East Cambridgeshire District Council Water Cycle Study Detailed ...

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Stage 2 Water Cycle Study: Final Report Sept 2011 26 Cambridgeshire Horizons East Cambridgeshire – Detailed WCS watercourse upstream of the discharge and several of the watercourses in the study area do not have suitable flow information to use in the assessment. In these cases, load standstill calculations have been used. Load standstill has also been used for calculation of discharge consents to tidal waters, due to the highly managed nature of fenland drainage systems. A summary of which methodology has been used for each WwTW is provided in Table 3-2 below. Table 3-2: Modelling Method used – summary Modelling Steps WwTW RQP used Load Standstill used Soham Burwell Bottisham Haddenham Witchford Littleport Little Downham Witcham The first stage of the modelling exercise was to establish the discharge consent standards that would be required to meet ‘No deterioration’; this would be the discharge consent limit that would need to be imposed on AWS immediately at the time that the growth causes the flow consent to be exceeded. No deterioration is an absolute requirement of the WFD and any development must not result in a decrease in quality downstream from the current status. The second stage was to establish the discharge consent standards that would be required to meet future Good Status under the WFD classification in the downstream waterbody. This assessment was only carried out for WwTW discharging to waterbodies where the current status is less than Good (i.e. currently Moderate, Poor or Bad). This would be the discharge consent standard that may need to be applied in the future, subject to the assessments of ‘technical feasibility’ and ‘disproportionate cost. Such assessment would be carried out as part of the formal Periodic Review process overseen by OFWAT in order to confirm that the proposed improvement scheme is acceptable. Modelling assumptions and input data Several key assumptions have been used in the water quality and consent modelling as follows: • the wastewater generation per new household is based on an assumed Occupancy Rate (OR) of 2.1 people per house 12 and an average consumption ion of 150 l/h/d (as set out in water use assumptions – section 1.6). The 150l/h/d figure makes an allowance for 12 For modelling purposes AWS uses 2.3p/d (persons per dwelling) for new properties but factor in a declining occupancy in existing properties to balance, at a regional level, forecasts of population growth and housing targets. This brings it in line with the 2.1p/d use din this detailed study. AWS have confirmed (Rob Morris email, Thu 30/06/2011 09:41) that they consider the approach taken in this study as conservative and suitable for WCS purposes. It is the same approach that has been promoted in all the WCS in the AWS region
Stage 2 Water Cycle Study: Final Report Sept 2011 27 Cambridgeshire Horizons East Cambridgeshire – Detailed WCS commercial use and use in schools and hospitals etc considered to represent increases in non-domestic use across the study area; • WwTW current flows were taken as the current consented dry weather flow (DWF). Future 2031 flows were calculated by adding the volume of additional wastewater generated by new dwellings (using an OR of 2.1, a consumption value of 150l/h/d and allowance for an increase in infiltration) to the current consented DWF value; • river flow data for the RQP modelling has been provided by the Environment Agency based on outputs from Low Flow Enterprise (LFE) models – data was provided as mean flow and Q95 13 ; • following discussion with the Environment Agency 14 it was established that the waterbody classifications and targets as provided in the River Basin Management Plan, would not be appropriate for this detailed assessment. This is because the RBMPs report a waterbody classification on a large spatial scale, whereas the actual quality of a watercourse local to a discharge may be different and needs to be considered at a local scale. Base data for modelling has therefore been provided by Environment Agency water quality planners. The WFD 'no deterioration' targets for each WwTW are the downstream status, for each water quality element, based on river monitoring data collected between 2006 and 2008. Where significant improvement has occurred since 2008, or is planned through confirmed RBMP measures, the 'no deterioration' target' is the planned status. It was requested by the Environment Agency that the actual data provided was used in preference over the published status in the RBMP. Details are provided in Appendix 2 along with the full results and outputs from the water quality modelling. • WwTW effluent quality data was not available for use in this study, therefore assumptions were applied to the discharge quality statistics ensuring consistent ratios between mean and standard deviation (or co-efficient of variation 15 ) for each parameter (see RQP print outs in Appendix 2 for details). • in order to calculate Load standstill values, where a P consent is not in place for a WwTW a starting assumption of a mean quality of discharge at 2mg/l was used 16 ; and • For the purposes of this study, the limits of conventionally applied treatment processes are considered to be: • 5mg/l for BOD; • 1mg/l for Ammoniacal-N; and • 1mg/l for Phosphate. The water quality modelling was then undertaken for the new growth figures; but, using the following steps: Step 1 – no deterioration A calculation was undertaken (using either RQP or load standstill) to determine if the receiving watercourse can maintain no deterioration downstream from the current quality with the proposed growth within limits of conventional treatment technology and what consent limits would be required. If no deterioration could be achieved, then a proposed discharge consent 13 Defined as the flow value exceeded 95% of the time i.e. a representation of low flows 14 Steve Hopper, Senior Environment Planning Officer (Water Quality), personal communication, email "RE: East Cambs and Fenland WCS - WFD classes" - Thu 03/06/2010 14:11 15 Approximately 1 for P, 0.5 for BOD and 0.33 for ammonia 16 This is a worst case assumption on the basis that many of the WwTW will not treat to this high level of P removal – therefore, if the assessment shows the stricter standard is achievable then it can be assumed that a solution will be feasible.
Page 1 and 2: East Cambridgeshire District Counci
Page 3 and 4: Table of Contents Cambridgeshire Ho
Page 5 and 6: Executive Summary Stage 2 Water Cyc
Page 7 and 8: Stage 2 Water Cycle Study: Final Re
Page 9 and 10: Surface Water Drainage Management S
Page 11 and 12: SWM5 - Linkages to SWMP and SFRA St
Page 13 and 14: Glossary of Acronyms and Abbreviati
Page 15 and 16: Abbreviation Description RTPI Royal
Page 17 and 18: 1.3 Stage 2 - Study Governance Stag
Page 21 and 22: • Surface Water Management Plan f
Page 23 and 24: 2 Proposed Growth 2.1 Preferred Gro
Page 25 and 26: 2.3 Employment Stage 2 Water Cycle
Page 27 and 28: Figure 2-1: Potential development s
Page 29: Relevant WwTW Stage 2 Water Cycle S
Page 33 and 34: WwTW Soham Burwell Bottisham Hadden
Page 36 and 37: 3.2.2 Results Discussion WwTW Soham
Page 38 and 39: WwTW Consent parameter Stage 2 Wate
Page 46 and 47: Table 3-7: Potential Impact of Clim
Page 48 and 49: 3.3 Ecological Appraisal Stage 2 Wa
Page 60 and 61: 3.4.1 Stage 2 network assessment re
Page 62 and 63: Site Description of potential waste
Page 64 and 65: Site Description of potential waste
Page 66 and 67: Bottisham Site Assessment Site Desc
Page 70 and 71: Impact on Supplies Stage 2 Water Cy
Page 76 and 77: Low flow taps and showers Stage 2 W
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Figure 4-1: A typical domestic rain
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Stage 2 Water Cycle Study: Final Re
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Medium Scenario The key assumptions
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Table 4-7: Details of new Build Spe
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WN Scenario New development Water u
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Operation of GWR £30 per annum 82
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Table 4-12: Estimated Cost of Neutr
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Figure 4-3: CO2 emissions from a
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4.4.7 Preferred strategy - delivery
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5 Surface Water Management 5.1 The
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• continuous surfaces with an inh
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5.5.1 Ecological opportunities Ely
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Site Stage 2 Water Cycle Study: Fin
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5.5.7 SuDS and groundwater protecti
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Lisle Lane, Ely 2.855 2.28 1,038 -
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Land rear of Fordham Road, Soham 2.
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6.3.3 Wastewater Network constraint
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6.4.4 Phasing Assessment Phase Dwel
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7.2 Climate Change and the Water Cy
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Directive/Legislation/Guidance Desc
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Key Additional development can be a
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Consents to achieve ‘Good Status
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MASS BALANCE CALCULATION: MONTE CAR
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LITTLEPORT STW Current Quality Cons
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HADDENHAM STW Current Quality Conse
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Sequencing Batch Reactor Stage 2 Wa
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Tertiary treatment Stage 2 Water Cy
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East Cambridgeshire WCS Flood Estim
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11 12 12 Is the discharged water on
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