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 – 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

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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

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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

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Appendices Appendix A – 3rd party borehole logs

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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, 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 . 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.

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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. 1.3 Limitations

1.3.1 This report has been completed with information provided by HS2 and third parties. It is subject to the limitations of information collected during the Water Features Survey and subsequent monitoring. Template no.: Uncontrolled when printed HS2‐HS2‐PM‐TEM‐000‐000004 Page 7

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1.3.2 The assessment of whether the desired yield could be obtained from the boreholes is intended to be indicative only; and should not be relied upon to complete an engineering feasibility assessment of this option. It does not constitute an evaluation of peak deployable output. 1.4 Data sources

1.4.1 Information on the study area has been collected from various sources, it includes:

 Water Features Surveys completed by HS2.

 BGS mapping.

 BGS borehole records.

 Information on borehole assets provided by Affinity Water.

1.4.2 Additional sources of information have been collected for this study:

 Environment Agency rainfall and river stage data.

 Environment Agency observation borehole data.

 Information from TWUL.

 Information from the local Environmental Health Officer.

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OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 2 Study Area Setting 2.1 Introduction

2.1.1 The study area is taken to be the area approximately 2 km from the Batchworth PS, as shown in Figure 1 overleaf. The principal geographic feature is the valley of the River Colne, which contains many flooded gravel pits. Ground levels vary from c. 90 mAOD on the surrounding hillsides, to c. 45‐47 mAOD in the valley floor. 2.2 Geology

2.2.1 The details of the key strata present are summarized in Table 1 further on.

2.2.2 The bedrock geology of the study area principally comprises Chalk bedrock, with some limited outcrops of London Clay and Lambeth Group deposits on the higher ground to the south‐east of Batchworth PS. The strata dip regionally at a gentle angle (i.e. a few degrees) to the south‐ east. No faults are shown on the 1:50 000 geological maps for the local area (BGS, 2015), but it is possible that unmapped discontinuities may be present, e.g. beneath the river valleys.

2.2.3 Superficial deposits are present in the valley floors of local drainage channels, comprising alluvium overlying Shepperton Gravels. Isolated Winter Hill Terrace gravel deposits and Head deposits are also present outside the main floodplains. There are some localised areas of landfilling: e.g. waste disposal sites are recorded beneath the sites of the Croxley and Cressacres lakes, c. 500m to the ENE of the Batchworth PS source.

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Figure 1 ‐ Study Area

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Table 1 ‐ Geology of Study Area

Type Formation Description Indicative Comment on Occurrence Thickness (m)

Super‐ Made Ground Variable – likely to comprise 0‐2 Likely to be present in the local urban area facial granular material beneath and at specific sites of emplacement, e.g. railway embankments and Railway embankments near the site and waste materials in landfills. in backfilled gravel pits in the Colne Valley, e.g. around Croxley Hall Farm.

Alluvium Fine, organic rich silts and 0‐ 2 Present in the valley floors of the Colne, clays with occasional gravel Gade and Chess, locally absent at sites of lenses. former gravel pits

Shepperton Gravel Sandy gravels with Est. 0‐5 Present in the valley floors of the Colne, occasional silt deposits Gade and Chess

Winter Hill Gravel Est. 0‐5 Present as isolated terrace deposits on hillsides

Solid London Clay Grey/brown silty clay. 0‐20 Present only beneath the hill approximately 1km to the south‐east of

Lambeth Group Interbedded silts, sands and 0‐10 Batchworth PS, underlying part of clays, gravel beds at base Batchworth Golf Club

Chalk Group: Seaford Firm white chalk with 0‐50 This formation forms most the bedrock and Newhaven conspicuous semi‐ outcrop/sub‐crop in the local area and is Formations continuous nodular and present beneath the valley floor, where it (undifferentiated) tabular flint seams. may be weathered. Hardgrounds and thin marls in the lowest beds.

Chalk Group: (Lewes Hard to very hard nodular 30‐35 Outcrops beneath the valleys of the Chess Formation) chalks and hardgrounds, with and part of the Colne Valley floor; and at interbedded soft to medium depth beneath the Seaford/Newhaven hard chalks Chalk.

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OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 2.3 Hydrogeology Hydrogeological properties of strata 2.3.1 The Hydrogeological properties of the local formations are summarized in Table 2 below, and the relationship of the geology to local surface water features and boreholes is depicted in a schematic section along the Colne Valley in Figure 2 overleaf.

Table 2 ‐ Hydrogeological Properties of Strata in Study Area

Type Formation Permeability Storage Comment

Alluvium Moderate to Moderate Occasional moderate permeability layers/lenses, but typically low Superficial Low permeability

Winter Hill High High Likely to have moderate/good connectivity to the underlying Chalk, Gravels depending on the extent of Chalk weathering. Likely to be in good hydraulic continuity with local lakes and rivers.

Solid London Moderate to Low Likely to restrict infiltration from the surface to the underlying Chalk Clay Low where present. Unlikely to act as a confining layer, given local water levels

Lambeth Low to Moderate Likely to restrict infiltration from the surface to the underlying Chalk Group Moderate where present. Unlikely to act as a confining layer, given local water levels/topography

Chalk High to Very Low Main aquifer for potable supply in the area. Likely to have significant High interconnection to local river systems and overlying Gravel aquifer. May be weathered to a lower permeability putty chalk in places in the river valley. Likely to have high transmissivity, particularly where faults/dissolution features: Affinity Water have indicated previous aquifer tests at Batchworth proved a very high transmissivity of 7,910 m2/d, which is suggestive of this situation being the case at the site. Piezometric and artesian heads in some boreholes indicate layering within the Aquifer and/or confinement at depth.

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Figure 2‐ Schematic Hydrogeological Cross Section through Study Area

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OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 Groundwater Flow Directions and Levels 2.3.2 Groundwater flow directions in the region have a flow trend to the east/south‐east, i.e. down dip. (HS2, 2017). A contoured plot produced during NEP investigations (shown in Figure 3 below) indicates the flow direction in the valley is approximately parallel to the River Colne (i.e. ESE), although the contours are beginning to diverge around Batchworth. The hydraulic gradient within the valley is relatively shallow.

Figure 3: Chalk Aquifer Water Level Contours in Local Area

Batchworth PS

2.3.3 Rest groundwater levels in the Colne Valley (as derived from data collected and described below) are typically 40‐45 mAOD. This is close to ground surface and artesian conditions are observed in some boreholes in the Chalk aquifer to the north‐east of the site (presumably due to semi‐confinement of deeper horizons in the Chalk), as described below.

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2.3.4 An example of a medium‐term regional groundwater level hydrograph is shown in Figure 4 below for Westerley OBH, located uphill, 1 km to the NW of Batchworth PS (location shown further on in Figure 6). This indicates a typical baseline annual fluctuation of the order of +/‐1 m, with the lowest level in this period recorded during the drought of 2011/12, at about 1 m below the mean level.

Figure 4 – Westerley OBH Long‐term Hydrograph

2.3.5 Natural groundwater level fluctuations closer to the river valleys would be expected to be attenuated relative to the interfluves, due to the moderating effect of surface water inflows/outflows and storage in the overlying alluvial gravel aquifer, as well as possible zones of higher transmissivity in the Chalk due to karstification of the aquifer. However, artificial influences may be greater there due to the operation of numerous public supply sources (including Batchworth PS).

2.3.6 There may also be distinct piezometric surfaces within the Chalk, due to layering/weathering and other discontinuities that either retard or enhance flow movement within the aquifer. Previous studies at Batchworth (HS2, 2016) have indicated a leaky response from the Chalk aquifer, with an attenuated pumping signal seen in the overlying Superficial deposits.

2.3.7 Groundwater levels in the valley gravels are likely to be shallow and an intermediate value between Chalk groundwater levels and surface water. The water level of local lakes is likely to reflect the balance between the surrounding gravel aquifer’s groundwater level and local Template no.: Uncontrolled when printed HS2‐HS2‐PM‐TEM‐000‐000004 Page 15

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inflows/outflow to/from the Colne, the Grand Union Canal (GUC); and other lakes, all of which appear to have some degree of interconnection through sluices and spillways.

2.3.8 The groundwater level in the Alluvium may be different and potentially perched above that of the gravels, due to low permeability horizons within it that restrict vertical movement of groundwater. 2.4 Hydrology

2.4.1 The study area contains several rivers and flooded gravel pits, the key surface water features in the study area are shown in Figure 5 below. The area typically receives 650 to 750 mm of rainfall a year.

Figure 5 – Key Surface Water Features in the Study Area

Rivers 2.4.2 The study area lies within the catchment of the River Colne, which flows south‐westwards past the site. It is fed by two significant tributaries upstream of Rickmansworth: the Gade and

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the Chess. There are also ditches within 250 m of the pump station that drain the Rickmansworth urban area.

2.4.3 Summary flow statistics for each surface water body are provided in Table 3 below. Baseline flows in the Colne are supported by the discharge from Maple Lodge Sewage Treatment Works, c. 3 km downstream of Batchworth: this works has a typical dry weather flow output of the order of 100 Ml/d.

Table 3 ‐ Local River Flows (as Ml/d)

River Gauge Name Catchment Area Q95 Q70 Q50 (km2)

Colne (c. 8 km upstream Berrygrove 352 13 33 48 of Rickmansworth)

Chess (nr. Rickmansworth 105 16 33 43 Rickmansworth)

Gade (nr. Croxley Green 184 33 61 79 Rickmansworth)

Colne (c. 3 km Denham 743 159 254 320 downstream Rickmansworth)

Grand Union Canal 2.4.4 The Grand Union Canal passes through the study area, running parallel to the Gade and the Colne Valley, downstream of Rickmansworth. It is interconnected with the River in places, and at other points is either fed from, or spills into the river system. Canals are usually lined where running over permeable formations, but it has not been established if this is the case in the locality. Lakes and ponds 2.4.5 There are several large lakes in the local area that are flooded gravel pits, principally Stockers Lake, Bury Lake and Batchworth Lake to the WSW of Batchworth PS; and lakes around Croxley Hall Farm and Cressacres Lake to the ENE. Further details on these were collected during the Water Features Survey for the pumping test and are provided in the following chapter. These lakes are typically unlined and in lateral continuity with local groundwater in the shallower superficial deposits, although it is likely that some have materials in their base and/or accumulated silt that may reduce the degree of hydraulic connection with the underlying aquifers.

2.4.6 There are also a series of lakes/ponds located on higher ground c. 750 m to the south of Batchworth PS, within Batchworth Golf Club: given their elevation, these may be lined/artificial, or perched on impermeable natural deposits.

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OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 2.5 Hydro‐ecology

2.5.1 The overall WFD status of local waterbodies is shown in Table 4 below. These indicate that the rivers in the study area are all in moderate condition, driven by poor chemical quality (phosphates) and the condition of specific ecological assemblages. The Chalk Aquifer is in poor condition due to the water resource balance of the aquifer and water quality.

2.5.2 There are four specific designated local habitat sites within 1.5 km of the source that are or may be groundwater dependent:

SSSI – (c. 1 km to the ENE of Batchworth PS., adjacent to Croxley Lake, shown in Figure 5 previously). This is a heathland habitat, partly dry heathland, but with a section of water‐dependent plant species towards its western end. It is in unfavourable condition and recovering: the key factor causing the current condition appears to be the lack of grazing at the site.

 Rickmansworth Aquadrome Local Nature Reserve (LNR)‐ (c. 250 m to the WSW of Batchworth PS at its closest point). This comprises Batchworth Lake, Bury Lake and surrounding woodland/grassland;

 Stockers Lake LNR‐ this comprises Stockers Lake and margins; and a small woodland area to the north‐west of the Colne;

 Withey Beds LNR, located 1.5 km to the W of Batchworth PS – This is a local conservation site that “supports a wide range of habitats including wet woodland, marsh, drier grassland and open ditches as well as the River Colne”.

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Table 4 ‐ WFD status of local waterbodies within Study Area

Feature Waterbody ID WFD Status Objective (2015 Driver for failure to achieve good (Cycle 2) unless stated) status

River Colne (Upstream GB 106039029840 Moderate Moderate Overall ecological condition, of Rickmansworth (from Confluence with appears to be driven primarily by Ver to Gade) macrophytes/phytobenthos and phosphate.

River Chess GB 106039029870 Moderate Moderate Overall ecological condition, (Chess) appears to be driven primarily by fish, macrophytes/phytobenthos and phosphate.

River Colne GB 106039023090 Moderate Good Overall ecological condition: (Downstream of (Chess to conf. appears to be driven primarily by Rickmansworth Thames) phosphate.

Grand Union Canal GB 70610185 Moderate Good (By 2027) Overall status driven by (Berkhamstead to “mitigation measures Maple Lodge) assessment”, although it is not clear what this refers to.

Chalk Aquifer GB 40601G601200 Poor Poor Overall status driven by (Mid Chilterns Chalk) “Groundwater dependent surface water body status, water balance and chemical status for drinking water protected areas”.

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OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 3 Water Features in Study area 3.1 Introduction

3.1.1 This chapter describes the water features survey (WFS) process for the site and the details collected during the water features survey in 2016; and the subsequent monitoring programme. 3.2 Water features survey specification

3.2.1 The WFS was completed based on a technical note from the EA prepared in August 2016 (EA, 2016). This stated that an appropriate survey radius was 1.5 km from the source, based on an initial calculation of a potential drawdown effect of up to 0.5 m at this distance from the Batchworth PS.

3.2.2 The EA identified four licensed abstractions in the area to be included in the WFS, with a view to completing an assessment of impacts. A further licence holder (Batchworth Golf Club) was also subsequently identified within this radius during the WFS (see below).

3.2.3 The licence details ascertained to date are summarised in Table 4 below, and the site locations are included as points on Figure 5 or Figure 6.

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Table 4 ‐ Abstraction License holders identified within the WFS radius

Licence Site Name Abstraction License Abstracted Permitted Purpose number Location(s) Holder Feature Abstraction quantities

28/39/28/ 0507 Croxley Hall TQ 0712 9445 to Assumed River Chess 20,263 m3/d; and Watercress Farm TQ 0648 9441 Croxley Hall 4,930,663 m3/yr. growing and Water Ltd. fish farming 28/39/28/ 0312 36 artesian wells at Chalk 20,457 m3/d; and Croxley Hall Farm, Groundwater 7,464532 m3/yr. between NGRs TQ 0673 9463, TQ 0701 9451, TQ 0715 9442 and TQ 0645 9432

28/39/28/ 0114 Juniper Hill TQ 056 934 Thames Water Chalk 54.6 m3/hour; Process PS (Juniper Hill PS) Groundwater water 681.9 m3/d; and

204,570 m3/yr.

28/39/28/0480 Stockers PS TQ 05048 93299 Affinity Water Chalk 56.8 m3/hour, Potable (BHs E1 and E2) Groundwater supply 9,092 m3/d.

The aggregate quantity of water authorised to be abstracted under this licence shall not exceed 32,120,000 m3/year.

28/39/28/0601/ Batchworth TQ 06630 932240 Trustees for Chalk 20 m3/hr; Spray R01 Golf Club and TQ 06940 the time being Groundwater Irrigation 3 92820 of Batchworth 400 m /d; Park Golf Club 40,000 m3/year.

3.2.4 The EA also identified that the local rivers/canals should be considered for monitoring, with a view to assessment of impacts, i.e. the:

 River Gade.

 River Colne.

 River Chess.

 Grand Union Canal.

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3.2.5 A series of 7 river level monitoring points were recommended in the EA technical note on the WFS (EA, 2016). A further 13 lakes and ponds were identified by the EA for assessment of impacts, as shown in Table 5 below, but no additional monitoring was requested.

Table 5 ‐ Lakes/Ponds identified by EA to be considered for monitoring within the WFS radius

Name NGR of closest point Distance from pumping test

Batchworth Lake TQ 05963 93946 340 m west

Bury Lake TQ 05497 93866 810 m west

Croxley Lake TQ 06601 94318 440 m northeast

Cressacres TQ 06548 94359 440 m northeast

Longwater TQ 06970 94386 780 m northeast

Kingfisher Pool TQ 07043 94360 830 m northeast

Unnamed lake 1 TQ 06961 94247 710 m northeast

Unnamed lake 2 TQ 07139 94338 900 m northeast

Unnamed lake 3 TQ 07186 94256 920 m northeast

Unnamed lake 4 TQ 07335 94242 1.1 km northeast

Unnamed lake 5 TQ 07508 94222 1.2 km northeast

Unnamed lake 6 TQ 07508 94286 1.2 km northeast

Unnamed lake 7 TQ 06460 94425 460 m north

3.2.6 Three Rivers council (the Local Authority) were also contacted in July 2017 to determine if there were any private, unlicensed potable abstractions in the local area (i.e. within 1.5 km of Batchworth PS) and they have confirmed that there are not.

3.3 Water features survey data collection

3.3.1 The WFS was completed in December 2016. This involved visiting the sites named above with a view to ascertaining further details and to review the practicality and merit of including them in the monitoring programme for the pumping test. Further details ascertained from the WFS and subsequently for the licensed abstraction points in the area are included in Table 6. Groundwater abstraction points and observation wells within 2 km of Batchworth PS are shown on Figure 6 below.

3.3.2 There is a further Affinity Water Chalk abstraction site called Mill End. This is 3 km to the WSW of Batchworth PS; and 1km to the NW of Stockers PS. This is of relevance, as pumping from it may influence water levels to the west of Batchworth PS, e.g. at Stockers OBH.

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Figure 6 – Licensed Groundwater Abstraction Sites and Observation Boreholes in vicinity of Batchworth PS

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Table 6 ‐ Details of Features ascertained during the Water Features Survey

Site & License Abstraction Point details Pump Comment Holder ascertained during WFS intake depth

Croxley Hall Surface water feeds fishing n/a – River source reported from site visit to be the Colne from Farm ‐ Surface lakes: Lake A‐D from: assumed the north, but may actually be sourced from the Chess, as water gravity the River Colne is to the south of the site, beyond the canal. i) Gated inflow and channel inflow only from River and; (ii) Passive overflow spill from the GUC

Croxley Hall i) Several artesian boreholes, n/a ‐ Holes overflowing during December 2016 site visit and Farm ‐ capped with bricks to restrict artesian Springs and borehole seen discharging into base of Groundwater overflow; flow only watercress beds. Discharge rates are unmeasured.

ii) Artesian boreholes sunk 2 borehole depths quoted from site visit: 30 m (point 7d in directly into cress bed base WFS report) and 100 m. Only one BGS borehole record for a 40 m‐deep borehole on this site at NGR 506540 194420, iii) Natural springs that included in Appendix A). Comment on log that it went sub‐ emerge into base of artesian during a 1940s drought and needed to be pumped. watercress bed and are assumed to feed Lake E

Juniper Hill PS Borehole in pump house Not BGS borehole record (in Appendix A) indicates there is a 61 (Thames Water) building. Licensed for process ascertained m‐deep borehole at the site. water, but not used for several years.

Stockers PS Abstraction boreholes are Not The site was an Affinity Water potable supply site, but has (Affinity Water) shown bordering Stockers ascertained not been used for abstraction for several years. adit Lake, but were not visited comprises two abstraction boreholes: BH2; and BH5, during 2016 site visit. connected via an adit. Stockers OBH is outside the adit and is an observation borehole.

Batchworth Golf Two boreholes, BH A and BH Not BH A is 87 m borehole (Plain casing to 20 m bgl as shown in Club B, c. 500 m apart, 750 m and ascertained the log in Appendix A).BH B is 62 m deep borehole. Mostly 1.25 km from Batchworth used during summer months, for irrigation. Drawdown of c. respectively 10 m observed in BH A during 2004 test at 10 m3/hr. RWL in unconfined Chalk

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OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 3.4 Monitoring agreed

3.4.1 Following provision of the WFS information, it was discussed with the EA and it is understood that it was agreed with the EA that monitoring during the pumping test would be completed at the following off‐site monitoring points (data loggers with periodic manual dips, unless stated):

 Cressacres Lake (Lake A above).

 Croxley Lake.

 Four boreholes at Croxley Hall Farm (“Shed”, “Ditch”, “Deep” and “Shallow”)

 Juniper Hill Pumping Station borehole.

 Stockers and Westerly OBHs (dips completed by HS2, logger data provided by Affinity Water and EA).

 Weekly spot flow gauging of the Canal adjacent to Rickmansworth; and of the Gade adjacent to the Grove PS.

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OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 4 2017 Pump Testing 4.1 Scope of testing and monitoring

4.1.1 The test comprised progressively increasing abstraction from Batchworth BH3 from early to mid‐March 2017, followed by a two‐week period of total abstraction of c. 24‐ 26 Ml/d from mid to the end of March. Abstraction in the weeks before and after the test was close to the current peak licence of 20.46 Ml/d. This is depicted in Figure 7 below, with the green and red dotted lines indicating the start and end of the testing period respectively. The flow was partly pumped in to supply, and partly discharged to the River Colne adjacent to the site.

4.1.2 Following the test, there was a fluctuating reduction in rates back down to 10 Ml/d in the early part of April. There were also clearly defined stepped rate increases in February preceding the test. Monitoring during both these periods provides useful background information on aquifer responses, and this data is included in the scope of the assessment below.

Figure 7 ‐ Pumping rates at Batchworth PS around the test period

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OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 Data Collection 4.1.3 Groundwater level logger data was collected between 9th February to around 4th April from Juniper Hill, Stockers, Croxley Hall Farm “Deep” and “Shallow “boreholes. A shorter period of logger data (6th March to the 5th April) from Croxley Lake, Cressacres Lake and the Croxley Hall Farm “Ditch” and “Shed” boreholes. Logger data has been obtained for Westerly OBH and Stockers OBH from mid‐February to the end of April. Level transducer and flow data for the individual Batchworth boreholes, as well as the total Batchworth abstraction rate has been obtained for the period of February to March. The available details of the off‐site monitoring points are summarized in Table 7 below.

Table 7 – Details of Off‐Site test groundwater monitoring points

Monitoring Est. Depth Response zone Inferred Screened Formation Point (mbgl)

Croxley Hall >100* Unknown ‐No log Chalk (and possibly Terrace Gravels) “Deep”

Croxley Hall 29.5* Unknown‐ No log Chalk (and possibly Terrace Gravels) “Shallow”

Croxley Hall 22* Unknown‐ No log Chalk (and possibly Terrace Gravels) “Ditch”

Croxley Hall 7* Unknown‐ No log Chalk (and possibly Terrace Gravels) “Shed”

Juniper Hill OBH 62 Unknown Chalk

Stockers OBH Unknown Unknown‐ No log Chalk

Westerley OBH >21* Unknown‐ No log Chalk

Moor Park Golf 90 30 to 90 m Chalk Club

*inferred from dips to base and/or water level reading

4.1.4 Local daily rainfall data has been obtained from the EA Chenies gauge, 8 km to the NNW of the site. River stage daily data has been obtained for the Chess at the EA Rickmansworth gauge, just upstream of Batchworth. 4.2 Antecedent conditions Rainfall and river flows 4.2.1 In the 6 months preceding the test, total rainfall was well below average and effective rainfall was slightly below average, (EA, 2017). In the week preceding the test, there was a moderate rainfall event that resulted in higher river flows during the first week of the test.

4.2.2 River Flows in the Thames at Kingston and in the Ver at Colney Street (15 km to the east of the site) were typically in the ‘below normal’ or ‘notably low range’ when compared to long

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term averages in the month prior to the test. At a more local level, recorded water levels in the Colne responded to the rainfall events prior to the test period, as mentioned above.

4.2.3 Local rainfall and river flows (in the Chess at Rickmansworth, just upstream of Batchworth) in and around the period of the pump test is depicted in the chart in Figure 8 below to illustrate the hydrological conditions around the test.

Figure 8 – Local rainfall and river levels around the testing period

Local source abstraction rates 4.2.4 Pumping rates at Mill End PS from February to April 2017 are shown in Figure 9. Rates typically fluctuated between 10 and 14 Ml/d prior to the test period.

4.2.5 Batchworth Golf Club abstraction during the period (if any) is assumed to be too small to influence water levels in any of the monitoring points. TWUL have confirmed that the Juniper Hill PS abstraction was not operational during the test (and hasn’t been in use for some time).

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Figure 9‐ Flow rates at Mill End around the testing period

Long‐term trends in groundwater monitoring. 4.2.6 As shown in Figure 10, water levels measured in the Westerley and Stockers OBH were in a very gentle recession or flat during February 2017, declining <0.1 m at both sites during this month.

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Figure 10 ‐ Water levels in Westerley and Stockers OBH around the testing period

4.2.7 The water level in Westerley OBH of c. 46.8 mAOD at the end of February 2017 appears to have been slightly below the long‐term average reported in the preceding 5 years (shown in Figure 4 previously); and approximately 0.5 m above the equivalent lowest water level in the 2011/2 drought.

4.2.8 Similarly, long‐term monitoring data for Stonor Park Chalk OBH, (a regional monitoring site 15 km to the west of the site), indicates that its groundwater level was also below normal for the time of year (EA, 2017). The nearer Ashley Green OBH (c. 10 km to the NW of Batchworth PS, was also abnormally low, being c. 7 m below its long‐term average, and close to the minimum for the 2007‐2017 period).

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OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 4.3 Prevalent Conditions during the test and recovery period Pumping rates from local sources 4.3.1 As shown previously in Figure 9, pumping rates at Mill End PS during the testing period were typically stable, being in the range of 10‐13 Ml/d, with lower rates of c. 8 Ml/d for a few days in mid‐March and for one day at the end of March (29/3/17). Thames Water have confirmed that Juniper Hill BH was not being pumped around the time of the test. Rainfall/River flows 4.3.2 As mentioned above, there was a period of slight to moderate rainfall just before the testing period, starting from 27th February 2017 and peaking on 4th March 2017, when 5 mm fell and river levels rose in response during the first few days of the test. There was a second period of slight to moderate amount of rainfall from the 19th to 22nd March, after which there was minimal rainfall until the beginning of May 2017. These rainfall events are reflected in the local stage variations measured in the Chess shown previously in Figure 8, noting that there are appears to be a lag of a few days for the daily flows for the larger events. Given the dry antecedent conditions, the river flows are likely to be towards the lower end of the flow range, i.e. close to the Q70, which is likely to be of the order of 100 Ml/d, the discharge flow into the river/canal (i.e. of the order of up to 10 Ml/d) might represent a small component of the overall river Colne flow at the discharge point, e.g. 10%, reducing to zero during the recovery period, when all the abstracted water was being pumped to supply.

4.3.3 In terms of direct aquifer rainfall recharge, the water situation report (EA, 2017) indicates that there was very low effective rainfall in March 2017; and almost none in April 2017. This indicates that the groundwater levels were unlikely to have been substantially affected by these events, unless they were in good and direct continuity with surface water (i.e. the shallowest part of the aquifer). Lake management 4.3.4 It is not known if there was any manual activation of sluices from the Colne into Cressacres Lake overspill from the GUC into the lakes; or transfer of water between the lakes during the pumping period. 4.4 Method for interpretation of test data

4.4.1 As the rates during the test were variable and the tested rates are likely to be comparable to the magnitude of licence increase sought, the approach adopted for the interpretation of the test data has been to examine the relative water level changes during the test, rather than to derive aquifer parameters using pump test curve analysis. It was determined that the nature of the response in the observation wells, the number of external influences and the changing pumping regime over the test period was such that such a quantitative pump test interpretation would provide little output of value to the overall analysis of the test period.

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4.4.2 For the purposes of the assessment, the test data for the required monitoring points have been considered for each significant change in pumping rates over the period for which monitoring data is available. These have been split into five periods, as shown in Figure 11:

1. (Pre‐test Period)

2. (Pre‐test Period) – stepped increase to a constant ~20 Ml/d from 28th Feb 2017 ‐ until 7th March (8 days)

3. Test Phase 1 ‐ Gradually increasing from 20 to 26 Ml/d from 7th March to 20th March (12 days)

4. Test Phase 2‐ Approximately constant abstraction at c. 26 Ml/d from 20th to 27th March inclusive (7 days)

5. Post‐Test Period (Recovery at ~20, declining to ~10 Ml/d)‐ 28th March to 3rd April (5 days)

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Figure 11 ‐ Sub‐division of test period for comparison of drawdown effects at test monitoring points

4.5 Measured water level changes

4.5.1 The water level observations at the monitoring locations to the east of Batchworth PS are shown in Figure 12 and 13 overleaf; and tabulated in Table 8 further on.

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Figure 12 ‐ Water Levels at Observation Sites to the east of Batchworth PS in February‐April 2017

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Figure 13 ‐Water Levels at Borehole observation sites to the west of Batchworth PS in February‐April 2017 (Juniper Hill LHS axis)

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Table 8 – Water level changes at monitored off‐site boreholes relative to the start of the test period

Test Phase Nominal Water level change at end of phase relative to start of Test (m) end of Phase Croxley Cress‐ Shallow Ditch BH Deep BH Shed BH Juniper Wester‐ Stockers Lake acres BH Hill ley OBH Deep Lake OBH OBH

Approx. Distance from Batchworth PS (metres)

400 400 650 800 900 900 900 900 1,400

Pre‐Test 8/3/17 0.00 0.00 0.00 0.00 0.00 0.00 nr 0.00 0.00 (Baseline) 1700 (just prior to test)

Test Ph 1 21/3/17 0.00 ‐0.01 ‐0.02 0.00 ‐0.05 ‐0.04 ‐0.57 ‐0.09 ‐0.07 1300

Test Ph 2 27/3/17 ‐0.02 +0.01 ‐0.02 +0.02 ‐0.01 0.00 ‐0.74 ‐0.12 ‐0.11 1200 (just before end of test)

Post Test 02/4/17 ‐0.06 +0.02 +0.04 0.00 ‐0.01 ‐0.01 ‐0.60 ‐0.09 ‐0.09 1400 nr = no record, positive values represent a rise in water levels.

Discussion: water levels in sites to the east of Batchworth PS 4.5.2 At the sites to the east of Batchworth PS (Croxley Lake, Cressacres Lake and the boreholes on Croxley Hall farm), there is an initial drop in water levels during the initial phase of the test, but these recover part‐way through the test. This may, at least in part, be due to the rainfall event beginning around the 19th/20th March, as site abstraction is relatively constant. The result being that the net change in water levels at these sites during the phase of the test when pumping rate increased is negligible, being just +/‐2 cm around the pre‐test starting value, as shown in Table 8 above.

4.5.3 At Croxley Hall Farm, the “Shallow” borehole (and possibly the “Ditch” BH) do seem to exhibit small spikes (i.e. c. 5 cm in magnitude) of water level rise during at least two periods of the test when there were very short reductions in Batchworth abstraction (response examples circled in Figure 12, with the instantaneous flow rate shown in Figure 14 further on), although some of these coincide with rainfall events and this may be at least partially contributing to the rise in levels corresponding to reduced abstraction from turbidity spikes. During the recovery period, water levels rise slightly in Croxley Hall Farm “Shallow” BH and Cressacres Lake, but are flat, or continue to fall slightly at the other sites. Overall, there is a possible, but

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not confirmed, hydraulic influence of the test in the Chalk groundwater beneath the Croxley Hall Farm area, albeit a very small one, if at all.

4.5.4 During the recovery period when abstraction had reduced, there is an inconsistent response: Croxley Lake continues to fall, the “Ditch”, “Deep” and “Shed” BH signals are relatively flat; and Cressacres Lakes shows a possible small rise. The only location that appears to show a clear recovery‐type signal is from the “Shallow” BH, where there is a rise of the order of 5‐10 cm after the test. There is no clear reason why this borehole shows an effect when compared to the others on the site, the only differentiating factor is that it is slightly closer to the PS than the other holes (hole depth does not appear to be a factor, with the limited construction information that is available).

4.5.5 Overall, the sites to the east of Batchworth do not show clear/consistent drawdown and recovery signals that would confirm that the water levels at those sites were substantially affected (i.e. by >10 cm) by the test. However, it is possible that smaller magnitude variations (i.e. <10 cm) effects seen at some of the monitoring sites in the area may have been caused by the test, e.g. at the “Shallow” BH, but other factors could have been influencing the water levels to a comparable or greater degree, e.g. the rainfall event from 19th to 23rd March and/or possibly active lake level management. Discussion: sites to the west of Batchworth PS 4.5.6 At the Westerly and Stockers sites, there is a small magnitude (i.e. c. 10 cm) net drop in water levels during the pumping phase of the test, and a possible trace of a small amount of recovery, although due to the background recession, there is no net recovery overall. This would suggest that these sites were not clearly in the zone of influence of the test and any effect is likely to be <10 cm in magnitude, if at all.

4.5.7 The Juniper Hill PS OBH exhibits a greater variation during the test than any of the other monitoring sites. Unfortunately, there is no logger data for the period immediately after the start of the test (as the logger dropped down the hole) but the data for the latter part of the test (i.e. mid to late March) does show a progressive drop in water levels and there is what appears to be a small recovery‐type signal at the end of the test, although the scale of the recovery (c. 0.15 m) is much less than the net drop of c. 0.6m during the pumping phase. There are also short‐term level spikes when Batchworth PS pumping rate temporarily dropped for short‐periods (see examples circled in Figure 14 below), and other similar smaller responses to pumping rate variations prior to the test. Some of these correspond with rainfall events and could be due to turbidity events causing reduced abstraction at Batchworth, but others do not. Overall, it appears that Batchworth PS pumping rate fluctuations do cause a minor effect on water levels at Juniper Hill, but the change during the test was modest, being of the order of 10s of cm.

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Figure 14 – Juniper Hill Water Levels vs. Instantaneous Batchworth PS Flow

Discussion: sites to the south west of Batchworth PS 4.5.8 There was no monitoring at sites to the SW of Batchworth planned during the test, but data from the Moor Hall BH, c 1.7 km to the SW of Batchworth, was being collected as part of local NEP investigations and has been included to indicate the scale of effect in this section of the aquifer. This data is graphed in Figure 15 overleaf.

4.5.9 A review of the data from Moor Hall shows that there was a slight rise in water level during the initial phase of the test when abstraction rates were increasing, followed by a steady drop during the second part of March. During the recovery phase at the end of the test, water levels continued to decline. These observations show that there was no discernible effect from pumping in this location.

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Figure 15 – Groundwater levels at Moor Hall borehole, February to April 2017

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OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 5 Environment Impact of Proposed Licence Variation

5.1.1 The potential environmental impact of the proposed change to the licence is discussed for the various features in the area below, based on the observations and interpretation described in the preceding chapters. 5.2 Potential to derogate licensed abstractions rights Croxley Hall Farm sources 5.2.1 It appears that the proposed variation could produce a very small reduction in water levels in the lakes and outflow from artesian boreholes, but this is likely to be very small (i.e. <0.1 m reduction in head), and it is likely that water levels would recover rapidly after the peak. The effect under drought conditions is likely to be similar, as the seasonal water level variation in the valley floor is likely to be muted; and the 2017 observations were made after a period of dry weather. It therefore appears unlikely that the proposed licenced variation at the tested rate would cause any significant derogation of the abstraction licence rights. Juniper Hill PS 5.2.2 The scale of potential net water level change above baseline at Juniper Hill PS appears likely to be of the order of 10s of cm. There is therefore some, but a small potential for derogation of this licence during drought conditions, but only if the Juniper Hill pump intake is set a small distance below drought pumped water level. TWUL have reported that the source has not been in use for several years and there are no plans to recommission it. Stockers PS 5.2.3 The scale of drawdown at Stockers PS is not clear from the test results, but observations there indicate that it is likely to be relatively small i.e. <0.1 m, if any. This source is not actively used and the very small scale of potential water level change implies that the risk of significant derogation of the abstraction rights from the proposed licence variation is low, noting that the source is in any case, an AW source and there is no intention to recommission it during the HS2 construction period. Batchworth Golf Club 5.2.4 The observations at the Moor Park Borehole (described previously in section 4.5.8) indicate that there was not a substantial drawdown propagating into the aquifer a substantial distance (e.g. c. 1.5 km) to the south‐west of the PS, although it is noted that one of the Golf Club boreholes is closer than this (c. 750m). However, observations at another off‐site borehole at a similar perpendicular distance from the valley floor (Westerley OBH) also did not indicate a discernible drawdown either. This may reflect the likelihood that the zone of high transmissivity in the Chalk aquifer (where pumping effects are likely to be more pronounced) runs parallel to the Colne Valley. It therefore appears unlikely that there is any significant risk Template no.: Uncontrolled when printed HS2‐HS2‐PM‐TEM‐000‐000004 Page 40

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of derogation of this source’s abstraction rights because of the proposed licence variation, even under drought conditions. 5.3 Review of potential to impact surface water features Rivers 5.3.1 The extent of the drawdown measured during the tests suggests that there would likely be some potential for a very minor localised loss of baseflow to the local river system due to de‐ pressurization of some sections of the Chalk aquifer. However, the effect is likely to be attenuated by the storage available in the overlying gravel aquifer and lakes near the site; and given the temporary nature of the proposed variation, the net loss of instantaneous flows in the river (if any) is likely to be much smaller than the proposed peak abstraction increase. Lakes/ponds 5.3.2 It is possible that there may have been a minor (i.e. few cm) net drop in water levels in some local lakes near the site during the peak abstraction period that could have been due to pumping, but levels recovered to the baseline after the peak abstraction had subsided.

5.3.3 In most situations (apart from extreme drought), any net drop from the additional abstraction would likely be well within the typical range of baseline variation. The active water level management of the lakes; and possible siltation that may be reducing connectivity with the underlying aquifers may be more significant in determining their water levels. It is therefore considered that this is unlikely to be a significant impact on the use/ecology of the lakes from the proposed licence change. Grand Union Canal 5.3.4 The Grand Union Canal may be lined and therefore have a poor connection to groundwater. If not, it is possible that there could be some minor increase in leakage rates at the higher abstraction rate tested, but the scale of drawdown observed in other features (e.g. lakes) suggest the effect on the canal would be small and it is noted that it will be maintained by upstream releases/inflows during dry weather. For short‐term peak abstractions, it appears unlikely that there would be a substantial impact on the canal from the proposed licence variation, even under drought conditions. Groundwater dependent eco‐systems 5.3.5 The scale of level changes in the Chalk beneath the more distant points to the west of the site (which is approximately 1km from the western boundary of the Croxley Common Moor SSSI) is likely to be <0.1 m, if at all. Any effect in the water level feeding the wetland is likely to be significantly attenuated by the overlying drift deposits and would in any case be short and temporary and unless in drought conditions, within the range of baseline fluctuation. The anticipated impact is therefore likely to be negligible.

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5.3.6 The potential water level changes at the lakes connected to the local LNRs (Rickmansworth Aerodrome, Stockers Lake, Withey Beds) would be similar to those stated for Lakes/Ponds above; and it is not anticipated that there would be any resultant ecological impacts. Water Quality 5.3.7 There are several contamination sources in the local area, e.g. landfills and a former gasworks that may have associated bodies of poor quality groundwater. No significant changes in chemical water quality during the test were seen that would indicate that any contamination plumes had been captured at the higher peak abstraction rate. Given that there is no proposed increase in the average rates, it appears unlikely that the variation would result in any increase in long‐term average migration rates of any bodies of contaminated groundwater from the surrounding area. 5.4 WFD compliance Surface water waterbodies 5.4.1 The primary drivers for WFD non‐compliance appear to be phosphate levels and the additional peak abstraction flow would not affect this issue. Any overall effect on the river flow is likely to be very temporary and flows would return to baseline after the peak abstraction period, noting the annual group licence total for other sources in the catchment will remain unchanged. It is not envisaged that the proposed licence variation would cause WFD non‐compliance. Groundwater waterbodies 5.4.2 WFD non‐compliance for the groundwater body (where resource is a contributing factor to its poor status) is unlikely as the variation would be for a temporary and short‐term abstraction, with no overall change in annual group licence abstraction limits.

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6.1 Batchworth PS borehole details

6.1.1 The construction details and condition information on the site boreholes from recent survey information provided by AW are shown in Table 9 below.

Table 9 –Details of Batchworth PS boreholes from most recent downhole surveys

Borehole: BH2 BH3 BH4 Date of most recent survey 2013 2014 2013 report Rising main length (m) 32 m 25 m 32 m Depth of Plain casing 32 mbgl 31 mbgl 33 mbgl (mbgl) Casing condition Minor encrustation, no Encrustation, but no signs Joints and shoe reported in signs of weeping joints, of weeping joints, iron good condition. Degree of minor corrosion of shoe. tubercles near base. Shoe encrustation not reported. in very poor condition. Base of Open Hole (mbgl) 91 m 92 m 108 m Condition comments Obstruction seen at 50m Minor cavities between 48 No signs of leakage at base during 2013 survey, but to 60 m bgl of plain casing. No depth reported in 2015 ops indication of manual indicates that it instability/collapse in open may have been fished out. hole. No video record available. *Based on dip datum provided by Affinity Water, less notional 0.5m height of dip datum height above ground level.

6.2 Assessment of potential yield

6.2.1 The water levels in the individual boreholes around the period of the test are shown in Figure 16 overleaf. A preliminary calculation of available headroom above the pump intake has been made using this information and the preliminary estimates of ground level and pump intake depth. This is shown in Table 10, also overleaf.

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Figure 16 ‐ Batchworth PS individual BH water levels around the period of testing (note: levels adjusted for clarity: see key)

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Table 10 – Preliminary calculation of headroom above the pump intake during the 2017 test

Parameter Borehole: BH2 BH3 BH4 Assumed Headplate elevation (mAOD)* 47.2 46.9 47.5 PWL during 2017 test at end of peak rate (mAOD) 21 mAOD @ 23.5 mAOD @ 27.5 mAOD 4Ml/d 17Ml/d @ 5Ml/d Estimated elevation of top of pump intake (mAOD)** c. 13 mAOD c. 20 mAOD c. 13.5 mAOD

Calculated headroom above pump intake during 2017 test @26Ml/d (m)** c. 8 m c. 3.5 m c. 14 m Potential for pump level DO constraint under drought conditions at tested Unlikely Possibly Unlikely rates for 14‐day peak duration, with current pump depth setting? *Provided by AW Jan 2018, **based on rising main length in Table 9, plus AW assumption of 2m distance between top of intake and collar flange (provided by AW).

6.2.2 Even given the uncertainties in the pump intake depth/ground level, it would appear likely that there is sufficient headroom above the pump intake in BH2 and BH4 to accommodate drought water levels and/or a slightly longer 26 Ml/d peak flow period than was tested in 2017, provided other external conditions and site operation prior to the increased flow period is similar to that experienced in the 2017 test.

6.2.3 However, in BH3, the available headroom above the pump intake is significantly less. It is noted that the drought pumped water levels may be c. 0.5 m below those seen in the 2017 test (see section 4.2.7 previously) and there is also likely to be a pump low level cut out sensor 1‐3 m above the intake. Thus, it is possible that the current pump intake and low‐level cut‐out depth could limit the yield of BH3 to slightly less than the tested 17 Ml/d for the proposed 14‐ day peak duration and/or under less favourable external/operational conditions. 6.3 Recommendations for confirmation of yield

6.3.1 It is recommended that:

 The exact pump intake depths at each Batchworth PS borehole are determined; and

 The achievability of the proposed peak is considered by AW using their existing Source Reliable Output (SRO) assessment for the site, as there may be other constraints on deepest advisable pumped water level (DAPWL) than pump intake depth alone.

6.3.2 If on further examination, the pump intake depth in BH3 is proven to be a potential yield constraint, there are at least two options to achieve the desired rate (26 Ml/d) from the site, e.g.:

 the BH3 pump & low‐level cut out depth could be increased by installing an additional length of rising main to take it a few metres deeper. (It may be inadvisable to lower it Template no.: Uncontrolled when printed HS2‐HS2‐PM‐TEM‐000‐000004 Page 45

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much further than this, i.e. close to the base of the casing, due to the potential for dislodgement of encrustation/corrosion around the base of the casing shoe); and/or

 complete works (if required) to increase the output capacity from BH2 or BH4 relative to that achieved during the test: it seems BH4 would be the best option of the two, as it has better drawdown/yield characteristics than BH2 and appears to be in better structural condition.

6.3.3 Other constraints (e.g. water quality, pump capacity, borehole condition, power supply and treatment/distribution) would also need to be considered to determine if the source peak week deployable output could be achieved.

6.3.4 If a peak abstraction rate higher than 26 Ml/d were required, this could likely be physically achieved if pumps were lowered, particularly if the PWL could be dropped below into the open hole section without causing raw water quality deterioration or structural failure of the borehole. However, this would require a review of historic (or new, if not available) individual borehole step test data to indicate their specific capacity at higher rates; and an assessment of the combined interference effects between the three pumping boreholes using an analytical solution.

6.3.5 Affinity Water have advised that they believe that the desired test yield could have been obtained had the turbidity problems not constrained the site output; and that this will be addressed via a treatment solution.

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OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 7 Conclusions 7.1 Potential for derogation of abstraction rights

7.1.1 The review of the test data has indicated that only one site (Juniper Hill PS) had a notable downward water level drop and subsequent rise that may be attributable to the test pumping. Notwithstanding this, the level change at that site was still relatively small (10s of cm), so there would only be potential for derogation if the intake is already very close to the pumped water level under drought conditions; and there was an intention to re‐use the site. At the other sites, the potential effect was generally either negligible or very small (i.e. of the order of less than 10 cm), and as such, the potential for significant derogation is small.

7.1.2 TWUL have confirmed that they do not have information on the pump intake depth at Juniper Hill readily to hand and that if derogation is a potential issue, this may need to be measured (e.g. by dipping down the rising main). Pumped water level at the Juniper Hill source would also need to be confirmed (or estimated). Alternatively, TWUL may be prepared to sign a consent to derogate the source and this would avoid the inconvenience of further investigations. 7.2 Potential for environmental impacts on surface water features/ecology

7.2.1 The test has indicated that there is unlikely to be any substantial effects on nearby water features or groundwater‐dependent ecology: effects are likely to be small in magnitude (if at all) and temporary. They are not likely to affect the WFD status of any local waterbodies. 7.3 Achievability of borehole target yield

7.3.1 The test pump proved that c. 26 Ml/d of raw water was obtainable from the boreholes at the source for at least a week during the conditions that were prevalent around the test period (i.e. slightly below average groundwater levels and abstraction in the range of 10‐20 Ml/d). However, the headroom above the BH3 pump intake may have been small during the test. Under less favourable conditions and/or for a slightly longer period of pumping at peak rate, it is possible that the BH3 low‐level cut out may start to act as a constraint on yield. Confirmation of the pump intake depths would assist in this evaluation.

7.3.2 It is also recommended that the intake depths are ascertained and the deployable output from the source is re‐evaluated by Affinity Water using the UKWIR methodology to confirm the deepest advisable pumped water level. If a potential pumping water level depth constraint in BH3 is confirmed or suspected, it may be possible to lower the BH3 submersible pump to remove this constraint; or another option could be to abstract more than the tested 5 Ml/d from BH4.

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OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 List of acronyms

AW Affinity Water

BGS British Geological Survey

BH Borehole

EA Environment Agency

DAPWL Deepest advisable pumped water level

GI Ground Investigation

GUC Grand Union Canal

LNR Local Nature Reserve

mAOD metres above ordnance datum

m b(a)gl metres (above) below ground level

Ml/d megalitres per day

NE Natural England

OBH Observation borehole

PS Pumping Station

PWL Pumped water level

SRO Source Reliable Output

SSSI Site of Special Scientific Interest

TWUL Thames Water Utilities Ltd.

WFD Water Framework Directive

WFS Water Features Survey

WQ Water quality

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OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 References

Reference Title BGS, 2005 Geology of the Beaconsfield District – a brief explanation of the geological map sheet 255, British Geological Survey

EA, 2016 Water Features Survey Requirements, Batchworth Pumping Station, 25/08/16, Environment Agency

EA, 2017 Monthly water situation report (Summary to June 2017), South east England, Environment Agency

HS2, 2016 Affinity Water Pumping Tests at Batchworth and The Grove ‐ scope and supporting information, HS2, 07/12/16

HS2, 2017a WR36 Water Features Survey Form (for a visit on 8/12/16)– Batchworth, v2, HS2

Hs2, 2017b Misbourne Hydrogeological Review, 1D107‐EDP‐EV‐REP‐CS02‐000001, HS2, June 2017

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OFFICIAL Affinity Water Sources – Batchworth Pumping Test Assessment Document no.: 1D107‐EDP‐EV‐REP‐CS01‐000001 Revision: P04 Appendix A

Logs of monitored third party boreholes

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Juniper Hill:

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Moor Park:

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