Crossness Combustion Facility Revised air quality assessment Thames Water Utilities Ltd

22 October 2020

5181760

Environmental permit variation application

Notice

This document and its contents have been prepared and are intended solely as information for Thames Water Utilities Ltd and use in relation to Crossness Combustion Facility Environmental Permit Variation Application. Atkins Limited assumes no responsibility to any other party in respect of or arising out of or in connection with this document and/or its contents. This document has 74 pages including the cover.

Document history Document title: Revised air quality assessment Document reference: 5181760 Origin- Author- Revision Purpose description ated Checked Reviewed ised Date Rev 1.0 Draft Final ME/JM JM/ME SH JD 24/02/20 Rev 2.0 Final ME SH SH JD 26/02/20 Rev 3.0 Revised for EA ME JM SH JD 22/10/20

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Contents

Chapter Page 1. Introduction 6 1.1. Report structure 6 2. Methodology 8 2.1. Modelling software 8 2.2. Meteorological data 8 2.3. Modelled receptors 9 2.4. Buildings and terrain 10 2.5. Source characteristics 10 2.6. Data sources 12 2.7. Model output 19 3. Baseline Conditions 22 3.1. Site setting 22 3.2. Monitoring data 22 3.3. Defra mapped backgrounds 23 3.4. Sensitive receptors 24 4. Impact Assessment 27 4.1. Introduction 27 4.2. Human receptors 27 4.3. Ecological receptors 48 5. Conclusions 55

Appendices 56 Appendix A. AER Operation 58 A.1. Results for AER Engines 58 Appendix B. Manufacturer’s data 63 B.1. MAN Paxman standby generators 63 B.2. MTU standby generators 65 B.3. Webster House Boilers 67 Appendix C. Non statutory ecological sites 69 C.1. Local nature reserves (LNR) 69 C.2. Sites of importance for nature conservation (SINCS) 69 C.3. Daily Mean NOX 73

Tables Table 2-1 - Site Surface Characteristics 9 Table 2-2 - Exhaust Characteristics – 3 No. CHP Engines and 2 No. CHP Boilers 13 Table 2-3 – Exhaust Characteristics – 4 No. MAN Paxman Standby Engines 15 Table 2-4 - Exhaust Characteristics – 2 No. MTU Standby Engines 16 Table 2-5 - Exhaust Characteristics – 2 No. Webster House Boilers 17 Table 2-6 - Exhaust Characteristics – 2 No. AER Engines 18

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Table 3-1 - Air Quality Assessment Criteria 22 Table 3-2 - Air Quality Monitoring Data for LB Bexley 23 Table 3-3 - DEFRA Mapped Annual Mean Concentrations (µg/m3) 23 Table 3-4 - Discrete Model Receptors for Human Health 24 Table 3-5 - Local wildlife sites within 2km 25 Table 4-1 - Background Pollutant Concentrations Used in the Assessment 27 Table 4-2 - Maximum Annual Average Concentrations of Nitrogen Dioxide – All Sources 28

Table 4-3 - Maximum Annual Average Concentrations of Particulate Matter (PM10) – All Sources 29 Table 4-4 - Maximum Hourly Average Concentrations of Nitrogen Dioxide – Routine Testing 31 Table 4-5 - Maximum Daily Average Concentrations of Particulate Matter – Routine Testing 34 Table 4-6 - Maximum 8 hour Average Concentrations of Carbon Monoxide –Routine Testing 35 Table 4-7 - Maximum 1 hour Average Concentrations of Carbon Monoxide – Routine Testing 36 Table 4-8 - Maximum 15 Minute Average Concentrations of Sulphur Dioxide – Routine Testing 37 Table 4-9 - Maximum Hourly Average Concentrations of Sulphur Dioxide – Routine Testing 37 Table 4-10 - Maximum Daily Mean Concentrations of Sulphur Dioxide – Routine Testing 38 Table 4-11 - Maximum Hourly Average Concentrations of Nitrogen Dioxide – Black Start Test 39 Table 4-12 - Maximum Daily Average Concentrations of Particulate Matter – Black Start Test 41 Table 4-13 - Maximum 8 hour Average Concentrations of Carbon Monoxide – Black Start Test 41 Table 4-14 - Maximum 1 hour Average Concentrations of Carbon Monoxide – Black Start Test 42 Table 4-15 - Maximum 15 Minute Average Concentrations of Sulphur Dioxide – Black Start Test 44 Table 4-16 - Maximum Hourly Average Concentrations of Sulphur Dioxide – Black Start Test 44 Table 4-17 - Maximum Daily Mean Concentrations of Sulphur Dioxide – Black Start Test 45 Table 4-18 – Ecological Impact Assessment – long term, sites within 2km 48 Table A-1 - Maximum Annual Average Concentrations of Nitrogen Dioxide – AER Engines 58

Table A-2 - Maximum Annual Average Concentrations of Particulate Matter (PM10) – AER Engines 58 Table A-3 - Maximum Hourly Average Concentrations of Nitrogen Dioxide – AER Engines 59 Table A-4 - Maximum Daily Average Concentrations of Particulate Matter – AER Engines 60 Table A-5 - Maximum 8 hour Average Concentrations of Carbon Monoxide – AER Engines 60 Table A-6 - Maximum 1 hour Average Concentrations of Carbon Monoxide – AER Engines 61 Table C-1 – Annual mean process contribution at LWS (µg/m3) 71 Table C-2 – Maximum 24-hour mean NOx concentration at LWS (µg/m3) 72 Table C-3 – Top 50 24 hour Average Concentrations of Oxides of Nitrogen (µg/m3) – All sources 73

Figures Figure 2-1 - London City Airport Wind Rose, 2013 to 2017 9 Figure 2-2 - Schematic of Modelled Structures and Stacks 10 Figure 3-1 - Selected Human (D) and Ecological (Green Shaded) Receptor Locations 26 Figure 4-1 - Maximum Annual Average Nitrogen Dioxide Concentrations, µg/m3 – 2014, All Sources 29 Figure 4-2 –Nitrogen Dioxide Maximum Hourly Mean Concentration, Routine Testing 33 Figure 4-3 – No. Exceedances of Nitrogen Dioxide Hourly Mean Standard – 2014, Black Start Test 47 Figure 4-4 - Maximum Annual Average Oxides of Nitrogen Concentrations, µg/m3 – 2014, All Sources 51 Figure 4-5 - Maximum Annual Average Sulphur Dioxide Concentrations, µg/m3 – 2014, All Sources 52

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Figure 4-6 - Maximum 24 hour Average Oxides of Nitrogen Concentrations, µg/m3, Scenario 2 53 Figure 4-7 - Maximum 24 hour Average Oxides of Nitrogen Concentrations, µg/m3, Scenario 3 54 Figure B-1 - MAN Paxman engine plate 63 Figure B-2 - MAN Paxman emission parameters 63 Figure B-3 - MAN Paxman stack testing results (September 2019) 64 Figure B-4 – MTU engine plate 65 Figure B-5 – MTU engine flow rate data 65 Figure B-6 – MTU engine emissions data 66 Figure B-7 – Webster House Boiler Plate 67 Figure B-8 – BS845-1 Boiler Calculation 68 Figure C-1 – Local nature sites (from GIGL website) 70

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1. Introduction

This revised air quality assessment, prepared by Atkins Ltd on behalf of Thames Water Utilities Limited (TWUL), has been produced in support of the Industrial Emissions Directive (IED) Section 1.1 A(1)(a) bespoke permit variation application for the Crossness Combustion Facility at Crossness Sewage Treatment Works (STW). As the site operates existing plant with an aggregated capacity of over 50 megawatt thermal input (MWth), an Environmental Permit (EP) variation is required under Schedule 1 of the Environmental Permitting Regulations1, to vary the regulated facility from a waste operation to an Installation. This is revision 3 of the report, which has been updated to remove the assessment of elective running, and to reflect a revised testing regime agreed by TWUL in response to the Environment Agency’s Schedule 5 notice. The plant to be permitted include combined heat and power engines and boilers utilising biogas generated by the thermal hydrolysis process (THP), standby diesel generators and diesel boilers. The assessment also considers the Advanced Energy Recovery (AER) demonstration facility which produces a fuel gas (syngas) from digestate generated by the on-site anaerobic digestion facility. The syngas is subsequently combusted in two new combined heat and power (CHP) engines on site. These will be subject to a separate variation application, but which are included here for completeness. The CHP plant engines and boilers and the standby plant operated by TWUL have a combined thermal input of approximately 60 MWth. The six Powerhouse standby diesel generators are used for emergency use only; they will no longer be used for export of electricity during periods of high power demand on the local network (e.g. Triad periods, Short Term Operating Reserve (STOR) and capacity market (CM) agreements). The Crossness STW is set within an area of mixed industrial, commercial and residential uses, near to the Abbey Wood and Thamesmead areas within the London Borough (LB) of Bexley. To the east of the site is a commercial and industrial area within Belvedere, to the south is Southmere Park, to the west are residential areas of Thamesmead and to the north is the River Thames. LB Bexley has declared a borough-wide air quality management area (AQMA) due to exceedances of the annual average nitrogen dioxide (NO2) and both the annual mean and daily average particulate matter (PM10) objectives at certain locations. This report describes the findings of a dispersion modelling study of the atmospheric emissions of oxides of nitrogen (NOx), particulate matter (both PM10 and PM2.5 size fractions), carbon monoxide (CO) and sulphur dioxide (SO2). The modelled increments to short-term and long-term ground level concentrations are evaluated in the context of the national air quality objectives, considering the existing ambient air quality. The revised assessment has considered the following scenarios: • Scenario 1 Long Term – Routine Operation: all routinely operated plant operating on an annual basis and a weighted contribution from standby sources; • Scenario 2 Short Term – Routine Testing: all routinely operated plant plus routine testing (maintenance and HV testing) of standby generators in line with the standard testing regime; and • Scenario 3 Short Term – Black Start Test: all routinely operated plant plus black start testing of standby generators. This study evaluates the environmental impact of air pollutant emissions on human health and ecological receptors, following the requirements of the risk assessment and dispersion modelling guidance for permit applications provided by the Environment Agency2,3, which applies to all bespoke permit applications. Supplementary technical air quality guidance for Specified Generators (SG) regulated under Schedule 25B4 published by the Environment Agency has also been referred to where appropriate. 1.1. Report structure This report presents the findings of an atmospheric dispersion modelling study of stack emissions from combustion sources at Crossness STW and evaluates the potential effects upon local receptors.

1 Statutory Instrument 2018 - No.110. The Environmental Permitting (England and Wales) (Amendment) Regulations 2018 2 Available at: https://www.gov.uk/guidance/environmental-permitting-air-dispersion-modelling-reports 3 Available at: https://www.gov.uk/guidance/air-emissions-risk-assessment-for-your-environmental-permit 4 Available at: https://consult.environment-agency.gov.uk/psc/mcp-and-sg- regulations/supporting_documents/Specified%20Generators%20Modelling%20GuidanceINTERIM%20FINAL.pdf

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The report documents the existing background air quality from published sources, characterises the atmospheric emissions from the installation, describes the operational regime and the approach used for the assessment of the emissions, and presents the results of the air dispersion modelling study. The results are presented graphically and the potential effects at human and ecological receptors are also tabulated and discussed. The report is set out as follows: • Section 2 presents the methodology used for the atmospheric dispersion modelling including the meteorological data, treatment of buildings and terrain, source emissions data, discrete model receptors and the relevant air quality criteria; • Section 3 presents information representative of the baseline conditions in the local area including any air quality monitoring and background pollutant levels; • Section 4 presents the results of the air dispersion modelling for the operational scenarios considered and assesses the impact on human health and ecological receptors; and • Section 5 provides conclusions to the study.

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2. Methodology 2.1. Modelling software The atmospheric dispersion modelling was undertaken using the latest version of the US EPA model AERMOD (19191), as incorporated by Trinity Consultants Inc. in the software BREEZE AERMOD. This model is the result of many years development by the US EPA and the American Meteorological Society. It has been developed as a regulatory model that incorporates the current understanding of atmospheric physical processes. This model is used by regulatory agencies, consultants and industry worldwide to assess the impact of air emissions from point, area, line, flare and volume sources. AERMOD simulates essential atmospheric physical processes and provides refined concentration estimates over a wide range of meteorological conditions and modelling scenarios. The modelling system includes: • an advanced meteorological pre-processor to compute site-specific planetary boundary layer parameters; • highly developed dispersion formulations that incorporate current planetary boundary layer understanding and variables for both convective and stable boundary inversions; • enhanced treatment of plume rise and plume penetration for elevated inversions allowing for effects of strong updrafts and downdrafts that occur in unstable conditions; • improved computation of vertical profiles of wind, turbulence and temperature; and • a “dividing streamline” approach for computations in complex terrain. AERMOD includes two data pre-processors for streamlining data input: AERMET, a meteorological pre- processor, and AERMAP, a terrain pre-processor. The model can address both local topography and building downwash effects concurrently, where relevant to the study. The model provides reasonable estimates over a wide range of meteorological conditions and modelling scenarios. The building downwash algorithms in AERMOD PRIME, using parameters calculated by the Building Parameter Input Program (BPIP), distinguish this model from earlier versions of AERMOD, which used a simpler procedure to address downwash. 2.2. Meteorological data The London City Airport meteorological station was deemed the most appropriate site with adequate records in the format required for the dispersion modelling study. This station is located approximately 6 km to the west of the Crossness STW. Hourly sequential meteorological data for the five-year period 2013 to 2017 were used in the dispersion model. The meteorological data file contains over 43,000 hourly records and, in accordance with best practice, is considered adequate to characterise local meteorology in terms of both extreme events and long-term average conditions. The model results presented thus robustly characterise the effects of the plant emissions on ambient concentrations due to both short-term (e.g. hourly) meteorological events and to long- term (e.g. annual) average meteorological conditions. In accordance with the US EPA modelling guidance, the near-field land use within a one-kilometre radius of the site was evaluated to determine the surface roughness length5. Land uses were specified by directional sector. The Bowen ratio6 and albedo7 were determined by the land use categories within the far-field, represented by a 10 x 10 km square centred on the site. A determination of the percentages of each type of land use was made based on inspection of Ordnance Survey mapping and aerial photography. The far-field land use proportions are simply averaged over the area and are independent of distance or direction from the site. Surface characteristics were specified to reflect the nature of the area surrounding the facility. In line with the latest US EPA guidance, the near-field land use within a one kilometre diameter circle was evaluated to determine the surface roughness length. Land uses may be specified by directional sector. The Bowen ratio and albedo were determined by the dominant land use categories within the far-field, a 10 by 10 kilometre square. A visual estimate of the percentages of each type of land use was made based on maps and aerial photographs. The land use proportions are simply averaged over the area and are independent of distance or direction from the site. Urban, cultivated land, deciduous woodland and water comprised 72%, 16%, 3% and

5 Surface roughness length is a measure of the height of obstacles to wind flow. It is not equal to the physical dimensions of obstacles but is generally proportional to them. 6 The Bowen ratio is a measure of the amount of moisture at the earth’s surface. This influences other parameters which in turn affect atmospheric turbulence. 7 Noon-time albedo is the fraction of incoming solar radiation reflected from the ground when the sun is directly overhead. Adjustments are made in AERMET to incorporate the variation in the albedo with solar elevation angle.

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9% respectively. The pre-processor generates appropriate default annual average values for these parameters based on the land use information. The derived values used for surface parameters are presented in Table 2- 1.

Table 2-1 - Site Surface Characteristics Sector Degrees Albedo Bowen Ratio Surface Roughness, m 105 to 304 Urban 0.21325 1.35675 1.0 304 to 105 Water 0.21325 1.35675 0.000075

The assessment used AERMOD recommended values where appropriate. A surface roughness value of 1.0 m was used to represent the majority of the urban/industrial landscape area surrounding the site, with a value of 0.000075 used to represent the River Thames to the north (which is over 600 metres wide at this point). The meteorological data was used to generate a five-year frequency distribution of wind speed and direction. The data is presented as a wind rose diagram in Figure 2-1. It is evident from the data that winds from the south-southwest and adjoining sectors are both the most frequent, with a secondary prevailing wind from the east. Figure 2-1 - London City Airport Wind Rose, 2013 to 2017

2.3. Modelled receptors Ground level concentrations were modelled using nested Cartesian receptor grids covering wide and local areas. A 100 m resolution grid over a wide area, 4 x 4 km, was used. An 8 x 8 km grid was also modelled at a 200 m resolution for receptors further afield. A boundary receptor network comprising almost 100 additional receptor locations was also established to evaluate maximum off-site concentrations. Discrete receptors were also specified to represent areas of public exposure. All sensitive receptors were modelled at a flagpole height of 1.5 m to represent breathing height. Sites of ecological interest relevant to the application were not included as discrete receptor points; instead, concentrations were derived from contour outputs. No sites of international and European importance were

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identified within 10 km of the site. Ecological receptors within 2 km of the site included SSSI, local nature reserves, ancient woodland and local wildlife sites. At the request of the Environment Agency in the subsequent Schedule 5 notice, predicted concentrations at seventeen specific Local Wildlife Sites (LWS) has been produced for this revised air quality assessment report. Contour plots were produced using the grid receptors to allow for subsequent inference of pollutant concentrations at any other locations of interest within the model domain (e.g. local sites of importance). 2.4. Buildings and terrain Buildings close to point source plume discharges that are more than 40% of the stack height may potentially cause downwash effects. The BPIP programme was used to calculate for each wind sector the direction specific building downwash parameters to be used by AERMOD PRIME in the dispersion calculations. Building height information was derived from schematics provided by TWUL or from LIDAR data at a resolution of 1 m. Details of the buildings included in the dispersion model are shown as a schematic in Figure 2-2. The emission sources are shown in light blue with buildings included in the model shown as blue blocks. Due to the number and complexity of buildings, 88 in total, detailed of the buildings are not provided in this report. Information on these can readily be evaluated from the model input file. Figure 2-2 - Schematic of Modelled Structures and Stacks

Terrain elevations for all model objects and receptors were used in the dispersion model, as derived from Ordnance Survey digital terrain data files (in “DEM” format). 2.5. Source characteristics

2.5.1. Emissions to air The Crossness site operates various combustion plant which have been considered in the air quality assessment. In line with EPR guidelines, and as agreed at the pre-application meeting with the Environment Agency local officer (25th November 2019) the detailed assessment has focussed on all combustion sources with a net thermal input exceeding 1 MWTH. The following sources have been included in the air dispersion model: • CHP Engines

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- A1 to A3 – 3 No. 4.7 MWTH MWM CHP engines, fuelled by site generated biogas; • CHP Boilers

- A4 to A5 – 2 No. 4.7 MWTH ICI CHP boilers, fuelled by site generated biogas or natural gas; • Standby Diesel Generators

- A8 to A11 – 4 No. MAN Paxman 5.2 MWTH engines, fuelled by diesel;

- A12 to A13 – 2 No. MTU 5.6 MWTH engines, fuelled by diesel; • Webster House Boilers

- A15 to A16 – 2 No. 0.5 MWTH Ideal Viceroy boilers, fuelled by fuel oil (diesel); • AER Plant Engines

2 No. 1.94 MWTH engines, fuelled by site produced syngas fuel (yet to be permitted).

The above list omits some installed combustion plant which are either not used or used only in unlikely operational or emergency situations. This includes the two redundant and unused English Electric engines and the site flares. Flare operation has not been included in the model for reasons outlined in detail below. The two flare stacks are installed to burn excess biogas when the CHP engines are not in operation. This is essential to maintain the biogas supply system pressure within safe limits under emergency circumstances. Biogas is preferentially burned in the engines or boilers; the flares are intended to be used in emergency scenarios only. The biogas fuelled combustion plant have a capacity of 77,784 Nm3/day (CHP Engines - 59,016 Nm3/day, CHP Boilers - 18,768 Nm3/day) exceeding the theoretical maximum STW biogas production rate of 73,079 Nm3/day. The biogas production rate is based on maximum throughput of the production process and as such is not always achieved. Typically, the STW biogas production allows for full operation of the CHP engines and operation of one of the two CHP boilers at 75% load, which demonstrates the low requirement for flare use. If biogas production does exceed combustion capacity, the flares, which effectively are low NOx burners with staged combustion at higher temperatures, are used. As NOx emissions per Nm3 of biogas combusted are approximately a third of that emitted by the CHP engines and boilers, pollutant emissions are greatest when the flares are not in use. Given that emission from the CHP engines and boilers is higher than that of the flares and the model assumes that more biogas is combusted than is available, an assessment that excludes the flares as operational is thus shown to be conservative.

Plant with a thermal input below 1 MWTH are deemed to have a low likelihood of off-site impacts due to their small size and limited operational hours, as agreed with the Environment Agency in a pre-application meeting, they have not been modelled or assessed. The assessment that is presented is conservative because it assumes the maximum theoretical operational hours and capacity of plant running simultaneously. For instance, there is insufficient biogas to operate all engines and boilers together, however the routine operational scenario has modelled all CHP plant, boilers and AER engines at maximum load, all emitting at their permitted limits. Therefore, the conservative approach to other combustion plant means the omission of small, temporary plant will not have a material effect on the model results.

The assessment considers emissions of NOx and CO and, where appropriate according to fuel type, PM10 and SO2.

2.5.2. Operational regime For the purposes of this conservative assessment, the 3 No. CHP engines, 2 No. CHP boilers, 2 No. Webster House boilers and 2 No. AER engines are assumed to run continually throughout the year. These are described as the “routine” sources. The MAN Paxman and MTU Standby Diesel Generators in the Powerhouse do not operate continuously as they are for emergency use only. They are operated at regular intervals throughout the year for testing purposes to ensure their availability in the event of an emergency. The maximum expected operating hours for these standby generators is fewer than 50 hours per engine, under the following conditions: • Routine/HV maintenance – up to 43.5 hours per engine, tested consecutively (each engine operated for 1.5 hours for no more than six hours per day, i.e. four tests per day at maximum expected duration);

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• Black Start Test – up to six hours duration, all engines operated concurrently once a year (maximum six hours per year); No two types of test would be undertaken at the same time. In an emergency event, such as loss of offsite power, all six engines would operate for up to one hour duration (this has not been modelled as it is a very rare occurrence and impact is covered by the black start test).

2.5.3. Model scenarios The dispersion model was run for the following scenarios: 1. Scenario 1 Long Term – Routine Operation: – emissions from routinely operated (i.e. continuous) combustion plant (CHP engines and boilers, Webster House boilers, and future AER engines) plus a factored contribution from, as a very conservative scenario, all standby generators operating together for comparison with annual mean criteria; 2. Scenario 2 Short Term - Routine Testing: emissions from routinely operated combustion plant together with routine testing of standby plant, run consecutively for up to six hours in a day (43.5 hours per engine per year) for comparison with short-term criteria; 3. Scenario 3 Short Term – Black Start Test: emissions from routinely operated combustion plant together with all six standby generators operating concurrently (black start test, one test per year for up to six hours in a day) for comparison with short-term criteria.

In addition, the modelled concentrations for the AER Plant Engines alone are presented for information purposes only in Appendix A; the results may be used to accompany a future application/variation for the AER Plant sources. To maintain a conservative assessment, both routine and standby (non-routine) plant have been assumed to run continuously in the dispersion model and compared to short-term assessment criteria. Where the modelling indicated a potential breach of the assessment criteria under this conservative scenario i.e. more than 18 hours’ exceedance at a receptor location, the Environment Agency’s recommended hypergeometric distribution methodology8 was used to evaluate the probability of the assessment level being exceeded. The results have been compared to relevant Ambient Air Directive (AAD) limit values and other air quality benchmarks for permitting set out in the Environment Agency’s online guidance for air emissions risk assessment. Both the process contribution (PC) and predicted environmental concentration (PEC, including background contribution) are presented. For the comparison to long term criteria, a weighting has been applied to derive the incremental contribution from the non-routine testing of standby plant over the course of a year. For the annual average calculations, the six standby engines were modelled as operating concurrently; however, most testing will be for single engines and thus it contributes to a more conservative approach. The modelled results are conservative and will overstate impacts at receptor locations for actual operation, in particular, for short-term exceedences as all hours of the year have been modelled. As such, if the modelled results are compliant with the air quality standards, there can be confidence that the impacts will be lower and therefore also compliant with the relevant air quality standards. 2.6. Data sources Primacy of information was discussed with the Environment Agency prior to the start of this assessment. The assessment has used a range of information sources with the assessment firstly using information from already approved and operational environmental permit, where appropriate. For new or previously unassessed combustion plant the hierarchy of preference, as specified by the Environment Agency, was adopted. The hierarchy is as follows: a. Emissions measurements from the specific unit under assessment b. Emissions data for the specific model as identified on the manufacturer’s specification data sheet, accounting for any likely degradation in performance (e.g. in older plant) if needed c. Emissions measurements from similar units in the TWUL portfolio d. Emission factors taken from the US EPA Compilation of Air Pollutant Emission Factors (AP-42), using data relevant to the specific type of plant

8 Environment Agency, Specified Generator modelling guidance-interim final (2018) https://consult.environment-agency.gov.uk/psc/mcp- and-sg-regulations/supporting_documents/Specified%20Generators%20Modelling%20GuidanceINTERIM%20FINAL.pdf

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e. Emission factors taken from the EMEP-EEA Air Pollutant Emission Inventory Guidebook 2016 Section 1.A.4 “Small Scale Combustion”, using data relevant to the specific type of plant, and taking any assumed abatement into account (emission factors from the Emission Inventory Guidebook typically refer to plant with a relatively high standard of control and abatement which would need to be taken into account when applying to plant installed at TWUL sites. As a result, emission factors from this source are lower in the hierarchy than option d (US EPA AP-42 guidebook) f. Emissions data for a comparable model, as identified on a specification data sheet g. Emissions limits expected to be specified in the permit (unlikely to be directly relevant, however, as would not be expected to reflect current operational conditions)

A similar order of priority was given to the derivation of exhaust flow parameters which included, in the following order of priority: • stack testing results (provided in Appendix B for standby engines); • manufacturers specification sheets (provided in Appendix B); and • stochiometric calculation of exhaust gases. Data relating to the maximum continuous rating operation of each combustion source, and the data sources are summarised in the following sections. Emissions of NOX, SO2, particulate matter and CO were all modelled for diesel fuelled plant. Environmental permits for gas phase plant do not typically consider particulate matter due to improved fuel mixing and complete combustion, however industry benchmark emission values were applied in this assessment for completeness.

2.6.1. CHP engines and boilers (A1 to A5) The modelled stack emission and flow rates for the three biogas fired CHP engines and two biogas boilers were taken from the Air Quality Assessment that accompanied the 2013 environmental permit application for the permitted CHP operation. Of the two scenarios presented in the 2013 Air Quality Assessment, Scenario 1, representing full operation of all combustion plant on biogas, was selected for this conservative assessment. Stack testing data is available for these sources and was compared with the data used for the permit application. The permit application data, which uses ELVs, provided a more conservative approach. This assessment has additionally included emissions of particulates, using indicative benchmark values in the absence of an ELV9. Data relating to the maximum continuous rating operation of the CHP engines and boilers is presented in Table 2-2. The five engine flues were modelled as a single discharge with a virtual diameter of 1.21 m, thus conserving the same cross-sectional area as the five physical flues.

Table 2-2 - Exhaust Characteristics – 3 No. CHP Engines and 2 No. CHP Boilers Parameter Engine (per unit) Boiler (per unit) Combined Flue No. of Units 3 2 - Grid Reference - - 548671.3, 180939.6 Stack height, m - - 45 Stack diameter, m 0.5 0.6 1.21 Actual discharge flow rate, Am3/s 3.9 4.3 20.1 Discharge velocity, m/s 19.7 15.1 17.5 Flue gas discharge temperature, C 180 247 208 Moisture content, % v/v 11.3 16.8 - Oxygen content, % v/v (dry basis) 7.8 2.6 -

Normalised flow rate, 273 K, 5% O2 (dry basis), 1.6 2.1 9.0 Nm3/s (4.31) (2) (5.66) (2) (24.3) (2)

9 Particulates are of limited concern for gas fired equipment, thus a screening approach was agreed at the pre-application meeting with EA local officer (telecon, 25/11/19)

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Parameter Engine (per unit) Boiler (per unit) Combined Flue

Oxides of nitrogen (as NO2) emission 500 100 - 3 concentration, mg/Nm at 5% O2 (185.5) (2) (37.1) (2) Particulate matter emission concentration, 10 (1) 10 (1) 10 (1) 3 mg/Nm at 5% O2 (3.7) (2) (3.7) (2) (3.7) (2) Carbon monoxide (CO) emission concentration, 1,400 50 - 3 mg/Nm at 5% O2 (519.5) (2) (18.6) (2)

Sulphur dioxide (SO2) emission concentration, 350 45 - 3 mg/Nm at 5% O2 (129.9) (2) (16.7) (2)

Oxides of nitrogen (as NO2) emission rate, g/s 0.79 0.21 2.78 Particulate matter emission rate, g/s - - 0.05 Carbon monoxide (CO) emission rate, g/s 2.2 0.1 6.81

Sulphur dioxide (SO2) emission rate, g/s 0.55 0.09 1.84

(1).No limit set in the Environmental Permit due to these being gas fired plant and no stack testing therefore undertaken for this pollutant. EPR1.01 benchmark value of 10 mg/Nm3 used as a conservative estimate of emissions for engines and boilers. (2) Both engines and boilers were presented in the 2013 assessment at 5% oxygen due to the presence of a combined flue. Number in brackets therefore represent the normalised flow rate/emission concentration at 15% O2 for both engines and boilers for comparison with MCPD reference conditions for the former.

To ensure that the 2013 Air Quality assessment provides conservative assessment, the emission rates and actual flow rates were compared to stack testing results. Data from stack testing in June 2019 demonstrated total combined flue NO2 and CO emission rates of 2.59 g/s and 4.22 g/s compared to modelled values of 2.78 g/s and 6.81 g/s respectively. As such, the emission rate used in the dispersion model is conservative. Hierarchy of information – • Permit application air quality assessment (based on manufacturer’s datasheets and agreed ELVs applicable under the 2013 permit application); • Permit emission rates, based upon ELV and compared to testing results (a); • Benchmark emission used for particulate matter as no ELV set in permit or requirement for testing (f).

2.6.2. MAN Paxman standby diesel generators (A8 to A11) Stack parameters and pollutant emission rates for the four MAN Paxman diesel standby generators, at rated load operation, were derived from manufacturer’s data and stack testing conducted on 11th September 2019. To maintain a conservative approach, the higher of either the measured or theoretical flow/emissions data were selected. Data relating to the maximum continuous rating operation of a single engine are summarised in Table 2-3. The NOX, particulate matter and SO2 emission concentrations were used to derive the emission rates presented. The individual engine flues are mounted on the roof of the Powerhouse building, providing an emission point approximately 1.5 m above the highest point of the building. A horizontal flue is fitted to the exhaust, facing northeast. To allow building influences to be modelled for all emission sources using the AERMOD building downwash module, emissions from these sources were modelled using the ‘horizontal point source’ option. The four engine flues were modelled as individual point sources as they are not sufficiently close together to have compound buoyancy influences.

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Table 2-3 – Exhaust Characteristics – 4 No. MAN Paxman Standby Engines Parameter Engines 1-4 No. of units 4 Grid Reference, m 1. 548736.6, 180731.0 2. 548748.0, 180724.5 3. 548764.9, 180714.8 4. 548775.1, 180709.2 Stack height, m (horizontal flues) 13.5 Stack diameter, m 0.48 (2) Actual discharge flow rate, Am3/s 8.43 (1) 5.35 (2) Discharge velocity, m/s 29.6 (2) Flue gas discharge temperature, °C 387 (1) 363 (2) 10.6 (1) Moisture content, % v/v 12.2 (2) 12.2 (1) Oxygen content, % v/v (dry basis) 10.6 (2) (1) 3 1.71 (4.57) Normalised flow rate, 273 K, 5% O2 (dry basis), Nm /s 1.31 (2) (3.52) (1) Oxides of nitrogen (as NO2) emission rate, g/kWh 10.75 (1) Oxides of nitrogen (as NO2) emission rate, g/s 5.97 Particulate matter emission rate, g/s 0.07 (2) Carbon monoxide (CO) emission rate, g/s 0.47 (2) (2) Sulphur dioxide (SO2) emission rate, g/s 0.07 3 (4) (1) (3) Oxides of nitrogen (as NO2) emission concentration, mg/Nm at 5% O2 3483 (1306) 2800 (2) (1050) (3) 3 (1) (3) Particulate matter emission concentration, mg/Nm at 5% O2 22 (8.2) 49 (2) (18.2) (3) 3 (2) (3) Carbon monoxide (CO) emission concentration, mg/Nm at 5% O2 134.6 (50.5) 3 (2) (3) Sulphur dioxide (SO2) emission concentration, mg/Nm at 5% O2 18.9 (7.1)

(1) Manufacturer’s data sheet. For NOx, 10.75 g/kWh, TWUL stated max 2000 kWe gives 5.97 g/s, far more 3 conservative than stack testing rate of 3.7 g/s. For PM, 22 mg/Nm assumed to be at 5% O2. (2) Data from stack testing conducted September 2019 (Appendix B). Note, stack test reports to 15% O2 reference conditions, manufacturer used 5% O2. (3) Number in brackets represents the normalised flow rate/emission concentration at 15% O2 (4) Not used in modelling, for information only. Manufacturer states 3279 mg/Nm3. Small difference due to alternative route of derivation from NOx emission in g/kWh. Very conservative compared to measured value.

Emission concentrations derived from the manufacturer’s datasheet were considerably above the measured values for NOx, the key pollutant of concern in this assessment. The higher NOx value presented above was therefore used in the model to maintain a highly conservative approach to assessment. Hierarchy of information: • Exhaust parameters and mass emissions from stack testing results (a); and • Emission concentrations provided by manufacturer (b), where more conservative.

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There are acknowledged to be minor discrepancies between the emission concentrations and normalised flow rates due to the mixture of data sources used. This does not affect the outcome of the assessment.

2.6.3. MTU standby diesel generators (A12 and A13) Stack characteristics and emissions data for the two MTU diesel standby generators, at rated load operation, were taken from comprehensive technical specifications for the 20V4000G63L engine, provided by the manufacturer. Data relating to the maximum continuous rating operation of a single engine are summarised in Table 2-4. The individual engine flues are mounted on the roof of the Powerhouse building, providing a position 1.5m above the highest point of the building. A horizontal flue is fitted to the exhaust, facing northeast. To allow building influences to be modelled for all emission sources using the AERMOD BPIP module, emission from these sources have been modelled using the ‘horizontal point’ option. The two engine flues were modelled as individual point sources as they are not sufficiently close together to have compound buoyancy influences.

Table 2-4 - Exhaust Characteristics – 2 No. MTU Standby Engines Parameter Engines 1 & 2 No. of units 2 Grid Reference, m 1.) 548722.8, 180738.8 2.) 548732.5, 180733.3 Stack height, m 13.5 Horizontal flue Stack diameter, m 0.48 Actual discharge flow rate, Am3/s 7.10 Discharge velocity, m/s 39.2 Flue gas discharge temperature, C 370 (1) Moisture content, % v/v 10 (2) (5) Oxygen content, % v/v (dry basis) 7.7 (2) (2) 3 1.83 Normalised flow rate, 273 K, 5% O2 (dry basis), Nm /s (4.93) (4) (3) Oxides of nitrogen (as NO2) emission rate, g/kWh 10.40 Particulate matter emission rate, g/kWh 0.04 (3) Carbon monoxide (CO) emission concentration, g/kWh 0.500 (3) (3) Sulphur dioxide (SO2) emission rate, g/kWh 0.002

Oxides of nitrogen (as NO2) emission rate, g/s 6.99 Particulate matter emission rate, g/s 0.03 Carbon monoxide (CO) emission rate, g/s 0.34

Sulphur dioxide (SO2) emission rate, g/s 0.001 (2) 3 (5) 3823 Oxides of nitrogen (as NO2) emission concentration, mg/Nm at 5% O2 (1419) (4) (2) 3 (5) 15 Particulate matter emission concentration, mg/Nm at 5% O2 (5) (4) (2) 3 (5) 184 Carbon monoxide (CO) emission concentration, mg/Nm at 5% O2 (68) (4) (2) 3 (5) <1 Sulphur dioxide (SO2) emission concentration, mg/Nm at 5% O2 (<1) (4)

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(1) Estimated temperature based on heat loss from 519°C exhaust temperature from the combustion chamber. (2) Not used in assessment as manufacturer data provided actual exhaust flow and emission rates in terms of power output (g/KWh) which were used to directly calculate model input in g/s (3) As stated on manufacturer datasheet (4) Number in brackets represents the normalised flow rate/emission concentration at 15% O2 but not used in the assessment so presented for information only (5) Assumption of 10% moisture in actual flow

Hierarchy of information: • Technical details from manufacturer’s full specification sheet (b); - Exhaust parameters based on stochiometric calculations based upon fuel use data; - No testing data for MTUs due to safety/accessibility (lack of testing ports due to type of engines); - One of the older standby generators (Paxman) was selected by TWUL for testing on basis that it would represent a worst case for emissions due to age; - Manufacturer’s data was comprehensive and preferred to a single test result for alternative engine; the calculated emission rate for NOx is conservative by comparison.

2.6.4. Webster House Boilers (A15 and A16) The modelled emission and flow rates for the Webster House diesel boilers, each at rated load operation of 0.54 MWTH, were taken from technical specifications for the Viceroy GTS9 boiler unit provided by the manufacturer. Emission testing of these relatively minor sources has not been undertaken due to site constraints including suitable access and safety. Instead, exhaust flow parameters were calculated based on the rated thermal input of the unit and emission rates were based upon MCPD limit values and EPR benchmark emission concentrations. These were compared with stack test data for diesel fired boilers at Mogden STW. Model input data relating to the maximum continuous rating operation of the diesel boilers are presented in Table 2-5. The two boiler flues were modelled as a single discharge with an effective stack diameter of 0.35 m, thus conserving the same cross-sectional area as the two physical flues.

Table 2-5 - Exhaust Characteristics – 2 No. Webster House Boilers Parameter Boiler (per unit) Combined Flue No. of Units 2 - Grid Reference - 548680.7, 180572.3 Stack height, m - 20 Stack diameter, m 0.25 0.35 Actual discharge flow rate, Am3/s 0.32 0.65 Discharge velocity, m/s 6.59 6.59 Flue gas discharge temperature, C 220 220 Moisture content, % v/v 10.4 10.4 Oxygen content, % v/v (dry basis) 2.97 2.97 Reference oxygen content 3% 3% 3 Normalised flow rate, 273 K, 3% O2 (dry basis), Nm /s 0.179 0.359 3 (1) Oxides of nitrogen (as NO2) emission concentration, mg/Nm 200 200 Total particulate matter emission concentration, mg/Nm3 (2) 15 15 Carbon monoxide (CO) emission concentration, mg/Nm3 (2) 150 150 3 (2) Sulphur dioxide (SO2) emission concentration, mg/Nm 175 175

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Oxides of nitrogen (as NO2) emission rate, g/s 0.036 0.072 Particulate matter emission rate, g/s 0.003 0.005 Carbon monoxide (CO) emission rate, g/s 0.027 0.054

Sulphur dioxide (SO2) emission rate, g/s 0.031 0.063

(1) MCPD limit at 3% reference oxygen (no limits set for boilers other than on NOx emissions) (2) EPR 1.01 benchmark (liquid fuel, new, 50-100 MWth)

Hierarchy of information sources: • Boiler details from manufacturers specification sheet (b); - Noting limited manufacturer's data available (output, flue temperature and volumetric flow rate at unspecified reference conditions); • Emissions limits expected to be specified in the permit (g); - Stack testing data not yet available due to safety and accessibility considerations however diesel boiler emission limits/benchmarks compared with Mogden STW (NOx 230, 128, 183 mg/Nm3; CO 12, 2, <1 mg/Nm3 – all at 3% oxygen); • Exhaust parameters based on stochiometric calculations based upon fuel use data (BS845-1:1987 standard boiler calculation sheet provided by manufacturer); - Fuel oil (BS2869 class D) was selected as the fuel type. The diesel used on site is commercial diesel (ADO) or gasoil (dyed) which meets the UK regulations for ultra low sulphur (ULS) diesel (specified at 10 mg/kg).

2.6.5. AER engines The modelled emission and flow rates for the AER engines (which will be subject to a future variation application) were provided by the manufacturer and are based upon the design volumetric flow rate of exhaust gases, and anticipated ELVs which meet MCPD limits. As the fuel for the engines is an end-of-waste syngas10, rather than a biogas, which is passed through a scrubbing system prior to use, the emissions of SO2 will be negligible and thus not modelled. The modelled scenario represents a conservative operating situation where both engines are run at 100% capacity. Data relating to the maximum continuous rating operation of the AER engines is presented in Table 2-6. The two engine flues were modelled as individual point sources as they are not sufficiently close together to have compound buoyancy influences.

Table 2-6 - Exhaust Characteristics – 2 No. AER Engines Parameter Engine 1 Engine 2 Grid Reference 548654, 181029 548661, 181025 Stack height, m 7.5 7.5 Stack diameter, m 0.30 0.30 Actual discharge flow rate, Am3/s 1.51 1.51 Discharge velocity, m/s 21.4 21.4 Flue gas discharge temperature, C 120 120 Moisture content, % v/v 10.9 10.9 Oxygen content, % v/v (dry basis) 7.5 7.5 Reference oxygen (dry) 15 15

10 To achieve End of Waste status the syngas will need to meet the Natural Gas Comparator Specification, which includes limits for sulphur content

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Parameter Engine 1 Engine 2

Normalised flow rate, 273 K, 5% O2 (dry 2.04 2.04 basis), Nm3/s (0.76) (4) (0.76) (4) (1) (1) Oxides of nitrogen (as NO2) emission 190 190 3 concentration, mg/Nm (at 15% O2) (500) (4) (500) (4) Particulate matter emission 10 (2) 10 (2) 3 concentration, mg/Nm (at 15% O2) (26.8) (4) (26.8) (4) Carbon monoxide (CO) emission 563 563 3 (3) concentration, mg/Nm (at 15% O2) (1509) (4) (1509) (4)

Oxides of nitrogen (as NO2) emission 0.39 0.39 rate, g/s Particulate matter emission rate, g/s 0.02 0.02 Carbon monoxide (CO) emission rate, 1.15 1.15 g/s (1) Equivalent to MCPD ELV (2) 3 Estimated from EPR 1.01 benchmark 20 mg/Nm for natural gas engine (5% O2) (3) Manufacturer’s datasheet (more conservative than LFTGN, no limit set in MCPD) (4) Number in brackets represents the normalised flow rate/emission concentration at 5% O2

Hierarchy of information applied: • Engine and exhaust parameters derived from manufacturers specification (b); - No stack testing data available as not yet an operational source (pending permit); • Emissions limits expected to be specified in the permit (g); - The source will use syngas so is not typically represented by common literature emission rates; - New combustion source, not yet operational, but will need to meet MCPD limit for NOx; - Syngas will be scrubbed for sulphur compounds as part of the production process and will need to meet the strict Natural Gas Comparator Specification to ensure End of Waste Status, therefore SO2 in the exhaust will be negligible and is excluded from the modelling study.

2.7. Model output

2.7.1. Process contributions The Environment Agency online risk assessment guidance3 states that modelled long-term increments to concentrations “Process Contributions” (PC) may be added to the background annual mean concentration to derive a “Predicted Environmental Concentration” (PEC), for comparison with criteria. For short-term, interpreted as hourly in line with Defra LAQM Guidance11, concentrations the PEC may be obtained by adding the process contribution to twice the background annual mean concentration. The Environment Agency’s methodology does not necessitate assessment of other localised pollution sources, e.g. roads and other combustion sources, as it focusses on wider scale impacts.

The Environment Agency “worst case” recommends conversion ratios for NOX and NO2 of 35% for short-term and 70% for long-term average concentrations. The modelled long-term process contribution may then be added to the background annual mean concentration. Operators may use lower conversion ratios if justified on a case specific basis for “high NOx” generators. For example, the Environment Agency’s Air Quality Modelling and Assessment Unit (AQMAU) guidance for large diesel generators12 suggests that 15% may be a more

11 Defra, Local Air Quality Management, Technical Guidance (TG16), February 2018. https://laqm.defra.gov.uk/documents/LAQM-TG16- February-18-v1.pdf 12 AQMAU (2016) Diesel generator short term NO2 impact assessment https://consult.defra.gov.uk/airquality/medium-combustion-plant- and-controls-on-generators/supporting_documents/Generator%20EA%20air%20dispersion%20modelling%20report.pdf

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appropriate ratio within 500 metres of the source. For a conservative assessment, 35% has been applied to all sources for the short-term and 70% for long term.

To estimate the 15 minute PC for SO2, a factor of 1.34 was applied to the hourly results, in accordance with Environment Agency guidance. In addition, online risk assessment guidance3 states that where a source does not operate all year round, a time weighted conversion should be applied to estimate the process contribution. To maintain the conservative nature of this assessment, the model has been run for all hours within each of five years (8760 hours); however, as each standby engine operation is limited to the maximum hypothetical operational envelope of 50 hours, a factor of 50/8760 has been applied to annual average outputs from those sources.

2.7.2. Statistical analysis Where the modelled hourly mean nitrogen dioxide PEC indicates that, for 19 or more hours per year, the air quality standard could be exceeded at a sensitive receptor over the full modelled operating envelope, and the number of operational hours would exceed 18, statistical analysis was undertaken. The hypergeometric probability distribution has been used for the statistical analysis, in line with Environment Agency guidance for specified generators13. The parameters for the analysis method include the number of hours where the total concentration exceeds the air quality standard, the number of operational hours per year and the defined operating envelope. According to that guidance, probabilities of: • 1% or less indicate exceedances are highly unlikely. • Less than 5% indicate exceedances are unlikely, provided the generator plant operational lifetime is no more than 20 years. • Greater than or equal to 5% indicate there is potential for the exceedances and may not be considered acceptable on a case-by-case basis. To understand the maximum number of times the hourly mean standard of 200 µg/m3 may be exceeded at a sensitive receptor, an exceedance threshold was calculated to represent the difference between the background concentration (twice the annual mean NO2 background concentration) and the assessed short- term standard. Where there are more than 18 modelled hourly exceedances of this threshold, assuming engines are operating constantly throughout the year, statistical analysis is required to understand the likelihood of exceedance under more realistic operating conditions. The cumulative hypergeometric distribution is calculated using the following equation:

Where • N is the sample size – the expected number of operational hours; • M is the population size - 8760 hours in the operating envelope; • E is the number of failures in the population - Modelled number of annual exceedance hours; and • K is the number of non-exceedance hours - K = M – e.

The results from this assessment require application of a factor of 2.5 to the calculated probability, as the facility has the potential to operate for several consecutive hours.

13 Environment Agency - Emissions from specified generators, Guidance on dispersion modelling for oxides of nitrogen assessment from specified generators. (https://consult.environment-agency.gov.uk/psc/mcp-and-sg- regulations/supporting_documents/Specified%20Generators%20Modelling%20GuidanceINTERIM%20FINAL.pdf) 13 uk-air.defra.gov.uk/data/laqm

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2.7.3. Ecological impacts An assessment of the effect of oxides of nitrogen, sulphur dioxide and nitrogen/acid deposition is required for designated ecological sites, in accordance with the Government guidance “Air Emissions Risk Assessment for Your Environmental Permit” as these sites may contain species that are sensitive to air pollution. 3 There is an objective for oxides of nitrogen (NOX) for the protection of vegetation of 30 µg/m as an annual mean concentration. The EU Ambient Air Quality Directive (AAD) requires that assessment of compliance with the limit values for the protection of vegetation is undertaken at locations more than twenty kilometres from towns with more than 250,000 inhabitants or more than five kilometres from other built-up areas, industrial installations or motorways. This objective does not apply in those areas where assessment of compliance with the limit value is not required. However, as the United Nations Economic Commission for Europe (UNECE) and the World Health Organisation (WHO) have set a critical level for NOX for the protection of vegetation, the Statutory Nature Conservation Agencies’ policy (in England, Natural England) is to apply the 30 µg/m3 criterion as a benchmark, on a precautionary basis, in internationally designated conservation sites and sites of special scientific interest (SSSIs). The Environment Agency’s Air Emissions Risk Assessment guidance14 specifies certain “target values” for air pollutants in addition to the statutory air quality objectives. There is a non-statutory short-term target value for the protection of vegetation and ecosystems, for oxides of nitrogen, of 75 µg/m3 as a daily average concentration; however, a value of 200 µg/m3 is suggested by the World Health Organisation (WHO)15 as appropriate in areas with low SO2 and ozone. In addition, critical loads for nitrogen and acid deposition have been set by the UNECE, that represent (according to current knowledge) the exposure below which there should be no significant harmful effects on sensitive elements of the ecosystem. Critical levels at all sensitive ecological receptor locations were compared to the assessment criteria14 to determine whether impacts can be discounted from further assessment based on the magnitude of the PC alone or. Pollutant concentrations were modelled at all local ecological receptors within 2 km of the site including those that were identified by the Environment Agency in the Schedule 5 notice. Where available on APIS for designated sites, the habitat type most sensitive to the impact of nutrient nitrogen and acid deposition was selected. The modelled PCs were compared to the assessment criteria to determine the likelihood of significant impacts. Impacts were considered insignificant where: For SSSIs: • “the short-term PC is less than 10% of the short-term environmental standard for protected conservation areas”; • “the long-term PC is less than 1% of the long-term environmental standard for protected conservation areas”. For all other locally designated ecological sites less stringent criteria are applied: • “the short-term PC is less than 100% of the short-term environmental standard”; • “the long-term PC is less than 100% of the long-term environmental standard”; Where the modelled results do not breach the relevant assessment criteria14 on the above precautionary basis, impacts can be dismissed as insignificant and no further assessment is required. Where the PC is in excess of the screening criteria, a more detailed assessment is required. This would involve an assessment against a habitat specific critical load for the location in question and combination of the PC with a suitable background deposition rate.

14 Environment Agency Online Risk Assessment Guidance, available at https://www.gov.uk/guidance/air-emissions-risk-assessment-for- your-environmental-permit (accessed February 2020) 15 World Health Organisation (WHO), 2000, Air Quality Guidelines for Europe, Second edition (CD ROM version). The Institute of Air 3 Quality Management (IAQM) suggests that 200 µg/m should be used unless in a high SO2 and O3 environment. “Experimental evidence 3 3 exists that the CLE decreases from around 200 µg/m to 75 µg/m when in-combination with O3 or SO2 at or above their critical levels. In the knowledge that short-term episodes of elevated NOx concentrations are generally combined with elevated concentrations of O3 or SO2, 75 µg/m3 is proposed for the 24 h mean”. http://www.euro.who.int/en/healthtopics/environment-and-health/air- quality/publications/pre2009/who-air-uality-guidelines-for-europe,-2nd-edition,-2000-cd-rom-version

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3. Baseline Conditions 3.1. Site setting The Crossness STW is located south of the River Thames between the areas of Thamesmead and Belvedere within LB Bexley. The surrounding area is of urban and industrial character with residential areas to the west and south. The closest residential properties to the site are located approximately 250 m from the western boundary of the STW. Other receptors include recreational areas at the western boundary and the Crossness Nature Reserve at, and partially within, the eastern boundary A review of the study area confirmed that: • LB Greenwich and LB Barking and Dagenham are within 1 km of the Crossness STW site; • AQMAs forming the whole administrative areas of LB Bexley, Greenwich and Barking and Dagenham are declared in relation to concentrations of NO2 (annual mean and hourly mean) and PM10 (24 hour mean). Air quality assessment criteria are summarised in Table 3-1.

Table 3-1 - Air Quality Assessment Criteria Pollutant Period Value Unit Comment Human health Nitrogen dioxide Annual mean 40 µg/m3 (NO2) Hourly mean 200 µg/m3 No more than 18 exceedances per year PM10 Annual mean 40 µg/m3 Daily mean 50 µg/m3 No more than 35 exceedances per year PM2.5 Annual mean 25 µg/m3 Carbon monoxide 8 hour mean 10 mg/m3 (CO) Hourly mean 30 mg/m3 Sulphur dioxide 15 min mean 266 µg/m3 No more than 35 exceedances per year (SO2) Hourly mean 350 µg/m3 No more than 24 exceedances per year Daily mean 125 µg/m3 No more than 3 exceedances per year Ecology Oxides of nitrogen Annual mean 30 µg/m3 (as NO2) Daily mean 75 µg/m3 EA risk assessment guideline 200 WHO guideline15 Sulphur dioxide Annual mean 20 µg/m3

3.2. Monitoring data Air quality monitoring data collected as part of the Local Air Quality Management (LAQM) process were reviewed to investigate current pollutant concentrations. Monitoring locations within 2 km of the Crossness STW were screened based on their classification and location to evaluate their potential to represent baseline conditions at receptors closest to the site. LB Bexley operate two continuous monitoring stations (CMS) in the vicinity of the Crossness STW. The CMS are located at: • Bexley Business Academy (BQ7) approximately 750m to the south; and • Belvedere Primary School (BX2), approximately 1.3km to the south east.

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Both the locations represent suburban areas away from the principal A road network and therefore representative of the conditions around Crossness STW. The monitoring data, summarised in Table 3-2, show that annual mean concentrations of NO2 and PM10 are consistently less than 75% of the AAD limit values. There were no exceedances of the NO2 hourly limit value and less than 35 exceedances of the daily mean PM10 AAD limit value.

Table 3-2 - Air Quality Monitoring Data for LB Bexley Location Pollutant 2014 2015 2016 2017 2018 3 BX2 - NO2 annual mean – µg/m 27 24 28 28 28 Belvedere Number of hours > 200 µg/m3 Primary School 0 0 0 0 0 3 PM10 annual mean – µg/m 17 14 14 17 19 3 Number of days > 50 µg/m 6 1 3 2 7 3 BQ7 - Bexley NO2 annual mean – µg/m 23 22 24 21 21 Business Number of hours > 200 µg/m3 Academy 0 0 0 0 0 3 PM10 annual mean – µg/m 19 18 15 15 15 3 Number of days > 50 µg/m 6 2 5 2 1

The pollutant concentrations measured at the CMS are representative of the majority of public receptors in the vicinity of the STW. Information is provided on the London Air website for a TEOM instrument also located at 3 Belvedere West location. For 2018, PM10 concentrations were reported as 15 µg/m , which is less than that reported at the BX2 location (19 µg/m3).

LB Bexley does not operate a network of diffusion tubes for NO2. The most recent results for 2013 are not deemed representative of current conditions, particularly in light of the improvement measures applied in London in recent years for traffic (e.g. Low Emission Zone). 3.3. Defra mapped backgrounds Estimates of background pollutant concentrations in the UK are available from the DEFRA local air quality website16. The background maps, which are a combination of measured and modelled data, are available for each 1 km grid square throughout the UK for a base year of 2017 and future years up to 2030.

The mapped concentrations for the grid square incorporating the site and the surrounding land based grid squares south of the River Thames are provided in Table 3-3. The data for NOx, NO2, PM10 and PM2.5 are for the year 2020; the data for CO and SO2 are for the year 2001 (no longer updated by DEFRA due to very low concentrations nationwide and thus conservative).

Table 3-3 - DEFRA Mapped Annual Mean Concentrations (µg/m3)

Grid Square X, m Y, m NOx NO2 PM10 PM2.5 CO SO2 Site centre 548500 180500 29.5 19.8 16.4 11.2 0.4 6.2 1 547500 181500 31.5 20.9 16.4 11.3 0.0 6.2 2 548500 181500 35.6 22.8 16.9 11.9 0.0 7.6 3 547500 180500 31.3 20.8 16.8 11.6 0.4 5.9 4 549500 180500 26.8 18.2 15.6 10.8 0.4 6.3 5 547500 179500 30.3 20.3 16.8 11.6 0.4 5.8 6 548500 179500 27.3 18.6 16.2 11.2 0.4 5.8 7 549500 179500 31.2 20.7 16.5 11.4 0.4 7.7

16 uk-air.defra.gov.uk/data/laqm

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Grid Square X, m Y, m NOx NO2 PM10 PM2.5 CO SO2 Maximum 35.6 22.8 16.9 11.9 0.4 7.7 Minimum 26.8 18.2 15.6 10.8 0.0 5.8

To maintain a conservative assessment, the CMS measured concentrations (maximum in five years) for NO2 and PM10 were used in preference to the DEFRA mapped backgrounds as they provided higher readings. Background concentrations for NOx, PM2.5, CO and SO2 were used in the absence of equivalent CMS monitoring data. Where more detailed assessment of ecological receptors was required, NOx concentrations for relevant ecological receptors were obtained from the DEFRA local air quality pages17. Where available, background nutrient nitrogen and acid deposition rates were obtained from the Air Pollution Information System (APIS) website and are averages for the years 2015 to 201718. 3.4. Sensitive receptors

3.4.1. Human health Selected representative receptors for human health (Receptors 1 to 21), were chosen based on their proximity to the site and sensitivity to air pollution, both over short and long-term exposure periods. These receptors are listed in Table 3-4 and represent the areas likely to be most affected by combustion plant emissions in the local area. The receptors were modelled at 1.5 metres above local ground level to represent breathing height.

Table 3-4 - Discrete Model Receptors for Human Health Receptor Receptor Description Grid Reference, m Classification ID Easting Northing D1 Lytham Close 548093 181290 Long Term Receptor D2 Cherbury Close 548028 181068 Long Term Receptor D3 Fleming Way 547890 180872 Long Term Receptor D4 Haldane Road 547758 180678 Long Term Receptor D5 Glendale Way 547469 180497 Long Term Receptor D6 Poplar Place (N) 547253 180377 Long Term Receptor D7 Poplar Place(S) 547284 180260 Long Term Receptor D8 Sewell Road 547278 180049 Long Term Receptor D9 Binsey Walk 547406 180066 Long Term Receptor D10 A2041/ Lynsham Drive 547318 179667 Long Term Receptor D11 Hartslock Drive 547762 179986 Long Term Receptor D12 St Katherines Road 547974 179889 Long Term Receptor D13 Yarnton Way 547624 179613 Long Term Receptor D14 Yarnton Way / Kale Rd 548190 179516 Long Term Receptor D15 Yarnton Way 548626 179370 Long Term Receptor D16 Waterfield Close 549475 179466 Long Term Receptor D17 Norman Road 549598 179651 Long Term Receptor D18 Crossness Visitor Centre19 548521 181075 Short Term Receptor

17 uk-air.defra.gov.uk/data/laqm 18 http://www.apis.ac.uk/, accessed February 2020 19 Visitor centre (D18) is within the STW boundary; it is open on Tuesdays and Sundays only for tours of up to 2 hours’ duration.

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Receptor Receptor Description Grid Reference, m Classification ID Easting Northing D19 Lytham Close Play Area 548115 181269 Short Term Receptor D20 Thamesmead Sports Club 547963 180625 Short Term Receptor D21 Crossway Park 547636 180477 Short Term Receptor

3.4.2. Ecological sites The assessment for ecological sites considers the relevant national (SSSI) and local (LNR, LWS, ancient/semi ancient woodlands) designations within 2 km of the site. These are shown in Figure 3-1, in green shading. There are no relevant European or Ramsar designations within 10 km. The closest nationally designated site is Abbey Wood SSSI, just within 2 km to the south. This is not relevant to the assessment as the SSSI citation describes it as being for geological interest only and does not therefore require assessment. The Abbey Wood SSSI is, however, coincident with an area of ancient woodland and local SINC (Lesnes Wood). The next nearest SSSI, Inner Thames Marshes, is outside the study area at over 2 km to the north east. There is one other statutory designated site within 2 km, the Crossness LNR, on the eastern site boundary. There are also a number of local, non-statutory sites of importance for nature conservation (SINCs) shown in Table 3-5 (note, these are not included in Figure 3-1 to ensure clarity of human health receptors).

Table 3-5 - Local wildlife sites within 2km Local wildlife site X Y River Thames and tidal tributaries LWS 548618 181086 Crossness Sewage Treatment Works Pond LWS 549176 180633 Erith Marshes LWS south 548514 180497 Erith Marshes LWS east 548937 180575 Erith Marshes LWS outside 1 548558 180330 Erith Marshes LWS outside 2 548527 180258 Thamesview Golf Course LWS 548403 181097 The Ridgeway LWS 548130 180674 Crossway Park and Tump 52 LWS 548065 180652 Southmere Park and Woodland LWS 548084 180231 Belvedere Dykes LWS 549671 180515 Crossways Lake Nature Reserve LWS 547859 181126 Goresbrook and the Ship & Shovel LWS 548053 182155 Ridgeway in Greenwich LWS 547309 180143 Lesnes Abbey Woods and Bostall Woods LWS 548380 178956.1 Tump 53 Nature Park LWS 546873 180430 Franks Park LWS 549611 178854 Twin Tumps and Thamesmere LWS 546636 180991 Gallions Reach Park LWS 546640 180513 Church Manorway Nature Area LWS/ Pirelli Site 550552 179423

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Figure 3-1 - Selected Human (D) and Ecological (Green Shaded) Receptor Locations

Inner Thames Marshes SSSI

Crossness LNR

Abbey Wood SSSI

(red lines indicate the site boundary and 2 km search radius)

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4. Impact Assessment 4.1. Introduction The results of the air dispersion modelling study are presented and interpreted in this section, for human health and ecological receptors. Results are tabulated and isopleth (contour) plots for selected pollutants are also presented to illustrate the pattern of dispersion across the study area. For Scenario 1, the assessment of compliance with long-term (annual mean) air quality criteria uses the maximum result from the five individual years of meteorological data and thus robustly characterises the range of dispersion conditions which may be encountered. The PC includes the contribution from emission sources that are typically run continuously all year round (CHP engines and boilers, Webster House boilers, and future AER engines) as well as a weighted contribution from the intermittent standby generator testing, based on the number of total hours’ operation per year for those engines (50 hours). For Scenarios 2 and 3, for comparison with short term criteria, both routine only sources and standby sources were modelled as fully operational throughout the year. This ensures that the least favourable hours of meteorology were included, although the standby engine testing will be restricted to site opening hours i.e. daytime, when dispersion conditions are more favourable. For the assessment of compliance with short term (daily, 8 hourly, hourly and 15 minute mean) air quality criteria, the maximum (100th percentile) concentration is provided from the full five year dataset. This assumes all standby engines are operational throughout the year, without a weighting. Where the reported PEC exceeds the criterion under consideration, the maximum number of exceedances of a threshold in a single calendar year has then been evaluated. Where appropriate, a statistical analysis is presented which considers the probability of the hours of operation coinciding with periods of unfavourable meteorological conditions such that exceedances could occur above the number allowed by the air quality objective.

4.1.1. Background The background concentrations selected for use in the assessment are summarised in Table 4-1. A correction has not been made to the background component taken from the CMS, i.e. the contribution from emissions from the existing combustion plant at Crossness STW is included already in this background, thus is a conservative approach.

Table 4-1 - Background Pollutant Concentrations Used in the Assessment Pollutant Averaging period Value Unit Source 3 NO2 Annual mean 28 µg/m Belvedere Primary School, CMS 2018 3 PM10 Annual mean 19 µg/m Bexley Business Park, CMS 2014 CO Annual mean 409 µg/m3 DEFRA map 2001 3 SO2 Annual mean 6.3 µg/m DEFRA map 2001

4.2. Human receptors

4.2.1. Scenario 1 – Long term

4.2.1.1. Nitrogen dioxide – annual mean The assessment of annual average nitrogen dioxide concentrations at human health receptor locations for the operation of routine and standby sources is presented in Table 4-2. The maximum modelled annual mean PC at each relevant receptor is presented and calculated as a percentage of the AAD limit value of 40 µg/m3. Both the annual concentration from routine sources and the expected weighted contribution from infrequently used engines (each of 50 hours per year) are provided. Each PC was combined added to the appropriate background concentration (28 µg/m3) to calculate the PEC. The PEC is presented as a percentage of the AAD limit value to inform the evaluation of modelled results at sensitive receptors.

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Table 4-2 - Maximum Annual Average Concentrations of Nitrogen Dioxide – All Sources

(1) 3 Receptor Location PC NO2, µg/m PC / NO2 PEC / ID AAD, PEC, AAD, % µg/m3 % Routine Standby Plant Plant D1 Lytham Close 1.0 <0.1 2.5 29.0 72.5 D2 Cherbury Close 0.8 <0.1 2.1 28.8 72.1 D3 Fleming Way 0.7 <0.1 1.9 28.8 71.9 D4 Haldane Road 0.5 <0.1 1.4 28.6 71.4 D5 Glendale Way 0.3 <0.1 0.8 28.3 70.8 D6 Poplar Place (N) 0.2 <0.1 0.6 28.2 70.6 D7 Poplar Place(S) 0.2 <0.1 0.6 28.2 70.6 D8 Sewell Road 0.2 <0.1 0.5 28.2 70.5 D9 Binsey Walk 0.2 <0.1 0.6 28.2 70.6 D10 A2041/ Lynsham Drive 0.1 <0.1 0.4 28.2 70.4 D11 Hartslock Drive 0.2 <0.1 0.6 28.3 70.6 D12 St Katherines Road 0.2 <0.1 0.6 28.3 70.6 D13 Yarnton Way 0.2 <0.1 0.4 28.2 70.4 D14 Yarnton Way / Kale Rd 0.2 <0.1 0.5 28.2 70.5 D15 Yarnton Way 0.2 <0.1 0.5 28.2 70.5 D16 Waterfield Close 0.1 <0.1 0.4 28.2 70.4 D17 Norman Road 0.1 <0.1 0.4 28.2 70.4 (1) Receptors D18 to D21 are not relevant locations for long-term public exposure so not presented

The modelled results at sensitive receptors show that: 3 • the maximum PC from routine sources as NO2 is 1.0 µg/m or 2.8% of the AAD limit value at Receptor D1; • the PC from routine sources is less than 0.4 µg/m3 (1% of the AAD limit value) in most of the surrounding area; • the weighted contribution from standby plant on an annual basis is very small (<0.1 µg/m3); • all PECs are well below, i.e. less than 75% of, the AAD limit, with a maximum at Receptor D1 (29.0 µg/m3). No correction has been made to the background component to remove the contribution from these existing plant at Crossness STW, thus the results are conservative. A contour plot for the routine sources for the year 2014, which gave the maximum concentration at a sensitive receptor, is presented in Figure 4-1. The results for the yet to be permitted AER engines alone are presented separately in Appendix A.

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Figure 4-1 - Maximum Annual Average Nitrogen Dioxide Concentrations, µg/m3 – 2014, All Sources

4.2.1.2. Particulate matter – annual mean The assessment of annual average PM10 concentrations for routine operation at human receptor locations is presented in Table 4-3. The maximum modelled PC at each receptor was combined with the selected background concentration (19 µg/m3) to calculate the PEC. Both the annual concentration from routine sources and the expected weighted contribution from infrequently tested standby engines are provided. 3 A comparison of the PEC with the AAD limit value of 40 µg/m for PM10 was made to inform the evaluation of modelled results at sensitive receptors.

Table 4-3 - Maximum Annual Average Concentrations of Particulate Matter (PM10) – All Sources

3 Receptor Location PM10, µg/m PC / PM10 PEC / ID AAD, PEC, AAD, % µg/m3 % Routine Standby Plant Plant D1 Lytham Close 0.1 <0.1 0.2 19.1 47.7 D2 Cherbury Close <0.1 <0.1 0.1 19.1 47.7

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3 Receptor Location PM10, µg/m PC / PM10 PEC / ID AAD, PEC, AAD, % µg/m3 % Routine Standby Plant Plant D3 Fleming Way <0.1 <0.1 0.1 19.1 47.6 D4 Haldane Road <0.1 <0.1 0.1 19.0 47.6 D5 Glendale Way <0.1 <0.1 <0.1 19.0 47.6 D6 Poplar Place (N) <0.1 <0.1 <0.1 19.0 47.5 D7 Poplar Place(S) <0.1 <0.1 <0.1 19.0 47.5 D8 Sewell Road <0.1 <0.1 <0.1 19.0 47.5 D9 Binsey Walk <0.1 <0.1 <0.1 19.0 47.5 D10 A2041/ Lynsham Drive <0.1 <0.1 <0.1 19.0 47.5 D11 Hartslock Drive <0.1 <0.1 <0.1 19.0 47.6 D12 St Katherines Road <0.1 <0.1 <0.1 19.0 47.6 D13 Yarnton Way <0.1 <0.1 <0.1 19.0 47.5 D14 Yarnton Way / Kale Rd <0.1 <0.1 <0.1 19.0 47.5 D15 Yarnton Way <0.1 <0.1 <0.1 19.0 47.5 D16 Waterfield Close <0.1 <0.1 <0.1 19.0 47.5 D17 Norman Road <0.1 <0.1 <0.1 19.0 47.5

The modelled results show that: 3 • The maximum PC as PM10 is 0.1 µg/m or 0.2% of the annual mean AAD limit value at Receptor D1; • At all other receptors the PC is less than 0.1% of the AAD limit value; • The PEC at all receptors is less than 50% of the AAD value, the maximum at Receptor D1 (19.1 µg/m3). The modelled concentrations at receptors are similar to CMS readings in the vicinity of the Crossness STW, i.e. less than 20 µg/m3. No correction has been made to the PEC calculation to remove the contribution from the Crossness STW, which is already in operation.

The pattern of distribution of particulate matter concentrations will follow that for NO2, but proportionately lower.

As a conservative assumption, particulate matter emission rates can also be assumed to represent the PM2.5 3 size fraction. As the modelled PM10 PEC is below 25 µg/m at all receptors, the PM2.5 AAD limit will also be met at all sensitive receptors.

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4.2.2. Scenario 2 – Short-term, Routine Testing

4.2.2.1. Nitrogen dioxide – 1 hour mean The assessment of short term NO2 concentrations at human health receptor locations for Scenario 2 is presented in Table 4-4. This scenario considered continuous operation of all routine combustion plant at the Crossness STW at full load for all hours of the day, concurrently with one standby engine to represent the individual testing regime. (Therefore, the results represent all engine testing but are conservative to ensure the highest result in any year at a discrete receptor is obtained). For Scenario 2, the results for a single engine A11 have been considered, which was selected as it gave the highest short-term results from the full five year dataset when compared with the other standby engines. The maximum modelled hourly mean PC at each receptor (the highest result from a five year meteorological dataset) was combined with twice the measured background concentration to calculate the PEC. 3 The NO2 hourly mean AAD limit value allows no more than 18 hourly exceedances of 200 µg/m . The number of exceedances presented in Table 4-4 represents the number of times the PEC (i.e. including background) is above the hourly limit value for the individual year of meteorological data giving the highest PC.

Table 4-4 - Maximum Hourly Average Concentrations of Nitrogen Dioxide – Routine Testing (1) Receptor Description NO2 PC, NO2 PEC , Breaches Max no. of > 1% ID µg/m3 µg/m3 AQO exceedances probability of AQS breach D1 Lytham Close 88.8 145 N 0 N D2 Cherbury Close 86.2 142 N 0 N D3 Fleming Way 44.1 100 N 0 N D4 Haldane Road 16.9 72.9 N 0 N D5 Glendale Way 12.2 68.2 N 0 N D6 Poplar Place (N) 11.2 67.2 N 0 N D7 Poplar Place(S) 10.9 66.9 N 0 N D8 Sewell Road 16.6 72.6 N 0 N D9 Binsey Walk 16.8 72.8 N 0 N D10 A2041/ Lynsham Drive 17.1 73.1 N 0 N D11 Hartslock Drive 16.3 72.3 N 0 N D12 St Katherines Road 14.8 70.8 N 0 N D13 Yarnton Way 15.3 71.3 N 0 N D14 Yarnton Way / Kale Rd 15.6 71.6 N 0 N D15 Yarnton Way 13.7 69.7 N 0 N D16 Waterfield Close 13.3 69.3 N 0 N D17 Norman Road 16.7 72.7 N 0 N D18 Crossness Visitor Centre 193 249 Y 18 N D19 Lytham Close Play Area 90.7 147 N 0 N D20 Thamesmead Sports Club 29.7 85.7 N 0 N D21 Crossway Park 14.0 70.0 N 0 N

(1) Calculated as the maximum hourly PC plus twice the annual mean NO2 background.

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The modelled results show that: • At off-site locations there were no instances where the hourly PEC was above 200 µg/m3; • The maximum hourly average total nitrogen dioxide concentration was in excess of 200 µg/m3 at one potentially sensitive receptor location on-site (Receptor D18, the Crossness Visitor Centre20). - The maximum number of exceedances in a single year was 18. It must be noted that all hours of the year were modelled to obtain this result, whereas the testing will be restricted to working (daytime) hours when dispersion conditions are typically better. Examination of the model files show very few of the maximum modelled receptor concentrations arose during working hours, during which visits would take place (the visitor centre is not publicly accessible and only open for a very limited number of days for organised visits, of short (2 hour) duration). As the maximum number of exceedances was equal to 18, at this infrequently accessed location, the calculation of the hypergeometric mean is not required.

A contour plot showing the maximum hourly NO2 concentration from the five year dataset, based on the source group for all routine sources and emission point A11, (the engine which returned the highest hourly result at a receptor), is presented in Figure 4-2. The area outside the 150 µg/m3 contour (i.e. approximately the AAD limit value minus twice the NO2 background) shows the that the AAD limit value would not be exceeded at sensitive off-site locations. There is a very limited area where the modelled results indicate that the hourly AAD objective may be exceeded downwind (to the northeast) beyond the STW boundary. Here, there is a footpath along the River Thames but it is not deemed to be a location where public exposure could either a) reasonably occur for periods of one hour or more or b) occur on a regular basis. As such, an assessment against the AAD limit value is not required.

20 Visits are limited to Tuesday and Sunday, maximum of 2 hours duration

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Figure 4-2 – Nitrogen Dioxide Maximum Hourly Mean Concentration – All Years, Routine Testing

4.2.2.2. Particulate matter – daily mean The impact assessment of short term (daily mean) PM10 concentrations at human receptor locations is presented in Table 4-5. This scenario considers the continuous operation of all routine combustion plant at the STW at full load for all hours of the day, plus one standby engine (note, this assumes engine runs continuously, no weighting has been applied in calculating the PC due to the low values). The maximum modelled daily mean PC at each receptor (from a five year dataset) was combined with the twice the measured background concentration to calculate the PEC. The PM10 daily mean AAD limit value allows up to 35 hourly exceedances of 50 µg/m3 in a calendar year. There are not expected to be any occasions in which the PEC (i.e. including background) is above the daily limit value for the individual year of meteorological data giving the highest PC. Even were the background component to be doubled, this would still be the case.

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Table 4-5 - Maximum Daily Average Concentrations of Particulate Matter – Routine Testing

Receptor ID Description 3 3 (1) Breaches AQO PM10 PC, µg/m PM10 PEC, µg/m

D1 Lytham Close 1.2 39.2 N D2 Cherbury Close 0.5 38.5 N D3 Fleming Way 0.6 38.6 N D4 Haldane Road 0.4 38.4 N D5 Glendale Way 0.2 38.2 N D6 Poplar Place (N) 0.2 38.2 N D7 Poplar Place(S) 0.2 38.2 N D8 Sewell Road 0.1 38.1 N D9 Binsey Walk 0.2 38.2 N D10 A2041/ Lynsham Drive 0.1 38.1 N D11 Hartslock Drive 0.2 38.2 N D12 St Katherines Road 0.2 38.2 N D13 Yarnton Way 0.1 38.1 N D14 Yarnton Way / Kale Rd 0.2 38.2 N D15 Yarnton Way 0.2 38.2 N D16 Waterfield Close 0.1 38.1 N D17 Norman Road 0.1 38.1 N D18 Crossness Visitor Centre 5.7 43.7 N D19 Lytham Close Play Area 1.3 39.3 N D20 Thamesmead Sports Club 0.5 38.5 N D21 Crossway Park 0.2 38.2 N

(1) Calculated as the maximum daily mean PC plus twice the annual mean PM10 background.

The modelled results show that: • The maximum hourly PEC is less than AAD limit value of 50 µg/m3 at all sensitive receptors.

• There are no exceedances of the daily mean standard hence the PM10 objective is met.

4.2.2.3. Carbon monoxide – 8 and 1 hour mean The impact assessment of short-term (eight hour) CO concentrations at human receptor locations is presented in Table 4-6. This scenario considers the continuous operation of all combustion plant at the STW at full load for all hours of the day, including one standby engine. No weighting has been applied in calculating the PC due to the low results. The maximum modelled eight hourly mean PC at each receptor (from a five year meteorological dataset) was combined with the mapped background concentration for the relevant grid square to calculate the PEC. The result presented is directly comparable to the 10,000 µg/m3 8 hour AAD limit value.

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Table 4-6 - Maximum 8 hour Average Concentrations of Carbon Monoxide –Routine Testing

Receptor ID Description CO PC, µg/m3 CO PEC, µg/m3 (1) Breaches AQO

D1 Lytham Close 149 966 N D2 Cherbury Close 50.5 868 N D3 Fleming Way 63.7 882 N D4 Haldane Road 29.5 848 N D5 Glendale Way 15.1 833 N D6 Poplar Place (N) 12.5 831 N D7 Poplar Place(S) 12.3 830 N D8 Sewell Road 14.1 832 N D9 Binsey Walk 14.7 833 N D10 A2041/ Lynsham Drive 12.2 830 N D11 Hartslock Drive 19.3 837 N D12 St Katherines Road 18.8 837 N D13 Yarnton Way 14.4 832 N D14 Yarnton Way / Kale Rd 17.1 835 N D15 Yarnton Way 17.3 835 N D16 Waterfield Close 10.6 829 N D17 Norman Road 9.5 828 N D18 Crossness Visitor Centre 545 1363 N D19 Lytham Close Play Area 156 974 N D20 Thamesmead Sports Club 56.9 875 N D21 Crossway Park 20.9 839 N (1) Calculated as the maximum eight hourly mean PC plus twice the annual mean CO background.

The modelled results show that: • The maximum 8 hourly PEC from the five-year dataset is less than AAD limit value of 10,000 µg/m3 at all sensitive receptors. • The PEC is less than 10% of the AAD limit value at all off site sensitive receptors. The impact assessment of short term (one hour) CO concentrations at human receptor locations is presented in Table 4-7. This scenario considered operation of all combustion plant at the STW at full load for all hours of the day, including one standby engine (no weighting applied). The maximum modelled one hourly mean PC at each receptor (from a five year meteorological dataset) was combined with the mapped background concentration for the relevant grid square to calculate the PEC. The result is directly comparable to the 30,000 µg/m3 hourly mean AAD limit value.

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Table 4-7 - Maximum 1 hour Average Concentrations of Carbon Monoxide – Routine Testing

Receptor ID Description CO PC, µg/m3 CO PEC, µg/m3 (1) Breaches AQO

D1 Lytham Close 513 1331 N D2 Cherbury Close 290 1108 N D3 Fleming Way 268 1086 N D4 Haldane Road 142 960 N D5 Glendale Way 74.1 892 N D6 Poplar Place (N) 61.9 880 N D7 Poplar Place(S) 57.7 876 N D8 Sewell Road 59.0 877 N D9 Binsey Walk 62.7 881 N D10 A2041/ Lynsham Drive 54.9 873 N D11 Hartslock Drive 69.9 888 N D12 St Katherines Road 70.5 889 N D13 Yarnton Way 54.0 872 N D14 Yarnton Way / Kale Rd 59.7 878 N D15 Yarnton Way 61.4 879 N D16 Waterfield Close 48.9 867 N D17 Norman Road 57.1 875 N D18 Crossness Visitor Centre 1160 1980 N D19 Lytham Close Play Area 500 1318 N D20 Thamesmead Sports Club 250 1068 N D21 Crossway Park 84.5 903 N (1) Calculated as the maximum hourly PC plus twice the annual mean CO background. The modelled results show that: • The maximum hourly mean PEC from the five-year dataset is less than AAD limit value of 30,000 µg/m3 at all sensitive receptors. • The PEC is less than 10% of the AAD limit value at all sensitive receptors.

4.2.2.4. Sulphur dioxide – 15 minute, 1 hour and 24 hour mean The assessment of short term (15 minute, hourly and daily mean) SO2 concentrations at human receptor locations are presented in Table 4-8, Table 4-9 and Table 4-10. This scenario considers the continuous operation of all routine combustion plant at the STW at full load for all hours of the day, including one standby engine. No weighting has been applied in calculating the PC due to the low values. The maximum modelled PC at each receptor (from a five year meteorological dataset) was combined with the mapped background concentration for the relevant grid square (6 µg/m3, doubled for assessment short-term criteria of 1 hour or less) to calculate the PEC.

The SO2 15 minute, hourly and daily AAD limit values allow no more than 35, 24 and three exceedances of 266 µg/m3, 350 µg/m3 and 125 µg/m3 AAD respectively. In no case did the highest short-term PC result in an exceedance.

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Table 4-8 - Maximum 15 Minute Average Concentrations of Sulphur Dioxide – Routine Testing

Receptor ID Description 3 3 (1) Breaches AQO SO2 PC, µg/m SO2 PEC, µg/m

D1 Lytham Close 5.4 18.1 N D2 Cherbury Close 8.1 20.7 N D3 Fleming Way 7.2 19.8 N D4 Haldane Road 6.1 18.8 N D5 Glendale Way 5.1 17.7 N D6 Poplar Place (N) 4.7 17.4 N D7 Poplar Place(S) 4.7 17.4 N D8 Sewell Road 4.6 17.2 N D9 Binsey Walk 4.7 17.4 N D10 A2041/ Lynsham Drive 4.2 16.9 N D11 Hartslock Drive 5.1 17.8 N D12 St Katherines Road 5.2 17.9 N D13 Yarnton Way 4.6 17.2 N D14 Yarnton Way / Kale Rd 4.9 17.5 N D15 Yarnton Way 4.8 17.5 N D16 Waterfield Close 4.6 17.2 N D17 Norman Road 4.8 17.5 N D18 Crossness Visitor Centre 8.7 21.3 N D19 Lytham Close Play Area 5.6 18.3 N D20 Thamesmead Sports Club 7.3 20.0 N D21 Crossway Park 5.3 18.0 N (1) Calculated as the maximum fifteen minute PC plus twice the annual mean SO2 background.

Table 4-9 - Maximum Hourly Average Concentrations of Sulphur Dioxide – Routine Testing

Receptor ID Description 3 3 (1) Breaches AQO SO2 PC, µg/m SO2 PEC, µg/m

D1 Lytham Close 4.1 16.7 N D2 Cherbury Close 6.0 18.7 N D3 Fleming Way 5.4 18.0 N D4 Haldane Road 4.6 17.2 N D5 Glendale Way 3.8 16.4 N D6 Poplar Place (N) 3.5 16.2 N D7 Poplar Place(S) 3.5 16.2 N D8 Sewell Road 3.4 16.1 N D9 Binsey Walk 3.5 16.2 N

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Receptor ID Description 3 3 (1) Breaches AQO SO2 PC, µg/m SO2 PEC, µg/m

D10 A2041/ Lynsham Drive 3.2 15.8 N D11 Hartslock Drive 3.8 16.5 N D12 St Katherines Road 3.9 16.5 N D13 Yarnton Way 3.4 16.1 N D14 Yarnton Way / Kale Rd 3.6 16.3 N D15 Yarnton Way 3.6 16.2 N D16 Waterfield Close 3.4 16.1 N D17 Norman Road 3.6 16.3 N D18 Crossness Visitor Centre 6.5 19.1 N D19 Lytham Close Play Area 4.2 16.8 N D20 Thamesmead Sports Club 5.5 18.1 N D21 Crossway Park 4.0 16.6 N (1) Calculated as the maximum hourly PC plus twice the annual mean SO2 background

Table 4-10 - Maximum Daily Mean Concentrations of Sulphur Dioxide – Routine Testing

Receptor ID Description 3 3 (1) Breaches AQO SO2 PC, µg/m SO2 PEC, µg/m

D1 Lytham Close 1.5 14.1 N D2 Cherbury Close 3.0 15.7 N D3 Fleming Way 2.9 15.5 N D4 Haldane Road 2.2 14.8 N D5 Glendale Way 1.4 14.1 N D6 Poplar Place (N) 1.2 13.8 N D7 Poplar Place(S) 1.1 13.8 N D8 Sewell Road 0.9 13.6 N D9 Binsey Walk 1.0 13.7 N D10 A2041/ Lynsham Drive 1.0 13.6 N D11 Hartslock Drive 1.5 14.1 N D12 St Katherines Road 1.7 14.3 N D13 Yarnton Way 1.1 13.7 N D14 Yarnton Way / Kale Rd 1.6 14.3 N D15 Yarnton Way 1.2 13.9 N D16 Waterfield Close 1.0 13.7 N D17 Norman Road 1.0 13.7 N D18 Crossness Visitor Centre 1.6 14.3 N

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Receptor ID Description 3 3 (1) Breaches AQO SO2 PC, µg/m SO2 PEC, µg/m

D19 Lytham Close Play Area 1.6 14.2 N D20 Thamesmead Sports Club 2.4 15.1 N D21 Crossway Park 1.6 14.2 N (1) Calculated as the maximum daily mean PC plus twice the annual mean SO2 background

The modelled results show that: • The maximum PECs from the five-year datasets are below the respective 15 minute, hourly and daily AAD limit values for SO2 at all sensitive receptors; • The short-term PECs are less than 10% of the AAD limit value at all sensitive receptors; • As there are no exceedances of the individual standards, all objectives are met.

4.2.3. Scenario 3 – Short term, black start test A third scenario has been modelled which considers the standby generator emissions operating concurrently in an annual black start test. This test lasts for six hours and is conducted only once a year. The results presented are for the maximum in a five year dataset thus are extremely conservative.

4.2.3.1. Nitrogen dioxide – 1 hour mean The assessment of short term NO2 concentrations at human health receptor locations during a black start test is presented in Table 4-11. This scenario considered operation of all combustion plant at the STW at full load for all hours of the day, including all standby plant (concurrent operation). The maximum modelled hourly mean PC at each receptor (from a five year meteorological dataset) was combined with twice the background concentration to calculate the PEC.

Table 4-11 - Maximum Hourly Average Concentrations of Nitrogen Dioxide – Black Start Test (1) Receptor Description NO2 PC, NO2 PEC , Breaches Max no. of > 1% ID µg/m3 µg/m3 AQO exceedances probability of AQS breach D1 Lytham Close 414.1 470.1 Y 48 N D2 Cherbury Close 410.5 466.5 Y 51 N D3 Fleming Way 204.2 260.2 Y 6 N D4 Haldane Road 79.5 135.5 N 0 N D5 Glendale Way 63.5 119.5 N 0 N D6 Poplar Place (N) 56.8 112.8 N 0 N D7 Poplar Place(S) 56.6 112.6 N 0 N D8 Sewell Road 74.2 130.2 N 0 N D9 Binsey Walk 77.1 133.1 N 0 N D10 A2041/ Lynsham Drive 80.1 136.1 N 0 N D11 Hartslock Drive 71.3 127.3 N 0 N D12 St Katherines Road 71.8 127.8 N 0 N D13 Yarnton Way 76.7 132.7 N 0 N

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D14 Yarnton Way / Kale Rd 65.0 121.0 N 0 N D15 Yarnton Way 65.8 121.8 N 0 N D16 Waterfield Close 63.8 119.8 N 0 N D17 Norman Road 77.7 133.7 N 0 N D18 Crossness Visitor Centre 768.2 824.2 Y 177 N D19 Lytham Close Play Area 423.7 479.7 Y 51 N D20 Thamesmead Sports Club 109.3 165.3 N 0 N D21 Crossway Park 68.8 124.8 N 0 N

(1) Calculated as the maximum hourly PC plus twice the annual mean NO2 background. The modelled results show that: 3 • The maximum NO2 PC is 768 µg/m at a sensitive receptor, Crossness Visitor Centre (D18);

• The maximum NO2 PC at the most affected residential receptor (D1) is less than half this value; 3 • The maximum hourly total NO2 concentration (PEC) is below 200 µg/m at most sensitive receptors. The number of exceedances represents the number of times the PEC (i.e. including background) is above the hourly limit value for the individual year of meteorological data giving the highest PC, based on the engines running all hours throughout that year. The black test run would only run once a year for six hours, therefore at most there would be six hours of exceedance (a purely hypothetical event as it assumes the six least favourable hours of meteorological data are concurrent with the test). 3 The NO2 hourly mean AAD limit value allows no more than 18 hourly exceedances of 200 µg/m . At the Crossness Visitor Centre (D18), the maximum annual number of exceedances for routine and black start testing was 18 and six hours respectively. Although in combination this is above the AAD limit value for more than 19 individual hours, it is highly unlikely that an exceedance at this location will occur due to: • The modelled assumption that all plant across the Crossness site, both routine and standby, are all running at full capacity during these hours of testing; • The modelled assumption that the standby plant, each of which operate for less than 50 hours in total, are tested during the least favourable hours of meteorological data, in a dataset of approximately 44,000 hours; • Testing would in fact be undertaken during working hours, when dispersion is typically improved whereas the highest hourly results occurred almost without exception during night-time; • The visitor centre is not publicly accessible and only open for a very limited number of days for organised visits, of short (two hour) duration; • The maximum hourly PCs from the two individually assessed scenarios may occur for the same hour of meteorological data while in practice, testing will not occur in parallel; Given these findings and the small margin of the potential exceedance at only one location that is within the installation boundary, there is an infinitesimally small probability that the AAD limit value would be breached here or indeed at any offsite location.

4.2.3.2. Particulate matter – daily mean The assessment of short term (daily mean) PM10 concentrations at human receptor locations is presented in Table 4-5. This scenario considers the continuous operation of all combustion plant at the STW at full load for all hours of the day, including all standby plant (no weighting has been applied in calculating the PC). The maximum modelled daily mean PC at each receptor (from a five year dataset) was combined with the measured background concentration to calculate the PEC. The PM10 daily mean AAD limit value allows up to 35 hourly exceedances of 50 µg/m3 in a calendar year. There are not expected to be any occasions in which the PEC (i.e. including background) is above the daily limit value for the individual year of meteorological data giving the highest PC.

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Table 4-12 - Maximum Daily Average Concentrations of Particulate Matter – Black Start Test

Receptor ID Description 3 3 Breaches AQO PM10 PC, µg/m PM10 PEC, µg/m

D1 Lytham Close 2.3 40.3 N D2 Cherbury Close 1.6 39.6 N D3 Fleming Way 1.0 39.0 N D4 Haldane Road 1.0 39.0 N D5 Glendale Way 0.7 38.7 N D6 Poplar Place (N) 0.5 38.5 N D7 Poplar Place(S) 0.5 38.5 N D8 Sewell Road 0.5 38.5 N D9 Binsey Walk 0.5 38.5 N D10 A2041/ Lynsham Drive 0.4 38.4 N D11 Hartslock Drive 0.6 38.6 N D12 St Katherines Road 0.6 38.6 N D13 Yarnton Way 0.4 38.4 N D14 Yarnton Way / Kale Rd 0.5 38.5 N D15 Yarnton Way 0.4 38.4 N D16 Waterfield Close 0.4 38.4 N D17 Norman Road 0.4 38.4 N D18 Crossness Visitor Centre 7.0 45.0 N D19 Lytham Close Play Area 2.3 40.3 N D20 Thamesmead Sports Club 1.3 39.3 N D21 Crossway Park 0.7 38.7 N

The modelled results show that: • The maximum hourly PEC is less than AAD limit value of 50 µg/m3 at all sensitive receptors.

• There are no exceedances of the daily standard hence the PM10 objective is met.

4.2.3.3. Carbon monoxide – 8 and 1 hour mean The assessment of short-term (8 hour) CO concentrations at human receptor locations is presented in Table 4- 6. This scenario considers the continuous operation of all combustion plant at the STW at full load for all hours of the day, including standby plant. No weighting has been applied in calculating the PC. The maximum modelled 8 hour mean PC at each receptor (from a five year meteorological dataset) was combined with the mapped background concentration for the relevant grid square to calculate the PEC. The result presented is directly comparable to the 10,000 µg/m3 8 hour AAD limit value.

Table 4-13 - Maximum 8 hour Average Concentrations of Carbon Monoxide – Black Start Test

Receptor ID Description CO PC, µg/m3 CO PEC, µg/m3 Breaches AQO

D1 Lytham Close 150.5 559.5 N

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Receptor ID Description CO PC, µg/m3 CO PEC, µg/m3 Breaches AQO

D2 Cherbury Close 57.0 466.0 N D3 Fleming Way 64.6 473.6 N D4 Haldane Road 31.4 440.4 N D5 Glendale Way 17.8 426.8 N D6 Poplar Place (N) 15.1 424.1 N D7 Poplar Place(S) 15.0 424.0 N D8 Sewell Road 15.2 424.2 N D9 Binsey Walk 16.1 425.1 N D10 A2041/ Lynsham Drive 13.3 422.3 N D11 Hartslock Drive 20.3 429.3 N D12 St Katherines Road 21.1 430.1 N D13 Yarnton Way 14.4 423.4 N D14 Yarnton Way / Kale Rd 17.6 426.6 N D15 Yarnton Way 19.5 428.5 N D16 Waterfield Close 12.4 421.4 N D17 Norman Road 13.6 422.6 N D18 Crossness Visitor Centre 544.5 953.5 N D19 Lytham Close Play Area 155.9 564.9 N D20 Thamesmead Sports Club 57.7 466.7 N D21 Crossway Park 22.1 431.1 N

The modelled results show that: • The maximum 8 hourly PEC from the five-year dataset is less than AAD limit value of 10,000 µg/m3 at all sensitive receptors. • The PEC is less than 10% of the AAD limit value at all sensitive receptors. The assessment of short term (hourly) CO concentrations at human receptor locations is presented in Table 4- 7. This scenario considered operation of all combustion plant at the STW at full load for all hours of the day, including standby plant. The maximum modelled hourly mean PC at each receptor (from a five year meteorological dataset) was combined with the mapped background concentration for the relevant grid square to calculate the PEC. The result is directly comparable to the 30,000 µg/m3 hourly mean AAD limit value.

Table 4-14 - Maximum 1 hour Average Concentrations of Carbon Monoxide – Black Start Test

Receptor ID Description CO PC, µg/m3 CO PEC, µg/m3 Breaches AQO

D1 Lytham Close 513.2 922.2 N D2 Cherbury Close 289.8 698.8 N D3 Fleming Way 268.0 677.0 N

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Receptor ID Description CO PC, µg/m3 CO PEC, µg/m3 Breaches AQO

D4 Haldane Road 142.1 551.1 N D5 Glendale Way 74.1 483.1 N D6 Poplar Place (N) 61.9 470.9 N D7 Poplar Place(S) 57.7 466.7 N D8 Sewell Road 59.1 468.1 N D9 Binsey Walk 62.7 471.7 N D10 A2041/ Lynsham Drive 54.9 463.9 N D11 Hartslock Drive 69.9 478.9 N D12 St Katherines Road 70.5 479.5 N D13 Yarnton Way 54.0 463.0 N D14 Yarnton Way / Kale Rd 59.8 468.8 N D15 Yarnton Way 61.6 470.6 N D16 Waterfield Close 48.9 457.9 N D17 Norman Road 57.1 466.1 N D18 Crossness Visitor Centre 1160.4 1569.4 N D19 Lytham Close Play Area 499.9 908.9 N D20 Thamesmead Sports Club 249.8 658.8 N D21 Crossway Park 84.5 493.5 N

The modelled results show that: • The maximum hourly PEC from the five-year dataset is less than AAD limit value of 30,000 µg/m3 at all sensitive receptors. • The PEC is less than 10% of the AAD limit value at all sensitive receptors.

4.2.3.4. Sulphur dioxide – 15 minute, 1 hour and 24 hour mean The impact assessment of short term (15 minute, hourly and daily mean) SO2 concentrations at human receptor locations are presented in Table 4-8, Table 4-9 and Table 4-10. This scenario considers the continuous operation of all combustion plant at the STW at full load for all hours of the day, including standby plant. No weighting has been applied in calculating the PC due to the low modelled values. The maximum modelled PC at each receptor (from a five year meteorological dataset) was combined with the mapped background concentration for the relevant grid square (6 µg/m3, doubled for assessment short-term criteria of one hour or less) to calculate the PEC.

The PEC is not directly comparable to the SO2 15 minute, hourly and daily AAD limit values, which allow no more than 35, 24 and 3 exceedances of 266 µg/m3, 350 µg/m3 and 125 µg/m3 AAD respectively. The number of exceedances represents the number of times the PEC (i.e. including background) is above the limit value for the individual year of meteorological data giving the highest PC.

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Table 4-15 - Maximum 15 Minute Average Concentrations of Sulphur Dioxide – Black Start Test

Receptor ID Description 3 3 Breaches AQO SO2 PC, µg/m SO2 PEC, µg/m

D1 Lytham Close 14.4 27.0 N D2 Cherbury Close 13.8 26.4 N D3 Fleming Way 8.6 21.3 N D4 Haldane Road 6.6 19.3 N D5 Glendale Way 5.7 18.4 N D6 Poplar Place (N) 5.2 17.9 N D7 Poplar Place(S) 5.3 17.9 N D8 Sewell Road 5.1 17.7 N D9 Binsey Walk 5.3 18.0 N D10 A2041/ Lynsham Drive 4.7 17.4 N D11 Hartslock Drive 5.8 18.5 N D12 St Katherines Road 6.0 18.6 N D13 Yarnton Way 5.1 17.8 N D14 Yarnton Way / Kale Rd 5.6 18.3 N D15 Yarnton Way 5.6 18.2 N D16 Waterfield Close 5.3 18.0 N D17 Norman Road 5.6 18.2 N D18 Crossness Visitor Centre 28.8 41.5 N D19 Lytham Close Play Area 14.7 27.3 N D20 Thamesmead Sports Club 7.9 20.6 N D21 Crossway Park 6.0 18.7 N

Table 4-16 - Maximum Hourly Average Concentrations of Sulphur Dioxide – Black Start Test

Receptor ID Description 3 3 Breaches AQO SO2 PC, µg/m SO2 PEC, µg/m

D1 Lytham Close 10.7 23.4 N D2 Cherbury Close 10.3 22.9 N D3 Fleming Way 6.4 19.1 N D4 Haldane Road 4.9 17.6 N D5 Glendale Way 4.3 16.9 N D6 Poplar Place (N) 3.9 16.6 N D7 Poplar Place(S) 3.9 16.6 N D8 Sewell Road 3.8 16.4 N D9 Binsey Walk 4.0 16.6 N

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Receptor ID Description 3 3 Breaches AQO SO2 PC, µg/m SO2 PEC, µg/m

D10 A2041/ Lynsham Drive 3.5 16.2 N D11 Hartslock Drive 4.4 17.0 N D12 St Katherines Road 4.5 17.1 N D13 Yarnton Way 3.8 16.5 N D14 Yarnton Way / Kale Rd 4.2 16.8 N D15 Yarnton Way 4.2 16.8 N D16 Waterfield Close 4.0 16.6 N D17 Norman Road 4.2 16.8 N D18 Crossness Visitor Centre 21.5 34.2 N D19 Lytham Close Play Area 11.0 23.6 N D20 Thamesmead Sports Club 5.9 18.6 N D21 Crossway Park 4.5 17.1 N

Table 4-17 - Maximum Daily Mean Concentrations of Sulphur Dioxide – Black Start Test

Receptor ID Description 3 3 Breaches AQO SO2 PC, µg/m SO2 PEC, µg/m

D1 Lytham Close 2.1 14.7 N D2 Cherbury Close 3.3 16.0 N D3 Fleming Way 3.3 15.9 N D4 Haldane Road 2.5 15.1 N D5 Glendale Way 1.6 14.2 N D6 Poplar Place (N) 1.3 14.0 N D7 Poplar Place(S) 1.3 14.0 N D8 Sewell Road 1.1 13.8 N D9 Binsey Walk 1.1 13.8 N D10 A2041/ Lynsham Drive 1.1 13.7 N D11 Hartslock Drive 1.7 14.3 N D12 St Katherines Road 1.8 14.5 N D13 Yarnton Way 1.2 13.9 N D14 Yarnton Way / Kale Rd 1.8 14.5 N D15 Yarnton Way 1.4 14.0 N D16 Waterfield Close 1.2 13.8 N D17 Norman Road 1.1 13.8 N D18 Crossness Visitor Centre 4.8 17.5 N

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Receptor ID Description 3 3 Breaches AQO SO2 PC, µg/m SO2 PEC, µg/m

D19 Lytham Close Play Area 2.1 14.8 N D20 Thamesmead Sports Club 2.7 15.4 N D21 Crossway Park 1.8 14.5 N

The modelled results show that: • The maximum PECs from the five-year datasets are below the respective 15 minute, hourly and daily AAD limit values for SO2 at all sensitive receptors; • The short-term PECs are less than 10% of the AAD limit value at all sensitive receptors; • As there are no exceedances of the individual standards, all objectives are met.

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Figure 4-3 – No. Exceedances of Nitrogen Dioxide Hourly Mean Standard – 2014, Black Start Test

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4.3. Ecological receptors An impact assessment has been undertaken for statutory and non-statutory designated ecological sites in the relevant study area (including SSSI, ancient woodland, local nature reserves and non-statutory local wildlife sites). There are no relevant European or Ramsar designations within 10 km.

4.3.1. Within 2 km

4.3.1.1. Scenario 1 - Long term The results for long term impact assessment for the two statutory designated ecological sites and the LWS are presented in Table 4-18. The modelled concentrations at individual LWS are provided in Appendix C, Table C- 1.

The contour plots in Figure 4-4 and Figure 4-5 show long term average concentrations of NOx and SO2 (each figure includes the additional weighted contribution from standby engines). These figures show that: • at the statutory designated sites within 2 km, the EA screening criterion (i.e. less than 100% of the critical level or load) is not breached; • the EA screening criterion will not exceeded at any non-statutory LWS (shown as hatched areas, with modelled receptor points as green triangles).

Table 4-18 – Ecological Impact Assessment – long term, sites within 2km Receptor PC concentration PC deposition (1) (µg/m3) (kg or keq/ha/yr) Annual Mean Annual Mean Nitrogen Sulphur Acidity NOX SO2 Crossness LNR <4 <0.3 1.15 1.14 0.15 Abbey Wood SINC <0.2 <0.1 0.06 0.38 0.03 / Ancient Woodland Range at LWS 0.1 -14 <0.1-0.8 4.03 3.03 0.48 (1) Calculated on a precautionary basis, using the AQTAG deposition velocities for woodland of 0.003 m/s and 0.024 m/s for NO2 and SO2 respectively. At non woodland locations, the impact would be half that presented.

The maximum modelled process contribution at a local site (14 µg/m3) occurs within the River Thames and tidal tributaries LWS. There is an extremely small area above 30 µg/m3 on the northern site boundary (not visible in the contour plot), however the LWS at this location is not sensitive to NOX, due to it comprising a river wall and the River Thames alluvial deposits which are regularly submerged at high tide. This must also be considered in light of the conservative nature of the modelling. There are no critical loads on APIS for acidity on saltmarsh or coastal/grazing marsh, which are considered the most appropriate habitats for the area immediately surrounding the Crossness STW where concentrations would be highest. The lowest nitrogen critical load identified on APIS for these general habitat types is 20 kg/ha/year21. Clearly, the maximum calculated nitrogen deposition rate in Table 4-18 (based on woodland) does not approach 100% of this value. On this basis, the impacts on local ecological sites can be considered insignificant and do not require further assessment.

4.3.1.2. Scenario 2 & 3 - Short term Due to the non-additive nature of emissions from the routine and standby sources over the short term, caution must be taken when interpreting the 24 hour mean results for “all sources”, as this represents a hypothetical scenario whereby all combustion sources, including the infrequently operated standby engines, are operational

21 http://www.apis.ac.uk/node/967

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throughout the least favourable day for dispersion in a five-year dataset. This does not present a scenario which is feasible, so must not be used to define compliance with the non-statutory daily mean critical level22. The assessment has considered both Scenario 2, representing TWUL’s revised routine testing regime and Scenario 3, representing black start testing. The scenarios considered consecutive and concurrent running respectively of the standby engines for up to six hours in a day. In each case, a factor of 6/24 has been applied to the maximum daily mean with all sources running and this has been added to the daily mean for routine only sources multiplied by a factor of 18/24. This is conservative since, for Scenario 2, on the second test day of testing, only two engines would need to be run for a total of three hours. For Scenario 2, a single engine A11 (one of the four MAN Paxman engines), was selected for inclusion in the model results interpretation, as it gave the highest short term results from the full five year dataset when compared with the other standby engines. It is noted that the emission concentration used in the assessment for the MAN Paxman engine, is the manufacturer’s figure which was substantially higher than the measured emission concentration. The maximum modelled results at discrete receptor locations representative of each LWS are provided in Table C-2 of Appendix C. The contour plots showing concentrations across the entire modelled domain are provided in Figure 4-6 and Figure 4-7. These show that the maximum concentrations at an LWS are: • Scenario 2 – Routine testing - Maximum outside the site boundary* – 110 µg/m3 - Maximum inside the site boundary – 75 µg/m3 • Scenario 3 – Black start test - Maximum outside the site boundary* – 340 µg/m3 - Maximum inside the site boundary – 250 µg/m3 *excludes the River Thames LWS which is not considered likely to be sensitive to air quality impacts due to its tidal nature and high tide covering the full extent of the designated area in the vicinity of Crossness STW. Despite the conservative approach to modelling, the maximum modelled process contribution for Scenario 2 exceeds the non-statutory guideline of 75 µg/m3 over a fraction of the Crossness LWS, just outside the northern site boundary. The WHO 24 hour mean non-statutory guideline23 of 200 µg/m3 (which is deemed to be more appropriate in areas with low SO2 and ozone) is not exceeded at any relevant location, on or off site. Consideration of these results must also be made in the context of where the maximum area of impact occurs i.e. a small stretch of the northern site boundary adjacent to the River Thames which is unlikely to be sensitive to NOX impacts. Furthermore, for Scenario 2 the daily mean would be lower than the values presented on days when only two engines are run. At all other locations the maximum concentration was 63 µg/m3, below the non-statutory UK guideline value of 75 µg/m3. For Scenario 3, a black start test, there is only a very small area beyond the site boundary which exceeds the non-statutory UK guideline value 75 µg/m3. Apart from an area within the Crossness LWS site where the maximum daily mean in a five year dataset is just above 200 µg/m3, the guideline value suggested by the WHO, all other locations are below this value. The highest result at an ecological receptor of 373 µg/m3 is over a very small area of the River Thames and tidal tributaries LWS, which is not deemed to be a sensitive location. The presented values represent the maximum 24 hour period, from a five year dataset, for the routinely operated combustion plant combined with a contribution from the standby engines. There is an extremely remote probability that the once a year, standby engines black start test would be run under the least favourable conditions for dispersion in a five-year dataset. An analysis of the top 50 results at the closest receptor to illustrate the very low probability of an exceedance in a single year is provided in Appendix C.3. Furthermore, the days giving rise to the maximum 24 hour mean for the routine and standby engines are unlikely to occur on the same day; in fact at the most affected receptor, the two highest results do not occur in the same year, and this further confirms the conservative nature of the results.

22 Rather than 75 µg/m3, the IAQM considers that the WHO15 guideline value of 200 µg/m3 is more appropriate for an assessment of short- term impacts in an environment where SO2 and ozone concentrations are not elevated. 23 World Health Organisation (WHO), 2000, Air Quality Guidelines for Europe, Second edition (CD ROM version). The Institute of Air 3 Quality Management (IAQM) suggests that 200 µg/m should be used unless in a high SO2 and O3 environment. “Experimental evidence 3 3 exists that the CLE decreases from around 200 µg/m to 75 µg/m when in-combination with O3 or SO2 at or above their critical levels. In the knowledge that short-term episodes of elevated NOx concentrations are generally combined with elevated concentrations of O3 or SO2, 75 µg/m3 is proposed for the 24 h mean”. http://www.euro.who.int/en/healthtopics/environment-and-health/air- quality/publications/pre2009/who-air-uality-guidelines-for-europe,-2nd-edition,-2000-cd-rom-version

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The results demonstrate that with TWUL’s revised routine testing regime, represented by Scenario 2 with standby engines tested on a sequential basis, rather than an equivalent period of concurrent testing, achieves a 65-80% reduction in the maximum 24 hour mean ground level NOx concentrations. On this basis, significant impacts are not expected at even the closest nature sites to the Crossness STW.

4.3.2. Beyond 2km

4.3.2.1. Long term To assess potential impacts at Ingrebourne Marshes and Inner Thames Marshes SSSIs, which lie fractionally beyond the 2 km study area, the gridded model results were used to identify maximum pollutant concentrations. These results represent continuous operation of all routine sources plus weighted contribution from standby plant operation (all six engines up to 50 hours per year) The contour plots in Figure 4-4 and Figure 4-5 show that the maximum long term average concentrations are:

• Annual mean maximum NOx PC (routine operation plus weighted contribution from standby plant): - < 0.6 µg/m3, or 2% of the 30 µg/m3 critical level;

• Annual mean SO2 maximum PC (routine operation plus weighted contribution from standby plant): - < 0.1 µg/m3, less than 1% of the 20 µg/m3 critical level; Using the deposition velocity for grassland type ecological receptors deposition rates are 0.085 kg N/ha/yr, 0.190 kg S/ha/yr and 0.018 keq/ha/yr. The PC is less than 1% of the lowest stated critical load for this habitat on APIS, 15 kg N/ha/yr (rich fens); no acidity critical loads are provided. Given these low annual mean PCs for concentration and deposition, which represent the maximum at any statutory designated ecological receptor beyond 2 km, long term impacts are not considered to be significant.

4.3.2.2. Short-term The contour plots for short-term average NOx concentrations (Figure 4-6 and Figure 4-7) show that the maximum short term PCs at receptors beyond 2 km are substantially less than 100% of the 75 µg/m3 non- statutory assessment level:

• 24-hour maximum NOX PC: - Scenario 2 – Routine testing : < 10 µg/m3; - Scenario 3 – Black Start < 25 µg/m3. On this basis, the modelled short -term contributions at statutory designated ecological receptors further than 2 km from the Installation boundary are not considered to be significant.

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Figure 4-4 - Maximum Annual Average Oxides of Nitrogen Concentrations, µg/m3 – 2014, All Sources

(includes weighted contribution from routine and black start testing)

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Figure 4-5 - Maximum Annual Average Sulphur Dioxide Concentrations, µg/m3 – 2014, All Sources

(includes weighted contribution from routine and black start testing)

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Figure 4-6 - Maximum 24 hour Average Oxides of Nitrogen Concentrations, µg/m3, Scenario 2

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Figure 4-7 - Maximum 24 hour Average Oxides of Nitrogen Concentrations, µg/m3, Scenario 3

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5. Conclusions

An air dispersion modelling study has been carried out in support of the Environmental Permit variation application for the Crossness Combustion Plant at the Crossness STW site. Dispersion modelling of various operational scenario was undertaken to estimate impacts at human and ecological receptor locations incorporating normal operation, routine standby engine testing and a once a year black start test. The air quality assessment has not identified any likelihood of breaches of long-term assessment criteria at human receptors under the long and short-term operational scenarios for any pollutant or averaging period. The air quality assessment, including operation of standby generators, identified that for hourly nitrogen dioxide, an exceedance of the air quality objective at sensitive receptors is extremely unlikely to occur. The short-term results for all other pollutants are well within the relevant assessment criteria at all offsite locations. At ecological sites, the annual impacts are not significant at either statutory or non-statutory sites within the study area. The likelihood of an exceedance of the non-statutory daily mean criterion is low, using a worst- case scenario approach (all standby plant operating concurrently). The interpretation of the significance of these impacts must also consider the conservative nature of the emissions characteristics and operational parameters used in the modelling. The long-term assessment overstates impacts because the of the following: • routine combustion equipment was modelled as operating for the full potential operating envelope, 8,760 hours every year (fewer operating hours are expected for some plant, due to the need for maintenance downtime); • the modelling assumes that all combustion plant operate at 100% capacity at all times (in reality, the site does not produce and store sufficient volumes of either biogas or syngas for all the routine combustion sources to be run contemporaneously at full capacity); and • all combustion plant were modelled to emit at the highest measured concentration or emission limit value, benchmark or manufacturer’s guarantee, continuously throughout the year. • all six standby generators were modelled as operating together at full capacity for 50 hours per year. This represents the worst-case situation but TWUL is committed to undertake the majority of testing sequentially to reduce impacts). The following additional conservative assumptions apply to the short-term assessment: • assumes standby engine testing occurs during the least favourable hours of meteorological data, in a dataset of nearly 44,000 hours; • testing is only typically carried out during working hours, when dispersion is typically improved whereas the highest hourly results occurred almost without exception during night-time; • the maximum hourly PCs from the two testing scenarios may occur for the same hour of meteorological data while in practice, testing will not occur in parallel; • the maximum 24 hour PCs from the two testing scenarios may not occur on the same day within the five year dataset and as such are not directly additive; • the standby engines may not always be tested at full capacity or for the full stated duration; • all sources, both routine and standby, emit at their maximum or permitted levels at all times; • the total hours (50) for standby operation for a standby engine in a year used in the assessment is a theoretical maximum. On the above basis, it is concluded that the impact of the combustion plant at the existing Crossness STW on local air quality is not significant.

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Appendices

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Appendix A. AER Operation

A.1. Results for AER Engines

Table A-1 - Maximum Annual Average Concentrations of Nitrogen Dioxide – AER Engines

(1) 3 Receptor Location PC NO2, µg/m PC / AAD, NO2 PEC, PEC / ID % µg/m3 AAD, % AER D1 Lytham Close 0.8 2.0 28.8 72.0 D2 Cherbury Close 0.4 1.1 28.4 71.1 D3 Fleming Way 0.3 0.9 28.3 70.9 D4 Haldane Road 0.2 0.5 28.2 70.5 D5 Glendale Way 0.1 0.2 28.1 70.2 D6 Poplar Place (N) 0.1 0.2 28.1 70.2 D7 Poplar Place(S) 0.1 0.2 28.1 70.2 D8 Sewell Road 0.1 0.2 28.1 70.2 D9 Binsey Walk 0.1 0.2 28.1 70.2 D10 A2041/ Lynsham Drive 0.0 0.1 28.0 70.1 D11 Hartslock Drive 0.1 0.2 28.1 70.2 D12 St Katherines Road 0.1 0.2 28.1 70.2 D13 Yarnton Way 0.0 0.1 28.0 70.1 D14 Yarnton Way / Kale Rd 0.1 0.1 28.1 70.1 D15 Yarnton Way 0.1 0.2 28.1 70.2 D16 Waterfield Close 0.1 0.1 28.1 70.1 D17 Norman Road 0.1 0.1 28.1 70.1 (1) Receptors D18 to D21 are not relevant locations for long-term public exposure so not presented

Table A-2 - Maximum Annual Average Concentrations of Particulate Matter (PM10) – AER Engines

Receptor Location PM10 PC, PC / AAD, PM10 PEC, PEC / ID µg/m3 % µg/m3 AAD, %

D1 Lytham Close 0.1 0.1 19.1 47.6 D2 Cherbury Close <0.1 0.1 19.0 47.6 D3 Fleming Way <0.1 0.1 19.0 47.6 D4 Haldane Road <0.1 <0.1 19.0 47.5 D5 Glendale Way <0.1 <0.1 19.0 47.5 D6 Poplar Place (N) <0.1 <0.1 19.0 47.5 D7 Poplar Place(S) <0.1 <0.1 19.0 47.5 D8 Sewell Road <0.1 <0.1 19.0 47.5

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Receptor Location PM10 PC, PC / AAD, PM10 PEC, PEC / ID µg/m3 % µg/m3 AAD, %

D9 Binsey Walk <0.1 <0.1 19.0 47.5 D10 A2041/ Lynsham Drive <0.1 <0.1 19.0 47.5 D11 Hartslock Drive <0.1 <0.1 19.0 47.5 D12 St Katherines Road <0.1 <0.1 19.0 47.5 D13 Yarnton Way <0.1 <0.1 19.0 47.5 D14 Yarnton Way / Kale Rd <0.1 <0.1 19.0 47.5 D15 Yarnton Way <0.1 <0.1 19.0 47.5 D16 Waterfield Close <0.1 <0.1 19.0 47.5 D17 Norman Road <0.1 <0.1 19.0 47.5

Table A-3 - Maximum Hourly Average Concentrations of Nitrogen Dioxide – AER Engines

3 (1) 3 Receptor Description NO2 PC, µg/m NO2 PEC , µg/m Breaches AQO ID D1 Lytham Close 60.9 116.9 N D2 Cherbury Close 34.4 90.4 N D3 Fleming Way 31.8 87.8 N D4 Haldane Road 16.9 72.9 N D5 Glendale Way 8.8 64.8 N D6 Poplar Place (N) 7.4 63.4 N D7 Poplar Place(S) 6.8 62.8 N D8 Sewell Road 7.0 63.0 N D9 Binsey Walk 7.4 63.4 N D10 A2041/ Lynsham Drive 6.5 62.5 N D11 Hartslock Drive 8.3 64.3 N D12 St Katherines Road 8.4 64.4 N D13 Yarnton Way 6.4 62.4 N D14 Yarnton Way / Kale Rd 7.1 63.1 N D15 Yarnton Way 7.3 63.3 N D16 Waterfield Close 5.8 61.8 N D17 Norman Road 6.8 62.8 N D18 Crossness Visitor Centre 137.7 193.7 N D19 Lytham Close Play Area 59.3 115.3 N D20 Thamesmead Sports Club 29.7 85.7 N D21 Crossway Park 10.0 66.0 N Maximum (2) 137.7 193.7 (2)

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(1) Calculated as the maximum hourly PC plus twice the annual mean NO2 background. (2) Not a relevant location for public exposure so no impact assessment presented

Table A-4 - Maximum Daily Average Concentrations of Particulate Matter – AER Engines

Receptor ID Description 3 3 Breaches AQO PM10 PC, µg/m PM10 PEC, µg/m

D1 Lytham Close 1.0 20.0 N D2 Cherbury Close 0.4 19.4 N D3 Fleming Way 0.4 19.4 N D4 Haldane Road 0.2 19.2 N D5 Glendale Way 0.1 19.1 N D6 Poplar Place (N) 0.1 19.1 N D7 Poplar Place(S) 0.1 19.1 N D8 Sewell Road 0.1 19.1 N D9 Binsey Walk 0.1 19.1 N D10 A2041/ Lynsham Drive 0.1 19.1 N D11 Hartslock Drive 0.1 19.1 N D12 St Katherines Road 0.1 19.1 N D13 Yarnton Way 0.1 19.1 N D14 Yarnton Way / Kale Rd 0.1 19.1 N D15 Yarnton Way 0.1 19.1 N D16 Waterfield Close 0.1 19.1 N D17 Norman Road 0.1 19.1 N D18 Crossness Visitor Centre 5.7 24.7 N D19 Lytham Close Play Area 1.1 20.1 N D20 Thamesmead Sports Club 0.3 19.3 N D21 Crossway Park 0.1 19.1 N Maximum (1) 6.6 25.6 (1) (1) Not a relevant location for public exposure

Table A-5 - Maximum 8 hour Average Concentrations of Carbon Monoxide – AER Engines

Receptor ID Description CO PC, µg/m3 CO PEC, µg/m3 Breaches AQO

D1 Lytham Close 147.8 556.8 N D2 Cherbury Close 47.0 456.0 N D3 Fleming Way 63.7 472.7 N D4 Haldane Road 29.5 438.5 N

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Receptor ID Description CO PC, µg/m3 CO PEC, µg/m3 Breaches AQO

D5 Glendale Way 15.0 424.0 N D6 Poplar Place (N) 12.2 421.2 N D7 Poplar Place(S) 11.1 420.1 N D8 Sewell Road 13.5 422.5 N D9 Binsey Walk 14.3 423.3 N D10 A2041/ Lynsham Drive 11.2 420.2 N D11 Hartslock Drive 18.0 427.0 N D12 St Katherines Road 18.0 427.0 N D13 Yarnton Way 14.3 423.3 N D14 Yarnton Way / Kale Rd 16.7 425.7 N D15 Yarnton Way 16.4 425.4 N D16 Waterfield Close 9.9 418.9 N D17 Norman Road 9.5 418.5 N D18 Crossness Visitor Centre 544.5 953.5 N D19 Lytham Close Play Area 154.2 563.2 N D20 Thamesmead Sports Club 54.7 463.7 N D21 Crossway Park 18.7 427.7 N Maximum (1) 544.5 953.5 (1) (1) Not a relevant location for public exposure

Table A-6 - Maximum 1 hour Average Concentrations of Carbon Monoxide – AER Engines

Receptor ID Description CO PC, µg/m3 CO PEC, µg/m3 Breaches AQO

D1 Lytham Close 513.2 1.7 N D2 Cherbury Close 289.8 1.0 N D3 Fleming Way 268.0 0.9 N D4 Haldane Road 142.1 0.5 N D5 Glendale Way 74.1 0.2 N D6 Poplar Place (N) 61.9 0.2 N D7 Poplar Place(S) 57.6 0.2 N D8 Sewell Road 58.9 0.2 N D9 Binsey Walk 62.7 0.2 N D10 A2041/ Lynsham Drive 54.9 0.2 N D11 Hartslock Drive 69.8 0.2 N

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Receptor ID Description CO PC, µg/m3 CO PEC, µg/m3 Breaches AQO

D12 St Katherines Road 70.5 0.2 N D13 Yarnton Way 54.0 0.2 N D14 Yarnton Way / Kale Rd 59.7 0.2 N D15 Yarnton Way 61.1 0.2 N D16 Waterfield Close 48.7 0.2 N D17 Norman Road 57.1 0.2 N D18 Crossness Visitor Centre 1160.4 3.9 N D19 Lytham Close Play Area 499.9 1.7 N D20 Thamesmead Sports Club 249.8 0.8 N D21 Crossway Park 84.5 0.3 N Maximum (1) 1160.4 5.4 (1) (1) Not a relevant location for public exposure

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Appendix B. Manufacturer’s data

B.1. MAN Paxman standby generators

Figure B-1 - MAN Paxman engine plate

Figure B-2 - MAN Paxman emission parameters

Pers comm MAN-ES, 28 November 2019: The exhaust gas flow data will be as follows for the two ratings shown on the engine data plate: 2165 kWb @ 1500 r/min = 7.99 m3/h 2365 kWb @ 1500 r/min = 8.43 m3/h

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Figure B-3 - MAN Paxman stack testing results (September 2019)

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B.2. MTU standby generators

Figure B-4 – MTU engine plate

Figure B-5 – MTU engine flow rate data

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Figure B-6 – MTU engine emissions data

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B.3. Webster House Boilers

Figure B-7 – Webster House Boiler Plate

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Figure B-8 – BS845-1 Boiler Calculation

Fuel Fuel Oil, BS2869, class D Flue Gas Composition % Data

GCV of Fuel by mass @ 15°C GCVm 43,938 kJ/kg Wet Boiler Type Hot Water

NCV of Fuel by mass @ 15°C NCVm 41,103 kJ/kg by vol. by mass Net Heat Input 543 kW

GCV of Fuel by volume @ 15°C GCVv 41,032 kJ/l CO2 12.09 18.31 Feedwater Temperature 10 °C

NCV of Fuel by volume @ 15°C NCVv 38,384 kJ/l H2O 10.39 6.44 Operating Pressure 6.00 barg 3 Density of Fuel @ 15°C and 1.01325 bar r 933.857 kg/m O2 2.70 2.97 Saturation Temperature 164.9 °C

Carbon Content of the fuel, by mass C 80.88 % N2 74.66 71.96 Actual Steam Consumption N/A kg/hr Hydrogen Content of the fuel, by mass H 11.06 % Dry Flowrate at Saturation Temperature 3,014 l/hr Oxygen Content of the fuel, by mass O 0.00 % by vol. by mass Flowrate at Saturation Temperature 0.84 l/s

Nitrogen Content of the fuel, by mass N 0.19 % CO2 13.49 19.57 Net Heat Input 543 kW

Sulphur Content of the fuel, by mass S 2.36 % H2O ~ ~ Gross heat required 632 kW

Gaseous Nitrogen Content of the fuel by mass N2 0.00 % O2 3.01 3.18 Fuel Consumption 51.78 kg/hr

Gaseous Oxygen Content of the fuel by mass O2 0.00 % N2 83.32 76.92 0.014 kg/s

Carbon Dioxide Content of the fuel by mass CO2 0.00 % SO2 1,323 ppm Gaseous volumetric fuel consumptions 55.4 l/hr Corr. are stated for 15°C and 1,013 mbar Specific Humidity of the Air w 0.00 kg/kg SO2 1,324 ppm 0.015 l/s Stoichiometric Air for the Fuel Ŵ 13.88 kg/kg 632 kWh

Moisture Content of the fuel as fired mH2O 5.51 %

Quantity of ashes and riddlings/ tonne of fuel burnt / hour (dry basis) M1 0 kg Fuel Cost 2 p/l

Quantity of dust and grit/ per tonne of fuel burnt / hour (dry basis) M2 0 kg No. Hours / day @ F&A output 24

Carbon content/ tonne of fuel burnt of ashes and riddlings (dry basis) a1 0 % No Days/ week 7

Carbon content/ tonne of fuel burnt of grit and dust (dry basis) a2 0 % No. of weeks 50 Volume of CO in the gases leaving the boiler (dry basis) 0.00 % Cost / day £26.61 Loss due to radiation, convection and conduction (based on GCV) 0.5 % Cost / week £186.30 Temperature of air entering the combustion system 25.0 °C Cost / year £9,315

Volumetric O2 Measuremant Basis Dry % O2 in flue 3.0 % Emissions Data

CombustionExcess Air a3 16.8 % CO2 output 153.5 kg/hr Mass of Combustion Products / kg fuel burn 16.19 kg 42.63 g/s

Mass flow rate of combustion products 838 kg/hr H2O output 54.0 kg/hr 0.233 kg/s 15.00 g/s

Flue Gas Temperature T3 220.0 °C Theoretical SO2 output 2.44 kg/hr 493.15 K 0.68 g/s

Flue Gas Density 0.72 kg/m³ Normalised to 25°C, 1.01325bara and 3% O 2 DVB 3,469 mg/m³

Volumetric flow rate of combustion products @ T3 1,165 m³/hr Absolute Pressure 1,013.25 mbar 0.324 m³/s Dewpoint 46.8 °C Normalised volumetric flow rate of combustion 645 Nm³/hr Sulphuric Acid dewpoint 145 °C products (@ 0°C & 1.013.25 mbar) 0.179 Nm³/s Chimney internal diameter 0.25 m

Efflux velocity @ T3 6.59 m/s BS845-1:1987 Boiler Thermal Efflux velocity corrected to 250°C 7.00 m/s Efficiency Gross Calorific Efficiency 85.92 % Net Calorific Efficiency 90.76 %

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Appendix C. Non statutory ecological sites

C.1. Local nature reserves (LNR) Local nature reserves • Crossness nature reserve http://discover-london.gigl.org.uk/site- Details.aspx?sID=OS_Bx_0269&sType=park • Lesnes Abbey Woods http://discover-london.gigl.org.uk/site-Details.aspx?sID=OS_Bx_0136&sType=park

C.2. Sites of importance for nature conservation (SINCS) In London, SINCs24,25 are designated as one of a hierarchy of types. • Sites of Metropolitan Importance are selected on a London-wide basis; • Sites of Borough Importance (Grade 1 and 2) are selected from candidates within each borough; • Sites of Local Importance are the lowest tier of sites, selected to redress any remaining local deficiencies.

Sites of metropolitan grade importance: • River Thames and Tidal Tributaries http://discover-london.gigl.org.uk/site- Details.aspx?sID=M031&sType=sinc • Erith Marshes http://discover-london.gigl.org.uk/site-Details.aspx?sID=M041&sType=sinc • Lesnes Abbey Woods and Bostall Woods http://discover-london.gigl.org.uk/site- Details.aspx?sID=M015&sType=sinc

Sites of borough grade I importance • Thamesview Golf Course http://discover-london.gigl.org.uk/site-Details.aspx?sID=BxBI14&sType=sinc • Crossways Lake http://discover-london.gigl.org.uk/site-Details.aspx?sID=BxBI01&sType=sinc

Sites of borough grade II importance • Southmere Park & Yarnton Way http://discover-london.gigl.org.uk/site- Details.aspx?sID=BxBII02&sType=sinc • Franks Park http://discover-london.gigl.org.uk/site-Details.aspx?sID=BxBI03&sType=sinc

Sites of local importance • Crossway Park http://discover-london.gigl.org.uk/site-Details.aspx?sID=BxL07&sType=sinc

24 https://www.gigl.org.uk/designated-sites/non-statutory-sincs/ 25 http://downloads.gigl.org.uk/website/Mapping%20Technical%20Note.pdf

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Figure C-1 – Local nature sites (from GIGL website)

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Table C-1 – Annual mean process contribution at LWS (µg/m3) Receptor Annual Mean Annual Mean PC NOX PC SO2 River Thames and tidal tributaries LWS 14.0 0.11 River Thames and tidal tributaries LWS centre point 8.9 0.24 Crossness STW Pond LWS 1.2 0.32 Erith Marshes LWS south 2.2 0.82 Erith Marshes LWS east 1.8 0.56 Erith Marshes LWS outside 1 1.3 0.45 Erith Marshes LWS outside 2 1.0 0.37 Thamesview Golf Course LWS 4.4 0.24 The Ridgeway LWS 1.7 0.53 Crossway Park and Tump 52 LWS 1.5 0.47 Southmere Park and Woodland LWS 0.7 0.27 Belvedere Dykes LWS 1.5 0.15 Crossways Lake Nature Reserve LWS 0.7 0.23 Goresbrook and the Ship & Shovel LWS 0.5 0.04 Ridgeway in Greenwich LWS 0.3 0.13 Lesnes Abbey Woods and Bostall Woods LWS 0.2 0.07 Tump 53 Nature Park LWS 0.3 0.11 Franks Park LWS 0.1 0.05 Twin Tumps and Thamesmere LWS 0.2 0.09 Gallions Reach Park LWS 0.2 0.10 Church Manorway Nature Area LWS/ Pirelli Site * 0.1 0.05

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Table C-2 – Maximum 24-hour mean NOx concentration at LWS (µg/m3) Receptor Routine Scenario 2 Scenario 3 Sources Routine Testing Black Start Routine (1) PC (2) Total PC (2) Total River Thames and tidal tributaries LWS 59.4 38.7 98.0 121.2 180.6 River Thames and tidal tributaries LWS 61.4 65.1 126.5 312.0 373.4 centre point Crossness STW Pond LWS 6.2 45.2 51.4 196.2 202.3 Erith Marshes LWS south 8.5 23.7 32.2 122.9 131.3 Erith Marshes LWS east 10.0 21.7 31.7 111.9 121.8 Erith Marshes LWS outside 1 6.9 17.8 24.7 87.8 94.7 Erith Marshes LWS outside 2 5.4 13.8 19.1 67.8 73.2 Thamesview Golf Course LWS 32.8 29.8 62.6 142.6 175.4 The Ridgeway LWS 8.6 9.8 18.4 48.8 57.4 Crossway Park and Tump 52 LWS 7.3 8.2 15.4 40.3 47.6 Southmere Park and Woodland LWS 3.9 4.9 8.9 24.6 28.5 Belvedere Dykes LWS 9.3 22.6 32.0 98.6 107.9 Crossways Lake Nature Reserve LWS 3.9 6.5 10.4 30.6 34.5 Goresbrook and the Ship & Shovel LWS 5.7 5.3 11.0 16.2 21.9 Ridgeway in Greenwich LWS 1.7 2.6 4.3 11.9 13.6 Lesnes Abbey Woods and Bostall Woods 1.2 1.5 2.7 6.6 7.8 LWS Tump 53 Nature Park LWS 1.5 2.4 3.8 10.9 12.4 Franks Park LWS 1.3 1.3 2.6 6.0 7.3 Twin Tumps and Thamesmere LWS 1.2 1.5 2.7 6.4 7.6 Gallions Reach Park LWS 1.4 2.2 3.6 9.8 11.2 Church Manorway Nature Area LWS/ 0.9 1.3 2.2 6.3 7.2 Pirelli Site * (1) Weighted by a factor of 18/24 to estimate the total for Scenario 2/3 (2) Weighted by a factor of 6/24 to estimate the total for Scenario 2/3

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C.3. Daily Mean NOx Further analysis was carried out to illustrate the low likelihood of an exceedance of the daily mean based on actual operating scenarios. Modelling was undertaken for Scenario 3 (black start test) at a single receptor location within the Crossness LNR representing the area of the maximum daily mean concentrations shown in Figure 4-7. The top 50 modelled daily mean concentrations were extracted from the five year model run, and are presented in Table C-3.

Table C-3 – Top 50 24 hour Average Concentrations of Oxides of Nitrogen (µg/m3) – All sources Top 24 Hour Mean (µg/m3) Year Occurrences in top 50 Min Max Average 2013 10 213.4 514.6 290.9 2014 9 209.2 425.8 282.8 2015 9 199.5 448.0 245.2 2016 6 241.6 385.4 286.7 2017 16 202.3 415.4 268.4

Of the top 50 results in the five year run, based on all routine plant operating concurrently with all standby engines, it is shown that 16 occur in year 2017 (column 2 of the table), but the overall daily maximum (515 µg/m3) occurred in 2013 (column 4). Note, these results are not weighted for the number of hours of black start testing thus are higher than those presented in Section 4.3.1. The top 24 hour results are only considering the top 50 out of 1,825 days at the most affected location. Concentrations across the great majority of the modelled period and modelled domain are lower than those in Table C-3. The intention of this exercise is to illustrate the sharp decline in daily average concentrations, even within this top fraction of results; the minimum is typically half of the maximum even within this small subset. This is because there are very few winds that would result in the highest concentrations at this closest receptor.

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