MITCHELL HILL, COTTENHAM ENVIRONMENTAL STATEMENT

7. Hydrology and Hydrogeology (including Flood Risk Assessment)

January 2018 HYDROLOGY & HYDROGEOLOGY

HYDROGEOLOGICAL AND HYDROLOGICAL ASSESSMENT FOR A PROPOSED QUARRY AT MITCHELL HILL

Report Reference: 2173/HIA Final January 2018

Report prepared for :

Frimstone Ashcroft Farm Main Road CRIMPLESHAM Norfolk PE33 9EB

Barkers Chambers • Barker Street • Shrewsbury • United Kingdom • S Y 1 1 S B T : 01743 355770 • F : 01743 357771 • E : [email protected]

Frimstone Mitchell Hill HYDROLOGICAL IMPACT ASSESSMENT

GENERAL NOTES

Title of report: Hydrogeological and hydrological assessment Site: Mitchell Hill Report ref: 2173/HIA Date: January 2018

Version Date Issued to Draft version 1 July 2017 Ted Clover Draft version 3 January 2018 Ted Clover Final 15 January Ted Clover

Author: Lawrence Brown BSc, MSc, FGS, CGeol Reviewer: Chris Leake BSc, MSc, FGS

This report has been prepared by Hafren Water Ltd for the named Client, with reasonable skill, care and diligence within the agreed scope and terms of contract. Hafren Water Ltd disclaims any responsibility to the client and others in respect of any matters outside the agreed scope of work. This report has been prepared for use by the client and others acting on their behalf. The report may be passed to regulators. This report does not constitute legal advice or opinion.

This report does not represent advice to third parties and no reliance is offered to third parties. No liability is accepted with regard to third parties. Reliance required by any specific Third Party must be agreed in writing with Hafren Water Ltd.

P:\Projects\Mitchell Hill (2173)\Reports\HIA\2173_HIA Final.docx

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CONTENTS

1 INTRODUCTION ...... 1

1.1 Background ...... 1 1.2 Location ...... 1 1.2.1 Site location ...... 1 1.3 Scope of assessment ...... 1 1.4 Data sources ...... 1 1.5 Methodology ...... 2 1.6 Qualifications and experience ...... 2

2 BASELINE CONDITIONS ...... 3

2.1 Landform ...... 3 2.2 Hydrology ...... 3 2.2.1 Rainfall ...... 3 2.2.2 Watercourses ...... 4 2.2.3 Waterbodies ...... 5 2.2.4 Springs ...... 6 2.2.5 Wells ...... 6 2.2.6 Surface water abstractions ...... 6 2.3 Consented discharges ...... 7 2.4 Sites of ecological and conservation interest ...... 7 2.4.1 Statutory sites ...... 7 2.4.2 Non-statutory sites ...... 8 2.5 Archaeology ...... 8 2.6 Landfill sites ...... 9 2.7 Water resource status ...... 9 2.8 Geology ...... 9 2.8.1 Regional ...... 9 2.8.2 Local...... 10 2.9 Hydrogeology ...... 11 2.9.1 Aquifer status and regional context ...... 11 2.9.2 Groundwater levels ...... 12 2.9.3 Groundwater quality ...... 14 2.9.4 Aquifer properties ...... 14 2.9.5 Groundwater abstractions ...... 14 2.9.6 Gravel Diggers Quarry ...... 14 2.10 Conceptual understanding ...... 15

3 PROPOSED DEVELOPMENT ...... 16

3.1 Mineral extraction ...... 16 3.2 Water management ...... 16 3.2.1 General...... 16 3.2.2 Groundwater ingress volumes ...... 17 3.2.3 Rainfall ...... 17 3.3 Restoration ...... 17

4 ASSESSMENT OF IMPACTS ...... 19

4.1 Methodology ...... 19 4.2 Baseline sensitivity ...... 19 4.3 Potential impacts during mineral extraction ...... 20

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4.3.1 Surface water levels ...... 20 4.3.2 Surface water flow ...... 21 4.3.3 Surface water quality...... 21 4.3.4 Groundwater levels ...... 22 4.3.5 Groundwater quality ...... 22 4.3.6 Wildlife sites ...... 23 4.3.7 Archaeology...... 23 4.3.8 Buildings ...... 23 4.3.9 Summary...... 23 4.4 Potential impacts following restoration ...... 24 4.4.1 General...... 24 4.4.2 Groundwater levels ...... 24 4.4.3 Water quality ...... 25 4.4.4 Surface water run-off ...... 25

5 WATER FRAMEWORK DIRECTIVE ASSESSMENT ...... 26

5.1 Introduction ...... 26 5.2 Location ...... 26 5.3 Surface water assessment ...... 27 5.3.1 Quantitative status ...... 27 5.3.2 Qualitative status ...... 27 5.3.3 Ecological status ...... 27

6 MITIGATION MEASURES AND RESIDUAL IMPACTS ...... 28

6.1 During mineral extraction ...... 28 6.1.1 Surface water quality...... 28 6.1.2 Surface water levels ...... 28 6.2 Post-restoration ...... 29 6.2.1 Groundwater levels ...... 29

7 CUMULATIVE IMPACTS ...... 30

8 SUMMARY AND CONCLUSIONS...... 31

TABLES

2173/HIA/T1: Rainfall Data from the Stretham rain gauge ...... 3 2173/HIA/T2: Historical rainfall data from MAFF Area 28 ...... 3 2173/HIA/T3: Consented discharges ...... 7 2173/HIA/T4: Regional stratigraphy ...... 10 2173/HIA/T5: Summary statistics for superficial deposits ...... 11 2173/HIA/T6: Assessment of impacts of quarry operations without mitigation measures...... 24

DRAWINGS

2173/HIA/01 Location 2173/HIA/02 Surface water features 2173/HIA/03 Surface water abstractions 2173/HIA/04 Landfills and discharge consents 2176/HIA/05 Sites of conservation interest 2173/HIA/06 Geology 2173/HIA/07 Groundwater level and monitoring boreholes 2173/HIA/08 Groundwater hydrographs

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APPENDICES

2173/HIA/A1 Assessment methodology 2173/HIA/A2 Water Framework Directive status of waterbodies 2173/HIA/A3 Borehole data 2173/HIA/A4 Groundwater level data 2173/HIA/A5 Proposed phasing and restoration plans 2173/HIA/A6 Dewatering calculations

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1 INTRODUCTION

1.1 Background

Frimstone Limited (‘Frimstone’) is applying for planning permission to undertake sand and gravel extraction from an area known as Mitchell Hill Common. The Application Area covers an area of approximately 72 hectares (ha) located 12 km to the north of Cambridge.

Hafren Water has been commissioned to undertake a hydrogeological and hydrological assessment in support of the Planning Application. The results of the assessment are presented in this report.

1.2 Location

1.2.1 Site location

The Application Area at Mitchell Hill Common (‘the Site’) lies to the west of the A10 approximately 12 km north of the northern outskirts of Cambridge and 4.2 km northeast of the village of Cottenham ( Drawing 2173/HIA/01 ). The area is low-lying and drained by a network of artificial drains managed by the Old West Internal Drainage Board.

The site is bounded to the north by the River Ouse, to the west partially by the B1049 (Twenty Pence Road) and partially by farmland, to the east by open fen farmland and Gravel Diggers Quarry and to the south by a mixture of farmland and residential properties. The northern half of the site is split by the Right Wing Drain (shown as ‘Engine Drain’ on Ordnance Survey maps), which flows from west to east.

1.3 Scope of assessment

The objectives of the investigation are as below:

. Determination of baseline conditions of the water environment at the site and its environs . Identification of potential impacts of the proposed mineral extraction . Assessment of the magnitude and significance of potential impacts of mineral extraction and the proposed subsequent restoration . Derivation of appropriate mitigation measures for any identified potential impacts

1.4 Data sources

The characteristics of the water environment have been investigated with the use of existing published data and reports, assessment of site data, a site visit and experience of other sites in broadly similar settings. The data sources used in the investigation are listed below:

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British Geological Survey (BGS) . 1:50,000 scale geological map for Cambridge, Sheet 188 . Geological borehole logs

Environment Agency . Licensed abstraction data . Groundwater level and quality data . Rainfall data . Topographic (LIDAR)

South Cambridgeshire District Council . Private water supplies

Frimstone Ltd . Borehole logs . Site plans . Groundwater level monitoring data

1.5 Methodology

Baseline conditions of the water environment have been defined by the collation and analysis of existing data and field observations. The potential effects of the proposed development upon the extant water environment have been assessed by reference to the baseline data and a series of matrices ( Appendix 2173/HIA/A1 ), developed to ensure a rigorous and consistent approach to the assessment of potential impacts. Mitigation measures have been proposed where appropriate.

1.6 Qualifications and experience

This report has been compiled by Lawrence Robert Brown, Principal Hydrogeologist with Hafren Water. He has over 20 years’ experience in groundwater assessment and management, most of which has been in a professional consultancy capacity.

He holds a Bachelor of Sciences degree in Geology from the City of London Polytechnic and a Master of Science in Mineral Production Management from Imperial College, London.

Lawrence brown been employed by Hafren Water since 2007. He is a Chartered Geologist (CGeol) and a Fellow of the Geological Society of London and is familiar with the Code of Conduct of the Geological Society.

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2 BASELINE CONDITIONS

2.1 Landform

The site is located on low-lying agricultural land drained by a network of artificial ditches. One of these ditches, Engine Drain, passes along part of the southern boundary and a second, Right Wing Drain, passes from west to east across the northern section of the site. In the area surrounding the site, ground levels vary from a low of around 1.2 metres above Ordnance Datum (mAOD) at Chear Fen to the northeast, to over 5 mAOD at Cottenham to the southwest.

Within the site, the highest ground is along the western and southwestern boundary where it is up to 2.8 mAOD. Ground elevation generally declines northwards towards the River Ouse where they are around 2 mAOD.

2.2 Hydrology

2.2.1 Rainfall

Average monthly rainfall data were obtained from the Environment Agency for the Stretham rain gauge, (Station ID 180704) located 3.5 km to the northeast of the site boundary at NGR TL 51600 72900. Average monthly rainfall for the period 1971 to 2000 is shown in Table 2173/HIA/T1 . Average annual rainfall over the period was 541.9 mm/a.

2173/HIA/T1: Rainfall Data from the Stretham rain gauge

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Rainfall 43 31.87 40.87 40.94 45.87 51.67 41.83 51.11 47.19 50.72 49.49 47.37 (mm)

Historical rainfall data and evapotranspiration data have also been obtained from MAFF Technical Bulletin 34 for this area (Area 28) and are shown in Table 2074/HIA/T2 . The rainfall range for this area was given as 510 to 730 mm with an average of 574 mm.

2173/HIA/T2: Historical rainfall data from MAFF Area 28 (mm) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Rainfall 48 38 38 37 44 47 56 60 49 49 58 50 PT 1 10 33 57 83 94 94 76 48 22 5 0 Eff.Rain. 47 28 5 0 0 0 0 0 1 27 53 50 PT – Potential Transpiration, Eff.Rain. – Effective rainfall

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2.2.2 Watercourses

The largest watercourse in the vicinity of the site is the River Great Ouse (referred to as the Old West River in this area), which flows from west to east to the north of the site. The flood defence embankment for the river forms the northern boundary of the site (Drawing 2173/HIA/02 ). A tributary of the River Great Ouse, Cottenham Lode, lies to the west of the site boundary and flows from southwest to northeast, joining the Great Ouse at Twenty Pence Cottage. Cottenham Lode is entirely artificial in nature, while the River Great Ouse has been heavily modified from its natural state. Both watercourses are contained within embankments.

Under the Water Framework Directive the River Great Ouse and Cottenham Lode fall within the Old West River Waterbody (ID GB205033043375), with a hydromorphological designation of ‘Heavily Modified’. A summary of the information provided in the Environment Agency’s Catchment Data Explorer is provided in Appendix 2173/HIA/A2 .

All the smaller watercourses in the vicinity of the site are anthropogenic in origin and relate to agricultural drainage. Management of these drains is the responsibility of the Old West and Waterbeach Internal Drainage Boards (IDB), both part of the Ely Group of IDBs. Water levels within these areas are maintained by a series of pumping stations which pump water into the River Great Ouse.

Old West IDB

The site itself lies within the Old West IDB, the eastern boundary of which passes along the A10. The largest drains in this catchment are Engine Drain, Beach Ditch and Right Wing Drain. These drains convey water draining from within the IDB northwards to the Chear Fen Engine Pumping Station, which discharges into the River Great Ouse. Pumping from Chear Fen is designed to maintain a summer water level at 0.7 mAOD and a winter level at 0.1 mAOD at the pumping station. It is understood that none of these ditches would have been lined when originally dug (pers comms IDB engineer).

Beach Ditch passes to the east of the site and adjacent to the A10. To the south it passes through the Cambridge Waste Management Park

Engine Drain passes along part of the southern boundary of the site and then northwards along the eastern boundary of Gravel Diggers Quarry.

North of Gravel Diggers, another drain, marked as ‘Engine Drain’ on the Ordnance Survey maps, but referred to as the Right Wing Drain by the IDB, joins from the west. This drain

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bisects the northern part of the site and survey data have recorded the invert level of the drain at -0.17 to -0.18 mAOD as it passes through the site. The catchment of the Right Wing Drain extends into the area west of Cottenham Lode.

A small drain, Fourth Sock Drain, flows from west to east close to the northern boundary of the site and discharges into Engine Drain at the Chear Fen pumping station.

Waterbeach IDB

East of the A10, drainage is within the Waterbeach Level IDB catchment. Drainage in this area is discharged into the River Cam via the Cam Pumping Station (NGR TL 53709 71473).

2.2.3 Waterbodies

Within the site there is a single waterbody (Ref ‘PA’ on Drawing 2173/HIA/02 ) within the site boundary, located close to the southern boundary and northwest of Elm Farm. The pond is relatively recent in origin and reported to have been dug into gravel and then lined with clay. Water levels were measured in the pond on 25 th April 2016 (0.93 mAOD) and 8 th May 2017 (0.80 mAOD), slightly higher than levels measured in the adjacent Engine Drain at the same time.

There are nine waterbodies outside the site and within 2 km of the site boundary, labelled P1 to P9 on Drawing 2173/HIA/02 . Ponds P1 to P6 are all located in the Old West IDB catchment. Ponds P7 and P8 lie on the north bank of the River Great Ouse and Pond P9 is in the Waterbeach IDB catchment.

. P1: A group of lakes located between the Twenty Pence Road and Cottenham Lode and about 50 m from the western boundary of the site at their closest. These lakes form the Twenty Pence Pit County Wildlife Site. . P2 is 250 m from the site boundary, close to the Twenty Pence Pit County Wildlife Site and west of Cottenham Lode. The form of the waterbody suggests that it represents flooded former sand and gravel workings. . P3 and P4 are located within the Waterbeach Waste Management Park and form part of the water management system inside the facility. . P5 is an artificial lake which lies next to an old unlined landfill site (Amey Ltd.) . P6 represents a group of lakes 1.6 km south of the site boundary and located immediately to the south of the Waterbeach Waste Management Park. They have been formed by the flooding of former gravel workings. Some of these now lie inside the Cambridge Science Park development.

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. P7 is a Marina development on the north bank of the River Great Ouse at Twenty Pence Cottage, 200 m north of the site boundary. . At P8 are a group of elongate waterbodies adjacent to the River Great Ouse, the largest is located on the north side of the river. . P9 is located 1.4 km to the south east of the site boundary

2.2.4 Springs

The Ordnance Survey map does not show the presence of any springs within 2 km of the site boundary.

2.2.5 Wells

There are no wells indicated on the Ordnance Survey map of the area.

2.2.6 Surface water abstractions

Licensed abstractions

The Environment Agency has provided details of licensed surface water abstractions within 3 km of the site centre (TL 270 120). There are five licences with abstraction points located within the Old West IDB catchment. Their locations are shown on Drawing 2173/HIA/03 and details are given below:

(a) Licence No 6/33/35/*S/0306/R01 allows abstraction from a number of reaches in the drains in the vicinity of the site. The licence allows abstraction of up to 72,727.27 m 3 annually and 3,636.36 m 3 daily for the purpose of spray irrigation between 1 st May and 31 st October each year.

(b) Licence N o AN/033/0035/007 permits abstraction from a single point on Engine Drain at TL 48028 70915. Abstraction is for 354.53 m 3/d and 9,857 m 3/a between April October each year.

(c) Licence No 6/33/34/*S/0012 allows abstraction from within a defined area of land at Chear Fen . Abstraction for direct spray irrigation is permitted between 1 st February and 31 st October each year. An abstraction volume of 6,768 m3/d and 237,323 m 3/a is shared with an area 2 km to the east within the Waterbeach IDB catchment.

(d) Licence N o 6/33/34/*S/0254 allows abstraction within the same defined area of land at Chear Fen as Licence N o 6/33/34/*S/0012. Abstraction is permitted between 1 st February and 31 st October each year for direct spray irrigation.

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(e) Licence N o 6/33/34/*S/0048 also allows abstraction within the previously defined area of land at Chear Fen. Abstraction is allowed between 1st March and 31 st October each year for direct spray irrigation. A total abstraction of 1,036.4 m 3/d and 29,180 m 3/a is allowed, shared between two other areas at Stretham Mere and Barway and Stretham as well as two river reaches, one on the Great Ouse at Chear Fen and a second on Upper Mill Drain near Barry Island.

2.3 Consented discharges

There are nine Environmental Permits for discharges in the Old West IDB catchment and within 2 km of the site boundary. Their locations are shown on Drawing 2173/HIA/04 and details summarised in Table 2176/HIA/T3.

2173/HIA/T3: Consented discharges Map NGR Permit Discharge Effluent Receiving Water ID Type Type D1 TL4962070110 PRCNF14443 SE UA Beach Ditch Trib of Ely Ouse D3 TL4888269021 NPSWQD006341 RB UA Great River Ouse D4 TL4820468416 PRCNF18031 SE UA The Beach Ditch D2 TL4776268873 NPSWQD002146 UZ TC Engine Drain D5 TL4894069000 PRCNF17219 SE UA Unnamed Trib of Beach Ditch D6 TL4991271141 PRCNF18091 TE UA Chear Lode D7 TL4958670079 PRCNF14386 TE UA Beach Ditch D8 TL4964070100 PR1NF3275 QC UA Beach Ditch TL4877269926 TC/BZ Engine Drain D9 EPR/FB3190VN DF TL4889970236 TC/TG Engine Drain tributary SE - Sewage disposal works – other RB - Industrial estates UA – Sewage discharge, final treated effluent UZ - Unspecified Waste Site TC – Trade discharges-site drainage TE - Domestic Property (Single) TG – Trade discharges-Mineral workings QC - Snack Bars, Cafes, etc BZ – Groundwater-unspecified DF – Mineral extraction

2.4 Sites of ecological and conservation interest

2.4.1 Statutory sites

There are no statutory ecological sites within 3 km of the site boundary.

The closest statutory sites are Cam Washes SSSI, 3.7 km to the east, Wicken Fen SSSI (also designated as SAC and RAMSAR sites), 5.3 km to the east and Stow Cum Quy Fen, 6.1 km to the southeast. These statutory sites are located in separate hydrological catchments to the site and upstream of any potential impacts that may result from discharges from the site.

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2.4.2 Non-statutory sites

There are four County Wildlife Sites within 3 km of the site: River Great Ouse, Beach Ditch and Engine Drain, Landbeach Pits Willow Wood and Twenty Pence Pit. Their locations are shown on Drawing 2173/HIA/05.

North of the site, the River Great Ouse CWS lies between the flood defence embankments providing narrow washlands along each bank of the river. The channel supports a wide variety of submerged, floating, marginal and wetbank species. The embankments support swamp and inundation grasslands in the wet areas and species-poor grassland in the drier areas.

Beach Ditch and Engine Drain CWS is designated for a number of reasons: it supports a population of a nationally scarce vascular plant species, it supports more than 5 submerged, floating and emergent species per 20 m stretch and more than 10 species per 20 m if wetbank flora are included.

Landbeach Pits Willow Wood CWS is an area of mature willow woodland, damp neutral grassland and reedbed with areas of temporary and permanent water. It is designated due to its invertebrate index, which is greater than 500.

Twenty Pence Pit CWS comprises a number of disused gravel pits which are in various stages of succession from open water to swamp and wet woodland. It is designated due to well- developed vegetation mosaics representing hydroseral zonation.

2.5 Archaeology

An archaeological survey 1 was undertaken by Cambridge Archaeological Unit between 7 November and 23 December 2016. An aerial photographic and geophysical survey identified an area of dense Roman settlement around Mitchell Hill Farm and consequently this area was excluded from the Application Area.

According to the survey report, there are four Scheduled Ancient Monuments (SAM) located within 2 km of the site (Drawing 2173/HIA/05). Car Dyke (SAM 224) is located 1.2 km south of the site boundary and represents the remains of a Roman Canal. Bullocks Haste (SAM 66) is the remains of a Roman settlement located approximately 1 km from the site boundary and west of Cottenham Lode. A second settlement, Chittering Hill (SAM13605), is located 1.2 km

1 Tabor, JL. 2017. Mitchell Hill Common, Cottenham, Cambridgeshire. An Archaeological Evaluation. Cambridge Archaeological Unit. Report N o 1364.

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east of the site. Denny Abbey is a monastic priory complex dating from the 12th to 16th centuries, located approximately 1.5km to the south-east of the proposed extraction area

2.6 Landfill sites

Locations of landfill sites in the vicinity of the site have been taken from the Government website environment.data.gov.uk. There are two authorised sites present within 2 km of the site boundary (shown in Drawing 2173/HIA/04):

. Waterbeach Waste Management Facility, Amey Cespa (East) Limited (now Amey LG Limited). The IPPC reference number for the site is CP3633YM . Donarbon Ltd – Dickersons, Donardon Limited. The site does not have an IPPC number. The Environmental Permit Reference is FP3190NH/V002.

2.7 Water resource status

According to the Environment Agency’s Cam and Ely Ouse Catchment Abstraction Management Plan (Environment Agency, May 2017) the site lies within the Old West Level dependent management Unit (LDMU). The licensing strategy within this unit states:

. No water available at low flows. . Water may be available at high flows subject to a Hands Off Flow (HoF) condition at AP17 (Denver Sluice). . A local level based cessation condition to protect Internal Drainage Board (IDB) drain levels may also be included. It may be possible to allow additional pumping when the HoF is enforced if the IDB are pumping water out (subject to IDB agreement). . Trading of recent actual quantities within IDB areas may be possible. Proposals will be considered on case by case basis in consultation with the relevant IDB.

The site lies within surface water Nitrate Vulnerable Zone S390, Ely Ouse and Cutoff channel.

2.8 Geology

2.8.1 Regional

The solid regional geology comprises a sequence of sedimentary strata which are generally inclined to the southeast. They comprise Jurassic and Cretaceous strata, separated by an unconformity. The regional solid geology is shown on Drawing 2173/HIA/06. The succession of the solid geology is shown in Table 2173/HIA/T4.

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2173/HIA/T4: Regional stratigraphy

Group Formation Lithology

Zig Zag Chalk Formation Chalk

Tottenhoe Stone Member Hardground Chalk Group West Melbury Marly Chalk Chalk Formation

Selbourne Group Gault Formation Clay or mudstone, sandy base

Lower Greensand Woburn Sands Formation Sandstone (or loose sand), Group glauconitic

Unconformity

Kimmeridge Clay Formation Mudstone, calcareous horizons in places, beds of argillaceous Ancholme Group limestone

Ampthill Clay Formation Mudstone, silty

The geological map shows that the site is underlain by the Kimmeridge Clay Formation.

The solid geology is partially concealed by superficial deposits comprising River Terrace Deposits (sand and gravel), peat and alluvium. Alluvium is associated with the two largest watercourses in the region: the River Cam and the River Great Ouse. Large continuous areas of peat are located to the east and northeast of the Site, the largest being in the vicinities of North Fen, Adventurers Fen, Swaffham Prior Fen and Wicken Sedge Fen.

The river terrace gravels in which the site is located form a linear north-south deposit stretching from just north of the River Ouse southwards towards Cambridge. The deposits vary from 1.2 to 2.5 km wide. To the south of the site the River Terrace Deposits have been worked for sand and gravel. The resulting voids have been restored either as open waterbodies, or used for landfilling.

2.8.2 Local

The local geology has been assessed using data provided by Frimstone from their mineral evaluation boreholes drilled in 2009/10 and recent infill drilling between the Engine Drain and the River Ouse. Additional data has also been provided from boreholes completed for the purpose of groundwater level monitoring. A summary of the data from the mineral evaluation boreholes is provided in Appendix 2173/HIA/A3 .

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The superficial deposits on-site are between 1.8 and 3.8 m thick and rest on the Kimmeridge Clay Formation, described as a firm, grey, silty clay.

The superficial deposits comprise between 0.4 and 2.1 m of soil and silty, sandy and stoney clay overlying between 1.0 and 3.0 of sand and fine to medium gravel with clay lenses. Summary statistics for these units are presented in Table 2173/HIA/T5.

2173/HIA/T5: Summary statistics for superficial deposits

Geological unit Overburden Sand and gravel Base of sand Elevation of base of Thickness thickness (m) and gravel sand and gravel (m) (mbgl) (mAOD) Min 0.4 1.0 1.8 -1.37 Max 2.1 3.0 3.8 2.52 Average 0.73 1.89 2.59 -0.06

The spatial variation in the thickness of the sand and gravel deposit is shown on Drawing 2173/HIA/A3. 1 (Appendix 2173/HIA/A3 ). The elevation of the base of the gravel is shown in Drawing 2173/HIA/A3 .2 . Reference to the geological map on Drawing 2173/HIA/06 shows that the area where the elevation of the base of the gravel rises above about 0.5 mAOD has been mapped as 2 nd Terrace Deposits, while the proposed site lies on the 1 st Terrace Deposits.

A summary of particle size distribution (PSD) analysis provided by Key Geosolutions Ltd. (KGS) gives an average composition of 40% gravel, 55% sand and 5% fines. Other PSD data are available from boreholes drilled by the Mineral Assessment Unit (MAU) in the 1970s and available on records held by the BGS. Some of these data for boreholes in and around the site are presented in Appendix 2173/HIA/A3. These indicate a poorly sorted gravelly sand with a low fines content.

2.9 Hydrogeology

2.9.1 Aquifer status and regional context

The Kimmeridge Clay present beneath most of the superficial deposits in the vicinity of the Site is argillaceous and therefore assumed to have very limited potential to store or transmit groundwater. There may be thin permeable limestone bands present within the Kimmeridge Clay, but these are unlikely to be significant in terms of the volume of groundwater flow. According to the Environment Agency’s Cam and Ely Ouse Abstraction Licensing Strategy

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(February, 2013), this area is classed as ‘Unproductive strata, including localised sand and gravel’ .

The only major permeable unit is the Woburn Sands Formation, which is classed by the Environment Agency as a Principal Aquifer. In this area, the Woburn Sands is part of the Cam and Ely Ouse Woburn Sands Waterbody (ID GB40501G445700). The current quantitative and qualitative status of this Waterbody is ‘Good’ ( Appendix 2173/HIA/A2 ). According to the Environment Agency’s Cam and Ely Ouse Abstraction Licensing Strategy (February, 2013), there is no water available for licensing from the confined or unconfined Greensand (Woburn Sands).

The Superficial River Terrace Deposits are classified by the Environment Agency as a Secondary A Aquifer. This aquifer has not been defined as a Waterbody for the purposes of the Water Framework Directive (WFD).

The base of the River Terrace aquifer is defined by the Kimmeridge Clay.

The site lies within groundwater nitrate vulnerable zone G144, Huntingdon River Gravels.

2.9.2 Groundwater levels

The Environment Agency does not monitor groundwater levels in the River Terrace Deposits. The nearest groundwater level monitoring point is at New Farm, Landbeach (TL46/001) located 1.8 km south of the site (at TL47866 66443), which monitors groundwater in the Woburn Sands Formation. Between September 1977 and June 2015 groundwater levels have varied between 2.54 and 3.77 mAOD (0.63 and 1.86 m below datum).

Groundwater levels for the sand and gravel deposit are available from a number of sources, as described below:

Mineral evaluation boreholes

Water strikes and standing water levels were recorded in the mineral evaluation boreholes drilled in 2009/10. The boreholes were not surveyed, but locations have been digitised from the available location plans and ground elevations estimated from LIDAR data. These data are provided in Appendix 2173/HIA/A3 . Groundwater levels are shown on Drawing 2173/HIA/07.

The groundwater levels recorded over most of the site are between 0.5 and 1.5 mAOD with some indication that levels are slightly lower along some of the surface drains and rise slightly

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between drains. Groundwater levels rise towards Mitchell Hill Farm reaching an elevation of around 3 mAOD at the farm.

Monitoring boreholes

Frimstone has installed seven groundwater monitoring boreholes around the site, the locations of which are shown on Drawing 2173/HIA/07. An eighth borehole (Borehole E) is located to the east of the Gravel Diggers site. Borehole logs are provided in Appendix 2173/HIA/A3 .

Monitoring of groundwater levels in these boreholes commenced in September 2016 and is currently undertaken monthly. The groundwater hydrographs are shown on Drawing 2173/HIA/08 and the data presented in Appendix 2173/HIA/A4 . At this stage the data record is too short to comment on long-term groundwater level variations.

Groundwater levels in boreholes B and C are over 1 m higher than the other six boreholes and reflects their location on the elevated ground around Mitchell Hill Farm, to the southwest of the site. Both boreholes had their highest water levels recorded in February and March, following which they declined, the lowest levels being recorded in July at borehole C and in October in borehole B. Groundwater levels have been rising in both boreholes since October 2017.

A similar pattern of variation to that in boreholes B and C can be seen in boreholes F and H. The remaining boreholes have shown different behaviours. At borehole D and G, maximum groundwater levels were observed in June and July 2017. Both these boreholes are adjacent to main drains and may be influenced by water levels in the drains, which are managed by the IDB. In borehole F, groundwater levels peaked between December 2016 and February 2017, but have declined since then, although they have risen slightly between November and December 2017.

Waterbeach Waste Management Park

Around the Waterbeach Waste Management Park (WWMP) groundwater levels in the River Terrace Deposits and limestone horizons in the Kimmeridge Clay are monitored by the landfill operator at up to 20 locations. These form part of the monitoring network around the landfill operation and are included as part of the monitoring programme required by the landfill site’s Environmental Permit.

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Groundwater level data were analysed in the 2010 HRA review (MLM Environmental, 2010). Groundwater flow in the River Terrace Deposits was reported to be in a northeasterly direction with a gradient of 0.0004. Within the limestone bands in the Kimmeridge Clay the data showed a flow to the east-northeast at a gradient of 0.0005.

2.9.3 Groundwater quality

There is no information on the general groundwater quality in the area, although the monitoring boreholes around the WWMP will be sampled as part of the landfill permit conditions. The presence of older, un-lined, dilute and disperse landfills within the WWMP is likely to have resulted in poorer quality groundwater than otherwise might be expected.

2.9.4 Aquifer properties

Analysis of the PSD data indicates the deposit is a poorly sorted gravelly sand with a low fines content. Literature data suggests that this type of deposit could have a hydraulic conductivity in the range 2 to 46 m/d.

There are no site specific data on aquifer properties of the River Terrace Deposits. However, an estimate can be made by using results from PSD analysis. PSD data from boreholes drilled in the 1970s by the Mineral Assessment Unit of the Institute of Geological Sciences have been analysed to estimate the hydraulic conductivity of the samples ( Appendix 2173/HIA/A3). The geometric means of the estimates range from 1.6 m/d to 38.4 m/d, with an average of 18 m/d, similar to the range provided in the literature.

2.9.5 Groundwater abstractions

There are no known licensed groundwater abstractions within a 2 km radius of the boundary of the Permitted Area.

Data provided by South Cambridgeshire District Council shows that there is only one private water supply within 2 km of the site boundary. This is located at Overbrook, Green End, Landbeach, approximately 1.5 km south of the site. Borehole records held by the British Geological Survey show that the abstraction is from the Woburn Sands Formation.

2.9.6 Gravel Diggers Quarry

Gravel Diggers Quarry lies immediately to the east of Long Drove and works the same superficial deposits as at the proposed Mitchell Hill site. The quarry covers approximately 29 ha. A limited amount of dewatering takes place from the quarry void, some of which is used for processing the sand and gravel on-site.

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The site has a discharge permit (Ref: EPR/FB3190VN ) to allow excess water to be discharged into Engine Drain at two locations, when required (Drawing 2173/HIA/04 ).

The site has planning permission for restoration with natural clay originating from the Waste Management Park and this should be completed by December 2019.

2.10 Conceptual understanding

The River Terrace Deposits form the local aquifer unit at the site. They are underlain by the Kimmeridge Clay, which forms an effective base to the aquifer.

Although regarded as a low permeability unit, the Kimmeridge Clay contains thin limestone horizons, which may permit some groundwater flow. However, this flow is unlikely to be of sufficient volume to be significant compared to flows in the sand and gravel.

The drainage ditches are considered to influence groundwater levels in the River Terrace Deposits and to act as a discharge point for the aquifer. Their presence will have acted to reduce the seasonal water level variation in the area. Groundwater flow in the sand and gravel is considered to be in a generally north-easterly direction towards the Chear Fen pumping station.

The presence of old dilute and disperse landfills to the south of the site means that the general background groundwater and surface water quality in the area is likely to be poor. It is understood that operations at the WWMP are intended to encapsulate much of the old dilute and disperse landfill and so water quality should improve in the long-term.

Dewatering in the proposed sand and gravel quarry will have local impact on groundwater levels in the River Terrace Deposits. There are no statutory wildlife sites within a sufficient distance to be impacted by dewatering in the proposed development. However, there are two County Wildlife Sites, Twenty Pence Pit and Engine Drain, located adjacent to the site.

There are three Scheduled Ancient Monuments within 1 km of the site boundary and an area of dense archaeological remains around Mitchell Hill Farm, immediately to the southwest of the site.

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3 PROPOSED DEVELOPMENT

3.1 Mineral extraction

Within the Mitchell Hill section, sand and gravel will be extracted to the full depth of the deposit. Mineral working will be undertaken in eight phases as summarised in Appendix 2173/HIA/A5 . Working will generally proceed from south to north, with the offices, processing plant and product stockpiles located in the southeast section. The final area of reserves to be worked will be that located beneath the processing plant (Phase 8). Mineral extraction is expected to take 12 years following commencement.

Mineral will be worked by excavator and transported to the processing area by dump trucks.

Processed material will be transported from the site via an access road passing along the northern and eastern sides of the Amey Cespa and Donarbon landfill areas to join the A10 at the Waste Management Park access roundabout.

Phases 3a and 5a will initially only be stripped to remove soils and the areas used to enable vehicular traffic to the processing area to travel over the uncovered gravel rather than the restoration materials.

3.2 Water management

3.2.1 General

During mineral extraction, groundwater flowing into the site, as well as incident rainfall, will need to be pumped off-site to facilitate safe and efficient working. It is proposed that water entering the site will be drained to a sump from where it will be pumped to a settlement lagoon prior to discharge to the external drainage system. The position of the drainage sump, and the discharge point, will change as the working area progresses northwards.

Where required, clay from the base of the workings will be placed against the sides of the excavation adjacent to the main IDB drains to prevent any significant leakage from the drains.

The gravel processing plant will require a water supply for gravel washing. It is anticipated that this will operate in a similar manner to the plant currently operating at Gravel Diggers. Process water may be taken either from the surface water and groundwater inflow to the void, or, in the event that these inflows are insufficient for the plant, from the nearby Engine Drain. In either case an abstraction licence will be required from the Environment Agency.

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Excess water from the site will be discharged into the surface water system. The exact position of the discharge is likely to vary based on the position of the workings at any time. It should also be noted that from 1 st January 2018, quarry dewatering will no longer be exempt from abstraction licensing. Therefore, an application will have to be made for a transfer licence to pump water from the sump(s) to the surface water system.

3.2.2 Groundwater ingress volumes

Groundwater flowing into the site will either be discharged into the surface water system, or partially used in the gravel processing operation. It is likely that groundwater inflows will be significantly reduced due to the mitigation measures used to prevent impacts to surrounding features. An estimate of the maximum inflow (with no mitigation) has been made assuming an area the size of Phases 2 and 3 (11 ha) is open at any one time. Details are provided in Appendix 2173/HIA/A6 .

Assuming a hydraulic conductivity of 18 m/d, the estimated groundwater inflow is of the order of 502 m3/d (or 5.8 l/s). If a maximum hydraulic conductivity of 46 m/d is assumed, then the groundwater inflow is estimated to increase to 816 m3/d (or 9.4 l/s).

3.2.3 Rainfall

Rainfall incident to the open area will also need to be removed. The volume to be removed will depend on the area required to be dewatered at any one time. As with the groundwater flow estimate, it has been assumed that two consecutive phases may be open at any one time as restoration will lag behind the extraction phase. The largest two consecutive phases are Phases 2 and 3, which cover an area of 182,800 m 2.

Details of the estimate are provided in Appendix 2173/HIA/A6 . Average daily rainfall flows are estimated to be between 2.93 l/s in January to 3.64 l/s in June, based on rainfall data from the Stretham rain gauge ( Table 2173/HIA/T1 ).

3.3 Restoration

Restoration of the site will be completed by infilling the void with imported inert material. The final landform is shown on Drawing CP/FRIM/MH/04 , reproduced in Appendix 2173/HIA/A5. Restoration will be progressive as the site is worked.

The proposed final landform for Phases 1 to 5 and Phase 8 is a north-south orientated elongate dome rising to around 5 mAOD. Phases 6 and 7 will be restored to a wetland area using suitable materials.

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Drainage ditches will be positioned around the periphery of the restored site with the dual purpose of removing surface water flow from the landform and preventing excessive rise in groundwater levels up-gradient of the site. Balancing ponds positioned around the site will ensure suitable discharge volumes are maintained. Further details are provided in the Flood Risk Assessment 2 accompanying the application.

2 Hafren Water, 2173/FRA, 2018.

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4 ASSESSMENT OF IMPACTS

4.1 Methodology

An assessment of the potential effects of the proposed mineral extraction at Mitchell Hill on the water environment within the site and its surrounds has been undertaken.

Potential impacts to the baseline and current conditions were assessed. Short-term (operational) and long-term (post-restoration) phases of site development were considered. The potential for unplanned incidents, such as spillage of hazardous substances, was also taken into account. The following factors were considered:

. Magnitude of the impact . Spatial extent of the impact . Frequency of the impacts . Timescale over which the impact may occur . Cumulative impacts . Sensitivity of the receiving environment

Mitigation measures and residual impacts have been considered as part of the assessment. The method of assessment is detailed in Appendix 2173/HIA/A1 together with the matrices used to provide a robust method of assessment. Mitigation measures and residual impacts are discussed in Section 5.

4.2 Baseline sensitivity

The site is located within a Secondary A Aquifer with clay beneath. The site does not lie within a Drinking Water Safeguard Zone, or a source protection zone (SPZ) and there are no groundwater abstractions from the aquifer within the IDB catchment.

The site is located within a surface water catchment defined by the surface water drainage system to Chear Fen Pumping Station, which discharges into the River Great Ouse. The drains within this catchment are used as a water source for licensed abstractions for crop irrigation. A number of these abstractions are permitted from drains immediately adjacent to the proposed development, or are downstream of the development. Two drains within the site are also identified as permitted locations for abstraction.

There are no statutory groundwater, or surface water, dependent sites of ecological interest down-gradient of the site. However, two County Wildlife Sites (CWS) are located immediately adjacent to the site boundary. Part of the Beach Ditch and Engine Drain CWS passes west to

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east through the site and the Twenty Pence Pit CWS lies adjacent to the western boundary of the site.

Archaeological remains are present on the slightly higher ground around Mitchell Hill Farm, although they have not been identified as specifically at risk from groundwater level changes.

The catchment sensitivity, based on the above hydrological, hydrogeological and environmental factors, is considered to be ‘Low’ to ‘Medium’ sensitivity.

4.3 Potential impacts during mineral extraction

4.3.1 Surface water levels

There is a small pond immediately adjacent to the southern boundary of Phase 2 of the development (labelled PA on Drawing 2173/HIA/02 ) and within the Planning Application area. This is an artificial pond and reported to be lined with clay. The pond is reported to have no particular ecological significance 3.

The sensitivity of the pond is considered to be ‘Low’, with a magnitude of impact of ‘Low’. The significance of effect is therefore ‘Minor’.

Water levels in the adjacent ditches, principally Engine Drain and Right Wing Drain may be reduced due to increased leakage from the drains as the mineral is dewatered in Phases 4 to 7. This could potentially have local impact on the conservation status of Beach Ditch and Engine Drain CWS, particularly in the summer when levels are lower and there is no pumping at Chear Fen. However, any impacts will occur on a relatively small length of the CWS in comparison to the total length of drain designated. Any water level changes as a result of the development are likely to be smaller in magnitude than changes made by the IDB as part of the drainage management.

Increased leakage from the drains is unlikely to impact significantly on the volume of water available for licensed abstractions.

The sensitivity of the surface water catchment at Right Wing Drain is considered to be ‘Medium’, with a magnitude of impact of ‘Low’. The significance of effect is therefore ‘Minor’.

In Phases 3 and 4 the extraction area is within 50 m of one of the ponds forming Twenty Pence Pit CWS. These ponds are likely to be in hydraulic connection with groundwater in the

3 Ward Associates, Ecological assessment of land at Mitchell Hill, Cambs. January 2018.

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gravel deposit and lowering of groundwater levels could induce flow out of the ponds with a consequent decline in water level. However, the maximum radius of influence of dewatering is only 64 m (as shown on Drawing 2173/HIA/A6.1) and it is considered that the impact on water levels is likely to be insignificant.

The sensitivity of the surface water catchment at Twenty Pence Pit is considered to be ‘Medium’, with a magnitude of impact of ‘Low’. The significance of effect is therefore ‘Minor’.

4.3.2 Surface water flow

The entire catchment is artificially managed by the IDB and flow in the drains will depend on the pumping regime at Chear Fen. This is considered to be the dominant control on flows in the drainage network.

Discharge from the site will be controlled to the greenfield run-off rate and no significant change to the overall flow regime is expected. Discharge will eventually enter the sections of the drainage system designated as the Beach Ditch and Engine Drain CWS.

The sensitivity of the surface water catchment is considered to be ‘Medium’, with a magnitude of impact of ‘Low’. The significance of effect is therefore ‘Minor’.

4.3.3 Surface water quality

Water pumped from the quarry will be discharged into the surrounding surface water drainage system. The point of discharge will vary as the various phases are worked, but ultimately the discharge will enter the Right Wing Drain, or Engine Drain.

There are potential impacts to surface water quality in the drains, and on the Beach Ditch and Engine Drain CWS in particular, in the unlikely event that there are accidental spills of hydrocarbons (fuels and lubricants) from mobile and static plant within the site. There are also licensed surface water abstractions downstream of the site which could be impacted by such releases.

Due to the presence of a County Wildlife Site downstream of the site, the catchment sensitivity is classed as ‘Medium’. The magnitude of impact of potentially poor quality water is assessed as ‘Medium’, resulting in a significance of ‘Moderate’ without any mitigation measures.

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There is a potential risk of accidentally including contaminated soil in the imported material, resulting in leaching of contaminants into the internal drainage system and consequently out of the site via the dewatering discharge.

However, the use of imported materials for restoration will require an Environmental Permit (EP) from the Environment Agency with acceptance criteria. This should act to reduce the risk of potentially contaminated material being imported. Other conditions on the source of material are also likely to be imposed as part of the environmental permitting.

For these reasons, the magnitude of impact from the restoration materials is considered to be ‘Low’ and with a catchment sensitivity of ‘Medium’ the significance of impact is considered to be ‘Minor’.

4.3.4 Groundwater levels

Impacts to groundwater levels are expected to be limited to a zone approximately 64 m from the dewatered void (assuming a high hydraulic conductivity for the gravel).

Up-gradient (south and west)

The groundwater is of limited sensitivity in this area. However, the Twenty Pence Pit CWS is within the radius of influence of dewatering and there are archaeological remains around Mitchell Hill Farm which may be at risk from groundwater level reduction. Potential impacts to these receptors are addressed in Sections 4.3.1 and 4.3.7 respectively.

Down-gradient (east)

The groundwater is not considered to be sensitive in this area as there are no receptors within the radius of influence of dewatering.

With a ‘Low’ sensitivity and ‘Low’ magnitude of impact, the significance of effect is considered to be ‘Minor’.

4.3.5 Groundwater quality

During mineral extraction, the site will be dewatered to maintain safe working conditions. Groundwater will, therefore, flow in towards the site. In the unlikely event of an accidental spillage of hydrocarbons (fuels and lubricants) within the site, the spilt material would be contained within the site. There is considered to be no risk to groundwater from accidental spillages.

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The groundwater is considered to be of ‘Low’ sensitivity, the magnitude of impact ‘Negligible’ and, therefore, the significance of effects as ‘None’.

4.3.6 Wildlife sites

Potential impacts to the County Wildlife Sites at Twenty Pence Pit and Beach Ditch and Engine Drain have been discussed above.

In the case of both sites the significance of effects has been classed as ‘Minor’ for water level and flow. For water quality the significance of effects has been classed as ‘Moderate’ without any mitigation measures.

4.3.7 Archaeology

Archaeological remains have been identified in the area around Mitchell Hill Farm. Groundwater levels at monitoring points B and C indicate groundwater levels are between 2.15 and 1.43 mbgl and potentially below the level of any remains.

The radius of impact from dewatering on groundwater levels is expected to be up to 64 m from the dewatered void, as shown on Drawing 2173/HIA/A6.1 . This is not expected to significantly encroach on the archaeological remains. There are already two groundwater monitoring boreholes in this area and monitoring will be continued during the life of the quarry.

This area is considered to have a sensitivity of ‘Low’ and a magnitude of impact from dewatering of ‘Low’ resulting in a significance level of ‘Minor’.

4.3.8 Buildings

The closest buildings to the site are at Elm Farm. The assessment of the impact of dewatering indicates that groundwater levels will not be lowered as a result of dewatering and there is no risk to buildings from subsidence.

4.3.9 Summary

A summary of the assessment is provided in Table 2173/HIA/T6 .

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2173/HIA/T6: Assessment of impacts of quarry operations without mitigation measures

Sensitivity Magnitude Significance Comments GROUNDWATER LEVELS Down-gradient Low Low Minor (east) Medium Low Minor Twenty Pence Pit CWS Up-gradient Potential impacts on (south and west) Low Low None waterlogged archaeological remains at Mitchell Hill Farm GROUNDWATER QUALITY Groundwater Low Negligible None Groundwater inflow (if any) will be into the quarry void during working SURFACE WATER LEVELS Fishing pond PA Low Low Minor Artificial clay-lined pond Engine Drain (south of Low Low Minor site) Right Wing Drain Medium Low Minor Part of Beach Ditch and Engine Drain CWS SURFACE WATER Flows Engine Drain Low Low Minor Right Wing Drain Medium Low Minor Beach Ditch and Engine Drain CWS SURFACE WATER QUALITY Suspended solids Medium Medium Moderate Engine Drain and Right Wing Drain Chemical Medium Medium Moderate

4.4 Potential impacts following restoration

4.4.1 General

During the period of mineral extraction, the site will be progressively restored with natural clay and imported inert fill.

Once gravel extraction has ceased, surrounding groundwater levels will rise and re- equilibrate with surface water. To assess the risks of the post-operational impacts, the sensitivity of the receptors will not change, but the magnitude of impacts and their significance may change. Impacts have been considered against conditions prior to quarry workings.

4.4.2 Groundwater levels

The periphery of the final void will be lined with natural clay derived from within the site. Therefore the restored site will present a barrier to groundwater flow. This could result in

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groundwater levels rising on the up-gradient (western and southwestern) side of the restored site.

Due to the increase in ground level proposed in the restoration plan, there will be a shallow depression between the slightly higher ground at Mitchell Hill Farm and the centre of the restored site, coincident with the edge of the clay fill. There is potential for raised groundwater levels, together with rainfall run-off from the restored area, to cause surface water flooding in this area.

The proposed land use in this area is agricultural and the sensitivity is considered to be ‘Low’ with a magnitude of impact of ‘Medium’. The significance of effect is considered to be ‘Minor’. However, without mitigation measures it is possible that this area could not be farmed.

4.4.3 Water quality

The risks of the use of imported inert material will be addressed by the conditions imposed on waste acceptance criteria in the event that an Environmental Permit is granted. No further mitigation measures are considered necessary to protect the general groundwater quality down-gradient of the site.

4.4.4 Surface water run-off

The low permeability nature of fill and the steeper slopes of the new landform will increase the amount of run-off and result in a flashy response to rainfall in the surrounding ditch network.

Details of how run-off will be controlled are provided in the Flood Risk Assessment 4.

4 Flood Risk assessment for a proposed quarry at Mitchell Hill, Cambridge. Hafren Water 2173/FRA, 2018

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5 WATER FRAMEWORK DIRECTIVE ASSESSMENT

5.1 Introduction

The Water Framework Directive (WFD) (2000/60/EC) was implemented in England and Wales by The Water Environment (Water Framework Directive)(England and Wales) Regulations 2003. The WFD requires that all European countries manage the water environment to consistent standards, which include:

. Prevent deterioration in the status of aquatic ecosystems, protect and improve the ecological condition of waters, . Subject to the criteria set out in the Directive, aim to achieve good status by 2021 or 2027 where it was not possible to have achieved this by 2015, . Meet the requirements of Water Framework Directive Protected Areas, . Promote sustainable use of water as a natural resource, . Conserve habitats and species that directly depend on water, . Reduce or phase out the release of individual pollutants or groups of pollutants that present a significant threat to the aquatic environment, . Progressively reduce the pollution of groundwater and prevent or limit the entry of pollutants, . Contribute to mitigating the effects of floods and droughts.

An assessment of the application is required to ensure that there are no impacts to the current or future status of the relevant waterbodies.

5.2 Location

The site lies within the Anglian River Basin District.

In terms of groundwater, there is no waterbody designation for the sand and gravel aquifer and therefore, no groundwater assessment under the Water Framework Directive has been undertaken for this aquifer. The closest groundwater unit is the Cam and Ely Ouse Woburn Sands (ID GB40501G445700), which crops out beneath superficial deposits approximately 600 m to the east of the site boundary.

The relevant surface water unit is the Old West River (GB205033043375), classed as a heavily modified waterbody. The 2015 ecological potential of the waterbody is ‘Moderate’ and the Chemical status is ‘Good’. There are no WFD Protected Areas in the catchment.

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5.3 Surface water assessment

5.3.1 Quantitative status

Dewatering of the site will be necessary for the operational period in order to remove groundwater inflow and surface water run-off. This water will be discharged into the existing surface water drainage system and none will be lost from the catchment.

The catchment is classed as heavily modified as the drainage system is artificial and water levels are controlled by pumping. It is considered that the proposals will have no impact on the quantitative status of the surface water waterbody.

5.3.2 Qualitative status

As dewatering is required, there will be a need to discharge water from the quarry into the surface water system. There is, therefore, potential for impact to the local qualitative status of the surface water due to the accidental release of hydrocarbons within the site.

It is considered that the pollution control procedures that will be adopted for fuel and oil handling and storage, will prevent water becoming contaminated and impacting on the qualitative status of the surface water system. The water management system will also prevent fine-grained suspended solids from being discharged into the surface water system.

There is a potential risk to water quality due to the presence of unsuitable imported material used to restore the site. The importation of material to the site will be undertaken using strict Waste Acceptance Criteria, that would be specified as part of the Environmental Permit required for the restoration. The conditions imposed will minimise the risk to water quality and prevent deterioration in the status of the waterbody.

5.3.3 Ecological status

There are no statutorily designated sites within the catchment. However, there are two County Wildlife Sites. The risk assessment has shown that neither of the sites is at significant risk from the development.

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6 MITIGATION MEASURES AND RESIDUAL IMPACTS

6.1 During mineral extraction

6.1.1 Surface water quality

Suspended solids

Incident rainfall and groundwater inflow will be drained and collected in an appropriate sump in the quarry floor and suspended material allowed to settle before the water is discharged into the external drainage network.

Fuels and lubricants

Impacts due to accidental spillages of fuels and oils from mobile plant will be mitigated by ensuring the following measures are taken: i) All refuelling of mobile plant will take place on hardstanding in the plant area, minimising the risk of spillages reaching the sand and gravel aquifer. ii) Fuel will be stored in a double sided tank located on a concrete base and bunded. iii) All plant will be maintained in accordance with best practice and manufacturer’s specification. Where possible, all maintenance will be carried out off-site or on areas of hardstanding. iv) Written procedures will be in place for responding to an accidental spill of hydrocarbons, which will minimise the risk to the environment.

With these measures in place, the magnitude of residual impacts on surface water quality during the operational phase of the proposed quarry are assessed as ‘negligible’ with a significance of effect of ‘Minor’.

6.1.2 Surface water levels

During mineral extraction, no potentially significant effects were identified on the Beach Ditch and Engine Drain CWS where it passes across the site (as Right Wing Drain), or in Twenty Pence Pit CWS. However, in the event that significant leakage is observed from the drains, or the ponds, into the site, there is sufficient natural clay material in the floor of the void to be able to line the side of the void with a low permeability barrier.

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6.2 Post-restoration

6.2.1 Groundwater levels

Potential impacts were identified in an area between Mitchell Hill Farm and the restored landform where there might be a potential for flooding from a combination of rising groundwater levels and increased surface run-off.

To address this problem, a perimeter ditch is proposed that would act to keep groundwater levels to a similar elevation as the pre-development level and capture any increased surface water run-off. The ditch would probably be constructed progressively during the operational period of the site and be completed by the time Phases 2 and 3 were being restored.

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7 CUMULATIVE IMPACTS

Cumulative impacts are those which result from incremental changes caused by past, present or future reasonably foreseeable developments.

The River Terrace Gravels have previously been worked within the Waterbeach Waste Management Park and in most cases replaced by low permeability fill, or more recently, fully lined landfills. Gravel is also currently being extracted at Gravel Diggers Quarry, which is located immediately to the east of the proposed development at Mitchell Hill.

The most significant impact on the water environment is likely to be the cumulative loss of the gravel deposits and the ability to store water within them. However, the gravel deposits are not utilised directly as a source of water and there are no licensed groundwater abstractions from the gravel.

Water levels in the drainage system are maintained at suitable levels by the IDB as a consequence of the operation of the Chear Fen pumping station.

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8 SUMMARY AND CONCLUSIONS

Frimstone is seeking Planning Permission for a sand and gravel quarry located at a site approximately 12 km north of Cambridge and 4.2 km northeast of the village of Cottington and immediately north of the Waste Management Park.

It is proposed to work the site dry and dewatering will be required. The site will be progressively restored to agriculture using a mixture of site derived soils and imported inert waste. The topography of the restored site will be raised in comparison with the existing ground level.

The site lies at elevations of between 2.0 and 2.8 mAOD and is within the Old West Internal Drainage Board. Surface water drains to a pumping station, Chear Fen, where water is pumped out of the catchment into the River Great Ouse. There are a number of licensed surface water abstractions between the site and the Chear Fen pumping station.

The proposed development is located on superficial River Terrace Deposits between 1 and 3 m thick resting on Kimmeridge Clay. The River Terrace Deposits are classed by the Environment Agency as a Secondary A aquifer, while the Kimmeridge Clay is classed as unproductive strata. There are no licensed groundwater abstractions or private water supplies from the River Terrace Deposits within 2 km of the site.

There are no statutory sites of ecological interest within 2 km of the site. However, three County Wildlife Sites are present in the vicinity, two of which, Beach Ditch and Engine Drain and Twenty Pence Pit, are immediately adjacent to the site boundary.

Groundwater flow in the River Terrace Deposits is in a general northeasterly direction, towards the Chear Fen pumping station. It is likely that maximum groundwater levels are controlled by land drains and the network of artificial drains in the catchment.

An assessment of impacts from the proposed site has been made with specific reference to the water environment including groundwater and surface water flows and quality, water abstractions and water dependent sites of ecological interest. Impacts of the proposed development have been assessed against the current conditions around the site, while impacts following restoration have been assessed against the pre-development situation.

During mineral extraction the significance of effect of most of the impacts identified are assessed as Minor. The exceptions are risks to surface water quality from accidental fuel or chemical spills inside the site. Mitigation measures for these impacts have been identified

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and include ensuring best practice is observed on-site in respect of handling and storage of chemicals and fuels.

Post-restoration impacts include raised groundwater levels up-gradient of the site which could cause groundwater to rise to ground level. The mitigation measure proposed is to provide a new surface water drain to lower groundwater levels.

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DRAWINGS

January 2018 Version: D1

3.5

3.0

2.5

A

B

C 2.0 D

E m AOD m F

1.5 G

H Client Frimstone Ltd, Ashcraft Farm, Main Road, 1.0 Crimplesham, Norfolk, PE33 9EB Title Groundwater hydrographs

Project Mitchells Hill 0.5 Drawing 2173/HIA/08 Version 1 Date Jan-18 Scale n/a

0.0 Barkers Chambers • Barker Street • Shrewsbury 01/09/2016 31/10/2016 31/12/2016 02/03/2017 02/05/2017 02/07/2017 01/09/2017 01/11/2017 01/01/2018 • United Kingdom • SY1 1SB E: [email protected] • T: 01743 355 770 Frimstone Mitchell Hill HIA

APPENDIX 2173/HIA/A1

Assessment methodology

Frimstone Ltd Mitchell Hill Impact assessment methodology

Method of assessment

The method of assessment of hydrological and aquatic effects has involved:

. Characterisation of the baseline environment . Determination of the sensitivity of key catchments and watercourses . Evaluation of the significance of predicted effects taking account of the magnitude of effects (before and after mitigation) . Evaluation of the sensitivity of the baseline environment affected

A rigorous and consistent approach to the assessment has been adopted using matrices to help classify sensitivity of the resource, and determine the scale and significance of effects.

Baseline sensitivity

The characterisation of the baseline water environment has involved the review of data and identification of sensitivities. The characterisation of catchment sensitivities has been guided by the matrix presented in Table 2173/HIA/A1.1 which lists indicative criteria.

The criteria for sensitivity are based approximately on hierarchy of factors relating to the quality of the aquatic environment. The criteria have been used to guide the analysis of the sensitivity of the baseline hydrological, hydrogeological and water quality environment.

Table 2173/HIA/A1.1: Catchment sensitivity classification Sensitivity category Sensitivity criteria Adjacent to Application Area Downstream/in catchment High sensitivity SSSI or Aquatic Natura 2000 site Aquatic Natura 2000 site or Wetland/watercourse habitat SSSI immediately of particular ecological downstream/ adjacent to importance site Highly vulnerable groundwater Significant peat deposits on sloping ground Medium sensitivity Wetland watercourse habitat Aquatic Natura 2000 site or of particular ecological SSSI further downstream of importance the catchment. Moderately vulnerable Sensitive locally designated groundwater site of ecological interest Significant peat deposits Low sensitivity Low vulnerability groundwater Superficial peat deposits Not sensitive No aquatic habitats or watercourses present No significant groundwater present

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Frimstone Ltd Mitchell Hill Impact assessment methodology

Impact prediction and evaluation

The prediction and assessment of effects on hydrology, hydrogeology and other aquatic resources has been undertaken using a series of tables to document the various potential impacts from aspects of the proposed project. Impacts have been predicted for the proposed development based on the guideline criteria for impact magnitudes set out in Table 2173/HIA/A1.2 .

Table 2173/HIA/A1.2: Impact magnitude Impact Guideline criteria magnitude High Total loss of, or alteration to, key features of the baseline resource such that post-development characteristics or quality would be fundamentally and irreversibly changed, eg watercourse realignment Medium Total loss of, or alteration to, key features of the baseline resource such that post-development characteristics or quality would be partially changed, eg in-stream permanent bridge works Low Small changes to the baseline resource which are detectable but the underlying characteristics or quality of the baseline situation would be similar to pre-development conditions, eg culverting of very small watercourses Negligible A very slight change from baseline conditions, which is barely distinguishable and approximates to the ‘no change’ situation, eg short-term compaction from plant movements

Using these criteria a series of generic impacts have been predicted for the proposed development. Residual effects have been predicted taking into account site-specific mitigation.

The significance of the predicted effects has been assessed in relation to the sensitivities of the baseline resource. A matrix of significance was developed to provide a consistent framework for evaluation and is presented in Table 2173/HIA/A1.3 . Guideline criteria for the various categories of effect are included in Table 2173/HIA/A1.4.

Table 2173/HIA/A1.3: Significance matrix Magnitude Sensitivity High Medium Low Negligible High Major Major Moderate Minor Medium Major Moderate Minor Minor Low Moderate Minor Minor None Negligible Minor Minor None None

Table 2173/HIA/A1.4: Significance of effects categories Significance Definition Guideline criteria None No detectable change to No effects on drainage patterns, the environment surface and groundwater quality or aquatic habitat

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Frimstone Ltd Mitchell Hill Impact assessment methodology

Table 2173/HIA/A1.4: Significance of effects categories Significance Definition Guideline criteria Minor A small but detectable Localised changes in drainage change to the patterns or groundwater flows, or environment changes resulting in minor and reversible effects on surface and groundwater quality or aquatic habitats Moderate A larger, but non- Changes in water quality or quantity fundamental change to affecting part of a catchment or the environment groundwaters of moderate vulnerability, or changes resulting in loss of conservation value to aquatic habitats or designated areas Major A fundamental change to Changes in water quality or quantity the environment affecting widespread catchments or groundwater reserves of strategic significance, or changes resulting in substantial loss of conservation value to aquatic habitats and designations

In the above classification, fundamental changes are those which are permanent, detrimental and would result in widespread change to the baseline environment.

The matrices used to guide the assessment have been applied with a degree of flexibility since the evaluation of effects would always be subject to particular location-specific characteristics which need to be taken into account. For this reason, the evaluation of impact significance, in particular, would not always correlate exactly with the cells in the relevant matrix where professional judgement and knowledge of local conditions may result in a slightly different interpretation of the impact concerned. Cumulative effects have been taken into account through prediction and evaluation of effects at a catchment-wide level.

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Frimstone Mitchell Hill HIA

APPENDIX 2173/HIA/A2

Water Framework Directive status of waterbodies

Frimstone Ltd Mitchell Hill Appendix A2 Water Framework Directive

Old West River: ID GB205033043375

Type River

Hydromorphological designation heavily modified

NGR TL4020674016

Length (km) 40.949

Catchment area (km2) 194.224

Water body classification

2013 Cycle 2 2015 Cycle 2 Objectives

Moderate Moderate Moderate by 2015 Overall Water Body

Moderate Moderate Moderate by 2015 Ecological

Good Good Good by 2015 Chemical

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Frimstone Ltd Mitchell Hill Appendix A2 Water Framework Directive

Cam and Ely Ouse Woburn Sands:

Chemical and quantitative classification for groundwater | 2015 Cycle 2 Quantitative status Chemical status

Number of water bodies Poor Good Poor Good

1 0 1 1 0

Ref: http://environment.data.gov.uk/catchment-planning/OperationalCatchment/1027

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Frimstone Mitchell Hill HIA

APPENDIX 2173/HIA/A3

Borehole data

Frimstone Ltd Mitchell Hill Appendix A3 Borehole data

Data from Mineral evaluation boreholes

Frimstone Ltd Mitchell Hill Appendix A3 Borehole data

Table 2173/HIA/A3.1 Data for mineral evaluation boreholes Gravel Water strike Standing water Saturated Ground level thickness BH_ID Easting Northing level Top Base Thick mAOD mbgl mbgl mAOD m mbgl mAOD mbgl mAOD m

Drilled September 2009

1 547556 270118 3.817 0.8 2.1 1.717 1.3 1.5 2.317 2 547709 270279 3.188 0.8 2.3 0.888 1.5 1.8 1.388 1.55 1.638 0.75 3 547846 270413 2.793 0.7 3 -0.207 2.3 2 0.793 4 547929 270532 2.803 0.7 3 -0.197 2.3 2 0.803 1.62 1.183 1.38 5 548092 270496 2.062 0.7 2 0.062 1.3 2 0.062 1.53 0.532 0.47 6 547945 270318 2.675 0.6 2.6 0.075 2 1.6 1.075 1.36 1.315 1.24 7 547792 270200 3.21 0.7 2.1 1.11 1.4 1.8 1.41 1.52 1.69 0.58 8 547704 270027 4.343 0.6 2.2 2.143 1.6 1.7 2.643 1.49 2.853 0.71 9 547814 269963 4.378 0.6 2.8 1.578 2.2 1.8 2.578 1.62 2.758 1.18 10 547918 270080 3.557 0.7 1.8 1.757 1.1 1.6 1.957 1.42 2.137 0.38 11 548000 270230 2.653 0.6 2.7 -0.047 2.1 1.7 0.953 1.42 1.233 1.28 12 548094 270162 2.51 0.6 2.8 -0.29 2.2 1.8 0.71 1.59 0.92 1.21 13 547977 269986 3.61 1.1 2.3 1.31 1.2 1.6 2.01 1.31 2.3 0.99 14 548147 270049 2.255 0.6 2.7 -0.445 2.1 1.9 0.355 1.61 0.645 1.09 15 548148 269911 2.362 0.6 2.3 0.062 1.7 1.7 0.662 1.28 1.082 1.02 16 548498 270858 2.057 0.6 3.2 -1.143 2.6 1.7 0.357 1.37 0.687 1.83 17 548675 270846 1.98 0.6 2.3 -0.32 1.7 1.4 0.58 1.14 0.84 1.16 18 548804 270841 1.673 0.8 1.9 -0.227 1.1 1.5 0.173 1.27 0.403 0.63 19 548822 270682 1.88 0.7 2.1 -0.22 1.4 1.7 0.18 1.51 0.37 0.59

Version: 1 January 18 Page A3.2 Frimstone Ltd Mitchell Hill Appendix A3 Borehole data

Table 2173/HIA/A3.1 Data for mineral evaluation boreholes Gravel Water strike Standing water Saturated Ground level thickness BH_ID Easting Northing level Top Base Thick mAOD mbgl mbgl mAOD m mbgl mAOD mbgl mAOD m

20 548681 270686 2.017 0.8 2 0.017 1.2 1.5 0.517 1.26 0.757 0.74 21 548519 270671 2.005 0.7 1.9 0.105 1.2 1.5 0.505 1.32 0.685 0.58 22 548876 270464 1.678 0.7 2 -0.322 1.3 1.6 0.078 1.31 0.368 0.69

23 548934 270639 1.885 2.1 2.1 -0.215 24 548854 270765 1.91 0.9 1.9 0.01 1 1.7 0.21 1.55 0.36 0.35 25 548917 270846 1.84 0.8 1.9 -0.06 1.1 1.6 0.24 1.19 0.65 0.71

Drilled May 2010 26 548251 269912 2.58 0.8 2.2 0.38 1.4 1.6 0.98 1.53 1.05 0.67 27 548234 270093 2.56 0.8 3.1 -0.54 2.3 1.4 1.16 1.32 1.24 1.78 28 548231 270275 2.607 0.7 2.7 -0.093 2 1.7 0.907 1.41 1.197 1.29 29 548244 270455 2.332 0.8 2.9 -0.568 2.1 1.7 0.632 1.47 0.862 1.43 30 548163 270403 2.312 0.7 2.6 -0.288 1.9 1.8 0.512 1.52 0.792 1.08 31 548119 270263 2.275 0.9 2.5 -0.225 1.6 1.8 0.475 1.63 0.645 0.87 32 548371 269913 2.535 0.7 3 -0.465 2.3 1.7 0.835 1.39 1.145 1.61 33 548345 270102 2.525 0.7 2.7 -0.175 2 1.6 0.925 1.19 1.335 1.51 34 548351 270282 2.367 0.7 2.6 -0.233 1.9 1.6 0.767 1.34 1.027 1.26 35 548360 270430 2.2 0.7 2.5 -0.3 1.8 1.7 0.5 1.51 0.69 0.99 36 548454 270401 2.225 0.7 2.5 -0.275 1.8 1.6 0.625 1.46 0.765 1.04 37 548462 270288 2.295 0.5 2.8 -0.505 2.3 1.7 0.595 1.51 0.785 1.29 38 548469 270104 2.445 0.7 3.6 -1.155 2.9 1.5 0.945 1.29 1.155 2.31

Version: 1 January 18 Page A3.3 Frimstone Ltd Mitchell Hill Appendix A3 Borehole data

Table 2173/HIA/A3.1 Data for mineral evaluation boreholes Gravel Water strike Standing water Saturated Ground level thickness BH_ID Easting Northing level Top Base Thick mAOD mbgl mbgl mAOD m mbgl mAOD mbgl mAOD m

39 548508 269920 2.39 0.7 3.4 -1.01 2.7 1.7 0.69 1.47 0.92 1.93 40 548421 270527 2.102 0.6 3.3 -1.198 2.7 1.7 0.402 1.48 0.622 1.82 41 548300 270551 2.122 0.5 2.8 -0.678 2.3 1.7 0.422 1.38 0.742 1.42 42 548182 270562 2.205 0.8 2.7 -0.495 1.9 1.6 0.605 1.37 0.835 1.33 43 548037 270566 2.213 0.7 2.4 -0.187 1.7 1.7 0.513 1.29 0.923 1.11 44 548039 270719 2.155 0.7 3.4 -1.245 2.7 1.7 0.455 1.4 0.755 2 45 548158 270715 2.227 0.7 2.8 -0.573 2.1 1.8 0.427 1.47 0.757 1.33 46 548294 270711 2.135 0.8 2.8 -0.665 2 1.7 0.435 1.36 0.775 1.44 47 548429 270708 2.125 0.7 3.5 -1.375 2.8 1.6 0.525 1.33 0.795 2.17 48 548395 270858 2.037 0.6 3.1 -1.063 2.5 1.6 0.437 1.32 0.717 1.78 49 548251 270863 1.983 0.4 2.6 -0.617 2.2 1.7 0.283 1.42 0.563 1.18 50 548056 270864 2.188 0.9 2.6 -0.412 1.7 1.7 0.488 1.5 0.688 1.1 51 547849 269834 4.323 0.8 1.8 2.523 1 1.6 2.723 1.21 3.113 0.59 52 548104 269716 3.025 0.8 3.8 -0.775 3 2 1.025 2.07 0.955 1.73 53 548158 269831 2.51 0.8 2.7 -0.19 1.9 1.8 0.71 1.6 0.91 1.1 54 547918 269912 4.105 0.6 2.6 1.505 2 1.7 2.405 1.36 2.745 1.24 55 548008 269824 3.142 0.7 2.6 0.542 1.9 1.7 1.442 1.29 1.852 1.31 NOTES: Boreholes were not surveyed and coordinates have been digitized d from locations shown on a plan and ground elevations from Environment Agency LIDAR data

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Frimstone Ltd Mitchell Hill Appendix A3 Borehole data

Particle size distribution from boreholes drilled by the Mineral Assessment Unit

TL46NE10 TL46NE15

100 100

90 90

80 80

70 sample depth 70

60 1.8 60 sample depth

50 2.8 50 1.8 2.2 40 3.8 40 4.8 30 30

20 20

10 10

0 0 0.01 0.1 1 10 100 0.01 0.1 1 10 100

TL46NE6 TL46NE8

100 100

90 90

80 80

70 70

60 sample depth 60 sample depth 50 1.7 1 50 40 40 2.5

30 30

20 20

10 10

0 0 0.01 0.1 1 10 100 0.01 0.1 1 10 100

TL47SE10 TL46NE7

100 100

90 90

80 80

70 70

60 sample depth 60 sample depth

50 2.2 50 2.1

40 3.2 40 2.4

30 30

20 20

10 10

0 0 0.01 0.1 1 10 100 0.01 0.1 1 10 100

Client Frimstone Ltd, Title Particle size distributions from Ashcraft Farm, MAU boreholes Main Road, Project Mitchells Hill Crimplesham, Barkers Chambers • Barker Street • Shrewsbury • Drawing 2173/HIA/A3.4 Version 1 United Kingdom • SY1 1SB Norfolk, PE33 9EB E: [email protected] • T: 01743 355 770 Date Jan-18 Scale n/a Frimstone Ltd Mitchell Hill Appendix A3 Borehole data

Borehole logs for groundwater observation borehole

Frimstone Mitchell Hill HIA

APPENDIX 2173/HIA/A4

Groundwater level data

Frimstone Ltd Mitchell Hill Appendix A4 Water level data

Table 2173/HIA/A4.1 Groundwater level monitoring

BH-ID A B C D E F G H

X 547920.7 547502.8 547765.3 548570.7 548889.6 548504.8 548429.5 548271.2

Y 270563.5 270064.1 269948.8 269891.1 270206.4 270624.6 270906.7 271113.2 Ground level 2.69 4.07 4.28 2.77 1.86 2.14 2.11 2

Datum 3.26 4.57 4.76 3.21 2.34 2.6 2.43 2.5 21/09/2016 1.93 1.33 1.94 2.63 1.91 2.85 2.6 0.61 1.99 0.35 1.81 0.79 1.91 0.52 1.48 1.02 04/10/2016 1.98 1.28 2.08 2.49 1.96 2.8 2.61 0.6 1.97 0.37 1.83 0.77 1.95 0.48 1.53 0.97 21/10/2016 1.97 1.29 2.1 2.47 1.98 2.78 2.62 0.59 1.97 0.37 1.85 0.75 1.96 0.47 1.51 0.99 01/11/2016 1.975 1.285 2.155 2.415 2.005 2.755 2.62 0.59 1.99 0.35 1.86 0.74 2.01 0.42 1.51 0.99 16/11/2016 1.86 1.4 1.83 2.74 1.92 2.84 2.605 0.605 1.93 0.41 1.79 0.81 2 0.43 1.26 1.24 01/12/2016 1.8 1.46 1.84 2.73 1.795 2.965 2.55 0.66 1.73 0.61 1.55 1.05 2.015 0.415 1.17 1.33 14/12/2016 1.71 1.55 1.7 2.87 1.68 3.08 2.545 0.665 1.44 0.9 1.456 1.144 1.95 0.48 0.995 1.505 21/12/2016 1.79 1.47 1.82 2.75 1.7 3.06 2.55 0.66 1.285 1.055 1.555 1.045 2.06 0.37 1.24 1.26 11/01/2017 1.72 1.54 1.715 2.855 1.6 3.16 2.54 0.67 1.31 1.03 1.48 1.12 2.05 0.38 1.075 1.425 07/02/2017 1.68 1.58 1.61 2.96 1.43 3.33 2.58 0.63 1.08 1.26 1.46 1.14 1.95 0.48 1.015 1.485 23/03/2017 1.7 1.56 1.63 2.94 1.44 3.32 2.59 0.62 1.11 1.23 1.53 1.07 1.99 0.44 1.2 1.3 27/04/2017 1.78 1.48 1.84 2.73 1.66 3.1 2.51 0.7 1.13 1.21 1.63 0.97 1.71 0.72 1.37 1.13 31/05/2017 1.8 1.46 1.87 2.7 1.75 3.01 2.46 0.75 1.23 1.11 1.7 0.9 1.69 ` 1.4 1.1 07/06/2017 1.845 1.415 1.875 2.695 1.86 2.9 2.4 0.81 1.29 1.05 1.81 0.79 1.625 0.805 1.38 1.12 30/07/2017 1.98 1.28 1.81 2.76 1.96 2.8 2.45 0.76 1.11 1.23 2.06 0.54 1.66 0.77 1.58 0.92 29/08/2017 1.9 1.36 1.885 2.685 1.9 2.86 2.62 0.59 1.3 1.04 2.1 0.5 1.85 0.58 1.38 1.12 28/09/2017 1.88 1.38 1.82 2.75 1.78 2.98 2.67 0.54 2.13 0.47 1.95 0.48 1.385 1.115 25/10/2017 1.92 1.34 1.94 2.63 1.85 2.91 2.67 0.54 2.23 0.37 2.08 0.35 1.475 1.025 28/11/2017 1.9 1.36 1.87 2.7 1.77 2.99 2.66 0.55 2.3 0.3 2.08 0.35 1.48 1.02 20/12/2017 1.76 1.5 1.75 2.82 1.6 3.16 2.65 0.56 2.25 0.35 2.09 0.34 1.3 1.2

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APPENDIX 2173/HIA/A5

Proposed phasing and restoration plans

Drain to prevent flooding from groundwater and surface water

RESTORATION PLAN CP/FRIM/MH04

SITE LAYOUT CP/FRIM/MH03

Frimstone Mitchell Hill HIA

APPENDIX 2173/HIA/A6

Dewatering calculations

Frimstone Appendix 2176/HIA/A6 Mitchell Hill Dewatering estimates

General

The working areas are indicated on Drawing 2176/HIA/A6.1. Elevations of the base of the sand and gravel are shown on Drawing 2176/HIA/A3.2 and assumed groundwater levels on Drawing 2176/HIA/06.

To assess the maximum likely dewatering volume, it has been assumed that two Phase could be open at any time due to the restoration lagging behind the gravel extraction, The largest potential open area would be a combined Phase 2 and 3, assuming no mitigation measures were in place, such as reducing inflow by placing clay against the side of the void.

Phases 2 and 3 have an area of 182,800 m3, which in equivalent to a circle with a diameter of 241 m.

Radius of influence

The extent of the zone of influence of dewatering for the open area can be estimated using the Sichardt equation assuming the excavation is represented by radial flow to a well of an equivalent diameter to the open area.

R0 = C.s.√k

Where C is a constant of 3000 for radial flow, R0 is the radius of influence (m), s the drawdown (m) and k the hydraulic conductivity (as m/s).

The saturated thickness of the sand and gravel varies from 0.35 m to 2.31 m (Table 2173/HIA/A3.1), with an average of 1.18 m.

In the absence of site data, the hydraulic conductivity of that sand and gravel deposit has been estimated from the available literature and estimates from analysis of particle size distribution data.

For this calculation a best estimate of 18 m/d has been used with an upper estimate of 46 m/d.

Substituting these values into the equation gives a radius of influence of 64 m for the maximum hydraulic conductivity of 46 m/d and a radius of 39 m for the best estimate of 18 m/d. These radii are shown on Drawing 2173/HIA/A6.1.

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Frimstone Appendix 2176/HIA/A6 Mitchell Hill Dewatering estimates

Groundwater inflow

Groundwater inflow has been estimated using the Theim equation and by assuming radial flow around a circular void of equivalent area to Phases 2 and 3.

Inflow to the equivalent well is given by:

. ( − ℎ ) = ln[ ]

Where,

Parameter Best estimate maximum Q flowrate = K hydraulic conductivity (m/s) = 2.0E-4 5.3E-4 (18 m/d) (46 m/d) H Initial groundwater head (m) = 1.18 1.18 hw target water level in excavation (m) = 0.25 0.25

R0 re + radius of influence (m) = 39 + 241 64 + 241 re radius of equivalent well (m) = 241 241

For steady-state inflows from the sand and gravel, groundwater inflow rates are estimated to be

• 502 m3/d (5.8 l/s). A best estimate of groundwater inflow based on the mid point of the range of hydraulic conductivity for the sand and gravel of 18 m/d.

• 816 m3/d (9.4 l/s). Estimate of maximum likely groundwater inflow based on the upper range of hydraulic conductivity for the sand and gravel of 46 m/d.

In practice inflow rates will be significantly lower due to various mitigation measures which will reduce the inflows.

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Frimstone Appendix 2176/HIA/A6 Mitchell Hill Dewatering estimates

Rainfall inflow

In the worst case situation, it is assumed that Phases 2 and 3 are open requiring the removal of incident rainfall by pumping. The area of these two phases is 182,800 m2. Average rainfall data are available from the Stretham rain gauge.

Details are shown below.

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Frimstone Appendix 2176/HIA/A6 Mitchell Hill Dewatering estimates

Rainfall ingress Catchment 182,806 m2

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Days 31 28 31 30 31 30 31 31 30 31 30 31 Av rainfall (mm) 43.0 31.9 40.9 40.9 45.9 51.7 41.8 51.1 47.2 50.7 49.5 47.4 Total rainfall (m 3) 7861 5826 7471 7484 8385 9446 7647 9343 8627 9272 9047 8660 Average Daily (m 3) 254 208 241 249 270 315 247 301 288 299 302 279 Flow rate (l/sec) 2.93 2.41 2.79 2.89 3.13 3.64 2.85 3.49 3.33 3.46 3.49 3.23

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