3.4 CLIMATE AND AIR QUALITY

Transcription

1 3.4 CLIMATE AND AIR QUALITY INTRODUCTION This chapter of the describes the Climate and the Air Quality in the existing environment surrounding the proposed development area and is divided into the following sub-sections; INTRODUCTION CLIMATE EXISTING ENVIRONMENT - Methodology - Receiving Environment ENVIRONMENTAL IMPACTS - Construction and Operational Phase Impacts - Worst-Case Scenario Impact - Do-Nothing Impact MITIGATION MEASURES - Construction and Operational Phase Mitigation RESIDUAL IMPACTS AIR QUALITY AND ODOUR EXISTING ENVIRONMENT General Air Quality - Methodology - Receiving Environment Odour - Methodology - Receiving Environment ENVIRONMENTAL IMPACTS General Air Quality - Impact Assessment Methodology - Construction Phase Impacts - Operational Phase Impacts - Worst-Case Scenario Impact - Do-Nothing Impact Odour - Impact Assessment Methodology - Construction Phase Impacts - Operational Phase Impacts - Worst-Case Scenario Impact - Do-Nothing Impact MITIGATION MEASURES General Air Quality - Construction Phase Mitigation - Operational Phase Mitigation Odour - Construction Phase Mitigation - Operational Phase Mitigation RESIDUAL IMPACTS AWN Consulting Limited were commissioned to conduct an assessment into likely impact on the climate and the air quality associated with the proposed plant. The specialist brief was to assess the current climate and air quality in the region of the development and to predict the impacts of the proposed development on air quality in future years. A copy of the specialist report is included as Appendix 5 of Volume III of this statement. 99

2 3.4.2 CLIMATE Existing Environment Methodology The methodology for the description of the current climate in the region of the proposed development is included on a desk study review on the data available from Met Eireann. Receiving Environment Regional Climate The dominant influence on Ireland's climate is the Atlantic Ocean. Consequently, Ireland does not suffer from the extremes of temperature experienced by many other countries at similar latitude. Average annual temperature is about 9 C. In the middle and east of the country temperatures tend to be somewhat more extreme than in other parts of the country. For example, summer mean daily maximum is about 19 C and winter mean daily minimum is about 2.5 C in these areas Mean annual wind speed varies between about 4 m/sec in the east midlands and 7 m/sec in the northwest. Strong winds tend to be more frequent in winter than in summer. Sunshine duration is highest in the southeast of the country. Average rainfall varies between about 1,000 and 1,250mm. With south westerly winds from the Atlantic dominating, rainfall figures are highest in the northwest, west and southwest of the country, especially over the higher ground. Rainfall accumulation tends to be highest in winter and lowest in early summer The annual number of days with more than 1 mm of rain varies between about 150 in the drier parts and over 200 in the wetter parts of the country. Met Éireann has station data going back to the 19th century for some dozens of stations Synoptic stations are those that observe and record all the surface meteorological data. These observations include temperature, relative humidity, sunshine, rainfall, wind and general weather. They report a mixture of snapshot hourly observations of the weather know as synoptic observations, and daily summaries of the weather known as climate observations and daily summaries of the weather known as climate observations. There are 15 synoptic stations scattered throughout the country, as listed in the table below. Table 3.4.1: Synoptic Stations in Ireland Station Name Latitude Longitude Height (m) Grid Ref VALENTIA OBSERVATORY V SHANNON AIRPORT R DUBLIN AIRPORT O MALIN HEAD C ROCHE'S POINT S.W.S W BELMULLET F CLONES H ROSSLARE T CLAREMORRIS M MULLINGAR II N KILKENNY S CASEMENT AERODROME O CORK AIRPORT W BIRR N KNOCK AIRPORT M Local Climate The nearest synoptic station to the proposed development is Belmullet. The station is located at Carne, Belmullet, Co. Mayo. The nearest town is Belmullet, situated 1 km to the east. The station opened in September The station is regarded as being particularly important because of its 100

3 location on the western fringe of Europe. Below are listed the climatic observations for Belmullet station for the period from 1961 and Table 3.4.2: Climatic observation for Belmullet station for the period TEMPERATURE (degrees Celsius) jan feb mar apr may jun jul aug sep oct nov dec year mean daily max mean daily min mean absolute max absolute min mean no. of days with air frost mean no. of days with ground frost RELATIVE HUMIDITY (%) jan feb mar apr may jun jul aug sep oct nov dec year mean at 0900UTC mean at 1500UTC SUNSHINE (hours) mean daily duration greatest daily duration mean no. of days with no sun RAINFALL (mm) jan feb mar apr may jun jul aug sep oct nov dec year mean monthly total greatest daily total mean no. of days with >= 0.2mm mean no. of days with >= 1.0mm mean no. of days with >= 5.0mm WIND (knots) jan feb mar apr may jun jul aug sep oct nov dec year mean monthly speed max. gust max. mean 10-minute speed mean no. of days with gales WEATHER (mean no. of days with..) jan feb mar apr may jun jul aug sep oct nov dec year snow or sleet snow lying at 0900UTC hail thunder fog Refer Figure Belmullet Meteorological Station: 1993, for relevant windrose data. 101

4 Environmental Impacts Construction and Operational Phase Impacts Due to the scale of the proposed development, during either construction phase or operational phase there are not any predicted impacts on the regional and local climate During the consultation process a number of the stakeholder raised queries relating to how the design of the would take climate change into consideration. To date there have been no firm policy decisions relating to the effects of climate change on drainage design criteria in Ireland. However, the Greater Dublin Strategic Drainage Study has indicated design consideration should be given to increasing rainfall intensities by 10%. In the west of Ireland, it could be assumed that rainfall figures may be higher. Having regard to the recent Environmental Research Centre publication for the Environmental Protection Agency, Implications of the EU Climate Change Protection for Ireland it is considered that the increase of 10% in rainfall intensities is an appropriate figure to utilise when considering the design horizon for this proposed development. In relation to the design implications of this figure the reader is advised to revert to Section of this statement Based on the nature and scale of the proposed development there is considered to be no impact of significance related to Ireland s commitments as a signatory to the Kyoto Protocol concerning the reduction of greenhouse gases to the environment. Worst-Case Scenario Impact Due to the nature and scale of the development, it is considered that there are no impacts arising which could affect the general climate of the area, either regionally or locally. Do-Nothing Impact If the development does not proceed, the general climate of the area would continue to be subject to existing prevailing influences. Mitigation Measures Construction and Operational Phase Since it is envisaged that the proposed facility will have no impacts on the regional and local climate, no specific mitigation measures are deemed necessary. Residual Impacts No significant residual impacts are envisaged. 102

5 AIR QUALITY AND ODOUR Existing Environment A GENERAL AIR QUALITY Methodology The methodology for the description of the general air quality in the existing environment is based on a desk based review of the relevant literature, with particular reference to the publication from the Environmental Protection Agency (2003) Air Quality Monitoring Annual Report Receiving Environment The proposed site of the waste water treatment plant is located on a rural section of land approximately 500m from Newport town and 200m from the coastline. The closest residential receptors are 2 no. properties approximately 400m to the northwest of the site, 1 no. property approximately 350m directly south of the site and 3 properties at the edge of Newport village, approximately 220m southeast of the site boundary [refer to Figure WWTP in Operation: predicted 98 th %ile Odour Concentrations (OU/m 3 )] Rural Ireland, of which the current region is typical, (which in the context of ambient air legislation is defined as rural areas and all towns with populations less than 15,000) is defined under ambient air quality legislation as a Zone D region. Zone D regions are considered areas of good air quality, which is reflected in the absence of a requirement for continuous air monitoring The current region in which the waste water treatment plant is proposed has no significant air emission sources with the prevailing westerly wind from the Atlantic ensuring that the area experiences low background air concentrations. Existing levels of NO 2, (Nitrogen Dioxide), CO 2 (Carbon Dioxide) and Benzene are likely to be very low. PM 10 (Particulates with a diameter of less than 10 microns) may be higher due to sea spray and other natural sources but will be significantly below the applicable standards in Ireland which are the EU Air Quality Directives 1999/30/EC and 2000/69/EC. The EU Directives have recently been adopted into Irish Legislation in the, Air Quality Standard Regulations, 2002 (S. I. No. 271 of 2002) Temperature is an important factor in terms of the rate of chemical and biochemical reactions. As the temperatures increases, oxygen becomes less soluble in water while the rate of biochemical reactions increases (rate of biological uptake and thus oxygen utilization doubles for every 10 C in temperature. Both of these factors lead to faster depletion of dissolved oxygen in summer months. As shown already in table 3.4.2, the 30-year average temperatures at Belmullet vary from a low of 5.6 C in February to a high of 14.1 C in August with a long-term mean of 9.6 C B ODOUR Methodology The methodology for the description of odour in the existing environment is based on a desk based review of the relevant literature, with particular reference to the publications from the UK/Scottish Environment Agency (2002) IPPC Draft Horizontal Guidance for Odour Part 1- Regulation and Permitting and IPPC Draft Horizontal Guidance for Odour Part 2 Assessment and Control. Receiving Environment General In terms of odour, the existing background will be dominated by the influence of the coastal location with sea spray and seaweed imparting a characteristic coastal odour. Although an existing background odour is present, odours are not generally additive i.e. a new odour cannot be added to an existing background odour to give a total odour. This is a result of the brain s ability to screen out existing odours and detecting a much lower new odour against this background. Thus, the existing odour is effectively ignored in the olfactometry assessment. 103

6 Meteorological Environment Wind speed is of key importance in dispersing both air and odour pollutants and for low level sources, such as sedimentation tanks and aeration basins, pollutant concentrations are inversely related to wind speed. Thus, odour levels will be greatest under very calm conditions and low wind speeds when movement of air is restricted. The frequency of these conditions is low. Data from the nearest appropriate meteorological station of Belmullet has been examined to identify the wind field pattern which will be indicative of conditions likely at Newport. For data collated during four representative years (1993, 95-97), the worst-case conditions occurred for approximately 1-2% of the time. The predominant wind directions in the worst-case year (1997) are south westerly with average wind speeds of approximately 3-5 m/s. Source of Odours in Wastewater Treatment Plants Wastewater has a discernible odour as does its degradation products. The degree to which the odour will cause a problem will depend on: The original components, The treatment and handling of the wastewater and products, and Extent to which they are exposed to the atmosphere The smell of wastewater results from its components which in the present case will generally be domestic sources (toilets, baths, sinks, dishwashers and washing machines). The mixture of odorous chemicals contains a range of aliphatic, aromatic and chlorinated hydrocarbons, derived from cleaning agents used in the home, solvents and odours associated with human waste (urea, ammonia, skatole and indole) Fresh wastewater has usually sufficient dissolved oxygen (DO) to prevent the generation of anaerobic compounds although oxidation of volatile organic compounds to alcohols, and in turn to aldehydes (which can be further oxidised to carboxylic acid and eventually carbon dioxide and water) and ketones may lead to the formation of odours under even aerobic conditions However, fresh wastewater generally does not cause an odour problem unless potential complainants are located very close to discharge points (typically less than 50 metres from the site boundary) or where industrial discharges are important (both of which are not relevant in this case) The majority of chemicals associated with odour problems develop in wastewater and waste sludges when they become anaerobic or septic (i.e when all the DO and nitrates have been used). Under anaerobic conditions, various reactions will occur: Fermentation of fats, polysaccharides and proteins to produce fatty acids, alcohols, aldehydes, ketones, ammonia, amines, mercaptans and suphides particularly important in stored sludges and sludge liquors where they may be the main source of odours. Reduction of sulphates by sulphate-reducing bacteria (SRB) with the production of hydrogen sulphide. Generally sulphate levels may be in the region of mg/l. Examples where sulphate reduction takes place include rising main sewers, sediments and slimes within tanks, grit channels, primary sedimentation tanks, slimes in high rate or overloaded biological filters, sludge storage tanks and gravity thickeners A complex range of factors are important in the rate of the two sets of reactions including retention time, temperature, ph value, redox potential, concentration of substrates and nutrients and the concentration of wastewater and sludges The presence of odorous substances in waste water does not necessarily mean that they will contribute to odour problems because the conditions under which they are transformed from liquid to gas are complicated. The factors which affect the amount of odorous gases released to atmosphere are: The solubility of the dissolved gases, Concentration of compounds in the gas and liquid phases, 104

7 Overall volumetric mass-transfer coefficient which is related to the mass transfer coefficient and the interfacial area - the rate of release at points of turbulence is very much greater than from quiescent surfaces, Temperature - solubility decreases and the rate of transfer increases with increasing temperature, and ph low ph values favour the emission of H 2 S, mercaptans and volatile fatty acids, while high ph values favour the emission of ammonia and reduced nitrogeneous compounds Examples of locations where there may be significant potential for release of odours are discharge point of rising main sewers, free drops of sludge into open holding tanks or over weirs, mechanical sludge thickening and dewatering plant, discharge points of septage sludges and discharge point of sludge liquors. Newport Waste Water Treatment Plant The Newport waste water treatment plant is likely to consist of an inlet works prior to aeration in an activated sludge aeration basin. Following secondary sedimentation, sludge may be thickened using a picket fence thickening tank and then dewatered in an enclosed building prior to disposal offsite In rising main sewers, respiration of wastewater and slimes rapidly depletes any dissolved oxygen and nitrates. Thus, sulphate reduction and fermentation may take place within the body of wastewater and on the slimes in the submerged sewer walls leading to odour releases at the discharge points Raw wastewater inlet channels can be a source of odour problems. Odours can be released from the discharge points, channels, screenings and grit removal. Screenings and grit can be odorous during storage and transfer, particularly if not washed after separation The storm water tank will be used for storm water flows and thus will not be in operation continually. Provided that the tank is clean after discharge of influent, odour emissions will not be significant Odours are removed from wastewater by adsorption of anaerobic compounds onto sludge floc and through biochemical oxidation. However, the aeration system will also strip odours from the mixed liquor with the off-gases having a characteristic musty odour The secondary sedimentation tanks are generally low in odour due to the low BOD load in the influent. However, odours can develop faster than primary sedimentation tanks due to the more biologically active, settled mixed liquor. Housekeeping to prevent accumulation of scum on water surface, sludge accumulation on walls and organic matter on effluent weir troughs will minimise odour formation. Withdrawal rates should provide for residence times not exceeding hours to avoid septic conditions in the settled sludge The amount of hydrogen sulphide and fermentation products generated will increase significantly with time of storage during sludge thickening. Depletion of residual dissolved oxygen occurs very rapidly because the number of micro-organisms in the sludge is several orders of magnitude higher than in wastewater whilst the availability of substrate per unit volume is much greater. The strength of sludge liquors will also increase with time. Environmental Impacts A GENERAL AIR QUALITY Impact Assessment Methodology In assessing the impact of the proposed development on general air quality AWN Consulting Limited utilised a desk-based literature review approach. Construction Phase Impacts Construction activities are likely to generate some dust emissions in the vicinity of the proposed development. Construction vehicles, generators etc., may also give rise to NO 2, PM 10, CO 2 and N 2 O emissions. In the case of dust, it is considered that on the implementation of an appropriate designed 105

8 dust minimisation plan in addition to the absence of nearby receptors (<220 m) should lead to no significant impact on sensitive receptors during the construction phase. As is the case regarding the operational phase emissions of NO 2, PM 10, CO 2 and N 2 O are considered insignificant. Operational Phase Impacts The primary impact on air quality will be the release of odour from the waste water treatment plant process and NO 2, PM 10 and Benzene emissions from vehicles travelling to and from the facility. The existing baseline concentration of these pollutants is significantly below the ambient air quality limit values (as the site is located in a Zone D region). The additional impact of site traffic will lead to an insignificant increase in the levels of NO 2, PM 10 and Benzene emissions. Thus, the cumulative impact of the baseline concentration and the additional concentration due to site traffic will lead to levels which are still significantly below the ambient air quality limit values as outlined in S.I. 271 of Thus, the impact of the scheme in terms of general air quality is not significant. Worst-Case Scenario Impact It is considered that the Worst-Case Scenario impact would arise from ineffective traffic and construction management resulting in the generation of significant air quality impacts. Do-Nothing Scenario Impact If the development does not proceed, the general air quality of the area would continue to be subject to existing prevailing influences. B ODOUR Impact Assessment Methodology Dispersion Modelling The United States Environmental Protection Agency (USEPA) developed AERMOD dispersion model has been used to predict the ground level odour concentrations (GLC) from the proposed Newport waste water treatment plant. The modelling incorporated the following features: Seventeen discrete receptors were identified near the proposed facility. In addition, boundary receptors locations were placed at the site boundary giving a total of 31 calculation points for each model case. All on-site buildings and significant process structures were mapped into the computer to create a three dimensional visualisation of the site and its emission point. AERMOD incorporates a meteorological pre-processor AERMET PRO. The AERMET PRO meteorological preprocessor requires the input of surface characteristics, including surface roughness (z 0 ), Bowen Ratio and albedo by sector and season, as well as hourly observations of wind speed, wind direction, cloud cover, and temperature. The values of albedo, Bowen Ratio and surface roughness depend on land-use type (e.g., urban, cultivated land etc) and vary with seasons and wind direction. The assessment of appropriate land-use type was carried out to a distance of 3km from the source location in line with USEPA recommendations. The source and emission data, including area source dimensions, gas volumes and emission temperatures have been incorporated into the model. Terrain has been included in the modelling. The immediate area on-site is relatively flat but has some slight changes in terrain to the northeast and southwest of the site The selection of the appropriate meteorological data has followed the guidance issued by the USEPA. A primary requirement is that the data used should have a data capture of greater than 90% for all parameters. The nearest representative meteorological station to the site is, as described already, Belmullet. Real meteorological data collected at Belmullet Meteorological Station from 1993,95-97 has been used as input to the model. Belmullet is located approximately 40km northwest of the site. The worst-case year (i.e the year which gives the highest ground level pollutant concentration relative to its limit value) has been used throughout this study, Year 1997 (Refer to 106

9 107 Figure Belmullet Meterological Station 1993, ). This will lead to higher concentrations than would be experienced in an average year. Selection of Odour Annoyance Threshold The exposure of the population to a particular odour consists of two factors; the concentration and the length of time that the population may perceive the odour. By definition, 1 ou/m 3 is the detection threshold of 50% of a qualified panel of observers working in an odour-free laboratory using odourfree air as the zero reference In the absence of specific Irish EPA guidance on odour, available guidance from the UK has historically been adopted. During the 1990 s in the UK, it was generally accepted that odour concentrations of between 5 and 10 ou/m 3 would give rise to a faint odour only, and that only a distinct odour (concentration of >10 ou/m 3 ) could give rise to a nuisance. In 1990, a survey of the populations surrounding 200 industrial odour sources in the Netherlands showed that there were no justifiable complaints when 98%ile compliance with an odour exposure standard of a faint odour (5-10 ou/m 3 ) was achieved Recent approaches to odour compliance criteria are moving away from a purely arithmetic approach to odour, based on odour concentration, to one where the dose-effect relationship is investigated. This dose-response relationship will depend on factors such as on the offensiveness of odour, the Peak/Mean (P/M) ratio and the sensitivity of the surrounding environment As part of the dose-response approach to odour assessment, the odour concentration is corrected to reflect the offensiveness and nature of the odour. Hangartner has produced a table which shows the concentration of various sources of odour that would need to be present to extract the same hedonic response as that from pure hydrogen sulphide. In the current context, the odour will be untreated WWTP odours (H 2 S, mercaptans, amines etc) and, as such, an annoyance threshold correction of 1 is considered appropriate It is also appropriate to apply a correction to the concentration component for land use, location and population intensity. The current location is in a relatively low population, rural environment. The sensitivity of the current environment would be viewed as relatively low both due to medium to high existing background odours [odours associated with coastal locations (sea weed etc), and agricultural odours] and because the opportunities for people to be affected by the odours are reduced due to the relatively low population density (relative to high density urban areas). The recommended corrected annoyance threshold for a low sensitivity environment is 10 ou/m 3 (compared to the standard annoyance threshold of 5 ou/m 3 ), which is the same as for a moderately sensitive environment. Thus, in this context, the correction factor for low or medium sensitivity environment is 2. In addition, the rural nature of the site may lead to the masking of the odour by the existing background odour and thus reduce the impact of the facility beyond the site boundary A further factor which needs to be considered in the assessment procedure is the P/M ratio likely due to emissions from the facility. With respect to the current scenario, which involves area sources, volume sources and wake-effected point sources a P/M ratio (based on a 1-hour averaging period) of 2.3 for both the near and far field is recommended In terms of selection of the appropriate percentile, the 98 th %ile has been most commonly applied in odour thresholds and standards. This represents a compromise between the use of very high percentiles which corresponds with the particular conditions which cause most odour complaints and the fact that the uncertainty of the model increases significantly at very high percentiles In summary, an appropriate assessment criteria for Newport waste water odour emissions in a rural setting taking into account the P/M ratio, annoyance threshold correction factor and the land-use correction factor, has been detailed hereafter. Odour annoyance threshold for Newport WWTP: = 5.0 ou/m 3 (default based on a 98 th %ile for H 2 S) x 1 ou/m 3 (no annoyance threshold correction factor relative to H 2 S) x 2 ou/m 3 (correction factor for low or medium sensitivity environment) x 1/ (2.3) ou/m 3 (P/M ratio for wake-affected point sources, area sources, volume sources) = 4.3 ou/m 3 (based on a 98 th %ile of hourly concentrations) = 4 ou/m 3 (based on a 98 th %ile of hourly concentrations) at the nearest sensitive receptor.

10 Construction Phase Impacts During the construction phase, odour impacts are not predicted due to the nature of the activities. Operational Phase Impact As described before, an odour modelling assessment has been carried out based on the specified design. Indicative plant specifications and layout have been assumed based on the specified design and based on similar plants and engineering calculations. Although based on the specified design with assumptions in regard to emission heights (assumed to be at 1.5m) and incorporating worst-case emission factors as outlined in Tables and below, the modelling will give an estimation of the likely impact of the facility in the surrounding environment. Indicative Emission Rates In the absence of specific plant and operational details, accurate emission rates cannot be derived. However, typical emission rates from a wide range of waste water treatment plants are available in the literature and will give an order of magnitude estimate of likely levels at the Newport waste water treatment plant. A recent review of over one hundred measurements (Frechen, 2000) is shown in Table hereunder. Table Overview of Specific Odorant Flow Rates from WWTP Sources Specific Odorant Flow Rate WWTP Source From (ou/m 2 h) To (ou/m 2 h) Aerated Grit Chamber ,000 Screenings 1,000 5,000 Sand From Grit Chamber 1,000 6,500 Primary Sedimentation Tank: surface 500 4,000 Primary Sedimentation Tank: weir area 500 5,000 Aeration tank: Anaerobic part 850 3,000 Aeration tank: Aerobic part 300 1,700 Final sedimentation tank Primary sludge thickener 12,000 35,000 Stabilised Sludge thickener 500 5,000 Stabilised Sludge, dewatered , The range of emission factors above assumes normal conditions at a well operated plant without major industrial influent. However, values outside of this range will occur where poor site management and overloading leads to septic conditions. In addition, some emission sources are particularly difficult to measure accurately. Area source (sedimentation tanks, aeration basins etc) emission factors are generally measured using wind tunnel systems by sweeping air across the surface at a sweep rate of approximately 1800 l/min. However, some literature studies have been sampled using isolation chambers (flux hoods) which have a significantly lower sweep rate (5 24 l/min). Comparisons between total odour emission rates using both sampling apparatuses show under-predictions of isolation chambers of up to 300 times in some cases. Process Emissions Emission sources for the model were based on the specimen design supplied by the project team. Odour emission rates used the highest of the range of values outlined for the specific odorant flow rate in Table This is likely to significantly over-estimate the impact of the facility in the surrounding environment. The details of the input parameters are provided in Table

11 Table Source Emission Details Emission Source Reference Estimated Cross-section area (m 2 ) Odour Emission Rate (ou/m 2.s) Aerated Grit Chamber Screenings Storm Tank Aeration tanks Sedimentation tanks Sludge thickener Stabilised Sludge, dewatered Odour Modelling Results For all averaging periods, the predicted odour concentration is the maximum concentration predicted either at the nearest residential receptor or at ground level. Odour emissions have been modelled for several different emission sources on-site which represents the main sources of odour from a welloperated WWTP. Emissions from these sources were modelled using the specified design for the proposed sources and using worst-case estimated emission data. Details of the 98 th %ile 1-hour mean odour concentrations at the nearest residential receptor and the contribution of each type of source to the overall concentrations are provided in Table The 98 th %ile of 1-hour mean odour concentrations at the nearest residential receptors are listed in Table Table Dispersion Model Results Contributions of each emission source to worst-case odour concentration Stack Reference Averaging Period Predicted Odour Concentration (ou/m 3 ) Worst-Case Receptor All Sources 98 th %ile of 1-hour means 0.37 Grit Channel 98 th %ile of 1-hour means 0.02 Screenings 98 th %ile of 1-hour means Flow Balancing Tank (1) 98 th %ile of 1-hour means 0.07 Aeration tanks 98 th %ile of 1-hour means 0.05 Final sedimentation tanks 98 th %ile of 1-hour means Sludge thickener 98 th %ile of 1-hour means 0.04 Stabilised Sludge, dewatered 98 th %ile of 1-hour means 0.17 (1) Assumed to have an emission rate of a primary sedimentation tank and as a worst-case to be filled 109

12 Table Dispersion Model Results Predicted odour concentration at worst-case receptors Receptor Location Predicted Odour Concentration (ou/m 3 ) 98 th %ile of 1-hour Means 1 SE of Site (E N ) 0.36 ou/m 3 2 SE of Site (E N ) 0.37 ou/m 3 3 SE of Site (E N ) 0.18 ou/m 3 4 NW of Site (E N ) 0.08 ou/m 3 5 S of Site (E N ) 0.11 ou/m 3 6 NW of Site (E N ) 0.13 ou/m The dispersion modelling results presented in Tables and show that the 98 th %ile of mean hourly concentrations is 0.37 ou/m 3 at the worst-case residential receptor, which is located to the south-east of the site. The greatest contribution to the overall odour emissions from the Newport WWTP at the worst-case residential receptor occurs from the sludge thickener and dewatering unit, aeration basin and flow balancing tank, with relatively minor contributions from the other sources. As the overall 98 th %ile of 1-hour mean concentrations is significantly below the 4 ou/m 3 assessment criteria which would give rise to nuisance, it is unlikely that odour emissions from the facility will cause a nuisance at the nearest residential receptor. Concentration Contours The geographical variation in ground level odour concentrations is illustrated as concentration contour in Figure Predicted 98 th Percentile of Mean Hourly Odour Concentrations. The concentrations listed in Table and are for the maximum odour concentrations to be predicted at any of the nearest residential receptors off-site. All other residential receptors are below these values. The maximum concentrations are generally observed to the southeast of the site. The concentration contours show where the maximum concentrations are predicted to occur and the reduction in concentration with distance away from the maximum. Worst-Case Scenario Impact It is considered that the Worst-Case Scenario Impact for the odour would arise from ineffective management of the plant and consequently the plant causing a significant odour impact. Do-Nothing Impact If the development does not proceed, the odour environment of the area would continue to be subject to existing prevailing influences. Mitigation Measures A GENERAL AIR QUALITY Construction Phase Mitigation The implementation of the dust minimisation plan in addition to the absence of nearby receptors (the distance to the nearest receptor is approximately 220 metres) will lead to no significant impact on sensitive receptors during the construction phase of the project. A dust minimisation plan (as part of 110

13 the Construction Management Plan) will be formulated for the construction phase of the project. A sample plan is included in Appendix 1.3 of the AWN Consulting technical report included in Appendix 5 of Volume III of this Statement. Operational Phase Mitigation Since the impact of the scheme during the operational phase in terms of general air quality is not significant, operational measures to mitigate air quality impacts are not required. B ODOUR Construction Phase Mitigations Since the impact of the scheme during the construction phase in terms of odour is not significant, measures to mitigate odour impacts are not required. Operational Phase Mitigation In general, odour control is accomplished in a sewage disposal works by proper operation of the various processes to ensure that the sewage is maintained in a fresh, aerobic condition throughout the treatment system. Specific measures which will be implemented to ensure odour nuisance does not occur, are outlined below: Designing to minimise odours will minimise the length of pumped sewers and ensure odours cannot escape outside the sewerage system. Design velocities of at least 1.0 m/s in conjunction with the short length of the rising main sewer in Newport (600m) will ensure that solids and grit accumulation in the sewer is reduced and that odour formation will not be a significant issue. Designing to minimise odours will avoid accumulation of grit and minimize height of discharge points Ensuring adequate aeration and mixing an adequate concentration of DO must be maintained especially at the point of fresh wastewater entry. Poor mixing can result in organic solids deposition in corners and along edges of the tank. Preliminary treatment processes will be cleaned frequently to remove any accumulated organic debris. Velocities of greater than 0.2m/s through grit chambers will be maintained to avoid deposition of organic solids with the grit. Regular cleaning of channels and general maintenance will be carried out. Flow balancing tank will be cleaned after discharge of influent. A scraper to remove scum on the surface of the sedimentation tanks will be incorporated into the design. The retention time in the sludge-thickening tank will be minimised to prevent odour formation. In order to reduce odour release, the dewatering unit will be contained within an enclosed building with the dewatered sludge transferred to a covered skip. A significant reduction in odour release can be achieved by minimising the height of drops over weirs and into tanks and channels or by selective covering at these locations. Installing a cover over weirs allows gaseous contaminants to accumulate in the headspace and thus retard emissions by reducing the concentration driving force It should also be noted that the appointed Contractor will be required to comply with the European Communities (Waste Water Treatment)(Prevention of Odours and Noise) Regulations, 2005, S.I. No. 787 of These Regulations set out specific reporting requirements to the Environmental Protection Agency in addition to setting out requirements for waste water treatment plants to be designed, constructed, operated and maintained so as to avoid causing nuisance from odour emissions. 111

14 A limit of = 4 ou/m 3 (based on a 98 th %ile of hourly concentrations) at the nearest sensitive receptor will be implemented for odour control at the waste water treatment plant site. The appointed Contractor will be required to develop an approved air dispersion model (i.e. AERMOD or equivalent as appropriate for odour dispersion modelling) to demonstrate the odour contribution from all significant odour sources (e.g. inlet works, sludge handling facilities, storm water storage, etc.) and can be controlled (and abated as considered appropriate) to achieve this limit value. Residual Impacts On effective implementation of the proposed mitigation measures, no residual impacts of significance are envisaged. 112