Quantifying Uncontrolled Landfill Gas Emissions from Two Florida ...

Executive Summary
Waste decomposition in a municipal landfill is a biological process which occurs over multiple
decades from initial waste placement. Use of leachate recirculation is getting more widespread
use in the U.S. because it results in accelerating waste decomposition and extending landfill air
space (allowing more waste to be deposited in the landfill). Differences in how leachate and
other liquids are added and how the site is designed and managed will lead to differences in the
quantity of landfill gas that is not collected and controlled. Some landfills are designed and
operated to minimize fugitive loss such as the landfill site in Yolo County, California where
liquid is not added until synthetic liners are in place surrounding the waste mass including the
top of the cell (http://www.yolocounty.org/). Other sites are operated to add liquid as soon as
waste is placed in the landfill at the working face (U.S. EPA, 2005a). With this type of
operation, there is no ability to collect and control fugitive loss.
There are limited data on which to base the performance of wet landfills to traditional landfill
operation (i.e., not leachate recirculation). The most extensive work to date was released in 2005
and evaluated gas extraction data from twenty-nine wet landfill sites (U.S. EPA, 2005b; Faour et
al., 2007). The data were used to develop inputs for gas generation using a first-order
decomposition rate equation. For a few sites there were longer term data to evaluate trends over
time. However, most of the data were from a single sampling event (only one point in time).
None of the sites provided data on potential fugitive loss such as delays in gas collection from
waste placement or leaks in the surface cover or landfill gas header pipes and extraction wells.
The purpose of this study is to evaluate fugitive loss from two different municipal landfills which
were reported to be operating as a wet or bioreactor landfill and have an area regarded as a
“control” cell (where no additional liquid was added). Fugitive methane emissions were
measured at both sites for the “wet” and “control” cells using optical remote sensing (ORS)
technology. Two different instruments were used - an open-path tunable diode laser (OP­
TDLAS) instrument by Boreal, Inc (the Gas-Finder 2.0) and an open-path Fourier transform
infrared (OP-FTIR) instrument by IMACC, Inc. The measurements were conducted using
vertical radial plume mapping (VRPM) to calculate net methane-flux emission values from the
top and side slopes of each landfill cell. In addition to the ORS measurements, SUMMA canister
samples were collected from the gas header pipes at the sites to obtain data on trace constituents
in landfills gas including non-methane organic compounds (NMOC), hydrogen sulfide, mercury,
and other hazardous air pollutants (HAPs).
Problems were encountered during the field test. An intercomparison study was planned to
ensure no bias in measurements when using two different ORS instruments (i.e., OP-FTIR and
TDL). A regression analysis indicated that the TDL-AS instrument indicating a potential 40%
bias. However, the very limited number of measurements (n = 7) and the poor regression
coefficient (r 2 = 0.20), raise questions as to the validity of the intercomparison results. Previous
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