Water Quality Assessment V2.0.Pdf

Water Quality Assessment

A.1 Introduction The increased discharge of effluent due to an increase in the population served by a WwTW may impact on the quality of the receiving water. The Water Framework Directive (WFD) does not allow a watercourse to deteriorate from its current class (either water body or element class). It is EA policy to model the impact of increasing effluent volumes on the receiving watercourse. Where the scale of development is such that a deterioration is predicted, a new Environmental Permit (EP) may be required for the WwTW to improve the quality of the final effluent, so that the extra pollution load will not result in a deterioration in the water quality of the watercourse. This is known as "no deterioration" or "load standstill". The Environment Agency operational instruction “Water Quality Planning: no deterioration and the Water Framework Directive”1 sets out a hierarchy for how the no-deterioration requirements should be implemented on inland waters:  deterioration exceeds 10% of existing water quality immediately downstream of the discharge. This 10% target is included, not because it is a statutory requirement of the WFD, but to ensure that all the environmental capacity is not taken up by one phase of development and there is sufficient capacity for future growth.  Deterioration beyond the class limit immediately downstream of the discharge. For example, a watercourse currently in the Moderate class for ammonia moving to Poor. For the purpose of this WCS, these two methods for determining deterioration immediately downstream of the point of discharge have been applied, based on the principle that the WCS should, where possible, guide development to locations where it will not lead to environmental deterioration or require investment with a low cost-benefit being required to prevent deterioration. If the receiving watercourse is classed as "Bad" then no further deterioration is permitted, and, again within this study, this rule has also been applied immediately downstream of the point of discharge. EA policy allows alternative definitions of deterioration to be applied where it can be demonstrated that meeting the above criteria would be technically infeasible or where the costs of achieving no- deterioration is disproportionate to the cost. These alternative definitions of deterioration include allowing up to 15% of the water body or 1.5 km of classified watercourse length (whichever is the lower amount) to be in worse condition than the overall status, and assessing class limit deterioration at a downstream monitoring point. Application of these alternative approaches was considered to be beyond the scope of this WCS. It is, however, anticipated that these alternative approaches may be applied by the sewerage undertakers in their negotiations with the Environment Agency to determine future consents. Anglian Water and Thames Water prepared a RAG analysis of the capacity and performance of all WwTWs within Aylesbury Vale which may see increased flows due to housing allocations. This analysis identified 17 WwTWs with potential future capacity issues due to growth. Aylesbury Vale requested that a water quality impact assessment should be carried out at these 15 WwTWs: Anglian Water  Buckingham  Great Horwood  Ivinghoe  Padbury  Stanbridgeford  Steeple Claydon  Whaddon  Wing Cublington  Winslow Thames Water

1 Environment Agency (2012) Water Quality Planning: no deterioration and the Water Framework Directive. Accessed online at http://www.fwr.org/WQreg/Appendices/No_deterioration_and_the_WFD_50_12.pdf on 03/10/2016

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 Aylesbury  Haddenham  Long Crendon  Stone  Waddesdon  Worminghall Note that Brackley and Cotton Valley WwTWs were excluded in this assessment as they are located outside of Aylesbury Vale, and both will receive the vast majority of their growth from South Northamptonshire and Milton Keynes respectively. This WCS assesses the potential water quality impacts due to growth in WwTW effluent flows and loads at the WwTW discharge points. Please note that, whilst the other WwTWs not considered in this assessment may have capacity within their consents to accommodate the planned growth scenarios, this does not necessarily imply that the watercourse would, with the existing consent, be able to meet Good Status. Additionally, it does not imply that future increases in discharges within the permitted consent would not lead to a deterioration occurring.

A.2 Standards The WFD targets for Good Ecological Status (GES) for Biological Oxygen Demand (BOD), Ammonia (NH4) and Phosphorus (P) set by the EA for lowland and high alkalinity water bodies are shown in Table 1 below. Table 1: WFD targets for lowland and high alkalinity water bodies Determinand Statistic Target BOD 90 percentile 5gm/l

NH4 90 percentile 0.6mg/l P Mean reach specific

The EA has provided WFD 2015 set catchment/reach specific targets for phosphorus. On this basis the following targets (see Table 2) have been used at the WwTW discharge points assessed: Table 2: Phosphorus targets for "Good" status by WwTW WwTW P mean mg/l Waterbody/ WQ point Buckingham 0.08 GB105033037920 Great Horwood 0.076 GB105033038200 Ivinghoe 0.073 GB105033030490 Padbury 0.077 GB105033038220 Stanbridgeford 0.12 GB105033030530 Steeple Claydon 0.073 GB105033038220 Whaddon 0.08 GB105033037870 Wing Cublington 0.073 GB105033030540 Winslow 0.076 GB105033030570 Aylesbury 0.066 GB106039030410 Haddenham 0.081 GB106039030270 Long Crendon 0.066 GB106039030410 Stone 0.081 GB106039030270 Waddesdon 0.08 GB106039030420 Worminghall 0.081 GB106039030340

A.3 Methodology

The contaminants assessed were Biological Oxygen Demand (BOD), Ammonia (NH4) and Phosphorus (P).

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The selected approach was to use the EA River Quality Planning (RQP) tool in conjunction with their recommended guidance documents. "Water Quality Planning: no deterioration and the Water Framework Directive" and "Horizontal Guidance". This uses a steady-state Monte Carlo Mass Balance approach where flows and water quality are sampled from modelled distributions based on data where available. The data required to run the RQP software were: Upstream river data:  Mean flow  95% exceedance flow  Mean for each contaminants  Standard deviation for each contaminant Discharge data:  Mean flow  Standard deviation for the flow  Mean for each contaminant River quality target data:  No deterioration target  'Good status' target

The above data inputs should be based on observations where available. In the absence of observed data EA guidance require that the following values were used:  Flow mean: 1.25*DWF  Flow SD: 1/3*mean  Quality data: permit values or assumed values recommended by the Environment Agency If observed river flows were not available these were obtained from an existing model or a low-flows estimation software. If observed water quality data were not available these were obtained from an existing model or a neighbouring catchment with similar characteristics, or the mid-point of the WFD class. The observed data available for WwTWs discharges were analysed in the statistical tool, Aardvark and the values reported as "less than" (these are samples where it was not possible to get an accurate value and a limit value was assigned) were multiplied by 0.5 as agreed with the EA.

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A.4 Study Objectives RQP models were required to be set up and run using the present-day and a single future scenario representing development of all draft site locations (housing and employment) which would drain to each WwTW as reported in Table 3 below. Table 3: present day and future scenarios to model

Mean DWF (Ml/d) WwTW Future growth Percentage Present day Future growth Total Change Buckingham 4.63 0.713 5.34 115% Great Horwood 0.54 1.537 2.08 385% Ivinghoe 1.33 0.106 1.44 108% Padbury 0.36 0.023 0.38 106% Steeple Claydon 0.951 0.059 1.01 106% Whaddon 0.214 0.651 0.86 404% Wing Cublington 0.85 0.080 0.93 109% Winslow 1.77 0.335 2.11 119% Stanbridgeford 3.10 0.057 3.16 102% Aylesbury 24.11 5.191 29.30 122% Haddenham 2.05 1.826 3.88 189% Long Crendon 0.58 0.076 0.66 113% Stone 0.99 0.075 1.06 108% Waddesdon 0.658 0.098 0.76 115% Worminghall 0.76 0.057 0.82 107%

The study was required to consider increase to effluent flows as a result of development in each settlement to assess the impact of the increased contaminant loads on the receiving watercourses. These results were required to assess the potential impact on the watercourse which could cause the failure of one of these targets: Good Ecological status (GES), no more than 10% deterioration and no class deterioration. Where a WCS is predicted to lead to a WFD class deterioration, or a deterioration of greater than 10%, or a 'good status' failure it is necessary to determine a possible future permit value which would prevent a class deterioration using the RQP function tool that calculates the required discharge quality according to the specific river target. Where failure was predicted for any of the other scenarios, and the present-day upstream river quality did not achieve 'good status', the model was re-run for present-day and future effluent flows assuming that the river had 'good status', in order to assess whether the planned growth could prevent the watercourse from meeting GES in the future. When a new consent value was calculated, due to a target failure, this was compared against the effluent quality that can be achieved using Best Available Technology (BAT). The EA advised the following permit values are achievable using Best Available Technology and that these values should be used for modelling all WwTW potential capacity irrespective of the existing treatment technology and size of the works:  BOD (95%ile) = 5 mg/l  Ammonia (95%ile) = 1mg/l  Phosphorus (mean) = 0.5 mg/l Note that phosphorus removal is the subject of ongoing national trials investigating novel techniques and optimisation of existing methods. This major study, which involves all UK water companies, is not due to report until 2017, therefore this assessment is based on the current assumption of BAT for phosphorus. Water companies and the EA are continuing to apply 0.5mg/l as representing BAT for phosphorous, until the study's results become available.

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This assessment did not take into consideration whether it Is feasible to upgrade each existing WwTW to BAT due to constraints of costs, timing, space, carbon costs etc. The increase of DWF for each Anglian Water WwTW was calculated by using an occupancy rate of 2.4 persons per dwelling and a consumption of 133 l/p/d as considered by the Water Resource Management Plans (WRMPs), with 95% of flow reaching the WwTW (it is assumed that this is intended to represent an allowance for base infiltration in the sewer flows). The increase of DWF for each Thames Water WwTW was calculated by using an occupancy rate of 2.5 persons per dwelling and a consumption of 125 l/p/d as considered by the Water Resource Management Plans (WRMPs), with 95% of flow reaching the WwTW.

A.5 Data Collection The datasets required to assess the discharge permits were the following:  River flow data (received from the EA)  River quality data (received from the EA)  Current WwTW permits (received from the EA)  RQP tool (received from the EA)  Existing water quality models: GIS SIMCAT model (received from the EA)  Current river classifications (received from the EA)

 2015 WFD river target for BOD, P and NH4 (received from the EA)  EA guidance documents (received from the EA)  WwTW flow and quality data (received from the EA)  WwTW discharge information e.g. location, receiving watercourse, etc. (received from the EA).

A.6 WFD Compliance Compliance against WFD targets for the scenarios modelled was calculated using the Present Day situation as the baseline. Compliance / or non-compliance is indicated on the results tables as follows:

Modelled water quality is Modelled water quality does not within the WFD target for the meet the WFD target for the determinand in question. determinand in question.

The status of the receiving watercourse is reported using the same traffic-colour used by the EA "Method statement for the classification of surface water bodies v3" as shown in Figure 1. The 'Ecological status' is defined as the lowest class element between the 'Biological quality elements', the 'general chemical and physiochemical quality elements' and the 'hydromorphological quality elements'. Each element is classified as bad, poor, moderate, good or high. The 'Chemical status' is defined as the lowest classed substance defined in the 'priority substances and other EU level dangerous substances'. Each substance is classified as fail or good. For each WwTW a summary table (based on Table 4) for the receiving watercourse reports the single status for BOD, NH4 and P, the overall status, the 2015 WFD classifications, and the overall objectives for the watercourse. The EA did not provide the 'Ecological' and 'Chemical' status.

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Table 4: Summary table representing 2015 status, watercourse status and its objectives

Overall BOD Ammonia Phosphorus

Overall Watercourse's Watercourse's Watercourse's 2015 status watercourse's status for BOD status for NH4 status for P status

Overall Watercourse's Watercourse's Watercourse's Objective watercourse's objective for BOD objective for NH4 objective for P objective

Figure 1: Classification of Surface Water from "Method statement for the classification of surface water bodies v3"

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A.7 Input Data The input data and RQP results tables in sections A.8 and A.9 used to summarise the modelling exercise the source of each component of the modelling data. The list below explains the meaning of the data sources referenced:  Low Flow software: values calculated using the Low Flow software.  Mid class "class": mid-point of the permissible pollutant concentrations for the watercourse's current classification. This was used when no observed data were available.  Assumed mid class "class": the mid class of the pollutant class is assumed. This was used when no observed and classification data were available.  Observed data: obtained from statistical analysis of observed data.  EA suggested value: valued used by the EA when no observed or consent data are available.  Calculated using AW parameters: an occupancy rate of 2.4 p/h, a water consumption of 133 l/p/d and a 95% flow reaching the work were used to calculate the future DWF (based on advice from Anglian Water  Calculated using TW parameters: an occupancy rate of 2.5 p/h, a water consumption of 125 l/p/d and a 95% flow reaching the work were used to calculate the future DWF (based on advice from Thames Water The DWF limit assessment was carried out by comparing the Dry Weather Flow (DWF) permit value against the 90-percentile flow (Q90) in accordance with the EA approach to calculating DWF2. The former was provided by the EA whilst the latter was calculated by JBA using the observed data provided. The DWF limit and Q90 are shown in Table 5 below (see relevant paragraphs for the data analysis details):

Table 5: DWF Permit Conditions

WwTW DWF Permit Conditions (m3/d) Buckingham 3700 Great Horwood 548 Ivinghoe 1066 Padbury 289 Steeple Claydon 791 Whaddon 162 Wing Cublington 680 Winslow 1417 Stanbridgeford 2482 Aylesbury 11504 Haddenham 440 Long Crendon 273 Stone 16 Waddesdon 251 Worminghall 821

The determinands consent limits were assessed by comparing the current limit against the RQP calculated value. These are reported on

2 An Improved Definition of Sewage Treatment Works Dry Weather Flow: http://pioneer.tynemarch.co.uk/tynemarch/publications/msciwemymp.pdf

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Table 6 below.

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Table 6: Determinands consent limits and RQP calculated values

BOD (mg/l) NH4 (mg/l) P (mg/l) 95%ile 95%ile Mean WwTW Scenario Modelled Modelled Modelled consent consent consent 95%ile 95%ile mean value value value Present 6.99 2.34 0.76 Buckingham 20 10 2 Future 6.99 2.34 0.76 Great Present 13.97 Not 5.26 Not 4.21 40 Horwood Future 13.97 Available 5.26 Available 4.21

Present 3.61 2.12 Not 4.34 Ivinghoe 13 3 Future 3.61 2.12 Available 4.34

Present 7.67 Not 10.87 Not 6.85 Padbury 20 Future 7.67 Available 10.87 Available 6.85

Steeple Present 13.88 2.46 Not 6.5 25 10 Claydon Future 13.88 2.46 Available 6.5

Whaddon Present 7.05 Not 3.67 Not 5.16 30 Future 7.05 Available 3.67 Available 5.16

Wing Present 11.94 5.7 Not 6.23 15 10 Cublington Future 11.94 5.7 Available 6.23

Present 9.22 4.44 Not 5.74 Winslow 15 5 Future 9.22 4.44 Available 5.74 Present 3.66 0.34 0.45 Stanbridgeford 20 12 2 Future 3.67 0.34 0.45

Present 4.54 0.49 Not 0.72 Aylesbury 10 2 Future 4.54 0.49 Available 0.72

Present 3.84 0.28 Not 3.37 Haddenham 50 20 Future 3.84 0.28 Available 3.37

Present 4.07 Not 0.57 Not 6.30 Long Crendon 30 Future 4.07 available 0.57 available 6.3

Present 15.7 7.08 Not 5.17 Stone 50 20 Future 15.7 7.08 Available 5.17

Present 15.05 Not 3.98 Not 5.22 Waddesdon 30 Future 15.05 available 3.98 available 5.22

Present 8.59 3.09 Not 5.56 Worminghall 12 5 Future 8.59 3.09 available 5.56

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A.8 Anglian Water WwTWs

A.8.1 Buckingham WwTW Buckingham WwTW discharges into the Great Ouse as shown in Figure 2. The status of the receiving watercourse is summarised in Table 7. Figure 2: Buckingham WwTW Discharge Location

Legend #* WRC !( WQ Point Detailed River Network WFD river classification High Good Moderate Poor Bad

BUCKINGHAM STW #*

01M07 !(

Contains OS data © Crown copyright and database right (2016)

Table 7: Great Ouse watercourse status and objectives

Overall BOD Ammonia Phosphorus 2015 Moderate High High Moderate status Not Objective High High Good available

Table 8 shows the input data and RQP results for Buckingham. The works has permitted values for DWF, BOD, NH4 and P and is currently operating within these limits. The works has slightly exceeded the DWF. Future scenarios predict that the work will still be operating within the limits for all pollutants.

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Table 8: Input data and RQP results for Buckingham WwTW

Present Day Future growth

Parameter Statistic River Source Deterioration RQP RQP WRC Source WRC Source Result Result

Mean 130.10 4.63 5.34 Calculated Low Flow Based on Flow (Ml/d) using AW SD Softw are 1.54 Permitted DWF 1.78 parameters 5%ile 33.61

Mean 1.39 Observed 3.08 3.08 Observed Observed Data Data Data BOD (mg/l) SD 0.80 2.03 2.43 2.03 2.45 1% Target 4.00 2015 WFD 90%ile Mean 0.05 Observed 0.72 0.72 Observed Observed Data Data Data NH4 (mg/l) SD 0.12 0.97 0.17 0.97 0.18 6% Target 0.30 2015 WFD 90%ile Mean 0.12 Observed 0.74 0.74 Observed Observed Data P (mg/l) SD 0.08 Data 0.43 0.15 0.43 Data 0.16 7% Target Mean 0.08 2015 WFD Mean 0.062 Assumed 0.74 0.74 Mid Class Observed Data P (mg/l) SD 0.062 Good 0.43 0.1 0.43

Target Mean 0.08 2015 WFD

The model results indicate that for BOD and NH4 there is no class deterioration and both pollutants meet the 2015 WFD target. Phosphate is the only pollutant which currently fails the WFD target with a Moderate status but there is no class deterioration. There are no deteriorations greater than 10% for Buckingham WwTW. The RQP model was used to calculate whether the watercourse could meet GES for Phosphate. The model results in Table 9 indicate that GES is not achievable for the present day or future flows, even assuming Good Ecological Status upstream and BAT at Buckingham WwTW without improving upstream water quality. Therefore, the watercourse is unable to meet GES as a consequence of current technological limits, not as a result of the proposed development.

Table 9: Discharge quality required to meet good WFD targets for P at Buckingham WwTW

WRC Pollutant Target Upstream river quality Scenario Mean SD 95%ile Conclusion

BAT Not Achievable Without Buckingham P 0.08 Moderate Future Grow th Not Achievable Improving Upstream Quality

BAT Not Achievable Without Buckingham P 0.08 Moderate Present Day Not Achievable Improving Upstream Quality

Buckingham P 0.08 Assumed Mid Class Good Present Day 0.43 0.24 0.89 Doesn’t Achieve BAT Target

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A.8.2 Great Horwood WwTW Great Horwood WwTW discharges into the Horwood Tributary as shown in Figure 3. The watercourse has a very small upstream catchment, and consequently the treated effluent provides the majority of the flow in the watercourse. The status of the receiving watercourse is summarised in Table 10. Figure 3: Great Horwood WwTW discharge location

Legend *# WRC !( WQ Point Detailed River Network WFD river classification High Good Moderate Poor GT.HORWOOD STW F/E Bad *#

Contains OS data © Crown copyright and database right (2016)

Table 10: Horwood Tributary watercourse status and objectives

Overall BOD Ammonia Phosphorus 2015 Moderate Good Good Poor status High by High by Good by Objective Moderate 2027 2027 2027

Table 11 shows the input data and RQP results for Great Horwood. The works has permitted values for DWF and BOD and is currently operating within these limits. Future scenarios predict that the work will still be operating within the limits for all the pollutants.

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Table 11: RQP inputs and results of Great Horwood WwTW

Present Day Future growth Parameter Statistic River Source Deterioration RQP RQP WRC Source WRC Source Result Result

Mean 0.02 0.54 2.08 Based on Calculated Low Flow Flow (Ml/d) SD 0.33 Permitted 1.262 using AW Softw are DWF parameters 5%ile 0.004

Mean 2.58 4.26 4.26 Mid Class Observed Observed Good Data Data BOD (mg/l) SD 1.55 5.89 9.59 5.89 9.95 4%

Target 5.00 2015 WFD 90%ile Mean 0.22 1.49 1.49 Mid Class Observed Observed Good Data Data NH4 (mg/l) SD 0.22 2.52 3.44 2.52 3.58 4% Target 0.60 2015 WFD 90%ile Mean 1.00 4.15 4.15 Mid Class Observed Observed Poor Data Data P (mg/l) SD 1.10 1.42 4.10 1.42 4.18 2% Target 0.076 2015 WFD Mean

Mean 0.085 Assumed 4.15 Observed Mid Class Data P (mg/l) SD 0.085 Good 1.42 4.07

Target 0.076 2015 WFD Mean

The model results indicate that all the pollutants fail to meet the 2015 target for both the present day and future scenarios. There is no class deterioration or deterioration of greater than 10% for any pollutants. However, for BOD, NH4 and P there is a deterioration within the 'Bad' ecological status class which is not permitted; revision of the permit is likely to be required. The RQP model was used to calculate whether the watercourse could achieve Good Ecological Status (GES) for BOD, NH4 and P. The model results in Table 12 indicates that GES is achievable for BOD. However, GES is not achievable for NH4 or P for the present day flows, even assuming Good status upstream and BAT at the WwTW for P without improving the upstream water quality. Therefore, the watercourse is unable to meet GES as a consequence of current technological limits, not as a result of the proposed development. Table 12: Discharge quality required to meet good WFD targets for P at Great Horwood WwTW

WRC Pollutant Target Upstream river quality Scenario Mean SD 95%ile Conclusion

Great Horw ood BOD 5 Good Future Grow th 2.20 2.66 7.01 Reaches BAT Target

Great Horw ood BOD 5 Good Present Day 2.25 2.73 7.20 Reaches BAT Target

Great Horw ood NH4 0.6 Good Future Grow th 0.25 0.36 0.88 Doesn't Reach Target

Great Horw ood NH4 0.6 Good Present Day 0.26 0.37 0.91 Doesn't Reach Target

Great Horw ood P 0.076 Poor Future Grow th 0.07 0.02 0.11 Doesn't Reach Target

Great Horw ood P 0.076 Poor Present Day 0.04 0.01 0.07 Doesn't Reach Target

Great Horw ood P 0.076 Assumed Mid Class Good Present Day 0.08 0.03 0.12 Doesn't Reach Target

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A.8.3 Ivinghoe WwTW Ivinghoe WwTW discharges into the Whistle Brook as shown in Figure 4. The status of the receiving watercourse is summarised in Table 13. Figure 4: Ivinghoe WwTW discharge location

Legend #* WRC !( WQ Point Detailed River Network WFD river classification High IVINGHOE STW Good #* Moderate Poor Bad

Contains OS data © Crown copyright and database right (2016)

Table 13: Whistle Brook watercourse status and objectives

Overall BOD Ammonia Phosphorus 2015 Moderate High High Poor status Not Objective High High Good available

Table 14 shows the input data and RQP results for Ivinghoe. The works has permitted values for DWF, BOD, and NH4 is currently operating within these limits. Future scenarios predict that the work will still be operating within the limits for all determinands.

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Table 14: Input data and RQP results for Ivinghoe WwTW

Present Day Future growth Parameter Statistic River Source Deterioration RQP RQP WRC Source WRC Source Result Result

Mean 2.70 1.33 1.44

Based on Calculated Low Flow Flow (Ml/d) SD 0.44 Permitted 0.48 using AW Softw are DWF parameters

5%ile 0.17

Mean 1.15 1.46 1.46 Mid Class Observed Observed High Data Data BOD (mg/l) 2.26 2.28 1% SD 0.69 1.13 1.13

Target 2015 4.00 90%ile WFD Mean 0.09 Mid Class 0.73 Observed 0.73 Observed High Data Data NH4 (mg/l) SD 0.05 0.77 0.88 0.77 0.91 3% Target 2015 0.30 90%ile WFD Mean 1.00 Mid Class 4.30 Observed 4.30 Observed Poor Data Data P (mg/l) SD 1.10 1.65 2.7 1.65 2.75 2% Target 2015 0.073 Mean WFD Mean 0.056 Mid Class 4.30 Observed Good Data P (mg/l) SD 0.056 1.65 2.23 Target 2015 0.073 Mean WFD The model results indicate that BOD is the only pollutant that meets the 2015 WFD target and there is no class deterioration. Both NH4 and P fail the WFD target but there is no class deterioration for either. There are no deteriorations greater than 10% for Ivinghoe, however for P there is a predicted deterioration within the 'Bad' ecological class which is not permitted; revision of the permit is likely to be required. The RQP model was used to calculate whether the watercourse could meet Good Ecological Status (GES) for NH4 and P. The model results in Table 15 indicates that GES is not achievable for the present day or future flows without improving upstream quality, even assuming Good status upstream and BAT at the WwTW. Therefore, the watercourse is unable to meet GES as a consequence of current technological limits, not as a result of the proposed development.

Table 15: Discharge quality required to meet good WFD targets for NH4 and P at Ivinghoe WwTW

WRC Pollutant Target Upstream river quality Scenario Mean SD 95%ile Conclusion

Ivinghoe NH4 0.3 Mid Class High Present Day 0.23 0.22 0.65 Doesn’t meet BAT target

BAT Not Achievable Without Ivinghoe P 0.073 Poor Future Grow th Not Achievable Improving Upstream Quality

BAT Not Achievable Without Ivinghoe P 0.073 Poor Present Day Not Achievable Improving Upstream Quality

BAT Not Achievable Without Ivinghoe P 0.181 Poor Future Grow th Not Achievable Improving Upstream Quality

BAT Not Achievable Without Ivinghoe P 0.181 Poor Present Day Not Achievable Improving Upstream Quality

Ivinghoe P 0.073 Assumed Mid Class Good Present Day 0.09 0.03 0.15 Doesn’t Meet BAT target

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A.8.4 Padbury WwTW Padbury WwTW discharges into the Padbury Brook as shown in Figure 5. The status of the receiving watercourse is summarised in Table 16. Figure 5: Padbury WwTW discharge location

Legend #* WRC !( WQ Point Detailed River Network WFD river classification High Good Moderate Poor Bad

PADBURY STW #*

Contains OS data © Crown copyright and database right (2016)

Table 16: Padbury Brook watercourse status and objectives

Overall BOD Ammonia Phosphorus 2015 Moderate High High Poor status Not Objective High High Good available

Table 17 shows the input data and RQP results for Padbury. The works has permitted values for DWF and BOD is currently operating within these limits. Future scenarios predict that the work will still be operating within the limits for all determinands.

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Table 17: Input data and RQP results for Padbury WwTW

Present Day Future growth Parameter Statistic River Source Deterioration RQP RQP WRC Source WRC Source Result Result

Mean 126.30 0.36 0.38 Based on Calculated Flow Low Flow SD 0.12 Permitted 0.13 using AW (Ml/d) Softw are DWF parameters 5%ile 14.16

Mean 1.41 6.07 6.07 Observed Observed Observed Data Data Data BOD (mg/l) SD 0.87 2.51 2.49 2.51 2.49 0%

Target 2015 4.00 90%ile WFD Mean 0.05 Observed 3.69 Observed 3.69 Observed Data Data Data NH4 (mg/l) SD 0.06 2.06 0.15 2.06 0.15 0% Target 2015 0.30 90%ile WFD Mean 0.51 Observed 6.77 Observed 6.77 Observed Data Data Data P (mg/l) SD 0.26 1.63 0.55 1.63 0.56 2% Target 2015 0.077 Mean WFD Assumed Mean 0.059 6.77 Observed Mid Class Data P (mg/l) SD 0.059 Good 1.63 0.11 Target 2015 0.077 Mean WFD

The model results indicate that BOD and NH4 both meet the 2015 WFD target and has no class deterioration. P is the only pollutant which fails the target but there is no class deterioration. There are no deteriorations greater than 10% for Padbury. The RQP model was used to calculate whether the watercourse could meet Good Ecological Status (GES) for P. The model results in Table 18 indicates that GES is not achievable for the present day or future flows with the current upstream water quality. However, GES could be achieved upstream, this could be maintained downstream of the WwTW for both the present-day and future growth scenarios, within the limits of current BAT. Therefore, development can be accommodated with a tighter permit and upgrade to treatment.

Table 18: discharge quality required to meet good WFD targets for P at Padbury WwTW

WRC Pollutant Target Upstream river quality Scenario Mean SD 95%ile Conclusion

BAT Not Achievable Without Padbury P 0.077 Poor Future Grow th Not Achievable Improving Upstream Quality

BAT Not Achievable Without Padbury P 0.077 Poor Present Day Not Achievable Improving Upstream Quality

BAT Not Achievable Without Padbury P 0.188 Poor Future Grow th Not Achievable Improving Upstream Quality

BAT Not Achievable Without Padbury P 0.188 Poor Present Day Not Achievable Improving Upstream Quality

Padbury P 0.077 Assumed Mid Class Good Future Grow th 2.57 0.61 3.67 Reaches BAT Target

Padbury P 0.077 Assumed Mid Class Good Present Day 2.70 0.64 3.85 Reaches BAT Target

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A.8.5 Stanbridgeford WwTW Stanbridgeford WwTW discharges into the Ouzel Brook as shown in Figure 6. The status of the receiving watercourse is summarised in Table 19. Figure 6: Stanbridgeford WwTW discharge location

Contains OS data © Crown copyright and database right (2016)

Table 19: Ouzel Brook watercourse status and objectives

Overall BOD Ammonia Phosphorus No 2015 Status Moderate High Poor Available Moderate No Objective High Poor by 2015 by 2015 Available

Table 20 shows the input data and RQP results for Stanbridgeford. The works has permitted values for DWF, BOD, and NH4 is currently operating within these limits. Future scenarios predict that the work will still be operating within the limits for all determinands.

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Table 20: Inputs and RQP Results for Stanbridgeford WwTW

Present Day Future growth Parameter Statistic River Source Deterioration RQP RQP WRC Source WRC Source Result Result

Mean 9.50 3.10 3.16 Based on Calculated Flow Low Flow SD 1.03 Permitted 1.050 using AW (Ml/d) Softw are DWF parameters 5%ile 0.95

Mean 1.47 3.17 3.17 Observed Observed Observed Data Data Data SD 0.87 2.74 2.74 BOD (mg/l) 3.66 3.67 0% Target 4.00 2015 WFD 90%ile

Mean 0.05 Observed 0.31 Observed 0.31 Observed Data Data Data NH4 (mg/l) 0.34 0.34 SD 0.11 0.42 0.42 0% Target 0.30 2015 WFD 90%ile Mean 0.27 Observed 0.72 Observed 0.72 Observed P (mg/l) SD 1.57 Data 0.74 Data 0.45 0.74 Data 0.45 0% Target Mean 0.12 2015 WFD Assumed Mean 0.085 0.72 Observed Mid Class Data P (mg/l) SD 0.085 Good 0.74 0.33

Target Mean 0.12 2015 WFD

The model results indicate that P fails to meet the 2015 targets. There are no class deteriorations or deteriorations greater than 10% for any of the pollutants. There are no deteriorations greater than 10% for Stanbridgeford. The RQP model was used to calculate whether the watercourse could meet Good Ecological Status (GES) for NH4 and P. The model results in Table 21 indicate that High Ecological Status would not be achievable for NH4 with the present day and future flows. For P, GES is also not achievable for the present day or future flows, even assuming GES upstream and BAT at the WwTW. Therefore, the watercourse is unable to meet GES as a consequence of current technological limits, not as a result of the proposed development. Table 21: Discharge quality required to meet good WFD targets for NH4 and P at Stanbridgeford WwTW

WRC Pollutant Target Upstream river quality Scenario Mean SD 95%ile Conclusion

Stanbridgeford NH4 0.30 High Future Grow th 0.27 0.32 0.85 Doesn’t Meet BAT target

Stanbridgeford NH4 0.30 High Present Day 0.27 0.33 0.86 Doesn’t Meet BAT target

BAT Not Achievable Without Stanbridgeford P 0.12 Poor Future Grow th Not Achievable Improving Upstream Quality

BAT Not Achievable Without Stanbridgeford P 0.12 Poor Present Day Not Achievable Improving Upstream Quality

Stanbridgeford P 0.25 Poor Future Grow th 0.22 0.20 0.60 Doesn’t Meet BAT target

Stanbridgeford P 0.25 Poor Present Day 0.22 0.20 0.60 Doesn’t Meet BAT target

Stanbridgeford P 0.12 Assumed Mid Class Good Future Grow th 0.17 0.16 0.49 Doesn’t Meet BAT target

Stanbridgeford P 0.12 Assumed Mid Class Good Present Day 0.18 0.17 0.49 Doesn’t Meet BAT target

2016s3990 - Water Quality Assessment v2.0 19

A.8.6 Steeple Claydon WwTW Steeple Claydon WwTW discharges into the Claydon Brook as shown in Figure 7. The status of the receiving watercourse is summarised in Table 22. Figure 7: Steeple Claydon WwTW discharge location

Legend #* WRC !( WQ Point Detailed River Network WFD river classification !( High Good 02M10 Moderate !( Poor Bad

STEEPLE CLAYDON STW #*

Contains OS data © Crown copyright and database right (2016)

Table 22: Steeple Claydon watercourse status and objectives

Overall BOD Ammonia Phosphorus 2015 Moderate High High Poor status Not Objective High High Good available

Table 23 shows the input data and RQP results for Steeple Claydon. The works has permitted values for DWF, BOD, and NH4 is currently operating within these limits. Future scenarios predict that the work will still be operating within the limits for all determinands.

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Table 23: Inputs and RQP results for Steeple Claydon WwTW

Present Day Future growth Parameter Statistic River Source Deterioration RQP RQP WRC Source WRC Source Result Result

Mean 58.46 0.951 1.01 Based on Calculated Flow Low Flow SD 0.317 Permitted 0.34 using AW (Ml/d) Softw are DWF parameters 5%ile 7.27

Mean 1.15 Mid Class 5.87 Observed 5.87 Observed High Data Data BOD (mg/l) SD 0.69 4.17 2.21 4.17 2.23 1% Target 2015 4.00 90%ile WFD Mean 0.09 Mid Class 0.94 Observed 0.94 Observed High Data Data NH4 (mg/l) SD 0.05 0.81 0.20 0.81 0.20 0% Target 2015 0.30 90%ile WFD Mean 0.127 Mid Class 6.43 Observed 6.43 Observed Poor Data Data P (mg/l) SD 0.127 1.46 0.34 1.46 0.35 3% Target 2015 0.073 Mean WFD Assumed Mean 0.056 6.43 Observed Mid Class SD 0.056 1.46 Data P (mg/l) Good 0.27 Target 2015 0.073 Mean WFD

The model results indicate that BOD and NH4 both meet the 2015 WFD target and has no class deterioration. P is the only pollutant which fails the target but there is no deterioration. There are no deteriorations greater than 10% for Steeple Claydon. The RQP model was used to calculate whether the watercourse could meet Good Ecological Status (GES) for Phosphate. The model results in Table 24 indicates that GES is not achievable for the present day or future flows. The watercourse could achieve Moderate Status using BAT and if GES could be achieved upstream, this could be maintained downstream of the WwTW for the present- day scenario, within the limits of current BAT. Therefore, development can be accommodated with a tighter permit and upgrade to treatment.

Table 24: discharge quality required to meet good WFD targets for P at Steeple Claydon WwTW

WRC Pollutant Target Upstream river quality Scenario Mean SD 95%ile Conclusion

BAT Not Achievable Without Steeple Claydon P 0.073 Poor Future Grow th Not Achievable Improving Upstream Quality

BAT Not Achievable Without Steeple Claydon P 0.073 Poor Present Day Not Achievable Improving Upstream Quality

Steeple Claydon P 0.181 Poor Future Grow th 1.63 0.36 2.28 Reaches BAT Target

Steeple Claydon P 0.181 Poor Present Day 1.71 0.38 2.40 Reaches BAT Target

Steeple Claydon P 0.073 Assumed Mid Class Good Present Day 0.55 0.12 0.77 Reaches BAT Target

2016s3990 - Water Quality Assessment v2.0 21

A.8.7 Whaddon WwTW Whaddon WwTW discharges into head of the Wealden Brook as shown in Figure 8. The watercourse has a very small upstream catchment, with a calculated mean daily flow of only 0.03Ml/D. Consequently the treated effluent provides the majority of the flow in the watercourse. The status of the receiving watercourse is summarised in Table 25. Figure 8: Whaddon WwTW discharge location

Legend *# WRC !( WQ Point WFD river classification High Good Moderate Poor Bad Detailed River Network

WHADDON STW F/E *#

Contains OS data © Crown copyright and database right (2016)

Table 25: Wealdon Brook watercourse status and objectives

Overall BOD Ammonia Phosphorus 2015 Moderate Good Good Poor status High by High by Good by Objective Moderate 2027 2027 2027

Table 26 shows the input data and RQP results for Whaddon. The works has permitted values for DWF and BOD and is currently operating within these limits. Future scenarios predict that the work will still be operating within these limits.

2016s3990 - Water Quality Assessment v2.0 22

Table 26: RQP inputs and results for Whaddon WwTW

Present Day Future growth Parameter Statistic River Source Deterioration RQP RQP WRC Source WRC Source Result Result

Mean 0.003 0.214 0.86 Based on Calculated Flow Low Flow SD 0.11 Permitted 0.44 using AW (Ml/d) Softw are DWF parameters 5%ile 0.001

Mean 2.58 3.10 3.10 Mid Class Observed Observed Good Data Data BOD (mg/l) SD 1.55 2.05 5.74 2.05 5.80 1%

Target 2015 5.00 90%ile WFD Mean 0.22 Mid Class 1.15 Observed 1.15 Observed Good Data Data NH4 (mg/l) SD 0.22 1.49 2.63 1.49 2.65 1% Target 2015 0.60 90%ile WFD Mean 1.00 Mid Class 5.09 Observed 5.09 Observed Poor Data Data P (mg/l) SD 1.10 1.62 5.1 1.62 5.15 1% Target 2015 0.08 Mean WFD Assumed Mean 0.085 5.09 Observed Mid Class Data P (mg/l) SD 0.085 Good 1.62 5.09 Target 2015 0.08 Mean WFD

The model results indicate that all pollutants fail to meet the 2015 WFD target for both the present day and future scenarios. There is also a predicted class deterioration for NH4. For P there is predicted deterioration within the 'Bad' ecological class which is not permitted; revision of the permit is likely to be required. The RQP model was used to calculate whether the watercourse could meet Good Ecological Status (GES) for BOD, NH4 and P. The model results in Table 27 indicate that GES would be achievable for BOD with the present day and future flows, assuming Good status upstream and BAT at the WwTW. However, for NH4 and P, GES is not achievable for the present day or future flows, even when assuming GES upstream and BAT at the WwTW. Therefore, the watercourse is unable to meet GES as a consequence of current technological limits, not as a result of the proposed development. Table 27: Discharge quality required to meet good WFD targets for P at Whaddon WwTW

WRC Pollutant Target Upstream river quality Scenario Mean SD 95%ile Conclusion

Whaddon BOD 5 Good Future Grow th 2.74 1.73 6.08 Reaches BAT Target

Whaddon BOD 5 Good Present Day 2.76 1.74 6.13 Reaches BAT Target

Whaddon NH4 0.6 Good Future Grow th 0.27 0.31 0.83 Doesn't Reach Target

Whaddon NH4 0.6 Good Present Day 0.27 0.31 0.83 Doesn't Reach Target

Whaddon P 0.08 Poor Future Grow th 0.08 0.02 0.12 Doesn't Reach Target

Whaddon P 0.08 Poor Present Day 0.07 0.02 0.10 Doesn't Reach Target

Whaddon P 0.08 Assumed Mid Class Good Present Day 0.08 0.02 0.13 Doesn't Reach Target

2016s3990 - Water Quality Assessment v2.0 23

A.8.8 Wing Cublington Wing Cublington WwTW discharges into the Wing Brook as shown in Figure 9. The status of the receiving watercourse is summarised in Table 28. Figure 9: Wing Cublington WwTW discharge location

Legend #* WRC !( WQ Point Detailed River Network

WFD river classification WING-CUBLINGTON ROAD STW High #* Good Moderate Poor Bad

ASTON ABBOTTS STW #*

Contains OS data © Crown copyright and database right (2016) Table 28: Wing Brook watercourse status and objectives

Overall BOD Ammonia Phosphorus 2015 Moderate High High Poor status Not Objective High High Good available

Table 29 shows the input data and RQP results for Wing Cublington. The works has permitted values for DWF, BOD, and NH4 is currently operating within these limits. Future scenarios predict that the work will still be operating within the limits for all determinands.

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Table 29: Input and RQP results for Wing Cublington WwTW

Present Day Future growth Parameter Statistic River Source Deterioration RQP RQP WRC Source WRC Source Result Result

Mean 1.47 0.850 0.93 Based on Calculated Flow Low Flow SD 0.283 Permitted 0.31 using AW (Ml/d) Softw are DWF parameters

5%ile 0.25

Mean 1.15 7.06 7.06 Mid Class Observed Observed High Data Data BOD (mg/l) SD 0.69 2.57 6.14 2.57 6.27 2%

Target 2015 4.00 90%ile WFD

Mean 0.09 Mid Class 3.45 Observed 3.45 Observed High Data Data NH4 (mg/l) SD 0.05 1.19 2.76 1.19 2.83 3% Target 2015 0.30 90%ile WFD Mean 1.000 Mid Class 6.17 Observed 6.17 Observed Poor Data Data P (mg/l) SD 1.100 1.51 3.37 1.51 3.37 0% Target 2015 0.073 Mean WFD Assumed Mean 0.056 6.17 Observed Mid Class Data P (mg/l) SD 0.056 Good 1.51 2.87 Target 2015 0.073 Mean WFD The model results indicate that all pollutants fail to meet the 2015 WFD targets and there is a class deterioration between the present day and future growth scenario for BOD. There are no deteriorations greater than 10% for Wing Cublington. However, for NH4 and P there is a predicted deterioration within the 'Bad' ecological class which is not permitted; revision of the permit is likely to be required. The RQP model was used to calculate whether the watercourse could meet Good Ecological Status (GES) for BOD, NH4 and P. The model results in Table 30 indicate that GES would be achievable for BOD with the present day and future flows, assuming High status upstream and BAT at the WwTW. However, for NH4 and P, GES is not achievable for the present day flows without improving upstream quality, even assuming GES upstream and BAT at the WwTW. Therefore, the watercourse is unable to meet GES as a consequence of current technological limits, not as a result of the proposed development. Table 30: Discharge quality required to meet good WFD targets for P at Wing Cublington WwTW

WRC Pollutant Target Upstream river quality Scenario Mean SD 95%ile Conclusion

Wing Cublington BOD 4 Mid Class High Future Grow th 4.35 1.55 7.23 Reaches BAT Target

Wing Cublington NH4 0.3 Mid Class High Future Grow th 0.33 0.11 0.53 Doesn’t meet BAT target

Wing Cublington NH4 0.3 Mid Class High Present Day 0.34 0.11 0.55 Doesn’t meet BAT target

BAT Not Achievable Without Wing Cublington P 0.073 Poor Future Grow th Not Achievable Improving Upstream Quality

BAT Not Achievable Without Wing Cublington P 0.073 Poor Present Day Not Achievable Improving Upstream Quality

BAT Not Achievable Without Wing Cublington P 0.181 Poor Future Grow th Not Achievable Improving Upstream Quality

BAT Not Achievable Without Wing Cublington P 0.181 Poor Present Day Not Achievable Improving Upstream Quality

Wing Cublington P 0.073 Assumed Mid Class Good Present Day 0.09 0.02 0.13 Doesn’t Meet BAT target

2016s3990 - Water Quality Assessment v2.0 25

A.8.9 Winslow WwTW Winslow WwTW discharges into the Claydon Brook as shown in Figure 10. The status of the receiving watercourse is summarised in Table 31. Figure 10: Winslow WwTW discharge location

Legend #* WRC !( WQ Point Detailed River Network WFD river classification High Good Moderate Poor Bad 02M54 !(

WINSLOW STW #*

Contains OS data © Crown copyright and database right (2016)

Table 31: Claydon Brook watercourse status and objectives

Overall BOD Ammonia Phosphorus 2015 Moderate High High Poor status Not Objective High High Good available

Table 32 shows the input data and RQP results for Winslow. The works has permitted values for DWF, BOD, and NH4 is currently operating within these limits. Future scenarios predict that the work will still be operating within the limits for all determinands.

2016s3990 - Water Quality Assessment v2.0 26

Table 32: Inputs and RQP Results for Winslow WwTW

Present Day Future growth Parameter Statistic River Source Deterioration RQP RQP WRC Source WRC Source Result Result

Mean 19.87 1.77 2.11 Based on Calculated Flow Low Flow SD 0.59 Permitted 0.70 using AW (Ml/d) Softw are DWF parameters 5%ile 1.38

Mean 1.15 Mid Class 3.77 Observed 3.77 Observed High Data Data SD 0.69 2.85 2.85 BOD (mg/l) 2.84 2.96 4% Target 2015 4.00 90%ile WFD

Mean 0.03 Observed 1.44 Observed 1.44 Observed Data Data Data NH4 (mg/l) SD 0.03 1.72 0.73 1.72 0.81 11% Target 2015 0.30 90%ile WFD Mean 1.00 Mid Class 5.69 Observed 5.69 Observed Poor Data Data P (mg/l) SD 1.10 1.07 1.9 1.07 2.02 6% Target 2015 0.076 Mean WFD Assumed Mean 0.056 5.69 Observed Mid Class Data P (mg/l) SD 0.056 Good 1.07 1.14 Target 2015 0.076 Mean WFD The model results indicate that NH4 and P fail to meet the 2015 targets and there is a class deterioration between the present day and future growth scenario for NH4. There is a deterioration of 4%, 11% and 8% for BOD, NH4 and P respectively. In addition, for P there is a deterioration within the 'Bad' ecological class which is not permitted; revision of the permit is likely to be required. The RQP model was used to calculate whether the watercourse could meet Good Ecological Status (GES) for NH4 and P. The model results in Table 33 indicates that GES would not be achievable for NH4 for the present day and future flows even with BAT at the WwTW. For P, GES is not achievable for the present day or future flows, even assuming GES and BAT at the WwTW. Therefore, the watercourse is unable to meet GES as a consequence of current technological limits, not as a result of the proposed development. Table 33: Discharge quality required to meet good WFD targets for P at Winslow WwTW

WRC Pollutant Target Upstream river quality Scenario Mean SD 95%ile Conclusion

Winslow NH4 0.3 Mid Class High Future Grow th 0.51 0.55 1.54 Doesn’t Meet BAT Target

Winslow NH4 0.3 Mid Class High Present Day 0.57 0.62 1.72 Doesn’t Meet BAT Target

BAT Not Achievable Without Winslow P 0.076 Poor Future Grow th Not Achievable Improving Upstream Quality

BAT Not Achievable Without Winslow P 0.076 Poor Present Day Not Achievable Improving Upstream Quality

BAT Not Achievable Without Winslow P 0.187 Poor Future Grow th Not Achievable Improving Upstream Quality

BAT Not Achievable Without Winslow P 0.187 Poor Present Day Not Achievable Improving Upstream Quality

Winslow P 0.076 Assumed Mid Class Good Present Day 0.16 0.03 0.21 Doesn’t Meet BAT Target

2016s3990 - Water Quality Assessment v2.0 27

New permit values were calculated for NH4 due to a deterioration of more than 10%. This was calculated using the present day result from the RQP calculation to prevent deterioration. Table 34 shows the results for the discharge quality to meet no deterioration. The new permit values cannot be reached using BAT for all pollutants. Table 34: WwTW discharge quality required to meet up to 10% or no class deterioration for Winslow

Parameter Worst Case Scenario Present Day Target Values required to meet target

Mean SD 95%ile BOD - - - - -

NH4 Future 0.73 1.32 1.42 3.96

P - - - - -

2016s3990 - Water Quality Assessment v2.0 28

A.9 Thames Water WwTWs

A.9.10 Aylesbury Aylesbury WwTW discharges into the River Thames as shown in Figure 11. The status of the receiving watercourse is summarised in Table 35. Figure 11: Aylesbury WwTW discharge location

Legend #* STW !( WQ Point PTAR0007 WFD!( river classification High PTAR0189 Good !( Moderate Poor PTAR0028 Bad !( Detailed River Network

PTAR0003 !( Aylesbury STW #*

Contains OS data © Crown copyright and database right (2016)

Table 35: River Thames watercourse status and objectives

Overall BOD Ammonia Phosphorus 2015 Moderate Good High Poor status Good by High by Good by Objective Moderate 2027 2021 2027

Table 36 shows the input data and RQP results for Aylesbury. The works has permitted values for DWF, BOD and NH4 and is currently operating within these limits. Future scenarios predict that the work will still be operating within these limits.

2016s3990 - Water Quality Assessment v2.0 29

Table 36: RQP inputs and results for Aylesbury WwTW

Present Day Future growth Parameter Statistic River Source Deterioration RQP RQP WRC Source WRC Source Result Result

Mean 0.83 24.11 29.30 Calculated Flow Low Flow Observed using TW (Ml/d) SD Softw are 10.98 Data 13.34 parameters 95%ile 0.12

Mean 1.79 Observed 2.30 Observed 2.30 Observed Data Data Data BOD (mg/l) SD 0.86 1.16 3.81 1.16 3.82 0% Target 2015 5.00 90%ile WFD Mean 0.057 Observed 0.13 Observed 0.13 Observed Data Data Data NH4 (mg/l) SD 0.063 0.28 0.31 0.28 0.31 0% Target 2015 0.30 90%ile WFD Mean 1.000 Mid Class 0.70 Observed 0.70 Observed Poor Data Data P (mg/l) SD 1.100 0.79 0.73 0.79 0.73 0% Target 2015 0.066 Mean WFD Mean 0.085 Assumed 0.70 Observed mid Good Data P (mg/l) SD 0.085 0.79 0.7 Target 2015 0.066 Mean WFD

The model results indicate that BOD meets the 2015 targets and there is no class deterioration between the present day and future growth scenario. Both NH4 and P do not meet their targets but there is no class deterioration. All pollutants have less than 10% deterioration thus a new permit is not necessary. The RQP model was used to calculate whether the watercourse could meet Good Ecological Status (GES) for NH4 and P. The model results in Table 37 indicate that GES is not achievable for the present day and future flows, even assuming GES upstream and BAT at the WwTW. Therefore, the watercourse is unable to meet GES as a consequence of current technological limits, not as a result of the proposed development. Table 37: Discharge quality required to meet good WFD targets for P at Aylesbury WwTW

WRC Pollutant Target Upstream river quality Scenario Mean SD 95%ile Conclusion

Aylesbury NH4 0.3 High Future Grow th 0.13 0.21 0.47 Doesn’t Meet BAT target

Aylesbury NH4 0.3 High Present Day 0.13 0.22 0.48 Doesn’t Meet BAT target

Aylesbury P 0.066 Poor Future Grow th 0.04 0.04 0.13 Doesn’t Meet BAT target

Aylesbury P 0.066 Poor Present Day 0.04 0.04 0.11 Doesn’t Meet BAT target

Assumed Mid Class Aylesbury P 0.066 Present Day 0.07 0.07 0.19 Doesn’t Meet BAT target Good

2016s3990 - Water Quality Assessment v2.0 30

A.9.11 Haddenham WwTW Haddenham WwTW discharges into the Scotsgrove Brook as shown in Figure 12. The status of the receiving watercourse is summarised in Table 38. Figure 12: Haddenham WwTW discharge location

Legend #* STW !( WQ Point WFD river classification High Good Moderate Poor Bad Detailed River Network

PTAR0032 !(

Haddenham STW #*

Contains OS data © Crown copyright and database right (2016)

Table 38: Scotsgrove Brook watercourse status and objectives

Overall BOD Ammonia Phosphorus 2015 Moderate Good High Poor status Good by High by Good by Objective Moderate 2027 2021 2027

Table 39 shows the input data and RQP results for Haddenham. The works has permitted values for BOD and NH4 and is currently operating within these limits. DWF exceeds the current consented limit. Future scenarios predict that the work will still be operating within the limits excluding DWF.

2016s3990 - Water Quality Assessment v2.0 31

Table 39: RQP inputs and results for Haddenham WwTW

Present Day Future growth Parameter Statistic River Source Deterioration RQP RQP WRC Source WRC Source Result Result Mean 0.25 2.05 3.88 Calculated Flow Low Flow Observed SD 0.92 1.74 using TW (Ml/d) Softw are Data parameters 5%ile 0.046

Mean 1.437 Observed 2.24 Observed 2.24 Observed Data Data Data BOD (mg/l) SD 0.54 0.84 3.18 0.84 3.29 3% 2015 Target 90%ile 5.00 WFD Mean 0.056 Observed 0.11 Observed 0.11 Observed Data Data Data NH4 (mg/l) SD 0.086 0.09 0.20 0.09 0.21 5% 2015 Target 90%ile 0.30 WFD Mean 1.00 Mid Class 3.30 Observed 3.30 Observed Poor Data Data P (mg/l) SD 1.10 1.56 3.13 1.56 3.23 4% 2015 Target Mean 0.081 WFD Mean 0.085 Assumed 3.30 Observed mid Good Data P (mg/l) SD 0.085 1.56 3.04 2015 Target Mean 0.081 WFD

The model results indicate that BOD and NH4 meet the 2015 targets and there is no class deterioration between the present day and future scenario. P fails the target, but there is no class deterioration. All pollutants have less than 10% deterioration. However, for P there is a predicted deterioration within the 'Bad' ecological class which is not permitted; revision of the permit is likely to be required. The RQP model was used to calculate whether the watercourse could meet Good Ecological Status (GES) for P. The model results in Table 40 indicate that GES is not achievable for the present day for future flows, even assuming GES upstream and BAT at the WwTW. Therefore, the watercourse is unable to meet GES as a consequence of current technological limits, not as a result of the proposed development.

Table 40: Discharge quality required to meet good WFD targets for P at Haddenham WwTW

WRC Pollutant Target Upstream river quality Scenario Mean SD 95%ile Conclusion

Haddenham P 0.081 Poor Future Grow th 0.03 0.01 0.05 Doesn’t reach BAT Target

BAT Not Achievable Without Haddenham P 0.081 Poor Present Day Not Achievable Improving Upstream Quality

Haddenham P 0.081 Assumed Mid Class Good Present Day 0.08 0.04 0.15 Doesn’t reach BAT Target

2016s3990 - Water Quality Assessment v2.0 32

A.9.12 Long Crendon WwTW Long Crendon WwTW discharges into the River Thames as shown in Figure 13. The status of the receiving watercourse is summarised in Table 41. Figure 13: Long Crendon WwTW discharge location

Legend #* STW !( WQ Point WFD river classification Long Crendon STW High #* Good Moderate Poor Bad Detailed River Network

Contains OS data © Crown copyright and database right (2016)

Table 41: River Thames watercourse status and objectives

Overall BOD Ammonia Phosphorus 2015 Moderate Good Good Poor status Good by High by Good by Objective Moderate 2027 2027 2027

Table 42 shows the input data and RQP results for Long Crendon. The works has permitted values for BOD and is currently operating within these limits. DWF exceeds the current consented limit. Future scenarios predict that the work will still be operating within the limits excluding DWF.

2016s3990 - Water Quality Assessment v2.0 33

Table 42: RQP inputs and results for Long Crendon WwTW

Present Day Future growth

Parameter Statistic River Source RQP RQP Deterioration WRC Source WRC Source Result Result Mean 1.74 0.58 0.660 Calculated Flow Low Flow Observed SD 0.19 0.21 using TW (Ml/d) Softw are Data parameters 5%ile 0.25

Mean 2.6 Mid Class 2.75 Observed 2.75 Observed SD 1.6 Good 0.71 Data 0.71 Data BOD (mg/l) 3.93 3.91 -1% Target 2015 5.00 90%ile WFD Mean 0.22 Mid Class 0.23 Observed 0.23 Observed Good Data Data NH4 (mg/l) SD 0.22 0.18 0.40 0.18 0.40 0% Target 2015 0.60 90%ile WFD Mean 1.000 Mid Class 6.13 Observed 6.13 Observed Poor Data Data P (mg/l) SD 1.100 1.16 2.81 1.16 2.95 5% Target 2015 0.066 Mean WFD Mean 0.085 Assumed 6.13 Observed mid Good Data P (mg/l) SD 0.085 1.16 2.38 Target 2015 0.066 Mean WFD

The model results indicate that all pollutants fail to meet the 2015 targets but there is no class deterioration or deterioration of greater than 10% between the present day and future scenarios However for P there is a predicted deterioration within the 'Bad' ecological class which is not permitted; revision of the permit is likely to be required. The RQP model was used to calculate whether the watercourse could meet Good Ecological Status (GES) for BOD, NH4 and P. The model results in Table 43 indicate that GES is achievable for BOD and NH4 for the present day and future flows with BAT applied at the WwTWs. For P, GES is not achievable for the present day flows, even assuming GES upstream and BAT at the WwTW. Therefore, the watercourse is unable to meet GES as a consequence of current technological limits, not as a result of the proposed development.

Table 43: Discharge quality required to meet good WFD targets at Long Crendon WwTW

WRC Pollutant Target Upstream river quality Scenario Mean SD 95%ile Conclusion

Long Crendon BOD 5 Good Future Grow th 4.91 1.25 7.18 Reaches BAT Target

Long Crendon BOD 5 Good Present Day 5.07 1.29 7.40 Reaches BAT Target

Long Crendon NH4 0.6 Good Future Grow th 0.53 0.39 1.29 Reaches BAT Target

Long Crendon NH4 0.6 Good Present Day 0.55 0.40 1.32 Reaches BAT Target

BAT Not Achievable Without Long Crendon P 0.066 Poor Future Grow th Not Achievable Improving Upstream Quality

BAT Not Achievable Without Long Crendon P 0.066 Poor Present Day Not Achievable Improving Upstream Quality

BAT Not Achievable Without Long Crendon P 0.066 Assumed Mid Class Good Present Day Not Achievable Improving Upstream Quality

2016s3990 - Water Quality Assessment v2.0 34

A.9.13 Stone WwTW Stone WwTW discharges into the Scotsgrove Brook as shown in Figure 14. The upstream catchment area is very small, and consequently the treated effluent contributes the majority of the flow in the Scotsgrove Brook. The status of the receiving watercourse is summarised Table 44. Figure 14: Stone WwTW discharge location

Legend #* STW !( WQ Point WFD river classification High Good STONE STW Moderate #* Poor Bad Detailed River Network

Table 44: Scotsgrove Brook watercourse status and objectives

Overall BOD Ammonia Phosphorus 2015 Moderate Good Good Poor status Good by High by Good by Objective Moderate 2027 2027 2027 Table 45 shows the input data and RQP results for Stone. The works has permitted values for BOD and NH4 and is currently operating within these limits. DWF exceeds the current consented limit. Future scenarios predict that the work will still be operating within the limits excluding DWF.

2016s3990 - Water Quality Assessment v2.0 35

Table 45: RQP inputs and results for Stone WwTW

Present Day Future growth Parameter Statistic River Source Deterioration RQP RQP WRC Source WRC Source Result Result

Mean 0.12 0.99 1.06 Calculated Flow Low Flow Observed SD 0.47 0.51 using TW (Ml/d) Softw are Data parameters 5%ile 0.016

Mean 2.6 9.87 9.87 Mid Class Observed Observed Good Data Data BOD (mg/l) SD 1.6 3.10 13.07 3.10 13.12 0%

Target 2015 5.00 90%ile WFD Mean 0.22 Mid Class 3.40 Observed 3.40 Observed Good Data Data NH4 (mg/l) SD 0.22 1.90 5.38 1.90 5.42 1% Target 2015 0.60 90%ile WFD Mean 1.10 Mid Class 5.10 Observed 5.10 Observed Poor Data Data P (mg/l) SD 1.00 1.53 4.78 1.53 4.81 0% Target 2015 0.081 Mean WFD Mean 0.085 Assumed 5.10 Observed mid Good Data P (mg/l) SD 0.085 1.53 4.69 Target 2015 0.081 Mean WFD The model results indicate that all pollutants fail to meet the 2015 targets but there is no class deterioration or deterioration of greater than 10% between the present day and future scenarios. However, for BOD, NH4 and P there is a deterioration within the 'Bad' ecological class which is not permitted; revision of the permit is likely to be required. The RQP model was used to calculate whether the watercourse could meet Good Ecological Status (GES) for BOD, NH4 and P. The model results in Table 46 indicate that GES is achievable for BOD with BAT. However, GES is not achievable for NH4 or P for the present day flows, even assuming Good status upstream and BAT at the WwTW. Therefore, the watercourse is unable to meet GES as a consequence of current technological limits, not as a result of the proposed development. Table 46: Discharge quality required to meet good WFD targets for P at Stone WwTW

WRC Pollutant Target Upstream river quality Scenario Mean SD 95%ile Conclusion

Stone BOD 5 Good Future Grow th 3.70 1.14 5.81 BAT target exceeded

Stone BOD 5 Good Present Day 3.70 1.14 5.80 BAT target exceeded

Stone NH4 0.6 Good Future Grow th 0.37 0.20 0.76 Doesn’t reach BAT Target

Stone NH4 0.6 Good Present Day 0.37 0.20 0.76 Doesn’t reach BAT Target

BAT Not Achievable Without Stone P 0.081 Poor Future Grow th Not Achievable Improving Upstream Quality BAT Not Achievable Without Stone P 0.081 Poor Present Day Not Achievable Improving Upstream Quality BAT Not Achievable Without Stone P 0.081 Assumed Mid Class Good Present Day 0.08 0.02 0.12 Improving Upstream Quality

A.9.14 Waddesdon WwTW Waddesdon WwTW discharges into the Fleet Marston Brook as shown in Figure 15. The

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upstream catchment area is very small, and consequently the treated effluent contributes the majority of the flow in the Fleet Marston Brook. The status of the receiving watercourse is summarised in Table 47. Figure 15: Waddesdon WwTW discharge location

Legend #* STW !( WQ Point WFD river classification High Good Moderate Poor Bad Detailed River Network

Waddesdon STW #*

Table 47: Fleet Marston Brook watercourse status and objectives

Overall BOD Ammonia Phosphorus 2015 Poor Good Good Poor status Good by Good by Good by Objective Poor 2027 2027 2027

Table 48 shows the input data and RQP results for Waddesdon. The works has permitted values for BOD and is currently operating within these limits. DWF exceeds the current consented limit. Future scenarios predict that the work will still be operating within the limits excluding DWF.

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Table 48: Inputs and RQP results for Waddesdon WwTW

Present Day Future growth Parameter Statistic River Source Deterioration RQP RQP WRC Source WRC Source Result Result

Mean 0.02 0.658 0.76 Calculated Flow Low Flow Observed SD 0.31 0.36 using TW (Ml/d) Softw are Data parameters 5%ile 0.003

Mean 2.6 9.05 9.05 Assumed Observed Observed mid Good Data Data BOD (mg/l) SD 1.6 3.17 13.08 3.17 13.10 0%

Target 2015 5.00 90%ile WFD Mean 0.22 Assumed 1.35 Observed 1.35 Observed mid Good Data Data NH4 (mg/l) SD 0.22 1.47 2.90 1.47 2.91 0% Target 2015 0.60 90%ile WFD Mean 1.1 Mid Class 5.14 Observed 5.14 Observed Poor Data Data P (mg/l) SD 1.0 1.84 5.11 1.84 5.12 0% Target 2015 0.08 Mean WFD Mean 0.085 Assumed 5.14 Observed SD 0.085 mid Good 1.84 Data P (mg/l) 5.08 Target 2015 0.08 Mean WFD

The RQP model was used to calculate whether the watercourse could meet GES for BOD, NH4 and P. The model results in

Table 49 indicate that GES is achievable for BOD. However, GES is not achievable for NH4 or P for the present day flows, even assuming Good status upstream and BAT at the WwTW. Therefore, the watercourse is unable to meet GES as a consequence of current technological limits, not as a result of the proposed development.

Table 49: Discharge quality required to meet good WFD targets for P at Waddesdon WwTW

WRC Pollutant Target Upstream river quality Scenario Mean SD 95%ile Conclusion

Waddesdon BOD 5 Good Future Grow th 3.46 1.19 5.67 BAT target exceeded

Waddesdon BOD 5 Good Present Day 3.47 1.19 5.68 BAT target exceeded

Waddesdon NH4 0.6 Good Future Grow th 0.28 0.28 0.82 Doesn’t reach BAT Target

Waddesdon NH4 0.6 Good Present Day 0.29 0.28 0.82 Doesn’t reach BAT Target

Waddesdon P 0.08 Poor Future Grow th 0.05 0.02 0.09 Doesn’t reach BAT Target

Waddesdon P 0.08 Poor Present Day 0.05 0.02 0.08 Doesn’t reach BAT Target

Waddesdon P 0.08 Assumed Mid Class Good Present Day 0.08 0.03 0.13 Doesn’t reach BAT Target

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A.9.15 Worminghall WwTW Worminghall WwTW discharges into the Worminghall Brook as shown in Figure 16. The upstream catchment area is very small, and consequently the treated effluent contributes the majority of the flow in the Worminghall Brook Brook. The status of the receiving watercourse is summarised in Table 50. Figure 16: Worminghall WwTW discharge location

Legend #* STW !( WQ Point WFD river classification High Good Moderate Poor Bad Detailed River Network

WORMINGHALL STW #*

PTAR0087 !(

Table 50: Worminghall Brook watercourse status and objectives

Overall BOD Ammonia Phosphorus 2015 Moderate Good Good Moderate status Good by High by Good by Objective Moderate 2027 2027 2027

Table 51 shows the input data and RQP results for Worminghall. The works has permitted values for DWF, BOD and NH4 and is currently operating within these limits. Future scenarios predict that the works will still be operating within these limits.

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Table 51: Inputs and RQP results for Worminghall WwTW

Present Day Future growth Parameter Statistic River Source Deterioration RQP RQP WRC Source WRC Source Result Result

Mean 0.05 0.76 0.82 Calculated Flow Low Flow Observed SD 0.50 0.54 using TW (Ml/d) Softw are Data 5%ile 0.005 parameters

Mean 2.6 Mid Class 4.16 Observed 4.16 Observed Good Data Data BOD (mg/l) SD 1.6 2.29 6.95 2.29 6.96 0% Target 2015 5.00 90%ile WFD Mean 0.22 Mid Class 1.55 Observed 1.55 Observed Good Data Data NH4 (mg/l) SD 0.22 0.80 2.49 0.80 2.50 0% Target 2015 0.60 90%ile WFD Mean 0.185 Mid Class 5.48 Observed 5.48 Observed Moderate Data Data P (mg/l) SD 0.185 1.84 5.26 1.84 5.28 0% Target 2015 0.081 Mean WFD Mean 0.084 Assumed 5.48 Observed Mid Good Data P (mg/l) SD 0.084 1.84 5.26 Target 2015 0.081 Mean WFD

The RQP model was used to calculate whether the watercourse could meet GES for BOD, NH4 and P. The model results in

Table 52 indicate that GES is achievable for BOD. However, GES is not achievable for NH4 or P for the present day flows, even assuming Good status upstream and BAT at the WwTW. Therefore, the watercourse is unable to meet GES as a consequence of current technological limits, not as a result of the proposed development.

Table 52: Discharge quality required to meet good WFD targets for P at Worminghall WwTW

WRC Pollutant Target Upstream river quality Scenario Mean SD 95%ile Conclusion

Worminghall BOD 5 Good Future Grow th 3.05 1.62 6.16 BAT target exceeded

Worminghall BOD 5 Good Present Day 3.05 1.62 6.16 BAT target exceeded

Worminghall NH4 0.6 Good Future Grow th 0.37 0.19 0.73 Doesn’t reach BAT Target

Worminghall NH4 0.6 Good Present Day 0.38 0.19 0.74 Doesn’t reach BAT Target

Worminghall P 0.081 Poor Future Grow th 0.08 0.02 0.12 Doesn’t reach BAT Target

Worminghall P 0.081 Poor Present Day 0.07 0.02 0.12 Doesn’t reach BAT Target

Worminghall P 0.081 Assumed Mid Class Good Present Day 0.08 0.03 0.13 Doesn’t reach BAT Target

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A.10 Summary and Conclusion

A.10.1 Method The increased discharge of effluent due to an increase in the population served by a Wastewater Treatment Works (WwTW) may impact on the quality of the receiving water. The Water Framework Directive (WFD) does not allow a watercourse to deteriorate from its current class (either waterbody or element class). It is Environment Agency policy to model the impact of increasing effluent volumes on the receiving watercourse. Where the scale of development is such that a deterioration Is predicted, a new permit may be required for the WwTW to improve the quality of the final effluent, so that extra pollution load will not result in a deterioration in the water quality of the watercourse. This is known as a "no deterioration" or "load standstill". During the preparation of this Water Cycle Study (WCS) 15 WwTWs were identified which are anticipated to receive significant future increases in wastewater flows as a result of development in their catchments. The assessment was undertaken using the EA's River Quality Planning (RQP) tool which enables a Monte-Carlo analysis to be undertaken at a single point of discharge to a watercourse. RQP models were set up and run for each WwTW, for the present-day situation and the future scenarios. Where failure was predicted for any of the scenarios, and the upstream water quality did not achieve 'good status' the model was re-run assuming that the river had 'good status'. The reason for this approach is to assess the actual impact of the effluent if the upstream point and/or diffuse sources were to be resolved.

A.10.2 Results Table 53 summarises the modelling results for passing or failing the following targets:  'Good Status',  'No deterioration greater than 10%';  'No class deterioration'.

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Table 53: RQP results summaries for passing or failing targets of: 'Good Status', 'No >10% Deterioration' and 'No Class Deterioration'.

Achieves 'Good Achieves 'No > 10% Achieves No 'Class Watercourse status' target? deterioration' target? deterioration' target? (Ww TW Scenario discharging into it) BOD NH4 P BOD NH4 P BOD NH4 P

Achieves good status No deterioration No class deterioration Key NA Up to 10% deterioration NA Fails good status More than 10% deterioration Class deterioration

Great River Ouse Present day yes yes no N/A N/A N/A N/A N/A N/A (Buckingham) Future grow th yes yes no 1% 6% 7% yes yes yes

Horw ood Tributary Present day no no no N/A N/A N/A N/A N/A N/A (Great Horw ood) Future grow th no no no 4% 4% 2% yes yes yes

Whistle Brook Present day yes no no N/A N/A N/A N/A N/A N/A (Ivinghoe) Future grow th yes no no 1% 3% 2% yes yes yes

Padbury Brook Present day yes yes no N/A N/A N/A N/A N/A N/A (Padbury) Future grow th yes yes no 0% 0% 2% yes yes yes

Claydon Brook Present day yes yes no N/A N/A N/A N/A N/A N/A (Steeple Claydon) Future grow th yes yes no 1% 0% 3% yes yes yes

Weald Brook Present day no no no N/A N/A N/A N/A N/A N/A (Whaddon) Future grow th no no no 1% 1% 1% yes yes yes

Wing Brook (Wing Present day no no no N/A N/A N/A N/A N/A N/A Cublington) Future grow th no no no 2% 3% 0% yes yes yes

Claydon Brook Present day yes no no N/A N/A N/A N/A N/A N/A (Winslow ) Future grow th yes no no 4% 11% 6% yes yes yes

Ouzel Brook Present day yes yes no N/A N/A N/A N/A N/A N/A (Stanbridgeford) Future grow th yes yes no 0% 0% 0% yes yes yes

River Thames Present day yes yes no N/A N/A N/A N/A N/A N/A (Aylesbury) Future grow th yes yes no 0% 0% 0% yes yes yes

Scotsgrove Brook Present day yes yes no N/A N/A N/A N/A N/A N/A (Haddenham) Future grow th yes yes no 3% 5% 4% yes yes yes

River Thames (Long Present day yes yes no N/A N/A N/A N/A N/A N/A Crendon) Future grow th yes yes no -1% 0% 5% yes yes yes

Scotsgrove Brook Present day no no no N/A N/A N/A N/A N/A N/A (Stone) Future grow th no no no 0% 1% 1% yes yes yes

Fleet Marston Brook Present day no no no N/A N/A N/A N/A N/A N/A (Waddesdon) Future grow th no no no 0% 0% 0% yes yes yes

Worminghall Brook Present day no no no N/A N/A N/A N/A N/A N/A (Worminghall) Future grow th no no no 0% 0% 0% yes yes yes

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A.10.3 Best Available Technology (BAT) assessment Where river targets failures occurred, the modelling results were compared against BAT to assess if improving the works to such level of performance could prevent the failure to occur. This assessment process has recently been set out in a guidance document by the Environment Agency's West Thames Area3. Whilst this document has no national status it provides a useful summary of how to interpret the results of the water quality assessment. This guidance is summarised in the flow chart below:

Figure 17: Water Quality assessment flow chart

The EA advised that the following permit values are achievable using Best Available Technology (BAT), and that these values should be used for modelling all WwTWs potential capacity irrespective of the existing treatment technology and size of the works:  BOD (95%ile) = 5mg/l  Ammonia (95%ile) = 1mg/l  Phosphorus (mean) = 0.5 mg/l

This does not take into consideration if it is feasible to upgrade each existing WwTW to such technology due to constraints of cost, timing, space, carbon cost etc.

3 Environment Agency West Thames Area (2015) Water Cycle Study Guidance and Requirements - West Thames Area.

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Table 54: Summary of results assuming BAT is applied

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Could the Could the Could the development development cause development prevent Watercourse cause a greater a deterioration in the water body from (WwTW) than 10% WFD class of any reaching GES? deterioration in element? WQ? Key See Figure 17 Good Ecological Status Predicted cannot be achieved for No class deterioration Great River deterioration is less P due to current is predicted. No Ouse than 10%. No technology limits. WwTW upgrade is (Buckingham) WwTW upgrade is Ensure proposed required required growth doesn’t cause significant deterioration. No class deterioration Good Ecological Status Predicted is predicted, however cannot be achieved for Horwood deterioration is less there is deterioration NH4 or P due to current Tributary (Great than 10%. No within the "Bad" class technology limits. Horwood) WwTW upgrade is for BOD, NH4 and P. Ensure proposed required WwTW upgrade is growth doesn’t cause likely to be required. significant deterioration. No class deterioration Good Ecological Status Predicted is predicted however cannot be achieved for deterioration is less there is deterioration P due to current Whistle Brook than 10%. No within the "Bad" class technology limits. (Ivinghoe) WwTW upgrade is for P. WwTW Ensure proposed required upgrade is likely to be growth doesn’t cause required. significant deterioration. If Good status could be achieved upstream this could be maintained downstream of the Predicted WwTW for both the No class deterioration deterioration is less present-day and future Padbury Brook is predicted. No than 10%. No growth scenarios, within (Padbury) WwTW upgrade is WwTW upgrade is the limits of current required. required BAT. Therefore, development can be accommodated with a tighter permit and upgrade to treatment. Good Ecological Status Predicted cannot be achieved for No class deterioration Claydon Brook deterioration is less P due to current is predicted. No (Steeple than 10%. No technology limits. WwTW upgrade is Claydon) WwTW upgrade is Ensure proposed required. required growth doesn’t cause significant deterioration. No class deterioration Good Ecological Status Predicted is predicted, however cannot be achieved for deterioration is less there is deterioration P due to current Weald Brook than 10%. No within the "Bad" class technology limits. (Whaddon) WwTW upgrade is for NH4 and P. Ensure proposed required. WwTW upgrade is growth doesn’t cause likely to be required. significant deterioration. No class deterioration Good Ecological Status Predicted is predicted, however cannot be achieved for Wing Brook deterioration is less there is deterioration NH4 or P due to current (Wing than 10%. No within the "Bad" class technology limits. Cublington) WwTW upgrade is for NH4 and P. Ensure proposed required. WwTW upgrade is growth doesn’t cause likely to be required. significant deterioration.

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Could the Could the Could the development development cause development prevent Watercourse cause a greater a deterioration in the water body from (WwTW) than 10% WFD class of any reaching GES? deterioration in element? WQ? Predicted deterioration is No class deterioration Good Ecological Status more than 10% for is predicted, however cannot be achieved for NH4. Proposed there is deterioration P due to current Claydon Brook development can be within the "Bad" class technology limits. (Winslow) accommodated with for P. WwTW Ensure proposed a tighter permit and upgrade is likely to be growth doesn’t cause upgrade to the required. significant deterioration. WwTW. Good Ecological Status Predicted cannot be achieved for No class deterioration deterioration is less P due to current Ouzel Brook is predicted. No than 10%. No technology limits. (Stanbridgeford) WwTW upgrade is WwTW upgrade is Ensure proposed required required growth doesn’t cause significant deterioration. Good Ecological Status Predicted cannot be achieved for No class deterioration deterioration is less NH4 or P due to current River Thame is predicted. No than 10%. No technology limits. (Aylesbury) WwTW upgrade is WwTW upgrade is Ensure proposed required. required. growth doesn’t cause significant deterioration. No class deterioration Good Ecological Status Predicted is predicted, however cannot be achieved for Scotsgrove deterioration is less there is deterioration P due to current Brook than 10%. No within the "Bad" class technology limits. (Haddenham) WwTW upgrade is for P. WwTW Ensure proposed required. upgrade is likely to be growth doesn’t cause required. significant deterioration. Good Ecological Status No class deterioration cannot be achieved for Predicted is predicted, however BOD, NH4 or P due to deterioration is less there is deterioration River Thame current technology than 10%. No within the "Bad" class (Long Crendon) limits. Ensure WwTW upgrade is for P. WwTW proposed growth required. upgrade is likely to be doesn’t cause required. significant deterioration. No class deterioration Good Ecological Status Predicted is predicted, however cannot be achieved for deterioration is less there is deterioration NH4 or P due to current Scotsgrove than 10%. No within the "Bad" class technology limits. Brook (Stone) WwTW upgrade is for BOD, NH4 and P. Ensure proposed required. WwTW upgrade is growth doesn’t cause likely to be required. significant deterioration. No class deterioration Good Ecological Status Predicted is predicted, however cannot be achieved for Fleet Marston deterioration is less there is deterioration NH4 or P due to current Brook than 10%. No within the "Bad" class technology limits. (Waddesdon) WwTW upgrade is for BOD, NH4 and P. Ensure proposed required. WwTW upgrade is growth doesn’t cause likely to be required. significant deterioration.

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The analysis undertaken looked at each treatment works and receiving watercourse in isolation. There is a theoretical risk that the cumulative impact of several treatment works, none of which would cause a significant deterioration at their point of discharge, could combine to create a deterioration further downstream. To assess the catchment-scale impact of increased discharges would require further analysis using the EA’s SAGIS-SIMCAT model. To properly undertake this type of assessment would also require a collaborative approach, bringing in growth from neighbouring districts. Given that Aylesbury Vale has eight neighbours this would be a significant undertaking, beyond the scope of this WCS. The Environment Agency, in collaboration with the water companies, are expected to undertake further catchment-scale modelling to support preparation of Business Plans for AMP7 (2020-2025). Potentially there may be scope for this additional modelling to further inform AVDC. If this is not possible due to timescales, specific catchment-scale analysis may be required by the Environment Agency. These could be undertaken with key neighbouring authorities, as follows:  River Ouse (including Buckingham) with Milton Keynes  River Ouzel with Central Bedfordshire and Milton Keynes  River Thame (including Aylesbury and Haddenham) with South Oxfordshire.

Table 54 reports information on the runs and the model results used to compare against BAT. Further explanation of the column headers can be found below:  Scenario: specifies the discharge flow and quality scenario data used as input in the RQP run;  Target: specifies the target to achieve;  Upstream river quality: specifies if the upstream river condition used for the run is the actual situation of if GES was assumed;  Mean, SD and 95%ile: these are the RQP tool output representing the discharge value required to meet the specific target. For BOD and NH4 the value to compare with BAT is the 95%ile whilst for P is the mean.

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Table 55: Runs and the model results used to compare against BAT

Upstream WwTW Pollutant Target River Scenario Mean SD 95%ile Conclusion Quality BAT Not Future Achievable Without Buckingham P 0.08 Moderate Not Achievable Growth Improving Upstream Quality BAT Not Present Achievable Without Buckingham P 0.08 Moderate Not Achievable Day Improving Upstream Quality Assumed Present Doesn’t Achieve Buckingham P 0.08 Mid Class 0.43 0.24 0.89 Day BAT Target Good Great Future Reaches BAT BOD 5 Good 2.20 2.66 7.01 Horwood Growth Target Great Present Reaches BAT BOD 5 Good 2.25 2.73 7.20 Horwood Day Target Great Future Doesn't Reach NH4 0.6 Good 0.25 0.36 0.88 Horwood Growth Target Great Present Doesn't Reach NH4 0.6 Good 0.26 0.37 0.91 Horwood Day Target Great Future Doesn't Reach P 0.076 Poor 0.07 0.02 0.11 Horwood Growth Target Great Present Doesn't Reach P 0.076 Poor 0.04 0.01 0.07 Horwood Day Target Assumed Great Present Doesn't Reach P 0.076 Mid Class 0.08 0.03 0.12 Horwood Day Target Good Mid Class Present Doesn’t Meet BAT Ivinghoe NH4 0.3 0.23 0.22 0.65 High Day target BAT Not Future Achievable Without Ivinghoe P 0.073 Poor Not Achievable Growth Improving Upstream Quality BAT Not Present Achievable Without Ivinghoe P 0.073 Poor Not Achievable Day Improving Upstream Quality BAT Not Future Achievable Without Ivinghoe P 0.181 Poor Not Achievable Growth Improving Upstream Quality BAT Not Present Achievable Without Ivinghoe P 0.181 Poor Not Achievable Day Improving Upstream Quality Assumed Present Doesn’t Meet BAT Ivinghoe P 0.073 Mid Class 0.09 0.03 0.15 Day target Good BAT Not Future Achievable Without Padbury P 0.077 Poor Not Achievable Growth Improving Upstream Quality

BAT Not Present Achievable Without Padbury P 0.077 Poor Not Achievable Day Improving Upstream Quality

BAT Not Future Achievable Without Padbury P 0.188 Poor Not Achievable Growth Improving Upstream Quality

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Upstream WwTW Pollutant Target River Scenario Mean SD 95%ile Conclusion Quality BAT Not Present Achievable Without Padbury P 0.188 Poor Not Achievable Day Improving Upstream Quality Assumed Future Reaches BAT Padbury P 0.077 Mid Class 2.57 0.61 3.67 Growth Target Good Assumed Present Reaches BAT Padbury P 0.077 Mid Class 2.70 0.64 3.85 Day Target Good BAT Not Steeple Future Achievable Without P 0.073 Poor Not Achievable Claydon Growth Improving Upstream Quality BAT Not Steeple Present Achievable Without P 0.073 Poor Not Achievable Claydon Day Improving Upstream Quality Steeple Future Reaches BAT P 0.181 Poor 1.63 0.36 2.28 Claydon Growth Target Steeple Present Reaches BAT P 0.181 Poor 1.71 0.38 2.40 Claydon Day Target Assumed Steeple Present Reaches BAT P 0.073 Mid Class 0.55 0.12 0.77 Claydon Day Target Good Future Reaches BAT Whaddon BOD 5 Good 2.74 1.73 6.08 Growth Target Present Reaches BAT Whaddon BOD 5 Good 2.76 1.74 6.13 Day Target Future Doesn't Reach Whaddon NH4 0.6 Good 0.27 0.31 0.83 Growth Target Present Doesn't Reach Whaddon NH4 0.6 Good 0.27 0.31 0.83 Day Target Future Doesn't Reach Whaddon P 0.08 Poor 0.08 0.02 0.12 Growth Target Present Doesn't Reach Whaddon P 0.08 Poor 0.07 0.02 0.10 Day Target Assumed Present Doesn't Reach Whaddon P 0.08 Mid Class 0.08 0.02 0.13 Day Target Good Wing Mid Class Future Reaches BAT BOD 4 4.35 1.55 7.23 Cublington High Growth Target Wing Mid Class Future Doesn’t meet BAT NH4 0.3 0.33 0.11 0.53 Cublington High Growth target Wing Mid Class Present Doesn’t meet BAT NH4 0.3 0.34 0.11 0.55 Cublington High Day target BAT Not Wing Future Achievable Without P 0.073 Poor Not Achievable Cublington Growth Improving Upstream Quality BAT Not Wing Present Achievable Without P 0.073 Poor Not Achievable Cublington Day Improving Upstream Quality BAT Not Wing Future Achievable Without P 0.181 Poor Not Achievable Cublington Growth Improving Upstream Quality BAT Not Wing Present Achievable Without P 0.181 Poor Not Achievable Cublington Day Improving Upstream Quality

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Upstream WwTW Pollutant Target River Scenario Mean SD 95%ile Conclusion Quality Assumed Wing Present Doesn’t Meet BAT P 0.073 Mid Class 0.09 0.02 0.13 Cublington Day target Good Mid Class Future Doesn’t Meet BAT Winslow NH4 0.3 0.51 0.55 1.54 High Growth Target Mid Class Present Doesn’t Meet BAT Winslow NH4 0.3 0.57 0.62 1.72 High Day Target BAT Not Future Achievable Without Winslow P 0.076 Poor Not Achievable Growth Improving Upstream Quality BAT Not Present Achievable Without Winslow P 0.076 Poor Not Achievable Day Improving Upstream Quality BAT Not Future Achievable Without Winslow P 0.187 Poor Not Achievable Growth Improving Upstream Quality BAT Not Present Achievable Without Winslow P 0.187 Poor Not Achievable Day Improving Upstream Quality Assumed Present Doesn’t Meet BAT Winslow P 0.076 Mid Class 0.16 0.03 0.21 Day Target Good Future Doesn’t Meet BAT Stanbridgeford NH4 0.30 High 0.27 0.32 0.85 Growth target Present Doesn’t Meet BAT Stanbridgeford NH4 0.30 High 0.27 0.33 0.86 Day target BAT Not Future Achievable Without Stanbridgeford P 0.12 Poor Not Achievable Growth Improving Upstream Quality BAT Not Present Achievable Without Stanbridgeford P 0.12 Poor Not Achievable Day Improving Upstream Quality Future Doesn’t Meet BAT Stanbridgeford P 0.25 Poor 0.22 0.20 0.60 Growth target Present Doesn’t Meet BAT Stanbridgeford P 0.25 Poor 0.22 0.20 0.60 Day target Assumed Future Doesn’t Meet BAT Stanbridgeford P 0.12 Mid Class 0.17 0.16 0.49 Growth target Good Assumed Present Doesn’t Meet BAT Stanbridgeford P 0.12 Mid Class 0.18 0.17 0.49 Day target Good Future Doesn’t Meet BAT Aylesbury NH4 0.3 High 0.13 0.21 0.47 Growth target Present Doesn’t Meet BAT Aylesbury NH4 0.3 High 0.13 0.22 0.48 Day target Future Doesn’t Meet BAT Aylesbury P 0.066 Poor 0.04 0.04 0.13 Growth target Present Doesn’t Meet BAT Aylesbury P 0.066 Poor 0.04 0.04 0.11 Day target

Assumed Present Doesn’t Meet BAT Aylesbury P 0.066 Mid Class 0.07 0.07 0.19 Day target Good

Future Doesn’t reach BAT Haddenham P 0.081 Poor 0.03 0.01 0.05 Growth Target

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Upstream WwTW Pollutant Target River Scenario Mean SD 95%ile Conclusion Quality BAT Not Present Achievable Without Haddenham P 0.081 Poor Not Achievable Day Improving Upstream Quality Assumed Present Doesn’t reach BAT Haddenham P 0.081 Mid Class 0.08 0.04 0.15 Day Target Good Future Reaches BAT Long Crendon BOD 5 Good 4.91 1.25 7.18 Growth Target Present Reaches BAT Long Crendon BOD 5 Good 5.07 1.29 7.40 Day Target Future Reaches BAT Long Crendon NH4 0.6 Good 0.53 0.39 1.29 Growth Target Present Reaches BAT Long Crendon NH4 0.6 Good 0.55 0.40 1.32 Day Target BAT Not Future Achievable Without Long Crendon P 0.066 Poor Not Achievable Growth Improving Upstream Quality BAT Not Present Achievable Without Long Crendon P 0.066 Poor Not Achievable Day Improving Upstream Quality BAT Not Assumed Present Achievable Without Long Crendon P 0.066 Mid Class Not Achievable Day Improving Good Upstream Quality Future BAT target Stone BOD 5 Good 3.70 1.14 5.81 Growth exceeded Present BAT target Stone BOD 5 Good 3.70 1.14 5.80 Day exceeded Future Doesn’t reach BAT Stone NH4 0.6 Good 0.37 0.20 0.76 Growth Target Present Doesn’t reach BAT Stone NH4 0.6 Good 0.37 0.20 0.76 Day Target BAT Not Future Achievable Without Stone P 0.081 Poor Not Achievable Growth Improving Upstream Quality BAT Not Present Achievable Without Stone P 0.081 Poor Not Achievable Day Improving Upstream Quality BAT Not Assumed Present Achievable Without Stone P 0.081 Mid Class 0.08 0.02 0.12 Day Improving Good Upstream Quality Future BAT target Waddesdon BOD 5 Good 3.46 1.19 5.67 Growth exceeded Present BAT target Waddesdon BOD 5 Good 3.47 1.19 5.68 Day exceeded Future Doesn’t reach BAT Waddesdon NH4 0.6 Good 0.28 0.28 0.82 Growth Target Present Doesn’t reach BAT Waddesdon NH4 0.6 Good 0.29 0.28 0.82 Day Target Future Doesn’t reach BAT Waddesdon P 0.08 Poor 0.05 0.02 0.09 Growth Target Present Doesn’t reach BAT Waddesdon P 0.08 Poor 0.05 0.02 0.08 Day Target Assumed Present Doesn’t reach BAT Waddesdon P 0.08 Mid Class 0.08 0.03 0.13 Day Target Good

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Upstream WwTW Pollutant Target River Scenario Mean SD 95%ile Conclusion Quality Future BAT target Worminghall BOD 5 Good 3.05 1.62 6.16 Growth exceeded Present BAT target Worminghall BOD 5 Good 3.05 1.62 6.16 Day exceeded Future Doesn’t reach BAT Worminghall NH4 0.6 Good 0.37 0.19 0.73 Growth Target Present Doesn’t reach BAT Worminghall NH4 0.6 Good 0.38 0.19 0.74 Day Target Future Doesn’t reach BAT Worminghall P 0.081 Poor 0.08 0.02 0.12 Growth Target Present Doesn’t reach BAT Worminghall P 0.081 Poor 0.07 0.02 0.12 Day Target Assumed Present Doesn’t reach BAT Worminghall P 0.081 Mid Class 0.08 0.03 0.13 Day Target Good

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A.10.4 Conclusions The following conclusions are drawn from this water quality impact assessment:  Haddenham, Long Crendon, Stone and Waddesdon are currently working above their DWF limits.

 The proposed growth is predicted to cause a greater than 10% deterioration for NH4 at Winslow. The deterioration at Winslow could be redressed by applying a tighter permit and upgrade to treatment, within the bounds of current technology.  At Great Horwood, Ivinghoe, Whaddon, Winslow, Haddenham, Long Crendon, Stone Waddesdon and Worminghall, modelling indicates that water quality is currently poor for at least one parameter immediately downstream of the treatment works, and would deteriorate as a result of growth, and therefore is likely to require a treatment upgrade. In most of these cases, the upstream catchment area is very small and consequently the treated effluent contributes the majority of the flow in the watercourse. In such cases, the EA may consider assessing compliance at a downstream water quality monitoring point, rather than immediately downstream of the treatment works outfall.  At all other works investigated, the proposed growth is not expected to lead to significant deterioration in water quality  It would be possible for the Padbury Brook to meet Good Status or Potential with a combination of improvements to upstream water quality and improvements to treatment within the limits of current BAT. At all other treatment works, GES or GEP could currently not be achieved for Phosphorous (and for BOD and Ammonia at a few works) due to the limitations of current Best Available Technology. In all cases, it is the technology limitations, not the proposed growth, which prevents the waterbody meeting GES/GEP, and therefore environmental capacity is not considered to place a limitation on growth. In these cases, it remains necessary to ensure that the proposed growth does not cause significant deterioration.  It is anticipated that improvements in Phosphorous removal technologies will lead to permits of annual mean concentrations down to 0.1mg/l, from AMP7 (2020-2025). If such technology were to be applied at Winslow, then the predicted deterioration could be prevented and environmental capacity would not be a constraint to growth. Results of national phosphorous removal trials, and the implications for future permits, are planned to be published in 2017. If an annual average of 0.1mg/l could be achieved, this would enable the majority of watercourses assessed to achieve, or be very close to achieving, GES/GEP. However, it is likely that technical feasibility and cost-benefit assessment would mean that 0.1mg/l would not be achievable at all small treatment works in the near future.  The river flow data used for Ivinghoe is from the AMP3 (2000-2005) period. Prior to final determination of a revised permit condition, it would be advisable to revise this with more recent data.  There may be potential for additional flows within the Great Horwood catchment being transferred to Swanbourne WwTW. Likewise, a proportion of flow at Whaddon could be transferred to Cotton Valley WwTW at Milton Keynes. Neither of these options have been tested.  The analysis undertaken looked at each treatment works and receiving watercourse in isolation. There is a theoretical risk that the cumulative impact of several treatment works, none of which would cause a significant deterioration at their point of discharge, could combine to create a deterioration further downstream. To assess the catchment-scale impact of increased discharges would require further analysis using the EA’s SAGIS- SIMCAT model. To properly undertake this type of assessment would also require a collaborative approach, bringing in growth from neighbouring districts. Given that Aylesbury Vale has eight neighbours this would be a significant undertaking, beyond the scope of this WCS.

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