Veolia ES Staffordshire Limited Project W2R: Energy Recovery Facility
12 Water Resources
12.1 Introduction
12.1.1 This ES Chapter determines the potential impacts on surface water and groundwater receptors, together with the flood risk associated with the proposed development of the ERF.
12.1.2 This ES Chapter draws upon and reviews the assessment and conclusions of the ES chapter on water resources prepared by Enviros in 2008 for the consented EfW facility, together with comments received and consultation responses ahead of the planning determination and in response to the scoping of the current ERF planning submission.
12.1.3 Consideration is given to potential impacts on surface water and groundwater hydrology and water quality, flood risk and surface water drainage during construction and operation of the proposed development. The need for site specific mitigation measures to protect the water environment are also identified and described. The nature of any residual risks that remain after mitigation has are discussed.
Overview of Potential Impacts
12.1.4 Impacts to the water environment resulting from the proposed ERF relate to four main issues:
• Erosion and sediment transport. • Chemical / effluent pollution events. • Alteration / interruption of surface water flows. • Alteration / interruption of groundwater flows.
Water Related Consultation Responses
12.1.5 The following stakeholders were consulted:
• British Waterways (BW). • Environment Agency (EA). • Staffordshire County Council (SCC). • South Staffordshire Water (SSW).
12.1.6 The guidance and comments provided by the stakeholders above have been taken into account and addressed within this assessment. Key guidance includes the request for a Flood Risk Assessment (FRA) by the EA and SCC. Correspondence from the EA indicating they are satisfied that the proposed development satisfies the Sequential Test is included in Annex A of the FRA (Appendix 12.1).
12.1.7 The EA and SSW requested that the contamination in the underlying soils be considered. Therefore the results from both the Phase 2 Site Investigation undertaken by Enviros, and a subsequent site investigation undertaken by MLM Environmental in 2009, have been considered with regards to contamination onsite being mobilised during the construction phase.
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12.2 Relevant Legislation and Policy Legislation
12.2.1 Guidance provided from the UK Technical Advisory Group (UKTAG) provides an overview of the environmental standards for water quality and hydromorphology arising from requirements set by the European Water Framework Directive (WFD), which was transposed into English and Welsh law in December 2003.
12.2.2 The activities associated with the construction of the proposed ERF will need to conform to existing water legislation in England, including the Environment Protection Act (1990), Environment Act (1995), Water Resources Act (1991), Land Drainage Act (1991) and the Water Act (2003). This is particularly relevant in relation to discharges to water and any engineering works or impoundments. These include the following requirements:
• Any significant dewatering activity will be subject to licensing by the Environment Agency (EA), under the Water Act (2003). • Any works in, under, over or within 7m of a watercourse will require a land drainage consent (from the EA). • Assurance that riparian owners common law rights to receive water is undiminished in quantity or quality.
Relevant Planning Policy
National Policy
12.2.3 PPS23: Planning and Pollution Control advises that any consideration of the quality of land, air or water and potential impacts arising from development, possibly leading to impacts on health, is capable of being a material planning consideration, in so far as it arises, or may arise from, or may affect any land use.
12.2.4 PPS25: Development and Flood Risk aims to ensure that flood risk is taken into account at all stages in the planning process to avoid inappropriate development in areas at risk of flooding, and to direct development away from areas of highest risk. Where new development is, exceptionally, necessary in such areas, policy aims to make it safe, without increasing flood risk elsewhere, and, where possible, reducing overall flood risk.
Regional Policy
12.2.5 In July 2010 the Secretary of State for Communities and Local Government informed councils and the Planning Inspectorate that the regional planning regime for England no longer forms part of the development plan for the purposes of the determination of planning applications. Guidance issued with the announcement advised that evidence that informed the preparation of the revoked Regional Strategies may still be a material consideration in planning decisions.
Local Policy
12.2.6 The saved policies of the South Staffordshire Local Plan (adopted December 1996) provide general development control policies which are used in a determination of a planning application. Saved policies relevant to water include:
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12.2.7 Policy BE25 which seeks to control the location of new development and advocates that:
“new buildings shall be located so as to avoid, or at least keep to the minimum…any increase in water…pollution, any loss of potable water and any deterioration in the function of river washlands or other flow protection measures”.
12.2.8 Policy BE27 has regard to the importance of the protection of the natural watercourse system and advocates that it will be protected:
“against adverse forms of development by seeking to prevent…drainage from development giving rise to substantial changes in the characteristic of surface water run-off unless adequate site works can be provided”.
12.2.9 Policy BE28 meanwhile relates specifically to the protection of groundwater resources and states that:
“proposals for development which could damage ground water resources and prevent the use of those resources will not normally be allowed”.
12.2.10 The Local Development Framework (LDF) will replace the South Staffordshire Local Plan once adopted. The Core Strategy is a fundamental component of the LDF and will set out core policies to guide future development within the district. The draft Core Strategy document was published in January 2010 and has since undergone public consultation. The timetable for the adoption of the Core Strategy document is mid 2011.
Guidance
12.2.11 With regard to hydrology, management of water-borne pollution and protection of ecologically sensitive areas, the EA has a statutory obligation to manage and control the pollution of water resources. Accordingly, it is reasonable to assume that the adoption of the EA’s Best Practice Guidelines and licensing of the plant under Environmental Permitting Regulations will prevent pollution to recognised standards and make any ‘significant’ impacts unlikely. The EA’s Pollution Prevention Guidelines (PPGs) are the principal documents used for guidance on preventing the contamination of surface waters from construction activities.
12.2.12 The PPGs relevant to this development include:
• PPG1: General Guide to the Prevention of Pollution. • PPG2: Above Ground Oil Storage Tanks. • PPG5: Works In, Near or Liable to Affect Watercourses. • PPG6: Working at Construction and Demolition Sites. • PPG7: Refuelling Facilities. • PPG8: Storage and Disposal of Used Oils. • PPG21: Pollution Incident Response Planning. • PPG26: Storage and Handling of Drums and Intermediate Bulk Containers.
12.2.13 Other relevant guidance includes:
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• Environment Agency Groundwater Protection: Policy and Practice document (2007). • Control of Water Pollution from Construction Sites. Guidance for Consultants and Contractors C532 (CIRIA). • Environmental Good Practice on Site C650 (CIRIA). • Sustainable Drainage Systems C609 Hydraulic, Structural and Water Quality Advice (CIRIA). • Designing for Exceedance in Urban Drainage C635 - Good Practice (CIRIA). • The SUDS Manual C697 (CIRIA). • Control of Water Pollution from Linear Construction Projects: Technical Guidance C649 (CIRIA).
12.2.14 A number of other guidance documents have also been reviewed as outlined in the following sections.
Waterways for Tomorrow (Defra 2000)
12.2.15 This document follows up the White Paper: A New Deal for Transport; Better for Everyone and sets out proposals for the future of inland waterways (the canals and navigable rivers of England and Wales).
12.2.16 The Government wants to promote the inland waterways, encouraging a modern, integrated and sustainable approach to their use. They want to encourage innovative uses such as water transfer and telecommunications. Transportation of waste by canal to the ERF has been considered but is not feasible (see ES Chapter 3).
Waterways for Everyone: The Government’s Draft Strategy for the Inland Waterways of England and Wales (2010)
12.2.17 Waterways for Everyone sets out the development of a successor document to the Waterways for Tomorrow policy document.
12.2.18 The document intends to set out a vision for how waterways can contribute to a wide range of public policy objectives, including:
• The natural environment – recognising the value of waterways as wildlife corridors and identifying the challenges to waterways management from environmental pressures; • Cultural heritage – the potential to harness heritage features to education, regeneration and tourism purposes; • Sustainable transport – explores the possibilities for developing more freight of passenger travel on waterways, and use of riverside paths for off road walking/ cycling and commuting;
12.2.19 Potential impacts on the natural environment of the canal are discussed in this ES Chapter. Potential impacts on the cultural heritage of the canal are discussed in Chapter 15. Transportation of waste by canal to the ERF has been considered but is not feasible (see ES Chapter 3).
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Planning a Future for Inland Waterways: A Good Practice Guide (Inland Waterways Amenity Advisory Council, 2001)
12.2.20 This Guide explains the contribution that inland waterways can make to regeneration and other projects, and highlights examples of good planning. It is not considered especially relevant to the proposed ERF.
Policy Advice Note: Unlocking the Potential and Securing the Future of Inland Waterways through the Planning System (Town and Country Planning Association with the support of British Waterways, 2009)
12.2.21 The purpose of this Policy Advice Note is to, inter alia :
• Highlight the different types of waterways that form the inland waterway network, including their different characteristics, roles, uses and functions; • Promote the contribution that inland waterways make to economic, social and environmental agendas; • Demonstrate how inland waterways contribute to the Government’s key policy objectives; • Highlight the public benefits generated by waterways so that they are fully appreciated by policy-makers and influencers, and by planners at all the different spatial levels; • Identify the key planning policy challenges and issues that need to be tackled in order to fully unlock the economic, social and environmental benefits of inland waterways and secure their long-term sustainability as a national asset; • Promote the need for a supportive planning policy framework for inland waterways at all the different spatial levels; and • Make recommendations to policy-makers and planners at the different spatial levels on how the planning system can help to secure the long-term future, and support the development, regeneration and improvement, of the inland waterways network.
12.2.22 It is not considered especially relevant to the proposed ERF.
Code of Practice for Works Affecting British Waterways (British Waterways, 2009)
12.2.23 This Code of Practice gives guidance and procedures to Developers, Local Authorities, Statutory Undertakers and others wishing to carry out works which affect the Waterways. It is not considered especially relevant to the proposed ERF as no works to the waterway are proposed.
12.3 Baseline Conditions Information Sources
12.3.1 Baseline data on water resources and flood risk in the vicinity of the proposed development site has been collated by reference to the following sources:
• British Geological Survey (BGS) Map: Geological Survey Map Drift Edition 1:63,360 – Sheet 153. • Ordnance Survey (OS) Landranger Map at 1:50,000 scale: No 127.
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• Groundwater Vulnerability Map 1: 100,000 – No 22. • Landmark Envirocheck Report (February 2010) provide data on surface water and groundwater abstractions and discharges. • Water Framework Directive (WFD) water quality data. Environment Agency website: www.environment-agency.gov.uk . • Groundwater Aquifer Designation Maps provide information on superficial drift and bedrock designation. Environment Agency website: www.environment-agency.gov.uk . • Groundwater Source Protection Zones Maps defines groundwater protection zones in relation to public water supply. Environment Agency website: www.environment-agency.gov.uk . • Flood Map. Environment Agency website: www.environment-agency.gov.uk .
12.3.2 Specifically commissioned reports and investigation undertaken at the site:
• MLM Environmental (October, 2009) Factual Ground Investigation Report. • Scott Wilson Flood Risk Assessment 2010 (Appendix 12.1). • Scott Wilson Surface Water Drainage Strategy 2010 (Appendix 4.1). • Enviros – Phase 1 and 2 Site Investigations. • Additional groundwater level data (2009 – 2010).
Site Setting
12.3.3 The site was previously used for sand and gravel extraction, is currently vacant and benefits from a planning permission for an EfW granted in 2009. The site is located off the east end of Enterprise Drive, adjacent to the Four Ashes Industrial Estate, Four Ashes, Staffordshire. The land to the south and east, including the mitigation land to the south, is predominantly rural with industrial areas to the west and north. A sewage sludge treatment works exists approximately 300 m to the east of the site (see Figure 12.1).
12.3.4 The Saredon Brook, a tributary of the River Penk, borders the southwest corner of the mitigation land and is located approximately 30 m from the site at its closest point. The Staffordshire and Worcestershire Canal lies approximately 150 m to the north of the site at its closest point. A marina associated with the Canal is located approximately 1 km to the east of the site (see Figure 12.1).
Surface Hydrology
Topography and Drainage
12.3.5 Ground levels on the site are predominantly between 98 m and 103 m aOD. The main area of the site is relatively uniform, sloping gently upwards to the north from 99.5 to 102.5m aOD. The only interruption to this is a slightly higher spoil heap area just above the bank in the centre south, of up to 102.5 m aOD. There is another spoil heap on the western boundary that rises to 101.8 m aOD. Ground levels gently rise along the western border up to the concrete batching plant. Moving along the southern and eastern borders of the site, a steep bank (3 m height) separates the site from the drain and farmland below.
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12.3.6 A series of drainage ditches run along the eastern and southern boundaries of the site before discharging to the Saredon Brook (see Figure 12.1). A small number of ponds are associated with the eastern drainage ditch. An ephemeral pond also occurs at the centre of the site, however, as this will be drained and built over, it is not considered further in this assessment.
12.3.7 Beyond the boundary of the site, three land drainage systems can be identified (see Figure 12.1). A land drain, which initiates from a spring approximately 650 m to the east of the site, flows south west, discharging into the Saredon Brook approximately 400 m to the east. A single tributary discharges to this land drain approximately 500 m to the east of the site.
12.3.8 A drain originating from the land to the east of the site is characterised by orange ochre that coats the bed and sides of the drain. The Phase 2 Site Investigation (Enviros Consulting, 2008) has shown no hazardous compounds to be present in this discharge.
12.3.9 The second land drain system exists on agricultural land to the southeast of the site, which discharges to the Saredon Brook through a network of small channels. The final land drain, which also discharges to the Saredon Brook, is located approximately 150 m to the south west of the site. This land drain is only 20 m in length and receives surface water runoff from the Four Ashes Industrial Estate.
12.3.10 A large pond is located up slope of the site, approximately 300 m, to the northeast of the site. A further pond is located approximately 250 m to the south of the Saredon Brook. The potential for contaminants arising from site activities to impact either of these ponds is limited. As surface water runoff drains to the southeast away from the pond located to the northeast, and the Saredon Brook provides an effective barrier to the pond 250 m to the south, intercepting potential contaminants generated on site, these ponds are not considered further within this assessment.
Significant Water Features
12.3.11 The Saredon Brook is classified as Main River and originates as Ridings Brook to the northeast of Cannock. This watercourse is 6.2 km long and drains a catchment area of 18 km 2, the majority of which is urban. The Saredon Brook flows in a south westerly direction, to the south of the site, discharging to the River Penk approximately 2 km downstream of the site.
12.3.12 The River Penk rises 4.8 km northwest of Wolverhampton, close to the town of Tettenhall, and flows in a north-westerly direction where it ends at its confluence with the River Sow.
12.3.13 The Staffordshire and Worcestershire Canal runs for approximately 74 km from the River Severn to the Trent and Mersey Canal at the Haywood Junction. As the canal is up gradient of the site, it is not considered within this assessment as there is no valid hydrological pathway to this receptor.
Surface Water Quality
12.3.14 The Water Framework Directive (WFD) aims to achieve good ecological health of surface water bodies. The WFD classification is based on a far wider range of assessments compared to the superseded General Quality Assessments (GQA) classification. The WFD reports on over 30 measures, grouped into ecological status (ecological status includes biological, chemical and hydromorphological elements).
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12.3.15 Annex B of the River Humber River Basin Management Plan 1 provides information relating to the current status of all the water bodies within the Humber River Basin District. Table 12.1 below provides a summary of the current status of the Saredon Brook and the Staffordshire and Worcestershire Canal in the vicinity of the site, together with the River Penk, both upstream and downstream of its confluence with the River Saredon.
Table 12.1 Summary of Water Framework Directive Water Body Status
Current Status
Water body Ecological Overall Hydro Water body ID (and reach) status/potential Overall physico morpholo Specific (and certainty biological chemical gical pollutants that status is less quality quality Quality quality than good) Saredon Brook
Moderate ecological GB104028046740 (Saredon Brook Moderate Good Not high Good potential from Source to River Penk) River Penk Upstream Bad ecological status GB104028046680 (River Penk from Bad Moderate Not high Good (very certain) Source to Saredon Brook) River Penk Downstream Moderate ecological (River Penk from GB104028047120 potential Good Moderate Not high High Saredon Brook to (very certain) River Sow)
Staffordshire and Moderate ecological Worcester Canal potential GB70410266 - Moderate - High (summit pond) (very certain)
12.3.16 Ecological status is recorded on the scale of high, good, moderate, poor or bad. ‘High’ denotes largely undisturbed conditions and the other classes represent increasing deviation from this natural condition.
12.3.17 Table 12.1 indicates that, with the exception of the upstream reach of the River Penk (GB104028046680), which is classified as having ‘Bad’ ecological status, all water body reaches in the vicinity of the site are classified as having a ‘Moderate’ ecological potential. This indicates that these watercourses have a moderate chemical or biological quality deviation from natural conditions.
12.3.18 With the exception of the River Penk (GB104028046680), all water bodies shown in Table 12.1 are classified as Heavily Modified Water Bodies (HMWBs). The physical characteristics of HMWBs have been substantially changed in character to facilitate their water use, such as navigation or land drainage. As changes to their hydromorphological characteristics necessary to
1 Available online at: http://wfdconsultation.environment-agency.gov.uk/wfdcms/en/humber/Intro.aspx
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achieve good surface water status would have a significant adverse impact on their water use they are instead classified as having good ecological potential 2.
Mains Supply and Sewers
12.3.19 No mains supply pipes, surface or foul sewer pipes are currently located within the site. A mains water supply pipe runs along the south of Enterprise Drive finishing in the hammerhead opposite the newly constructed Dell development. A branch pipe runs down Latherford Close to the west, which is down gradient of the site.
12.3.20 The surface water sewer beyond the site boundary initiates along Enterprise Drive in the region of the hammerhead opposite the newly constructed Dell development and flows west along this road. Along with flow coming from the east along Enterprise Drive the surface water sewer flows south down Aspley Close approximately 200 m west of the site. A second section initiates in Latherford Close, 150 m west of the site, and flows south then west, where it joins with the first section to discharge to Saredon Brook.
12.3.21 The foul sewers in the area run past (but not through) the sewage treatment works located 300 m east of the site before a pressurised sewer runs up-gradient towards the site. The construction of ‘The Dell’ development, involved the relocation of the pressurised foul sewer from within the northern boundary of the Dell site to beneath a roadway constructed along the boundary fence between the ‘The Dell’ development and the site. The 2007 FRA indicates that the ground height above this sewer will be between 102 m and 103 m aOD. From here the foul sewer runs down Enterprise Drive and Latherford Close (where there is a pumping station).
Geology and Hydrogeology
Geology
12.3.22 A review of the Ground Investigation Report undertaken by MLM Environmental (MLM Environmental, 2009) provides the following summary on ground conditions underlying the site.
12.3.23 Made Ground is encountered between 1.0 – 5.4 m below ground level (bgl). Generally, Made Ground is present to depths in excess of 3.0m bgl. The greatest thickness of Made Ground was experienced in the eastern part of the site. The Made Ground comprises a clayey gravelly sand to a sandy gravelly clay, with variable silt, sand and gravel content. The gravel element comprised sandstone, brick, concrete, quartzite, ash, limestone, clinker, ceramics, glass, wood and charcoal.
12.3.24 Superficial deposits were encountered underlying the Made Ground. The superficial deposits were a variable material comprising of sand, clay and gravel. The gravel element comprised fine to cobble sized quartzite and sandstone.
12.3.25 Underlying the superficial deposits, and to the completion of the boreholes at a maximum depth of 25m bgl, the Wildmoor Sandstone Formation (of the Sherwood Sandstone Group) was encountered as a very weakly cemented extremely weak to moderately weak red banded green, yellow and grey fine grained locally gravely sandstone. The gravel element comprised quartzite.
2 Further information on HMWBs is available online at: http://www.wfduk.org/UKCLASSPUB/LibraryPublicDocs/gep_hmwb_final
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Hydrogeology
12.3.26 The Environment Agency Groundwater Aquifer Designation Maps 3 for the area indicate that the superficial drift deposits underlying the southern part of the site and the ecological mitigation land are classified as a Secondary Aquifer (A). Superficial deposits of this nature are categorised as:
”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”.
12.3.27 The bedrock underlying the entire site is classified as a Principal Aquifer of the Sherwood Sandstone Group, which is categorised as:
“layers of rock or drift deposits that have high intergranular 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. In most cases, principal aquifers are aquifers previously designated as major aquifer”.
12.3.28 The Environment Agency Groundwater Vulnerability Map 4 indicates that the overlying sands and gravels are shown to be of high leaching potential. This means they are able to transmit a wide range of pollutants due to rapid drainage and low attenuation potential, which may impact shallow groundwater should a pollution event occur. The Ground Investigation Report (MLM, 2009) indicates that groundwater levels on the site range from 3 m bgl in the north to 1.5 m bgl in the south of the site.
12.3.29 Further groundwater monitoring has been undertaken on the mitigation land to the south of the site, north of Saredon Brook for the period September 2009 to March 2010. Groundwater levels in this area are all less than 1 m bgl.
12.3.30 The site is also located within a designated Nitrate Vulnerable Zone (NVZ) under the Nitrates Directive. NVZs are areas where groundwater may potentially contain nitrate concentrations of greater then 50 mg/l (if preventative action was not taken).
12.3.31 The site is located within a Zone II area (Outer Source Protection Zone (SPZ)), which is defined by a 400 day travel time from any point below the water table. SPZs are associated with important potable sources of water, such as public water supply borehole. The zones are defined on the basis of the area identified as the source of water (i.e. the catchment area to the borehole and the time taken for the water to reach the borehole).
Existing Contamination
On Site
12.3.32 The 2008 ES provides a summary of the Phase II Land Quality Assessment (Enviros Consulting, 2008) which indicates that there is no widespread soil contamination on the site, although elevated levels of PAHs were found in one localised sample. The PAHs are thought to be caused by the presence of coal.
3 Available online: www.environment-agency.gov.uk 4 Environment Agency Groundwater Vulnerability Map Sheet 22, South Staffordshire & East Shropshire, 1997
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12.3.33 Leachate testing has shown widespread leachable ammonium concentrations, which were found at relatively low levels. Isolated occurrences of arsenic and benzo(a)pyrene also occur but do not form significant point sources of widespread controlled water pollution.
12.3.34 Isolated occurrences of groundwater pollution (PAHs, TPH, nickel, boron, ethyl benzene and xylene) have been reported. These do not form significant point sources of widespread controlled water pollution. Widespread, but relatively low levels of ammonium have been detected in the shallow groundwater. Elevated levels of COD in the groundwater have also been found. At the time of the 2008 survey it was thought that the source of the elevated COD and ammonium levels may be the foul sewer located off-site in the land adjacent to the north.
Off Site
12.3.35 An existing concrete batching plant is in operation immediately adjacent to the north west of the site. The 2008 ES indicates that there have been historic discharges of washout material and surplus concrete on adjoining land and the site area.
Abstractions and Discharges
12.3.36 The Envirocheck Report (February 2010) indicates a total of 11 licensed discharge consents within 1 km of the site (see Figure 12.2). Eight discharge consents are to surface waters and two to groundwater. The closest discharge is by Lafarge Aggregates Ltd to the Saredon Brook. The discharge information for three discharge consent licences is not supplied within the Envirocheck Report.
12.3.37 There are 18 water abstraction licenses (11 for surface water and 7 for groundwater) held at 21 locations within 2 km of the site (see Figure 12.2). Water is abstracted for industrial, agricultural and domestic purposes. There are four licensed groundwater abstractions within 1 km of the site. The Envirocheck Report indicates that the closest abstraction license is held by Redland Aggregates Limited immediately south of the site on the ecological mitigation land. The Envirocheck Report states that water abstraction is from the Saredon Brook and is used for mineral washing. It is expected that this license dates from the time that the site was used as a sand and gravel quarry and that no water is currently abstracted in this location. One potable water abstraction is undertaken 1.3 km from the site by South Staffordshire Water Plc at Slade Heath pumping station.
Flood Risk
12.3.38 The Environment Agency Flood Map 5 indicates that the site is located in Flood Zone 1 indicating that flooding from major fluvial or tidal sources is unlikely. Land immediately beyond the southwest corner of the site, on the ecological mitigation land, is located within Flood Zone 3, however, this fluvial flood source is not considered to pose a potential flood risk to the proposed development.
12.3.39 PPS25 defines the flood zones as:
• Zone 1 – land assessed as having a less than 1 in 1000 annual probability of river or sea flooding in any year (<0.1%).
5 Available online: www.environment-agency.gov.uk
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• Zone 2 – land assessed as having between a 1 in 100 and 1 in 1000 annual probability of river flooding (1% - 0.1%) or between a 1 in 200 and 1 in 1000 annual probability of sea flooding (0.5% - 0.1%) in any year. • Zone 3 – land assessed as having a 1 in 100 year or greater annual probability of river flooding (>1%) or a 1 in 200 or greater annual probability of flooding from the sea (>0.5%) in any year.
12.3.40 Planning Policy 25 (PPS25)6: Development and Flood Risk specifies that planning applications for development proposals of 1 ha or greater in Flood Zone 1 and all proposals for new development located in Flood Zone 2 and Flood Zone 3 should be accompanied by an FRA. It has therefore been necessary to prepare a FRA for this site, which is presented in Appendix 12.1.
Designated Sites
12.3.41 The Four Ashes Pit is located 660 m to the west of the site and is a nationally designated Site of Special Scientific Interest (SSSI). The Four Ashes Pit is an important geological feature, however the site is not considered to be water dependent and is not considered further within this assessment.
12.4 Methodology
12.4.1 The methodology used for this ES is consistent with the 2008 ES (prepared by Enviros). In the absence of any standard criteria for undertaking water resource assessments, assessment criteria have been adapted from the Department for Transport, Transport Appraisal Guidance (2003). This methodology takes into account the magnitude, sensitivity and significance of predicted impacts/effects on the water environment.
Water Resources Methodology
Magnitude
12.4.2 The magnitude of a potential impact is assessed based on the amount and intensity of disturbance and duration (i.e. whether permanent or temporary) (see Table 12.2). In this assessment consideration of likelihood is incorporated into a final risk based assessment (see Table 12.5).
Table 12.2 Impact Magnitude Criteria – Water Resources
Magnitude Definition Negligible Unquantifiable or unqualifiable change in hydrological / hydrogeological conditions (including water quality). Minor Detectable but minor change to hydrological / hydrogeological conditions. Water quality/quantity standards less than threshold and unlikely to affect most sensitive receptors. Moderate Detectable change to hydrological / hydrogeological conditions resulting in non- fundamental temporary or permanent consequential changes. Some deterioration in
6 Available online: http://www.communities.gov.uk/publications/planningandbuilding/pps25floodrisk
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Magnitude Definition water quality/quantity likely to temporarily affect most sensitive receptors. High Fundamental change to hydrological / hydrogeological conditions (including deterioration in water quality/quantity) resulting in temporary or permanent consequential changes.
Sensitivity
12.4.3 Sensitivity is based on the degree of environmental response to any particular impact, together with the value of the water feature or resource (e.g. a Principal Aquifer or nearby abstraction borehole should be considered more sensitive to any impact than a Non Aquifer) (see Table 12.3).
Table 12.3 Sensitivity Criteria – Water Resources
Sensitivity Definition Negligible Environment is insensitive to impact, no discernible changes e.g. non-aquifer where little or no effect on groundwater could occur. Low Environment responds in a minimal way such that only minor changes are detectable e.g. surface water features present at some distance (>500m) or groundwater resource with minimal sensitivity e.g. Minor Aquifer. Medium Environment clearly responds to effect(s) in quantifiable and / or qual ifiable manner e.g. reasonable proximity to a surface water course (within 500m), abstraction point, or Major Aquifer or sited on a Minor Aquifer. High Environment is subject to major change(s) due to impact e.g. adjacent to, or within 100m of, a sensitive watercourse or sited directly upon a Major Aquifer / Source Protection Zone (SPZ).
Significance
The significance of a specific potential effect on a water feature or resource is then derived by considering the associated the magnitude and sensitivity (see Table 12.4).Table 12.4Table 12.4 Significance Matrix – Water Resources
Magnitude Sensitivity
Negligible Low Medium High Negligible Insignificant Insignificant Insignificant Insignificant Minor Insignificant Minor Minor Moderate Moderate Insignificant Minor Moderate High High Insignificant Moderate High Very High
Risk Assessment Methodology
12.4.4 The Source-Pathway-Receptor model has been adopted to undertake this assessment. Firstly potential ‘sources’ of contamination based on a review of historic, existing and proposed site uses (contaminated land, potential spillages during construction or operational phases) have been identified. Considerations such as the nature and likely extent of the contamination have also been taken into account.
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12.4.5 The presence of contamination does not always infer a risk. It is the exposure pathway that determines the risk to the receptor and the effective consequence of exposure. A pathway which transports the contaminants to the receptor, generally involves conveyance via soil, water or air, or, in some cases, direct contact.
12.4.6 The varying effect that a hazard has on an individual ‘receptor’ depends largely on the sensitivity of the receptor. Receptors include any people, animal or plant populations, or natural or economic resources that are within the range of the potential spread of the source, and which are connected to the source by a transport pathway. Although in this instance the assessment is principally concerned with surface water and groundwater receptors.
12.4.7 By considering the source, pathway and receptor, an assessment has been made for each contaminant type, on a receptor by receptor basis, with reference to the significance and degree of risk. In assessing this information, a judgement has been made as to whether the source contamination can reach a receptor, and whether it is of a major or minor significance. The exposure risks are assessed against the present site conditions (i.e. the ‘Do Nothing Scenario’).
12.4.8 The environmental risk guidance document ‘Guidelines for Environmental Risk Assessment and Management’ 7 first published by the Department for the Environment in 1995 states that the designation of risk is based upon a consideration of both:
• The likelihood of an event; (takes into account both the presence of the hazard and receptor and the integrity of the pathway); and • The severity of the potential significance (takes into account both the potential severity of the hazard and the sensitivity of the receptor).
12.4.9 Table 12.5 shows how the risk rating is achieved by combining the likelihood of the event and the degree of significance.
Table 12.5 Risk Assessment Matrix – Water Resources
Likelihood Significance
Insignificant Minor Moderate High Unlikely Very low risk Very low risk Low risk Moderate / low risk Low likelihood Very low risk Low risk Moderate / low risk Moderate risk Likely Low risk Moderate / low risk Moderate risk High risk High likelihood Low risk Moderate risk High risk Very high risk
12.4.10 A description of the varying degrees of associated risk, shown in the risk assessment matrix (see Table 12.5), is provided in Table 12.6 below.
Table 12.6 Risk Criteria – Water Resources
Term Description Very low risk The presence of an identified hazard does not give rise to the potential to cause
7 Available online at: http://www.defra.gov.uk/environment/quality/risk/eramguide/index.htm
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Term Description significant harm to a designated receptor. Low risk It is possible that harm could arise to a designated receptor from an identified hazard but it is likely that, at worst, this harm, if realised, would normally be minor.
Moderate risk It is possible that, without appropriate remedial action, harm could arise to a designated receptor, but it is relatively unlikely that any such harm would be high, and if any harm were to occur it is more likely that such harm would be relatively minor.
High risk Harm is likely to arise to a designated receptor from an identified hazard at the site without appropriate remedial action.
Very high risk There is a high likelihood that severe harm could arise to a designated receptor from an identified hazard at the site without appropriate remedial action.
12.4.11 The assessment of likely significant impacts of the proposed ERF, both within and outside the site, is initially based on potential impact before mitigation. Levels of assessed impact which are moderate or above will require mitigation/management to reduce the level of impact to negligible or low levels.
Flood Risk Assessment Methodology
12.4.12 The primary assessment tool within a flood risk assessment should be the sequential test as set out in Tables D1 and D2 of PPS25. Such an assessment however, deals almost exclusively with the risks associated with tidal and fluvial sources and not the full range of flooding sources identified in Annex C of PPS25.
12.4.13 In addition to this, the sequential test does not provide guidance for assessing the impact of mitigation and residual risk subsequent to development, as required by Annex G of PPS25.
12.4.14 Therefore in order to allow for the wider assessment of flood risk this more generalised assessment methodology has been developed. It should be noted that where applied to fluvial and tidal sources the results of the assessment should be cross checked against the results of the sequential test.
Risk Assessment Methodology – Flood Risk
12.4.15 In line with guidance set out in PPS25, the key to the classification is that the designation of significance (or risk) is based upon the consideration of:
• The sensitivity of the receptor – takes into account the nature of the development or receptor and its likely response to increased risk. • The magnitude of the potential hazard (i.e. severity) – takes into account the potential severity and nature of the flooding. • The probability of occurrence (i.e. likelihood) – takes into account both the presence of the hazard and receptor, and the integrity of the pathway.
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Sensitivity
12.4.16 When considering new developments, the classification of sensitivity is based (where possible) directly on the sequential test as set out within Table D2 of PPS25. When considering off site impacts there is a general assumption that all developments are highly sensitive. This assumption can however typically be relaxed when considering ‘Water Compatible’ development or undeveloped land. Given this the sensitivity of the receptor is ranked as shown in Table 12.7.
Table 12.7 Classification of Sensitivity of Receptor – Flood Risk
Sensitivity of New development Off site receptor Very low Flood attenuation features. - Low Water compatible* developments. - Moderate Less vulnerable* developments. Undeveloped land. High More vulnerable* developments. Other access routes. Very High Highly vulnerable* developments. All built development unless mitigating circumstances exist.
Key access routes. *For definition of terms see Table D2 of PPS25.
Magnitude
To classify the magnitude of the potential effects it is necessary to look at the nature and scale of the individual impacts. These include, but are not confined to, the extent of flooding, the depth of flooding, the duration of flooding and the velocity of flood waters. For new developments the assessment is based on the likely post development situation, for off site receptors it is based solely on the likely deterioration resulting from the development. Given this the magnitude of the potential effect is then ranked as shown below in Table 12.8.Table 12.8
Table 12.8 Classification of Magnitude of Potential Hazard – Flood Risk
Magnitude of New development Off site potential hazard Negligible No potential for flooding, or no identifiable No likely increase in flood severity at any off impact of flooding. site location.
Very low Planned or permitted flooding that does not - adversely impact the built development.
Low All of the following criteria achieved: Likely, but unquantifiable small increases of • Flood depths below 0.3m, flood depths, durations, flow velocities or • Likely flood duration below one extent. hour • Flood proofing measures planned
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Magnitude of New development Off site potential hazard Medium Any one of the following criteria achieved: Any other measurable increase of flood • Flood depths between 0.3m and depths, durations, flow velocities or extent. 1m • Flood flow velocity greater than 0.15m/s • Likely flood duration in excess of one hour • Any restrictions to access and egress
High Any one of the following criteria achieved: Any marked (>10%) increase in flood depth, • Flood depths greater than 1m flood flow velocity or flood duration. • Flood flow velocities greater than 0.45m/s Any change in flood extent that impacts • Likely flood duration in excess of additional properties including access. 24 hours
Significance
12.4.17 Table 12.9 shows how the magnitude of the hazard and the sensitivity of the receptor are combined to determine the significance of the potential effect.
Table 12.9 Matrix for Determining the Significance of the Potential Effect – Flood Risk
Magnitude of Sensitivity of receptor potential hazard Very low Low Medium High Very high Negligible Negligible Negligible Negligible Negligible Negligible Very low Negligible Very low Very low Low Low Low Very low Very low Low Moderate Moderate Medium Very low Low Moderate Moderate High High Low Moderate Moderate High High
Classification of Probability of Occurrence
12.4.18 To classify the probability of occurrence for a potential effect it is necessary to understand how regularly a given event or outcome will occur. This can be assessed in a number of ways including assessments based on historical data, quantitative analysis, or experience from other similar sites. Often this assessment will be based on standard guidance. The magnitude of the potential effect is then ranked as shown below in Table 12.10.
Table 12.10 Classification of Probability of Occurrence – Flood Risk
Probability of Potential effect occurrence Very low It is unlikely that any consequence will ever arise.
Low It is unlikely that any consequence would arise within the lifetime of the development.
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Probability of Potential effect occurrence Equivalent to an annual probability of less than 0.1% or Flood Zone 1*.
Medium Circumstances are such that an event is possible in the medium term and likely over the long term, although not necessarily inevitable.
Equivalent to an annual probability between 0.1 and 1% (0.1 and 0.5% for tidal) or Flood Zone 2*.
High Any consequence would appear likely in the medium term and inevitable in the long term (lifetime of the development).
Equivalent to an annual probability of flooding of greater than 1% (0.5% for tidal) or Flood Zone 3*.
*For definition of terms see Table D1 of PPS25.
Risk Assessment
12.4.19 Once the magnitude of the potential effect and probability of occurrence have been assessed these are then combined using a risk matrix (Table 12.11) to assess the flood risk of each potential effect.
Table 12.11 Risk Matrix – Flood Risk
Magnitude of potential Probability of occurrence effect Very low Low Medium High Negligible Negligible Negligible Negligible Negligible Very low Negligible Very low Low Low Low Very low Low Low Moderate Moderate Low Low Moderate High High Low Moderate High High
12.4.20 Typically flood risks assessed as low, or less are considered acceptable. If the assessment results in moderate or high risk, additional mitigation measures will be required to facilitate development.
12.4.21 In some situations the risk assessment procedure will result in an artificially low assessment of risk. This is particularly the case in situations where consequences of very rare flooding (i.e. breach scenarios) are so extreme that any residual risk, however low, should not be allowed. In such instances the assessed risk should be elevated. Such decisions must always be accompanied by detailed justification.
12.5 Incorporated Mitigation
12.5.1 Several pollution prevention and drainage management features are inherent within the design of the proposed ERF. The main mitigation feature will be the carrying out of all operations within a
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building and on hardstanding. Other mitigation measures which will provide protection to surrounding water features are as follows:
• Waste will be stored inside the waste bunker / tipping hall, which will help to prevent accidental release of waste which could result in it being transported to local water courses. • The waste bunker is to be constructed from reinforced concrete rendering it waterproof and so preventing potential seepage to groundwater. • All storage silos will be filled and emptied by bulk tankers or refuse collection vehicles within the building envelope, which will be help prevent accidental releases of substances to the aquatic environment. • Dust will be careful controlled under a dust suppression scheme (see Appendix 4.5) preventing release to the aquatic environment. • Incinerator bottom ash (IBA) and flue gas treatment (FGT) residues will be transferred to vehicles within the building envelope and so reduce the potential of release to the surface waters. • The water treatment plant to be used during the initial fill of boiler and small volumes of system top up will be located within a bunded area, with additional bunded storage areas to store the boiler water treatment chemicals. • All chemical substances and hazardous materials are to be stored in accordance with legislation and Environment Agency guidelines. • The filling of storage tankers will be through a sealed system, within the building envelope, to prevent powder from being released. • Ammonia/Urea for use in NOx control, will be stored in a suitable container with a vent scrubber system and pressure relief valve, these will be stored in a bunded area which will have a 110% capacity of the storage tank. • All diesel fuel and lubrication oils will be stored in bunded areas, diesel will be contained within double skinned tanks. Bunded areas will have a 110% capacity of the storage tank. • Accidental discharge of process waters and contaminated waters will be diverted to a wastewater storage pit. This may be re-used in the process, transported off-site for treatment disposal or treated and to discharged to foul water sewer. • The drainage system will incorporate interceptors to prevent the pollution of surface water bodies. • Additionally, the use of Sustainable Drainage Systems (SUDS) will assist with the attenuation of any polluting surface water runoff. • Finished Floor Levels (FFLs) will be at least 0.3 m above surrounding ground level reducing risk from flooding. • The facility will be operated in accordance with an Environmental Permit.
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12.6 Impact Assessment Effects During Construction
12.6.1 Impacts to the hydrological environment that typically arise from construction processes are generally relevant for any development activity irrespective of location. Potential impacts are detailed in the paragraphs below
Mobilisation of Sediments
12.6.2 Unmitigated construction sites typically result in an increase in the mobilisation of sediments in surface water runoff from the development areas. This derives from the removal of vegetation, open soil surfaces, ground disturbance, stockpiles of soil and other construction materials, and the erosion caused by the movement of heavy plant and other traffic on temporary access roads (or unprotected) surfaces.
12.6.3 Higher sediment loads may be washed into local watercourses where sediment will start to settle. If the sediment load is sufficiently high, aquatic vegetation can be smothered, alterations may occur to the bed profile/conveyance of the channel, and/or can lead to the blockage of culverts or other structures through which the water flows.
12.6.4 Where soils and/or sediments are contaminated from previous land use, the mobilisation of sediments may cause surface pollution.
Contamination of Groundwater
12.6.5 Construction at the site will require the use and storage of a wide range of hydrocarbons and other chemicals. The construction will also involve delivery of materials by heavy goods vehicles and the use of construction plant on the site.
12.6.6 Spillage or uncontrolled disposal of hydrocarbons or other chemicals in any areas of the site could result in contamination of the shallow groundwater beneath the site.
12.6.7 Contamination during construction could also occur through the mobilisation of existing contamination on site (e.g. dewatering, drawing shallow contaminated groundwater into deep excavations).
Contamination of Surface Water
12.6.8 As with potential contamination to groundwater, construction will involve the use and storage of hydrocarbons and other chemicals, along with the presence of delivery vehicles and mechanised construction plant. Spillage or uncontrolled disposal of hydrocarbons or other chemicals in any areas of the site could rapidly lead to pollution of surface water runoff from the site either from hard-standing surfaces or via contaminated groundwater (see above) infiltrating into the drainage system.
12.6.9 Erection of concrete structures during the construction phase may cause cement material to enter watercourses; some polluted water could be generated through concrete washout. Discharging cement based products or water polluted with concrete into any surface water body, groundwater or surface water drain without prior consent is an offence under the Water Resources Act 1991. Where works are in close proximity to watercourses, silt run-off to
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watercourses could result, which may physically damage fish, smother vegetation and the river bed, alter the water’s pH and mobilise pollutants.
12.6.10 If the amount of pollution were significant, or if the nature of the pollutant was toxic, such spillages could result in a significant deterioration in the water quality of runoff from the site. This in turn would impact upon the receiving waters and have the potential to cause adverse impacts on aquatic ecology.
Dewatering
12.6.11 Proposed construction at the site will require excavation/piling for building foundations and excavations for the waste bunker. There is the potential for groundwater to seep into such excavations. In order to allow construction to continue, some dewatering would be required in the immediate vicinity of the excavation.
12.6.12 This activity may impact surface water flows, draw in contaminated water from off site, open pathways between shallow groundwater and the major aquifer and result in contaminated water requiring appropriate disposal.
12.6.13 Table 12.12 provides a summary of the assessment of potential construction (and decommissioning) impacts prior to mitigation.
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Table 12.12 Construction (and Decommissioning) Phase Impacts (Not Including Mitigation)
Nature of Pathway Receptor Sensitivity of Magnitude of Significance of Likelihood Risk Impact Receptor Impact Impact
Erosion / Direct surface water Drainage network Low Moderate Minor Likely Moderate / low risk Sediment runoff and associated Loading ponds Direct surface water Saredon Brook Medium Moderate Moderate Likely Moderate risk runoff
Surface water flow River Penk Medium Negligible Insignificant Unlikely Very low risk via Saredon Brook
Reduction Mobilisation of Drainage network Low Moderate Minor Likely Moderate / low risk in Water existing and associated Quality contamination ponds
Mobilisation of Saredon Brook Medium Moderate Moderate Likely Moderate risk existing contamination
Mobilisation of River Penk Medium Negligible Insignificant Unlikely Very low risk existing contamination
Mobilisation of Secondary Aquifer Low Moderate Minor Likely Moderate / low risk existing (A). (Shallow contamination groundwater)
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Nature of Pathway Receptor Sensitivity of Magnitude of Significance of Likelihood Risk Impact Receptor Impact Impact
Reduction Mobilisation of Principal Aquifer High High High Likely High risk in Water existing Quality contamination Surface water Drainage network Low Moderate Minor Low likelihood Low risk runoff and associated ponds Direct discharge
Surface water Saredon Brook Medium Moderate Moderate Low likelihood Moderate / low risk runoff
Direct discharge
Surface water River Penk Medium Negligible Insignificant Unlikely Very low risk runoff
Direct discharge
Direct infiltration to Secondary Aquifer Low Minor Minor Low likelihood Low risk ground (A). (Shallow groundwater)
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Nature of Pathway Receptor Sensitivity of Magnitude of Significance of Likelihood Risk Impact Receptor Impact Impact
Reduction Infiltration through Principal Aquifer High Minor Moderate Low likelihood Moderate / low risk in Water overlying superficial Quality drift deposits Dewatering Infiltration through Saredon Brook Medium Minor Minor Unlikely Very low risk – Flow baseflow alteration
Infiltration through Secondary Aquifer Low Moderate Minor Unlikely Very low risk baseflow (A). (Shallow groundwater)
Infiltration from Principal Aquifer High Negligible Insignificant Low likelihood Very low risk shallow groundwater
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12.6.14 Table 12.12 indicates that the majority of impacts have been classed as low risk or lower. Contamination of the Principal Aquifer through the mobilisation of existing contamination in the Secondary Aquifer has been classed as high risk. However, this risk is likely to be already present without development as the geology and hydrogeology baseline conditions (see section 12.3) indicate that the superficial deposits of the Secondary Aquifer appears to be in hydraulic continuity with the Principal Aquifer.
12.6.15 Also of concern is the erosion/sediment loading through direct surface water runoff to the drainage network and associated ponds and Saredon Brook, where the risk is classed as moderate / low and moderate risk respectively.
12.6.16 There is also a moderate / low risk to the Saredon Brook and the Principal Aquifer from direct discharges of pollutants that may affect water quality. Note that major excavations (e.g. for the waste bunker) are likely to require dewatering and off-site disposal if mitigation is not applied.
Effects During Operation
12.6.17 On-site and off-site impacts to the hydrological environment that could potentially arise during the operation of the proposed ERF are discussed below.
12.6.18 Impacts are assessed with consideration of the incorporated mitigation measures inherent in the design of the ERF (see Section 12.5) but not further mitigation.
Sediment Runoff Increase
12.6.19 The increase in built hard surface areas (e.g. concrete) can lead to flushing effects, whereby site runoff mobilises sediment accumulated over time. This sediment would then be discharged into the local drainage system and could lead to sedimentation in the channels, or smothering within the system.
12.6.20 The potential effect of an increase in sedimentation over time would reduce channel capacity, could lead to blockages in culverts and other structures, and could cause an adverse ecological impact by smothering stream beds and reducing light infiltration.
12.6.21 However, as the site surface currently consists of unconsolidated made ground, it is unlikely that sediment loadings could increase through replacing these surfaces with hardstanding. Therefore, this issue has not been considered further within the assessment.
Contamination from Process Waste
12.6.22 Process waste / by-products in the form of FGT residues, IBA, waste oils and lubricants has the potential to create contamination on and off site if operational practices are not developed and managed efficiently. This waste could both be flushed from the site as surface water runoff or by wind potentially affecting the local watercourses and shallow groundwater.
12.6.23 Any contamination would likely remain within the shallow groundwater for longer periods when compared to local watercourses due to the flushing effect experienced in surface waters during high flows.
Pollution of Site Runoff by Oils and Hydrocarbons
12.6.24 Routine use / presence of lorries, cars and other vehicles across the site and on access routes and associated accidental spills or minor leaks all have the potential to contaminate runoff in the
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locality with hydrocarbons or other chemicals. This could then be flushed through the system during heavy rainfall or high flows within the watercourses which could then lead to contamination of receptors downstream of the site.
12.6.25 If such contamination occurred, it could lead to degradation of water quality in the downstream receptors and associated ecological damage. However, as contaminants are mobilised during heavy rainfall and high flows in the watercourses they are likely to be substantially diluted, thus reducing the associated risk.
Pollution of Site Runoff by Gritting
12.6.26 Site access roads are likely to be treated with salt during winter periods for safety purposes to prevent ice forming on roads. During subsequent melts or rainfall this becomes entrained and dissolved in site runoff potentially polluting downstream receptors.
12.6.27 If such contamination were to occur it could lead to the temporary degradation of the water quality downstream and ecological damage. However, any gritting that may be necessary will not be any more extensive than for the existing public road network. Furthermore, the periods of potential contamination are limited to the winter months which tend to be associated with high rainfall resulting in greater levels of dilution than in the summer, and therefore reducing the associated risk.
Contamination of Shallow Groundwater
12.6.28 Routine use of heavy goods vehicles, cars and other vehicles across the site as well as oils and chemicals being stored and utilised on site all have the potential to create contamination which could then infiltrate into the shallow groundwater either through cracks in hardstanding, or through runoff onto non-developed areas.
12.6.29 Given the permeability of the shallow geology it is likely that there could be some migration of any released contamination, particularly with regards to shallow groundwater.
Contamination from Imported / Treated Waste
12.6.30 Waste imported to, and stored on, the site for treatment has the potential to cause contamination. Any liquid wastes / leachates could seep into shallow groundwater through cracks in hardstandings or bunkers or runoff into local watercourses. Accidental releases of the waste, or waste leachates, to watercourses or groundwater could potentially cause deterioration of water quality and smothering and / or entrapment of aquatic ecology. Releases of significant amounts of litter could also be visually unacceptable on watercourses.
12.6.31 Any contamination would likely remain within the shallow groundwater for longer periods when compared to local watercourses due to the flushing effect experienced in surface waters during high flows.
12.6.32 Table 12.13 provides a summary of the potential operational phase pollution related impacts prior to mitigation.
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Table 12.13 Operational Phase Impacts (Including Incorporated Mitigation in the ERF Design but Excluding Additional Mitigation)
Source Nature of Pathway Receptor Sensitivity of Magnitude of Significance of Likelihood Risk Impact Receptor Impact Impact
Site Contamination Surface water Drainage network Low Moderate Minor Unlikely Very low risk (operations by oils and runoff and associated and storage) hydrocarbons ponds Uncontrolled discharge Surface water Saredon Brook Medium Moderate Moderate Unlikely Low risk runoff
Uncontrolled discharge Surface water flow River Penk Medium Negligible Insignificant Unlikely Very low risk via Saredon Brook
Direct infiltration to Secondary Aquifer Low Moderate Minor Unlikely Very low risk ground (A). (Shallow groundwater)
Infiltration through Principal Aquifer High Minor Moderate Unlikely Very low risk overlying superficial drift deposits
Contamination Surface water Drainage network Low Moderate Minor Unlikely Very low risk by process runoff and associated waste ponds Uncontrolled discharge
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Source Nature of Pathway Receptor Sensitivity of Magnitude of Significance of Likelihood Risk Impact Receptor Impact Impact
Site Contamination Surface water Saredon Brook Medium Moderate Moderate Unlikely Low risk (operations by process runoff and storage) waste Uncontrolled discharge Surface water flow River Penk Medium Negligible Insignificant Unlikely Very low risk via Saredon Brook
Direct infiltration to Secondary Aquifer Low Moderate Minor Unlikely Very low risk ground (A). (Shallow groundwater)
Infiltration through Principal Aquifer High Minor Moderate Unlikely Low risk overlying superficial drift deposits Road Contamination Surface water Drainage network Low Moderate Minor Likely Low risk Maintenance by gritting runoff and associated ponds
Surface water Saredon Brook Medium Moderate Moderate Likely Moderate risk runoff
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Source Nature of Pathway Receptor Sensitivity of Magnitude of Significance of Likelihood Risk Impact Receptor Impact Impact
Waste Contamination Surface water flow River Penk Medium Negligible Insignificant Unlikely Very low risk delivery and by gritting via Saredon Brook operation of plant Direct infiltration to Secondary Aquifer Low Minor Minor Low Likelihood Low risk ground (A). (Shallow groundwater) Infiltration through Principal Aquifer High Negligible Insignificant Unlikely Very low risk overlying superficial drift deposits Contamination Surface water Drainage network Low Moderate Minor Unlikely Very low risk from delivery runoff and associated waste ponds Surface water Saredon Brook Medium Moderate Moderate Unlikely Low risk runoff
Surface water flow River Penk Medium Negligible Insignificant Unlikely Very low risk via Saredon Brook
Direct infiltration to Secondary Aquifer Low Moderate Minor Unlikely Very low risk ground (A). (Shallow Groundwater) Infiltration through Principal Aquifer High Minor Moderate Unlikely Low risk overlying superficial drift deposits
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12.6.33 Although some of the potential impact significances are rated as moderate, when taking the likelihood into account all risks from the operation of the site are classified as low risk or lower, other then the risk to Saredon Brook from contamination from gritting operations, which is rated as moderate.
Flood Risk
Flood Risk Assessment
12.6.34 A FRA in line with PPS25 has been undertaken for the proposed ERF, which is provided in full in Appendix 12.1 and summarised in the following sections. The FRA draws upon the 2007 FRA (prepared by Enviros).
Sequential Test
12.6.35 The site is located in Flood Zone 1 (see Table 12.10) indicating that flooding from major fluvial or tidal sources is not likely. Land immediately beyond the southwest corner of the site is located within Flood Zone 3, however, this fluvial flood source is not considered to pose a potential flood risk to the proposed development.
12.6.36 The sequential test as set out in PPS25 states that development for waste treatment is appropriate in Flood Zone 1. In support of this Annex A of the FRA (Appendix 12.1) provides correspondence from the EA in 2008 indicating that they would have no objection in terms of flood risk to the proposed development. However, the EA have stipulated that the following should be incorporated:
• Where fencing is proposed along the watercourse a minimum of 6 m from the top of the bank of the river for future possible maintenance access is required. • Permitted development rights are removed for the area shown to be at risk of flooding (this is not considered relevant as the site is entirely located within Flood Zone 1 – the 2007 FRA initially assessed a different site boundary which put part of the site in Flood Zone 3).
Sensitivity of Receptors
12.6.37 The sensitivity of the proposed development of the ERF can be based on the flood risk vulnerability classification as set out within Table D2 of PPS25, where waste treatment plant is classified as ‘less vulnerable development’. Given this the development sensitivity has been defined as medium. Those areas not being developed will be ‘water compatible development’ and thus will have a low sensitivity.
12.6.38 When considering off site receptors there is a general assumption that all developments are highly sensitive to any increase in flood risk and, therefore, it is important that any adverse off- site impacts on flood severity or frequency are avoided.
Risk Assessment
12.6.39 PPS25 requires that all potential sources of flooding that could affect the proposed development be considered. This section considers all of the potential sources as listed in Annex C (Forms of Flooding) of PPS25.
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Saredon Brook
12.6.40 The EA Flood Map shows that the site is located within Flood Zone 1. This indicates that the annual risk of flooding to this area of the site from Saredon Brook is less than 1 in 1000 year (0.1% annual probability). Land within Flood Zone 3 is located immediately beyond the south western boundary of the site, on the ecological mitigation land. The detailed topographic data provided for this assessment (Figure 3 of the FRA, Appendix 12.1) indicates that land located within Flood Zone 3 is below 98 m aOD.
12.6.41 The proposed development is predominantly located in areas above 100 m aOD. Therefore, there is effectively a 2 m difference in elevation between the 1 in 100 year event flood water level and the development.
12.6.42 In addition, whilst detailed topographic information for the opposite bank of the river is not available, the Ordnance Survey 1:25,000 map indicates that the ground is lower on the opposing bank. Thus, if floods exceeding the predicted 1 in 100 year event were to occur, flood waters would extend southwards onto the open lower land rather than onto the site.
12.6.43 Based on existing ground levels on the site and the location of the proposed development on land above 100 m aOD the probability of flooding from this source to the ERF is considered low.
12.6.44 Using Flood Zone 2 as a surrogate for Flood Zone 3 with climate change it can be seen that when considering the effects of climate change the Flood Zone 3 extent would remain beyond the southern boundary of the site.
12.6.45 Therefore, this conclusion is not modified by allowing for possible climate change effects. The overall risk from the brook is therefore assessed as low to the site and very low to the development.
Ponds Off Site
12.6.46 No pathways are identified for ponds off site.
Tidal
12.6.47 Flood risk from tidal sources is very low due to the site's inland location and elevation approximately 100 m aOD.
Overland Flow
12.6.48 The site is on a gentle slope to south with no steep slopes in close proximity to the site. No potential pathways are therefore identified for flooding from overland flow.
Drainage and Mains Supply
12.6.49 A failure of one of the surface water drains/sewers or mains supply could potentially occur, for example due to very high system flows after a major storm event or a collapse within the system itself. There is a small possibility that such an event up gradient of the site to the northwest could cause surface flooding. The position of the mains water and surface water sewers, however, is such that any such flood waters, if they were to occur, would not be likely to flow onto the site, but would flow directly south to the Saredon Brook.
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12.6.50 Also, the surface water sewers around the site are not extensive and are not expected to convey significant rates of flow. In case of a system collapse the total volume of flood waters would not be large.
12.6.51 Whilst the likelihood of a flood event due to failure of the local drainage system cannot be easily quantified, it is conservatively assessed as of medium probability. The magnitude of impact should it occur is considered to be negligible, thus the overall flood risk is also negligible.
Foul Sewers
12.6.52 The recent construction of the ‘Dell’ development involved the relocation of the foul sewer.
12.6.53 The foul sewer is still located up-gradient of the site but is unlikely to carry significant flow. Thus, should flooding occur it is not predicted to be above low magnitude. Again, the likelihood of such an event occurring is assessed as medium and so the overall risk is low.
Groundwater
12.6.54 The sands and gravels on site are underlain by low permeability glacial drift that is unlikely to transmit significant volumes of water. The site is on a gentle slope to the south and overlooks low lying land to the east and south. It is not at the base of any significant slope.
12.6.55 With consideration of these factors, it has been determined that the potential for flooding to occur from seepage is low. Should it occur, due to the small volume likely to be present, the impact would be very low and therefore so would the overall risk.
Artificial
12.6.56 The EA Flood Map does not consider man-made canals as they cut across catchments. Canals do not usually have significant flow and do not generally flood as they can be managed through the use of locks. However, there is a possibility that vandalism, a blockage or structural failure of the Staffordshire and Worcestershire Canal could result in a build up of water and overland flow up and above the edge of the canal to the site.
12.6.57 However, the canal is not embanked, is located 150 m north of the site on relatively level ground and is monitored and controlled by British Waterways (who can operate emergency sluices in the event of an accident). The probability of flooding from such an event reaching the site is considered to be very low, and the resulting impact, should it occur, is also considered to be very low. Combined, the overall risk of flooding from this source is very low.
Increased Surface Water Runoff
12.6.58 The existing site is undeveloped. Therefore, an increase in impermeable surfaces due to development of the ERF will lead to higher peak flows from the site, which will discharge either directly or indirectly to the Saredon Brook increasing flood risk to third parties downstream.
12.6.59 The sensitivity of the receptor is classed as medium, and a medium magnitude of potential. The resulting impact is moderate. There is high probability of occurrence, with a resulting high risk of flooding of downstream receptors. The results of the FRA are summarised in Table 12.14.
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Table 12.14 Flood Risk Summary (Not Including Mitigation)
Flood Source Pathway Receptor Sensitivity Magnitude of Probability of Flood Risk potential effect occurrence Fluvial Saredon Brook Flows in excess of site Low Low Low Low channel capacity
Flows in excess of Development Moderate Very low Very low Negligible channel capacity
Ponds and drains Blockage and Development Moderate Negligible Medium Negligible on site excedance of channel/retention area
Drainage Mains water Pipe burst and overland Development Moderate Negligible Medium Negligible flow
Surface drains Blocked and surcharge Development Moderate Negligible Medium Negligible and sewers followed by overland flow Foul sewers Blocked and surcharge Development Moderate Low Medium Low followed by overland flow Groundwater Underlying sands Higher groundwater Development Moderate Very low Very low Negligible and gravels levels expressed at surface
Artificial Staffordshire and Blockage and Development Moderate Very low Very low Negligible sources Worcestershire surcharge followed by Canal overland flow Increased Development Increased surface Saredon Brook Moderate Moderate High High impermeable water runoff floodplain areas
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12.6.60 Typically risks assessed to be low, or less, are acceptable whereas risks assessed to be moderate or high require additional mitigation or management to enable development to proceed.
12.6.61 All the risks to the proposed ERF development are assessed as low or lower. There is a low risk of flooding from foul sewers up-gradient of the site. Although the risk is low, it is recommended that Finished Floor Levels (FFLs) be at least 0.3 m above the surrounding ground level, as was proposed in the design for the consented EfW facility. No additional mitigation is required in terms of flood risk to the development.
12.6.62 As the proposed development will result in an increase in the hardstanding area on site compared with existing conditions, surface water runoff from the site is likely to increase. The flood risk posed to downstream receptors by this increase in surface water runoff has been assessed as high, and therefore, additional mitigation is required.
12.7 Additional Mitigation Mitigation During Construction
12.7.1 Mitigation measures during construction will help to manage any identified negative impacts deemed to be significant. If possible, works should be avoided, or sensibly managed, in accordance with adverse ground and / or weather conditions occurring such as heavy rainfall or waterlogged soils.
12.7.2 A Construction Environmental Management Plan (CEMP) will be prepared by Clugston prior to work commencing on the site (an outline CEMP can be found in Appendix 4.7). This will contain detailed information regarding the techniques and methods that will be used to limit the impact of the construction phase on the water environment. The CEMP will also include details of any monitoring proposed.
Mobilisation of Sediments
12.7.3 Specific guidance in dealing with silt arising from construction activities is contained within the EA’s PPG5. A number of measures could be put in place in order to minimise the actual transport of silt into surface water features including:
• Use of sediment traps and installing settlement ponds or tanks where practical. • Directing runoff into designated vegetated ground to reduce silt and suspended solids before discharge off site. • Use of designed drainage filters. • Provision of track or road side drainage channels with small dams to assist with silt retention. • Bulk materials such as aggregate, topsoil and excavated arisings will be stored in designated areas away from watercourses. Where stockpiles are located in the vicinity of watercourse a minimum 5 m buffer strip should be in place to reduce pollution risks. • Bunding (either earth bunds, cut-off ditches or other forms of diversion) or sheeting of stockpiles will be used to minimise the potential for silt laden run-off. Where appropriate silt fences or straw / rock barriers at the toe of the stockpile would be put in place to mitigate runoff during rainfall events. A silt fence comprises a geotextile filter fabric, straw bales or a combination of both, installed in the path of runoff and can filter out heavy sediments.
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Groundwater and Surface Water Resources and Contamination
12.7.4 The storage of polluting materials should be kept to a minimum where practicable, and where less hazardous or inert materials are available these should be specified. For example, construction materials containing sulphides or cement which could potentially alter the pH of runoff will be avoided and the use of biodegradable hydraulic oils could be considered for construction plant. In addition, absorbent mats/pads, absorbent granules and sand could be made available, and site operatives trained in their use, to deal with any spillages.
12.7.5 Further measures should be adopted include locating mobile plant at least 20 m from water features. Further, the positioning of fuel storage tanks and other potentially polluting materials and maintenance facilities should be on bunded areas of hardstanding with dedicated drainage systems. The bunded areas should be protected from direct rainfall by organic mulch or a temporary sward, and stored materials on site should be checked regularly for containment integrity (both primary and secondary), quantity stored and security of storage.
12.7.6 Construction of concrete structures during the construction phase should be monitored to prevent cementitious material entering any watercourses. Pre-cast work or permanent formwork will reduce the amount of in-situ concreting required. Ready mix suppliers should be used in preference to on-site batching.
12.7.7 Washing out of concrete wagons or other equipment used in concreting operations should be undertaken in designated contained washout areas. These should be located away from all watercourses, drains and groundwater protection zones, and should be impermeable. Due to the SPZ within the area, washout water should be contained and removed from site for treatment as liquid waste.
Dewatering
12.7.8 Any significant excavations that are required during the construction process, principally excavation of the made ground and sandstone for the waste bunker, will need to incorporate measures to control the ingress of groundwater. This depends on the permeability of the sandstone and therefore the amount of water that may ingress into the excavation. Pre- construction abstraction trials (see Appendix 4.3) will take place in order to define the construction method and any mitigation required, in consultation with the Environment Agency. The different construction methods are expected to comprise the following:
• High water flow – sheet piling then grouting to minimise water ingress into the excavation. • Low water flow / high levels of contaminated groundwater – sheet piling then grouting to minimise water ingress into the excavation; collection of contaminated water and either treatment prior to discharge to stream / ground, discharge to foul sewer or tankering off site for disposal. • Low water flow / low or no levels of contaminated groundwater – open excavation; collection of water and discharge to stream / ground via silt trap.
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12.7.9 Permission for any dewatering activities will need to be sought from the EA under the terms of the Water Act 2003 8 in advance of construction commencing.
12.7.10 Mass concrete foundations for other elements of the development would require similar groundwater control measures to avoid the need for significant dewatering. Piled foundations using continuous flight auger piles bearing on to the Sherwood Sandstone could be adopted to minimise contaminated perched water being transferred to the underlying aquifer.
12.7.11 Table 12.17 provides a summary of mitigated construction phase impacts to the water environment.
Mitigation During Operation
Pollution from Process Wastes
12.7.12 Management of waste removal should be undertaken with due caution to prevent pollution release. Any transfer of IBA or FGT residue will take place within the building envelope to help prevent accidental release. Emergency response plans should be prepared to ensure that minimal waste is released should an accident occur. The SUDS system described below (see 12.7.21) will also provide some level of protection from waste entering the water environment.
Pollution of Site Runoff and Groundwater by Oils and Hydrocarbons
12.7.13 Any operational activities that carry significant risk of oils / hydrocarbon spillage must comply with the EA’s PPG1 and PPG5. If activities such as refuelling occur on the site, additional measures (e.g. oil interceptors, bunded areas) proportionate to the risks posed should be put in place.
12.7.14 Such measures could include construction of a facility to isolate drainage from that area and undertaking regular checks / monitoring of any discharge. Any such activity would, however, be subject to a separate task specific environmental risk assessment under the Environmental Permitting Regulations regime and associated licences from the EA.
Pollution from Gritting
12.7.15 Salt gritting of local roads and the site should only take place at intervals when required during the winter period. Spreading should be minimal and carried out with due sensitivity.
Contamination from Delivered Waste
12.7.16 Sound management and adoption of standard good working practices should be undertaken during all transfer of waste from delivery vehicles to the plant and all waste handling should occur within the building. Waste should be stored appropriately to ensure accidental release does not occur. Emergency response plans should be prepared to ensure that minimal waste or leachate is released should an accident occur.
12.7.17 Implementation of these mitigation measures will ensure that residual impacts on the identified receptors and their significance are minimised. Table 12.18 provides a summary of mitigated operational phase impacts to the water environment.
8 Available online at: http://www.defra.gov.uk/environment/quality/water/legislation/index.htm
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Flood Risk Mitigation
Drainage Policy
12.7.18 PPS25 states that as well as assessing risk to a development, the risk of flooding arising from a development should be considered. In general, site development reduces the permeability of the site, increasing the volume and rate of water running off the site, potentially increasing flood risk to third parties.
12.7.19 Paragraph 5.54 of the PPS25 Practice Guide provides guidance on the management of surface water generated on site to ensure flood risk to third parties does not increase post development:
“For the range of annual flow rate probabilities up to and including the one per cent annual exceedance probability (1 in 100 years) event, including an appropriate allowance for climate change, the developed rate of runoff into a watercourse, or other receiving body, should be no greater than the existing rate of runoff for the same event”.
12.7.20 To ensure post development runoff rates do not exceed existing site runoff rates over the developments lifetime, appropriate drainage arrangements are required on site. Annex F of PPS25 promotes the use of Sustainable Drainage Systems (SUDS) in new developments to manage surface water generated on site.
Sustainable Drainage Systems
12.7.21 The incorporation of SUDS should be assessed on a site by site basis, taking into consideration the physical characteristics of the catchment (e.g. slope), the nature of the rainfall event, the hydrology of the catchment, and the presence of any pollutants.
12.7.22 Examples of potential SUDS include:
• Source control measures - including rainwater harvesting, green/living roofs and water butts (where possible). • Filter strips and swales - which are vegetated features that hold and drain water mimicking natural drainage patterns (Due to health and safety, design and maintenance issues, swales are not considered suitable onsite). • Filter drains and porous pavements - to allow rainwater and runoff to infiltrate into permeable material below ground and provide storage if needed (where infiltration is shown to be appropriate for use onsite). • Basins and ponds - to hold excess water after rain and allow controlled discharge that avoids flooding.
12.7.23 The Surface Water Drainage Strategy prepared by Scott Wilson (Appendix 4.1) and summarised within the updated Flood Risk Assessment (Appendix 12.1) indicates that the use of infiltration techniques on the site is limited based on previous infiltration tests carried out in the vicinity of the site. Therefore the Surface Water Drainage Strategy is principally based on attenuation. The Surface Water Drainage Strategy is summarised below to inform this ES chapter.
Surface Water Drainage Strategy
12.7.24 The Surface Water Drainage Strategy is principally based on two attenuation ponds; one in the southeast corner of the site (the southern pond) and one in the northern extent of the site (the
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northern pond) (see Appendix 4.1 Annex A) with further temporary attenuation provided by a living roof (approximate living roof area 0.8 ha).
12.7.25 The proposed living roof and attenuation ponds are deemed acceptable to provide sufficient biodiversity benefits to the site when compared to the existing development. Therefore the site will comply with PPS25 and local policies D2, in particular item (g) 9.
12.7.26 The site has been separated into two drainage areas, one area draining into the northern pond and one draining into the southern pond. The reference greenfield runoff rates for the 1 in 100 year return period rainfall event from each drainage area have been calculated and are provided below in Table 12.15.
Table 12.15 Greenfield Runoff Rates for Each Site Drainage Area
Drainage Area Name Surface Area (ha) Greenfield runoff rate (l/s)
Northern area 0.86 2.8 Southern area 1.35 4.4
12.7.27 To ensure that greenfield runoff rates from the site are not exceeded for rainfall events up to and including the 1 in 100 year return period, over the lifetime of the development (incorporating a 20% increase in peak rainfall intensity) attenuation volumes, as shown in Table 12.16 will be required.
Table 12.16 Required Attenuation for Each Site Area During the 1% Annual Probability Storm Event, Inclusive of Climate Change
Drainage Area Reference runoff rate (l/s) Required Attenuation (m 3) Minimum Pond Name Dimensions Area (m 2) Depth (m) Northern area 3.3 752 835 0.9 Southern area 4.4 1,358 1,030 1.4
12.7.28 The main receptor for surface water runoff discharging from the proposed SUDS features would be the small ditch that flows south along the eastern boundary of the site, before turning west along the southern boundary. This ditch joins the Saredon Brook to the south west of the site.
12.7.29 In order to comply with PPS25 and its Practice Guide, the ponds and drainage system should include a design for exceedance. This would reduce the chance of flood water inundating the buildings in the unlikely event that a storm of greater magnitude than the 1% annual probability event (inclusive of climate change) was to occur. It would also offer some protection against a blockage of the drainage system. In order to design for exceedance, it is recommended that detailed designs should consider constructing the ponds with excess storage capacity.
12.7.30 The recommendation that FFLs within the development are set a minimum of 0.3 m above surrounding ground levels will also provide mitigation so that the parking and roads flood and not the building.
9 http://www.staffordshire.gov.uk/NR/rdonlyres/43E17862-4CBA-48B8-AE95- FE1B8DB661FA/61655/StructurePlanExplanatoryMemorandum7802savedpolicie.pdf
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Table 12.17 Construction (and Decommissioning) Phase Environmental Impact with Mitigation
Source Nature of Pathway Receptor Sensitivity of Magnitude of Significance of Likelihood Risk Impact Receptor Impact Impact
Site Erosion / Direct surface Drainage network Low Minor Minor Low likelihood Low risk Development sediment loading water runoff and associated ponds Direct surface Saredon Brook Medium Minor Minor Low likelihood Low risk water runoff
Surface water flow River Penk Medium Negligible Insignificant Unlikely Very low risk via Saredon Brook
Water quality Mobilisation of Drainage network Low Minor Minor Unlikely Very low risk existing and associated contamination ponds Mobilisation of Saredon Brook Medium Minor Minor Unlikely Very low risk existing contamination Mobilisation of River Penk Medium Negligible Insignificant Unlikely Very low risk existing contamination
Mobilisation of Secondary Aquifer Low Minor Minor Low likelihood Low risk existing (A). (Shallow contamination groundwater)
Mobilisation of Principal Aquifer High Negligible Minor Low likelihood Low risk existing contamination
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Source Nature of Pathway Receptor Sensitivity of Magnitude of Significance of Likelihood Risk Impact Receptor Impact Impact
Site Water Quality Surface water Drainage network Low Negligible Insignificant Unlikely Very low risk Development runoff and associated ponds Direct discharge Surface water Saredon Brook Medium Negligible Insignificant Unlikely Very low risk runoff
Direct discharge Surface water flow River Penk Medium Negligible Insignificant Unlikely Very low risk via Saredon Brook
Direct infiltration to Secondary Aquifer Low Minor Minor Unlikely Very low risk ground (A). (Shallow groundwater) Infiltration through Principal Aquifer High Negligible Insignificant Unlikely Very low risk overlying superficial drift deposits
Dewatering – Infiltration through Saredon Brook Medium Negligible Insignificant Unlikely Very low risk Flow alteration baseflow
Infiltration through Secondary Aquifer Low Minor Minor Unlikely Very low risk baseflow (A). (Shallow groundwater)
Infiltration from Principal Aquifer High Negligible Insignificant Low likelihood Very low risk Secondary Aquifer (A). (Shallow groundwater)
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Table 12.18 Operational Phase Environmental Impact with Mitigation
Source Nature of Pathway Receptor Sensitivity of Magnitude of Significance of Likelihood Risk Impact Receptor Impact Impact
Site Pollution by oils Surface water Drainage network Low Negligible Insignificant Unlikely Very low risk (operations and runoff and associated and storage) hydrocarbons ponds Direct discharge Surface water Saredon Brook Medium Negligible Insignificant Unlikely Very low risk runoff
Direct discharge Surface water flow River Penk Medium Negligible Insignificant Unlikely Very low risk via Saredon Brook
Direct infiltration to Secondary Aquifer Low Negligible Insignificant Unlikely Very low risk ground (A). (Shallow groundwater) Infiltration through Principal Aquifer High Insignificant Insignificant Unlikely Very low risk overlying superficial drift deposits Road Pollution by Surface water Drainage network Low Minor Minor Low likelihood Low risk Maintenance gritting runoff and associated ponds
Surface water Saredon Brook Medium Minor Minor Low likelihood Low risk runoff
Surface water flow River Penk Medium Negligible Insignificant Unlikely Very low risk via Saredon Brook
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Source Nature of Pathway Receptor Sensitivity of Magnitude of Significance of Likelihood Risk Impact Receptor Impact Impact
Road Pollution by Direct infiltration to Secondary Aquifer Low Negligible Insignificant Unlikely Very low risk Maintenance gritting ground (A). (Shallow groundwater) Infiltration through Principal Aquifer High Negligible Insignificant Unlikely Very low risk overlying superficial drift deposits Site Pollution by Surface water Drainage network Low Negligible Insignificant Unlikely Very low risk (operations process waste runoff and associated and storage) ponds Direct discharge Surface water Saredon Brook Medium Negligible Insignificant Unlikely Very low risk runoff
Direct discharge Surface water flow River Penk Medium Negligible Insignificant Unlikely Very low risk via Saredon Brook
Direct infiltration to Secondary Aquifer Low Negligible Insignificant Unlikely Very low risk ground (A). (Shallow groundwater)
Infiltration through Principal Aquifer High Negligible Insignificant Low likelihood Very low risk overlying superficial drift deposits
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Source Nature of Pathway Receptor Sensitivity of Magnitude of Significance of Likelihood Risk Impact Receptor Impact Impact
Waste Contamination Surface water Drainage network Low Negligible Insignificant Unlikely Very low risk delivery and from delivered runoff and associated operation of waste ponds plant Surface water Saredon Brook Medium Negligible Insignificant Unlikely Very low risk runoff
Surface water flow River Penk Medium Negligible Insignificant Unlikely Very low risk via Saredon Brook
Direct infiltration to Secondary Aquifer Low Negligible Insignificant Unlikely Very low risk ground (A). (Shallow groundwater) Infiltration through Principal Aquifer High Negligible Insignificant Unlikely Very low risk overlying superficial drift deposits
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12.8 Residual Effects and Conclusion
12.8.1 Given the additional mitigation set out above, all effects for the construction, operation and decommissioning of the proposed ERF can be mitigated to a minor level of significance. The risks of effects are also reduced to low risk or less.
12.8.2 All operations will occur on hardstanding or within a building providing the underlying Principal Aquifer and surface waters with significant protection from pollution incidents. Incorporation of standard best practice during the construction works and during operation will also ensure that no major pollution incidents occur and thus protect the aquifer and surface waters.
12.8.3 Although no significant flood risks to the development have been identified, finished floor levels will be raised to reduce risks further. In addition, appropriate SUDS will be employed to ensure the development does not contribute to flooding of downstream receptors. With regards to flood risk, the application of SUDS will ensure runoff from the site will remain at greenfield rates, resulting in no impact on flood risk.
12.9 Comparison of Predicted Environmental Effects of Proposed ERF with Consented EfW
12.9.1 Minor differences in the baseline conditions have been noted, but these are mainly concerned with updated methodologies used to categorise surface water and groundwater features. For example the Environment Agency has published new Aquifer Designation maps which replace the previously used Groundwater Vulnerability maps. The previously known Major and Minor Aquifers are now known as Principal and Secondary Aquifers respectively. Although the terminology has changed the actual status of the underlying aquifers remains unchanged.
12.9.2 The methodology used to categorise river quality status has also been updated since the assessment of the consented EfW facility. The Environment Agency General Quality Assessment has been superseded by the Water Framework Directive classification system. However, a comparison of the two classification systems suggests that the river quality of the identified watercourse – the Saredon brook – remains at a similar status.
12.9.3 In respect of water resources impacts, there would be no significant difference between the consented EfW facility and the ERF now proposed. It should be noted that the Enviros assessment considered that the risk of flooding to the site from the Saredon Brook was high, whilst the flood risk to the development itself was very low. Since the site is entirely within flood zone 1 this assessment has found the flood risk to the site to be low and the flood risk to the development to be negligible.
12.10 References
Enviros Consulting Limited, 2008. Four Ashes Phase 2 Land Quality Assessment. Prepared for Staffordshire County Council, April 2008. MLM, 2009, Site at Four Ashes, Factual Ground Investigation Report. Prepared for Staffordshire County Council, October 2009.
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