Environmental Statement Section Template. It is also associated with the Melbourn Rock, due to the greater density of open, well developed discontinuities within these hard brittle

WATER ENVIRONMENT 11

CONTENTS Introduction ............................................................................................................ 11-2 Policy Context ........................................................................................................ 11-2 Methodology .......................................................................................................... 11-3

Sources of Information ....................................................................................... 11-5 Baseline Conditions ............................................................................................... 11-5

Geology .............................................................................................................. 11-5 Hydrogeology ..................................................................................................... 11-6 Hydrology ......................................................................................................... 11-11

Assessment of Potential Impacts ......................................................................... 11-12 Summary of Proposed Development ................................................................ 11-12 Potential Geological Impacts ............................................................................ 11-12 Potential Impacts on Water Quality ................................................................... 11-12 Potential impacts on Groundwater Flow Regime .............................................. 11-13 Potential Impacts on the Hydrological Regime .................................................. 11-14 Summary of Unmitigated Potential Impacts ...................................................... 11-15

Identification of Appropriate Mitigation Measures ................................................. 11-17 Prevention of Pollution ...................................................................................... 11-17 Surface Water Management Scheme & Flood Risk .......................................... 11-18

Residual Effects ................................................................................................... 11-19 Conclusions ......................................................................................................... 11-21


Filching Quarry 11-2 SLR Consulting Limited

INTRODUCTION

11.1 This section of the ES considers the local geology, hydrogeology and hydrology of the application site and surrounding area. In particular, it identifies potential hydrogeological and hydrological impacts associated with the proposed quarry restoration and sets out mitigation measures to ameliorate the identified impacts.

11.2 Unmitigated impacts are considered for the initial assessment assuming that no mitigation is in place, before discussing appropriate mitigation measures and reassessing potential residual impacts. The assessment is based on a detailed baseline description of the local geological, hydrogeological and hydrological regimes.

11.3 In accordance with the requirements of PPS25 – Development and Flood Risk, a Flood Risk Assessment (FRA) and surface water management scheme are also presented as technical appendices to the Environmental Statement (please see Technical Appendix 11 Volume 4).

POLICY CONTEXT

11.4 The proposals for the development of the application site have had due regard to technical guidance, relevant Pollution Prevention Guidelines and other codes of best practice in order to limit the potential for contamination of ground and surface waters, the potential for flooding to be caused by the development, and other potential impacts. This assessment has therefore been completed in accordance with the following guidance:

Environmental Permitting (England and Wales) Regulations 2010;

Environment Act 1995;

the Environment Agency’s (EA) statutory obligations over the management and control of pollution into water;

the Environment Agency’s Groundwater Protection: Policy and Practice (GP3)

EC Water Framework Directive (2000/60/EC);

Flood and Water Management Act 2010;

Eurocode 7 Geotechnical Design – Part 2 Ground Investigation and Testing, BS EN1997/2:2007;

Environmental Good Practice on Site C650 (CIRIA 2005);

The Sustainable Urban Drainage Manual – Best Practice Manual. CIRIA Report C697, 200;

Institute of Hydrology Flood Estimation Handbook CD ROM, Version 3, 2009; and

Planning Policy Statement 25: Development and Flood Risk, Published by Department for Communities and Local Government, March 2010.

11.5 The Pollution Prevention Guidelines identified below are the principal documents used for guidance on preventing water pollution and erosion from construction activities and are produced by the Environment Agency (EA) and are available via the EA’s website (www.environment-agency.gov.uk):



PPG1: General Guide to the Prevention of Pollution;

PPG2: Above Ground Oil Storage Tanks;

PPG3: Use and Design of Oil Separators in Surface Water Drainage Systems;

PPG4: Disposal of Sewage where no Mains Drainage is Available;

PPG5: Works in, Near, or Liable to Affect Watercourses;

PPG6: Working at Construction and Demolition Sites;

PPG8: Storage and Disposal of Used Oils;

PPG18: Managing Firewater and Major Spillages;

PPG21: Pollution Incident Response Planning;

PPG22: Dealing with Spillages on Highways; and

PPG23: Maintenance of Structures over Water.

11.6 Relevant planning polices at the national and local levels are considered in Chapter 4 of this Environmental Statement.

METHODOLOGY

11.7 The methodology applied in the assessment is a qualitative risk assessment methodology, in which the probability of an impact occurring and the magnitude of the impact, if it were to occur, are considered. This approach provides a mechanism for identifying the areas where mitigation measures are required, and for identifying mitigation measures appropriate to the risk presented by the development. This approach allows effort to be focused on reducing risk where the greatest benefit may result. The assessment of risk is outlined in Table 11-1.



Table 11-1 Matrix used to Estimate Risk

Probability of Occurrence

Magnitude of Potential Impacts Severe Moderate Mild

Negligible

High High High Medium Low

Medium High Medium Low Near zero

Low Medium Low Low Near zero

Negligible Low Near zero Near zero Near zero

11.8 The definition of degrees of magnitude of potential impacts in terms of hydrogeology and hydrology are detailed in Table 11-2.

Table 11-2 Magnitude of Potential Geological, Hydrogeological and Hydrological Impacts

Magnitude Examples of Potential Impacts

Negligible No impact or alteration to existing important geological environs; No alteration or very minor changes with no impact to watercourses, hydrology, hydrodynamics, erosion and sedimentation patterns; No alteration to groundwater recharge, flow mechanisms or water levels; and No pollution or change in water chemistry to either groundwater or surface water.

Mild Some loss of soils with no long term impact; Minor or slight changes to the watercourse, hydrology or hydrodynamics; Changes to site resulting in slight increase in runoff well within the drainage system capacity; Minor changes to groundwater recharge, flow mechanisms or water levels; Minor changes to erosion and sedimentation patterns; and Minor changes to the water chemistry.

Moderate Slope failure or instability which may cause foundation problems, loss of extensive areas of peat or agricultural soil, damage to important geological structures/features; Some fundamental changes to watercourses, hydrology or hydrodynamics; Changes to site resulting in an increase in runoff within system capacity; Moderate changes to groundwater recharge, flow mechanisms or water levels; Moderate changes to erosion and sedimentation patterns; and Moderate changes to the water chemistry.

Severe Slope failure or instability which causes loss of life, permanent degradation and loss of important geological feature. Wholesale changes to watercourse channel, route, hydrology or hydrodynamics; groundwater flow regime or water levels; Changes to site resulting in an increase in runoff with flood potential and also significant changes to erosion and sedimentation patterns; and Major changes to the water chemistry or hydro-ecology.



Sources of Information

11.9 The following sources of information have been consulted in order to investigate the hydrogeology and hydrology of the application site and surrounding area:

Ordnance Survey, 1:50,000 Landranger Sheet 199 Eastbourne & Hastings;

Landmark Information Group Ltd (Landmark), Envirocheck Report 31821772_1_1, 9th July 2010;

results of a site investigation completed by SLR Consulting Limited at Filching Quarry in November 2010;

Environment Agency (EA) website (www.environment-agency.gov.uk) for details of river quality, groundwater source protection zones and flooding;

British Geological Survey (BGS) 1:50,000 scale Sheet 334 Solid & Drift (Eastbourne);

British Geological Survey (BGS) 1:50,000 scale Sheet 319 Solid & Drift (Lewes);

Hydrogeological Map of South Downs and part of the Weald. 1:100,000 BGS 1978;

National Rivers Authority, Policy and Practise for the Protection of Groundwater, Groundwater Vulnerability Sheet 46 East Sussex (1:100,000);

Institute of Hydrology Flood Estimation Handbook CD ROM, Version 3, 2009;

MAFF (1975): Climate and Drainage Technical Bulletin 34;

Wealden District Council1 and the Eastbourne Borough Council2 for details of private water abstractions;

discussions with South East Water;

British Geological Survey, The Physical Properties of Minor Aquifers in England and Wales, Technical Report WD/00/04, Environment Agency R & D Publication 68, 2000;

site specific infiltration testing (January 2011); and

site visit by an experienced hydrogeologist.

BASELINE CONDITIONS

Geology

Regional Geology

11.10 Review of the published geological maps confirms that Filching Quarry is developed within the Cretaceous Chalk. Extracts from the geological maps are shown on Drawing No. 11-1. The stratigraphy of the site is summarised in Table 11-3 and discussed below.

1 Telephone conversation with Richard Finton, Environmental Health Officer for Wealden

District Council on the 12th July 2010.

2 Email from Julie Huckling, Environmental Heath Department, Eastbourne Borough Council

on 12th July 2010



Table 11-3 Site Stratigraphy

Age Formation Unit Typical

Thickness Typical Description

Cretaceous

Middle Chalk

Middle Chalk (generic)

Up to 65m

Massive, hard, well-jointed, white or yellowish, thickly

bedded chalk with occasional/rare nodular beds

Melbourn Rock 4-6m Hard, creamish coloured

nodular marl bed

Lower Chalk

Plenus Marls 3m

Thin sequence of alternating chalk and marl. Slightly greyish

green very marly beds.

Lower Chalk (generic)

Approx. 60m

Massive off-white, marly Chalk with interbedded thin marl

partings.

11.11 The published geological maps indicate that the quarry extends down through the Middle Chalk, Melbourn Rock, Plenus Marls and Lower Chalk succession, with the Lower Chalk in the quarry base.

11.12 The site lies on the southern limb of the regional Wealden anticlinal structure. The bedrock strata generally dip to the south-south-west. The geological map does not show any major faults within the vicinity of the site.

11.13 The SLR Site Investigation in November 2010 found that the Lower Chalk within the quarry was weak to moderately strong cream coloured chalk which weathers with mechanical friction to a clayey texture. The site investigation factual report is included as Appendix 11/1.

Hydrogeology

Aquifer Characteristics

11.14 The Cretaceous Chalk is classified by the Environment Agency as a principle aquifer3. Principle aquifers are described as “layers of rock or drift deposits that have high inter-granular and/or fracture permeability – meaning they usually provide a high level of water storage. They may support water supply and/or river base flow on a strategic scale.”

11.15 The soils in the vicinity of the site are classified by the Environment Agency4 as High Leaching Potential – “Soils which readily transmit liquid discharges because they are either shallow, or susceptible to rapid flow directly to rock, gravel or groundwater”.

3 Environment Agency website, visited 8

th July 2010, www.environment-agency.gov.uk.

4 Environment Agency, 1996: Policy and Practice of the Protection of Groundwater.

Groundwater Vulnerability Map Sheet 46 East Sussex.



11.16 The published regional hydrogeological map5 for the area and the Major Aquifer Properties Manual6 indicate the following about the Cretaceous Chalk:

porosity is typically between 20 and 35% for the Middle Chalk and between 9.7-46.5%, for the Lower Chalk;

permeabilities for the matrix average 6.3x10-4m/day, which is extremely low, and it can be inferred that the permeability of the Chalk matrix (i.e. intrinsic permeability) is negligible with respect to the permeability of the chalk fracture systems;

transmissivity values vary from less than 16m2/d to 9,500m2/d where fissures are open and well developed. Typically transmissivity lies in the range 230 to 1,600m2/d.

11.17 Given the low intrinsic permeability of the Chalk, as noted above, the majority of groundwater flow takes place through discontinuities (fractures, fissures and bedding planes) typically associated with the harder Chalk horizons. Groundwater flow is also increased within the valley features, due to the typically greater density of discontinuities and solution features.

11.18 The greatest permeability in the Chalk is typically found in the zone of water table fluctuation, where dissolution can enhance the apertures of the discontinuities. It is also associated with the Melbourn Rock, due to the greater density of open, well developed discontinuities within these hard brittle beds.

11.19 Due to the higher permeability of the Melbourn Rock and the low permeability of the underlying Plenus Marl, springs often occur at the outcrop of the Melbourn Rock / Plenus Marl interface.

11.20 Permeabilities obtained from the 2010 Site Investigation illustrate a range between 1.17x10-5 and 2.10x10-4m/sec.

Recharge Mechanisms

11.21 Filching Quarry lies within MAFF Agroclimate Area 38S7, which indicates that the long term average annual rainfall is 836mm with a range of 750mm to 910mm.

11.22 The effective rainfall, reported by MAFF as winter excess rain, is 330mm per annum. This represents the amount of rainfall that is available for surface run-off, underdrainage and deep seepage.

5 British Geological Survey, 1978. Hydrogeological Map of the South Downs and Adjacent

Parts of the Weald. Scale 1:100,000. 6 British Geological Survey, 1997. The physical properties of major aquifers in England and

Wales. Technical Report WD/97/34. 7 Ministry of Agriculture, Fisheries and Food (MAFF), 1975, Technical Bulletin 34 – Climate

and Drainage.



Groundwater Levels and Flows

11.23 The Hydrogeological map for the region indicates that the site is located close to the regional groundwater divide of the Chalk aquifer, which is orientated in a north-west to south-east direction. An excerpt from the Hydrogeological map is shown in Drawing No. 11-2.

11.24 The locations of the boreholes installed as part of the November 2010 Site Investigation are shown on Drawing 11-4 and hydrographs are included in Appendix 11/2.

11.25 The groundwater monitoring data gathered between November 2010 and January 2011 for the Chalk monitoring boreholes installed at the application site ranged in elevation between 39.9mAOD in borehole BH A/10 and 34.87mAOD in borehole BH C/10. The lowest point of the quarry floor lies at c.43mAOD, indicating that during this period groundwater elevations were below the quarry base. Anecdotal evidence suggests that the base of the quarry void can contain minor ponded surface water on occasions during the winter months. It is possible that this ponded surface water may also include a minor groundwater component reflecting seasonally high groundwater levels lying just above the quarry base. However, during the majority of the year the base of the quarry is dry. Groundwater flow direction is towards the north-east, as illustrated on Drawing No. 11-4.

11.26 Groundwater monitoring data collected since 1977 from three Chalk boreholes, located at Jevington GWTW, Folkington Old Rectory and Deep Dean BH No.2, have been provided by the Environment Agency. These monitoring locations are shown on Drawing No. 11-3 and hydrographs are presented within Appendix 11/3. These monitoring data indicate the following:

Jevington GWTR (located c.1.4km to the south): Groundwater elevations range between c.28 and 64.5mAOD. (Datum: 74.55mAOD)

Folkington Old Rectory (located c.1km to the north-north-west): Groundwater elevations range up to c.44.5mAOD and also extend below the basal elevation of the borehole at c. 29.9mAOD. (Datum 65.71mAOD).

Deep Dean Borehole (located c.2.6km to the west-south-west: Groundwater elevations range between c.9 and c.24.6mAOD. (Datum 53.28mAOD).

11.27 Water levels at these three locations show a wide range that is likely to reflect both seasonal variations in addition to drawdown influences from the large public groundwater abstractions in the vicinity.

Source Protection Zones, Groundwater Abstractions, Use and Quality

11.28 Groundwater quality data for the three Chalk monitoring boreholes installed at the application site in November 2010 indicate groundwater quality is good quality and typically lies within UK Drinking Water Standards, although elevated ammoniacal nitrogen has been detected with a maximum of 6.4mg/l



in BH B/10. No Hazardous Substances have been detected within these three monitoring boreholes. Groundwater quality data is included in Appendix 11/4.

11.29 A total of three licensed abstractions have been identified within a 2km radius of the site, of which one is from surface water8. The abstraction locations are shown on Drawing No. 11-3 and are summarised in Table 11-4, below.

11.30 The application site is located within the total catchment of a Groundwater Source Protection Zone (SPZ), which is associated with seven public abstractions operated by South East Water Plc that are located to the north-east, south-south-west, south and south-east, as shown in Drawing No. 11/3. Licence details for these abstractions provided by the Environment Agency are included within Appendix 11/5.

11.31 The edge of the nearest outer SPZ, which is associated with the Filching Pumping station (Filching Shaft No. 2 – see Table 11-4, below), is located approximately 290m to the north-east of the application site. The edge of the inner SPZ associated with the same abstraction is located approximately 375m to the north-east of the application site. South East Water has confirmed that this abstraction comprises an adit system within the Chalk bedrock to the north-west of the Filching Pumping Station.

11.32 Historically, groundwater abstracted from the Filching Pumping Station adit system (Filching Shaft No. 2 – see Table 11-4, below) has been pumped to the Crane Down service reservoir, located approximately 340m to the north-east of the application site, form where the water has been gravity fed to the distribution system.

11.33 It is understood9 that this abstraction is not currently in use due to water quality problems (cryptosporidium) associated with livestock grazing on the Chalk catchment area. It is also understood that it is very unlikely that this abstraction will be used to help meet public water supply requirements by South East Water in the future due to the water quality problems.

11.34 It has been confirmed with the Wealden District Council10 and the Eastbourne Borough Council11 that there are no private water abstractions within 2km of the application site.

11.35 There are two discharge consents within a 2km radius of the site and these are summarised in Table 11-5, below and shown on Drawing No 11-3.

8 Envirocheck Report, July 2010.

9 SLR telephone conversation with Phil Harpen of South East Water on 1

st September 2010.

10 Telephone conversation with Richard Finton, Environmental Health Officer for Wealden

District Council on the 12th July 2010.

11 Email from Julie Huckling, Environmental Heath Department, Eastbourne Borough Council

on 12th July 2010


Filching Quarry – Volume 3 11-10 SLR Consulting Limited

Table 11-4

Licensed Abstractions within a 2km Radius of Filching Quarry

ID (Drawing No. 11-3)

Name of Holder

Licence Number

Grid Reference

Distance from Site

Source Purpose

Permitted Annual Yield

(m3/year)

Filching Shaft No. 2

South East Water Plc

10/41/151301

556980 103130

541m

Filching Shaft No. 2 Chalk

Groundwater

Public Water Supply – Potable Water Supply – Direct

Abstraction now ceased due to Cryptosporidium

problems.

10364880 (combined

licence including 5 other Chalk groundwater abstractions.

Filching Shaft No. 1

556830 103540

727m

Filching Shaft No. 1 Chalk

Groundwater

Public Water Supply – Potable Water Supply – Direct

Abstraction now ceased due to Cryptosporidium

problems.

S1 South East Water Plc

151301D 556830 103535

722m Surface Water –

Pond or Lake Additional Purpose: Public

Water Supply

Note: Information obtained from Landmark Envirocheck Report, July 2010.

Table 11-5

Discharge Consents within a 2km Radius of Filching Quarry

ID (Drawing No. 11-3)

Name of Holder

Reference Number

OS Grid Reference

Distance from Site

Receiving Water Discharge Type

D1 Mr D Vassie & Mrs W Baxter

P11930 556230 102990

132m Land/Soakaway Final Treated Effluent –

Not water company

D2 Mr & Mrs Bates P12522 556520 103040

139m Land/Soakaway Final Treated Effluent –

Not water company

Note: Information obtained from Landmark Envirocheck Report, July 2010



Hydrology

11.36 The proposed development lies on the east - west watershed of the South Downs, close to the northerly scarp slope.

11.37 The proposed development is located near the head, and on the northern side, of a ‘dry valley’ which extends in a generally south-west to north-east direction within the northerly scarp, dropping in elevation to the north-east.

11.38 Other dry valleys are present within the northerly scarp, and also to the south of the proposed development. These features reflect the high permeability of the underlying Chalk which prevents the development of permanent surface water features within these valleys.

11.39 The Ordnance Survey (OS) mapping indicates that there are no surface water drainage features within 200m of the proposed development. The closest identified surface water feature on the OS map is located approximately 250m to the north-east near a reservoir located on Crane Down. A second surface water feature, possibly a small pond, is identified near Filching Manor, approximately 425m east-north-east of the proposed development. Both these surface water features are isolated from the main drainage system with the Eastbourne area.

11.40 The closest permanent surface water drainage features are associated with the east-south-east to west-north-west spring line, located to the north-east of the proposed development. At its closest point the spring line is located c.500m to the north-east near Filching Manor and former Filching Shaft No.2 public abstraction. The spring line corresponds with the Gault Clay/Lower Chalk contact running along the foot of the South Downs northerly scarp slope. These springs flow in a north-easterly direction and join the drainage system within the Eastbourne area.

Flood Risk

11.41 A detailed assessment of the flood risk to the site is presented in Appendix 11/6. The Flood Risk Assessment has been completed in accordance with guidance set out in PPS25 (2010).

11.42 The Environment Agency’s Flood Zone Maps indicate the entire site to be located within Flood Zone 1, which represents an annual probability of less than 0.1% of a flood occurring in any one year.

11.43 Table D.3 of Planning Policy Statement 25: Development and Flood Risk (PPS25) sets out that the proposed landfill is designated as a ‘more vulnerable’ use and is appropriate in Flood Zones 1 and 2. The proposed development is therefore in accordance with the requirements of the Sequential Test as set out within PPS25.

11.44 The application site is currently an open quarry and does not benefit from any formal surface water drainage. It is recognised that the proposed development would decrease the area of current storage potential within the



application site and therefore increase the volume of surface water runoff from the site. However, the long term (restored) surface water runoff rates will not be significantly greater than those prior to site development. It is, however, proposed that enhanced management of excess surface water runoff would be provided within the site to ensure no increase in off-site runoff rates or flood risk to the site or third party land. Details are included within the FRA (refer to Appendix 11/6).

ASSESSMENT OF POTENTIAL IMPACTS

11.45 This sub-section identifies the potential impacts of the proposed development on the geological, hydrogeological and hydrological environments and via risk assessments, establish whether or not those impacts are significant.

11.46 It also assesses the likelihood of occurrence of each identified impact. The results of this assessment are summarised in Table 11-7. It should be noted that the magnitude of the impact has been assessed as described in Table 11-2.

Summary of Proposed Development

11.47 A detailed description of the proposed development is presented in Section 3 above; in summary, the proposed development includes the following:

inert materials imported into the siite will be used to stabilise the sideslopes of the quarry;

once stabilisation has been achieved, an inert landfill will be constructed within the remaining void, and infilled in order to restore the quarry site;

the base and sideslopes of the inert landfill will include an engineered mineral liner.

Potential Geological Impacts

11.48 Site investigations have indicated that the proposed development footprint is underlain by Lower Chalk, while Middle Chalk, Melbourn Rock, Plenus Marls and Lower Chalk strata are present within the quarry side walls. Therefore there are no impacts related to loss of soils.

11.49 This section does not consider the stability risks associated with the development; however it is noted that a stability risk assessment has been completed to assess impacts of the proposed development on the side slope stability of the application site (please Technical Appendix 12, Volume 4)

Potential Impacts on Water Quality

11.50 Without the incorporation of mitigation measures the construction and operation of the proposed development has the potential to impact on



groundwater quality. This would be from the risk of contaminated runoff being generated from the following potential sources:

accidental spillage of raw materials, fuels and lubricants, required over the short term by construction plant and over the medium term from operation of the facility;

potential release of contaminated liquid from waste deposited in the landfill that is not truly inert;

increase in suspended solids; and

contaminated runoff from vehicle movement areas.

11.51 It is considered that in the short to medium term the likelihood for untreated runoff associated with roads and landfill areas from leaving the site and entering the Chalk groundwater is medium’ to ‘high’ unless appropriate mitigation measures are employed. The magnitude of impact under these conditions is assessed as ‘moderate to ‘severe’, as the Environmental Permitting Regulations could be breached. The overall impact is therefore considered to be a ‘medium’ to high’ significance to water quality. Therefore mitigation measures are proposed as discussed below.

11.52 The absence of any surface water features within the vicinity of the site, and the presence of the underlying Chalk aquifer with its associated relatively high permeability, would prevent any untreated runoff associated with the application site from reaching surface waters. Mitigation measures are however proposed as an additional safeguard, as discussed below.

11.53 Unless appropriate mitigation measures are employed with regard to the operation and design of the inert landfill, there is potential for impacts on groundwater quality due to possible leachate generated from waste accidently accepted at the site which is not truly inert. The potential receptors for these impacts are the groundwater abstractions and groundwater fed surface water drainage systems downstream of the application site. Given the nature of the inert waste stream, without mitigation the probability of occurrence is considered to be ‘negligible’ to ‘low’, while the magnitude of impact could be ‘moderate’ to ‘severe’ with a corresponding ‘near zero’ to ‘medium’ level of overall risk. Mitigation measures are therefore considered necessary, as detailed below.

Potential impacts on Groundwater Flow Regime

11.54 Under current conditions the base of the quarry lies above the active groundwater system within the Chalk aquifer. Available information indicates that the large public groundwater abstractions located to the south-south-west, south and south-east, as shown in Drawing No. 11-3, could potentially influence groundwater elevations should these abstractions cease. However, given the substantial distances between the application site and these abstractions, together with the site setting, it is considered that the likelihood of occurrence of altering the groundwater flow regime as a result of the proposed development and possible rise in groundwater elevations due to changes in operating regime of the public abstraction boreholes can be assessed as ‘negligible’. This assessment takes into consideration the small footprint of the application site compared to the surrounding Chalk



catchments, and the high permeability of the Chalk bedrock, which would prevent any significant groundwater damming effects should Chalk groundwater elevations rise above the base of the proposed development. The magnitude of impact is assessed as ‘negligible’ with a corresponding ‘near zero’ level of overall risk. No mitigation measures are therefore required.

11.55 The likelihood of occurrence of significantly altering or reducing the groundwater recharge within the landfill footprint would be ‘negligible’, given the small footprint of the proposed development compared to the extensive area of the regional Chalk aquifer. Also, effective rainfall generated on the inert landfill would ultimately enter the underlying groundwater within the Chalk aquifer following infiltration. The magnitude of impact is assessed as ‘negligible’ with a corresponding ‘near zero’ level of overall risk. No additional mitigation measures are therefore required.

Potential Impacts on the Hydrological Regime

11.56 The development of the site has the potential to significantly alter the local hydrological regime, possibly resulting in locally increased surface water runoff rates and volumes arising from increased topographical relief and the import of materials with a higher runoff coefficient than that of the natural chalk grassland which predominates the wider area.

11.57 As noted above, the absence of any surface water features within the vicinity of the site, and the presence of the underlying Chalk aquifer with its associated relatively high permeability, would likely prevent runoff associated with the application site from reaching surface waters with no consequent impacts on their hydrological regimes arising from development proposals.

11.58 Any localised increased surface water runoff would be expected to drain into the underlying Chalk bedrock, which has been confirmed by infiltration testing carried out at the site – refer to Appendix 11/6 - to exhibit high infiltration potential on the south-eastern site boundary (lowest topographical point within the site once the quarry has been infilled and restored).

11.59 Measures are proposed to mitigate potential increases in surface water runoff rates and volumes and to prevent increased flood risk at the site or to third party land. These include intercept drainage, attenuation storage and infiltration. This is discussed in greater detail below and within the Flood Risk Assessment located at Appendix 11/6.

11.60 A summary of the potential sources of flooding and a review of the potential risk posed by each source at the application site is presented in Table 11-6 below.

Table 11-6

Potential Risk Posed by Flooding Sources

Potential Impact

Potential Flood Risk

to Application

Reasoning for Decision



Site

Fluvial / Tidal Flooding No. The site is located within Flood Zone 1 and as such is not considered to be at risk from fluvial

or tidal flooding.

Flood defence breach (Failure)

No The site is remote from any watercourses

protected by flood defences.

Flooding from rising / high groundwater

No

Anecdotal evidence suggests that the base of the quarry void can contain minor ponded

surface water on occasions during the winter months. This is slow to drain due to

compaction of the quarry floor and the presence of silts within this chalk layer,

although it is also possible that there may also be a minor groundwater component reflecting

seasonally high groundwater levels. During the majority of the year the base of the quarry is

dry.

Overland flow flooding Yes

Potential overland flow originates from surface water runoff discharged from restored areas

and from elevated landform to the north of the site post-restoration.

Flooding from artificial drainage systems

No No utility pipelines or water storage structures

are found within the vicinity of the site. Flooding due to infrastructure failure

No

11.61 It is considered that there is a ‘high’ probability of increased surface water runoff post restoration which could cause a ‘moderate’ impact. The significance of this impact has the potential to be ‘high’ without mitigation.

Summary of Unmitigated Potential Impacts

11.62 The unmitigated potential impacts are summarised in Table 11-7 below.

Table 11-7 Summary of Unmitigated Potential Impacts

Potential Impact

Spatial and

Temporary impact

Probability of

Occurrence

Magnitude of Impact

Significance of Impact

Mitigation Required

Water Quality Contaminated runoff (fuels and polluting liquids) entering groundwater

Local, Short to Medium

Term Medium to High

Moderate to Severe

Medium to High Yes

Leakage of potential leachate from the inert waste to groundwater

Local, Short to Long Term

Negligible to Low

Moderate to Severe

Near Zero to Medium

Yes

Groundwater Flow Regime Alteration of


Negligible Negligible Near Zero No



groundwater flow regime due to footprint of application site

Reduction of groundwater recharge


Negligible Negligible Near Zero No

Hydrological Flow Regime & Flooding Overland flow flooding from surface water runoff

Local, Long Term

High Moderate High Yes

Flooding from other sources

Local, Long Term

Negligible Moderate Near Zero No



IDENTIFICATION OF APPROPRIATE MITIGATION MEASURES

11.63 Mitigation measures to address the potential impacts detailed above in Table 11-7 are described below. These measures either reduce the likelihood of an event occurring, or reduce the magnitude of the consequences if the event does occur. It should be noted that several of the mitigation measures proposed below would have a positive effect on more than one potential impact.

11.64 A number of operational mitigation measures and best available techniques

have been incorporated into the scheme design, which would reduce the potential risk to ground and surface water.

11.65 Implementation of the mitigation measures described below would lead to a ‘near zero’ to low’ level of overall risk.

Prevention of Pollution

11.66 The following pollution prevention measures would be required:

during construction there would be heavy plant and machinery required on site. As a result, best working practices and measures to protect the water environment would be adopted, including those set out in the Environment Agency’s Pollution Prevention Guidance (as detailed in paragraph 11.5 above);

in accordance with PPG02 all on-site fuel and chemical storage would be bunded and located above ground;

an emergency spill response kit would be maintained on site;

a vehicle management system / road markings would be put in place wherever possible during construction and operation to reduce the potential conflicts between vehicles and thereby reduce the risk of collision;

a speed limit would be enforced on site to reduce the likelihood and significance of any collisions;

all soils would be stored in accordance with the relevant guidance (such as PPG1, PPG5 and PPG6). Where necessary, ditches would be cut to capture runoff from areas generating clay and silt laden runoff to allow for settlement of fines (clay and silt fractions) prior to infiltration into the Chalk. These ditches would be sized accounting for the requirements of PPS25: Development and Flood Risk;

the source of all inert materials for stabilisation of the quarry sides, landfill construction and restoration would be known, and confirmed to be uncontaminated prior to acceptance at the site;

the inert landfill design would be in accordance with the Landfill Directive and would include a sidewall and basal geological barrier;

the landfilling using ‘inert waste’ would be carried out under the auspices of an Environmental Permit for an Inert Landfill; and

the inert waste brought to site would be carefully inspected prior to tipping, in order to ensure that it was inert. The waste streams would also be confirmed to be inert by a strict regime of testing to ensure that they met the Waste Acceptance Criteria for inert wastes.



11.67 It is noted that a quantitative Hydrogeological Risk Assessment would also be required in support of the Environmental Permit application for the proposed landfill at the site. The HRA would:

need to be accepted by the Environment Agency prior to approval of the Environmental Permit;

demonstrate that even under the unlikely instance that a rogue load of waste is accepted at the site, the site would remain compliant with the Environmental Permitting Regulations 2010; specifically that the site would not result in Hazardous Substances entering groundwater nor in the introduction of Non-hazardous Pollutants so as to cause pollution;

outline Essential and Technical Precautions to ensure the site accepts only inert wastes; and

identify a programme of requisite surveillance measures that would allow the performance of the site to be judged against the conclusions of the HRA, to ensure that the installation remains in compliance with the Regulations. These would include a groundwater monitoring plan and identification of appropriate groundwater trigger and control levels

Surface Water Management Scheme & Flood Risk

11.68 The effect of the development on surface water flood risk has been assessed separately in detail in Appendix 11/6.

11.69 In order to mitigate flood risk from surface water sources the following surface water management measures are proposed at the site:

surface water attenuation storage (203m3) sized to accommodate surface water runoff from return period rainfall events up to and including 100 years;

intercept drainage designed to convey surface water runoff from the site to the storage area and sized to accommodate runoff rates from return period rainfall events up to and including 30 years;

overland flowpaths to convey surface water runoff from the site to the storage area for return period rainfall events between 30 and 100 years;

30% uplift in peak rainfall intensity and volume has been included in the sizing of all surface water conveyance and storage areas to account for climate change;

infiltration measures for the disposal of surface water runoff from site in accordance with the use of sustainable drainage techniques (SuDS) wherever practicable;

intercept drainage to prevent off-site impacts on the surface water runoff regime at the application site; and

flow control measures within the site, including bunds to slow the flow of surface water runoff. This serves a dual purpose slowing flows and increasing sedimentation upstream of the storage area, whilst containing water within the site and maximising the infiltration potential within the surface water storage area.

11.70 The above measures are set out in greater detail in the Site Specific Flood Risk Assessment located at Appendix 11/6.



RESIDUAL EFFECTS

11.71 Overall, it is concluded that with incorporation of the proposed mitigation measures, there would be no significant residual impacts arising from the proposed development with respect to geology, groundwater and surface water.

11.72 A summary of the residual effects and the proposed mitigation measures are presented overleaf in Table 11-8.



Table 11-8 Summary of Proposed Mitigation and Residual Effects

Potential Impact Spatial and Temporal

Impact

Probability of

Occurrence

Magnitude of Impact

Significance of Impact

Proposed Mitigation Measures

Mitigated Probability

of Occurrence

Mitigated Magnitude of Impact

Residual Significance

of Impact

Water Quality

Contaminated runoff (fuels and polluting

liquids) entering groundwater

Local, Short to Medium Term

Medium to Medium

Moderate to Severe

Medium to High

Inspections, maintenance, interceptors, traffic

management system, spill response plan, bunding, SuDs, discharge controls

etc.

Negligible Moderate to

Severe Near Zero to

Low

Leakage of potential leachate from the inert waste to groundwater


Negligible to Low

Moderate to Severe

Near Zero to Medium

Landfill design in accordance with the

Landfill Directive, to include basal and sidewall geological barriers.

Negligible Moderate to

Severe Near Zero to

Low

Hydrological Regime & Flooding

Overland flow flooding from surface water

runoff

Local, Long Term

High Moderate High

Surface water management system to include incept drainage

channels and an infiltration basin

Negligible Moderate Near Zero to

low



CONCLUSIONS

11.73 The geological, groundwater and surface water regimes at the application site have been assessed with reference to information held by the British Geological Survey, the Environment Agency, Local Authorities and South East Water Plc. This information has been supplemented with site specific investigation information and a site walkover survey.

11.74 The potential impacts of the proposed development upon the geological,

hydrogeological and hydrological environment have been identified and assessed, and where appropriate, mitigation measures have been incorporated into the design of the development.

11.75 All aspects of the construction and operation of the site would be in

accordance with best practice guidance.

11.76 It is concluded that with incorporation of the proposed mitigation measures,

there would be no significant residual impacts arising from the proposed

development with respect to geology, groundwater and surface water.

Documents

Environmental Statement Section Template. It is also associated with the Melbourn Rock, due to the greater density of open, well developed discontinuities within these hard brittle