Waverley Borough Council Water Quality Assessment
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Waverley Borough Council Waverley Borough Council Water Quality Assessment 23 June 2017 Amec Foster Wheeler Environment & Infrastructure UK Limited 3 © AMEC Environment & Infrastructure UK Limited Contents Glossary 6 Summary 7 1. Introduction 9 1.1 Purpose of the Water Quality Assessment 9 1.2 Aims and objectives 9 1.3 Local Plan and the growth areas 10 2. Water Quality Assessments 12 2.1 Overview 12 2.2 Assessment methodology 12 Data collation 12 Baseline data 13 Growth Scenarios 16 Use of Simcat and River Quality Planning (RQP) tool 17 Graphical representation of Results 17 Overall assumptions and caveats for all water quality assessments 18 3. Results 20 3.1 Overview 20 3.2 Cranleigh, Alfold, Dunsfold, Ewhurst, Hascombe and Dunsfold Aerodrome Growth Areas 20 Upstream impacts 20 No deterioration – preventing class deterioration 20 No deterioration – limiting in class deterioration to below the 10% threshold 20 Length of river impacted 21 Getting to Good (or 2027 objective) 21 Downstream impacts beyond main water body 21 Indicative permit calculations 21 Impact of quicker housing growth 22 3.3 Elstead, Peper Harow and Thursley Growth Areas 24 Upstream impacts 24 No deterioration – preventing class deterioration 24 No deterioration – limiting in class deterioration to below the 10% threshold 24 Length of river impacted 24 Getting to Good (or 2027 objective) 24 Downstream impacts beyond main water body 24 Indicative permit calculations 25 3.4 Farnham, Churt, Dockenfield, Frensham and Tilford Growth Areas 27 Upstream impacts 27 No deterioration – preventing class deterioration 27 No deterioration – limiting in class deterioration to below the 10% threshold 27 Length of river impacted 27 Getting to Good (or 2027 objective) 27 Downstream impacts beyond main water body 28 Indicative permit calculations 28 3.5 Godalming, Busbridge, Hambledon, Witley Growth Areas 30 Upstream impacts 30 No deterioration – preventing class deterioration 30 No deterioration – limiting in class deterioration to below the 10% threshold 30 Length of river impacted 30 Getting to Good (or 2027 objective) 30 23 June 2017 Doc Ref. ERea008i3R 4 © AMEC Environment & Infrastructure UK Limited Downstream impacts beyond main water body 31 Indicative permit calculations 31 3.6 Bramley and Wonersh Growth Areas 33 Upstream impacts 33 No deterioration – preventing class deterioration 33 No deterioration – limiting in class deterioration to below the 10% threshold 33 Length of river impacted 33 Getting to Good (or 2027 objective) 33 Downstream impacts beyond main water body 34 Indicative permit calculations 34 3.7 Haslemere Growth Area 36 Upstream impacts 36 No deterioration – preventing class deterioration 36 No deterioration – limiting in class deterioration to below the 10% threshold 36 Length of river impacted 36 Getting to Good (or 2027 objective) 36 Downstream impacts beyond main water body 36 Indicative permit calculations 36 3.8 Chiddingfold Growth Area 38 Upstream impacts 38 No deterioration – preventing class deterioration 38 No deterioration – limiting in class deterioration to less than 10% from baseline 38 Getting to Good (or 2027 objective) 38 Downstream impacts beyond main water body 38 Indicative permit calculations 39 3.9 Dry Weather flow assessments 40 4. Conclusions 42 5. References 43 Table 1 Summary of the indicative permit standards for phosphate (annual average), BOD (95th percentile) or ammonia (95th percentile) required to get water bodies to Good Ecological Status or prevent deterioration downstream WwTWs that serve growth areas in the Waverley Local Plan. 8 Table 1.1 Growth Areas and their planned housing growth along with the relevant wastewater treatment works. 10 Table 2.1 Data collated and its purpose for the water quality assessments 13 Table 2.2 Water Framework Directive classifications for Surface Water Bodies (2015 Cycle) 14 Table 2.3 Water Framework Directive Standards for water quality (in mg\l) at sample points assessed for the seven WwTWs Error! Bookmark not defined. Figure 1.1 Growth Areas Figure 2.1 Example graph showing the Simcat model results for the water quality impacts of future housing growth due to one wastewater treatment works. 18 Figure 3.1 Modelled changes in concentrations (in mg/l), of phosphates (A - Average), BOD (B - 90%ile) and Ammonia (C - 90%ile) down the Cranleigh Waters from the upstream sample point PWER0004 to downstream sample point PWER0006, due to growth. Please note: A lack of deterioration can mean that the baseline is indistinguishable from the predicted impact line. 23 Figure 3.2 Modelled changes in concentrations (in mg/l), of Phosphates (A - Average), BOD (B - 90%ile) and Ammonia (C - 90%ile) down the River Wey from the upstream sample point PWER0110 to the end of the modelled Simcat reach downstream of Elstead WwTW, due to growth. Please note: A lack of deterioration can mean that the baseline is indistinguishable from the predicted impact line. 26 Figure 3.3 Modelled changes in concentrations (in mg/l), of Phosphates (A - Average), BOD (B - 90%ile) and Ammonia (C - 90%ile) down the River Wey from the head of the Simcat reach to downstream sample point PWER0126, due to growth. Please note: A lack of deterioration can mean that the baseline is indistinguishable from the predicted impact line. 29 Figure 3.4 Modelled changes in concentrations (in mg/l), of Phosphates (A - Average), BOD (B - 90%ile) and Ammonia (C - 90%ile) down the River Wey from the upstream sample point PWER0029 to downstream sample point PWER0151, due to growth. Please note: A lack of deterioration can mean that the baseline is indistinguishable from the predicted impact line. 32 Figure 3.5 Modelled changes in concentrations (in mg/l), of Phosphates (A - Average), BOD (B - 90%ile) and Ammonia (C - 90%ile) down the Cranleigh Waters from the upstream sample point PWER0006 to the end of the modelled Simcat reach, due to growth. Please note: A lack of deterioration can mean that the baseline is indistinguishable from the predicted impact line. 35 Figure 3.6 Modelled changes in concentrations (in mg/l), of Phosphates (A - Average), BOD (B - 90%ile) and Ammonia (C - 90%ile) down the South Wey from the head of the reach to downstream sample point PWER0026, due to growth. Please note: A lack of deterioration can mean that the baseline is indistinguishable from the predicted impact line. 37 23 June 2017 Doc Ref. ERea008i3R 5 © AMEC Environment & Infrastructure UK Limited Appendix A Input data and modelling outputs (Excel workbook) Appendix B WFD water body and growth area maps 23 June 2017 Doc Ref. ERea008i3R 6 © AMEC Environment & Infrastructure UK Limited Glossary BAT Best Available Technology BOD Biological Oxygen Demand BC Borough Council dpa dwellings per annum GES Good Ecological Status m2 Square meters mg/l Milligrams per litre Ml/d Mega litres per day P Phosphorous RQP River Quality Planning Tool RBMP River Basin Management Plan SIMCAT Environment Agency water quality model WFD Water Framework Directive WQA Water Quality Assessment WwTW Wastewater Treatment Works 23 June 2017 Doc Ref. ERea008i3R 7 © AMEC Environment & Infrastructure UK Limited Summary Waverley Borough Council (referred to as the Council in this report) identified twenty two growth areas for sustainable growth in the Waverley Local Plan to help meet their housing needs, including proposals for up to 9,383 homes, to be built by 2032. As part of the evidence base to support the Plan the Council commissioned a Water Cycle Study (WCS, Capita, 2016). The WCS aimed to identify if the housing growth could impact on water quality of rivers in the area through increased discharges of treated sewage effluent from the major wastewater treatment works. This initial WCS did identify potential constraints to housing growth. To investigate these constraints further a new Water Quality Assessment (WQA) was commissioned by the Council to clarify the potential constraints and any future impacts on water quality related to housing growth within Waverley Borough that is linked to the wastewater treatment works (WwTWs) at Chiddingfold, Cranleigh, Elstead, Farnham, Godalming, Haslemere and Shamley Green. Any impacts were to be investigated in line with the WCS guidance1 and Water Framework Directive objectives (WFD) as set out in the Thames and South East River Basin Management Plans (RBMPs), specifically: to identify the impacts on water quality in receiving watercourses from future housing growth downstream of the seven WwTWs (i.e. from increases in discharges of treated sewage effluent from 2015 onwards); clarify if future housing growth will impact on the WFD objectives below No Deterioration in class of any element. Ensuring the WFD water bodies can achieve the 2027 objectives as set out in the 2015 RBMPs Limiting in class deterioration to less than a 10% deterioration threshold from current conditions (an aspirational objective set by the Environment Agency) model the potential future discharge permit standards from the WwTWs to reverse potential deterioration in downstream river quality; and identify if there are any cumulative impacts from increases in discharges from WwTWs within the same catchment. For all growth areas housing numbers were provided for each growth period used in the WQA (i.e. 2016- 2020, 2021-2026 and 2027-2032). For the WQA increases in effluent based on assumed occupancy rates for the housing numbers were calculated and added to the current volume of treated effluent discharged from the relevant WwTWs. The impact of this increase in treated