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MSE Air Quality Assessment (Including Odour) for Proposed Change of Use Development

Contents

1 Introduction ............................................................................................................................................ 1 2 Purpose of this Report ....................................................................................................................... 1 3 Baseline Description ........................................................................................................................... 1 4 Emissions to Atmosphere from the Proposed Development ................................................. 3 5 Legislation and Policy......................................................................................................................... 4 6 Atmospheric Dispersion Modelling of Emissions from the Gas Engines ........................... 5 7 Atmospheric Dispersion Modelling of Odour Release ............................................................. 9 8 Conclusions ......................................................................................................................................... 11

Tables Table 1 Market Harborough Automatic Monitoring Station, 2004 & 2005........................................2 Table 2 Emission Source Parameters ..............................................................................................6 Table 3 Modelled Emissions Data ....................................................................................................6 Table 5 Maximum Predicted Environmental Concentration of Modelled Pollutants.........................8

Figures Figure 1 Location of Proposed Development ....................................................................................1 Figure 2 Annual Average NO2 Predicted Environmental Concentration Arising from Emissions from

the Two Gas Engines ..........................................................................................................8 Figure 3 Environment Agency Guidance Note H4 Odour Assessment Criteria ..............................10 Figure 4 Hourly Average 98th Percentile Odour Ground-Level Concentration (Odour Units) ........11

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1 Introduction 1.1 Chelveston Renewable Energy Ltd (CREL) proposes to build a Biomass Plant to

generate electricity for export to the national grid, using engines powered by fuel

gas from an associated anaerobic digestion process. The generators will be

housed within existing buildings on a site formerly occupied by the Ministry of

Defence (MOD) as part of a radio listening post, and formerly a USAF air base.

In addition, the development will include a new building where waste will be

received on site and processed for treatment in the anaerobic digestion process.

2 Purpose of this Report 2.1 This report describes the current state of air quality within the area surrounding

the proposed Biomass Plant, and gives an indication of the potential impact of

emissions to atmosphere on air pollutant concentrations locally. Consideration is

also given to the potential impact of fugitive odour release within the surrounding

area.

3 Baseline Description 3.1 The location of the proposed Biomass Plant is on former MOD land to the south-

west of the village of Chelveston, Bedfordshire (See Figure 1).

Figure 1 Location of Proposed Development

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3.2 The site is in a rural location and is currently used for agricultural purposes.

There are no industrial activities within approximately 10 kilometres of the site,

and the nearest major road systems are the A6 to the west and the A45 to the

north; both of which are ~5 km away.

3.3 The site is in an elevated position located on a “plateau” that overlooks the

surrounding area. The “plateau” is ~30 metres above the surrounding area.

Accordingly, the site is well “ventilated” by the prevailing south-westerly winds

and is exposed to pollutant concentrations that may be categorised as “Rural

Background”.

Existing Air Quality

3.4 Estimates of existing background air quality data for the proposed site were

obtained from the National Air Quality Archive. The proposed development site is

considered to be a rural background site in terms of air quality designation. The

nearest rural background site in the National Network of air quality monitoring

stations operated by DEFRA is at Market Harborough, (NGR 483300, 295900)

situated ~32 km north-west of Chelveston. Measured data for nitrogen dioxide

(NO2), oxides of nitrogen (NOX) and ozone (O3) from this site were used in the

atmospheric dispersion modelling study discussed later in this report.

3.5 Carbon monoxide (CO), oxides of nitrogen (NOX) and ozone (O3) are also

monitored at Market Harborough and the data for 2004 and 2005 are presented

in Table 1. The data presented are the annual average of the average monthly

measured values (i.e. the monthly average value for January, plus the monthly

average value for February, plus… the monthly average value for December

over twelve months, divided by twelve).

Table 1 Market Harborough Automatic Monitoring Station, 2004 & 2005

Year* Carbon

Monoxide (mg m-3)

Nitric Oxide

(µg m-3)

Nitrogen Dioxide (µg m-3)

Nitrogen Oxides as Nitrogen Dioxide

(µg m-3)

Ozone (µg m-3)

2004 0.28 1.6 12.8 14.8 53.1

2005 0.24 1.4 12.6 14.1 47.1

2008* - - 11.7* - -

* Projected forward from 2005 data using the DEFRA “Year Adjustment Calculator”

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3.6 The measured data for the Market Harborough monitoring station indicate that

the 2005 annual average NO2 concentration was 12.6 µg m-3, equivalent to

~32% of the 40 µg m-3 objective limit. Using the DEFRA Year Adjustment

Calculator, this value was projected forward to 2008 to give an estimated

background NO2 concentration for the area of 11.7 µg m-3. This value was used

in the assessment for NO2.

Air Quality Management Areas

3.7 Local Authorities are required to undertake a statutory review of air quality within

their areas and if there is a risk of exceeding an Air Quality Standard or Objective

Value then they are required to declare an Air Quality Management Area

(AQMA). The Local Authorities closest to the development site are Bedford

Borough Council and East Northamptonshire Borough Council.

3.8 East Northamptonshire Borough Council has undertaken an assessment of the

air quality within the Borough and concluded that there was no requirement to

declare an AQMA.

3.9 Bedford Borough Council has declared four AQMAs. Three of these were located

within the town with the fourth is situated in Great Barford, to the east of Bedford.

The AQMAs are located approximately 20 km from the proposed development

site and are considered to be too far away to be directly affected significantly by

emissions from the proposed development.

3.10 There are no odour sources associated with the existing activities undertaken on

the development site that may cause an off-site impact, other than general

agricultural odours associated with the management of sheep and cattle. The

nearest receptors (dwellings) are situated approximately 2 km from the centre of

the proposed Biomass Plant development.

4 Emissions to Atmosphere from the Proposed Development 4.1 The proposed Biomass Plant development comprises an anaerobic digestion

(AD) plant plus associated gas engines. Some of the biomass materials to be

processed may be odorous and odour management is proposed using a bio-bed

filter. Consideration has been given to the potential impact on local air quality of

release to atmosphere of pollutants and odour from the above processes.

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Emissions from Gas Engines

4.2 Biogas generated by the AD plant will be combusted in two dedicated gas

engines capable of generating up to ~1.5 MWe of electricity. Emissions from the

combustion of the biogas will be discharged to atmosphere via dedicated stacks.

Emissions from Anaerobic Digestion Liquids Storage

4.3 Liquid fertiliser from the AD Plant will be stored on site in enclosed tanks prior to

land spreading when the prevailing meteorology allows. As the tanks will be fully

enclosed, the potential of odorous releases is considered to be negligible and no

assessment has been carried out of this potential source.

Odorous Releases from Biomass Storage

4.4 Biomass materials delivered to site for treatment in the AD plant will be stored

temporarily in the main building prior to transfer to the digesters. The building will

be completely enclosed and will operate under negative pressure in order to

prevent fugitive release of odour. Potentially odorous air will be drawn

continuously from the main building by an induced draft (ID) fan and vented to

atmosphere via a wood chip bio-filter. Consideration has been given to the

potential impact of fugitive odour release from the bio-filter.

5 Legislation and Policy National Air Quality Strategy

5.1 In 2001 the UK Government and devolved administrations for Scotland, Wales

and Northern Ireland published the Air Quality Strategy (AQS). This strategy set

air quality standards and objectives for eight key air pollutants that must be

achieved between 2003 and 2008. Local Authorities are charged with the task of

working towards the objectives for seven of these pollutants. The standards and

objectives are subject to regular review taking into account the latest information

on the health effects of air pollution as well as technical and policy

developments.

5.2 The Strategy’s objectives for particles (PM10), benzene and carbon monoxide

were reviewed in 2000/01, in particular, to take account of the latest health

evidence and advice on the impact of particles on people’s health and of

developments in Europe. Following this review, a consultation paper was

published by the UK Government and devolved administrations setting out

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proposals to introduce tighter objectives for those pollutants and to introduce, for

the first time, an objective for PAHs.

5.3 In England, the AQS is translated in The Air Quality (England) Regulations (2000)

and subsequent amendments. For those objectives which are included in

regulations for the purposes of local air quality management (LAQM), each Local

Authority is required to work towards the achievement of the objectives in their

area.

5.4 The air quality standards and objectives defined within the original 2001 AQS and

as amended following consultation in 2003 are presented in Appendix 1. These

standards were used as the benchmark against which estimates of air quality

impacts were made. For the emissions from the gas engines, the pollutants

considered were those covered by the relevant Environment Agency guidance

for combustion processes subject to regulation.

Odour Regulatory Controls

5.5 Statutory nuisance legislation is covered by Part III of the Environmental

Protection Act 1990 and includes issues relating to odour. Odour issues are

regulated by the Local Authority, however PPC processes regulated by the

Environment Agency incorporate odour within the permitted emission inventory

resulting in odour regulation shifting from the remit of the Local Authority to the

Environment Agency. The Anaerobic Digestion process will most likely require a

PPC Permit prior to operation and odour management will form an integral part

of the operation of the plant.

5.6 The Environment Agency has developed guidance for assessing and controlling

offensive odours and published PPC Horizontal Guidance Note H4. This

guidance applies to all PPC Permitted processes. The principles of odour

management as specified in Guidance Note H4 will be applied to the operation of

the Biomass Plant and its associated treatment processes.

6 Atmospheric Dispersion Modelling of Emissions from the Gas Engines 6.1 Detailed air dispersion modelling has been undertaken using Version 3.3 of the

ADMS model, developed in the UK by Cambridge Environmental Research

Consultants (CERC). The purpose of the modelling was to assess the potential

impact of pollutant emissions from the biomass plant on local air quality. The

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assessment considered the potential impact on local air quality of emissions of

SO2, NOX, CO and particles from the gas engines.

Emissions Data

6.2 The proposed biomass development comprises two principal air pollutant point

sources, namely the two gas-fired engines. The source data, based on data for

similar-sized landfill gas engines, are presented in Table 2.

Table 2 Emission Source Parameters

Parameter Engine 1 Engine 2

Stack Height (m) 7 7

Stack Diameter (m) 0.3 0.3

Temperature (oC) 450 450

Efflux Velocity (m/s) 40 40

Volume Flow Rate (m3/s) 2.8* 2.8*

Location (x,y) 500670,268848 500668,268843

* Value Calculated by ADMS

Table 3 Modelled Emissions Data

Substance Engine 1 (g/s) Engine 2 (g/s)

NOX 0.53 0.53

SO2 0.055 0.055

CO 1.49 1.49

Particles (PM10) 0.0055 0.0055

6.3 Pollutant emissions data were not available for the proposed gas engines,

therefore, data for the engines were derived from emissions standards for landfill

gas engines in DEFRA1 and Environment Agency2 guidance. The emission

standards were translated into mass emission rates as shown in Table 3.

1 DEFRA, Quantification of the Health Consequences of Emissions, www.defra.gov.uk/environment/waste/research/health/pdf/health-report4.pdf 2 Environment Agency, 2004, LFTGN 08 Guidance for Monitoring Landfill Gas Emissions

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Sensitivity Analysis

6.4 A sensitivity analysis of the significance of the model input parameters was

undertaken. This included evaluation of the surface roughness (a measure of

low-level atmospheric turbulence associated with land use) and meteorological

data for different years (2001 through to 2005 inclusive). The conclusions were

as follows:

• The appropriate surface roughness was 0.5m

• Building effects should be modelled

• 2004 meteorological data resulted in the highest predicted ground-level concentrations

6.5 The results from the model are discussed within the context of the Air Quality

Objective Values detailed in Appendix 1.

Results from Detailed Atmospheric Dispersion Modelling

6.6 Detailed atmospheric dispersion modelling was undertaken to assess the

potential impact on local air quality of pollutant emissions from the gas engines.

The ADMS 3.3 dispersion model was used for the assessment and was

undertaken based on the results of the sensitivity analysis reported above. The

results are based upon a 50m resolution output.

6.7 Predicted Environmental Concentrations for NO2 were calculated using the

following formulae recommended by the Environment Agency.

Equation 1 Calculation of Annual Average NO2 Predicted Environmental Concentration

(Annual NOX Modelled x 0.7) + Annual NO2 Monitored

Equation 2 Calculation of Hourly Average NO2 Predicted Environmental Concentration

(Hourly NOX Modelled x 0.35) + (Annual NO2 Monitored x 2) 6.8 Process Contribution data from the ADMS output file were used in conjunction

with the 2008-projected background NO2 value of 11.7 µg m-3 to calculate

Predicted Environmental Concentrations for NO2 for the area around the

Biomass Plant.

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6.9 The worst case modelling assumed that the process was operating at full

capacity (i.e. two engines operational concurrently). The results are presented

below in Table 4

Table 4 Maximum Predicted Environmental Concentration of Modelled Pollutants

Pollutant Statistic Objective Limit (µg m-3)

Predicted Environmental Concentration (µg m-3)

Annual Average 40 ~25 NO2 *

Hourly Average 200 ~30

15 Minute Average 266 ~33**

Hourly Average 350 ~29**

SO2

Daily Average 125 ~15**

CO 8 Hourly Average 10,000 720**

Daily Average 50 µg m-3 0.5** Particles

Annual Average 40 µg m-3 0.2**

* NO2 concentrations calculated according to Environment Agency protocols (See Appendix 2) ** Process Contribution (µg m-3)

6.10 The following discussion relates to NO2 only which is considered to be the most

significant pollutant associated with the emissions from the gas engines.

6.11 Modelling the emissions from two engines, with a release height of 7m, operating

simultaneously resulted in a maximum predicted annual average NO2 ground-

level concentration of ~25 µg m-3 compared to a background of 11.7 µg m-3

(Table 5). This value was predicted to occur close to the point of release and

decreased rapidly as the plume migrates away from the engine stacks.

6.12 The annual average NO2 ground-level concentration is plotted in Figure 2 and

shows that the annual average NO2 objective limit of 40 µg m-3 was not

exceeded. Figure 2 also shows that Predicted Environmental Concentrations of

NO2 are expected to be close to the background level by the time the emissions

from the gas engines have migrated towards nearby residential properties. The

model predicted that the hourly average concentration would be ~30 µg m-3,

representing ~15% of the 200 µg m-3 hourly average Objective Value.

Figure 2 Annual Average NO2 Predicted Environmental Concentration Arising from Emissions from the Two Gas Engines

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6.13 The results of predicted ground-level concentration of the other pollutants (SO2,

CO and PM10) released from the combustion plant indicate that they are unlikely

to have a significant impact on local air quality in the vicinity of the proposed

Biomass Plant.

7 Atmospheric Dispersion Modelling of Odour Release

Assessment for Odour

7.1 It was not possible to undertake detailed atmospheric dispersion modelling for

odour as there were no data available to indicate what the likely odour

concentration will be from the bio-filter. However, qualitative comments are

provided based upon a similar assessment undertaken for a bio-filter at a

rendering site, where odours will be considerably stronger than those likely to be

associated with the operations at Chelveston. Accordingly, the conclusions

probably represent an overly pessimistic assessment of the likely impact of

fugitive odour from the bio-filter proposed for the Biomass Plant.

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7.2 Environment Agency Guidance Note H4 recommends the assessment criteria

presented in Figure 3 in relation to the description of the offensiveness of odours.

The materials to be accepted on site for treatment in the AD Process may have

offensive odours and accordingly an assessment level of 1.5 OUE is the

appropriate benchmark for assessment.

7.3 Environment Agency Guidance Note H4 recommends that the basis for

assessment should be the 98th percentile of hourly average values. In other

words, there are 175 allowable exceedences of the 1.5 OUE assessment level in

any one year period; any more than this and there is an indication that odour

management requires improvement.

7.4 In the absence of measured data for odour release from the bio-bed filter, and in

order to provide a qualitative assessment for fugitive odour from the Biomass

Plant, data from the modelling of a similar situation at a rendering plant were

used.

7.5 An odour emission value of 420 OUE m-3 with a release temperature of 15 ºC was

used to estimate the potential impact of odour in relation to the 1.5 OUE

assessment level. The results from the previous study were adjusted to reflect

the relative sizes of the two bio-filters.

Figure 3 Environment Agency Guidance Note H4 Odour Assessment Criteria

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7.6 The results from the qualitative odour modelling are shown in Figure 4 and

indicate that odour is unlikely to be a problem at nearby residential properties.

The red contour line indicates the extent of the 1.5 OUE limit, and as can be

seen, none of the nearby residential properties are within the shaded area.

Figure 4 Hourly Average 98th Percentile Odour Ground-Level Concentration (Odour Units)

7.7 In light of the results from the qualitative modelling, it is considered that fugitive

odour release from the bio-filter is unlikely to give rise to complaints from nearby

residents.

8 Conclusions

8.1 An assessment has been undertaken of the potential impact of the proposed

Biomass Plant on local air quality, including odour. Detailed atmospheric

dispersion modelling was undertaken to determine the potential magnitude of the

impact of emissions from gas engines within the proposed plant. The modelling

concluded that emissions from the gas engines would not result in any

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exceedences of the National Air Quality Strategy objective limits for the modelled

pollutants (NO2, SO2, CO, PM10). The results indicated that pollutant

concentrations associated with emissions from the gas engines were likely to be

close to background levels by the time they have migrated towards nearby

residential properties.

8.2 In the absence of measured odour data for the proposed bio-filter, results from a

similar assessment for a rendering site where odour strength is likely to be

considerably higher than that associated with the AD Process at Chelveston.

Accordingly, the results from the current assessment are likely to portray an

overly pessimistic picture of the impact of fugitive odour release from the bio-filter

at Chelveston. Emissions data were modified to take account of the relative sizes

of the bio-filters at each location. The results indicated that the fugitive release of

odour from the bio-filter associated with the Biomass Plant was unlikely to be a

cause for concern at nearby residential properties Accordingly, it is considered

that there is unlikely to be a significant impact associated with fugitive odour from

the Biomass Plant.

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MSE Air Quality Assessment for Proposed Change of Use Development

Appendix 1 National Air Quality Standards and Objectives

Pollutant Jurisdiction Objective Measured as To be achieved by All Authorities 16.25 µg/m3 Running Annual Mean 31 December 2003 Authorities in England and Wales only

5 µg/m3 Annual Mean 31 December 2010 Benzene

Authorities in Scotland and Northern Ireland only a

3.25 µg/m3 Running Annual Mean 31 December 2010

1,3-Butadiene 2.25 µg/m3 Running Annual Mean 31 December 2003 Authorities in England, Wales and Northern Ireland only a

10.0 mg/m3 Maximum daily running 8 Hour Mean

31 December 2003 Carbon monoxide

Authorities in Scotland only 10.0 mg/m3 Running 8 Hour Mean b 31 December 2003 0.5 µg/m3 Annual Mean 31 December 2004 Lead 0.25 µg/m3 Annual Mean 31 December 2008 200 µg/m3 Not to be exceeded more than 18 times

per year 1 Hour Mean 31 December 2005 Nitrogen dioxide c

40 µg/m3 Annual Mean 31 December 2005 Nitrogen Oxides** (V) 30 µg/m3 Annual Mean 31 December 2000 Ozone* 100 µg/m3 Daily maximum of running 8 hour mean

not to be exceeded more than 10 times per year

Running 8 Hour Mean 31 December 2005

50 µg/m3 Not to be exceeded more than 35 times per year

24 Hour Mean 31 December 2004 Particles (PM10)(gravimetric)d

All authorities

40 µg/m3 Annual Mean 31 December 2004 50 µg/m3 Not to be exceeded more than 7 times

per year 24 Hour Mean 31 December 2010 Authorities in Scotland only e

18 µg/m3 Annual Mean 31 December 2010 Greater London f 50 µg/m3 Not to be exceeded more than 10 times

per year 24 Hour Mean 31 December 2010

Greater London f 23 µg/m3 Annual Mean 31 December 2010 Greater London f 20 µg/m3 Annual Mean 31 December 2015

Particles (PM10)

Rest of England, Wales and Northern Ireland f


24 Hour Mean 31 December 2010

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MSE Air Quality Assessment for Proposed Change of Use Development

Pollutant Jurisdiction Objective Measured as To be achieved by Rest of England, Wales and Northern

Ireland f20 µg/m3 Annual Mean 31 December 2010


15 Minute Mean 31 December 2005





(V) 20 µg/m3 Annual Mean 31 December 2000

Sulphur dioxide

(V) 20 µg/m3 Winter Mean (01 October - 31 March)

31 December 2000

Notes: a. In Northern Ireland none of the objectives are currently in regulation. Air Quality (Northern Ireland) Regulations are scheduled for consultation early in 2003. b. The Quality Objective in Scotland has been defined in Regulations as the running 8 Hour mean, in practice this is equivalent to the maximum daily running 8 Hour mean c. The objectives for nitrogen dioxide are provisional. d. Measured using the European gravimetric transfer sampler or equivalent. e. These 2010 Air Quality Objectives for PM 10 apply in Scotland only, as set out in the Air Quality (Scotland) Amendment Regulations 2002. f. New particle objectives for England, Wales, Northern Ireland and Greater London not included in Regulations µg/m3 - micrograms per cubic metre mg/m3 - milligrams per cubic metre *Ozone is not included in the Regulations ** Assuming NOx is taken as NO2 (V) These standards are adopted for the protection of vegetation and ecosystems. All of the remainder are for the protection of human health.

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