br />
include five locations along the ECIS from downstream of the Mission and Jesse drop<br />
structure to upstream of the USC drop structure; the ECIS siphon at Jefferson Boulevard<br />
and La Cienega Boulevard; the NORS/ECIS Junction; the NCOS Siphon at I-405 and the<br />
NORS Siphon at I-405.<br />
With the additional flow diverted into the NOS from the NORS, the upstream end of the<br />
NOS siphon and the NOTF location are predicted to experience positive pressure buildup<br />
under the assumption that the NOTF <strong>ATF</strong> is currently not being run pending ongoing<br />
public involvement efforts;<br />
The diversion of 30 cfs from NOS to COS will not cause additional areas of concern in<br />
the study sewers. However, the addition of the wastewater flow in the COS may cause<br />
positive pressure buildup along the COS.<br />
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3.0 SEWER SIPHON STUDY<br />
Previous City sampling efforts have shown that headspace air pressures in the NCOS are typically<br />
at or below atmospheric levels, whereas in the NORS they are highly positive. Other samplings<br />
conducted by the City have also resulted in the conclusion that the source of this positive air<br />
pressure is the air dragged in the headspace of the NORS to the siphon located under the I-405.<br />
Field samplings from a total of twelve maintenance holes (see Figure 3 below) were collected<br />
over a period of time in the summer of 2009 followed by physically connecting the NORS and<br />
NCOS interceptors with a 200-foot, 36-inch diameter, and corrugated HDPE duct laid aboveground<br />
in Culver City. Air flow and air velocity samples were taken for a period of several days<br />
which was identified as the passive ventilation phase.<br />
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Figure 3 - Detailed Sampling Location Map<br />
Following that phase, the duct was separated to permit the installation of a fan. During this active<br />
duct phase, more air pressure and air velocity data were collected to measure the effect of the fan<br />
air withdrawal from the NORS to the NCOS with fan speed varying between 5000 and 12,500<br />
cfm.<br />
<strong>Final</strong>ly, the permanent 24-inch/42-inch diameter air duct connecting the upstream ends of the<br />
siphons of the NOS and NCOS near the 405 Freeway was plugged to test the differential air<br />
pressure.<br />
Figure 4 depicts the baseline pressure data recorded on the NORS and NCOS during the first<br />
week of testing. The most notable feature of this data set is the difference between the average<br />
differential air pressures on the NORS and NCOS.<br />
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Figure 4 - Baseline Air Pressure<br />
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Figure 5 - Passive Air Duct Connection Data<br />
Figure 5 shows the effects of the passive 36-inch diameter duct connection explained previously<br />
in this report between the NORS and NCOS maintenance holes. The duct was connected on July<br />
20, 2009. The most notable feature of this data set is that MH 535-05-016 on the NCOS was the<br />
location whose air pressure was most visibly affected by the passive duct connection.<br />
Differential air pressure data recorded along the NCOS and NORS interceptors during the active<br />
ventilation phase of the duct test are presented graphically in Figure 6.<br />
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Figure 6 - Combined NORS-NCOS Air Pressure with Fan Active<br />
1<br />
Combined NORS NCOS Air Pressure 8/18/09 ‐ 8/27/09<br />
With Fan Active (Installed 8/18/09)<br />
0.8<br />
0.6<br />
Air Pressure (in. wc)<br />
0.4<br />
0.2<br />
The data indicates that the most significant effect of the active ventilation exercise was measured<br />
in the downstream reach of the NCOS (MH 535-09-009). At this location, the average pressure<br />
between the passive and active ventilation phases increased by 1.51 inches of water column as a<br />
result of the fan operation.<br />
The following provides a summary of the findings of the NORS/NCOS duct connection study:<br />
<br />
<br />
<br />
<br />
0<br />
‐0.2<br />
‐0.4<br />
‐0.6<br />
‐0.8<br />
During baseline testing, the average pressure levels at all locations measured were lower<br />
while the NORS/ECIS <strong>ATF</strong> was turned on.<br />
The passive air duct connection resulted in the NORS and NCOS coming to equilibrium<br />
with respect to differential air pressure. The pressures in the NCOS generally increased<br />
and the pressures in the NORS generally decreased.<br />
Actively forcing air from the NORS into the NCOS resulted in an increase in pressure in<br />
the NCOS that is deemed to be unacceptably high. The pressures in the NORS were not<br />
reduced significantly as a result of active ventilation.<br />
The cause of the negative pressures in the NCOS was likely due to either one or both of<br />
two factors:<br />
o<br />
o<br />
NCOS US of Duct Cxn (535‐05‐016)<br />
NORS Culver City Park (535‐05‐021)<br />
NORS DS of Duct Cxn (535‐13‐007)<br />
NCOS DS of Duct Cxn (535‐09‐009)<br />
NORS US of Duct Cxn (DS of NOTF) (535‐09‐006)<br />
NORS ECIS Jnc (535‐09‐022)<br />
8/18/09 8/19/09 8/20/09 8/21/09 8/22/09 8/23/09 8/24/09 8/25/09 8/26/09 8/27/09 8/28/09<br />
Time<br />
The presence of a permanent air duct that connects the NOS to the NCOS<br />
Low flow conditions that were in effect along the NCOS as a result of upstream<br />
flow diversions into the NORS due to the then ongoing rehabilitation of the NOS<br />
It should be noted that, during the sampling effort, a diversion was in effect that redirected all the<br />
NOS flow to the NORS. The project team determined that additional sampling would be needed<br />
when the diversion to the NORS is removed.<br />
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4.0 DROP STRUCTURES STUDY<br />
Drop structures in sewer collection systems are known to be the locations of odor problems as a<br />
result of increased air pressures caused by the rapid vertical drop of sewage within the structures.<br />
The increased air pressures often result in release of the odorous air to the outside with<br />
subsequent odor complaints.<br />
The purpose of the drop structure study was to evaluate the impact of drop structures on the sewer<br />
differential air pressures (difference in air pressure between inside and outside the sewer), under<br />
current conditions and planned modifications. This study focused on measuring and examining<br />
differential air pressures at the four existing sewer drop structures in the City's wastewater<br />
collection system:<br />
<br />
<br />
<br />
Division<br />
Humboldt<br />
Mission and Jesse<br />
23 rd and San Pedro<br />
A baseline condition was established, which consisted of measuring the sewer differential air<br />
pressures along a route starting at the Division drop structure and ending at a maintenance hole in<br />
the Culver City Park as depicted in Figure 7.<br />
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Figure 7 - Drop Structure Baseline Pressure<br />
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This was followed by the physical plugging of the return air lines at each drop structure in order<br />
to measure the impact on the differential air pressures at the drop structure and downstream<br />
sewer. The purpose was to examine the impact of each return line upon differential air pressure<br />
at the structure and in the system. The results of that test are summarized in Figure 8.<br />
Figure 8 - Drop Structure Air Return Line Plugged Pressure<br />
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<strong>Final</strong>ly, flow management (diversion/redistribution resulting in less flow into Humboldt and more<br />
flow into Mission & Jesse) was introduced to the system and more differential air pressure data<br />
was collected to valuate the effect of increased/decrease flow on the differential air pressures at<br />
the structures. Results are shown on Figure 9.<br />
Figure 9 - Drop Structure Pressure with Flow Management<br />
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During theses three different phases, Air Treatment Facilities (<strong>ATF</strong>) at Mission & Jesse and 23 rd<br />
& San Pedro were turned on and off several times in order to study their impact on the air<br />
pressure.<br />
The following provides a summary of site-specific pressure responses to the various<br />
manipulations performed during the study.<br />
<br />
<br />
<br />
Plugging the air return lines generally resulted in increasing pressures along the entire<br />
NEIS/ECIS tunnel alignment. There was some evidence of slight decrease in pressure<br />
immediately upstream of the drop structure.<br />
Allowing less flow through the Humboldt drop structure into the NEIS and more flow<br />
being directed into the ECIS via the Mission and Jesse Drop Structure (by removing the<br />
stop log at the two locations), generally resulted in decreasing pressures on the NOS.<br />
Those locations where the pressures didn’t decrease remained at atmospheric levels.<br />
The <strong>ATF</strong>’s generally reduce pressures along the entire length of the NEIS/ECIS tunnel.<br />
Noticeable pressure reductions occur when the <strong>ATF</strong>’s are turned on. Noticeable pressure<br />
increases occur when the <strong>ATF</strong>’s are turned off.<br />
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5.0 TOTAL NON-METHANE HYDROCARBON STUDY<br />
In recent history, the City of Los Angeles (City) has encountered increasing public concern to<br />
sewer odors, and has been working to improve odor control in several areas identified by local<br />
community groups. Formal, permanent air treatment facilities (<strong>ATF</strong>s) for seven areas with known<br />
or predicted odor “areas of concern” were including in a 2004 Collection System Settlement<br />
Agreement (CSSA) that the City entered into with the United States Environmental Protection<br />
Agency (USEPA), Santa Monica Baykeeper, and others. The CSSA included several<br />
requirements including the installation and operation of interim and permanent air treatment<br />
facilities. Permanent <strong>ATF</strong>s are in the final stages of construction at two of the seven targeted<br />
areas. The location of the five remaining proposed <strong>ATF</strong>s need to be reevaluated based on the<br />
effect of wastewater flow diversions on interceptor headspace air pressure; reported performance<br />
issues and continued odor complaints at several of the locations. Accordingly, the City has<br />
embarked on a study to determine the number and location of the new proposed <strong>ATF</strong>s, assess the<br />
performance of the interim odor control facilities, and decide on the <strong>ATF</strong> technologies. This<br />
Technical Memorandum (TM) summarizes the monitoring results for parameters of interest<br />
conducted at the five proposed <strong>ATF</strong> locations where interim odor control facilities are currently<br />
operating at four of the locations. No control is provided at23rd and San Pedro, the fifth location.<br />
In some cases, existing interceptor odor control facilities and <strong>ATF</strong>s have air permit limits for total<br />
non-methane hydrocarbons (TNMHC) in their exhaust. A single distinct exhaust limit value is<br />
listed in each site’s air permit. The various sites have different individual permit limit values.<br />
Those permit values vary from 18 to 36 parts per million by volume in air (ppm v ). All of these<br />
existing <strong>ATF</strong>s are required to meet a hydrogen sulfide stack exhaust limit of 1 ppm v , with the<br />
exception of the Decotah Street facility which has an exhaust H 2 S permit limit of 0.6 ppm v .<br />
Given that future air pollution permits similar to the existing air permit limits for TNMHC and<br />
hydrogen sulfide, the City wants to have a greater understanding of the composition of the sewer<br />
headspace air at the five interim odor control facility locations so that permanent <strong>ATF</strong> systems<br />
can be designed to meet the likely future air permit requirements. Parameters of interest include:<br />
TNMHC, speciated volatile organic compounds (VOCs), hydrogen sulfide, and total reduced<br />
sulfur compounds. The interim air permits for the existing operating odor control facilities and<br />
<strong>ATF</strong>s require analysis of VOCs by South Coast Air Quality Management District (SCAQMD)<br />
test methods, including the use of SCAQMD Method 25.3 to analyze for TNMHC.<br />
A sampling/analysis program was conducted in April <strong>2010</strong> at the following five interim odor<br />
control facility locations where raw untreated sewer air and the exhaust from the odor control<br />
facilities were assessed.<br />
<br />
<br />
<br />
<br />
<br />
<br />
North East Interceptor Sewer (NEIS) – Richmond (Richmond)<br />
North Outfall Relief Sewer (NORS) –ECIS (NORS-ECIS)<br />
NEIS – Humboldt (Humboldt)<br />
East Central Interceptor Sewer (ECIS) – Mission & Jesse (Mission & Jesse)<br />
ECIS - 23 rd Street & San Pedro (23 rd & San Pedro)<br />
Note that the interim <strong>ATF</strong> at 23 rd and San Pedro was physically removed well before our<br />
sampling program started. As a result, the raw sewer air space was sampled and analyzed<br />
for all the same parameters of interest as the other locations.<br />
Air samples were analyzed for the following parameters:<br />
<br />
Total non-methane hydrocarbons (TNMHC)<br />
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Speciated volatile organic compounds (VOCs)<br />
Hydrogen Sulfide (H 2 S) by Jerome Meter<br />
Continuous H 2 S by OdaLog unit<br />
Speciated organic reduced sulfur compounds<br />
The TNMHC, speciated VOCs and total reduced sulfur compound analyses were conducted by an<br />
independent laboratory. The speciated VOC and speciated organic reduced sulfur compound<br />
analyses were conducted in order to provide an understanding of the compounds that makeup the<br />
TNMHC air sample results. Hydrogen sulfide, in addition to the grab sample evaluation with a<br />
Jerome Meter, was also monitored in the sewer at each location using a continuous monitor with<br />
data-logging capabilities (OdaLog).<br />
The City has shown interest in using a hand-held VOC measuring device as an alternative to<br />
running Method 25.3 to determine TNMHC. A photoionization detector (PID) was used to<br />
analyze samples and the results were compared to TNMHC results.<br />
Following is a summary of findings from the sampling/analytical effort:<br />
At all locations, the odor control facility inlet (raw sewer air) and exhaust Method 25.3<br />
results were below the air permit TNMHC emission limits of 18 to 36 ppm v , except at<br />
Humboldt where the inlet and exhaust concentrations were 23.0 and 18.4 ppmC,<br />
respectively. This is graphically displayed in Figure 10. It is believed that the higher<br />
TNMHC and elevated hydrogen sulfide activated carbon exhaust concentrations are due<br />
to spent carbon at the Humboldt odor control facility. It is expected that if the carbon<br />
was still effective the exhaust TNMHC and hydrogen sulfide results would be notably<br />
reduced. The figure below, Total Non-Methane Hydrocarbon VOS Sampling Result<br />
Summary illustrates inlet and exhaust TNMHC concentrations relative to the permit limit<br />
range of 18 to 36 ppm v .<br />
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Figure 10 - Total NMHC VOC Sampling Result Summary<br />
<br />
<br />
<br />
The percentage of speciated VOCs which accounted for Method 25.3 VOCs ranged from<br />
approximately 32% to approximately 100% except for locations where apparent sampling<br />
interferences occurred at the Humboldt inlet/exhaust, and at Mission & Jesse.<br />
There was limited correlation between PID readings and TNMHC results produced by<br />
Method 25.3 results. Given that a PID’s reading is dependent on the compounds present,<br />
the City should consider using an alternative hand-held field measurement monitor if a<br />
substitute for Method 25.3 is desired.<br />
The short term grab sampling of the odor control facility inlet or raw sewer air hydrogen<br />
sulfide concentrations ranged from approximately 2 ppm v (at Richmond) to >50 ppm v (at<br />
Mission & Jesse and 23 rd & San Pedro). Figure 11 below, Hydrogen Sulfide Sampling<br />
Results Summary, illustrates the odor control facility inlet and exhaust hydrogen sulfide<br />
concentrations and the average OdaLog readings.<br />
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Figure 11 – Hydrogen Sulfide Sampling Results Summary<br />
<br />
The carbon adsorbers at Richmond and NORS-ECIS were providing hydrogen sulfide<br />
removals of > 99%. The carbon at Humboldt appeared to be exhausted, with an exhaust<br />
hydrogen sulfide concentration of 11.7 ppm v .<br />
An overview of hydrogen sulfide control technologies as a function of inlet concentration in<br />
general, and the values measured in this study are presented in Figure 12. Carbon is generally<br />
cost-effective at inlet concentrations less than 10 ppm v . Biofilters are cost-effective at inlet<br />
concentrations up to 50 ppm v and greater. At higher concentrations however, the biofilter media<br />
degradation accelerates. Bio-trickling filters are cost-effective at inlet concentrations of 20 ppm v<br />
and higher, which indicates some overlap for the two biological systems. Figure 12, Hydrogen<br />
Sulfide Emission Control Overview, can be used as a basis to evaluate control technologies in the<br />
next phase of this project.<br />
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Figure 12 - Hydrogen Sulfide Emission Control Overview<br />
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6.0 <strong>ATF</strong> STUDY<br />
The <strong>ATF</strong> <strong>Study</strong> was conducted after all field tests were performed and the associated Technical<br />
Memorandum described the results of the analysis of the data collected for the <strong>ATF</strong> Review<br />
<strong>Study</strong>. It includes<br />
<br />
A summary of the field test conducted for the study, including the siphons and drop<br />
structures<br />
<br />
<br />
<br />
<br />
<br />
The results of the airflow modeling for current conditions and future scenarios<br />
Recommendations for an <strong>ATF</strong> location, drop structure modifications and flow diversion<br />
based on the results of observations and analysis following the field data collection<br />
Characterization data from five of the seven locations identified in the 2004 Collection<br />
System Settlement Agreement<br />
Various available technologies for controlling nuisance related odors and air emissions<br />
that are associated with wastewater collection systems<br />
Recommended technology for the <strong>ATF</strong> at Mission and Jesse.<br />
6.1 <strong>ATF</strong> Locations<br />
The following are the general conclusions that may be drawn from analyzing pressure data<br />
recorded during the drop structure field study with the various system modifications described in<br />
the technical memorandum.<br />
<br />
The existing interim air scrubbers generally reduce pressures along the entire length of<br />
the NEIS/ECIS tunnel. This appears to be especially the case with the Mission and Jesse<br />
interim scrubber. Measurable pressure reductions occur in the NEIS/ECIS tunnel when<br />
this interim scrubber is turned on. Measurable pressure increases occurred in the<br />
NEIS/ECIS tunnel system when the Mission and Jesse interim scrubber was turned off.<br />
<br />
<br />
<br />
The Humboldt interim scrubber only appears to affect pressures in its immediate vicinity<br />
Plugging the air return line plugs generally resulted in increasing pressures along the<br />
entire NEIS/ECIS tunnel alignment<br />
The stop logs removal decreasing the flow at Humboldt and increasing it at Mission &<br />
Jesse generally resulted in decreasing pressures on the NOS. Those locations where the<br />
pressures didn’t decrease remained at atmospheric levels.<br />
6.2 Air Emissions Characteristics<br />
To obtain emissions characterization data from five of the seven locations identified in the 2004<br />
Collection System Settlement Agreement (CSSA) that the City entered into with the USEPA,<br />
Santa Monica Baykeeper, and others, a monitoring plan was developed. The remaining two<br />
locations were not included in this characterization plan since the City determined to move ahead<br />
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with constructing <strong>ATF</strong>s at these sites. Those <strong>ATF</strong>s have been constructed, have passed their<br />
performance tests, and are about to be commissioned. The monitoring plan included sampling at:<br />
North East Interceptor Sewer (NEIS) – Richmond<br />
North Outfall Relief Sewer (NORS) – NORS – ECIS<br />
NEIS – Humboldt<br />
East Central Interceptor Sewer (ECIS) – Mission & Jesse<br />
ECIS – 23 rd Street & San Pedro<br />
The samples collected at these five locations were analyzed for the following parameters:<br />
Hydrogen sulfide (H 2 S)<br />
TNMHC<br />
Speciated volatile organic compounds (VOCs)<br />
Speciated organic reduced sulfur compounds<br />
The following analytical methods were used to determine the concentrations of the various<br />
specific compounds and classes of compounds:<br />
TNMHC - SCAQMD Method 25.3<br />
Speciated volatile organic compounds - EPA Method TO – 15 and 12 Modified<br />
Speciated organic reduced sulfur compounds - ASTM 5504<br />
These methods were carefully selected to identify those compounds that together made up the<br />
TNMHC value, and to ensure that the two approaches reached a similar endpoint.<br />
For more details on the sample collection, the analytical procedures, and the analytical results the<br />
reader is referred to the Total Non-Methane Hydrocarbon Monitoring Results Technical<br />
Memorandum (TM) submitted in draft to the City in June <strong>2010</strong>.<br />
The analytical results for the samples collected from the manhole at Mission and Jesse where the<br />
interceptor odorous air is extracted and forwarded to the interim odor control system (consisting<br />
of activated carbon) are presented in Table 1. Table 1 includes those analytical results that are<br />
directly related to permit limits. For information on speciated organic compounds and reduced<br />
sulfur compounds refer to the TNMHC TM.<br />
Table 1 - Mission & Jesse Interceptor Raw Emissions Characterization Results<br />
<br />
Parameter<br />
TNMHC – Methods 25.3 (ppmC) 1 14.0<br />
Non-VOCs (ppmC) 1 0.47<br />
Adjusted Method 25.3(ppmC) 1 13.53<br />
Hydrogen Sulfide (ppm)<br />
Grab Sample >50 2<br />
OdaLog Unit 4<br />
• Minimum<br />
• Average<br />
• Maximum<br />
1<br />
ppm C – parts per million as carbon.<br />
2<br />
The monitoring device, Jerome Meter, has a upper H 2 S limit of 50 ppm.<br />
3<br />
The monitoring device, OdaLog, has a lower detection limit of 0.25 ppm.<br />
4<br />
The OdaLog unit was placed in the interceptor maintenance hole.<br />
Mission & Jesse Analytical Results<br />
6.3 Air Emissions Control Technologies<br />
Many different technologies are available for controlling nuisance related odors and air emissions<br />
that are associated with wastewater collection systems. Each technology has a niche when it is<br />
most suitable to provide the level of control required to reduce off-site odor impacts. The degree<br />
of control required at any one site is dependent on several factors, including, but not limited to:<br />
physical setting; metrological conditions, topography of the land surrounding the odor control<br />
site; proximity of the nearest neighbors and/or nearest sensitive receptors; permit requirements<br />
established by South Coast Air Quality Management District (SCAQMD); and unobstructed view<br />
of the air treatment facility (<strong>ATF</strong>). These factors will need to be considered when evaluating the<br />
many different control technologies. The challenge is identifying the most cost effective, viable<br />
control technology that will achieve the goal of the City of Los Angeles (City) and comply with<br />
the limits established in the air permit for each site.<br />
The most commonly applied air control technologies used today that were suitable to this study<br />
include the following:<br />
<br />
Wet scrubbing<br />
<br />
<br />
Biotrickling<br />
Activated Carbon<br />
<br />
Combinations<br />
For a more detailed description of the technology, please refer to the <strong>ATF</strong> TM that is part of this<br />
study.<br />
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7.0 RECOMMENDATIONS<br />
7.1 <strong>ATF</strong><br />
No forced air treatment system is recommended for Division, Humboldt, Richmond and 23 rd &<br />
San Pedro. Since the Mission & Jesse drop structure appeared to be the primary conduit through<br />
which the NEIS/ECIS tunnel relieved its air pressure back into the NOS upstream, a permanent<br />
<strong>ATF</strong> is therefore recommended for this location.<br />
7.2 Drop Structure Modifications<br />
The pressures in the NOS upstream approach sewer were reduced slightly as a result of plugging<br />
the air return line at all the drop structures. There is evidence that installation of a flow regulation<br />
device (“dampler”) in the air return line of the drop structure, such as an adjustable damper may<br />
be beneficial. However, it is recommended to complete the drop structure model testing before<br />
finalizing the damper concept. Such a device would give BOS the flexibility to adjust the amount<br />
of air that is allowed to flow through the air return line under current or future operational<br />
conditions.<br />
Additional modifications to the Mission and Jesse Drop Structure could include installing two<br />
curtains or similar flexible devices. One curtain would be installed at the downstream end of the<br />
plunge pool; the other curtain would be installed on the NEIS just upstream of the junction with<br />
the Mission and Jesse drop structure as shown in Figure 13. However, these decisions should be<br />
delayed pending the outcome of the hydraulic model study.<br />
An additional air pickup should also be designed and constructed for the recommended Mission<br />
and Jesse <strong>ATF</strong>. This air pickup would be located along the NEIS tunnel just upstream of the<br />
recommended NEIS curtain. This additional air pickup is shown in Figure 13.<br />
Figure 13 - Mission & Jesse Additional Air Pickup<br />
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7.3 Flow Diversion<br />
The system air pressures appeared to react favorably to less flow through the Humboldt drop<br />
structure into the NEIS and more flow being directed into the ECIS via the Mission and Jesse<br />
Drop Structure. This was accomplished by removing the stop log at the two locations, which<br />
allowed the approach flows in the NOS to split naturally between that sewer and the NEIS. It is<br />
therefore recommended that the stop logs be configured at Humboldt in such a manner that a<br />
minimum amount of flow is directed into the NEIS and to be configured at Mission & Jesse in<br />
such a manner that a maximum amount of flow is directed into the ECIS. This would likely<br />
result in less air being dragged into the NEIS and therefore, lower air pressures in the NEIS/ECIS<br />
tunnel system.<br />
An overall graphic summary of the recommendations for the NEIS/ECIS drop structure locations<br />
between the Division Drop Structure and the ECIS Jefferson Siphon is presented in Figure 14<br />
below.<br />
Figure 14 - NEIS/ECIS Recommendation Summary<br />
These above recommendations must be revisited following the completion of the pending<br />
physical model testing. Additionally the effects of the recommendations should be verified<br />
with a full scale fan test field study aimed at verifying the effect of the combination of the<br />
adjustable air plugging devices and the recommended <strong>ATF</strong> at Mission and Jesse.<br />
7.4 Technology<br />
Based on the monitoring results from the TNMHC study, the discussions on the technologies, and<br />
the comparison tables of advantages and disadvantages for each of the individual control<br />
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technologies, the recommended technology for the Mission and Jesse location is a two stage,<br />
combination system consisting of:<br />
<br />
First Stage - Biotrickling filter<br />
<br />
<br />
<br />
<br />
Second Stage - Activated Carbon<br />
The biotrickling filter will remove 99% of the influent H2S and limited other reduced<br />
sulfur compounds, and the carbon will: remove any residual H2S down to the low<br />
parts per billion (ppb) concentrations (Well below the projected permit limit of 1.0<br />
ppm.); remove any residual reduced sulfur and odorous compounds; and reduce the<br />
levels of VOCs. This will comply with the permit conditions and keep nuisance odors<br />
from impacting the surrounding communities.<br />
This recommended full air treatment facility is necessary in order to treat the elevated<br />
levels of influent H 2 S concentrations, the modest concentrations of VOCs and the<br />
remaining odorous organic and inorganic compounds. Implementing this two-stage,<br />
combination, air emissions control system will minimize any risk facing the City with<br />
respect to permit compliance and being a good neighbor.<br />
As presented in Section 5- Determine Air Flow, the actual air flow to be treated by the<br />
<strong>ATF</strong> is yet to be established. In the interim it is projected that a 20,000 cfm flow rate<br />
would be necessary at this recommended Mission and Jesse <strong>ATF</strong>. The <strong>ATF</strong> attributes<br />
will depend on the vendor providing the <strong>ATF</strong> units and the design criteria developed<br />
by the design engineer in coordination with the City staff.<br />
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APPENDIX A<br />
Air Treatment Facility (<strong>ATF</strong>) Review<br />
Draft <strong>Final</strong> <strong>Report</strong><br />
Comments by the Independent Odor Expert – Dirk Apgar<br />
October <strong>2010</strong><br />
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Air Treatment Facility (<strong>ATF</strong>) Review<br />
Draft <strong>Final</strong> <strong>Report</strong><br />
Comments by the Independent Odor Expert – Dirk Apgar<br />
October <strong>2010</strong><br />
Contents<br />
Introduction ..................................................................................................................................... 1<br />
Airflow Modeling <strong>Study</strong> ................................................................................................................. 2<br />
Sewer Siphon Duct Connection <strong>Study</strong> ............................................................................................ 4<br />
Drop Structure <strong>Study</strong> ...................................................................................................................... 7<br />
Total Non-Methane Hydrocarbon <strong>Study</strong> ........................................................................................ 9<br />
Air Treatment Facility <strong>Study</strong> ........................................................................................................ 12<br />
Recommendations of the <strong>ATF</strong> Review <strong>Study</strong> Draft <strong>Final</strong> <strong>Report</strong> ................................................ 15<br />
General Remarks and Conclusions of the Independent Odor Expert ........................................... 16
Introduction<br />
This paper is intended to provide a constructive critique of the City of Los Angeles’ Air<br />
Treatment Facility Technical Draft <strong>Final</strong> <strong>Report</strong> (<strong>Report</strong>). The <strong>Report</strong> summarizes the technical<br />
memoranda produced during the City’s Air Treatment Facility (<strong>ATF</strong>) Review <strong>Study</strong>, which was<br />
conducted to develop an understanding of the causes of odor problems originating from the<br />
City’s wastewater conveyance system and reach conclusions on methods of controlling those<br />
nuisance odor problems.<br />
Under the original Collection System Settlement Agreement (CSSA), the City had planned to<br />
construct seven new <strong>ATF</strong>s to help control odors from the wastewater conveyance system. Of the<br />
seven, two have almost been completed (Jefferson & La Cienega and 6000 Jefferson), but design<br />
and construction of the remaining five was placed on hold pending the outcome of the <strong>ATF</strong><br />
Review. As part of the review, the City reevaluated the location and necessity of the five<br />
remaining proposed <strong>ATF</strong>s based on the effect of changing wastewater flows through its<br />
interceptors and the associated effect on sewer headspace air pressure, measured performance of<br />
the interim carbon scrubber based <strong>ATF</strong>s, and continued odor complaints. <strong>Final</strong> recommendations<br />
on the location and technologies to be used in a single <strong>ATF</strong> at the Mission and Jesse site were<br />
reported as a result of the <strong>ATF</strong> Review. The determination of the size of the <strong>ATF</strong> will be made<br />
during the design process for the new facility utilizing information the City will obtain through<br />
testing of a drop structure scale model similar to the structure at Mission and Jesse.<br />
The City has undergone a significant level of work in an attempt to develop an understanding of<br />
the airflow and air pressurization within its wastewater conveyance system. It is rare that this<br />
level of effort is seen within the United States or, for that matter, worldwide. While the City and<br />
its consulting engineering firms have many capable technical experts, it is important to<br />
understand that estimating the causes and effects of the airflow dynamics in complex sewer<br />
systems and the resulting likelihood of odor emissions and impacts can only be done within a<br />
broad range of accuracy. It is possible that while odor impacts may be diminished, communities<br />
may continue to experience odors even with the activation of the two <strong>ATF</strong>s currently nearing<br />
completion, modification of wastewater flow patterns, and the implementation of the<br />
recommended <strong>ATF</strong> at Mission and Jesse. As the <strong>ATF</strong>s at Jefferson & La Cienega and 6000<br />
Jefferson are brought up to their design airflow capacities, neighboring citizens should be able to<br />
assess their ability to control odor emissions and impacts in their community.<br />
Below is a summary of the major components of the <strong>ATF</strong> Review <strong>Study</strong>. Each has been<br />
discussed previously in comments by the Independent Odor Expert with input by<br />
Community Liaison, The City Project.<br />
1
Airflow Modeling <strong>Study</strong><br />
The Airflow Modeling <strong>Study</strong> (Modeling <strong>Study</strong>) was conducted by the City in an attempt to better<br />
understand how flowing wastewater influences the movement of the free air in the sewer system<br />
and better predict where odor emissions may occur. The model created in this instance relied on<br />
major assumptions regarding the City’s existing sewer system. As with all models, the<br />
conclusions of the study can only be as good as the assumptions upon which it is based. The<br />
usefulness of the Modeling <strong>Study</strong> results should not be summarily discounted, however, they<br />
should be viewed as being within a broad range of accuracy and should not be viewed as precise<br />
or as the only information that should be used to locate and size <strong>ATF</strong>s for odor control.<br />
The movement of air above wastewater in a sewer is largely dependent on the viscous drag of the<br />
liquid on the gas. Viscous drag is the force exerted on the air by the moving water due to friction.<br />
Air movement is also influenced by the ambient air pressure and movement outside the sewer,<br />
heating or cooling of the air, and obstructions within the sewer. As moving air meets an<br />
obstruction it can be compressed, resulting in increased sewer air pressure. If the air pressure<br />
internal to the sewer is higher than that of the surrounding atmosphere, there is the potential for<br />
foul air to escape and cause nuisance odor impacts in the community.<br />
The stated scope of the Modeling <strong>Study</strong> was to create a model that could identify odor “hot<br />
spots” under several potential wastewater flow scenarios. These hot spots are not points of actual<br />
or even modeled odor impacts, but locations in the sewer system where the model indicates<br />
airflow is likely to be restricted. According to the <strong>Study</strong>, past experience has shown that airflow<br />
restrictions are the primary cause of high air pressure in the sewer. Since we know high sewer<br />
pressure (in comparison to lower atmospheric pressure) can cause foul air to escape, being able<br />
to predict possible locations of sewer airflow obstruction/high air pressure, is one way to predict<br />
the location of odor impacts in the community.<br />
To estimate where these hot spots could occur, the City’s engineering team used a pair of<br />
computer models to understand wastewater flow conditions and developed a third model to<br />
estimate how flowing wastewater would cause air to move within the sewer and where that<br />
movement may become restricted. It was explicitly stated that the airflow model is not intended<br />
to model air differential pressure, but only to identify hot spots as defined above.<br />
Modeling Methodology<br />
The City used commercially available computer software to model and analyze wastewater flows<br />
under various conditions. They developed an additional computer program that used the output<br />
of the wastewater flow predicting software to estimate where the characteristics of the sewers<br />
and the flowing wastewater could result in a location where the capacity of the system to carry<br />
air would become restricted. In that case, a “hot spot” was identified.<br />
The Modeling <strong>Study</strong> explains that the airflow model was developed assuming only that the<br />
movement of the wastewater is responsible for air movement within the sewer. The airflow<br />
model calculates the airflow capacity within a segment of the sewer based on the wastewater<br />
velocity, the depth of wastewater, and the geometry of the pipe. Based on that information, the<br />
airflow velocity is estimated as a fraction of the wastewater velocity. That fraction varies with<br />
depth of the wastewater and the diameter of the sewer. The volumetric airflow is calculated by<br />
2
multiplying the air velocity by the cross section of the free air space. The airflow is similarly<br />
calculated for the next downstream sewer segment. If the first segment’s airflow is greater than<br />
the second segment’s, it is assumed that the potential for compression of the air exists. If the<br />
difference in airflows in the two segments is greater than 2,000 cubic feet per minute (cfm) a hot<br />
spot is identified.<br />
Modeling Assumptions and Accuracy<br />
The City’s model is based on the assumption that flowing wastewater is the only influence<br />
causing air to move within the sewer. This phenomenon is well documented and could provide a<br />
reasonable first estimate of airflow. However, while the drag of flowing wastewater has a<br />
significant influence on sewer airflow, air pressure up and downstream of the sewer segment<br />
modeled can also have a profound effect on air movement as can the effects of air buoyancy and<br />
friction between the moving air and the sewer wall. A stated limitation of the model is that it<br />
does not account for back pressure effects from siphons, drop structures, slope reductions or<br />
junction structures. The effect of air treatment facilities on airflow is also ignored by the model.<br />
All models predict reality with some degree of error and the absolute accuracy of the City’s<br />
model is difficult to gage. Field data was collected in an attempt to determine if the model was<br />
predicting those areas where pressurization of the sewer air was occurring. Air pressure was<br />
monitored at six locations where hot spots were predicted by the model. Data from one of the<br />
locations was discounted due to the strong effect of the air treatment facility at the Hyperion<br />
wastewater treatment plant. Data from the remaining five locations did show good correlation<br />
between the modeled and real-world conditions. However, only locations identified by the model<br />
to have a build-up of pressure were sampled. It would have been helpful if locations that the<br />
modeled airflows indicated lower or neutral pressure were also monitored. This would have<br />
provided additional insight to the model’s accuracy.<br />
Model Analysis and Hot Spot Identification<br />
Analysis to identify hot spots and estimate the airflow within certain sewer sections was<br />
performed using three different wastewater flow scenarios. These represented the current and<br />
possible future sewer configurations that would divert flows from the North Outfall Relief Sewer<br />
(NORS) to the North Outfall Sewer (NOS) and from the NOS to the Central Outfall Sewer<br />
(COS). For each of these three scenarios, the airflow model was used to identify hot spots based<br />
on a 48-hour period using typical weekday and weekend wastewater flows.<br />
The <strong>Study</strong> states that the airflow rate within the sewer is one of the design criteria for any future<br />
air treatment facility. This is a reasonable statement. Knowledge of the sewer airflow is<br />
necessary to determine the rate of air extraction by an <strong>ATF</strong> to lower the pressure in the sewer to<br />
prevent odor emissions. Current airflow rates were estimated at several locations that appear to<br />
be associated with known odor problems. Airflows at the upstream ends of the North Central<br />
Outfall sewer (NCOS) and NORS siphons near the I-405 freeway and five drop structures were<br />
modeled. The <strong>Study</strong> states that actual airflow rates can differ from the model-estimated rates due<br />
to the disregard of <strong>ATF</strong> ventilation and airline effects. The <strong>Study</strong> reports the modeled airflows<br />
for eleven locations near the NCOS, NORS, and the drop structures for each of the three<br />
wastewater flow scenarios.<br />
3
Some of the model-identified hot spots were dismissed due to known actual conditions. Those<br />
locations that were dismissed were those known or assumed to be affected by <strong>ATF</strong>s and<br />
therefore not sources of odor problems. Under the current wastewater conveyance system<br />
configuration, nine hot spot locations identified by the model were considered valid. Six of these<br />
hot spots were located on the East Central Interceptor Sewer (ECIS), one was on the<br />
NORS/ECIS Junction, and the remaining two were on the NCOS and NORS siphons at I-405.<br />
When modeling the two potential future sewer configurations, three additional hot spots were<br />
identified on the ECIS, one at the NOS siphon and one immediately downstream of the North<br />
Outfall Treatment Facility (NOTF) on the NOS.<br />
General Remarks and on the Airflow Modeling <strong>Study</strong><br />
The City’s engineering team has produced a model to estimate airflows and hot spot sites of<br />
potentially high pressure within the sewer system. The model estimates the airflow based on the<br />
assumption that air movement is only due to the viscous drag on the air by moving wastewater<br />
and ignores several other significant parameters. However, given the state of the art of sewer<br />
airflow modeling, it is not an unreasonable way to gain insight into the potential for air pressure<br />
increases, potential locations of odorous emissions, and to understand the magnitude of the air<br />
volumes moving within the sewer. The estimate of the volumetric airflow is important to<br />
quantify so that air treatment facilities can be sized to neutralize the potential for high air<br />
pressure at the model identified hot spots.<br />
Given the current state of the art of modeling airflow within sewers, it is important to corroborate<br />
modeled information with real world data and observations. The City’s team has conducted some<br />
field data collection that indicates their model is capable of identifying points of air<br />
pressurization within the sewer. These locations are compared with odor complaint locations in<br />
the <strong>ATF</strong> <strong>Study</strong> (discussed later in this paper) to further verify the validity of the model.<br />
From the information in the Modeling <strong>Study</strong>, one can conclude that, as a first estimate, the<br />
airflow model provides a reasonable estimate within a broad range of accuracy. The model was<br />
used in the <strong>ATF</strong> <strong>Study</strong> along with field data and observations as an aid to determining the need,<br />
location, and size of <strong>ATF</strong>s.<br />
Sewer Siphon Duct Connection <strong>Study</strong><br />
The stated purpose of the Sewer Siphon Duct Connection <strong>Study</strong> (Siphon Duct <strong>Study</strong>) was to<br />
examine the effect that existing interceptor siphons located under the I-405 freeway have on<br />
airflow dynamics in the interceptor collection system. The interceptor collection system<br />
discussed in the Siphon Duct <strong>Study</strong> is made up of the North Outfall Relief Sewer (NORS), East<br />
Central Interceptor Sewer, North Central Outfall Sewer (NCOS) and the North Outfall Sewer<br />
(NOS).<br />
The focus of the Siphon Duct <strong>Study</strong> was to examine the potential benefit of adding a duct to<br />
connect the air spaces of the NORS and NCOS. Because the NORS airspace has been shown to<br />
have consistently higher than atmospheric pressure and the NCOS lower than atmospheric<br />
pressure, it was hoped that the two could be connected, allowing air to flow from the high to low<br />
pressure sewers and decrease the odorous emissions from the NORS. Earlier investigation on this<br />
topic was described in the City’s NORS Siphon Air Line Feasibility <strong>Study</strong>. After that work was<br />
4
produced, additional investigatory tasks were accomplished and documented in the Sewer Duct<br />
<strong>Study</strong> that reports on the findings and conclusions based on an analysis of the data collected.<br />
In addition to examining the effects of joining the NORS and NCOS air spaces, the Siphon Duct<br />
<strong>Study</strong> also reports on the affects of blocking an existing permanent air duct that joins the NCOS<br />
and the NOS. This was done in an attempt to understand why the NCOS is at a consistently low<br />
pressure.<br />
Rational and Methodology of Siphon <strong>Study</strong><br />
The City and its consulting engineers formulated the Siphon <strong>Study</strong> to perform air pressure<br />
measurements in the as-built (no NORS/NCOS air duct connection) to establish a baseline data<br />
set. The air duct would then be installed and air allowed to flow freely between the NORS and<br />
NCOS while additional air pressure data and airflow measurements through the duct were<br />
recorded. After the free airflow data was collected a fan would be place in the air duct forcing air<br />
from the NORS into the NCOS to determine if that scenario would provide positive results with<br />
respect to controlling odors. In order to gain an understanding of the affect the existing air<br />
treatment facilities’ extraction of air from the sewers had on air pressure and flow within the<br />
sewer system under these various scenarios they would be cycled on and off during the data<br />
gathering period.<br />
Baseline Data Collection Phase<br />
The baseline air pressure measurements were taken over approximately three week’s time<br />
beginning in early June of 2009. During that time the NORS was consistently pressurized<br />
between approximately 0 to 0.4 inches water column with an average of approximately 0.2<br />
inches water column. There were almost daily excursions of the NORS pressure below 0 inches<br />
water column, but for the most part it was positively pressurized with respect to the atmosphere.<br />
The NCOS baseline pressure measurements were taken simultaneously with the measurements in<br />
the NORS. The NCOS data showed that that sewer’s air space was consistently lower in pressure<br />
than the surrounding atmosphere with an average pressure of approximately -0.39 inches of<br />
water column.<br />
The pressure of 1 inch of water column is literally the pressure exerted by water one inch below<br />
its surface. This may seem slight but the ventilation of air requires very slight pressure<br />
differences. Pressure in heating and air conditioning systems are typically measured in these<br />
units. Significant air volumes can be moved with differential pressures in the 0 to 1 inch water<br />
column range and the pressures measured in the NORS and NCOS could reasonably be assumed<br />
to have the capability to transfer large volumes of air between the two sewers. This justified the<br />
further investigation of the efficacy of allowing that to occur with the air duct connection.<br />
Further baseline data collection was taken while the NORS/ECIS <strong>ATF</strong> system was turned off so<br />
that its 10,000 cfm capacity was not being extracted from just upstream of the NORS/ECIS<br />
junction. During that time the data revealed that the pressure in the two sewers was higher than it<br />
was when the AFT was turned on as one would expect. The pressure measurement data taken<br />
from the NCOS showed that the <strong>ATF</strong>’s influence could be detected miles from the point at which<br />
5
the air was extracted from near the NORS/ECIS junction. This data could prove useful in the<br />
locating and sizing of future AFT facilities.<br />
Passive Air Duct Connection Data Collection Phase – Description and Critique<br />
A 36-inch duct was used to connect maintenance holes on the NORS and NCOS. This allowed<br />
the higher pressure in the NORS to be relieved while causing air in the range of 3,000 to 3,500<br />
cfm to flow into the NCOS and raising the pressure in that sewer. The increase in pressure in the<br />
NCOS was significant, rising from an average of -0.39 to +0.03 inches water column, while the<br />
pressure in the NORS decreased by only 0.06 inches wc from 0.20 to 0.14 inches wc. The<br />
decrease in pressure in the NORS could result in fewer odor emissions but the increasing<br />
pressure in the NCOS could result in odor emissions from that sewer.<br />
During the passive air duct connection pressure monitoring, the NORS/ECIS and Jefferson <strong>ATF</strong>s<br />
were cycled on and off. When the scrubbers (rated at 10,000 cfm each) were extracting air from<br />
the sewers, the airflow from the NORS into the NCOS was from 3,000 to 3,500 cfm as<br />
mentioned above. With those interim <strong>ATF</strong>s turned off, the airflow dropped to approximately half<br />
those values and the pressure increased by 0.1 and 0.17 in the NORS and NCOS respectively.<br />
This would indicate that the effect of the air extraction by the <strong>ATF</strong>s has a more profound effect<br />
on the NCOS than on the NORS in the vicinity of the duct connection.<br />
Active Air Duct Connection (Forced Ventilation) Data Collection Phase – Description<br />
and Critique<br />
During the active air duct data collection phase, an axial flow fan was placed in the 36 inch<br />
diameter duct to extract air from the NORS and force it into the NCOS. The apparent intention of<br />
this phase was to determine if mechanically extracting air would relieve more pressure from the<br />
NORS than during the passive ventilation phase and what affect would be seen in the NCOS.<br />
The fan was operated to achieve target airflows of 5,000, 7,500, 10,000 and 12,500 cfm.<br />
As a result of the active ventilation described above, three significant and related issues became<br />
evident. First, and most importantly, the average pressure in the NCOS became very high at 1.5<br />
inches wc above that found in the passive ventilation test. Second, the pressure in the NCOS<br />
fluctuated extremely between the positive and negative pressure values indicating that very<br />
unpredictable odorous emissions could come from the NCOS with the forced ventilation option.<br />
Third, there was only a minor benefit to the pressure condition in the NORS with the average<br />
pressure decreasing by only about -0.03 inches wc in that sewer.<br />
The fact that the active ventilation led to only a small reduction in the NORS average pressure<br />
while the NCOS became so highly and erratically pressurized leads to the conclusion that the<br />
active air duct connection is not a viable option for controlling odors in the NORS/NCOS<br />
system.<br />
Air Duct Isolation between NOS and NCOS – Description and Critique<br />
With the information obtained from the investigation and data gathering described above, the<br />
reason for the consistent negative pressure in the NCOS still remained unclear. The City’s team<br />
determined that additional sampling would be needed to determine the cause. It was decided to<br />
6
lock the airflow in the permanent air duct that connects the NCOS to the NOS near their<br />
respective siphons under the I-405 freeway. It was reasoned that this would allow the team to<br />
determine if the low pressures in the NCOS were influenced by the NOS.<br />
The permanent air duct was blocked and pressure monitors were used to record pressure data for<br />
a period of approximately two weeks. Pressure in the NCOS was observed to not change<br />
appreciably while the pressure in the NOS markedly increased. This would indicate that the<br />
NCOS was not influenced by the NOS but that the opposite was true. The NCOS influenced the<br />
NOS pressures, keeping them lower as a result of the air duct being open.<br />
One additional conclusion was noted in the Siphon Duct <strong>Study</strong>. That was that the low flow<br />
conditions in the NCOS at the time the data was being collected were the cause of the negative<br />
pressures in that sewer. It would be reasonable to assume that the lack of high pressure would<br />
result from the low flow conditions but there are likely additional factors that lead to negative<br />
pressure in the NCOS. These lower than atmospheric pressures could be caused by wind passing<br />
over maintenance holes causing air to flow out of openings in their lids, temperature differences<br />
between the sewer air and the surrounding atmosphere or sewer conditions upstream of the<br />
pressure data collection area that may influence the NCOS near the I-405 freeway siphon.<br />
General Remarks on the Siphon Duct <strong>Study</strong><br />
Understanding the dynamics of airflow and pressure distribution is necessary to effectively<br />
control wastewater conveyance system odors. Good real-world data helps engineers locate, and<br />
size air treatment facilities for appropriate foul air extraction and treatment to minimize odor<br />
emissions from sewers and adequately treat the air prior to its discharge to the neighborhood.<br />
The Siphon Duct <strong>Study</strong> provides some of the fundamental information that will aid with the final<br />
design of odorous air management and control systems.<br />
Complete understanding of the airflow characteristics in a sewer system is never achievable but<br />
it is possible to move forward with good designs based on limited knowledge. Information<br />
regarding the way wastewater flow influences airflow and pressure distributions in the sewers<br />
was not included in the Siphon Duct <strong>Study</strong>. That topic was covered in the Airflow Modeling<br />
<strong>Study</strong> (discussed above).<br />
In a separate NORS Siphon Air Line Feasibility <strong>Study</strong>, the City concluded that installing a<br />
permanent duct between the NORS and NCOS could provide partial relief of the high pressure in<br />
the NORS and that an attractive aspect of this alternative is its simplicity and relatively low cost.<br />
That study indicates that it would cost approximately $200,000 to install the permanent duct. The<br />
work in the Sewer Siphon Duct Connection <strong>Study</strong> would support this conclusion.<br />
Drop Structure <strong>Study</strong><br />
The purpose of the Drop Structure <strong>Study</strong> was to develop a better understanding of how<br />
wastewater flowing through drop structures influences the pressure of the free air space in the<br />
structure and connecting sewers. The Drop Structure <strong>Study</strong> also examined the affect turning on<br />
and off various interim air treatment facilities had on the sewer air pressure.<br />
7
A drop structure is necessary when the elevation of a sewer must change abruptly. This can be<br />
required at the confluence of two sewers when one is higher than the other. Air above the<br />
flowing wastewater is dragged in the approach sewer and with the flow falling into the drop<br />
structure. This action can cause high pressures to develop if the moving air is obstructed from<br />
traveling downstream from the drop structure. To help alleviate this problem an air return line<br />
connecting the bottom and top of the drop structure is often included in the design. The City had<br />
observed that drop structures with these air return lines often had high pressures in their<br />
approach sewers and that at least one drop structure without a return line operated with an<br />
approach sewer having air pressure lower than atmospheric. Those sewers with high pressures<br />
could cause odors to escape and impact the local community while the low air pressure sewer<br />
would be unlikely to be offensive.<br />
Due to the observed air pressures in and around the drop structures, the City performed a series<br />
of tests to measure the effects of (1) blocking the air return lines, (2), modifying wastewater<br />
flows, and (3) cycling the relevant interim carbon scrubber <strong>ATF</strong>s off and on to measure the<br />
effects on air pressures upstream and downstream of five drop structures. 1<br />
The Drop Structure <strong>Study</strong>’s additional stated objective was to identify potential changes to the<br />
planned odor control strategies and methods to control odorous air releases in the proximity of<br />
the drop structures.<br />
Investigation Procedures<br />
The City’s team conducted a series of experiments in the field that first involved measuring the<br />
air pressure in the sewers as they are currently built and operated to obtain baseline data. Data<br />
was gathered in the North Outfall Sewer (NOS) and Eagle Rock Interceptor Sewer (ERIS)<br />
approaches to the drop structures, in the drop structures, and in the North Outfall Relief Sewer<br />
(NORS), East Central Interceptor <strong>Sewers</strong> (ECIS) and North East Interceptor Sewer (NEIS) on<br />
the downstream side of the drop structures.<br />
The air return lines were then blocked with inflatable plugs to prevent airflow from the bottom of<br />
the drop structures from flowing back to the top of the drop structures. As this was done,<br />
additional air pressure data was collected. Then, wastewater flows through the drop structures<br />
were manipulated by removing barriers known as stop logs within diversion structures in the<br />
sewers. These diversion structures, as the name implies, are used to divert flow from one sewer<br />
to another. <strong>Final</strong>ly, while the air return lines were blocked and the flows manipulated in the drop<br />
structures, the interim <strong>ATF</strong>s at the Humboldt and Mission and Jesse locations were cycled on<br />
and off. Air pressure data was collected to determine if the air they extracted from the sewer<br />
would influence the air pressures in the drop structures as well as the upstream and downstream<br />
sewers.<br />
1 The drop structures tested were located at Division, Humboldt, Mission & Jesse, and 23 rd San<br />
Pedro and the University of Southern California (USC).<br />
8
General Remarks on the Drop Structure <strong>Study</strong><br />
The City of Los Angeles has gone to considerable effort to understand how sewer air pressure is<br />
influenced by drop structure design, wastewater flow, and operation of interim <strong>ATF</strong>s. While<br />
there is good information that can be derived from the data collected, there is no one obvious<br />
conclusion from the information obtained that will allow a clear decision to be made regarding<br />
the solution to the problem of air emissions from the sewers and the odor impacts that result.<br />
This is not to say that the information is not valuable; the information should reasonably lead to<br />
better informed engineering decisions. What can be gleaned from the data is that a number of<br />
changes that each contribute a little to the solution could be made to lower the probability of<br />
odor emissions.<br />
The most significant conclusion that can be drawn from examining the Drop Structure <strong>Study</strong> is<br />
that it will likely be necessary to use more appropriately sized and located <strong>ATF</strong>s to remove air<br />
from the sewers and thus reduce the high pressures that result in uncontrolled odor emissions. As<br />
long as such high pressures exist in the sewers, uncontrolled emissions are virtually certain.<br />
Because none of the methods investigated in the Drop Structure <strong>Study</strong> (including blocking air<br />
return lines and manipulating wastewater flows), could dependably achieve a substantial and<br />
consistent reduction in air pressure, the only real alternative is to remove more sewer air with<br />
<strong>ATF</strong>s.<br />
The information obtained in the Drop Structure <strong>Study</strong> was used to help initially size and locate<br />
<strong>ATF</strong>s. <strong>Final</strong> <strong>ATF</strong> locations and sizes should be determined after scale drop structure model<br />
testing in the City’s hydraulics laboratory and through a formal pre-design and design process.<br />
Total Non-Methane Hydrocarbon <strong>Study</strong><br />
The City is required under the terms of the CSSA to install and operate interim and permanent<br />
<strong>ATF</strong>s for the control of odors from the sewers. These <strong>ATF</strong>s must have permits issued by the<br />
South Coast Air Quality Management District (SCAQMD) that will allow the City to build and<br />
operate the facilities. Permits of this type place limits on <strong>ATF</strong> pollutant emissions that could<br />
have nuisance or human health effects. As part of its <strong>ATF</strong> Review, the City monitored total nonmethane<br />
hydrocarbons (TNMHC) and odorous compounds in the sewer air and produced a<br />
technical memorandum summarizing its finding.<br />
Some organic 2 pollutants that may be emitted from the <strong>ATF</strong>s can react in the atmosphere<br />
forming ozone (O 3 ), which is one of the first pollutants regulated under the Clean Air Act. The<br />
concentration of O 3 in the City’s air is higher than the regulatory limit. As a result, the City is<br />
considered a non-attainment area for that pollutant by the United States Environmental<br />
Protection Agency (US EPA). The SCAQMD limits emissions of these organic pollutants as a<br />
way to limit the production and concentration of O 3 . The existing interim <strong>ATF</strong>s are required to<br />
meet SCAQMD TNMHC and hydrogen sulfide (H 2 S) emission concentration limits described in<br />
their permits. Future permanent <strong>ATF</strong>s will certainly have limits on these pollutants as well.<br />
2 Substance whose molecules contain one or more carbon atoms with the exception of<br />
carbonates, cyanides, carbides, and a few others.<br />
9
As part of the City’s <strong>ATF</strong> Review, the City wanted to gain knowledge about the pollutants in the<br />
sewer air that the new <strong>ATF</strong>s would be treating and about the ability of the interim <strong>ATF</strong>s to<br />
control these pollutants. This would allow the City to determine if the interim <strong>ATF</strong> technology<br />
(carbon bed scrubbers) could be used as part of the new <strong>ATF</strong> systems. The purpose of the work<br />
was the following:<br />
Understand the characteristics of the air pollutants in the sewer air that would be treated<br />
by the new <strong>ATF</strong>s;<br />
Determine if the concentrations of the various organic compounds in the sewer air<br />
summed to a similar value as that determined by the SCAQMD TNMHC testing method;<br />
Determine if there were organic compounds in the sewer air that should not be included<br />
in the calculation of the TNMHC concentration;<br />
Compare the measured pollutant concentrations in the interim <strong>ATF</strong> exhaust against the<br />
SCAQMD permit limits;<br />
Assess the pollutant removal efficiency of the interim <strong>ATF</strong>s; and<br />
Determine if a handheld device could be used to measure TNMHC concentrations<br />
Sampling and Analysis of Sewer Air Pollutants<br />
The City simultaneously extracted air samples for analysis by several laboratory methods. Two<br />
EPA methods, TO-12 and TO-15, were used to determine the concentration of specific organic<br />
compounds, SCAQMD Method 25.3 was used to quantify TNMHC concentration, and American<br />
Society for Testing and Materials (ASTM) Method D5504 was used to quantify sulfur compound<br />
concentrations in the sewer air. In addition to these methods, H 2 S data monitors were used to<br />
spot check and collect concentration data over extended periods. A handheld photo-ionization<br />
detector (PID) was also used with hopes that it could be used as an alternative to Method 25.3 for<br />
measuring TNMHC concentrations.<br />
Pollutants in the Air Stream<br />
The two EPA methods yielded a great deal of information about which organic compounds are<br />
present in the sewer air that made up the interim <strong>ATF</strong> inlet airstream and in the exhaust air<br />
streams. The information about the individual compounds is valuable in that it could be used in<br />
the evaluation of future <strong>ATF</strong> technologies for controlling their emission into the atmosphere at<br />
concentrations acceptable to the SCAQMD. The pollutants identified by these methods probably<br />
contribute only slightly to the total sewer odor given the concentrations reported. The sulfurous<br />
compounds identified by the ASTM method are likely the main cause of sewer odors in these air<br />
streams.<br />
The City was interested if the EPA methods would find some compounds that do not cause O 3<br />
production in the atmosphere, but could influence the TNMHC value determined by the<br />
SCAQMD method. If the EPA methods did find such compounds, that could call into question<br />
the permit limit on TNMHC concentration that SCAQMD uses to limit atmospheric O 3 levels.<br />
Ultimately, discounting the influence of those non-O 3 producing compounds did not appreciably<br />
change TNMHC concentration, so the SCAQMD method appears to be a reasonable way of<br />
finding the concentration.<br />
10
Using the information obtained by the EPA methods, the total carbon in the organic compounds<br />
was summed and compared to the TNMHC value obtained by the SCAQMD Method 25.3. The<br />
values determined by the two methods differed by as much as a factor of five and were not<br />
consistent between sites. Examination of the Method 25.3, TO-12, and TO-15 did provide<br />
information on which compounds most influenced the TNMHC concentrations. This information<br />
could be used in the selection of <strong>ATF</strong> technology if it is deemed necessary to lower the<br />
concentration of those most influential compounds to meet the permit limits.<br />
The interim <strong>ATF</strong>s were able to control the emission of H 2 S and TNMHC to their individual<br />
permit limits at all locations with the exception of the Humboldt interim <strong>ATF</strong>. The concentration<br />
of TNMHC in the exhaust stream was measured at 18.4 parts per million as carbon (ppmC). This<br />
exceeded the permit limit of 18 ppmC. The Technical Memorandum states that the relatively<br />
high exhaust concentration was likely due to the fact that the carbon was spent, which means that<br />
it was past the end of its useful life. This is a reasonable conclusion since the other interim <strong>ATF</strong>s<br />
sampled were able to adequately control the TNMHC emissions to levels below the permit<br />
limits. Simply installing fresh carbon should allow the Humboldt interim <strong>ATF</strong> to meet the permit<br />
limit.<br />
A handheld PID was used to sample the sewer air to determine if that type of device could be<br />
used to measure TNMHC concentrations rather than the more cumbersome SCAQMD method<br />
25.3. The handheld PID would have the advantage of providing almost instantaneous values at<br />
the <strong>ATF</strong> locations, whereas the SCAQMD method requires that samples be taken to a laboratory<br />
for analysis and it can take weeks to obtain results. Unfortunately, the information from the two<br />
methods compared poorly so it is not likely that use of the PID will provide its desired advantage<br />
unless a suitable correction factor could be used to convert the PID readings. The SCAQMD<br />
would have to accept such a methodology.<br />
General Remarks on the TNMHC <strong>Study</strong><br />
The City conducted a substantial effort and developed an understanding of the types and<br />
concentrations of pollutants that are treated by the interim <strong>ATF</strong>s that have been installed for odor<br />
control. Because the SCAQMD places permit limits on the emission of TNMHC and hydrogen<br />
sulfide, the City monitored the inlet and outlet airstreams of the existing interim <strong>ATF</strong>s. It was<br />
shown that these current systems, based on carbon bed scrubbers, can be effective in meeting the<br />
permit requirements.<br />
The monitoring and analysis did show that there were some organic compounds that influence<br />
the TNMHC concentrations but do not contribute to O 3 production in the atmosphere, which is<br />
what the permit limit is intended to prevent. However, this influence was slight and will not<br />
likely change the requirement to limit the TNMHC emissions.<br />
The interim <strong>ATF</strong>s were shown to be capable of removing pollutants with sufficient efficiency to<br />
meet their permit requirements. This is not to say that the currently installed interim <strong>ATF</strong>s have<br />
provided adequate relief from odor impacts on the community, but only that the permit<br />
conditions can be met. In one case the permit limit for TNMHC was exceeded and was likely due<br />
to the need for new carbon. In a similar manner, hydrogen sulfide and other odorous compounds<br />
can be emitted if the carbon in these devices is not changed with adequate frequency.<br />
11
A handheld PID was tested as a simple means of determining TNMHC concentrations. The<br />
initial conclusion of the draft TNMHC Technical Memorandum was that the PID was not likely<br />
an adequate tool for determining permit compliance. However, the final version raises the<br />
possibility of using a PID with an appropriate calibration curve that would allow the instrument’s<br />
output to be correlated to SCAQMD Method 25.3 results, but it also recommends further work to<br />
determine if this is feasible and that an alternative but unnamed hand-held device may provide<br />
better service.<br />
The City was able to gain some useful information regarding the composition of the sewer air<br />
and the various testing methods for organic air pollutants and TNMHC concentrations that are<br />
available. It also verified that the interim <strong>ATF</strong> carbon bed scrubber technology was adequate for<br />
meeting its current permit limits.<br />
Air Treatment Facility <strong>Study</strong><br />
The Air Treatment Facility Technical Memorandum (<strong>ATF</strong> Tech Memo) was produced to justify<br />
the selection of future <strong>ATF</strong> locations, technologies, and foul air treatment volumes. The <strong>ATF</strong><br />
Tech Memo is based on the earlier work (and related technical memoranda) on sewer drop<br />
structure air pressure studies, airflow modeling, and analytical testing of non-methane<br />
hydrocarbons and inorganic odorous compounds such as hydrogen sulfide (H 2 S), all of which<br />
comprise the broader <strong>ATF</strong> Review <strong>Study</strong> and are discussed in detail above.<br />
Under the original CSSA, the City had planned to construct seven new <strong>ATF</strong>s to help control<br />
odors from the wastewater conveyance system. Of these seven, two have almost been completed,<br />
but design and construction of the remaining five was placed on hold pending the outcome of the<br />
City’s <strong>ATF</strong> Review. The City has continued to treat foul air from the sewers with interim <strong>ATF</strong>s<br />
based on carbon filtration while the <strong>ATF</strong> Review has been conducted. As a result of the work,<br />
the City is recommending proceeding with only one of the originally planned but yet un-built<br />
<strong>ATF</strong>s.<br />
Field Testing of Sewer Air Pressure<br />
The City has conducted what could be considered a very large scale set of tests to characterize<br />
the air pressure within its sewer system in its study on differential air pressure at drop structures.<br />
In that study the City conducted measurements on sewer air pressure to determine how it was<br />
influenced by the changing of wastewater flows through and around drop structures, installation<br />
of airflow blocking devices in and near drop structures, and the operation of existing interim<br />
<strong>ATF</strong>s. The pressure data collected provided some insight to how each of these influenced air<br />
pressure in and around the drop structures. While the City was able to draw some general<br />
conclusions about how each of these might influence air pressures, there was no one clear<br />
solution that would lower sewer air pressure to the point that odor emissions would be<br />
completely eliminated. This should not be viewed as an unreasonable result. Due to the complex<br />
network of sewer connections and the dynamic character of wastewater flow, air pressures vary<br />
widely and significantly within sewers. It would indeed be the rare case where any sewer<br />
operator could completely eliminate the potential for odor emissions.<br />
12
Sewer Airflow Modeling<br />
The City developed a model to estimate where odor emissions from the sewers might occur. The<br />
model used by the City to predict wastewater flows was used to estimate the velocity and depth<br />
of water in connecting segments of the sewers. Based on the information provided by this model,<br />
a second model was developed to predict where changes in the air space geometry from one<br />
segment to another indicated a reduction in the amount of air that could be conveyed from an<br />
upstream to a downstream segment. Where this occurred, the potential for odor emission was<br />
predicted. This was a reasonable method of arriving at a first estimate of odor emission locations.<br />
That said, the modeling of airflow in sewers and the points of emissions has proven to be<br />
difficult and, at best, only a rough estimate of each can be expected.<br />
The odor emission locations were overlaid on a map in the <strong>ATF</strong> Tech Memo with the location of<br />
odor complaints received between the months of October 2008 to September 2009. There<br />
appeared to be some correlation between the predicted points of emissions and the registered<br />
odor complaints. However, not all clusters of complaints corresponded to predicted emission<br />
points. Also, it is not possible to show how all real odor emissions and impacts correlate to the<br />
predicted emission points because not all true impacts result in complaints formally registered<br />
with the City.<br />
<strong>ATF</strong> Locations Recommendations<br />
Based on the results of the airflow modeling discussed above, the City developed<br />
recommendations on the methods of reducing air pressure within the various sewers in the<br />
vicinity of drop structures. Of the four <strong>ATF</strong>s originally recommended for installation at drop<br />
structures, only the <strong>ATF</strong> at the Mission and Jesse site is now being recommended for<br />
construction by the City. No mention of the originally planned <strong>ATF</strong> at NORS/ECIS is made in<br />
the draft <strong>ATF</strong> Tech Memo.<br />
In addition to the <strong>ATF</strong> at the Mission and Jesse site, modifications in the drop structures and<br />
adjacent sewers are being recommended. These include the use of flow diversion devices known<br />
as stop logs to modify the flow patterns in the sewers to minimize pressure in and around the<br />
drop structures. They also include the installation of airflow prevention devices that would be<br />
installed in the drop structure air return lines and plastic curtains in the sewers to prevent<br />
pressurization of the air spaces downstream of the drop structures.<br />
The <strong>ATF</strong> Tech memo also recommends that air pressure tests be conducted in the sewer in the<br />
vicinity of the newly constructed <strong>ATF</strong> treating air from the East Central Interceptor Sewer<br />
(ECIS) Jefferson Siphon. It is further recommended that if the operation of that <strong>ATF</strong> does not<br />
result in satisfactory pressure reductions along the North Outfall Relief Sewer (NORS) that the<br />
city should initiate a fan test along the NORS between the siphon at the Fox Hills Mall and the<br />
Culver City Park. The purpose of that test would be to determine how much air would need to be<br />
extracted from the NORS to reduce the air pressure within the sewer and thereby control odor<br />
emissions.<br />
13
Determining <strong>ATF</strong> Airflows Required to Control Odor Emissions<br />
The <strong>ATF</strong> Tech Memo projects that it would be necessary to extract 20,000 cubic feet per minute<br />
(cfm) of air at Mission and Jesse to lower sewer air pressure and control odors at that location. It<br />
further recommends that the City conduct airflow tests on a scale model of a sewer drop structure<br />
in its hydraulics laboratory to better estimate the actual airflow necessary. This should provide a<br />
deeper understanding of what <strong>ATF</strong> airflows would be required and result in a more efficient <strong>ATF</strong><br />
design to be developed. At this writing the City is modifying a physical scale model of a drop<br />
structure in its hydraulics laboratory to conduct this testing.<br />
Identification of Air Emission Control Technologies<br />
The <strong>ATF</strong> Tech Memo describes commonly applied air pollution control devices used for<br />
controlling wastewater odors. Using the information gained in the TNMHC study, the City<br />
evaluated the ability of various air emission control technologies to control odors from the<br />
wastewater conveyance system. With the exception of biotrickling filters and carbon adsorbers,<br />
all of the technologies are eliminated from consideration as viable for the normally unstaffed<br />
wastewater conveyance facility locations such as the Mission and Jesse site.<br />
Recommendations of the <strong>ATF</strong> Tech Memo<br />
The ultimate recommendation set forth in the <strong>ATF</strong> Tech Memo is that a combination of a<br />
biotrickling filter and a carbon adsorber be used to control odors from the Mission and Jesse drop<br />
structure and surrounding sewers near that location. Information in the <strong>ATF</strong> Tech Memo<br />
indicates that high levels of hydrogen (H 2 S) sulfide gas can be present in the foul air from this<br />
part of the sewer. A biotrickling filter should be capable of removing virtually all of H 2 S from<br />
the foul air stream. Use of a carbon adsorber to remove most of the residual odors that are not<br />
removed by the biotrickling filter should provide very good control of odors that are introduced<br />
to the <strong>ATF</strong>.<br />
General Remarks on the <strong>ATF</strong> Tech Memo<br />
The City’s engineering team has developed recommendations to construct one additional <strong>ATF</strong> at<br />
Mission and Jesse. Odor control technologies and methods for estimating foul air treatment<br />
volumes are also recommended for that single location that should provide good odor control<br />
based on the City’s findings and assumptions are correct. Of the remaining four sites originally<br />
proposed for <strong>ATF</strong>s, it has been recommended that only wastewater flow patterns be modified<br />
and air flow prevention devices be placed in the sewers to prevent the build-up of high air<br />
pressures.<br />
With the information assembled by the City’s team, it is not possible to definitively state that the<br />
reduced number of <strong>ATF</strong>s, changes to wastewater flow patterns, and installation of airflow<br />
prevention devices will or will not adequately control odors from the sewers. One could not<br />
make such a definitive statement even if all five of the originally proposed <strong>ATF</strong>s were<br />
determined to be necessary by the City’s team. The state of the art of odor control from sewers is<br />
not yet sufficient to make such strong conclusions even with the large amount of information and<br />
knowledge gained in the process of the City’s <strong>ATF</strong> Review <strong>Study</strong>. However, it would be safe to<br />
14
say that five well designed, carefully located and adequately maintained <strong>ATF</strong>s would provide<br />
better odor control than a single <strong>ATF</strong>.<br />
The City has constructed and is near final completion of <strong>ATF</strong>s at Jefferson and La Cienega and<br />
6000 Jefferson. The City’s team has recommended that sewer air pressure monitoring be<br />
conducted after these are completed to determine air pressures along the North Outfall Relief<br />
Sewer. This would be a prudent course of action to determine how much the high air pressures<br />
have been relieved in that sewer and how far away from the <strong>ATF</strong> the air pressures remain<br />
acceptably low within the sewer. It would also be prudent to measure air pressures in the sewers<br />
connected to the new <strong>ATF</strong>s to obtain additional knowledge that could be used in the design of<br />
future <strong>ATF</strong>s.<br />
Of the seven originally proposed conveyance system <strong>ATF</strong>s, two are nearing completion and one<br />
is being proposed. It will be possible to determine if these are adequate to control odors that have<br />
been impacting the surrounding communities after they are fully operational. Typical public<br />
works projects in the size range of the <strong>ATF</strong> design and installation can be expected to take<br />
between three and five years to move from initial authorization to completion. Because these<br />
timelines can be considered long, the City should move with forward soon with design and<br />
installation of the recommended <strong>ATF</strong> at the Mission and Jesse site. With the completion of the<br />
two newly constructed <strong>ATF</strong>s, the City should quickly test how the airflow extracted from the<br />
sewers influences pressures in the conveyance system.<br />
Recommendations of the <strong>ATF</strong> Review <strong>Study</strong> Draft <strong>Final</strong> <strong>Report</strong><br />
The <strong>ATF</strong> Review <strong>Study</strong> Draft <strong>Final</strong> <strong>Report</strong> (<strong>Report</strong>) pulls together the findings of and makes<br />
recommendations based upon the previously discussed airflow modeling, drop structure, siphon,<br />
TNMHC, and <strong>ATF</strong> technical memorandum. The most significant recommendation set forth in<br />
the <strong>Report</strong> is that of the seven originally planned <strong>ATF</strong>s four will not be built. These were at the<br />
drop structures located at Division, Humboldt, Richmond and 23 rd & San Pedro. The City’s<br />
justification for building only an <strong>ATF</strong> at the Mission and Jesse site is that it is the drop structure<br />
through which the NEIS/ECIS tunnel appeared to relieve pressure back into the NOS.<br />
The installation of the <strong>ATF</strong> at the Mission & Jesse site would likely not be sufficient in and of<br />
itself to alleviate odor emissions from the drop structure and the connecting sewers.<br />
Modifications to the drop structure are also being recommended to prevent air from being carried<br />
away from the structure by the flowing wastewater and to allow the interim and future <strong>ATF</strong> to<br />
efficiently capture foul air from the structure. Plastic curtains are recommended to prevent<br />
airflow from the bottom of the drop structure into the downstream NEIS. A damper at the top of<br />
the drop structure air return line will prevent the air movement induced by the water falling in<br />
the drop structure to pressurize the upstream NOS. A new foul air pick-up point that is being<br />
recommended at the bottom of the drop structure will, in conjunction with the damper, allow the<br />
<strong>ATF</strong> to efficiently capture air from the structure. <strong>Final</strong> decisions regarding these recommended<br />
modifications will be made by the City with information obtained from testing water and airflow<br />
in a scale model drop structure in its hydraulics laboratory.<br />
Changes to wastewater flow patterns in the NOS and NEIS are also being recommended. The<br />
City found that air pressures were lower when more of the wastewater was allowed into the NOS<br />
past the Division, Humboldt and Richmond drop structures and into the ECIS through the drop at<br />
15
Mission & Jesse. Removing stop logs in the diversion structures to accomplish this has been<br />
recommended. This would seem a reasonable conclusion based on what is known about the<br />
airflow and pressurization dynamics in and around drop structures. The recommendation has<br />
been made to revisit these conclusions after the physical testing of the drop structure testing in<br />
the City’s hydraulics laboratory.<br />
General Remarks and Conclusions of the Independent Odor Expert<br />
The City of Los Angeles Bureau of Sanitation has undergone a large study of the cause of odor<br />
emissions from its wastewater conveyance system. Conclusions have been drawn based on air<br />
pressure data gathered during physical manipulation of the system to change wastewater flow<br />
patterns and change potential airflow pathways in the sewers. Computer modeling based on<br />
wastewater flow and sewer geometry has been conducted to estimate where airflow restrictions<br />
could cause the air to be pressurized and emitted to the neighborhoods above the sewers. Foul air<br />
testing has been conducted to determine the chemical species that need to be controlled by air<br />
treatment facilities. Studies of this breadth and depth are indeed rare and can yield good<br />
information regarding the cause and effects of odor emissions and impacts. However, the state of<br />
the art in modeling of airflow dynamics in sewers will only allow for general conclusions to be<br />
drawn on results that lie within a broad range of accuracy. There is much art left in the science of<br />
wastewater conveyance system odor control and solutions must still be made based on inference<br />
by those with real world experience and knowledge based on past successful and unsuccessful<br />
attempts to control sewer odor emissions and impacts.<br />
The City’s plan forward is to complete the two <strong>ATF</strong>s currently under construction at Jefferson<br />
and La Cienega and at 6000 Jefferson and to construct only one of the originally recommended<br />
five additional <strong>ATF</strong>s. Given the information provided in the <strong>ATF</strong> study technical memorandums<br />
on the various studies this does not appear to be an unreasonable approach. However, as<br />
mentioned above, because these conclusions are based on a range of accuracy is very broad, only<br />
the installation and operation of these improvements will allow the neighbors and the City to<br />
determine if they will be successful in preventing odor impacts in the community. With the full<br />
scale operation of the two <strong>ATF</strong>s currently in construction, the community should soon be able to<br />
determine if these projects will provide relief from sewer odors. It remains to be seen if these<br />
efforts will be sufficient or if additional measures will be required to provide the community<br />
with sufficient relief from sewer odors.<br />
16
Technical Memorandum - FINAL<br />
Team<br />
City of Los Angeles<br />
Department of Public Works<br />
Bureau of Sanitation<br />
Air Treatment Facility (<strong>ATF</strong>) Review <strong>Study</strong><br />
AIRFLOW MODELING STUDY<br />
FINAL<br />
November <strong>2010</strong><br />
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Table of Contents<br />
Executive Summary ...................................................................................................................... 4<br />
1.0 Scope and Objectives ........................................................................................................ 4<br />
2.0 Approach ............................................................................................................................ 7<br />
3.0 Background ........................................................................................................................ 7<br />
3.1 Existing Hydraulic Model – MIKE URBAN and MIKE View ............................................ 7<br />
3.2 Need for Customized Airflow Model Development ......................................................... 7<br />
4.0 Airflow Modeling ................................................................................................................. 7<br />
4.1 Methodology ................................................................................................................... 7<br />
4.2 Model Assumptions & Limitations ................................................................................. 12<br />
5.0 Model Verification ............................................................................................................. 12<br />
5.1 Analysis of Current Conditions ..................................................................................... 12<br />
5.2 Field Data Collection .................................................................................................... 14<br />
5.3 Discussions .................................................................................................................. 16<br />
6.0 Analysis ............................................................................................................................ 18<br />
6.1 Estimated Airflow Rates ............................................................................................... 18<br />
6.1.1 Scenario 1: Current System Flow ............................................................................... 19<br />
6.1.2 Scenario 2: Flow Diversion from NORS to NOS ......................................................... 20<br />
6.1.3 Scenario 3: Flow Diversion of 30 cfs from NOS to COS ............................................. 21<br />
6.2 Area of Concern Location Identifications ...................................................................... 22<br />
7.0 Conclusions ...................................................................................................................... 24<br />
List of Tables<br />
Table 1 – Implemented Air-to-Wastewater Velocity Ratios ........................................................... 8<br />
Table 2 – Computed Airflow Capacity Differentials for Selected Sampling Sites ....................... 13<br />
Table 3 - Air Differential Pressure Data ...................................................................................... 16<br />
Table 4 – Estimated Airflow Flow Rate Summary ....................................................................... 19<br />
Table 5 - Estimated Airflow Flow Rate Summary ....................................................................... 20<br />
Table 6 - Estimated Airflow Flow Rate Summary ....................................................................... 21<br />
Table 7 – Model Predicted Areas of Concern for Current System (Scenario 1) ......................... 22<br />
Table 8 – Additional Areas of Concern for Scenario 2 & Scenario 3 .......................................... 23<br />
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List of Figures<br />
Figure 1 - System Map .................................................................................................................. 6<br />
Figure 2 - OPTools Startup GUI .................................................................................................. 10<br />
Figure 3 - OPTools Scenario Manager ....................................................................................... 10<br />
Figure 4 – Selected Sampling Sites for Airflow Model Verification ............................................. 13<br />
Figure 5 – Photo for Site 1 .......................................................................................................... 14<br />
Figure 6 – Photo for Site 2 .......................................................................................................... 14<br />
Figure 7 - Photo for Site 3 ........................................................................................................... 14<br />
Figure 8 - Photo for Site 6 ........................................................................................................... 14<br />
Figure 9 - Photo for Site 5 ........................................................................................................... 15<br />
Figure 10 - Photo for Site 6 ......................................................................................................... 15<br />
Figure 11 - Air Differential Pressure Data ................................................................................... 16<br />
Figure 12 - Correlation between Model Results and Field Data ................................................. 17<br />
Figure 13 – Odor Area of Concern Location Map ....................................................................... 24<br />
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EXECUTIVE SUMMARY<br />
The City of Los Angeles has a long history of implementing proactive and innovative steps to<br />
control odors from its interceptor collection system including using chemical addition to control<br />
odors with an extensive use of magnesium hydroxide. Recently, the City has been working to<br />
improve odor control in several areas identified by local community groups. Air treatment<br />
facilities (<strong>ATF</strong>s) with known or predicted odor “areas of concern” were included in the 2004<br />
Collection<br />
System Settlement Agreement (CSSA).<br />
The Airflow Modeling Technical Memorandum provides documentation of the developed airflow<br />
model and presents the modeling results for the City’s current interceptor system configurations<br />
and the two planned wastewater flow diversion scenarios. The benefits of the airflow modeling<br />
study include supporting the findings in other studies and evaluating the impact of the identified<br />
future operational changes in terms of odor areas of concern. However, the airflow modeling<br />
results are not intended to be the sole material for the evaluations of the proposed <strong>ATF</strong>s and any<br />
recommendations for <strong>ATF</strong> installation. Based on the airflow modeling results, it is determined<br />
that:<br />
<br />
<br />
<br />
Under the current system configurations, nine areas of concern are predicted. These<br />
include five locations along the ECIS from downstream of the Mission and Jesse drop<br />
structure to upstream of the USC drop structure; the ECIS siphon at Jefferson Boulevard<br />
and La Cienega Boulevard; the NORS/ECIS Junction; the NCOS Siphon at I-405 and the<br />
NORS Siphon at I-405.<br />
With the additional flow diverted into the NOS from the NORS, the upstream end of the<br />
NOS siphon and the NOTF location are predicted to experience positive pressure buildup<br />
under the assumption that the NOTF <strong>ATF</strong> is currently not being run pending ongoing<br />
public involvement efforts;<br />
The diversion of 30 cfs from NOS to COS will not cause additional areas of concern in<br />
the study sewers. However, the addition of the wastewater flow in the COS may cause<br />
positive pressure buildup along the COS.<br />
1.0 SCOPE AND OBJECTIVES<br />
For the purposes of this technical memorandum, an odor “area of concern” is defined as a<br />
location in the wastewater collection systems where airflow bottleneck occurs in the sewer pipe<br />
headspace. Past experience has shown that these locations are typically the primary cause of<br />
positive differential air buildup in large diameter gravity pipe sewer systems. Positive differential<br />
air pressure buildup results in the release of odorous air to atmosphere, thereby resulting in odor<br />
complaints.<br />
The scope of the airflow modeling study is to identify the odor areas of concern under current<br />
conditions and examine the impact of the two planned wastewater flow diversion scenarios as<br />
follows:<br />
1. Flow diversion from NORS back to NOS<br />
2. Flow diversion of 30 cubic feet per second (cfs) from NOS to COS.<br />
Based on the scope, the interceptor sewers to be analyzed include ECIS, LCIS, LCSFVRS,<br />
NCOS, NEIS, NORS, NOS, WHIS, W<strong>LA</strong>IS, and WRS. Figure 1 shows the locations of the study<br />
area and the study sewers. The analyzed interceptor sewers included approximately 1,100 pipe<br />
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segments, in which 60 % of the segments have circular cross sections and the remaining segments<br />
have other cross sections such as rectangular ones or semi-elliptical ones.<br />
In order to satisfy the requirements of the study scope, the principal objectives of this study are<br />
determined to be:<br />
1. Developing an airflow model with capabilities to identify odor areas of concern;<br />
2. Utilizing the developed airflow model to perform analysis for the current system<br />
conditions and the two aforementioned planned flow diversion scenarios.<br />
It should be noted that the developed airflow model is not intended to model air differential<br />
pressure by any means but to identify the odor areas of concern only.<br />
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Figure 1 - System Map<br />
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2.0 APPROACH<br />
In order to achieve the first study objective, i.e. developing an airflow model, a conceptual<br />
airflow modeling methodology was established to form the core of the airflow model. A<br />
customized computer program was then implemented using the modeling methodology. Lastly,<br />
an airflow model was developed using the data representing the desired conditions. To confirm<br />
the usefulness of the model for this particular system, the model results were compared with some<br />
field data which were collected in the study system.<br />
With the aim of accomplishing the second objective, the developed airflow model was prepared<br />
and run for the three desired scenarios. It is expected that the model results can be used to identify<br />
the odor areas of concern for the study system.<br />
3.0 BACKGROUND<br />
3.1 Existing Hydraulic Model – MIKE URBAN and MIKE View<br />
The City uses MIKE URBAN to evaluate the hydraulic capacities in the existing interceptor<br />
system, so as to evaluate the needs for capital improvements, and analyze the hydraulic effects of<br />
operational changes. MIKE URBAN is a hydraulic modeling software package that is created by<br />
DHI Water and Environment (DHI) and is considered as a fully dynamic model for simulating<br />
sanitary sewer flows. It is capable of simulating complex hydraulics in wastewater collection<br />
systems, including back water effects. Similar to other dynamic models, MIKE URBAN can<br />
produce time series flow, depth and velocity information in the simulation results.<br />
MIKE View is a visualization tool developed by DHI for model results from its hydraulic<br />
modeling software packages including MIKE URBAN. It is a freeware and the user can<br />
download the installation file directly from DHI’s website. This cost free option is particularly<br />
useful for anyone who only needs to review or use the model results for any purpose. In order to<br />
review the MIKE URBAN model results in MIKE View, one simply imports the MOUSE result<br />
file where all the time series data are stored.<br />
3.2 Need for Customized Airflow Model Development<br />
MIKE URBAN does not have built-in capabilities of modeling airflow and predicting odor areas<br />
of concern for wastewater collection systems. In order for the City to model these effects in the<br />
Los Angeles interceptor system, a customized tool needed to be developed.<br />
4.0 AIRFLOW MODELING<br />
4.1 Methodology<br />
In order to identify the locations in the sewer system with potential for odor complaints referred<br />
to herein as odor “areas of concern”, a customized computer program called OPTools (Odor<br />
Predictive Tools) was developed as a part of this study. The program uses empirical surface drag<br />
equations to estimate air flow capacities in the sewer headspace, and calculates the difference in<br />
airflow capacities for consecutive sewer segments to identify locations with potential for positive<br />
air pressure buildup.<br />
The hypotheses in this modeling methodology are that:<br />
1. A decrease in the airflow capacity from one segment to the next creates a situation for<br />
positive air pressure build up in the sewer;<br />
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2. The higher the decrease in airflow capacity from one segment to the next should result in<br />
a higher positive pressure build up between the two segments.<br />
The above hypotheses are intuitive because the incoming air from the upstream segment cannot<br />
be conveyed through the downstream segment by means of drag forces alone and therefore<br />
requires a pressure buildup to assist in its conveyance.<br />
Airflow capacity was calculated as headspace cross sectional area multiplied by airflow velocity.<br />
Equation (1)<br />
<br />
The Headspace Cross Sectional Area was calculated as the difference between the pipe cross<br />
sectional area and the wastewater flow area, which were calculated based on the imported sewer<br />
network and hydraulic output information.<br />
In a partially full gravity sewer, Air Velocity was assumed to be induced entirely by surface drag<br />
forces that occurs at the air-water interface from the wastewater flow and was estimated to be a<br />
certain fraction of the sewer flow velocity, depending on the water depth ratios (d/D). This<br />
approach ignored the pressure head differential effect in the headspace and the effect of sewer<br />
pipe roughness and therefore some differences between modeled and actual headspace airflows<br />
may occur.<br />
Table 1 summarizes the air-to-water velocity ratios at given wastewater depth ratio ranges which<br />
were implemented in the OPTools for the circular cross sections, the semi-elliptical cross<br />
sections, and the Burns-McDonnel cross sections. These air-to-water velocity ratios were<br />
determined based on the previous field experience obtained during the previous projects with the<br />
City. During the previous projects with the City, the same ratios were successfully applied to<br />
estimate airflow for several gravity interceptors that are currently being ventilated, including the<br />
NCOS upstream of the Jefferson Siphon and two locations on the LCSFVRS; an upstream<br />
location at Sierra Bonita in West Hollywood and a downstream location at the Genesee Siphon.<br />
A constant air-to-water velocity ratio of 0.35 was applied to rectangular cross sections and other<br />
special cross sections, including arch shapes, elliptical shapes and pipes with known sediment<br />
deposits. This is deemed to be a reasonable assumption given a limited amount of supportive field<br />
experience with such cross sections.<br />
Table 1 – Implemented Air-to-Wastewater Velocity Ratios<br />
OPTools<br />
Air/Wastewater Velocity Ratios for<br />
Circular, Semi-Elliptical, and Burns-McDonnel Cross Sections<br />
Depth Ratio (d/D)<br />
Air/Wastewater Velocity Ratio<br />
Less than 0.1 0.15<br />
Between 0.1 and 0.2 0.25<br />
Between 0.2 and 0.48 0.35<br />
Between 0.48 and 0.75 0.6<br />
Between 0.75 and 0.85 0.35<br />
Larger than 0.85 0.15<br />
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The change in airflow capacity is termed “Airflow Capacity Differential” (ACD) given by:<br />
Equation (2)<br />
<br />
<br />
As shown in Equation 2, Airflow Capacity Differential at any given point in the modeled<br />
interceptor system is computed as the difference between the cumulative incoming airflow<br />
capacity and the airflow capacity in the downstream pipe. It should be noted that all the model<br />
nodes were assumed to be fully sealed and therefore there is no term accounting for the airflow<br />
exchange with the external atmosphere in the Equation 2.<br />
A decrease in airflow flow capacity or a positive ACD value indicates that the downstream pipe<br />
has insufficient capacity to convey the incoming airflow, resulting in positive pressure buildup.<br />
Conversely, a negative ACD value implies a potential negative pressure location.<br />
With the introduction of the term “Airflow Capacity Differential” or “ACD”, the study<br />
hypotheses can be restated as follows:<br />
<br />
<br />
A positive Airflow Capacity Differential or ACD results in positive air pressure in the<br />
sewer;<br />
The higher the Airflow Capacity Differential or ACD, the higher the positive pressure<br />
buildup potential will be.<br />
Given the approximate nature of the calculations, computed Airflow Capacity Differential less<br />
than 2,000 cubic feet per minute (cfm) were not taken as being significant with regards to<br />
potential for positive pressure buildup. Therefore a threshold value of 2,000 cfm was used for<br />
identifying odor areas of concern. With this approach, all the pipes with computed Airflow<br />
Capacity Differential of more than 2,000 cfm were identified as potential odor area of concern<br />
locations.<br />
Airflow Capacity Differential was calculated at the upstream ends of the sewer pipe segments.<br />
The computer program developed to perform the calculations, OPTools, received input data from<br />
MIKE URBAN and MIKE View. Two sets of data sources were required to perform the<br />
calculations. These were the sewer network data set and the hydraulic output data set. The sewer<br />
network data set contains attributes specifically for the sewer pipes, including pipe identifiers,<br />
upstream and downstream node identifiers, pipe geometry data, etc. This information was<br />
imported from the MIKE URBAN models. The hydraulic output data set included wastewater<br />
depths, wastewater velocities, and wastewater flows. This information was imported from the<br />
MIKE View models.<br />
A graphical user interface (GUI) was developed which allows the user to load input data, run case<br />
scenarios, and view, export or print the outputs. Optionally, the output can be linked with<br />
Geographic Information System (GIS) to present the results graphically. Figure 2 and Figure 3<br />
depict the GUIs of OPTools. In the back end, OPTools uses Microsoft Access 2003 as its<br />
database engine to store the data.<br />
A user guide that comes with the OPTools installation has been created and will be made<br />
available for step-by-step instructions.<br />
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Figure 2 - OPTools Startup GUI<br />
Figure 3 - OPTools Scenario Manager<br />
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4.2 Model Assumptions & Limitations<br />
The following assumptions and limitations are inherent in the above-described modeling<br />
methodology used in this study. For each assumption, an explanation of the related model<br />
limitations is included.<br />
1. The computed airflow capacities are estimates. This could lead to some differences<br />
between modeled and actual headspace airflows.<br />
2. The model does not account for any active or passive <strong>ATF</strong> or passive air line ventilation<br />
effects. Therefore, the number of resultant area of concern locations may be conservative;<br />
3. In identifying the areas of concern, the approach does not account for any backpressurization<br />
effects from headspace airflow constrictions such as siphons, drop<br />
structures, diameter reductions, slope reductions, or junction structures. The model will<br />
predict the locations in the interceptor system where airflow obstructions are most likely<br />
to occur (i.e., the locations of the source of positive differential air pressure buildup).<br />
In order to identify the zones of influence of the <strong>ATF</strong>s and the back pressure effects from the<br />
downstream headspace airflow obstructions, some field pressure testing can be performed to<br />
compensate for the model limitations in identifying odor areas of concern.<br />
5.0 MODEL VERIFICATION<br />
5.1 Analysis of Current Conditions<br />
In order to develop confidence in the ability of the model to identify odor areas of concern, the<br />
OPTools program was run to identify locations of significant positive Airflow Capacity<br />
Differential in the system. According to the hypothesis of the aforementioned airflow modeling<br />
methodology, we should measure a corresponding positive sewer air pressure at these locations.<br />
Moreover, we expect there to be a positive correlation between the Air Capacity Differential and<br />
the measured sewer air pressure.<br />
The OPTools run used the sewer network and hydraulic information, which were extracted from<br />
the City MIKE URBAN export file and the MIKE View model representing the current system<br />
configurations. A 24-hour model run in 15-minute time steps, representing a typical weekday<br />
condition, was performed for the following sewers:<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
ECIS<br />
LCIS<br />
LCSFVRS<br />
NCOS<br />
NEIS<br />
NORS<br />
NOS<br />
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WHIS<br />
W<strong>LA</strong>IS<br />
WRS.<br />
Based on the model results, six locations, including two on NOS, two on WHIS, one on W<strong>LA</strong>IS,<br />
and one on WRS, were identified to have positive Airflow Capacity Differentials though their<br />
computed Airflow Capacity Differentials are distinctively different. These locations were<br />
subsequently chosen to be the sampling sites to verify the hypothesis made in the modeling<br />
methodology. Figure 4 shows the locations of the locations where air pressure sampling was<br />
performed. The computed Airflow Capacity Differentials and pertinent information for these sites<br />
are summarized in Table 2.<br />
Figure 4 – Selected Sampling Sites for Airflow Model Verification<br />
Table 2 – Computed Airflow Capacity Differentials for Selected Sampling Sites<br />
Site No. Model Pipe ID Model<br />
Upstream<br />
Node ID<br />
Interceptor<br />
Name<br />
Computed<br />
Average 1<br />
ACD (cfm)<br />
Computed<br />
Maximum 2<br />
ACD (cfm)<br />
Computed<br />
Minimum 3<br />
ACD (cfm)<br />
1 5630121556208053A 56301215 NOS 736 1193 134<br />
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2 5340714553407144A 53407145 W<strong>LA</strong>IS 560 869 133<br />
3 5340800653408024A 53408006 WRS 1440 1903 551<br />
4 5170217851702191A 51702178 WHIS 902 1045 577<br />
5 5180824451808167A 51808244 WHIS 864 1288 417<br />
6 5360903753609200A 53609037 NOS 782 1037 234<br />
Notes:<br />
1. The average ACD was based on all the ACD values calculated at 15-minute increment<br />
over the entire 24-hour model run<br />
2. The maximum ACD was calculated to be the highest ACD value over the entire 24-hour<br />
model run;<br />
3. The minimum ACD was calculated to be the lowest ACD value over the entire 24-hour<br />
model run;<br />
5.2 Field Data Collection<br />
Air differential pressures at the six locations were collected for two-weekday periods from 3/10 to<br />
3/12, <strong>2010</strong> at two-minute intervals. It should be noted that the data loggers were installed at six<br />
alternative maintenance holes, each of which are located immediately upstream of the originally<br />
selected maintenance holes due to accessibility reasons. This adjustment should not have a<br />
significant effect on the quality of the data collected for the purposes of this model verification<br />
effort.<br />
The data loggers used in the field are the SmartReader Plus 4 LPD, manufactured by ACR<br />
Systems. The operating ranges of these units are between 2.0 inch of water column and -2.0<br />
inches of water column according to the manufacturer’s specifications. Photos showing the<br />
vicinity of each sampling site are presented in Figures 5 to 10.<br />
Figure 5 – Photo for Site 1<br />
(Pershing Dr. North of Rees St.)<br />
Figure 6 – Photo for Site 2<br />
(Venice Blvd. and Overland Ave.)<br />
Figure 7 - Photo for Site 3 Figure 8 - Photo for Site 6<br />
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(Jasmine Ave. South of Regent St.)<br />
(Norton Ave South of 8 th St.)<br />
Figure 9 - Photo for Site 5<br />
(Venice Blvd. West of San Vicente Blvd.)<br />
Figure 10 - Photo for Site 6<br />
(Bronson Ave. South of 41 st St.)<br />
The collected air different pressure results were summarized in Figure 11 and Table 3.<br />
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Figure 11 - Air Differential Pressure Data<br />
Table 3 - Air Differential Pressure Data<br />
Location ID Maintenance<br />
Hole ID<br />
Average Pressure<br />
(in.wc)<br />
Max Pressure<br />
(in.wc)<br />
Min Pressure<br />
(in.wc)<br />
1 56301209 -1.62 -0.24 -2.37<br />
2 53407074 0.019 0.13 -0.19<br />
3 53404122 0.096 0.29 -0.02<br />
4 51702134 0.014 0.12 -0.03<br />
5 51705210 0.064 0.17 -0.04<br />
6 53609063 0.024 0.11 -0.18<br />
5.3 Discussions<br />
Figure 11 and Table 3 show that all the sampling sites except the site No. 1 have positive average<br />
and maximum differential air pressure over the sampling period. It is noted that the <strong>ATF</strong> at<br />
Hyperion is approximately 13,000 feet downstream of the sampling location No.1 and the <strong>ATF</strong> at<br />
the Hyperion wastewater treatment plant is running continuously throughout the year under<br />
normal conditions. Additionally, it is believed that the sewers are tightly sealed in the vicinity as<br />
they are elsewhere in the system. Therefore, the <strong>ATF</strong> at the Hyperion wastewater treatment plant<br />
is believed to be the cause of the negative pressure observed at the sampling location No. 1.<br />
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Therefore, the above results support the hypothesis that we can expect positive sewer air pressure<br />
in locations where positive airflow capacity differentials are calculated.<br />
In order to test the hypothesis that higher airflow capacity differentials correspond to higher<br />
positive differential air pressure, the computed airflow capacity differentials were plotted against<br />
the measured air differential pressure as shown in Figure 12. Because of the potential <strong>ATF</strong><br />
influence on sampling site No.1, that location is not included in this figure. As shown in Figure<br />
12, the field differential air pressure increases with the modeled differential airflow for site 2, 6, 5<br />
and 3 but not for site 4. It is suspected that the outside influences such as unknown ventilation in<br />
the vicinity could be the cause of the relatively low pressure observed at site 4.<br />
In order to verify and quantify the linearity between the two variables, a trend line along with the<br />
computed coefficient of determination (R 2 ) is generated using a linear regression function in<br />
Microsoft Excel 2007. As shown in Figure 12, a R 2 value of 0.69 was computed and it is deemed<br />
to be a reasonable indicator of the correlation and linearity between the computed airflow<br />
capacity differentials and the field air differential pressure. As a result, the higher differential air<br />
pressure potential would be expected at locations with higher airflow capacity differentials in the<br />
model.<br />
In summary, subject to the limitations described, the developed airflow model is considered to be<br />
an adequate tool for broadly locating odor area of concern in the sewer systems.<br />
Figure 12 - Correlation between Model Results and Field Data<br />
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6.0 ANALYSIS<br />
This section summarizes the analysis which was conducted using the airflow model, including the<br />
estimated airflow rates at several key locations and the area of concern identifications.<br />
Three wastewater flow scenarios were analyzed as listed below using the provided MIKE<br />
URBAN and the MIKE View models as the data sources.<br />
<br />
<br />
Scenario1: Current system configurations. The MIKE View model was calibrated based<br />
on the flow conditions in the summer moths of 2008. In this scenario, the NOS is dry<br />
from Diversion 2 downstream to just north of I-405;<br />
Scenario 2: Future flow diversion from NORS back to NOS at Diversion 2. The same<br />
dry weather wastewater flow conditions that were used in Scenario 1 were applied. Refer<br />
to Figure 1 for the location of Diversion 2.<br />
Scenario 3: Future flow diversion of 30 cubic feet per second (cfs) from NOS to COS.<br />
The same dry weather wastewater flow conditions as used in Scenario 1 were applied.<br />
Refer to Figure 1 for the location of the diversion weir. It should be noted that the flow is<br />
still being diverted into the NOS at Diversion 2 in this scenario.<br />
For each scenario, the airflow model was set up to run for a 48-hour period using typical weekday<br />
and weekend flows in 15-minute time intervals.<br />
6.1 Estimated Airflow Rates<br />
Airflow rate in the sewer headspace is one of the design criteria for any future <strong>ATF</strong> design. This<br />
section documents the estimated airflow rates at several locations listed below using the<br />
developed airflow model for each of the three flow scenarios.<br />
<br />
<br />
<br />
<br />
Upstream end of the NCOS siphon at the 405 freeway;<br />
Upstream end of the NORS siphon at the 405 freeway;<br />
Upstream end of the <strong>LA</strong> Cienega/Jefferson <strong>ATF</strong> on ECIS;<br />
Upstream end of the Division drop structure on ERIS (shallow approach interceptor<br />
sewer);<br />
Upstream ends of the Humboldt drop structure on both NEIS (deep tunnel) and NOS (<br />
shallow approach outfall sewer);<br />
<br />
<br />
<br />
Upstream ends of the Mission and Jesse drop structure on both NEIS (deep tunnel) and<br />
NOS (shallow approach outfall sewer);<br />
Upstream ends of the 23 rd and San Pedro drop structure on both ECIS (deep tunnel) and<br />
NOS (shallow approach outfall sewer);<br />
Upstream end of the USC drop structure on ECIS (deep tunnel)<br />
It should be noted that the reported airflow rates in this section were estimated solely based on the<br />
drag-induced airflow capacities as mentioned in Section 4.1. Because the airflow capacity<br />
calculation disregards ventilation effects from <strong>ATF</strong>s and air lines and pressure differential effects,<br />
the actual airflow rates in the field can differ from the estimated airflow rates presented herein.<br />
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6.1.1 Scenario 1: Current System Flow<br />
The estimated airflow rates for the current system configurations based on the provided MIKE<br />
View file are shown in Table 4. Note the estimated airflow rate values were rounded to the<br />
nearest hundred.<br />
Location<br />
Description<br />
US of NCOS<br />
Siphon at I-405<br />
US of NORS<br />
Siphon at I-405<br />
US of La<br />
Cienega/Jefferson<br />
<strong>ATF</strong> on ECIS<br />
US of Division<br />
on ERIS (surface<br />
channel)<br />
US of Humboldt<br />
on NEIS (deep<br />
tunnel)<br />
US of Humboldt<br />
on NOS (surface<br />
channel)<br />
US of M&J on<br />
NEIS (deep<br />
tunnel)<br />
US of M&J on<br />
NOS (surface<br />
channel)<br />
US of 23&SP on<br />
ECIS (deep<br />
tunnel)<br />
US of 23&SP on<br />
NOS (surface<br />
channel)<br />
US of USC on<br />
ECIS (deep<br />
tunnel)<br />
Table 4 – Estimated Airflow Flow Rate Summary<br />
for Current Conditions (Scenario 1)<br />
Model Pipe ID<br />
MIKE<br />
URBAN<br />
Average<br />
Wastewater<br />
Flow (cfs)<br />
Estimated<br />
Average<br />
Airflow<br />
(cfm)<br />
Estimated<br />
Maximum<br />
Airflow<br />
(cfm)<br />
Estimated<br />
Minimum<br />
Airflow<br />
(cfm)<br />
5590500455905005A 96.7 5,200 5,900 4,300<br />
5590500655905007A 318.6 10,500 14,400 8,300<br />
5350321353502178A 105.1 11,800 13,800 7,900<br />
4681215646816116A 5.4 600 900 500<br />
4950924349509244A 5.4 600 800 400<br />
4950911249509106A 22.7 1,600 1,700 1,000<br />
5150918751513122A 28.1 3,600 5,100 2,700<br />
5151312551513132A 19.5 1,000 1,100 700<br />
5370317753703203A 28.1 2,200 3,000 1,000<br />
5370319953703200A 51.4 4,100 4,400 2,700<br />
5370518053705183A 79.5 5,000 6,200 3,400<br />
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6.1.2 Scenario 2: Flow Diversion from NORS to NOS<br />
The estimated airflow rates for the scenario of diverting the wastewater flow back into the NOS<br />
from the NORS are presented in Table 5. Note the estimated airflow rate values were rounded to<br />
the nearest hundred. It is understood that this flow diversion affects mainly the wastewater flow<br />
in the NORS, which is downstream of the Diversion 2 structure. Comparing Table 4 and 5, the<br />
wastewater flow in the NORS at I-405 (pipe segment 5590500655905007A) dropped by<br />
approximately 35% from 318 cfs to 203 cfs, however, the estimated average airflow rate<br />
decreases only by approximately 10 % from 10,500 cfm to 9,400 cfm, which is considered<br />
insignificant.<br />
Location<br />
Description<br />
US of NCOS<br />
Siphon at I-405<br />
US of NORS<br />
Siphon at I-405<br />
US of La<br />
Cienega/Jefferson<br />
<strong>ATF</strong> on ECIS<br />
US of Division<br />
on ERIS (surface<br />
channel)<br />
US of Humboldt<br />
on NEIS (deep<br />
tunnel)<br />
US of Humboldt<br />
on NOS (surface<br />
channel)<br />
US of M&J on<br />
NEIS (deep<br />
tunnel)<br />
US of M&J on<br />
NOS (surface<br />
channel)<br />
US of 23&SP on<br />
ECIS (deep<br />
tunnel)<br />
US of 23&SP on<br />
NOS (surface<br />
channel)<br />
US of USC on<br />
ECIS (deep<br />
Table 5 - Estimated Airflow Flow Rate Summary<br />
for Flow Diversion from NORS to NOS (Scenario 2)<br />
Model Pipe ID<br />
MIKE<br />
URBAN<br />
Average<br />
Wastewater<br />
Flow (cfs)<br />
Estimated<br />
Average<br />
Airflow<br />
(cfm)<br />
Estimated<br />
Maximum<br />
Airflow<br />
(cfm)<br />
Estimated<br />
Minimum<br />
Airflow<br />
(cfm)<br />
5590500455905005A 103.4 7,200 7,400 6,700<br />
5590500655905007A 203.5 9,400 14,200 7,200<br />
5350321353502178A 129.8 12,400 14,100 8,400<br />
4681215646816116A 5.3 600 900 500<br />
4950924349509244A 5.3 400 800 200<br />
4950911249509106A 50.9 1,700 2,800 1,600<br />
5150918751513122A 56.2 4,900 5,300 3,100<br />
5151312551513132A 23.4 1,000 1,100 600<br />
5370317753703203A 56.2 3,600 5,200 1,400<br />
5370319953703200A 50.6 4,000 4,400 2,500<br />
5370518053705183A 106.9 6,000 7,500 4,800<br />
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tunnel)<br />
6.1.3 Scenario 3: Flow Diversion of 30 cfs from NOS to COS<br />
The estimated airflow rates for the scenario of diverting 30 cfs wastewater flow into the COS<br />
from the NOS are summarized in Table 6. Note the estimated airflow rate values were rounded to<br />
the nearest hundred.<br />
This flow diversion mainly reduces the wastewater flow in the NOS and the downstream NCOS.<br />
Because the diverted flow is marginal, the estimated airflow rate into the NCOS siphon is very<br />
similar to the one computed for the Scenario 2.<br />
Location<br />
Description<br />
US of NCOS<br />
Siphon at I-405<br />
US of NORS<br />
Siphon at I-405<br />
US of La<br />
Cienega/Jefferson<br />
<strong>ATF</strong> on ECIS<br />
US of Division<br />
on ERIS (surface<br />
channel)<br />
US of Humboldt<br />
on NEIS (deep<br />
tunnel)<br />
US of Humboldt<br />
on NOS (surface<br />
channel)<br />
US of M&J on<br />
NEIS (deep<br />
tunnel)<br />
US of M&J on<br />
NOS (surface<br />
channel)<br />
US of 23&SP on<br />
ECIS (deep<br />
tunnel)<br />
US of 23&SP on<br />
NOS (surface<br />
channel)<br />
US of USC on<br />
ECIS (deep<br />
tunnel)<br />
Table 6 - Estimated Airflow Flow Rate Summary<br />
for Flow Diversion of 30cfs from NOS to COS (Scenario 3)<br />
Model Pipe ID<br />
MIKE<br />
URBAN<br />
Average<br />
Wastewater<br />
Flow (cfs)<br />
Estimated<br />
Average<br />
Airflow<br />
(cfm)<br />
Estimated<br />
Maximum<br />
Airflow<br />
(cfm)<br />
Estimated<br />
Minimum<br />
Airflow<br />
(cfm)<br />
5590500455905005A 86.4 7,100 7,300 6,600<br />
5590500655905007A 201.1 9,400 14,000 7,400<br />
5350321353502178A 127.4 12,300 14,100 8,400<br />
4681215646816116A 5.3 600 900 500<br />
4950924349509244A 5.3 400 900 200<br />
4950911249509106A 49.0 1,700 1,700 1,600<br />
5150918751513122A 54.3 4,800 5,300 3,100<br />
5151312551513132A 22.9 1,000 1,100 600<br />
5370317753703203A 54.3 3,500 5,600 1,300<br />
5370319953703200A 50.1 4,000 4,400 2,500<br />
5370518053705183A 104.5 5,900 7,500 4,700<br />
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6.2 Area of Concern Location Identifications<br />
This section will discuss the model results related to the area of concern location predictions.<br />
As discussed in Section 4.1, all the pipes with a computed airflow capacity differential above<br />
2,000 cfm will be identified as the areas of concern by the airflow model. However, some of the<br />
areas of concern identified by the airflow model were filtered out manually based on some known<br />
system information. This primarily includes any pipes identified as area of concern candidates<br />
where <strong>ATF</strong> effects are known to be significant. This adjustment will avoid overly-conservative<br />
predictions.<br />
The following locations were identified to be odor area of concern candidates by the airflow<br />
model but were filtered out due to known <strong>ATF</strong> effects on the pipes. It should be noted that these<br />
locations can be potential odor areas of concern without the current <strong>ATF</strong>s near these locations as<br />
mentioned below in operation.<br />
<br />
<br />
<br />
<br />
Candidates on the LCSFVRS were disregarded due to the negative pressures<br />
currently induced on this pipe by the Genesee and Sierra Bonita <strong>ATF</strong>s;<br />
Candidates on the pipe segment upstream of the NCOS siphon on Rodeo Dr. just<br />
west of La Cienega were disregarded due to the temporary <strong>ATF</strong> that is<br />
withdrawing air from that pipe segment;<br />
Pipes that are within 2,000 ft of the <strong>ATF</strong> at the Hyperion WWTP were removed<br />
from the area of concern list. The pressure data collected during model<br />
verification at maintenance hole Site No. 1, which is approximately 13,000<br />
upstream of the WWTP, showed that location’s headspace to be under negative<br />
pressure;<br />
Pipes that are within 500 feet of the interim <strong>ATF</strong> at Rodeo Road and Martin<br />
Luther King Jr. Boulevard are removed from the area of concern list. It is<br />
assumed that this <strong>ATF</strong> keeps negative pressure in the upstream NOS and south<br />
branch NOS pipes.<br />
The area of concern locations for the current system (Scenario 1) are presented in Table 7. Note<br />
the reported airflow capacity differential values were rounded to the nearest hundred. In total,<br />
there are 9 locations where the airflow model predicts potential positive pressure buildup. As<br />
discussed in Section 4.1, airflow capacity differential is caused by insufficient downstream pipe<br />
airflow capacities. The potential causes of the insufficient downstream pipe capacities include<br />
diameter reduction, slope reduction, increase of wastewater flow, sudden headspace and velocity<br />
reduction due to back water effects, and/or siphons with undersized air jumper lines.<br />
Area of<br />
concern<br />
ID<br />
HS-1<br />
HS2<br />
Table 7 – Model Predicted Areas of concern for Current System (Scenario 1)<br />
Location Descriptions<br />
Immediately upstream of<br />
the 23 rd & San Pedro Drop<br />
Structure on ECIS<br />
Model Pipe ID/<br />
Upstream Node ID<br />
5370317753703203A<br />
53703177<br />
5370830353703177A<br />
53708303<br />
Computed<br />
Average<br />
ACD (cfm)<br />
Computed<br />
Maximum<br />
ACD (cfm)<br />
Computed<br />
Minimum<br />
ACD (cfm)<br />
2,600 3,400 1,700<br />
2,000 7,400 1,200<br />
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HS-3<br />
HS-4<br />
HS-5<br />
HS-6<br />
Downstream of the 23 rd &<br />
San Pedro Drop Structure<br />
on ECIS at 31 st St. and<br />
Trinity St.<br />
Upstream of the USC<br />
drop structure on ECIS<br />
on Exposition Blvd. just<br />
east of Figueroa St.<br />
Downstream of the<br />
Mission & Jesse Drop<br />
Structure on ECIS on<br />
Santa Fe Ave. just north<br />
of 8 th St.<br />
ECIS Siphon at Jefferson<br />
Blvd. and La Cienega<br />
Blvd.<br />
5370617853705181A<br />
53706178<br />
5370518753705180A<br />
53705187<br />
5151313553801134A<br />
51513135<br />
5350217853502178_<br />
DummyA<br />
53502178<br />
2,400 4,900 1,500<br />
4,100 5,900 3,100<br />
3,400 4,200 2,500<br />
3,200 3,800 2,400<br />
HS-7 NORS/ECIS Junction 5350902253509011A<br />
53509022<br />
HS-8 NCOS Siphon at I-405 55905005_55905005<br />
_Dummy_1<br />
55905005<br />
HS-9 NORS Siphon at I-405 55905007_Dummy55<br />
909301<br />
55905007_Dummy<br />
7,100 11,800 4,400<br />
2,500 3,100 2,000<br />
5,000 7,000 2,800<br />
Based on the model results for the Scenario 2, diverting flow from NORS back to NOS, all the<br />
areas of concern as predicted for the current system are still identified to be area of concern<br />
locations. In addition, a few more areas of concern are identified due to this flow diversion. The<br />
additional areas of concern are summarized in Table 8. Note the reported airflow differential<br />
values were rounded to the nearest hundred. As expected, the NOS siphon at I-405 is identified as<br />
a area of concern by the model. The NOTF location is included as one of the areas of concern<br />
under the assumption that the NOTF <strong>ATF</strong> is currently not being run pending ongoing public<br />
involvement efforts. It is believed that the two additional areas of concern on ECIS are caused by<br />
the increased wastewater flow in the ECIS.<br />
Area of<br />
concern<br />
ID<br />
HS-10<br />
HS-11<br />
Table 8 – Additional Areas of concern for Scenario 2 & Scenario 3<br />
Location Descriptions<br />
Downstream of the<br />
USC Drop Structure<br />
on ECIS on<br />
Exposition Blvd. just<br />
west of Arlington Ave.<br />
Immediately<br />
downstream of the<br />
NOTF on NOS<br />
Model Pipe ID/<br />
Upstream Node ID<br />
5360621753606219A<br />
53606217<br />
5350902053509017A<br />
53509020<br />
Computed<br />
Average<br />
ACD (cfm)<br />
Computed<br />
Maximum<br />
ACD (cfm)<br />
2,000 3,400 ‐800<br />
Computed<br />
Minimum<br />
ACD (cfm)<br />
3,300 3,800 2,000<br />
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HS-12 NOS Siphon at I-405 56008065_56008150<br />
_Dummy<br />
56008065<br />
HS-13<br />
Upstream of USC<br />
Drop Structure on<br />
ECIS on Grand Ave.<br />
just south of 35 th St.<br />
5370518153705188A<br />
53705181<br />
4,400 5,500 2,900<br />
2,100 3,100 ‐1,500<br />
For the Scenario 3, in general, the airflow model predicts similar results as the Scenario 2. All the<br />
areas of concern identified for the Scenario 2 are still identified to be potential areas of concern<br />
points in the system by the model.<br />
A map showing the locations of the thirteen areas of concern identified by the airflow model is<br />
shown in Figure 13.<br />
Figure 13 – Odor Areas of Concern Location Map<br />
7.0 CONCLUSIONS<br />
An airflow model was developed as a tool to compute airflow capacities in the sewer pipes and<br />
identify potential odor areas of concern for the wastewater collection systems. The developed<br />
airflow model leverages the existing City-owned hydraulic modeling software packages, i.e.<br />
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MIKE URBAN and MIKE View, to provide data input for the airflow modeling. The tool can be<br />
used to evaluate the system responses in terms of the drag-induced airflow capacities and odor<br />
areas of concern to operational changes of the wastewater flow provided the corresponding MIKE<br />
URBAN and MIKE View models are available.<br />
In order to increase confidence in the model results, differential air pressure data was collected at<br />
several locations. With the collected field data, it has been shown that the developed airflow<br />
model is an adequate tool for modeling the airflow in this particular system. Three modeling<br />
scenarios were analyzed using the developed airflow model, including:<br />
<br />
<br />
Current system configurations under typical dry weather flow conditions.<br />
Future flow diversion from NORS back to NOS under the same flow conditions;<br />
Future flow diversion of 30 cfs from NOS to COS under the same flow conditions.<br />
For each scenario, the airflow model was set up to run for a 48-hour period, including the typical<br />
weekday and weekend wastewater flow data provided in the corresponding MIKE View file, in<br />
15-minute time step. The conclusions based on the airflow modeling results are summarized as<br />
follows:<br />
<br />
<br />
<br />
Under the current system configurations, nine areas of concern are predicted. These<br />
include five locations along the ECIS from downstream of the Mission and Jesse drop<br />
structure to upstream of the USC drop structure; the ECIS siphon at Jefferson Boulevard<br />
and La Cienega Boulevard; the NORS/ECIS Junction; the NCOS Siphon at I-405 and the<br />
NORS Siphon at I-405.<br />
With the additional flow diverted into the NOS from the NORS, the upstream end of the<br />
NOS siphon and the NOTF location are predicted to experience positive pressure buildup<br />
under the assumption that the NOTF <strong>ATF</strong> is currently not being run pending ongoing<br />
public involvement efforts;<br />
The diversion of 30 cfs from NOS to COS will not cause additional areas of concern in<br />
the study sewers. However, the addition of the wastewater flow in the COS may cause<br />
positive pressure buildup along the COS.<br />
It should be noted that the model results presented herein are not viewed with absolute confidence<br />
but rather an aid to help understand the system airflow dynamics and can be used to identify<br />
where odor emission might occur.<br />
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Appendix A<br />
Acronyms and Abbreviations<br />
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ACRONYMS AND ABBREVIATIONS<br />
ACD<br />
<strong>ATF</strong><br />
COS<br />
CSSA<br />
ECIS<br />
LCIS<br />
LCSFVRS<br />
NCOS<br />
NEIS<br />
NOS<br />
NOTF<br />
NORS<br />
WHIS<br />
W<strong>LA</strong>IS<br />
WRS<br />
Airflwo Capacity Differential<br />
Air Treatment Facility<br />
Central Outfall Sewer<br />
Collection System Settlement Agreement<br />
East Central Interceptor Sewer<br />
La Cienega Interceptor Sewer<br />
La Cienega San Fernando Relief Sewer<br />
North Central Outfall Sewer<br />
North East Interceptor Sewer<br />
North Outfall Sewer<br />
North Outfall Treatment Facility<br />
North Outfall Replacement Sewer<br />
Wilshire-Hollywood Interceptor Sewer<br />
West Los Angeles Interceptor Sewer<br />
Westwood Relief Sewer<br />
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Technical Memorandum – FINAL<br />
Team<br />
City of Los Angeles<br />
Department of Public Works<br />
Bureau of Sanitation<br />
Air Treatment Facility (<strong>ATF</strong>) Review <strong>Study</strong><br />
SEWER SIPHONS TECHNICAL MEMORANDUM<br />
DUCT CONNECTION STUDY<br />
FINAL<br />
November <strong>2010</strong><br />
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Table of Contents<br />
Executive Summary ...................................................................................................................... 5<br />
1.0 Introduction and Purpose ................................................................................................... 5<br />
2.0 Sampling Setup .................................................................................................................. 5<br />
2.1 Locations Sampled ......................................................................................................... 6<br />
2.2 Schedule ....................................................................................................................... 10<br />
2.3 Roles and Responsibilities ........................................................................................... 12<br />
3.0 Field Sampling ................................................................................................................. 13<br />
3.1 Baseline Data Collection .............................................................................................. 13<br />
3.1.1 Data Logger Installation ........................................................................................ 15<br />
3.1.2 Baseline Data Download ....................................................................................... 16<br />
3.2 Ductwork Installation .................................................................................................... 16<br />
3.2.1 Passive Ventilation Phase ..................................................................................... 17<br />
3.2.2 Active Ventilation Phase ........................................................................................ 20<br />
4.0 Test Results ..................................................................................................................... 22<br />
4.1 Baseline Phase Air Pressure Data ............................................................................... 22<br />
4.2 Passive Duct Phase Air Pressure Data ........................................................................ 27<br />
4.3 Active Duct Phase Air Pressure Data ........................................................................... 33<br />
4.4 Findings ........................................................................................................................ 37<br />
5.0 Air Duct Isolation between NOS and NCOS .................................................................... 38<br />
5.1 Sampling & Air Duct Isolation ....................................................................................... 38<br />
5.2 Locations to be Sampled .............................................................................................. 39<br />
5.3 Schedule ....................................................................................................................... 42<br />
5.4 Roles and Responsibilities ........................................................................................... 43<br />
5.5 Test Results .................................................................................................................. 44<br />
6.0 Additional Siphon Sampling ............................................................................................. 47<br />
7.0 Conclusions ...................................................................................................................... 51<br />
List of Tables<br />
Table 1 Air Phase Sampling Parameter ....................................................................................... 6<br />
Table 2 - Sampling Location and Descriptions ............................................................................. 6<br />
Table 3 - Air Duct Connection Locations .................................................................................... 10<br />
Table 4 - Overall Sampling Schedule ......................................................................................... 11<br />
Table 5 - Detailed Ventilation Schedule ...................................................................................... 11<br />
Table 6 - Grab Sample Pressure Data ........................................................................................ 14<br />
Table 7 - Summary of Baseline Air Pressure Data Recorded in NCOS and NORS, 6/2/09 to<br />
6/9/09 .......................................................................................................................................... 23<br />
Table 8 – Summary of Baseline Air Pressure Data Recorded in NCOS and NORS, 6/9/09 to<br />
6/24/09 ........................................................................................................................................ 24<br />
Table 9 - Summary of Air Pressure Data Recorded in NCOS and NORS, 7/20/09 to 7/24/09,<br />
Passive Ventilation Phase .......................................................................................................... 27<br />
Table 10 - Comparison of Data Summary for Pressure Recorded from 7/20/09 to 7/22/09 ....... 30<br />
Table 11 - Summary of Air Pressure Data Recorded in NCOS and NORS, 7/24/09 to 7/27/09,<br />
Passive Ventilation Phase .......................................................................................................... 31<br />
Table 12 - Summary of Air Pressure Data Recorded in NCOS and NORS, 7/27/09 to 8/3/09,<br />
Passive Ventilation Phase .......................................................................................................... 33<br />
Table 13 - Summary of Air Pressure Data Recorded in NCOS and NORS, 8/18/09 to 8/24/09,<br />
Active Ventilation Phase ............................................................................................................. 35<br />
Table 14 - Summary of Air Pressure Data Recorded in NCOS, NORS and NOS, 8/10/09 to<br />
8/18/09, Passive Ventilation Phase ............................................................................................ 36<br />
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Table 15 - Summary of Air Pressure Data Recorded in NCOS, NORS and NOS, 8/18/09 to<br />
8/24/09, Passive Ventilation Phase ............................................................................................ 36<br />
Table 16 - Air Pressure Sampling Locations ............................................................................... 39<br />
Table 17 - Overall Sampling Schedule ....................................................................................... 42<br />
Table 18 - Summary of Air Pressure Data Recorded During Duct Isolation <strong>Study</strong> ..................... 44<br />
Table 19 – Sampling Locations and Description ......................................................................... 48<br />
Table 20 – Culver City/Baldwin Hills and San Fernando Valley Air Pressure Data Summary .... 50<br />
List of Figures<br />
Figure 1 - Detailed Sampling Location Map .................................................................................. 9<br />
Figure 2 - Maintenance Hole 535-09-022 ................................................................................... 15<br />
Figure 3 - Maintenance Hole 535-13-007 ................................................................................... 15<br />
Figure 4 - Maintenance Hole 535-05-016 ................................................................................... 15<br />
Figure 5 - Maintenance Hole 535-09-009 ................................................................................... 15<br />
Figure 6 - Maintenance Hole 535-05-021 ................................................................................... 15<br />
Figure 7 - Maintenance Hole 535-09-006 ................................................................................... 15<br />
Figure 8 - Duct Connection ......................................................................................................... 16<br />
Figure 9 - NORS Maintenance hole of Duct Connection ............................................................ 16<br />
Figure 10 - NCOS Maintenance hole of Duct Connection .......................................................... 16<br />
Figure 11 - Air Velocity Measurement ......................................................................................... 16<br />
Figure 12 - Air Velocity Measurements in Duct ........................................................................... 18<br />
Figure 13 - Maintenance hole 560-12-145 .................................................................................. 19<br />
Figure 14 - Maintenance hole 559-05-005 .................................................................................. 19<br />
Figure 15 - Maintenance hole 535-06-132 .................................................................................. 19<br />
Figure 16 - Maintenance hole 535-09-017 .................................................................................. 19<br />
Figure 17 - “Special Manhole” ..................................................................................................... 19<br />
Figure 18 - Maintenance hole 535-09-017 .................................................................................. 19<br />
Figure 19 - Fan Installation ......................................................................................................... 20<br />
Figure 20 – Fan Prep .................................................................................................................. 20<br />
Figure 21 - Fan Installation Complete ......................................................................................... 20<br />
Figure 22 – Fan Control Panel .................................................................................................... 20<br />
Figure 23 - Sound Abatement ..................................................................................................... 21<br />
Figure 24 -- Installation Complete ............................................................................................... 21<br />
Figure 25 - Fan Test Complete ................................................................................................... 21<br />
Figure 26 - Baseline Air Pressure ............................................................................................... 22<br />
Figure 27 - Detail 24 hours Baseline ........................................................................................... 23<br />
Figure 28 - NORS NCOS Air Pressure with NORS/ECIS <strong>ATF</strong> Shut Off ..................................... 24<br />
Figure 29 - Air Pressure (Absolute Value) Difference between NORS and NCOS .................... 25<br />
Figure 30 - 24-hour Period Combined Data on 6/19/09 .............................................................. 26<br />
Figure 31 - Passive Air Duct Connection Data ........................................................................... 27<br />
Figure 32 - Passive Duct Air Pressure Data ............................................................................... 28<br />
Figure 33 - Average Passive Air Velocity .................................................................................... 29<br />
Figure 34 - Average Passive Air Flow ......................................................................................... 29<br />
Figure 35 - NORS NCOS Passive Duct Test Air Pressure Data................................................. 31<br />
Figure 36 - NORS NCOS Air Pressure with Passive Duct Connection....................................... 32<br />
Figure 37 - Air Velocity Measurements in Duct ........................................................................... 33<br />
Figure 38 - Air Velocity Measurements in Duct (2) ..................................................................... 34<br />
Figure 39 - Combined NORS-NCOS Air Pressure with Fan Active ............................................ 35<br />
Figure 40 - Combined Air Pressure 8/18 to 8/27 ........................................................................ 36<br />
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Figure 41 - Schematic of 24-inch/42-inch Air Duct and Special MH Flap Installation ................. 38<br />
Figure 42 - Air Duct Isolation with plywood and rubber flap ........................................................ 39<br />
Figure 43 - Sampling Location Map for Air Duct Isolation ........................................................... 40<br />
Figure 44 - Maintenance Hole 559-05-005 ................................................................................. 41<br />
Figure 45 - Maintenance Hole 535-05-016 ................................................................................. 41<br />
Figure 46 - Maintenance Hole 535-09-009 ................................................................................. 41<br />
Figure 47 - Maintenance Hole Special MH ................................................................................. 41<br />
Figure 48 - Maintenance Hole 535-13-002 ................................................................................. 41<br />
Figure 49 - Maintenance Hole 559-05-008 ................................................................................. 41<br />
Figure 50 - Maintenance Hole 560-08-056, Downstream of NOS Siphon .................................. 42<br />
Figure 51 - NOS/NCOS Duct Isolation Air Pressure Data .......................................................... 44<br />
Figure 52 - Typical Baseline Air Pressure Data .......................................................................... 45<br />
Figure 53 – Pressure Effects of <strong>ATF</strong> Shutoffs ............................................................................ 46<br />
Figure 54 - NORS Modeled Wastewater Flow Comparison........................................................ 47<br />
Figure 55 - Post Flow Diversion NORS Air Pressure .................................................................. 48<br />
Figure 56 - Post Flow Diversion NOS Air Pressure in Baldwin Hills ........................................... 49<br />
Figure 57 - NOS Air Pressure US of Radford Siphon ................................................................. 49<br />
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EXECUTIVE SUMMARY<br />
The City of Los Angeles has a long history of implementing proactive and innovative steps to<br />
control odors from its interceptor collection system including using chemical addition to control<br />
odors with an extensive use of magnesium hydroxide. Recently, the City has been working to<br />
improve odor control in several areas identified by local community groups. Air treatment<br />
facilities (<strong>ATF</strong>s) with known or predicted odor “hot spots” were included in the 2004 Collection<br />
System Settlement Agreement (CSSA).<br />
The NORS/NCOS Duct Connection Test Technical Memorandum presents the results of the<br />
HDR Team regarding the effect that the existing interceptor siphon located under the 405<br />
Freeway has on airflow dynamics in the interceptor collection system. In order to accomplish the<br />
task, field samplings from several maintenance holes were collected over a period of time<br />
followed by physically connecting the NORS and NCOS interceptors with a 200-foot, 36-inch<br />
diameter, and corrugated HDPE duct laid above-ground in Culver City. Air flow and air velocity<br />
samples were taken for a period of several days which was identified as the passive ventilation<br />
phase. Following that phase, the duct was separated to permit the installation of a fan. During<br />
this active ventilation phase, more air pressure and air velocity data were collected to measure the<br />
effect of the fan air withdrawal from the NORS discharge to the NCOS with fan speed varying<br />
between 5000 and 12,500 cfm. <strong>Final</strong>ly, the permanent air duct that connects the headspace of the<br />
upstream ends of the siphons of the NOS and NCOS near the 405 Freeway was plugged to test<br />
the differential air pressure between the two interceptors. This air duct is comprised of two<br />
sections: A 24-inch high by 57-inch wide rectangular section that connects the NOS to a “Special<br />
Manhole” and a 42-inch diameter round section that connects the NCOS to the “Special<br />
Manhole”. The “Special Manhole”, as it is called out in the NCOS as-built drawings, is the<br />
transition point between these two sections of the permanent air duct.<br />
The results of these tests and findings are described in this document.<br />
1.0 INTRODUCTION AND PURPOSE<br />
Previous City sampling efforts have shown that headspace air pressures in the NCOS are typically<br />
at or below atmospheric levels, whereas in the NORS they are highly positive. Previous sampling<br />
efforts conducted by the City have also resulted in the conclusion that the source of this positive<br />
air pressure is the air dragged in the headspace of the NORS to the siphon located under the 405<br />
Freeway. The air that is carried in the open headspace of the NORS to the siphon cannot pass<br />
through the siphon and positive differential air pressure builds from there to points upstream<br />
along the NORS alignment. Because the NORS and NCOS alignments are essentially parallel to<br />
one another, the possibility exists of physically connecting the headspaces of these two sewers<br />
(between nearby maintenance holes on each) with a short run of flexible duct in order to test the<br />
effectiveness of depressurizing the NORS through such a connection. The purpose of this study<br />
is to test the feasibility and effectiveness of relieving this positive air pressure from the NORS<br />
into the NCOS.<br />
2.0 SAMPLING SETUP<br />
Data collection instruments that were used during the sampling effort are shown in Table 1. The<br />
air pressure sampling consisted of continuous data collection at two-minute intervals during four<br />
separate periods at the locations shown in Table 2. Using two-minute intervals, the differential air<br />
pressure data loggers have the capacity to log data for approximately two weeks apiece.<br />
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The instruments were installed from the surface, and entry into maintenance holes or structures<br />
was not required. The instrument installations were temporary and generally took place by<br />
suspension from a maintenance hole rim, step or lid.<br />
The quantity of air transferred through the flexible duct from the NORS to the NCOS, both in<br />
passive and active ventilation modes, was determined by the use of a hot-wire anemometer. A<br />
sampling port was cut into the flexible duct connecting the two sewers through which air velocity<br />
readings were taken across the cross section of the duct. This was done both in the vertical and<br />
horizontal directions in the cross section and is further described in the Field Sampling section of<br />
this memo.<br />
Table 1 Air Phase Sampling Parameter<br />
Parameter Field Data Logger Purpose<br />
Headspace Air Pressure ACR Smart Reader Plus 4<br />
To locate and quantify areas of positive<br />
pressure and allow for qualitative<br />
verification of computer airflow model<br />
To subsequently calculate the amount of air<br />
Air Velocity in Flexible Duct Hot-wire anemometer that passes between the NORS and NCOS<br />
under both passive and active ventilation<br />
conditions<br />
2.1 Locations Sampled<br />
In general, continuous differential air pressure sampling locations were selected based on the<br />
following criteria:<br />
<br />
<br />
<br />
<br />
Locations along the NORS upstream of the NORS Siphon<br />
Locations where previous air pressure testing had indicated that a backpressure<br />
relationship, due to a positive differential air pressure buildup, exists that is likely related<br />
to the NORS Siphon<br />
Locations upstream on the NCOS and NORS from proposed air duct connections<br />
Locations downstream on the NCOS and NORS from proposed air duct connections<br />
Detailed information on field sampling locations is presented in Table 2. A map of the locations<br />
sampled is presented in Figure 1.<br />
Table 2 - Sampling Location and Descriptions<br />
Session MH Number Sewer Field Notes<br />
1 535-09-022 NORS This maintenance hole is the first maintenance hole<br />
upstream of the air duct connection on NORS and is<br />
located at the NORS/ECIS carbon <strong>ATF</strong> site. The<br />
maintenance hole has an inner plate and the data logger in<br />
the protective case was placed on top of it. On August 5,<br />
2009, in order to prevent the tubing connected to the<br />
negative terminal from being pinched off by the ribs under<br />
the maintenance hole cover, the tubing was shortened.<br />
1 535-13-007 NORS This maintenance hole is the first maintenance hole<br />
downstream of the air duct connection on NORS and is<br />
located in the dirt shoulder behind the sound wall on<br />
Stocker Street. The maintenance hole has an inner plate<br />
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Session MH Number Sewer Field Notes<br />
and the data logger in the protective case was placed on<br />
top of it.<br />
1 535-05-016 NCOS This is an alternate location due to access difficulty with<br />
the originally selected maintenance hole and is the second<br />
maintenance hole located upstream of the duct connection<br />
maintenance hole of the NCOS interceptor. This<br />
maintenance hole is adjacent to the skate park on the<br />
Jefferson Boulevard. The data logger was secured to the<br />
underside of the maintenance hole cover through a<br />
pickhole with a rope, bolts and a p-trap assembly. On the<br />
field trip to reset the logger on August 18, 2009, it was<br />
found that the barbed hose connection was disconnected<br />
from the p-trap; this was likely caused by heat and/or<br />
moisture and caused the glue to melt. The p-trap assembly<br />
was replaced with a threaded one and the bottom of the<br />
new p-trap was sealed with duck tape without the water<br />
filled u shaped PVC pipe since no rainfall was expected.<br />
1 535-09-009 NCOS This maintenance hole is downstream of the air duct<br />
connection on the NCOS and is on the south side of the<br />
Physical Education Complex at West <strong>LA</strong> College. The<br />
maintenance hole does not have an inner plate and a p-trap<br />
assembly was installed originally in order to secure the<br />
logger. It was found that the bottom part of the p-trap was<br />
disconnected on a couple of occasions when crews went to<br />
download data and reset the logger. Therefore, on July 23,<br />
2009, the p-trap was removed and instead, the tubing<br />
connected to the negative terminal with brass hose<br />
connection was secured directly on the maintenance hole<br />
cover through the pickhole. It was found on a couple of<br />
occasions on August 5 and 18, 2009, that the maintenance<br />
hole cover was tarred but the vent of the hose connection<br />
and the tubing were cleaned on site.<br />
1 535-05-021 NORS This is the first maintenance hole upstream of<br />
NORS/ECIS Junction. The maintenance hole is located in<br />
Culver City Park. The maintenance hole has an inner plate<br />
and the data logger in the protective case was placed on<br />
top of it. On August 5, 2009, in order to prevent the tubing<br />
connected to the negative terminal from being pinched off<br />
by the ribs under the maintenance hole cover, the tubing<br />
was shortened.<br />
1 535-09-006 NORS This maintenance hole is the first one upstream of the<br />
NORS/ECIS Junction and downstream of the North<br />
Outfall Treatment Facility (NOTF). It is within the Turner<br />
Construction property boundary on Jefferson Boulevard.<br />
The maintenance hole has an inner plate and the data<br />
logger in the protective case was placed on top of it.<br />
2 560-12-145 NCOS This maintenance hole is located on the downstream end<br />
of the NCOS siphon and is on the east side of Sepulveda<br />
Boulevard between Howard Hughes Parkway and Center<br />
Drive. This maintenance hole has no inner plate. In order<br />
to properly install the p-trap assembly on the maintenance<br />
hole cover, the City replaced the existing maintenance<br />
hole cover, which had one pickhole, with one that has two<br />
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Session MH Number Sewer Field Notes<br />
pickholes.<br />
2 559-05-005 NCOS This maintenance hole is located on the upstream end of<br />
NCOS siphon and is in the southeast corner of the<br />
intersection of Bristol Parkway and Green Valley Circle.<br />
There is no inner plate in place and the data logger with a<br />
p-trap assembly was installed as done in previously<br />
similar setups.<br />
2 535-06-132 NORS This maintenance hole is located at the intersection of Ivy<br />
Way and Perham Drive. The maintenance hole has an<br />
inner plate and the data logger in the protective case was<br />
placed on top of it.<br />
2 535-09-017 NOS This maintenance hole is located in a commercial parking<br />
lot where the NOS connects with NOTF. The maintenance<br />
hole has no inner plate and has only one pickhole. The<br />
data logger in the protective case was secured through a<br />
rope. The tubing connected to the negative terminal with<br />
brass tee assembly was secured on the maintenance hole<br />
cover through the a pickhole.<br />
2 “Special MH” 42” Air<br />
Vent Line<br />
This is designated as a “Special MH” in the NCOS asbuilt<br />
drawing set. The maintenance hole is located on a<br />
dedicated air ventilation duct that connects the upstream<br />
end of the NOS siphon and the upstream end of NCOS<br />
siphon. The maintenance hole serves as a transition<br />
between a 24-inch diameter section of the air duct that<br />
connects to the NOS and a 42-inch diameter section that<br />
connects to the NCOS. The maintenance hole has an inner<br />
plate and the data logger in the protective case was placed<br />
on top of it.<br />
2 535-06-090 NCOS This maintenance hole is located just downstream of the<br />
Rodeo and La Cienega NCOS siphon on the east side of<br />
Jefferson Boulevard. This maintenance hole has no inner<br />
plate and the data logger p-trap assembly was installed<br />
here as in similarly configured locations.<br />
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Figure 1 - Detailed Sampling Location Map<br />
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The air pressure effects of a 36-inch diameter air duct connection were measured at the same<br />
maintenance holes in which air pressure data had been taken during the baseline sampling period.<br />
The duct was connected to the rims of the two maintenance holes shown in Table 3. Maintenance<br />
hole 535-09-011 (NORS) was connected to maintenance hole 535-09-008 (NCOS). This location<br />
is just east of the intersection of Freshman Dr. and Sophomore Dr. just north of West <strong>LA</strong> College<br />
in Culver City. This location was chosen due to the proximity of the two sewers to one another as<br />
well as the low probability of traffic disruptions during the testing. Approximately 200 linear feet<br />
separate maintenance holes 535-09-011 on the NORS and 535-09-008 on the NCOS. Prior to<br />
commencing the sampling effort, two field inspections were performed by City and the HDR<br />
team staff in order to assess and confirm the feasibility of performing the duct connections at the<br />
West <strong>LA</strong> College location.<br />
Table 3 - Air Duct Connection Locations<br />
Sampling Locations<br />
Location MH Number Notes<br />
Freshman Dr. at Sophomore Dr.; just north of<br />
West <strong>LA</strong> College<br />
535-09-011<br />
535-09-008<br />
NORS maintenance hole<br />
NCOS maintenance hole<br />
(Approx. linear distance = 200<br />
feet)<br />
2.2 Schedule<br />
There were two distinct, baseline data gathering sessions carried out for this sampling effort. The<br />
locations and sessions during which differential air pressure data were measured at each location<br />
are listed in Table 2<br />
Baseline Session 1 lasted approximately one week. One day was needed to install all the data<br />
loggers and another day to remove all the data loggers at the end of Session 2.<br />
Downloading of data from Session 1 and programming of the data loggers for Session 2 was<br />
performed in the field approximately seven days after the instruments were installed. An overall<br />
sampling schedule is presented in Table 4. A detailed ventilation schedule, covering both the<br />
passive and active ventilation tests, is presented in Table 5.<br />
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Task<br />
Table 4 - Overall Sampling Schedule<br />
Session 1<br />
Baseline Air Pressure<br />
Start Date<br />
06/02/09<br />
End Date<br />
06/09/09<br />
Session 2<br />
Air Duct Effect Testing<br />
Start Date<br />
07/20/09<br />
Install Air Pressure Data Loggers Day 1 Day 2 n/a n/a<br />
All Data Loggers installed and<br />
logging data<br />
Day 2 Day 7 n/a n/a<br />
Download Baseline Air Pressure<br />
Data in Field; Reprogram Day 7 Day 7 n/a n/a<br />
Instruments for Session 2<br />
Install 36-inch diameter flexible<br />
duct to maintenance holes n/a n/a *Day 1 n/a<br />
referenced in Table 3<br />
Retrieve Instruments and<br />
disassemble conduits<br />
n/a n/a n/a Day 4<br />
End Date<br />
8/24/09<br />
Table 5 - Detailed Ventilation Schedule<br />
Task<br />
Connect ductwork to NORS &<br />
NCOS maintenance holes<br />
Disconnect ductwork from<br />
NORS & NCOS maintenance<br />
holes<br />
Connect 10,000 cfm fan to 36-<br />
inch duct; begin air withdrawal<br />
Shut off fan; disassemble and<br />
remove ductwork, fan and<br />
generator<br />
Passive Ventilation<br />
Start Date<br />
7/20/09<br />
9:00 am<br />
Day 1<br />
n/a<br />
n/a<br />
End Date<br />
7/27/09<br />
Active Ventilation<br />
Start Date<br />
8/19/09<br />
End Date<br />
8/24/09<br />
n/a n/a n/a<br />
3:00 pm<br />
Day 2<br />
n/a<br />
n/a<br />
9:00 am<br />
Day 3<br />
n/a n/a n/a<br />
n/a<br />
n/a<br />
3:00 pm<br />
Day 4<br />
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2.3 Roles and Responsibilities<br />
The sampling activities were a joint effort between the HDR/Malcolm Pirnie team, its sub (GK &<br />
Associates) and City BOS staff. The roles and responsibilities for each of the three included the<br />
following:<br />
HDR/Malcolm Pirnie<br />
<br />
<br />
<br />
<br />
<br />
Prepare all instruments for data logging<br />
Installation of all data logging instruments<br />
Data downloads from all instruments<br />
Retrieval of all data instruments<br />
Data compilation, organization and analysis<br />
Documentation of results<br />
GK & Associates<br />
<br />
<br />
<br />
<br />
<br />
Support HDR/MP representatives in accessing, closing and properly sealing all<br />
maintenance holes accessed during this sampling effort (see 2009 Field Ops Workshop<br />
presentation for details)<br />
Arrange for procurement and fabrication (where necessary on appurtenant equipment) of<br />
10,000 cfm fan, portable generator and minimum 200-linear feet of 36-inch diameter<br />
flexible ductwork<br />
Connect approximately 200-linear feet of 36-inch flexible ductwork to maintenance holes<br />
shown in Table 3 according to schedule outlined in Table 5<br />
Operation of hot-wire anemometer during both passive and active ventilation efforts;<br />
record subsequent air velocity readings in daily field log.<br />
Set up 10,000 cfm fan, portable generator and approximately 200-linear feet of 36-inch<br />
flexible ductwork to maintenance holes shown in Table 3 according to schedule outlined<br />
in Table 5.<br />
Operate fan and portable generator according to schedule outlined in Table 5.<br />
<br />
Remove fan, generator, ductwork and all appurtenant equipment following completion of<br />
testing.<br />
City BOS Staff<br />
<br />
Accompany HDR/MP staff in field during instrument installation/removal and fan<br />
operation during normal working hours.<br />
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3.0 FIELD SAMPLING<br />
This section describes the field sampling that was conducted to collect air pressure data. The<br />
sampling was performed according to the schedule as described in Table 4 and Table 5. During<br />
Baseline Session 1, six maintenance holes were used to install data loggers to collect air pressure<br />
data. After reviewing the passive ventilation results, an additional six maintenance holes were<br />
proposed for Baseline Session 2 to further assess the extent of the passive and active ventilation.<br />
The descriptions of each sampling maintenance hole are included in Table 2. Figure 1 provides a<br />
map showing the locations of the maintenance holes where the data loggers and the ductwork<br />
were installed.<br />
3.1 Baseline Data Collection<br />
Three weeks’ worth of baseline differential air pressure data were collected from June 2 to June<br />
24, 2009 in the six maintenance holes listed previously in Table 2. Grab sample pressure data<br />
were also collected during each field trip using a hand-held manometer. This grab sample data is<br />
summarized in Table 6. Detailed information on the continuous differential air pressure data<br />
collected is presented in Section 4.0 (Test Results).<br />
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Table 6 - Grab Sample Pressure Data<br />
Maintenance<br />
Hole<br />
Information<br />
Data Collected on 06/02/09<br />
(Tuesday)<br />
Data Collected on 06/09/09<br />
(Tuesday)<br />
Data Collected on 06/25/09<br />
(Thursday)<br />
Data Collected on 07/14/09<br />
(Tuesday)<br />
Data Collected on 07/27/09<br />
(Monday)<br />
MH Number<br />
Differential<br />
Pressure<br />
(inch of water<br />
column)<br />
Time of<br />
Pressure<br />
Measurem<br />
ent<br />
Differential<br />
Pressure<br />
(inch of water<br />
column)<br />
Time of<br />
Pressure<br />
Measurem<br />
ent<br />
Differential<br />
Pressure<br />
(inch of water<br />
column)<br />
Time of<br />
Pressure<br />
Measurem<br />
ent<br />
Differential<br />
Pressure<br />
(inch of water<br />
column)<br />
Time of<br />
Pressure<br />
Measurem<br />
ent<br />
Differential<br />
Pressure<br />
(inch of water<br />
column)<br />
Time of<br />
Pressure<br />
Measurem<br />
ent<br />
NORS ECIS Jnc<br />
535‐09‐022<br />
0.28 10:10 AM 0.35 9:36 AM 0.25 9:30 AM 0.19 10:42 AM 0.04 10:15 AM<br />
NORS DS of<br />
Duct Cxn<br />
(535‐13‐007)<br />
0.28 10:30 AM 0.38 10:18 AM 0.28 10:00 AM 0.26 10:26 AM 0.16 9:00 AM<br />
NCOS US of<br />
Duct Cxn<br />
(535‐05‐016)<br />
‐0.16 8:50 AM ‐0.12 8:28 AM ‐0.3 9:40 AM ‐0.31 10:54 AM 0.05 8:10 AM<br />
NCOS DS of<br />
Duct Cxn<br />
(535‐09‐009)<br />
‐0.4 10:57 AM ‐0.3 10:34 AM ‐0.4 10:05 AM ‐0.28 10:10 AM ‐0.08 9:40 AM<br />
NORS Culver<br />
City Park<br />
(535‐05‐021)<br />
0.35 9:31 AM 0.35 8:53 AM 0.3 8:48 AM 0.19 11:24 AM 0.13 8:35 AM<br />
NORS US of<br />
Duct Cxn<br />
(535‐09‐006)<br />
0.28 9:52 AM 0.33 9:58 AM 0.26 9:20 AM 0.29 9:00 AM 0.1 8:00 AM<br />
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3.1.1 Data Logger Installation<br />
Six data loggers were initially installed to record baseline differential air pressure data on June 2,<br />
2009 at the sampling locations indicated above. City staff was present at the time to provide<br />
guidance on the exact sampling locations that were proposed. Photographs taken at each sampling<br />
location are presented in Figure 2 through Figure 7.<br />
Figure 2 - Maintenance Hole 535-09-022 Figure 3 - Maintenance Hole 535-13-007<br />
Figure 4 - Maintenance Hole 535-05-016 Figure 5 - Maintenance Hole 535-09-009<br />
Figure 6 - Maintenance Hole 535-05-021 Figure 7 - Maintenance Hole 535-09-006<br />
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3.1.2 Baseline Data Download<br />
The Baseline Session 1 pressure data was downloaded on site in the field and the data loggers<br />
were reset and reinstalled at the same locations on June 9, 2009. The Baseline Session 2 pressure<br />
data was downloaded on June 25, 2009 and all the data loggers were temporarily removed.<br />
3.2 Ductwork Installation<br />
The duct connection from the NORS to the NCOS was completely constructed on July 20, 2009.<br />
Figure 8 through Figure 11 present pictures of the duct connection in the field. The connection<br />
between the two interceptors was performed with a 36-inch diameter, corrugated HDPE duct laid<br />
above-ground.<br />
Figure 8 - Duct Connection<br />
Figure 9 - NORS Maintenance hole of Duct<br />
Connection<br />
(taken from west to east)<br />
(taken from east to west)<br />
Figure 10 - NCOS Maintenance hole of<br />
Duct Connection<br />
Figure 11 - Air Velocity Measurement<br />
(taken from west to east)<br />
(taken from east to west)<br />
On July 20, 2009, the GK field crew began the duct installation just before 8:00 am. The fence<br />
was removed and the lower part of the fence was cut on one side and then unscrewed to allow for<br />
the duct to pass through. The backhoe was used to move each segment of the duct into place.<br />
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Once everything was lined up, the segments on the NORS side were joined together. Joint<br />
lubricant was applied to the gaskets, and then a truck was backed up to one side of the duct and<br />
used as an anchor, while the backhoe applied pressure on the other side to push the segments<br />
together.<br />
The city crew arrived to assist in opening the NCOS maintenance hole. With the city’s<br />
supervision, a backhoe was employed to apply the force necessary to lift the cover off. An inner<br />
plate underneath the maintenance hole cover was found to be severely corroded and had to be<br />
broken into pieces to be removed. After the cover was removed, the 90 degree duct fitting was<br />
mounted over the hole and anchored into the concrete surrounding it. The backhoe was used to<br />
level out the dirt leading from the maintenance hole to the fence. The remaining duct segments<br />
were joined together, and then connected to the 90 degree fitting. Air/water tight foam was<br />
sprayed around the base of the 90 degree fitting to form a seal around the maintenance hole.<br />
Once the 90-degree fitting was connected to the duct, air could clearly be felt being drawn into<br />
the open end of the duct into the NCOS. Measurements were taken to cut the last segment before<br />
joining it to the NORS maintenance hole. Once the segment was cut, the other 90 degree fitting<br />
was prepared to be bolted over the NORS maintenance hole. The cover was removed; the 90<br />
degree bend was connected to the duct and then anchored over the NORS maintenance hole into<br />
the asphalt. The foam was sprayed around the connection to seal it. Sandbags were setup to help<br />
reinforce various spots along the duct. The backhoe scooped dirt up against the base of the duct<br />
on the NCOS end to make it more stable. Following completion of the duct connection to both<br />
maintenance holes, the site was cleaned up; a temporary piece of fence was put up above the duct<br />
to prevent access on to private property near the NCOS maintenance hole and all remaining<br />
equipment was loaded onto the vehicles.<br />
In order to record the pressure data after the duct connection was completed, all six data loggers<br />
were reset and reinstalled at the original locations on July 14, 2009. The pressure data was<br />
downloaded on July 23 and 27, 2009.<br />
3.2.1 Passive Ventilation Phase<br />
The first test performed following the installation of the 36-inch diameter duct was to measure the<br />
transfer of air from the NORS to NCOS through the duct connection while simultaneously<br />
logging differential air pressure in the maintenance holes listed in Table 2. The air transfer for<br />
this portion of the test was due to the difference in differential air pressure between the NORS<br />
and the NCOS.<br />
Air Velocity Measurement<br />
In order to assess the airflow through the duct connection, air velocity grab samples through the<br />
duct were taken every hour from July 21 through July 24, 2009 by GK Associates. During each<br />
hourly sampling effort, a total of twelve readings were taken in the duct cross section: six<br />
readings across the horizontal direction and six readings across the vertical direction. A graphic<br />
depiction of the cross section of the air duct, and the locations in it where air velocity readings<br />
were taken, is presented in Figure 12. The air velocity readings taken horizontally and vertically<br />
across the cross section of the duct did not vary significantly during the test; therefore the<br />
subsequent airflow calculations were taken to be accurate and valid.<br />
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Figure 12 - Air Velocity Measurements in Duct<br />
Additional Air Pressure Sampling Locations<br />
After reviewing the air pressure data collected at the six original sampling locations and the air<br />
velocity data collected in the duct, an additional six air pressure sampling locations were added to<br />
further assess the extent of the passive and active ventilation. Before installing the data loggers at<br />
these additional locations, reconnaissance was scheduled for August 5, 2009 to assess the<br />
accessibility and feasibility of the proposed maintenance holes. After reconnaissance, the six data<br />
additional loggers were installed on August 10, 2009. All sampling locations are shown in Figure<br />
1 and listed in Table 1. The photos for the additional locations are shown in Figure 13 through<br />
Figure 18.<br />
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Figure 13 - Maintenance hole 560-12-145 Figure 14 - Maintenance hole 559-05-005<br />
Figure 15 - Maintenance hole 535-06-132 Figure 16 - Maintenance hole 535-09-017<br />
Figure 17 - “Special Manhole” Figure 18 - Maintenance hole 535-09-017<br />
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3.2.2 Active Ventilation Phase<br />
Following the passive ventilation test, the duct was separated to permit a fan to be inserted in-line<br />
between the two duct sections (Figure 19 through Figure 22). During the next 4 days, air pressure<br />
data and air velocity data were recorded to measure the effect of the fan air withdrawal from the<br />
NORS to the NCOS. The fan speed was varied in order to achieve planned withdrawal rates of<br />
5,000, 7,500, 10,000 and 12,500 cfm.<br />
Figure 19 - Fan Installation<br />
Figure 20 – Fan Prep<br />
Figure 21 - Fan Installation Complete<br />
Figure 22 – Fan Control Panel<br />
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Figure 23 - Sound Abatement<br />
Figure 24 -- Installation Complete<br />
Figure 25 - Fan Test Complete<br />
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4.0 TEST RESULTS<br />
4.1 Baseline Phase Air Pressure Data<br />
This section provides a summary of baseline air pressure data recorded on the NORS and NCOS<br />
prior to connecting the 36-inch diameter duct at West <strong>LA</strong> College.<br />
Figure 26 - Baseline Air Pressure<br />
The baseline pressure data recorded on the NORS and NCOS during the first week of testing is<br />
presented in Figure 26. The most notable feature of this data set is the difference between the<br />
average differential air pressures on the NORS and NCOS. As shown in Figure 26, the average<br />
pressure of the locations measured on the NORS was approximately 0.2 inches w.c., whereas the<br />
average pressure of the locations measured on the NCOS was approximately -0.39 inches of w.c.<br />
This represents an average pressure difference between the two interceptors of approximately<br />
0.59 inches w.c. These results confirm air pressure testing results conducted by BOS<br />
immediately prior to this round of testing during which it was discovered that pressures on the<br />
NCOS were well below atmospheric. This data is summarized numerically in Table 7.<br />
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Table 7 - Summary of Baseline Air Pressure Data Recorded in NCOS and NORS, 6/2/09 to 6/9/09<br />
Maintenance Hole Baseline session 1 6/2 - 6/9<br />
Description MAX MIN AVG STD DEV<br />
NCOS US of Duct Cxn (535-05-016) 0.05 -0.57 -0.38 0.08<br />
NCOS DS of Duct Cxn (535-09-009) -0.01 -0.69 -0.41 0.08<br />
NORS Culver City Park (535-05-021) 0.11 -0.07 0.01 0.03<br />
NORS DS of Duct Cxn (535-13-007) 0.84 -0.09 0.22 0.09<br />
NORS US of Duct Cxn (DS of NOTF) (535-09-006) 0.72 -0.02 0.19 0.09<br />
NORS ECIS Jnc (535-09-022) n/a n/a n/a n/a<br />
The data in Table 7 show that air pressures along the NORS reached levels as high at 0.84 inches<br />
w.c. and that pressures on the NCOS were as low as -0.69 inches w.c. Note that no usable data<br />
was recorded at the NORS ECIS junction location due to a pinched-off tube on the data logger<br />
used in that maintenance hole.<br />
Under normal operating conditions, diurnal air pressure trends in Los Angeles interceptors are<br />
generally believed to be a function of diurnal wastewater flow trends, therefore the general<br />
similarities in diurnal trends that are observed between the two interceptors are not surprising.<br />
Even more interesting to observe, however, are the similarities in minute trends along the two<br />
interceptors. For example, significant variations in pressure activity were recorded on June 3 rd in<br />
both interceptors. Numerous examples of this can be seen in the data chart presented in Figure<br />
27. Other, similar occurrences will be described later in this section.<br />
Figure 27 - Detail 24 hours Baseline<br />
1<br />
0.8<br />
0.6<br />
Combined NORS NCOS Baseline Air Pressure Data 6/3/09<br />
Prior to Passive Duct Connection<br />
NCOS US of Duct Cxn (535‐05‐016)<br />
NORS Culver City Park (535‐05‐021)<br />
NORS DS of Duct Cxn (535‐13‐007)<br />
NCOS DS of Duct Cxn (535‐09‐009)<br />
NORS US of Duct Cxn (DS of NOTF) (535‐09‐006)<br />
Air Pressure (in. wc)<br />
0.4<br />
0.2<br />
0<br />
‐0.2<br />
‐0.4<br />
‐0.6<br />
‐0.8<br />
12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM<br />
Time<br />
A second baseline pressure session was conducted between 6/9/09 and 6/24/09. During this<br />
approximate 2-week period the 10,000 cfm interim NORS/ECIS <strong>ATF</strong> was purposely shut off in<br />
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order to observe the differential air pressure effects, if any, on the NORS and NCOS. Figure 28<br />
presents a chart of the pressure data recorded on the NORS and NCOS during this period.<br />
Figure 28 - NORS NCOS Air Pressure with NORS/ECIS <strong>ATF</strong> Shut Off<br />
Air Pressure (in. wc)<br />
1<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
0<br />
‐0.2<br />
Combined NORS NCOS Air Pressure Data<br />
Baseline Session 2<br />
NCOS US of Duct Cxn (535‐05‐016)<br />
NORS Culver City Park (535‐05‐021)<br />
NORS DS of Duct Cxn (535‐13‐007)<br />
NORS US of Duct Cxn (DS of NOTF) (535‐09‐006)<br />
‐0.4<br />
‐0.6<br />
‐0.8<br />
6/8/09 6/10/09 6/12/09 6/14/09 6/16/09 6/18/09 6/20/09 6/22/09 6/24/09 6/26/09<br />
Time<br />
The most notable feature of this data set is the overall pressure differences between the period<br />
when the NORS/ECIS <strong>ATF</strong> was shut off (6/9 to 6/15) and when it was turned back on (6/15 to<br />
6/24). The average pressure levels at all locations measured were lower while the <strong>ATF</strong> was<br />
turned on. The differences in average pressure for these two <strong>ATF</strong> operation conditions are shown<br />
in Table 8. It is interesting to note that this effect was measured on both the NORS and the<br />
NCOS even though the air for this <strong>ATF</strong> is being drawn off of a point just upstream of the<br />
NORS/ECIS junction. This indicates that the <strong>ATF</strong> has an effect on the NCOS through a common<br />
headspace upstream of the NORS/ECIS junction.<br />
Table 8 – Summary of Baseline Air Pressure Data Recorded in NCOS and NORS, 6/9/09 to 6/24/09<br />
Maintenance Hole NORS/ECIS Shut OFF 6/9 - 6/15 NORS/ECIS Turned ON 6/15 - 6/24 OFF-to-ON<br />
Description MAX MIN AVG STD DEV MAX MIN AVG STD DEV ΔAVG.<br />
NCOS US of Duct Cxn<br />
(535-05-016) -0.05 -0.46 -0.34 0.07 0.32 -0.57 -0.41 0.08 -0.07<br />
NCOS DS of Duct Cxn<br />
(535-09-009) n/a n/a n/a n/a n/a n/a n/a n/a n/a<br />
NORS Culver City Park<br />
(535-05-021) 0.1 -0.07 0.01 0.02 0.03 -0.08 -0.01 0.03 -0.02<br />
NORS DS of Duct Cxn<br />
(535-13-007) 0.44 0.00 0.25 0.09 0.42 0.03 0.17 0.07 -0.08<br />
NORS US of Duct Cxn<br />
(DS of NOTF)<br />
(535-09-006) 0.37 -0.2 0.18 0.09 0.35 -0.06 0.09 0.07 -0.09<br />
NORS ECIS Jnc<br />
(535-09-022)<br />
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Figure 29 - Air Pressure (Absolute Value) Difference between NORS and NCOS<br />
0.8<br />
Difference Btwn Average NORS & NCOS Air Pressure<br />
Baseline Session 2<br />
0.7<br />
Air Pressure Difference (in. wc)<br />
0.6<br />
0.5<br />
0.4<br />
0.3<br />
0.2<br />
0.1<br />
0<br />
6/8/09 6/10/09 6/12/09 6/14/09 6/16/09 6/18/09 6/20/09 6/22/09 6/24/09 6/26/09<br />
Time<br />
The chart presented in Figure 29 shows the absolute value difference between the average<br />
measured air pressures on the NORS and the average measured air pressures on the ECIS for the<br />
second baseline data gathering phase which lasted from 6/9/09 to 6/24/09. The maximum values<br />
are approximately 0.65 inches w.c.; the minimum values are approximately 0.4 inches w.c. and<br />
the average values are approximately 0.55 inches w.c.<br />
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Figure 30 - 24-hour Period Combined Data on 6/19/09<br />
0.6<br />
0.4<br />
Combined NORS NCOS Baseline Data, Session 2<br />
6/19/09<br />
NCOS US of Duct Cxn (535‐05‐016)<br />
NORS Culver City Park (535‐05‐021)<br />
NORS DS of Duct Cxn (535‐13‐007)<br />
NORS US of Duct Cxn (DS of NOTF) (535‐09‐006)<br />
Air Pressure (in. wc)<br />
0.2<br />
‐0<br />
‐0.2<br />
‐0.4<br />
‐0.6<br />
12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM<br />
Time<br />
The chart in Figure 30 shows the combined data for the 24-hour period on 6/19/09. The most<br />
notable feature of this data set is the severe upward spike in air pressure that was measured on the<br />
NCOS between approximately 9:45 am and 10:45 am. The air pressure changes approximately<br />
0.6 inches w.c. during that time period; from -0.3 to 0.3 inches w.c. It is interesting that a similar,<br />
albeit less severe, effect was measure on the NORS during the same time interval. One possible<br />
explanation for this phenomenon is that the 40,000 cfm chemical <strong>ATF</strong> which had been ventilating<br />
the NOS south of West <strong>LA</strong> College was either temporarily turned off or its air pathway to the<br />
NCOS via the 42-inch diameter ventilation pipe that connects the NOS and the NCOS was<br />
temporarily blocked.<br />
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4.2 Passive Duct Phase Air Pressure Data<br />
Figure 31 shows the effects of the passive 36-inch diameter duct connection explained previously<br />
in this report between the NORS and NCOS maintenance holes.<br />
Figure 31 - Passive Air Duct Connection Data<br />
The duct was connected on July 20, 2009. The most notable feature of this data set is that MH<br />
535-05-016 on the NCOS (depicted by the red line on the chart in Figure 31) was the location<br />
whose air pressure was most visibly affected by the passive duct connection. The average<br />
pressure increased from -0.15 inches of water column to approximately 0.0 inches of water<br />
column following the duct connection between the NORS and NCOS. The pressure data<br />
recorded during this initial four-day period following the duct installation is summarized in Table<br />
9.<br />
Table 9 - Summary of Air Pressure Data Recorded in NCOS and NORS, 7/20/09 to 7/24/09, Passive<br />
Ventilation Phase<br />
Maintenance Hole Passive Duct Cxn 7/20 - 7/24<br />
Description MAX MIN AVG STD DEV<br />
NCOS US of Duct Cxn (535-05-016) 0.25 -0.21 0.01 0.07<br />
NCOS DS of Duct Cxn (535-09-009) 0.11 0.08 0.10 0.01<br />
NORS Culver City Park (535-05-021)<br />
NORS DS of Duct Cxn (535-13-007) 0.48 0 0.19 0.08<br />
NORS US of Duct Cxn (DS of NOTF) (535-09-006) 0.49 0.02 0.19 0.08<br />
NORS ECIS Jnc (535-09-022) 0.45 0 0.15 0.08<br />
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The data presented in Table 9 clearly show that the highest pressures were recorded in the NORS<br />
during this time period. The average pressures were approximately 0.19 inches w.c. on the<br />
NORS.<br />
Figure 32 - Passive Duct Air Pressure Data<br />
Figure 32 shows pressure data over a three day period during the passive duct connection phase<br />
of the test. Also the time interval during which the NORS/ECIS and Jefferson Siphon <strong>ATF</strong>s were<br />
shut down is shown. The data presented suggest that the shutdown of the <strong>ATF</strong>s had a measurable<br />
effect on both the NORS and the NCOS; in particular the pressures on both interceptors increased<br />
by approximately 0.125 inches of water column during this time interval when compared to<br />
similar pressures recorded the day before the <strong>ATF</strong> was shut down.<br />
Figure 33 and Figure 34 show the velocity readings and corresponding airflows, respectively,<br />
recorded in the 36-inch diameter duct during the passive air test. The average velocity and<br />
airflow during the passive test was approximately 450 fpm and 3,300 cfm, respectively, with the<br />
exception of 0930 to 1800 hours on July 22 nd . The NORS/ECIS and Jefferson Siphon <strong>ATF</strong>s,<br />
were temporarily shut-down during this time period. The 10,000 cfm NORS/ECIS and Jefferson<br />
Siphon <strong>ATF</strong>s are approximately 0.25 mile and 1.0 mile, respectively, upstream of the two<br />
maintenance holes that were connected by the above-ground duct. The average velocity and<br />
corresponding airflow through the 36-inch diameter duct decreased to approximately 225 fpm and<br />
1,500 cfm, respectively, during this time interval.<br />
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Figure 33 - Average Passive Air Velocity<br />
Average Passive Air Velocity Through NORS/NCOS Duct<br />
600<br />
500<br />
400<br />
Velocity (ft/min)<br />
300<br />
200<br />
100<br />
NORS/ECIS and<br />
Jefferson Scrubbers<br />
Shut-off Period<br />
0<br />
7/21/2009 7/22/2009 7/23/2009 7/24/2009 7/25/2009<br />
Figure 34 - Average Passive Air Flow<br />
4000<br />
Average Passive Air Flow Through NORS/NCOS Duct<br />
3500<br />
3000<br />
Air Flow (cfm)<br />
2500<br />
2000<br />
1500<br />
1000<br />
500<br />
NORS/ECIS and<br />
Jefferson Scrubbers<br />
Shut-off Period<br />
0<br />
7/21/2009 7/22/2009 7/23/2009 7/24/2009 7/25/2009<br />
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A summary of the pressure data taken between 0930 and 1800 hours on July 20 th , July 21 st and<br />
July 22 nd is presented in Table 10.<br />
Table 10 - Comparison of Data Summary for Pressure Recorded from 7/20/09 to 7/22/09<br />
Two Days Prior to<br />
7/20 & 7/21 (0930 to 1800 hrs.)<br />
<strong>ATF</strong>s Shut Down MAX MIN AVG STD DEV<br />
NCOS US of Duct Cxn (535-05-016) 0.08 -0.21 -0.05 0.04<br />
NCOS DS of Duct Cxn (535-09-009) 0.11 0.09 0.09 0.05<br />
NORS Culver City Park (535-05-021) n/a n/a n/a n/a<br />
NORS DS of Duct Cxn (535-13-007) 0.37 0.08 0.17 0.05<br />
NORS US of Duct Cxn (DS of NOTF) (535-09-<br />
006) 0.37 0.1 0.18 0.05<br />
NORS ECIS Jnc (535-09-022) 0.35 0.03 0.13 0.08<br />
7/22 (0930 to 1800 hrs.)<br />
During <strong>ATF</strong>s Shut Down MAX MIN AVG STD DEV ΔAVG.<br />
NCOS US of Duct Cxn (535-05-016) 0.24 -0.07 0.11 0.05 0.17<br />
NCOS DS of Duct Cxn (535-09-009) 0.11 0.1 0.10 0.00 0.01<br />
NORS Culver City Park (535-05-021) n/a n/a n/a n/a n/a<br />
NORS DS of Duct Cxn (535-13-007) 0.47 0.08 0.27 0.07 0.10<br />
NORS US of Duct Cxn (DS of NOTF) (535-09-<br />
006) 0.47 0.09 0.28 0.07 0.10<br />
NORS ECIS Jnc (535-09-022) 0.45 0.03 0.23 0.08 0.10<br />
The data presented in Table 10.suggest that the 10,000 cfm NORS/ECIS <strong>ATF</strong> and the 10,000 cfm<br />
Jefferson siphon <strong>ATF</strong> have a more pronounced effect on the pressures in the upstream reach of<br />
the NCOS than on the NORS. This is made apparent by comparing the change in average<br />
pressures along the NORS to that on the NCOS upstream of the 36-inch diameter duct connection<br />
(535-05-016). During the <strong>ATF</strong>s shut-down period (0930 to 1800 hours on July 22 nd ), the average<br />
pressure along the NORS increased by 0.10 inches of water column as compared to the same time<br />
period during the previous two days (0930 to 1800 hours on July 20 th and July 21 st ); however the<br />
average pressure in the NCOS at maintenance hole 535-05-016 increased by 0.17 inches of water<br />
column during the same three-day time period.<br />
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Figure 35 - NORS NCOS Passive Duct Test Air Pressure Data<br />
Figure 35 is a continuation of the pressure data set presented previously in Figure 32. It shows<br />
the effects of the passive 36-inch diameter duct connection explained previously in this report<br />
between the NORS and NCOS maintenance holes.<br />
As shown in Table 11, the highest average air pressures were recorded in the NORS, where the<br />
values were between 0.07 and 0.12 inches of water column. As previously seen during other<br />
testing sessions, the lowest average air pressures were in the NCOS, where the average values<br />
recorded were between -0.03 and 0.03 inches water column. As was shown during the initial<br />
stage of the passive test the most stark pressure changes occurred in the NCOS. Because the<br />
pressures in the NORS decreased (albeit slightly) and the pressures in the NCOS increased<br />
significantly during the passive phase, this suggests that the combined system had come to some<br />
equilibrium as a possible result of the passive duct connection. This equilibrium phenomenon is<br />
more clearly shown when one compares the data presented in Figure 36 to that presented<br />
previously in Figure 26.<br />
Table 11 - Summary of Air Pressure Data Recorded in NCOS and NORS, 7/24/09 to<br />
7/27/09, Passive Ventilation Phase<br />
Maintenance Hole Passive Duct Cxn 7/24 - 7/27<br />
Description MAX MIN AVG STD DEV<br />
NCOS US of Duct Cxn (535-05-016) 0.13 -0.12 -0.03 0.04<br />
NCOS DS of Duct Cxn (535-09-009) 0.29 -0.09 0.03 0.06<br />
NORS Culver City Park (535-05-021) n/a n/a n/a n/a<br />
NORS DS of Duct Cxn (535-13-007) 0.36 0 0.12 0.06<br />
NORS US of Duct Cxn (DS of NOTF) (535-09-006) 0.35 0 0.11 0.06<br />
NORS ECIS Jnc (535-09-022) 0.32 -0.05 0.07 0.06<br />
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The chart presented previously in Figure 26 showed that the average air pressures measured in the<br />
NORS during the first week of June, 2009 were approximately 0.2 inches of water column during<br />
the initial week of baseline pressure data recording. The pressures measured in the NCOS during<br />
that same time period, were approximately -0.39 inches of water column. The data presented in<br />
Figure 36 show that by the last week of July, 2009, after the 36-inch diameter passive duct had<br />
been installed for approximately 1 week, the average air pressure in the NORS had been reduced<br />
to 0.14 inches of water column; representing a change of -0.06 inches of water column. The<br />
average air pressures in the NCOS had increased to 0.03 inches of water column; representing a<br />
change of +0.42 inches of water column.<br />
Figure 36 - NORS NCOS Air Pressure with Passive Duct Connection<br />
A numerical summary of the air pressure data shown in Figure 36 is presented in Table 12.<br />
Included in this data table is a column showing the change in average pressure at each location<br />
between the baseline pressure data phase in June, 2009 (shown in Table 7) and the end of the<br />
passive duct connection pressure recording phase at the end of July, 2009. The data in Table 12<br />
also show that the most significant changes in average pressure were recorded on the NCOS. The<br />
average increases in pressure were between 0.39 and 0.46 inches of water column along that<br />
sewer. The NORS pressure changes were much smaller by comparison. The average pressure in<br />
the first maintenance hole downstream of the duct connection (MH 535-09-006), was reduced by<br />
-0.08 inches of water column; however this still resulted in an average differential air pressure of<br />
0.14 inches of water column at that location. Very little change in effect was recorded at the<br />
Culver City Park maintenance hole (MH 535-05-021) and the maintenance hole upstream of the<br />
duct connection (MH 535-09-006); however it is interesting to note that two of these locations did<br />
experience a slight decrease in pressure, whereas the Culver City Park maintenance hole<br />
experienced a slight increase in pressure This difference in reactions along the NORS is likely<br />
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due to the fact that the NORS reach on which the Culver City Park maintenance hole is situated<br />
was essentially carrying no flow at the time of this test.<br />
Table 12 - Summary of Air Pressure Data Recorded in NCOS and NORS, 7/27/09 to 8/3/09,<br />
Passive Ventilation Phase<br />
Maintenance Hole Passive Duct Cxn 7/27 - 8/3 BL to Pass<br />
Description MAX MIN AVG STD DEV ΔAVG.<br />
NCOS US of Duct Cxn (535-05-016) 0.09 -0.09 0.01 0.02 0.39<br />
NCOS DS of Duct Cxn (535-09-009) 0.24 -0.07 0.05 0.06 0.46<br />
NORS Culver City Park (535-05-021) 0.22 0.02 0.04 0.01 0.03<br />
NORS DS of Duct Cxn (535-13-007) 0.33 0.02 0.14 0.06 -0.08<br />
NORS US of Duct Cxn (DS of NOTF)<br />
(535-09-006) 0.31 0.02 0.13 0.06 -0.06<br />
NORS ECIS Jnc (535-09-022) 0.29 -0.07 0.09 0.06 n/a<br />
4.3 Active Duct Phase Air Pressure Data<br />
The air velocity data recorded in the 36-inch diameter duct during the active ventilation phase of<br />
this study is presented graphically in Figure 37 (which references the chart in Figure 38). The<br />
data indicate that the targeted airflows were met for each portion of the test.<br />
On the afternoon of August 20 th , the team had planned to increase the airflow from the NORS to<br />
the NCOS to the maximum allowed by the fan, 15,000 cfm; however the anemometer that was<br />
being used in the field indicated that only approximately 8,400 cfm was being moved through the<br />
36-inch diameter duct.<br />
Figure 37 - Air Velocity Measurements in Duct<br />
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The following day, August 22 nd , a replacement anemometer was used to measure velocity through<br />
the duct. The fan was still running at the same speed as it had been the previous day. The<br />
replacement instrument indicated, as shown graphically in Figure 38, that the target airflow was<br />
being met. It was surmised by field personnel that the first anemometer had likely been<br />
inadvertently exposed to moisture which had gathered at the bottom of the 36-inch diameter duct,<br />
thus causing it to fail to report accurate velocity readings on the afternoon of August 21 st .<br />
Figure 38 - Air Velocity Measurements in Duct (2)<br />
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Differential air pressure data recorded along the NCOS and NORS interceptors during the active<br />
ventilation phase of the duct test are presented graphically in Figure 39. A summary of the<br />
numerical data for the same locations is presented in Table 13.<br />
Figure 39 - Combined NORS-NCOS Air Pressure with Fan Active<br />
1<br />
Combined NORS NCOS Air Pressure 8/18/09 ‐ 8/27/09<br />
With Fan Active (Installed 8/18/09)<br />
0.8<br />
0.6<br />
Air Pressure (in. wc)<br />
0.4<br />
0.2<br />
0<br />
‐0.2<br />
‐0.4<br />
‐0.6<br />
‐0.8<br />
Table 13 - Summary of Air Pressure Data Recorded in NCOS and NORS, 8/18/09 to<br />
8/24/09, Active Ventilation Phase<br />
Maintenance Hole<br />
NCOS US of Duct Cxn (535‐05‐016)<br />
NORS Culver City Park (535‐05‐021)<br />
NORS DS of Duct Cxn (535‐13‐007)<br />
NCOS DS of Duct Cxn (535‐09‐009)<br />
NORS US of Duct Cxn (DS of NOTF) (535‐09‐006)<br />
NORS ECIS Jnc (535‐09‐022)<br />
8/18/09 8/19/09 8/20/09 8/21/09 8/22/09 8/23/09 8/24/09 8/25/09 8/26/09 8/27/09 8/28/09<br />
Fan Test<br />
8/18 - 8/24<br />
Passive<br />
to Active<br />
Baseline to<br />
Active<br />
STD<br />
DEV ΔAVG. ΔAVG.<br />
Description MAX MIN AVG<br />
NCOS US of Duct Cxn (535-05-016) 0.09 0.02 0.05 0.01 0.04 0.43<br />
NCOS DS of Duct Cxn (535-09-009) 2.16 -0.61 1.57 0.85 1.51 1.97<br />
NORS Culver City Park (535-05-021) 0.19 -0.03 0.07 0.04 0.04 0.08<br />
NORS DS of Duct Cxn (535-13-007) 0.34 -0.12 0.10 0.07 -0.04 -0.10<br />
NORS US of Duct Cxn (DS of NOTF)<br />
(535-09-006) 0.4 -0.1 0.10 0.08 -0.03 -0.02<br />
NORS ECIS Jnc (535-09-022) 0.39 -0.14 0.06 0.08 -0.03 0.06<br />
Time<br />
The data presented in Figure 39 and Table 13 indicates that the most significant effect of the<br />
active ventilation exercise was measured in the downstream reach of the NCOS (MH 535-09-<br />
009). At this location, the average pressure between the passive and active ventilation phases<br />
increased by 1.51 inches of water column as a result of the fan operation. Except for the Culver<br />
City Park maintenance hole (535-05-021), the average pressures on the NORS were only changed<br />
by approximately -0.03 inches of water column. The average pressure at the Culver City Park<br />
maintenance hole was increased by 0.04 inches of water column.<br />
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Following the analysis of air pressure data recorded during the June/July baseline period and the<br />
initial passive ventilation test, the decision was made to conduct pressure testing in four<br />
additional maintenance holes between August 18 th and August 27 th . The results of this additional<br />
testing are presented graphically in Figure 40 and summarized in Table 14 and Table 15.<br />
Figure 40 - Combined Air Pressure 8/18 to 8/27<br />
1<br />
0.8<br />
0.6<br />
Combined NORS NCOS Air Pressure 8/18/09 ‐ 8/27/09<br />
With Fan Active (Installed 8/18/09)<br />
NORS Ivy Way (535‐06‐132)<br />
NOS Warehouse (535‐09‐017)<br />
NCOS Green Valley (at siphon)<br />
NOS/NCOS Vent Line near NOS ("Special MH")<br />
Air Pressure (in. wc)<br />
0.4<br />
0.2<br />
0<br />
‐0.2<br />
‐0.4<br />
‐0.6<br />
‐0.8<br />
8/9/09 8/11/09 8/13/09 8/15/09 8/17/09 8/19/09 8/21/09 8/23/09 8/25/09<br />
Table 14 - Summary of Air Pressure Data Recorded in NCOS, NORS and NOS, 8/10/09 to<br />
8/18/09, Passive Ventilation Phase<br />
Maintenance Hole Passive Ventilation Test 8/10 - 8/18<br />
Description MAX MIN AVG STD DEV<br />
NORS Ivy Way (535-06-132) 0.37 0.00 0.14 0.07<br />
NCOS Green Valley (at siphon) 0.25 -0.14 0.03 0.04<br />
NOS Warehouse (535-09-017) 1.97 -1.35 0.37 0.31<br />
NOS/NCOS Vent Line near NOS ("Special MH") 0.08 -0.49 -0.27 0.13<br />
Time<br />
Table 15 - Summary of Air Pressure Data Recorded in NCOS, NORS and NOS, 8/18/09 to<br />
8/24/09, Passive Ventilation Phase<br />
Maintenance Hole Active Ventilation Test 8/18 - 8/24<br />
Pass to<br />
Fan<br />
Description MAX MIN AVG STD DEV ΔAVG.<br />
NORS Ivy Way (535-06-132) 0.33 -0.04 0.09 0.07 -0.04<br />
NCOS Green Valley (at siphon) 2.18 -2.25 0.23 1.10 0.20<br />
NOS Warehouse (535-09-017) 0.65 0.02 0.39 0.22 0.02<br />
NOS/NCOS Vent Line near NOS<br />
("Special MH") -0.04 -0.39 -0.21 0.07 0.06<br />
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As with the data presented previously in Figure 39 and Table 13, the data presented in Figure 40<br />
and Tables 14 and 15 indicate that the most significant pressure effect of the active ventilation<br />
between the NORS and the NCOS was measured in the segment of the NCOS downstream of the<br />
duct connection. At the NCOS Green Valley maintenance hole (559-05-005) the average<br />
pressure increased 0.2 inches of water column between the active and passive duct ventilation<br />
portions of the test. This maintenance hole is located at the head house of the siphon on the<br />
NCOS at Centinela. This is not as high as the pressure increase measured further upstream on the<br />
NCOS at MH 535-09-009; however this can likely be explained by the presence of air jumpers at<br />
the NCOS siphon and the 42-inch diameter air ventilation duct that connects the NCOS siphon to<br />
the NOS siphon.<br />
4.4 Findings<br />
The following provides a summary of the findings of the NORS/NCOS duct connection study:<br />
<br />
<br />
<br />
<br />
During baseline testing, the average pressure levels at all locations measured were lower<br />
while the NORS/ECIS <strong>ATF</strong> was turned on. This effect was measured on both the NORS<br />
and the NCOS even though the air for this <strong>ATF</strong> is being drawn off of a point just<br />
upstream of the NORS/ECIS junction.<br />
The passive air duct connection resulted in the NORS and NCOS coming to equilibrium<br />
with respect to differential air pressure. The pressures in the NCOS generally increased<br />
and the pressures in the NORS generally decreased; however the increase in the NCOS<br />
was significantly greater than the decrease along the NORS.<br />
Actively forcing air from the NORS into the NCOS resulted in an increase in pressure in<br />
the NCOS that is deemed to be unacceptably high. The pressures in the NORS were not<br />
reduced significantly as a result of active ventilation.<br />
The cause of the negative pressures in the NCOS was likely due to either one or both of<br />
two factors:<br />
• The presence of a permanent air duct that connects the NOS to the NCOS<br />
• Low flow conditions that were in effect along the NCOS as a result of upstream<br />
flow diversions into the NORS due to the then ongoing rehabilitation of the NOS<br />
Based on the analysis of the results presented in this report, the project team determined that<br />
additional sampling would be needed in order to determine the most likely cause of negative<br />
pressures in the NCOS. Specifically, the team decided that the possible air pressure effects due<br />
to the permanent air duct that connects the NOS to the NCOS would need to be investigated. The<br />
procedures, results and conclusions of that investigation are presented in Section 5.0 of this<br />
report.<br />
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5.0 AIR DUCT ISO<strong>LA</strong>TION BETWEEN NOS AND NCOS<br />
The upstream ends of the siphons of the NOS and NCOS near the 405 Freeway are connected via<br />
a permanent 24-inch/42-inch diameter air duct which was part of the construction of the NCOS.<br />
The purpose of this sampling is to test the differential air pressure results of plugging this 24-<br />
inch/42-inch diameter duct; thereby isolating the NOS from the NCOS. Recent sampling efforts<br />
have shown that differential air pressures in the NCOS are typically at or below atmospheric<br />
levels, whereas in the past they have been highly positive. By plugging this air duct and<br />
simultaneously testing the air pressures along the NOS and the NCOS, air pressure conditions<br />
along the NOS will be either ruled out or confirmed as the likely source of the negative air<br />
pressures currently existing in the NCOS.<br />
5.1 Sampling & Air Duct Isolation<br />
The air pressure sampling consisted of continuous data collection at two-minute intervals over an<br />
approximate two-week period at the locations shown in Table 1. Using two-minute intervals,<br />
ACR SmartReader Plus 4 data loggers have the capacity to log data for approximately two weeks.<br />
The data logging instruments were installed from the surface, and entry into maintenance holes or<br />
structures were not required for their installation. Installations was temporary and generally took<br />
place by suspension from a maintenance hole rim, step or lid without damage to any liners or<br />
protective coatings.<br />
A crew from GK & Associates was deployed in the field to isolate the 24-inch high by 57-inch<br />
wide rectangular section of the air duct. Note that the plug installation involved a confined space<br />
entry into the access structure. A schematic showing this air duct connection, the flap, and the<br />
special maintenance hole is presented in Figure 41. In the field, the air duct was isolated using<br />
plywood and rubber flap and sealed with expanding foam as shown in Figure 42.<br />
Figure 41 - Schematic of 24-inch/42-inch Air Duct and Special MH Flap Installation<br />
“Special MH”<br />
24-inch high by 57-inch<br />
wide rectangular duct<br />
to NOS<br />
42-inch diameter<br />
air duct to NCOS<br />
24-inch plywood<br />
and rubber flap<br />
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Figure 42 - Air Duct Isolation with plywood and rubber flap<br />
5.2 Locations to be Sampled<br />
In general, continuous differential air pressure sampling locations were selected based on the<br />
following criteria:<br />
<br />
<br />
<br />
Locations along the NCOS previously sampled both before and during the recently completed<br />
passive and active air duct connection test between the NCOS and NORS<br />
Locations along the NOS previously sampled during the recently completed active air duct<br />
connection test between the NCOS and NORS<br />
A location on the NOS approximately halfway between those which were previously sampled<br />
during the recently completed active air duct connection test between the NCOS and NORS<br />
Table 16 presents the differential air pressure sampling locations. Each sampling location<br />
represents a maintenance holes.<br />
Table 16 - Air Pressure Sampling Locations<br />
Air Pressure Sampling Locations<br />
Location MH Number Sewer<br />
MH at upstream end of NCOS siphon; Green Valley Circle 559-05-005 NCOS<br />
MH at skate park; Jefferson Blvd. 535-05-016 NCOS<br />
MH in front of West <strong>LA</strong> College gymnasium 535-09-009 NCOS<br />
MH along air duct that connects the NCOS to the NOS “Special MH” NOS<br />
Culver City; MH approximately near intersection of Bernardo 535-13-002 NOS<br />
and Eveward.<br />
MH at upstream end of NOS siphon; Fox Hills Dr. 559-05-008 NOS<br />
MH at downstream end of NOS siphon; near Arizona Cir. 560-08-056 NOS<br />
A map showing the sampling locations is presented in Figure 43.<br />
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Figure 43 - Sampling Location Map for Air Duct Isolation<br />
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The photos of the seven sampling maintenance holes are shown in Figure 44 to Figure 50.<br />
Figure 44 - Maintenance Hole 559-05-005 Figure 45 - Maintenance Hole 535-05-016<br />
Figure 46 - Maintenance Hole 535-09-009<br />
Figure 47 - Maintenance Hole Special MH<br />
Figure 48 - Maintenance Hole 535-13-002 Figure 49 - Maintenance Hole 559-05-008<br />
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Figure 50 - Maintenance Hole 560-08-056, Downstream of NOS Siphon<br />
The air pressure effects of plugging the air duct connection between the NOS and the NCOS was<br />
measured on both sewers simultaneously. The duct can be accessed via the so-called “special<br />
MH” referenced in Table 16. This “special MH” is located on an unpaved parcel in the northwest<br />
corner of the intersection of Fox Hills Drive and Green Valley Circle.<br />
5.3 Schedule<br />
There were two distinct sessions envisioned for this sampling effort. Session 1 involved<br />
gathering baseline differential air pressure data at the locations listed in Table 16. Session 2 was<br />
similar to Session 1, except that the air pressure effects of the plugged air duct connection<br />
described above was measured at the same maintenance holes in which the baseline air pressure<br />
data had been taken during Session 1. Table 17 summarizes these two sessions.<br />
Table 17 - Overall Sampling Schedule<br />
Session 1<br />
Baseline Air Pressure<br />
Session 2<br />
Air Duct Effect Testing<br />
Task<br />
Install Air Pressure Data<br />
Loggers<br />
All data loggers installed<br />
and logging data<br />
Plug air duct connecting<br />
the NOS to the NCOS<br />
All data loggers installed<br />
and logging data<br />
Retrieve data logging<br />
instruments and<br />
disassemble duct plug<br />
Start Date<br />
10/26/09<br />
End Date<br />
11/2/09<br />
Start Date<br />
11/2/09<br />
Day 1 Day 1 n/a n/a<br />
Day 2 Day 7 n/a n/a<br />
End Date<br />
11/9/09<br />
n/a n/a Day 8 Day 14<br />
n/a n/a Day 8 Day 14<br />
n/a n/a n/a Day1 4<br />
Session 1 lasted approximately one week. Approximately one day was needed to install all the<br />
data loggers. Approximately one day was needed to remove all the data loggers at the end of<br />
Session 2.<br />
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The data download was performed immediately after the instruments were removed following the<br />
completion of Session 2. The flap was removed on or immediately after the day that Session 2<br />
was completed.<br />
5.4 Roles and Responsibilities<br />
The sampling activities were a joint effort between the HDR/Malcolm Pirnie team, its sub (GK &<br />
Associates) and City BOS staff. The roles and responsibilities for each of the three include the<br />
following:<br />
HDR/Malcolm Pirnie<br />
Preparation of all instruments for data logging<br />
<br />
<br />
<br />
Installation of all data logging instruments<br />
Data downloads from all instruments<br />
Retrieval of all data instruments<br />
Data compilation, organization and analysis<br />
GK & Associates (or designated sub-contractor)<br />
Support of HDR/MP representatives in accessing, closing and properly sealing all<br />
maintenance holes accessed during this sampling effort (see 2009 Field Ops Workshop<br />
presentation for details)<br />
<br />
<br />
Arranging for procurement of inflatable sewer plug capable of plugging the 24-inch diameter<br />
air duct that connects the NOS to the NCOS; also arranging for procurement of air<br />
compressor; generator and all confined space entry equipment necessary to perform ingress<br />
and egress into the “Special MH” and inserting and inflating the plug in the field. Note that<br />
the “Special MH” constitutes the point along the layout at which the air duct diameter<br />
changes from 24-inches to 42-inches. For the purposes of this test it would be preferable for<br />
the 24-inch diameter section of the duct to be plugged. This is due to the fact that a<br />
differential air pressure logger was placed in the “Special MH” which was intended to record<br />
the pressure results with and without the headspace pressure effects of the NOS.<br />
Performing confined space entry into “special MH”; inserting and inflating, and subsequently<br />
deflating and removing, 24-inch diameter air duct plug according to plug manufacturer’s<br />
recommended procedures and the schedule. The static air pressure inside the plug should be<br />
monitored by GK field crew personnel (or their designated sub-contractor) once per day<br />
during Session 2 to ensure that the plug does not deflate prematurely during this time period.<br />
The daily pressure reading should be recorded and submitted to HDR at the end of Session 2.<br />
These pressure readings can be performed using a dedicated, liquid filled type static air<br />
pressure gage that would be installed following plug inflation. The gauge can remain in place<br />
during the entire Session 2 period.<br />
City BOS Staff<br />
<br />
Accompany HDR/MP staff in field during instrument and plug installation/removal<br />
during normal working hours.<br />
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5.5 Test Results<br />
A chart showing a graphical representation of the pressure data recorded at all locations during<br />
the entire two-week test is presented in Figure 51. A statistical summary of this data is presented<br />
in Table 18. A chart showing typical baseline pressure data is presented in Figure 52.<br />
Figure 51 - NOS/NCOS Duct Isolation Air Pressure Data<br />
Table 18 - Summary of Air Pressure Data Recorded During Duct Isolation <strong>Study</strong><br />
Locations Baseline Duct Plugged <strong>ATF</strong>s OFF<br />
NOS - Bernardo at<br />
Eveward<br />
NOS Siphon Inlet<br />
(Alt.)<br />
NOS-Siphon<br />
Outlet (Alt.)<br />
NOS/NCOS Vent<br />
Line near NOS<br />
("Special MH")<br />
NCOS DS of Duct<br />
Cxn (535-09-009)<br />
Max Min Avg Max Min Avg Δ Max Min Avg Δ<br />
Avg.<br />
Avg.<br />
0.14 -0.42 -0.04 0.14 -0.12 -0.01 0.03 0.08 -0.13 -0.01 0.03<br />
0.15 -0.42 -0.02 0.16 -0.08 0.01 0.03 0.11 -0.09 0.02 0.04<br />
0.03 -0.11 0.00 0.03 -0.01 0.01 0.01 0.02 -0.01 0.01 0.01<br />
0.25 -1.50 -0.27 0.16 -0.98 -0.36 -<br />
0.09<br />
-0.06 -0.49 -0.30 -0.02 -0.49 -0.33 -<br />
0.03<br />
0.03 -0.92 -0.39 -0.12<br />
-0.03 -0.38 -0.23 -0.07<br />
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Figure 52 - Typical Baseline Air Pressure Data<br />
The most noticeable pressure change effect took place at the “Special MH” located on the<br />
NOS/NCOS vent line following the installation of the duct isolation device on the vent line. The<br />
average air pressure at that location was reduced by approximately 0.1 inches of water column.<br />
The other noticeable pressure effect was recorded on the two maintenance holes along the NOS<br />
upstream of the siphon, namely the Bernardo at Eveward maintenance hole and the NOS Siphon<br />
Inlet maintenance hole. At those two locations, the minimum pressures were increased by<br />
approximately 0.3 inches of water column. This was likely related to the air draw effect from the<br />
negative headspace air pressures along the NCOS. This NCOS air draw effect was cut-off from<br />
the NOS once the NOS/NCOS vent line was blocked off on 11/1/09.<br />
A graphical representation of the pressure effects of the planned 24-hour NORS/ECIS and NOTF<br />
<strong>ATF</strong> shut-off is presented in Figure 53.<br />
The most noteworthy recorded effect of the <strong>ATF</strong> shut-off occurred on the NCOS at MH 535-09-<br />
009. This is the first maintenance hole downstream of the 36-inch flexible duct connection that<br />
was installed as part of the NORS/NCOS test described previously in this report. The average<br />
pressure at that location increased by 0.11 inches of water column following the planned <strong>ATF</strong><br />
shut-down. This is similar to the pressure responses to NORS/ECIS <strong>ATF</strong> shut-down events<br />
during the passive and active duct ventilation study described previously in this report.<br />
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Figure 53 – Pressure Effects of <strong>ATF</strong> Shutoffs<br />
The main conclusion drawn from the duct isolation study is that the negative pressures previously<br />
recorded along the NCOS were not a function of any pressure activity along the NOS. Isolating<br />
the permanent air duct that connects those two interceptors at their respective siphons in Culver<br />
City did not result in a significant reduction in air pressure along the NCOS. It did, however<br />
result in a significant increase in the minimum pressures along the NOS.<br />
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6.0 ADDITIONAL SIPHON SAMPLING<br />
In August, <strong>2010</strong> additional air pressure sampling was performed in the following two general<br />
areas:<br />
<br />
<br />
Culver City/Baldwin Hills area on the NORS and NOS<br />
San Fernando Valley upstream of the Radford Siphon on the NOS<br />
The purpose of the sampling in the Culver City/Baldwin Hill area was to perform an analysis of<br />
air pressures in the NORS as a follow-up subsequent to flow diversions away from the NORS to<br />
the recently rehabilitated NOS. Prior to the flow diversion to the NOS, the average dry weather<br />
flows (ADWF) in the NORS were approximately 325 cfs. Following the diversion of flows to the<br />
NOS, the ADWF in the NORS was reduced to 200 cfs. These flow values were provided to the<br />
consultant team by BOS from the MIKE Urban hydraulic model that is maintained by BOS staff.<br />
These flow differences are depicted graphically in Figure 54.<br />
Figure 54 - NORS Modeled Wastewater Flow Comparison<br />
Wastewater Flow (cfs)<br />
450<br />
400<br />
350<br />
300<br />
250<br />
200<br />
150<br />
100<br />
NORS Modeled Wastewater Flow Comparison<br />
Avg =<br />
325<br />
Avg<br />
=<br />
200<br />
2009 (Pre NOS<br />
Activation)<br />
<strong>2010</strong> (Post NOS<br />
Activation)<br />
50<br />
0<br />
12:00 AM<br />
4:00 AM<br />
8:00 AM<br />
12:00 PM<br />
4:00 PM<br />
8:00 PM<br />
12:00 AM<br />
4:00 AM<br />
Time<br />
Table 19 provides information on the locations of pressure sampling, both in the Culver<br />
City/Baldwin Hill area and in the San Fernando Valley.<br />
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Table 19 – Sampling Locations and Description<br />
MH Number Sewer Field Notes<br />
Culver City/Baldwin Hill Area<br />
535-05-021 NORS Culver City Park<br />
535-09-006 NORS US of above-ground duct connection<br />
535-09-022 NORS NORS/ECIS scrubber<br />
535-13-007 NORS DS of above-ground duct connection<br />
559-05-006 NORS Bristol N. of Hannum<br />
535-02-155 NOS Rodeo E. of Kalisman<br />
535-03-156 NOS Rodeo W. of Cochran<br />
San Fernando Valley<br />
442-08-091 NOS 2 nd MH US of Radford Siphon<br />
442-08-090 NOS 3 rd MH US of Radford Siphon<br />
Findings<br />
The air pressure data recorded during this round of sampling is presented graphically in Figures<br />
55, 56 and 57. The data is summarized in Table 20.<br />
Figure 55 - Post Flow Diversion NORS Air Pressure<br />
0.5<br />
Post Flow Diversion NORS Air Pressure<br />
0.4<br />
0.3<br />
Air Pressure (inches WC)<br />
0.2<br />
0.1<br />
0<br />
‐0.1<br />
‐0.2<br />
‐0.3<br />
‐0.4<br />
NORS Culver City Park (MH 535‐05‐021)<br />
NORS US of Duct Cxn (DS of NOTF) (535‐09‐006)<br />
NORS ECIS Scrubber<br />
NORS DS of Duct Cxn (535‐13‐007)<br />
NORS at Bristol N of Hannum<br />
8/16/10 8/18/10 8/20/10 8/22/10 8/24/10 8/26/10<br />
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Figure 56 - Post Flow Diversion NOS Air Pressure in Baldwin Hills<br />
Post Flow Diversion NOS Air Pressure in Baldwin Hills<br />
0.5<br />
0.4<br />
0.3<br />
Air Pressure (inches WC)<br />
0.2<br />
0.1<br />
0<br />
‐0.1<br />
‐0.2<br />
‐0.3<br />
‐0.4<br />
NOS Rodeo E. of Kalisman<br />
NOS Rodeo W. of Cochran<br />
8/16/10 8/18/10 8/20/10 8/22/10 8/24/10 8/26/10<br />
Figure 57 - NOS Air Pressure US of Radford Siphon<br />
NOS Air Pressure US of Radford Siphon<br />
0.5<br />
0.4<br />
Air Pressure (inches WC)<br />
0.3<br />
0.2<br />
0.1<br />
0<br />
‐0.1<br />
‐0.2<br />
‐0.3<br />
‐0.4<br />
NOS 3rd MH US of Radford Siphon<br />
NOS 2nd MH US of Radford Siphon<br />
8/16/10 8/18/10 8/20/10 8/22/10 8/24/10 8/26/10<br />
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Table 20 – Culver City/Baldwin Hills and San Fernando Valley Air Pressure Data Summary<br />
MH Number Sewer Air Pressure (inches WC)<br />
Culver<br />
City/Baldwin<br />
Hills Area<br />
MAX MIN AVG STD DEV Pre to Post<br />
Flow Diversion<br />
ΔAVG.<br />
535-05-021 NORS 0.29 -0.17 0.06 0.07 0.05<br />
535-09-006 NORS 0.27 -0.08 0.05 0.06 -0.14<br />
535-09-022 NORS 0.3 -0.1 0.05 0.07 n/a<br />
535-13-007 NORS 0.42 -0.3 -0.01 0.16 -0.23<br />
559-05-006 NORS 0.34 -0.12 0.07 0.08 n/a<br />
535-02-155 NOS 0.22 -0.36 -0.01 0.06 n/a<br />
535-03-156 NOS 0.2 -0.41 -0.02 0.02 n/a<br />
San Fernando<br />
Valley<br />
442-08-091 NOS 0.11 -0.01 0.05 0.02 n/a<br />
442-08-090 NOS 0.18 -0.09 0.00 0.01 n/a<br />
As shown in Table 20, significant changes in the recorded average pressures along the NORS<br />
were recorded between the pre-diversion period in June 2009, when the NORS was operating<br />
near capacity, and the post-diversion period in August <strong>2010</strong>, by which time over 30% of the<br />
NORS flows had been diverted to the NOS. There was a slight, albeit negligible increase in<br />
average pressure at maintenance hole 535-05-021 (in Culver City Park); however significant<br />
reductions in pressure were achieved at maintenance hole 535-09-006 and at maintenance hole<br />
535-13-007. Reductions in average pressures at these two locations were -0.14 and -0.23 inches<br />
of water column, respectively. These pressure reductions were likely due to the increase in<br />
available headspace in the NORS that resulted from the reduction in flows in that interceptor.<br />
Average pressures were also quite low in the NOS in the vicinity of Baldwin Hills. Pressure were<br />
near atmospheric at MH 535-03-156, on Rodeo just west of Cochran during the entire testing<br />
period, with one exception early in the testing period. Average pressures were also near<br />
atmospheric on the NOS at MH 535-02-155 on Rodeo east of Kalisman; however it is unclear<br />
why the fluctuations at this location were significantly greater than those recorded west of<br />
Cochran.<br />
The pressures recorded just upstream of the Radford Siphon on the NOS in the San Fernando<br />
Valley were very near atmospheric during the entire one week testing period. This is not<br />
surprising given the presence of an actively ventilated carbon scrubber at the upstream end of the<br />
siphon. These results indicate that the scrubber is maintaining acceptable pressure levels in the<br />
NOS in this area; thereby not allowing positive air pressure to build in the NOS upstream of the<br />
siphon.<br />
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7.0 CONCLUSIONS<br />
The purpose of the NOS/NCOS duct isolation study was to determine whether the negative<br />
pressures recorded along the NCOS were being caused by pressure effects along the NOS by<br />
isolating the permanent in-ground duct that connects the NOS to the NCOS. The following<br />
provides a summary of the additional findings of the NORS/NCOS duct connection study<br />
subsequent to the completion of the NOS/NCOS duct isolation study:<br />
<br />
<br />
<br />
<br />
<br />
<br />
Isolating the permanent air duct that connects those two interceptors at their respective<br />
siphons in Culver City did not result in a significant increase in air pressure along the NCOS.<br />
It did, however result in a significant increase in the minimum pressures along the NOS.<br />
The negative pressures previously recorded along the NCOS did not appear to be a function<br />
of any pressure activity along the NOS.<br />
The negative pressure conditions along the NCOS appeared to have been influencing the<br />
pressures along the NOS between the siphon and the NOTF via the permanent duct<br />
connection between the two interceptors, thus potentially keeping the pressures along the<br />
NOS lower than they normally would be when flow is reintroduced back to the NOS.<br />
Both <strong>ATF</strong> ventilation activity and the presence of the NOS/NCOS permanent air duct were<br />
ruled out as causes of the negative pressures recorded along the NCOS; therefore the most<br />
likely cause of these low pressure conditions was the low flow conditions that were in effect<br />
along the NCOS during that time.<br />
Flow diversions away from the NORS to the NOS appear to have resulted in significant<br />
pressure reductions on the NORS<br />
The Radford Siphon carbon scrubber appears to be maintaining air pressure levels very near<br />
atmospheric in the immediate upstream reaches of the NOS in the San Fernando Valley.<br />
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Technical Memorandum – FINAL<br />
Team<br />
City of Los Angeles<br />
Department of Public Works<br />
Bureau of Sanitation<br />
Air Treatment Facility (<strong>ATF</strong>) Review <strong>Study</strong><br />
DIFFERENTIAL AIR PRESSURE STUDY<br />
AT DROP STRUCTURES<br />
TECHNICAL MEMORANDUM<br />
November <strong>2010</strong><br />
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Table of Contents<br />
Executive Summary ...................................................................................................................... 4<br />
1.0 Introduction and Overview ................................................................................................. 4<br />
1.1 Purpose .......................................................................................................................... 5<br />
1.2 Expected Behavior ......................................................................................................... 5<br />
2.0 Sampling and Testing Setup .............................................................................................. 6<br />
2.1 Data Collection Locations ............................................................................................... 6<br />
2.2 Schedule ....................................................................................................................... 11<br />
2.3 Roles and Responsibilities ........................................................................................... 15<br />
3.0 Field Activities .................................................................................................................. 16<br />
3.1 Data Logger Installation ................................................................................................ 16<br />
3.2 Plug Installations .......................................................................................................... 19<br />
3.3 Flow Management ........................................................................................................ 21<br />
4.0 Collected Data and Results .............................................................................................. 22<br />
4.1 Division Drop Structure ................................................................................................. 22<br />
4.2 Humboldt Drop Structure .............................................................................................. 27<br />
4.3 Mission and Jesse Drop Structure ................................................................................ 31<br />
4.4 23 rd and San Pedro Drop Structure .............................................................................. 36<br />
4.5 USC Drop Structure ...................................................................................................... 40<br />
4.6 Systemwide Downstream ............................................................................................. 44<br />
4.7 Findings ........................................................................................................................ 48<br />
4.7.1 General Observations ........................................................................................... 48<br />
4.7.2 Division Drop Structure & Vicinity .......................................................................... 48<br />
4.7.3 Humboldt Drop Structure & Vicinity ....................................................................... 49<br />
4.7.4 Mission and Jesse Drop Structure & Vicinity ......................................................... 49<br />
4.7.5 23 rd and San Pedro Drop Structure & Vicinity ....................................................... 50<br />
4.7.6 USC Drop Structure & Vicinity ............................................................................... 50<br />
4.7.7 Systemwide Downstream Interceptors .................................................................. 50<br />
5.0 Conclusions ...................................................................................................................... 52<br />
List of Tables<br />
Table 1 - Air Pressure Sampling Locations ................................................................................. 10<br />
Table 2 - Overall Sampling Schedule ......................................................................................... 12<br />
Table 3 – Differential Air Pressure Data (inches of water) at the Division Drop Structure .......... 23<br />
Table 4 - Humboldt Drop Structure Recorded Field Data ........................................................... 28<br />
Table 5 - Mission and Jesse Drop Structure Recorded Field Data ............................................. 32<br />
Table 6 - 23rd and San Pedro Drop Structure Recorded Field Data .......................................... 37<br />
Table 7 - USC Drop Structure Recorded Field Data ................................................................... 41<br />
Table 8 - Systemwide Downstream Recorded Field Data .......................................................... 45<br />
List of Figures<br />
Figure 1 – Location of the Air Pressure Data Loggers for the Drop Structures Sampling ............. 8<br />
Figure 2 - Location of the Air Pressure Data Loggers Downstream ............................................. 9<br />
Figure 3 – Timeline of Pressure Data Collection at Drop Structures and Sewer Conditions ...... 11<br />
Figure 4 - Schematic of Data Logger Installation at Division Drop Structure .............................. 13<br />
Figure 5 - Schematic of Data Logger Installation at Humboldt Drop Structure ........................... 14<br />
Figure 6 - Schematic of Data Logger Installation at Mission and Jesse Drop Structure ............. 14<br />
Figure 7 - Schematic of Data Logger Installation at 23rd and San Pedro Drop Structure .......... 15<br />
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Figure 8 – Data Logger Installation Kit ........................................................................................ 17<br />
Figure 9 - Manhole 49514241 ..................................................................................................... 17<br />
Figure 10 - Data Logger Installed ............................................................................................... 17<br />
Figure 11 - Manhole 49509106 ................................................................................................... 17<br />
Figure 12 - Installing Data Logger ............................................................................................... 17<br />
Figure 13 – Manhole 51509154 .................................................................................................. 17<br />
Figure 14 - Manhole 51513136 ................................................................................................... 18<br />
Figure 15 - Manhole 51513137 ................................................................................................... 18<br />
Figure 16 - Manhole 53503213 .................................................................................................. 18<br />
Figure 17 - Manhole 53703199 ................................................................................................... 18<br />
Figure 18 - Manhole 53703199 Installed .................................................................................... 18<br />
Figure 19 - Manhole 53706178 .................................................................................................. 18<br />
Figure 20 - Plug Delivery ............................................................................................................ 19<br />
Figure 21 - Plug Discharge ......................................................................................................... 19<br />
Figure 22 - Plug Installation with Crane ...................................................................................... 19<br />
Figure 23 - Plug Insertion in M/H ................................................................................................ 19<br />
Figure 24 - Adjustment to Plug ................................................................................................... 20<br />
Figure 25 - Plug Installation Complete ........................................................................................ 20<br />
Figure 26 - View of Plug in Air Return Line ................................................................................. 20<br />
Figure 27 - Installation of Data Loggers ...................................................................................... 20<br />
Figure 28 - Removal of the Stop Log .......................................................................................... 21<br />
Figure 29 - Stop Log Location ..................................................................................................... 21<br />
Figure 30 - Division Drop Structure Upstream Average Pressure .............................................. 24<br />
Figure 31 - Division Drop Structure Downstream Average Pressure .......................................... 25<br />
Figure 32 - Division Drop Structure Average Pressure ............................................................... 25<br />
Figure 33 - Humboldt Drop Structure Upstream Average Pressure............................................ 28<br />
Figure 34 - Humboldt Drop Structure Downstream Average Pressure ....................................... 29<br />
Figure 35 - Humboldt Drop Structure Average Pressure ............................................................ 29<br />
Figure 36 - Mission and Jesse Drop Structure Upstream Average Pressure ............................. 32<br />
Figure 37 - Mission and Jesse Drop Structure Downstream Average Pressure ......................... 33<br />
Figure 38 - Mission and Jesse Drop Structure Average Pressure .............................................. 33<br />
Figure 39 - 23rd and San Pedro Drop Structure Upstream Average Pressure ........................... 37<br />
Figure 40 - 23rd and San Pedro Drop Structure Downstream Average Pressure ...................... 38<br />
Figure 41 - 23rd and San Pedro Drop Structure Average Pressure ........................................... 38<br />
Figure 42 - USC Drop Structure Upstream Average Pressure ................................................... 41<br />
Figure 43 - USC Drop Structure Downstream Average Pressure ............................................... 42<br />
Figure 44 - USC Drop Structure Average Pressure .................................................................... 42<br />
Figure 45 - Systemwide Downstream Jefferson Siphon Upstream Average Pressure ............... 45<br />
Figure 46 - Systemwide Downstream NORS/ECIS Junction (ECIS) Average Pressure ............ 46<br />
Figure 47 - Systemwide Downstream NORS/ECIS Junction (NORS) Average Pressure .......... 46<br />
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EXECUTIVE SUMMARY<br />
The City of Los Angeles has a long history of implementing proactive and innovative steps to<br />
control odors from its interceptor collection system including using chemical addition to control<br />
odors with an extensive use of magnesium hydroxide and sodium hydroxide. Recently, the City<br />
has been working to improve odor control in several areas identified by local community groups.<br />
Air treatment facilities (<strong>ATF</strong>s) with known or predicted odor “hot spots” were included in the<br />
2004 Collection System Settlement Agreement (CSSA).<br />
The present Technical Memorandum evaluates the impact of drop structures on the sewer<br />
differential air pressures (difference in air pressure between inside and outside the sewer and the<br />
ambient air), under current conditions and planned modifications. This study focused on<br />
measuring and examining differential air pressures at the four existing sewer drop structures in<br />
the City's wastewater collection system:<br />
<br />
<br />
<br />
Division<br />
Humboldt<br />
Mission and Jesse<br />
23 rd and San Pedro<br />
A baseline condition was established, which consisted of measuring the sewer differential air<br />
pressures along a route starting at the Division drop structure on the Northeast Interceptor Sewer<br />
(NEIS) and ending at a maintenance hole in Culver City Park on the North Outfall Relief Sewer<br />
(NORS). This was followed by the physical plugging of the return air lines at each drop structure<br />
in order to measure the impact on the differential air pressures at the drop structures, on the North<br />
Outfall Sewer (NOS) approach pipelines and downstream deep tunnels. The purpose was to<br />
examine the effectiveness of each return line in air recirculation at the structure. <strong>Final</strong>ly, flow<br />
management (diversion/redistribution) was introduced to the system and more differential air<br />
pressure data was collected to valuate the effect of increased flow on the differential air pressures<br />
at the structures. During theses three different phases, Air Treatment Facilities (<strong>ATF</strong>) at Mission<br />
& Jesse and Humboldt were turned on and off several times in order to study their impact on the<br />
air pressure.<br />
It was determined that:<br />
Plugging the air return lines in the drop structures generally resulted in increasing<br />
pressures along the entire NEIS/ECIS tunnel alignment<br />
<br />
<br />
<br />
Plugging the air return lines generally resulted in maintaining atmospheric pressure levels<br />
in the NOS approach sewers, with the exception of the approach to the Mission and Jesse<br />
drop structure, where pressures initially increased along the NOS, then gradually<br />
decreased over time<br />
Adjusting stop logs generally resulted in decreasing pressures on the NOS. Those<br />
locations where the pressures didn’t decrease remained at atmospheric levels.<br />
The <strong>ATF</strong>’s generally reduce pressures along the entire length of the NEIS/ECIS tunnel.<br />
Noticeable pressure reductions occur when the <strong>ATF</strong>’s are turned on. Noticeable pressure<br />
increases occur when the <strong>ATF</strong>’s are turned off.<br />
1.0 INTRODUCTION AND OVERVIEW<br />
A drop structure is a manmade structure to pass water or wastewater to a lower elevation while<br />
controlling the energy and velocity of the flow. The purpose of the air return line in a drop<br />
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structure is to attenuate the pumping effect of the flow going down the drop shaft. Drop<br />
structures in sewer collection systems are potential locations of odor problems as a result of<br />
increased air pressures caused by the rapid vertical drop of sewage within the structures and the<br />
backpressurization caused by interconnection to the receiving tunnel. The increased air pressures<br />
often result in release of the odorous air to the neighborhood with subsequent odor complaints.<br />
1.1 Purpose<br />
The purpose of this TM is to better understand the sewer differential air pressures and<br />
fluctuations at the drop structures, and examine the impact of the following measures upon the<br />
differential air pressures:<br />
1. Blocking of the return air lines at each drop structure<br />
2. Increasing / decreasing the wastewater flow at each drop structure<br />
3. Operating (cycling off and on) the existing interim carbon scrubbers<br />
The broader objective is to identify any potential changes to the planned odor control strategies<br />
and methods to control odorous air release in the proximity of the drop structures.<br />
After collecting baseline measurements, return airlines within the drop structures were plugged in<br />
order to evaluate the effect that they have on air pressures within the structures and subsequently<br />
in the NORS, East Central Interceptor Sewer (ECIS) and the approach sewers such as the NOS<br />
and Eagle Rock Interceptor Sewer (ERIS). Several operation scenarios were also performed<br />
including diverting flows at the Humboldt and the Mission and Jesse drop structures and<br />
adjusting on/off status of the carbon scrubber at Humboldt and Mission and Jesse drop structures<br />
and the damper at the Humboldt drop structure, which together will facilitate understanding of the<br />
air movement as well as the zone of influence near each drop structure.<br />
1.2 Expected Behavior<br />
Previous studies performed on the interceptor system in Central Los Angeles have resulted in<br />
observations which showed that differences in observed positive differential air pressure<br />
phenomena in a given sewer over an extended time period could be directly correlated to<br />
wastewater flow volumes. For example, during times when flows are higher, differential air<br />
pressure tends to be higher and vice versa. This has been shown to be true not only with respect<br />
to diurnal flow patterns, but also before and during periods when flows have been diverted from<br />
one interceptor to another.<br />
In addition, previous differential air pressure readings taken on the approach sewer that carries<br />
flow into the USC Drop Structure on the ECIS have shown that the approach pipe headspace is<br />
under almost constant negative pressure. Unlike all other NEIS and ECIS drop structures, the<br />
USC Drop Structure has no air return line connecting the receiving chamber to the top of the<br />
vertical drop shaft; therefore there would be no open conduit for positive differential air pressure<br />
to travel into the shallow, upstream approach pipe.<br />
It was therefore theorized that the positive air pressure and subsequent odor complaints that occur<br />
primarily along the NOS could be better understood by conducting a series of tests that would<br />
involve the following system manipulations:<br />
<br />
<br />
Plugging the air return lines in place at the Division, Humboldt, Mission & Jesse and<br />
23rd & San Pedro drop structures along the NEIS and ECIS<br />
Adjusting stop logs in place at the Humboldt and the Mission & Jesse drop structures on<br />
the NEIS and ECIS, respectively to allow more flows to enter the drop structure at<br />
Mission and Jesse<br />
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In conjunction with these two primary manipulations, various ON/OFF tests were to be staged<br />
with the interim carbon scrubbers at the Humboldt and Mission & Jesse drop structures.<br />
Given the previously described system pressure observations, the expected results at the start of<br />
the drop structure study were as follows:<br />
<br />
<br />
Plugging the air return lines would reduce the pressures along the shallow, approach<br />
sewers at each drop structure location<br />
Plugging the air return lines would result in an increase in differential air pressure along<br />
the NEIS and ECIS alignments<br />
Adjusting stop logs at Humboldt and Mission and Jesse would result in less air dragged<br />
into the NEIS at Humboldt and more air dragged into the ECIS at Mission and Jesse.<br />
The results of the drop structure test, compared to the expected results, were as follows:<br />
<br />
<br />
<br />
Plugging the air return lines did significantly reduce the differential air pressures on the<br />
NOS approach sewer at Mission &Jesse. Other NOS pressures at Humboldt and 23rd &<br />
San Pedro remained near atmospheric levels throughout the entire duration of the study.<br />
The pressure at the Division drop structure was significantly reduced as a result of<br />
plugging the air return line at that location.<br />
Plugging the air return lines did result in significant differential air pressure increases<br />
along the entire NEIS/ECIS alignment.<br />
Stop log adjustments at Humboldt and Mission and Jesse, in conjunction with all air<br />
return lines being plugged, appeared to result in an overall reduction in the amount of air<br />
dragged into the NEIS and ECIS. This was evidenced by the difference in air pressures<br />
between the Mission and Jesse and Humboldt drop structures when comparing the<br />
plugged condition versus the combined plugged and stop log adjustment condition.<br />
2.0 SAMPLING AND TESTING SETUP<br />
The air pressure data collection consisted of continuous pressure recording at two-minute<br />
intervals over two one-week periods at the locations shown in Table 1. ACR SmartReader Plus 4<br />
data loggers were used, which at a two-minute interval setting, have the capacity to log data for<br />
approximately two weeks. The data loggers were visited every two weeks to download the<br />
collected data, after which they were replaced with fresh data loggers in the maintenance holes<br />
for additional data collection.<br />
The data logging instruments were installed from the surface, which meant that entry into<br />
maintenance holes or structures was not required for their installation. Installations were<br />
temporary and generally took place by suspending the instruments from a maintenance hole rim,<br />
step or lid without damage to any maintenance hole liners or protective coatings.<br />
2.1 Data Collection Locations<br />
In general, the locations of the differential air pressure data loggers were selected as follows:<br />
<br />
<br />
<br />
Within each drop structure, locations in the drop shafts immediately above the<br />
connections with the air return lines;<br />
First manhole immediately upstream of each drop structure in the NEIS/ECIS tunnel and<br />
on the approach sewers;<br />
First manhole immediately downstream of each drop structure in the NEIS/ECIS tunnel;<br />
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Manholes upstream and downstream of the USC drop structure on ECIS;<br />
Additional manholes near each drop structure if needed;<br />
One manhole upstream of Jefferson siphon on ECIS<br />
Manholes upstream of NORS/ECIS junction;<br />
Figure 1 and Figure 2 show the location of the differential air pressure data loggers relative to the<br />
drop structures and in downstream sewers. Table 1 provides the location details for each<br />
differential air pressure data logger. Each data logger was installed at maintenance holes<br />
referenced in Table 1. Figure 3 shows the pressure data collection timeline for the different sewer<br />
conditions tested (baseline, return line plugs, scrubbers on/off, and flow management). Figures 4,<br />
5 and 6 show the location of the differential air pressure data logger within each drop structure.<br />
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Figure 1 – Location of the Air Pressure Data Loggers for the Drop Structures Sampling<br />
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Figure 2 - Location of the Air Pressure Data Loggers Downstream<br />
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Table 1 - Air Pressure Sampling Locations<br />
Group Manhole ID Sewer Description Street 1 Street 2<br />
Inner<br />
Cover<br />
46812156 ERIS<br />
First manhole upstream of<br />
Division drop structure CYPRESS AVE CAZADOR ST NO<br />
46816116 ERIS/NEIS Division drop structure<br />
SAN<br />
FERNANDO RD<br />
R/W<br />
NW/O<br />
DIVISION ST YES<br />
Division<br />
46713313 NEIS<br />
First manhole downstream of<br />
Division drop structure<br />
(1400 BLK)SAN<br />
FERNANDO RD<br />
NW/O ARVIA<br />
ST<br />
YES<br />
49505144 NEIS<br />
First manhole upstream of<br />
Humboldt drop structure on<br />
NEIS<br />
SAN<br />
FERNANDO RD<br />
N/O FIGUEROA<br />
ST (Home<br />
Depot)<br />
YES<br />
49509108 NOS/NEIS<br />
First manhole upstream of<br />
Humboldt drop structure on<br />
NOS<br />
W/O SAN<br />
FERNANDO RD<br />
N/O<br />
HUMBOLDT ST YES<br />
49509106 NEIS Humboldt drop structure<br />
W/O SAN<br />
FERNANDO RD<br />
N/O<br />
HUMBOLDT ST YES<br />
Humboldt<br />
49514241 NEIS<br />
Manhole midway between<br />
Humboldt and Mission/Jesse MAIN ST AVE 21 YES<br />
51505288 NEIS<br />
First manhole upstream of<br />
Mission/Jesse drop structure<br />
on NEIS MISSION RD KEARNEY ST YES<br />
51509154 NOS<br />
First manhole upstream of<br />
Mission/Jesse drop structure<br />
on NOS MISSION RD 6TH ST NO<br />
51513137 NEIS Mission/Jesse drop structure<br />
W/O MISSION<br />
RD N/O JESSE ST YES<br />
Mission and Jesse 51513136 ECIS<br />
First manhole downstream of<br />
Mission/Jesse drop structure SANTA FE AVE N/O 7TH PL YES<br />
23rd and San<br />
Pedro<br />
USC<br />
Systemwide<br />
Downstream<br />
Effects<br />
53703177 ECIS<br />
53702211 NOS<br />
First manhole upstream of<br />
23rd/San Pedro drop<br />
structure on ECIS<br />
Second manhole upstream of<br />
23rd/San Pedro drop<br />
(1100 BLK)<br />
22ND ST<br />
E/O GRIFFITH<br />
AVE<br />
YES<br />
structure on NOS TRINITY ST S/O 23RD ST Unknown<br />
First manhole upstream of<br />
23rd/San Pedro drop<br />
SAN PEDRO W/O SAN<br />
structure on NOS<br />
ST ALLEY PEDRO ST YES<br />
53703199 NOS/ECIS<br />
23rd/San Pedro drop<br />
SAN PEDRO<br />
53703200 ECIS structure<br />
ST R/W 23RD ST YES<br />
First manhole downstream of<br />
23rd/San Pedro drop<br />
W/O TRINITY<br />
53706178 ECIS structure<br />
31ST ST ST<br />
YES<br />
First manhole upstream of<br />
53705181 ECIS USC drop structure GRAND AVE S/O 35TH ST YES<br />
EXPOSITION E/O MENLO<br />
53705184 ECIS USC drop structure<br />
BLVD N/RDWY AVE<br />
YES<br />
First manhole downstream of EXPOSITION<br />
53607171 ECIS USC drop structure<br />
BLVD N/R <strong>LA</strong> SALLE ST YES<br />
Upstream of Jefferson JEFFERSON W/O<br />
53503213 ECIS Siphon<br />
BLVD<br />
COCHRAN YES<br />
Upstream of NORS/ECIS <strong>LA</strong> CIENEGA<br />
53506116 ECIS Junction on ECIS<br />
BLVD A<strong>LA</strong>DDIN ST YES<br />
Upstream of NORS/ECIS JEFFERSON CULVER CITY<br />
53505021 NORS Junction on NORS<br />
BLVD R/W PARK<br />
YES<br />
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2.2 Schedule<br />
There were three distinct sessions for the sampling effort. Session1 involved collecting baseline<br />
differential air pressure data with the scrubber turned on or off at the locations listed in Table 1.<br />
Session 2 was similar to Session 1, except that the return airline at each drop structure was<br />
plugged in an attempt to evaluate the air ventilation effectiveness through these existing return<br />
airlines. Session 3 consisted of monitoring the air pressures under several flow diversion<br />
scenarios along with the installation of a curtain at 23 rd and San Pedro. The purpose of the curtain<br />
was to isolate the headspace between the NOS approach sewer at 23 rd and San Pedro and the<br />
ECIS tunnel.<br />
Session 1 lasted four weeks (from 2/16/<strong>2010</strong> to 3/16/<strong>2010</strong>) and included delays due to rain and<br />
contractor contract preparation. Session 2 started on 3/16/<strong>2010</strong> with the installation of the fist<br />
plug at Division. Sampling of air pressure with plugs installed lasted from 3/16/<strong>2010</strong> to 4/1/<strong>2010</strong>.<br />
Session 3, consisting of flow management, started on 4/2/<strong>2010</strong> and lasted till 5/4/<strong>2010</strong>. The<br />
curtain was installed on 4/29/<strong>2010</strong> and removed on 5/7/<strong>2010</strong>. Figure 3graphically depicts the<br />
timeline of the sampling sessions including the scrubbers’ on/off conditions at both Humboldt<br />
and Mission and Jesse.<br />
Figure 3 – Timeline of Pressure Data Collection at Drop Structures and Sewer Conditions<br />
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Table 2 below shows the overall data collection schedule.<br />
Event<br />
Table 2 - Overall Sampling Schedule<br />
Event Period<br />
Session 1<br />
Baseline Scenarios<br />
(Scrubber on/off)<br />
Start Date<br />
2/16/<strong>2010</strong><br />
End Date<br />
3/16/<strong>2010</strong><br />
Session 2<br />
Plug Test Scenarios<br />
Start Date<br />
3/16/<strong>2010</strong><br />
End Date<br />
4/2/<strong>2010</strong><br />
Session 3<br />
Flow Management<br />
/Curtain Test Scenarios<br />
Start Date<br />
4/2/<strong>2010</strong><br />
Install Air Pressure Data 2/16 to 2/17 n/a n/a n/a n/a n/a n/a<br />
Loggers<br />
All data loggers installed and n/a Day 1 Day 29 n/a n/a n/a n/a<br />
logging data for Session 1<br />
Plug return airlines/Session 2 3/16, 3/19, 3/24, 3/30 n/a n/a Day 29 Day 45 n/a n/a<br />
begins<br />
Reset data loggers 3/2, 3/3 and 3/23, n/a n/a n/a n/a n/a n/a<br />
3/24<br />
All data loggers reset and n/a n/a n/a Day 29 Day 45 n/a n/a<br />
logging data/Session 2<br />
continues<br />
Adjust stop logs at Humboldt 4/2 and 4/13 n/a n/a n/a n/a Day 46 Day 57<br />
and M&J/Session 3 begins<br />
Reset data loggers 4/2, 4/3 and 4/20,<br />
4/21<br />
n/a n/a n/a n/a n/a n/a<br />
Install curtain at 23 rd and San<br />
Pedro<br />
All data loggers reset and<br />
logging data/Session 3<br />
continues<br />
Retrieve data loggers/Remove<br />
plugs/Remove curtain/Back to<br />
normal operations<br />
End Date<br />
5/7/<strong>2010</strong><br />
Day 75<br />
n/a n/a n/a n/a n/a n/a<br />
4/29<br />
n/a n/a n/a n/a n/a Day 46 Day 80<br />
Day 77 to Day 85<br />
(5/7 to 5/12)<br />
n/a n/a n/a n/a n/a n/a<br />
Figure 4 thru Figure 7 below graphically show the drop structures and locations within each<br />
where pressure monitors were installed. An existing access maintenance hole at the Division<br />
Drop Structure is not depicted in Figure 4.<br />
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Figure 4 - Schematic of Data Logger Installation at Division Drop Structure<br />
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Figure 5 - Schematic of Data Logger Installation at Humboldt Drop Structure<br />
Figure 6 - Schematic of Data Logger Installation at Mission and Jesse Drop Structure<br />
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Figure 7 - Schematic of Data Logger Installation at 23rd and San Pedro Drop Structure<br />
2.3 Roles and Responsibilities<br />
The sampling activities were a joint effort between the HDR/Malcolm Pirnie team, its<br />
subcontractor (E2) and City BOS staff. The roles and responsibilities for each of the three<br />
included the following:<br />
HDR/Malcolm Pirnie<br />
Prepare all instruments for data logging<br />
E2<br />
<br />
<br />
<br />
<br />
<br />
<br />
Installation of all data logging instruments<br />
Data downloads from all instruments<br />
Retrieval of all data instruments<br />
Data compilation, organization and analysis<br />
Documentation of results<br />
Support HDR/MP representatives in accessing, closing and properly sealing all<br />
maintenance holes accessed during this sampling effort (see 2009 Field Ops Workshop<br />
presentation for details)<br />
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City BOS Staff<br />
Accompany HDR/MP staff in field during instrument installation/removal and fan<br />
operation during normal working hours.<br />
Adjust scrubber/damper status<br />
City Designated Contractor<br />
Procure inflatable plug capable of plugging the 42-inch diameter return airline at the<br />
Division drop structure<br />
<br />
<br />
<br />
<br />
Procure inflatable plug capable of plugging the 78-inch diameter return airline at the<br />
Mission and Jessie drop structure<br />
Procure inflatable plug capable of plugging the 78-inch diameter return airline at the 23 rd<br />
and San Pedro drop structure<br />
Procure inflatable plug capable of plugging the 54-inch diameter return airline at the<br />
Humboldt drop structure<br />
Perform confined space entry into the four drop structures; insert and inflate, and<br />
subsequently deflate and remove each of the four return air line plugs described<br />
previously in this section according to plug manufacturer’s recommended procedures and<br />
the schedule.<br />
Adjust stop logs at Humboldt and Mission and Jesse diversion structures during phase 3<br />
flow management test<br />
<br />
If necessary, install and remove the air curtain at 23rd and San Pedro drop structure<br />
3.0 FIELD ACTIVITIES<br />
This section describes the field activities that were performed to collect the differential air<br />
pressure data. The sampling was performed according to the schedule as described in Table 2.<br />
3.1 Data Logger Installation<br />
Twenty two data loggers were installed to record baseline differential air pressure data on<br />
February 16 and 17, <strong>2010</strong> at the data collection locations indicated in Table 1above. City staff<br />
were present at the time to provide guidance on the exact sampling locations that were proposed.<br />
Photographs taken at various data logger locations are presented in Figure 8 through Figure 19.<br />
Due to the length of the data collection period, the recorded data in the data loggers was<br />
periodically downloaded and then reset. In general, the data loggers were reset every two weeks<br />
to accommodate a two minute sampling sequence.<br />
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Figure 8 – Data Logger Installation Kit Figure 9 - Manhole 49514241<br />
Figure 10 - Data Logger Installed Figure 11 - Manhole 49509106<br />
Figure 12 - Installing Data Logger<br />
Figure 13 – Manhole 51509154<br />
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Figure 14 - Manhole 51513136 Figure 15 - Manhole 51513137<br />
Figure 16 - Manhole 53503213 Figure 17 - Manhole 53703199<br />
Figure 18 - Manhole 53703199 Installed<br />
Figure 19 - Manhole 53706178<br />
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3.2 Plug Installations<br />
Following the baseline session, plugs were installed in the air return lines of the four drop<br />
structures (Division 3/16/10, Humboldt 3/19/10, Mission and Jesse 3/24/10 and 23 rd and San<br />
Pedro 3/30/10). The plugs were installed in order to evaluate the effect that they have on the<br />
differential air pressures within the structures and subsequently in the NORS and ECIS sewers<br />
themselves. The plugs were installed sequentially, starting at the Division drop structure and data<br />
was collected for 3 days before plugging the next one. City contractor Murray Company installed<br />
the plugs supported by City staff.<br />
Figure 20 - Plug Delivery<br />
Figure 21 - Plug Discharge<br />
Figure 22 - Plug Installation with Crane<br />
Figure 23 - Plug Insertion in M/H<br />
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Figure 24 - Adjustment to Plug<br />
Figure 25 - Plug Installation Complete<br />
Figure 26 - View of Plug in Air Return Line<br />
Figure 27 - Installation of Data Loggers<br />
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3.3 Flow Management<br />
Following the plug installation, the third session of the field differential pressure data collection<br />
was under way. Stop logs at two drop structures (Mission and Jesse, and 23 rd and San Pedro)<br />
were removed. During the first week of May, two stop logs were reinserted into the upstream<br />
NOS approach diversion at Humboldt.<br />
Stop log removals at Humboldt and Mission and Jesse resulted in a reduction of flow to the NEIS<br />
via the Humboldt drop structure and additional flow to the NEIS via the Mission and Jesse drop<br />
structure.<br />
The removal at the 23 rd and San Pedro drop structures brought additional flow to the NOS.<br />
Figure 28and Figure 29 show the removal of the stop log at Mission and Jesse.<br />
Figure 28 - Removal of the Stop Log<br />
Figure 29 - Stop Log Location<br />
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4.0 COLLECTED DATA AND RESULTS<br />
This section provides the results of the field data collection. Data is compiled by drop structures<br />
and spans the length of the data collection period covering all three sessions of baseline, plugs<br />
and flow management.<br />
The large amount of data recorded over three months by each of the 22 data loggers collecting<br />
pressure readings every two minutes were processed to calculate the minimum, average, and<br />
maximum values. To calculate the average value, five time intervals were established first to<br />
divide a 24 hour period of a day. For each time interval, an average value was calculated using<br />
all 2-minute readings in that time period. <strong>Final</strong>ly, the average value for that day was calculated as<br />
the average of the time intervals. The results are provided as tables and figures in this section.<br />
Each logger was essentially dormant during the approximate time period between March 3 rd and<br />
March 8 th , <strong>2010</strong>. This is reflected in the data sets by the flat line at the atmospheric pressure level<br />
in each chart; however this time period was disregarded when calculating statistical summaries<br />
for each data set.<br />
4.1 Division Drop Structure<br />
Three data loggers were installed in the locations listed below.<br />
<br />
<br />
<br />
MH 46812156, 270 feet US of Division drop structure on ERIS<br />
MH 46713313, 2,900 feet DS of Division drop structure on NEIS<br />
MH 46816116, Division drop structure on NEIS<br />
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(Note that in the figure above, US means “Upstream” and DS means “Downstream”)<br />
Table 3 – Differential Air Pressure Data (inches of water) at the Division Drop Structure<br />
Division Drop Structure Ups tream Downstream Drop Structure<br />
ERIS at MH<br />
46812156<br />
NEIS at MH<br />
46713313<br />
ERIS /NEIS at MH<br />
46816116<br />
Sewer Condition<br />
Min Avg Max Min Avg Max Min Avg Max<br />
Baseline<br />
Start<br />
2/16/<strong>2010</strong><br />
End<br />
3/16/<strong>2010</strong> 0.2 0.23 0.28 -0.21 0.17 0.51 -0.35 -0.11 0.06<br />
Plug<br />
Installed<br />
3/16/<strong>2010</strong><br />
Removed<br />
5/6/<strong>2010</strong> 0.22 0.24 0.29 -1.14 0.17 0.68 -2.36 -1.19 -0.1<br />
Stop Logs<br />
Removed<br />
4/2/<strong>2010</strong><br />
Reinstalled<br />
5/4/<strong>2010</strong> n/a n/a n/a -1.14 0.18 0.68 -2.3 -1.08 -0.11<br />
Note: The logger at manhole 46812156 was removed and stopped recording on<br />
3/24 due to extreme low pressure observed exceeding ACR logger limit<br />
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The following three figures summarize the differential air pressure recorded at the maintenance<br />
holes at Division.<br />
Figure 30 - Division Drop Structure Upstream Average Pressure<br />
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Figure 31 - Division Drop Structure Downstream Average Pressure<br />
Figure 32 - Division Drop Structure Average Pressure<br />
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Plug Effect: The positive pressures recorded at the ERIS manhole during the baseline testing<br />
period were likely the result of air being forced up into the drop structure air return line from the<br />
NEIS tunnel, which was also under positive pressure. The plugged air return duct at the Division<br />
drop structure resulted in an extremely negative pressure at the upstream ERIS manhole. During<br />
field data download activities approximately two weeks after the air return line plug insertion at<br />
the Division drop structure, field crew members noted that the pressures at this location were well<br />
below the minimum -2.45 inches w.c. that the ACR data loggers are able to record. This was<br />
likely due to the fact that the approach pipe from the ERIS to the drop structure had been denied<br />
its primary source of headspace air when the plug was inserted in the drop structure air return<br />
line. The drag induced by the flowing wastewater on the drop structure approach pipe headspace<br />
therefore drew a vacuum in the upstream manhole. Crew member observations of airflow into<br />
this manhole confirmed that the pressures here were extremely negative. The plugged air return<br />
duct at the Division drop structure generally resulted in an increasing pressure trend on the NEIS<br />
just downstream of the drop structure. Once the plug was removed, the pressure on the NEIS MH<br />
at this location was immediately reduced to near baseline levels. The plugged air return duct at<br />
the Division drop structure clearly resulted in a severe pressure reduction at the drop structure.<br />
Once the plug was removed, the pressure at this location immediately increased to near baseline<br />
levels.<br />
Stop Log Removal: The pressure on the NEIS MH at this location showed a slight reduction<br />
trend during the stop log removal period. The pressure on the NEIS MH at this location remained<br />
fairly constant during the stop log removal period, during which time flows were directed away<br />
from the Humboldt drop structure and towards the Mission and Jesse drop structure. This was<br />
likely due to the fact that the NOS flow at the Humboldt drop structure was diverted away from<br />
the NEIS due to the stop log removal, thereby resulting in less air being dragged into the drop<br />
structure and into the NEIS.<br />
Scrubbers on/off: The scrubber at the Humboldt drop structure has a slight pressure reduction<br />
effect on the Division drop structure and a slight effect on the NEIS downstream of the Division<br />
drop structure. Several instances shown on the chart show direct, albeit slight, pressure increase<br />
effects when the scrubber was turned off and pressure decrease effects when the scrubber was<br />
turned back on.<br />
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4.2 Humboldt Drop Structure<br />
Four data loggers were installed at the locations shown in the map below.<br />
MH 49505144, 2,800 feet US of Humboldt drop structure on NEIS<br />
MH 49509108, 60 feet US of Humboldt drop structure on NOS<br />
MH 49514241, 4,800 feet DS of Humboldt drop structure on NEIS<br />
MH 49509106, Humboldt drop structure on NEIS<br />
(Note that in the figure above, US means “Upstream” and DS means “Downstream”)<br />
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Table 4 - Humboldt Drop Structure Recorded Field Data<br />
Humboldt Drop Structure Upstream Downstream<br />
Sewer Condition<br />
Min Avg Max Min Avg Max Min Avg Max Min Avg Max<br />
Baseline<br />
Start End<br />
2/16/<strong>2010</strong> 3/19/<strong>2010</strong><br />
Scrubber Off 2/16/<strong>2010</strong> 3/4/<strong>2010</strong> 0.01 0.42 0.77 -0.50 -0.16 0.04 0.05 0.50 1.00 -0.27 0.05 1.48<br />
Scrubber On 3/4/<strong>2010</strong> 3/10/<strong>2010</strong> 0.27 0.41 0.59 -0.19 -0.09 0.04 0.24 0.41 0.76 -0.04 0.02 0.10<br />
Scrubber Off 3/10/<strong>2010</strong> 3/19/<strong>2010</strong> -0.04 0.20 0.57 -0.23 -0.11 0.02 0.22 0.52 1.07 -2.42 -0.14 2.30<br />
Plug<br />
Installed<br />
3/19/<strong>2010</strong><br />
Removed<br />
5/6/<strong>2010</strong><br />
Scrubber On 3/19/<strong>2010</strong> 3/22/<strong>2010</strong> -0.03 0.13 0.33 -0.27 -0.14 -0.01 0.24 0.61 0.92 -2.42 -1.92 0.05<br />
Scrubber Off 3/22/<strong>2010</strong> 4/2/<strong>2010</strong> 0.11 0.57 1.07 -0.29 -0.05 0.09 0.49 1.03 1.66 -2.42 -0.80 0.06<br />
Stop Logs<br />
Removed<br />
4/2/<strong>2010</strong><br />
Reinstalled<br />
5/4/<strong>2010</strong><br />
NEIS at MH<br />
49505144<br />
NOS at MH<br />
49509108<br />
NEIS at MH<br />
49514241<br />
Drop Structure<br />
NEIS/NOS at MH<br />
49509106<br />
Scrubber On 4/2/<strong>2010</strong> 4/7/<strong>2010</strong> 0.26 0.55 1.27 -0.18 0.00 0.09 0.75 1.14 1.88 -2.43 -1.84 0.34<br />
Scrubber Off 4/7/<strong>2010</strong> 4/9/<strong>2010</strong> 0.41 0.70 1.08 0.01 0.03 0.05 1.02 1.57 2.09 -2.41 -1.84 0.09<br />
Scrubber On 4/9/<strong>2010</strong> 4/13/<strong>2010</strong> 0.17 0.44 1.15 -0.11 0.01 0.05 0.73 1.15 1.80 -2.42 -2.23 0.08<br />
Scrubber Off 4/13/<strong>2010</strong> 4/19/<strong>2010</strong> 0.29 0.60 1.11 -0.01 0.03 0.05 0.80 1.29 2.01 -2.42 -2.28 0.04<br />
Scrubber On 4/19/<strong>2010</strong> 4/28/<strong>2010</strong> 0.08 0.64 1.12 -0.13 0.02 0.21 0.58 1.17 1.96 -2.43 -2.34 -1.67<br />
Scrubber Off 4/28/<strong>2010</strong> 5/4/<strong>2010</strong> 0.25 0.66 1.02 -0.01 0.02 0.06 0.83 1.11 1.58 -2.41 -2.27 -0.65<br />
The following three figures summarize the differential air pressure recorded at Humboldt.<br />
Figure 33 - Humboldt Drop Structure Upstream Average Pressure<br />
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Figure 34 - Humboldt Drop Structure Downstream Average Pressure<br />
Figure 35 - Humboldt Drop Structure Average Pressure<br />
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Plug Effect: The plugged air return ducts generally resulted in an increasing pressure trend in<br />
both the upstream and downstream maintenance holes on the NEIS. This was likely due to the<br />
fact that the interceptor system could not relieve its buildup of air pressure through the plugged<br />
drop structure air return lines and that more air was likely being dragged into the tunnel system<br />
from the Division and Humboldt drop structures. The pressure increase recorded at the NOS,<br />
however, was very minimal. This indicates that the momentum of flowing wastewater into the<br />
drop structure would not allow a significant air back pressurization into the NOS. Once the plug<br />
was removed, the pressure on the NEIS MH upstream of this location was immediately reduced<br />
to near baseline levels. The pressure at the drop structure remained at very low levels following<br />
plug removal. It is unclear why the pressure at the drop structure did not immediately increase<br />
back to near the baseline atmospheric level following plug removal at the air return line; however<br />
it could be that this was delayed and began to occur after the instrument was removed. The<br />
instrument removal time is depicted in the chart by the straight vertical line that terminates at the<br />
atmospheric pressure level just after May 12 th .<br />
Stop Log Removal: During the baseline pressure test phase, four stop logs were in place on the<br />
NOS side of the upstream diversion into the Humboldt drop structure. The pressure fluctuations<br />
in the NOS manhole just upstream of the Humboldt drop structure generally flattened after the<br />
stop logs were removed at the drop structure, but remained near atmospheric levels. This further<br />
indicates that the wastewater flow momentum into the drop structure would not allow a back<br />
pressurization effect to occur in the NOS. Pressures remained very near atmospheric levels from<br />
the day the stop logs were removed until the end of the test period. The pressure trends on the<br />
NEIS MH upstream of the drop structure remained fairly constant during the stop log removal<br />
period; however once the stop logs were re-installed an immediate reduction in pressure was<br />
recorded. A minimal downward trend in pressure was recorded at the maintenance hole<br />
downstream of the Humboldt drop structure during the stop log removal period. Pressures<br />
remained well below atmospheric levels at the drop structure itself. This indicates that from an<br />
air pressure perspective, the volume of flow entering the drop structure during the stop log<br />
removal period was optimal. The negative pressures recorded at the drop structure could have<br />
been lower than the minimum -2.42 recorded as this is very near the lower limit of the pressure<br />
data logging instruments.<br />
Scrubbers on/off: The scrubber at the Humboldt drop structure clearly has a slight pressure<br />
reduction effect on the NEIS MH upstream of that location; on the NEIS MH downstream of that<br />
location and at the drop structure itself. Several instances shown on the data charts show direct,<br />
albeit slight, pressure increase effects when the scrubber was turned off and slight pressure<br />
decrease effects when the scrubber was turned back on.<br />
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4.3 Mission and Jesse Drop Structure<br />
Four data loggers were installed at the locations shown in the map below.<br />
MH 51505288, 5,000 feet US of Mission & Jesse drop structure on NEIS<br />
MH 515009154, 800 feet US of Mission & Jesse drop structure on NOS<br />
MH 51513136, 1,600 feet DS of Mission & Jesse drop structure on ECIS<br />
MH 51513137, Mission & Jesse drop structure on ECIS<br />
(Note that in the figure above, US means “Upstream” and DS means “Downstream”. Also note<br />
that the NEIS and NOS are very close together and almost parallel making it difficult to see that<br />
those two sewer lines in the figure.)<br />
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Table 5 - Mission and Jesse Drop Structure Recorded Field Data<br />
Mission and Jesse Drop Structure Upstream Downstream Drop Structure<br />
Sewer Condition<br />
Min Avg Max Min Avg Max Min Avg Max Min Avg Max<br />
Start End<br />
Baseline<br />
2/16/<strong>2010</strong> 3/24/<strong>2010</strong><br />
Scrubber Offtart2/16/201 3/4/<strong>2010</strong> 0.00 0.30 0.70 -0.40 0.27 0.57 -0.02 0.31 0.60 0.05 0.29 0.53<br />
Scrubber On 3/4/<strong>2010</strong> 3/10/<strong>2010</strong> -0.15 0.30 0.58 0.94 1.07 1.23 0.18 0.33 0.57 0.20 0.30 0.47<br />
Scrubber Off 3/10/<strong>2010</strong> End3/24/<strong>2010</strong>-0.54 0.10 0.56 0.79 1.59 2.17 0.08 0.32 0.70 0.09 0.19 0.43<br />
Plug<br />
Installed<br />
3/24/<strong>2010</strong><br />
Removed<br />
5/5/<strong>2010</strong><br />
Scrubber On 3/24/<strong>2010</strong> 3/26/<strong>2010</strong> -0.30 0.39 0.65 0.76 1.21 2.22 0.23 0.57 0.83 0.09 0.22 0.47<br />
Scrubber Off 3/26/<strong>2010</strong> 4/2/<strong>2010</strong> 0.05 0.38 0.79 1.36 1.89 2.16 0.42 0.83 1.42 0.09 0.34 0.67<br />
Stop Logs<br />
Removed<br />
4/13/<strong>2010</strong><br />
Reinstalled<br />
5/4/<strong>2010</strong><br />
NEIS @ MH<br />
51505288<br />
NOS @ MH<br />
51509154<br />
ECIS @ MH<br />
51513136<br />
NEIS @ MH<br />
51513137<br />
Scrubber On 4/2/<strong>2010</strong> 4/7/<strong>2010</strong> -0.48 0.27 0.88 1.13 1.54 1.84 0.56 1.00 1.72 0.03 0.21 0.67<br />
Scrubber Off 4/7/<strong>2010</strong> 4/9/<strong>2010</strong> 0.26 0.75 1.13 1.18 1.44 1.61 1.04 1.54 2.14 0.09 0.46 0.89<br />
Scrubber On 4/9/<strong>2010</strong> 4/13/<strong>2010</strong> -0.02 0.47 0.91 -0.68 1.23 1.72 0.53 1.45 2.09 0.07 0.27 0.60<br />
Scrubber Off 4/13/<strong>2010</strong> 4/19/<strong>2010</strong> 0.19 0.64 1.17 0.85 1.19 1.54 1.16 1.80 2.28 -0.10 0.22 0.66<br />
Scrubber On 4/19/<strong>2010</strong> 4/28/<strong>2010</strong> -0.02 0.39 1.16 0.82 1.39 2.10 1.12 1.92 2.29 -0.10 0.07 0.52<br />
Scrubber Off 4/28/<strong>2010</strong> 5/4/<strong>2010</strong> 0.09 0.39 0.79 1.57 1.77 2.08 2.01 2.20 2.32 -0.11 0.07 0.41<br />
The three figures below summarize the air pressure recorded at the MHs at Mission & Jesse.<br />
Figure 36 - Mission and Jesse Drop Structure Upstream Average Pressure<br />
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Figure 37 - Mission and Jesse Drop Structure Downstream Average Pressure<br />
Figure 38 - Mission and Jesse Drop Structure Average Pressure<br />
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Plug Effect: The plugged air return duct at the Mission & Jesse drop structure generally resulted<br />
in an increasing pressure trend in the upstream maintenance hole on the NEIS; on the ECIS<br />
maintenance hole downstream of Mission & Jesse and in the drop structure itself. This was likely<br />
due to the fact that the interceptor system was not able to relieve air pressure buildup through the<br />
plugged NOS approach pipes at the drop structures. As plugs were inserted in the Division and<br />
Humboldt drop structures along the NEIS upstream of Mission and Jesse between 3/16/10 and<br />
3/19/10, the pressures in the NOS approach sewer upstream of Mission and Jesse began to<br />
increase significantly. This pressure increase was likely exacerbated by the presence of an<br />
approximate 30% diameter constriction along the NOS in the first maintenance hole upstream of<br />
the one in which the pressure testing was occurring. As the air from the NEIS/ECIS tunnel<br />
backpressurization effect filled the upstream NOS, the diameter reduction caused a constriction in<br />
the available headspace in the upstream NOS, resulting in higher than normal pressures.<br />
However the plug insertion at the Mission and Jesse drop structure on 3/23/10 appears to have<br />
caused a significant decreasing pressure trend along the same upstream NOS reach between the<br />
tested maintenance hole and the Mission and Jesse drop structure. This trend, which resulted in<br />
pressures being reduced from approximately 2.2 inches of water column down to approximately<br />
0.8 inches of water column, lasted for over four weeks. This gradual pressure reduction was<br />
likely due to the fact that the source of positive pressure-causing backpressurization air from the<br />
NEIS/ECIS tunnel in the NOS was denied by the presence of the plug at Mission & Jesse. Once<br />
the plugs at all drop structures were removed, the pressures on the NEIS MH upstream of this<br />
location and at the drop structure were immediately reduced to near baseline levels. Following<br />
plug removal, the pressures at the downstream maintenance hole on the ECIS and at the upstream<br />
NOS approach sewer maintenance hole were reduced as well.<br />
Stop Log Removal: The pressure trends on the NEIS MH upstream of the drop structure showed<br />
a general decreasing trend during the stop log removal period. This was likely due to the fact that<br />
less air was being dragged into the NEIS from the NOS approach at Humboldt. The pressure<br />
trends at the ECIS maintenance hole downstream of Mission and Jesse showed a general<br />
increasing trend during the stop log removal period. This was likely due to the fact that air was<br />
being dragged into the ECIS at Mission and Jesse through the NOS approach sewer during the<br />
stop log removal period, something that normally does not occur when the Mission and Jesse stop<br />
logs are in place. The pressure trends at the drop structure itself, showed a general decreasing<br />
trend during the stop log removal period. More air was being dragged into the Mission and Jesse<br />
drop structure through the NOS, causing lower pressures at the top of the drop structure. The<br />
data presented in Figure 37 provides further evidence that more air appeared to be dragged into<br />
the system at Mission and Jesse than is the case when the stop logs are in place. The pressures<br />
recorded at that ECIS maintenance hole, MH 515-13-136, could have actually been greater than<br />
those recorded. The maximum values recorded during the stop log removal period were very<br />
near the maximum value that the instruments are able to record.<br />
Scrubbers on/off: The scrubber at the Mission & Jesse drop structure clearly has a pressure<br />
reduction effect on the NEIS MH upstream of that location; the downstream ECIS manhole and at<br />
the drop structure itself. The recorded air pressure data show direct air pressure increases when<br />
the scrubber was turned off and pressure reduction effects when the scrubber was turned back on.<br />
The pressure on the NOS was reduced significantly during the approximately 40-day period that<br />
the plugs were in place and the stop logs were removed. The only exception to this trend was<br />
during a 10-to-15 day period between April 19th and May 2nd during which time the pressure<br />
rose in the NOS. This could have been a reaction to the absence of stop logs at the Mission and<br />
Jesse drop structure. In the immediate aftermath of stop log removal at Mission and Jesse,<br />
enough air was eventually dragged into the drop structure at that location to cause an increase in<br />
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air pressure in the NOS approach sewer over a ten day period. It is theorized that not enough<br />
wastewater flow momentum was being generated in the NOS approach to physically impede this<br />
eventual air back pressure effect, hence the 10-day lag period between the removal of the Mission<br />
and Jesse stop logs and the increase in air pressure that appeared to begin on April 20th.<br />
A pressure reduction phenomenon was recorded on March 17th that did not appear to be caused<br />
by any planned manipulation to the drop structures or interceptor flow control system. In<br />
discussing this phenomenon with BOS staff, it was learned that a damper was fully closed on the<br />
Humboldt <strong>ATF</strong> air duct header during a routine inspection on that day. This could have directly<br />
caused the recorded reduction in pressure.<br />
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4.4 23 rd and San Pedro Drop Structure<br />
Five data loggers were installed at the locations shown in the map below.<br />
MH 53703177, 1,700 feet US of 23rd & San Pedro drop structure on ECIS<br />
MH 53702211, 700 feet US of 23rd & San Pedro drop structure on NOS<br />
MH 53703199, 100 feet US of 23rd & San Pedro drop structure on NOS<br />
MH 53706178, 2,800 feet DS of 23rd & San Pedro drop structure on ECIS<br />
MH 53703200, 23rd & San Pedro drop structure on ECIS<br />
(Note that in the figure above, US means Upstream and DS means Downstream)<br />
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Baseline<br />
Plug<br />
Table 6 - 23rd and San Pedro Drop Structure Recorded Field Data<br />
23rd and San Pedro Drop Structure<br />
Sewer Condition Min Avg Max Min Avg Max Min Avg Max Min Avg Max<br />
Start End<br />
2/16/<strong>2010</strong> 3/30/<strong>2010</strong> -0.10 0.25 0.70 -1.22 0.10 1.74 0.25 0.58 0.95 -0.25 0.03 0.36<br />
Installed<br />
3/30/<strong>2010</strong><br />
Installed<br />
4/29/<strong>2010</strong><br />
ECIS @ MH<br />
53703177<br />
Upstream<br />
NOS @ MH<br />
53703199<br />
Downstream<br />
ECIS @ MH<br />
53706178<br />
Drop Structure<br />
ECIS @ MH<br />
53703200<br />
Removed<br />
4/30/<strong>2010</strong> 0.15 0.49 1.11 -0.22 0.05 0.12 0.01 0.68 1.50 -0.70 -0.14 0.12<br />
Removed<br />
5/7/<strong>2010</strong> 0.02 0.23 0.70 -0.10 0.04 0.10 0.25 0.48 0.93 -2.23 -0.99 0.13<br />
Curtain<br />
Note: The raw data for the logger at manhole 53706178 (31st & Trinity) from 2/16 to 3/24<br />
was not used due to erroneous data observed and obstruction during retrieval on 3/2 and 3/3<br />
The three figures below summarize the air pressure recorded at the MHs at 23 rd & San Pedro.<br />
Figure 39 - 23rd and San Pedro Drop Structure Upstream Average Pressure<br />
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Figure 40 - 23rd and San Pedro Drop Structure Downstream Average Pressure<br />
Figure 41 - 23rd and San Pedro Drop Structure Average Pressure<br />
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Plug Effect: The plug inserted at the 23 rd and San Pedro drop structure generally resulted in<br />
increasing pressures along the ECIS and a reduction in pressure at the drop structure itself. The<br />
plugged air return ducts on the three upstream drop structures generally resulted in an increasing,<br />
albeit slight, pressure trend at the upstream ECIS maintenance hole and a slight decreasing<br />
pressure trend at the drop structure By the time the last plug was inserted (at the 23rd and San<br />
Pedro drop) the pressures at the upstream location had increased by approximately 0.5 inches w.c.<br />
Once the last plug was removed, the pressures at the upstream ECIS maintenance hole and at the<br />
drop structure were immediately reduced to near baseline levels.<br />
A car was parked over the maintenance hole on the ECIS downstream of the 23rd and San Pedro<br />
drop structure for several days during the early part of the plug test. As a result it is difficult to<br />
ascertain the overall pressure trend at this location as a result of the insertion of all three plugs in<br />
air return lines at the three drop structures; however a significant increase in air pressure was<br />
recorded at this location following the installation of the air plug at 23rd and San Pedro.<br />
Stop Log Removal: The pressure on the ECIS at this location showed a slight reduction trend at<br />
the upstream ECIS maintenance hole; and at the drop structure during the stop log removal<br />
period. A significant reduction trend at the downstream ECIS maintenance hole was recorded<br />
while the stop logs were removed.<br />
Scrubbers on/off: The scrubber at the Mission & Jesse drop structure has a pressure reduction<br />
effect on the ECIS maintenance holes upstream and downstream of the 23rd and San Pedro drop<br />
structures. Several instances shown on the data charts show direct, albeit slight, pressure<br />
increase effects when the scrubber was turned off and pressure decrease effects when the scrubber<br />
was turned back on. Similar, albeit very slight, pressure effects were recorded at the 23rd and<br />
San Pedro drop structure.<br />
Curtain Installation: As shown in Figures 39 and 40, increases in air pressure were recorded at<br />
the maintenance holes just upstream and downstream of the 23rd and San Pedro drop structure<br />
during the curtain installation period while the plug was still in place at the drop structure. This<br />
was likely due to the fact that the source of ECIS pressure relief was sealed off.<br />
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4.5 USC Drop Structure<br />
Three data loggers were installed at the locations shown in the map below.<br />
MH 53705181, 2,800 feet US of USC drop structure on ECIS<br />
MH 53607171, 5,300 feet DS of USC drop structure on ECIS<br />
MH 53705184, USC drop structure on ECIS<br />
(Note that in the figure above, US means “Upstream” and DS means “Downstream”)<br />
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Baseline<br />
Plugs<br />
Table 7 - USC Drop Structure Recorded Field Data<br />
USC Drop Structure Upstream Downstream<br />
Stop Logs<br />
Sewer Condition<br />
Min Avg Max Min Avg Max Min Avg Max<br />
Start End<br />
2/16/<strong>2010</strong> 3/16/<strong>2010</strong> 0.01 0.32 0.67 -0.44 0.17 0.78 -2.28 -1.82 0.04<br />
Installed Removed<br />
3/16/<strong>2010</strong> 4/2/<strong>2010</strong> 0.01 0.39 0.93 -0.84 0.35 0.90 -2.29 -1.79 -1.09<br />
Removed<br />
4/2/<strong>2010</strong><br />
ECIS @ MH<br />
53705181<br />
ECIS MH @<br />
53607171<br />
Drop Structure<br />
ECIS @ MH<br />
53705184<br />
Reinstalled<br />
5/4/<strong>2010</strong> 0.06 0.49 1.15 -1.01 0.18 0.93 -2.24 -1.78 -1.07<br />
The three figures below summarize the air pressure recorded at the MHs at the USC drop<br />
structure.<br />
Figure 42 - USC Drop Structure Upstream Average Pressure<br />
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Figure 43 - USC Drop Structure Downstream Average Pressure<br />
Figure 44 - USC Drop Structure Average Pressure<br />
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Plug Effect: The plugged air return ducts on the upstream Division, Humboldt, Mission and<br />
Jesse and 23 rd and San Pedro drop structures generally resulted in an increasing pressure trend at<br />
the USC drop structure and at the two maintenance holes on the ECIS upstream and downstream<br />
of the USC drop structure. Once the last plug was removed, the pressures at these three<br />
locations were immediately reduced to near baseline levels. This was likely due to the fact that<br />
the interceptor system could no longer relieve its pressure buildup through the NOS approach<br />
sewers into the upstream drop structures.<br />
Stop Log Removal: The pressure on the ECIS upstream and downstream of the USC drop<br />
structure showed a significant reduction trend during the stop log removal period. A slight<br />
pressure reduction was recorded at the drop structure itself during the stop log removal period.<br />
One possible explanation for this is that the NOS approach sewer at Humboldt could be a more<br />
significant contributor of air drag into the NEIS/ECIS system when NOS flows are being directed<br />
to the Humboldt drop structure, compared to the amount of air dragged by the NOS into the<br />
NEIS/ECIS system when flows are directed to the Mission and Jesse drop structure. Once the<br />
stop logs were removed at Humboldt, flow was able to pass through the NOS away from the drop<br />
structure unimpeded, thereby reducing the amount of air dragged into the NEIS at Humboldt and<br />
potentially reducing the overall system pressurization increase trend that had begun following<br />
introduction of the air line return plugs at the Division, Humboldt and Mission and Jesse drop<br />
structures.<br />
Scrubbers on/off: The scrubber at the Mission & Jesse drop structure clearly has a pressure<br />
reduction effect on the ECIS upstream and downstream of the USC drop structure. Several<br />
instances shown on the pressure charts show direct pressure increase effects when the scrubber<br />
was turned off and pressure decrease effects when the scrubber was turned back on. As with<br />
other systems changes, slight pressure reduction effects were recorded at the drop structure itself<br />
when the Mission & Jesse <strong>ATF</strong> was turned on.<br />
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4.6 Systemwide Downstream<br />
Three data loggers were installed at the locations shown in the map below.<br />
MH 53503213, 2,400 feet US of Jefferson Siphon on ECIS<br />
MH 53506116, 5,300 feet US of NORS/ECIS junction on ECIS<br />
MH 53505021, 8,000 feet US of NORS/ECIS junction on NORS<br />
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Systemwide Downstream<br />
Table 8 - Systemwide Downstream Recorded Field Data<br />
Downstream<br />
ECIS @ MH<br />
53503213<br />
Downstream<br />
ECIS @ MH<br />
53506116<br />
Downstream<br />
NORS @ MH<br />
53505021<br />
Sewer Condition<br />
Min Avg Max Min Avg Max Min Avg Max<br />
Baseline<br />
Start End<br />
2/16/<strong>2010</strong> 3/16/<strong>2010</strong> -0.42 -0.08 0.33 -0.56 0.11 0.45 -0.04 0.09 0.48<br />
Plugs<br />
Installed Removed<br />
3/16/<strong>2010</strong> 4/2/<strong>2010</strong> -0.44 -0.16 0.10 -0.37 0.08 0.48 0.00 0.08 0.22<br />
Stop Logs<br />
Removed Reinstalled<br />
4/2/<strong>2010</strong> 5/4/<strong>2010</strong> -0.47 -0.25 0.16 -2.35 0.08 0.73 -0.40 0.06 0.55<br />
The three figures below summarize the air pressure recorded at the MHs downstream of the drop<br />
structures.<br />
Figure 45 - Systemwide Downstream Jefferson Siphon Upstream Average Pressure<br />
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Figure 46 - Systemwide Downstream NORS/ECIS Junction (ECIS) Average Pressure<br />
Figure 47 - Systemwide Downstream NORS/ECIS Junction (NORS) Average Pressure<br />
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Plug Effect: The plugged air return ducts on the four upstream drop structures at Division,<br />
Humboldt, Mission and Jesse and 23 rd and San Pedro generally resulted in a slight increasing<br />
pressure trend at the maintenance hole upstream of the ECIS Jefferson Siphon, on the ECIS<br />
between the siphon and the NORS/ECIS junction and on the NORS upstream of the NORS/ECIS<br />
junction. This was likely due to the fact that the interceptor system could not relieve air pressure<br />
buildup through the NOS approach sewers at the upstream drop structures. Once the last plug<br />
was removed, the pressures at the downstream system locations were immediately reduced to<br />
near baseline levels.<br />
Stop Log Removal: The pressures on the ECIS from just upstream of the Jefferson Siphon to the<br />
NORS/ECIS junction showed a general reduction trend during the stop log removal period. As<br />
with other locations along the studied interceptor system, one possible explanation for this is that<br />
the NOS approach sewer at Humboldt could be a more significant contributor of air drag into the<br />
NEIS/ECIS system when NOS flows are being directed to the Humboldt drop structure,<br />
compared to the amount of air dragged by the NOS into the NEIS/ECIS system when flows are<br />
directed to the Mission and Jesse drop structure.. Once the stop log was removed at Humboldt,<br />
flow was able to pass through the NOS away from the drop structure unimpeded; thereby<br />
reducing the amount of air dragged into the NEIS at Humboldt and therefore reduced the overall<br />
interceptor system pressure. As explained previously, more air appeared to be dragged into the<br />
system at Mission and Jesse than is the case when the stop logs are in place, as evidenced by the<br />
data recorded at ECIS MH 515-13-136 (see Figure 37).<br />
Scrubbers on/off: The scrubber at the Mission & Jesse drop structure has a slight pressure<br />
reduction effect on the two ECIS maintenance holes. Several instances shown on the chart show<br />
direct pressure increase effects when the scrubber was turned off and pressure decrease effects<br />
when the scrubber was turned back on. No effects due to NEIS/ECIS drop structure <strong>ATF</strong> activity<br />
are discernable on the NORS upstream of the NORS/ECIS junction. The NORS/ECIS junction<br />
<strong>ATF</strong> had been off between mid-February and mid-April due to maintenance issues. The scrubber<br />
was turned back on April 12th. An initial reduction in air pressure was recorded when the<br />
scrubber was turned back on.<br />
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4.7 Findings<br />
The following conclusions are drawn from analyzing pressure data recorded during the drop<br />
structure field study from February <strong>2010</strong> to May <strong>2010</strong>. The General Observations apply to all<br />
drop structures, and their immediate upstream and downstream vicinities, that were studied.<br />
Explanations for location-specific phenomena that are not believed to have occurred as a result of<br />
events described in the General Observations section are provided in each location-specific<br />
section.<br />
4.7.1 General Observations<br />
The plugged air lines at the drop structures generally resulted in a gradual buildup of air pressure<br />
in the NEIS/ECIS system that began when the plugs were inserted at the drop structures and<br />
continued until the stop logs were removed at the Humboldt and Mission and Jesse NOS<br />
diversions. This is likely primarily due to the fact that the plugs did not allow air pressure<br />
buildup in the tunnel system to be relieved through the NOS approach sewer segments.<br />
During the stop log removal period of the study, the air return plugs were still in place at the drop<br />
structures. During the stop log removal phase, pressures in the NEIS/ECIS system were<br />
generally, gradually reduced. This was likely due to the fact that NOS flow at the Humboldt drop<br />
structure was diverted away from the NEIS due to the stop log removal, thereby resulting in less<br />
air being dragged into the drop structure and into the NEIS. The exception to this appeared to be<br />
at ECIS MH 515-13-136, which is immediately downstream of the Mission and Jesse drop<br />
structure. Pressures generally increased at this location during the stop log removal period. This<br />
is likely due to more air being dragged into the ECIS at Mission and Jesse than is the case when<br />
the stop logs are in place.<br />
The <strong>ATF</strong>’s generally reduce pressures by 0.1 to 0.25 inches of water column along the entire<br />
length of the NEIS/ECIS tunnel. Discernable pressure reductions occur when the <strong>ATF</strong>’s are<br />
turned on. Discernable pressure increases occur when the <strong>ATF</strong>’s are turned off. This indicates<br />
that the <strong>ATF</strong>’s are removing some air from the NEIS/ECIS system.<br />
The following provides summary descriptions of the pressure observations at each drop structure<br />
at their immediate upstream and downstream vicinities<br />
4.7.2 Division Drop Structure & Vicinity<br />
<br />
<br />
Division Drop Structure: The most favorable pressure conditions (i.e., lowest air<br />
pressures) were achieved at this location, as well as the maintenance holes immediately<br />
upstream (on the ERIS) and downstream (on the NEIS), when the plugs were in place in<br />
all four drop structure air return lines. Also, removing the stop logs at Humboldt and<br />
Mission and Jesse NOS diversions did not cause significant air pressure increases at this<br />
location. This was likely due to the fact that the NOS flow at the Humboldt drop<br />
structure typically drags a significant amount of air into the NEIS. During the stop log<br />
removal period flows were being diverted away from the NEIS at Humboldt. This<br />
resulted in less air being into the NEIS than is normally the case when the Humboldt stop<br />
logs are in place.<br />
ERIS: Once the plug was in place at the Division Drop Structure, the air pressures on the<br />
ERIS just upstream of the drop structure became too negative for the ACR instruments to<br />
properly record. This was likely due to the fact that the ERIS approach to the Division<br />
drop structure had been denied positive backpressurization from the NEIS when the plug<br />
was inserted in the drop structure air return line. The drag induced by the flowing<br />
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wastewater on the approach pipe headspace therefore drew a vacuum in the upstream<br />
manhole. This indicates that they were at -2.5 inches w.c. maximum.<br />
NEIS: The lowest air pressures were recorded on the NEIS just downstream of the drop<br />
structure when the plugs were in place in all four drop structure air return lines. This was<br />
likely due to the fact that this segment of the NEIS is the furthest away from several<br />
potential sources of positive air pressurization (i.e. other drop structures and siphons)<br />
along the NEIS/ECIS alignment. Also, diverting flows away from the Humboldt drop<br />
structure resulted in a decreasing air pressure trend at this location. As explained<br />
previously, this was likely due to the fact that a net reduction in air drag into the NEIS<br />
occurred when the NOS flows were diverted away from the Humboldt drop structure.<br />
4.7.3 Humboldt Drop Structure & Vicinity<br />
<br />
<br />
<br />
<br />
The most favorable pressure conditions (i.e., lowest air pressures) were achieved at this<br />
location when the plugs were in place in all four drop structure air return lines. Also,<br />
removing the stop logs at the Humboldt and Mission and Jesse NOS diversions did not<br />
cause significant air pressure increases at this location.<br />
NEIS: The pressures on the 2 NEIS maintenance holes immediately upstream and<br />
downstream of this location increased as a result of the presence of plugs in the four drop<br />
structure air return lines.<br />
NOS: The air pressure on the NOS at the Humboldt diversion was generally well below<br />
or right at atmospheric during the entire duration of the field study. The most favorable<br />
(i.e., lowest) pressure conditions were recorded while the stop logs were removed and the<br />
plugs were in place at the drop structure air return lines.<br />
Noticeable reductions in air pressure were recorded on the NOS, NEIS and at the<br />
Humboldt drop structure when the Humboldt <strong>ATF</strong> was in operation, although the<br />
pressures in the NEIS tunnel in the vicinity of Humboldt remained positive.<br />
4.7.4 Mission and Jesse Drop Structure & Vicinity<br />
<br />
<br />
<br />
Mission and Jesse Drop Structure: The lowest air pressure conditions were achieved at<br />
this location when the plugs were in place in all four drop structure air return lines and<br />
the NOS stop logs had been removed at both this drop structure and the Humboldt<br />
location.<br />
NEIS/ECIS: The pressures on the two maintenance holes immediately upstream and<br />
downstream of this location increased as a result of the presence of plugs in the four drop<br />
structure air return lines. The pressure at the ECIS maintenance hole immediately<br />
downstream of this location also increased as a result of stop log removals at Humboldt<br />
and Mission and Jesse. The pressure at the NEIS maintenance hole immediately<br />
upstream of this location generally decreased as a result of stop log removals at<br />
Humboldt and Mission and Jesse.<br />
NOS: The air pressure on the NOS at the Mission and Jesse diversion decreased<br />
significantly during the plug insertion and stop log removal period of this study. The<br />
exception to this was during an approximate 15 day period toward the end of this testing<br />
period during which the pressures exhibited an increasing trend. This was likely due to<br />
more air being dragged into system at this location than is normally the case with the stop<br />
logs in place; however it also indicates that this is a primary source of pressure relief for<br />
the tunnel system.<br />
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Noticeable reductions in air pressure were recorded on the NEIS, ECIS and at the<br />
Mission and Jesse drop structure when the Mission and Jesse <strong>ATF</strong> was in operation.<br />
4.7.5 23 rd and San Pedro Drop Structure & Vicinity<br />
<br />
<br />
<br />
<br />
<br />
23rd and San Pedro Drop Structure: The lowest air pressure conditions were achieved at<br />
this location when the plugs were in place in all four drop structure air return lines and<br />
the NOS stop logs had been removed at both the Mission and Jesse and the Humboldt<br />
locations. The pressure in the drop structure was approximately atmospheric during the<br />
baseline period. The pressures went below atmospheric shortly after the plug was<br />
inserted in the air return line at this drop structure.<br />
ECIS: The pressures on the 2 ECIS maintenance holes immediately upstream and<br />
downstream of this location increased as a result of the presence of plugs in the four drop<br />
structure air return lines. The pressures at these maintenance holes generally decreased<br />
during the stop log removal test.<br />
NOS: The air pressure on the NOS at the 23rd and San Pedro diversion decreased<br />
slightly during the plug insertion and stop log removal period of this study. The<br />
pressures were generally near atmospheric for the majority of the entire drop structure<br />
testing period.<br />
The curtain installation at 23 rd and San Pedro did not result in a significant pressure<br />
change at the 23 rd and San Pedro drop structure. A slight, albeit measurable, pressure<br />
reduction trend was recorded on the maintenance holes upstream and downstream of the<br />
drop structure on the ECIS during the curtain installation period. This indicates that the<br />
curtain might have isolated a small source of air into the ECIS through the drop structure.<br />
Noticeable reductions in air pressure were recorded on the ECIS and at the 23rd and San<br />
Pedro drop structure when the Mission and Jesse <strong>ATF</strong> was in operation.<br />
4.7.6 USC Drop Structure & Vicinity<br />
<br />
<br />
<br />
USC Drop Structure: The air pressures at the drop structure did not appear to be<br />
significantly affected by any system-wide manipulations to the <strong>ATF</strong>s, drop structure air<br />
return lines or interceptor stop logs. This is likely due to the fact that there is no air<br />
return line on this drop structure which, if there was one in place, would provide a source<br />
of back pressurization from the ECIS tunnel.<br />
ECIS: Compared to upstream locations along the ECIS and NEIS, there were very little<br />
changes to overall pressures immediately upstream or downstream of the USC drop<br />
structure on the ECIS as a result of the planned system-wide manipulations.<br />
Noticeable reductions in air pressure were recorded on the ECIS immediately upstream<br />
and downstream of the USC drop structure when the Mission and Jesse <strong>ATF</strong> was in<br />
operation.<br />
4.7.7 Systemwide Downstream Interceptors<br />
<br />
<br />
The lowest air pressure conditions were achieved during the stop log removal period.<br />
Upstream of Jefferson Siphon (ECIS): The pressures at this location were at or below<br />
atmospheric levels for the majority of the study period. The air pressures at this location<br />
slightly increased during the period that the air return line plugs were in place at the four<br />
drop structures. During the time period that the plugs were in place and the stop logs<br />
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were removed from Humboldt and Mission and Jesse the air pressure generally decreased<br />
at this location and remained below atmospheric. There also appears to have been a<br />
direct correlation between the interim scrubbers being turned off and on and increases<br />
and decreases, respectively, in pressure levels at this location.<br />
NORS/ECIS Junction Upstream (ECIS): The air pressures generally increased when the<br />
plugs and stop logs were in place. Once the stop logs were removed the pressures<br />
exhibited a general downward trend. Following plug removal and stop log re-insertion<br />
the pressures went to near atmospheric.<br />
NORS/ECIS Junction Upstream (NORS): The pressures in the NORS maintenance hole<br />
immediately upstream of the NORS/ECIS junction increased slightly during the time in<br />
which the plugs were in place in the four drop structure air return lines. The pressures at<br />
these maintenance holes generally decreased and fluctuated more significantly in the<br />
negative direction during the stop log removal test. During this time period, on April<br />
12 th , the NORS/ECIS scrubber was brought back online, which could have resulted in the<br />
fluctuating pressure conditions. Following plug removal and stop log re-insertion the<br />
pressures went below atmospheric with some slight spikes above atmospheric levels;<br />
however these pressure conditions were generally lower than those recorded during the<br />
baseline condition when the scrubber was out of service.<br />
Reductions in air pressure were recorded at each of these three locations when the<br />
Mission and Jesse <strong>ATF</strong> were in operation. The most notable example was at the ECIS<br />
location upstream of the NORS/ECIS junction.<br />
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5.0 CONCLUSIONS<br />
The following provides a summary of the conclusions drawn from the Findings presented in this<br />
report:<br />
<br />
<br />
<br />
<br />
<br />
The plugs inserted in the air return lines in the drop structures generally resulted in<br />
increasing pressures along the entire NEIS/ECIS tunnel alignment. The plugs also<br />
generally resulted in a reduction in pressure along the NOS approach sewer into the<br />
Mission and Jesse Drop Structure. The NOS diversions into the Humboldt and 23 rd and<br />
San Pedro drop structures didn’t display pressure reductions, but remained near<br />
atmospheric levels during the plug insertion test period.<br />
The stop logs removal generally resulted in decreasing pressures on the NOS along that<br />
segment that discharges into the Mission and Jesse drop structure. One anomaly was<br />
recorded during the stop log removal test along this segment. The pressure increased<br />
over an approximate four-day period about half-way through the stop log test. This<br />
increase phenomenon was not observed at other locations. As with the air return line<br />
plug insertions at drop structures, those locations where the pressures didn’t decrease<br />
remained at atmospheric levels during this part of the test period, such as the NOS<br />
approach segments at Humboldt and 23 rd and San Pedro. When the stop logs are in place<br />
at Humboldt and Mission and Jesse, NEIS/ECIS tunnel pressure primarily appears to be<br />
relieved through the Mission and Jesse NOS approach sewer.<br />
The <strong>ATF</strong>’s generally reduce pressures by 0.1 to 0.25 inches of water column along the<br />
entire length of the NEIS/ECIS tunnel. Discernable pressure reductions occur when the<br />
<strong>ATF</strong>’s are turned on. Discernable pressure increases occur when the <strong>ATF</strong>’s are turned<br />
off.<br />
The curtain installation at the NOS diversion structure just upstream of the 23 rd and San<br />
Pedro drop structure resulted in increases in air pressure on the ECIS tunnel at the<br />
maintenance holes just upstream and downstream of the drop structure while the plug<br />
was still in place at the drop structure. This was likely due to the fact that the source of<br />
ECIS air pressure relief was sealed off in the vicinity due to the presence of both the plug<br />
and the curtain.<br />
In general the drop structures appeared to have the following effects on the air pressures<br />
in the NEIS/ECIS and the NOS approach sewers during plug insertion and flow<br />
management operations:<br />
o<br />
o<br />
o<br />
o<br />
Air is drawn into the NEIS/ECIS tunnel system from the NOS approach sewers<br />
through the drop structures, causing positive pressurization of the NEIS/ECIS<br />
tunnel system<br />
The air return lines in the drop structures tend to have a pressure reduction effect<br />
on the NEIS/ECIS tunnel system; likely due to the drop structure air return lines<br />
acting as conduits for backpressure relief from the NEIS/ECIS tunnel system<br />
The Humboldt drop structure appears to be a more significant contributor of air<br />
into the NEIS/ECIS system than does the Mission and Jesse drop structure. Air<br />
pressures increased only slightly on the NOS approach to Humboldt, yet even<br />
then remained near or below atmospheric, during the entire duration of the drop<br />
structure testing period<br />
The Mission and Jesse drop structure appears to serve as the primary relief<br />
pressure relief point for the NEIS/ECIS system. When the stop logs are in place<br />
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o<br />
at this location, the vertical drop shaft and the air return line appear to serve as a<br />
conduit for air back-pressurization on the NOS upstream of the drop structure.<br />
Plugging the air return line caused a gradual reduction in pressure along that<br />
reach of the NOS; however, once the stop logs were removed and wastewater<br />
flow was allowed to enter unimpeded into the Mission and Jesse drop, the<br />
pressures gradually increased along the NOS approach into Mission and Jesse.<br />
This was likely due to an increased air backpressure effect in the ECIS due to the<br />
upstream flow diversions.<br />
The pressures in the Humboldt and 23 rd and San Pedro NOS approach pipes were<br />
very near atmospheric before and during the air line plug test.<br />
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Technical Memorandum – FINAL<br />
Team<br />
City of Los Angeles<br />
Department of Public Works<br />
Bureau of Sanitation<br />
Air Treatment Facility (<strong>ATF</strong>) Review <strong>Study</strong><br />
TOTAL NON-METHANE HYDROCARBON<br />
MONITORING RESULTS TECHNICAL<br />
MEMORANDUM<br />
FINAL<br />
November <strong>2010</strong><br />
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Table of Contents<br />
Executive Summary ...................................................................................................................... 4<br />
1.0 Introduction and Purpose ................................................................................................... 9<br />
2.0 Air Permits ........................................................................................................................ 12<br />
3.0 Sampling Setup ................................................................................................................ 17<br />
3.1 Sample Locations and Schedule .................................................................................. 17<br />
3.2 Sampling Equipment, Measurement Parameters and Analytical Methods ................... 18<br />
3.2.1 Sampling Equipment and Measurement Parameters ............................................ 18<br />
3.2.2 Analytical Methods ................................................................................................ 20<br />
3.2.3 <strong>ATF</strong> Inlet Air Velocity Measurements and Air Flow Rates ..................................... 23<br />
4.0 Collected Data and Sampling Results .............................................................................. 25<br />
4.1 Richmond ..................................................................................................................... 25<br />
4.2 NORS-ECIS .................................................................................................................. 32<br />
4.3 Humboldt ...................................................................................................................... 38<br />
4.4 Mission and Jesse ........................................................................................................ 49<br />
4.5 23 rd and San Pedro ....................................................................................................... 55<br />
4.6 Summary ...................................................................................................................... 60<br />
5.0 Comparison of Current and Historical Data ..................................................................... 65<br />
List of Tables<br />
Table 1 - <strong>ATF</strong> TNMHC Emission Limits ...................................................................................... 12<br />
Table 2 - Summary of the Permits .............................................................................................. 14<br />
Table 3 -Sampled Locations and Dates ...................................................................................... 17<br />
Table 4 - TO-15 Compound List ................................................................................................. 21<br />
Table 5 - TO-12 Modified Compound List ................................................................................... 22<br />
Table 6 - ASTM 5504 Measured Compounds ............................................................................ 23<br />
Table 7 - Richmond - TNMHC, VOC and H2S Sample/Analytical Results ................................. 27<br />
Table 8 - Richmond TO-15 Sample/Analytical Results ............................................................... 28<br />
Table 9 - Richmond TO-12 Modified Results .............................................................................. 29<br />
Table 10 - NORS-ECIS TNMHC, VOC and H2S Sample/Analytical Results.............................. 33<br />
Table 11 - NORS-ECIS TO-15 Sample/Analytical Results ......................................................... 34<br />
Table 12 - NORS-ECIS TO-12 Modified Results ........................................................................ 35<br />
Table 13 - Humboldt TNMHC, VOC and H 2 S Sample/Analytical Results ................................... 44<br />
Table 14 - Humboldt TO-15 Sample/Analytical Results .............................................................. 45<br />
Table 15 - Humboldt Inlet <strong>ATF</strong> Reduced Sulfur Compounds ...................................................... 45<br />
Table 16 - Humboldt TO-12 Modified Results ............................................................................. 46<br />
Table 17 - Mission & Jesse TNMHC, VOC and H2S Sample/Analytical Results ........................ 50<br />
Table 18 - Mission & Jesse TO-15 Sample/Analytical Results ................................................... 51<br />
Table 19 - Mission & Jesse <strong>ATF</strong> Inlet Reduced Sulfur Compounds ........................................... 51<br />
Table 20 - Mission & Jesse TO-12 Modified Results .................................................................. 52<br />
Table 21 - 23rd & San Pedro TNMHC, VOC and H 2 S Sample/Analytical Results ...................... 56<br />
Table 22 - 23rd & San Pedro TO-15 Sample/Analytical Results ................................................ 57<br />
Table 23 - 23rd & San Pedro TO-12 Modified Results ............................................................... 58<br />
Table 24 - Total NMHC, VOC and H 2 S Sample/Analytical Results Summary ............................ 61<br />
Table 25 - Comparison of <strong>2010</strong> and 2009 Total VOC Data (ppb v ) ............................................. 66<br />
Table 26 - Comparison of <strong>2010</strong> and 2009 Reduced Sulfur Data (ppm v ) .................................... 66<br />
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List of Figures<br />
Figure 1 - Interim <strong>ATF</strong> and Monitoring Location Map ................................................................. 18<br />
Figure 2 - Sampling Train Schematic .......................................................................................... 19<br />
Figure 3 – Air Sampling Train ..................................................................................................... 19<br />
Figure 4 - Richmond <strong>ATF</strong> (1) ...................................................................................................... 30<br />
Figure 5 - Richmond <strong>ATF</strong> (2) ...................................................................................................... 30<br />
Figure 6 - Richmond <strong>ATF</strong> (3) ...................................................................................................... 31<br />
Figure 7 - NORS ECIS <strong>ATF</strong> (1) ................................................................................................... 36<br />
Figure 8 - NORS ECIS <strong>ATF</strong> (2) ................................................................................................... 36<br />
Figure 9 - NORS ECIS <strong>ATF</strong> (3) ................................................................................................... 37<br />
Figure 10 - Humboldt <strong>ATF</strong> (1) ..................................................................................................... 47<br />
Figure 11 - Humboldt <strong>ATF</strong> (2) ..................................................................................................... 47<br />
Figure 12 - Humboldt <strong>ATF</strong> (3) ..................................................................................................... 48<br />
Figure 13 - Humboldt <strong>ATF</strong> (4) ..................................................................................................... 48<br />
Figure 14 - Mission and Jesse <strong>ATF</strong> (1) ....................................................................................... 53<br />
Figure 15 - Mission and Jesse <strong>ATF</strong> (2) ....................................................................................... 53<br />
Figure 16 - Mission and Jesse <strong>ATF</strong> (3) ....................................................................................... 54<br />
Figure 17 - 23rd and San Pedro (1) ............................................................................................ 59<br />
Figure 18 - 23rd and San Pedro (2) ............................................................................................ 59<br />
Figure 19 - TNMHC VOC Results Summary .............................................................................. 62<br />
Figure 20 - Hydrogen Sulfide Sampling Result Summary .......................................................... 63<br />
Figure 21 - Hydrogen Sulfide Emission Control Overview .......................................................... 64<br />
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EXECUTIVE SUMMARY<br />
In recent history, the City of Los Angeles (City) has encountered increasing public concern to<br />
sewer odors, and has been working to improve odor control in several areas identified by local<br />
community groups. Formal, permanent air treatment facilities (<strong>ATF</strong>s) for seven areas with known<br />
or predicted odor “hot spots” were including in a 2004 Collection System Settlement Agreement<br />
(CSSA) that the City entered into with the United States Environmental Protection Agency<br />
(USEPA), Santa Monica Baykeeper, City of El Segundo, and others. The CSSA included several<br />
requirements including the installation and operation of interim and permanent air treatment<br />
facilities. Permanent <strong>ATF</strong>s are in the final stages of construction at two of the seven targeted<br />
areas. The location of the five remaining proposed <strong>ATF</strong>s need to be reevaluated based on the<br />
effect of wastewater flow diversions on interceptor headspace air pressure; reported performance<br />
issues and continued odor complaints at several of the locations. Accordingly, the City has<br />
embarked on a study to determine the number and location of the new proposed <strong>ATF</strong>s, assess the<br />
performance of the interim odor control facilities, and decide on the <strong>ATF</strong> technologies. This<br />
Technical Memorandum (TM) summarizes the monitoring results for parameters of interest<br />
conducted at the five proposed <strong>ATF</strong> locations where interim odor control facilities are currently<br />
operating at four of the locations and no control is provided a the fifth location.<br />
In some cases, existing interceptor odor control facilities and <strong>ATF</strong>s have air permit limits for total<br />
non-methane hydrocarbons (TNMHC) in their exhaust. A single distinct exhaust limit value is<br />
listed in each site’s air permit. The various sites have different individual permit values. Those<br />
permit values vary from 18 to 36 parts per million by volume in air (ppm v ). All of these existing<br />
<strong>ATF</strong>s are required to meet a hydrogen sulfide stack exhaust limit of 1 ppm v , which with the<br />
exception of the Decotah Street facility has an exhaust H 2 S permit limit of 0.6 ppm v . Given the<br />
existing air permit limits for TNMHC and hydrogen sulfide, the City wants to have a greater<br />
understanding of the composition of the sewer headspace air at the five interim odor control<br />
facility locations so that permanent <strong>ATF</strong> systems can be designed to meet future air permit<br />
requirements. Parameters of interest include: TNMHC, speciated volatile organic compounds<br />
(VOCs), hydrogen sulfide, and total reduced sulfur compounds. The interim air permits for the<br />
existing operating odor control facilities and <strong>ATF</strong>s require analysis of VOCs by South Coast Air<br />
Quality Management District (SCAQMD) test methods, including the use of SCAQMD Method<br />
25.3 to analyze for TNMHC.<br />
A sampling/analysis program was conducted in April <strong>2010</strong> at the following five interim odor<br />
control facility locations where raw untreated sewer air and the exhaust from the odor control<br />
facilities were assessed.<br />
<br />
<br />
<br />
<br />
<br />
North East Interceptor Sewer (NEIS) – Richmond (Richmond)<br />
North Outfall Relief Sewer (NORS) –ECIS (NORS-ECIS)<br />
NEIS – Humboldt (Humboldt)<br />
East Central Interceptor Sewer (ECIS) – Mission & Jesse (Mission & Jesse)<br />
ECIS - 23 rd Street & San Pedro (23 rd & San Pedro)<br />
Note that the interim <strong>ATF</strong> at 23 rd and San Pedro was physically removed well before our<br />
sampling program started. As a result, the raw sewer air space was sampled and analyzed<br />
for all the same parameters of interest.<br />
Air samples were analyzed for the following parameters:<br />
<br />
Total non-methane hydrocarbons (TNMHC)<br />
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Speciated volatile organic compounds (VOCs)<br />
Hydrogen Sulfide (H 2 S) by Jerome Meter<br />
Continuous H 2 S by OdaLog unit<br />
Speciated organic reduced sulfur compounds<br />
The TNMHC, speciated VOCs and total reduced sulfur compound analyses were conducted by an<br />
independent laboratory. The speciated VOC and speciated organic reduced sulfur compound<br />
analyses were conducted in order to provide an understanding of the compounds that makeup the<br />
TNMHC air sample results. Hydrogen sulfide, in addition to the grab sample evaluation with a<br />
Jerome Meter, was also monitored in the sewer at each location using a continuous monitor with<br />
data-logging capabilities (OdaLog).<br />
While reviewing the analytical results in subsequent paragraphs, please keep in mind that the<br />
SCAQMD Method 25.3 results will be used to determine compliance with the permit limits. The<br />
speciated results were developed to gain a better understanding of the general compounds that<br />
make up the TNMHC value resulting from Method 25.3 and are not used to directly demonstrate<br />
compliance with any permit limits. Due to the variable nature of sewer gases and the cocktail of<br />
compounds present at all different concentrations, a direct equal correlation between Method 25.3<br />
and speciated analyses results is not anticipated nor expected.<br />
The City has shown interest in using a hand-held VOC measuring device as an alternative to<br />
running Method 25.3 to determine TNMHC. A photoionization detector (PID) was used to<br />
analyze samples and the results were compared to TNMHC results.<br />
Following is a summary of findings from the sampling/analytical effort:<br />
At all locations, the odor control facility inlet (raw sewer air) and exhaust Method 25.3<br />
results were below the air permit TNMHC emission limits of 18 to 36 ppm v , except at<br />
Humboldt where the inlet and exhaust concentrations were 23.0 and 18.4 ppmC,<br />
respectively. This is graphically displayed in Figure ES-1. It is believed that the higher<br />
TNMHC and elevated hydrogen sulfide activated carbon exhaust concentrations are due<br />
to spent carbon at the Humboldt odor control facility. It is expected that if the carbon<br />
was still effective the exhaust TNMHC and hydrogen sulfide results would be notably<br />
reduced. The figure below, Total Non-Methane Hydrocarbon VOS Sampling Result<br />
Summary illustrates inlet and exhaust TNMHC concentrations relative to the permit limit<br />
range of 18 to 36 ppm v .<br />
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Figure ES-1<br />
<br />
<br />
<br />
The percentage of speciated VOCs which accounted for Method 25.3 VOCs ranged from<br />
approximately 32% to approximately 100% except for locations where apparent sampling<br />
interference occurred at the Humboldt inlet/exhaust, and at Mission Jesse. The speciated<br />
compounds were determined by EPA Method TO-15, EPA Method TO-12 Modified, and<br />
by a reduced sulfur scan (ASTM 5504) and were expressed as parts per million by<br />
volume by the laboratory. The Method 25.3 results are expressed as ppm as Carbon<br />
(ppmC). In order to compare the speciated results to the Method 25.3 results, the<br />
speciated results were converted to ppmC by multiplying by the volumetric concentration<br />
by the number of carbon atoms in each compound, per EPA guidance. After converting<br />
all the speciated results to ppmC, these compounds were totaled and were compared to<br />
the Method 25.3 results, by calculating a quotient, (ppmC-Speciated)/(ppmC- Method<br />
25.3).<br />
There was limited correlation between PID readings and TNMHC results produced by<br />
Method 25.3 results. Given that a PID’s reading is dependent on the compounds present,<br />
the City should consider using an alternative hand-held field measurement monitor if a<br />
substitute for Method 25.3 is desired.<br />
The short term grab odor control facility inlet or raw sewer air hydrogen sulfide<br />
concentrations ranged from approximately 2 ppm v (at Richmond) to >50 ppm v (at<br />
Mission & Jesse and 23 rd & San Pedro). Figure ES-2, Hydrogen Sulfide Sampling<br />
Results Summary, illustrates the odor control facility inlet and exhaust hydrogen sulfide<br />
concentrations and the average OdaLog readings.<br />
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Figure ES-2<br />
<br />
The carbon adsorbers at Richmond and NORS-ECIS were providing hydrogen sulfide<br />
removals of > 99%. The carbon at Humboldt appeared to be exhausted, with a unit<br />
exhaust hydrogen sulfide concentration of 11.7 ppm v .<br />
An overview of hydrogen sulfide control technologies as a function of inlet concentration in<br />
general, and the values measured in this study are presented in Figure ES-3. Carbon is generally<br />
cost-effective at inlet concentrations less than 10 ppm v . Biofilters are cost-effective at inlet<br />
concentrations up to 50 ppm v and greater. At higher concentrations however, the biofilter media<br />
degradation accelerates. Bio-trickling filters are cost-effective at inlet concentrations of 20 ppm v<br />
and higher, which indicates some overlap for the two biological systems. The Figure below,<br />
Hydrogen Sulfide Emission Control Overview, can be used as a basis to evaluate control<br />
technologies in the next phase of this project.<br />
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Figure ES-3<br />
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1.0 INTRODUCTION AND PURPOSE<br />
Management of a large wastewater collection system presents many challenges and the control of<br />
odors is an increasingly demanding challenge for most owners. The City of Los Angeles (City)<br />
has an extensive collection system that is over 9700 km (6,000 miles) in length with several areas<br />
that present unique odor control challenges. In addition, the City has a long history of<br />
implementing proactive and innovative steps to control odors from its interceptor collection<br />
system including a long and successful history of using chemical addition to proactively control<br />
odors. Unfortunately, chemical addition alone has been unable to eliminate the release of odors<br />
and total non-methane hydrocarbon (TNMHC) from the interceptors. In recent history, the City<br />
has encountered increasing public sensitivity to sewer odors, and they have been working to<br />
improve odor control in several areas identified by local community groups. Air treatment<br />
facilities (<strong>ATF</strong>s) for seven areas with known or predicted odor “hot spots” were including in a<br />
2004 Collection System Settlement Agreement (CSSA) that the City entered into with the United<br />
States Environmental Protection Agency (USEPA), Santa Monica Baykeeper, City of El<br />
Segundo, and others. The CSSA includes several requirements related to operations,<br />
maintenance, capital improvement, and odor control. A key component included the<br />
implementation and operation of interim and permanent air treatment facilities, in addition to the<br />
existing odor control systems and methods currently operating.<br />
Although two out of seven of the proposed permanent <strong>ATF</strong>s were located in areas that were<br />
clearly identified as current and proposed future interceptor hot spots, five of the proposed <strong>ATF</strong>s<br />
locations needed to be reevaluated based on planned future interceptors expansion and<br />
wastewater flow diversions. Accordingly, the City has embarked on a study to determine the<br />
number of and location of the new proposed <strong>ATF</strong>s, assess the performance of the interim odor<br />
control facilities, and decide on the <strong>ATF</strong> technologies. This Technical Memorandum (TM) will<br />
examine the parameters of concern that the <strong>ATF</strong>s will have to control based on monitoring the<br />
existing five interim odor control facility locations.<br />
The City has an extensive network of several major interceptors. Those interceptors consist of<br />
shallow and deep pipelines, including drop structures that convey the wastewater and the airspace<br />
of the various interceptors. The interceptors also include inverted siphons that were constructed<br />
to get around major structures such as interstate highways, rivers and railroad/utility structures.<br />
All of these features not only complicate the location of the <strong>ATF</strong>s, but they also contribute to the<br />
production of odors and the stripping of odors and other volatile organic compounds.<br />
Odors released from the interceptor collection system have been the trigger for odor complaints<br />
and have served to get the attention of the community and the local air regulators, the South Coast<br />
Air Quality Management District (SCAQMD). Existing interceptor odor control facilities and<br />
<strong>ATF</strong>s are required to meet hydrogen sulfide, and in some cases TNMHC limits in their exhaust.<br />
Although the City is ultimately concerned about odors, they must also address TNMHC<br />
emissions whose limits are based on human health affects and/or the total accumulation of<br />
volatile organic compounds (VOCs) in the atmosphere. The City and the surrounding air basin<br />
are in a non-attainment area for Federal (USEPA) ozone ambient air quality standards and must<br />
reduce the levels of ambient ozone by restricting ozone precursors like VOCs. Current odor<br />
control facility and <strong>ATF</strong> permits have a single district exhaust TNMHC and H 2 S limit value in<br />
each site’s air permit. The district exhaust limit is different from site to site. The permit values<br />
range from 18 to 36 ppm v for TNMHC and from 0.6 to 1.0 ppm for H 2 S. The five locations<br />
identified in the CSSA where monitoring will be conducted are:<br />
<br />
<br />
North East Interceptor Sewer (NEIS) – Richmond (Richmond)<br />
North Outfall Relief Sewer (NORS) –ECIS (NORS-ECIS)<br />
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NEIS – Humboldt (Humboldt)<br />
East Central Interceptor Sewer (ECIS) – Mission & Jesse (Mission & Jesse)<br />
ECIS - 23 rd Street & San Pedro (23 rd & San Pedro)<br />
Interim odor control systems consisting of fans and carbon adsorption units were initially<br />
installed at all five of these locations. The interim odor control system installed at 23 rd & San<br />
Pedro has since been removed in response to neighborhood odor complaints. The carbon media<br />
was being consumed quite rapidly by the high concentrations of hydrogen sulfide (H 2 S) and other<br />
odorous and non-odorous compounds. It was determined that it was less of an off-site odor<br />
problem when the interim carbon system was shut completely off. After the system was shut off<br />
and the odor complaints dropped noticeably, the City decided to remove the system from this site.<br />
Nevertheless, this remains one of the original recommended <strong>ATF</strong> locations that will be monitored<br />
during this task of the project.<br />
The City provided several permits that were associated with odor control systems throughout<br />
their interceptor network. Among the permits provided by the City were those for the four<br />
interim odor control systems located at the proposed <strong>ATF</strong> sites. Each of the permits was issued<br />
by the SCAQMD, the regional air permitting authority, to construct/operate the interim odor<br />
control facilities. The permits each have a maximum allowable hydrogen sulfide emission<br />
concentration of 1 part per million by volume (ppm v ) and a single district TNMHC limit that<br />
varies from 18 to 36 ppm v .<br />
Given the permit limits for hydrogen sulfide and TNMHC for the existing odor control facilities<br />
and <strong>ATF</strong>s, and the anticipated permit limits for future proposed <strong>ATF</strong>s, the City wants to have a<br />
greater understanding of the composition of the sewer headspace air at the five interim odor<br />
control facility locations so that permanent <strong>ATF</strong> systems, if placed at the same locations, can be<br />
designed to meet any future air permit requirements. Parameters of interest include: hydrogen<br />
sulfide, total reduced sulfur compounds, and volatile organic compounds (VOCs). The interim<br />
permits require analysis of VOCs by SCAQMD test methods, including SCAQMD Method 25.3.<br />
Method 25.3 reports the total VOC content of the air as carbon, expressed as ppmC.<br />
A sampling/analysis program was conducted in April <strong>2010</strong> at the five interim odor control facility<br />
locations noted above where raw untreated sewer air and the exhaust from the activated carbon<br />
vessels were assessed.<br />
The purpose and objectives of this TM include:<br />
<br />
<br />
<br />
<br />
<br />
Monitoring the five locations previously identified in the CSSA where initially interim<br />
odor control facilities have been installed.<br />
Understanding what the untreated air characteristics are at the five locations.<br />
Monitoring and collecting samples at the inlet and exhaust from the five existing interim<br />
odor control facilities.<br />
Analyzing the samples collected for the following parameters:<br />
o Hydrogen Sulfide (H 2 S)<br />
o Total non-methane hydrocarbons (TNMHC)<br />
o Speciated volatile organic compounds (VOCs)<br />
o Speciated organic reduced sulfur compounds<br />
Evaluating whether the result from the general sum of the speciated compounds is<br />
consistent with the results from the total non-methane hydrocarbon testing (TNMHC).<br />
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Determining whether there are compounds identified by the speciated analysis that are<br />
not technically considered VOCs and should therefore is subtracted from the TNMHC<br />
values.<br />
Comparing the measured values from this task against similar monitoring conducted by<br />
the City at these and/or other odor control facilities and <strong>ATF</strong> locations.<br />
Comparing the measured values from this task for the interim odor control facilities<br />
controlled exhaust against the air permit limits at the same site, and in general against air<br />
permit limits for other odor control facilities and <strong>ATF</strong>s.<br />
Assessing the removal efficiency of the existing interim odor control facilities relative to<br />
H 2 S and TNMHCs.<br />
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2.0 AIR PERMITS<br />
Air permits for interim air pollution control systems were issued by SCAQMD for the following<br />
locations:<br />
<br />
<br />
<br />
Richmond<br />
NORS-ECIS<br />
Humboldt<br />
Mission & Jesse<br />
Permits to construct were also issued for future, permanent odor control systems. The following<br />
summarizes permit limits for the interim and permanent odor control systems:<br />
<br />
<br />
The maximum hydrogen sulfide emission concentration is 1 part per million by volume<br />
(ppm v ) for the interim and permanent systems<br />
The maximum TNMHC emission limits are summarized in Table 1 for the indicated<br />
facilities. No TNMHC limits were set for other facilities. No justification or reason was<br />
provided by SCAQMD for the difference in TNMHC permit limits for the different sites.<br />
Reviewing the actual permits it would appear that different permit writers may have been<br />
involved pursuant to the inconsistencies in the language of the permit. However, it is<br />
more than likely that a consistent TNMHC load has been designated for each site and the<br />
limits reflect the allowable concentrations given the anticipated air flows.<br />
Table 1 - <strong>ATF</strong> TNMHC Emission Limits<br />
<strong>ATF</strong> Location<br />
TNMHC Limit<br />
(ppm v )<br />
North Central Outfall Sewer (NCOS) 30<br />
NORS-ECIS 30<br />
La Cienega – San Fernando Valley Sewer 36<br />
ECIS Inverted Siphon 18<br />
<br />
<br />
A source test was required within 180 days of initial operation to test for the following<br />
parameters using SCAQMD procedures:<br />
o Total sulfur as hydrogen sulfide<br />
o TNMHC<br />
o Speciated organics<br />
o Air flow rate, moisture, temperature<br />
There was consistency in the requirement to speciate organic species. However, there was<br />
some inconsistency in the stated methods recommended to be used to conduct these<br />
analyses. For instance, in some cases the requirement to speciate the organic compounds<br />
is stated as “typical sewer gas organic species using approved methods.” In other<br />
instances speciated is stated in the terms, “speciated using Methods 8015/8021 and 8260,<br />
or other approved methods.” Methods 8015, 8021 and 8260 were designed for liquid and<br />
solid waste matrices. While these methods can be used to analyze for VOC in air<br />
samples, EPA Method TO-15 was written for ambient air samples with lower<br />
concentration VOCs and would be the more appropriate method to use.<br />
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The requirement to measure total organics also varied. In some instances the<br />
measurement of TNMHC was stated, in others, total organic compounds was stated.<br />
A permit had been issued for an odor control system for the 23 rd and San Pedro location, but this<br />
unit was removed in 2008 and relocated to the North Outfall Treatment Facility (NOTF) located<br />
at 10127 Jefferson Blvd, Culver City, CA.<br />
Table 2 is a summary of the permits. It is divided into two sections: the upper section (2A) lists<br />
the permits for the interim odor control facilities; and the lower section (2B) lists permits for the<br />
permanent <strong>ATF</strong>s.<br />
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Table 2 - Summary of the Permits<br />
Table 2A<br />
Air Permit Summary For City of Los Angeles, Dept. of Public Works, Bureau of Sanitation, Interceptor Collection System, Interim Air Treatment Facilities<br />
Carbon<br />
Air Treatment Facility Location Air Flow Rate Treatment<br />
Operating<br />
H2S Limit<br />
Operating<br />
TNMHC<br />
Limit<br />
Carbon<br />
Change-<br />
Out H2S<br />
Threshold<br />
Change-<br />
Out<br />
TNMHC<br />
Threshold<br />
Source Test in Accordance w/<br />
SCAQMD Test Procedures<br />
Within 180 days of Iniitial<br />
Operation<br />
(cfm) (ppmv) (ppmv) (ppmv) (ppmv)<br />
NEIS - Richmond 886 N Mission Rd, Los Angeles, CA 90023 10,000<br />
NORS ECIS 10100 Jefferson Blvd., AFT #804, Culver City, CA 90232 10,000<br />
NEIS - Humboldt 303 1/2 N. San Fernando, Los Angeles, CA 90031 10,000<br />
ECIS - Mission & Jesse<br />
633 S. Mission Road, Los Angeles, CA 90023<br />
10,000<br />
Weekly<br />
Monitoring<br />
During<br />
Operation<br />
Permit Type<br />
Mist Eliminator, One carbon<br />
adsorber, one fan 1.0 na 0.8 na In/Out H2S Construct/Operate 6/28/2005<br />
Total Sulfur as H2S<br />
TNMHC<br />
"Typical Sewer Gas Organic<br />
Species" (speciated organics)<br />
Air flow rate, moisture,<br />
temperature<br />
Demister, One carbon<br />
adsorber, one fan 1.0 na 0.8 na In/Out H2S Construct/Operate 7/2/2004<br />
Total Sulfur as H2S<br />
"Total Organic Compounds"<br />
Speciated using: Methods<br />
8015/8021 and 8260, or other<br />
SCAQMD method<br />
Air flow rate, moisture,<br />
temperature<br />
Mist Eliminator, One carbon<br />
adsorber, one fan 1.0 na 0.8 na In/Out H2S Construct/Operate 6/28/2005<br />
Total Sulfur as H2S<br />
TNMHC<br />
"Typical Sewer Gas Organic<br />
Species" (speciated organics)<br />
Air flow rate, moisture,<br />
temperature<br />
Demister, One carbon<br />
adsorber, one fan 1.0 na 0.8 na In/Out H2S Construct/Operate 7/2/2004<br />
Total Sulfur as H2S<br />
"Total Organic Compounds"<br />
Speciated using: Methods<br />
8015/8021 and 8260, or other<br />
SCAQMD method<br />
Air flow rate, moisture,<br />
temperature<br />
Permit<br />
Date<br />
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Air Permit Summary For City of Los Angeles, Dept. of Public Works, Bureau of Sanitation, Interceptor Collection System, Additional Air Treatment Facilities<br />
Carbon<br />
Operating<br />
TNMHC<br />
Limit<br />
Carbon<br />
Change-<br />
Out H2S<br />
Threshold<br />
Change-<br />
Out<br />
TNMHC<br />
Threshold<br />
Source Test in Accordance w/<br />
SCAQMD Test Procedures<br />
w/iin 180 days of Iniitial<br />
Operation<br />
Name Location Air Flow Rate Treatment<br />
Operating<br />
H2S Limit<br />
(cfm) (ppmv) (ppmv) (ppmv) (ppmv)<br />
NCOS (Interim)<br />
NCOS (Future)<br />
5900 1/2 W Jefferson Blvd., Traffic Island, Los Angeles, CA<br />
90016 10,000<br />
Oil/Grease Trap, three (3)<br />
biotrickling filters (parallel),<br />
mist eliminator, two (2)<br />
6000 Jefferson Blvd, Los Angeles, CA 90016 (North Central<br />
Outfall Sewer (NCOS Inverted Siphon and air line along<br />
Jefferson Blvd. Near Holdrege Ave.)<br />
carbon trains (two series<br />
vessels in parallel), two fans<br />
12,000 (one standby) 1.0 30 0.9 27<br />
NORS-ECIS (Future) 9940 Jefferson Blvd., Culver City, CA 90232 12,000 Demister, Oil/Grease Trap,<br />
three (3) biotrickling filters<br />
(parallel), two (2) carbon<br />
trains (two series vessels in<br />
parallel), two fans (one<br />
standby)<br />
Weekly<br />
Monitoring<br />
During<br />
Operation<br />
Permit Type<br />
Demister, One carbon<br />
adsorber, one fan 1.0 na 0.8 na In/Out Construct/Operate 7/2/2004<br />
Total Sulfur as H2S<br />
"Total Organic Compounds"<br />
Speciated using: Methods<br />
8015/8021 and 8260, or other<br />
SCAQMD method<br />
Air flow rate, moisture,<br />
temperature<br />
Permit<br />
Date<br />
Bio-Trickiling Filter In/Out,<br />
Carbon Train outlet H2S, TNMHC Construct 7/17/2007<br />
Total Sulfur as H2S<br />
"Total Organic Compounds"<br />
Speciated organic compounds<br />
using SCAQMD method<br />
Air flow rate, moisture,<br />
temperature<br />
1.0 30 0.9 27 In/Out H2S, TNMHC (or<br />
otherwise appv'd<br />
frequency)<br />
Total Sulfur as H2S<br />
"Total Organic Compounds"<br />
Construct 1/11/2007<br />
"Speciated organic compounds"<br />
Air flow rate, moisture,<br />
temperature<br />
North Outfall Treatment Facility<br />
(NOTF) 10127 Jefferson Blvd., Culver City, CA 90232<br />
Mist Eliminator, One carbon<br />
10,000 adsorber, one fan 1.0 na 0.8 na TO-15 H2S Construct/Operate 8/13/2008<br />
La Cienega-San Fernando Valley<br />
Relief Sewer<br />
Table 2B<br />
1403 N. Gardner St., Los Angeles, CA 90046 10,000 Mist eliminator, one carbon<br />
adsorber<br />
1.0 36 0.9 34 In/Out H2S, TNMHC Construct 7/12/2007<br />
Total Sulfur as H2S<br />
Total organics<br />
Speciated organics<br />
Air flow rate, moisture,<br />
temperature<br />
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Table 2B (con't)<br />
Air Permit Summary For City of Los Angeles, Dept. of Public Works, Bureau of Sanitation, Interceptor Collection System, Additional Air Treatment Facilities<br />
Operating<br />
TNMHC<br />
Limit<br />
Carbon<br />
Change-<br />
Out H2S<br />
Threshold<br />
Carbon<br />
Change-<br />
Out TNMHC<br />
Threshold<br />
Name Location Air Flow Rate Treatment<br />
Operating<br />
H2S Limit<br />
(cfm) (ppmv) (ppmv) (ppmv) (ppmv)<br />
3410 S La Cienega, Los Angeles, CA 90016 20,000 Oil/Grease Trap 1.0 18 0.9 16<br />
ESIC Inverted Siphon - La Cienega /<br />
San Fernando Vally Interceptor<br />
Sewer<br />
Five (5) biotrickling filters<br />
(parallel), mist eliminator<br />
Source Test in Accordance w/<br />
SCAQMD Test Procedures<br />
w/iin 180 days of Iniitial<br />
Operation<br />
In/Out<br />
Total Sulfur as H2S<br />
Weekly<br />
Monitoring<br />
During<br />
Operation<br />
Permit Type<br />
Permit<br />
Date<br />
H2S, TNMHC Construct 1/11/2007<br />
ESIC Inverted Siphon - La Cienega /<br />
San Fernando Vally Interceptor<br />
Sewer<br />
3410 S La Cienega, Los Angeles, CA 90016<br />
10,000<br />
Ballona Creek Pumping Plant 5550 Inglewod Blvd., PP 654, Los Angeles, CA 90030 5,000<br />
ng 4250 N. Radford, Studio City, CA 91604 5,000<br />
Dacotah Pumping Station 1164 Dacotah St., Los Angeles, CA 90023 3,000<br />
Various Locations in SCAQMD 5,000<br />
Various Locations in SCAQMD 5,000<br />
Notes:<br />
na = not applicable<br />
ng = not given in permit<br />
Four (4) parallel carbon trains<br />
(two vessels in series per<br />
train), two fans (one standby)<br />
Total organics compounds<br />
Speciated organic compounds<br />
Air flow rate, moisture,<br />
temperature, bio-trickling filter<br />
solution flow rate and pH, diff.<br />
pressure<br />
Demister, One carbon<br />
adsorber, one fan 1 na 0.8 na In/Out H2S Construct/Operate 7/2/2004<br />
Total Sulfur as H2S<br />
Total organics compounds<br />
Speciated organic compounds<br />
using EPA Methods 8015/8021<br />
and 8260, or other approved<br />
SCAQMD methods<br />
Air flow rate, moisture,<br />
temperature<br />
Mist Eliminator, one carbon<br />
adsorber, one fan 1.0 na 0.8 na In/Out H2S Construct/Operate 6/28/2005<br />
Total Sulfur as H2S<br />
TNMHC<br />
"Typical Sewer Gas Organic<br />
Species" (speciated organics)<br />
Air flow rate, moisture,<br />
temperature<br />
Prefilters, carbon adsorber,<br />
one fan 1.0 na 0.8 na na H2S Construct/Operate 2/23/2005<br />
Mist eliminator,carbon<br />
adsorber, one fan 1.0 na 0.8 na In/Out H2S Construct/Operate 6/28/2005<br />
Total Sulfur as H2S<br />
TNMHC<br />
"Typical Sewer Gas Organic<br />
Species" (speciated organics)<br />
Air flow rate, moisture,<br />
temperature<br />
Pre-filters, carbon adsorber,<br />
one fan 1.0 na 0.8 na na na Construct/Operate 2/23/2005<br />
Pre-filters, carbon adsorber,<br />
one fan 0.6 na 0.5 na na H2S Operate 11/5/2004<br />
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3.0 SAMPLING SETUP<br />
The sampling was conducted per the Total Non-Methane Hydrocarbon VOC and H 2 S Draft<br />
Sampling Plan dated April <strong>2010</strong>, and as described in this document.<br />
3.1 Sample Locations and Schedule<br />
The locations sampled and sample dates are listed in Table 3. Also included in the table is the<br />
location as called-out on the sewer air treatment systems map prepared by the City of Los<br />
Angeles, Sanitation Department of Public Works. This map appears in Appendix A. Figure 1<br />
shows the sample locations<br />
As is the case in most collection systems, it was expected that hydrogen sulfide emissions in the<br />
City of Los Angeles collection system follows a diurnal cycle, and it was assumed that the<br />
mechanisms that drives the volatilization of hydrogen sulfide also applies to the release of VOCs.<br />
In order to determine the time of day to conduct the sampling, a hydrogen sulfide measurement/<br />
device with data-logging ability was suspended in the headspace of the inlet manhole at each<br />
<strong>ATF</strong> location before the sampling began. OdaLog units were used and are described below in the<br />
hydrogen sulfide measurement section below. The sample times determined from the recorded<br />
hydrogen sulfide concentrations are summarized in Table 3.<br />
Location - Description<br />
NEIS – Richmond. Interim carbon<br />
scrubber<br />
NORS ECIS – Interim carbon<br />
scrubber<br />
NEIS – Humboldt. Interim carbon<br />
scrubber<br />
ECIS – Mission & Jesse. Interim<br />
carbon scrubber<br />
ECIS – 23 rd & San Pedro. Interim<br />
carbon scrubber removed.<br />
Table 3 -Sampled Locations and Dates<br />
Interceptor Air Treatment<br />
System Map Location No.<br />
Sample Date-<br />
Time<br />
2 4/22/10 -<br />
12:30<br />
7 4/22/10 –<br />
18:45<br />
1 4/23/10 –<br />
7:30<br />
3 4/23/10 –<br />
12:00<br />
4 4/23/10 –<br />
14:30<br />
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Figure 1 - Interim <strong>ATF</strong> and Monitoring Location Map<br />
3.2 Sampling Equipment, Measurement Parameters and<br />
Analytical Methods<br />
3.2.1 Sampling Equipment and Measurement Parameters<br />
Air samples were collected for analysis from a continuous air stream that was pulled from the<br />
<strong>ATF</strong> inlet, <strong>ATF</strong> exhaust, or <strong>ATF</strong> inlet manhole using an air pump. A generator was used to run<br />
the pump. The <strong>ATF</strong> inlet manhole was sampled at Mission & Jesse because the carbon of its<br />
<strong>ATF</strong> was being replaced during the sampling; and as noted above the <strong>ATF</strong> at 23 rd and San Pedro<br />
had been removed. For air samples collected from the <strong>ATF</strong> inlet, a threaded fitting was installed<br />
in one of the inlet duct sample ports, ½” (inside diameter) Teflon tubing was connected via a<br />
Swagelock fitting to this threaded fitting and the other end of the tubing was connected to the<br />
suction side of the air pump. Tee fittings were installed in the ½” Teflon tubing and a line from<br />
each Tee was run to two Summa canisters, which were used to collect samples for the TNMHC<br />
samples and volatile organic compound (VOC) analyses as discussed below. The air volume<br />
pulled by the air pump was approximately 300 times greater than the air volume collected in the<br />
Summa canisters which enabled the simultaneous filling of both Summa canisters. Air samples<br />
were also collected from the air pump discharge for additional analyses. Figure 2 is a schematic<br />
of the sampling train. Figure 3 is a photograph of one of the sampling trains.<br />
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Figure 2 - Sampling Train Schematic<br />
Figure 3 – Air Sampling Train<br />
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For air samples collected from the <strong>ATF</strong> exhaust, ½” Teflon tubing was connected to the threaded<br />
pressure port located on the exhaust stack or exhaust plenum downstream of the carbon bed and<br />
samples were collected as described above for the <strong>ATF</strong> inlet. Samples were collected from the<br />
<strong>ATF</strong>s’ inlet and exhaust simultaneously.<br />
At Mission & Jesse and 23 rd & San Pedro, air samples were collected by placing approximately<br />
20 lineal feet of the ½” Teflon sample tubing down into the manhole which connected to the<br />
sample train setup as described for the <strong>ATF</strong> inlet and exhaust<br />
3.2.2 Analytical Methods<br />
The analytical methods used to characterize the raw untreated sewer air and the <strong>ATF</strong> exhaust air<br />
were based upon SCAQMD permits for the <strong>ATF</strong>s and the City’s interest in understanding the<br />
composition of these air streams. The permits had two common emission limits as noted above:<br />
TNMHC and hydrogen sulfide.<br />
The permits require TNMHC is to be measured by SCAQMD Method 25.3 which oxidizes<br />
volatile organic compounds (VOCs) to carbon dioxide, reduces the carbon dioxide to methane,<br />
and measures the methane with a flame ionization detector. The method uses a gas<br />
chromatographic system to separate methane and ethane from the analysis because these<br />
compounds are recognized as not contributing to photochemical reactions. The air streams were<br />
analyzed by Method 25.3, and three additional methods in order to understand the organic<br />
compounds present in the subject air streams before their conversion to methane: EPA Method<br />
TO-15, EPA TO-12 Modified and ASTM 5504. These methods are described below.<br />
The City has received approval to use a photo-ionization detector (PID) device as an alternative<br />
method to measure the VOCs in the <strong>ATF</strong> exhaust air streams. PIDs have varying sensitivities to<br />
different compounds. Given this varying sensitivity, the use of a PID as an alternative to Method<br />
25.3 was evaluated as part of this study.<br />
The following paragraphs describe the test methods used:<br />
Total Non-Methane Hydrocarbon Compounds: Samples were collected/analyzed using<br />
SCAQMD Method 25.3 by an independent outside laboratory, Atmospheric Analysis &<br />
Consulting (AAC), Ventura, CA. Per this method, the air sample was passed through a<br />
condensate trap chilled in ice and then collected in a 6-liter evacuated stainless steel sample<br />
canister (Summa canister). The purpose of the condensate trap is to remove carbon dioxide and<br />
moisture which may contribute to a positive interference. The condensate was analyzed for total<br />
carbon and inorganic carbon. Total organic carbon (TOC) is determined by taking the difference<br />
of these values and is expressed as parts per million as carbon (ppmC). The air collected in the<br />
Summa canister was passed through a gas chromatographic column which separated carbon<br />
monoxide, carbon dioxide, methane, ethane and ethylene from the other organic compounds<br />
present, referred to as non-methane, non-ethane organic compounds (NMNEOC). The remaining<br />
compounds were then oxidized to carbon dioxide, reduced to methane and analyzed by a flame<br />
ionization detector (FID). The results were reported as ppmC. Samples were collected over 1-<br />
hour through the use of a flow controller that was provided with the Summa canister. See<br />
Appendix B for the analytical reports from AAC.<br />
EPA Method TO-15: Samples were collected in a 6-liter evacuated sample Summa canister and<br />
were analyzed by gas chromatography/mass spectrometry (GC/MS) to identify the compounds<br />
present by the laboratory, AAC. Prior to analysis, the sample was first concentrated<br />
cryogenically. Water was then removed using a hydrophobic drying system before being<br />
analyzed by the GC/MS system. Table 4 lists the compounds identified by this analytical<br />
method. Samples were collected over 1-hour using a flow controller at the same time samples<br />
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were collected for analysis by SCAQMD 25.3. See Appendix B for the analytical reports from<br />
AAC.<br />
Chlorodifluoromethane<br />
Propylene<br />
Dichlorodifluoromethane<br />
Chloromethane<br />
1,2-Dichloro-1,1,2,2 tetrafluoroethane<br />
Vinyl chloride<br />
Methanol<br />
1,3-Butadiene<br />
Bromomethane<br />
Chloroethane<br />
Dichlorofluoromethane<br />
Ethanol<br />
Vinyl Bromide<br />
Acetone<br />
Trichlorofluoromethane<br />
Isopropanol<br />
Acrylonitrile<br />
1,1-Dichloroethylene<br />
Methylene Chloride<br />
Allyl Chloride<br />
Carbon Disulfide<br />
1,1,2-Trichloro-1,2,2-trifluoroethane<br />
t-1,2-dichloroethylene<br />
1,1-dichloroethane<br />
MTBE<br />
Vinyl Acetate<br />
2-butanol (MEK)<br />
cis-1,2-dichloroethylene<br />
Hexane<br />
Chloroform<br />
Ethyl Acetate<br />
Tetrahydrofuran<br />
1,2-dichloroethane<br />
1,1,1-trichloroethane<br />
Table 4 - TO-15 Compound List<br />
Benzene<br />
Carbon Tetrachloride<br />
Cyclohexane<br />
1,2-Dichloropropane<br />
Bromodichloromethane<br />
1,4-Dioxane<br />
Trichloroethene<br />
2,2,4-trimethylpentane<br />
Heptane<br />
cis-1,3-dichloropropene<br />
4-methyl-2-pentanone (MIBK)<br />
Trans-1,3-dichloropropene<br />
1,1,2-trichloroethane<br />
Toluene<br />
2-Hexanone<br />
Dibromochloromethane<br />
1,2-Dibromoethane<br />
Tetrachloroethene<br />
Chlorobenzene<br />
Ethylbenzene<br />
m,p-xylenes<br />
Bromoform<br />
Styrene<br />
1,1,2,2-Tetrachloroethane<br />
o-xylene<br />
Ethylotoluene<br />
1,3,5-trimethylbenzene<br />
1,2,4-trimethylbenzene<br />
Benzyl chloride<br />
1,3-dichlorobenzene<br />
1,4-dichlorobenzene<br />
1,2-dichlorobenzene<br />
1,2,4-trichlorobenzene<br />
Hexachlorobutadiene<br />
TO-12 Modified: This method is based on the methodology developed to measure ozone<br />
precursors as part of the Clean Air Act Amendments (Title 40 Code of the Federal Register, Part<br />
58). The amendments require States to establish Photochemical Assessment Monitoring Stations<br />
(PAMS). As a result this method is also referred to as the PAMS protocol. Fifty seven (57) VOCs<br />
are measured which consist of aliphatic and aromatic hydrocarbons generally having a carbon<br />
number in the range C 2 through C 12 . The sample is passed through a gas chromatographic column<br />
and then into a flame ionization detector (FID). A retention-time multi-component calibration<br />
standard is used to identify the compounds and the FID response to each compound is calibrated<br />
using propane. Concentrations are reported as parts per billion as carbon (ppbC). Table 5 is a list<br />
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of compounds measured by this analytical method. See Appendix B for the analytical reports<br />
from AAC.<br />
Ethylene<br />
Acetylene<br />
Ethane<br />
Propylene<br />
Propane<br />
Isobutane<br />
l-Butene<br />
n-Butane<br />
Trans-2-Butene<br />
Cis-2-Butene<br />
Isopentane<br />
1-Pentene<br />
n-Pentane<br />
Isoprene<br />
trans-2-Pentene<br />
cis-2-Pentene<br />
2,2-Dimethylbutane<br />
Cyclopentane<br />
2,3-Dimethylbutone<br />
2-Methylpentane<br />
3-Methylpentane<br />
1-Hexene<br />
n-Henane<br />
Methylcyclopentane<br />
2,4-Dimethylpentane<br />
Benzene<br />
Cyclohexane<br />
2-Methylhexane<br />
Table 5 - TO-12 Modified Compound List<br />
2,3-Dimethylpentane<br />
3-Methylhexane<br />
2,2,4-Trimethylpentane<br />
n-Heptane<br />
Methylcyclohexane<br />
2,3,4-Trimethylpentane<br />
Toluene<br />
2-Methylheptane<br />
3-Methylheptane<br />
n-Octane<br />
Ethylbenzene<br />
m/p-Xylenes<br />
Styrene<br />
o-Xylene<br />
Nonane<br />
Isopropylbenzene<br />
n-Propylbenzene<br />
m-Ethyltoluene<br />
p-Ethyltoluene<br />
1,3,5-Trimethylbenzene<br />
o-Ethyltoluene<br />
1,2,4-Trimethylbenzene<br />
n-Decane<br />
1,2,3-Trimethylbenzene<br />
m-Diethylbenzene<br />
p-Diethylbenzene<br />
n-Undecane<br />
n-Dodecane<br />
Handheld Photo-ionization Detector (PID): Air samples were collected in Tedlar bags and<br />
analyzed by a handheld PID, a Mini-Rae 2000, manufactured by Rae Systems. The unit was<br />
calibrated using isobutylene at a concentration of 100 ppm v . Measurements are expressed as<br />
ppm v. However they are actually ppm v equivalents as isobutylene. A PID uses an ultraviolet lamp<br />
to emit photons which ionizes compounds. The unit that was used had lamp with an ionization<br />
potential of 10.6 millivolts, which is the most commonly used. The instrument response is<br />
proportional to the concentration of compounds which become ionized. It is noted that only a<br />
fraction of the compounds present are typically ionized because the PID’s sensitivity to different<br />
compounds varies. The order of a PID’s sensitivity to different types of compounds, from greater<br />
to less sensitivity is as follows: aromatic compounds, olefins, ketones, ethers, amines, sulfur<br />
compounds, esters, aldehydes, alcohols, aliphatics, chlorinated aliphatics and ethane. The<br />
sensitivity of compounds is expressed as a correction factor (CF). When measurements of<br />
mixtures are made, the reading should be adjusted by the CF for each compound present. The<br />
overall CF for an air sample containing multiple compounds would be,<br />
CF (Mix) = 1/(X i /CF i + X j /CF j + X k /CF k …)<br />
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The instrument’s reading would then be multiplied by the correction factor to yield the volumetric<br />
concentration equivalents as isobutylene.<br />
For example, with an air sample containing 5% benzene (CF=0.53) and 95% n-hexane (CF=4.3),<br />
the CF (Mix) would be,<br />
CF (Mix) = 1/(0.05/0.53 + 0.95/4.3) = 3.2<br />
A reading of 100 would then be multiplied by 3.2 to yield 320 ppm v equivalents as isobutylene.<br />
Reduced Sulfur Compounds: Air samples were collected from the <strong>ATF</strong> air inlet streams in a<br />
Tedlar bag and were analyzed for reduced sulfur compounds by the laboratory, AAC. The<br />
method used, ASTM 5504, analyzes for 20 reduced sulfur compounds by using gas<br />
chromatography (GC) and a sulfur chemiluminescence detector (SCD). The compounds this<br />
method measures are listed in Table 6. See Appendix B for the analytical reports from AAC.<br />
Table 6 - ASTM 5504 Measured Compounds<br />
Hydrogen Sulfide<br />
Carbonyl Sulfide<br />
Methyl Mercaptan<br />
Ethyl Mercaptan<br />
Dimethyl Sulfide<br />
Carbon Disulfide<br />
Isopropyl Mercaptan<br />
tert-Butyl Mercaptan<br />
n-Propyl Mercaptan<br />
Ethyl Methyl Sulfide<br />
Thiophene<br />
Isobutyl Mercaptan<br />
Diethyl Sulfide<br />
Butyl Mercaptan<br />
Demethyl Disulfide<br />
3-Methylthiophene<br />
Tetrahydrothiophene<br />
2-Ethylthiophene<br />
2,5-Dimethylthiophene<br />
Diethyl Disulfide<br />
Hydrogen Sulfide: Hydrogen sulfide was measured using two different types of field<br />
measurement devices. OdaLog units were suspended in the manholes that exhaust to the <strong>ATF</strong><br />
units, and at the 23 rd & San Pedro manhole that discharged to the <strong>ATF</strong> before it was removed, in<br />
order to determine when elevated concentrations occur within the diurnal cycle, so that the<br />
sampling could be scheduled as discussed above. The units were left in the manholes for three<br />
days to record data for the daily cycle and then up to two additional days until the sampling was<br />
complete. These devices are intrinsically safe, utilize an electro-chemical sensor, have a lower<br />
detection limit of 0.25 ppm v and depending on the model, can measure up to 50, 200, or a 1,000<br />
ppm v . They have data-logging capabilities and were programmed to take a measurement once per<br />
minute.<br />
A low level monitor, the Jerome Meter, manufactured by Arizona Instruments, was used to<br />
measure hydrogen sulfide collected in Tedlar bags. The bags were analyzed immediately onsite.<br />
(The same bags were analyzed by the PID unit during the sampling event.) The Jerome Meter has<br />
a measurement range of 0.003 to 50 ppm v .<br />
3.2.3 <strong>ATF</strong> Inlet Air Velocity Measurements and Air Flow Rates<br />
Velocity measurements were made of the inlet air stream to the <strong>ATF</strong>s at Richmond, NORS-ECIS,<br />
Humboldt and Mission & Jesse. The measurements were made using an Airdata Multimeter<br />
ADM-860 and a pitot tube. The inlet duct at these locations has two sample ports 90 degrees<br />
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apart from each other. A traverse across the duct was made using both ports. The average<br />
velocity was multiplied by the inlet duct cross sectional area (diameter = 24”) to determine the<br />
inlet air flow rate.<br />
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4.0 COLLECTED DATA AND SAMPLING RESULTS<br />
While reviewing the analytical results in subsequent paragraphs, please keep in mind that the<br />
SCAQMD Method 25.3 results will be used to determine compliance with the permit limits. The<br />
speciated results were developed to gain a better understanding of the general compounds that<br />
make up the TNMHC value resulting from Method 25.3 and are not used to directly demonstrate<br />
compliance with any permit limits. Due to the variable nature of sewer gases and the cocktail of<br />
compounds present at all different concentrations, a direct equal correlation between Method 25.3<br />
and speciated analyses results is not anticipated nor expected.<br />
4.1 Richmond<br />
Method 25.3/Speciated VOCs: The Richmond VOC sample/analytical results by Method 25.3<br />
are 3.8 and 4.8 ppmC for the inlet and exhaust, respectively, as shown in Table 7. These values<br />
are relatively low as compared to the permit emission limits in Table 1 (18 to 36 ppm v ).<br />
However, it is noted that the exhaust TNMHC concentration exceeded the inlet concentration<br />
indicating the carbon is exhausted for its VOC removal capacity. Every attempt was made to<br />
sample the inlet and exhaust simultaneously. Accordingly, the difference in inlet and exhaust<br />
Method 25.3 values cannot be readily explained by highlighting the continuous odor and<br />
TNMHC variability in the interceptor headspace. In this situation, although the difference in<br />
values is merely 1.0 ppm, the activated carbon may be the cause. It is theorized that when<br />
activated carbon becomes saturated with long chain organic compounds, some of those<br />
compounds can be displaced while others can be broken releasing intermediate compounds. The<br />
displaced and additional intermediate compounds could account for the increase in the exhaust<br />
levels. Fortunately, the inlet and exhaust levels are well below any anticipated TNMHC permit<br />
limits.<br />
It is believed the reason greater concentrations were being measured in the exhaust than the inlet<br />
is that the carbon had reached saturation for some compounds. At this condition, compounds in<br />
the inlet were displacing compounds on the carbon which were then measured in the exhaust. The<br />
VOCs breaking through the carbon had a higher concentration than the inlet.<br />
The sum of the VOC speciated compounds results from the TO-15, TO-12 Modified and ASTM<br />
5504 were compared to the Method 25.3 results. In order to make this comparison, the TO-15<br />
and ASTM 5504 results, which were reported in volumetric concentrations for each compound,<br />
had to be converted to ppmC, the reporting basis for the Method 25.3 results. Per EPA guidance,<br />
volumetric concentrations are converted to ppmC by multiplying by the number of carbon atoms<br />
in each compound.<br />
This conversion was made for the TO-15 and ASTM 5504 results which were then expressed as<br />
total speciated VOC as ppmC (Table 7). There are eleven (11) compounds that are measured by<br />
both the TO-15 and TO-12 Modified methods. When this comparison was made, TO-15<br />
compounds that were also reported by the TO-12 Modified method were excluded from the<br />
summation. In addition, the VOCs which were measured and have negligible photochemical<br />
activity were subtracted from the Method 25.3 and the TO-15 results. Comparisons of Method<br />
25.3 and total speciated VOCs for the inlet and exhaust are as follows:<br />
<br />
Richmond <strong>ATF</strong> Inlet. The total speciated VOC concentration for the Richmond <strong>ATF</strong> inlet<br />
was 3.66 ppmC which slightly exceeded the Method 25.3 value, 3.29 ppmC. The ratio of<br />
speciated VOCs/Method 25.3 VOCs was 1.11 (Table 7). Given the limits of the precision<br />
and accuracy of the analytical methods, the speciated VOCs account for the Method 25.3<br />
VOCs. The required relative percent difference (RPD) for laboratory control spikes for<br />
Method 25.3, TO-15 and TO-12 Modified is +/- 25%. Compounds with concentrations<br />
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above 100 ppbC, key speciated compound contributors, which contributed to the inlet VOCs<br />
are: propane, isobutane, n-butane, and isopentane (Table 9). The total speciated VOC<br />
concentrations are shown in Table 7. For a complete list of speciated compounds with<br />
measured concentrations refer to Tables 8 and 9.<br />
Richmond <strong>ATF</strong> Exhaust. The total speciated VOC concentration for the Richmond <strong>ATF</strong><br />
inlet was 3.66 ppmC which slightly exceeded the Method 25.3 value, 3.29 ppmC. The ratio of<br />
speciated VOCs/Method 25.3 VOCs was 1.11 (Table 7). Given the limits of the precision<br />
and accuracy of the analytical methods, the speciated VOCs account for the Method 25.3<br />
VOCs. The required relative percent difference (RPD) for laboratory control spikes for<br />
Method 25.3, TO-15 and TO-12 Modified is +/- 25%. Compounds with concentrations<br />
above 100 ppbC, key speciated compound contributors, which contributed to the inlet VOCs<br />
are: propane, isobutane, n-butane, and isopentane (Table 9). The total speciated VOC<br />
concentrations are shown in Table 7. For a complete list of speciated compounds with<br />
measured concentrations refer to Tables 8 and 9.<br />
Non-VOCs. The TO-15 analytical list includes numerous compounds which do not participate in<br />
photochemical reactions that produce ozone. EPA excludes 51 of these compounds from its<br />
definition of VOCs. Method 25.3 excludes two of these compounds, methane and ethane.<br />
Acetone, methylene chloride and tetrachloroethylene which are included on the EPA non-VOC<br />
list were measured at Richmond. Acetone was detected in the <strong>ATF</strong> inlet. Methylene chlorine and<br />
tetrachloroethylene were below the detection limit of the inlet but were measured in the exhaust.<br />
The concentration of these compounds is summarized in Table 7. The adjusted Method 25.3<br />
results for the inlet and exhaust which accounts for the subtraction of the methylene chloride and<br />
acetone are given in Table 7.<br />
Table 8 and Table 9 summarize the TO-15 and TO-12 Modified results, respectively. TO-15<br />
results were reported by the laboratory in units of ppb v and were converted to units of ppbC.<br />
PID Results: The PID results for the <strong>ATF</strong> inlet and exhaust which were 2.04 and 0.25 ppmC,<br />
respectively. The ratio of the PID/Method 25.3 values for the inlet and exhaust were 0.54 and<br />
0.05, respectively, showing a low bias for both the inlet and exhaust air streams, but relatively<br />
greater correlation for the inlet air as compared to the exhaust air. (Table 7)<br />
Hydrogen Sulfide and Reduced Sulfur Results:<br />
The Jerome Meter hydrogen sulfide inlet and exhaust concentrations were 2.29 and
Measured Air Flow Rate: The fan was not operating during the sampling. Air was being moved<br />
through the <strong>ATF</strong> using the positive pressure of the collection system. The measured air flow rate<br />
at the <strong>ATF</strong> inlet was 1,120 cfm. This compares to rated system capacity of 10,000 cfm.<br />
Figure 4 thru Figure 6 are photographs of the Richmond <strong>ATF</strong>, and sampling and velocity<br />
measurement effort.<br />
Table 7 - Richmond - TNMHC, VOC and H2S Sample/Analytical Results<br />
Analytical Method Richmond Inlet Richmond Exhaust<br />
TNMHC<br />
Method 25.3, ppmC 3.80 4.80<br />
TNMHC Removal Efficiency By Carbon<br />
Adsorber<br />
Exhaust Conc. > Inlet Conc.<br />
Non VOCs<br />
Acetone, ppmv/ppmC 0.164/0.492
Table 8 - Richmond TO-15 Sample/Analytical Results<br />
Compound<br />
Richmond Inlet Richmond Inlet Richmond Exhaust Richmond Exhaust<br />
(ppbv) (ppbC) (ppbv) (ppbC)<br />
Methanol 27.6 27.6 40.5 40.5<br />
Ethanol 24.6 49.2 294 588.0<br />
Acetone
Table 9 - Richmond TO-12 Modified Results<br />
Compound<br />
Richmond Inlet Richmond Exhaust<br />
(ppbC)<br />
(ppbC)<br />
ETHYLENE 8.1 6.8<br />
Acetylene
Figure 4 - Richmond <strong>ATF</strong> (1)<br />
Figure 5 - Richmond <strong>ATF</strong> (2)<br />
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Figure 6 - Richmond <strong>ATF</strong> (3)<br />
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4.2 NORS-ECIS<br />
Method 25.3/Speciated VOCs: The NORS-ECIS VOC sample/analytical results by Method 25.3<br />
are 15.2 and 3.9 ppmC for the inlet and exhaust, respectively, as shown in Table 10. These values<br />
are relatively low as compared to the emission limits in Table 1 (18 to 36 ppm v ). The TNMHC<br />
removal efficiency of the carbon adsorber was 74%.<br />
Using the approach described for Richmond, the VOCs measured by method 25.3 were compared<br />
to the speciated VOC results:<br />
<br />
NORS-ECIS <strong>ATF</strong> Inlet: The total speciated VOC concentration for the NORS-ECIS <strong>ATF</strong><br />
inlet adjusted for non-photochemically active VOCs was 8.42 ppmC which is approximately<br />
58% of the Method 25.3 value (Table 10). However, if the measured speciated and Method<br />
25.3 results are viewed with their allowable range given the +/- 25% RPD limits for these<br />
methods, the speciated VOCs account for the Method 25.3 VOCs. Compounds with<br />
concentrations above 100 ppbC, key speciated compound contributors, which contributed to<br />
the inlet VOCs are: ethanol, acetone, methylene chloride, chloroform (Table 11); and<br />
propane, isobutane, n-butane, isopentane, methylcyclohexane, toluene, 2-methylheptane, 3-<br />
methylheptane, n-octane, m/p-xylenes, o-xylene, nonane, n-propylbenzene, m-ethyltolune, p-<br />
ethyltoluene,1,3,5-trimethylbenzene, o-ethyltoluene, 1,2,4-trimethybenzene, n-decane, 1,2,3-<br />
trimethylbenzene, n-undecane and n-dodecane (Table 12). For a complete list of speciated<br />
compounds with measured concentrations refer to Tables 11 and 12.<br />
NORS-ECIS <strong>ATF</strong> Exhaust: The total speciated VOC concentration for the NORS-ECIS<br />
<strong>ATF</strong> exhaust was 3.25 ppmC, which is approximately 80% of the Method 25.3 concentration.<br />
As noted for the inlet, if the measured speciated and Method 25.3 results are viewed with<br />
their allowable range given the +/- 25% RPD limits for these methods, the speciated VOCs<br />
account for the Method 25.3 VOCs. Ethanol at a concentration of 1,476 ppbC had the highest<br />
VOC concentration in the exhaust. Other compounds above a concentration of 100 ppbC, key<br />
speciated compound contributors, that contributed to the exhaust VOCs are: propane,<br />
isobutane, and n-butane. For a complete list of speciated compounds with measured<br />
concentrations refer to Tables 11 and 12.<br />
Non-VOCs. The non-VOCs, acetone, methylene chloride and tetrachloroethylene were<br />
measured at NORS-ECIS. Their concentrations and the adjusted Method 25.3 results are<br />
summarized in Table 10.<br />
Table 11 and Table 12 summarize TO-15 and TO-12 Modified Results, respectively. TO-15<br />
results were reported by the laboratory in units of ppb v and were converted to units of ppbC.<br />
PID Results. The PID results for the <strong>ATF</strong> inlet and exhaust were 8.45 and 0.40 ppmC,<br />
respectively. The ratio of the PID/Method 25.3 values for the inlet and exhaust were 0.56 and<br />
0.10, respectively, showing a low bias for both the inlet and exhaust air streams, but relatively<br />
greater correlation for the inlet air as compared to the exhaust air. The PID and Method 25.3<br />
results shown for the NORS-ECIS is similar to that shown for Richmond. Table 10)<br />
Hydrogen Sulfide and Reduced Sulfur Results<br />
The Jerome Meter hydrogen sulfide inlet and exhaust concentrations were 22.2 and 0.005 ppm,<br />
respectively, resulting in greater than 99% removal (Table 10).<br />
An OdaLog unit was placed in the NORS-ECIS <strong>ATF</strong> manhole from April 19 to 23. The average,<br />
maximum and minimum hydrogen sulfide concentrations were, 32, 67 and < 0.25 ppm v , as<br />
summarized in Table 10. The NORS-ECIS OdaLog graph appears in Appendix C.<br />
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The only reduced sulfur compound measured in the <strong>ATF</strong> inlet in addition to hydrogen sulfide<br />
was methyl mercaptan at a concentration of 0.584 ppm v .<br />
Measured Air Flow Rate: The fan was operating during the sampling. The measured air flow<br />
rate at the <strong>ATF</strong> inlet was 9,190 cfm. This compares to the rated system capacity of 10,000 cfm.<br />
Figure 7 thru Figure 9 are photographs of the NORS-ECIS <strong>ATF</strong> and the sampling effort.<br />
Table 10 - NORS-ECIS TNMHC, VOC and H2S Sample/Analytical Results<br />
Analytical Method<br />
NORS ECIS Inlet<br />
NORS ECIS<br />
Exhaust<br />
TNMHC<br />
Method 25.3, ppmC 15.2 3.90<br />
TNMHC Removal Efficiency By Carbon Adsorber 74%<br />
Non VOCs<br />
Acetone, ppmv/ppmC 0.130/0.390 99%<br />
OdaLog Results<br />
Average Hydrogen Sulfide, ppm 32 ns 2<br />
Maximum Hydrogen Sulfide, ppm 67 ns 2<br />
Minimum Hydrogen Sulfide, ppm
Table 11 - NORS-ECIS TO-15 Sample/Analytical Results<br />
Compound<br />
NORS-ECIS<br />
Inlet<br />
NORS-ECIS<br />
Inlet<br />
NORS-ECIS<br />
Exhaust<br />
NORS-ECIS<br />
Exhaust<br />
(ppb v ) (ppbC) (ppb v ) (ppbC)<br />
Chlorodifluoromethane 18.4 18.4 16.2 16<br />
Chloromethane 43.7 43.7 42.4 42<br />
Methanol 44.8 44.8 53.5 54<br />
Chloroethane 23.9 47.8 29.0 58<br />
Ethanol 180 360 738 1476<br />
Acetone 130 390
Table 12 - NORS-ECIS TO-12 Modified Results<br />
Compound<br />
NORS-ECIS Inlet NORS-ECIS Exhaust<br />
(ppbC)<br />
(ppbC)<br />
Ethylene 25.3 20.2<br />
Acetylene
Figure 7 - NORS ECIS <strong>ATF</strong> (1)<br />
Figure 8 - NORS ECIS <strong>ATF</strong> (2)<br />
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Figure 9 - NORS ECIS <strong>ATF</strong> (3)<br />
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4.3 Humboldt<br />
Method 25.3/Speciated VOCs: The Humboldt VOC sample/analytical results for Method 25.3<br />
are 23.0 and 18.4 ppmC for the inlet and exhaust, respectively, as shown in Error! Not a valid<br />
bookmark self-reference.. The exhaust concentration is just above the emission limits in<br />
Table 1. The TO-15 and TO-12 Modified data were reviewed to determine if one or more<br />
compounds at Humboldt may have caused this increase. As is discussed below, the only<br />
measured compound that may have contributed to this higher Method 25.3 value is ethanol,<br />
however, due to the interference described below, the actual ethanol concentration in the inlet and<br />
exhaust air streams is not known. The TNMHC removal efficiency of the carbon absorber was<br />
20% indicating the carbon has approached its VOC adsorption capacity. The likely TNMHC<br />
removal efficiency with fresh carbon will vary based on the make-up of the inlet air stream, but<br />
can generally be expected to range from 70 to over 90% removal from typical wastewater<br />
environments.<br />
<br />
Humboldt <strong>ATF</strong> Inlet: The sum of the speciated VOC results from the TO-15, TO-12<br />
modified and ASTM 5504 were compared to the Method 25.3 results with VOCs having<br />
negligible photochemical activity subtracted (Table 13). The total speciated VOC<br />
concentration for the Humboldt <strong>ATF</strong> inlet was 115 ppmC which is approximately five times<br />
greater than the Method 25.3 results.<br />
This is believed to be the result of condensate which accumulated at the Tee where the ½”<br />
Teflon tubing air line connected to the ¼” Teflon branch line that ran to the Summa canister<br />
used for the TO-15 and TO-12 Modified analysis. It is believed that this condensate absorbed<br />
a disproportionate amount of ethanol from the total air stream being moved by the air pump<br />
which in turn was released into the air stream being directed to the TO-15 and TO-12<br />
Modified canister. This hypothesis is supported by the high ethanol concentration of 54,700<br />
ppb v in the TO-15 results for the Humboldt inlet air stream (see<br />
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Table 14). This compares to ethanol concentrations in the Richmond inlet and exhaust; and<br />
the NORS-ECIS inlet and exhaust that are all considerably less than 1,000 ppb v (refer to<br />
Tables 8 and 11).<br />
In addition to the ethanol already noted, compounds with concentrations above 100 ppbC<br />
which contributed to the inlet VOCs are acetone, ethyl acetate, tetrachloroethylene (<br />
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Table 14); and propane, isobutane, n-butane, and isopentane (Table 16).<br />
Humboldt <strong>ATF</strong> Exhaust: The total speciated VOC concentration for the Humboldt <strong>ATF</strong><br />
inlet was 66.6 ppmC which is approximately 3.7 times greater than the Method 25.3 results.<br />
This is believed to be the result of the same condensate accumulation mechanism as was<br />
described for the elevated total speciated VOC concentration in the <strong>ATF</strong> inlet TO-15 and TO-<br />
12 Modified samples. An ethanol concentration of 31,100 ppmC was reported for the TO-15<br />
results for the NORS-ECIS inlet air stream (see<br />
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Table 14). In addition to ethanol, compounds with concentrations above 100 ppbC, key<br />
speciated compound contributors, which contributed to the exhaust VOCs are: acetone,<br />
toluene (<br />
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Table 14); and, propane, isobutane, and isopentane (see Table 16). For a complete list of<br />
speciated compounds with measured concentrations refer to Tables 14 and 16.<br />
Non-VOCs: The non-VOCs, acetone, methylene chloride and tetrachloroethylene were<br />
measured at Humboldt. Their concentrations and the adjusted Method 25.3 results are<br />
summarized in Error! Not a valid bookmark self-reference..<br />
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Table 14 and Table 16 summarize the TO-15 and TO-12 Modified results, respectively. TO-15<br />
results were reported by the laboratory in units of ppb v and were converted to units of ppbC.<br />
PID Results: The PID results for the <strong>ATF</strong> inlet and exhaust which were 12.0 and 5.57 ppmC,<br />
respectively. The ratio of the PID/Method 25.3 inlet and exhaust were 0.52 and 0.30, respectively,<br />
showing a low bias for both the inlet and exhaust air streams, but relatively greater correlation for<br />
the inlet air as compared to the exhaust air, similar to the results for Richmond and NORS-ECIS.<br />
Hydrogen Sulfide and Reduced Sulfur Results:<br />
<br />
The Jerome Meter hydrogen sulfide inlet and exhaust concentrations were 19.1 and 11.7 ppm,<br />
respectively, resulting in a 38% removal efficiency. Such a low removal efficiency suggests<br />
that the carbon in this system should be replaced. Inlet and exhaust readings should be taken<br />
on at least one other event to verify the need to replace the carbon.<br />
An OdaLog unit that was placed in the Humboldt <strong>ATF</strong> manhole from April 19 to 23. The<br />
average, maximum and minimum H 2 S concentrations were, 6.5, 51 and < 0.25 ppm v ,<br />
respectively, as shown in Table 13. The Humboldt OdaLog graph appears in Appendix C.<br />
Two reduced sulfur compounds other than hydrogen sulfide were measured and are summarized<br />
in Table 15.<br />
Measured Air Flow Rate: The fan was operating during the sampling. The measured air flow<br />
rate at the <strong>ATF</strong> inlet was 12,940 cfm. This compares to a rated system capacity of 10,000 cfm.<br />
Figure 10 thru Figure 13 are photographs of the Humboldt <strong>ATF</strong> and the sampling effort.<br />
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Table 13 - Humboldt TNMHC, VOC and H 2 S Sample/Analytical Results<br />
Analytical Method Humboldt Inlet Humboldt Exhaust<br />
TNMHC<br />
Method 25.3, ppmC 23.0 18.4<br />
TNMHC Removal Efficiency by Carbon Adsorber 20%<br />
Non VOCs<br />
Acetone, ppmv/ppmC 0.063/0.190 0.077/0.230<br />
Methylene Chloride, ppmv/ppmC 0.14/0.14 0.007/0.007<br />
Total Non VOCs, ppmC 0.204 0.237<br />
Adjusted Method 25.3, ppmC 22.80 18.16<br />
Speciated Results as Carbon<br />
TO - 15, ppmC 112.9 65.07<br />
TO - 12 Modified, ppmC 1.83 1.87<br />
ASTM 5504, ppmC 0.55 ns 1<br />
Total Speciated, ppmC 115.3 66.9<br />
Ratio: Speciated VOCs/Method 25.3 VOCs 5.0 3.6<br />
PID Results<br />
PID, ppm v 12.0 5.57<br />
Ratio: PID/Method 25.3 0.52 0.30<br />
Hydrogen Sulfide Results<br />
Hydrogen Sulfide, ppm 19.1 11.7<br />
Hydrogen Sulfide Removal Efficiency By Carbon<br />
Adsorber 39%<br />
OdaLog Results<br />
Average Hydrogen Sulfide, ppm 6.5 ns 1<br />
Maximum Hydrogen Sulfide, ppm 51 ns 1<br />
Minimum Hydrogen Sulfide, ppm
Table 14 - Humboldt TO-15 Sample/Analytical Results<br />
Compound<br />
Humboldt<br />
Inlet<br />
Humboldt<br />
Inlet<br />
Humboldt<br />
Exhaust<br />
Humboldt<br />
Exhaust<br />
(ppb v ) (ppbC) (ppb v ) (ppbC)<br />
Chlorodifluoromethane
Table 16 - Humboldt TO-12 Modified Results<br />
Compound<br />
Humboldt Inlet Humboldt Exhaust<br />
(ppbC)<br />
(ppbC)<br />
Ethylene 22.7 18.5<br />
Acetylene 11.5 10.3<br />
Ethane 3190 2810<br />
Propylene
Figure 10 - Humboldt <strong>ATF</strong> (1)<br />
Figure 11 - Humboldt <strong>ATF</strong> (2)<br />
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Figure 12 - Humboldt <strong>ATF</strong> (3)<br />
Figure 13 - Humboldt <strong>ATF</strong> (4)<br />
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4.4 Mission and Jesse<br />
Method 25.3/Speciated VOCs: The <strong>ATF</strong> was not in operation during the sampling of Mission &<br />
Jesse because its carbon was being replaced. Therefore, only the sewer air was sampled by<br />
placing a sample line approximately 20 feet down into the manhole which exhausts to the <strong>ATF</strong><br />
inlet. The inlet sample/analytical result for Method 25.3 was 14.0 ppmC, as shown in Table 17<br />
which is less than the TNMHC emission limits in Table 1.<br />
The total speciated VOC concentration for the Mission & Jesse sewer exhaust was 24.1 ppmC<br />
with VOCs having negligible photochemical activity subtracted. This concentration exceeds the<br />
Method 25.3 results by 1.8 times (see Table 17). As described for Humboldt, this greater total<br />
speciated VOC concentration is attributed to condensate that accumulated at the Tee where the<br />
½” Teflon tubing air line connected to the ¼” Teflon branch line that ran to the Summa canister<br />
used for the TO-15 and TO-12 Modified analysis. This condensate absorbed a disproportionate<br />
amount of ethanol from the total air stream being moved by the air pump, which in turn was<br />
released into the air stream being directed to the TO-15 and TO-12 Modified canister. The<br />
ethanol concentration of this air stream was 5,480 ppb v (Table 18). The TO-15 compound with<br />
the next highest concentration was toluene at 837 ppb v .<br />
Compounds with concentrations above 100 ppbC, key speciated compound contributors, which<br />
contributed to the inlet VOCs are: acetone, toluene, m & p-xylene (Table 18); and propane,<br />
isobutene, n-butane, isopentane, toluene, o-xylene, m-ethyltoluene, p-ethyltoluene, n-decane,<br />
1,2,3-trimethylbenzene, n-undecane. For a complete list of speciated compounds with measured<br />
concentrations refer to Tables 18 and 20.<br />
Table 18 and Table 20 summarize the TO-15 and TO-12 Modified Results, respectively. TO-15<br />
results were reported by the laboratory in units of ppb v and were converted to units of ppbC.<br />
Non VOCs: The non-VOCs, acetone, methylene chloride and tetrachloroethylene were measured<br />
at Mission & Jesse. Their concentrations and the adjusted Method 25.3 results are summarized in<br />
Table 17.<br />
PID Results: The PID results for the sewer exhaust to the <strong>ATF</strong> inlet was 13.0 ppmC. The ratio of<br />
the PID/Method 25.3 values of 0.9, which shows a better correlation than for the inlet at<br />
Richmond, NORS-ECIS and Humboldt. (Table 17)<br />
Hydrogen Sulfide and Reduced Sulfur Results:<br />
<br />
<br />
The Jerome Meter hydrogen sulfide sewer exhaust concentration was >50 ppm, which is<br />
greater than the Jerome Meter’s measurement range (Table 17).<br />
An OdaLog unit was placed in the Humboldt <strong>ATF</strong> manhole from April 19 to 23. The average,<br />
maximum and minimum hydrogen sulfide concentrations were 16.5, 87 and < 0.25 ppm v ,<br />
respectively, as shown in Table 17. The Mission & Jesse OdaLog graph appears in Appendix<br />
C.<br />
Two reduced sulfur compounds other than hydrogen sulfide were measured and are<br />
summarized in Table 19.<br />
Measured Air Flow Rate. As noted above the <strong>ATF</strong> was not in operation during the sampling.<br />
As a result the velocity was measured on a subsequent visit. The calculated air flow rate at the<br />
<strong>ATF</strong> inlet was 5,150 cfm. This compares to rated system capacity of 10,000 cfm.<br />
Figure 14 thru Figure 16 are photographs of the Mission & Jesse <strong>ATF</strong> and sampling effort.<br />
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Table 17 - Mission & Jesse TNMHC, VOC and H2S Sample/Analytical Results<br />
Analytical Method<br />
Mission & Jesse Inlet<br />
TNMHC<br />
Method 25.3, ppmC 14.0<br />
Non VOCs<br />
Acetone, ppm v /ppmC 0.154/0.462<br />
Methylene Chloride, ppm v /ppmC 0.008/0.008<br />
Total Non VOCs, ppmC 0.162/0.47<br />
Adjusted Method 25.3, ppmC 13.53<br />
Speciated Results as Carbon<br />
TO - 15, ppmC 12.35<br />
TO - 12 Modified, ppmC 11.40<br />
ASTM 5504, ppmC 0.95<br />
Total Speciated VOCs, ppmC 24.7<br />
Ratio: Speciated VOCs/Method 25.3 1.8<br />
PID Results<br />
PID, ppm v 13.0<br />
Ratio: PID/Method 25.3 0.9<br />
Hydrogen Sulfide Results<br />
Hydrogen Sulfide, ppm >50<br />
OdaLog Results<br />
Average Hydrogen Sulfide, ppm 16.5<br />
Maximum Hydrogen Sulfide, ppm 87<br />
Minimum Hydrogen Sulfide, ppm
Table 18 - Mission & Jesse TO-15 Sample/Analytical Results<br />
Compound<br />
Mission & Jesse Inlet Mission & Jesse Inlet<br />
(ppb v )<br />
(ppbC)<br />
Chlorodifluoromethane 1.7 2<br />
Chloromethane 2.2 2<br />
Ethanol 5480 10960<br />
Acetone 154 462<br />
Isopropyl Alcohol 15.5 47<br />
Methylene Chloride 8.4 8<br />
Carbon Disulfide 14.6 15<br />
2-Butanone (MEK) 9.3 37<br />
Hexane 4.1 25<br />
Chloroform 80.2 80<br />
Ethyl Acetate 11.4 46<br />
Benzene 1.8 11<br />
Cyclohexane 2.0 12<br />
Bromodichloromethane 12.9 13<br />
Trichloroethene 8.7 17<br />
2,2,4-Trimethylpentane 7.9 63<br />
Heptane 6.3 44<br />
Toluene 837 5859<br />
Dibromochloromethane 8.4 8<br />
Tetrachloroethylene 68.4 137<br />
Ethylbenzene 38.9 311<br />
m- & p-Xylenes 159 1272<br />
Bromoform 2.0 2<br />
Styrene 5.4 43<br />
o-Xylene 35.6 285<br />
4-Ethyltoluene 1.9 17<br />
1,3,5-Trimethylbenzene 2.5 23<br />
1,2,4-Trimethylbenzene 7.2 65<br />
1,4-Dichlorobenzene 17.0 102<br />
Table 19 - Mission & Jesse <strong>ATF</strong> Inlet Reduced Sulfur Compounds<br />
Compound<br />
(ppmv)<br />
Methyl Mercaptan 0.826<br />
Dimethyl Sulfide 0.063<br />
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Table 20 - Mission & Jesse TO-12 Modified Results<br />
Compound<br />
Mission & Jesse Inlet<br />
(ppbC)<br />
Ethylene 33.5<br />
Acetylene 9.8<br />
Ethane 4010<br />
Propylene 13.0<br />
Propane 821<br />
Isobutane 285<br />
1-Butene 15.4<br />
n-Butane 147<br />
Isopentane 195<br />
n-Pentane 86.1<br />
2,2-Dimethylbutane 6.9<br />
2,3-Dimethylbutane 10.4<br />
2-Methylpentane 14.3<br />
3-Methylpentane 25.1<br />
n-Hexane 28.9<br />
Methylcyclopentane 16.4<br />
2,4-Dimethylpentane 8.4<br />
Benzene 11.2<br />
Cyclohexane 12.9<br />
2-Methylhexane 20.0<br />
2,3-Dimethylpentane 15.3<br />
3-Methylhexane 28.6<br />
2,2,4-Trimethylpentane 72.3<br />
n-Heptane 45.8<br />
Methylcyclohexane 73.6<br />
2,3,4-Trimethylpentane 44.2<br />
Toluene 6020<br />
2-Methylheptane 23.3<br />
3-Methylheptane 16.0<br />
n-Octane 129<br />
Ethylbenzene 339<br />
m/p-Xylenes 1350<br />
o-Xylene 305<br />
Nonane 98.3<br />
Isopropylbenzene 3.8<br />
n-Propylbenzene 21.0<br />
m-Ethyltoluene 140<br />
p-Ethyltoluene 236<br />
1,3,5-Trimethylbenzene 38.2<br />
o-Ethyltoluene 14.4<br />
1,2,4-Trimethylbenzene 75.1<br />
n-Decane 106<br />
1,2,3-Trimethylbenzene 239<br />
n-Undecane 105<br />
n-Dodecane 98.8<br />
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Figure 14 - Mission and Jesse <strong>ATF</strong> (1)<br />
Figure 15 - Mission and Jesse <strong>ATF</strong> (2)<br />
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Figure 16 - Mission and Jesse <strong>ATF</strong> (3)<br />
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4.5 23 rd and San Pedro<br />
Method 25.3/Speciated VOCs: The <strong>ATF</strong> was removed from this location in 2008. Therefore,<br />
the sewer air was sampled by placing a sample line approximately 20 feet down into the manhole<br />
which had exhausted to the <strong>ATF</strong> inlet. The inlet sample/analytical results for Method 25.3 was<br />
16.4 ppmC, as shown in Table 21 which is less than the TNMHC emission limits of Table 1.<br />
The total speciated VOC concentration for the 23 rd & San Pedro sewer exhaust was 11.4 ppmC<br />
with the VOCs having negligible photochemical activity subtracted. This concentration is 70% of<br />
the Method 25.3 results (see Table 21). Given the RPD limits of the methods used to measure the<br />
speciated VOCs and of Method 25.3, the measured speciated VOCs account for the Method 25.3<br />
VOCs. Compounds with concentrations above 100 ppbC, key speciated compound contributors,<br />
which contributed to the inlet VOCs are: acetone, methylene chloride, chloroform, 1,2-<br />
dichloroethane, toluene (Table 22); propane, isobutene, n-butane, isopentane, n-pentane, toluene,<br />
n-octane, ethylbenzene, m/p-xylene, o-xylene, nonane, n-propylbenzene, m-ethyltoluene (Table<br />
23). For a complete list of speciated compounds with measured concentrations refer to Tables 22<br />
and 23.<br />
Table 22 and Table 23 summarize the TO-15 and TO-12 Modified Results, respectively. TO-15<br />
results were reported by the laboratory in units of ppb v and were converted to units of ppbC.<br />
Non VOCs: The non-VOCs, acetone, methylene chloride and tetrachloroethylene were measured<br />
at 23rd & San Pedro. Their concentrations and the adjusted Method 25.3 results are summarized<br />
in Table 21.<br />
PID Results: The PID results for the sewer exhaust was 18.5 ppmC. The PID/Method 25.3 ratio<br />
was 1.13 (Table 21). The ratio of the PID/Method 25.3 values of 1.13, which shows a slightly<br />
high bias for the PID relative to Method 25.3, but a better correlation than for the inlets at<br />
Richmond, NORS-ECIS and Humboldt.<br />
Hydrogen Sulfide and Reduced Sulfur Results:<br />
<br />
The Jerome Meter hydrogen sulfide inlet sewer exhaust concentration was >50 ppm (see<br />
Table 21).<br />
An OdaLog unit that was placed in the 23 rd & San Pedro <strong>ATF</strong> manhole from April 19 to 23.<br />
The average, maximum and minimum hydrogen sulfide concentrations were, 34.5, 101, and <<br />
0.25 ppm v , respectively, as summarized in Table 21. The 23 rd & San Pedro OdaLog graph<br />
appears in Appendix C.<br />
The only reduced sulfur compound measured in the sewer exhaust other than hydrogen<br />
sulfide was methyl mercaptan at a concentration of 0.617 ppm.<br />
Figure 17 and Figure 18 are photographs of the 23 rd & San Pedro location and sampling effort.<br />
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Table 21 - 23rd & San Pedro TNMHC, VOC and H 2 S Sample/Analytical Results<br />
Analytical Method<br />
23rd & San Pedro<br />
TNMHC<br />
Method 25.3, ppmC 16.4<br />
Non VOCs<br />
Acetone, ppm v /ppmC 0.138/0.414<br />
Methylene Chloride, ppm v /ppmC 0.308/0.308<br />
Total Non VOCs, ppmC 0.722<br />
Adjusted Method 25.3, ppmC 15.7<br />
Speciated Results as Carbon<br />
TO - 15, ppmC 5.01<br />
TO - 12 Modified, ppmC 6.64<br />
ASTM 5504, ppmC 0.62<br />
Total Speciated VOCs, ppmC 12.3<br />
Ratio: Speciated VOCs/Method 25.3 0.7<br />
PID Results<br />
PID, ppm v 18.5<br />
PID/Method 25.3 1.13<br />
Hydrogen Sulfide Results<br />
Hydrogen Sulfide, ppm >50<br />
OdaLog Results<br />
Average Hydrogen Sulfide, ppm 34.5<br />
Maximum Hydrogen Sulfide, ppm 101<br />
Minimum Hydrogen Sulfide, ppm 0<br />
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Table 22 - 23rd & San Pedro TO-15 Sample/Analytical Results<br />
Compound<br />
San Pedro & 23rd St. San Pedro & 23rd St.<br />
(ppb v )<br />
(ppbC)<br />
Chlorodifluoromethane 6.1 6<br />
Chloromethane 44.8 45<br />
Methanol 54.6 55<br />
Chloroethane 42.6 85<br />
Ethanol 1110 2220<br />
Acetone 138 414<br />
Isopropyl Alcohol 39.6 119<br />
Methylene Chloride 308 308<br />
Carbon Disulfide 20.1 20<br />
2-Butanone (MEK) 5.4 22<br />
Hexane 5.2 31<br />
Chloroform 173 173<br />
Ethyl Acetate 3.9 15<br />
1,2-Dichloroethane 173 346<br />
Bromodichloromethane 20.3 20<br />
Trichloroethene 10.8 22<br />
2,2,4-Trimethylpentane 2.6 21<br />
Heptane 6.2 43<br />
Toluene 104 728<br />
Dibromochloromethane 14.3 14<br />
Tetrachloroethylene 90.1 180<br />
Ethylbenzene 12.3 98<br />
m- & p-Xylenes 40.5 324<br />
Bromoform 4.3 4<br />
o-Xylene 17.4 139<br />
4-Ethyltoluene 16.0 144<br />
1,3,5-Trimethylbenzene 32.2 290<br />
1,2,4-Trimethylbenzene 55.3 498<br />
1,4-Dichlorobenzene 10.1 61<br />
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Table 23 - 23rd & San Pedro TO-12 Modified Results<br />
Compound<br />
23 rd & San Pedro<br />
(ppbC)<br />
Ethylene 32.2<br />
Acetylene 26.4<br />
Ethane 1170<br />
Propylene 16.4<br />
Propane 322<br />
Isobutane 139<br />
n-Butane 106<br />
Isopentane 106<br />
n-Pentane 106<br />
Isoprene 8.0<br />
2,2-Dimethylbutane 5.5<br />
2,3-Dimethylbutane 8.1<br />
2-Methylpentane 22.1<br />
3-Methylpentane 17.4<br />
n-Hexane 33.4<br />
2,4-Dimethylpentane 5.9<br />
Benzene 9.3<br />
Cyclohexane 11.7<br />
2-Methylhexane 14.8<br />
2,3-Dimethylpentane 12.8<br />
3-Methylhexane 23.2<br />
2,2,4-Trimethylpentane 24.6<br />
n-Heptane 41.2<br />
Methylcyclohexane 79.5<br />
Toluene 785<br />
2-Methylheptane 90.4<br />
3-Methylheptane 81.5<br />
n-Octane 224<br />
Ethylbenzene 108<br />
m/p-Xylenes 329<br />
o-Xylene 172<br />
Nonane 205<br />
Isopropylbenzene 29.6<br />
n-Propylbenzene 222<br />
m-Ethyltoluene 527<br />
p-Ethyltoluene 398<br />
1,3,5-Trimethylbenzene 395<br />
o-Ethyltoluene 254<br />
1,2,4-Trimethylbenzene 616<br />
n-Decane 368<br />
1,2,3-Trimethylbenzene 192<br />
m-Diethylbenzene 16.2<br />
p-Diethylbenzene 39.2<br />
n-Undecane 261<br />
n-Dodecane 154<br />
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Figure 17 - 23rd and San Pedro (1)<br />
Figure 18 - 23rd and San Pedro (2)<br />
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4.6 Summary<br />
Table 24 is a summary of the TNMHC, VOC and hydrogen sulfide sample/analytical results for<br />
the five locations. Following is a summary of findings from the sampling/analytical effort:<br />
<br />
<br />
<br />
<br />
<br />
<br />
At all locations, the <strong>ATF</strong> inlet (raw sewer air) and <strong>ATF</strong> exhaust air Method 25.3 results were<br />
below the air permit TNMHC emission limits of Table 1 (obtained from various interceptor<br />
<strong>ATF</strong> permits the City provided) except at Humboldt where the inlet and exhaust<br />
concentrations were 23.0 and 18.4 ppmC, respectively. This is graphically displayed in<br />
Figure 19. As noted below in Table 24 with regard to the exhaust hydrogen sulfide emission<br />
concentration, it appears that the carbon of the Humboldt <strong>ATF</strong> is used up. It is expected that<br />
if the carbon was still effective the exhaust Method 25.3 and hydrogen sulfide results would<br />
be notably reduced. Figure 19 illustrates inlet and exhaust TNMHC concentrations relative to<br />
the permit limit range of Table 1 (18 to 36 ppm v ).<br />
The percentage of speciated VOCs which accounted for Method 25.3 VOCs ranged from<br />
approximately 32% to approximately 100% except for locations where sampling<br />
interferences occurred and a disproportionate amount of ethanol was collected in the TO-<br />
15/TO-12 Modified Summa canister, i.e., at the Humboldt inlet/exhaust, and Mission &<br />
Jesse. The speciated compounds were determined by EPA Method TO-15, EPA Method TO-<br />
12 Modified, and by a reduced sulfur scan (ASTM 5504) and were expressed as parts per<br />
million by volume by the laboratory. The Method 25.3 results were expressed as ppm as<br />
Carbon (ppmC). In order to compare the speciated results to the Method 25.3 results, the<br />
speciated results were converted to ppmC by multiplying by the volumetric concentration by<br />
the number of carbon atoms in each compound, per EPA guidance. After converting all the<br />
speciated results to ppmC, these compounds were totaled and were compared to the Method<br />
25.3 results, by calculating a quotient, (ppmC-Speciated)(ppmC-Method 25.3).<br />
Some consistency was shown between the PID and Method 25.3 results expressed as a<br />
PID/Method 25.3 ratio. For the inlet at Richmond, NORS-ECIS and Humboldt, the<br />
PID/Method 25.3 ratio ranged from 0.52 to 0.56. There was less consistency of the<br />
PID/Method 25.3 ratio on the exhaust of these locations, with the ratio ranging from 0.05 to<br />
0.30. Additional work is needed to evaluate whether a calibration curve can be developed to<br />
be used by the staff to effectively monitor exhaust TNMHC concentrations instead of using<br />
SCAQMD Method 25.3. The City should also consider investigating whether an alternative<br />
hand-held device can provide improved service.<br />
The short term grab <strong>ATF</strong> inlet or raw sewer air hydrogen sulfide concentrations ranged from<br />
approximately 2 ppm v (at Richmond) to >50 ppm v (at Mission & Jesse and 23 rd & San<br />
Pedro). Figure 20 illustrates the <strong>ATF</strong> inlet and exhaust hydrogen sulfide concentrations and<br />
the average OdaLog readings.<br />
The carbon adsorbers at Richmond and NORS-ECIS were providing hydrogen sulfide<br />
removals of > 99%. The carbon at Humboldt appeared to be exhausted, with an exhaust<br />
hydrogen sulfide concentration of 11.7 ppm v .<br />
Figure 21 serves as an overview of hydrogen sulfide control technologies as a function of<br />
inlet concentration in general, and the values measured in this study. Carbon is generally<br />
cost-effective at inlet concentrations less than 10 ppm v . Biofilters are cost-effective at inlet<br />
concentrations up to 50 ppm v and grater. At higher concentrations however, the biofilter<br />
media degradation may accelerate. Bio-trickling filters are cost-effective at inlet<br />
concentrations of 20 ppm v and higher, which indicates some overlap for the two biological<br />
systems. Figure 21 can be used as a basis to evaluate control technologies in the next phase<br />
of this project.<br />
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Analytical Method/Parameter<br />
Table 24 - Total NMHC, VOC and H 2 S Sample/Analytical Results Summary<br />
Richmond<br />
Inlet<br />
Richmond<br />
Exhaust<br />
NORS<br />
ECIS Inlet<br />
NORS ECIS<br />
Exhaust<br />
Humboldt<br />
Inlet<br />
Humboldt<br />
Exhaust<br />
Mission &<br />
Jesse Inlet<br />
San Pedro<br />
& 23rd St.<br />
Method 25.3, ppmC 3.80 4.80 15.2 3.90 23.0 18.4 14.0 16.4<br />
TO - 15, ppmC 1.42 0.11 2.23 1.72 112.9 65.07 12.35 5.01<br />
TO - 12 Modified, ppmC 2.61 1.45 6.33 1.53 1.83 1.87 11.40 6.64<br />
ASTM 5504, ppmC 0.14 ns 0.58 ns 0.55 ns 0.95 0.62<br />
Total Speciated VOCs, ppmC 4.17 1.55 9.14 3.25 115.3 66.9 24.7 12.3<br />
Ratio Speciated VOCs/Method 25.3 1.10 0.32 0.60 0.83 5.0 3.6 1.8 0.7<br />
PID, ppm v 2.04 0.25 8.45 0.40 12.0 5.57 13.0 18.5<br />
PID/Method 25.3 0.54 0.05 0.56 0.10 0.52 0.30 0.9 1.13<br />
Hydrogen Sulfide, ppm 2.29 50 >50<br />
Sewer OdaLog Results<br />
Average Hydrogen Sulfide, ppm 9.5 nm 32 nm 6.5 nm 16.5 34.5<br />
Maximum Hydrogen Sulfide, ppm 26 nm 67 nm 51 nm 87 101<br />
Minimum Hydrogen Sulfide, ppm
Figure 19 - TNMHC VOC Results Summary<br />
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Figure 20 - Hydrogen Sulfide Sampling Result Summary<br />
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Figure 21 - Hydrogen Sulfide Emission Control Overview<br />
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5.0 COMPARISON OF CURRENT AND HISTORICAL DATA<br />
The City conducted sampling/analyses at <strong>ATF</strong>s within their collection system in 2009 including<br />
the locations that were the focus of this study. The locations sampled included the scrubber inlet<br />
and exhaust of the <strong>ATF</strong>s. The samples were analyzed by EPA Method TO-14 which measures<br />
for 39 VOCs and by SCAQMD 307-91 which analyzes for 10 sulfur compounds including<br />
hydrogen sulfide and sulfur dioxide. (The 2009 sample results are in Appendix D). As noted in<br />
Section 3 of this report, the <strong>2010</strong> samples were analyzed for VOCs by TO-15 and for 20 reduced<br />
sulfur compounds by ASTM 5504. The analytical results from the 2009 sampling/analytical were<br />
compared to the results from the <strong>2010</strong> sampling effort.<br />
Because the TO-14 analysis measured for 39 compounds and the TO-15 analysis measured for 68<br />
compounds, the results of the TO-14 and TO-15 results were compared as follows:<br />
<br />
A list was made of all the compounds for which there were detectable results from the TO-14<br />
analytical results. A truncated list of TO-15 compounds was then made that matched the TO-<br />
14 list.<br />
The concentration of all the compounds from the TO-14 and TO-15 results were then totaled.<br />
These total concentrations are compared in Table 25.<br />
The results are summarized as follows:<br />
The maximum concentration was measured in <strong>2010</strong> at the Mission & Jesse <strong>ATF</strong> inlet of<br />
1,279 ppb v<br />
Inlet concentrations in 2009 and <strong>2010</strong> ranged from 2 to 421 ppb v , and 81 to 1,279 ppb v ,<br />
respectively.<br />
The exhaust concentrations in 2009 and <strong>2010</strong> ranged from 26 to 151 ppb v and 9 to 147 ppb v ,<br />
respectively.<br />
A comparison of the 2009 total sulfur results and the <strong>2010</strong> reduced sulfur results are summarized<br />
as follows:<br />
<br />
<br />
<br />
Results from the 2009 sampling effort reports the presence of carbonyl sulfide in numerous<br />
samples ranging in concentration from 0.40 to 0.96 ppm v , with a method detection limit of<br />
0.088 ppm v . Whereas no carbonyl sulfide was measured in any of the <strong>2010</strong> samples, where<br />
the sample reporting limit was 0.050 ppm v . (See Table 26)<br />
In addition to hydrogen sulfide, methyl mercaptan and dimethyl sulfide were the only other<br />
reduced sulfur compounds measured. The range of methyl mercaptan detected in 2009 and<br />
<strong>2010</strong> ranged from 0.59 to 0.96 ppm v and 0.139 to 0.826 ppm v , respectively. Dimethyl sulfide<br />
was measured in <strong>2010</strong> at concentrations of 0.055 and 0.063 ppm v .<br />
The 2009 and <strong>2010</strong> results are generally similar except for the presence of carbonyl sulfide in<br />
the 2009 data and dimethyl sulfide in the <strong>2010</strong> data.<br />
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Table 25 - Comparison of <strong>2010</strong> and 2009 Total VOC Data (ppb v )<br />
Richmond<br />
Inlet<br />
Richmond<br />
Exhaust<br />
Comparison of <strong>2010</strong> and 2009 Total VOC Data (ppb v )<br />
NORS<br />
ECIS<br />
Inlet<br />
NORS<br />
ECIS<br />
Exhaust<br />
Humboldt<br />
Inlet<br />
Humboldt<br />
Exhaust<br />
Mission &<br />
Jesse Inlet<br />
Mission &<br />
Jesse<br />
Exhaust<br />
San Pedro<br />
& 23rd St.<br />
Inlet<br />
2009 Data/TO-14 248 147 270 48 2 9 366 165 421 5<br />
<strong>2010</strong> Data/TO-15 81 26 591 112 181 151 1279
Appendix A<br />
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Appendix B<br />
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Appendix C<br />
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Appendix D<br />
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Technical Memorandum – FINAL<br />
Team<br />
City of Los Angeles<br />
Department of Public Works<br />
Bureau of Sanitation<br />
Air Treatment Facility (<strong>ATF</strong>) Review <strong>Study</strong><br />
AIR TREATMENT FACILITY<br />
TECHNICAL MEMORANDUM<br />
FINAL<br />
November <strong>2010</strong><br />
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TABLE OF CONTENTS<br />
Executive Summary .............................................................................................................................. 3<br />
1. Introduction .................................................................................................................................. 4<br />
2. Field Testing ................................................................................................................................. 5<br />
3. Modeling .................................................................................................................................... 13<br />
4. <strong>ATF</strong> Locations Recommendation ............................................................................................... 14<br />
5. Determine Air Flows .................................................................................................................. 23<br />
6. Air Emissions Characterization .................................................................................................. 24<br />
7. Identify Air Emission Control Technologies.............................................................................. 28<br />
8. Recommendations ...................................................................................................................... 44<br />
LIST OF FIGURES<br />
Figure 1 – Base Map ............................................................................................................................. 4<br />
Figure 2 - Baseline Pressure ................................................................................................................. 6<br />
Figure 3 - Sampling with Air Return Lines Plugged .............................................................................. 7<br />
Figure 4 - Sampling with Stop Logs Removed ...................................................................................... 8<br />
Figure 5 – Odor Complaint Locations and Predicted Odor Areas of Concern .................................... 13<br />
Figure 6 - Additional Air Pickup ........................................................................................................... 17<br />
Figure 7 - NEIS/ECIS Recommendation Summary ............................................................................ 19<br />
Figure 8 - Detailed Recommendations Descriptions (1) ..................................................................... 20<br />
Figure 9 - Detailed Recommendations Descriptions (2) ..................................................................... 20<br />
Figure 10 - OdaLog Continuous H2S Data Logging Results .............................................................. 26<br />
Figure 11 - Wet Scrubbing Process Schematic .................................................................................. 32<br />
Figure 12 - Biotrickling Filter Process Schematic ............................................................................... 36<br />
Figure 13 - Dual Bed Activated Carbon Process Schematic .............................................................. 39<br />
LIST OF TABLES<br />
Table 1 - Mission & Jesse Interceptor Raw Emissions Characterization Results ............................... 25<br />
Table 2 - Wet Scrubbing Emissions Control: Advantages & Disadvantages ..................................... 33<br />
Table 3 - Biotrickling Filter Emissions Control: Advantages and Disadvantages ............................. 38<br />
Table 4 - Activated Carbon Emissions Control: Advantages & Disadvantages ................................ 42<br />
Table 5 - Preliminary <strong>ATF</strong> Attributes ................................................................................................. 45<br />
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Executive Summary<br />
The City of Los Angeles has a long history of implementing proactive and innovative steps to<br />
control odors from its interceptor collection system including using chemical addition to control<br />
odors with an extensive use of magnesium hydroxide. Recently, the City has been working to<br />
improve odor control in several areas identified by local community groups. Air treatment facilities<br />
(<strong>ATF</strong>s) with known or predicted odor “areas of concern” were included in the 2004 Collection<br />
System Settlement Agreement (CSSA).<br />
The Technical Memorandum describes the results of the analysis of the data collected for the <strong>ATF</strong><br />
Review <strong>Study</strong> and includes<br />
<br />
<br />
<br />
<br />
<br />
<br />
A summary of the field test conducted for the study, including the siphons and drop<br />
structures<br />
The results of the airflow modeling for current conditions and future scenarios<br />
Recommendations for an <strong>ATF</strong> location, drop structure modifications and flow diversion<br />
based on the results of observations and analysis following the field data collection<br />
Characterization data from five of the seven locations identified in the 2004 Collection<br />
System Settlement Agreement<br />
Various available technologies for controlling nuisance related odors and air emissions that<br />
are associated with wastewater collection systems<br />
Recommended technology for the <strong>ATF</strong> at Mission and Jesse.<br />
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1. Introduction<br />
A study of air flow in the City's wastewater collection system was conducted between January 2008<br />
and August <strong>2010</strong>. This Technical Memorandum presents the results of the study on Air Treatment<br />
Facilities (<strong>ATF</strong>s) and provides recommendations for locations, size and technology for <strong>ATF</strong>s in<br />
order to provide satisfactory odor relief to the collection system. Figure 1 below shows the system<br />
under study. It includes NEIS, NOS, ECIS, NORS and NCOS starting at the Division drop structure<br />
downstream to the 405 freeway.<br />
Figure 1 – Base Map<br />
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2. Field Testing<br />
Large sets of data were collected between July 2009 and May <strong>2010</strong> to measure internal differential<br />
air pressure in the interceptors (difference in air pressure between inside and outside the sewer) and<br />
evaluate sewer headspace ventilation dynamics. These data have been used to determine the<br />
locations in the interceptor system where high positive air pressures cause odorous air to be released<br />
to the atmosphere and, therefore where odorous air should be withdrawn and treated. The data<br />
collection in the field included sewer siphons and drop structures.<br />
Field tests at drop structures were conducted to evaluate the impact of drop structures on the sewer<br />
differential air pressures, under current conditions and planned modifications. The effort was<br />
focused on measuring and examining differential air pressures at the four existing sewer drop<br />
structures in the City's wastewater collection system:<br />
<br />
<br />
<br />
<br />
Division<br />
Humboldt<br />
Mission and Jesse<br />
23 rd and San Pedro<br />
A baseline condition was established, which consisted of measuring the sewer differential air<br />
pressures along a route starting at the Division drop structure and ending at a maintenance hole in the<br />
Culver City Park. This was followed by the physical plugging of the return air lines at each drop<br />
structure in order to measure the impact on the differential air pressures at the drop structure and<br />
downstream sewer. The purpose was to examine the impact of perceived air circulation in each<br />
return line at the structure upon upstream and downstream differential pressures in the sewer system.<br />
<strong>Final</strong>ly, flow management (diversion/redistribution to increase/decrease the flow at the drop<br />
structures) was introduced to the system and more differential air pressure data was collected to<br />
valuate the effect on the differential air pressures at the drop structures and sewer system. During<br />
theses three different phases, interim air scrubbers at Mission & Jesse and 23 rd & San Pedro were<br />
turned on and off several times in order to study their impact on the air pressure.<br />
Figures 2 to 4 show the results of the field pressure measurements under the above-described<br />
scenarios<br />
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Figure 2 - Baseline Pressure<br />
Figure 2 shows the results of the baseline field pressure measurements of the drop structure sampling<br />
for the period between 2/21/10 and 2/27/10. The three values shown for each maintenance hole are<br />
the measured Minimum, Average, and Maximum differential air pressures over the data collection<br />
period. During baseline measurements, the interim air scrubbers were turned off and the air return<br />
line in the drop structures were open (not plugged).<br />
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Figure 3 - Sampling with Air Return Lines Plugged<br />
Figure 3 shows the results of the field pressure measurements of the drop structure sampling when<br />
the air return lines were all plugged. The period of measurement is between 3/31/10 and 4/1/10. The<br />
three values shown for each maintenance hole are the measured Minimum, Average, and Maximum<br />
differential air pressures over the data collection period. Data shows that when the air return lines<br />
are all plugged, there is a measureable increase in the differential air pressure in the NEIS<br />
accumulating at the Mission and Jesse drop structure.<br />
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Figure 4 - Sampling with Stop Logs Removed<br />
Figure 4 shows the results of the field pressure measurements for the drop structure sampling when<br />
the air return lines were all plugged and the stop logs removed at Humboldt and Mission & Jesse<br />
drops. The period of measurement is between 4/20/10 and 4/27/10. The removal of the stop logs<br />
resulted in diverting more flow into the Mission & Jesse drop structure. The three values shown for<br />
each maintenance hole are the measured Minimum, Average, and Maximum differential air<br />
pressures over the data collection period. Data shows that when the air return lines are all plugged<br />
and the stop logs removed, there is a measurable increase in air pressure in the NEIS accumulating at<br />
the Mission and Jesse drop structure.<br />
General Conclusions<br />
The following are the general conclusions that may be drawn from analyzing pressure data recorded<br />
during the drop structure field study with the various system modifications described above.<br />
<br />
The existing interim air scrubbers generally reduce pressures along the entire length of the<br />
NEIS/ECIS tunnel. This appears to be especially the case with the Mission and Jesse interim<br />
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scrubber. Measurable pressure reductions occur in the NEIS/ECIS tunnel when this interim<br />
scrubber is turned on. Measurable pressure increases occurred in the NEIS/ECIS tunnel<br />
system when the Mission and Jesse interim scrubber was turned off.<br />
<br />
<br />
<br />
The Humboldt interim scrubber only appears to affect pressures in its immediate vicinity<br />
Plugging the air return line plugs generally resulted in increasing pressures along the entire<br />
NEIS/ECIS tunnel alignment<br />
The stop logs removal decreasing the flow at Humboldt and increasing it at Mission & Jesse<br />
generally resulted in decreasing pressures on the NOS. Those locations where the pressures<br />
didn’t decrease remained at atmospheric levels.<br />
The following provides a summary of site-specific pressure responses to the various manipulations<br />
performed during the study. For more detail on the effects of these tests, the reader is directed to the<br />
TM created for this project titled, “Differential Air Pressure <strong>Study</strong> at Drop Structures”.<br />
<br />
Division Drop Structure & Vicinity<br />
o<br />
o<br />
Measurable reductions in air pressure were recorded on the NEIS downstream of<br />
this drop structure when the Humboldt interim scrubber was in operation.<br />
Once the plug was in place at the Division Drop Structure, the air pressures on the<br />
ERIS just upstream of the drop structure became too negative for the pressure<br />
recording instruments to properly record. This meant that the differential pressures<br />
were less than -2.0 inches water column, which is the recording limit of the<br />
instruments.<br />
<br />
Humboldt Drop Structure & Vicinity<br />
o<br />
o<br />
Measurable reductions in air pressure were recorded on the upstream of the<br />
Humboldt Drop Structure on the NEIS and at the Humboldt drop structure itself<br />
when the Humboldt interim scrubber was in operation. A slight reduction was<br />
recorded on the NOS maintenance hole at Humboldt when the Humboldt interim<br />
scrubber was turned on. The air pressure on the NOS at the Humboldt diversion was<br />
generally well below or right at atmospheric during the entire duration of the field<br />
study.<br />
The most favorable pressure conditions (i.e., lowest air pressures) were achieved at<br />
the Humboldt Drop Structure location (not in the tunnel) when the plugs were in<br />
place in all four drop structure air return lines. Also, removing the stop logs at the<br />
Humboldt and Mission and Jesse NOS diversions did not cause significant air<br />
pressure increases at this location (decreasing the flow at Humboldt and increasing it<br />
at Mission & Jesse).<br />
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Richmond Drop Structure<br />
o<br />
Due to the fact that there is no flow entering the Richmond Drop Structure, no<br />
pressure testing was performed at or near this drop structure.<br />
<br />
Mission and Jesse Drop Structure & Vicinity<br />
o<br />
o<br />
o<br />
o<br />
Measurable reductions in air pressure were recorded on the NEIS, ECIS and at the<br />
Mission and Jesse drop structure when the Mission and Jesse interim scrubber was<br />
in operation.<br />
The lowest air pressure conditions were achieved at the Mission and Jesse Drop<br />
Structure itself when the plugs were in place in all four drop structure air return lines<br />
and the NOS stop logs had been removed at both this drop structure and the<br />
Humboldt location (decreasing the flow at Humboldt and increasing it at Mission &<br />
Jesse). This resulted in more flow, and consequently more air, being directed<br />
through the Mission and Jesse Drop Structure than was the case during the baseline<br />
period.<br />
The pressures on the 2 maintenance holes on the NEIS immediately upstream and<br />
downstream of the drop structure increased as a result of the presence of plugs in the<br />
four drop structure air return lines. The pressure at the maintenance hole<br />
immediately downstream of this location also increased during the entire duration of<br />
the stop log removal test. The pressure at the maintenance hole immediately<br />
upstream of this location generally decreased during the stop log removal test<br />
(decreasing the flow at Humboldt and increasing it at Mission & Jesse).<br />
The air pressure on the NOS at the Mission and Jesse diversion increased<br />
significantly immediately upon insertion of the plugs in the Division and Humboldt<br />
drop structure air return lines. The pressure on the NOS decreased significantly<br />
during the Mission and Jesse plug insertion and the stop log removal period of this<br />
study.<br />
<br />
23 rd and San Pedro Drop Structure and Vicinity<br />
o<br />
o<br />
Measurable reductions in air pressure were recorded on the ECIS and at the 23 rd and<br />
San Pedro drop structure when the Mission and Jesse interim scrubber was in<br />
operation. The pressures on the NOS approach sewer at this location were generally<br />
near atmospheric for the majority of the entire drop structure testing period.<br />
The lowest air pressure conditions were achieved at this location when the plugs<br />
were in place in all four drop structure air return lines and the NOS stop logs had<br />
been removed at both the Mission and Jesse and the Humboldt locations.<br />
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o<br />
The pressures on the 2 maintenance holes on ECIS immediately upstream and<br />
downstream of this location increased as a result of the presence of plugs in the four<br />
drop structure air return lines. The pressures at these maintenance holes generally<br />
decreased during the stop log removal test.<br />
<br />
USC Drop Structure and Vicinity<br />
o<br />
o<br />
Measurable reductions in air pressure were recorded on the ECIS immediately upstream<br />
and downstream of the USC drop structure when the Mission and Jesse interim scrubber<br />
was in operation. The air pressures at the drop structure did not appear to be<br />
significantly affected by any system-wide manipulations to the interim scrubbers, drop<br />
structure air return lines or interceptor stop logs.<br />
Compared to upstream locations along the ECIS and NEIS, there were few changes to<br />
overall pressures immediately upstream or downstream of the USC drop structure on the<br />
ECIS as a result of the stop log manipulations or air return line plug insertions.<br />
<br />
Systemwide Downstream Interceptors<br />
o<br />
o<br />
o<br />
o<br />
o<br />
When the Mission and Jesse interim scrubber was in operation, reductions in air<br />
pressure were recorded at each of the three maintenance holes tested in this vicinity.<br />
The most notable example was at the ECIS location upstream of the NORS/ECIS<br />
junction.<br />
The lowest air pressure conditions were achieved while the stop logs were removed<br />
(decreasing the flow at Humboldt and increasing it at Mission & Jesse) at the<br />
Humboldt and Mission and Jesse diversions to the NOS.<br />
Upstream of Jefferson Siphon (ECIS): The air pressures at the drop structure did not<br />
appear to be significantly affected by the air return line plug insertions at the four<br />
drop structures. During the time period that the plugs were in place and the stop<br />
logs were removed from Humboldt and Mission and Jesse the air pressure generally<br />
decreased at this location and remained below atmospheric. Once the plugs were<br />
removed and the stop logs were put back into place, the pressure began to fluctuate<br />
more wildly and went above atmospheric frequently.<br />
NORS/ECIS Junction Upstream (ECIS): The air pressures generally increased when<br />
the plugs and stop logs were in place. Once the stop logs were removed the<br />
exhibited a general downward trend. Following plug removal and stop log reinsertion<br />
the pressures went to near atmospheric.<br />
NORS/ECIS Junction Upstream (NORS): The pressures in the NORS maintenance<br />
hole immediately upstream of the NORS/ECIS junction increased slightly as a result<br />
of the presence of plugs in the four drop structure air return lines. The pressures at<br />
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these maintenance holes generally decreased and fluctuated more significantly<br />
during the stop log removal test. Following plug removal and stop log re-insertion<br />
the pressures went below atmospheric.<br />
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3. Modeling<br />
An Airflow Modeling application program was developed to model the airflow in the system under<br />
study. The modeling included the City’s current interceptor system configurations and the two<br />
planned wastewater flow diversion scenarios, thus evaluating the impact of the identified future<br />
operational changes by pointing to locations with potential for positive pressure. Such locations can<br />
result in odor issues and were termed “odor areas of concern”. The airflow modeling results were<br />
intended to assist in the evaluation of the proposed <strong>ATF</strong>s and any recommendations for <strong>ATF</strong><br />
installation.<br />
Based on the airflow modeling results and under the current system configurations, nine areas of<br />
concern are predicted. These include five locations along the ECIS from downstream of the Mission<br />
and Jesse drop structure to upstream of the USC drop structure; the ECIS siphon at Jefferson<br />
Boulevard and La Cienega Boulevard; the NORS/ECIS Junction; the NCOS Siphon at I-405 and the<br />
NORS Siphon at I-405. The results of the modeling are depicted in Figure 5 below.<br />
Figure 5 – Odor Complaint Locations and Predicted Odor Areas of Concern<br />
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4. <strong>ATF</strong> Locations Recommendation<br />
As part of the 2004 Collection System Settlement Agreement (CSSA), the <strong>ATF</strong> Review <strong>Study</strong> was<br />
initiated to study the airflow in the City’s wastewater collection system. The following<br />
recommendations are put forth based on conclusions drawn from the results of the <strong>ATF</strong> Review<br />
<strong>Study</strong>. The recommendations are divided among the various locations and sections of the<br />
NEIS/ECIS interceptor that were studied during the various phases of the overall project. Within<br />
each section specific recommendations on forced air treatment systems, modifications to drop<br />
structures and flow diversions are presented.<br />
<br />
Division Drop Structure & Vicinity<br />
o<br />
o<br />
This drop structure drops the flow from ERIS upstream to NEIS downstream<br />
<strong>ATF</strong>: The drop at the Division Drop structure does not appear to result in a significant<br />
air back-pressurization of the ERIS approach sewer; therefore no forced air treatment<br />
system is recommended for this location.<br />
o Drop Structure Modifications: The pressures in the ERIS upstream approach sewer<br />
were reduced significantly as a result of plugging the air return line at the Division Drop<br />
Structure. This indicates that plugging the air line at the Division drop structure is<br />
beneficial. However, given the unknown impact of future flow conditions, the<br />
permanent plugging of the air return line is not recommended. Therefore, in order to<br />
provide control and flexibility, there is evidence that installation of a flow regulation<br />
device in the air return line of this drop structure, such as an adjustable damper<br />
may be beneficial. However, it is recommended to complete the drop structure model<br />
testing before finalizing the damper concept. This would maintain negative pressures on<br />
the ERIS. Such a device would give BOS the flexibility to adjust the extent of plugging<br />
(amount of air that is allowed to flow through the air return line) under current or future<br />
operational conditions.<br />
o<br />
Flow Diversion: Since the ERIS is the only sewer that flows into and terminates at this<br />
drop structure, flow diversion recommendations are not applicable at this location.<br />
<br />
Humboldt Drop Structure & Vicinity<br />
o<br />
o<br />
This drop structure drops the flow from NOS upstream to NEIS downstream<br />
<strong>ATF</strong>: The interim scrubber at this location only appeared to significantly affect the air<br />
pressures in the NEIS between the Division Drop Structure and the Humboldt Drop<br />
Structure. Also it did not appear to significantly reduce the pressures in the NOS, which<br />
were near or just below atmospheric levels throughout the duration of the study;<br />
therefore no forced air treatment system is recommended for this location.<br />
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o<br />
o<br />
Drop Structure Modifications: The pressures in the NOS upstream approach sewer were<br />
reduced slightly as a result of plugging the air return line at the Humboldt Drop<br />
Structure. There is evidence that installation of a flow regulation device in the air<br />
return line of this drop structure, such as an adjustable damper may be beneficial.<br />
However, it is recommended to complete the drop structure model testing before<br />
finalizing the damper concept. As with the Division Drop Structure, such a device<br />
would give BOS the flexibility to adjust the amount of air that is allowed to flow through<br />
the air return line under current or future operational conditions.<br />
Flow Diversion: The system air pressures appeared to react favorably to the stop log<br />
removal at this location; which allowed approach flows in the NOS to split naturally<br />
between that sewer and the NEIS. This resulted in less flow through the Humboldt drop<br />
structure into the NEIS. It is therefore recommended that the stop logs be<br />
configured at this location in such a manner that a minimum amount of flow is<br />
directed into the NEIS via Humboldt. This would likely result in less air being<br />
dragged into the NEIS and therefore, lower air pressures in the NEIS/ECIS tunnel<br />
system.<br />
<br />
Richmond Drop Structure<br />
o<br />
o<br />
o<br />
<strong>ATF</strong>: Since there is no shallow approach sewer discharging flows into this drop<br />
structure, the structure cannot serve as a pathway for air backpressurization into such a<br />
sewer; therefore no forced air treatment system is recommended for this location.<br />
Drop Structure Modifications: Although there is no shallow sewer discharging flows<br />
into this drop structure, there is evidence that installation of a flow regulation device in<br />
the air return line of this drop structure, such as an adjustable damper may be<br />
beneficial. However, it is recommended to complete the drop structure model testing<br />
before finalizing the damper concept. Such a device would be available for future air<br />
backpressurization adjustments as a contingency if a shallow approach sewer is<br />
connected to this drop structure in the future.<br />
Flow Diversion: Because there is no shallow approach sewer currently discharging<br />
flows into the Richmond Drop Structure, flow diversion recommendations for this<br />
location are not applicable at this time.<br />
<br />
Mission and Jesse Drop Structure & Vicinity<br />
o<br />
o<br />
This drop structure drops the flow from NOS upstream to NEIS downstream<br />
<strong>ATF</strong>: The interim scrubber at this location appeared to reduce the air pressures along<br />
the majority of the NEIS and ECIS alignment. Also, this drop structure appeared to be<br />
the primary conduit through which the NEIS/ECIS tunnel relieved its air pressure back<br />
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into the NOS upstream. A permanent <strong>ATF</strong> is therefore recommended for this<br />
location if the structure modifications and flow adjustment do not work.<br />
o<br />
Drop Structure Modifications: During the time the air return lines at Division and<br />
Humboldt were plugged, the pressures in the NOS upstream approach sewer at Mission<br />
and Jesse increased significantly. Once the Mission and Jesse air return line was also<br />
plugged, the pressure along the NOS at this location began to reduce significantly. There<br />
is evidence that installation of a flow regulation device in the air return line of this<br />
drop structure, such as an adjustable damper may be beneficial. However, it is<br />
recommended to complete the drop structure model testing before finalizing the damper<br />
concept. As with the Division and Humboldt Drop Structures, such a device would give<br />
BOS the flexibility to adjust the amount of air that is allowed to flow through the air<br />
return line under current or future operational conditions and prevent air from<br />
backpressuring the NOS approach sewer via this location.<br />
<br />
<br />
Additional modifications to the Mission and Jesse Drop Structure should include installing<br />
two curtains or similar flexible devices. One curtain should be installed at the downstream end<br />
of the plunge pool; the other curtain should be installed on the NEIS just upstream of the<br />
junction with the Mission and Jesse drop structure as shown in Figure 6.<br />
An additional air pickup should also be designed and constructed for the recommended<br />
Mission and Jesse <strong>ATF</strong>. This air pickup would be located along the NEIS tunnel just upstream<br />
of the recommended NEIS curtain. This additional air pickup is shown in Figure 6.<br />
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Figure 6 - Additional Air Pickup<br />
The purpose of the curtain on the NOS would be to isolate the common headspace between the drop<br />
structure and the ECIS tunnel. This would allow the recommended <strong>ATF</strong> at this location to fully<br />
capture the air that would be carried with the NOS flows into the drop structure, thereby reducing the<br />
amount of air dragged into the ECIS tunnel and helping to maintain reduced pressures along the<br />
NOS approach sewer to Mission and Jesse.<br />
The recommended curtain on the NEIS would serve to isolate the air dragged by the NEIS from the<br />
Mission and Jesse Drop Structure and ECIS headspaces. An additional air pickup point on the<br />
upstream side of the NEIS curtain would direct odorous air from the NEIS to the recommended <strong>ATF</strong><br />
for this location.<br />
<br />
Flow Diversion: The system air pressures appeared to react favorably to the stop log removal at<br />
this location; which allowed approach flows in the NOS to split naturally between that sewer and<br />
the NEIS. This resulted in more flow being directed into the ECIS via the Mission and Jesse<br />
Drop Structure. It is therefore recommended that the stop logs be configured at this location<br />
in such a manner that a maximum amount of flow is directed into the ECIS via Mission<br />
and Jesse. This would likely result in more air being dragged into the drop structure and<br />
therefore, lower air pressures in the NOS approach sewer and the NEIS/ECIS tunnel system.<br />
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This air would be isolated in the drop structure due to the recommended damper and curtain<br />
devices and captured by the recommended <strong>ATF</strong>.<br />
<br />
23 rd and San Pedro Drop Structure and Vicinity<br />
o<br />
o<br />
o<br />
o<br />
This drop structure drops the flow from NOS upstream to ECIS downstream<br />
<strong>ATF</strong>: Following the removal of the interim scrubber at this location, odor complaints<br />
have been significantly reduced in the near vicinity. Also, pressure testing conducted<br />
during the drop structure study indicated that this structure is not a significant source of<br />
backpressurization into the shallow NOS approach sewer; therefore no forced air<br />
treatment system is recommended for this location.<br />
Drop Structure Modifications: The pressures in the shallow NOS approach sewer were<br />
reduced slightly as a result of plugging the air return line at the 23 rd and San Pedro Drop<br />
Structure. There is evidence that installation of a flow regulation device in the air<br />
return line of this drop structure, such as an adjustable damper may be beneficial.<br />
However, it is recommended to complete the drop structure model testing before<br />
finalizing the damper concept. As with the Division, Humboldt and Mission and Jesse<br />
drop structures, such a device would give BOS the flexibility to adjust the amount of air<br />
that is allowed to flow through the air return line under current or future operational<br />
conditions.<br />
Flow Diversion: Flows should be allowed to split naturally between the NOS and the<br />
approach sewer to the 23 rd and San Pedro Drop Structure in the upstream diversion<br />
structure<br />
<br />
USC Drop Structure and Vicinity<br />
o<br />
No modifications or operational recommendations are necessary at this drop<br />
structure.<br />
An overall graphic summary of the recommendations for the NEIS/ECIS drop structure locations<br />
between the Division Drop Structure and the ECIS Jefferson Siphon is presented in Figure 7.<br />
Detailed descriptions of the rationale for each site recommendation are presented graphically in<br />
Figures 8 and 9.<br />
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Figure 7 - NEIS/ECIS Recommendation Summary<br />
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Figure 8 - Detailed Recommendations Descriptions (1)<br />
Figure 9 - Detailed Recommendations Descriptions (2)<br />
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These above recommendations must be revisited following the completion of the pending physical<br />
model testing. Additionally the effects of the recommendations should be verified with a full scale<br />
fan test field study aimed at verifying the effect of the combination of the adjustable air plugging<br />
devices and the recommended <strong>ATF</strong> at Mission and Jesse.<br />
Since there is evidence that the source of pressure in the shallow approach sewers emanates from the<br />
NEIS/ECIS tunnel system, adjustable air plugging devices in the air return lines could provide a<br />
beneficial effect to control the back pressurization effect from the tunnel to the shallow approach<br />
sewers, i.e. NOS.<br />
Since the purpose is to reduce the backpressurization effect into the shallow approach and given the<br />
fact that the system is dynamic and will change in the future, the City may want to have the<br />
flexibility to adjust the air flow through the return air line using adjustable air plugging devices.<br />
There was evidence in the approach sewers at Division and Mission & Jesse of a downward trend of<br />
air pressure once the return lines were plugged at Division and Mission & Jesse. However given the<br />
fact that the plugging of the air return lines at the four drop structures increased the pressure in the<br />
NEIS/ECIS tunnel, it is recommended that the City conduct a full scale fan test to verify the sizing of<br />
an <strong>ATF</strong> at Mission and Jesse in order to reduce the amount of positive pressure in the tunnel and to<br />
verify the backpressurization reduction effects of adjustable air plugging devices.<br />
<br />
Systemwide Downstream Interceptors<br />
The City is in the process of initiating several odor control measures downstream of the<br />
ECIS Jefferson Siphon. These include the startup of a 20,000 cfm <strong>ATF</strong> at Jefferson and La<br />
Cienega and the installation of headspace isolation curtains at Diversion Structures 1, 2 and<br />
3 in the Baldwin Hills/Culver City area. The purpose of the <strong>ATF</strong> is to ventilate the ECIS<br />
both upstream and downstream of the Jefferson Siphon. The purpose of the curtains is to<br />
isolate the NORS headspace from the interceptors that discharge flows into it through the<br />
three diversion structures. In addition to this, an interim scrubber is currently ventilating the<br />
NORS and the ECIS at the NORS/ECIS junction. Furthermore, flows have been diverted<br />
away from the NORS towards the NOS in recent months following the completion of the<br />
NOS rehab in the Culver City area. It is generally believed that these flow diversions will<br />
relieve the significantly high air pressures that have been recorded in the NORS during NOS<br />
rehab.<br />
Given these numerous odor control-related measures, the following recommendations are<br />
put forth for the NORS:<br />
o<br />
The City should conduct differential air pressure testing along the NORS to<br />
determine the effects of the flow diversions, curtain installations and effect of the 20,000<br />
cfm ECIS Jefferson Siphon <strong>ATF</strong>. This data should be compared to pressure data taken<br />
on the NORS before these measures were put into place, specifically that data which was<br />
recorded during Spring/Summer, 2009 as part of this study.<br />
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If the planned odor control measures do not result in satisfactory pressure reductions<br />
along the NORS, the City should initiate a fan test along the NORS between the siphon<br />
at Fox Hills Mall and Culver City Park. The fan should be configured to withdraw air<br />
from a maintenance hole just upstream of the siphon while differential air pressure data<br />
loggers are recording data in the upstream reaches of the NORS. If this proves successful at<br />
reducing pressures to acceptable levels, an <strong>ATF</strong> should be designed and constructed just<br />
upstream of the siphon.<br />
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5. Determine Air Flows<br />
It is premature to estimate the effective air flow that would be necessary to capture, contain and treat<br />
the odors and emissions at the Mission and Jesse location. Follow-on work on a simulated drop<br />
structure at the City’s hydraulics laboratory will provide additional insight into the patterns of air<br />
flow and the flow rates for a similar, but not identical arrangement to the Mission and Jesse drop<br />
structure. To pinpoint the air extraction flows that will be required to achieve the desired impact at<br />
the Mission and Jesse location and beyond, a fan test is warranted.<br />
Simulating actual conditions in the field and setting up a monitoring program to document the extent<br />
of the impact resulting from extracting air from the interceptor will verify the flow rate requirements,<br />
and reduce any second guessing or speculation on what the air extraction flow rate should be. In the<br />
interim it is projected that a 20,000 cfm flow rate would be required at this recommended Mission<br />
and Jesse <strong>ATF</strong>.<br />
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6. Air Emissions Characterization<br />
To obtain emissions characterization data from five of the seven locations identified in the 2004<br />
Collection System Settlement Agreement (CSSA) that the City entered into with the USEPA, Santa<br />
Monica Baykeeper, City of El Segundo, and others, a monitoring plan was developed. The<br />
remaining two locations were not included in this characterization plan since the City determined to<br />
move ahead with constructing <strong>ATF</strong>s at these sites. Those <strong>ATF</strong>s have been constructed, have passed<br />
their performance tests, and are about to be commissioned. The monitoring plan included sampling<br />
at:<br />
North East Interceptor Sewer (NEIS) – Richmond<br />
North Outfall Relief Sewer (NORS) – NORS – ECIS<br />
NEIS – Humboldt<br />
East Central Interceptor Sewer (ECIS) – Mission & Jesse<br />
ECIS – 23 rd Street & San Pedro<br />
The samples collected at these five locations were analyzed for the following parameters:<br />
Hydrogen sulfide (H 2 S)<br />
TNMHC<br />
Speciated volatile organic compounds (VOCs)<br />
Speciated organic reduced sulfur compounds<br />
Hydrogen sulfide was analyzed in the field with two devices: a hand-held H 2 S monitor (Jerome<br />
meter) was used to measure untreated interceptor air samples collected in Tedlar sample bags; and a<br />
continuous H 2 S data logging device (OdaLog) was inserted in a manhole location at each site to<br />
represent the untreated air emissions from the interceptors. The remaining parameters were collected<br />
according to strict sampling protocol requirements in various containers (Summa canisters and<br />
Tedlar® bags and shipped by courier to a local laboratory for analysis. Whereas most of these<br />
parameters were collected as grabs or over a limited short duration time frame (1-hour), the OdaLog<br />
continues logging H 2 S monitors was left in place for several days to record the diurnal variation of<br />
H 2 S concentrations in the interceptor.<br />
The following analytical methods were used to determine the concentrations of the various specific<br />
compounds and classes of compounds:<br />
<br />
<br />
<br />
TNMHC<br />
o SCAQMD Method 25.3<br />
Speciated volatile organic compounds<br />
o EPA Method TO – 15<br />
o EPA Method TO – 12 Modified<br />
Speciated organic reduced sulfur compounds<br />
o ASTM 5504<br />
These methods were carefully selected to identify those compounds that together made up the<br />
TNMHC value, and to ensure that the two approaches reached a similar endpoint. The speciated<br />
compounds were also examined to assess whether any of these particular compounds indentified<br />
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should not be classified as a VOC based on their inability to be converted by sunlight into ozone, or<br />
the pronouncement by USEPA that they were not photochemically reactive and therefore<br />
dropped/not included on USEPA’s list of VOC’s.<br />
For more details on the sample collection, the analytical procedures, and the analytical results the<br />
reader is referred to the Total Non-Methane Hydrocarbon Monitoring Results Technical<br />
Memorandum (TM) submitted in draft to the City in June <strong>2010</strong>. The final version of that TM will be<br />
submitted as part of the final project report.<br />
The analytical results for the samples collected from the manhole at Mission and Jesse where the<br />
interceptor odorous air is extracted and forwarded to the interim odor control system (consisting of<br />
activated carbon) are presented in Table 1. Table 1 includes those analytical results that are directly<br />
related to permit limits. For information on speciated organic compounds and reduced sulfur<br />
compounds refer to the TNMHC TM. [As a point of reference, on the day that the samples were<br />
collected at Mission and Jesse the odor control system was not operating. The activated carbon fan<br />
was shut off to allow for removing the spent carbon from the vessel and replacing it with virgin<br />
carbon.]<br />
The results of the OdaLog, continuous H 2 S monitoring from the interceptor airspace is presented in<br />
Figure 10.<br />
Table 1 - Mission & Jesse Interceptor Raw Emissions Characterization Results<br />
Parameter<br />
Mission & Jesse Analytical Results<br />
TNMHC – Methods 25.3 (ppmC) 1 14.0<br />
Non-VOCs (ppmC) 1 0.47<br />
Adjusted Method 25.3(ppmC) 1 13.53<br />
Hydrogen Sulfide (ppm)<br />
Grab Sample >50 2<br />
OdaLog Unit 4<br />
• Minimum<br />
Figure 10 - OdaLog Continuous H2S Data Logging Results<br />
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The unadjusted TNMHC results and the adjusted results, 14.0 and 13.53 ppmC, respectively, are<br />
below the range of current percent limits for operating odor control systems of 18.0 to 36.0 ppmC.<br />
Accordingly, these uncontrolled results are lower than the potential discharge/exhaust levels even<br />
before any control system is used. Based on previous monitoring results from several years ago, the<br />
City was concerned that the TNMHC results here would be higher. With the presence of an air<br />
treatment system, it is expect that the concentrations will be even lower than these uncontrolled<br />
values.<br />
For H 2 S, the grab sample results, >50 ppm, compares well to the concentrations recorded by the<br />
OdaLog unit, squarely between the average concentrations of 16.5 ppm and the maximum<br />
concentration of 87.0 ppm. The H 2 S concentration from Mission and Jesse were the second highest<br />
recorded among the five locations that were monitored during this task. The concentrations recorded<br />
at 23 rd Street and San Pedro were higher, with an average of 34.5 ppm and a maximum value of<br />
greater than 100 ppm. Nevertheless, the concentrations recorded at Mission and Jesse are elevated<br />
enough to be of concern to the City and demonstrate a need for the selection of a consistent,<br />
permanent and effective H 2 S control system.<br />
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7. Identify Air Emission Control Technologies<br />
Many different technologies are available for controlling nuisance related odors and air emissions<br />
that are associated with wastewater collection systems. Each technology has a niche when it is most<br />
suitable to provide the level of control required to reduce off-site odor impacts. The degree of<br />
control required at any one site is dependent on several factors, including, but not limited to: physical<br />
setting; metrological conditions, topography of the land surrounding the odor control site; proximity<br />
of the nearest neighbors and/or nearest sensitive receptors; permit requirements established by South<br />
Coast Air Quality Management District (SCAQMD); and unobstructed view of the air treatment<br />
facility (<strong>ATF</strong>). These factors will need to be considered when evaluating the many different control<br />
technologies. The challenge is identifying the most cost effective, viable control technology that will<br />
achieve the goal of the City of Los Angeles (City) and comply with the limits established in the air<br />
permit for each site.<br />
Existing odor control systems and <strong>ATF</strong>s that are operating at various locations across the City’s<br />
interceptor network systems have air permits issued by SCAQMD. All the air permits include a<br />
discharge/exhaust limit for hydrogen sulfide ranging from 0.6 to 1.0 part per million by volume in air<br />
(ppm). Some of the permits, but not all also have discharge/exhaust limits for total non-methane<br />
hydrocarbons (TNMHC), but the limits vary from 18 to 36 ppmC. Although the City is ultimately<br />
concerned about odors, they must also address TNMHC emissions whose limits are based on human<br />
health affects and/or the total accumulation of volatile organic compounds (VOCs) in the<br />
atmosphere. The City and the surrounding air basin are in a non-attainment area for Federal<br />
(USEPA) ozone ambient air quality standards and reduce the levels of ozone being emitted by<br />
restricting ozone processors like VOCs/ TNMHCs. It is fully anticipated that any air emissions<br />
control system and/or <strong>ATF</strong> that will be designed and constructed moving forward from today will<br />
continue to include H 2 S and TNMHC limits. Accordingly, the technology, or combination of<br />
technologies, that will be constructed at any site must have the ability to remove both constituents to<br />
comply with the permit limits. The existing permit to operate the interim odor control system at<br />
Mission & Jesse has a discharge/exhaust H 2 S limit of 1.0 ppm and no limit for TNMHC.<br />
The City’s goal for sites that require odor control systems and/or <strong>ATF</strong>’s are:<br />
<br />
<br />
<br />
<br />
<br />
Comply with all regulatory requirements<br />
Keep collection system nuisance odors from impacting residents, drivers and visitors.<br />
Capture and treat the odors to eliminate fugitive nuisance odor releases to the open<br />
atmosphere<br />
Reduce odor complaints from the surrounding neighborhoods<br />
Be a good neighbor.<br />
Understanding the goals, needs and requirements for odor and emissions control at a site helps to<br />
establish the initial framework for the identification of viable control alternatives. Characterization<br />
of the emissions at the interceptor area of concern area(s) is the final critical piece of background<br />
information necessary to move forward with selecting the right air emissions control technology.<br />
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The prime role of the air control technologies is to address the moderately high concentrations of<br />
H 2 S in the Mission and Jesse inlet air stream. The technology must be capable of consistently<br />
reducing the average (16.5 ppm) and the maximum (87.0 ppm) concentration of H 2 S to less than 1<br />
ppm. Accordingly, a technology on its own or in combination must be capable of achieving a 99%<br />
reduction of inlet H 2 S concentration. At a removal efficiency of 99% for these monitored H 2 S<br />
concentration, the City will be able to comply with the anticipated SCAQMD 1 ppm air permit<br />
discharge/exhaust limit, with a safety factor. Keep in mind that the SCAQMD air permit is based on<br />
a one hour standard. Referring to Figure 6-1, the maximum concentration of 87.0 ppm was a one<br />
time, short term (less than an hour) recorded value. No sustained, high H 2 S concentrations were<br />
observed for the four days that the OdaLog was in place monitoring the airspace of the maintenance<br />
hole on the interceptor at the Mission and Jesse location. The HDR Team recommends that the City<br />
continue to monitor the H 2 S concentrations at the Mission and Jesse location to verify the readings<br />
recorded during this TNMHC study and to ensure that the technology to be constructed here is<br />
capable of complying with the anticipated SCAQMD discharge/exhaust limit of 1.0 ppm of H 2 S.<br />
The most commonly applied air control technologies used today include:<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
Wet scrubbing<br />
Biofilter<br />
Biotrickling<br />
Bioscrubbing<br />
Activated Carbon<br />
Ionization<br />
Dilutions/Entrainment<br />
<br />
Combinations<br />
An initial screening of these technologies can eliminate several that are not viable for the conditions<br />
presented above. In addition to the ability of the air control technology to remove H 2 S, odors and<br />
some degree of TNMHC, selection of the control system must consider the conditions under which<br />
the system will operate, including but not limited to:<br />
<br />
<br />
<br />
<br />
<br />
Remote location of the installation<br />
Unmanned operation of the site<br />
Situated in the community where safety is of paramount importance<br />
Access to utilities (water, electrical service)<br />
The site has no natural sight barriers to prevent the facilities from being visible from the<br />
street and beyond<br />
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What is the footprint of any technology or combination being considered and is their<br />
enough space at the site to support it<br />
With the railroad so close at grade, are there any special concerns, permits or approvals<br />
that may be required before moving forward with construction.<br />
Will access to the site be restricted, and/or will there be enough space to easily operate<br />
and maintain the facilities<br />
<br />
Does the air treatment systems need to be placed below grade in a building structure, or<br />
can it be constructed at grade without impacting the nearest residents<br />
The following technologies have been eliminated from further consideration for the reasons<br />
provided:<br />
<br />
<br />
<br />
Biofilter – Biofilters are better suited for conditions where H 2 S concentrations are lower<br />
than 87.0 ppm. In addition, the space required to erect a biofilter based technology would<br />
take a larger footprint than any of the other technologies listed.<br />
Bioscrubbing – Bioscrubbing is a technology that has not been embraced by the<br />
wastewater industry partly because of the increased operation and maintenance attention<br />
required of the separate aerated oxidation tank (biological reactor) where the recirculated<br />
mixed liquor solution is deposited and treatment occurs. Bioscrubbers are better suited to<br />
remove organic odors since the bioreactor supports heterotrophic microorganisms.<br />
Ionization – Ionization is a technology that has become more visible in the last few years.<br />
Although performance claims have been made by the manufacturers, very limited<br />
documented evidence of removal efficiency performance, for H 2 S and odors, are<br />
available. Recent inquiries for information by a research study sponsored by the Water<br />
Environment Research Foundation (WERF) which reviewed several thousand articles,<br />
reports and gray literature, received no response. As a result, undocumented technologies<br />
are not viable options for further consideration.<br />
<br />
Dilution/Entrainment – The solution to pollution is dilution does not work for wastewater<br />
discharge permits, but for controlling H 2 S odors and reducing off-site impacts it can.<br />
This technology becomes non-viable when specific compound discharge limits are in<br />
place (like H 2 S) and the exhaust concentrations exceed them. The potential for that<br />
condition to occur here exists. Therefore, this technology has also been eliminated.<br />
The remaining four technologies will be discussed in more detail below.<br />
(1) Wet Scrubbing<br />
The leading odor control technology over the last 25 years is wet scrubbing. It has proven that it<br />
can be an effective method for controlling traditional odors associated with wastewater<br />
operations. Although it has taken many forms over the years, such as cross-flow and atomizing<br />
mist, the vertical, packed-tower, counter-current systems have been the most popular. Newer<br />
designs that address concerns with the height of the system have tried to retain the best features<br />
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in a more compact, low-profile version. Regardless, the fundamental principles of the wet<br />
scrubber remain the same. Wet scrubbing consists of a physical-chemical process that removes<br />
odorous parameters from the inlet air stream. A chemical scrubbant solution is distributed over a<br />
bed of plastic inert media. The most common make-up of the chemical scrubbant solution<br />
besides the base component of water is caustic and sodium hypochlorite. Other chemicals have<br />
been used, such as chlorine dioxide or hydrogen peroxide, but they have not shared the same<br />
level of success.<br />
The overriding principles of a wet scrubber are to bring the odorous air flow in direct contact<br />
with the chemical scrubbant solution. In achieving this contact, the odor causing compounds are<br />
removed from the air stream and the treated air is discharged from the exhaust stack into the<br />
atmosphere. The odorous compounds are removed from the air by absorption into the scrubbant<br />
solution. The key odorous constituent normally associated with wastewater operations is H 2 S.<br />
H 2 S is very soluble in high pH solutions. By raising the pH of the scrubbant solution by adding<br />
caustic, the H 2 S and other soluble odor compounds are absorbed into the liquid scrubbant<br />
solution. To maintain a strong mass transfer driving force, sodium hypochlorite is also added to<br />
the scrubbant solution. The sodium hypochlorite converts the absorbed H 2 S into sulfate and<br />
prevents it from being re-stripped from the liquid phase either in the scrubber, or after the liquid<br />
is drained from the scrubber and the pH drops as it combines with the lower pH interceptor<br />
collection system waters.<br />
To enhance the contact between the odorous air stream and the scrubbant solution, plastic media<br />
are used. The plastic media, which have taken on many different shapes, sizes and<br />
configurations, are designed to provide the maximum amount of surface area in the smallest<br />
volume while also achieving as little pressure drop as possible. The air is forced to pass through<br />
a torturous path of media whose surface is coated with the scrubbant solution. It is at this<br />
air/liquid interface that the contact and absorption (mass transfer) of the odors occurs.<br />
Figure 11 illustrates a single stage vertical, packed-tower, wet chemical scrubber. The odorous<br />
air is fed into the air plenum at the lower part of the tower just above the sump where the<br />
scrubbant solution ends up after it has passed through the plastic media. The air plenum is an<br />
open, unobstructed area of the scrubber just below the plastic media. The air plenum serves to<br />
reduce the velocity of the inlet air flow, equalize the air volume and force it upwards evenly over<br />
the cross-section of the scrubber, thereby utilizing the full plastic media bed.<br />
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Figure 11 - Wet Scrubbing Process Schematic<br />
The scrubbant solution is recirculated through the wet scrubber and is distributed over the top of<br />
the plastic media bed through nozzles attached to a pipe network. To freshen the recirculating<br />
scrubbant solution, fresh water and chemical are constantly being fed, and an equal amount of<br />
solution is blown down to drain. The make-up water being fed is generally held at a constant<br />
rate. The chemicals are added on a demand basis, usually dictated by instrumentation that<br />
measures the pH, ORP and/or the concentration of H 2 S or chlorine in the exhaust. The fresh<br />
make-up water and chemical ensure an optimal mass transfer driving force for the odorous<br />
compounds to be absorbed into the liquid and ensure the effectiveness and efficiency of the odor<br />
control technology.<br />
Wet scrubbers are good at optimizing the removal of H 2 S under varying diurnal concentrations.<br />
The physical-chemical wet scrubber design allows it to quickly respond to changes in odor<br />
concentrations. Wet scrubbers are able to achieve 99% removal of H 2 S inlet concentrations.<br />
Manufacturers of wet scrubbers will guarantee a 99% removal efficiency of inlet H 2 S<br />
concentrations of 10 ppm v or greater. For concentrations less than 10 ppm v , they will only<br />
guarantee a low discharge concentration of 0.1 ppm v .<br />
The wet scrubber performance history for removing other reduced sulfur compounds is not<br />
consistently good. Depending on the specific reduced sulfur compound and its inlet<br />
concentration, documented removal efficiencies can range from 50 to 90+%. In situations where<br />
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the predominant odorous compounds are reduced sulfur compounds other than H 2 S, wet<br />
scrubbing may not be the optimal odor control technology selection.<br />
Removal of VOC compounds in wet scrubbers is poor. Generally, only those highly soluble<br />
VOC compounds are removed in a wet scrubber, others pass through and out the exhaust. Note<br />
that wet scrubbers were intended to be odor control devices and most VOCs do not contribute to<br />
odor conditions (the odor detection threshold limit of VOC compounds are several orders of<br />
magnitude greater than H 2 S and reduced sulfur compounds).<br />
Table 2 presents a list of advantages and disadvantages of wet scrubbing as an emissions control<br />
technology.<br />
Table 2 - Wet Scrubbing Emissions Control: Advantages & Disadvantages<br />
Wet Scrubber<br />
Advantages<br />
Disadvantages<br />
Physical-Chemical process<br />
Uses hazardous chemical<br />
Small footprint<br />
Safety is an issue<br />
Automatic chemical feed<br />
Mechanically intensive<br />
Recirculates scrubbant solution<br />
Poor VOC removals<br />
Proven track record<br />
Continuous blowdown<br />
Thousands of installations<br />
Scale build-up<br />
Familiarity of mechanical system<br />
Removes CO 2 (sink for caustic)<br />
Effective H 2 S/odor removal<br />
More labor intensive<br />
Inherent capacity for variable loads Greater degree of O&M<br />
Can reduce chemical in off odor season Calibration needed on probes<br />
Single stack discharge<br />
More systems to monitor<br />
No acclimation time required<br />
Must take system out of service to acid wash<br />
Visible odor control device<br />
Chlorine odor in exhaust<br />
Less subject to upsets<br />
Waste chemical in blowdown<br />
Easy to monitor exhaust<br />
Hard water causes scale<br />
Hazardous chemical truck deliveries through<br />
streets<br />
Despite the ability of wet scrubbing to achieve the prime role of the air control technology of<br />
99% removal of H 2 S, and the small footprint it would require, other features make it a less<br />
favorable candidate for final consideration at the Mission and Jesse location, for example:<br />
<br />
<br />
Wet scrubbing is the most mechanically intensive technology, incorporating a fan,<br />
recirculating pump, and multiple chemical metering pumps, in addition to chemical<br />
storage tanks, and instrumentation and control systems. Each of these systems requires<br />
maintenance and servicing on a routine basis to ensure reliability and continued effective<br />
service.<br />
Wet scrubbing uses hazardous chemicals in sodium hypochlorite and sodium hydroxide<br />
to maintain operations. These hazardous chemicals delivered by tanker truck and stored<br />
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on site in FRP tanks, represent a safety concern at a remote, unmanned location such as<br />
the Mission and Jesse site. Extra precautions are necessary to ensure the City staff and<br />
surrounding community are safe in the event of a spill, accident or premeditated act by<br />
outside forces.<br />
<br />
Wet scrubbing may occasionally require that the plastic media be acid washed to remove<br />
scale build-up, generally calcium carbonate based. The frequency of acid washing and<br />
the duration of this process will depend on how the system is operated. The higher the<br />
operating pH, the greater the chance that scaling will occur, and the more frequent that<br />
acid washing will be necessary. The duration will depend on the effectiveness of the<br />
previous acid wash and the degree of build-up since the last acid wash was performed.<br />
Acid washing demands that the wet scrubber be taken out of service. As a result, a<br />
redundant wet scrubber would be required for this technology option.<br />
Collection system odorous air streams normally contain elevated concentrations of CO 2 .<br />
CO 2, like H 2 S, consumes sodium hydroxide and can significantly increase the chemical<br />
demand to remove a compound that is neither an odor concern, nor a VOC.<br />
<br />
The Chemicals in the wet scrubbing systems blow-down may create a problem with<br />
disposal as the pH of that stream is generally greater than the allowable sewer discharge<br />
ordinance pH.<br />
Pursuant to these limitations associated with chemical safety, O&M, remote/unmanned site,<br />
scaling, extraneous compound chemical demand, blow-down disposal, and necessary<br />
redundancy requirements, wet scrubbing will not be considered further as a viable air control<br />
technology for the Mission and Jesse location.<br />
(2) Biotrickling Filter<br />
Treating odors using microorganisms is not a new technology. In fact, using microorganisms in<br />
a soil filter or a trickling filters dates back to the 1940’s, however, development of this<br />
technology did not emerge on the US market as a viable and marketable technology until the<br />
1990’s. Since then, biofilters achieved greater acceptance initially and biotrickling filters were<br />
slower to be recognized. Today both technologies, biofiltration and biotrickling filters are<br />
accepted technologies, are provided by vendors across the US, and have become the control<br />
technology of choice in the wastewater market area replacing the wet scrubbing alternatives<br />
because of their ability to achieve compliance with H 2 S and odor requirements without using<br />
hazardous chemicals and for a lower annual operating cost.<br />
Biotrickling filters consist of a containment vessel with some form of inorganic media to support<br />
microbial growth. That inorganic media may be a basic lava rock, plastic media or proprietary<br />
material. Initial research work with biotrickling filters demonstrated that standard landscape<br />
lava rock provided a rough and uneven surface filled with crevices and pores that supported the<br />
attachment and growth of a microbial slime layer that was not easily dislodged. Subsequently,<br />
non-uniform unit plastic media that is high-density but very light in weight when compared to<br />
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lava rock was introduced and has proven to be extremely effective as a truly robust biotrickling<br />
filter media. This plastic media can be stacked in vertical stages to minimize the overall<br />
footprint of this technology. The media is resistant to plugging and many vendors will provide a<br />
guarantee that the media will last at least 10 years before needing replacement. When<br />
replacement is needed, the media can easily and readily be removed in one piece by lifting it out<br />
of the vessel and quickly inserting the new media.<br />
The typical biotrickling filter functions much like a conventional chemical packed-bed wet<br />
scrubber, with the exceptions that no hazardous chemical is used. (Refer to Figure 12). The<br />
odorous foul air enters the bottom of the vessel, just above the water-based solution that is used<br />
to recirculate over the media, and just below the supported media. The open space or plenum<br />
where the odorous foul air enters the biotrickling filter allows for a reduction in air flow velocity,<br />
a build-up of positive pressure, and even distribution of the foul air as it pushes upward and<br />
evenly across the full cross-sections of the media bed. Based on the positioning and<br />
extent/layering of this media, whether lava rock, plastic or some other proprietary blend, the<br />
odorous air is forced to go through a torturous path of media where it consistently comes in<br />
contact with the liquid film coating the outside surface area of the media. The media is kept<br />
moist by applying a nutrient rich water-based solution from a distribution network above the<br />
media. The air stream flows upward through the media and the water-based solution passes<br />
downward. This counter-current, air liquid flow maximizes the operation of the biotrickling<br />
filter. The downward flow of the water-based solution not only delivers the nutrients required by<br />
the microorganisms living and working in the liquid film layer on the media, but also acts to<br />
remove dead layers and sloughing from the media into the sump where it can be removed from<br />
the system, and keeps the media wet. This is important because the air passing over the media<br />
has a tendency to dry it out.<br />
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Figure 12 - Biotrickling Filter Process Schematic<br />
Exhaust<br />
Media<br />
Inlet<br />
Air<br />
Stream<br />
Nutrients<br />
Temperature<br />
Control<br />
Blowdown<br />
The nutrient rich, water-based solution distributed at the top of the media can be designed as a<br />
once through system or it can be recirculated. When biotrickling filters are located at wastewater<br />
treatment plants where plant effluent is available, plentiful and can be readily used, once through<br />
systems are normally designed. The need for nutrient supplement is not typically necessary as<br />
the plant effluent will often have enough nutrients remaining. However, when plant effluent is<br />
not an option and potable water is all that is available, adding nutrients are critical and<br />
recirculating/recycling the solution is advised/recommended.<br />
The biotrickling filter is a biological reactor that removes H 2 S. The biomass is primarily living<br />
as attached growth on the media and not in the recirculated solution. Biotrickling filters rely on<br />
the growth of a thin biofilm on the surface of the media. The H 2 S and other compounds are<br />
absorbed or dissolved in the water matrix and diffuse into the biofilm, where the biological<br />
culture can aerobically degrade them. The biofilm must stay thin to avoid anaerobic activity,<br />
thereby making suitable biomass sloughing mechanisms necessary for a productive and effective<br />
control system. The bacteria that will be found operating in biotrickling filters with elevated<br />
levels of H 2 S are autotrophic.<br />
Microbiologists use the term autotrophic to identify this general type of bacteria that use<br />
inorganic compounds for their energy and carbon sources. In contrast, heterotrophic organisms<br />
must use organic compounds for both their energy and carbon needs. Autotrophic bacteria<br />
obtain their carbon from carbon dioxide gas dissolved in the water in which they live.<br />
Autotrophs consume inorganic compounds for energy such as sulfur based compounds<br />
(hydrogen sulfide [H 2 S], sulfide [HS - ]). Once inside the cell wall, biological processes act on<br />
these compounds to extract energy for use by bacteria. Once the energy is extracted through<br />
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their particular metabolic process, a converted and oxidized byproduct of the compound is<br />
released.<br />
Examples of common autotrophic bacteria are Thiobacillus. They consume H 2 S gas and the<br />
released product is sulfuric acid (H 2 SO 4 ). The latter process is also responsible for corrosion of<br />
concrete and metal surfaces exposed to H 2 S gas in wastewater systems.<br />
Autotrophic bacteria typically have a thin cell wall to allow free movement of chemicals in and<br />
out of the cell. They also prefer to live as single cells in suspended culture or as thin sheets of<br />
cells on surfaces so that a maximum cellular surface area is exposed to collect food and<br />
nutrients. Therefore, autotrophic bacteria do not clump together or form thick masses of cells<br />
like heterotrophs. Autotrophic bacteria are also efficient nutrient scavengers and can efficiently<br />
recycle nutrients in dead cells around them. Because autotrophic bacteria do not get as much<br />
energy from the conversion of inorganic chemicals as heterotrophic bacteria get from organic<br />
compounds, they must convert more chemicals at a faster rate. Autotrophic bacteria can,<br />
therefore, quickly assimilate and convert large quantities of inorganic compounds. This latter<br />
ability lends to rapid conversion of H 2 S gas in sewers to sulfuric acid and destruction of the<br />
wastewater infrastructure.<br />
Because of their ability to rapidly remove inorganic compounds, biological odor control<br />
technologies like biotrickling filters use autotrophic organisms to remove inorganic odor<br />
compounds such as H 2 S, and have proven that they can consistently achieve 99+% removal of<br />
H 2 S with the latest synthetic plastic media. Some autotrophic organisms can also degrade some<br />
low molecular weight organic compounds such as carbon disulfide, methyl mercaptan, and ethyl<br />
mercaptan. However, in the case of organic compounds, autotrophs degrade only the functional<br />
sulfur groups of the compound leaving the carbon-carbon bonds untouched.<br />
The biotrickling filter process schematic presented in Figure 12 illustrates the ability to provide<br />
temperature control ahead of the biotrickling filter to maintain the system at a uniform<br />
temperature that optimizes the performance of the microorganisms. For the City of Los Angeles,<br />
this option would not necessary.<br />
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Table 3 presents a list of the advantages and disadvantages of a biotrickling filter as an emissions<br />
control technology.<br />
Table 3 - Biotrickling Filter Emissions Control: Advantages and Disadvantages<br />
Biofilter<br />
Advantages<br />
Disadvantages<br />
Environmentally friendly<br />
Very poor non-H2S removal<br />
Green technology<br />
Larger footprint<br />
No chemicals<br />
Short circuiting<br />
Few mechanical pieces<br />
Requires post polishing step<br />
Low maintenance<br />
Must add nutrients<br />
Minimal monitoring<br />
Low pH blowdown<br />
Removes H 2 S<br />
Extended detention times<br />
Biological treatment<br />
Subject to upsets<br />
Low annual operating cost<br />
Biological process<br />
Non-hazardous media<br />
Need second stage for other odors/VOCs<br />
Minor adjustments needed<br />
Need CO2 in air flow/water supply<br />
Capable of treating variable H2S loads Short track record<br />
Robust microorganisms<br />
Requires acclimation period<br />
Proven media effectiveness<br />
Standby units must be operated<br />
Long detention time in media<br />
Less appropriate for low H2S levels<br />
Because the biotrickling filter would be an excellent control mechanism for H 2 S and some of the<br />
other reduced sulfur based compounds, but not very effective for other odorous compounds and<br />
VOCs, implementing this technology would require adding a second stage for residual odor<br />
removal and some VOC reduction. This is especially important to reduce the impact of odors on<br />
the surrounding community at the Mission and Jesse location.<br />
The sustainable operation of the biotrickling filter (no chemicals, minimal mechanical<br />
equipment, low operating cost in comparison to other odor control technologies, etc.) together<br />
with its ability to remove high and variable concentrations of H 2 S support the application of this<br />
technology at the Mission and Jesse location.<br />
(3) Activated Carbon<br />
The oldest of the three odor control technologies under evaluation, activated carbon, has proven<br />
that it can be a viable odor control alternative. Using a different removal process when<br />
compared to wet scrubbing and biotrickling filters, it is generally capable of providing the most<br />
complete removal of wastewater treatment plant odors, and is often found in a second stage<br />
polishing arrangement.<br />
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Unlike wet scrubbing and biofilters, activated carbon is a dry operating system that relies on<br />
adsorption rather than absorption. The preferred optimal operating point for the inlet odorous air<br />
stream moisture content is 50% relative humidity (RH), with some activated carbons on the<br />
market today capable of operating up to 75% RH. Too much moisture in the odorous air stream<br />
is not good since the moisture then competes for sites on the activated carbon along with the<br />
odorous compounds that we are looking to remove.<br />
Activated carbon odor control is a very simple system consisting of the following elements:<br />
<br />
<br />
<br />
<br />
Foul air fan<br />
Vessel<br />
Activated carbon<br />
Exhaust stack<br />
The foul air fan pushes the odorous air into an open volume within the vessel, a plenum. The<br />
plenum reduces the velocity of the inlet air and prepares the air flow to be evenly distributed<br />
across the full cross-section of the activated carbon bed. The odorous air passes through the<br />
carbon bed at a velocity of 50 to 65 feet per minute and the odorous air compounds are adsorbed<br />
onto the carbon surface. The treated air is then released through an exhaust stack into the<br />
atmosphere. Figure 13 illustrates a typical, dual bed, activated carbon odor control system.<br />
Figure 13 - Dual Bed Activated Carbon Process Schematic<br />
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Activated carbon has a finite capacity for removing various compounds from the air. Once that<br />
capacity is reached, the activated carbon needs to be replaced. Some activated carbons can be<br />
regenerated in place, but the only capacity that is restored is for H 2 S and not other reduced sulfur<br />
compounds or VOCs. If the odorous air flow does not have a dominant H 2 S component, the use<br />
of a regenerable activated carbon is not warranted and the selected carbon should be virgin<br />
activated carbon.<br />
Some compounds have less capacity for being removed by activated carbon. It is important to<br />
understand the characteristics of the odorous air treated in order to determine the limiting<br />
odorous compound so the estimated activated carbon bed life can be determined. Understanding<br />
the duration of the activated carbon bed life will help determine the bed replacement frequency,<br />
which is important in assessing the operating costs for activated carbon odor control. Hydrogen<br />
sulfide is commonly used to assess bed life, and replacement frequency.<br />
Different activated carbons are on the market today, including:<br />
<br />
<br />
<br />
Virgin<br />
Caustic impregnated<br />
Catalytic<br />
The type of carbon selected will depend on the characteristics of the odorous air flow. Virgin<br />
carbon is the oldest and most traditional carbon that would be used for volatile and odorous<br />
organic compounds, but has a relatively low capacity for H 2 S. Impregnated carbons applied at<br />
wastewater operations are usually impregnated with an alkali, such as sodium hydroxide or<br />
potassium hydroxide, a chemical that promotes a reaction with adsorbed acidic compounds like<br />
H 2 S. These impregnates enhance the activated carbon’s removal efficiencies and capacities for<br />
H 2 S removal. Catalytic carbons have finer pore structure, giving it a higher density and greater<br />
adsorption capacity for H 2 S than unimpregnated carbons. Because of its catalytic nature, most<br />
(more than 90%) of the H 2 S reacts to form sulfates which is water soluble and could be removed<br />
by washing the carbon with water. Again, this regeneration only removes H 2 S related<br />
constituents. From a cost perspective, virgin carbon is the least costly and catalytic is the most<br />
expensive.<br />
Two concerns have been expressed by owners of activated carbon odor control systems: bed<br />
fires and disposal of the used carbon. Bed fires are only a legitimate concern when impregnated<br />
carbon is being used. The caustic solution used to impregnate the carbon can cause an<br />
exothermic reaction when combined with moisture, from the ambient air for example. This can<br />
create high enough heat for ignition to occur if the fans are not operating. The fans would tend<br />
to dissipate the heat. However, when the fans are off and the activated carbon bed is not sealed<br />
off, allowing air to breathe through the bed, fires have been known to occur. These conditions<br />
do not exist in virgin and catalytic carbons, and therefore are less susceptible to bed fires.<br />
The proper way to dispose of activated carbon once it is spent depends on the type of carbon, the<br />
characteristics of the inlet odorous air, and the compounds adsorbed. The carbon should be<br />
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tested to determine compliance with RCRA regulations. The results will determine how the<br />
carbon should be disposed. Impregnated carbon is likely to be considered hazardous due to the<br />
caustic impregnate used. Virgin and catalytic carbons can be thermally regenerated, and so may<br />
be removed by the supplier of the replacement carbon and not disposed of but re-used.<br />
To economize on the space requirements for activated carbon odor control systems, dual bed<br />
vessels are available (see Figure 7-3). Dual bed vessels provide two, generally three foot deep<br />
activated carbon beds in a single vessel. This allows for twice the flow in the same footprint as a<br />
single bed vessel. The space requirements for activated carbon lie in between wet scrubbing and<br />
biotrickling filters.<br />
Activated carbon odor control systems often require an in-line particulate filter before the carbon<br />
vessel to avoid plugging of the carbon, particularly when it is used as the prime/single odor<br />
control device when treating wastewater collection system air streams that contain aerosol<br />
particulates of oil and grease, and free moisture. Plugging created by the unwanted particulate<br />
matter build-up can cause uneven distribution of the air, unused sections of the activated carbon<br />
bed, and an increase in pressure drop.<br />
Pursuant to the nature of an activated carbon odor control system, no controls (other than for the<br />
fans) or chemicals are needed. There is no way to regulate the degree of control for activated<br />
carbon. Activated carbon works to remove all the compounds it is capable of when it passes<br />
through its bed, whether that removal is necessary or not. This can result in a shorter bed life<br />
and more frequent carbon replacements.<br />
Activated carbon is capable of removing the typical wastewater related odors, H 2 S (to levels<br />
greater than 99%) and other reduced sulfur compounds, as well as VOCs. Although activated<br />
carbon can remove reduced sulfur compounds, in some instances the removal capacity is much<br />
less than that associated with H 2 S. This means that these compounds could break through the<br />
bed before the capacity to remove H 2 S is reached. The question with activated carbon, then, is<br />
not whether it can effectively remove H 2 S, VOCs and other odorous compounds, as it has<br />
demonstrated in the past that it is still the best technology of those identified earlier at removing<br />
these compounds to very low levels. The potential drawback with activated carbon is its finite<br />
capacity for removal. If the activated carbon media needs to be replaced too frequently, the<br />
advantages it has over other technologies are likely to disappear. At the same time, pursuant to<br />
its ability to provide the best exhaust quality, applying activated carbon as a second stage and<br />
polishing device, because of the higher degree of control necessary for facilities and locations<br />
like Mission and Jesse that are stuck in the middle of the community, can be extremely positive<br />
and effective in demonstrating that this air control facility will be able to consistently achieve the<br />
SCAQMD permit limits and the odor demands of the public.<br />
As a prime air emissions control system, activated carbon is not suitable at the Mission and Jesse<br />
location. The results from the monitoring study identified average concentrations of H 2 S of 16.5<br />
ppm over the several days of continuous data recording. Any time that average concentrations of<br />
H 2 S approach and exceed 10 ppm, the application is not appropriate for activated carbon. The<br />
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activated carbon would need to be regenerated in place and/or replaced too frequently to make<br />
this application cost-effective. Pursuant to the remote location of the Mission and Jesse site,<br />
changing the carbon frequently also creates a logistical problem for staff who need to know<br />
when the carbon must be changed (requiring more often system monitoring) and coordinate with<br />
the vendor on when it will be done.<br />
Table 4 presents a list of the advantages and disadvantages of an activated carbon system as an<br />
emissions control technology.<br />
Table 4 - Activated Carbon Emissions Control: Advantages & Disadvantages<br />
Activated Carbon<br />
Advantages<br />
Disadvantages<br />
Simple system<br />
Carbon disposal<br />
Minimal mechanical pieces<br />
Finite capacity<br />
Proven technology<br />
Comparatively high pressure drop<br />
Effective H 2 S/odor removal<br />
Moisture concerns<br />
Dry system<br />
No operating flexibility<br />
Simple monitoring<br />
Potential bed fires with impregnated carbon<br />
Good polishing unit<br />
One fan per vessel<br />
Low maintenance<br />
Must monitor for bed capacity<br />
Moderate footprint<br />
Regeneration byproducts require special handling<br />
No acclimation required<br />
Replacing carbon<br />
Long track record<br />
No reserve capacity<br />
Reliable performance<br />
Two exhaust stacks per dual bed unit<br />
Preferred final polishing technology Always removes everything<br />
Combinations<br />
Combinations consist of multiple odor control technologies linked together to provide for more<br />
complete control of the inlet odorous gases. Combinations are commonly applied when the inlet<br />
odorous gas concentrations exceed the ability of a single control technology to achieve compliance;<br />
or, when one technology is not able to achieve necessary removal efficiencies of all identified<br />
odorous compounds; or, in the case of wet scrubbers or biotrickling filters, the exhaust gas has a<br />
residual odor associated with it that may or may not be representative of the feed gas. Feasible<br />
combinations for the technologies under consideration in this study would be:<br />
<br />
<br />
<br />
<br />
Wet scrubbing and activated carbon<br />
Biotrickling filter and activated carbon<br />
Biotrickling filter and wet scrubbing<br />
According to the discussions of the technologies above, wet scrubbing is not a technology<br />
that is well suited for the service in a remote location such as Mission and Jesse for the<br />
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easons provided. Biotrickling filters will remove H 2 S, and activated carbon will remove<br />
H2S, VOCs and other odors, but operating as individual emissions control technologies they<br />
would not be able to satisfy the needs of the City nor the community. However, taking<br />
advantage of the best attributes of each technology<br />
<br />
<br />
<br />
<br />
Excellent H 2 S removal capability of biotrickling filters<br />
Sustainable, low energy, low O&M features of biotrickling filters<br />
Polishing capability of activated carbon to remove residual odors, H 2 S and VOCs<br />
The combination of biotrickling filters and activated carbon make for a successful, low risk<br />
solution to the air emissions treatment at Mission and Jesse.<br />
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8. Recommendations<br />
Based on the monitoring results from the TNMHC study, the discussions on the technologies, and<br />
the comparison tables of advantages and disadvantages for each of the individual control<br />
technologies, the recommended technology for the Mission and Jesse location is a two stage,<br />
combination system consisting of:<br />
<br />
<br />
<br />
<br />
<br />
First Stage - Biotrickling filter<br />
Second Stage - Activated Carbon<br />
The biotrickling filter will remove 99% of the influent H2S and limited other reduced sulfur<br />
compounds, and the carbon will: remove any residual H2S down to the low parts per billion<br />
(ppb) concentrations (Well below the projected permit limit of 1.0 ppm.); remove any<br />
residual reduced sulfur and odorous compounds; and reduce the levels of VOCs. This will<br />
comply with the permit conditions and keep nuisance odors from impacting the surrounding<br />
communities.<br />
This recommended full air treatment facility is necessary in order to treat the elevated levels<br />
of influent H 2 S concentrations, the modest concentrations of VOCs and the remaining<br />
odorous organic and inorganic compounds. Implementing this two-stage, combination, air<br />
emissions control system will minimize any risk facing the City with respect to permit<br />
compliance and being a good neighbor.<br />
As presented in Section 5- Determine Air Flow, the actual air flow to be treated by the <strong>ATF</strong> is<br />
yet to be established. In the interim it is projected that a 20,000 cfm flow rate would be<br />
necessary at this recommended Mission and Jesse <strong>ATF</strong>. The <strong>ATF</strong> attributes will depend on<br />
the vendor providing the <strong>ATF</strong> units and the design criteria developed by the design engineer<br />
in coordination with the City staff.<br />
A preliminary estimate of the <strong>ATF</strong> attributes are presented in Table 5.<br />
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Table 5 - Preliminary <strong>ATF</strong> Attributes<br />
City of Los Angeles<br />
Department of Public Works – Bureau of Sanitation<br />
Air Treatment Facility Review <strong>Study</strong><br />
Preliminary <strong>ATF</strong> Attributes<br />
Value<br />
Air Flow Rate, cfm 20,000<br />
Number of Biotrickling Filters<br />
@ Contact Time of 20 seconds (27s)* (Includes one standby<br />
unit)<br />
@ Contact Time of 14 seconds (20s)* (Includes one standby<br />
3<br />
unit)<br />
Diameter, feet 12<br />
Number of Activated Carbon Vessels<br />
@ Single Carbon Media Bed (Includes one standby unit) 4<br />
@ Dual Carbon Media Bed (Includes one standby unit) 3<br />
Diameter, feet 12<br />
Number of Fans<br />
Single Carbon Media Bed 4<br />
Horsepower per Fan 30<br />
Dual Carbon Media Beds 3<br />
Horsepower per Fan 40<br />
<br />
* The contact time with the standby unit operating.<br />
The number of biotrickling filters was developed based on a contact time and the air<br />
emissions flow of 20,000 cfm. Two contact times, 14 and 20 seconds, were applied and are<br />
consistent with literature, experience and vendor designs. The contact times were developed<br />
without the standby unit in operation. Accordingly, with the standby unit in operation, which<br />
would represent the normal operating condition, the contact times would increase to 20 and<br />
27 seconds, respectively. The standby biotrickling filter unit would be operating under<br />
normal conditions for the because the time to reach acclimation for one of these units can be<br />
as long as a few weeks, and if it has to take over for another operating unit it must be ready to<br />
do so at any time. This is where biological units differ from physical-chemical systems such<br />
as wet scrubbing and dry adsorption systems like activated carbon. These systems can be<br />
waiting in the wings until they are needed before turning them on to provide the necessary<br />
service.<br />
The activated carbon vessels were based on an average face velocity through the media of 55 to 60<br />
feet per minute (fpm) and the overall flow of 20,000 cfm. This face velocity range is a standard<br />
design criteria in the industry and is selected to optimize the size of the vessel and the pressure drop<br />
across the media. Pressure drop, which equates to energy and operating cost, increases with<br />
increasing face velocity. Using these criteria, carbon vessels can consist of either a single or dual<br />
bed construction which would require four (4) and three (3) vessels, respectively. There will be a fan<br />
4<br />
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for each carbon vessel. As a result, under the single bed approach, four (4) fans at 30 horsepower<br />
(hp) each would be necessary. Under the dual bed scenario, three (3) fans at 40 hp would be needed.<br />
These <strong>ATF</strong> attributes are preliminary but do provide insight into the initial system configuration of<br />
the Mission and Jesse <strong>ATF</strong>.<br />
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