odour modelling assessment

Oaktree Environmental Limited Unit 5, Oasis Park, 19 Road One, Winsford, Cheshire CW7 3RY

Tel: 01606 558833 Fax: 01606 861182 E-mail: [email protected] Web: www.oaktree-environmental.co.uk

Registered in the UK - Company No. 4850754

CRES Biogas Ltd

Document ref. 2263-1291-A

Oaktree Environmental Ltd

Proposed Anaerobic Digestion Plant off Goostrey Lane, Twemlow

Odour Modelling Assessment

Version 1.4

24th August 2011

CRES Biogas Ltd Version 1.4 Odour Modelling Assessment 24th August 2011

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Document History: Version Issue date Status Written by Reviewed by

1.1 12th July 2011 Draft David Young

1.2 19th August 2011 Draft David Young

1.3 23rd August 2011

Internal Draft Issued to Client David Young

1.4 24th August 2011 Final David Young


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LIST OF CONTENTS

1 NON TECHNICAL SUMMARY ................................................................ 4

2 INTRODUCTION ......................................................................................... 5

2.1 SCOPE OF WORK ................................................................................................................................................. 5 2.2 SITE LOCATION ................................................................................................................................................... 5 2.3 PROPOSED ACTIVITIES ........................................................................................................................................ 5

3 ODOUR LEGISLATION AND RELEVANT GUIDANCE ..................... 7

3.1 CONSULTED DOCUMENTS ................................................................................................................................... 7 3.2 REGULATION OF ODOUR WITHIN THE UNITED KINGDOM .................................................................................. 7 3.3 ODOUR ASSESSMENT CRITERIA .......................................................................................................................... 7

4 BASELINE POSITION .............................................................................. 10

4.1 CURRENT BACKGROUND ODOUR ..................................................................................................................... 10 4.2 SENSITIVE RECEPTORS ...................................................................................................................................... 10

5 MODELLING METHODOLOGY ........................................................... 12

5.1 MODEL DESCRIPTION ....................................................................................................................................... 12 5.2 MODEL INPUTS.................................................................................................................................................. 12 5.3 MODEL VERIFICATION ...................................................................................................................................... 19 5.4 MODEL SCENARIOS ........................................................................................................................................... 19 5.5 MODEL UNCERTAINTY ..................................................................................................................................... 20

6 MODELLING RESULTS .......................................................................... 21

7 CONCLUSIONS .......................................................................................... 23

List of Tables Table 1 Identified Odour Sensitive Receptor Locations ............................................................................................................ 10 Table 2 Emission Source Parameters for Biofilter Stack ........................................................................................................... 16 Table 3 Emission Source Parameters for Cattle Slurry Tank During Slurry Delivery ............................................................. 16 Table 4 Building and Structure Heights ..................................................................................................................................... 17 Table 5 Parameters for Surface Roughness, Albedo and Bowen Ratio .................................................................................... 19 Table 6 Modelled Scenarios ....................................................................................................................................................... 20 Table 7 Maximum Modelled 98th Percentile 1-Hour Mean Odour Concentrations .................................................................. 21 Table 8 Maximum Modelled 98th Percentile 1-Hour Mean Odour Concentrations at Sensitive Receptor Locations ............. 21

List of Appendices

Appendix 1 - Site Location and Layout Appendix 2 - Sensitive Receptor Locations Appendix 3 - Odour Contour Profiles Appendix 4 - Wind Roses Appendix 5 - EA Detailed Dispersion Modelling Requirements Checklist


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Glossary AD Anaerobic Digestion ADMS Atmospheric Dispersion Modelling System AMS American Meteorological Society BPIP Building Input Profile Program CH4 Methane CO2 Carbon Dioxide DEFRA Department for Environment, Food and Rural Affairs EA Environment Agency ELV Emission Limit Value EPA Environmental Protection Agency EPR Environmental Permitting (England and Wales) Regulations 2010 LA Local Authority NGR National Grid Reference OE Oaktree Environmental Ltd. OS Ordnance Survey OU Odour Unit UK United Kingdom US United States


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1 Non Technical Summary

Detailed dispersion modelling has been undertaken to identify potential impacts as a

result of odour emissions from a proposed Anaerobic Digestion plant to be located off

Goostrey Lane, Twemlow, Holmes Chapel. Resulting odour concentrations have been

predicted to be significantly below the worst case assessment criteria at all identified

sensitive receptor locations. Furthermore, no exceedences of the worst case assessment

criteria for odour have been predicted at any location surrounding the proposed plant.

Therefore, negligible odour impacts have been predicted as a result of plant operation.


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2 Introduction 2.1 Scope of Work

2.1.1 An odour modelling assessment has been undertaken in support of a planning

application being submitted for the proposed operation of an Anaerobic Digestion

(AD) plant to be located off Goostrey Lane, Twemlow, Holmes Chapel. The

assessment has been undertaken to predict the potential odour impacts at surrounding

human receptor locations as a result of the proposed operations. Detailed dispersion

modelling has been undertaken to predict likely resulting ground level odour

concentrations surrounding the proposed plant, which have been compared with the

relevant assessment criteria for odour. This has enabled a judgement to be made over

whether the plant is likely to have potential to cause statutory nuisance in terms of

odour.

2.2 Site Location

2.2.1 The site is located at approximate National Grid Reference (NGR) 378067, 368995.

Reference should be made to Appendix 1 Figure 1 for a map illustrating the site

location and surrounding area.

2.3 Proposed Activities

2.3.1 CRES Biogas Ltd are applying for planning permission to develop a Community

Renewable Energy Scheme. This will include development of an AD Plant.

2.3.2 AD is a biological process, which breaks down organic matter within biodegradable

wastes in the absence of oxygen, through the actions of a variety of micro-organisms.

The result of these processes is the production of biogas, which consists predominantly

of methane (CH4) and carbon dioxide (CO2) and a useable digestate product which has

environmental benefits when used in place of fertilisers. It is proposed to utilise the

biogas to power internal combustion engines for the production of electricity and heat.

The electricity produced will be exported to the National Grid. Once operational, the


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applicant will investigate possible uses for heat produced from the process, if a

suitable use can be found.

2.3.3 The feedstocks to be used will include agricultural wastes including dairy slurry and

poultry litter, maize, waste grass and food wastes. It is currently proposed to develop

the plant in two phases. During the initial phase, the wastes used will include dairy

slurry, maize, grass and poultry litter. During the second phase, the plant will also

utilise food wastes. It is currently anticipated that once fully developed, the plant will

accept the following quantities of waste:

• 15,000 tonnes cattle slurry;

• 4,000 tonnes poultry manure;

• 1,800 tonnes maize;

• 2,000 tonnes grass; and,

• 24,000 tonnes food waste.

2.3.4 Assessment of potential odour impacts within this report has been undertaken on the

basis of the fully developed plant, in order to ensure a worst case scenario.


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3 Odour Legislation and Relevant Guidance

3.1 Consulted Documents

3.1.1 The following documentation has been consulted for the purpose of this current

assessment:

• Additional Guidance for H4 Odour Management: How to Comply with your

Environmental Permit, Environment Agency, 2011; and,

• The Environmental Permitting (England and Wales) Regulations 2010.

3.2 Regulation of Odour Within the United Kingdom

3.2.1 There are no legislative standards or limits for regulating the concentration of odour in

ambient air. Odour is difficult to quantify and its impact is subjective since the

response of individuals and groups of people to the same odour can vary significantly.

The Local Authority (LA) is obliged, where statutory complaint about odour nuisance

is made, to take steps to investigate in accordance with Part III of the Environmental

Protection Act (1990). The assessment of odour made within this assessment gives

consideration to the potential for the proposed plant to cause statutory nuisance.

3.3 Odour Assessment Criteria

3.3.1 As outline above, odour is difficult to quantify and it’s impacts are highly subjective.

To simplify this problem, odour concentrations can be expressed as the number of

odour units per metre cubed of air (OU.m-3). Odour units are the measure of odour

concentration within a compound/mixture of compounds and can be determined by

means of olfactometry. For any given compound/mixture of compounds, 1OU.m-3 is

the point above which the compound(s) can be detected. However, some odours are

more offensive than others. For example an odour concentration of 1OU.m-3 resulting

from a chocolate manufacturing process would be considered less offensive than from

a biological landfill. Therefore, odour annoyance potential criteria have been

developed by the Environment Agency (EA), which are known as benchmark levels

for odour, above which there would be considered to be potential for odour annoyance.


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The benchmarks are based upon the 98th percentile of hourly average concentrations

for odour modelled over a year at a site installation/boundary as follows:

• 1.5 odour units for the most offensive odours;

• 3 odour units for moderately offensive odours; and,

• 6 odour units for less offensive odours.

3.3.2 EA H4 guidance provides broad categorisation of odour offensiveness as follows:

• Most offensive – processes involving decaying animals or fish remains, processes

involving sceptic effluent or sludge, and biological landfill odours;

• Moderately offensive – intensive livestock rearing, fat frying (food processing),

sugar beet processing and well aerated green composting; and,

• Less offensive – brewery, confectionary, coffee roasting and bakery.

3.3.3 Any modelled odour concentrations above the relevant thresholds for the relevant

process concerned indicates the likelihood of unacceptable odour impacts.

3.3.4 The issue when assessing potential odour impacts from an AD plant, such as the

current proposal, is categorising the potential offensiveness of odours. It is clear from

the EA H4 guidance that green wastes, chicken and dairy litter mostly aptly fall under

the ‘moderately offensive odours’ category, and therefore a benchmark of 3OU.m-3 is

most appropriate. The issue lies with potentially putrescible wastes such as catering

waste, which has the potential to create more offensive odours, in which case a

benchmark of 1.5OU.m-3 might be considered more appropriate. However, all food

waste will be delivered to site within enclosed HGVs, and deposited into an enclosed

reception building which will be operated under negative pressure with odours

controlled using biofiltration before release to atmosphere. The very nature of the

biofiltration system means that residual odours exiting the biofilter would likely have a

‘woody/peaty smell’, in which case a benchmark level of 3OU.m-3 is considered more

appropriate. However, in order to provide a highly conservative, worst case

assessment, an odour benchmark level of 1.5OU.m-3 has been used within this


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assessment. This ensures significant margin of safety in design to prevent odour

impacts at off-site sensitive receptor locations.


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4 Baseline Position 4.1 Current Background Odour

4.1.1 The proposed site is located in a rural location and there are no industrial processes or

waste sites which might be considered potential sources of odour in close proximity.

Therefore, background levels of odour in the vicinity of the site, other than general

agricultural smells associated with farming processes are considered to be negligible.

4.2 Sensitive Receptors 4.2.1 Discrete sensitive human receptors have been identified for inclusion within the

model. Table 1 contains a list of all identified sensitive receptors within the vicinity of

the plant, which would be sensitive to odour. Where these are referred to in the report,

they are identified as O1 to O25. Reference should be made to Appendix 2 for a

graphical representation of receptor locations. The identified NGR for each receptor

represents the nearest point to the proposed site boundary in order to ensure a ‘worst

case’ assessment.

Table 1 Identified Odour Sensitive Receptor Locations Odour

Receptor

Identifier

Odour Sensitive Receptor Description

National Grid Reference (m)

X Y

O1 Residential receptor on Goostrey Lane 378138 368869







O8 Residential receptor on Twemlow Lane 378095 368757





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Odour

Receptor

Identifier

Odour Sensitive Receptor Description

National Grid Reference (m)

X Y






O17 Blue Slate Farm 377771 368833

O18 Residential receptor on Station Road 378285 369614

O19 New Farm 378896 369248

O20 Blackden Manor Farm 378882 369188

O21 Blackyard Farm 378836 368944

O22 Thornfields Cottage 378275 368746

O23 Hiverley Cottage 378416 368739

O24 Hiverley (Residential receptor) 378460 368756

O25 Hermitage Turkey Farm 376773 369074


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5 Modelling Methodology 5.1 Model Description

5.1.1 The potential air quality impact that may arise through emissions of odour during

operation of the AD plant has been quantified using AERMOD, which is a steady

state, next generation, dispersion model. AERMOD was developed jointly by the

American Meteorological Society (AMS) and the United States (US) Environmental

Protection Agency (EPA) Regulatory Model Improvement Committee. The AERMOD

model is a development from the ISC(Industrial Source Complex) 3 dispersion model

and incorporates improved dispersion algorithms and pre-processors to integrate the

impact of meteorology and topography within the modelling output, and is approved

for use in the UK by the EA. The version of AERMOD that has been used for this

current assessment is Lakes Environmental ISC-AERMOD View Version 6.7.1. The

model has been run using the most recent version of the AERMOD executable file,

11103.

5.2 Model Inputs

5.2.1 Emission Sources

5.2.1.1 Reference should be made to Appendix 1 Figure 2 for a graphical representation of the

proposed site layout. The AD process itself is sealed and therefore there is limited

potential for odour to escape from the process. The main operations which have the

potential to create odour include the delivery and handling of wastes prior to entry to

the AD process and the storage and handling of digestate and biogas evolved from the

AD process.

5.2.1.2 There are no emission limit values for odour and since the site is not yet operational, it

is not possible to monitor site odour emissions. In the absence of such information,

estimations of odour emissions from the various identified sources have to be made.

However, it should be noted that the estimations made are based upon a combination

of odour monitoring data reported elsewhere at similar plants and in the case of the


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biofilter, design residual odour concentrations provided by the technology provider for

the site.

5.2.1.3 Plant efficiency and odour control are directly interrelated parameters. Therefore,

since it is in operator interest to maximise efficiency of the plant, this in turn means

that odour generation is minimised. The principal odour abatement measures which

will be used at the plant are as follows:

• The use of a two stage digestion process with a lengthy 114.3 day retention time

ensures minimal residual gas content of digestate, whilst also providing good

opportunity for the complete stabilisation of the digestate to ensure that sulphur

containing compounds are broken down to minimise potential for generation of

odourous compounds such as hydrogen sulphide;

• Gas flow to engines will be carefully controlled to maximise combustion

efficiency and ensure biogas is not directly released to atmosphere;

• Use of the latest, most efficient technology for methane extraction to ensure

highest possible capture of methane;

• Food and poultry waste will be delivered to and stored within an enclosed

reception building, operated under negative pressure, with odour controlled using

a biofiltration system;

• Cattle slurry will be stored within an enclosed tank, only vented during slurry

delivery;

• Storage of dewatered digestate will be within an enclosed building;

• Storage of liquid digestate will be within an enclosed storage tank;

• Covering of inactive silage clamp surfaces with suitable sheeting; and,

• An Odour Management Plan (OMP) will be implemented on site, as part of the

conditions of the permit to operate.

5.2.1.4 The waste reception building will be operated under negative pressure and fitted with a

biofiltration system which will control odour before release to atmosphere. A residual

odour concentration of 2000OU.m-3 has been used to derive the odour emission rate

from the biofilter stack, which is the maximum odour concentration which the


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technology provider for the site has indicated can be achieved from the biofilter1. This

is considered to provide a worst case assessment for odour emissions likely to arise

from the waste reception building. It is currently anticipated that there will be up to 3

air changes per hour within the waste reception building, which will result in up to

35,712m3 of air being exhausted from the biofilter stack each hour, which equates to

an exit flow rate of 9.92m3.s-1. Based upon the biofilter odour emission concentration

of 2000OU.m3, an odour emission rate of 19,831.7OU.s-1 has been calculated for the

biofilter stack. It is currently anticipated that the stack internal diameter will be 0.65m,

whilst an efflux temperature of 298K has been assumed.

5.2.1.5 The cattle slurry tank will be enclosed. However, there is potential for odour emission

during the unloading of slurry into the tank within vented displaced air. Based upon

values reported elsewhere2, an emission factor of 200OU.m-3 is considered to provide

a worst case assessment. It is currently expected that slurry will be delivered to site

within 12 tonne capacity tankers, up to 4 times each day. Each delivery is expected to

take approximately 10 minutes. Based upon this data, the peak odour emission rate

during slurry delivery has been calculated to be 4OU.s-1. It has been assumed that

odours will be continuously released at this concentration in order to ensure a

conservative, worst case assessment.

5.2.1.6 It is currently anticipated that the dewatering and storage of solid digestate will be

undertaken within an enclosed building. Liquid digestate will be stored within an

enclosed tank. As such, it is not considered that odour emissions from these

operations will be significant. However, it is not expected that the dewatered solid

substrate or liquid digestate will have significant potential for odour generation, once it

has undergone two stages of digestion.

5.2.1.7 The AD process involves breaking down of odour-making substances and organisms

within the digestate, whilst the majority of the methane within the waste ends up

within the biogas which is captured and burnt within the engines to produce electricity.

It has been reported by measurements elsewhere that the end substrate (digestate) from 1 Email communication from David Castle, ATS, dated 8th August 2011. 2 Odour and Bioaerosol Risk Assessment, Proposed Anaerobic Digestion, Whitwell, Derbyshire, Alkane Energy

PLC, 2010.


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AD is not significantly odourous3. The retention time of waste within the digestion

process is expected to be 114.3 days across a two stage digestion process which is

considered significantly longer duration than is required to sufficiently minimise odour

potential of the digestate. On this issue, reference should be made to the previous

Department for Environment, Food and Rural Affairs (DEFRA) Code of Good

Agricultural Practice for the Protection of Air4, which indicates that odours from

digestate can be reduced by up to 80%, after a 12-20 day retention time. It is currently

anticipated that the retention time at the proposed plant will be over 5 times longer

than this in duration. The proposed two stage, 114.3 day digestion process will ensure

a high level of methane removal whilst providing good opportunity for complete

break-down of odour-making substances within the digestate, such as sulphur

containing compounds. As such, potential odour emissions from digestate storage,

handling and transfer off-site are considered to be negligible and have not been

considered further in this assessment.

5.2.1.8 Maize and grass may be stored within a silage clamp near to the waste reception

building. If silage is stored on site, the top surface and inactive face of the clamp

would be covered at all times. There would be potential for odour from the open face

of the silage clamp and during transfer of material into and out of the clamp. However,

the magnitude of such odour emissions would be limited since the area of silage which

would be disturbed each day would be relatively small. Furthermore, maize and grass

silage would be described to have an ‘agricultural’ smell, and would be no more

significant than on commercial farms which use silage as animal forage. As such, the

potential for odour impact from the silage, should this be stored on site, would be

considered to be negligible. Therefore, odour emissions from silage have not been

considered further in this assessment.

5.2.1.9 The biogas used to power the Combined Heat and Power (CHP) units will be stored

within a regulated vessel. Flow of the biogas to the CHP units will be carefully

3 Air Quality Assessment of Proposed Agricultural Anaerobic Digester at Denham Estate, Near Bury St Edmunds,

Suffolk, ADAS, 2009. 4 Code of Good Agricultural Practice for the Protection of Air, Ministry of Agriculture, Fisheries and Food, Welsh

Office Agriculture Department, 1998.


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regulated to prevent gas being vented to atmosphere. Therefore, no odour emissions

are likely to arise from the biogas used to power the CHP units.

5.2.1.10 Table 2 and Table 3 contain the emission parameters used as model inputs for each

emission source modelled. Reference should be made to the site layout drawing in

Appendix 1 for an illustration of the location of emission points modelled.

Table 2 Emission Source Parameters for Biofilter Stack Process Parameter Value

Stack internal diameter (m) 0.65

Stack height (m) 12.2

Expected stack volumetric flowrate (m3.s-1) 9.92

Expected stack efflux velocity (m.s-1) 29.9

Expected stack efflux temperature (K) 298 Odour concentration in biofilter exhaust gas (OU.m-3) 2,000

Odour emission rate from biofilter Stack (OU.s-1) 19,831.7

Table 3 Emission Source Parameters for Cattle Slurry Tank During Slurry Delivery Process Parameter Value

Vent diameter (m) 0.3

Vent height (m) 2.5 Expected vent volumetric flowrate during slurry delivery (m3.s-1) 0.02

Expected vent exit velocity during slurry delivery (m.s-1) 0.283

Temperature of vented air (K) 298

Odour concentration in displaced air (OU.m-3) 200 Odour emission rate from slurry tank vent (OU.s-1) 4

5.2.2 Building Downwash

5.2.2.1 On-site building structures and heights were digitised within the model from proposed

site layout and elevation plans. As the closest buildings to the emissions sources, these

would be expected to have an influence on pollutant dispersion. Table 4 contains


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information on building heights used within the model. Reference should be made to

Appendix 1 Figure 2 for a site layout plan depicting structure locations, whilst

Appendix 1 Figure 3 shows a 3-dimensional illustration of the structures digitised

within the model, in relation to the surrounding area. The tanks on site which will be

used as digesters are situated within a part earth bunded compound, partially below

ground. The heights specified in the table below are structure heights relative to

ground level, and not absolute structure heights from base.

Table 4 Building and Structure Heights

Building Description Max Height (m)

Waste reception building 12.2

Slurry reception tank 2.5

Primary Digester 1 4.5

Primary Digester 2 4.5

Secondary Digester 1 4.5



Digestate Storage Tank 4.5

Food Waste Buffer Tank 6.7

Liquids Buffer Tank 6.7

Gas Holder 5.4

CHP No.1 0.99

CHP No. 2 0.99

Pasteurisation Tank 5.5

Flare 2.95

Digestate solids store 7

5.2.2.2 The integrated Building Profile Input Programme (BPIP) module within AERMOD

was used to assess the potential impact of building downwash upon predicted

dispersion characteristics. Building downwash occurs when turbulence, induced by

nearby structures, causes pollutants emitted from an elevated source to be displaced


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and dispersed rapidly towards the ground, resulting in elevated ground level

concentrations. All building structures were input into the BPIP processor.

5.2.3 Assessment Area

5.2.3.1 A uniform cartesian receptor grid was used to define the modelling domain over an

area of 1500m by 1500m, centred on the biofilter stack location at a grid spacing of

25m.

5.2.4 Meteorological Data

5.2.4.1 Meteorological data used in this assessment was obtained from Manchester

meteorological station, including missing cloud cover data from Liverpool.

Manchester met station is located approximately 15km to the North-North-East of the

proposed site.

5.2.4.2 Five years of meteorological data observed between 2005 and 2009 were used within

the assessment. This is in accordance with EA guidance and ensures a worst case

assessment. Data was provided by ADM Ltd, an established distributor of met data

within the UK. The AERMET processor within AERMOD was used to process the

data to be site specific. US EPA guidance on processing met data for use within

AERMOD states that land use up to 1km upwind from a site should be considered

when determining surface roughness characteristics, whilst for Bowen ratio and

albedo, land use types within a 10km by 10km area centred over the site should be

considered5. The land use over the 10km by 10km area is dominated by rural and

cultivated land, which make up approximately 90% of the land coverage. The

remaining 10% consists of buildings and trees. AERMOD guidance states that albedo

and bowen ratio should be calculated as the arithmetic and geometric mean

respectively of land use types over the 10km by 10km grid, not weighted by direction

or distance. In terms of surface roughness, between 0º and 120º and between 160º and

360º, a surface roughness factor of 0.15 has been assigned, appropriate for scattered

trees, hedges and buildings. Between 120º and 160º, a surface roughness factor of 0.5

5 AERMOD Implementation Guide, US EPA, 2009.


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has been assigned, to account for the large amount of buildings and trees dominating

landuse within this sector.

5.2.4.3 The parameters use to process the meteorological data are contained within Table 5.

Table 5 Parameters for Surface Roughness, Albedo and Bowen Ratio Parameter Directional Sector Value

Surface Roughness

0º -120º 0.15

120º -160º 0.5

160º - 360º 0.15

Albedo All 0.2481

Bowen Ratio All 0.8633

5.2.4.4 In order to ensure a ‘worst-case scenario’, the model was run for each year of met

data, with the highest predicated odour concentrations at each sensitive receptor

location over the five years of data used to determine potential impacts.

5.2.5 Terrain Data

5.2.5.1 Topographical features can have a significant impact on pollutant dispersion. The

model incorporated 1:50,000 Ordnance Survey (OS) digital terrain data. The

AERMAP function within AERMOD was used to process the terrain data in order to

assign elevations to all sources, structures and receptors.

5.3 Model Verification 5.3.1 It was not possible to verify model results as the plant is not yet operational.

5.4 Model Scenarios 5.4.1 The scenarios modelled are contained within Table 6. It was assumed that the plant

will be operational continuously for 24-hours per day, 365 days per year with no shut

down periods. This ensures a worst-case assessment since the plant is expected to be

operational for an average of 8,000 hours per annum.


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Table 6 Modelled Scenarios

Pollutant Modelled Scenarios

Odour 98th percentile, 1-hour mean

5.5 Model Uncertainty 5.5.1 It is widely accepted that there can be a significant degree of uncertainty in predictions

made by any atmospheric dispersion model, which needs to be taken into account

when assessing modelled results. A previous study by the EA6 presented the results of

an intercomparison study between AERMOD and the Atmospheric Dispersion

Modelling System (ADMS), which is another widely used next generation dispersion

model. The test protocol developed by the EA examined the response of the two

models under individual weather conditions. Simple counts were made of the ratios of

maximum concentrations obtained from both models. 28% of the maximum calculated

concentrations differed by a factor of more than 2, with 15% of the ADMS/AERMOD

ratios being high (>2) and 13% of the ratios being low (<0.5). Given the above,

caution should be applied when assessing the results obtained from any dispersion

model, without verification/validation.

6 Evaluation of Atmospheric Dispersion Models: AERMOD, Environment Agency, 2000.


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6 Modelling Results

6.1 Table 7 contains the maximum modelled 98th percentile 1-hour mean odour

concentrations surrounding the plant. Table 8 contains the maximum predicted 98th

percentile 1-hour mean odour concentrations at sensitive receptor locations. The model

was run for each year of met data between 2005 and 2009 - the odour concentrations

reported below are the maximum modelled from the 5 years of data, in order to ensure

a worst case assessment.

Table 7 Maximum Modelled 98th Percentile 1-Hour Mean Odour Concentrations

Year

Maximum Modelled 98th Percentile 1-Hour Mean Odour Concentration at Ground Level

(OU.m-3)

Maximum Modelled 98th Percentile 1-Hour Mean Odour Concentration As

Percentage of Benchmark (%)

2005 1.41 94.00 2006 1.40 93.33 2007 1.33 88.67 2008 1.34 89.33 2009 1.41 94.00

Table 8 Maximum Modelled 98th Percentile 1-Hour Mean Odour Concentrations at Sensitive Receptor Locations

Receptor


(OU.m-3)



O1 0.73 48.75 O2 0.78 51.83 O3 0.68 45.05 O4 0.49 32.61 O5 0.45 29.88 O6 0.45 30.17 O7 0.57 38.09 O8 0.38 25.58 O9 0.27 18.01 O10 0.25 16.64 O11 0.26 17.21


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Receptor


(OU.m-3)



O12 0.26 17.28 O13 0.24 16.32 O14 0.28 18.79 O15 0.39 26.01 O16 0.39 26.19 O17 0.35 23.07 O18 0.21 14.07 O19 0.12 8.19 O20 0.14 9.08 O21 0.19 12.76 O22 0.58 38.35 O23 0.48 32.21 O24 0.44 29.50 O25 0.03 2.09

6.2 As is indicated, no exceedence of the worst case benchmark criteria for odour is

predicted at any location surrounding the proposed plant. Furthermore, modelled

results show resulting odour concentrations are likely to be significantly below the

worst case benchmark level at all sensitive receptor locations. As such, no significant

odour impacts are predicted as a result of operation of the proposed AD plant.

Confidence in these predictions are high, since they have been obtained from site

specific dispersion modelling.


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7 Conclusions

7.1 Detailed dispersion modelling has been undertaken to assess the potential odour

impacts arising as a result of operation of a proposed AD plant to be located off

Goostrey Lane, Twemlow, Holmes Chapel.

7.2 The modelling results have shown that impacts from odour emissions will not be

significant. No exceedence of the worst case benchmark assessment level for odour

has been predicted at any location surrounding the plant. Furthermore, the modelling

has shown that resulting odour concentrations will be significantly below the most

stringent assessment benchmark at all identified sensitive receptor locations.


Appendix 1

Site Location and Layout Plan


Appendix 2

Sensitive Receptor Locations


Appendix 3

Odour Contour Profiles


Appendix 4

Wind Roses


Appendix 4 Figure 1 - Wind speed and frequency observed at Manchester Ringway during 2005

Appendix 4 Figure 2 – Wind speed and frequency observed at Manchester Ringway during 2006



NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

WIND SPEED (m/s)

>= 11.1

8.8 - 11.1

5.7 - 8.8

3.6 - 5.7

2.1 - 3.6

0.5 - 2.1

Calms: 7.32%



Appendix 5

EA Detailed Dispersion Modelling Requirements

Checklist


Appendix 5 Table 1 EA Air Dispersion Modelling Report Checklist

Item √/X Reason for Omission

Location Map √

Site plan √

List of emissions modelled

and relevant air quality

guidelines

√

Details of modelled

scenarios √

Details of relevant ambient

concentrations used √

Model description and

justification √

Special model treatments

used √

Table of emission

parameters used √

Details of modelled domain

and receptors √

Details of meteorological

data used (including origin)

and justification

√

Details of terrain treatment √

Details of building

treatment √

Sensitivity analysis √ (Worst case results from

5 years of meteorological

data used)

Assessment of impacts √

Model input files X

Can be provided on

request

odour modelling assessment

Documents

odour assessment criteria

odour legislation

regulation of odour

draft david young

final david young cres

client david young

current background odour

modelling methodology