Hydrology and Hydrogeology

HYDROGEOLOGY AND HYDROLOGY 10

CONTENTS Introduction ............................................................................................................ 10-1 Policy Context ........................................................................................................ 10-1 Methodology .......................................................................................................... 10-2

Sources of Information ....................................................................................... 10-3 Baseline Conditions ............................................................................................... 10-4

Geology .............................................................................................................. 10-4 Hydrogeology ..................................................................................................... 10-6 Hydrology ........................................................................................................... 10-9

Assessment of Potential Impacts ......................................................................... 10-11 Summary of Proposed Development ................................................................ 10-11 Potential Impacts on Water Quality ................................................................... 10-11 Potential impacts on Groundwater Flow Regime .............................................. 10-13 Potential Impacts on Hydrological Regime ....................................................... 10-14 Summary of Unmitigated Potential Impacts ...................................................... 10-15

Identification of Appropriate Mitigation Measures ................................................. 10-16 Prevention of Pollution ...................................................................................... 10-16 Surface Water Management Scheme ............................................................... 10-17 Flood Risk Assessment .................................................................................... 10-17

Residual Effects ................................................................................................... 10-18 Conclusions ......................................................................................................... 10-20


Kingswood ERF – Volume 3 10-1 SLR Consulting Limited

INTRODUCTION

10.1 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 Energy Recovery Facility (ERF) which has been described in Section 3, and sets out mitigation measures to ameliorate the identified impacts.

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

10.3 Finally, in accordance with the requirements of Planning Policy Statement 25: Development and Flood Risk, a flood risk assessment (FRA) and outline surface water management scheme are also presented.

POLICY CONTEXT

10.4 The proposals for the development of the application site have had 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. The development of the application site would therefore be in accordance with the following:

Environmental Permitting (England and Wales) Regulations 2007;

Environment Act 1995;

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

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

Control of Water Pollution from Construction Sites SP156 – Guide to Good Practice (CIRIA 2002);

Control of Pollution from Construction Sites C532 – Guidance for Consultants and Contractors (CIRIA 2001);

Code of Practice for Site Investigations, BS5930 or Eurocode 7;

Environmental Good Practice on Site C650 (CIRIA 2005);

CIRIA Report C609 Sustainable Drainage Systems – Hydraulic, Structural and Water Quality Advice, 2004;

Sustainable Urban Drainage Systems – Best Practice Manual. CIRIA Report C523, 2001;

Sustainable Urban Drainage Systems – Design Manual for England and Wales. CIRIA Report C522, 2000

The Sustainable Urban Drainage Systems Manual. CIRIA Report C697, 2007; and

Planning Policy Statement 25: Development and Flood Risk, Published by Department for Communities and Local Government, December 2006.



10.5 The Pollution Prevention Guidelines identified below are the principal documents used for guidance on preventing water pollution and erosion from construction activities 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.

10.6 Relevant planning polices at the national and local level are considered in Section 4 above.

METHODOLOGY

10.7 A qualitative risk assessment methodology has been applied, in which the probability that an impact occurs and the magnitude of the impact, if it were to occur, are considered. These are combined to determine the „Significance‟ of the impact. 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. Mitigation is considered necessary where the significance of the impact is assessed as „medium‟ or higher. The assessment is outlined in Table 10-1 below.

Table 10-1 Matrix used to Identify the Significance of an Impact

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

10.8 The definition of „degrees of magnitude‟ of potential impacts in terms of hydrogeology and hydrology are detailed overleaf in Table 10-2.



Table 10-2 Magnitude of Potential Hydrogeological and Hydrological Impacts

Magnitude Potential Impact

Negligible

No alteration or very minor changes with no impact to watercourses, hydrology, hydrodynamics, erosion and sedimentation patterns; No alteration to groundwater recharge or flow mechanisms; 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 erosion and sedimentation patterns; and Minor changes to the water chemistry.

Moderate

Some fundamental changes to watercourses, hydrology or hydrodynamics; Changes to site resulting in an increase in runoff within system capacity; Moderate changes to erosion and sedimentation patterns; and Moderate changes to the water chemistry of surface runoff and groundwater.

Severe

Wholesale changes to watercourse channel, route, hydrology or hydrodynamics; 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

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

British Geological Survey Sheet 154 – Lichfield (1:63360 Scale) Drift Edition, 1954 reprinted in 1971;

Environment Agency, Policy and Practice for the Protection of Groundwater, Groundwater Vulnerability Map 22 – South Staffordshire & East Shropshire;

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;

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

Environment Agency Information Request, June 2009;

Cannock Chase District Council Information Request, June 2009;

GroundSure report, March 2009;

Various consultancy Site Investigation reports for the site including:

o VHE, Kingswood Lakeside Phase1 Earthworks Report, October 2003; o SESL, Ground Investigation Zone C – Kingswood Lakeside,

November 2003; o Peter Cowsill, Kingswood Lakeside Zone C, Collapse Settlement

Report, January 2008; and o Peter Cowsill, Kingswood Lakeside Zone C, Trial Surcharge Draft

Geotechnical Appraisal, 2009.

Ministry of Agriculture, Fisheries and Food (MAFF), Technical Bulletin 34 Climate and Drainage (1976);

Centre of Ecology and Hydrology (CEH Wallingford), Flood Estimation Handbook CD ROM (2006) (FEH);



Halcrow Group Limited, April 2008, Cannock Chase District Council, Strategic Flood Risk Assessment for Local Development Framework;

Severn Trent Water for details of local public sewerage network; and

Staffordshire County Council for details of the as-built surface water drainage on Kingswood Lakeside Industrial Estate.

BASELINE CONDITIONS

Geology

Regional Geology

10.10 The published geological map1 for the area indicates that the application site is underlain by Boulder Clay, which in turn is underlain by Carboniferous Middle Coal Measures. However the natural geology has been disturbed by historic open cast mining within the application site and surrounding area.

10.11 Open cast mining occurred on site between 1957 and 1972 and is understood to have reached depths of 45m to 55m below ground level (bgl). Overburden was used to infill the mine void by 1977 to 1978. A desk study is presented as Appendix 10/1 which reviewed the geotechnical constraints relating to the development of the application site. The ground improvement and remedial measures discussed in the document were initiated around the time that the report was completed and many of the comments have been addressed.

10.12 This document was used to inform the decision making process regarding the purchase of the site.

10.13 The geotechnical remedial works are on-going at the time of writing with the results indicating a marked improvement in the geotechnical properties of the backfill on which the final development will take place. The current remedial works are due for completion in November 2010.

10.14 An extract of the published geological map is presented as Drawing KW10/1.

10.15 A summary of the geology in the vicinity of the application site is presented in Table 10-3 below.

Table 10-3 Summary of Geology in the Vicinity of the Application Site

Era Unit Description Typical Thickness

Recent Mine Infill

Overburden from open cast mining – sandstone, shale, seatearth and clay

45m-55m

Carboniferous Middle Coal Measures

Cyclic sequences of shale, sandstone,

seatearth, coal and limestone.

200m

1 British Geological Survey Sheet 154-Lichfield (1:63360 Scale) Drift Edition, 1954 reprinted in 1971



10.16 The overburden comprises a mixture of sandstone, shale, siltstone, mudstone, residual soils and clay. Due to the nature of the coal seams and the method of backfill the overburden is very heterogeneous.

10.17 The Coal Measures group comprises cyclic sequences of sandstone, siltstones, limestones and mudstones, with frequent coal seams, residual soil horizons and ironstones.

10.18 The sandstones are typically pale grey and are generally lenticular, passing laterally as well as vertically into siltstones and mudstones. Sandstones associated with the occasional major channels may be up to 20km wide, tens of kilometres long and greater than 8m thick, often cross-bedded with erosive bases, which may be marked by conglomerates. Sandstones associated with minor channels are up to 1km wide, several kilometres long and up to 8m thick and finer grained containing siltstones and mudstones to varying degrees.2

10.19 The grey siltstones and mudstones are typically fine-grained and often ochreous weathered. The sporadic limestones are also fine grained and characteristically marly and are typically found more frequently in the Lower Coal Measures.

10.20 The geology of the area forms a north-south trending anticlinal structure2. The general regional dip of the coal bearing strata is to the north-west3.

10.21 There are no Sites of Special Scientific Interest (SSSI), Special Areas of Conservation (SAC), Special Protection Areas (SPA) or Regionally Important Geological Sites (RIGS) in the vicinity of the application site.

Local Geology

10.22 The application site is located at National Grid Reference (NGR) SJ 994 086 and consists of an historic open cast coal mine which was infilled in the late 1970‟s. The Cannock Canal ran through the north-east of the application site and was excavated in 1962 to 1964 to enlarge the open cast mine.

10.23 The Coal Authority Reports show eleven underground mine workings beneath the application site between 60m and 320mbgl3.

10.24 Due to the depth and nature of the infilled material at the site, settlement and stability issues have been addressed fully. Various studies and intrusive site investigations have been undertaken. The main site investigations3 are mentioned below:

an inundation trial as part of the initial development; a small scale grouting inundation trial May 2006; a large scale grouting and inundation pilot in 2007; and

a rolling surcharge 2008 to 2010.

10.25 As part of the investigations a number of boreholes and piezometers were drilled and in the majority of cases a mixture of pulverised flue ash and water

2 BGS, The physical properties of minor aquifers in England and Wales. Technical Report WD/00/4. 2000

3 SLR Desk Study Options Assessment. October 2008.



was injected via the boreholes into the made ground as grout as part of the mitigation measures.

10.26 As such the site is increasingly anisotropic with regards to porosity and permeability. The rolling surcharge will also have decreased the permeability of the made ground.

10.27 A number of boreholes where drilled on site during the 2003 SESL4 site investigation. All the boreholes recorded made ground to a maximum depth of 39mbgl. Water observed during the site investigation was between 23mbgl and >39mbgl.

10.28 There used to be a former open-cast tailings lagoon in the south-east corner of the application site and this area will typically contain finer fill than the rest of the site, and will therefore have a lower permeability.3

Hydrogeology

Aquifer Characteristics

10.29 The published Groundwater Vulnerability Map5 for the region classifies the geology beneath the application site as a Minor Aquifer (variably permeable). Minor Aquifers can be fractured or potentially fractured rocks which do not have a high primary permeability, or other formations of variable permeability including unconsolidated deposits. They are generally important for local supplies and base flow to rivers.

10.30 The NRA regional appendix6 classifies the Coal Measures as a Minor Aquifer and states “these rocks consist of cyclic sequences of shale, seatearths, sandstones, coals and limestones. Most sandstones are micaceous, lenticular and well cemented and each acts as an independent aquifer. In consequence the yields that can be obtained are very variable, but may be locally important. Springs supporting surface water are common.”

10.31 An extract of the Groundwater Vulnerability map6 is presented on Drawing KW10/2.

10.32 The Environment Agency7 has recently updated the Aquifer classification system. Under the new classification the geology beneath the application site comprises a Secondary A Aquifer – permeable layers capable of supporting water supplies at a local rather than strategic scale, and in some cases forming an important source of base flow to rivers. These are generally aquifers formerly classified as minor aquifers.

10.33 The physical properties of minor aquifers in England and Wales2 book describes the South Staffordshire Coal field as “Impermeable argillaceous rocks predominate in the coal measures group whilst sandstone horizons which could act as aquifers are generally thin, well-cemented and laterally

4 Staffordshire Engineering Services Laboratory, Ground Investigation Zone C, Kingswood Lakeside, November 2003.

5 Environment Agency, Policy and Practice for the Protection of Groundwater, Groundwater Vulnerability Map 22 –

South Staffordshire & East Shropshire (1:100,000 Scale) 6 National Rivers Authority, now the Environment Agency, Policy and Practice for the Protection of Groundwater,

Regional Appendix, Severn Trent Region 7 Environment Agency website, www.environment-agency.gov.uk



impersistant. Both the argillaceous strata and well-cemented sandstones possess minimal primary porosity. Groundwater flow occurs in joints and fractures in the sandstones, often having been enhanced by mining subsidence.” It is also noted that high groundwater yields are possibly due to greater amounts of structural deformation in the vicinity of the Sedgely-Dudley anticline.

10.34 It is noted that the above classifications apply to the Coal Measures. The application site is underlain by 45m-55m of mine infill which has been subject to a series of grouting and stabilisation measures. The infill material will therefore display laterally variable permeability and porosity.

Recharge Mechanisms

10.35 The Flood Estimation Handbook (FEH)8 data indicates that the average annual rainfall at the application site is 699mm.

10.36 The site lies within MAFF Agroclimate9 area 20, which suggest a mean total annual rainfall of 695mm. The reported effective annual rainfall (excess winter rain) varies between 75mm and 405mm per year with an average of 230mm per year.

10.37 The Environment Agency10 has two rainfall gauges in the vicinity of the application site: one at Rodbaston (approximately 7.8km to the west-north-west) and one at Cannock Chase (approximately 8.5km to the north-east of the application site). The data is summarised below in Table 10-4.

Table 10-4 Environment Agency Long Term Average Rainfall Statistics (mm)

Location Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total

Rodbaston 56.9 38.9 43.7 52.3 53.3 62.5 62.7 57.4 58.6 67.2 59.2 64.6 677.4

Cannock Chase

84.2 32.1 42.1 47.7 61.4 59.2 59.6 60.8 62.1 80.8 78.4 77.2 745.4

10.38 The Rodbaston data covers the period October 1985 to August 2009. For the time period January 1986 to December 2008, total annual rainfall ranges between 497mm/year and 900mm/year, with an average annual rainfall of 680mm/year. The minimum monthly rainfall over the period was 0mm in February 1998 and the maximum monthly rainfall was 180.8mm in June 2007.

10.39 The Cannock Chase data covers the period August 2002 to August 2009 although complete data sets are only available for 2003 and 2008. During these years the total annual rainfall was 552mm and 886mm respectively. The minimum monthly rainfall over the period was 6mm in July 2003 and the maximum monthly rainfall was 175mm in August 2004.

8 The Institute of Hydrology, Flood Estimation Handbook (FEH) CD ROM version 2, 2006

9 Ministry of Agriculture, Food and Fishery (MAFF), 1976, Climate and Drainage, Technical Bulletin 34, HMSO,

London 10

Data from Environment Agency Information Request, EA Ref – MC17559 dated 12th August 2009.



10.40 Incident rainfall within the application site would infiltrate preferentially in areas of higher permeability fill. In areas of lower permeability fill material at surface or sub-surface, incident rainfall would preferentially form surface water runoff or shallow seepages. The 2003 VHE Report11 mentions surface water draining off-site through the southern boundary.

Groundwater Levels and Flows

10.41 The Environment Agency has a groundwater monitoring borehole in the area, which is located 3.8km to the west of the application site. The observed groundwater level ranges from 112.40m AOD to 115.51m AOD over the data period (July 1969 to March 2009), with an average of 114.05m AOD. Groundwater levels have generally been recorded between 112.5m AOD to 114.5m AOD since 1990.

10.42 Groundwater flow within the Coal Measures is likely to preferentially occur within the more permeable units, such as sandstones, rather than in the fine grained siltstones and mudstones. However, since the sandstones are typically thin and lenticular with little connectivity, groundwater flow will be influenced by fracture aperture size, frequency, interconnectivity and orientation.

10.43 The groundwater level measurements within the 2003 SESL report4 indicate that groundwater levels beneath the application site are approximately 23m to 40m below ground level.

10.44 The recorded groundwater level at the adjacent Poplars Landfill to the north of the application site is higher and indicates that the groundwater at the application site is depressed3 by approximately 20m. The cause of this localised depression of groundwater levels is believed to be linked to the Coal Authority abstraction which is dewatering the old underground mine workings.

10.45 The 2006 Cowsill Report12 concluded that the maximum potential rebound for the groundwater level beneath the application site would be to a level of 12m bgl to 20m bgl.

10.46 There are no springs noted on the 1:25,000 Ordnance Survey map13 of the area, showing groundwater is typically below ground level.

Source Protection Zones, Groundwater Abstractions, Use and Quality

10.47 The application site does not lie within or near a Groundwater Source Protection Zone (SPZ)7. The closest SPZ is associated with an abstraction within Cannock Chase, the outer boundary of the total catchment area (SPZ III) lies approximately 1.7km to the north.

10.48 Cannock Chase District Council14 is not aware of any private groundwater abstractions within 2km of the application site.

11 VHE, Kingswood Lakeside Phase 1 Earthworks Report, October 2003. 12

Peter Cowsill Ltd (2006), Kingswood Lakeside, Zone C, Collapse Settlement Prevention – Trial Treatment Report. 13

Ordnance Survey, Explorer sheet 244, Cannock Chase & Chasewater, 1:25,0000 scale



10.49 There is one licensed groundwater abstraction reported within 2km of the application site10. Details are presented in Table 10-5 below and the location is shown on Drawing KW10/2.

Table 10-5 Summary of Licensed Groundwater Abstractions within 2km of the Application

Site

Ref Licence Number

Licence Holder

NGR Purpose Source

G1 03/28/03/0253 The Coal Authority

SJ 89630934

Environmental – Transfer Between

Sources

Mid Cannock Colliery Borehole

10.50 The Environment Agency does not monitor groundwater quality in the vicinity of the application site10.

10.51 No groundwater quality data are available for the application site. However, typically groundwater found within the coal measures is of poor quality with generally elevated iron and manganese concentrations due to the mineral composition of the deposits. Groundwater at the application site will also be influenced by the fill as well as the nearby historic workings.

Hydrology

Local Hydrology

10.52 The application site is located to the immediate east of Leacroft Lake, an established local water feature. Several attenuation/settlement ponds associated with the Poplars Landfill site are located to the north of the application site beyond a raised bund. An attenuation pond designed to attenuate runoff from the application site is located to the south, beyond Blakeney Way. Further details of this attenuation pond are provided below.

10.53 There are no surface water courses in the immediate vicinity of the application site. Newlands Brook rises approximately 1.5km north-east of the application site and flows in a southerly direction to a large pond located approximately 500m to the south-east of the application site. Wash Brook enters this pond from a southerly direction. The outlet of the pond is to the west and is known as Wash Brook; this flows beneath the M6 Toll road and continues in a westerly direction passing approximately 500m south of the application site.

10.54 Leacroft Lake appears to be an isolated water body which is not fed by a water course or groundwater, as water levels are approximately 140m AOD (close to ground level).

Abstraction Licenses and Surface Water Quality

10.55 The Environment Agency10 has advised that there are two licensed surface water abstractions within a 2km radius of the application site. Details are presented in Table 10-6 below.

14

Various communications during July/August 2009 with differing departments of the council.



Table 10-6 Summary of Licensed Surface Water Abstractions within 2km of the Application

Site

Ref Licence Number

Licence Holder

NGR Purpose Source

S1 03/28/03/

0122 T Gameson

and Sons Ltd SJ 978089

Industrial, Commercial and Public Services – Process

Water Ridings Brook

S2 03/28/03/

0166 J S Holford &

Sons SK

00850823 Agriculture – Spray Irrigation

- Direct Swan Farm

10.56 The Environment Agency does not monitor surface water quality within the vicinity of the application site and there are no site specific surface water quality data.

Surface Water Flows and Discharge Consents

10.57 The Environment Agency10 has confirmed there are nine licensed discharge consents within a 2km radius of the application site. Details are presented in Table 10-7 and the locations are shown on Drawing KW10/2.

Table 10-7 Summary of Licensed Discharge Consents within 2km of the Application Site

Ref Consent No. Licence Holder

NGR Purpose

D1 T/03/21370/O No. 266

Walsall Road SJ 98860 07221

Sewerage Network – Sewers – water company

D2 T/03/21371/O No. 36 Hilton

Lane SJ 98860 07220


D3 T/03/00250/O Cheslyn Hay SJ 98900 07700 Sewerage - Undefined

D4 T/03/21311/O 103 Walsall

Road SJ 98810 07770


D5 T/03/20196/O Littlewood Pumping Station

SJ 98080 08100 Sewerage Network – Pumping

Station – water company

D6 T/03/11341/T Former Mid

Cannock Colliery

SJ 98640 08900 Reservoir/Borehole Site

D7 T/03/12884/O New

Bridgetown SPS

SJ 97620 08770 Sewerage Network – Pumping

Station – water company

D8 T/03/21298/O Surrey

Close/Devon Road

SJ 98670 09760 Sewerage Network – Sewers –

water company

D9 T/03/22175/S The Fluer De

Lys SK 00880 07300 Sewage disposal works - other

Flood Risk

10.58 A detailed Flood Risk Assessment (FRA) and Surface Water Management Plan have been prepared for the application site and are presented in Appendix 10/2. The FRA has been completed in accordance with guidance presented in PPS25 – “Development and Flood Risk”.



10.59 Review of the Environment Agency‟s Flood Zone Maps confirms that the application site is entirely located within Flood Zone 1 (low probability of flooding). Land within Flood Zone 1 has a less than 0.1% (1 in 1000 year) probability of fluvial flooding in any one year.

10.60 The application site is currently undeveloped and therefore does not benefit from any formal surface water drainage. It is recognised that the proposed development would increase the area of hard standing within the application site and therefore increase the rates and volumes of surface water runoff. In order to ensure there is no increased flood risk off-site, an appropriate surface water management plan is included within the FRA (Appendix 10/2).

ASSESSMENT OF POTENTIAL IMPACTS

10.61 This sub-section identifies the potential impacts of the proposed development on the hydrogeological and hydrological environments. It also assesses the likelihood of occurrence of each identified impact. The results of this assessment are summarised in Table 10-9. It should be noted that the magnitude of the impact has been assessed as described in Table 10-2.

Summary of Proposed Development

10.62 A detailed description of the proposed development of the ERF and operations is provided in Section 3 of this Volume. For the purposes of this section, a summary of the key development aspects which may impact the baseline hydrology and hydrogeology of the site is provided below:

construction and operation of an ERF and associated infrastructure including ancillary buildings, offices, visitor centre etc.;

o hardstanding would be provided to the entrance, weighbridge, car parking and all vehicle movement areas;

o the proposed depth of the bunker is 127.5m AOD (16.5m below the tipping hall floor);

o all process plant and waste handling would be housed within buildings / halls on site. A separate enclosed hardstanding area is proposed for bottom ash storage/recycling; and

o the floor of all buildings would be positively drained in a sealed system to collection tanks on site and/or the foul sewer.

construction and operation of an on site incinerator bottom ash (IBA) recycling facility.

redistribution of surface deposits (mine overburden) to allow construction of the EfW plant and landscaping of the surrounding area;

creation of attenuation pond, reed beds and fire water pond on site; and

Potential Impacts on Ground and Surface Water Quality

10.63 Without the incorporation of mitigation measures the construction and operation of the ERF has the potential to impact on surface water and 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 longer term from



operation of the facility and from the vehicles moving around the site, including the accidental spillage of potentially polluting liquids;

increase in suspended solids during the construction phase resulting from the proposed earthworks;

potential washout of pollutants by fire fighting water in the unlikely event of a fire at site;

potential release of contaminated liquid from the waste bunker, incinerator bottom ash area, fire fighting water storage area or process water; and

the change in land use may result in contaminated runoff from the incinerator bottom ash, weighbridges and vehicle movement areas.

10.64 The probability of groundwater contamination due to a leak or spill of pollutants during construction in the absence of mitigation measures and adherence to the good practice techniques is considered to be ‘low’ due to the thickness of the unsaturated zone and the short time period involved. The magnitude of impact is assessed as being ‘moderate’ to ‘severe’, as the Groundwater Regulations 2009 could be breached. It is noted, however that groundwater is approximately 20m bgl and the unsaturated zone would provide opportunity for retardation and biodegradation. The overall impact is considered to be ‘low’ to ‘medium’.

10.65 The likelihood of surface water contamination due to a leak or spill of pollutants during construction is considered to be ‘medium’ in the absence of mitigation measures and adherence to the good practice techniques. This is due to the proposed discharge of surface water runoff, via the dedicated surface water management scheme, to a local watercourse. The magnitude of impact is assessed as being ‘moderate’ to ‘severe’. The likelihood of suspended solids entering the surface water during construction without mitigation measures is considered to be ‘high’ due to ground disturbance associated with construction. The magnitude of impact is assessed as being ‘moderate’ to ‘severe’. The overall impact is therefore considered to be to ‘medium’ to ‘high’ to surface water quality without the incorporation of suitable mitigation methods.

10.66 The likelihood of contaminated runoff occurring during operation of the site without mitigation measures or good practice techniques is considered to be ‘medium’ to ‘high’ due to the longer time period during which there is a risk. The magnitude of impact is assessed as being ‘moderate’ to ‘severe’, as the Groundwater Regulations 2009 could be breached. The overall impact is therefore considered to be to ‘medium’ to ‘high’. Without appropriate mitigation there is potential for pollutants to enter surface water and groundwater.

10.67 In the event of a fire at site there is potential (if there is no mitigation) for uncontrolled discharge of contaminated water from site which could infiltrate to groundwater or discharge to surface water features off site. The probability of the fire water discharging is considered to be ‘low’. The magnitude of impact is assessed as being ‘moderate’ to ‘severe’. The overall impact is therefore considered to be ‘low’ to ‘medium’ in the absence of mitigation.

10.68 Without appropriate mitigation there is potential for an uncontrolled release of polluting liquid from the waste bunker, incinerator bottom ash area and process water to enter groundwater or surface water. The probability of the



polluting liquid discharging is considered to be ‘low’ to ‘medium’. The magnitude of impact is assessed as being ‘moderate’ to ‘severe’. The overall impact is therefore considered to be ‘low’ to ‘high’ in the absence of mitigation.

10.69 It is also possible that in the short, medium and long term hydrocarbon pollution from untreated runoff associated with roads and car parking areas could cause issues for water quality without suitable mitigation. The risk of pollution entering surface water and groundwater during long term operation is considered to be a ‘high’ probability due to the utilisation of the areas. The magnitude is assessed as ‘moderate’ to ‘severe’ with a ‘high’ significance to water quality without the incorporation of suitable mitigation methods.

10.70 There is a possibility that artifically lowered groundwater levels at the application site may rebound due to the cessation of groundwater dewatering. Should groundwater levels rise to natural levels there is a possibility of changes to groundwater chemistry. Whilst the infill is overburden from the mining operations and therefore the chemistry is likely to be similar to the natural ground, there is a ‘low’ possibility of any rising groundwater mobilising a pocket of potential contaminants with a ‘mild to moderate’ magnitude of impact on groundwater quality. This gives a ‘low’ overall level of groundwater quality risk to the development following any groundwater level rise.

Potential impacts on Groundwater Flow Regime

10.71 Given the site setting it is considered that the proposed development would have a limited impact on the groundwater flow regime for the following reasons:

the limited extent of the site in comparison to the regional extent of the Coal Measures in the area;

the complex layered nature of the Coal Measures Secondary A aquifer;

the on-going nearby Coal Authority groundwater abstraction of the coal measures with groundwater levels currently approximately 20mbgl;

the relatively low permeability of the heterogeneous and anisotropic mine infill with associated existing stability mitigation measures such as grout injection and compaction; and

the depth of the water table in relation to the proposed development.

10.72 It is concluded that the likelihood of occurrence of altering/reducing the groundwater recharge and the local groundwater flow regime due to increased hardstanding and as a result of foundation or waste bunker construction to 16.5m bgl would be ‘negligible’ and the magnitude of impact would be „negligible’ with a corresponding ‘near zero’ level of overall risk.

10.73 The application site is elevated with respect to the local topography, with a sharp topographic fall of approximately 15m in elevation to the south towards the M6 toll road. Therefore, the probability of flooding due to groundwater levels rising if dewatering ceases is considered to be ‘negligible’ and the magnitude of impact to be ‘moderate’. Therefore the overall risk would be considered ‘near zero’.



10.74 In the event that groundwater levels rebound due to the cessation of dewatering, the impact of the proposed development on groundwater flow has been assessed. The likelihood of occurrence of an impact on the natural groundwater flow in the localised area due to the presence of the foundations and waste bunker of the proposed development is ‘medium’ due to the predicted depth the groundwater will rebound to (12-20mbgl12) and the depth of the waste bunker (16.5mbgl). The magnitude of impact is ‘mild’ due to the small footprint of the bunker. Therefore the impact on groundwater flow (should the groundwater rebound) is considered to have a ‘low’ level of overall risk to the development.

Potential Impacts on Hydrological Regime

10.75 The development of the site through the inclusion of impermeable roof and external hardstanding etc. has the potential to alter the local hydrological regime with the potential effects including:

increased quantity and rate of runoff from the site, which may cause localised flooding.

10.76 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 10-8 below.

Table 10-8 Potential Risk Posed by Flooding Sources

Potential Source Potential Flood Risk to Application Site?

Reasoning for Decision

Fluvial/Tidal flooding

No

The site is located within Flood Zone 1 and as such is not considered to be at risk from fluvial flooding. The nearby Leacroft Lake is approximately 140mAOD, it is not linked to any other surface water features. The site topography is approximately 141-145mAOD, and drainage from the site will be linked to the existing surface water attenuation pond (Balancing Pond No. 2) for the Kingswood Lakeside Business Park which is approximately 5m below ground level to the south of the application area.

Flood defence breach (Failure)

No The site is remote from any watercourses protected by flood defences.

Flooding from rising / high groundwater

Yes Groundwater beneath the application site is artificially suppressed by pumping associated with historic coal mining.

Overland flow flooding

No

The application site occupies relatively elevated ground. No off-site catchment area identified. Runoff from restored areas of the adjacent Poplars Landfill will be managed by the landfill‟s surface water management scheme (an elevated bund separates the sites). No issues identified within the Cannock Chase District Council SFRA.



Potential Source Potential Flood Risk to Application Site?

Reasoning for Decision

Flooding from artificial drainage

systems No

Local foul and surface water drainage is to the south of the application site with manhole elevations of approximately 135mAOD, compared with site topography of approximately 145mAOD.

Flooding due to infrastructure

failure No Not applicable.

10.77 It is considered that there is a ‘high’ probability of increased surface water runoff during the short, medium and long term which could cause a ‘moderate to severe’ impact. The significance of this impact has the potential to be ‘high’ if not mitigated against.

10.78 The table highlights the potential of flood risk with regards to rising groundwater. This has already been considered in the groundwater flow impact section and the FRA (Appendix 10/2).

Summary of Unmitigated Potential Impacts 10.79 The unmitigated potential impacts are summarised in Table 10-9 below.

Table10-9

Summary of Unmitigated Potential Impacts

Potential Impact Spatial and Temporal

Impact


Magnitude of Impact

Significance of Impact

Mitigation Required?

Hydrogeological Regime

Contaminated runoff including hydrocarbons and leakage of fuels entering groundwater

Local, Short and Long Term

Low to High Moderate to

Severe Low to High Yes

Leakage from waste bunker into groundwater


Low to Medium

Moderate to Severe

Low to High Yes

Reduction in groundwater recharge and directional change to Groundwater Flow

Regional, Long Term

Negligible Negligible Near Zero No

Flooding due to groundwater rebound

Local, Long Term

Negligible Moderate Near Zero No

Alterations to groundwater flow should rebound occur

Local, Long Term

Medium Mild Low No

Alterations to groundwater quality should rebound occur

Local, Long Term

Low Mild to

Moderate Low No

Hydrology

Contaminated runoff including suspended solids, hydrocarbons and leakage of fuels entering surface waters



Severe Low to High Yes



Potential flood risk to the site


Negligible Negligible Near Zero No, See FRA in Appendix

10/2

Increased rate of runoff from site


High Moderate to

Severe High

Yes, See FRA in Appendix

10/2

Uncontrolled discharge of fire fighting water into groundwater or off-site surface water features


Low Moderate to

Severe Low to Medium Yes

IDENTIFICATION OF APPROPRIATE MITIGATION MEASURES 10.80 Mitigation measures to address the potential impacts detailed above in Table

10-9 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.

10.81 It is considered that the potential for occurrence of pollution of surface water or groundwater by raw materials, fuels, other potentially polluting liquids and contaminated runoff when the site is operational would be limited by good practice techniques.

10.82 A number of operational mitigation measures and best available techniques have been incorporated into the scheme design, which will reduce the potential risk to ground and surface water.

Prevention of Pollution

during construction there would be heavy plant and machinery required on site and as a result it is appropriate to adopt best working practices and measures to protect the water environment, including those set out in the Environment Agency‟s Pollution Prevention Guidance (as detailed in paragraph 10.4 and 10.5 above);

in accordance with PPG02 all on-site fuel and chemical storage would be bunded or if below ground contained within double skinned tanks;

any underground fuel or chemical piping would be either double skinned or laid in concrete ducts;

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; and

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



Surface Water Management Scheme

surface water management would seek to control the drainage from the development using sustainable drainage techniques (SuDS);

it is proposed that where possible rainfall runoff would be harvested for use in on-site processes;

it is proposed that runoff from areas of roof that cannot be harvested would be discharged with attenuation off site;

surface waters within the on site south-east attenuation pond would be discharged off site via surface water ditches to the Kingswood Business Park attenuation pond (Balancing Pond No. 2) south of the site;

it is proposed that runoff from areas of external kerbed hardstanding would be passed through a hydrocarbon and silt interceptor prior to being discharged off site via attenuation to the Kingswood Business Park attenuation pond;

it is proposed that drainage from the waste handling areas would be positively drained to sealed tanks (which would be subject to routine inspection) prior to water re-circulation within the process, any disposal would be to sewer or to tanker for disposal off-site at an appropriately licensed facility;

it is proposed that drainage from the incinerator bottom ash area would be positively drained to a sealed settlement tank (which would be subject to routine inspection) prior to water being discharged to the south-east attenuation pond;

the volume of fire water required would be minimised by the use of targeted fire fighting devices (e.g. sprinklers, mists, inert gases and foams);

water for fire fighting would be kept in a lined pond with an overspill outlet to the south-east attenuation pond;

secondary containment (in accordance with PPG18) would be provided in the south-east attenuation pond;

an emergency shut-off valve and low permeability lining (e.g. engineered clay or similar) would be provided to the south-east attenuation pond so that, in the event of a fire at site fire fighting water can be contained in the SuDS pond.

Flood Risk Assessment

10.83 Measures have been proposed in the site design (detailed in Appendix 10/2)

to manage and control surface water runoff so that development of the site will not pose an increased flood risk to users of the site or downstream land and property.

10.84 It is concluded therefore that with respect to flooding the development would

pose no increased flood risk. 10.85 The effect of the development on flood risk has been assessed separately in

detail in Appendix 10/2. This appendix also includes details of all surface water management mitigation measures proposed at the site and detail above.



RESIDUAL EFFECTS 10.86 Overall, it is concluded that, with respect to groundwater and surface water,

there would be no significant residual impacts associated with the development with incorporation of the above proposed mitigation measures (see Table 10-10 overleaf).


Kingswood ERF – Volume 3 10-19 SLR Consulting Ltd

Table 10-10 Summary of Proposed Mitigation and Residual Effects

Potential Impact Spatial and Temporal

Impact


Magnitude of Impact

Significance of Impact

Proposed Mitigation Measures

Mitigated Probability of Occurrence

Mitigated Magnitude of

Impact

Residual Significance of

Impact

Hydrogeological Regime

Contaminated runoff including hydrocarbons and leakage of fuels entering groundwater



Severe Low to High

Maintenance, traffic management, bunding, separation of waste and

incinerator bottom ash areas with settlement tanks, spill response kits, hydrocarbon

and silt traps etc

Low Low Low

Leakage from waste bunker into groundwater


Low to Medium Moderate to

Severe Low to High Sealed bunker Low Low Low

Hydrological Regime

Contaminated runoff including suspended solids, hydrocarbons and leakage of fuels entering surface waters



Severe Low to High

Maintenance, traffic management, bunding, separation of waste and

incinerator bottom ash areas with settlement tanks, spill response kits, hydrocarbon

and silt traps etc

Low Moderate Low

Increased rate of runoff from site


High Moderate to

Severe High

Adoption of SuDS techniques

Low Mild Low

Uncontrolled discharge of fire fighting water into groundwater or off-site surface water features


Low Moderate to

Severe Low

Targeted fire fighting measures, primary storage

pond and secondary containment in lined lagoon

with shutoff valve

Low Mild to

Moderate Low


Kingswood ERF – Volume 3 10-20 SLR Consulting Ltd

CONCLUSIONS 10.87 The geological environment, coupled with the 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 others as detailed in paragraph 10.9. This information has been supplemented with site specific investigation information.

10.88 The application site consists of an historic open cast coal mine of

approximately 55m depth which has been infilled by overburden. The Coal Board has confirmed there are worked coal seams up to a depth of 320m beneath the site.

10.89 The groundwater is currently artificially lowered at the application site to

approximately 23m-40m below ground level due to Coal Authority dewatering of old mine workings.

10.90 There are no surface water features on the application site although Leacroft

Lake exists to the west of the site. Currently the application site does not benefit from any formal surface water drainage.

10.91 The potential impacts of the proposed development upon the hydrogeological

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

10.92 A flood risk assessment for the proposed development has been prepared.

10.93 Mitigation measures have been proposed to ensure that development and operation of the site would be in accordance with best practice guidance.

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

accordance with best practice guidance.

Documents

Hydrology and Hydrogeology