1MC04 Main Works - Contract Lot S2

Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 MDL Code: None

Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035

Revision Author Checked by Approved by Date Reason for approved revision

C01 Lourds Michael Mark Gaby Christiane 19/06/2020 For Acceptance Anthonypillai / Chendorain Hof Phoebe Chappell C02 Lourds Michael Carlos Gómez Steven Anthonypillai Chendorain Bodenham RNSP WP Final Re-Submission

SECURITY CLASSIFICATION: OFFICIAL

Handling instructions: None

Revision changes, authorisation and reason for issue records:

Revision Author Date Checked by Date Approved by Date Reason for revision authored checked approved C01.1 Lourds 06/03/2020 Michael 30/03/2020 Mark Gaby / Richard 30/03/2020 First Issue Anthonypillai / Chendorain Patten Phoebe Chappell

C01.2 Lourds 16/04/2020 Michael 27/04/2020 Mark Gaby / 27/04/2020 For Acceptance Anthonypillai / Chendorain Christiane Hof Phoebe Chappell C01.3 Lourds 10/06/2020 Michael 19/06/2020 Mark Gaby / 19/06/2020 RNSP - WP Anthonypillai / Chendorain Christiane Hof Phoebe Chappell C02.1 Lourds 08/02/2021 Michael 09/02/2021 Carlos Gómez / Anthonypillai Chendorain Steven Bodenham RNSP WP Final Re-Submission

Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

Contents

1 Introduction 2 1.1 Context 2 1.2 Report Contents 3 1.3 Associated Documents 3 2 Methodology 5 3 Data 5 3.1 Ground Investigations 5 3.2 Baseline Data Requirements 6 4 Regional Geology and Hydrogeology 6 5 Local Geology and Hydrogeology 7 5.1 Geology 7 5.2 Hydrogeology 9 6 Conceptual Hydrogeological Site Model (CSM) 10 6.1 Summary of Ruislip Northern Sustainable Placement (RNSP) Western Mound 10 6.2 Baseline Conditions 12 7 Risk Evaluation 17 8 List of Acronyms and Abbreviations 20 9 References 22 Appendix A - Drawings 24 Appendix B - Groundwater Contours and Levels 25 Appendix C - Groundwater Quality Data 26 Appendix D - Risk Methodology 27 1 Methodology 27 Appendix E - Chalk Dissolution Features - Additional Details 30 1 Summary 30 2 Additional Details 30

Template no.: HS2-HS2-IM-TEM-000-000265 Page 1 Uncontrolled when printed

1.1.1 The Ruislip Northern Sustainable Placement (RNSP) is located around 2.4km to the west of Ruislip, with the centre of the RNSP at an approximate location of 507104.4, 188401.5. It is part of the wider Ruislip Sustainable Placement (RSP; shown in Figure 1), which will be the onsite location for disposal of surplus excavated material to avoid causing environmental effects that would otherwise be associated with the offsite disposal of that material. The material will be derived from a single source and will consist predominately of naturally occurring Clay excavated from the Copthall Tunnel area. It will be deposited in two locations across the RNSP, known as the Western and Eastern mounds.

Figure 1 - Location map showing both the Western and Eastern mounds of the Northern Sustainable Placement Area

1.1.2 This note provides a hydrogeological risk assessment (HRA) in relation to the proposed Western mound of the RNSP. It is one of a suite of documents that together will be submitted to the Environment Agency (EA) as part of an environmental permit for landfill applications for the RNSP. Applications for the Western and Eastern mounds will be submitted separately.

1.1.3 Given the permit application for the Western and Eastern mounds will now be submitted separately, a hydrogeological risk assessment will be conducted for both RNSP mounds

Template no.: HS2-HS2-IM-TEM-000-000265 Page 2 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

individually. Therefore, this report supersedes the previous HRA for the RNSP, previously known as the Northern Sustainable Placement Area (Northern SPA) [17], which considered both the Western and Eastern mounds together.

1.1.4 Nevertheless, the overall hydrogeological conceptual model and site characterisation will be the same as for Eastern mound, only the risks will be assessed in isolation, confined to the proposed Western mound boundary.

1.1.5 The intent of this document is to provide a factual presentation of available baseline data, and to evaluate and assess hydrogeological risks due to the placement of material as described in this report. This report is not intended to provide an exhaustive discussion of existing baseline conditions.

1.1.6 The term ‘S2’ included in the title of this assessment refers to Lot S2 for Phase 1 of the HS2 scheme. Lot S2 extends from the western end of the proposed Old Oak Common Station and includes tunnels, shafts, a large crossover box excavation, portal structures, cuttings and embankments. 1.2 Report Contents

1.2.1 This report is structured as follows:

• Section 1: Introduction,

• Section 2: Methodology,

• Section 3: Data,

• Section 4: Regional Geology and Hydrogeology,

• Section 5: Local Geology and Hydrogeology,

• Section 6: Conceptual Hydrogeological Site Model (CSM),

• Section 7: Risk Evaluation. 1.3 Associated Documents

1.3.1 This report should be read in conjunction with the following documents:

• Environmental Setting and Site Design Report (ESSD) [9],

• Environmental Permit Application Form parts A, B2, B4, F1,

• Environmental Monitoring Plan [19],

• Site Operating Plan (SOP) [20],

• Stability Risk Assessment [21],

Template no.: HS2-HS2-IM-TEM-000-000265 Page 3 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

• Management Systems and Procedures [22].

Template no.: HS2-HS2-IM-TEM-000-000265 Page 4 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02 2 Methodology 2.1.1 The assessment of hydrogeological risk associated with the Western mound is based on the following:

• Review of available ground investigation data (including groundwater monitoring data performed at a minimum of quarterly intervals from February 2017 through December 2019),

• Development of a Conceptual Hydrogeological Site Model (CSM),

• Semi-quantitative assessment of risks. A semi-quantitative assessment of risk is considered appropriate given the nature of the single source waste material to be placed, and the relatively low permeability nature of both the waste material and ground conditions at the RSP (as described below). Appendix D provides a summary of the risk assessment ranking methodology. 3 Data 3.1 Ground Investigations

3.1.1 The HS2-commissioned main ground investigation within S2 is formed from several works packages. The data used in this report is primarily from the North-West Ruislip (NWR) ground investigation and the South Package B (SPB) ground investigation. The details of the factual reports issued on completion of these investigations are listed in Table 1:

Report Name Date / Revision Document No.

NWR Final Factual Report 12th April 2019 / P02 1G089-FES-GT-REP-000-000019

SPB Final Factual Report 26th September 2018 / P04 1G107-FES-GT-REP-000-000010

Table 1 - GI data received relevant to the RNSP Western mound

3.1.2 Association of the Geotechnical and Geoenvironmental Specialists (AGS) data and the Final Factual Report is available for the NWR package which covers Copthall Tunnel to the west of Breakspear Road South. The NWR ground investigation data has been used to assist in characterising the ground conditions and hydrogeology of the West Ruislip tunnel portal.

3.1.3 In situ tests specified for the NWR package include variable head permeability testing and groundwater monitoring. Laboratory test results available in the Final Factual Report for the NWR package include Particle Size Distribution (PSD), consolidation tests and shear strength.

3.1.4 In situ field testing and monitoring for SPB package that is considered useful for hydrogeological characterisation includes in situ falling head tests with standpipe piezometers and measurement of water pressure by vibrating wire piezometers.

Template no.: HS2-HS2-IM-TEM-000-000265 Page 5 Uncontrolled when printed

3.2.1 In support of the environmental permit for landfill application for the RNSP Western mound, baseline data has been compiled as follows:

• Groundwater quality and water level monitoring has been performed at four installations at the limits of the RNSP (i.e. both the Western and Eastern mounds) at a minimum of quarterly intervals between February 2017 and December 2019,

• Surface water monitoring has been performed at four installations between May 2017 and February 2018.

3.2.2 Ground gas baseline monitoring has not been conducted for the following reasons:

• The material to be used for waste placement will be material from a single source consisting predominately of naturally occurring Clay excavated from the Copthall Tunnel area,

• Only non-organic soils would be placed at the RNSP Western mound. Any organic material encountered would be segregated separately and disposed elsewhere,

• Given the single source nature of the waste, and in the absence of a source of ground gas (in other words, no organic material will be used), there is no discernible source of gas generation in the waste material. 4 Regional Geology and Hydrogeology

4.1.1 The London Basin is a widely easterly plunging syncline structure between the Chiltern Hills to the north and the North Downs in the south [4]. Throughout the region, there are widespread yet spatially sporadic Superficial Deposits compromising Gravels, Sands, Clays and Peat layers. These have originated over the past 2-3Ma and include the River Terrace Deposits [5]. The Superficial Deposits overlie the London Clay Formation.

4.1.2 The London Clay Formation is underlain by the Harwich Formation, Lambeth Group (Reading Formation and Upnor Formation), Thanet Formation (absent in the west of the London Basin) and White Chalk Subgroup. Sediments deposited in the basin include an important aquifer for groundwater supply to London and its surrounding areas [4].

4.1.3 Within the London Basin, generally there are two aquifers within 150m below the ground surface, known as the Upper and Lower Aquifers. The Upper Aquifer is present in the Made Ground and River Terrace Deposits overlying the London Clay Formation. The Lower Aquifer comprises the sandy portions of the Upnor Formation of the lower Lambeth Group and the Thanet Formation (together known as the Basal Sands), in addition to the White Chalk Subgroup (Seaford Chalk Formation).

Template no.: HS2-HS2-IM-TEM-000-000265 Page 6 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

4.1.4 The Seaford Chalk Formation is classified by the EA as a Principal Aquifer, whereas the Lambeth Group and the Harwich Formation are Secondary A Aquifers [6]. Groundwater flow within the Seaford Chalk Formation is governed by a number of factors including weathering grade and discontinuity spacing and aperture size but is generally a dual porosity system [2] with highest flows occurring along fractures and other discontinuities. Drawing A1 in Appendix A shows the Chalk Piezometric Surface across the London Basin.

4.1.5 Due to the low permeability of the London Clay Formation, it is considered to act as an aquitard which is confining the combined Harwich Formation, Lambeth Group and Seaford Chalk Formation.

4.1.6 In the 19th century and first half of the 20th century, the Chalk aquifer had been exploited significantly due to increased industrialisation and the associated expansion of groundwater sources [1]. At the peak of abstraction in the 1960s, groundwater levels beneath central London had fallen to 88m below sea level [1]. Gradual rebound of the water table in the latter half of the 20th century as a result of reduced abstraction has now enabled water levels in most regions within the London basin to stabilise [1]. 5 Local Geology and Hydrogeology 5.1 Geology

5.1.1 According to the published 1:50,000 scale geological digital maps [7], the regional overview indicates an absence of Superficial Deposits and solid geology comprising the London Clay Formation and Lambeth Group within the RNSP Western mound site boundary. The Thanet Formation is not present across the RNSP, as it is absent in the west of the London Basin. Further detail regarding the stratigraphy can be found in Table 2 and Drawing A2 in Appendix A, the latter showing a cross section derived from HS2 investigation boreholes.

5.1.2 No faults are indicated to be present at or in the vicinity of the site. Superficial Deposits 5.1.3 According to the cross section, thin (less than 2m) Superficial Deposits are present comprising Made Ground and Alluvium. In the west of the site, there is a thin layer of Topsoil overlying Alluvium which is between 0.9 and 1.7m thick.

5.1.4 Thin (less than 1m) artificial deposits (i.e. Made Ground) are found across the site overlying the Topsoil and Alluvium. Made Ground is described as brown and grey slightly sandy gravelly Clay, with angular to sub rounded fine to coarse Flint and Brick Gravel.

5.1.5 Topsoil was encountered in ML025-RC048, ML025-RC049 and ML025- RC051 at a top elevation ranging from 51 to 60mOD. This stratum was typically described as grass over soft brown slightly sandy slightly gravelly Clay, with sub-angular to rounded fine to coarse Flint Gravel.

Template no.: HS2-HS2-IM-TEM-000-000265 Page 7 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

5.1.6 Alluvium was encountered in all exploratory holes in a thickness between 0.9m and 1.7m. This was typically described as stiff to soft light brown / yellow mottled grey slightly sandy slightly gravelly Clay with Sand being fine to coarse, and sub-angular and sub-rounded fine to coarse Flint Gravel. Some fissures are noted in ML025-RC048.

5.1.7 The Topsoil will be stripped from the footprint of the landfill prior to the construction of the artificially established geological barrier [9].

Borehole Made Top Soil Alluvium Harwich and London Upnor and Reading Seaford Chalk Ground (mbgl) (mbgl) Clay Formations Formations (Lambeth Formation (mbgl) (Thames Group) (mbgl) Group) (mbgl) (mbgl)

ML024-RC012 0-0.5m NP 0.5-2m 2-18.45m 18.45-33.45m 33.45-34.95m

ML025-RC048 NP 0-0.3m 0.3-1.2m 1.2-4.2m 4.2-20.2m 20.2-21.7m

ML025-RC049 NP 0-0.3m 0.3-1.65m 1.65-3.75m 3.75-19.35m 19.35-21.5m

ML025-RC051 NP 0-0.4m 0.4-2.1m 2.1-11.7m 11.7-29.05m 29.05-31m

Note: NP means not present

Table 2 - Summary of the local geology encountered from the four boreholes across the RNSP Harwich and London Clay Formations (Thames Group) 5.1.8 The Thames Group is formed of the London Clay Formation which overlies the Harwich Formation. The Thames Group was encountered in all exploratory holes at top elevations ranging from 49 to 60mOD. The thicknesses of these strata range from 2m to 16.45m.

5.1.9 The London Clay Formation is absent in the western most borehole (ML025-RC049), appears at borehole ML025-RC045, and thickens to around 16m at the easternmost borehole (ML024- RC012). Where present, the base elevation of the London Clay Formation ranges from 44mOD to 51mOD. The London Clay Formation is typically described as firm to stiff fissured brown mottled orangish brown and bluish grey slightly sandy Clay with occasional Claystones. The fissures are noted as extremely closely to very closely spaced, planar and smooth.

5.1.10 The Harwich Formation of the Thames Group (which is normally found below the London Clay Formation) has been encountered across the site and ranges in thickness from 1 to 2.5m with a base elevation ranging from 43 to 51mOD. The Harwich Formation is described as stiff brown locally grey silty sandy Clay, locally gravelly. The sandy components are classified as fine to coarse. Upnor and Reading Formations (Lambeth Group) 5.1.11 Underlying the Harwich Formation is the Lambeth Group ranging in thickness from 15 to 17m and with a base elevation ranging from 27 to 34mOD. The Lambeth Group is texturally highly heterogenous due to deposition within a terrestrial and coastal setting. However, the only

Template no.: HS2-HS2-IM-TEM-000-000265 Page 8 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

units of the Lambeth Group identified on this site are the Lower Mottled Clay of the Reading Formation, Sand channels within the Lower Mottled Clay, and the Upnor Formation.

5.1.12 At the site, the Lower Mottled Clay is described as stiff to very stiff fissured slightly sandy yellowish brown to red mottled bluish grey and black Clay. The thickness of the Lower Mottled Clay is around 13m but includes Sand channels towards its base.

5.1.13 Sand channels identified towards the base of the Lower Mottled Clay consist of a mixture of silty Sand, Sand, and clayey Sand1, with a thickness of around 4 to 5m (except for the easternmost borehole, ML024-RC012, where no Sand channel was encountered). Where Sand channels have been encountered, there is aat least 11 to 24m of Clay or silty Clay (from the Lower Mottled Clay, Harwich Formation, London Clay Formation, and/or Alluvium) overlying the unit.

5.1.14 The Sand channels of the lower Lambeth Group are excluded from the Basal Sands as they are not considered to be in direct hydraulic connectivity with the Lower Aquifer. This distinction is limited to the sandy portions of the Upnor Formation and the Thanet Formation (the latter of which is not present at the RNSP).

5.1.15 At the site, the Upnor Formation is described as dark greenish grey mottled dark brownish slightly gravelly clayey Sand and interbedded very stiff fissured greenish brown mottled greenish grey or bluish grey Clay and sandy Clay. The Clay fissures are very closely spaced planar and smooth. Seaford Chalk Formation 5.1.16 Underlying the Lambeth Group is the Seaford Chalk Formation of the White Chalk Subgroup. The Seaford Chalk Formation was encountered in all exploratory holes to an unproven depth. This Formation is typically described as very weak to weak low to high density white Chalk with occasional thin beds of nodular Flint. Fractures are very closely to medium spaced, planar, and smooth. In some shallower locations (ML025-RC049 and ML025- RC012), this unit is described as a structure-less Chalk composed of slightly gravelly silty Sand. ML025-RC051 notes extremely weak to weak Siltstone with frequent Chalk and Flint clasts. 5.2 Hydrogeology

5.2.1 The majority of the RNSP Western mound is located in a Source Protection Zone (SPZ) as shown in Drawing A3 (Appendix A).

5.2.2 ML024-RC012 and ML025-RC049 are located within the limits of the SPZ-1 and have installations in order to define baseline groundwater quality and levels in the SPZ-1 area.

1 At ML025-RC049 the interval identified as Clayey Sand was described in the borehole log as ‘thinly laminated to medium interbedded fissured brown mottled Clay, Silt and Sand. Conservatively this has been depicted as Clayey Sand on Drawing A2 in Appendix A.

Template no.: HS2-HS2-IM-TEM-000-000265 Page 9 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

5.2.3 There are no known public or private licensed groundwater abstraction wells in proximity to the RNSP site boundary except for the Ickenham Well, which is owned by Affinity Water. This permitted abstraction well lies in the SPZ-1, however it is not currently in operation and the closest edge of the RNSP is more than 500m away from the nearest adit. A query has been raised to Hillingdon Council by SCS in order to identify any abstractions not known to the EA, but due to the Covid-19 pandemic the Council had not been able to respond by the time of writing.

5.2.4 The Western mound is located within the Colne River catchment. The Newyears Green Bourne bounds the RNSP to the west. A drain that discharges into the Newyears Green Bourne crosses the area of the proposed RNSP from east to west. The Newyears Green Bourne discharges in to the Savay Lake (or also known as Harefield No. 2 Lake) approximately 1.2km to the south-west of the RNSP. The Savay Lake is part of the complex of water bodies of the Colne Valley [9]. The Environmental Statement (ES) for the HS2 South Ruislip to Ickenham section describes Newyears Green Bourne as ‘a small stream which runs within a ditch through fields and is largely shaded by the adjacent scrub and hedgerows’. The stream has a very low water level and is often dry in places [9].

5.2.5 The Eastern mound is located within the River Pinn catchment. The nearest watercourse within this catchment is located approximately 50m to the east of the Eastern mound area. This unnamed watercourse is a direct tributary to the River Pinn (where, at its closest, the River Pinn is around 770m away) [9]. Regardless of the proximity, these features are not in hydraulic connection to underlying aquifer units. Surface water drainage is discussed elsewhere [11].

5.2.6 Within the Lambeth Group, groundwater flow is intergranular matrix flow whereas within the Seaford Chalk Formation there is a dual porosity system where fracture flow controls permeability. The Chalk is the Principal Aquifer in this site which is assumed to be in hydraulic connectivity with the Basal Sands.

5.2.7 As discussed in detail below, groundwater flow is to the southeast across the site with a low hydraulic gradient in the order of 0.007. The local conditions are consistent with the regional hydrogeology. 6 Conceptual Hydrogeological Site Model (CSM) 6.1 Summary of Ruislip Northern Sustainable Placement (RNSP) Western Mound

6.1.1 The RNSP Western mound is one of four mounds designed to accept excavation or tunnelling materials generated during construction of the Lot S2 tunnel and associated assets. The RSP (Northern and Southern) is locally sited to reduce the environmental impacts associated off-

Template no.: HS2-HS2-IM-TEM-000-000265 Page 10 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

haul of these materials (i.e. trucking, etc.). In particular, the RNSP is designed to accept low permeability (i.e. Clay) inorganic materials excavated from a single source area (namely from the Copthall Tunnel excavation).

6.1.2 The identified Source-Receptor-Pathways (SPRs) relevant to the RNSP Western mound are summarised in Table 3. The risks associated with the identified SPRs are assessed in Section 7.

6.1.3 For characterisation of the material to be placed at the RNSP Western mound, refer to the Materials Management Study - Copthall Tunnel S2 [16].

Source Pathway Receptor

Unanticipated chemical contaminants Groundwater movement through the Groundwater within the underlying within the sustainable placement geological barrier and unsaturated zone Principal Aquifer mounds into the Lower Aquifer

Surface water which has been altered The movement of surface water as run-off Nearby surface water bodies as a result of unanticipated chemical from the Western mound including creeks, streams and rivers constituents within the placed material

Table 3 - Identified SPRs relevant to the RNSP Western mound

6.1.4 The design of the RNSP Western mound is described in the ESSD [9] but will generally consist of the following:

• Non-organic soil material taken from a single material source (from excavated naturally occurring soil at the Copthall Tunnel site) placed within the limits of the Western mound,

• Following a Topsoil strip from the footprint of the landfill, the material will be placed on the ground surface. No soil material will be placed below the water table,

• An impermeable artificially established geological barrier at the base of the waste material, comprised of non-organic single source Clays, compacted to achieve a permeability of less than 1x10-7m/s. The barrier will be 1m thick, tested to confirm compliance with the Landfill Directive. For further information on the characterisation and physical properties of the geological barrier, refer to the SOP [20].

6.1.5 The natural material underlying the RNSP Western mound generally consists of the following:

• At least of 9.8m of Lower Mottled Clay within the Lambeth Group forming a naturally impermeable barrier,

• An underlying Principal Aquifer (the Chalk) in apparent hydraulic connectivity with the overlying Basal Sands. A portion of the Chalk aquifer is within a SPZ-1 (see Drawing A3, Appendix A),

• The aquifer from which the groundwater is abstracted (the Seaford Chalk Formation and Newhaven Chalk Formation) is confined below the London Clay Formation and

Template no.: HS2-HS2-IM-TEM-000-000265 Page 11 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

Lambeth Group. As stated before, the inert material being deposited is already present over the Chalk.

6.1.6 The designation of the SPZ-1 in this area is due to the proximity of the Ickenham Well and its associated adits. Although the well is not currently in use, Affinity Water has indicated that it may in future reinstate abstraction from the well and will retain its license to operate this well for the foreseeable future. 6.2 Baseline Conditions Permeability of Geological Barrier 6.2.1 The waste material taken from the nearby Copthall Tunnel will be required to meet a suitable permeability (k) for the material to be used as the geological barrier.

6.2.2 Laboratory permeability testing (using a triaxial cell) was performed on three samples of London Clay Formation from depths between 9 and 13mbgl taken from the Copthall Tunnel. These permeabilities represent the small-scale permeability through a 200mm sample and therefore are not indicative of the larger scale in situ effective permeability within the London Clay Formation in the Copthall Tunnel area, which may be affected by higher permeability layers (e.g. Sand channels). The test results indicated k between 9.4x10-12 and 1.3x10-10m/s [8]. In addition, laboratory permeability testing using a triaxial cell are generally assumed to be more representative of vertical permeability (albeit at a small scale).

6.2.3 Variable Head tests were also conducted during borehole installation at the Copthall Tunnel within the London Clay Formation. The testing, performed at a depth ranging from 45mOD to 64mOD, resulted in a permeability ranging from 2x10-9 to 2x10-7m/s [12].

6.2.4 The Harwich Formation located in the Copthall Tunnel region, also had in situ permeability testing carried out which resulted in a permeability value of 6x10-9m/s [12].

6.2.5 The Lambeth Group from the Copthall Tunnel had 14 in situ permeability tests located in the Lower Mottled Clay and 2 in situ permeability tests located in the Upnor Formation. The tests in the Lower Mottled Clay resulted in values ranging from 7.2x10-9 to 2x10-6m/s [12]. The tests located in the Upnor Formation resulted in values ranging from 8x10-10 to 2.1x10-7m/s [12].

6.2.6 Given the observed range from variable head testing and the target permeability of less than 1x10-7m/s, the artificially established geological barrier design shall specify that only soils classified as Clay will be used in its construction. Permeability at RNSP Western Mound 6.2.7 Permeability of material above the Chalk and Basal Sands at the RNSP Western mound has been estimated from particle size distribution (PSD) data as summarised in Table 4. With the exception of samples collected from the Harwich Formation, all other material would be considered impermeable and with estimated hydraulic conductivity values at 3x10-8m/s or less.

Template no.: HS2-HS2-IM-TEM-000-000265 Page 12 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

6.2.8 Given the low permeability nature of the materials above the Chalk and Basal Sands, groundwater recharge from the overlying ground surface is negligible.

Borehole Sample Sample Estimated Hydraulic Geological Classification Depth (mbgl) Elevation (mOD) Conductivity (m/s) ML024-RC012 1.10 60.80 3.5x10-10 Superficial Deposits

ML025-RC048 1.10 53.66 2.9x10-10 Superficial Deposits

ML025-RC049 1.00 50.23 2.7x10-8 Superficial Deposits

ML025-RC051 1.10 58.88 1.6x10-9 Superficial Deposits

ML024-RC012 11.66 50.22 3.6x10-10 London Clay Formation

ML025-RC051 3.84 56.14 3.6x10-10 London Clay Formation

ML025-RC051 8.56 51.42 3.9x10-10 London Clay Formation

ML024-RC012 17.93 43.95 7.0x10-7 Harwich Formation

ML025-RC048 2.90 51.86 2.8x10-8 Harwich Formation

ML025-RC051 11.32 48.66 3.4x10-6 Harwich Formation

ML024-RC012 24.02 37.86 3.8x10-10 Reading Formation - Lower Mottled Clay

ML024-RC012 30.00 31.88 4.4x10-10 Reading Formation - Lower Mottled Clay

ML025-RC048 8.86 45.90 1.8x10-8 Reading Formation - Lower Mottled Clay

ML025-RC048 17.70 37.06 5.0x10-10 Reading Formation - Lower Mottled Clay

ML025-RC049 4.50 46.73 6.1x10-10 Reading Formation - Lower Mottled Clay

ML025-RC049 9.09 42.14 4.5x10-10 Reading Formation - Lower Mottled Clay

ML025-RC049 16.15 35.08 2.4x10-8 Reading Formation - Lower Mottled Clay

ML025-RC051 17.31 42.67 1.3x10-9 Reading Formation - Lower Mottled Clay

Note: Permeabilities estimated from PSD data based on Hydro Sieve [10] where arithmetic mean has been used from available methods.

Table 4 - Estimated permeability from PSD data from soils collected at the RNSP (both Western and Eastern mounds) Surface Water 6.2.9 Within the limits of the RNSP Western mound, there is no interaction between surface water and the deep aquifer. Given the low permeability nature of the materials above the Chalk and Basal Sands in the RNSP Western mound, and since the natural watercourses are assumed to not be in hydraulic continuity with the Chalk, groundwater recharge from the overlying ground surface is negligible. Surface water will flow through shallow deposits and into the nearest surface drainage points.

Template no.: HS2-HS2-IM-TEM-000-000265 Page 13 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

6.2.10 Hydrological impacts of the RNSP Western mound on surface run-off is discussed elsewhere in the ESSD Report [9]. Groundwater Levels 6.2.11 Groundwater level monitoring has been performed within the Basal Sands overlying the Chalk since February 2017. Drawing B3 and Table B1 (Appendix B) provide results of groundwater level monitoring. Given the hydraulic connectivity with the underlying Chalk, these water levels are also representative of the Chalk aquifer.

6.2.12 Groundwater flow direction and gradient has been estimated during two periods (16th Feb 2017 and 22nd May 2018). Flow and gradient maps provided in Appendix B (Drawings B1 and B2) illustrate a prevailing flow direction to the southeast, which is consistent with regional groundwater flow. The estimated groundwater gradient across the site is considered to be relatively low, ranging from 0.005 (on 22nd May 2018) to 0.0075 (on 16th Feb 2017).

6.2.13 Groundwater level monitoring data from 10th April 2019 was also plotted and the gradient found to be 0.006: in line with previous values. Flow direction was still prevailing to the southeast.

6.2.14 During construction and post-construction, groundwater levels will continue to be monitored. For further information on requisite groundwater monitoring related to the construction of the RNSP, see the Groundwater Monitoring Plan S1 and S2 [18]. Groundwater Quality 6.2.15 Groundwater quality has been monitored on a quarterly basis at all four installations since February 2017. Prior to construction commencing in 2020, baseline groundwater quality data will consist of at least 14 sampling events at each installation over three years taken at roughly quarterly frequency. Groundwater quality will continue to be monitored following the construction of the RNSP Western mound in accordance with permit conditions as required by the EA.

6.2.16 As previously agreed between HS2 and the EA, Lambeth Group installations have been used as surrogates for Chalk Group installations for monitoring groundwater quality within the lower aquifer, as response zones are within the lower half of the Lambeth Group in all installations.

6.2.17 Table C1 provides baseline groundwater quality data and Figure C1 (both Appendix C) shows groundwater quality trend plots for selected analytes as compared to Drinking Water Standards (DWS) or other Environmental Quality Standards (EQS). Trends are only provided for analytes which have had exceedances above the screening criteria during baseline monitoring.

6.2.18 Evaluation of trends in groundwater quality will be performed following the completion of the RNSP Western mound in accordance with EA requirements.

Template no.: HS2-HS2-IM-TEM-000-000265 Page 14 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

6.2.19 While statistically relevant trends are not explicitly used within the monitoring programme, trends will be qualitatively reviewed when reviewing additional groundwater level and groundwater quality data. Where trends appear to be qualitatively present, statistical trend analysis (such as Mann-Kendall or Theil-Sen methods) may be used to evaluate the relevance of the trend.

6.2.20 As illustrated in Drawing A3, two installations are located within the SPZ-1 area. These installations provide sufficient coverage of baseline groundwater conditions for the following reasons:

• The material to be placed at both the RNSP Western and Eastern mounds will be an inert, low permeability, single-source material,

• One installation (ML025-RC048,) located at the edge of the Western mound and up gradient of the SPZ-1, provides information on the quality of the groundwater entering the SPZ-1. Installation ML025-RC049 is located at the down gradient edge of the Western mound of the RNSP, providing information on the quality of groundwater after passing beneath the RNSP. Even if the abstraction well associated with the SPZ-1 becomes operational (which would force a change in groundwater flow towards the south-southwest), these monitoring wells will still serve the same function,

• Given the lack of surface recharge at both the RNSP Western and Eastern mounds (see above), there is no viable pathway from emplaced material to impact the underlying aquifer.

6.2.21 Based on this information, baseline groundwater quality is sufficient to define baseline groundwater quality conditions (particularly considering the low risk nature of the RNSP as discussed below). Recommended Groundwater Screening Levels 6.2.22 Once site work begins, newly collected groundwater quality data will be compared against baseline groundwater quality data in order to evaluate changes to hydrogeological conditions.

6.2.23 To form the basis for assessing groundwater monitoring data, control and trigger levels from the EA’s ‘Hydrogeological Risk Assessment for Landfills and the Derivation of Control and Trigger Levels’ [14] have been adopted. Any deviations from these pre-defined levels will be assessed using the methodology described in Figure 2.

6.2.24 According to the EA guidance, control levels have been defined as: “a specific assessment criteria that are used to determine whether a landfill is performing as designed and are intended to bring to attention of site management to the development of adverse trends in the monitoring data. They are a test of the significance of a deviation from baseline groundwater conditions, which is used to determine whether a landfill is performing as designed. Control levels should be

Template no.: HS2-HS2-IM-TEM-000-000265 Page 15 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

regarded as an ‘early warning system’ to enable appropriate investigation or corrective measures to be implemented, rather than as an indication that groundwater pollution has occurred” [14].

6.2.25 The control levels have been derived to be suitable for the specific monitoring location, considering other influencing factors such as historical groundwater contamination, natural variation in groundwater quality, and baseline trends in groundwater chemistry. As control levels are defined as a significant deviation from baseline trends, the following formula has been used to calculate the control level for each analyte:2

Control Level = Mean groundwater parameter concentration + (2.5*STDV).

6.2.26 Trigger levels are higher concentration criteria than control levels and have been defined by the EA as “criteria at which significant adverse environmental effects have occurred. Such effects would be consistent with the groundwater being polluted” [14]. Consequently, trigger levels have been calculated using the following formula:

Trigger Level = Mean groundwater parameter concentration + (4*STDV).

6.2.27 For analytes which have not had an exceedance above the DWS during baseline monitoring, the trigger level has instead been constrained to the DWS.

6.2.28 Comparison of monitoring data with the derived control levels for each analyte should be conducted at every monitoring occurrence [14]. The monitoring frequency will also be derived based on baseline groundwater quality data. The monitoring frequency may need to be altered if the analyte concentration either increases or approaches trigger levels. If the trigger level is breached, then the site operator should notify the EA at the earliest opportunity.

6.2.29 A summary of the evaluation process that will occur during construction and operation is as follows:

• Comparison of observed monitoring results against established control levels every time monitoring data is collected,

• If observed concentrations are close to exceeding control levels, further data review will be performed to evaluate whether the exceedance is a result of site activities,

• If the further data review concludes the rising concentrations are due to site activities, the monitoring frequency needs to be increased and control measures should be implemented,

• If trigger levels are breached, the site operator will notify the EA and remediation measures will be executed.

2 The control and trigger level formulas have been adopted at each borehole for each monitored analyte to: 1) ensure that baseline results are all within the selected trigger levels; and 2) that the number of control level exceedances has been reasonably minimised. Where less than 3 detections occur, then no control or trigger levels were adopted. Where outliers were identified in the baseline data, they were excluded from the statistical analysis, unless the outlier is within the range of the other monitoring installations for a specific analyte.

Template no.: HS2-HS2-IM-TEM-000-000265 Page 16 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

Figure 2 - Flowchart illustrating responses to breach of defined action levels

6.2.30 The EA will be consulted throughout the process illustrated above. Alterations to the monitoring plan will be agreed between the site operator and the EA. If required, a remediation plan will be developed and implemented if trigger level exceedances are concluded to be due to site activities.

6.2.31 Existing screening criteria derived from DWS or EQS are listed in Appendix C. Following the conclusion of the baseline monitoring programme, screening levels will be finalised using the method described above. Selected groundwater monitoring trigger levels based on the existing monitoring data are provided in Appendix B for groundwater quality concentrations. The list of groundwater quality monitoring analytes and minimum reporting levels is provided in the Environmental Monitoring Plan [13]. 7 Risk Evaluation 7.1.1 Two potential hydrogeological risks have been identified resulting from the construction of the RNSP Western mound: (1) deterioration of groundwater quality in underlying aquifers; and (2) geotechnical impacts associated within dissolution features which could potentially exist within the Chalk. The evaluation of risk associated with these identified risks are discussed below. Table 5 provides a summary of the risk evaluation.

Template no.: HS2-HS2-IM-TEM-000-000265 Page 17 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

Hazard Potential Impacts Likelihood Consequence Risk Magnitude

1 Contaminated waste is mistakenly Deterioration of Very Low Medium Low placed within RNSP Western groundwater mound and migrates to underlying quality Chalk aquifer

2 Collapse of dissolution features None (no receptors Very Low Low Low due to placement of additional exist) load from waste material

Note: A description of the risk methodology is provided in Appendix D.

Table 5 - Summary of hydrogeological risk evaluation

7.1.2 The principal hydrogeological risk is related to the potential deterioration of groundwater quality of the underlying aquifer (in particular, groundwater within the SPZ-1). The risk is considered to be low based on the following:

• The material to be placed at both the RNSP Western and Eastern mounds will be an inert, low permeability, single-source material,

• A hydraulic barrier will be placed at the base of the RNSP Western mound which severs the pathway of downward migration,

• There is a significantly impermeable natural hydraulic barrier present within the Lower Mottled Clay of the Lambeth Group, providing an additional barrier to downward migration, and

• Groundwater monitoring installations are in-place and can be used to confirm groundwater quality following construction of the RNSP Western mound.

7.1.3 The presence of dissolution features within the Chalk could potentially lead to ground settlement at surface following the placement of material for mound construction. The settlement, in this case, is the result of the additional load from the placement of material leading to a collapse within the dissolution features. Where settlement occurs, nearby structures may be at risk of structural impacts from the induced settlement. At the RNSP Western mound site, this risk is considered insignificant for the following reasons:

• The site is in an area identified to be of negligible risk of rock dissolution,

• There are no planned structures within the limits of the RNSP Western mound. Thus, should any settlement occur, there is no structural receptor to be impacted,

• The Chalk at this location is confined and thus will remain saturated. The presence of saturated groundwater conditions minimises the risk of collapse, as dissolution features are less stable where unsaturated,

Template no.: HS2-HS2-IM-TEM-000-000265 Page 18 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

• The top of the Chalk layer is at least 19m (or greater) below the ground surface. Thus, there will be some spread of the load applied from the mounds through the overlying material, reducing the load applied to the Chalk,

• As the Chalk is overlain by 19m of material, should there be any of collapse of voids within the Chalk, impacts may not propagate to the ground surface depending on the size of the void due to bulking effects.

7.1.4 For more detail on the evaluation of risk associated with Chalk dissolution features, refer to Appendix E.

7.1.5 A qualitative assessment of the full lifecycle of the Western mound has been considered in this HRA. Given that the source of the material is non-organic naturally occurring Clay from a single source, there is no expectation of long-term changes to the chemical disposition of the Western mound. Thus, the conclusions provided in this HRA are assumed to be appropriate for the life of the mound. In addition, given that post-construction monitoring will be in-place, any changes to groundwater as identified by exceedances in selected control and trigger levels will prompt a review of conditions, and if required, implementation of identified mitigation measures.

Template no.: HS2-HS2-IM-TEM-000-000265 Page 19 Uncontrolled when printed

Symbol/Abbreviation Description

AGS Association of Geotechnical and GeoEnvironmental Specialists – refers to a data format used to transfer site investigation information and results that is independent of software or hardware

BGS British Geological Survey

CSM Conceptual Site Model

DH Design House

DWS Drinking Water Standard

EA Environment Agency

EQ Environmental Quality

ES Environmental Statement

ESSD Environmental Setting and Site Design

GIR Ground Investigation Report

HRA Hydrogeological Risk Assessment

HS2 High Speed Two

GI Ground Investigation

k Permeability

mbgl Meter(s) below existing ground level

mOD Meter(s) above Ordnance Datum

MWCC Main Works Civils Contractor (MWCC)

NWR Northwest Ruislip

PSD Particle Size Distribution

RC Rotary core hole

RNSP Ruislip Northern Sustainable Placement

RSP Ruislip Sustainable Placement

SCS Construction Joint Venture SKANSKA, COSTAIN, STRABAG

SOP Site Operating Plan

SP Standpipe piezometer

SPA Sustainable Placement Area

SPB South Package B

Template no.: HS2-HS2-IM-TEM-000-000265 Page 20 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

Symbol/Abbreviation Description

SPR Source-Receptor-Pathway

SPZ Source Protection Zone

VW Vibrating wire piezometer

Template no.: HS2-HS2-IM-TEM-000-000265 Page 21 Uncontrolled when printed

[2] https://www.bgs.ac.uk/research/groundwater/waterResources/thames/chalk.html [accessed August 2018]

[3] British Geological Survey, 1997, The physical properties of major aquifers in England and Wales (Technical Report WD/97/34)

[4] ESI, 2013, London Basin Aquifer: NumericalmODel Report

[5] British Geological Survey, London and the Thames Valley [Accessed https://www.bgs.ac.uk/downloads/start.cfm?id=2921, August 2018]

[6] http://apps.environment-agency.gov.uk/wiyby/default.aspx [accessed August 2018]

[7] http://mapapps.bgs.ac.uk/geologyofbritain/home.html [accessed August 2018]

[8] HS2, 2018, Ground Investigation Report: Copthall Tunnel and Harvil Road, 1MC04-SCJ-GT- REP-000009

[9] SCS, 2020, Environmental Setting and Site Design Report (ESSD) - Western Mound - Ruislip Northern Sustainable Placement S2, 1MC04-SCJ-EV-REP-SS05_SL07-000002, C01

[10] HydrogeoSieveXL, 2015, University of Kansas

[11] HS2, 2018, Drainage Design Report s2, 1MC04-SCJ-DR-REP-S002-000002

[12] HS2, 2018, Final Factual Report West Ruislip, 1G089-FES-GT-REP-000-000019

[13] HS2, 2018, 1MCo4 Main Works - Contract Lot S2, Environmental Monitoring Plan, Sustainable Placement Area (North) S2

[14] EA, 2003, Hydrogeological Risk Assessment for Landfills and the Derivation of Control and Trigger Levels

[15] EA, 2003, Guidance on Monitoring of Landfill Leachate, Groundwater and Surface Water

[16] SCS, 2019, Materials Management Study - Copthall Tunnel S2, 1MC04-SDH-GT-NOT- SS05_SL07-000002, C01

[17] SCS, 2018, Northern Sustainable Placement Area (SPA) - Hydrogeological Risk Assessment (HRA) S2, 1MC04-SCJ-EV-RIA-SS05_SL07-000001, C02

[18] SCS, 2020, Groundwater Monitoring Plan S1 and S2, 1MC03‐SCJ‐EV‐PLN‐S001‐000030, C03

[19] SCS, 2020, Environmental Monitoring Plan - Western Mound - Ruislip Northern Sustainable Placement S2, 1MC04-SCJ-EV-PLN-SS05_SL07-000002, C01

Template no.: HS2-HS2-IM-TEM-000-000265 Page 22 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

[20] SCS, 2020, Site Operating Plan (SOP) - Western Mound - Ruislip Northern Sustainable Placement S2, 1MC04-SCJ-EV-PLN-SS05_SL07-000001, C01

[21] SCS, 2020, Stability Risk Assessment - Western Mound - Ruislip Northern Sustainable Placement S2, 1MC04-SCJ-EV-ASM-SS05_SL07-000002, C01

[22] SCS, 2020, Management Systems and Procedures - Western Mound - Ruislip Northern Sustainable Placement S2, 1MC04-SCJ_SDH-EV-PRO-SS05_SL07-000001, C01

Template no.: HS2-HS2-IM-TEM-000-000265 Page 23 Uncontrolled when printed

Template no.: HS2-HS2-IM-TEM-000-000265 Page 24 Uncontrolled when printed

OFFICIAL A3 505500 506500 507500 508500 509500 510500 511500 512500 513500 514500 515500 516500 517500 518500 519500 520500 521500 522500 523500 524500 525500 526500 527500 528500 529500 530500 531500 532500 533500 534500 535500 536500 537500 1 0 : 5 3 : 5

Legend 1

0 0 0 2 5 7 ° 0 2 9 ! / 1

Ruislip Northern Sustainable 6 0 / 1

Placement Western and Eastern 1 0 0

5 Mounds 6 9 1 Ruislip Northern Sustainable 0 0

5 Placement Site Boundary

5 D 9 1 O m Chalk Piezometric Surface

0 0 0

5 4 4 9 1 0 0 5 3 9 1 0 0 5 2 9 1 0 0 5 1 9 1 0 0 5 0 9 1 0 0 5

9 RNSP 8 1 D O 0 0 5

8 m 8

1 0 3 0 0 5 7 8 1 0

0 5 6 8 1

D C01 2018-08-24 LA LMCA MG/RPLA

0 D 0 O 5 O 5

8 m m 1 20 0 1 D Issue Date By Chkd Appd D O 0

0 O

5 m 4 m 8 0 0 Metres 1 -1 0 1,300 2,600 5,200 0 0 5 3 8 1 0 0 5 2 8 1 0

0 D 5 1

8 O 1 Arup m 13 Fitzroy Street,

0 0 London, 0

5 2 W1T 4BQ, 0

8 - United Kingdom 1 Client 0 0

5 D 9 O HS2 Ltd 7 m 1 -30 0 0 5 8 7 1 Job Title 0 0

5 HS2 S1 & S2 7 7

1 D 0mO 0

0 Drawing Title 5 6 7 1 Regional Hydrogeological Map 0 0 5 5 7 1 0 0 5 4 7 1

Scale at A3 0 0

5 0 3 mO 1:100,000 7 D 1 Job No Drawing Status 0 0

5 256905/6 For Issue 2 7 1 Drawing No Issue 0

0 A1 C01 5 1 7

1 Contains OS data © Crown Copyright and database right 2019

\\global.arup.com\london\ILG\JOBS\256000\256905-00 HS2 Phase 1 D&B - S1\05 Other Team Members\GEO\50_Design_analysis\02 GIS\01_mxd\20200325-HS2_Hydrogeology.mxd © Arup RUISLIP NORTHERN SUSTAINABLE PLACEMENT A3 506500 507000 507500 6 0 : 6 2 : 3 1 Legend 0 2

° 0

! 2 / 3 0 / 7 A! Groundwater Boreholes 2 Source Protection Zone 1 Asset Type Mitigation Earthworks

! ML025-RC051 A EASTERN MOUND 0 0 5 8 8 1

C01 2020-01-16 PC PMCC MG/RPPC

WESTERN MOUND ! Issue Date By Chkd Appd ML025-RC048A Metres

0 50 100 200

Arup 13 Fitzroy Street, ! London, A W1T 4BQ, ML025-RC049 United Kingdom Client ! HS2 Ltd ML024-RC012 A

Job Title HS2 S1 & S2

Drawing Title

Ruislip Northern Sustainable Placement 0 0

0 Location Map with respect to Source 8 8 1 Protection Zone

Scale at A3 1:3,750

Job No Drawing Status 256905/6 For Issue

Drawing No Issue Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User A3 C01 Community

\\global\london\G_E\Jobs\70000\71910-02\Hydrogeology\Jobs\HS2 S1 & S2\60 - GIS\Data\20200325-SPA groundwater_monitoring.mxd © Arup Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02 Appendix B - Groundwater Contours and Levels

Template no.: HS2-HS2-IM-TEM-000-000265 Page 25 Uncontrolled when printed

OFFICIAL A3 506500 507000 507500 2 3 : 5 2 : 3 1

Legend 0 2

° 0

! 2 / 3 0 /

! Groundwater Boreholes 7 A 2 Source Protection Zone 1 Prevailing Groundwater Flow Direction

Groundwater Contours (mOD) 16th Feb 2017 Asset Type ! Mitigation Earthworks ML025-RC051 A EASTERN MOUND

40 0 0 5 8 8 1

9.5 3

C01 2020-03-27 PC PMCC MG/RPPC

9 WESTERN MOUND ! 3 Issue Date By Chkd Appd ML025-RC048A Metres

0 50 100 200

38.5

Arup 7.5 13 Fitzroy Street, ! 3 London, A W1T 4BQ, ML025-RC049 United Kingdom Client ! HS2 Ltd ML024-RC012 A

Job Title HS2 S1 & S2

Drawing Title

Ruislip Northern Sustainable Placement 0 0

0 Groundwater Monitoring Contours 8 8 1 16th February 2017

Scale at A3 1:3,750

Job No Drawing Status 256905/6 For Issue

Drawing No Issue Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User B1 C01 Community

\\global\london\G_E\Jobs\70000\71910-02\Hydrogeology\Jobs\HS2 S1 & S2\60 - GIS\Data\20200325-SPA groundwater_monitoring.mxd © Arup A3 506500 507000 507500 7 2 : 6 2 : 3 1

Legend 0 2

° 0

! 2 / 3 0 /

! Groundwater Boreholes 7 A 2 Source Protection Zone 1 Prevailing Groundwater Flow Direction

Groundwater Contours (mOD) 22nd May 2018 Asset Type ! Mitigation Earthworks ML025-RC051 A EASTERN MOUND 40 0 0 5 8 8 1

.5 39

C01 2020-03-27 PC PMCC MG/RPPC

WESTERN MOUND ! Issue Date By Chkd Appd ML025-RC048A 9 3 Metres

0 50 100 200

.5 38

Arup 38 13 Fitzroy Street, ! London, A W1T 4BQ, ML025-RC049 United Kingdom Client ! HS2 Ltd ML024-RC012 A

Job Title HS2 S1 & S2

Drawing Title

Ruislip Northern Sustainable Placement 0 0

0 Groundwater Monitoring Contours 8 8 1 22nd May 2018

Scale at A3 1:3,750

Job No Drawing Status 256905/6 For Issue

Drawing No Issue Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User B2 C01 Community

\\global\london\G_E\Jobs\70000\71910-02\Hydrogeology\Jobs\HS2 S1 & S2\60 - GIS\Data\20200325-SPA groundwater_monitoring.mxd © Arup Table B1 - Groundwater Levels

Water Depth Borehole Sampling Date Geology mbgl mOD 18-Jan-17 22.96 38.92 26-Jan-17 24.10 37.78 26-Jan-17 24.10 37.78 03-Feb-17 24.21 37.67 07-Feb-17 24.30 37.58 07-Feb-17 24.30 37.58 16-Feb-17 24.90 36.98 16-Feb-17 24.90 36.98 21-Feb-17 24.17 37.71 22-Mar-17 24.18 37.70 19-Apr-17 24.44 37.44 15-May-17 24.39 37.49 14-Jun-17 24.37 37.51 17-Jul-17 24.55 37.33 Lower Lambeth Group ML024-RC012 29-Aug-17 24.49 37.39 including Upnor 26-Sep-17 24.61 37.27 Formation 24-Oct-17 24.59 37.29 21-Nov-17 24.53 37.35 18-Dec-17 24.74 37.14 15-Jan-18 24.28 37.60 14-Feb-18 24.32 37.56 20-Mar-18 24.50 37.38 22-May-18 24.28 37.60 25-Jun-18 24.43 37.45 24-Jul-18 24.48 37.40 21-Aug-18 24.38 37.50 26-Sep-18 25.12 36.76 10-Apr-19 25.02 36.86 12-Nov-19 23.66 38.22 18-Jan-17 15.34 39.42 27-Jan-17 15.37 39.39 31-Jan-17 15.13 39.63 07-Feb-17 15.27 39.49 16-Feb-17 15.2 39.56 16-Feb-17 15.2 39.56 23-Feb-17 15.23 39.53 22-Mar-17 15.23 39.53 19-Apr-17 15.34 39.42 15-May-17 15.36 39.40 18-May-17 14.81 39.95 13-Jun-17 15.31 39.45 19-Jul-17 15.32 39.44 22-Aug-17 15.46 39.30 Lower Lambeth Group ML025-RC048 26-Sep-17 15.52 39.24 including Upnor 24-Oct-17 15.52 39.24 Formation 21-Nov-17 15.47 39.29 18-Dec-17 15.55 39.21 15-Jan-18 15.27 39.49 15-Feb-18 15.4 39.36 19-Mar-18 15.35 39.41 22-May-18 15.25 39.51 25-Jun-18 15.39 39.37 24-Jul-18 15.31 39.45 16-Aug-18 15.34 39.42 26-Sep-18 15.55 39.21 10-Apr-19 15.25 39.51 26-Sep-19 15.48 39.28 22-Oct-19 15.67 39.09 Water Depth Borehole Sampling Date Geology mbgl mOD 27-Jan-17 13.40 37.83 27-Jan-17 13.40 37.83 01-Feb-17 13.40 37.83 01-Feb-17 13.40 37.83 07-Feb-17 13.40 37.83 07-Feb-17 13.40 37.83 16-Feb-17 13.40 37.83 16-Feb-17 13.40 37.83 23-Feb-17 13.30 37.93 23-Feb-17 13.30 37.93 22-Mar-17 13.23 38.00 19-Apr-17 13.37 37.86 15-May-17 13.33 37.90 18-May-17 13.24 37.99 13-Jun-17 13.38 37.85 Lower Lambeth Group ML025-RC049 19-Jul-17 13.43 37.80 including Upnor 22-Aug-17 13.59 37.64 Formation 26-Sep-17 13.58 37.65 24-Oct-17 13.48 37.75 21-Nov-17 13.40 37.83 18-Dec-17 13.66 37.57 15-Jan-18 13.06 38.17 15-Feb-18 13.03 38.20 19-Mar-18 12.95 38.28 22-May-18 12.49 38.74 25-Jun-18 12.72 38.51 24-Jul-18 13.23 38.00 16-Aug-18 13.33 37.90 26-Sep-18 13.64 37.59 10-Apr-19 19.00* 32.23* 26-Sep-19 13.53 37.70 12-Jan-17 19.76 40.22 19-Jan-17 19.99 39.99 27-Jan-17 19.68 40.30 01-Feb-17 19.58 40.40 07-Feb-17 19.96 40.02 16-Feb-17 19.30 40.68 16-Feb-17 19.30 40.68 23-Feb-17 19.52 40.46 21-Mar-17 19.87 40.11 19-Apr-17 20.10 39.88 19-Apr-17 20.10 39.88 15-May-17 20.09 39.89 14-Jun-17 20.10 39.88 14-Jun-17 20.10 39.88 Lower Lambeth Group 17-Jul-17 20.28 39.70 ML025-RC051 including Upnor 22-Aug-17 20.26 39.72 Formation 26-Sep-17 20.39 39.59 24-Oct-17 20.36 39.62 23-Nov-17 20.18 39.80 18-Dec-17 20.57 39.41 15-Jan-18 20.07 39.91 14-Feb-18 20.06 39.92 20-Mar-18 20.31 39.67 22-May-18 19.80 40.18 25-Jun-18 20.02 39.86 24-Jul-18 19.95 39.93 21-Aug-18 20.17 39.71 26-Sep-18 20.42 39.46 10-Apr-19 20.00 39.88 22-Oct-19 20.52 39.36

Table B1 Notes: *This data point has been excluded from the analysis as it is considered to be an outlier and likely represents a transcription error in the field. Groundwater Level Trends Across the RNSP

ML025-RC048 ML025-RC049 ML025-RC051 38 Groundwater Level (mOD) ML024-RC012

36 26 Nov 16 14 Jun 17 31 Dec 17 19 Jul 18 04 Feb 19 23 Aug 19

Sampling Date

Drawing B3 Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02 Appendix C - Groundwater Quality Data

Template no.: HS2-HS2-IM-TEM-000-000265 Page 26 Uncontrolled when printed

OFFICIAL Table C1

Ortho EPH >C10- Ethyl- Nitrate as Nitrite as Borehole Sampling Date Quarter Amm. N As B Ba Be Benzene Ca Cd Cl - Cyanide Cr 3+ Cr 6+ Cu DO EC Fe Hg K Mg Mn N Na Ni Phos- 40 benzene NO N 3 phate as P Unit mg/l µg/l µg/l µg/l µg/l µg/l mg/l µg/l mg/l µg/l µg/l µg/l µg/l mg/l µS/cm µg/l µg/l µg/l µg/l mg/l mg/l µg/l mg/l mg/l µg/l mg/l mg/l mg/l Screening Criterion 0.30 10 1,000 NC NC 1.0 NC 5.0 250 1.0 4.7 3.4 1.0 NC NC NC 20 200 0.070 NC NC 50 NC NC 4.0 50 0.50 NC DWS 0.39 10 1,000 NC NC 1.0 NC 5.0 250 50 NC 50 2,000 NC NC NC NC 200 1.0 NC NC 50 NC NC 20 50 0.50 NC AA-EQS 0.30 50 2,000 NC NC 10 NC 0.25* 250 1.0 4.7 3.4 1.0 NC NC NC 20 1,000 NC NC NC 123 NC NC 4.0 NC NC NC MAC-EQS NC NC NC NC NC 50 NC 1.50^ NC 5.0 32 NC NC NC NC NC 200 NC 0.070 NC NC NC NC NC 34 NC NC NC Well Specific Control Level 2.5 1.7 713 131 NA NA 279 NA 229 53 NA NA 4.4 14 2,836 88 NA 11,340 NA 24 130 1,121 5.9 104 13 3.6 0.36 0.75 Well Specific Trigger Level 3.4 2.1 794 180 NA NA 334 NA 301 81 NA NA 6.3 18 3,422 129 NA 15,769 NA 29 157 1,491 7.9 130 18 5.0 0.50 1.1 07-Feb-17 Q1 2017 2.0 1.6 540 110 0.050 0.50 190 0.050 79 0.80 0.50 3.5 2.5 8.8 1,930 89 0.50 2,000 0.0050 19 92 590 4.3 80 8.5 1.1 0.018 0.020 17-May-17 Q2 2017 2.0 0.69 610 46 0.050 0.50 290 0.015 88 0.050 0.50 3.5 3.0 10 2,530 5.0 0.50 1,300 0.0050 24 140 560 3.5 93 8.1 2.1 0.052 0.0050 17-Jul-17 Q3 2017 1.3 0.78 660 16 0.050 0.50 160 0.015 77 71 0.50 3.5 1.1 9.5 1,810 12 0.50 2,300 0.070 16 83 270 2.4 55 3.1 2.3 0.25 0.020 21-Nov-17 Q4 2017 1.1 0.86 580 19 0.050 0.50 150 0.015 100 0.30 0.50 3.5 1.0 10 1,460 5.0 0.50 3,000 0.0050 16 69 340 4.0 45 2.9 0.050 0.018 0.0050 20-Mar-18 Q1 2018 0.96 1.1 610 83 0.050 0.50 190 0.015 120 0.20 0.50 3.5 0.20 8.8 1,910 5.0 0.50 6,400 0.0050 16 86 970 2.5 73 7.2 0.91 0.018 0.010 22-May-18 Q2 2018 0.0075 1.4 480 54 0.050 0.50 190 0.015 97 0.050 0.50 3.5 1.7 4.0 1,840 5.0 0.50 4,500 0.010 14 82 970 1.9 88 8.6 1.0 0.41 0.0050 ML024-RC012 25-Jun-18 Q2 2018 0.63 1.1 520 120 0.050 0.50 200 0.015 110 0.050 0.50 3.5 0.50 4.4 2,010 37 0.50 31 0.0050 17 87 19 4.7 75 13 0.26 0.056 0.10 24-Jul-18 Q3 2018 1.3 0.87 630 48 0.050 0.50 200 0.015 110 0.40 0.50 3.5 0.20 5.3 1,880 5.0 0.50 7,400 0.0050 16 91 550 2.8 43 3.5 0.79 0.018 1.0 21-Aug-18 Q3 2018 0.92 0.62 620 27 0.050 0.50 180 0.015 91 0.80 0.50 3.5 1.1 8.5 1,640 5.0 0.50 310 0.0050 17 86 400 1.3 53 2.1 0.35 0.018 0.0050 26-Sep-18 Q3 2018 1.1 0.63 550 29 0.050 0.50 170 0.015 110 0.10 0.50 3.5 1.0 6.6 1,570 71 0.50 7,200 0.0050 16 80 450 0.50 53 1.9 0.50 0.043 0.030 24-Oct-18 Q4 2018 1.4 1.1 630 40 0.050 0.50 220 0.015 98 1.3 0.50 3.5 2.7 2.9 1,580 5.0 0.50 6,500 0.0050 17 80 430 0.50 58 2.8 0.12 0.018 0.040 27-Nov-18 Q4 2018 0.71 1.1 500 32 0.050 0.50 150 0.015 89 0.50 0.50 3.5 0.20 8.9 1,460 5.0 0.50 8,000 0.0050 17 61 530 2.4 47 3.2 1.5 0.018 0.030 18-Dec-18 Q4 2018 0.0075 1.1 560 33 0.050 0.50 160 0.015 98 1.6 0.50 3.5 4.0 7.9 2,810 5.0 0.50 6,200 0.0050 10 72 550 3.3 47 4.0 1.1 0.11 0.0050 12-Nov-19 Q4 2019 0.74 1.2 600 29 0.050 0.50 150 0.010 270 5.0 0.50 2.5 0.25 2.7 1,600 5.0 0.50 270 0.025 19 87 430 1.4 69 3.1 3.6 0.0084 0.033 Well Specific Control Level 6.1 9.7 463 169 NA NA 803 0.8 480 39 7.5 NA 82 14 6,621 161 NA 27,655 0.077 378 684 6,097 19 211 58 13 0.33 0.80 Well Specific Trigger Level 9.1 14 571 239 NA NA 1,056 1.1 616 59 11 NA 122 18 8,173 228 NA 41,723 0.11 540 916 8,736 27 262 75 18 0.50 1.2 20-Feb-17 Q1 2017 0.0075 6.7 190 0.070 0.050 0.50 200 0.59 220 3.5 4.1 3.5 55 9.0 3,040 60 0.50 4,100 0.040 220 120 260 0.50 180 21 1.2 0.018 0.78 18-May-17 Q2 2017 0.55 12 280 130 0.050 0.50 140 0.94 270 7.4 7.7 3.5 110 2.1 2,620 150 0.50 2,600 0.050 390 35 100 15 80 23 2.0 0.018 0.90 13-Jun-17 Q2 2017 0.57 1.9 270 16 0.050 0.50 480 0.070 220 0.050 0.50 3.5 3.9 10 4,880 5.0 0.50 450 0.090 41 390 610 2.9 130 17 5.2 0.018 0.030 19-Jul-17 Q3 2017 0.15 1.7 320 18 0.050 0.50 400 0.14 490 19 6.4 3.5 12 8.2 4,870 72 0.50 540 0.030 45 340 600 2.6 160 30 12 0.018 0.0050 22-Aug-17 Q3 2017 0.22 1.6 240 19 0.050 0.50 530 0.080 180 12 0.50 3.5 6.8 8.9 4,740 56 0.50 100 0.0050 51 390 770 2.9 78 32 8.9 0.048 0.020 21-Nov-17 Q4 2017 0.29 0.94 480 17 0.050 0.50 460 0.015 280 1.4 0.50 3.5 2.7 11 4,270 5.0 0.50 1,400 0.030 54 330 1,300 4.7 130 32 0.050 0.018 0.0050 19-Mar-18 Q1 2018 7.2 1.5 270 33 0.050 0.50 420 0.040 260 1.3 1.8 3.5 7.0 8.9 4,450 5.0 0.50 1,900 0.0050 91 320 1,800 19 140 41 5.2 0.077 0.040 22-May-18 Q2 2018 0.0075 0.81 300 31 0.050 0.50 490 0.040 240 0.050 0.50 3.5 3.8 7.2 5,100 80 0.50 38,000 0.0050 62 490 2,400 5.3 150 40 11 0.018 0.0050 ML025-RC048 25-Jun-18 Q2 2018 0.16 1.6 300 70 0.050 0.50 600 0.070 300 0.050 0.50 3.5 2.5 4.9 5,100 5.0 0.50 130 0.010 55 450 620 3.0 150 35 0.84 0.018 0.060 24-Jul-18 Q3 2018 0.73 1.4 360 75 0.050 0.50 350 0.34 270 0.60 0.50 3.5 9.7 4.7 5,100 55 0.50 830 0.010 54 240 2,700 2.5 150 44 1.7 0.048 0.20 16-Aug-18 Q3 2018 0.15 0.49 320 190 0.050 0.50 510 0.015 340 0.70 0.50 3.5 3.1 8.7 4,940 51 0.50 270 0.0050 48 490 1,300 1.6 150 33 1.1 0.018 0.13 26-Sep-18 Q3 2018 0.76 1.1 280 29 0.050 0.50 440 0.030 170 0.10 0.50 3.5 3.8 4.3 4,760 65 0.50 520 0.0050 47 410 780 1.2 150 19 3.0 0.018 0.030 24-Oct-18 Q4 2018 1.1 3.2 360 83 0.050 0.50 46 0.050 210 55 3.4 3.5 14 3.0 2,720 110 0.50 2,300 0.0050 4.4 130 2,100 3.6 100 48 1.2 0.039 0.10 27-Nov-18 Q4 2018 0.84 1.5 240 69 0.050 0.50 350 0.015 39 1.9 0.50 3.5 3.0 6.8 3,370 110 0.50 18,000 0.0050 160 200 6,900 7.5 110 39 0.15 0.018 0.030 18-Dec-18 Q4 2018 0.0075 1.7 210 44 0.050 0.50 180 0.050 210 2.4 1.1 3.5 16 9.0 2,370 67 0.50 2,800 0.0050 130 130 3,300 5.7 81 33 4.8 0.49 0.0050 10-Apr-19 Q1 2019 0.021 0.24 260 24 0.050 0.50 680 0.010 280 5.0 0.50 2.5 0.25 NA 4,600 5.0 0.50 140 0.025 85 560 250 0.99 170 3.3 4.4 0.024 0.010 22-Oct-19 Q4 2019 0.082 1.3 220 34 0.050 0.50 210 0.010 220 5.0 0.50 2.5 3.9 4.3 2,500 5.0 0.50 170 0.025 52 170 380 3.1 80 27 2.6 0.042 0.096 16-Jan-20 Q1 2020 5.7 5.2 170 51 0.050 0.50 380 0.040 340 5.0 U/S U/S 1.8 1.3 3,200 5.0 0.50 1,500 0.025 350 150 4,400 15 98 18 4.5 0.075 0.20 Well Specific Control Level 5.5 3.5 363 100 NA NA 288 NA 691 44 NA NA 3.4 13 2,410 102 NA 23,124 0.042 18 111 600 36 125 8.3 5.9 0.21 0.18 Well Specific Trigger Level 8.3 5.0 466 136 NA NA 334 NA 934 66 NA NA 4.6 16 2,672 152 NA 35,528 0.057 22 133 910 54 152 12 7.7 0.31 0.26 07-Feb-17 Q1 2017 0.70 0.55 120 43 0.050 0.50 130 0.015 270 0.30 0.50 3.5 0.20 7.8 2,050 5.0 0.50 110 0.020 8.5 31 84 49 27 2.4 1.9 0.018 0.0050 18-May-17 Q2 2017 0.0075 0.40 150 31 0.050 0.50 250 0.040 240 0.050 0.50 3.5 1.9 8.7 2,260 5.0 0.50 25 0.0050 15 89 5.5 1.3 91 1.5 3.2 0.018 0.0050 13-Jun-17 Q2 2017 0.0075 0.80 150 27 0.050 0.50 210 0.015 240 0.40 0.50 3.5 0.60 11 2,130 5.0 0.50 89 0.030 12 71 13 1.6 78 2.0 2.1 0.018 0.0050 19-Jul-17 Q3 2017 0.017 0.68 180 29 0.050 0.50 220 0.015 270 57 6.4 3.5 1.4 6.5 2,100 49 0.50 100 0.030 11 76 9.2 2.4 90 1.2 2.1 0.018 0.0050 22-Aug-17 Q3 2017 0.016 0.69 170 28 0.050 0.50 240 0.015 200 34 0.50 3.5 0.80 9.2 2,160 13 0.50 61 0.020 13 87 11 1.4 92 1.8 3.9 0.018 0.030 21-Nov-17 Q4 2017 0.44 1.3 220 27 0.050 0.50 210 0.015 580 2.6 0.50 3.5 1.2 11 1,950 5.0 0.50 250 0.020 11 75 20 4.4 84 3.7 2.4 0.018 0.0050 19-Mar-18 Q1 2018 7.5 0.35 160 27 0.050 0.50 240 0.015 350 0.10 0.50 3.5 0.50 9.0 2,090 5.0 0.50 170 0.0050 13 77 14 20 90 1.3 2.9 0.13 0.010 22-May-18 Q2 2018 0.0075 0.36 140 30 0.050 0.50 230 0.015 800 0.050 6.1 3.5 2.9 5.8 2,100 5.0 0.50 320 0.0050 11 78 6.3 1.8 98 1.6 5.0 0.018 0.0050 ML025-RC049 25-Jun-18 Q2 2018 3.1 3.6 370 97 0.050 0.50 180 0.015 200 0.050 0.50 3.5 1.0 4.8 1,810 5.0 0.50 160 0.0050 14 64 1.5 9.2 73 9.6 2.0 0.018 0.080 24-Jul-18 Q3 2018 0.24 0.45 210 78 0.050 0.50 230 0.015 280 0.50 0.50 3.5 0.80 9.1 2,020 5.0 0.50 270 0.010 11 71 13 2.4 53 1.0 3.0 0.018 0.21 16-Aug-18 Q3 2018 0.062 0.080 160 97 0.050 0.50 230 0.015 350 2.2 0.50 3.5 0.70 9.2 1,960 130 0.50 87 0.0050 12 78 13 1.3 80 1.4 2.4 0.018 0.13 26-Sep-18 Q3 2018 0.10 0.30 170 34 0.050 0.50 220 0.015 170 0.050 0.50 3.5 1.9 7.0 1,920 67 0.50 93 0.0050 12 75 12 1.2 76 0.60 3.0 0.018 0.030 22-Oct-18 Q4 2018 0.74 0.36 170 40 0.050 0.50 190 0.015 190 0.50 0.50 3.5 2.6 5.4 2,080 36 0.50 580 0.030 12 87 15 0.50 96 1.6 3.8 0.018 0.0050 27-Nov-18 Q4 2018 2.1 2.8 290 37 0.050 0.50 170 0.015 140 0.30 0.50 3.5 1.8 5.5 1,630 5.0 0.50 35,000 0.0050 15 50 810 14 66 4.6 0.47 0.018 0.030 18-Dec-18 Q4 2018 0.0075 2.6 290 31 0.050 0.50 190 0.015 180 0.30 0.50 3.5 2.8 8.7 1,690 5.0 0.50 6,700 0.0050 6.5 65 430 5.9 65 6.2 4.3 0.29 0.0050 10-Apr-19 Q1 2019 0.85 0.075 240 24 0.050 0.50 200 0.010 190 5.0 0.50 2.5 1.0 NA 1,700 5.0 0.50 2.0 0.025 15 79 18 0.69 91 2.8 3.1 0.0056 0.010 26-Sep-19 Q3 2019 0.18 0.075 110 23 0.050 0.50 230 0.010 240 5.0 0.50 2.5 1.6 7.6 1,900 5.0 0.50 96 0.025 15 87 5.9 0.50 91 1.1 3.5 0.022 0.053 16-Jan-20 Q1 2020 0.0075 0.075 120 25 0.050 0.50 240 0.010 250 5.0 0.50 2.5 0.8 3.3 2,000 5.0 0.50 2 0.025 14 92 4.8 0.60 93 0.25 5.2 0.0027 0.064 Well Specific Control Level 1.6 1.3 917 101 NA NA 516 NA 324 31 NA NA 5.1 14 5,731 93 NA 118,763 NA 31 395 905 6.2 218 11 8.5 0.072 0.21 Well Specific Trigger Level 2.1 1.8 1,000 144 NA NA 653 NA 381 46 NA NA 7.3 18 7,375 137 NA 166,927 NA 37 506 1,192 8.7 271 17 13 0.10 0.31 07-Feb-17 Q1 2017 0.60 1.2 770 97 0.050 0.50 360 0.070 260 0.40 1.6 3.5 5.1 9.7 3,820 87 0.50 44,000 0.0050 27 250 670 3.6 170 4.5 0.050 0.018 0.020 17-Jul-17 Q3 2017 0.84 0.58 670 9.5 0.050 0.50 360 0.015 200 41 0.50 3.5 0.20 10 3,690 23 0.50 14,000 0.040 18 260 450 1.3 140 1.6 2.1 0.018 0.0050 22-Aug-17 Q3 2017 0.92 0.49 680 13 0.050 0.50 380 0.015 230 8.9 0.50 3.5 0.50 9.2 4,030 5.0 0.50 28,000 0.0050 23 290 610 2.3 99 2.5 11 0.018 0.0050 23-Nov-17 Q4 2017 0.32 0.080 540 16 0.050 0.50 290 0.015 210 2.2 0.50 3.5 4.1 5.6 0.50 5.0 0.50 29,000 0.0050 18 210 440 3.1 140 1.7 1.1 0.018 0.0050 20-Mar-18 Q1 2018 0.047 0.26 180 82 0.050 0.50 120 0.015 150 0.050 0.50 3.5 0.40 8.6 1,100 5.0 0.50 82,000 0.0050 9.1 46 0.11 7.2 27 1.3 0.69 0.066 0.010 22-May-18 Q2 2018 0.55 0.20 610 13 0.050 0.50 340 0.015 290 0.050 0.50 3.5 1.0 4.3 3,940 5.0 0.50 100,000 0.0050 20 280 600 1.5 160 2.2 2.5 0.070 0.0050 ML025-RC051 25-Jun-18 Q2 2018 0.48 0.25 550 70 0.050 0.50 340 0.015 260 0.050 0.50 3.5 0.50 8.1 3,280 48 0.50 310 0.0050 19 240 100 1.0 130 1.9 0.17 0.018 0.080 24-Jul-18 Q3 2018 0.66 0.24 610 12 0.050 0.50 250 0.015 210 0.30 0.50 3.5 0.40 8.3 3,230 10 0.50 34,000 0.0050 18 41 460 1.5 110 1.5 0.33 0.018 0.25 21-Aug-18 Q3 2018 0.67 1.2 640 14 0.050 0.50 350 0.015 240 0.40 0.50 3.5 1.4 9.4 3,420 5.0 0.50 32,000 0.070 22 250 460 1.2 140 2.0 1.8 0.018 0.0050 26-Sep-18 Q3 2018 0.82 0.31 520 18 0.050 0.50 330 0.015 280 0.050 0.50 3.5 1.5 5.7 3,380 86 0.50 43,000 0.0050 22 230 570 0.50 160 1.0 0.50 0.018 0.030 24-Oct-18 Q4 2018 1.6 0.24 690 23 0.050 0.50 60 0.040 230 3.0 0.50 3.5 2.5 2.5 3,570 5.0 0.50 37,000 0.0050 24 250 560 1.1 170 1.6 0.30 0.018 0.030 27-Nov-18 Q4 2018 0.39 0.39 390 20 0.050 0.50 330 0.015 200 0.20 0.50 3.5 1.3 9.3 2,910 5.0 0.50 97,000 0.0050 18 200 450 1.5 120 1.3 0.050 0.018 0.050 18-Dec-18 Q4 2018 0.0075 0.39 480 17 0.050 0.50 260 0.015 200 0.60 2.1 3.5 2.2 8.6 2,810 5.0 0.50 37,000 0.0050 12 180 500 1.5 110 1.7 1.0 0.018 0.0050 22-Oct-19 Q4 2019 0.66 0.22 480 17 0.050 0.50 310 0.010 270 5.0 0.50 2.5 1.8 7.0 3,200 5.0 0.50 19 0.025 21 220 290 2.4 130 15 1.1 0.011 0.056 16-Jan-20 Q1 2020 0.42 0.24 430 11 0.050 0.50 240 0.010 200 5.0 0.50 2.5 1.8 2.4 2,500 5.0 0.50 35 0.025 21 210 240 0.50 120 0.7 2.7 0.044 0.11 Phenol Sulphate Total Total Borehole Sampling Date Quarter P PAHs Pb pH (Mono- Se TDS TOC Toluene Total Cr TSS V Xylene Zn as SO Alkalinity Hardness hydric) 4 Unit µg/l µg/l µg/l pH Units µg/l µg/l mg/l mg/l mg/l µg/l mgCaCO3/l µg/l mgCaCO3/l mg/l µg/l µg/l µg/l Screening Criterion NC 0.10 1.2 NC 7.7 10 250 NC NC 74 NC 50 NC NC 60 30 13 DWS NC 0.10 10 6.0 to 9.0 NC 10 250 NC NC NC NC 50 NC NC NC NC NC AA-EQS NC NC 1.2 NC 7.7 NC 400 NC NC 74 NC NC NC NC 60 30 13" MAC-EQS NC NC 14 6.0 to 9.0 46 NC NC NC NC 380 NC NC NC NC NC NC NC Well Specific Control Level 1,397 NA 0.86 7.9 5.6 3.3 1,039 2,159 6.5 NA 495 0.73 1,231 2,967 3.7 NA 44 Well Specific Trigger Level 1,397 NA 1.2 8.2 7.7 4.8 1,332 2,597 9.0 NA 580 1.0 1,479 4,447 5.4 NA 62 07-Feb-17 Q1 2017 220 NA 0.045 8.0 0.25 2.7 740 1,500 4.1 0.50 310 0.13 851 1,300 4.5 0.50 44 17-May-17 Q2 2017 36 NA 0.51 7.3 0.25 1.1 1,000 2,100 5.0 0.50 330 0.55 1,320 90 0.70 0.50 15 17-Jul-17 Q3 2017 55 NA 0.23 7.5 1.1 1.7 510 1,400 2.3 0.50 340 0.13 746 27 1.9 0.50 6.8 21-Nov-17 Q4 2017 64 NA 0.71 7.5 0.25 0.29 390 1,100 2.2 0.50 330 0.13 646 88 0.30 0.50 5.0 20-Mar-18 Q1 2018 310 NA 0.045 7.2 4.0 0.28 800 1,700 4.2 0.50 340 0.13 821 370 0.30 0.50 33 22-May-18 Q2 2018 990 NA 0.12 7.3 0.75 0.37 590 1,500 3.5 0.50 410 0.60 809 41 0.30 0.50 12 ML024-RC012 25-Jun-18 Q2 2018 33 NA 0.72 7.3 4.4 0.32 650 1,500 4.2 0.50 360 0.13 853 630 0.70 0.50 25 24-Jul-18 Q3 2018 290 NA 0.25 7.4 0.75 0.59 620 1,500 1.9 0.50 360 0.13 881 43 0.30 0.50 11 21-Aug-18 Q3 2018 260,000 NA 0.18 7.4 0.75 1.3 460 1,200 0.50 0.50 330 0.51 806 19 0.90 0.50 3.4 26-Sep-18 Q3 2018 640 NA 0.24 7.3 0.75 0.13 360 1,200 0.50 0.50 330 0.48 768 19 0.70 0.50 8.5 24-Oct-18 Q4 2018 1,100 NA 0.29 7.5 0.75 0.13 400 1,200 2.0 0.50 330 0.13 887 22 0.30 0.50 13 27-Nov-18 Q4 2018 840 NA 0.045 7.3 0.75 0.48 330 1,100 0.50 0.50 310 0.13 638 400 0.30 0.50 8.7 18-Dec-18 Q4 2018 700 NA 0.45 7.2 0.75 0.13 370 1,200 0.50 0.50 330 0.13 697 260 0.80 0.50 16 12-Nov-19 Q4 2019 10 NA 0.10 7.4 5.0 3.1 509 1,800 NA 0.50 530 0.10 734 3,700 0.10 0.50 3.0 Well Specific Control Level 2,991 NA 24 7.7 12 7.0 4,905 7,099 207 NA 667 7.1 4,761 4,325 14 NA 166 Well Specific Trigger Level 4,286 NA 36 8.0 17 9.7 6,803 9,105 303 NA 809 10 6,313 6,349 21 NA 244 20-Feb-17 Q1 2017 1,900 NA 16 7.4 0.50 7.8 660 2,400 190 0.50 430 NA 995 540 10 0.50 8,900 18-May-17 Q2 2017 2,100 NA 33 7.5 0.25 3.5 240 2,000 210 0.50 440 7.7 496 98 18 0.50 170 13-Jun-17 Q2 2017 100 NA 0.24 7.2 0.25 4.7 2,700 4,800 14 0.50 480 0.50 2,800 21 2.8 0.50 16 19-Jul-17 Q3 2017 120 NA 0.23 7.2 0.25 2.5 2,400 4,700 30 0.50 320 6.4 2,390 200 5.0 0.50 22 22-Aug-17 Q3 2017 55 NA 0.16 7.0 0.25 1.7 44 4,400 21 0.50 410 0.52 2,960 59 3.5 0.50 15 21-Nov-17 Q4 2017 48 NA 1.0 7.1 1.1 2.6 1,700 3,900 26 0.50 420 0.53 2,510 48 0.30 0.50 12 19-Mar-18 Q1 2018 180 NA 0.28 7.1 3.1 1.1 2,600 5,100 42 0.50 430 1.8 2,360 3,300 2.6 0.50 18 22-May-18 Q2 2018 1,600 NA 0.12 7.1 0.75 0.93 2,600 5,200 13 0.50 430 0.78 3,250 16 1.2 0.50 10 ML025-RC048 25-Jun-18 Q2 2018 33 NA 0.64 7.0 4.1 3.7 3,100 5,200 9.3 0.50 390 0.13 3,350 550 1.6 0.50 33 24-Jul-18 Q3 2018 370 NA 1.7 7.2 0.75 1.4 2,700 5,000 8.1 0.50 410 0.81 1,850 260 1.4 0.50 160 16-Aug-18 Q3 2018 1,600 NA 0.20 7.1 0.75 0.99 3,900 5,000 6.2 0.50 420 0.27 3,280 240 1.5 0.50 60 26-Sep-18 Q3 2018 830 NA 0.28 7.4 0.75 1.1 1,700 4,900 5.0 0.50 320 0.53 2,790 120 2.0 0.50 12 24-Oct-18 Q4 2018 1,200 NA 1.2 7.7 0.75 1.2 760 2,100 60 0.50 320 3.4 646 55 4.7 0.50 71 27-Nov-18 Q4 2018 1,400 NA 0.18 7.2 0.75 1.1 1.8 2,400 31 0.50 360 0.58 1,710 2,600 2.6 0.50 8.6 18-Dec-18 Q4 2018 680 NA 0.64 7.4 0.75 0.98 590 1,900 34 0.50 400 1.1 982 29 3.6 0.50 19 10-Apr-19 Q1 2019 10 NA 0.10 7.1 5.0 3.7 3,760 4,100 NA 0.50 650 0.10 3,990 2,000 0.50 0.50 0.25 22-Oct-19 Q4 2019 54 NA 0.70 7.3 5.0 2.3 886 2,200 NA 0.50 430 0.90 1,240 3,900 2.3 0.50 4.4 16-Jan-20 Q1 2020 2,690 NA 2.6 7.4 16 3.9 1,010 2,300 NA 0.50 670 1.1 1,540 3,100 6.2 0.50 4.0 Well Specific Control Level 1,840 NA 0.75 7.4 6.3 7.7 608 1,961 38 NA 588 5.8 1,160 16,836 3.5 NA 31 Well Specific Trigger Level 2,700 NA 1.1 7.6 7.7 10 748 2,287 56 NA 693 8.7 1,355 25,096 5.0 NA 44 07-Feb-17 Q1 2017 41 NA 0.045 7.2 2.2 0.74 320 1,400 51 0.50 390 0.13 450 940 0.30 0.50 0.65 18-May-17 Q2 2017 29 NA 0.43 7.1 0.80 4.5 380 1,600 4.4 0.50 400 0.43 983 2.5 1.1 0.50 13 13-Jun-17 Q2 2017 9.0 NA 0.045 7.3 0.25 4.9 400 1,500 7.0 0.50 500 0.13 826 7.0 2.1 0.50 6.8 19-Jul-17 Q3 2017 39 NA 0.090 7.3 0.25 4.7 430 1,100 2.9 0.50 420 6.4 861 2.5 3.9 0.50 4.0 22-Aug-17 Q3 2017 36 NA 0.045 7.0 0.25 4.5 390 1,500 1.5 0.50 400 0.13 968 23 2.7 0.50 5.9 21-Nov-17 Q4 2017 9.0 NA 0.90 7.0 1.8 4.4 340 1,300 1.4 0.50 420 0.13 845 63 0.30 0.50 5.2 19-Mar-18 Q1 2018 24 NA 0.045 7.0 1.4 3.9 510 1,800 6.3 0.50 420 0.13 909 17,000 0.30 0.50 2.5 22-May-18 Q2 2018 930 NA 0.16 7.1 0.75 4.3 560 1,800 3.4 0.50 420 6.1 905 6.5 1.0 0.50 4.0 ML025-RC049 25-Jun-18 Q2 2018 22 NA 0.47 7.1 4.3 1.6 300 1,200 4.0 0.50 390 0.13 721 6,500 1.1 0.50 27 24-Jul-18 Q3 2018 170 NA 0.32 7.2 2.8 3.9 410 1,400 2.8 0.50 410 0.32 871 44 0.70 0.50 26 16-Aug-18 Q3 2018 1,400 NA 0.20 7.1 0.75 3.4 520 1,400 2.2 0.50 400 0.27 886 35 0.30 0.50 26 26-Sep-18 Q3 2018 680 NA 0.23 7.1 2.6 3.0 230 1,400 1.3 0.50 400 0.49 866 2.5 0.90 0.50 12 22-Oct-18 Q4 2018 1,000 NA 0.21 7.3 0.75 3.2 330 1,400 1.1 0.50 420 0.52 831 21 0.80 0.50 12 27-Nov-18 Q4 2018 1,600 NA 0.20 7.2 0.75 1.9 220 1,100 1.4 0.50 400 0.13 642 17,000 0.70 0.50 4.9 18-Dec-18 Q4 2018 1,300 NA 0.14 6.9 0.75 2.3 280 1,700 1.9 0.50 390 0.13 745 5,200 1.2 0.50 6.9 10-Apr-19 Q1 2019 10 NA 0.10 7.1 5.0 5.0 353 1,300 NA 0.50 630 0.10 829 3,300 0.10 0.50 0.70 26-Sep-19 Q3 2019 27 NA 0.10 7.1 5.0 7.1 378 1,100 NA 0.50 360 0.20 921 1.0 0.30 0.50 11 16-Jan-20 Q1 2020 10 NA 0.10 7.0 5.0 5.6 418 1,500 NA 0.50 260 0.20 967 5,100 0.20 0.50 1.6 Well Specific Control Level 3,837 NA 0.88 8.1 5.8 4.6 2,987 4,356 33 NA 667 2.0 2,759 10,186 3.7 NA 57 Well Specific Trigger Level 5,674 NA 1.2 8.8 7.7 6.6 3,996 5,298 49 NA 793 3.0 3,462 15,517 5.4 NA 81 07-Feb-17 Q1 2017 460 NA 0.21 7.6 0.25 1.5 1,600 3,400 42 0.50 510 1.6 1,930 970 4.0 0.50 58 17-Jul-17 Q3 2017 93 NA 0.11 7.1 0.25 1.4 1,400 2,800 3.1 0.50 550 0.13 1,980 74 2.2 0.50 6.5 22-Aug-17 Q3 2017 160 NA 0.045 7.0 1.2 0.55 2,000 3,400 3.1 0.50 510 0.27 2,160 120 2.2 0.50 6.4 23-Nov-17 Q4 2017 150 NA 0.23 5.8 0.25 0.13 750 2,600 3.4 0.50 470 0.13 1,570 98 0.30 0.50 12 20-Mar-18 Q1 2018 4,800 NA 0.090 7.3 2.1 0.96 200 1,000 3.2 0.50 270 0.13 478 14,000 0.30 0.50 33 22-May-18 Q2 2018 1,900 NA 0.10 7.0 0.75 0.40 1,600 3,400 3.8 0.50 530 0.33 2,020 120 0.30 0.50 8.7 ML025-RC051 25-Jun-18 Q2 2018 25 NA 0.80 7.0 4.0 0.13 1,300 2,600 4.1 0.50 440 0.13 1,850 290 0.30 0.50 43 24-Jul-18 Q3 2018 350 NA 0.22 7.8 0.75 0.44 1,100 3,200 2.2 0.50 490 0.13 802 120 0.30 0.50 4.6 21-Aug-18 Q3 2018 350 NA 0.83 7.0 0.75 4.8 3,200 2,900 3.2 0.50 490 0.13 1,910 140 1.5 0.50 4.8 26-Sep-18 Q3 2018 700 NA 0.48 7.1 0.75 0.42 830 3,000 1.8 0.50 490 1.1 1,780 49 0.30 0.50 20 24-Oct-18 Q4 2018 970 NA 0.20 7.2 0.75 0.28 1,100 3,400 4.8 0.50 500 0.13 1,200 76 0.30 0.50 11 27-Nov-18 Q4 2018 990 NA 0.22 6.9 0.75 0.74 990 2,500 1.6 0.50 450 0.13 1,640 200 0.30 0.50 10 18-Dec-18 Q4 2018 660 NA 0.20 7.1 0.75 0.26 1,000 2,500 2.4 0.50 440 2.1 1,370 160 0.90 0.50 11 22-Oct-19 Q4 2019 10 NA 0.10 6.9 5.0 3.1 1,400 2,900 NA 0.50 440 0.10 1,680 1,900 0.10 0.50 1.6 16-Jan-20 Q1 2020 10 NA 0.30 7.0 5.0 2.8 1,130 2,200 NA 0.50 260 0.20 1,470 1,200 0.10 0.50 19 Table C1 Notes:C1 Notes:

Well Specific Control Level - Mean groundwater parameter concentration + (2.5*STDV) Well Specific Trigger Level - Mean groundwater parameter concentration + (4*STDV) Where the result for the chemical constituent is less than detectable level, half the non-detect value is used The greater value of 'Free Cyanide' and 'Total Cyanide' has been retained as 'Cyanide'

Screening Criteria: DWS - Drinking Water Standards - The Water Supply (Water Quality) Regulations 2016 EQS - Environmental Quality Standards - Water Framework Directive (WFD) 2015 (values based on long term mean or annual average EQS) UK EQS values not listed in WFD 2015 are taken from EA operational EQS and/or SEPA non-statutory EQS (criteria are based on annual average EQS) AA-EQS - Annual Average EQS MAC-EQS - Maximum Allowable Concentration EQS SEPA - Non-statutory EQS (WAT-SG-53) (criteria based on annual average EQS)

Formatting Key: Italic and grey fill - outlier (not included in statistical analysis) Red font - exceeds Screening Criterion Grey font - less than detectable level (half the non-detectable value used in statistical analysis) Yellow fill - greater than Well Specific Control Level (mean groundwater parameter concentration + (2.5*STDV) )

Abbreviation: Full Name: Amm. N - Ammoniacal Nitrogen as N As - Arsenic B - Boron Ba - Barium Be - Beryllium Ca - Calcium Cd - Cadmium CI- - Chloride Cr - Chromium, Cr3+ - trivalent Chromium, Cr6+ - hexavalent Chromium Cu - Copper DO - Dissolved Oxygen EC - Electrical Conductivity EPH - Extractable Petroleum Hydrocarbons, >C10-40 - hydrocarbons with Carbon content in the range of 10 to 40 per molecule Fe - Iron Hg - Mercury K - Potassium Mg - Magnesium Mn - Manganese N - Nitrogen NA - Not analysed Na - Sodium NC - No criterion Ni - Nickel

NO3 - Nitrate P - Phosphorus PAH - Polycyclic Aromatic Hydrocarbons Pb - Lead Se - Selenium

SO4 - Sulphate TDS - Total Dissolved Solids TOC - Total Organic Carbon TSS - Total Suspended Solids U/S - Unsuitable sample V - Vanadium Zn - Zinc

*^ Cadmium (Cd) EQS values: Water hardness - *AA-EQS (µg/l) ^MAC-EQS (µg/l) CaCO3/l < 40 mg/l ≤ 0.080 ≤ 0.45 40 to < 50mg/l 0.080 0.45 50 to < 100mg/l 0.090 0.60 100 to < 200mg/l 0.15 0.90 ≥ 200mg/l 0.25 1.50

" Zinc (Zn) AA-EQS value = 10.9 + ABC µg/l: ABC (Ambient Background Concentrations) forABC zinc (µg/l) Thames 2 Drawing C1 - Groundwater Quality Trends

A 8 Screening 7 Criterion 6 ML024-RC012 5 ML025-RC048 4 ML025-RC049 3

2 ML025-RC051 Ammoniacal Nitrogen Nitrogen Ammoniacal

Concentration as N (mg/l) as N Concentration 1 0 Jan-17 Aug-17 Feb-18 Sep-18 Mar-19 Oct-19 Sampling Date

B 14 Screening 12 Criterion ML024-RC012 10 8 ML025-RC048 6 ML025-RC049 4 ML025-RC051

2 Arsenic Concentration (µg/l) Concentration Arsenic 0 Jan-17 Aug-17 Feb-18 Sep-18 Mar-19 Oct-19 Sampling Date

C 900 Screening 800 Criterion 700 ML024-RC012 600 500 ML025-RC048 400 300 ML025-RC049 200 ML025-RC051 100

Chloride Concentration (mg/l) Concentration Chloride 0 Jan-17 Aug-17 Feb-18 Sep-18 Mar-19 Oct-19 Sampling Date

D 80 Screening 70 Criterion 60 ML024-RC012 50 ML025-RC048 40 30 ML025-RC049 20

Cyanide, Total (µg/l) Total Cyanide, ML025-RC051 10 0 Jan-17 Aug-17 Feb-18 Sep-18 Mar-19 Oct-19 Sampling Date

E 150000 Screening Criterion ML024-RC012 100000 ML025-RC048

ML025-RC049 50000

ML025-RC051 Iron Concentration (µg/l) Concentration Iron 0 Jan-17 Aug-17 Feb-18 Sep-18 Mar-19 Oct-19 Sampling Date

F 35 Screening 30 Criterion 25 ML024-RC012

20 ML025-RC048 15 ML025-RC049 10

5 ML025-RC051 Lead Concentration (µg/l) Concentration Lead 0 Jan-17 Aug-17 Feb-18 Sep-18 Mar-19 Oct-19 Sampling Date G 8000 Screening 7000 Criterion 6000 ML024-RC012 5000

4000 ML025-RC048

3000 ML025-RC049 2000

Manganese Concentration (µg/l) Concentration Manganese 1000 ML025-RC051 0 Jan-17 Aug-17 Feb-18 Sep-18 Mar-19 Oct-19 Sampling Date

H 60 Screening Criterion 50 ML024-RC012 40

ML025-RC048 30

20 ML025-RC049 Nickel Concentration (µg/l) Concentration Nickel 10 ML025-RC051

0 Jan-17 Aug-17 Feb-18 Sep-18 Mar-19 Oct-19 Sampling Date I 4,500 Screening 4,000 Criterion

(mg/l) 3,500 4 ML024-RC012 3,000

2,500 ML025-RC048 2,000 1,500 ML025-RC049 1,000 ML025-RC051

500 Sulphate Concentration as as SO Concentration Sulphate 0 Jan-17 Aug-17 Feb-18 Sep-18 Mar-19 Oct-19 Sampling Date

J 10,000 Screening Criterion 1,000 ML024-RC012

100 ML025-RC048

10 ML025-RC049

Zinc Concentration (µg/l) Concentration Zinc 1 ML025-RC051

0 Jan-17 Aug-17 Feb-18 Sep-18 Mar-19 Oct-19 Sampling Date

Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02 Appendix D - Risk Methodology 1 Methodology

1.1.1 Risks have been quantified in terms of the likelihood of occurrence and the consequence, as defined in the tables below.

Likelihood Descriptor Comment/clarifications

High Repeated occurrences expected; Expected. Very likely to occur in the short term and almost certain to occur over the long term. Repeated occurrences expected based on experience in comparable industries.

Medium Can be expected to occur several times; An event is possible, but not inevitable, in the short Likely. term, and likely over the long term.

Low Infrequent occurrence; Possible. The event occurring is by no means certain in the long term and is less likely in the shorter term.

Very Low Very rare, but possible. The event is possible, but very unlikely to occur.

Table D1 - Likelihood scale for risk assessment

Consequence Descriptor Additional comments/clarifications

High A major incident resulting in significant damage Fatality, serious injury or short term (acute) risk to to the environment and/or equipment and/or human health. harm to people. Significant pollution or exacerbation of existing historical contamination.

Irreversible adverse change to an ecological receptor.

Excessive drilling problems or equipment loss/damage and project delays leading to double the proposed investigation cost or more.

Medium Moderate, localized effect on people, the Lost time accidents or moderate risk to human environment, and/or equipment in the vicinity health. of the incident. Moderate effect on a sensitive water resource characterized by a breach of regulatory standard.

A significant effect on an ecological receptor or ecosystem.

Excessive drilling problems or equipment loss/damage and project delays leading to up to double the proposed investigation cost.

Template no.: HS2-HS2-IM-TEM-000-000265 Page 27 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

Consequence Descriptor Additional comments/clarifications

Low Minor incident which may breach a regulatory Minor injuries or low risk to human health. standard but is localized with no significant impact on the environment, people, or No effect on a high sensitivity environmental equipment. receptor, some effect on low sensitivity receptor. Drilling problems or equipment loss/damage and project delays resulting in up to 50% of the proposed investigation cost.

Very Low Very minor incident, manageable under existing Very minor injuries or no short-term risk to human controls. health.

No effect on a high sensitivity environmental receptor, minor effect on low sensitivity receptor.

Minor cost or program related cost increases (less than 10% of the proposed investigation cost).

Table D2 - Consequence scale for risk assessment

High Low Medium High High

Medium Low Medium Medium High

Low Low Low Medium Medium Likelihood Very Low Low Low Low Medium

Very Low Low Medium High

Consequence

Table D3 - Risk magnitude matrix

1.1.2 In this assessment, based on professional judgement, significant risks are those assessed to be either Medium or High. Where significant adverse risks have been identified, further mitigation is likely to be required, as identified in Table D4. The mitigation measures put in place should be managed to ensure risks are as low as practically possible (ALARP).

Risk magnitude Description/action

High There is a high to medium probability that the risk may be realized. Additional mitigation is required as a priority and may include further investigation/assessment to understand and, if appropriate, reassess the significance of the risk.

Medium Risks must be acted upon, but do not pose an immediate threat and thus the project can continue while the risk response measures are integrated and/or performed. Additional mitigation may be required and mitigation may require further investigation/assessment to understand, and, if appropriate, reassess the significance of the risk.

Template no.: HS2-HS2-IM-TEM-000-000265 Page 28 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

Risk magnitude Description/action

Low Risks may not require additional responses – it may be effective enough simply to monitor the risk to ensure that it does not arise during the project.

Table D4 - Risk magnitude description

Template no.: HS2-HS2-IM-TEM-000-000265 Page 29 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02 Appendix E - Chalk Dissolution Features - Additional Details 1 Summary 1.1.1 The presence of dissolution features within the Chalk could potentially lead to ground settlement at the surface following the placement of material for mound construction. The settlement, in this case, would be the result of the additional load from the placement of material leading to a collapse within the dissolution features. Should ground settlement occur, nearby structures may be at risk of structural impacts from the induced settlement.

1.1.2 At the RNSP Western mound site, this risk is considered insignificant for the following reasons:

• There are no planned structures within the limits of the RNSP Western mound. Thus, should any settlement occur, there is no structural receptor to be impacted,

• The site is in an area identified to be of negligible risk of rock dissolution. 2 Additional Details

2.1.1 This review provides further information on the potential presence of dissolution features below the RNSP Western mound. The BGS has developed maps which categorize risk of rock dissolution; which is largely based on the presence of surface or near surface rock formations, such as the Chalk.

2.1.2 Figure E1 illustrates that the site (at the 1:50,000 resolution of the map shown) is adjacent to an area where there is a ‘moderate to significant’ risk’3 that dissolution features exist. However, as indicated above, the Chalk, at the location of the RNSP does not outcrop and is

3 While the site is visibly adjacent to a green ‘significant risk’ zone, there is also a small yellow ‘moderate’ risk zone.

Template no.: HS2-HS2-IM-TEM-000-000265 Page 30 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

overlain by at least 19m of other material (see Figure E2 and Drawing A2). In fact, given the low risk nature of the geological conditions at the RNSP Western mound with respect to dissolution features, the site area has been excluded in the risk mapping by the BGS (as indicated in Figure E1).

Figure E1 - Site location as shown on the BGS Solution Potential Map (Contains British Geological Survey materials © NERC 2018)

Template no.: HS2-HS2-IM-TEM-000-000265 Page 31 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

Figure E2 - BGS Geological Map (Contains British Geological Survey materials © NERC 2018) with identified natural cavity locations

2.1.3 Within the site vicinity, one historic dissolution feature has been recorded, the location of which is around 400m south of the RNSP (see Figure E2). The feature, as recorded in the HS2 GIS database, has been listed as a ‘solution widened joint’ and ‘a fissure x 2’. With respect to this identified location, the following is noted:

• No information has been recorded within the HS2 database of any negative impacts to ground conditions or surface structures,

• The identified location is not within the RNSP Western mound site boundary, and

• The presence of a solution widened joint or fissure, at the identified location, would be present below the overlying Lambeth Group and London Clay Formation. Thus, as noted above, the risk of surface impacts is not likely to be significant as a result of this identified feature.

Template no.: HS2-HS2-IM-TEM-000-000265 Page 32 Uncontrolled when printed

OFFICIAL Document Title: Hydrogeological Risk Assessment (HRA) - Western Mound - Ruislip Northern Sustainable Placement S2 Document no.: 1MC04-SCJ_SDH-GT-REP-SS05_SL07-000035 Revision: C02

2.1.4 Additional information on the presence and likelihood of dissolution has been provided in a Groundsure survey, shown in Figure E3. Figure E3 clearly shows that the limits of the RNSP fall within an area identified to be of negligible risk of rock dissolution.

2.1.5 On 7 August 2018, Arup discussed the location of the RNSP Western mound with Affinity Water, who operate the nearest abstraction well, known as the Ickenham Well. The Ickenham Well is a group of three vertical boreholes interconnected with horizontal adits, some of which are 350m in length. However, the closest edge of the RSP is still more than 500m from the nearest adit. Thus, there are no risks associated with the presence of the Ickenham Well on the RNSP.

Ruislip Northern Sustainable Placement

Figure E3 - Site location in relation to ground dissolution of soluble rocks risk (adapted from Groundsure 2018)

Template no.: HS2-HS2-IM-TEM-000-000265 Page 33 Uncontrolled when printed

OFFICIAL