The Wrexham (Gas Fired Power Station) Order
6.2.8 Volume 2: Environmental Statement Chapter 8: Air quality
Planning Act 2008 The Infrastructure Planning (Applications: Prescribed Forms and Procedure) Regulations 2009
PINS Reference Number: EN010055 Document Reference Number: 6.2.8 Regulation Number: 5(2) (a) Lead Author: Atkins
Revision: Date: Description: 0 March 2016 Submission version
SEC6-ES Vol1_A4 chapterTabs.indd 9 15/03/2016 10:49
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Chapter 8 Air quality
INTRODUCTION
8.1 This chapter describes the potential effects of the Wrexham Energy Centre (WEC or Scheme) on ambient (outdoor) air quality. Good air quality is important for human health and the health of other living organisms, both animal and vegetable. The quality of air is determined by the concentration of pollutants it contains, in relation to established health based criteria. A pollutant is essentially a substance in the wrong place, at the wrong time, and at the wrong concentration. Pollution can be more formally defined as the introduction of a substance or form of energy into the environment that is likely to cause damage to the environment or those living within it.
8.2 The air quality assessment contained in this chapter considers the effects of direct and indirect emissions of air pollutants during the construction, operation (including maintenance) and decommissioning phases of the Scheme. Short-term and long- term pollutant concentrations are evaluated in the context of relevant ambient air quality criteria set for the protection of human health and ecology, taking into account where appropriate the existing background situation
8.3 The main element of this air quality assessment is an atmospheric dispersion modelling study of emissions to atmosphere from the Stacks of the Power Station Complex element of the Scheme. This has been carried out in line with national policy and permitting guidance32 to assess the potential effects of changes to ground level concentrations on human health and the environment. Likely significant environmental effects resulting from changes to local air quality due to vehicle movements associated with construction and operational activities have been evaluated and a qualitative assessment of dust emissions from construction and decommissioning evaluated has also been undertaken.
Air pollutants
8.4 The assessment of the likely significant environmental effects associated with the Scheme addresses the combustion products discharged in the flue gases from the Stacks, principally oxides of nitrogen (NOx) and carbon monoxide (CO). NOx and CO are the only pollutants with Emission Limit Values (ELVs) in the Industrial Emissions Directive (IED) for natural gas fired CCGT combustion plants (IED Annex V Part 2).
32 Environment Agency/DEFRA (2016) “Air Emissions Risk Assessment for your environmental permit”. Available at https://www.gov.uk/guidance/air-emissions-risk-assessment-for-your-environmental-permit. Horizontal guidance produced by the Environment Agency for permitting is supported by NRW (https://naturalresources.wales/apply-for-a-permit/environmental-permitting-regulations- guidance/horizontal-guidance/?lang=en)
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8.5 Emissions of NOx from natural gas fired CCGTs are the lowest for any thermal generating plant33. The choice of CCGT technology in itself mitigates air pollution and as such is considered to be embedded mitigation within the design of the Scheme.
8.6 Natural gas contains extremely low levels of sulphur and particulates resulting in 34 negligible emissions of both sulphur dioxide (SO2) and particulate matter (PM) . The natural gas entering turbines is subject to filtration to avoid damage to the equipment and thereby reducing particulate matter in the fuel gas even further. The inherently low emissions of these pollutants from gas fired turbines is reflected in the fact that the European Industrial Emissions Directive (IED) (2010/75/EU) has not specified emission limits for these pollutants for gas fired turbines. As has been agreed during consultation with the regulator and EHO, emissions of these two pollutants are not assessed in the model.
8.7 This approach is supported by National Policy Statement (NPS) EN-2, which states that ‘fossil fuel generating stations are likely to emit nitrogen oxides (NOx) and sulphur oxides (SOx), although SOx emissions from gas-fired generating stations may be negligible.’
8.8 The air pollutant of most relevance in the context of this assessment is therefore nitrogen dioxide (NO2), a secondary pollutant formed from the oxides of nitrogen which will be discharged from the gas turbines. Road traffic associated with the Scheme will also emit oxides of nitrogen as well as fine particles known as PM10 and PM2.5. These pollutants are the most likely to be present at concentrations close to or above their statutory limit values in areas of the UK, and are hence the focus of the assessment of vehicle emissions associated with the Scheme.
8.9 In addition, dust emissions (including the particles that give rise to soiling, and to human health and ecological effects) may arise during construction and decommissioning of the Scheme, and the effects associated with this are assessed in this chapter of the ES.
Key Policies, Legislation and Guidance
National Policy Statements
Overarching National Policy Statement for Energy (EN-1)
8.10 NPS EN-1 (Section 5.2) requires that applications for new energy infrastructure should consider any significant air emissions, their mitigation and any residual
33 Environment Agency Technical Guidance for Combustion Activities (EPR1.01) available at https://www.gov.uk/government/publications/combustion-activities-additional-guidance 34 http://chp.decc.gov.uk/cms/gas-turbines-10 .
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effects, including taking account of any significant emissions associated with road traffic associated with the development. The assessment should present the predicted absolute emission levels (post mitigation), and report on existing air quality and the relative change in air quality due to the proposed development. Any potential eutrophication impacts (adverse effects on sensitive ecosystems) should also be considered.
8.11 Furthermore, the Environmental Statement (ES) should consider the potential for release of dust emissions, during construction, operation and decommissioning, and recommend measures for preventing or mitigating such emissions (NPS EN-1 Part 5.6).
8.12 NPS EN-1 also highlights the requirement for the assessment of environmental impacts to include cumulative effects of the proposed development when considered with existing pollution sources in and around the Site, and whether these would make the development unacceptable, particularly in relation to statutory environmental quality limits (Part 4, paragraph 4.10.7).
National Policy Statement for Fossil Fuel Electricity Generating Infrastructure (EN-2)
8.13 NPS EN-2 sets out specific considerations in relation to air emissions from fossil fuel generating stations, and their regulation through the Environmental Permitting (England and Wales) Regulations 2010 (as amended) ("EPR"). It notes that SOx emissions from gas-fired generating stations may be negligible.
National Policy Statement for Gas Supply Infrastructure and Gas and Oil Pipelines (EN-4)
8.14 NPS EN-4 states that the effects of gas emissions should be assessed and advises that applicants should follow the generic considerations on these issues set out in NPS EN-1.
Planning Policy Wales (Edition 8, January 2016)
8.15 The land use planning system is integral to improving air quality, and Planning Policy Wales (PPW)35 contains a number of measures to ensure Local Planning Authorities incorporate air quality considerations into planning decisions.
8.16 Paragraph 8.1.9 of PPW states that “Development plan policies and decisions on planning applications should take into account statutory air quality objectives, together with the results of air quality reviews and assessments and any Air Quality Management Plans or Area Action Plans.”
8.17 Paragraph 13.10.3 of PPW states the following in respect of Air Quality Management Areas and improving the quality of air:
35 http://gov.wales/docs/desh/publications/160104planning-policy-wales-edition-8-en.pdf
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“Where pollution considerations, which may be relevant to a pollution control authorisation or licence or result from the need to comply with any statutory environmental quality standards or objectives, affect the use and development of land they can be material planning considerations. This provision extends to air quality objectives set out under Part IV of the Environment Act 1995 and the local authority’s action plans for Air Quality Management Areas […] The weight attached to such considerations will depend on the scope of the pollution control system in each case and the effect on land use and amenity”.
8.18 Paragraph 13.12.1 states further that:
“The potential for pollution affecting the use of land will be a material consideration in deciding whether to grant planning permission. Material considerations in determining applications for potentially polluting development are likely to include:
location, taking into account such considerations as the reasons for selecting the chosen site itself;
impact on health and amenity;
the risk and impact of potential pollution from the development, insofar as this might have an effect on the use of other land and the surrounding environment (the environmental regulatory regime may well have an interest in these issues, particularly if the development would impact on an Air Quality Management Area or a SAC);
prevention of nuisance;
impact on the road and other transport networks, and in particular on traffic generation; [….]”
8.19 PPW therefore makes clear that, when deciding to grant permission for a development, Local Planning Authorities should be satisfied that any remaining pollution concerns are capable of being dealt with under the other pollution regimes, making use of planning conditions or obligations where appropriate.
8.20 Paragraph 13.12.3 states in this regard that:
“Planning authorities may use planning conditions or obligations to meet planning aims to protect the environment where these are pertinent to the development proposed. It is important for planning authorities to understand the scope and purpose of conditions that can be imposed by pollution authorities so as to ensure that planning conditions neither duplicate nor conflict with such conditions. Proposed development should be
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designed wherever possible to prevent adverse effect to the environment but as a minimum to limit or constrain any effects that do occur”.
UK Air Quality Plan
8.21 The UK government has set out a plan for reducing nitrogen dioxide emissions in towns and cities as part of its commitment to meeting the EU air quality directive requirements36. The individual air quality plans set out targeted local, regional and national measures which aim to achieve improvements in air quality. The associated documents include 38 zone plans, a UK overview document, a list of national measures and a technical report. Implementation of the plan and progress on delivering improved air quality across the country will be monitored both through formal reporting processes and through continued engagement with local authorities, industry, and other relevant parties.
8.22 It is proposed to introduce Clean Air Zones in five cities in England where only the cleanest vehicles will be allowed to circulate. Local authorities can also adopt Clean Air Zones as a way to focus their action to improve air quality.
8.23 In Wales, there were four zones and agglomerations in exceedance of the limit values in 2013. There is only one location, a section of road in the South Wales zone, which is predicted to exceed the nitrogen dioxide limit value beyond 2020. Reducing the contribution of transport to air pollution and other harmful emissions is one important objective of the Welsh Government’s Transport Strategy. The interventions aim to reduce the use of private motor vehicles and increase active travel and the use of integrated public transport, and supporting highway schemes designed to reduce traffic congestion.
Legislation
Air Quality Directive and Regulations
8.24 Air quality criteria can be readily divided into two groups; those that are mandatory and those that are designed for guidance. Mandatory criteria that apply to the UK are the objectives from the 2007 Air Quality Strategy (AQS) for England, Scotland, Wales and Northern Ireland, and the Directive 2008/50/EC on ambient air quality and cleaner air for Europe ("Air Quality Directive") limit values, which are incorporated into national legislation, as listed below.
8.25 The following legislation is relevant to air quality regulation specifically within Wales:
36 https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/486636/aq-plan-2015- overview-document.pdf
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the Air Quality (Wales) Regulations 2000 (No. 1940 (Wales 138) as amended), which enact the air quality objectives applicable to local air quality management (LAQM) in Wales;
the Air Quality Standards (Wales) Regulations 2010 (No. 1433 (Wales 126)), which implements mandatory legislative air quality criteria for human health and vegetation, set in EU Directive 2008/50/EC; and
critical levels for the protection of vegetation for oxides of nitrogen based on the work of the United Nations Economic Commission for Europe (UNECE) and World Health Organisation (WHO), as incorporated into the Air Quality Standards (Wales) Regulations 2010 (No. 1433 (Wales 126)).
Industrial Emissions Directive and Regulatory Control
8.26 The Directive on industrial emissions (integrated pollution prevention and control) (recast) – 2010/75/EU, the “Industrial Emissions Directive” (IED), entered into force on 6th January 2011. The purpose of the IED is “to achieve a high level of protection for the environment taken as a whole” from the potentially harmful effects of industrial activities. It does so for many activities by requiring each of the industrial installations concerned to have a permit from the competent authority. In Wales this is Natural Resources Wales (NRW) or, for smaller installations, the relevant local authority.
8.27 The IED is a recast of seven existing directives including the Integrated Pollution Prevention and Control Directive (IPPC, 2008/1/EC) and sectoral directives including those on waste incineration (WID, 2000/76/EC), solvent emissions (199/13/EC) and large combustion plant (LCPD, 2001/80/EC) (the latter will be repealed from 1st January 2016). It is transposed into UK law through the Environmental Permitting (England and Wales) Regulations 2010 (SI 2010/675) (as amended).
8.28 Combustion installations fall under the remit of the IED if the aggregated thermal input of all combustion plant on site discharging emissions via a common stack exceeds 50 MW. As the electrical output of the Scheme is up to 299 MWe, it will be regulated under the IED and will require an Environmental Permit (EP) to operate. The permit will limit the pollutant concentrations in flue gas discharges to air from the Stacks during the operation of the Scheme.
8.29 It is anticipated that pollutant emissions from the Scheme will be required to meet the limit values specified in Part 2 of Annex V of the IED for new gas turbines. The details of the pollutants regulated and the specific emission limits applicable are summarised in Table 8.1. The IED limits are in units of milligrams per normal cubic metre (mg/Nm3), where the normalised reference conditions specified in the IED for gas turbines are 273K, 101.3 kPa, 15% oxygen, on a dry basis.
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Table 8.1: Emission limit values and benchmarks (mg/Nm3) for natural gas fired turbines
Source NOx CO SO2 PM10 Comment IED Annex V Part 50 100 - - Only applies above 70 % load 2 Limit Value EPR 1.01 20-50 100 10 5 No daily average value should benchmark exceed the benchmark value. 95% of all hourly averages over a defined period, e.g. a calendar year do not exceed 200% of the benchmark
8.30 The changes brought in by the IED were transposed into national legislation in England and Wales in February 2013 through the EPR. The Scheme comprises a listed activity under Schedule 1 of the EPR.
8.31 The Environment Agency sector guidance note for Combustion Activities (EPR 1.01)37 provides emission benchmarks, referred to as “achievable concentrations”, for CCGT facilities for two IED regulated pollutants NOx and CO. These emission benchmarks are shown in the final row in Table 8.1 above.
8.32 The Power Station Complex will be required to operate within conditions specified by NRW in the relevant EP, subject to the operator’s EP application having satisfactorily demonstrated the use of best available techniques (BAT) to protect the environment. The EP conditions will include inter alia limits to the flue gas concentrations of the pollutants emitted from the Stacks.
8.33 In addition to ensuring that the proposed development meets the requirements of BAT, NRW in their regulatory role have regard to numerous other national and international standards and obligations which must either be safeguarded through or, at least, taken into account in setting EP conditions. As the Scheme falls within the scope of the IED, the EP is anticipated to reflect the stringent IED emission limit values as a minimum standard for atmospheric discharges.
Air quality strategy
8.34 The 2007 AQS for England, Scotland, Wales and Northern Ireland provides details of national air quality standards and objectives for a number of local air pollutants.
8.35 The standards define the pollutant concentrations below which health effects are unlikely to be experienced, even by the most sensitive members of the population. These are based upon recommendations of the Expert Panel on Air Quality Standards (EPAQS). The objectives are targets for concentrations of air pollutants,
37 https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/297003/geho0209bpin-e- e.pdf
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which take account of the costs and benefits of achieving the standard. In the case of short-term targets, the permissible number of hours or days above the objective concentration is also specified. The number of permissible “exceedances” is considered when determining compliance with the short-term objectives over an annual period.
8.36 The AQS objectives also implement the requirements of European Directives on air quality. The first European Community (EC) air pollution limit values were introduced in the 1980s. These contained limit values that must be attained and more stringent, but non-obligatory, guideline values. In June 2008, the Air Quality Directive came into force, merging the previous Air Quality Framework Directive and the first three daughter directives and introduced new objectives for PM2.5. It was transposed into Welsh legislation by the Air Quality Standards (Wales) Regulations 2010 (No. 1433 (Wales 126)).
8.37 It should be noted that the assessment against AQS objectives should only apply in locations where there may be relevant public exposure i.e. these human health objectives are applicable where members of the public may be exposed to pollutant levels for periods equal to or exceeding the averaging periods set for these criteria. Locations of relevant exposure include building façades of residential premises, schools, public buildings and medical facilities; places of work (other than certain community facilities) are excluded.
Human health criteria
8.38 The air quality criteria for the protection of human health are presented in Table 8.2. These are the 2007 AQS objectives, which are the same as the EU limit values which have been transposed into national legislation (and are to be achieved by the same date unless otherwise indicated with square brackets).
Table 8.2: Air quality criteria Pollutant Objective Nitrogen dioxide, Hourly average concentration should not exceed 200 µg/m3 more than NO2 18 times a year Annual mean concentration should not exceed 40 µg/m3 24-hour mean concentration should not exceed 50 µg/m3 more than PM10 35 times a year Annual mean concentration should not exceed 40 µg/m3 PM2.5 UK (except Scotland): annual mean concentration should not exceed 25 µg/m3 by 2020 [2015].
Carbon monoxide, Maximum daily running eight-hour mean concentration should not CO exceed 10,000 µg/m3
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Pollutant Objective
Notes: [ ] denotes EU Limit Value compliance date in UK Regulations
8.39 As SO2 emissions from gas-fired generating stations are expected to be negligible and there are no IED limit values for new gas fired turbines, this pollutant has not been assessed.
Ecological criteria
8.40 Limit values are also set in the Air Quality Directive for the protection of vegetation and ecosystems. These limit values (also referred to as “critical levels”) are based on the work of the UNECE and WHO and have been incorporated into the Air Quality Standards (Wales) Regulations 2010 (No. 1433 (Wales 126)).
8.41 Assessment of compliance with the critical levels for the protection of vegetation is required at locations more than 20 km from towns with more than 250,000 inhabitants or more than 5 km from other built-up areas, industrial installations or motorways. According to the 2010 Welsh air quality regulations, the AQS objectives for vegetation do not apply in these areas where assessment of compliance with the European limit value is not required; however, as the UNECE and the WHO have set a critical level for NOx for the protection of vegetation, the Statutory Nature Conservation Agencies’ (in Wales, Natural Resources Wales (NRW)) policy is to apply the 30 µg/m3 critical level as a benchmark, on a precautionary basis, at all sites.
8.42 The Environment Agency and DEFRA guidance: “Air Emissions Risk Assessment Guidance” (published 2 February 2016) provides an additional, non-statutory critical level for oxides of nitrogen of 75 µg/m3 as a daily mean, which is based on the WHO guideline value for the protection of vegetation and ecosystems.
8.43 Critical loads for nitrogen and acid deposition have been set by the UNECE. A critical load is a quantitative estimate of a level of exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur, according to present knowledge. Critical loads vary by type of habitat and species. The critical load for nitrogen deposition (eutrophication) is given as a range and is quoted in units of kg N/ha/year. A single critical load is quoted for acidification, in keq/ha/year for both nitrogen and sulphur deposition fluxes.
8.44 Site-specific critical loads for eutrophication and acidification are held on the Air Pollution Information System (APIS) website (www.apis.ac.uk). Background rates of nitrogen and acid deposition are also available from the website for a three-year period average, 2010 to 2012, for five by five kilometre areas.
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Dust
8.45 There are no statutory quantitative controls or limits on general dust emissions from construction sites. Dust levels that are substantially elevated above the norm can cause annoyance. This commonly relates to increased rates of dust deposition on exposed surfaces and/or soiling (discolouration / contamination), although less commonly the term may relate to levels that are “prejudicial to health”, including airborne dust.
Local Air Quality Management
8.46 Under Part IV of the Environment Act 1995 all local authorities are responsible for Local Air Quality Management (LAQM), the mechanism by which the Government’s air quality objectives are to be achieved. As part of this LAQM role, local authorities are required to periodically review air quality in their area and to assess present and likely future air quality against the objectives defined in the 2010 Welsh Regulations. Where a local authority anticipates an objective may be breached within its area, it must designate an Air Quality Management Area (AQMA) and develop an action plan to reduce air pollution levels. Under the LAQM regime, a local authority is responsible for regular review and assessment of local air quality, reports on which are published following public consultation and review by the Department for Environment, Food and Rural Affairs (DEFRA).
8.47 The LAQM system is currently (as of 2016) undergoing consultation to increase its focus on supporting local authorities to take action, in particular on priority pollutants such as nitrogen dioxide.
8.48 Statutory responsibility for achieving EU limit values rests with the Secretary of State and local authorities have no responsibility for achieving the national air quality criteria, although they should contribute to this through local action plans designed to reduce pollution levels in AQMAs.
8.49 Individual actions by local authorities to address nitrogen dioxide are set out in each of the 38 air quality zone plans that accompany the overall UK air quality plan.
Guidance
8.50 Air quality guidance, prescriptive and non-prescriptive, produced by inter alia DEFRA, Natural Resources Wales, the Environment Agency, Highways England, the Institute of Air Quality Management (IAQM) and Environmental Protection UK (EPUK) is used in the assessment of air quality in the UK. The following key documents have been used in the assessment of the likely significant effects on air quality arising from the Scheme:
Natural Resources Wales (2014) How to comply with your environmental permit: additional guidance for combustion activities (EPR 1.01) – one of a
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series of additional guidance for Part A (1) activities listed in Schedule 1 of the EPR, describes BAT and provides emission benchmarks.
The Environment Agency and DEFRA guidance: “Air Emissions Risk Assessment Guidance” (published 2 February 2016) gives advice on assessing the impact of releases to air from listed activities when applying for a bespoke permit under the EPR. This guidance is also supported by NRW.
Environment Agency (2010) Air Quality Technical Advisory Group (AQTAG) 06 - guidance on how to carry out a quantitative assessment using short range modelling for emissions to air arising from an industrial process in order to fulfil the requirements of the Habitats Regulations. This guidance is also supported by NRW.
Department of Environment, Food and Rural Affairs (DEFRA) (2009) Local Air Quality Management Technical Guidance (LAQM.TG (09)) – guidance designed to support local authorities in England, Wales, Scotland and Northern Ireland in carrying out their duties under the Environment Act 1995, to review and assess air quality in their area on a regular basis. This document supersedes all previous technical guidance documents and is supported by web-based spreadsheet tools, helpdesks and supporting websites.
Highways Agency (as was) (2007) Design Manual for Roads and Bridges, Volume 11 Environmental Assessment, Section 3 Environmental Assessment Techniques, Part 1 (HA 207/07) Air Quality - Advice note providing guidance on the assessment of the impact that road projects may have on local and regional air quality. It includes a calculation method to estimate local pollutant concentrations and regional emissions for air including those for carbon. This guidance is also relevant to the assessment of road traffic emissions in Wales.
Institute of Air Quality Management (IAQM) (2014) Guidance on the assessment of dust from demolition and construction - provide guidance for developers, their consultants and environmental health practitioners on how to undertake a construction impact assessment (including demolition and earthworks as appropriate).
Environmental Protection UK and IAQM (2015) Land-Use Planning & Development Control: Planning for Air Quality– provides guidance on dealing with air quality within the development control process, advice on when an air quality assessment is required, and guidance on describing the magnitude of air quality impacts and on assessing their significance.
8.51 Some local authorities also produce Supplementary Planning Guidance which gives additional information on the requirements for air quality assessment and construction impacts. In the case of Wrexham County Borough Council (WCBC) no such guidance is in place.
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Realistic worst case scenario for assessment
8.52 For the assessment of air quality, the “realistic worst case” scenario from within the Scheme parameters (described in chapters 4 and 5 of this ES) is set out in Table 8.3 below. The 2+1 arrangement with two separate Stacks represents the “realistic worst case” for potential operational air quality impacts because it provides the least favourable dispersion characteristics and, as a result, gives higher estimates of ground level pollutant concentrations and deposition rates than an arrangement with a single stack. A discussion of tolerances and implications of variations in these parameters is provided from paragraph 8.75 and in Appendix 8.2.
8.53 For construction dust, the “realistic worst case” is to assume that dust raising activities could be anywhere within and up to the boundary of the Order Land. This provides a conservative assessment as it encompasses more receptors within the relevant distances than if, for example, only the specific boundaries of the construction laydown areas were to be considered. The assessment of the 2+1 arrangement with two separate Stacks is also the “realistic worst case” for assessment of construction and operational vehicle emissions, as it requires a larger building footprint and dimensions.
8.54 Other, conservative assumptions are highlighted throughout this chapter, which ensure a robust approach to the assessment.
Table 8.3: Parameters defining the “realistic worst case scenario” for air quality assessment Parameter Definition Number of stacks 2 Number of gas turbines 2 Number of HRSGs 2 Number of steam generators 1 Height of stacks up to 50 m Diameter of stacks Up to 5 m internal diameter and 6.5 m externally Buildings Maximum dimensions as defined in chapter 4 Construction activities Anywhere within the limits of the Order Land
ASSESSMENT METHODOLOGY
Construction
Dust emissions
8.55 Construction activities can give rise to dust emissions under particular circumstances if not effectively managed. The Scheme has the potential to affect nearby receptors due to dust generated from the construction of the Power Station
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Complex, Gas Connection (laying of the gas pipeline) and AGI; fugitive emissions from haulage routes and lay down areas on site; or the tracking out of dust from heavy goods vehicles (HGV) onto the local road network.
8.56 There are no statutory national or European criteria relating to dust, nor is there a standard methodology for the assessment of potential dust effects. The quantity and distribution of dust emissions varies according to type, duration and location of activity, weather conditions and the effectiveness of suppression (mitigation) measures.
8.57 Guidance produced by the Institute of Air Quality Management (IAQM) for the assessment of dust from demolition and construction is widely used by air quality practitioners38. The guidance presents a framework for a risk-based approach to the assessment of dust emissions from demolition and construction sites. The assessment of dust emissions is considered in the context of the overall scale and nature of the development and the potential sensitivity of neighbouring land uses. Professional judgement is required when undertaking this qualitative assessment. The application of professional judgement is an industry-accepted methodology when assessing the effects of dust emissions; it is for the professional to evaluate the potential risk of dust emissions for the site in question, based on the likely emission magnitude, assess these in the context of the risk assessment matrix and apply professional judgement as to the significance of the potential effects.
8.58 It is assumed when undertaking the assessment without mitigation in place, that measures required by legislation will be employed as a minimum. The IAQM guidance presents a number of industry standard good practice control measures that are considered to be “highly recommended” or “desirable” for the site risk categories as determined through the assessment process.
8.59 There are four key steps in the assessment process:
Step 1 – Screen the requirement for a more detailed assessment by identifying if there are: human receptors within 350 m of the boundary of the site and/or within 50 m of the route(s) used by construction vehicles on the public highway up to 500 m from the site entrance; ecological receptors within 50 m of either the boundary of the site and/or of the route(s) used by construction vehicles on the public highway up to 500 m from the site entrance. No further assessment is required if no such receptors are identified within these distances.
- Sensitive ‘human’ receptors are defined as residential dwellings or industrial/commercial premises that may have a particular sensitivity to dust deposition e.g. vehicle showrooms, food manufacturers, or electronics manufacturers.
38 Holman et al. (2014) IAQM Guidance on the assessment of dust from demolition and construction, Institute of Air Quality Management, London.
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- ‘Ecological’ receptors include sites with statutory designations e.g. Ramsar Sites, SPA, SAC and SSSI, as well as non-statutory sites such as LWS39 and/or locations with very specific sensitivities e.g. horticultural operations.
Step 2 – Assessment of the risk of dust impacts i.e. risk of dust arising in sufficient quantities to cause annoyance and/or health and/or ecological effects, by considering the area around the site in the context of potential dust sources and distances to nearby receptors. This step is carried out for each of the defined activities: demolition, earthworks, construction, and trackout (mud deposited on the road from road vehicles leaving the site). Sub steps 2A and 2B feed into Step 2C:
- Step 2A – The potential dust emission magnitude (‘large’, ‘medium’ or ‘small’) is determined according to the level of risk arising from each site, which is dependent on the scale and nature of works. Suggested criteria for each magnitude category are provided in IAQM guidance although professional judgement and a precautionary approach must be employed.
- Step 2B – The sensitivity of the surrounding area is defined for each of the three different effects, dust soiling; human health; and ecological, as ‘high’, ‘medium’ or ‘low’ depending on the receptor type and distance from the source. In addition, for the effect on human health, background PM10 concentrations are taken into account. The definitions are provided in Tables 2, 3 and 4 of the IAQM guidance, which are reproduced in Appendix 8.1.
- Step 2C - Tables 6 to 9 in the IAQM guidance, also reproduced in Appendix 8, are used to define the risk of impact based on the dust emission magnitude (from Step 2A) and sensitivity of the area (from Step 2B).
Step 3 – Determine site specific mitigation as appropriate for the identified risk of dust impact. The IAQM guidance advises (in section 8.2) that the mitigation as appropriate for the highest risk category should be applied.
Step 4 – Assessment of residual dust effects, after the application of the site specific mitigation. Once mitigation has been applied, there should not be any significant adverse effects. Slight and negligible effects are not considered to be significant.
Step 5 – Prepare the dust assessment report.
8.60 The IAQM approach is deliberately conservative such that further assessment beyond Step 1 is required for most schemes.
39 In Wrexham, these may be referred to as County Wildlife Sites (CWS) or simply wildlife sites but for the purposes of this report are referred to as LWS.
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8.61 Further detail on the IAQM methodology, including criteria to determine impact magnitude, receptor sensitivity and significance of effects, is provided in Appendix 8.1.
8.62 The IAQM distance bands for receptor identification have been applied from the boundary of the Order Land for a conservative assessment of off-site receptors in line with a “realistic worst case” approach. The example definitions provided in the guidance for demolition, earthworks, construction and trackout dust magnitude have been interpreted using a precautionary approach.
Construction traffic emissions
8.63 Additional vehicle movements generated during the Scheme construction phase have the potential to influence local air quality at sensitive receptors (both human health and ecological) that are located within 200 m of the centreline of an affected road40.
8.64 The EPUK & IAQM development control guidance (2015)41 provides indicative criteria for identifying affected roads and as such where a further assessment of the impact of traffic associated with a development or scheme on air quality may be appropriate. The criteria to identify an affected road that are relevant to construction works are:
a change in Light Duty Vehicles (LDV) (cars and small vans <3.5 tonnes gross vehicle weight) flow of more than 100 Annual Average Daily Traffic (AADT) within or adjacent to an AQMA or more than 500 AADT elsewhere;
a change in Heavy Duty Vehicle (HDV) (goods vehicles and buses >3.5 tonnes gross vehicle weight) flow of more than 25 AADT within or adjacent to an AQMA or more than 100 AADT elsewhere;
realignment of roads, i.e. changing the proximity of receptors to traffic lanes where the change in distance is 5 m or more and the road is within an AQMA.
8.65 If none of the criteria are met, then the EPUK & IAQM guidance advises there should be no requirement to carry out an air quality assessment for the impact of the development on the local area, and the impacts can be considered to be insignificant. It should be noted that the guidance states “passing a screening criterion does not automatically lead to the requirement for a Detailed Assessment” and that in some instances a qualitative assessment will be sufficient in order to draw a conclusion.
40 Traffic contribution to pollutant concentration reduces with increased distance from the road, with negligible effect beyond 200 m. See Figure C1 of DMRB42 41 Environmental Protection UK (2015) Land Use Planning & Development Control: Planning for Air Quality
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8.66 Similarly, the Highways Agency's (as was) Design Manual for Roads and Bridges (DMRB) section on air quality assessment42 sets out change criteria to determine the need for assessment. For construction vehicles (i.e. HGVs) an increase of more than 200 per day (as a two-way flow), where that change would be in place for more than six months, requires further assessment. If none of the roads in the network meet any of the traffic change criteria or there are no properties or relevant ecological sites near affected roads, then the impact of the development can be considered to be “neutral” in terms of local air quality (i.e. not significant), and no further assessment is needed.
8.67 If one or more of these criteria is exceeded, a qualitative or quantitative assessment of the effect on local air quality should be undertaken, for instance using the DMRB spreadsheet-based screening tool or a detailed model. Should such assessment be required, data used in the assessment are:
two way AADT flows, average vehicle speeds and fleet composition in terms of LDV and HDV43;
road type (either motorway / 'A' road, urban road or rural road);
distance between the receptor façade and road centreline where receptors are within 200 metres of affected roads; and
background annual mean pollutant concentrations, obtained from the DEFRA maps of air quality44 or actual measurements made by the relevant local authority.
8.68 It has been agreed through consultation with WCBC that the DMRB screening tool is an appropriate method for quantitative assessment, should it be required (see Appendix 8.3). Technical guidance produced by DEFRA45 has also been referred to in undertaking the assessment as this represents industry best practice.
8.69 The construction assessment considers traffic flows in a future year (2018, based on the draft construction programme provided in chapter 4). Future baseline forecasts account for assumed growth in existing traffic over time and flows from planned or committed developments, i.e. they are projections above the measured baseline flows derived from surveys (see chapter 7 Transport and Traffic). Estimates with and without the potential volume of construction traffic to be generated by construction of the Scheme have been provided.
42 Highways Agency (2007) Design Manual for Roads and Bridges, Volume 11, Section 3, Part 1 ‘Air Quality’. 43 Heavy Duty Vehicle: defined as vehicles with a gross weight above 3.5 tonnes, including heavy goods vehicles (HGVs), buses and coaches 44 © Crown 2014 copyright DEFRA via http://laqm.defra.gov.uk licensed under the Open Government Licence (OGL). http://www.nationalarchives.gov.uk/doc/open-government-licence/version/2/ 45 DEFRA (2009) Local Air Quality Management Technical Guidance (LAQM TG.09)
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8.70 As part of the Scheme mitigation strategy a temporary on-site concrete batching plant will be considered for use (if possible), so as to obviate the need for a high volume of material deliveries associated with the concrete pouring stage of the construction programme. Therefore, two scenarios are considered in the peak construction year for the Scheme without and with an on-site concrete batching plant.
Construction plant emissions
8.71 The Scoping Report for the Scheme did not identify construction plant emissions as a potential significant issue for consideration at EIA stage. The Scoping Opinion did not request that an assessment of construction plant emissions be made, hence it is not assessed in detail. However, for robustness an outline qualitative assessment has been undertaken with reference to the expected sources and distance to receptors.
8.72 Consideration is given to mitigation measures relevant to non-road mobile machinery (NRMM) which will be incorporated into the Construction & Environmental Management Plan (CEMP), in the “Mitigation Measures” section of this chapter.
Operation
Stack emissions
8.73 The potential for operational effects on air quality relates mainly to the stack flue gas emissions from the Scheme. A detailed dispersion modelling study addressing stack emissions to atmosphere during the operation of the Scheme has been carried out in accordance with established industry best practice. Technical guidance produced by DEFRA46 has been referred to in undertaking the assessment.
8.74 The study uses the engineering design developed for the Power Station Complex of the Scheme comprising the “realistic worst case” site layout, building dimensions and stack parameters, allowing for a conservative assessment within a ‘Rochdale Envelope’ approach. A description of the Scheme is presented in chapter 4 of this ES. The specific input data used in the dispersion modelling study are described in the sub-sections below.
Model choice
8.75 The dispersion modelling study was carried out using the United States Environmental Protection Agency (US EPA) model AERMOD version 14134. This model is the result of many years’ development by the US EPA and the American
46 DEFRA (2009) Local Air Quality Management Technical Guidance (LAQM TG.09)
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Meteorological Society. It has been developed as a regulatory model that incorporates the current understanding of atmospheric physical processes. This “new generation” model is used by regulatory agencies, consultants and industry worldwide to assess the impact of air emissions from point, area, line, flare and volume sources. The model is commonly used in the UK for planning and regulatory applications; its use is accepted by NRW as being fit for purpose47.
8.76 The AERMOD programme simulates essential atmospheric physical processes and provides refined estimates of pollutant concentrations over a wide range of meteorological conditions and modelling scenarios. The modelling system includes:
an advanced meteorological pre-processor to compute site-specific planetary boundary layer (PBL) parameters;
highly developed dispersion formulations that incorporate current PBL understanding and variables for both convective and stable boundary inversions;
enhanced treatment of plume rise and plume penetration for elevated inversions allowing for effects of strong updrafts and downdrafts that occur in unstable conditions;
improved computation of vertical profiles of wind, turbulence and temperature; and
a “dividing streamline” approach for computations in complex terrain.
8.77 AERMOD includes two data pre-processors for streamlining data input: AERMET, a meteorological pre-processor, and AERMAP, a terrain pre-processor. The model can address both local topography and building downwash effects concurrently, where relevant to the study. The model provides reasonable estimates over a wide range of meteorological conditions and modelling scenarios. The building downwash algorithms in AERMOD, using parameters calculated by the Building Profile Input Program (BPIP), distinguish this model from earlier versions of AERMOD, which used simpler procedures to address downwash.
Stack arrangement
8.78 The final design of the Power Station Complex of the Scheme will be determined on best available techniques (BAT) and consideration of the best available capacity and efficiency combinations. At this time, the following configurations of the Power Station Complex have been put forward by the project engineers as the two most likely configurations of the CCGT:
47 http://www.welshairquality.co.uk/documents/seminars/328100928_7_EA_Permitting.pdf
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a 2+1 arrangement, with two gas turbines and heat recovery steam generators (HRSG), one steam turbine, and a generator for each turbine; and
a 1+1 arrangement, with a single larger gas turbine with one HRSG, one steam turbine, and two separate generators.
8.79 The exemplar gas turbine technology options associated with the above two configurations are:
a GE 206FA combined cycle dual gas turbine unit of 235 MWe output, comprising two 6FA gas turbines, each with their own HRSG and an associated exhaust stack(s) (individual or combined); and
an Alstom GT13E2 combined cycle unit of approximately 290 MWe output, with a single gas turbine and single HRSG configuration and a single exhaust stack.
8.80 For these two configurations, there are three possible Stack arrangements:
a 2+1 arrangement, with two separate stacks;
a 2+1 arrangement, with two flues combined in a single outer stack; and
a 1+1 arrangement, with a single stack.
8.81 The height of the Stack for the Scheme is up to 50 m, as this is the upper limit considered acceptable from an engineering and technical perspective as well as from a landscape and visual impact perspective (as assessed in chapter 10).
8.82 The overriding factor when determining the “realistic worst case” stack height for use in the air quality assessment, is the need to ensure adequate dispersion such that the achievement of mandatory air quality criteria is not compromised. Whilst a lower stack would tend to give higher concentrations of air pollutants at ground level, and hence could be considered as the “worst case”, the air quality practitioner must have regard to the minimum height that would be acceptable to the regulator, who requires that BAT is demonstrated for the dispersion of emissions. This underlines the need for a “realistic” element to the so-called “worst case” and restricts the range of stack heights that may be acceptable from a permitting perspective. It would not be realistic to base the modelling for the EIA on a very low stack height simply because this gives more conservative results.
8.83 An HMIP D148 calculation was undertaken to determine the minimum appropriate stack height for each of the three arrangements. The D1 calculation is a simple and versatile method that takes account of the stack discharge characteristics (in particular, momentum, buoyancy and pollutant emission rates), the size of nearby
48 HMIP (1993) Guidelines on Discharge Stack Heights for Polluting Emissions, Technical Guidance Note (Dispersion) D1, ISBN 0 11 752794 7. This document is out-of-print, but is available from the British Library
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structures (maximum building dimensions for the design of the Power Station Complex were used) and their arrangement. It also considers ambient pollutant concentrations.
8.84 The HMIP D1 calculation gives a useful starting point for a detailed modelling study, which also takes into account additional factors such as detailed meteorological and terrain data, the precise building layout and the location, direction and height of sensitive receptors. The minimum stack height given by HMIP D1 was verified and refined through dispersion modelling, an approach that is in line with NRW expectations, to determine a height that provides adequate protection of human health and the environment.
8.85 A description of the HMIP D1 calculations and initial modelling work is presented in Appendix 8.2. In summary, the 2+1 arrangement with separate stacks was found to give the most conservative ground level concentrations at human health and ecological receptors. A stack height range of 46 to 50 m was deemed, by means of initial dispersion modelling sensitivity tests, to be acceptable for this arrangement. There is no significant difference in the results for the 50 m Stack with those for the 46 m stack for annual average concentrations, however due to the subtleties of the frequency distribution of wind speed and direction, a 50 m stack height gives rise to slightly higher maximum short-term concentrations at a human health receptor. For the purposes of the EIA, the 50 m height was selected for the realistic “worst case”, which provides a conservative indication of ground level pollutant concentrations resulting from the Power Station Complex stack emissions.
8.86 The Original Equipment Manufacturer (OEM) will need to demonstrate to NRW that the final stack height provides adequate environmental protection. This is shown in the results section of this chapter and supporting information in Appendix 8.2, to be achievable for a 2+1 arrangement with a Stack of up to 50 m.
Stack parameters
8.87 The stack discharge characteristics for the Power Station Complex, for a 2+1 arrangement (e.g. two GE 206FA gas turbines) with separate stacks, are summarised in Table 8.4. Calculations of flue gas parameters were based on the net thermal input of the CCGT technology and the typical molar composition of the natural gas fuel, to derive the fuel mass flow rate. The fuel specification representative of that supplied in the UK is that provided by GE (comprising 89.2% methane by volume, ethane and other compounds). The exhaust mass flow rates were taken from the GE 206FA gas turbine manufacturer’s specification.
8.88 The stack diameter can affect the dispersion of pollutants as it influences velocity. The available range is between the manufacturer’s specification of 4.5 m internal diameter and a maximum of 6.5 m external diameter, which is based on visual considerations. Rather than simply selecting the value which gives the lowest velocity, and hence the highest ground level concentrations, due regard must be
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given to the recommended minimum exit velocity of 10 m/s. An internal diameter of 5 m gave higher ground level concentrations than those for 4.5 m, whilst still maintaining an exit velocity of more than 10 m/s and not diverging too far from the manufacturer’s data specification for an individual flue stacks (which will be based on design considerations such as gas pressure). Hence an internal diameter of 5 m was selected for dispersion modelling purposes as part of the “realistic worst case” scenario.
8.89 It is assumed that heat will be recovered from the CCGT exhaust and hence the exit temperature of the flue gases will be in the region of 90°C. This is a conservative scenario as it represents a high degree of heat recovery (which may not be possible to deliver in practice) leading to a low thermal buoyancy of the plume, which will lead to less effective dispersion.
8.90 The stack emissions addressed in the modelling study are those regulated in the IED i.e. NOx and CO. The inherently clean gas turbine technology will meet BAT and will ensure that under normal operations the Power Station Complex will operate below the limits specified previously in Table 8.1. As described earlier in this chapter, emissions of SO2 and PM10 will inherently be negligible due to the nature of natural gas as the fuel and hence were not included in the detailed modelling study. This approach has been agreed with NRW and WCBC EHO.
Table 8.4: Scheme stack discharge characteristics for a 2+1 arrangement Parameter Value (each stack) Location of stack (National Grid Ref.), m 339020, 350369 339021, 350350 Height of release point above ground level, m 50 Flue diameter at exit point, m 5 Net thermal input, MW 430.6 Rated net output, MW (combined cycle) 239.4 Exhaust gas temperature, K 363.15 Exhaust gas exit velocity, m/s 12.8 Actual exhaust gas flow rate, m3/s 252.0 Oxygen content of actual gas flow, % 14.6 Water content of actual gas flow, % 6.5 Exhaust gas flow rate at IED reference conditions 189.0 (273 K, 101.3 kPa, 11% O2 dry basis), Nm3/s Oxides of nitrogen emission concentration, mg/Nm3 50 Carbon monoxide emission concentration, mg/Nm3 100 Oxides of nitrogen emission rate, g/s 9.44 Carbon monoxide emission rate, g/s 18.9
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8.91 The annual average mass emission rates (g/s) of NOx and CO were derived from the normalised flow rate of 189 Nm3/s and the IED emission concentration daily average limit values shown in Table 8.4.
8.92 For the purposes of comparison with long-term AQS objectives, a conservative assumption has been made that emissions from the Stacks will be discharged at the maximum permissible daily concentration specified in the IED, and that the gas turbines will operate at full load throughout the year, 24 hours a day i.e. 8760 hours in total. In practice, the plant performance is expected to be better than IED requires, and regulated substances will typically be emitted at somewhat lower concentrations than those forming the basis of this assessment.
8.93 Depending on the final chosen operational arrangement of the Power Station Complex, the number of operational hours may be fewer than 8760 per year49. As a result of annual maintenance, there will be a period of one to four weeks shut down in any given year which will lead to a slightly lower annual average ground level concentration for any pollutant.
8.94 For comparison with the short-term (hourly) objective of nitrogen dioxide, in addition to the assessment based on continuous operation at the daily IED limit value of 50 mg/Nm3 (which represents normal operation and is the gas turbine manufacturers’ guaranteed performance) an even more conservative, hypothetical scenario has been considered at the request of the NRW permitting officer (who was advised by the NRW air quality modelling and risk assessment team (AQMRAT), see correspondence in Appendix 8.3). This scenario uses an emission concentration 3 of 100 mg/Nm which is twice the daily IED limit value for NOx. This upper limit is based on the means of assessment of compliance set out in IED Annex V Part 4, which states that “95 % of all the validated hourly average values over the year do not exceed 200 % of the relevant emission limit values”.
Buildings
8.95 Buildings close to point source plume discharges that are more than 40% of the stack height may potentially cause downwash effects. The BPIP programme (as referred to in paragraph 8.70) was used to calculate for each wind sector the direction specific building downwash parameters for the stack to be used by AERMOD PRIME in the dispersion calculations. The notional height of the Power Station Complex structures that could affect the downwash parameters and hence included in the model are:
HRSG building 1 & 2 as a solid structure of 33 m (maximum height of 35m including silencers)
49 If the number of operational hours were to be lower, for example the Scheme supports peak demand only, short term emissions may be higher during each start up and shut down event but it is still considered that the overall annual average result would be lower compared to full load operation throughout the year at the IED limit.
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Gas turbine building (height to ridge) 25m
Steam turbine building 21m
Heat Network Interface building 15m
Air cooled condensers 26m (13m condensers elevated on stilts 13m above ground level)
8.96 These maximum building dimensions incorporate the ‘Rochdale Envelope’ with regard to the layout of the Power Station Complex. The modelling study is not sensitive to small changes in the position of the Power Station Complex within the Order Limits, where the stacks are fixed relative to the position of the closest buildings.
8.97 Terrain elevations for all model objects and receptors (see next section) were used in the dispersion model, as derived from Ordnance Survey digital terrain (DEM) data files. The stacks and closest buildings were entered in the model at the same height of 30 m AOD.
Meteorological data
8.98 The joint frequency distribution of wind speeds and directions is a matter for consideration regarding the dispersion of pollutants from all source types. The meteorological station considered to be most representative of conditions at the Scheme, and with adequate records, is located at Hawarden Airport. This station is approximately 15 km to the north north-west of the Stacks of the Power Station Complex.
8.99 Meteorological data for the period 2007 to 2011 for the Hawarden station are presented as a wind rose in Insert 8.1 and shown in Table 8.16 in the Baseline section of this chapter. The use of this station was agreed by email with the WCBC EHO as appropriate (see Appendix 8.3). The Isycoed air quality monitoring site (see Baseline section) has a wind gauge fitted but this is not currently functional; there is no weather gauge on the Victoria Road monitoring station.
8.100 The meteorological pre-processor AERMET was used to process the data and estimate the necessary boundary layer parameters50 for use in the dispersion modelling study. The data were processed to take account of the location of the
50 The atmospheric boundary layer is that region between the earth’s surface and the overlying, free flowing atmosphere. The fluxes of heat and momentum drive the growth and structure of this boundary layer. The depth of this layer and the dispersion of pollutants within it are influenced on a local scale by surface characteristics, such as the roughness of the underlying surface, the reflectivity of the surface (albedo) and the amount of moisture available at the surface (Bowen ratio). From these inputs AERMET calculates several boundary layer parameters which in turn influence pollutant dispersion, including surface friction velocity, sensible heat flux, Monin-Obukhov length, daytime mixing layer height and nocturnal surface layer height, and the convective velocity scale
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meteorological station and surroundings of the Scheme. These parameters, together with observed near-surface wind and temperature data, were used to model how pollutants disperse in the atmosphere.
8.101 Surface characteristics were specified to reflect the nature of the area surrounding the Power Station Complex Site. According to latest EPA guidance, the near-field land use within a 1 km radius centred on the Stack was evaluated to determine the surface roughness length51. Land use may be specified by directional sectors of 30 degrees; in this case two sectors represented by urban and cultivated land are appropriate.
8.102 The Bowen ratio52 and albedo53 were determined by the dominant land use categories within the far-field, a 10 km by 10 km area centred on the Scheme Stacks. A subjective determination of the percentages of each type of land use was made based on maps and aerial photographs. The land use proportions are simply averaged over the area and are independent of distance or direction from the Scheme. The categories of cultivated land, urban and water comprised 85, 14 and one percent respectively. Based on the land use information, the AERMET pre- processor generated the appropriate default annual average values shown in Table 8.5.
Table 8.5: Surface characteristics used in the AERMOD model Sector Degrees Type Surface Albedo Bowen roughness (m) ratio 1 148 – 320 Urban 1.000 0.2692 0.874 2 320 - 148 Cultivated land 0.0725 0.2692 0.874
Modelled receptors
8.103 It is custom and practice in dispersion modelling that ground level concentrations are calculated using receptor grids that vary in spacing. A dense receptor “grid” is often placed around the facility's boundary to capture all high concentrations along the fenceline. As the distance from the site increases, the receptor grid density decreases. By using this approach, a denser receptor grid is placed closer to the source(s) where the highest concentrations are likely to be, and a less dense grid is further from the source(s) to account for any high concentrations that may be located further away from the site.
51 The surface roughness length is a measure of the height of obstacles to wind flow. It is not equal to the physical dimensions of obstacles, but is generally proportional to them. 52 The Bowen ratio is a measure of the amount of moisture at the earth’s surface. This influences other parameters which in turn affect atmospheric turbulence. 53 Noon-time albedo is the fraction of incoming solar radiation reflected from the ground when the sun is directly overhead. Adjustments are made in AERMET to incorporate the variation in the albedo with solar elevation angle
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8.104 For the purposes of this study, ground level concentrations were modelled using both Cartesian receptor grids and boundary receptors. In total, over 2,000 receptor points were modelled. A Cartesian grid 6.0 km by 6.0 km wide at 250 m resolution was used to capture concentrations further from the Scheme. This grid was placed slightly off centre in order to reflect the prevailing wind direction; the extent was set so as to ensure that all potentially significant increments to pollutant concentrations (i.e. more than 1% of criteria) were captured. In a local area around the Scheme a second grid of smaller extent but higher resolution (50 m) was included to ensure that the maximum ground level concentrations closer to the Site were modelled. Receptor points at 25 m intervals along the boundary of the Power Station Complex Site were also included to capture high concentrations on the fenceline.
8.105 A selection of representative sensitive locations has also been included in the model as discrete receptors to aid the interpretation of results beyond the Order Land and to ensure the highest concentrations relevant to public exposure are identified (as set out in DEFRA TG(09) guidance). The receptors were chosen based on their sensitivity, proximity to the Scheme and the direction of the prevailing wind. These receptors are discussed at paragraph 8.168. An individual receptor point may be representative of a single property or several in close proximity. Note that this is not intended to be an exhaustive list, as the dispersion modelling also encompasses, as described above, two regular receptor grids which cover the areas in between these discrete points and further afield.
8.106 Maximum concentrations at locations relevant only to short-term exposure, such as the local public rights of way (PRoW), such as footpaths, and which extend over a wider area, were identified from the contour plots hence they are not specified in the table of modelled receptors (Table 8.14).
8.107 The Environment Agency’s Air Emissions Risk Assessment guidance requires an air quality assessment to also address effects on designated ecological sites. An evaluation is made of modelled concentrations against critical levels specified for oxides of nitrogen and against critical loads for rates of nitrogen and acid deposition. Ecological receptors included in the model are discussed at paragraph 8.170.
Comparison with criteria
8.108 For the assessment of human health effects, the results of the modelling study are interpreted in accordance with Environment Agency’s Air Emissions Risk Assessment guidance and the criteria therein. The guidance provides long-term and short-term criteria for numerous air pollutants. These criteria are an indicator of the concentration that can be considered to be acceptable for a particular substance. The criteria refer to the EU AAD limit values and national AQS objectives (where available) and where appropriate supplements these with Environmental Assessment Levels (EALs) derived from other sources, for example Health and
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Safety Executive Occupational Exposure Limits. All the pollutants considered in this assessment are contained within the UK AQS due to their potential effect on human health and the environment. The supplementary EALs for specific substances are referred to later in this chapter in the discussion of the results of the dispersion modelling study.
8.109 The interpretation of the modelled concentrations resulting from the oxides of nitrogen emissions, in terms of estimating the consequent nitrogen dioxide concentrations, requires an additional assessment. The NOx emissions from combustion processes are released almost entirely in the form of NO. As the plume travels and mixes with air, the NO slowly oxidises to form NO2. This slow atmospheric reaction depends upon the availability of both ozone and sunlight to proceed. The plume travel time to the nearest residential receptors is in the order of several minutes only, thus restricting the degree of oxidation. A secondary reaction with oxygen may take place without sunlight, but this is extremely slow and hence is not a relevant consideration in the context of the study area for the Scheme.
8.110 For the relatively short distances between the Stacks of the Power Station Complex and the most affected receptors (in this case, less than 1 km), a conversion factor of up to 20% is regarded as being a reasonable assumption for short term averaging periods. Studies of oxidation rates in power station plumes found conversions below 20% for distances of up to at least 2 km from the source, other than during high ozone episodes54.
8.111 Nevertheless, guidance produced by the Environment Agency’s Air Quality Modelling and Assessment Unit (AQMAU) on conversion ratios for NOx and NO2 provides a series of “screening procedures”. The AQMAU note suggests a phased approach, initially a “screening/worst case scenario” using unrealistically high conversion ratios of 50% for short-term and 100% for long-term average concentrations. The second phase of this approach is termed a “worst case scenario” [sic] and it is these conversion ratios of 35% for short-term and 70% for long-term average concentrations that are considered to be established industry practice.
8.112 The AQMAU “worst case scenario” approach has been applied in the assessment.
8.113 The modelled long-term process contribution thus derived may then be added to the background annual mean concentration. The Air Emissions Risk Assessment guidance advocates a pragmatic approach, in which short-term NO₂ concentrations obtained with this conversion factor are added to twice the background annual mean concentration and compared to the relevant air quality objective.
54 Janssen L.H.J.M., van Wakeren J.H.A., van Durren H. and Elshout A.J. (1988) A classification of NO oxidation rates in power plant plumes based on atmospheric conditions. Atmospheric Environment 22, 43 55.
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8.114 The Air Emissions Risk Assessment guidance advises short term concentrations are calculated on the same basis as the corresponding environmental standards e.g. over the same averaging period or percentile. The comparison of the maximum hourly concentration for NO2 is a conservative approach, as the objective allows for 18 exceedances of the standard per calendar year (often expressed as the 99.79th percentile of hourly means).
8.115 Rates of nitrogen and acid deposition (also known as deposition fluxes) for comparison with critical loads for the protection of vegetation and ecosystems, are calculated from modelled concentrations; firstly, by multiplying by the relevant deposition velocity, then by unit conversion factors. The deposition velocities vary by pollutant and land cover type. Technical guidance on the detailed modelling approach for appropriate assessment for emissions to air, published by the Air Quality Technical Advisory Group (AQTAG) of the Environment Agency55, is used in the assessment of ecological effects in terms of nitrogen and acid deposition.
Transport emissions
8.116 The methodology used for the assessment of emissions from transport on local air quality during operation of the Scheme follows that described above for the construction phase and as agreed with the EHO for WCBC (see Appendix 8.3).
8.117 An assessment of the change in concentrations of NO2 and PM10 at sensitive receptors as a result of vehicle movements is required if the EPUK/IAQM (2015) indicative criteria (described previously in paragraph 8.64; note this may not necessitate a detailed, fully quantitative assessment) and/or DMRB criteria for affected roads are exceeded with the Scheme in place.
8.118 The relevant DMRB change criteria for the operational phase are:
road alignment will change by five metres or more;
daily traffic flow (two way) will change by 1,000 AADT or more;
HDV flows (two way) will change by 200 AADT or more;
daily average speed will change by 10 kph or more; or
peak hour average speed will change by 20 kph or more.
8.119 If changes in traffic with the Scheme meet one or more of the DMRB change criteria, pollutant concentrations are then estimated at representative receptors on the affected road network and compared with the relevant air quality criteria. If the
55 Environment Agency Air Quality Technical Advisory Group (AQTAG) (2010). Technical Guidance on detailed modelling approach for an appropriate assessment for emissions to air, Version 10.
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change criteria are not met, it can be concluded that there would be a “neutral” effect (in line with DMRB para 3.14), i.e. an insignificant effect on local air quality and further assessment need not be carried out.
8.120 Additional vehicle movements arising from staff journeys, routine deliveries and maintenance activities during operation of the Scheme are discussed in chapter 7, and assessed at paragraph 8.249 in this chapter.
Study area
Dust
8.121 The study area for the construction dust assessment is set in line with IAQM guidance. For human receptors, this is up to:
350 m from the Power Station Complex Site boundary;
350 m from the Gas Connection Route boundary;
50 m either side of haul routes up to 500 m from the Power Station Complex Site access;
50 m either side of haul routes up to 500 m from the Gas Connection Route access.
8.122 For ecological receptors, the study area extends up to:
50 m from the Power Station Complex Site boundary;
50 m from the Gas Connection Route;
50 m either side of haul routes up to 500 m from the Power Station Complex Site access;
50 m either side of haul routes up to 500 m from the Gas Connection Route access.
Transport
8.123 The study area for traffic emissions during construction and operation, for both human and ecological receptors, extends
200 m either side of the centreline of roads “affected” by the Scheme (where “affected” is as defined by the DMRB and/or EPUK/IAQM change criteria).
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Stack emissions
8.124 The study area for the Stack emissions is:
a Cartesian receptor grid covering an area approximately 3.0 x 3.0 km in all directions around the Stacks, at 250m resolution (determined to be appropriate extent and density from initial modelling studies);
a Cartesian receptor grid in a local area covering an area approximately 1.5 x 1.5 km around the Power Station Complex Site at 50 m resolution (determined to be appropriate extent and density from initial modelling studies) and boundary receptor points at 25m intervals along the Power Station Complex Site;
discrete receptor points for human health, relevant to long and short-term public exposure, selected according to the shape of the plume in order to identify most affected receptors in proximity to the Scheme Stack (nominally within 2 km of the Power Station Complex Site);
SAC, SPA and Ramsar sites up to 15 km from the Power Station Complex Site (the search distance for coal- and oil-fired power stations has been conservatively applied in this assessment in response to statutory nature consultee comments); and
SSSI, LNR, NNR, LWS and ancient woodland up to 2 km from the Power Station Complex Site.
Data sources
8.125 The air quality assessment uses the data and information from:
Atkins’ engineers and likely technology providers, to derive Stack emission characteristics from the Scheme for input to the dispersion model;
Chapter 4, with regard to the description of construction activities, to undertake the dust assessment and building dimensions for the emissions modelling; and
Chapter 7, with regard to data and assumptions for construction and operational traffic flows.
8.126 Information on existing ambient air quality i.e. baseline conditions, has been taken from:
Local authority LAQM reports:
- WCBC LAQM Progress Reports 2012, 2013 and 2014;
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- WCBC LAQM Updating and Screening Assessment 2015; - CWCC LAQM Progress Reports 2013 and 2014
- CWCC LAQM Updating and Screening Assessment 2015;
monitoring data provided by the WCBC EHO;
UK Air Information Resource website56;
Air Quality for Wales website57;
DEFRA background pollution maps58; and
APIS website 59.
8.127 Information on ecological sites, status and sensitive habitat types has been derived from:
Chapter 11;
DEFRA “Magic” 60 website;
Forestry Commission Ancient Woodland Inventory website61;
WCBC scoping response for local wildlife sites; and
APIS website.
Cumulative developments
8.128 Chapter 5 of this ES sets out the cumulative scenarios applicable to the assessment of the effects of the Scheme in combination with other development proposals.
8.129 The traffic data for the assessment of cumulative impacts are described in more detail in chapter 7.
8.130 In undertaking the assessment of cumulative effects, consideration has been given to what would be the “realistic worst case” scenario during each Scheme phase, construction and operation. This consideration included a review of the additional volume of vehicle movements generated under each scenario, the potential for dust
56 http://uk-air.defra.gov.uk/ 57 http://www.welshairquality.co.uk/ 58 http://uk-air.defra.gov.uk/data/laqm-background-home 59 http://www.apis.ac.uk/ 60 http://magic.defra.gov.uk/ 61 http://maps.forestry.gov.uk/imf/imf.jsp?site=fcwales_ext&
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raising activities (construction only) and number of sensitive receptors both on and off site. The cumulative assessment has also considered changes in location of sources and receptors that may occur under each scenario which may change the conclusion of the main study. It was assumed, for the purposes of a conservative assessment (‘realistic worst case’), that the construction phases for all developments will be concurrent, as will the operational phases.
8.131 The approach to assessment of cumulative effects applies the methodologies and significance criteria as agreed in consultation with the EHO for WCBC for the assessment of the Scheme itself. These were described in earlier sections of this chapter for construction dust (paragraph 8.50) and traffic emissions (paragraph 8.55). Where appropriate, assessment of cumulative effects is made by means of qualitative comment with reference to the results from the main assessment.
8.132 The cumulative effects of construction requiring assessment are construction dust and vehicle emissions. The cumulative effects of operation requiring assessment are stack emissions (with regard to new receptors in the area62) and traffic emissions. The total vehicle movements generated, the number of sensitive receptors as well as location of sources, buildings and receptors which may change the findings of the study of the Scheme itself, have been considered.
Consultation on methodology
Scoping Report
8.133 The Scoping Report for the Scheme did not identify construction plant emissions as a potential significant issue for consideration at EIA stage. The Scoping Opinion did not request that an assessment of construction plant emissions be made, hence it is not assessed in detail. However, an outline qualitative assessment has been undertaken with reference to the expected sources and distance to receptors
Consultation and Scoping Opinion
8.134 The Scoping Report for the Scheme concluded that, with regard to air quality, the following potential effects on nearby sensitive receptors should be assessed in more detail in the EIA and presented in the ES:
operational emissions from the Stacks;
fugitive dust emissions during construction and demolition of the Scheme; and
62 The EHO at WCBC has confirmed (Appendix 8.3) there are no known planned developments with stack emissions other than a small unit associated with the new prison; it was agreed this will not lead to cumulative effects with the Scheme due to distance and difference in stack height.
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traffic emissions during construction and operation of the Scheme.
8.135 PINS and other stakeholder comments pertaining to air quality have been identified and taken into consideration in this assessment. The overall methodology has been agreed in consultation with WCBC's environmental health officer (EHO) and the NRW permitting officer (who was advised by AQMRAT) (See Appendix 8.3).
8.136 A summary of the consultation for air quality is provided in Table 8.6. A summary of the responses to air quality matters raised in the Scoping Opinion is provided in Table 8.7.
Table 8.6: Items identified within the consultation undertaken for air quality Date Description Additional comments 22.11.2012 Discussion with Paul Campini (air quality Provided diffusion tube data for officer at WCBC) regarding approach to Hugmore Lane and list of Part A2 assessment and local monitoring data. and B processes regulated by the WCBC. 03.01.13 Response from WCBC to the Previous Local wildlife sites within 2km Scoping Report requested: including W337 have been - Consideration of wildlife site W337; considered in the air quality and assessment. - Adherence to Environment Agency All relevant current guidance and guidance and policy relating to air policy documentation has been dispersion modelling; referenced in preparation of the WCBC also noted that the Isycoed air ES. quality monitoring station is likely to The approach to modelling has remain operational. been undertaken in line with Environment Agency guidance (Air Emissions Risk Assessment, and other publications from AQMAU and AQTAG), which is supported by NRW. The scope of dispersion modelling has been agreed with NRW. 09.01.13 Previous Scoping Opinion from the Short term receptors (e.g. access Secretary of State received; the advice roads, local footpaths, PRoW) are and recommendations have been considered. considered for the EIA and included in The scope of dispersion modelling the ES (see Table 8.7 below). has been agreed with the EHO and NRW.
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Date Description Additional comments 02.16 EHO confirmed that application of the - latest IAQM/EPUK (2015) guidance would be appropriate and noted that the Isycoed CMS ceased to operate from January 2016
Table 8.7: Items identified within the Scoping Opinion relating to air quality Scoping opinion requirement Comment 3.16 - The ES should clearly define and justify The study areas for all aspects of the air the study areas used for all aspects of the air quality assessment are presented from quality assessment. paragraph 8.121 to 8.124. Air quality and dust levels should be The assessment of construction dust considered not only on site but also off site, considers all relevant receptors in including along access roads, local footpaths accordance with the published IAQM and other PRoW methodology. This includes an assessment of trackout of dust 500m from the site entrance. Table 8.18 identifies a local public right of way as a receptor. See also Table 8.14. 3.17 - The pollutants to be considered in the Appropriate consultation was made with the assessment, the extent of the study area, the EHO at WCBC dealing with air quality. See for baseline data and assessment methodologies example paragraphs 8.99, 8.154 and 8.216 should be agreed with Wrexham County (Email correspondence also presented within Borough Council’s environmental health Appendix 8.3). officers and Natural Resources Wales (NRW). The most recently available monitoring data was requested from the EHO to determine baseline air quality conditions. At their request, the Isycoed CMS has been used to provide the background values for the stack emissions study. Methodology was also discussed with the permitting officer at NRW (based on the advice of AQMRAT). See for example paragraphs 8.75, 8.216, 8.230, 8.229 (E-mail correspondence presented in Appendix 8.3). 3.17 - The applicant’s attention is also drawn Specific responses at end of this table. to the comments from NRW, Wrexham Preparation of the Air Quality chapter of the County Borough Council (WCBC), Isycoed ES has considered comments received from Community Council and Public Health PHE. The text in the introduction to this England in Appendix 2 of this report. chapter provides a robust justification for the pollutants assessed. 3.18 – The Scoping Report states that a Given the current lack of a detailed Schedule detailed schedule of works and construction of works and Construction programme, the
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Scoping opinion requirement Comment programme is not available. The SoS advises methodology for “realistic worst case” that this must be clearly explained in the ES assessment of the Scheme is adopted including any assumptions that have been throughout. The assessment has been made made when conducting the assessment of air within the principles of a ‘Rochdale quality impacts during construction Envelope’. Justification of a robust assessment is also provided at paragraph 8.73 3.19 - The inter-relationship between the The traffic data used in the air quality traffic and transport assessment and the air assessment uses data presented in the traffic quality assessments should be clearly assessment chapter. This is explained in explained in the ES. each section of the ES where appropriate, for example paragraph 8.206. 3.20 - The SoS expects that at least an The Draft CEMP is included in Appendix 19.1 outline/draft CEMP should be provided as an annex to the ES; it should be clear exactly which mitigation measures will be delivered by implementation of the CEMP. 3.21 - The implications of stack height and Stack height and discharges are addressed dispersion of emissions need to be clearly within paragraphs 8.87 to 8.94 and in Table explained. 8.4.To be read in conjunction with the rest of the chapter. 3.21 - The SoS recommends that dispersion The methodology for “worst case” modelling considers a range of possibilities assessment of operational emissions is and seeks to ensure that the ‘worst case’ presented throughout including at scenario is assessed, for example the ‘worst paragraphs 8.52 to 8.54 and 8.82 to 8.85. case’ may occur as a short term impact. The The assessment has been made within the intention to use a realistic ‘worst case principles of a ‘Rochdale Envelope’. scenario’ in terms of the power station is Justification of a robust assessment is also noted; the applicant should refer to SoS provided at paragraph 8.73. comments in section two of this opinion regarding the approach to the assessment of worst case. 3.22 - The SoS agrees that it will be necessary Statutory and non-statutory sites have been to consider statutory and non-statutory addressed. The ES presents a full wildlife sites within the likely zone of assessment of air quality effects on all influence, based on Environment Agency relevant sites of ecological interest including (EA) guidance. The applicant’s attention is statutory sites out to 15km and non- also drawn to comments from NRW and statutory sites (LWS) within 2km. WCBC in Appendix 2. Paragraphs 8.173 and Table 8.15 of this chapter identify non-statutory ecological sites considered in the air quality assessment. 3.23 – The ES should meet the requirements The assessment of operational and of paragraph 4.10.7 of NPS EN-1 to the cumulative effects of the Scheme presented
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Scoping opinion requirement Comment satisfaction of the SoS in order for a DCO to in the ES chapter for air quality meets these be granted. requirements. 3.24 – The applicant’s attention is drawn to A phone conversation between the principal the comments from NRW in Appendix 2 permitting officer at NRW and the Scheme encouraging the applicant to begin air quality specialist took place on 17th July discussions with them as soon as possible in 2014. Written confirmation was provided in relation to the grant of an environmental email for forwarding to AQMRAT. A permit. response from NRW was received on 26th August and the AQMRAT comments contained within that response have been taken on board in the approach to modelling where appropriate. CWC requested two additional discrete Two additional receptor points included in receptor points be included in the stack model as requested, at Lane End and Crewe emissions modelling, acknowledging Hill. See Table 8.14. however that effects are unlikely to occur beyond 2km. Isycoed Community Council requested that Modelling included receptors in both Isycoed “air dispersion modelling should be carried village and Cheshire (as requested by CWC). out including any effect on adjoining The wider model grid was designed to cover communities including across the border into all relevant locations, including adjoining Cheshire” communities.
Assessment criteria
Dust
8.137 The IAQM Dust Guidance (2014) is the appropriate reference for determining the risk of dust effects and their significance. The risk of effects is assessed taking account of the factors that define the magnitude of the dust source and the sensitivity of the surrounding area. The overall pattern of potential risks is set out within a “summary dust risk table” (based on the example in Table 10 of the guidance) and suitable mitigation then recommended (see chapter 19, Mitigation Summary), for a summary of the mitigation that will be delivered). The IAQM recommends that significance is only assigned to the effect after considering the dust raising activity with mitigation in place. The interpretation of significance is based on professional judgement of a suitably qualified air quality professional. The guidance acknowledges that, as appropriate site-specific mitigation measures will have been defined for the risk presented by the project under consideration, the residual effect will - for most sites - be ’not significant’.
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Traffic emissions
8.138 For traffic emissions, the need for an assessment is initially based on whether the DMRB and/or EPUK / IAQM criteria for affected roads are exceeded. Should those criteria not be exceeded, effects can be considered as ‘neutral’ (DMRB paragraph 3.14) which for the purposes of EIA is deemed insignificant. Should further assessment be required, the results are interpreted through a comparison of estimated total pollutant concentrations with relevant AQS objectives, taking into account existing background concentrations and the magnitude of change due to the Scheme.
8.139 Descriptors for magnitude of change due to changes in ambient concentrations of pollutants at individual receptors, and guidance for the interpretation of the significance of these effects, are provided in the EPUK/IAQM Guidance (2015). The changes in concentration are grouped according to the percentage change relative to the so-called Air Quality Assessment Level (AQAL), and the description of that change, in terms of whether it is slight, moderate or substantial, or negligible, depends upon the absolute concentration in relation to the air quality objective of interest. The descriptors are provided in Table 6.3 in the guidance (repeated in Table 8.8 below in relation to the Scheme in relation to annual mean NO2 and particulate matter). The term AQAL is used to include air quality objectives or limit values, where these exist. These descriptors are intended for individual receptors only; the overall significance is determined using professional judgement.
8.140 The guidance states that, in most cases, the assessment of impacts for a proposed development will be governed by long-term exposure and hence it may not be necessary to define the significance of effects by reference to short-term impacts. Background concentrations are less important in determining the severity of impact for short term concentrations, not least because the peak concentrations attributable to the source and the background are not additive.
8.141 The guidance notes that the Environment Agency uses a threshold criterion of 10% of the short term AQAL as a screening criterion for the maximum short term impact (i.e. one hour or less). This is considered by EPUK/IAQM to be a reasonable value to define an impact that is sufficiently small in magnitude to be regarded as having an insignificant effect. With regard to impacts expressed using an averaging time of a day, peak short term concentrations from an elevated source in the range 10-20% of the relevant AQAL, can be described as being of small magnitude, those in the range 20-50% as medium and those above 50% as large. These will be the maximum concentrations experienced in any year and the severity of this impact can be described as slight, moderate and substantial respectively, without the need to reference background / baseline concentrations.
8.142 For the purposes of this EIA, changes of negligible or slight (adverse) severity are deemed – individually – to be not significant. However, as explained in the
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EPUK/IAQM guidance, any judgement on the overall significance of effect of a development must take into account such factors as:
the existing and future air quality in the absence of the development;
the extent of current and future population exposure to the impacts; and
the influence and validity of any assumptions adopted when undertaking the prediction of impacts.
Table 8.8: Air quality impact descriptors for individual receptors (Extract from EPUK/IAQM Guidance) Long term average Percentage change in concentration relative to AQAL, % concentration at receptor <1% 2 - 5% 6 - 10% >10%
75% or less of AQAL Negligible Negligible Slight Moderate 76 - 94% of AQAL Negligible Slight Moderate Moderate 95 - 102% of AQAL Slight Moderate Moderate Substantial 103 – 109% of AQAL Moderate Moderate Substantial Substantial 110% or more of AQAL Moderate Substantial Substantial Substantial
Stack emissions
8.143 The results of the dispersion modelling study of Stack emissions are interpreted in the first instance, in accordance with Environment Agency Air Emissions Risk Assessment Guidance with reference to the relevant EU limit values and target values, AQS objectives and EALs in the context of existing background concentrations. Where a modelled increment is less than 1% of the long-term objective or less than 10% of the short term objective, it can be considered insignificant. A result, in excess of this arbitrary and conservative screening criterion does not imply that it is significant; rather it suggests that a more detailed consideration of total concentrations is required. The results are evaluated against AQS objectives and EU Limit Values for human health, as well as – where appropriate – EALs, in the context of existing background concentrations. The EPUK/IAQM criteria shown in Table 8.8 above are used to interpret the significance of these results.
8.144 The modelled annual average oxides of nitrogen concentrations are evaluated in a similar manner in the context of critical levels for the protection of vegetation and ecosystems. Rates of nitrogen deposition at the nearest sensitive ecological sites are assessed with reference to background deposition rates and the APIS recommended critical loads. Where the calculated nitrogen deposition rate increases by less than 1% of the critical load or background rate, Environment
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Agency advice is that this can be interpreted as insignificant63. Nonetheless, it should be noted that an increase of 1% or more does not indicate that the increment is either significant or unacceptable, merely that a more detailed interpretation of the data is required. This may require, for instance, consideration of the extent of the area above 1%, the status or condition of the designated site, or the specific location of protected species within the site.
8.145 In relation to the assessment of the effects of the Stack emissions on the non- statutory local designations, the Environment Agency ‘Operational Instruction 66- 1264 states that where the modelled increment i.e. the process contribution (PC) is less than the critical level itself, it can be considered to be insignificant. This is deemed sufficient to demonstrate the application of BAT and no further assessment is required. However, in response to AQMRAT comments, the total Predicted Environmental Concentration (PEC) is reported herein for all site types.
Inherent mitigation
Power Station Complex
8.146 Mitigation considered integral to the design and considered in the assessment of impacts includes:
use of natural gas combined with the latest CCGT technology to ensure inherently low emissions of NOx and negligible emissions of SO2 and PM10;
improvements in vehicle emission technology over time, as a result of measures introduced at a national level implementing European Directives;
car sharing between construction workers travelling to the site; and
application of dust mitigation measures as required by legislation.
Gas connection
car sharing between construction workers travelling to the site; and
63 The IAQM position statement on impact assessment of sensitive habitats (http://www.iaqm.co.uk/text/position_statements/aq_impacts_sensitive_habitats.pdf) states that the Environment Agency has accepted that there is a level of emission from an installation so low such that its impact would constitute an ‘inconsequential effect’, when considered in isolation or in combination with the background or other sources. The Environment Agency, in developing their risk assessment guidance, chose to set this level at 1% of the relevant criterion, which in the context of ecological impacts is typically the critical level for vegetation or the critical load for the habitat being considered. NRW supports Environment Agency guidance for permitting. 64 Environment Agency. Operational Instruction 66_12: Simple assessment of the impact of aerial emissions from new or expanding IPPC regulated industry for impacts on nature conservation
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application of mitigation measures for the control of dust required by legislation.
Difficulties encountered compiling information
8.147 The Infrastructure Planning (Environmental Impact Assessment) Regulations 2009, Schedule 4, Part 1 requires at paragraph 23 that applicants provide “An indication of any difficulties (technical deficiencies or lack of know-how) encountered by the applicant in compiling the required information.”
8.148 Uncertainty at this stage as to how the final Power Station Complex will be configured (1+1 or 2+1) and a final design, has been suitably managed through robust and “realistic worst case” assumptions based on an initial modelling study for the most likely configurations. The configuration used in the model is that which gave rise to the higher ground level concentrations of pollutants in air. The assumption of full load operation throughout the year, and the application of a higher oxides of nitrogen emission rate when estimating short-term concentrations, to account for alternative means of operation, ensures a conservative assessment.
8.149 In the absence of published Environmental Statements for the other committed developments, assumptions have had to be made by the transport and traffic consultants when undertaking the cumulative impact assessment. The assumptions relevant to the cumulative assessment (described in chapter 7) are considered to be realistic and reasonable for the purposes of ensuring a robust assessment.
BASELINE INFORMATION
Local Air Quality Management
8.150 The Scheme is located within the boundaries of WCBC on the eastern boundary of the Wrexham Industrial Estate, which is approximately 5.5 km east of the centre of Wrexham.
8.151 The Wrexham Industrial Estate (WIE) is the largest industrial estate within the county borough boundary; approximately 220 businesses are based there, 20 of which hold either a local authority or NRW Environmental Permit. Industrial premises in the immediate vicinity of the Scheme include a large logistics warehouse and distribution centre operated by Norbert Dentressangle directly to the south, and the Kellogg’s food manufacturing complex to the west. Both of these processes are emitters of oxides of nitrogen.
8.152 There are no AQMAs within the WCBC administrative area. The Scheme is approximately 2 km west of the Cheshire West and Chester Council (CWCC) administrative boundary. CWCC has declared two AQMAs, at Ellesmere Port and in
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Chester; neither would be affected by the Scheme as they are over 15km to the north.
Monitoring data
8.153 Measurements of pollutant concentrations can be made by deploying analytical instruments that measure continuously and record average concentrations over specified time intervals, called continuous monitoring sites (CMS). Simpler passive sampling devices, such as diffusion tubes, absorb pollutants over a longer time period and are subsequently analysed at a laboratory to give an average concentration for the sampling period. National survey results from both types of monitoring are published on the “Air Quality in Wales” website.
8.154 Within WCBC, a CMS located at Isycoed (grid reference 339720, 350514) operated until January 2016. It was classified as an urban industrial site around 60 m west of the B5130 within the grounds of St Paul’s School and was approximately 450m south-east of the proposed location for the Stacks for the Power Station Complex. There is in addition a CMS on Victoria Road (grid reference 332865, 349909) close to Wrexham town, at a roadside location approximately 6 km west of the Stacks. Both sites are part of the Automatic Urban and Rural Network (AURN) of stations in the UK, hence the Quality Assurance / Quality Control (QA/QC) of the data is high. The EHO at WCBC has specifically requested that the historic readings from the Isycoed CMS are used to provide representative background data for the study, as it is the closest to the Scheme and represents an urban industrial setting outside of the town centre.
8.155 The locations of local air quality monitoring sites (CMS and diffusion tubes) are shown in Figure 8.2. No additional baseline surveys have been carried out for the assessment of air quality of the Scheme, as the publicly data available from the local authority reports and the aforementioned CMS are sufficient to establish existing conditions in the Scheme study area (as agreed with WCBC EHO by email dated March 2014, see appendix 8.3).
8.156 Data for the seven-year period 2009-2015 for NO2 recorded by the two CMS are presented in Table 8.9. Annual mean concentrations were well below65 the national AQS objective in all years; there were no exceedances of the short-term standard at either site. Over the monitoring period presented, the results have remained fairly consistent at the Victoria Road CMS with a slight increasing trend at Isycoed in recent years.
65 Defined in IAQM / EPUK Guidance 2015 as less than 75% of the AQAL value, in this case 40 µg/m3.
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Table 8.9: Nitrogen dioxide concentrations measured at Isycoed and Victoria Road CMS Averaging period 2009 2010 2011 2012 2013 2014 2015 1. Isycoed Annual Average, µg/m3 8.8 7.8 7.0 9.4 9.8 12.4 12.5^ No. of exceedances of 0 0 0 0 0 0 0 1-hour standard (200 µg/m3) 2. Victoria Road Annual Average, µg/m3 21.3 24.2 19.2 20.2 21.8 21.1 19.1^ No. of exceedances of 0 0 0 0 0 0 0 1-hour standard (200 µg/m3) ^ Note: 2015 CMS data contains 3 months of provisional data as of 16/02/16
8.157 Particulate matter (PM10) is measured gravimetrically at both the Isycoed CMS and the Victoria Road CMS; the Victoria Road site also records PM2.5, the finer fraction of particulate matter with a more stringent health-based standard. Concentrations of both pollutants measured in recent years are presented in Table 8.10. Annual mean concentrations of PM10 and PM2.5 were well below the national AQS objective in all years; the number of exceedances was less than the short-term objective.
Table 8.10: Particulate matter concentrations measured at Isycoed and Victoria Road CMS Averaging period 2009 2010 2011 2012 2013 2014 1. Isycoed Annual Average µg/m3 18.2* 14.5* 16.1* 16.7 21.8 15.8^ No. of exceedances of 0 0 6 8 13 7^ 24-hour standard (50 µg/m3) 2. Victoria Road PM10 Annual Average 15.2 14.3 17.7* 15.1 17.1 14.3 (µg/m3) No. of exceedances of 4 0 14 4 12 8 24-hour standard (50 µg/m3) PM2.5 Annual Average - 9.8 10.4 9.3 9.8 9.4 (µg/m3) * Data capture rate below 75% ^ Value is subject to change pending a final check to be conducted by WCBC
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8.158 WCBC operates a network of 23 passive diffusion tube monitoring sites equipped 66 with diffusion tubes sampling NO2 . In consultation with the WCBC EHO, three monitoring sites within approximately 2 km of the Power Station Complex Site were identified as being representative of conditions in the vicinity of the Scheme. These locations are shown in Figure 8.2. The results for these sites may be appropriate when interpreting the results of the assessment of road traffic emissions.
8.159 The NO2 diffusion tube sampling site closest to the Scheme is on Hugmore Lane, a roadside location north of the Wrexham Industrial Estate. Until 2012, Hugmore Lane was one of the main access roads for the industrial estate and carried a high volume of HGVs. Concentrations at the Hugmore Lane diffusion tube site are similar to those measured at the Victoria Road CMS (a roadside location) but are higher than at the Isycoed CMS.
8.160 The concentrations at Hugmore Road show an overall increase from 2008 to 2011, which could be partly due to changes in vehicle emissions of primary NO2 and increase in traffic volume over time. In July 2012 a new road (the A5156 Industrial Estate Road) linking Wrexham Industrial Estate with the A534 in the north was opened. This resulted in reduced traffic flows on the former Hugmore Lane access and a notable decrease in NO2 concentrations at this site was observed following opening of the bypass. The monitoring site was closed at the end of 2013.
8.161 A new diffusion tube monitoring site in Llan-y-Pwll was set up in January 2013 at a roadside location off the A5156, one of the main roads onto the Wrexham Industrial Estate and which has an AADT of around 17,500, of which 13% is HGVs. Another new roadside monitoring site was set up in 2012 at Marchwiel on the A525 through Overton, approximately 1km south west of the Pentre Maelor housing estate, which is approximately 2 km south west of the Power Station Complex Site.
8.162 Annual average, bias adjusted NO2 concentrations for Hugmore Lane for the six- year period 2008-2013 are presented in Table 8.11 below, together with available data for the two newer sites in recent years. The results, all of which represent roadside locations, are well below the AQS objective of 40 µg/m3. The result at Llan y Pwll is very similar to that recorded at Hugmore Lane, prior to the opening of the new Industrial Estate Road (N) to the industrial estate.
8.163 The closest monitoring location to the Scheme operated by CWCC is in Malpas, some 10 km to the south east of the Order Land67. This roadside site measured a 3 NO2 concentration of 16.6 µg/m in 2011, similar to that measured at Marchwiel in 2013.
66 2013 Air Quality Progress Report for Wrexham County Borough Council. May 2013 67 From Cheshire West and Chester website, page accessed 11/09/14 http://www.cheshirewestandchester.gov.uk/residents/pests_pollution_food_safety/pollution_and_air_quality /air_quality_monitoring/diffusion_tube_map.aspx
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Table 8.11: WCBC Nitrogen dioxide diffusion tube monitoring results, µg/m3 I Site Grid reference 2008 2009 2010 2011 2012 2013 2014 D 3 Hugmore Lane 337700, 21 21 24 27 23 24 - 351800 4 Marchwiel 335407, - - - - 14 16 17 347890 5 Llan y Pwll 335359, - - - - - 26 23 352178
Mapped data
8.164 An alternative source of background pollutant concentration are the maps available from the DEFRA website. These maps are produced based on the extrapolation and interpolation of empirical measurements and modelled dispersion of, amongst other sources, transport and industry and are a useful source in the absence of suitable monitoring data. The maps are available for every 1 km grid square in Great Britain for future years up to 2025, for NOx, NO2 and PM10, and for the year 2001 for CO (and SO2). The estimated background concentrations for the grid squares across which the Scheme lies are presented in Table 8.12 for the year 2014.
8.165 Annual mean background concentrations are well below (i.e. less than 75% of, as defined in EPUK/IAQM guidance) the AQS objectives for human health and vegetation for all pollutants. The concentrations of NO2 are broadly consistent with the measurements made at Isycoed CMS in the last two years. As requested by the EHO at WCBC the CMS site is used to provide NO2 data for the assessment of Stack emissions. For the assessment of dust (which requires a value for PM10), the values in Table 8.12 are preferred as they cover a wider area, reflecting the larger extent of the study area to be considered for the Gas Connection. The concentrations are again broadly consistent with the CMS data.
Table 8.12: DEFRA mapped annual mean background concentrations for 2014, µg/m3
Grid Square NOx NO2 PM10 PM2.5 CO 339500,350500 14.6 11.1 14.1 9.2 105 (Site and Gas Connection) 339500,349500 15.1 11.5 14.4 9.3 104 (Gas Connection) 339500,348500 11.5 8.9 13.0 8.6 102 (Gas Connection) 338500, 348500 13.6 10.5 14.1 9.0 102 (Gas Connection) 338500, 347500 11.0 8.6 13.7 8.7 99 (Gas Connection)
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Grid Square NOx NO2 PM10 PM2.5 CO National / EU criteria 30 40 40 25 - Note: CO converted from DEFRA 2001 value to an estimate for 2010 using factor of 0.432. 68
Nitrogen and acid deposition
8.166 The background pollutant concentrations and nitrogen and acid deposition rates as available from Air Pollution Information System (APIS) are presented in Table 8.13 below for the designated sites under consideration. The APIS habitat type was selected in consultation with the project ecologists at Atkins, who have themselves consulted with the nature conservation bodies (including NRW) or advice of which to select. The overriding consideration has been to ensure a conservative approach, therefore only the most sensitive habitat(s) have been assessed. For oxides of nitrogen, background concentrations from DEFRA mapping are also shown and, since they are more conservative overall, have been used in the assessment. It is noted that existing rates of nitrogen deposition already exceed critical levels for certain habitat types identified within the Scheme study area
8.167 The preference in the case of oxides of nitrogen of the mapped background data over monitoring data is appropriate because of the spatial coverage of the ecological assessment, which extends in a 15 km radius from the Scheme stacks in all directions, hence applying a single measurement to distant designated sites would be inappropriate as it would be most unlikely to be representative of local conditions. Furthermore, designated ecological sites are typically in more rural locations than monitoring sites, therefore the use of an industrial background measurement such as that from the Isycoed CMS would be overly conservative.
Table 8.13: DEFRA and APIS background concentrations and deposition rates
Designated site Site interest NOx Deposition rate Critical load† feature(s) concentration (maximum)* (µg/m3) DEFRA APIS Nitrogen Acid N Nitrogen Acid N (kg/ha/yr) (keq (kg/ha/yr) (keq /ha/yr) /ha/yr) Midland Meres Raised and 12.68 13.45 22.68 1.62 5-10 0.68 and Mosses blanket bog Ramsar Phase 2 (D1) - Vicarage Moss Midland Meres Valley mires, 9.51 8.16 25.48 1.82 10-15 1.08 and Mosses poor fens and Ramsar Phase 2 transition mires
68 Carbon monoxide only available for the year 2001. Adjustment factor is taken from DEFRA Technical Guidance LAQM TG (03), in accordance with the approach described at: http://laqm.defra.gov.uk/review-and- assessment/tools/background-maps.html#YAF
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Designated site Site interest NOx Deposition rate Critical load† feature(s) concentration (maximum)* (µg/m3) DEFRA APIS Nitrogen Acid N Nitrogen Acid N (kg/ha/yr) (keq (kg/ha/yr) (keq /ha/yr) /ha/yr) - Hanmer Mere (D2) River Dee and Mixed 10.80 9.82 61.32 4.38 10 3.07 Bala Lake SAC, woodland (G) SPA and SSSI - to east River Dee and Water course 10.00 9.03 24.22 1.75 3-10^ n/a Bala Lake SAC, of plain to SPA and SSSI montane levels - to south (H3260) Berwyn and Raised and 8.98 8.32 25.48 1.82 5-10 0.66 South Clwyd blanket bog Mountains SAC (D1) Johnstowns Raised and 14.73 11.88 18.06 1.29 5-10 n/a Newt Site SAC blanket bog (D1) Wrexham Non- 19.63 11.91 24.78 1.77 10-15 4.74 Industrial Estate Mediterranean LWS - Bryn Lane dry acid and neutral closed grassland (E1.7) Wrexham Non- 19.63 11.91 24.78 1.77 10-15 4.74 Industrial Estate Mediterranean LWS - Cefn Park dry acid and neutral closed grassland (E1.7) Broadleaved 19.63 11.91 44.52 3.18 10-20 1.76 woodland (G1) Wrexham Broadleaved 19.56 11.91 44.52 3.18 10-20 1.76 Industrial Estate woodland (G1) LWS - Erlas Black Wood Peter’s Dingle Broadleaved 11.46 11.91 44.52 3.18 10-20 1.76 LWS & Parkey woodland (G1) Lodge AW Bridgeway Broadleaved 19.56 11.91 44.52 3.18 10-20 1.76 Centre AW woodland (G1) Redwither Wood Broadleaved 26.35 11.91 44.52 3.18 10-20 1.76 AW woodland (G1) Notes: * Information relating to SACs and SSSIs taken from the “Site Relevant Critical Loads” section of the APIS website; values for non-statutory sites obtained using the “search by location” function. † Recommended values within range for use in the air pollution impact assessment were taken from http://www.apis.ac.uk/indicative-critical-load-values ^ NRW have advised the River Dee is “Water courses of plain to montane levels containing Ranunculion fluitantis and Callitricho-Batrachion vegetation”. NRW have advised all of the features of this SAC/SPA are
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aquatic so there are no nitrogen critical loads that can be applied hence the Ranunclion water course feature and the floating water plantain that you referred to below are not relevant. The project ecologists have also advised that water plantain is not likely to be present anywhere except Bala Lake. For a hypothetical worst case assessment, it is assumed to be potentially present in a section to the south of the Scheme hence the critical load for floating water plantain is applied here purely for a theoretical assessment of risk.
Receptors
Human health
8.168 The closest settlement to the Order Land for the Scheme is the village of Isycoed approximately 400 m to the east of the Gas Connection Route. There are some properties located closer to the Scheme on the B5130 approximately 250 m to the east of the Power Station Complex Site. There are a few isolated residential properties closer to the Order Land on Bryn Lane and Oak Road to the south and south west respectively. The Pentre Maelor housing estate is approximately 2 km to the south-west of the Power Station Complex Site. The nearest PRoW to the Power Station Complex Site is footpath ISY / 18, running east-west between Isycoed and Bryn Lane; at its closest point it is approximately 15 m from the Power Station Complex Site and is crossed by the Gas Connection Route. PRoW SESS / 25 is close to the AGI and crossed by the Gas Connection Route.
8.169 A list of receptor points representing locations of relevant short and long-term exposure is provided in Table 8.14. Note that this is not intended to be an exhaustive list of all relevant properties that could be affected by Stack emissions from the Power Station Complex; the dispersion model also includes two Cartesian receptor grids which cover intermediate areas in the near field as well as receptors further afield up to several kilometres away. The table shows the distance of each receptor to the Stacks (depicted as the blue dots within the Order Land in Figure 8.1). The receptor points are shown graphically in Figure 8.1 as purple stars.
Table 8.14: Air Quality Human Health Receptors and Distance (m) from the Stack, Scheme and Gas Connection Route ID Receptor description Easting Northing Distance to Distance to Distance to Gas Scheme Power Station Connection Stacks^ Complex Site Route 1 Harcourt, Ridleywood 339529 351144 935 505 885 Road 2 Plum Tree Farm, B5130 339832 350314 815 260 165 3 Marshley Farm, B5130 339719 350663 760 255 415 4 4 - 6 Bryn Lane 338920 350737 390 245 815 5 Little Acorns, Bryn Lane 338475 350886 755 630 1270
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ID Receptor description Easting Northing Distance to Distance to Distance to Gas Scheme Power Station Connection Stacks^ Complex Site Route 6 Bryn Cottages, Bryn 338809 349527 860 740 735 Lane 7 Kelloggs factory, Bryn 338894 350461 160 80 715 Lane 8 Higher Oak, Oak Road 339731 348843 1675 1385 120 9 Cae Bryner Farm, B5130 340032 349429 1375 910 315 10 St Pauls School, B5130 339981 349993 1030 455 245 11 Lower Oak Farm, Oak 339252 349070 1310 1150 135 Road 12 Parkey Lodge 338566 348197 2210 2090 60 13 Maesgwyn Farm 340517 350995 1625 1115 1125 14 Oakfields, Isycoed 340100 350117 1105 520 385 15 Pentre Maelor, Bridge 337294 348994 2200 2100 1285 Road S 16 Gorton Hall, Llan-Y-Pwll 337334 351974 2335 2205 2825 17 Hugmore Lane Farm 337761 351961 2035 1900 2490 18 Parkey Farm 338026 347837 2715 2590 335 19 Lane-end, Shocklach 342880 349530 3950 3365 3155 20 Crewe Hill 342070 352720 3855 3345 3445 21 Footpath ISY / 18 339615 350221 610 15 0 Note: Distances in bold type indicate receptors also relevant to the dust assessment ^ Distance provided is from the midpoint of the Scheme Stacks to the maximum modelled ground level concentration, which may not always be the shortest distance to the group of receptors identified.
Ecological Receptors
8.170 The Air Emissions Risk Assessment Guidance from the Environment Agency recommends that designated conservation sites need only be considered where they fall within set distances of the activity:
Special Protection Areas (SPAs), Special Areas of Conservation (SACs) or Ramsar sites within 10 km of the installation (or up to 15 km for coal- or oil-fired power stations); and
Sites of Special Scientific Interest (SSSIs), National Nature Reserves (NNRs), Local Nature Reserves (LNRs) and ancient woodland, as well as non-statutory local wildlife sites (LWS) within 2 km of the installation.
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8.171 An evaluation is then made of modelled concentrations against critical levels specified for oxides of nitrogen and of nitrogen deposition and acid deposition rates against critical loads.
8.172 The GIS website “Magic”, managed by DEFRA, was used to identify national, European and international designated sites in the above described search areas. Within 15 km of the Power Station Complex Site, the following relevant sites were identified:
Midland Meres and Mosses Ramsar (Phase 2) - a discrete series of lowland open water and peatland sites in the north-west Midlands. The 16 component sites include open water bodies (meres), the majority of which are nutrient-rich with associated fringing habitats; reed swamps, fen, carr and damp pasture. The component SSSI units within 15 km are Vicarage Moss, Hanmer Mere and Llyn Bedydd and more detail is provided below;
- Vicarage Moss is of special interest for a mixture of raised mire (bog), swamp, wetland and wet woodland plant communities.
- Hanmer Mere is a naturally nutrient rich mere supporting water plants, of special interest for its standing water.
- Llyn Bedydd69 is a small ‘mere’ developed in a natural depression, and of special interest for its standing water and wet woodland.
River Dee and Bala Lake SAC and SPA - special interest habitats of relevance to air quality include rivers with floating vegetation and saltmarsh transition habitats, with good tree cover along the banks. In the Cheshire plains it displays typical characteristics of lowland river types with shallow gradients flowing over nutrient rich soils. The stretch of the River Dee closest to the Scheme is classified as a water course of plain to montane levels containing the Ranunculion fluitantis and Callitricho-Batrachion vegetation. The species floating water-plantain Luronium natans is only present in Bala Lake, which is approximately 45 km south east of the Scheme Order Limits. Woodland/grassland habitats are listed for the coincident SSSI of the same name (NRW have advised these are not site features but are important when assessing impacts on the wider countryside as required under NERC Act 2006 S40).
Berwyn and South Clwyd Mountains SAC – Annex I habitats that are a primary reason for selection of this site are the European dry heath and blanket bogs. Annex I habitats present as a qualifying feature, but not a primary reason for selection of this site are: semi-natural dry grasslands and scrubland and transition mires and quaking bogs.
69 Owing to Hanmer Mere being of lesser distance than Llyn Bedydd to the Scheme, yet in a similar direction and with a similarly sensitive habitat, only Hanmer Mere is included in the assessment tables.
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Johnstown Newt Site SAC - not designated for habitats but for great crested newts. Surrounding land supports scrub and planted trees, grassland, and tall ruderal vegetation, important foraging and over wintering areas for adult and juvenile amphibia. The majority (45%) of the habitat present is broadleaved deciduous woodland while only 1% is classified as bog, marshes and fens.
8.173 There are no statutory designated sites of national or local importance within 2 km of the Power Station Complex Site, nor within 50 m of the Gas Connection Route (for construction impacts).
8.174 The following non-statutory sites have been identified within 2 km of the Order Land:
Wrexham Industrial Estate LWS (W337), which is composed of three sub units:
- Bryn Lane - a strip of species-rich unmanaged grassland beside a ditch to the south west of the Power Station Complex Site;
- Cefn Park - a complex mosaic of scrub, grassland and tall herb at an area of derelict land to the south of the Power Station Complex Site, with a mosaic of woodland and damp grassland adjacent to the River Clywedog, dominated by hawthorn with alder and willow;
- Erlas Black Wood a pocket of ancient broadleaved woodland (ID 30640) dominated by mature oak to the west of the Power Station Complex Site;
Peter’s Dingle LWS (W319), an ash/oak woodland along a brook to the south, co-incident with Parkey Lodge ancient woodland;
Ancient woodland (unique IDs given in brackets) at:
Bridgeway Centre (ID 33412) to the south west;
Parkey Farm and Parkey Lodge to the south (IDs 33342-44), the latter set partially within Peter’s Dingle LWS;
Redwither Wood (ID 30646) to the north west; and
Clays Plantation (ID 37168) to the north west.
8.175 Cefn Park LWS (W316) including ancient woodland at Big Wood lies just beyond 2 km west of the Power Station Complex Site. It is not included in the air quality assessment as it is more than 2km from the Power Station Complex Site; however, the impact here will be similar to that for Redwither Wood given the distance and direction from the Scheme Stacks.
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8.176 A summary of these sites and their distances to the Stacks, the Power Station Complex Site and the Gas Connection Route is provided in Table 8.15 below. Please note that for the Stacks, the distance is between the centre point of the stacks and the location of the modelled maximum ground level concentration of pollutants.
8.177 Ecological receptors within relevant search distances of the Power Station Complex Site and Gas Connection Route are shown graphically in Figure 8.1 (letters A to I, green stars; those furthest afield are shown in inset boxes).
Table 8.15: Air Quality Ecology Receptors and Distance (m) from the Stack, Power Station Complex Site and Gas Connection Route ID Receptor Easting Northing Distance Distance to Distance to to Scheme Power Gas Stacks^ Station Connection Complex Route* Site* A1 Wrexham Industrial 338923 349912 460 10 610 Estate LWS - Bryn Lane A2 Wrexham Industrial 338700 349475 940 815 85 Estate LWS - Cefn Park A3 Wrexham Industrial 337773 349971 1305 1185 1540 Estate LWS - Erlas Black Wood B1 Midland Meres and 336200 353780 4430 4280 4865 Mosses Ramsar Ph 2 - Vicarage Moss SSSI B2 Midland Meres and 345310 340020 12105 11695 10240 Mosses Ramsar Ph 2 - Hanmer Mere SSSI C1 River Dee and Bala 341392 350059 2390 1810 1660 Lake SAC, SPA and SSSI - east C2 River Dee and Bala 340870 347310 3570 3180 2125 Lake SAC, SPA and SSSI - south D Peter’s Dingle LWS 339026 348217 2145 1930 190 E Parkey Farm & Lodge 338238 347902 2580 1940 40 Ancient Woodland F Bridgeway Centre 337517 349407 1780 1690 1300 Ancient Woodland G Redwither Wood and 337040 350690 2010 1865 2515 Clays Plantation
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ID Receptor Easting Northing Distance Distance to Distance to to Scheme Power Gas Stacks^ Station Connection Complex Route* Site* Ancient Woodland H Berwyn and South 327200 349870 11830 11780 11245 Clwyd Mountains SAC I Johnstown Newt SAC 331260 346990 8460 8290 6990 Note: Distances in bold type indicate receptors relevant to the dust assessment ^ Distance provided is from the midpoint of the Scheme Stacks to the maximum modelled ground level concentration, which may not always be the shortest distance to the ecological site. *The distance to the Order Limits is the shortest distance to the ecological site boundary.
8.178 Within the Power Station Complex Site, there are two great crested newt breeding ponds. These are considered separately in the Ecology chapter as the sites are not designated.
8.179 There is only one statutory designated site within 200 m of main roads within a 5 km radius of the Scheme. The statutory site of relevance is the River Dee SAC, SPA and SSSI, which lies adjacent to the A534, approximately 3km to the north east of the Power Station Complex Site and adjacent to the A525, approximately 3 km to the south of the Gas Connection Route. Non-statutory sites are within 200 m of potentially affected roads but are not considered in the assessment of vehicle emissions, in accordance with DMRB guidance.
Meteorological data
8.180 The meteorological data from Hawarden Airport for the five-year period 2007 to 2011 used in the modelling study are presented as frequency distribution of wind speed and direction in Table 8.16 and as a wind rose diagram in Insert 8.1 below, which presents an excerpt from Figure 8.3.
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Insert 8.1: Wind Rose Diagram for Hawarden Airport, 2007 to 2011
8.181 There is a primary prevailing wind from the south-south-east and a secondary prevailing wind from the north west. Winds occur more often than the average sector frequency of 6.1% (including calms) for the three sectors from south east through to south, and the five sectors from the south west to north west. The three sectors in the south east account for almost 30% of all winds, compared to 18% for the evenly distributed case. Winds from the north to east-south-east are particularly uncommon; the five sectors from north through to east only generate 7% of all winds, just over the evenly distributed case for a single sector. Winds from the west-south-west and adjoining sectors account for the majority of high wind speeds (> 8.23 m/s).
Table 8.16: Relative Frequency Distribution of Wind Speed and Direction, (%) Direction Degree Wind speed (m/s) < 1.54 1.54 - 3.09 - 5.14 - 8.23 - > 10.8 Total 3.09 5.14 8.23 10.8 N 0.0 0.57 0.47 0.73 0.09 0.01 0.00 1.88 NNE 22.5 0.34 0.27 0.54 0.11 0.00 0.00 1.27 NE 45.0 0.32 0.39 0.59 0.21 0.02 0.00 1.54 ENE 67.5 0.26 0.27 0.57 0.23 0.01 0.00 1.34 E 90.0 0.21 0.23 0.57 0.21 0.01 0.00 1.23
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Direction Degree Wind speed (m/s) < 1.54 1.54 - 3.09 - 5.14 - 8.23 - > 10.8 Total 3.09 5.14 8.23 10.8 ESE 112.5 0.42 0.58 0.94 0.32 0.03 0.00 2.28 SE 135.0 0.93 1.42 3.08 1.07 0.09 0.00 6.58 SSE 157.5 1.61 2.80 6.31 2.19 0.18 0.01 13.09 S 180.0 1.57 1.75 3.64 1.38 0.11 0.01 8.46 SSW 202.5 0.92 0.80 1.81 0.96 0.14 0.02 4.66 SW 225.0 0.74 0.83 2.82 2.00 0.48 0.21 7.08 WSW 247.5 0.60 0.95 3.57 2.13 0.70 0.27 8.22 W 270.0 0.61 0.87 3.37 1.99 0.42 0.12 7.37 WNW 292.5 0.85 1.23 3.33 1.88 0.34 0.04 7.66 NW 315.0 1.39 2.25 4.61 2.01 0.16 0.01 10.43 NNW 337.5 1.04 1.43 2.72 0.70 0.06 0.00 5.95 Total 12.38 16.53 39.19 17.47 2.74 0.69 89.02 Calms 10.66 Missing 0.32 Total 100.00
POWER STATION COMPLEX SITE ASSESSMENT
Potential effects
Pollutants
8.182 The sources and effects of the air pollutants that are the subject of this air quality assessment are outlined below.
Oxides of nitrogen
8.183 The majority of oxides of nitrogen emitted from vehicles and combustion processes are in the form of nitric oxide (NO), which oxidises rapidly in the presence of ozone to form nitrogen dioxide (NO2). Nitric oxide does not have any observable effect on human health at the range of concentrations found in ambient air. In high concentrations NO2 can cause inflammation of the airways; it also enhances the response to allergens in sensitive individuals.
8.184 Elevated concentrations of oxides of nitrogen can have an adverse effect on vegetation, including leaf or needle damage and reduced growth. Deposition of pollutants derived from oxides of nitrogen emissions contribute to acidification and/or eutrophication of sensitive habitats.
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Particulate matter
8.185 Particulate matter in vehicle exhaust gases and from combustion processes includes carbon nuclei onto which a wide range of compounds are adsorbed. Particulate matter with a mean aerodynamic diameter of less than 10 µm is referred to as PM10. Particulate matter appears to be associated with a range of symptoms of ill health including effects on the respiratory and cardiovascular systems, on asthma and on mortality. Reviews by WHO and Committee on the Medical Effects of Air Pollutants (COMEAP) have suggested exposure to a finer fraction of particles (PM2.5) (which typically make up around two thirds of PM10 emissions and concentrations) give a stronger association with the observed ill health effects.
Carbon monoxide
8.186 Carbon monoxide (CO) is a partial combustion product found in vehicle exhaust and combustion gases. Exposure to very high concentrations of CO may temporarily restrict the oxygen carrying capacity of the blood; the CO thus adsorbed in the bloodstream is exhaled and reduces to normal levels within a few hours in a normal clean atmosphere. The ambient air quality objective for CO is set at a level well below that at which there may be any adverse physiological effects. Following the widespread introduction of catalytic converters on vehicles, there are no areas within the UK that are at risk of breaching the AQS objective for CO. Even at busy roadside locations CO concentrations are well below the AQS objective. The excess air supplied to combustion processes is optimised to ensure good fuel combustion and hence CO emissions are minimised. There are no effects on human health due to the concentrations found in ambient air.
Dust
8.187 Dust is the generic term for solid particles that can be suspended in the atmosphere. Demolition and construction activities have potential to create airborne dust. Dust emissions from a site may be mechanically generated (e.g. due to earth movements or block cutting) or blown by the wind from exposed surfaces, and have the potential to cause higher than normal levels of dust deposition in the surrounding area. Over a period of time, in the absence of effective control measures, cumulative dust deposition may become noticeable and cause concern.
8.188 Dust that may deposit in the local area close to a source of fugitive dust comprises particles between 10 and 75 µm in diameter, the larger size particles settling to the ground within a few tens of metres from the source. Small particles settle more slowly over a larger area and therefore contribute relatively little to the general ambient dust levels. Such particles are also more susceptible to being blown away. Excessive accumulations of dust on exposed surfaces, particularly in residential locations, may cause a perceived loss of amenity and give rise to public complaint.
8.189 Construction and demolition activities have the potential to generate dust through materials handling and vehicular movements within the site. Dry ground may also
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be subject to wind erosion. Dust emissions from construction sites potentially arise from a range of diffuse sources and are termed 'fugitive emissions'. Fugitive dust emissions can lead to a localised increase in dust deposition rates that may potentially cause soiling of cars, windows and other surfaces.
Construction
Construction dust emissions
8.190 The Power Station Complex Site construction activities which may give rise to dust emissions include: demolition of existing structures and hardstanding; earthworks; handling and disposal of spoil; wind-blow from stockpiles of particulate material; handling of loose construction materials; and construction vehicles travelling on un- surfaced haul routes. Once generated, the emissions may be transported beyond the construction site boundary if not properly controlled or mitigated at source. Larger particles may be carried to, and then deposited at, nearby properties depending on the particle size and distance between the source and the receptor. If the particles are deposited in a significant quantity or over a continued period of time, loss of amenity may result.
8.191 The Scheme will be constructed over a period of 36 months, with different stages of the works overlapping within the 36-month period. Construction will begin with enabling works, including site set-up and ground/earth works, which will take in the region of up to 8 - 10 months. The activities during this phase include removal of any existing structures and removal of existing areas of hardstanding and site levelling. This may incorporate the crushing of material using and on-site crusher (see chapter 4 for further detail).
8.192 Construction of the Power Station Complex will be undertaken over a period of approximately 2 years (months 8 to 28), with commissioning taking a further 11 months (months 25 to 36). The construction phase will include excavation work for foundations, filling and piling. It is possible that there will be a concrete batching plant on site. In addition, there will be movement of vehicles over made and unmade surfaces within the Power Station Complex Site, and activities associated with the movement of earth and fill material within the Power Station Complex Site boundary. The subsequent stages are likely to involve a much lower level of potentially dusty activities.
8.193 An assessment in line with IAQM guidance of the potential effects of dust raising activities has been carried out, in the context of receptor sensitivity and distance from source, and prevailing meteorological conditions. The assessment of dust emission magnitude for the Power Station Complex (IAQM Step 2A) is presented in Table 8.17; the magnitude was estimated based on the information in chapter 4, as summarised above. This comprises the first step in the IAQM dust assessment method, and informs the rest of the assessment.
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Table 8.17: Scheme - dust emission magnitude Activity Factors determining dust emission magnitude Dust emission magnitude Demolition Potentially dusty demolition material (any existing Large structures and areas of hardstanding), possible on-site crushing and screening Earthworks Total site area >10,000 m2, >10 heavy earth Large moving vehicles active at any one time Construction Total building volume >100,000 m3, potential for Large an on-site concrete batching plant Track out >50 HDV outward movements in any one day Large
8.194 Having determined, on a precautionary basis, the dust emission magnitude to be large for each activity, the sensitivity of the area was defined (IAQM Step 2B). This process was undertaken with reference to the examples presented in the IAQM Guidance (Boxes 6 to 9) and through the application of professional judgement by a suitably qualified assessor. While the IAQM tables appear prescriptive, the guidance notes that additional factors may also be relevant, such as the presence of pre-existing screening, meteorological conditions, local topography and duration of impact.
8.195 The results of Step 2B are set out in Table 8.18 to Table 8.20 for dust soiling, human health and ecological effects. Only those receptors relevant to the assessment of dust effects i.e. within 350 m of the Power Station Complex Site (50 m for ecological receptors) or 50 m of roads affected by trackout (up to 500 m from the site access on Bryn Lane), are presented in these tables. Figure 8.1 shows the distance screening bands for dust assessment for the Scheme including the Power Station Complex Site.
8.196 Note that the assessment took account of all potentially sensitive locations within 350 m of the Power Station Complex Site. These are taken account of in the total number of receptors in the third column of the following tables, with each entry assigned to a specific receptor location (identified in Table 8.14 and Table 8.15 and shown in Figure 8.1).
8.197 The overall sensitivity of the study area (i.e. 350 metres from the site boundary or 50m from trackout) is shown in the final column of each table. When determining the overall sensitivity of an area, IAQM advises that only the highest level of sensitivity from the table needs to be considered, for the total number of receptors within the stated distance.
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Table 8.18: Scheme - Sensitivity of the area to dust soiling effects on people and property results Receptor Receptor Number of Distance from Sensitivity of sensitivity receptors source area 2) Plum Tree Farm, High 14 255m from Power B5130 + other nearby Station Complex properties Site, 3) Marshley Farm, >50m of trackout B5130 + other nearby properties LOW 4) 4-6 Bryn Lane High 3 245m from Power (10-100 high Station Complex sensitivity Site, receptors <350m <50m of trackout of Power Station 7) Kellogg’s factory High 1 80m from Power Complex Site and (car park) * Station Complex <10 receptors for Site, trackout) <50m of trackout 21) Public right of way Low 1 15m from Power ISY /18 Station Complex Site, >50m trackout Note: The Kellogg’s food product manufacturing plant is considered of high sensitivity due to the potential for indirect soiling effects on the property (including the staff car park). The operator will already have in place their own control measures to prevent ambient fugitive dust ingress to their premises from naturally occurring particulates in ambient air. Workers will be covered by occupational exposure regulations hence it is not considered a relevant receptor for human health impacts
Table 8.19: Scheme - Sensitivity of the area to human health impacts Receptor Receptor Number of Distance from Sensitivity of sensitivity receptors source area 2) Plum Tree Farm, High 14 255m from Power LOW B5130 + other nearby Station Complex (10-100 high properties Site, sensitivity 3) Marshley Farm, >50m of trackout receptors <350m B5130 + other nearby of boundary and properties <10 receptors for 4) 4-6 Bryn Lane High 3 245m from Power trackout) Station Complex Site, <50m of trackout 21) Public right of way Low >1 15m from Power ISY /18 Station Complex Site,
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Receptor Receptor Number of Distance from Sensitivity of sensitivity receptors source area >50m of trackout Note: Background concentrations DEFRA mapped values 14.1 to 15.9 µg/m3. Urban industrial concentrations of PM10 measured by CMS at Isycoed are also less than 24 µg/m³ (see Baseline section)
Table 8.20: Scheme - sensitivity of the area to ecological impacts Receptor Receptor Distance from source Sensitivity of sensitivity area A1) Wrexham Low <20m from Power Station LOW Industrial Estate LWS Complex Site (1 low sensitivity – Bryn Lane <20m of trackout receptor)
8.198 The closest sensitive residential properties (considered highly sensitive receptors in accordance with IAQM guidance) to the Power Station Complex Site are located 245 m to the north west at 4-6 Bryn Lane (receptor 4), and are within 50 metres of the track out route. These properties are in line with the prevailing south easterly winds. Certain properties on the B5130 (represented by receptors 2 and 3) are similar distances away and are aligned with the secondary north westerly prevailing wind.
8.199 There are no residential receptors within 100 m of the Power Station Complex Site itself, 100m being the distance within which dust particles are most likely to be deposited in the absence of effective mitigation (Figure 8.1). There is, however, the Kelloggs manufacturing facility which is considered to be highly sensitive in terms of soiling (due to the presence of a car park) and which is less than 100 m to the west. There is one footpath assessed to be of low sensitivity within 20 m, which is aligned with the secondary north westerly prevailing wind.
8.200 The only relevant ecological receptor is the Bryn Lane unit of the non-statutory Wrexham Industrial Estate LWS (receptor A1 immediately to the south west of the Scheme). Winds from the north to east could potentially carry material towards this site, although winds from this quadrant are extremely infrequent. The LWS is considered to be of low sensitivity, in line with IAQM guidance.
8.201 Taking account of the total number of receptors, their sensitivity and their distance from Power Station Complex Site, the study area is assessed to be of overall “low” sensitivity for dust soiling, human health and ecological impacts, for all activities. The IAQM methodology suggests that the highest level of sensitivity from each potential impact type (dust soiling, human health, ecological) is carried forward when determining the risk of dust impacts (Step 2C). In this assessment, the sensitivity of the area affected by construction works is deemed in accordance with IAQM guidance (Table 2 and Table 3) to be “low” in each case, owing to the limited
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number of high sensitivity receptors in close proximity to the work areas and the low PM10 background concentration.
8.202 The risk of dust impacts (with no mitigation measures applied beyond those required by legislation) is defined by combining the dust emission magnitude for each of the four activity types, with the sensitivity of the surrounding area, in accordance with the matrices presented in Tables 6 to 9 of the IAQM Guidance (reproduced in Appendix 8.1). The assessment itself and the summary table of findings are presented in Table 8.21 and Table 8.22 respectively.
Table 8.21: Scheme - Determination of dust risk for impact type Potential impact Dust magnitude Sensitivity of area Dust risk Dust soiling Demolition Large Low Medium Earthworks Large Low Low Construction Large Low Low Track out Large Low Low Human Health Demolition Large Low Medium Earthworks Large Low Low Construction Large Low Low Track out Large Low Low Ecology Demolition Large Low Medium Earthworks Large Low Low Construction Large Low Low Track out Large Low Low
Table 8.22: Scheme - Summary Dust Risk Table to Define Site Specific Mitigation Potential impact Risk Demolition Earthworks Construction Trackout Dust Soiling Medium Low Low Low Human Health Medium Low Low Low Ecological Medium Low Low Low
8.203 Overall, construction of the Power Station Complex presents a “medium” risk of dust impact during the demolition phase and a “low” risk of impact during the subsequent phases of earthworks, construction and associated trackout. Recommended measures for the control of dust emissions at low and medium risk sites are provided in the section on mitigation which are included in a draft CEMP.
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The full listing from the IAQM guidance from which these measures have been taken is presented in Appendix 8.1.
8.204 In view of the fact that: appropriate mitigation for the defined level of risk is set out in the draft CEMP and will be adopted in the construction of the Scheme; such measures will be applied and managed effectively; and the construction dust emissions themselves will be temporary and intermittent in nature, it is considered that the effect of construction dust emissions on local air quality will not be significant.
Construction traffic emissions
8.205 The delivery of construction materials, removal of excavated material and worker access to the Power Station Complex Site will take place via the local road network. This assessment considers whether the associated increases in traffic flow associated with construction of the Power Station Complex could affect local air quality.
8.206 The transport assessment undertaken for the Scheme including the Power Station Complex is described in detail in chapter 7. Construction traffic will access the Power Station Complex Site via the A534 Wrexham Road, and A5156 Link Road (“Industrial Estate Road”) and onto Bryn Lane north of the Site access. Construction traffic will not use Bryn Lane to the south of the Power Station Complex Site access.
8.207 It has been estimated in chapter 7 that the peak volume of HGV construction traffic would comprise 55 HGVs accessing the Power Station Complex Site per day (i.e. 55 arrivals, 55 departures). This produces an increase in the two-way AADT flow on Bryn Lane and the A5156 Link Road of 110 HGV movements. In addition to the HGV movements, a peak of 600 workers would be required on site daily, resulting in a two-way increase on Bryn Lane of approximately 600 LDVs. In making this estimate, it was assumed that, as a minimum, two workers would share one vehicle. There would be no material change in average speeds or road alignment as a result of the works for the Power Station Complex Site.
8.208 Despite the additional increase in vehicle movements on the local road network during construction of the Power Station Complex, neither the increase in HGVs nor the total increase as a two way AADT flow exceeds the DMRB criteria on any road, in line with the fact that the Power Station Complex Site is located on the Wrexham Industrial Estate. On this basis, the air quality impact can be deemed to be “neutral” (in line with DMRB paragraph 3.14) i.e. insignificant for all receptor types, both human health and ecological.
8.209 The indicative EPUK/IAQM criteria for a change in LDVs and HDVs are both marginally exceeded. Given the low mapped background concentrations in the area (Table 8.12) which are equal to less than half the AQALs for NO2 and PM10 and with roadside concentrations (Table 8.9) equal to less than 75% of the AQALs, further quantitative assessment is not deemed necessary and the air quality impact can be
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considered insignificant. (A quantitative assessment of the cumulative effect of traffic emissions has been undertaken, see paragraph 8.312 to 8.352).
8.210 A theoretical estimate has been made of traffic flows in the absence of an on-site concrete batching facility. Over a period of three days, up to 300 HGVs would require access to the site per day (i.e. 300 arrivals and 300 departures or 600 HGVs as a two-way flow). This very temporary situation would not contribute to a material change in average pollutant concentrations over the course of a year70.
8.211 Delivery of abnormal loads may require the temporary closure of small sections of road. These abnormal deliveries would be few in number and would likely take place overnight, hence they would not contribute to a material change in local pollutant concentrations which are already well below AQS objectives.
Construction plant emissions
8.212 At this stage in the Power Station Complex design, a detailed inventory of the equipment that will be used within the Power Station Complex during the construction phase is not available. It is expected that there will be emissions from diesel or petrol powered generators and Non-Road Mobile Machinery (NRMM), for example bulldozers, crushers, mobile cranes, and other construction machinery. The majority of emission sources will be located within the Power Station Complex Site itself and/or nearby laydown areas.
8.213 The low level nature of the sources means that whilst there may be a temporary increase in ground level concentrations of NO₂ and PM10 close to the release point, such an increase is unlikely to be material beyond the limits of the Order Land. The closest residential properties are over 200 m from the Order Land, and further still from the Power Station Complex Site.
8.214 In view of the fact that the construction plant emissions will be temporary and intermittent in nature, and in light of existing background concentrations which are well below the AQS objectives, it is concluded that the effect of construction plant emissions on local air quality will not be significant.
8.215 Plant such as crushers are regulated by WCBC under the EPR regulations, as discussed in the subsequent section of this chapter concerning Mitigation Measures.
70 The equivalent change in AADT over the course due to this temporary increase for 3 days of a year is 5
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Operation
Stack emissions
8.216 A quantitative assessment of the potential effects of the operation of the Power Station Complex on local air quality, in terms of stack emissions to atmosphere, has been carried out. The assessment was undertaken by means of a dispersion modelling study, and considers the effects on human health and ecological receptors within the study areas defined previously. The pollutant emissions considered are those regulated by the IED for new gas turbines, i.e. NOx and CO. The approach to modelling has been agreed with the WCBC EHO and NRW/AQMRAT (see Appendix 8.3).
8.217 The model was set up to report the maximum hourly, 8-hourly, 24-hourly and annual average pollutant concentrations found at each point on the receptor grid. As a five-year meteorological data file was used the maximum hourly result is the highest in over 43,800 hours processed and the maximum annual result is the highest of the five years individually modelled. The model results presented thus robustly characterise the potential “worst case” effects of the Stack emissions on ambient concentrations due to both extreme short-term meteorological events and to long-term average meteorological conditions.
8.218 It is also assumed that the Power Station Complex will be maintained in accordance with the manufacturer's specification. Occasional, short term periods of shut down for the purposes of routine and annual maintenance activities (as outlined in chapter 4) will result in periods of a few days to a few weeks when the CCGT facility does not operate. This will not materially affect the findings presented herein. The results of the operational assessment presented below are based on continuous running of the gas turbines at 100% load throughout the year which gives a conservative answer for long-term averages. The potential excursions from IED emission limits that are allowed during temporary shut-down and start-up are accommodated for in a hypothetical scenario, which examines the hourly results using an emission rate of 200% of the IED emission limit for oxides of nitrogen.
Human health assessment
8.219 The following sections present a short description of the pattern of dispersion, and a discussion of the results at the closest sensitive receptors, which are tabulated for the highest results at sensitive receptors. The results for each pollutant and averaging period are also presented graphically in the form of contour plots overlaid on an Ordnance Survey base map.
8.220 The results of the dispersion modelling study for the human health assessment are tabulated in Table 8.23, Table 8.24 and Table 8.25. Each table presents the maximum ground level concentration modelled for each pollutant (the process contribution or PC), at each discrete receptor included in the model. Each table also
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shows the assessment criterion (EU limit value, AQS objective or EAL; all referred to as EAL for simplicity), the percentage that the PC is of the criterion, the background concentration, the total predicted environmental concentration (PEC), and the percentage that the PEC is of the assessment criterion. The results are interpreted in the context of the relevant air quality criteria (EU limit and target values, AQS objectives and EALs) and existing background concentrations.
8.221 The annual average concentration of NO2 measured at the Isycoed CMS in 2014 is used in the assessment as the background component to calculate the PEC, as requested by the EHO. For CO, the annual average concentrations from DEFRA background maps are used.
Nitrogen dioxide
8.222 The maximum modelled annual average ground level concentrations of NO2 resulting from the continuous 100% rated operation of the Power Station Complex gas turbines are shown graphically in Figure 8.4. The contour plot demonstrates the dispersion pattern of ground level concentrations beyond the Order Land. Each value plotted is the highest of the five individual annual average concentrations modelled at each receptor point. The effects of the Stack emissions are relatively 3 localised, the highest concentrations in the order of 1.4 µg/m as NO2, occurring approximately 500 m to the north east and south east of the Stacks, over farmland west of the B5130. There is a secondary maximum of around 1.2 µg/m3 at a distance of 400 m to the north west of the Stacks in the vicinity of receptor 4. These areas of high concentration reflect the long-term frequencies of winds depicted in the wind rose in Insert 8.1 (excerpt of Figure 8.3).
8.223 The results at representative sensitive receptors are shown in Table 8.23. The highest modelled ground level concentration is found at receptor 3 at Marshley, representative of a small group of properties on the B5130 approximately 760 m to the north east of the Stacks. The maximum modelled increment to annual mean oxides of nitrogen at this location is 1.9 µg/m3. A conservative “worse case” [sic] estimate assumes 70% of the oxides of nitrogen are converted to NO2, the modelled 3 increment of NO2 at this residential receptor is calculated to be 1.3 µg/m . A similar concentration is modelled at receptor 2, representing properties including Plum Tree Farm on the B5130 a little over 800 m from the Stacks. At receptor 1, on Ridley Wood Road further to the north east, the NO2 increment decreases to below 1.0 µg/m3.
3 8.224 Adding a measured background concentration of NO2 of 12.3 µg/m to the maximum modelled annual mean concentration at receptor 3 gives a PEC of 13.6 µg/m3, or one third of the EU limit value and AQS objective for annual mean NO2.
8.225 Within the secondary area of maximum concentrations where concentrations are in 3 the order of 1 µg/m as NO2, there are two residential properties, including receptor
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4. The annual mean increase in NO2 is equivalent to 2.5% of the AQS objective; the PEC at this location is 13.3 µg/m3 or one third of the annual mean criterion.
8.226 The effect of the Stack emissions on long-term average NO2 concentrations at human health receptors is assessed as negligible, in line with EPUK/IAQM impact descriptors (Table 8.8), as the maximum modelled increments are less than 5% of the AQS objective and the total concentrations in the assessment year are less than 75% of the AQS objective.
8.227 The maximum modelled hourly average NO2 concentrations are shown in Figure 8.5. The value depicted at each receptor grid location is the highest hourly average found in the five years of meteorological data used71. The results at individual sensitive receptors are shown in Table 8.24. Applying the “worse case” [sic] 35% conversion to NO2, the increments are equivalent to less than 10% of the AQS objective at all sensitive receptors.
8.228 The maximum modelled hourly average increment to ground level oxides of nitrogen concentration is 43.3 µg/m3. This result, the highest in five years of meteorological data, is found at receptor 4, at the junction of Bryn Lane with Ridley Wood Road. The equivalent hourly average ground level NO2 concentration is calculated to be 15.2 µg/m3 or less than 10% of the EU limit value and AQS standard 3 for hourly NO2 of 200 µg/m . According to Environment Agency and EPUK/IAQM guidance, this can be considered insignificant.
8.229 Modelled process contributions at the location of the PRoW to the east (receptor 21), and all other locations where short-term exposure may occur, are also less than 10% of the air quality standard.
8.230 At the request of NRW AQMRAT, a hypothetical assessment has been made allowing for an emission rate for short-term, hourly oxides of nitrogen emissions of 100 mg/m3. This is considered to be a very conservative, hypothetical estimate at twice the IED limit and the manufacturer’s performance guarantee. However, as this is the basis upon which compliance with the IED may be measured, this upper bound has been used to factor the short-term concentrations such as may temporarily arise for very short periods (a few hours at most) during start-up and shut-down for maintenance.
3 8.231 On this basis, at receptor 4, the NO2 process contribution would be 30.3 µg/m . Adding twice the annual average background concentration gives a PEC of 54.9 µg/m3. This PEC is just over one quarter of the short-term AQS standard of
71 Reporting the maximum hourly concentrations at each receptor is recognised by AQMRAT at NRW to be a conservative approach, as it will give a higher result than the 99.79th percentile (18th highest value, so used because the air quality objectives allows 18 measured exceedances per year). As the statistical basis for the modelled 99.79th percentile result would be entirely different to that which would be measured at a static continuous analyser, it is appropriate that the maximum value is reported herein.
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200 µg/m3. The EU limit value and AQS objective allows for 18 exceedances each year of this standard
8.232 The short-term effect on human health from the Scheme stack emissions is assessed as negligible, as it will not lead to any exceedances of the hourly AQS objective at any relevant receptor location. This assessment is extremely robust as it assumes that oxides of nitrogen are emitted at twice the limit value set in the IED, and that the occasional maintenance periods are combined with the worst hours of meteorological data in a five-year data set; furthermore, a conservative background value has been used to calculate total concentrations in a rural area.
Table 8.23: Maximum annual average nitrogen dioxide concentrations at human health receptors
ID PC NOx, PC NO2, PC /EAL, PEC NO2, PEC /EAL, µg/m3 µg/m3 % µg/m3 % 1 1.1 0.8 1.9 13.1 32.7 2 1.7 1.2 2.9 13.5 33.7 3 1.9 1.3 3.2 13.6 34.0 4 1.5 1.0 2.6 13.3 33.3 5 0.9 0.6 1.6 12.9 32.4 6 0.3 0.2 0.5 12.5 31.2 7 0.2 0.1 0.3 12.4 31.0 8 0.4 0.3 0.8 12.6 31.5 9 1.0 0.7 1.7 13.0 32.5 10 1.5 1.0 2.6 13.3 33.3 11 0.3 0.2 0.6 12.5 31.3 12 0.1 0.1 0.2 12.4 30.9 13 0.8 0.6 1.5 12.9 32.2 14 1.3 0.9 2.3 13.2 33.1 15 0.1 0.1 0.2 12.4 30.9 16 0.3 0.2 0.5 12.5 31.2 17 0.5 0.3 0.8 12.6 31.6 18 0.1 <0.1 0.1 12.3 30.9 19 0.3 0.2 0.4 12.5 31.2 20 0.3 0.2 0.5 12.5 31.2
Table 8.24: Maximum hourly average nitrogen dioxide concentrations at human health receptors
ID PC NOx, PC NO2, PC /EAL, PEC NO2, PEC /EAL, µg/m3 µg/m3 % µg/m3 % 1 23.0 8.0 4.0 32.6 16.3 2 27.5 9.6 4.8 34.2 17.1 3 27.3 9.6 4.8 34.2 17.1 4 43.3 15.2 7.6 39.8 19.9 5 31.4 11.0 5.5 35.6 17.8
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ID PC NOx, PC NO2, PC /EAL, PEC NO2, PEC /EAL, µg/m3 µg/m3 % µg/m3 % 6 17.2 6.0 3.0 30.6 15.3 7 21.1 7.4 3.7 32.0 16.0 8 16.3 5.7 2.9 30.3 15.2 9 22.1 7.7 3.9 32.3 16.2 10 22.0 7.7 3.8 32.3 16.1 11 12.8 4.5 2.2 29.1 14.5 12 8.6 3.0 1.5 27.6 13.8 13 20.0 7.0 3.5 31.6 15.8 14 23.6 8.2 4.1 32.8 16.4 15 11.2 3.9 2.0 28.5 14.3 16 12.6 4.4 2.2 29.0 14.5 17 13.5 4.7 2.4 29.3 14.7 18 9.7 3.4 1.7 28.0 14.0 19 16.0 5.6 2.8 30.2 15.1 20 16.0 5.6 2.8 30.2 15.1 21* 33.1 11.6 5.8 36.2 18.1
* PRoW, non-residential receptor only relevant to hourly exposure
Carbon monoxide
8.233 The maximum eight hourly average ground level concentrations of CO are depicted in Figure 8.6. The results at individual sensitive receptors are shown in Table 8.25.
8.234 The maximum eight-hourly average concentration at a sensitive receptor is 45.4 µg/m3 at receptor 2, representing properties including Plum Tree Farm on the B5130 to the east of the Scheme Stacks. The results at all relevant locations are negligible as they are less than 1% of the EU limit value and AQS objective of 10,000 µg/m3; hence any effects of the Scheme stack emissions on human health are considered to be negligible.
Table 8.25: Maximum short-term carbon monoxide concentrations at human health receptors ID Eight hourly mean PC CO, PC /EAL, µg/m3 % 1 30.4 0.3 2 45.4 0.5 3 43.5 0.4 4 45.1 0.5 5 37.5 0.4 6 23.2 0.2
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ID Eight hourly mean PC CO, PC /EAL, µg/m3 % 7 13.0 0.1 8 13.8 0.1 9 28.3 0.3 10 36.0 0.4 11 15.4 0.2 12 7.2 0.1 13 17.7 0.2 14 32.0 0.3 15 7.7 0.1 16 10.4 0.1 17 14.2 0.1 18 4.9 <0.1 19 7.1 0.1 20 7.0 0.1 21* 59.9 0.6
* PRoW, non-residential receptor only relevant to hourly exposure
Oxides of nitrogen
8.235 The modelled annual average oxides of nitrogen concentrations are shown graphically in Figure 8.7 while the results at specific receptors are provided in Table 8.26. The table shows the annual average ground level concentration of oxides of nitrogen (PC) at the relevant sensitive ecological receptors, and the proportion that the Stack emissions contribute to the EU target value as a critical level (CL) of 30 µg/m3. For the statutory sites, the background concentrations, total concentrations (PEC), and proportion that PEC is of the critical level, are also presented. The background concentrations used are the DEFRA mapped values, shown previously in Table 8.13.
Table 8.26: Annual average oxides of nitrogen concentrations at ecological sites
ID Site name PC NOx, PC/CL, PEC NOx, PEC/CL, µg/m3 % µg/m3 % A1 Wrexham Ind. Estate LWS 0.37 1.2 20.0 66.7 A2 Wrexham Ind. Estate LWS 0.25 0.8 19.9 66.3 A3 Wrexham Ind. Estate LWS 0.16 0.5 19.7 65.7 B1 Midland Meres & Mosses Ramsar 0.22 0.7 12.9 43.0 B2 Midland Meres & Mosses Ramsar 0.08 0.3 9.6 31.9 C1 River Dee & Bala Lake SAC – East 0.48 1.6 11.3 37.6 C2 River Dee & Bala Lake SAC - South 0.19 0.6 10.2 34.0
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D Peters Dingle LWS 0.13 0.4 11.6 38.6 E Parkey Farm and Parkey Lodge 0.07 0.2 11.0 36.8 ancient woodland F Bridgeway Centre ancient 0.13 0.4 19.7 65.6 woodland G Redwither ancient woodland 0.10 0.3 26.4 88.2 H Berwyn and South Clwyd Mountains 0.01 <0.1 9.0 30.0 SAC I Johnstown Newt SAC 0.04 0.1% 14.8 49.2
8.236 The maximum contribution from the Stack emissions to annual average concentrations of oxides of nitrogen is found at receptor C1, which represents the banks of the River Dee and Bala Lake SAC to the east. All of the designated features of the SAC are aquatic hence as agreed with NRW, critical levels are not applicable to these features. The JNCC website72 notes the SAC general site character as comprising 2% woodland and 2% grassland. NRW has confirmed that the woodland and grassland features to be important for when assessing impacts on the wider countryside but are not designated features and so a consideration of the modelled results is made in this regard.
8.237 The modelled increment at C1 is just under 0.5µg/m3, or less than 2% of the vegetation critical level for oxides of nitrogen of 30 µg/m3. At this location, the PEC including background is equal to 11.3 µg/m3, just one third of the critical level. The effect of the Power Station Complex on these non-designated features can be considered not to be significant. Modelled increments at the River Dee further to the south near Bangor (C2), are less than 0.3 µg/m3 and can be considered insignificant.
8.238 At no other international or European designated site within 15 km of the Power Station Complex does the PC exceed the 1% screening criterion. At Midland Meres & Mosses Ramsar Phase 2 (B1 and B2), modelled increments to ground level concentrations of oxides of nitrogen are 0.2 µg/m3 or less. At Berwyn and South Clwyd Mountains SAC (H), and Johnstown Newt SAC (I), the modelled contributions are equivalent to 0.1% or less of the critical level of 30 µg/m3. Such contributions are considered to be negligible.
8.239 The maximum modelled annual mean increment due to Stack emissions from the Power Station Complex at a non-statutory site occurs at Wrexham Industrial Estate LWS (receptor A1), the unit closest to the Power Station Complex on Bryn Lane. The 3 PC is 0.37 µg/m or a fraction over 1% of the NOx critical level. The PEC is calculated to be 20 µg/m3 or exactly two thirds of the critical level. The impact at this site (A1) and other non-statutory LWS and ancient woodland can be considered to be insignificant.
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8.240 The maximum modelled increment to daily mean oxides of nitrogen at any site occurs to the south of the Power Station Complex over part of the Wrexham Industrial Estate LWS (receptor A2). The increment here is 5.1 µg/m3, or less than 10% of the short-term, non-statutory critical level set in Environment Agency Air Emissions Risk Assessment guidance of 75 µg/m3. As such, the contribution from the Stack emissions at all sites can be considered insignificant.
Deposition rates
8.241 Given that the process contributions of oxides of nitrogen from the Stacks of the Power Station Complex are insignificant (i.e. less than 1% of the critical level) at all statutory designated sites with relevant features, and do not exceed the critical level at the non-statutory LWS, further assessment in terms of nutrient and acid deposition is not strictly necessary. This is because of the linear relationship between oxides of nitrogen and nitrogen deposition. An increment of 0.3 µg/m3 as oxides of nitrogen is equivalent to a deposition rate of less than 0.05 kg N/ha/yr, which itself is equal to 1% or less of the lowest critical load for the habitat types relevant to this assessment (5 kg N/ha/yr). It follows that an increment of up to 30 µg/m3 at a non-statutory site will give an increment in terms of nitrogen deposition of less than 100% of the lowest critical load, thus demonstrating BAT.
8.242 Nonetheless, for the purposes of this EIA, an estimation of nitrogen and acid deposition at all designated sites has been carried out to inform the ecological impact assessment. In undertaking this calculation, all NOx was conservatively assumed to be NO2. The AQTAG deposition velocity for grassland or forest was used as appropriate for the habitat type. The results of the calculation are presented in Table 8.27, which also shows the contribution of the Scheme as a percentage of the recommended critical loads for nitrogen and acid deposition73.
Table 8.27: Nitrogen and acid deposition at ecological sites ID PC Ndep, CL Ndep PC/CL PC N acid, CL Nacid^, PC/CL kg/ha/yr kg/ha/yr % keq/ha/yr keq/ha/yr % A1 0.05 10 0.5 0.004 4.74 0.1 A2 0.07 10 0.7 0.005 1.77 0.3 A3 0.05 10 0.5 0.003 1.77 0.2 B1 0.03 5 0.6 0.002 0.683 0.3 B2 0.02 10 0.2 0.002 1.08 0.1 C1 0.14 10 1.4 0.010 3.07 0.3 C2 0.03 3 0.9 0.002 n/a n/a D 0.04 10 0.4 0.003 1.76 0.2 E 0.02 10 0.2 0.001 1.76 0.1
73 Recommended values within nutrient nitrogen critical load ranges for use in air pollution impact assessments. http://www.apis.ac.uk/sites/default/files/downloads/APIS%20critical_load_range_document_0.pdf
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ID PC Ndep, CL Ndep PC/CL PC N acid, CL Nacid^, PC/CL kg/ha/yr kg/ha/yr % keq/ha/yr keq/ha/yr % F 0.04 10 0.4 0.003 1.76 0.2 G 0.03 10 0.3 0.002 1.76 0.1 H <0.01 5 <0.1 <0.001 0.66 <0.1 I 0.01 5 0.1 <0.001 n/a n/a
* n/a = No comparable habitat with established critical load estimate available ^ for statutory sites, APIS MinCL MaxN, for non-statutory sites, CL MaxN.
8.243 The contribution of the Scheme Stack emissions to the critical load for nitrogen deposition is insignificant at around 1% or less at all locations74.
8.244 The highest incremental nitrogen deposition rate is found at the River Dee and Bala Lake SAC receptor C1. The EC Directive Annex 1 habitat that is a primary reason for the selection of the River Dee and Bala Lake SAC is “water courses of plain to montane levels containing Ranunculion fluitantis and Callitricho-Batrachion vegetation”. The project ecologists have advised that floating water-plantain is not present at this location and NRW have confirmed that there are no other critical levels or loads relevant to the assessment as all designated features are aquatic.
8.245 At receptor C1, the appropriate critical load is that for broadleaved woodland to which the Stack emissions contribute 1.4%. There is no relevant critical load for improved grassland, the other priority habitat identified from MAGIC for this receptor (and which comprises just 2% of the SAC). At location C1, the background deposition rate is 61.32 kg/ha/yr, to which the Stack emissions for the Power Station Complex contribute less than 0.2%.
8.246 At location C2, south of the Power Station Complex Site, a hypothetical worst case assessment has been made for nitrogen deposition by comparing the result to the most stringent critical load for floating water plantain which is conservatively assumed to be present at this location. The contribution from the Power Station Complex Site is shown in Table 8.27 to be less than 1% of critical load for this species. The integrity of this feature of the SAC is therefore not considered to be affected and the Power Station Complex Stack emissions considered insignificant.
8.247 The contribution of Stack emissions to the critical load for acid deposition is insignificant at all sites, as the incremental deposition rates are less than 1% of the criteria. At Site B2, Midland Meres and Mosses Phase 2 Ramsar (Hanmer Mere SSSI), the modelled increment is 0.1% of the MinCLMaxN for fens and mires. It may hence be concluded that other sections of the international designated site beyond 15 km of the Stacks and broadly in the same direction of the Power Station Complex would be subject to similarly insignificant increments.
74 This interpretation is made in line with the IAQM position statement on assessment at sensitive habitats http://www.iaqm.co.uk/text/position_statements/aq_impacts_sensitive_habitats.pdf
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8.248 None of the calculated nitrogen or acid deposition rates at the non-statutory local sites exceed 1% of the relevant critical loads, hence results at these sites can also be considered insignificant.
Road transport
8.249 It has been assumed in the transport and traffic assessment (chapter 7) that a maximum of 30 staff will work at the Scheme once operational, operating on a two shift basis resulting in a maximum of 30 arrivals and 30 departures throughout the day i.e. a two way AADT of 60 LDVs. A robust assumption of one HGV accessing the site per day has been made to allow for routine maintenance and repairs. The total number of either LDV or HGVs accessing the site during routine operation and maintenance exceeds neither the DMRB nor EPUK/IAQM change criteria. It can thus be assumed without further assessment that there will be a “neutral” impact on air quality as a result of the additional vehicle movements generated during routine operation and maintenance of the Scheme. The effect on human health and vegetation will be insignificant.
8.250 A temporary increase in vehicle flows due to annual maintenance activities is described in chapter 4. Due to the very low numbers and short time periods involved, there would be no material effect on local pollutant concentrations during such work and the achievement of AQS objectives will not be compromised.
Decommissioning
8.251 During decommissioning of the Power Station Complex, there will be potential for dust emissions from locations where demolition is taking place. Following the operational life of the Scheme, anticipated to be approximately 35 years, site decommissioning will involve demolition of site structures. There will also be works compounds on the Power Station Complex Site, likely to incorporate stockpiles of recovered materials and the use of mobile plant including concrete crushers. Materials handling and transportation for disposal off-site may generate dust, particularly from un-surfaced haul routes within the site.
8.252 During the decommissioning phase, short-term emissions to atmosphere may arise through the use of temporary energy supply equipment, through dust raising activities during demolition and as a result of exhaust emissions from the transport of workers and material.
8.253 Decommissioning of the Power Station Complex is likely to produce similar effects to those identified for construction dust. The dust assessment for the construction stage is thus considered to be applicable to demolition operations during decommissioning. At decommissioning, the site is likely to be of medium risk given the size of the development and likely use of crushing and screening equipment, as is commonplace in demolition of facilities of this nature and scale. The main difference at decommissioning as opposed to during the construction phase will be
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the presence of new receptors, and hence the number and location of sensitive receptors may change. There remain a number of unknown factors associated with decommissioning, including future guidance and standards, the location and number of future receptors, air pollutant concentrations and prevailing best practice methods at the time of decommissioning. It is recommended that prior to decommissioning an assessment is undertaken in the light of the extant baseline and regulatory regime.
8.254 The existing receptors relevant to the decommissioning phase are as described previously for construction dust. Given the current distance between the Power Station Complex Site and the closest sensitive receptors, it is considered unlikely that there would be any potential for dust emissions beyond the Power Station Complex Site during decommissioning of the Scheme, with appropriate mitigation measures in place.
8.255 Emissions from the Scheme Stacks will cease upon decommissioning. The previous section showed that there will be no significant effect on human health and vegetation when the Scheme is operational, hence the effect of decommissioning on local air quality is likely to be not significant.
Mitigation measures
Construction
8.256 The impact assessment for construction dust concluded that the Power Station Complex Site comprises a “medium” risk site during the demolition phase (including enabling works) and a “low” risk site for the subsequent construction phases. The mitigation measures specified below are taken from IAQM Guidance (full listing is provided in Appendix 8.1) where they are identified as being “highly recommended” for the risk level determined through assessment. Implementation of such measures will ensure that the production and dispersion of dust during the construction of the Power Station Complex is kept to an absolute minimum. The following measures are included in the draft CEMP (Appendix 19.1).
8.257 Site management measures should include:
displaying the name of accountable persons (e.g. Site Environment Manager) and head or regional office information on the site boundary;
recording all dust and air quality complaints, identify cause(s), take appropriate measures to reduce emissions in a timely manner, and record the measures taken;
making the complaints log available to the WCBC EHO as required; and
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recording any exceptional incidents that cause dust and/or air emissions, either on- or offsite, and the action taken to resolve the situation in the log book.
8.258 Monitoring activities should include:
carrying out regular site inspections to monitor compliance with the draft CEMP (Appendix 19.1), record inspection results, and make an inspection log available to the WCBC EHO as required; and
increasing the frequency of site inspections by a nominated individual accountable for air quality and dust issues on site when activities with a high potential to produce dust are being carried out and during prolonged dry or windy conditions.
8.259 Preparing and maintaining the site should comprise:
planning site layout so that machinery and dust causing activities are located away from receptors, as far as is possible;
erecting solid screens or barriers around dusty activities or the site boundary that are at least as high as any stockpiles on site; and
avoiding site runoff of water or mud.
8.260 Demolition (i.e. enabling works to remove existing structures and hardstanding) should include:
ensuring effective water suppression is used during demolition operations. Hand held sprays are more effective than hoses attached to equipment as the water can be directed to where it is needed. In addition, high volume water suppression systems, manually controlled, can produce fine water droplets that effectively bring the dust particles to the ground; and
bagging and removing any biological debris or damp down such material before demolition.
8.261 Operations should consider:
only using cutting, grinding or sawing equipment fitted or in conjunction with suitable dust suppression techniques such as water sprays or local extraction, e.g. suitable local exhaust ventilation systems;
ensuring an adequate water supply on the site for effective dust/particulate matter suppression/mitigation, using non-potable water where possible and appropriate;
using enclosed chutes and conveyors and covered skips;
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minimising drop heights from conveyors, loading shovels, hoppers and other loading or handling equipment and use fine water sprays on such equipment wherever appropriate; and
avoiding bonfires and burning of waste materials.
8.262 As noted in the assessment section, mobile crushing equipment can be a source of dust and is regulated by the Unitary Authorities in Wales, under the Environmental Permitting (England and Wales) Regulations 2010 (SI 2010 No. 675) (as amended). Equipment should be designed and operated in accordance with the most recent version of DEFRA’s Process Guidance Note 3/16(12) for Mobile Crushing and Screening75.
8.263 With regard to the control of emissions from operating vehicle/machinery and sustainable travel, the following measures are proposed:
ensuring all vehicles switch off engines when stationary - no idling vehicles; and
avoiding the use of diesel or petrol powered generators and use mains electricity or battery powered equipment where practicable.
8.264 The above are the “highly desirable” measures only; the IAQM guidance contains other “desirable” measures such as the covering of vehicles entering and leaving site to prevent escape of materials during transport and the installation of wheel washing systems (both noted in the CEMP), which should be considered in particular in light of the potential for cumulative impacts (see paragraph 8.333).
8.265 NRMM used on site should be fitted with a type approved engine which meets the emission standards set in the Non-Road Mobile Machinery (Emission of Gaseous and Particulate Pollutants) Regulations 1999 (SI 1999/1053) (as amended). The placement of diesel or petrol powered generators should consider proximity to nearby receptors and ensure that the exhaust discharges vertically and is unimpeded.
8.266 The dust mitigation methods will be incorporated into a CEMP, a draft CEMP is included as Appendix 19.1 to the ES. The level of detail will depend on the risk, and will include as a minimum the “highly recommended” measures recommended in this document. Further “desirable” measures may also be included as appropriate. The CEMP may include monitoring of dust deposition, real-time PM10 continuous monitoring and/or visual inspections.
8.267 The transport and traffic assessment in relation to air quality determined that there would will be a neutral effect on air quality due to additional construction traffic movements. The theoretical peak of up to 300 HGVs requiring access to the site per day (i.e. 300 arrivals and 300 departures or 600 HGVs as a two-way flow, for up to a
75 Process Guidance Note 3/16 (12) Mobile crushing and screening. DEFRA. September 2012.
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three-day period, may be reduced if on-site concrete batching is employed. If this approach is employed, such operations will be undertaken using enclosed plant regulated in accordance with DEFRA’s Process Guidance Note 3/01(12)76 and permitted by WCBC under the Environmental Permitting (England and Wales) Regulations 2010 (SI 2010 No. 675) (as amended).
Operation
8.268 No further measures are proposed in addition to those incorporated in the Power Station Complex design. CCGT technology is inherently clean and the use of natural gas as a fuel ensures the stringent emission limits for NOx and CO, as set in the IED, will be met.
8.269 The number of vehicle movements during the operational phase of the Scheme is negligible hence further mitigation beyond those measures at the national level to control vehicle emissions are not required.
Decommissioning
8.270 The dust mitigation measures as outlined above for the construction phase of the Power Station Complex should be put in place during site decommissioning to reduce the risk of transport of dust beyond the Power Station Complex Site boundary, particularly with regard to demolition activities including crushing. The proposed mitigation methods should be incorporated into a CEMP, in line with the legislation applicable at the time.
Residual effects
Construction
8.271 Given the dust suppression measures to be implemented on the Scheme site during the construction phase of the Power Station Complex, as set out in the draft CEMP (Appendix 19.1), it is unlikely that there will be any significant adverse effects due to dust deposition beyond the Order Land.
8.272 The effect of construction traffic emissions on air quality was determined to be neutral hence there will be no significant residual effects.
76 Process Guidance Note 3/01(12) Statutory guidance for blending, packing, loading, unloading and use of cement. DEFRA. September 2012
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Operation
8.273 None of the AQS objectives or EALs for human health or ecology will be exceeded as a result of Stack emissions from the Power Station Complex, therefore there will be no residual effects on sensitive receptors. The residual incremental contribution of Stack emissions to critical loads is negligible in the context of existing background deposition rates at ecological sites, including where the critical load is already exceeded.
8.274 The effect of traffic emissions on air quality was determined to be negligible hence there would be no significant residual effects.
Decommissioning
8.275 No material effects are anticipated from dust emissions beyond the Scheme Order Limits for the Power Station Complex, with a comprehensive CEMP in place.
GAS CONNECTION ROUTE AND AGI ASSESSMENT
Potential effects
Pollutants
8.276 The main air pollutant relevant to the assessment of the Gas Connection and Above Ground Installation (AGI) is dust, with minor emissions of NOx and PM10 from construction and maintenance vehicle exhausts.
Construction dust emissions
8.277 The approach to the dust assessment for the Gas Connection follows that for the Power Station Complex described in the previous section.
8.278 The Gas Connection Route is approximately 3,400 m in length extending south from the Power Station Complex Site to the AGI, which is to be constructed at the Maelor Gas Works. Construction of the Gas Connection will generally comprise cut and cover operations, with directional drilling where the pipeline crosses beneath Oak Road and the River Clywedog. The volume of material to be excavated for the 1m wide x 1m deep trench is 5,114 m3 or approximately 6,400 tonnes of soil.
8.279 All construction operations will take place within the Gas Connection Route defined by the Order Land. Access points will be from the south east corner of the Power Station Complex Site, via gated access points on the north and south sides of Oak Road, and from the Maelor Gas Works Access Road, off the B5130.
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8.280 Excavators and other plant will use the haul road that will be put in place within the Gas Connection Route.
8.281 An assessment in line with IAQM guidance of the potential effects of dust raising activities has been carried out in the context of receptor sensitivity and distance from source, and prevailing meteorological conditions. The assessment of dust emission magnitude for the Gas Connection (IAQM Step 2A) is presented in Table 8.28; the magnitude was estimated based on the information in chapter 4, as summarised above. This comprises the first step in the IAQM dust assessment method, and informs the rest of the assessment.
Table 8.28: Gas connection - dust emission magnitude Activity Factors determining dust emission magnitude Dust emission magnitude Demolition No demolition works associated with pipeline N/A construction Earthworks <20,000 tonnes of total material to be moved, <5 Small heavy earth moving vehicles active at any one time Construction Approximately 3.4 km of pipeline to be laid but Small no significant associated infrastructure works. Track out <10 HDV/HGV outward movements in any one Medium day; potentially >100m unpaved road length
8.282 Having determined the dust emission magnitude, the sensitivity of the area needs to be defined. This process is set out in Table 8.29, Table 8.30 and Table 8.31 for each impact type, and has been undertaken using the same approach as for the Power Station Complex Site construction dust assessment.
8.283 In considering the potential for effects from trackout (of medium magnitude), it should be noted that the Gas Connection Route will primarily be accessed from the north from within the Power Station Complex Site, and from the south via the AGI Site at Maelor Gas Works. Vehicles egressing from these two sites will travel more than 200 m over private access roads before reaching the public highway. Therefore, assessment of trackout is only relevant for the properties within 200 m of the gated access points on Oak Road (see Table 8.29 below), where construction vehicles will exit directly onto the public highway.
Table 8.29: Gas connection - sensitivity of the area to dust soiling effects on people and property Receptor Receptor Number of Distance from source Sensitivity of sensitivity receptors area 2) Plum Tree Farm High 8 165m from GC Route LOW + other properties on (10-100 high B5130 sensitivity
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Receptor Receptor Number of Distance from source Sensitivity of sensitivity receptors area 8) Higher Oak, Oak High 3 120m from GC Route; receptors Road 20-50m from Oak <350m) + Ourholme Road, <200m from trackout 9) Cae Bryner Farm High 6 315m from GC Route + properties to south on B5130 to Oak Road 10) St. Paul’s Primary High 12 245m from GC Route School, B5130 + other properties on B5130 11) Lower Oak Farm, High 3 120m from GC Route; Oak Road 20-50m from Oak + The Orchard, Lower Road <200m from site Oak access for trackout 12) Parkey Lodge High 6 60m from GC Route + Nant Cottage, (closest property) 1-3 Talwrn Cottages, Talwrn House 18) Parkey Farm High 1 335m from GC Route 21) Footpath ISY / 18 + Low >1 0m from GC Route Footpath SESS / 25
Table 8.30: Gas connection - sensitivity of the area to human health impacts Receptor Receptor Number of Distance from source Sensitivity of sensitivity receptors area 2) Plum Tree Farm High 8 165m from GC Route + other properties on B5130 8) Higher Oak, Oak High 3 120m from GC Route; Road 20-50m from Oak + Ourholme Road <200m from LOW trackout (10-100 high 9) Cae Bryner Farm High 6 315m from GC Route sensitivity + properties to south receptors on B5130 to Oak Road <350m) 10) St. Paul’s Primary High 12 245m from GC Route School, B5130 + other properties on B5130 11) Lower Oak Farm, High 3 120m from GC Route; Oak Road 20-50m from Oak
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Receptor Receptor Number of Distance from source Sensitivity of sensitivity receptors area + The Orchard, Lower Road <200m from site Oak access for trackout 12) Parkey Lodge High 6 60m from GC Route + Nant Cottage, (closest property) 1-3 Talwrn Cottages, Talwrn House 18) Parkey Farm High 1 335m from GC Route 21) Footpath ISY / 18 + Low >1 0m from GC Route Footpath SESS / 25 Note: DEFRA mapped background concentrations < 24 µg/m³ for all relevant grid squares. Urban background concentrations of PM10 measured by Isycoed CMS < 24 µg/m³ (see Baseline section).
Table 8.31: Gas Connection - Sensitivity of the area to ecological impacts Receptor Receptor Distance from source Sensitivity of sensitivity area A2) Wrexham Industrial Low >50 m from GC Route N/A Estate LWS – Cefyn <50 m from Oak Road but >200m Park from access for trackout E) Parkey Lodge & Low 40 m from GC Route Low Parkey Farm ancient >50 m trackout woodland
8.284 Most residential receptors are located over 100m from the boundary of the Gas Connection Route (the distance within which most particulate material will settle). The only receptor identified within this distance is Parkey Lodge, located 60 m from the Gas Connection Route and in line with the prevailing south easterly wind. Higher Oak and properties on the B5130 are aligned with the secondary north westerly prevailing wind, but are all over 100 m from the Gas Connection Route boundary. A few properties are within 50 m of Oak Road and less than 200 m from the Gas Connection Route access point at this location; as such they may be affected by trackout in the absence of appropriate mitigation.
8.285 The only relevant ecological receptor is the non-statutory ancient woodland designation at Parkey Farm and Parkey Lodge at the southern end of the Gas Connection Route. The secondary north westerly prevailing wind could potentially carry dusty material towards this site, however only a very small portion is within 50 m (ID 33342). The section of ancient woodland coincident with Peter’s Dingle LWS is around 200 m away at its closest point.
8.286 Taking account of the total number of receptors, their sensitivity and their distance from the Gas Connection Route, and background PM10 concentrations, the study
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area is considered of overall “low” sensitivity for all activities and impacts. The summary findings are presented in Table 8.32.
Table 8.32: Gas connection - outcome of defining sensitivity of the area Potential Sensitivity of the surrounding area impact Earthworks Construction Trackout Dust Soiling Low Low Low Human Health Low Low Low Ecological Low Low Low
8.287 The risk of dust effects (with no mitigation applied beyond measures required by legislation) is defined by combining the dust emission magnitude for each of the four activity types, with the sensitivity of the surrounding area in accordance with the matrices presented in Tables 6 to 9 of the IAQM Guidance. The assessment and summary findings are presented in Table 8.33 and Table 8.34 below.
8.288 Overall, construction of the Gas Connection and AGI presents negligible risk of dust impact during the earthworks and construction phases and a “low” risk of impact from trackout. Appropriate measures for the control of trackout from low risk sites are provided in the section on mitigation.
Table 8.33: Gas connection - determination of dust risk for each impact type Dust magnitude Sensitivity of area Dust risk Dust soiling Earthworks Small Low Negligible Construction Small Low Negligible Track out Medium Low Low Human Health Earthworks Small Low Negligible Construction Small Low Negligible Track out Medium Low Low Ecology Earthworks Small Low Negligible Construction Small Low Negligible Track out Medium Low Low
Table 8.34: Gas connection - summary dust risk table to define site-specific mitigation Potential Risk impact Earthworks Construction Trackout Dust Soiling Negligible Negligible Low Human Health Negligible Negligible Low
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Ecological Negligible Negligible Low
Construction traffic emissions
8.289 This assessment considers whether the temporary increases in traffic flow could affect local air quality.
8.290 The transport of material and worker access to and from the Gas Connection Route will take place via the local road network. The traffic and transport assessment undertaken for the Scheme is described in detail in chapter 7. Access to the Gas Connection Route would typically be either from the Power Station Complex Site or the Maelor Gas Works, with minimal vehicular access from Oak Road.
8.291 The volume of additional construction traffic due to construction of the Gas Connection is in the order of up to 10 HGV trips daily (10 arrivals, 10 departures) and up to 10 light vehicle trips daily (10 arrivals, 10 departures) for staff. These flows are anticipated to occur for a two-week period during the early stages of construction work and one week after completion of the Gas Connection works.
8.292 The resultant increases in two-way daily vehicle movements do not exceed either the DMRB or EPUK/IAQM criteria for quantitative assessment and the impact is short term. No further assessment is therefore required and the impact on local air quality of construction vehicle emissions associated with the Gas Connection can be deemed to be “neutral” (in line with DMRB paragraph 3.14) and insignificant in line with EPUK/IAQM (2015). The effect on all receptor types, both human health and ecological, will be insignificant.
Construction plant emissions
8.293 At this stage in the design, a detailed inventory of the equipment that will be used on site during the construction phase of the Gas Connection and AGI is not available. It is expected that there will be emissions from diesel or petrol powered generators and NRMM, for example excavators, bulldozers, and other construction machinery. The majority of emission sources will be located within the Gas Connection Route.
8.294 The low level nature of the sources means that whilst there may be a temporary increase in ground level concentrations of NO₂ and PM10 close to the release point, such an increase is unlikely to be material beyond the Order Land. The closest residential properties are over 100 m from the Order Land boundary, with the exception of Receptor 12, Parkey Lodge, which is 60 m from the Gas Connection Route.
8.295 In view of the fact that the construction plant emissions will be temporary and intermittent in nature, and in light of existing background concentrations which are
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well below the AQS objectives, it is concluded that the effect of temporary construction plant emissions on local air quality will not be significant.
Operation
8.296 There will be no direct or indirect emissions to air from the operation of the Gas Connection and AGI. There may be occasional visits for repairs or maintenance, but these are considered to be negligible in the context of the EPUK / IAQM criteria for affected roads. Associated vehicle emissions will have negligible effect on human health and vegetation during operation and maintenance.
Mitigation measures
Construction
8.297 The impact assessment for construction dust concluded that the Gas Connection presents a “low” risk for trackout and negligible for all other phases. The IAQM “highly recommended” mitigation measures for a low risk site were presented previously in the assessment for the Power Station Complex and are also in the draft CEMP (Appendix 19.1). The application of these measures across all associated construction work including that for the Gas Connection will ensure that the generation and dispersion of dust during the construction phase is kept to an absolute minimum, in particular due to the proximity of the route to sensitive human receptors and ecological sites.
8.298 Similarly, the measures for NRMM emissions as described previously for the Power Station Complex are equally applicable to the Gas Connection.
8.299 Given the proximity of the construction works to a small area of ancient woodland, and to Parkey Lodge and nearby properties, particular attention to screening, control and monitoring of emissions (both in relation to dust and construction plant) at this location will be required.
8.300 These mitigation methods will be incorporated into a CEMP, a draft CEMP is included as Appendix 19.1 to this ES including dust mitigation measures.
8.301 The effect of construction traffic emissions on air quality was determined to be neutral hence there is no need for mitigation measures.
Operation
8.302 There will be no direct and negligible indirect emissions to air from the operation (including maintenance) of the Gas Connection hence mitigation is not required.
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The land where the Gas Connection is to be made will be returned to agricultural land.
Residual effects
Construction
8.303 With the application of measures set out in the draft CEMP, it is unlikely that there will be any significant adverse effects due to trackout or NRMM emissions beyond the Gas Connection Route.
8.304 The effect of construction traffic emissions on air quality was determined to be neutral hence there will be no significant residual effects.
Operation
8.305 There will be no direct and negligible indirect emissions to air from the operation (including maintenance) of the Gas Connection.
COMBINED RESIDUAL EFFECTS
Construction
8.306 The dust assessment for the Gas Connection found that only trackout presents a “low” risk; all other activities will be of negligible consequence. Combined effects of the Power Station Complex, the Gas Connection would not occur for trackout as the same properties would not be affected.
8.307 The application of IAQM “highly recommended” mitigation measures for the relevant level of risk across all Scheme construction areas will ensure that the production and dispersion of dust during the construction phase is kept to an absolute minimum. With a CEMP, it is unlikely that there will be any residual adverse effects due to dust deposition.
8.308 The in-combination traffic flows from both the Power Station Complex and Gas Connection will not exceed DMRB assessment criteria. The EPUK/IAQM (2015) indicative criteria are marginally exceeded for both LDVs and HDVs (HGVs). In the context of the low background concentrations in the area (Table 8.12), less than half the AQALs for NO2 and PM10, and with roadside concentrations (Table 8.9) equal to less than 75% of the AQALs, quantitative assessment is not deemed necessary and the air quality impact can be considered insignificant.
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Operation
8.309 There is no potential for combined residual effects during operation as there are no direct and negligible indirect operational emissions from the Gas Connection and AGI.
Decommissioning
8.310 There is no potential for combined residual effects of dust or traffic emissions as the Gas Connection will not be demolished but purged of any gas residue and left in- situ.
CUMULATIVE EFFECTS
8.311 The Electrical Connection is not part of the Application for the Scheme, but will be required for the export of electricity. It is thus assumed that works will be undertaken broadly at the same time as the Scheme construction works. To ensure that a robust assessment is carried out in the ES a number of realistic assumptions have been made regarding the electrical connection works as set out below:
8.312 The Electrical Connection is likely to consist of underground cabling between the Scheme’s electrical switchgear located within the Power Station Complex and the existing Marchwiel substation, located on Abbey Road on the Wrexham Industrial Estate.
8.313 The wider existing electrical distribution network will also need upgrading to accommodate the new generation. This is likely to consist of works to the existing Marchwiel substation, re-stringing of existing pylons between Legacy and Wrexham substations, replacement of the existing portal frame towers between Legacy and Marchwiel substations and laying of underground cables. Once completed the electrical network which currently serves the Wrexham Industrial Estate will have increased capacity and resilience from that which exists presently.
8.314 The final technical solution for the Electrical Connection will be determined at a later date by SPEN in their role as statutory undertaker for electrical infrastructure in the area. Any works associated with the Electrical Connection will be consented through the appropriate and lawful consenting regime. Further details of the Electrical Connection and the consultation undertaken with SPEN to date are detailed in the Grid Connection Statement (Document Ref: 8.1).
8.315 The North Wales Prison on the Firestone Site will accommodate 2,100 adult male inmates. Construction of the prison will be complete prior to the commencement of Scheme construction works. Once operational, it is expected to introduce additional traffic, predominantly cars, to the area. As agreed with the WCBC EHO, the cumulative assessment considers the introduction of new sensitive receptors to
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the area once the prison is operational, and therefore is considered in the context of exposure to Stack emissions for the Power Station Complex. There will be a CHP unit associated with the prison, but due to its small size it was agreed it would not have a cumulative impact with the Scheme. The WCBC EHO was not aware of any other developments with a significant combustion element that would require assessment of cumulative effects with those of Scheme.
8.316 The Kingmoor Park North development for a storage and distribution warehouse is expected to introduce additional traffic, in particular HGVs, to the area once operational as well as during the construction phase.
8.317 The construction of a solar photovoltaic array up to 4 MW in capacity on land at Pickhill Bridge Farm, Cross Lanes, Wrexham will last for 12 weeks, during which time it will introduce additional traffic to the area. Once operational there will be no staff based on site and no emissions to atmosphere, hence this phase is not assessed for air quality.
Construction
8.318 The assessment of cumulative construction effects has considered the “realistic worst case” scenario i.e. construction of the Scheme concurrently with the following local development proposals:
construction of the Electrical Connection for the Scheme;
construction of the Kingmoor Park North development (storage and distribution warehouse);
operation of the North Wales Prison at the former Firestone Factory site; and.
construction of the Pickhill Bridge Farm Solar Array.
Construction dust emissions
8.319 The assessment of construction dust is made in line with IAQM guidance and considers the potential for change to receptor sensitivity and/or dust emission magnitude. It considers those receptors which may be affected by the Scheme construction works in addition to those associated with the Electrical Connection works and/or the Kingmoor Park North development and/or the Pickhill Bridge Farm Solar Photovoltaic Array, and whether or not additional mitigation is warranted.
8.320 The anticipated Electrical Connection works may terminate at the Marchwiel substation (see Figure 5.1). In considering the cumulative effects of construction dust it has been determined that there are no human health receptors located
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within 350 m of both the Order Land and the anticipated Electrical Connection works (construction of new substation and laying of underground cabling to connect to the Scheme). A parcel of Wrexham Industrial Estate LWS adjacent to Bryn Lane (receptor A1) lies within 50 m of both the anticipated underground cabling connection works and the Power Station Complex Site.
8.321 The anticipated overhead Electrical Connection upgrade is expected to extend south on its existing alignment though Cefn Park, the largest parcel of the Wrexham Industrial Estate LWS (receptor A2), and south east towards Peter’s Dingle LWS (receptor D). A single residential property at Talwrn that falls within 350m of both the Gas Connection Route and the anticipated Electrical Connection. Neither the Cefyn Park unit of the Wrexham Industrial Estate LWS (receptor A2), nor Peter’s Dingle LWS (receptor D) falls within 50m of both the anticipated Electrical Connection and Gas Connection Route. Therefore, concurrent construction activities are not expected to give rise to cumulative effects of dust emissions at these ecological receptors.
8.322 The anticipated underground element of the Electrical Connection between the Marchweil and Wrexham substations is located over 350 m from the Order Land and therefore cumulative effects of dust emissions generated during concurrent construction of these proposals are not anticipated.
8.323 The Kingmoor Park North development is located immediately to the north of the Power Station Complex Site. The air quality assessment for the Kingmoor Park North development includes proposals for appropriate mitigation measures to control the effect of dust generated during the construction phase. In addition, the planning appeal decision document77 states “No development shall be commenced until a scheme of dust mitigation measures has been submitted to and approved in writing by the Local Planning Authority.”
8.324 Properties located at Marshley on the B5130 (Receptor 2) and those on the corner of Bryn Lane with Ridley Wood Road (Receptor 4), are within 350m of both the Power Station Complex Site and Kingmoor Park North. Concurrent construction activities at these two locations could therefore result in these properties being exposed to cumulative effects of construction dust emissions from both sites. None of these properties are within 100m of both the Power Station Complex Site and the Kingmoor Park North Site.
8.325 The Pickhill Bridge Farm Solar Array development will be located within the agricultural land at Pickhill Bridge Farm immediately south of the River Clywedog and 1.7 km to the north east of Cross Lanes. The site will be intersected by the Gas Connection Route and the access track will run parallel to the Gas Connection Route for approximately 300 m south west. In addition, replacement / restringing of overhead electrical pylons will be undertaken parallel to the eastern boundary of
77 http://www.wrexham-power.com/downloads/Appeal-Decision-plus-Plans.pdf
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the proposed Solar Array site, however, there are no relevant receptors within 350 m of the pylon works, Solar Array and Gas Connection works to consider for cumulative effects of construction dust.
8.326 In considering the cumulative effects of construction dust the only human health receptor located within 350 m of the anticipated Solar Array site is Parkey Farm Lodge (receptor 12). Concurrent construction activities at the locations of the Solar Array site and the Gas Connection Route could therefore result in this property being exposed to cumulative effects of construction dust emissions from both sites, although neither site is within 100 m of the receptor.
8.327 Overall, there is no change to dust emission magnitude for the earthworks and construction categories, which were assessed to be large for the Scheme alone and thus remain as large. The sensitivity of the area to dust soiling and human health effects remains low due to the limited number of receptors to be considered. There is no change to the risk of dust impact. It is assumed that appropriate dust mitigation measures will be implemented during underground cabling works associated with construction of the electrical connection to the Scheme, during construction of Kingmoor Park North and during construction of the Solar Array. No additional mitigation is required for cumulative impacts beyond those measures proposed in the main assessment.
8.328 Bryn Lane will be used by construction vehicles accessing the Scheme as well as the Kingmoor Park North and Solar Array developments. Construction vehicles for the Solar Array will exit the site via the proposed temporary access track and south on the unclassified local access road to the B5130. There will be fewer than 10 HGV movements daily associated with the Solar Array, thus in accordance with IAQM Guidance, trackout from this ‘small’ site may only extend to 50 m on the public highway from the site exit and will therefore not affect any receptors on Bryn Lane. Assuming appropriate dust mitigation measures will be implemented during construction at each respective site, there will be no change in the dust magnitude for trackout and the risk of cumulative dust impact will remain low. Nonetheless, IAQM “desirable” measures for low risk sites including wheel washing systems at the Power Station Complex Site exit could be implemented to minimise the potential for cumulative effects of trackout at the nearest properties on Bryn Lane.
Construction traffic emissions
8.329 An increase in vehicle movements is expected for the anticipated Electrical Connection works, with peak daily traffic movements in the order of 14 HGVs and 82 LDVs on the new Industrial Estate Road (N) (see chapter 7). This is considered to represent the “realistic worst case” for air quality.
8.330 As part of the Electrical Connection, underground cables are anticipated to be installed between the Wrexham substation and the Marchweil substation; this work may incur temporary road closures. As these works will take place over a short
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period of approximately 3 months, and given the low background levels in the study area, they have not been considered in the “realistic worst case” scenario for air quality.
8.331 Detailed information on the volume of construction traffic was not presented in the planning application for the Kingmoor Park North development78. In the absence of such data, assumptions of traffic flows were made based on the professional judgment of the traffic engineers at Atkins79. For the purpose of this assessment it is assumed that construction traffic for the Kingmoor Park North development will take the same route as the Power Station Complex construction traffic, i.e. arriving from the north via the A534, A5156 (Industrial Estate Road) and onto Bryn Lane.
8.332 The planning application for the Pickhill Bridge Farm Solar Array outlines that during construction there will be approximately 30 LDV movements and up to 4 HDV movements per day in the area over a 12-week period (including a 2 week enabling phase). Access to the site for construction vehicles will be from the B5130 via an unclassified road running north through Parkey Lodge Farm then through a temporary opening in the hedge of the western boundary of the proposed site.
8.333 A summary of the traffic data used in the assessment of cumulative construction traffic vehicle emissions to atmosphere is presented in Error! Reference source not found. below for the year 2018: a future baseline, all planned developments (“realistic worst case” cumulative scenario for the Scheme including construction traffic for the Power Station Complex, Gas Connection, Electrical Connection, Kingmoor Park North and Solar Array;) and future total flows including operational traffic associated with the prison. The future baseline (2018) flows include anticipated increases in traffic as a result of growth over time. A growth factor of 1.0442 was provided by the traffic engineers to estimate 2018 AADT flows from 2014 AADT.
Table 8.35: Affected road network due to cumulative construction traffic in 2018 Link Baseline Cumulative traffic Total AADT HGV AADT HGV AADT HGV A534 (W) 20,680 2,090 914 264 21,594 2,354 A534 (E) 8,154 1,263 256 0 8,410 1,263 Industrial Estate Road 15,312 1,900 1,170 264 16,482 2,164 (N) Bryn Lane (N) 3,743 699 908 252 4,651 951 Bryn Lane (E) 2,884 528 808 152 3,692 680
78 The Royal Haskoning Noise and Air Quality report (2011) indicates that Kingmoor construction traffic would equate to “A maximum of 100 HGV movements per day during the Concrete pouring phase of the construction”. No data on LGV flows is available. 79 As is deemed appropriate, in accordance with paragraph 3.6 of the DMRB (HA207/07).
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Link Baseline Cumulative traffic Total AADT HGV AADT HGV AADT HGV Access Road 450 71 750 130 1,200 201
8.334 The cumulative increases in construction traffic exceed one or more of the DMRB criteria on Industrial Estate Road, Bryn Lane and the A534 (W). One or more of the more stringent EPUK/IAQM indicative criteria are exceeded on all roads except the A534 (E). Further assessment of the potential cumulative impact of construction traffic on air quality has been undertaken through reference to existing local traffic flows, air quality monitoring data and a simple calculation using the DMRB screening tool to determine the likely magnitude of change.
8.335 The annual average concentration of NO2 recorded at the roadside CMS on Victoria Road80 in 2014 was 21.1 µg/m3, just over half the AQS objective. According to DfT statistics for the same year81, Victoria Road (A5152) at this location carried an AADT of 9,705 (comprising 5% HDVs). Annual traffic flows on Bryn Lane have been determined from the automatic traffic counts conducted as part of the traffic and transport assessment in chapter 7 of this ES. The measured weekday flow on Bryn Lane (N) in 2014 was 4,203 (16% HDVs), which is less than half that on Victoria Road hence roadside NO2 concentrations may be expected to be even lower on Bryn Lane.
8.336 Background concentrations of NO2 in the area (as indicated by DEFRA mapping in Table 8.12 and as measured at the Isycoed CMS) are less than 50% of the AQAL, while the measured roadside concentration on Victoria Road (Table 8.9), a more heavily trafficked road in Wrexham (albeit with a lower percentage of HGVs) is still well below (less than 75% of) the AQAL.
8.337 A simple screening calculation using the DMRB screening tool, using the incremental traffic data for Bryn Lane (N), shows that at a distance of 10 m from the road centreline, the increase due to cumulative development traffic will be less than 3 1 µg/m as NO2 or less than 5% of the AQAL. It can thus be determined that the total concentrations at properties on this road will remain well below the AQAL for NO2. The EPUK/IAQM guidance classifies such an impact as negligible.
8.338 There may also be a cumulative effect of construction traffic at properties on the A5156 Industrial Estate Road due to vehicles accessing the Kingmoor Park North development and the Power Station Complex Site from the north. The 2014 annual mean NO2 concentration at a roadside location in Llan-y-Pwll off the A5156 (the main road onto the Wrexham Industrial Estate from the A483T) was 23 µg/m3 (see
80 The EHO at WCBC gave a preference for use of the Isycoed CMS in the Stack assessment, however it is appropriate (in the professional opinion of the assessor) for the traffic assessment to refer to a roadside measurement in order to ensure a conservative assessment of change in concentrations at sensitive receptors where only the increment in emissions from additional road traffic is calculated. 81 https://data.gov.uk/dataset/gb-road-traffic-counts
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Table 8.11). This road carries an AADT of over 15,000 of which 13% is HGV traffic. The nearest property to new Industrial Estate Road (N) is on Hugmore Lane, over 40 m from the new road centreline, at which point the pollutant concentration will be lower due to a reduced contribution from road traffic emissions82.
8.339 A simple screening calculation using the DMRB screening tool was undertaken to estimate the emissions from the incremental traffic on the A5156 (Industrial Estate Road). This shows that the increase in concentration at the nearest property on Hugmore Lane due to cumulative development traffic on the new Industrial Estate 3 Road (N) will be less than 1 µg/m as NO2 or less than 5% of the AQAL. The total concentration at this location will thus remain at less than 75% of the AQAL; the EPUK/IAQM guidance classifies such an impact as negligible.
8.340 On this basis, and in recognition of the temporary nature of the cumulative increase in traffic during construction of the Scheme and the “realistic worst case” scenario adopted, the impact of cumulative development traffic on local air quality during the construction phase can be considered not significant.
Operation
8.341 The assessment of cumulative effects of the operational phase of the Scheme with other local development proposals has considered the following scenarios:
presence of a new sensitive receptor at the North Wales Prison at the former Firestone Factory site (as agreed with WCBC EHO to be included); and
additional vehicle movements associated with the Kingmoor Park North development and North Wales Prison.
8.342 There will be negligible emissions from the anticipated Electrical Connection once operational, with just occasional maintenance vehicles requiring access at points along the anticipated Electrical Connection Route. The Electrical Connection is hence not considered further regarding the operational phase of the Scheme for cumulative effects.
Operational traffic emissions
8.343 The traffic assessment presented in the ES for the North Wales Prison suggests that, when the prison is operational, the staff and visitors will generate an additional 1,158 LDV movements as a two-way daily flow. Of these, only 15% (174 as an AADT) will be on the same roads as the traffic associated with the Scheme. The Scheme operational traffic on the new Industrial Estate Road (N) (60 LDV as a two- way flow) is approximately one third of that generated by the prison.
82 See Figure C1 in Annex C of the DMRB (HA207/07).
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8.344 The traffic generated by the Kingmoor Park North development once operational has been estimated by the traffic engineers to give a two way AADT of 415, which would travel north and south on Bryn Lane. The operation traffic was assessed in the planning application for the Kingmoor Park North development to have a negligible impact on local air quality.
8.345 A summary of the traffic data used in the assessment of cumulative operational traffic emissions is presented in Table 8.36 below for the year 2018: a future baseline, all planned developments (“realistic worst case” cumulative scenario for the Scheme including the Power Station Complex Site and the Gas Connection) and future total flows. The future baseline flows include anticipated increases in traffic as a result of growth over time. The assessment year of 2018 is assumed.
Table 8.36: Affected road network due to cumulative operational traffic in 2018 Link Baseline Cumulative traffic Total AADT HGV AADT HGV AADT HGV A534 (W) 20,680 2,090 345 20 21,025 2,110 A534 (E) 8,154 1,263 136 7 8,290 1,270 Industrial Estate Road (N) 15,312 1,900 481 28 15,793 1,928 Bryn Lane (N) 3,743 699 307 28 4,050 726 Bryn Lane (E) 2,884 528 232 32 3,116 560 Access Road 450 71 62 2 512 73
8.346 The cumulative operational traffic from all developments, either as an increase in LDV, HDV/HGV or total daily movements, will not exceed either DMRB or the more stringent EPUK/IAQM change criteria on any road around the Scheme. The impact of cumulative development traffic on local air quality may hence be considered as “neutral” and the effect on sensitive receptors within 200 m of the local road network will be insignificant.
Stack emissions
8.347 The new industrial warehouse proposed building at the Kingmoor Park North development will not affect Stack emissions in terms of building downwash effects, as these are dominated by the Power Station Complex structures closest to the Stacks.
8.348 The North Wales Prison will introduce new sensitive receptors to the study area for Stack emissions. The detailed modelling study of Stack emissions found that NO2 concentrations in the Pentre Maelor area (represented by Receptor 15) would be just 0.2% of the long-term AQS objective and 2% of the short-term AQS standard. The effect of Stack emissions from the Power Station Complex on new receptors at the North Wales Prison is considered to be insignificant.
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Decommissioning
8.349 The potential for cumulative dust emissions during decommissioning of the Scheme, and in particular the Power Station Complex, will be managed through appropriate mitigation measures, in line with legislation and best practice at the time of undertaking.
8.350 Upon decommissioning, emissions from the Stacks will cease. There will be no direct or indirect emissions to air from the operation of the Gas Connection, AGI or anticipated Electrical Connection hence the cumulative effect of decommissioning is considered to be negligible.
Additional Mitigation
8.351 No additional mitigation measures have been identified as being required as a result of this cumulative assessment.
CONCLUSIONS
8.352 This chapter has assessed the potential impacts of the Scheme on air quality and evaluated the potential for effects on sensitive receptors, for a “realistic worst case” following the “Rochdale Envelope” principle. It considered, both separately and in combination, the direct and indirect effects of air pollutants associated with the Power Station Complex and those of the Gas Connection, during the construction, operation (including maintenance) and decommissioning phases. It included a discussion of relevant legislation and policy, a review of baseline air quality conditions, identification of sensitive receptors, impact assessment, mitigation measures, residual effects and consideration of the potential for cumulative impacts.
8.353 The main component of the assessment was a study of the potential effects of the emissions to atmosphere from the Stacks on the local environment during operation. The assessment also considered emissions from road transport during construction and operation, and dust emissions during the construction and decommissioning phases. The effect of these emissions on nearby human health and ecological receptors was addressed.
8.354 Baseline air quality in the vicinity of the Scheme is considered to be good. All of the AQS objectives are met at nearby monitoring sites, including those located at the roadside. There are no AQMAs in the WCBC area, and those in CWC are over 15 km away. Existing rates of nitrogen deposition already exceed critical levels for certain habitat types identified within the Scheme study area.
8.355 The assessments of effects of dust emissions during the construction phases of the Scheme were undertaken - both separately and together for the Power Station Complex and Gas Connection - in line with IAQM guidance. Each considered the risk
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of dust effects in the context of the overall scale and nature of the Scheme and the sensitivity of neighbouring land uses. The Scheme was determined to be of “low” risk for all stages other than demolition of the Power Station Complex, which was of “medium” risk. Suitable mitigation measures were recommended for such categories. No residual effects relating to dust emissions are anticipated at sensitive receptors beyond the Order Land, with a CEMP in place incorporating best practice measures for the control of dust. On that basis, all residential, commercial and sensitive industrial properties together with ecological receptors are likely to remain unaffected by dust throughout the construction period.
8.356 Road traffic emissions were considered in accordance with the DMRB and EPUK/IAQM methodologies for air quality assessment. Changes to traffic flow data during construction and operation of the Scheme were evaluated against the criteria therein and determined to have a “neutral” impact on local pollutant concentrations and as such, an insignificant effect on local receptors for human health and ecology.
8.357 Stack emissions were assessed by means of a detailed air dispersion modelling study for the pollutants regulated under the IED. The AERMOD model was used to estimate maximum ground level concentrations of pollutants at nearby residential and ecological receptors. As well as a “realistic worst case” 2+1 arrangement and 50 m stack height, the study used several conservative assumptions regarding emissions i.e. constantly at the IED limits, 24 hours a day throughout the year and “worse case” [sic] conversion ratios for oxides of nitrogen to NO2.
8.358 On that robust basis, it has been demonstrated that the Stack emissions will not lead to any exceedances of statutory air quality criteria at sensitive receptors. Total concentrations (including the background contribution) of NO2 and carbon monoxide will continue to be below respective AQS objectives at locations of sensitive receptors for human health. The effect of Stack emissions is, in line with EPUK guidance, which is considered to be not significant. Ecological effects of oxides of nitrogen and nitrogen deposition at statutory and non-statutory sites were found to be insignificant, for all international sites of importance as well at national and local sites.
8.359 The air quality assessment has considered the potential for cumulative impacts of the Scheme with those of the anticipated Electrical Connection, the Kingmoor Park North development, the North Wales Prison and the Pickhill Bridge Farm Solar Array. It was found that the dust risk category for the Site would not increase even if all developments were to be concurrent. Cumulative effects of traffic movements are considered not to be significant. Future pollutant concentrations at all receptors, including at the new North Wales Prison site, will remain below AQS objectives and cumulative effects of the Scheme emissions are hence considered to be insignificant.
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8.360 The conclusions of the Air Quality assessment are that the Scheme in isolation and cumulatively would not result in any likely significant effects on air quality.
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