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Southern Water EP Application

Bexhill and Hastings WTW CHP Plant Air Dispersion Modelling Report

October 2012


Southern Water EP Application

Bexhill and Hastings WTW CHP Plant Air Dispersion Modelling Report

October 2012 Notice

This document and its contents have been prepared and are intended solely for Southern Water Services Limited’s information and use in relation to the Environmental Permitting Application for the CHP plant at Bexhill and Hastings Wastewater Treatment Works.

Atkins Limited assumes no responsibility to any other party in respect of or arising out of or in connection with this document and/or its contents.

Document History

JOB NUMBER: 5103447.079 DOCUMENT REF: Southern CHP Bexhill and Hastings AQ_v0_draft final

0 Draft Final RW/RG SH/RW SH JAK 12/10/12

Revision Purpose Description Originated Checked Reviewed Authorised Date


Contents Section Page Executive Summary 5

1. Introduction 6

1.1 Background 6

1.2 Report structure 6

2. Existing Conditions 7

2.1 Introduction 7

2.2 Pollutants 7

2.3 Air quality criteria 7

2.4 Local air quality review and assessment 8

2.5 Monitoring data 9

2.6 Background maps 9

2.7 Pollutant deposition rates 10

3. Methodology 11

3.1 Dispersion modelling 11

3.2 Emissions to air 15

3.3 Modelled receptors 16

3.4 Interpretation of results 18

4. Results 21

4.1 Oxides of Nitrogen 21

13.2 Carbon monoxide 27

14. Conclusions 28

List of Tables

Table 2.1 - Air Quality Strategy Objectives 8

Table 2.2 - Nitrogen Dioxide Concentrations in Study Area, µg/m3 9

Table 2.3 - DEFRA Mapped Background Concentrations, µg/m3 10

Table 3.1 - Relative Frequency Distribution of Wind Speed and Direction, (%) 12

Table 3.2 - Surface Characteristics 14

Table 3.3 - Engine Stack Emissions Characteristics 16

Table 3.4 - Human Health Receptor Locations 16

Table 3.5 - Ecological Sites within 1 km Radius from Stack 18

Table 4.1 - Annual Average NOx Concentrations and Estimated Total NO2 Concentrations 22

Table 4.2 - Annual Average NOx Concentrations at Ecological Sites 23

Table 4.3 - Nitrogen and Acid Deposition Rates and Comparison with Critical Loads 24

Table 4.4 - Maximum Hourly NOx Concentrations and Estimated Total NO2 Concentrations 26

Table 4.5 - Daily Average NOx Concentrations at Ecological Sites 26

Table 4.6 - Maximum Hourly and 8-hourly Carbon Monoxide Concentrations 27

List of Figures

Figure 3.1 - Wind Rose Diagram for Herstmonceux, 2005 to 2009 13


Figure 3.2 - Stack and Building Layout 3D Schematic 15

Figure 3.3 - Locations of Nearest Sensitive Receptors 17

Figure 4.1 - Maximum Annual Average Oxides of Nitrogen Concentrations, µg/m3 21

Figure 4.2 - Maximum Hourly Average Oxides of Nitrogen Concentrations, µg/m3 25


Executive Summary

An air dispersion modelling study has been carried out to support the Environmental Permit application for the proposed combined heat and power (CHP) engine at the Bexhill and Hastings wastewater treatment works. The engine will utilise biogas produced from the on-site anaerobic sludge digestion process, to generate up to 772 kW of electricity as well as providing recovered heat for use in the process.

The Bexhill and Hastings works lie within the boundary of the East Sussex County Council, in a predominantly rural setting between the towns of Bexhill and Hastings. The site is bounded to the south by Pebsham Farm, to the east by a landfill site, the south east by Haven Holiday Park and the west by the edge of Bexhill, an urban area called Pebsham; in other directions the land is mainly rural with the coast approximately 1.5 kilometres to the south . The site is not located within an air quality management area. Background air quality in the area is good, with air quality objectives met by some margin. .

Dispersion modelling of the engine emissions was undertaken using the United States Environmental Protection Agency atmospheric dispersion model, AERMOD version 12060. Five years of meteorological data from Herstmonceux were used in the study. The modelling assumed continuous operation of the CHP engine on biogas, throughout the year. The input data for the study used values derived from information provided by Cogenco, the suppliers of the MTU 38 litre spark ignition biogas engine, and Southern Water. The manufacturer’s emission concentrations for oxides of nitrogen and carbon monoxide, which meet the Environment Agency emission benchmarks for landfill gas engines, were used to estimate emission rates for these pollutants.

The model results demonstrated that the stack emissions of oxides of nitrogen and carbon monoxide from the CHP will not affect the achievement of the relevant air quality strategy objectives for human health. At the nearest receptors close to the site boundary, the estimated total annual and hourly mean nitrogen dioxide concentrations, including the existing background concentration, were estimated to remain at less than a third of the relevant air quality strategy objectives. The effects of carbon monoxide emissions were found to be negligible as they contribute less than half a percent to the short-term EALs. On this basis, the facility emissions are considered to be not significant in terms of human health effects.

The effects of the facility on the nearest ecological sites are considered to be insignificant in terms of concentrations of oxides of nitrogen, and nitrogen and acid deposition. In particular, the achievement of the air quality objective for vegetation and the lower critical load values at the Combe Haven SSSI, 360 metres to the north of the facility, will not be affected.

The assessment was based on a number of conservative assumptions. The engine was modelled as if operating continuously throughout the year at full load, ignoring any temporary shut downs. Environment Agency “worse case” assumptions regarding conversion of oxides of nitrogen to nitrogen dioxide were applied. The uncertainty in the modelling is considered to be small in comparison with the overall scale of the safety factors built into the above assumptions and hence the conclusions drawn are robust.

Bexhill and Hastings WTW CHP Air Dispersion Modelling Report


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1. Introduction 1.1 Background

This report, undertaken on behalf of Southern Water Services (SWS), supplements the information in the Environmental Permitting application for the addition of a combined heat and power (CHP) plant at Bexhill and Hastings Wastewater Treatment Works (WTW) in East Sussex. As the CHP plant utilises biogas produced from the on-site sludge digestion process and is of less than three megawatts thermal input, it is scheduled as a Waste Operation in the Environmental Permitting (England and Wales) Regulations (SI 2010 No 675)1 and requires a permit to be issued by the Environment Agency.

The facility will comprise a Cogenco-packaged MTU biogas spark-ignition engine 8V4000L62FB of 38 litre displacement and two Strebel boilers which are capable of running on natural gas or biogas. The CHP facility is expected to be fully utilised 24 hours a day throughout the year. Typical planned operation is for the engine to run at full load on biogas. It is not planned routinely to operate the boilers on biogas; overall usage is anticipated to be less than ten percent of the time. The boilers are not therefore considered in this dispersion modelling.

1.2 Report structure This report presents an atmospheric dispersion modelling study of the stack emissions from the combustion of biogas in the CHP engine, in order to evaluate the potential effects of those emissions on the local atmospheric environment.

The report focuses on the emissions to air of oxides of nitrogen (NOx) discharged in the stack exhaust. The modelled short-term and long-term ground level concentrations are evaluated in the context of the air quality objectives and other relevant criteria, taking into account the existing ambient air quality. Emission rates have been estimated on the basis of manufacturer’s data, empirical calculations and the relevant emission limit values. The engine exhaust also contains trace amounts of carbon monoxide (CO) and non-methane volatile organic compounds (VOCs). Although emissions of these substances are generally of negligible environmental effect, emissions of carbon monoxide have nonetheless been addressed. Sulphur dioxide is not considered in this detailed modelling study as sulphur in the form of hydrogen sulphide is removed in the digesters as a result of ferric chloride dosing.

The report documents the atmospheric emissions from CHP engine, summarises the existing background air quality from published sources, documents the approach used for the assessment of the emissions and presents the results of the air dispersion modelling study. The results are presented graphically and the potential effects at the nearest residential properties are also tabulated and discussed.

The report is set out as follows:

• Section 2 discusses the role of the local authority with regard to air quality management, and describes the relevant air quality criteria and the existing ambient air quality;

• Section 3 presents the methodology used for the dispersion modelling including the meteorological data and buildings used, the source emissions data, the discrete model receptors, and the interpretation of the results with regard to both human health and ecological receptors;

• Section 4 presents the results of the air dispersion modelling; and • Section 5 provides conclusions to the study.

1 http://www.legislation.gov.uk/uksi/2010/675/contents/made



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2. Existing Conditions 2.1 Introduction

The Bexhill and Hastings WTW CHP stack is located at 576617, 109397, within the boundary of the Rother District Council, in a predominantly rural setting between the towns of Bexhill and Hastings. The site is bounded to the south by Pebsham Farm, to the east by a landfill site, the south east by Haven Holiday Park and the west an urban area called Pebsham on the outskirts of Bexhill. In other directions and mainly north of the WTW site the land is rural/cultivated while the coast is approximately 1.5 kilometres south of the site.

Data on existing air quality in the vicinity of the WTW have been drawn from the following sources:

• local authority review and assessment studies;

• the Sussex Air Partnership website2;

• Department of the Environment, Food and Rural Affairs (DEFRA) local air quality management pages3; and

• the UK-AIR website4.

2.2 Pollutants Nitrogen dioxide (NO2) is a secondary pollutant produced by the oxidation of nitrogen monoxide (NO). Nitrogen monoxide and nitrogen dioxide are collectively termed NOx. In high concentrations nitrogen dioxide can affect the respiratory system. Nitrogen monoxide does not have any observable effect on human health at the range of concentrations found in ambient air. High levels 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.

Carbon monoxide is a partial combustion product found in vehicle exhaust and combustion gases. The ambient air quality standard for carbon monoxide is set at a level well below that at which there may be any adverse physiological effects. Since the widespread introduction of catalytic converters on vehicles, there are no areas within the UK that are at risk of breaching the air quality objective for carbon monoxide. Even at busy roadside locations carbon monoxide concentrations are well below the standard and there are no effects on human health due to the concentrations found in ambient air.

2.3 Air quality criteria The Government’s Air Quality Strategy (AQS) for England, Scotland, Wales and Northern Ireland provides details of national air quality standards and objectives for a number of local air pollutants including nitrogen dioxide and carbon monoxide. These criteria are defined in the Air Quality Standards Regulations 2010 SI 2010/1001. These regulations implement the EU Directive 2008/50/EC on ambient air quality and cleaner air for Europe (the Air Quality Directive).

The air quality standards define the level of pollution 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 air quality objectives are targets for air pollution concentrations 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

2 http://www.sussex-air.net/ 3 http://defra.gov.uk/environment/quality/air/airquality/index.htm 4 http://uk-air.defra.gov.uk/



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days above the objective concentration is also specified. The number of permissible “exceedences” is considered when determining compliance with the short-term objectives over an annual period. Local authorities are not legally obliged to achieve the air quality objectives. They are, however, required to work towards the objectives by drawing up action plans setting out the measures they intend to take in pursuit of them.

It should be noted that the air quality criteria only apply in locations where there may be a ‘relevant exposure’. 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.

The relevant air quality objectives for the protection of human health for the purposes of this assessment are presented in Table 2.1.

Table 2.1 - Air Quality Strategy Objectives

Pollutant Criteria

Nitrogen dioxide Hourly average concentration should not exceed 200 µg/m3 more than 18 times a year

Annual mean concentration should not exceed 40 µg/m3

Carbon monoxide Running eight-hour mean concentration should not exceed 10,000 µg/m3

There are also objectives for the protection of vegetation of 30 µg/m3 oxides of nitrogen as an annual mean concentration. The EU Air Quality Directive requires that assessment of compliance with the limit values for the protection of vegetation is undertaken at locations more than twenty kilometres from towns with more than 250,000 inhabitants or at locations more than five kilometres from other built-up areas, industrial installations or motorways. This objective does not apply in those areas where assessment of complicance with the limit value is not required. However, as the United Nations Economic Commission for Europe (UN ECE) and the World Health Organisation (WHO) have set a critical level for NOx for the protection of vegetation, the Statutory Nature Conservation Agencies’ policy (in England, Natural England) is to apply these criteria as a benchmark, on a precautionary basis, in internationally designated conservation sites and sites of special scientific interest (SSSIs).

The Environment Agency Horizontal Guidance Note H1 (Annex F)5 specifies certain environmental assessment levels (EALs) for air pollutants for the protection of human health, in addition to the statutory air quality objectives. For the purposes of this report, the short-term EAL for carbon monoxide of 30,000 µg/m3 as an hourly mean is relevant, as is the vegetation-based EAL for oxides of nitrogen of 75 µg/m3 as a daily mean.

2.4 Local air quality review and assessment 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 periodically to review air quality in their area and to assess the present and likely future air quality against the objectives defined in Regulations. Where a local authority anticipates an objective is expected to be breached within their district, they must designate an Air Quality Management Area (AQMA) and develop an action plan to improve pollution levels. Under the LAQM regime, a local authority is

5 Horizontal Guidance Note H1 Environmental Risk Assessment (Annex F), Environment Agency, April 2010



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responsible for regular review and assessment of local air quality, reports on which are published following public consultation and review by DEFRA.

Rother District Council’s latest review and assessment of air quality is described in the 2010 Annual Progress Report6. No AQMAs have been declared within the borough. Hastings Borough Council declared an AQMA in 2004 related to exceedences of the 24-hour objective for PM10 on Bexhill Road.

2.5 Monitoring data The closest automatic air quality monitoring stations (CMS) which are part of the Sussex Air Quality Network and in proximity to the WTW site are Hastings Fresh Fields, Hastings Bulverhythe, and Rother De La Warr. These sites are all classified as “roadside” however, the Fresh Fields station is on a rural road in close proximity to the WTW facility and hence is considered relevant to the study. Table 2.2 shows the air quality monitoring data for the years 2009 to 2011 for these sites (note that 2011 data for Fresh Fields is partial as the site was closed on 2nd April).

The Lullington Heath rural background station in Wealden, part of the national automatic monitoring network managed by DEFRA, is considered to be most representative of conditions around Bexhill and Hastings WTW site. The data for this site are presented in Table 2.2 and show that background NO2 is well below the annual mean AQS objective for this pollutant.

There were no exceedences of the hourly standard of 200 µg/m3 at either the Fresh Fields or Lullington CMS in the last three years.

The 2012 Update and Screening Assessment report for Rother District Council reports diffusion tube monitoring data for the year of 2011. Table 2.2 shows the results for the two urban background monitoring locations nearest to the WTW site.

Table 2.2 - Nitrogen Dioxide Concentrations in Study Area, µg/m 3

Location Grid reference

Distance/ direction from site

Site type 2009 2010 2011

Fresh Fields CMS

577036 108726

800 m SE Roadside 15.9 17.8 19.7*

Lullington Heath CMS

553800 101600

24 km W Rural 10.4 10.2 7.5

Hillside Road DT

574004, 108238

2.85 km SW Urban Background

- - 20.3

Downlands Avenue DT

573482, 107804

3.52 km SW Urban Background

- - 19.6

* three month average

2.6 Background maps Estimates of background pollutant concentrations in the UK are available from the DEFRA local air quality pages7. The background estimates, which are a combination of measured and modelled data, are available for each one kilometre grid square throughout the UK for a base year of 2008 and future years up to 2020. Updated estimates using monitoring and meteorological

6 http://www.iwight.com/living_here/environment/environmental_health/environmental_protection/air_quality/3progress.asp 7 http://laqm.defra.gov.uk/review-and-assessment/tools/background-maps.html



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data for the year 2010 are also now available for use; these contain the most recent information for vehicle derived oxides of nitrogen.

Annual background concentrations for the year 2012 (taken from the revised maps for NOx and NO2) for the grid square containing the WTW (576500, 109500) are given in Table 2.3.

Table 2.3 - DEFRA Mapped Background Concentrations, µg/m 3

Substance Background Concentration

Oxides of nitrogen 14.32

Nitrogen dioxide 11.07

Carbon monoxide 115*

Notes

* Published value is 0.238 mg/m3 for 2001; adjusted to year 2010 by factor of 0.483

The mapped background concentration for nitrogen dioxide is very similar to the measurement made at Lullington Heath, as would be expected as both are background sites. The DEFRA estimated background concentrations given in Table 2.3 have been used in the assessment as they are considered to be representative of conditions around the WTW.

2.7 Pollutant deposition rates The Air Pollution Information System (APIS) site relevant critical load (SRCL) website8 contains estimates of background concentrations and deposition rates for use in ecological assessments. These concentrations are a three year period average (2006 to 2008) for the relevant 5 by 5 kilometre areas. In addition, background rates of nitrogen and acid deposition have been downloaded for the main habitat types at each ecological site. The data for the grid square covering the ecological sites considered in this assessment are presented in Table 2.4.

Table 2.4 - Background Concentrations and Depositio n Rates at Ecological Sites

Grid reference Oxides of nitrogen,

µg/m 3

Nitrogen deposition

kg N/ha/year

Acid deposition keq/ha/year

12.6 (arable)

1.22 (N: 0.9, S: 0.32)

575000, 105000 17.1 25.62

(woodland) 2.21

(N: 1.83 , S: 0.38)

8 http://www.apisdev.ceh.ac.uk/, accessed 10/10/2012



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3. Methodology 3.1 Dispersion modelling

The dispersion modelling of emissions from the CHP plant was carried out using the United States Environmental Protection Agency (US EPA) model AERMOD PRIME version 120609. This model is the result of many years development by the US EPA and the American Meteorological Society. It has been developed as a regulatory model that incorporates the current understanding of atmospheric physical processes. This 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.

AERMOD simulates essential atmospheric physical processes and provides refined concentration estimates 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 parameters;

• highly developed dispersion formulations that incorporate current planetary boundary layer 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.

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 PRIME, using parameters calculated by the Building Parameter Input Program (BPIP), distinguish this model from earlier versions of AERMOD, which used simpler procedures to address downwash.

3.1.1 Meteorological data An appropriate meteorological station with adequate records in the format required for the dispersion modelling study is Herstmonceux. This station is located at 50.9 N, 0.317E and is approximately 9 kilometres to the north west of the application site, which is at 50.857 N, 0.508 E.

Hourly sequential meteorological data for the five-year period 2005 to 2009 from Herstmonceux were used in the dispersion modelling. The meteorological data file contains over 43,000 hourly records, and is quite adequate to characterise local meteorology in terms of both extreme events and long-term average conditions.

AERMET, the meteorological pre-processor, was used to process the data and estimate the necessary boundary layer10 parameters for dispersion calculations in AERMOD. The data were

9 AERMOD software provided by Trinity Consultants Inc, http://www.breeze-software.com/ 10 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. From these inputs AERMET calculates severable boundary layer



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processed to take account of the location and surroundings of the meteorological station and of the modelled facility. These parameters, together with observed near-surface wind and temperature data, were used to model how pollutants disperse in the atmosphere.

The processed meteorological data were used to generate a five-year frequency distribution of wind speed and direction. The data are shown in Table 3.1 and presented as a wind rose diagram in Figure 3.1.

Table 3.1 - Relative Frequency Distribution of Wind Speed and Direction, (%)

Direction Speed, m/s

Bearing Degree ≤≤≤≤1.54 1.54 to

3.09 3.09 to

5.14 5.14 to

8.23 8.23 to 10.80 >>>>10.80 Total %

N 0.0 1.81 1.15 1.73 0.28 0.00 0.00 4.98

NNE 22.5 2.54 1.77 2.40 0.23 0.00 0.00 6.94

NE 45.0 3.66 1.92 2.20 0.18 0.00 0.00 7.96

ENE 67.5 2.87 2.26 2.28 0.23 0.00 0.00 7.64

E 90.0 1.11 0.85 0.95 0.08 0.00 0.00 2.98

ESE 112.5 0.67 0.40 0.48 0.00 0.00 0.00 1.55

SE 135.0 0.83 0.54 0.20 0.00 0.00 0.00 1.57

SSE 157.5 1.12 0.92 0.46 0.08 0.00 0.00 2.58

S 180.0 1.32 1.32 1.25 0.21 0.01 0.00 4.11

SSW 202.5 1.35 1.02 1.66 0.93 0.18 0.02 5.16

SW 225.0 1.98 1.78 4.54 3.10 0.52 0.05 11.97

WSW 247.5 2.70 2.85 6.73 2.39 0.10 0.01 14.78

W 270.0 2.90 3.02 4.15 1.29 0.08 0.00 11.44

WNW 292.5 2.24 1.49 1.01 0.16 0.00 0.00 4.90

NW 315.0 1.52 1.96 1.31 0.17 0.00 0.00 4.95

NNW 337.5 1.39 1.06 1.28 0.23 0.00 0.00 3.97

Total % 30.01 24.27 32.63 9.56 0.92 0.09 97.49

Calms 1.44

Missing 1.07

Total % 100.00

Were the wind to be equally distributed from each directional sector, the frequency would be almost 6% in each sector excluding calms.

It is evident from the data for these years that there is a pronounced prevailing wind from the west south west and the two adjoining sectors. Winds from these three sectors between the west and the south west occur for over 38% of the time, more than twice as frequent as the evenly

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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distributed case. There is a secondary prevailing wind from the north east and adjoining sectors; the wind frequency from these three sectors is 22.5%. There are fewer high wind speeds from this secondary prevailing wind sector compared to the prevailing wind direction, but relatively more low speed winds. Winds from the north north west sector are relatively infrequent, as are those from the south east and adjoining sectors.

Figure 3.1 - Wind Rose Diagram for Herstmonceux, 20 05 to 2009

The meteorological data pre-processor AERMET was used to create the site-specific surface and upper air hourly sequential data files required by AERMOD. The AERMET processing takes account of the location and surroundings of the meteorological station and of the modelled facility.

In accordance with the latest US EPA guidance, the near-field land use within a one kilometre radius of the site was evaluated to determine the surface roughness length11. Land uses may be specified by directional sector; in this case two sectors were designated as either predominantly urban or cultivated land. The Bowen ratio12 and albedo13 were determined by the land use categories within the far-field, a 10 by 10 kilometre square. A determination of the percentages of each type of land use was made based on inspection of maps and aerial photographs. The land use proportions are simply averaged over the area and are independent of distance or direction from the site. The land use percentages within this area were: water (37%), deciduous woodland (9%), cultivated (22%) urban (32%).

11 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. 12 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. 13 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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The pre-processor generates appropriate default annual average values for these parameters based on the land use information. The values used are presented in Table 3.2.

Table 3.2 - Surface Characteristics

Direction Degrees

Land Type Albedo Bowen Ratio Roughness Length, m

208 - 238 Urban 0.1992 0.93 1.0000

238 - 208 Cultivated Land 0.1992 0.93 0.0725

3.1.2 Receptors Ground level concentrations were modelled using nested Cartesian receptor grids covering wide and local areas. A 50 metre resolution grid over a wide area was used in combination with a local grid of 25 metre resolution. The high-resolution local grid improves the spatial resolution of the model results in those areas subject to the highest concentrations close to the site boundary. Receptors were set at 25 m intervals on the site boundary. Discrete receptors were also specified for certain nearby properties where exposure of the public may occur, and designated ecological sites.

The model was set up to report the maximum hourly, eight hourly and annual average concentrations found at each receptor. As AERMOD was run with a five-year meteorological data file the maximum hourly result at each receptor is therefore the highest in over 43,000 hours processed. The results presented thus robustly characterise the effects of the plant emissions on ambient concentrations during the most extreme meteorological events and those due to long-term average meteorological conditions.

Terrain heights for all receptors were imported into the model from Ordnance Survey digital elevation files.

3.1.3 Building downwash Buildings close to point source plume discharges that are more than 40% of the stack height may potentially cause downwash effects. The BPIP programme was used to calculate for each wind sector the direction specific building downwash parameters to be used by AERMOD PRIME in the dispersion calculations.

The structures included in the model are shown in Figure 3.2; the view is from the north west. Building heights were estimated from measurements taken during a site visit.

The large building in the left of Figure 3.2 below is the main site building. On the right hand side of the figure, i.e. towards the north of the site, there are three sludge digester tanks. The containerised CHP which is the subject of this study is the small rectangular structure shown in the centre of the figure closest to the digester tanks; the light blue CHP stack is evident on this structure. The CHP is located close to two other small structures which are redundant generator units.



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Figure 3.2 - Stack and Building Layout 3D Schematic

3.2 Emissions to air For the purpose of this assessment it is assumed that the engine will operate continuously at full load throughout the year, ignoring temporary shut-down periods for maintenance. It is not planned routinely to operate the boiler on biogas; overall usage is anticipated to be less than ten percent of the time. For this reason, the boiler has not been included in the modelling study.

3.2.1 MTU spark ignition engines The MTU 8V4000L62FB gas engine is an eight cylinder turbocharged spark ignition engine of 38.13 litres displacement. It has a thermal input of 1.838 kW and an electrical output of 772 kW. The engine specification quotes an oxides of nitrogen emission concentration of 500 mg/Nm3 and a carbon monoxide emission concentration of 739 mg/Nm3, at reference conditions and 5% oxygen, dry basis. Technical information from the manufacturer was used to derive the input data for the modelling study. The discharge velocity was calculated from the actual wet flow rate and the stack diameter as advised by Cogenco Ltd.

The emissions data are summarised in Table 3.3 together with the other stack parameters. The stack height was set at the maximum permitted height of 15 metres due to its proximity to (within 20 metres of) the main site building which is itself 13 metres high. The primary digester tanks are slightly lower at 14 metres.



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Table 3.3 - Engine Stack Emissions Characteristics

Parameter Value

OS grid reference 576617,109397

Stack height, m 15.0

Stack diameter, m 0.250

Flue gas discharge temperature, K 433.15

Discharge velocity, m/s 29.1

Actual discharge flow rate, am3/s 1.427

Normalised flow rate, 5% O2 dry basis, Nm3/s 0.606

Oxygen content of flue gas, % vol 8.8

Moisture content of flue gas, % 11.2

Oxides of nitrogen (as NO2) emission rate, g/s 0.303

Carbon monoxide emission rate, g/s 0.448

3.3 Modelled receptors Human health

The nearest receptors where long-term exposure to pollutant emissions from the facility may occur are to the south west at Filsham House and to the south at Pebsham Farm House. The residential area of Pebsham is further to the south west. There are no sensitive human health receptors to the north or east but there are residential properties over a kilometre to the south east of the CHP stack on Bexhill Road.

Selected representative receptors (1 to 4) used in the modelling are shown in Table 3.4 and in Figure 3.3 below. Short-term exposure of members of the public may also occur on the playing fields to the south east.

Table 3.4 - Human Health Receptor Locations

Grid Reference Distance/direction Ref Receptor

Easting, m Northing, m from CHP

1 Little Worsham Farm 576035 109511 590 m WNW

2 Filsham House 576311 109163 390 m SW

3 Pebsham Farm House 576539 109029 380 m S

4 382 Bexhill Road 577300 108528 1100 m SE



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Figure 3.3 - Locations of Nearest Sensitive Receptor s

576000 576500 577000 577500

Eastings, m

108500

109000

109500

110000

Nor

thin

gs, m

1

23

4

A

B

C

D EF

G

BX_receptors 09/10/12

© Crown copyright, All rights reserved. 2012 Licence number 0100031673

Ecological

An assessment of the effect of pollutant deposition is required for designated ecological sites, in accordance with Environment Agency Horizontal Guidance Note H1 (Annex F), as these sites may contain species that are sensitive to air pollution.

The H1 guidance requires that European and internationally designated sites within a 10 kilometre radius and nationally designated sites within a two kilometre are considered. Given the very small size of the CHP engine, and the area of influence that the exhaust emissions will have, only sites within one kilometre are required by the Environment Agency to be assessed for waste operations. The relevant sites are summarised in Table 3.5. Locations A to G represent the ecological sites within one kilometre of the WTW that were included in the modelling study as discrete receptors. These receptors are shown above in Figure 3.3.



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Table 3.5 - Ecological Sites within 1 km Radius from Stack

ID Site name Site type Location Description

A Pebsham Wood Ancient woodland 130 m to WSW (closest point

576492,109354)

Ancient woodland

B Roundacre Wood Ancient woodland 940 m to WSW (closest point

575729,109078)

Ancient woodland

C Combe Wood Ancient woodland 760 m to WNW (closest point

575877,109588)

Ancient woodland

D, E Combe Haven SSSI (Unit 4) 360 m to N (closest point D 576699,109749)

Neutral grassland - lowland

F, G Combe Haven / Filsham Reed Bed

SSSI (Unit 5) / LNR

1000m to NE (closest point F 577538,109790)

Fen/marsh – lowland Reed bed

3.4 Interpretation of results

3.4.1 Human health assessment The modelled long-term increments to concentrations (“Process Contributions”, PC) may be added to the background annual mean concentration to derive a “Predicted Environmental Concentration” (PEC). For short-term concentrations this value may be obtained by adding the PC to twice the background annual mean concentration. This approach is described in the Environment Agency Horizontal Guidance Note H1 (Annex F).

In order for an assessment to be made against the air quality objective for nitrogen dioxide, an additional step is required to convert the oxides of nitrogen, principally in the form of NO, to nitrogen dioxide.

The oxides of nitrogen emissions from engines are almost entirely in the form of nitrogen monoxide. 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 local receptors depicted 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 local study area.

For the short travel distances between the point of release from the CHP stack and the nearest sensitive receptors, a conversion factor of up to 20% is regarded as being an appropriately conservative assumption for short term averaging periods. Studies by Janssen14 of oxidation rates in power station plumes found conversions below 20% for distances of up to at least two kilometres from the source, other than during high ozone episodes. Given the lower rate of oxidation at night time, it appears reasonable to assume that long-term average conversion factors would in fact be lower than the short-term daytime factor.

14 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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Environment Agency guidance15 produced by the 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 the proposed approach is termed a “worse case scenario” sic and it is recommended that conversion ratios of 35% for short-term and 70% for long-term average concentrations are considered. The modelled long-term PC may then be added to the background annual mean concentration. The guidance does not present any empirical basis for this procedure, nor indeed is there any evidence to suggest that conversion ratios are higher for long-term averaging periods.

The third stage does advise that operators may use lower conversion ratios if justified on a case specific basis.

The second phase ratios of 35% for short-term and 70% for long-term average concentrations have been applied below.

3.4.2 Ecological assessment An assessment of the effect of the facility emissions at nature conservation sites was undertaken to assess whether the objective for oxides of nitrogen for the protection of vegetation of 30 µg/m3 annual mean would be exceeded. In accordance with H1 guidance, concentrations of less than 1% of this critical level are considered to be insignificant and no further assessment need be undertaken.

For the ecological sites where the modelled increment to oxides of nitrogen concentrations are found to be more than 1% of the objective i.e. over 0.3 µg/m3, the dry nitrogen deposition rate may be calculated, using Equation 1 below.

Equation 1 – Calculation of Nitrogen Deposition

Deposition rate (kg N/ha/yr) = NOx conc. * deposition velocity(a) * 14/46 * 31557600/100000 (a) taken from AQTAG 0616 = 0.0015 m/s, for grassland, 0.003 for woodland.

The modelled increment to the nitrogen deposition rate is then added to the background rate of nitrogen deposition (taken from the APIS SRCL website17). The total rate is compared with the relevant UN ECE critical load for the habitat of interest. Ranges for critical loads rather than fixed values are used to allow for natural variation, uncertainties about deposition values and temporal variability of available data.

An assessment is also required of the acid deposition rate for comparison with critical loads for acid deposition. This value may be calculated using the conversion rate for nitrogen deposition specified in AQTAG06 guidance.

Where the calculated nitrogen or acid deposition rate increases by less than 1% of the critical load or background rate, Natural England advises that this can be interpreted as being not significant. However, it should be noted that an exceedence of this criterion would not indicate that the increment is either significant or unacceptable, merely that a more detailed interpretation of the data is required.

For ancient woodland, local and national nature reserves and non-statutory local wildlife sites the PC is compared with 100% of the relevant EAL and an estimation of the PEC is not required. This

15 http://www.environment-agency.gov.uk/static/documents/Business/noxno2conv2005_1233043.pdf 16 Environment Agency Air Quality Technical Advisory Group - Technical Guidance on detailed modelling approach for an appropriate assessment for emissions to air, AQTAG 06. April 2010. Version 10. 17 www.apis.ac.uk – critical loads obtained on 22/08/12



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is in accordance with the latest Environment Agency guidance for the assessment of nature sites (published in Operational Instruction 66_12, issued May 2012).



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4. Results 4.1 Oxides of Nitrogen

4.1.1 Long-term average results The maximum modelled annual average oxides of nitrogen concentrations are shown graphically in Figure 4.1. Each value plotted is the five year annual average concentration modelled for each receptor point. The small red dot located to the north east of the grey buildings denotes the stack.

Figure 4.1 - Maximum Annual Average Oxides of Nitro gen Concentrations, µg/m 3

576000 576500 577000

Eastings, m

108500

109000

109500

110000

Nor

thin

gs, m

BX99_NX_A 09/10/12


The contour plot demonstrates the dispersion pattern of off-site long-term average concentrations, reflecting the windrose as shown in Figure 3.1. The effects of the engine emissions are quite localised, the highest increments to ground level concentrations occurring on the site boundary to the north east of the stack. The general pattern of dispersion extends furthest to the south west



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reflecting the relatively high frequency of low wind speeds from the north east. The prevailing west south westerly winds are also reflected in the higher concentrations to the east north east of the stack. Increments to ground level concentrations fall to 1 µg/m3 approximately four hundred metres or less of the point of release.

Human health assessment

The maximum modelled increments to annual average oxides of nitrogen concentrations (i.e. the PCs) at each sensitive receptor are listed in the third column of Table 4.1. The highest modelled increment of 1.17 µg/m3 is found at the Filsham House receptor to the south west of the CHP. Applying the 70% conversion ratio for the AQMAU “worse case scenario”, this is equivalent to 0.8 µg/m3 as nitrogen dioxide, or 2.0% of the annual mean AQS objective. The PEC for nitrogen dioxide, which includes a background contribution of 11.1 µg/m3, is shown in the penultimate column of Table 4.1. The PEC at Filsham House is estimated to be 11.9 µg/m3, less than a third of the AQS objective.

Table 4.1 - Annual Average NO x Concentrations and Estimated Total NO 2 Concentrations

Ref Receptor PC NOx

µg/m 3

PC NO2,

µg/m 3

PC as % of

EAL

PEC NO2

µg/m 3

PEC as % of

EAL

1 Little Worsham Farm 0.07 0.05 0.1 11.1 27.8

2 Filsham House 1.17 0.82 2.0 11.9 29.7

3 Pebsham Farm House 0.51 0.35 0.9 11.4 28.6

4 382 Bexhill Road 0.05 0.04 0.1 11.1 27.8

The estimated total nitrogen dioxide concentrations using this conservative procedure demonstrate that at all sensitive receptors where there may be a relevant long-term exposure, concentrations are well below the AQS objective. The increments due to the facility emissions therefore do not affect the achievement of this criterion.

Ecological assessment

The modelled increments to concentrations of oxides of nitrogen at the closest ecological sites are summarised in Table 4.2. In accordance with current Environment Agency guidance for the assessment of nature sites, the calculation of PEC is only required at national or European sites, and so is presented in columns 5 and 6 for receptors D to G only.



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Table 4.2 - Annual Average NO x Concentrations at Ecological Sites

Ref Receptor PC NOx

µg/m 3

PC as % of

EAL

PEC NOx

µg/m 3

PEC as % of

EAL

A Pebsham Wood 2.68 8.9 - -

B Roundacre Wood 0.30 1.0 - -

C Combe Wood 0.04 0.1 - -

D Combe Haven 0.37 1.2 17.5 58

E Combe Haven 0.42 1.4 17.5 58

F Combe Haven / Filsham Reed Bed 0.30 1.0 17.4 58

G Combe Haven / Filsham Reed Bed 0.21 0.7 17.3 58

Table 4.2 shows that at receptor A, the Pebsham Wood ancient woodland, at the point where it lies adjacent to the WTW site boundary, the PC for oxides of nitrogen is 2.68 µg/m3 or 8.9% of the objective for vegetation of 30 µg/m3. This increment is much less than 100% of the critical level and can be considered insignificant. The increments at the other ancient woodland sites (receptors B and C) are an order of magnitude or more lower.

The PCs modelled at the Combe Haven SSSI (receptors D to G, including the Filsham Reed Bed LNR) are an extremely small fraction of the EAL at 1.4% or less. Receptor E is subject to the highest increment of 0.42 µg/m3. The PEC at this location is less than two thirds of the critical level for vegetation and is dominated by the background contribution of 17.1 µg/m3. As is evident in Figure 4.1, the NOx concentrations decrease rapidly with increasing distance from the site and hence concentrations will be considerably lower across the designated area as a whole.

The modelled increments at all sites would not affect the achievement of the vegetation objective and the effect of the facility is considered to be insignificant.

Assessment of deposition

The results for nitrogen and acid deposition at each of the ecological sites considered in the assessment are presented in Table 4.3. In accordance with Environment Agency guidance, assessment of the PEC has only been undertaken at national or European sites.

The highest modelled PC at the Combe Haven SSSI (Receptor E, in Unit 4) is equivalent to a nitrogen deposition rate of 0.061 kg/ha/yr at Unit 4; this is an area of neutral grassland for which no critical loads are specified on the APIS SRCL website. A comparison may be made with the critical load range for hay meadows of 20 to 30 kg/ha/yr; the PC is a negligible fraction of this range, contributing just 0.2% to 0.3%. The highest nitrogen deposition rate at Combe Haven SSSI where it is coincident with the Filsham Reed Bed LNR (Receptor F, in Unit 5) is 0.043 kg/ha/yr; the critical load range for this habitat is 10 to 15 kg/ha/yr (mires and poor fens). The modelled increment is equivalent to 0.3% to 0.4% of the upper and lower extents of this range and is considered to be negligible. On this basis there would be no adverse effect of the facility emissions at any location within the designated site. An assessment of the PEC is not required.

The maximum nitrogen-derived acid deposition rate at any point within the SSSI is estimated to be 0.004 keq/ha/yr at Receptor E within Unit 4, which is equivalent to 0.4% of the critical load for acid grassland of 1.143 keq/ha/yr (as the MinCLMaxN). On the basis of these negligible contributions, there would be no material effect on acid deposition rates and soil quality within the designated



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site and the conservation objective would not be compromised. An assessment of the PEC is not required.

At the ancient woodland sites, the maximum contribution to a critical load for nitrogen deposition occurs at Pebsham Wood (Receptor A), where the PC is equal to around 4 to 8% of the relevant critical load range of 10 to 20 kg N/ha/year. The maximum contribution to the acid critical load for woodlands is less than 2% at Pebsham Wood. It is evident from Table 4.3 that the corresponding results for Roundacre Wood (Receptor B) and Combe Wood (Receptor C) are considerably lower. The results at these locally important sites are considered to be negligible as the increments are just a small percentage of the EAL.

Table 4.3 - Nitrogen and Acid Deposition Rates and Comparison with Critical Loads

Site C

N dep

Critical load

PC as % of

CL C

acid dep

MinCL MaxN

PC as % of

CL

kg N/ha/y

kg N/ha/y

% keq/ha/y keq/ha/y %

A 0.772 10 - 20 3.9 - 7.7 0.055 2.94 1.9

B 0.086 10 - 20 0.4 - 0.9 0.006 2.94 0.2

C 0.012 10 - 20 0.06 - 0.12 0.001 2.94 <0.1

D 0.053 20 - 30 0.2 - 0.3 0.004 1.143 0.3

E 0.061 20 - 30 0.2 - 0.3 0.004 1.143 0.4

F 0.043 10 - 15 0.3 - 0.4 0.003 1.143 0.3

G 0.030 10 - 15 0.2 - 0.3 0.002 1.143 0.2

13.1.1 Short-term average results The modelled maximum hourly average oxides of nitrogen concentrations due to facility emissions are shown below Figure 4.2. Note that the value depicted at each receptor grid location is the highest hourly average concentration found in over 43,000 hours of meteorological data processed by the dispersion model.

The effects of the emissions on short-term concentrations are also relatively localised, the highest concentration occurring in an uninhabited location just beyond on the site boundary to the north north west of the stack. Concentrations decrease rapidly with increasing distance from the site.



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Figure 4.2 - Maximum Hourly Average Oxides of Nitro gen Concentrations, µg/m3

576000 576500 577000

Eastings, m

108500

109000

109500

110000

Nor

thin

gs, m

BX99_NX_H 10/10/12


Human health assessment

The AQMAU “worst case scenario” sic assumption of 35% conversion was used to estimate short-term incremental nitrogen dioxide concentrations to allow a comparison with the AQS objective, which allows for 18 exceedences of an hourly standard of 200 µg/m3.

The maximum modelled increments to hourly average oxides of nitrogen concentrations (i.e. the PCs) at each sensitive receptor are listed in the third column of Table 4.4. The highest modelled increment of 32 µg/m3 is found at Filsham House, to the south south west of the site boundary. Using conservative assumptions, this is equivalent to 11 µg/m3 as nitrogen dioxide, as shown in the fourth column of Table 4.4.



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Table 4.4 - Maximum Hourly NO x Concentrations and Estimated Total NO 2 Concentrations

Ref Receptor PC NOx

µg/m 3

PC NO2

µg/m 3

PC as % of

EAL

PEC NO2

µg/m 3

PEC as % of

EAL

1 Little Worsham Farm 17.6 6.2 3.1 28.3 14.2

2 Filsham House 31.6 11.1 5.5 33.2 16.6

3 Pebsham Farm House 19.4 6.8 3.4 28.9 14.5

4 382 Bexhill Road 5.7 2.0 1.0 24.2 12.1

The total nitrogen dioxide concentration (PEC) shown in the penultimate column of the above table was obtained by adding twice the mapped background nitrogen dioxide concentration of 11.07 µg/m3, to 35% of the oxides of nitrogen modelled increment. The result at Filsham House is 33 µg/m3, or one sixth of the AQS standard of 200 µg/m3.

At Little Worsham Farm, Pebsham Farm House and at Bexhill Road the nitrogen dioxide PCs are less than 10% of the criterion and hence are assessed to be insignificant.

The total nitrogen dioxide concentrations estimated using this conservative procedure demonstrate that at all residential receptors where there may be a relevant exposure over a short-term time period, concentrations are substantially below the hourly standard for nitrogen dioxide and would therefore not compromise meeting the AQS objective.

At the playing fields to the south east of the facility, hourly NOx concentrations are less than 18 µg/m3 i.e. lower than the result reported for Receptor 3 in Table 4.4. On this basis, short-term exposure at the playing fields would not be adversely affected as concentrations would remain well below the hourly standard.

Ecological assessment

The maximum increments to daily average oxides of nitrogen concentrations at the closest boundary of the ecological sites are summarised in Table 4.5.

Table 4.5 - Daily Average NO x Concentrations at Ecological Sites

Ref Receptor PC NOx µg/m 3

PC as % of EAL

A Pebsham Wood 29.6 40

B Roundacre Wood 4.5 6.0

C Combe Wood 2.0 2.6

D Combe Haven 6.1 8.1

E Combe Haven 2.8 3.7

F Combe Haven / Filsham Reed Bed 2.0 2.7

G Combe Haven / Filsham Reed Bed 2.2 2.9

The PCs are shown in the third column of Table 4.5, and as a percentage of the 75 µg/m3 daily mean EAL for the protection of vegetation and ecosystems in the fourth column. At the ancient



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woodland sites (Receptors A to C) the PCs are insignificant as they are less than 100% of the EAL. At the Combe Haven SSSI (Receptors D to G), the PCs are insignificant as they are less than 10% of the short-term EAL.

13.2 Carbon monoxide The maximum incremental hourly and eight-hourly concentrations for carbon monoxide at nearby residential receptors are shown in Table 4.6.

Table 4.6 - Maximum Hourly and 8-hourly Carbon Mono xide Concentrations

Ref Receptor PC Hourly Mean µg/m 3

PC as % of

EAL

PC 8-hourly Mean µg/m 3

PC as % of

EAL

1 Little Worsham Farm 26 <0.1 6.6 <0.1

2 Filsham House 47 0.16 29 0.29

3 Pebsham Farm House 29 0.10 17 0.17

4 382 Bexhill Road 8.5 <0.1 3.4 <0.1

The highest maximum modelled carbon monoxide concentrations were found at Filsham House where the hourly average is 47 µg/m3 and the eight-hourly average is 29 µg/m3. This maximum hourly average is less than 0.2% of the short-term EAL of 30,000 µg/m3 and the highest maximum eight-hourly average is less than 0.3% of the AQS standard of 10,000 µg/m3.

These results for carbon monoxide are substantially below the respective criteria and are an order of magnitude below the 10% threshold described in H1, and are therefore considered to be negligible. No further calculation of the PEC has been undertaken.



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14. Conclusions An air dispersion modelling study has been carried out to supplement the Environmental Permit application for the biogas-fuelled CHP plant at Bexhill and Hastings WTW. The study addresses the operation of the Cogenco-packaged MTU 8V4000L62FB engine on biogas, used to generate electricity on site.

The results demonstrate that the stack emissions of oxides of nitrogen and carbon monoxide from the biogas-fuelled CHP will not affect the achievement of the relevant air quality strategy objectives for either human health or vegetation.

At the nearest residential receptor Filsham House, approximately 400 metres to the south west of the site boundary, the estimated total annual mean nitrogen dioxide concentration, including the existing background concentration, was shown to remain well below (less than a third of) the AQS objective. The highest increment to nitrogen dioxide hourly concentrations was also found at Filsham House, where the total including background was shown to be less than a sixth of the AQS objective.

The effects of carbon monoxide emissions are negligible as at most they contribute less than one percent to the short-term EALs. The maximum increments are an order of magnitude below the H1 threshold at which process contributions may be considered to be negligible.

The effects of the facility on the nearest ecological sites are considered to be insignificant in terms of concentrations of oxides of nitrogen, and nitrogen and acid deposition. In particular, the achievement of the air quality objective for vegetation and the critical loads for deposition at the nearby Combe Haven SSSI will not be affected.

The assessment was based on a number of conservative assumptions. The engine was modelled as if operating continuously throughout the year at full load. The engine emission rates used for oxides of nitrogen and carbon monoxide were based upon emission concentrations as specified in the manufacturer’s data sheet. The AQMAU “worse case” assumptions regarding conversion of oxides of nitrogen to nitrogen dioxide were applied.

The conclusions drawn are therefore very robust. The model results are all below the relevant criteria. The uncertainty in the modelling is considered to be small in comparison with the overall scale of the safety factors built into the above assumptions.



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Southern Water EP Application Bexhill and Hastings …...5103447/Southern CHP Bexhill and Hastings...

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