Sola ADC Lenses IPPC Licence Application

Dispersion Modelling Report

31 January 2006 Final

Issue Nu 3 45078530

Final Report Jsnuwy 31 .doc

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Sola ADC Lenses IPPC Licence Application Dispersion Modelling Report

Name Signature

Project Title:

Report Title:

Date

Project No:

Report Ref:

Status:

Issue No Date 1

2

Client Contact Name:

Details of Revisions

Original issue

Revised Draft

Sola ADC Lenses IPPC Licence Application

Dispersion Modelling Report

45078530

Final

Martin Butler

Client Company Name: Issued By: URS Ireland Ltd

Sola ADC Lenses

4th Floor, lveagh Court 6 - 8 Harcourt Road Dublin 2

Document Production 1 Approval Record

Issue No: 3

Prepared by

Checked bY

Approved by

Ian Marnane

Gerard Kelly

9

Fergus Hayes 3 1 IO 1 IO6

C ( I' I . v

Position

Project Manager

Project Director

Operations Manager

FimI Report January 31 .doc 31 January 2006

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e 1 I 1 1 1 I I

Sola ADC Lenses IPPC Licence Applicatlon Dispersion Modelling Report

LIMITATION

URS has prepared this Report fot the sole use of Sola ADC Lenses in accordance with the Agreement under which our services were performed. No other warranty, expressed or implied, is made as to the professional advice included in this Report or any other services provided by us. This Report may not be relied upon by any other party without the prior and express written agreement of URS. Unless otherwise stated in this Report, the assessments made assume that the sites and facilities will continue to be used for their current purpose without significant change. The conclusions and recommendations contained in this Report are based upon information provided by others and upon the assumption that all relevant information has been provided by those parties from whom it has been requested. Information obtained from third parties has not been independently verified by URS, unless otherwise stated in the Report.

COPYRIGHT

6 This Report is the copyright of URS Ireland Limited. Any unauthorised reproduction or usage by any person other than the addressee is strictly prohibited.

Final Report Janualy 3 l . d ~ Final 31 January 2006

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Sola ADC Lenses IPPC Licence Application URS Dispersion Modelling Report

CONTENTS

Section

1.

1.1. 1.2. 1.3.

2.

2.1. 2.2. 2.3. 2.4. 2.5. 2.6.

3.

4.

4.1. 4.2. 4.3. 4.4.

INTRODUCTION .. , .... .... .... , .... .... .... .... .... .... , ... , ... . ... . ... , ... , .... .... . ... . ... . .... .._. . ._. . ._. .

Page No

........ *. 1

Background .......................................................................................................................l Site Operations ................................................................................................................. 1 The Dispersion Model ....................................................................................................... 2

MODEL INPUTS ................................................,....-.............-...-....,,,..,........ . ............... ....3

Meteorological Data ....... .... ,....___.___......__. ._. ._.......___._... ................. .__. .___._... .... .__. .__. ......... ... 3 Topography . . . . . . . , . . . , , . . . , . . . , . . . , , . . . . . . . , . . , . . . . . . . . . . . , , . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . __..__.... 6 Building Effects ................................................................................................................. 6 Emission Point Data ......................................................................................................... 7 Model Outputs ................................................................................................................ 11 Dispersion Modelling Assumptions and Limitations .....,.___.___..... .__. .___..... .... ..__......... .... ,. 12

AIR QUALITY GUIDELINE VALUES ............................................................................ I3

MODEL RESULTS AND DISCUSSION ............................................... ........................ I 5

Introduction __..___. .__. .__. ..... .__. .__............. ,.__.___.__.. .._. .__. .... .__. .__. ................. .___.__.. .... . ._. ._....... 15 Results ............................................................................................................................ 15 Additional Modelling and Sensitivity Assessment (Scenario B & C) _.~_~. . . . . . .~ . . .~~.~. . . . .~~.~~ 15 Discussion and Recommendations ... .__. ._.. .... .__. .... .....___......... .... ..._.___. .... .... . ... . .... .... .... .. 17

Appendix A - AOMS Model Information

Final Report January 3l.doc Page i 31 Januaty 2006 Final

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t -3 Sola ADC Lenses IPPC Licence Appllcatlon Dispersion Modellinn Re~ort

i.

1.1.

1.2.

INTRODUCTION

Background

URS Ireland has been requested by Sota ADC Lenses (hereafter referred to as Sola) to complete dlspersion modelling of emissions from a number of point sources at the Sola plant in Wexford. This report will form part of the appbtion to the Environmental Protection Agency (EPA) for an Integrated Pollution Prevention and Control (IPPC) licence.

The EPA requested the completion of dispersion modelling for the site in a letter to Sola dated December Zd 2005. The requested information was as follows:

Provide an environmental impact analysis (i.e. air emissions modelling assessment) of the maximum emissions to air (for moving the fwe vents on the rear wall of Plant 2 on the western boundary to a mom suitable location) including details of the maximum predicted ground level concentration for any new. and retained existing, emissions to alr,

Demonstrate the adequacy of the stack heights for the dispersion of emissions from all new, and retained existing, air emission points.

The air dispersion model is to be appropriate and all assumptions must be appropriate to the plant situation and surrounding environment. In addition, take into consideratbn any other solvent emissions on or off site that may have an impact on these results.

This dispersion modelling report has been prepared to meet the above requirements. However, in dation to the thlrd bullet point above and ihe requirement to take into consideration solvent emissions from off-site locations, no such data was available at present, as no ambient air monitoring data for the site area was identified.

Site Operations

There are few operations on site which would result in release of solvents to atmosphere.

Two s p e d ~ c sources have been included, namely:

4 Emission Point A2-1. This is the only Major Emission Point specified in the Hcence application. This emission point receives any vapour phase emissions f r m two monomer mixing vessels and a number of monomer storage vessels. Vessels are held under vacuum during mixing operations and are pressurised during emptying or filling. Site management report that the only time when emissions are likely to occur is during the Initial period when the mixing vessels are placed under vacuum (typically takes less than five minutes) and when vessels are being emptied or filled (again of short duration). The mixing stage itself takes approximately 3 hours with negligible emissions reported during this period.

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URS Sola ADC Lenses IPPC Licence Application Dispersion Modelling Report

I .3.

As requested by the EPA dispersion modelling of a proposed new emission point from the oven area in Plant 2 (known as Stack 19) is also included in the assessment. At present this Is released through five ground level vents which are Included as minor emission points in the IPPC licence application. Them emission points extract air from the semi-finished oven area and also frwn the general production area in plant 2. The main period when emissions would be expected would be when ovens are opened. Oven are opened only at the start and end of the curlng period (approximately 21 hours), with the ovens being open for approximately 2 minutes. 12 ovens are typically in use at any one time.

There are other minor emission points at the site, however in practice such sources would typically not require assessment using dispersion modelling. These mlnor emission points would include solvent emissions from lens coating processes and from fume cupboards.

The Dispedon Model

The dispersion model used for this study is ADMS 3.3, developed by Cambridge Environmental Research Consultants in the UK. This model Is widely used in the UK, Ireland and Europe, and has been employed by URS in a wide range of modelling applications, including for the purposes of regulatory submission to the €PA (e.g. in relation to IPCllPPC licensed sites). Further details on the model are included in Appendix A.

Modelling of the emissions is carried out for each hour of a three year period of meteorological data taken from Rosslare, In order to identify the worst-case ground level concentrations for each compound released from the stacks. The identified worst-case ground level concentrations can then be compared to available ground level conwntration guideline values.

Section 2 of this report describes the model Inputs and outputs, Section 3 details the available ground level concentration guideline values, while Section 4 presents the results of the modelling study.

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2.

2.1.

MODEL INPUTS

Meteorological Data

Prevailing weather conditions can have a significant impact on ground level concentrattons of compounds released to air from stacks. Wind speed and direction, in particular, impact the location and magnitude of the maximum ground level cunc;entrations.

A range of meteorological parameters is monitored by Met Eireann at thelr synoptic monitoring stations, including wind speed, wind direction, temperature, rainfall, doud cover and humidity. There are significant variations between dimrent stations in Ireland hence it is important that a station is chosen which is representative of the area under investigation. The Sola site is located within 2 kilometres of the Wexford coast line. The meteorological data from the Rosslare synoptic monitoring station was identified as being representative of the mstgorological conditions at the site. The Rosslare monitoring station is situated approximately 13 kilometres southeast of the Sola site, within 500 metres of the coastline. In order to ensure that a range of likely meteorological conditions are induded in the modelling assessment, thrm complete years of hourly meteoroloQical data are induded in the assessment, for 2001,2002 and 2003.

The required meteorological input parameters for the model are:

I Windspeed;

Wind direction;

Temperature;

Cloud cover;

Month, day and hour data.

A summary of the temperature, wind speed and cloud cover data for each of the years is presented below, while wind roses for each year are induded in Figures 2.1,2.2 and 2.3. Cloud cover is measured in ‘oktas’, 0 to 8 shows the fraction, in oktas, of the celestial dome covered by all clouds.

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Sofa ADC Lenses 1PPC Licence Application Dispersion Modelling Report

Table 2.1 : Summary of meteorological data for Rosslare Monitoring Station

I I

Average Cloud Cwer (Oktas) 5.22 5.50 5.15

Minimum Wind Spaed (M) 0.00 0.00 0.00 I I I

Average Wind Sped (mls) 5.18 5.67 5.42

Maximum Wind sped (Ws) 20.1 0 17.50 15.90

Minimum Tmpsmtufe r C ) -1.20 1.70 -0.30 I

Average Temperaturn eC) 1 Ob3 11.20 t l . l i I I I

1 I 1 1 Maxlmum Temperature f'C] 22.90 22.20 24.20 I

1 I i I

Figure 2.1 : MO1 wind rose for Rodare meteomlogical station

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Fagure 2.2: 2002 wind rose for Rodare meteomlogical station

lm

I I -- 0 1.5 Xl 51 42 errs

Figure 2.3: 2003 wind COSB for R d a m meteorological station

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URS Sola ADC lenses IPPC LIcence Application Dispersion Modelling Report

2.2.

2.3.

Local topography can have a significant impact on the dispersion of released materials. The ADMS model is capable of including topographical data, if required. There are two parameters that c8n be employed in the model to describe local topography, as detailed below.

Surface Rorrghness

This parameter is specified in all modelling assessments. Surface roughness describes the degree of ground turbulence caused by the passage of winds across surface shctures. Ground turbulence is greater in urban areas than in rural areas, for example, due to the presence of tall buildings.

The area surrounding the Soia site includes some other commercialflight Industrial sites and private houses. Based on visits to the site a surface roughness value of 0.5 metres has been conservatively chosen which is typical of suburbadparkland areas and is considered to represent typical surface roughness in the site area.

Complex Terrain

The presence of steep hills (known as complex terrain) in the vicinity of a site can effect dispersion of emlssions. A gradient of 1 A0 or greater is normally taken as the criteria for inclusion of terrain in a modelling assessment. The topography in the immediate vicinity of the site is generally flat, wlth the gradient decreasing slightly In the area to the south of the site. It is expected that the highest ground level concentrations will occur within 150 metres of the site hence the overall impact of changes in surrounding topography are not expected to be significant compared to the impact of factors such as sits buitdings (see Section 2.3).

Building Effects

Buildings and other structures can have a significant impact on the dispersion of materials released to air. The main &fed is to entrain pollutants into the wvity (leeward side) of the building, which is isolated from the main flow and in which a reversal of flow can occur. This can result In rapid grounding of undiluted plumes.

Typically buildings are considered to have an impact on dispersion if the building height is greater than 40 % of the stack height.

The main buildings on the site have been included in the assessment as it is considered that the buildings are likely to have an impact on plume dispersion due to their location and height. Input of highly accurate dimensions for different areas of site buildings is not necessary, wlth a simplified building layout and consernative dimension specifcatlon typically being used in the assessment. For the purposes of the Sola site the site buildings have been broken up into the three main plant areas, namely Plant 1, 2 and 3, respectively. The approximate dimensions of the buildings induded in the modelling assessment are included in Table 2.2. The model representation of the buildings with respect to the air emission point are included in Figure 2.4.

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2.4.

Table 2.2: Dimensions for krlldings induded in the assessment

Figure 2.4: Model repserrtation of site buildings, boundary and erniskm points included in the model

€mission Point Data

FoaoWing diswssions with Sola, two emidon points am taken into account as part of this assessment. as detailed in fable 2.3. Emisslon point A2-1 is the only major mission point at the Sola site, however as requesled by the €PA the five vent from the own ama

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Sola ADC Lenses IPPC Llcence Application Dispersion Modelling Report

in Plant 2 have also been included in the modelling assessment. The modelling Is completed based on these five release points being rerouted through a single stack, known a5 Stack 19, which is currently in place (and unused} at the site.

As Stack A2-1 is the only stack classified as a Major emission point, it is also the only emission point with an emission limit (based on TA Luff 1986 organics emlssion Ilmlts). For the purposes of this assessment emissions from the ovens (hereafter referred to as Stack 19) are also dassifmd into TA Luft Class I , II and Ill (as available measurement data for this emission source are also specified as TA Luft Class 1, It and Ill), however there are no specific emission limits at present for this emission point.

Emissions monitoring data for Stack A2-1 and one of the five oven area vents are presented in Table 2.4. This illustrates that the emissions from A2-1 are significantly below the current TA Luff I986 organlcs emission limits specified in the existing licence (Reg. No. 62). The licence allows a mass Row limit for TA Luft Class 1, II and Ill of 0.1 kglhour, 2 kglhour and 3 kghour, respectively. Sased on the low measured emission levels and the infrequent emissions from A2-1 (see Section 1.2) the modelling assessment is based on worst-case measured emissions from both release points as detailed in Table 2.4 (results are only presented for one of the current 5 oven release vents, hence for Stack 19 emissions the maximum measured emission is multiplied by 5). This is taken as modelling Scenario A.

Table 2.5 presents the details of height, diameter and exit velocities assumed In the model. The emission velocities for both stacks is assumed to be negligible in the modelling exercise due to the nature of the release points (A2-I has a 'Chinese Hat' cover while Stack 19 releases slightly downwards and is reflected ofT the surrounding roof area).

Solvent emissions from other mlnor emission points at the plant are understood to be infrequent and of a low mass emission rate. Use of dispersion modelling techniques for determination of the impacts of such emission points is not considered appropriate. A more suitable approach may be to carry out boundary monitoring of VOC concentrations over a 2 week period using passive sampling techniques to determlne the impact of ongoing site operations on ambient VOC concentrations.

Final Report Janrrsfy 3 l . h 31 January 2006

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URS Sola ADC Lenses IPPC Licence Appllcatlon Dispersion Modelling Report

Table 2.3: Stack Descriptions

1 A2-1

A3-11, A3-I2 - TO Be Released through single stack

Major

Minor

I I

Notes: classmGltiom based on T

Descrlptlon

Extract from mixing processes in Plant 1

General extiaction from Plant 2 oven area and general production area

Luff 19%

Emissions

TA Lufl Class 1 - Acrolein, Carbon Tetrachloride, allyl alcohol

TA Luff Class II - Toluene, hexane, acetonitrile

TA Luft Class Ill - Acetone, IPA, Cydo hexane

TA Luft Class I - Acrolein, allyl alcohol

TA Luft Class II - Toluene

TA Luft Class ill -Acetone, cyclohexane, ethyl acetate

Cainpwnds emitted based on revlew of m t monitoiing reports completed at the site Allyl alcohol clonsidered to ba TA Luft Class I m p w n d {allhaugh not spaeifiwlly listed in Annex E of TA tuft 1W) as TA Luft dassification is based on environmental impad with allyl alcohol displaying a dmliar leml of toxicity to the other Class I mpounds Hexane and acetonitrile are considered to be TA luft Class II wmpwnds (althwgh not spedfically tlsted in Annex E of TA Luff 19%) as TA tuft d s s s i h t h is based on environmental Impact, with M of these compwnds dbplaylng B toxiaty (based on OEL value) cwnpsrsble to other Class II campoundS.

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Parameter A2-1 I 9

Helght above roof level {m) 2.6 1 .o

Diameter (m) 0.1 2.05

Assumed exit velocity for modelling (mi')

Reported exit velocity (ms")

0.1 0.1

8.1 - 18.1 1.7 - 2.5

Release temperature ("C) 14 14

Sola ADC Lenses IPPC Licence Application URS Dispersion Modelling Report

Table 2.4: (maximum m

tl oring events :oncentration and mass flow data for 5 most recent moni ass flow events in bold italics)

Stack

=4 2 . 8 ~ t

A2-1

A24

A2-1

A2.1

A2-1

c 1.7 x 10 Oven vent

Oven vent

0.02

Oven vent

Oven vent

0.89 4.5x lo" 0.06 3.9 x io" 2.49 Oven vent

Table 2.5: Stack parameters employed in the modelling exercise

n

I 1 I

Notes:

Stack iQ Is squara section duct, hawever for modelling purposes a drwtar dud of the same surface area is mumed. The exit docity for stack 19 wlll depend on the catlng of the new exbadion fan installed. Due to the nature of the currently Installed vents and kns the measurement of the existing flow mtes Is unreliable (very turbulent ftow). A oombined flw rste for the five emission paint is estimated at 20,000 - 30,oQo Mahout (giving the vetdtles rspMted above). Emission rates for Stack 19 based on data from five separate monitoring events (a single mnt monitored on each msion). The rnaxlmllrn measursd emission rate has been muttiplied by 5 to estimate me maximum likely emission rate for Stack 19.

I

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2.5.

Stack A2-I is fitted with a ‘dlntlse hat‘ tVpe mln mver, while Stad! 19 is release at a slight dwvnward anas whieh will be FeRedSd off the surmunding rwf area. As the vertical exit wdodly Is llmlted an both stacks a m k s e veW of 0.1 mls is m e d to take a m n t of thb.

Model Outputs

The ADMS model set-up allows definition of a grid of receptor points at which the grouna level concentrations of the specified mmpounds are calculated by the model. For the purposes of this assessment, a square grid is taken, stretching to a distance of 500 metres to the north, south, east and west from the centre of the site, with a total of 960 receptor points (approximate 30 metre spacing between points). The receptor grid is illustrated in Figure 2.5.

The model calculates the concentrations for each hour of meteoroiogical data for each receptor point and #en calculates user defined statistics, h i c h in the -se of this modelling assessment is the maximum single hourly concentration at each receptor throughout the year.

For the purposes of this assessment only results for off-site loations are calculated.

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2.6.

Figure 2.5: Receptor Grid for Model Output

Dispersion Modelling Assumptions and Limitations

In practic;e emissions from Stack A2-1 am infrequent due to the nature of operations at the site (see Section 1.2). The mixing process associated with Stack A2-1 Is cam& out under vacuum, hem the most significant period of emissions is when the mixing vassels are being placed under vacuum and when the mixed material is being taken M R o f

associated storage vessels. However, as a conservative approach to the modelling exercise it is assumed that emissions are continuous at the stated level throughout the complete year.

The model --up also assumes that both sources are emitting sbnultaneoprsly and continuously at these meurimum levels.

The model outputs are also consenratively chosen, in that the OEU40 guideline value is compared tu the single hahest hourly Oarslte ground lewd concentreaiOn for the Crwnwe

year.

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URS Sola ADC Lenses IPPC Licence Application Dispersion Modelling Report

3. AIR QUALITY GUlDELINE VALUES

In order to assess the impact of the compounds released k m the stack it is necessary to compare the pfedrcted ground level concentrations to available amblent air quality limit values, or in the absence of statutory limit values to wmpare the predicted concentrations to available guideline values.

The model has been set-up to model emissions to air as TA Luft Class I, 11 and 111 compounds (based on TA Luft 1986) as emissions data for specific compounds are not available. while the current licence limits are also specified for each TA Luft Organics Class. There are no specific air quality limits available for TA tuft Class I, II and 111. In addition, no statutory limits were identified for any of the TA Luft compounds listed in Table 2.3, although guideline values can be derived as follows:

8-hour Occupational Exposure Limits (OELs) divided by a factor of 40. OELs are taken from the 2002 Code of Practice for the Safety, Heatth and Welfare at Work (Chemical Agents) Regulations, 2001. These OEL gutdeline values can then be compared to the maximum single predicted hourly concentration (i.e. the 100* permntile value) for each of the modelled years of meteorological data.

As an initial conservative approach to assessment of the model outputs the specific compound with the lowest guideline value within each TA Luff Class is taken as representative of that class.

The OEL derived guideline values for the compounds identified in Table 2.3 are presented in Table 3.1 below.

Final Repwt January 31 .doc 31 .Isnumy 2W

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Dispersion Modelling Report

Table 3.1: Available guideline values for emitted compounds kg/rn3)

Compound OEt derived guideline value 1

TA Luft Class I

Acrolein 6.25

Allyl alcohol 25

Carbon Tetrachloride 31 5

I

TA Luft Class II

Hexane 1,750

Acetonitrile 1,750 I

Toluene 4,700

TA Luft Class 111

Cyclohexane 8,500

IPA 24,500 I

AoetWI9 30,250

Ethyl acetate 35,000

Final Report January 31 .doc Page 14 31 JMw 2M16 Flnal

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4.

4.1.

4.2.

4.3.

MODEL RESULTS AND DISCUSSION

Introduction

The results for the scenario described in Section 2.4 is presented in Section 4.2. while these results are discussed in Section 4.4. Additional scenarios are also assessed in Section 4.3, as an example of how a number of minor variations to the existing stacks can provide improved dispersion of the releases to air and a reduction in ground level concentrations.

Tabular results are presented far off-site receptors only.

Results

Results for Scenario A

This scenario assumes continuous emissions from both stacks at Ehe maximum measured emission rate.

The resulting ground level concentrations for TA Luft Class I, IJ and Ill compounds are presented in Table 4.1. The concentrations are conservatively compared to the compound within that class with the lowest ground level guideline value (see Table 3.1).

Table 4.1: Maximum predicted ground level concentrations based on Scenario A

TA Luft Class I TA tuft Class II TA Luft Class 111

1 DOm Percenttle (1 -hour maximum concentration)

Guideline Value 6.25 1,750 8,500

2001 53.8 90.9 239.2

2002 61.0 104.3 273 .%

2003 41.6 70.4 185.1

Additional Modelling and Sensitivity Assessment (Seenarto B & C)

The stack configuration at the site results in poor dispersion of the emissions due to a relatively low stack height (Stack 19 in particular) and negligible vertical exit velocity (both stacks).

An additional modelling scenario was completed. taken as Scenario 6, which employed the same emissions data as Scenario A, with the exception of the followlng changes to the stack parameters:

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0 Both stack allowed to release vertically (unimpeded by covers or bends in the pipewark), which will result in a greater ‘effective stack height’ for both stacks due to the increased vertical exit velocity;

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Increase in height of Stack 19 to 10 metres (from approximately 8 metres) to allow increased release height and lower the impact due to building effects {see Section 2.3).

This model was run for a single year of meteorological data (ZOOl), to demonstrate the relative changes In ground level concentrations which may be expected as a result of these alterations. The results of this scenarlo are presented in Table 4.2.

Table 4.2: Maximum predicted ground level concentrations based on Scenario B (results for Scenario A are also presented for comparison)

TA Luft Mass I TA Luft Cfass II TA Luft Class 111

lootn Percentlle (1 -hour maximum concentration)

Guldeline Value 6.25 1,750 8,500

2001 - Scenario 8 7.1 12.1 31.8

2001 - Scenario A 53.8 90.9 239.2

In order to identify the impact that further stack height increases would have on ground level concentrations an additional scenario (Scenario C) was run, with the same inputs as Smnario 8, with the following exception:

Increased stack height for both Stack 19 and Stack A2-1 to 13 metres from original heights used in Scenario A of 8.1 metres and 11.6 metres, respectively.

The results for Scenario C are presented in Table 4.3, with results from Scenario B also being presented for the purposes of comparison.

Table 4.3: Maximum predicted ground level concentrations based on Scenario C (results for Scenarlo 8 are also presented for comparison)

TA Luft Class I TA Luft Class 11 TA Luft Class 111

1 OOm Percentile (I -hour maximum concentration)

Guideline Value 6.25 1,750 8,500

2001 - Scenario C 4.82 8.14 21.41

2001 - Scenario 8 7.1 12.1 31 ‘8

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4.4. Discussion and Recommendations

Scenatio A

This is based on maximum montoring data for both stacks and although based on highly conservative input data, this scenarh still provides the most realistic assessment of the impact due to emissions from Stacks A2-1 and 19.

The results for TA Lufl Class II and Ill are M o w the applicable guideline values.

Acrolein, which exhibits a very low guideline value, is the representative compound chosen for TA Luff Class 1. The resultant maximum TA Luft Class I ground level concentratlons for Scenario A exceed the guideline value for acrolein by a factor of approximately 10, This is based on acrolein emission at the maximum measured TA Luft Class I emission rate for the complete year (i.e. 8,760 hours per annum), while in practice significant emissions of acrolein are likely to be less frequent, given that elevated emissions occur only at certain times (see Section 1.2) . Figure 4.1 presents an isopleth plot detailing the locatlon of the maximum ground level concentrations. This illustrates that the maximum concentrations occur very close to the sources, with concentrations diminishing raplidly with distance from the site boundary. The approximate location of the closest sensitlve receptor (a residence adjacent to the northwest boundary of the site) is indicated in Figure 4.1. Figure 4.2, based on the input data for Scenario C, indicates reduced ground level concentrations in the region of this receptor and at all off-site locations, illustrating that minor changes In the stack layout and height will result in lower ground level concentrations.

In order to improve the overall accuracy of the modelling assessment it may be of use to complete additional speciated monitoring on A2-1 and on the proposed Stack 19. This will allow a more detailed and accurate comparison with applicable guideline values.

Completion of ambient monitoring of acrolein concentrations may also be of use in determining actual ground level concentrations in the vicinity of the site (e.g. use of passive sarnpllng tubes (if available) to collect ambient samples over a 1 to 2 week period).

GeneraUScenarJo B & C

The current stack layout for both stack results in negligible upward plume manenturn and consequent poor dispersion. Dispersion of the releases from the stack a n be improved by implementing a number of small changes as illustrated in Section 4.3. As the model is now set up for the site it can be employed to determine the impact of any proposed alterations to the parameters for Stack A2-1 and Stack 19.

The proposed changes to the Stack for Scenario 6 result in a significant reduction in ground level concentrations of TA Luft Class I organics, which results in a predicted ground level concentration close to the OEL derived limit value for acrolien. The additional changes for Scenario C result in a predicted worst-case TA Luft Class t concentration below the acrolein guidellne value.

. , . .". , . ,. , . . . . . . - . .. - - . . . . .

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Once detailed design information is available for Stack 19 a detailed assessment can be completed to determine the actual impact and to assess the impact of any potential changes to the stack parameters compared to the modelled scenarios.

It is considered that some additional speciated monitoring data is required for Stack A2-1 {during periods where emissions are known to be occurring) to determine me approximate concentrations of individual hydrocarbons within the emissions. Additional monitoring on Stack I 9 would also be of use, once the five existing emission points have been consolidated into Stack 19 (to confirm the accuracy of the input data employed in the model).

Finally, it should be noted that the modelled scenarios provide estimated ground level concentrations for a hypothetical scenario based on the rerouting of current emissions through a proposed single stack (Stack 19). Therefore the reported concentrations may not be an accurate estimate of current ground level concentrations.

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Figure 4.1: IsupMh concentration (Wm? plot for maximum Scenario A TA Luff Class 1 hourly concentration, 2001 meteorological data

Grid Coordinates, Metres (East)

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Grid Coordinates, Metres (North)

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Appendix A = ADMS Model Information

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Appendix A 4DMS Model Information

The ADMS model is an advanced modelling system which requires a variety of input data to ensure realistic predictions of ground level concentrations due to stack emissions. Required inputs indude building dimension data, terrain dah, surface mqhness data, source data (Stack height, diameter, flow rate, emission rates for each compound to be modelled), meteorological data and receptor data.

This assessment considers the impad of releases of substances fram the slacks. No account is taken of the effect of any fugitive or acdde-1 releases. Air dispersion rnwlek are used for calculating air pollution concentrations given infomation about the pollutant emissions and the nature of the atmosphere (factors affecting the dispersion and dilution In the atmosphere). The resultant pollutant concentrations can be compared with air quali standards, objectives or guidelines.

AOMS is a Windows based programme, which requires inputs on a number of tabs for a variety of different parameters. An example of one of the tabs is presented in the screenshot below. This is the s c m n where the source prametea am described.

The impact of a release on the environment wiH be dependent on many fadors, including:

0 the rate of release of each substance;

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other release characteristics, such a5 release location, release velocity and the temperature of the released material;

e the physical properties of the released substance (such as its physical form or particle size);

the chemical properties of the released substances;

the nature of the receiving medium, particularly its dispersive and transfer cbaracteristim and how these vary with time;

ambient concentrations of released substances already present in the environment;

the locations of receptors in the environment sensitive to the released substances; and

the degree of sensitivity of these receptors to enhanced concentrations of released substances.

To quantify these effects and to establish the predicted ground level concentrations of species emitted from on-site sources, URS has undertaken detailed air dispersion modelling for the site. The selected model for use in this assessment is ADMS3, produced by Cambridge Environmental Research Consultants (CERC). This model is a 'new-generation' model, which represents local meteorological conditions in 8 more technically correct way than the older models that utilise semi-empirical stability classes. The main features of ADMS3 are:

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all on-site sources can be modelled together in the same run, to provide an integrated assessment of the whole site;

site-specific hourly sequential meteorological data is used in the modelling assessment to provide worst-case ground level concentrations for realistic condttions;

meteorology is treated in a more comprehensive way than in early dispersion models, using the Monin-Obukhov length instead of the semi-empirical stability classes;

worst-case conditions can be modelled e.g. adverse combinations of meteorology and emissions, which could result in pollution episodes;

effects such 8s steep terrain, coastline and building effects can be taken into account;

model outputs can be calculated for a wide range of averaging periods and percentiles, allowing direct comparison wlth all relevant ambient air pollutant standards and objectives.

The ADMS3 model takes a range of parameters including stack dimensions, emission conditions and representative meteorological data, and calculates the maximum

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concentrations at specified intervals from the emission source using sequential computer algorithms. It is generally considered that air dispersion models are conservative models, over-predicting ground level concentrations. All results quoted in this report are the maximum values predicted by the model, and therefore in the opinion of URS represent the worst case.

The use of an advanced model such as ADMS3 rather than a simpler screening model is considered the best available analytical techntque and enables the incorporation of terraln and building effects on dispersion (if required).

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