Affinity Water Sources – Batchworth Pumping Test Assessment Document No.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 Contents
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Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision Author Checked by Approved by Date approved Reason for revision P01 Richard Mike Barker Mike 26/10/17 n/a Winstanley Hutchinson P02 Richard Mike Barker Mike 2/2/18 For acceptance ‐ Winstanley Hutchinson after Affinity Water Comments P03 Richard Mike Barker Mike 2/2/18 For acceptance‐ Winstanley Hutchinson After EA comments Po4 Richard Mike Barker Mike 5/3/18 For acceptance‐ Winstanley Hutchinson After further AW Comments SECURITY CLASSIFICATION: OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 Contents Executive Summary 6 1 Introduction 7 1.1 Background 7 1.2 Scope of study 7 1.3 Limitations 7 1.4 Data sources 8 2 Study Area Setting 9 2.1 Introduction 9 2.2 Geology 9 2.3 Hydrogeology 12 2.4 Hydrology 16 2.5 Hydro‐ecology 18 3 Water Features in Study area 20 3.1 Introduction 20 3.2 Water features survey specification 20 3.3 Water features survey data collection 22 3.4 Monitoring agreed 25 4 2017 Pump Testing 26 4.1 Scope of testing and monitoring 26 4.2 Antecedent conditions 27 4.3 Prevalent Conditions during the test and recovery period 31 4.4 Method for interpretation of test data 31 4.5 Measured water level changes 33 5 Environment Impact of Proposed Licence Variation 40 5.2 Potential to derogate licensed abstractions rights 40 5.3 Review of potential to impact surface water features 41 5.4 WFD compliance 42 6 Review of Potential Source Yield 43 6.1 Batchworth PS borehole details 43 6.2 Assessment of potential yield 43 6.3 Recommendations for confirmation of yield 45 7 Conclusions 47 Template no.: Uncontrolled when printed HS2‐HS2‐PM‐TEM‐000‐000004 Page 2 OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 7.1 Potential for derogation of abstraction rights 47 7.2 Potential for environmental impacts on surface water features/ecology 47 7.3 Achievability of borehole target yield 47 List of acronyms 48 References 49 Appendix A 50 Logs of monitored third party boreholes 50 Template no.: Uncontrolled when printed HS2‐HS2‐PM‐TEM‐000‐000004 Page 3 OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 List of figures Figure 1 ‐ Study Area Figure 2‐ Schematic Hydrogeological Cross Section through Study Area Figure 3 – Groundwater Level Contours in Local Area Figure 4 ‐ Westerley OBH Long‐term Hydrograph Figure 5 ‐ Key Surface Water Features in the Study Area Figure 6 ‐ Pump Test Monitoring Points Figure 7 ‐ Pumping rates at Batchworth PS around the test period Figure 8 ‐ Local rainfall and river flows around the testing period Figure 9‐ Flow rates at Mill End around the testing period Figure 10 ‐ Water levels in Westerley and Stockers OBH around the testing period Figure 11 ‐ Sub‐division of test period for comparison of drawdown effects at test monitoring points Figure 12‐ Water Levels at Observation Sites to the east of Batchworth PS in February‐April 2017 Figure 13 ‐ Water Levels at Borehole observation sites to the west of Batchworth PS in February‐April 2017 Figure 14 ‐ Juniper Hill Water Levels vs. Instantaneous Batchworth PS Flow Figure 15 – Moor Hall Park Borehole Levels February‐April 2017 Figure 16 ‐ Batchworth PS individual BH water levels around the period of testing List of tables Table 1 ‐ Geology of Study Area Table 2 ‐ Hydrogeological Properties of Strata in Study Area Table 3 ‐ Local River Flows (as Ml/d) Table 4 ‐ WFD status of local waterbodies within Study Area Table 5 ‐ Abstraction License holders identified within the WFS radius Table 6 ‐ Lakes/Ponds identified by EA within WFS radius Table 7 ‐ Details of Licensed Abstraction Points Table 8 – Water level changes at off‐site monitoring points during the test period Table 9 ‐ Assumed details of Batchworth PS boreholes from test and most recent downhole surveys Template no.: Uncontrolled when printed HS2‐HS2‐PM‐TEM‐000‐000004 Page 4 OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 Appendices Appendix A – 3rd party borehole logs Template no.: Uncontrolled when printed HS2‐HS2‐PM‐TEM‐000‐000004 Page 5 OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 Executive Summary The HS2 route in the Colne Valley, Hertfordshire passes very close to several Affinity Water (AW) groundwater abstractions. It has been identified that certain HS2 construction activities could pose a temporary risk to abstracted water quality at these supplies. HS2 and Affinity Water are investigating options to mitigate these risks, including: shutting down a vulnerable source for several years during the HS2 construction phase; and increasing output capacity at other AW groundwater sources to maintain customer supplies. One source where alternative abstraction capacity has been identified is Batchworth Pumping Station, a groundwater source near Rickmansworth. AW aims to have the facility to temporarily increase the output from this source for short periods during the HS2 construction period. This would involve an increase to the daily licensed rate from the current value of 20.46 Ml/d (with no change to the annual group licence total). A pumping test at Batchworth has been performed to assess the feasibility of this option and to collect information to support an abstraction licence variation application. This testing was completed in spring 2017 and a peak abstraction rate of c. 26 Ml/d was achieved. Atkins / CH2M / SENER has been commissioned by the EDP JV, on behalf of High Speed 2 Ltd, to: assess the environmental impacts of the proposed increase in abstraction; and to complete a preliminary review of whether this yield could be obtained from the boreholes under drought conditions. The review of the test data has indicated that the potential effect seen in the monitored features was generally either negligible or very small (i.e. of the order of less than 10 cm), except at Juniper Hill PS, where a modest effect was observed. This is a Thames Water site that has a (presently) disused groundwater abstraction for process water. However, there would only be potential for licence derogation of the Thames licence if their intake is already close to the pumped water level under drought conditions. It appears that there is unlikely to be any other significant licence derogations or adverse effects on nearby water features with groundwater‐dependent ecology from the proposed licence variation. The test proved that a peak yield from the source of at least 26 Ml/d was possible for 1 week and at least 24 Ml/d for 2 weeks under the prevalent conditions at the time of the test (i.e. when groundwater levels were below average and the site had been operating at 10 to 20 Ml/d in the preceding weeks). It is possible that there may be some limitations on a 26 Ml/d 2‐week abstraction, due to the current BH3 pump depth, particularly under drought conditions. Confirmation of the intake depth and re‐evaluation of source deployable output by AW would determine if further action (e.g. lowering of the pump) is required to achieve 26 Ml/d. Template no.: Uncontrolled when printed HS2‐HS2‐PM‐TEM‐000‐000004 Page 6 OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 1 Introduction 1.1 Background 1.1.1 The HS2 route in the Colne Valley, Hertfordshire passes very close to several Affinity Water (AW) groundwater abstractions, most notably the source at Blackford. It has been identified that certain construction activities pose a temporary risk to abstraction from this source, and to others further afield. 1.1.2 HS2 and Affinity Water have agreed a plan to mitigate the risk to Blackford. Currently, this is envisaged as: a medium term (c. 30 month) shut down of Blackford during a period of the HS2 construction phase; increased short‐term abstraction from other Affinity Water sources in the area to compensate; and an import of treated water from Thames Water Utilities Ltd. (TWUL). 1.1.3 One source where additional abstraction capacity could be obtained is Batchworth Pumping Station (PS), a groundwater source near Rickmansworth, located further up the Colne Valley, approximately 5 km to the north of Blackford PS. Affinity Water intend to temporarily increase the licensed daily abstraction rate from this source, with no change to the annual group licence total. This would allow it to provide additional supply capacity during the HS2 construction period. It is anticipated that proposed peak abstraction would need to cover two consecutive periods of supply‐demand deficit of up to one week each, i.e. approximately 14 days in total: these periods are likely to occur during the summer months when demand is mostly likely to spike, but could potential occur at other times of the year, as operational needs arise. 1.1.4 A pumping test was scoped at Batchworth to assess the feasibility of this option and to collect information for an environmental assessment to support a licence variation. This testing was completed in spring 2017 and an abstraction rate of c. 26 Ml/d was sustained. 1.2 Scope of study Atkins / CH2M / SENER has been commissioned by the EDP JV, on behalf of High Speed 2 Ltd, to prepare a report to: assess the environmental impacts of the proposed increase in abstraction using the data collected as part of the pump test; and complete a review of whether the desired yield could be obtained from the Batchworth boreholes.