2 AIR QUALITY IMPACT

2.1 Introduction

2.1.0.1 Air quality is considered as one of the key environmental issues of concern during both construction and operational phases of the proposed project. During the construction phase, there will be potential dust impacts on existing and future sensitive receivers from the construction activities undertaken at the project site. During the operational phase, traffic emission impacts from vehicles travelling on the proposed road network on nearby sensitive receivers would be a major environmental issue of concern.

2.1.0.2 This section presents the assessments on construction phase dust impacts and the operational phase traffic emission impacts.

2.2 Legislation, Policies, Plans, Standards and Criteria

2.2.0.1 The air quality impact assessment criteria make reference to the Hong Kong Planning Standards and Guidelines (HKPSG), the Air Pollution Control Ordinance (APCO) (Cap.311), and Annex 4 of the Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM).

2.2.0.2 The APCO (Cap.311) provides powers for controlling air pollutants from a variety of stationary and mobile sources and encompasses a number of Air Quality Objectives (AQOs). Currently AQOs stipulate concentrations for a range of pollutants namely sulphur dioxide (SO2), total suspended particulates (TSP), respirable suspended particulates (RSP), nitrogen dioxide (NO2), carbon monoxide (CO), photochemical oxidants, and lead (Pb). The AQOs are listed in Table 2.1.

Concentration in micrograms per cubic metre¹

Notes:

1 Measured at 298 K and 101.325 kPa.

2 Not to be exceeded more than three times per year.

3 Not to be exceeded more than once per year.

4 Arithmetic mean.

5 Respirable suspended particulates means suspended particulates in air with a nominal aerodynamic diameter of 10 micrometres or smaller.

6 Photochemical oxidants are determined by measurement of ozone only.

7 Not an AQO but is a criteria for evaluating air quality impacts as stated in Annex 4 of EIAO-TM.

2.2.0.3 The HKPSG specify buffer distances between sources of pollution and sensitive land uses to ensure acceptable air quality at the sensitive land uses. Examples of recommended buffer distances extracted from the HKPSG for relevant source and sensitive land use combinations are given in Table 2.2 below. The actual buffer distances required to avoid adverse air quality impacts associated with Deep Bay Link (DBL) would be reviewed based on the findings of this assessment.

2.2.0.4 For construction dust, Annex 4 of EIAO-TM specifies a TSP limit in air over an 1-hour period of 500 µgm-3. The maximum acceptable TSP concentration averaged over a 24-hour period is 260 µgm-3, as defined in the AQOs.

2.2.0.5 The Air Pollution Control (Construction Dust) Regulation specifies processes that require special control. Contractors and site agents are required to inform EPD and adopt dust reduction measures while carrying out "Notifiable Works" or "Regulatory Works" as defined under the regulation. Works relevant to this Project include:

• Site formation;
• Demolition of building;
• Construction of the foundation of roadworks;
• Construction of the superstructure of roadworks; and
• Other road construction work.

2.3 Description of Environment

2.3.0.1 The vicinity of the northern part of the study area is mostly rural in nature and become more urbanised in the southern part. Existing air quality in the area is influenced by emissions from:
 

• Road network within and around the study area; and
• Construction activities within and around the study area.

2.3.0.2 Further away to the west of the study area are some major existing air pollution sources namely the Shenzhen Ma Wan Power Station, the Hong Kong Black Point Power Station, and the Hong Kong Castle Peak Power Station. They are located at about 11km, 8km, and 10km from Ngau Hom Shek respectively. Future major stack emissions include the Waste-to-Energy Facilities (WEF), the Sludge Treatment Facility (STF), and the Animal Carcass Treatment Facility (ACTF) planned in Nim Wan at about 6km southwest of Ngau Hom Shek. All these future facilities are currently under planning, their locations may be subject to change and that the decision to proceed with these facilities has not yet been made. Locations of the existing major stack emission sources and the currently proposed locations of the planned major stack emission sources are shown in Figure 2.14.

2.3.0.3 There is currently no EPD-operated air quality monitoring station located in the area. Historical air quality monitoring data from the nearest station, namely the rooftop Yuen Long station operated by EPD are taken to examine the historical trend of the air quality condition in the vicinity of the study area.

2.3.0.4 The last three published years of air quality monitoring data, namely 1998, 1999 and 2000 at Yuen Long station are tabulated in Table 2.3.

Note: N/M - Not Measured.

Monitoring results exceeded AQO are shown as bold characters.

2.3.0.5 The monitoring results in Table 2.3 show that nitrogen dioxide and particulates have been the major air pollutants of concern in the area. The reasons may be due to the high traffic emissions from road network and the dust emissions from construction activities in the area. The annual average concentrations of both TSP and RSP exceeded the AQOs from 1998 to 2000. Exceedances of the hourly and/or daily AQOs for nitrogen dioxide were recorded in 1998 and 1999. Nevertheless, in view of the Government's continuous effort in improving the air quality in Hong Kong, the air quality standards in Hong Kong is expected to be sustainable and improving in the future. The recorded levels of sulphur dioxide remained low and were below 35% of the respective AQOs from 1998 to 2000.

2.3.0.6 Apart from EPD's monitoring stations, the China Light & Power Co. Ltd (CLP) also operate a number of monitoring stations in the Yuen Long and Tuen Mun areas to assess the ambient levels of sulphur dioxide and nitrogen dioxide in the vicinity of their power generating stations in the western part of Tuen Mun. The monitoring results of 1998 to 2000 are tabulated in Table 2.4.

Note:

(1) The 24-hour AQO level for sulphur dioxide was exceeded once in June 1999 at the Butterfly Estate station.

(2) The 24-hour AQO for nitrogen dioxide was violated in 1999 because the 24-hour AQO level was exceeded three times in December 1999 at the Tuen Mun station.

2.3.0.7 The monitoring results of CLP showed some geographical variations of the sulphur dioxide and nitrogen dioxide levels in the Tuen Mun and Yuen Long area. Nevertheless, the monitoring results are generally in line with the corresponding monitoring results recorded at EPD's Yuen Long monitoring station. One exception is the sulphur dioxide levels recorded at CLP's Au Tau station; relatively higher sulphur dioxide concentrations were recorded in 1998 and 1999 which might be due to the industrial emissions scattered over the Au Tau area.

2.4 Air Quality Sensitive Receivers and Assessment Points

2.4.0.1 The study area for this air quality impact assessment is defined by a distance of 500m from the boundary of the project site as shown in Figure 2.1. Existing and future air sensitive receivers (ASRs) located in the proximity of the project site which may be subjected to potential air quality impacts of the project are presented in Tables 2.5 and 2.6 respectively. For the purpose of this assessment, it was assumed that existing ASRs located within the works limit/land resumption limit of the DBL project would be resumed and were not included in this assessment.

2.4.0.2 Planned/committed ASRs in the future were identified with reference to relevant Outline Zoning Plans, Outline Development Plans, Layout Plans and other published plans in relation to the Planning and Development on Northwest New Territories. These include the proposed Hung Shui Kiu New Development Area (HSKNDA) and some local planned private developments.

2.4.0.3 More than 250 representative assessment points among these existing and future ASRs tabulated in Tables 2.5 and 2.6 were selected for the air quality impact assessment. Locations of the ASRs and the assessment points are shown in Figure 2.1. Existing ASRs in areas encircled by the proposed Lam Tei Interchange would be resumed together with the proposed Route 10 Northern Section project.

2.5 Assessment Methodology

2.5.0 Construction Phase

2.5.0.1 In order to assess the potential dust impacts associated with the construction of DBL, potential sources of air emissions from the construction sites were identified. Dust mitigation measures stipulated in the Air Pollution Control (Construction Dust) Regulation which are relevant to the associated construction activities were then identified and presented in this report.

2.5.0.2 Apart from the construction of DBL, there are a number of major projects planned in the vicinity of the study area which might cause cumulative construction phase impacts to the environment. These planned projects include Shenzhen Western Corridor, Yuen Long Highway Widening, Hung Shui Kiu New Development Area, Route 10 Northern Section, and San Wai Sewage Treatment Works Expansion and Upgrading. The scope of these projects and their tentative construction program were identified and presented in Section 2.6.0.

2.5.0.3 Audit and monitoring program during the construction phase of this project were formulated and are included in the Environmental Monitoring and Audit Manual prepared under this study.

2.5.1 Operational Phase

Review of Vehicle Fuel Standards for Mainland and Hong Kong

 2.5.1.1 It is noted that the fuels currently marketed in Mainland are in general of a lower quality (that is, higher in sulphur content) compared with the vehicle fuels currently marketed in Hong Kong. It is anticipated that this will remain the case in the near future. Since the quality of fuels would have a direct effect on the tailpipe emissions of vehicles, its effect on those Hong Kong vehicles fuelled with Mainland fuels and travelling from Mainland to Hong Kong through Shenzhen Western Corridor (SWC) and then onto DBL should also be addressed in this assessment.

2.5.1.2 A review on the vehicle fuel standards for Mainland and Hong Kong was undertaken and is presented below and summarised in Table 2.7.

Mainland

2.5.1.3 Light diesel fuels standard before 2002 (GB 252-1994): sulphur content ranges from not more than 1.0% for qualified product to not more than 0.5% for Grade 1 product and not more than 0.2% for excellent product.

2.5.1.4 Latest light diesel fuels standard enacted on 1 January 2002 (GB 252-2000): sulphur content not more than 0.2% for all light diesel fuels.

2.5.1.5 Standards of petrol for motor vehicles before 2000 (GB 484-93): sulphur content not more than 0.15%. Lead content not more than 0.35g/L for Grade 90 and not more than 0.45g/L for Grades 93 and 97.

2.5.1.6 Production of leaded petrol was not allowed after 1 January 2000, and sales and use of leaded petrol were banned after 1 July 2000.

2.5.1.7 Latest standards of unleaded petrol for motor vehicles enacted on 1 January 2000 (GB 17930-1999): sulphur content not more than 0.10%, sulphur content not more than 0.08% for Beijing, Shanghai, and Guangzhou after 1 July 2000 and for the whole country after 1 January 2003.

Hong Kong

2.5.1.8 In accordance with Schedule 1 of the Air Pollution Control (Motor Vehicle Fuel) Regulation, the sulphur content of vehicle diesel should not be more than 0.05% before 2001 and has revised to not more than 0.035% on 1 January 2001. However, it is noted that ultra low sulphur diesel (0.005% sulphur content) has currently become the only motor diesel sold at all the petrol filling stations in Hong Kong instead of 0.035% sulphur content as stipulated in the Regulation.

2.5.1.9 Leaded petrol was banned in 1999. In accordance with Schedule 2 of the Air Pollution Control (Motor Vehicle Fuel) Regulation, the sulphur content of unleaded petrol should not be more than 0.05% before 2001 and has revised to not more than 0.015% on 1 January 2001.

Emission Inventories

Traffic Emissions from Open Roads

2.5.1.10 The traffic on all major existing and planned roads within the study area were included in this assessment. Free flowing traffic with no queuing was assumed. Free flow traffic conditions are normally adopted for traffic air quality impact assessments to represent the prevailing traffic conditions on the roads over the averaging period of 1 hour or 24 hours although occasional short-term congestion could occur.

2.5.1.11 For the section of Deep Bay Link to the north of Hung Shui Kiu Interchange, the vehicle fleet was divided into four different vehicle categories namely car, bus, non-container truck goods vehicle (non-CT GV), and container truck (CT). For the purpose of this assessment, the percentage split of non-CT GV was taken as 50% light goods vehicle (LGV) and 50% heavy goods vehicle (HGV). The percentage of LGV among all the GV (including container truck) is about 22%. A sensitivity test was undertaken to determine the change in potential air quality impact for a lower percentage of LGV on SWC and the section of DBL to the north of Ha Tsuen Interchange (approx. 800m portion of DBL). This sensitivity test assumed only 12% of all GV (including container truck) as LGV, and the other 88% of the GV would be heavy goods vehicles (HGV) and container trucks. Details of the sensitivity test are presented in Appendix 2D.

2.5.1.12 For other roads modelled in this assessment, the traffic forecast provided information on the total flow and the percentage of goods vehicle. With reference to the Third Comprehensive Transport Study (CTS3) 2016 matrices (before cross-boundary adjustments), the percentage split of goods vehicle for the afternoon peak hour flow is approximately 44% LGV and 56% HGV. For Yuen Long Highway, the percentage split of goods vehicle for the afternoon peak hour flow was predicted to be about 32% LGV and 68% HGV. These assumptions were taken in vehicle emission calculations as input to the air quality modelling.

2.5.1.13 Among the traffic pollutants, oxides of nitrogen (NOX), respirable suspended particulates (RSP), carbon monoxide (CO), and sulphur dioxide (SO2) are the major traffic air pollutants of concern and are assessed in this study. For lead, as indicated in the review above, use and marketing of leaded petrol had been banned in both Hong Kong and Mainland in 1999 and 2000 respectively. Lead pollution due to vehicle tailpipe emissions should not be a concern in the future and is not assessed in this study.

2.5.1.14 With reference to the review above on the fuel standards between Mainland and Hong Kong, the quality of vehicle fuels in Mainland is lower compared with Hong Kong at present and in near future. Higher tailpipe emissions would thus be expected for those Hong Kong vehicles travelling from Mainland to Hong Kong and fuelled with Mainland fuels.

2.5.1.15 Table 2.8 below tabulated the Fleet Average Emission Factors for Cross Boundary Vehicles and Fleet Average Emission Factors for Hong Kong Vehicles - Euro IV and V Model provided by EPD for year 2011 (the last future year forecasted). The emission factors for cross boundary vehicles refer to the tailpipe emissions of those Hong Kong vehicles fuelled with Mainland fuels.

2.5.1.16 In this assessment, it is assumed that all vehicles travelling on the entire road network modelled in this assessment (including sections of SWC, DBL, YLH, planned roads in HSKNDA, other existing roads etc) would be fuelled with Mainland fuels. This is a very conservative assumption taken only for the purpose of this assessment. The higher emission factors for cross boundary vehicles tabulated above in Table 2.8 were taken in this air quality impact assessment. No speed correction or other adjustment has been made.

2.5.1.17 Sensitivity test was undertaken to examine the worst-case year in term of vehicle tailpipe emissions from 2005 (year of commissioning of DBL) to year 2021. For years beyond 2011, the estimated emission factors for year 2011(the last future year with EPD forecasted fleet average emission factors) were adopted in this assessment as conservative estimates. The use of beyond year 2011 traffic flow with year 2011 Fleet Average Emission Factors is a conservative estimate of the impact without taking into account the improvement in the Fleet Average Emission Factors beyond year 2011.

2.5.1.18 Peak hourly traffic may vary for morning and afternoon at some parts of the DBL. The main reasons for choosing afternoon peak hourly traffic are: i) DBL mainly serves cross-boundary traffic for which the peak is in the afternoon; and ii) the total emissions over the entire DBL are higher in the afternoon considering the flow and length of the road involved. The case may be different for HSKNDA and Yuen Long Highway. Table 2.9 below tabulates the predicted afternoon peak hour traffic flow for years 2005 to 2021 on major roads considered in this assessment. Tables 2.10 to 2.13 tabulate the corresponding total vehicle tailpipe emissions of NOX, RSP, CO and SO2 respectively from these major roads.

Table 2.9 Predicted Afternoon Peak Hour Traffic Flow (in vehicles per hour)

Note: SWC = Shenzhen Western Corridor

DBL = Deep Bay Link

HTI = Ha Tsuen Interchange

HSKI = Hung Shui Kiu Interchange

LTI = Lam Tei Interchange

Table 2.10 Estimated Afternoon Peak Hour Total NO_X Emissions (in gram per km per hour)

Note: SWC = Shenzhen Western Corridor

DBL = Deep Bay Link

HTI = Ha Tsuen Interchange

HSKI = Hung Shui Kiu Interchange

LTI = Lam Tei Interchange

Note: SWC = Shenzhen Western Corridor

DBL = Deep Bay Link

HTI = Ha Tsuen Interchange

HSKI = Hung Shui Kiu Interchange

LTI = Lam Tei Interchange

Note: SWC = Shenzhen Western Corridor

DBL = Deep Bay Link

HTI = Ha Tsuen Interchange

HSKI = Hung Shui Kiu Interchange

LTI = Lam Tei Interchange

Note: SWC = Shenzhen Western Corridor

DBL = Deep Bay Link

HTI = Ha Tsuen Interchange

HSKI = Hung Shui Kiu Interchange

LTI = Lam Tei Interchange

2.5.1.19 As shown in Table 2.9, the predicted peak hour traffic flow for year 2021 on all major road sections are the highest among other years from the year of commissioning of SWC and DBL (year 2005). Tables 2.10 to 2.12 indicated that the NOx, RSP and CO emissions for year 2021 on all major road sections are also the highest among the other years. However, comparison in Table 2.13 showed that the SO2 emissions from major road sections would be the highest at year 2007 or 2008 regardless of lower traffic flows on the roads. This is largely related to the conservative assumption made in deriving the Fleet Average Emission Factors that 0.2% sulphur diesel would be used in Mainland until the 0.05% sulphur diesel become the diesel standard in Mainland in year 2009.

2.5.1.20 Nevertheless, NOx and RSP would be the major traffic air pollutants of concern and the predicted traffic flows and NOx and RSP emissions are the highest on major road sections in year 2021. Year 2021 was therefore taken as the representative year for this air quality impact assessment. For potential worst-case SO2 impacts due to vehicle emissions, assessment is undertaken based on the predicted 2021 SO2 levels and the percentage difference in SO2 emissions between year 2007/2008 and 2021. Details of the year 2021 afternoon peak hour traffic forecast are included in Appendix 2A.

Stack Emissions from other Major Air Pollution Sources

2.5.1.21 Major existing air pollution sources further away include the Shenzhen Ma Wan Power Station, the Hong Kong Black Point Power Station, and the Hong Kong Castle Peak Power Station which are located at about 11km, 8km, and 10km respectively from Ngau Hom Shek. Future major stack emissions include the Waste-to-Energy Facilities (WEF), the Sludge Treatment Facility (STF), and the Animal Carcass Treatment Facility (ACTF) planned in Nim Wan at about 6km southwest of Ngau Hom Shek. All these future facilities are currently under planning, their locations may be subject to change and that the decision to proceed with these facilities has not yet been made. Locations of the existing major stack emission sources and the currently proposed locations of the planned major stack emission sources are shown in Figure 2.14. For the purpose of this assessment, it is anticipated that these stack emissions would contribute to the future cumulative impacts of NOX, RSP, and SO2 in the area. CO emissions from these stacks are relatively small in quantity compared with the above three pollutants and should not constitute major cumulative impacts at distant area. CO emissions from these stacks are thus not included in this assessment.

2.5.1.22 With reference to the EIA Report on Shenzhen Ma Wan Power Station and the Air Modelling Assessment Report in Ha Pak Nai, Feasibility Study of Waste-to-Energy Incineration Facilities, and the ongoing Additional Study of Waste-to-Energy Facilities, details of the stack emissions are summarised in Table 2.14.

Table 2.14 Summary of Stack Emissions from Major Existing and Planned Sources

Dispersion Modelling

Traffic Emissions from Open Roads

2.5.1.23 The United States Environmental Protection Agency (USEPA) approved CALINE4 dispersion model was used to assess traffic emissions impact from existing and planned road network. In the dispersion model, for most part of the study area, meteorological conditions of Pasquill stability class D, mixing height of 500 metres, and horizontal wind direction standard deviation of 18 degrees were adopted for daytime hours (7am to 7pm). For nighttime hours (7pm to 7am the following day), meteorological conditions of Pasquill stability class F, mixing height of 500 metres, and horizontal wind direction standard deviation of 5.5 degrees were adopted. Surface roughness coefficient of 100cm was taken in the CALINE4 model to calculate the worst-case 1-hour average concentrations.

2.5.1.24 For the northern part of the study area around Ngau Hom Shek, in view of the large portion of water surface and small portion of rolling terrain in the area, surface roughness coefficient of 20cm was taken in the CALINE4 model. The horizontal wind direction standard deviations for daytime hours (Pasquill stability class D) and nighttime hours (Pasquill stability class F) were taken as 13 degrees and 4 degrees accordingly.

2.5.1.25 Similar meteorological conditions were taken in the USEPA approved Industrial Source Complex Short Term 3 (ISCST3) model on modelling the traffic emissions from Route 10 northern portals, ventilation shafts, and toll plaza. Detailed calculations of the emission rates of the Route 10 Northern Section traffic emission sources are included in Appendix 2B.

2.5.1.26 In view of the constrain of the CALINE4 model in modelling highly elevated roads, the road heights of elevated road sections in excess of 10m high above local ground or water surface were set to 10m in the CALINE4 model. This approach effectively brings the emission sources closer to the ground level where there are more traffic emissions. More conservative predictions would therefore be expected at the worst-affected ASRs at or close to ground level.

2.5.1.27 Secondary air quality impacts arising from the implementation of roadside noise mitigation measures namely vertical noise barriers and vertical noise barriers with canopies were incorporated into the air quality model.

2.5.1.28 It is assumed that, with the installation of vertical noise barriers, all the traffic pollutants generated from the mitigated road section would be emitted from the top of the noise barriers. In the CALINE4 model, the elevation of the mitigated road section was set to the elevation of the barrier top, the width of mixing zone was set to the actual width of the road due to physical obstruction of the barrier walls, and the road type was set to 'fill'. No correction or adjustment to the receiver heights was made in the model.

2.5.1.29 For vertical noise barriers with canopies, it is assumed that the dispersion of the traffic pollutants would in effect be similar to physically shifting the mitigated road section towards the central divider. The traffic pollutants were assumed to be emitted from the top of the canopies. In the CALINE4 model, the alignment of the mitigated road section was shifted by a distance equal to the covered extent, the elevation of the mitigated road section was set to the elevation of the barrier top, the width of mixing zone was set to the actual width of the road due to physical obstruction of the barrier walls, and the road type was set to 'fill'. No correction or adjustment to the receiver heights was made in the model.

2.5.1.30 A schematic diagram of the modelled road network is shown in Appendix 2B.

Stack Emissions from other Major Air Pollution Sources

2.5.1.31 The USEPA approved ISCST3 model was used to model the dispersion of major stack emissions. The model assumed the algorithm for "rural" mode, with the stack tip downwash component. The gradual plume rise option was adopted.

Concentration Calculations

2.5.1.32 The worst-case 1-hour average NO2, CO, SO2 concentrations and the worst-case 24-hour average NO2, RSP and SO2 concentrations were calculated at each representative assessment point to check the compliance with the respective AQOs. Assessment heights adopted in this assessment are 1.5m, 10m, 20m, 30m, 50m, 75m and 100m above ground. 1.5m is the average height of human breathing zone. Depends on the actual height of each specific assessment point, the assessment heights were taken as 1.5m up to just over the maximum height of the specific assessment point.

2.5.1.33 For road traffic emissions, a daily profile of road traffic prepared by the traffic engineer as shown in Table 2.15 was taken for the calculation of predicted concentrations.

2.5.1.34 The hourly average concentrations for road traffic emissions calculated by the dispersion models were based on the predicted 2021 afternoon peak hour traffic flow. In order to calculate the hourly average concentration for each hour of the day, the CALINE4 and ISCST3 hourly average concentrations due to emissions from the road network were multiplied by the factors listed in Table 2.15 above to produce the hourly average concentration for each hour of the day. The hourly average concentrations of NO2 were calculated using the Ozone Limiting Method. Tailpipe NO2 emission was assumed to be 7.5% of NOX and the background ozone concentration was taken as 57 mgm-3 derived from the EPD monitoring data for rural and new development area.

2.5.1.35 For major stack emissions, the NO2/NOx ratio of 0.83 was adopted in this assessment with reference to the Janssen formula (Atmospheric Environment, Vol.22, No.1, pp.43-53, 1988) under an ambient ozone concentration of 57 µgm-3 for rural and new development area derived from EPD's monitoring data.

2.5.1.36 Historical wind data from Lau Fau Shan meteorological station for year 1996 to 2000 was used in the calculation of the worst-case 1-hour and worst-case 24-hour average concentrations. For each hour of a year, the wind direction from the historical data was taken at 10-degree resolution. Calm hours (hours with wind speed less than 1m/s) were disregarded in accordance with Section 9.3.4 of the Guideline on Air Quality Models, USEPA.

2.5.1.37 In the CALINE4 model run, the historical meteorological data were categorised into stability class D (wind speed classes 1, 2, 4m/s) and stability class F (wind speed classes 1, 2, 4m/s). In the ISCST3 model run, the historical meteorological data were categorised into stability class A (wind speed classes 1, 2, 3m/s), stability class B (wind speed classes 1, 2, 3, 4, 5m/s), stability class C (wind speed classes 1, 2, 3, 4, 5, 8, 10m/s), stability class D (wind speed classes 1, 2, 3, 4, 5, 8, 10, 15, 20m/s), stability class E (wind speed classes 1, 2, 3, 4, 5m/s), and stability class F (wind speed classes 1, 2, 3, 4m/s).

2.5.1.38 For example, in the CALINE4 model, for wind speed less than 2m/s, the wind speed was conservatively converted to 1m/s in the model. For wind speed equal to or larger than 2m/s but less than 4m/s, the wind speed was conservatively converted to 2m/s in the model. For wind speed equal to or larger than 4m/s, the wind speed was converted to 4m/s in the model.

2.5.1.39 The hourly average concentration due to open road emissions and stack emissions for each assessment point was then calculated as described above based on the converted wind direction and wind speed. The maximum 1-hour average and 24-hour average concentrations over the five years were then taken as the worst-case concentrations for the assessment points.

2.5.1.40 Cumulative impacts were calculated by adding the predicted concentrations for each hour of the day from:

• CALINE4 modelling results of open roads traffic emissions (from Deep Bay Link and other major roads in the area including SWC, Route 10 Northern Section, Yuen Long Highway, and roads within the future HSKNDA);
• ISCST3 and CALINE4 modelling results of traffic emissions from Route 10 northern portals, ventilation shafts, and toll plaza; and
• ISCST3 modelling results of major existing and planned stack emissions.

2.5.1.41 After all, background NO2 and RSP concentrations of 67.9 µgm-3 and 64.8 µgm-3 respectively were added to the results calculated above to produce the worst-case concentrations. These background concentrations are predicted at EPD's Yuen Long monitoring station for year 2016, based on the Third Comprehensive Transport Study (CTS3). For SO2, a background concentration of 13 µgm-3 derived from EPD's monitoring data for rural area was taken in the calculation. For CO, the highest 1-hour average CO concentration of 5400 µgm-3 recorded among all EPD's monitoring stations in year 2000 was added to modelling results as a very conservative background concentration.

2.5.1.42 According to the above description, the modelling approach adopted in this assessment takes into account the historical wind data from a representative meteorological station near the study area. Instead of using a simple worst-case meteorological condition normally adopted in typical screening assessment, this refined modelling approach predicts the potential air quality impact with reference to categorised meteorological conditions and the historical meteorological data. More realistic predictions would thus be expected from this modelling approach.

2.5.2 Accuracy, Uncertainty, and Limitations of Models

2.5.2.1 The ISC model and the CALINE model used in this assessment are two of the air quality models recommended for regulatory applications with reference to USEPA. They are also the models listed in EPD's "Guidelines on Choice of Models and Model Parameters". These two models had been widely used and accepted for the air quality impact assessment of numerous approved EIA reports on EPD's EIAO Register. With reference to USEPA's "Guideline on Air Quality Models", the preferred models, including ISC and CALINE model, may be used without a formal demonstration of applicability provided they satisfy the recommendation for regulatory use.

2.5.2.2 Besides, a discussion included in USEPA's guideline regarding use of uncertainty in decision making states that: "……. it is easiest and tends to ensure consistency if the decision-maker confines his judgement to use of the "best estimate" provided by the modeler (i.e. , the design concentration estimated by a model recommended in this guideline or an alternate model of known accuracy). This is an indication of the practical limitations imposed by current abilities of the technical community." Given that the models used in this assessment are the recommended models of USEPA as well as EPD, we therefore consider that the Air Quality Objectives should be compared with the "best estimate" produced by these recommended models for compliance checking and decision making purposes.

2.5.2.3 Moreover, with reference to the review of fuel standards between Mainland and Hong Kong presented in this EIA Report, the quality of vehicle fuels in Mainland is lower compared with Hong Kong at present and in near future. Higher tailpipe emissions would thus be expected for those Hong Kong vehicles travelling from Mainland to Hong Kong and fuelled with Mainland fuels. The proportion of vehicles fuelled with Mainland fuels is uncertain. For the purpose of this assessment, it was assumed that all vehicles travelling on the entire road network included in the air quality model would be fuelled with Mainland fuels. This is a very conservative assumption taken only for the purpose of this assessment.

2.5.2.4 Furthermore, the vehicle fleet average emission factors for year 2011 (the latest available emission factors in the future) were adopted in this assessment for year 2021 with the highest predicted traffic flow. The use of year 2011 vehicle emission factors is another conservative assumption without taking into account the possible future reduction in vehicle emissions due to improvement both in fuel quality and in vehicle technology.

2.5.2.5 To conclude, this air quality impact assessment provided the conservative "best estimate" produced by the models recommended by both USEPA and EPD. Given the practical limitations imposed by current abilities of the technical community on air quality modeling, these estimates should be used for direct compliance checking to ensure consistency in the decision making process.

2.6 Identification, Prediction and Evaluation of Potential Impacts

2.6.0 Construction Phase

2.6.0.1 The construction work of DBL could be divided into the following work tasks and areas:

1) Deep Bay Link Mainline
The road layout of the mainline is a dual-3-lane carriageway. However, due to bifurcation of slip roads, the deck is generally wider than 2 lanes in each direction. A twin box section for the mainline is therefore proposed. Typical span length will be 40m with monolithic reinforced concrete column.

2) Ramps in Lam Tei Interchange Connecting to Yuen Long Highway
All ramps at Lam Tei Interchange would be constructed by cast-in-situ method. They can be constructed simultaneously with the Mainline.

3) Precast Yard for Segmental Launching Method
The segmental construction requires a precast yard for fabrication of the concrete segments and the curing and storage of the completed concrete segments. There would be approximately 2500 numbers of segments which may required up to 4 production lines. The size of a fabrication yard will be approximately 500 m2 and the storage yard will be approximately 700 m2 allowing the stacking up of segments.

It is also considered to import concrete segments from Mainland China instead of setting up a precast yard. This would require a barging point at Tuen Mun for shipping the concrete segments and an initial proposal is to use the same barging point as for SWC Project. Only potential noise impact is expected in this case. For details, please refer to Section 3.4.1.31.

4) Concrete Batching Plant
Concrete batching plant would be used for the project which would be located at the loop encircles by ramps at Lam Tei Interchange and at Ha Tsuen Interchange which are away from nearby sensitive receivers.

5) Haul Road Construction traffic
Since there is no large-scale site formation nor cut-and-fill works for DBL, the construction traffic generated would be small.

2.6.0.2 The construction of DBL alignment typically involves piling, pile cap construction, pier construction and superstructure construction. For the construction of superstructure, two methods of construction are considered for viaducts, namely the segmental launching method and the span by span cast in-situ method. The mainline of DBL together with the ramps cross over Yuen Long Highway, KCRC West Rail and Castle Peak Road where falsework will be high and where bridge decks are fairly straight will best be constructed by segmental launching methods. Other ramps not crossing major roads and where falseworks are low, conventional span by span cast in-situ method would be used.

2.6.0.3 The proposed construction methods of DBL are not likely to generate significant dust emissions, with proper dust suppression measures, in particular those relevant measures set out in the Air Pollution Control (Construction Dust) Regulation as discussed in Section 2.7 below, adverse dust impacts due to the construction works of this project is not expected.

2.6.0.4 Apart from the construction of DBL, there are a number of major projects planned in the vicinity of the study area which might cause cumulative construction phase impacts to the environment. The tentative construction programs of these projects are listed below:

Project Anticipated Programme
Deep Bay Link 2003-2006
Shenzhen Western Corridor* 2003-2005
Yuen Long Highway Widening* 2003-2005
Hung Shui Kiu New Development Area* 2004-2010
Route 10 Northern Section* 2004-2007
San Wai Sewage Treatment Works Expansion and Upgrading* 2004-2007

* The actual implementation programme will be subject to the individual study and Government's decision.

Shenzhen Western Corridor (SWC)

2.6.0.5 The northern end of DBL will be connected to the Shenzhen Western Corridor (SWC) at Ngau Hom Shek. SWC is a proposed highway carrying a dual-3 carriageway crossing Deep Bay to connect HKSAR and Shenzhen on the Mainland side. Implementation of SWC project is synchronised with the implementation of DBL.

2.6.0.6 The same project proponent namely Highways Department is responsible for the two adjoining projects. The construction dust mitigation measures recommended in this report for DBL construction would also be applicable to SWC and should be fully implemented to mitigate the potential cumulative construction dust impacts in Ngau Hom Shek area.

Yuen Long Highway Widening

2.6.0.7 Yuen Long Highway (YLH) is a dual two-lane highway serving as a trunk route between Tuen Mun and Yuen Long. It will be widened to dual three-lane standard under the project "Widening of Yuen Long Highway between Lam Tei and Shap Pat Heung Interchange" and its related EIA Report was completed in December 2001. DBL will be connected to YLH via Lam Tei Interchange.

2.6.0.8 According to the current programme, the widening works will be carried out in parallel with the works for DBL. There would likely be cumulative construction phase impacts around the Lam Tei Interchange area. The construction dust mitigation measures recommended in this report for DBL construction would also be applicable to YLH widening and should be fully implemented.

Route 10 - North Lantau to Yuen Long Highway (Route 10)

2.6.0.9 Route 10 - North Lantau to Yuen Long Highway (Route 10) is a proposed dual three-lane highway between Lam Tei and Lantau. The project will include construction of a 1.7 km long suspension bridge crossing Ma Wan Channel, a 1.65 km long tunnel at Tai Lam Chung and interchanges with Tuen Mun Road and a 4.1 km long tunnel at Lam Tei and interchanges with Deep Bay Link and Yuen Long Highway.

2.6.0.10 The project is divided into two sections i.e. the Southern Section from North Lantau to So Kwun Wat and the Northern Section from So Kwun Wat to Lam Tei. The southern end of DBL is planned to be connected to Route 10 via Lam Tei Interchange.

2.6.0.11 There would likely be cumulative impacts during construction phase for areas near the R10 tunnel portal and toll plaza in conjunction with DBL. It is understood that the construction schedule for Route 10 Northern Section would be revised to a later time. The relevant construction dust mitigation measures recommended in this report for DBL construction would also be applicable to Route 10 Northern Section construction and should be fully implemented.

Hung Shui Kiu New Development Area (HSKNDA)

2.6.0.12 The Hung Shui Kiu New Development Area (formerly known as Hung Shui Kiu Strategic Growth Area) is located in the Tuen Mun -Yuen Long Corridor and centred on a newly proposed KCRC West Rail station. It is planned to accommodate residential developments and ancillary GIC facilities, education facilities, commercial developments, container back-up area, and other regional infrastructures.
2.6.0.13 There would likely be cumulative dust impacts during concurrent construction of both DBL and HSKNDA. Practicable and effective construction dust mitigation measures should be implemented, in particular, in areas with significant dust generating activities and in areas in close proximity to sensitive receivers. With the implementation of proper dust suppression measures, adverse cumulative dust impacts at sensitive receivers are not expected.

San Wai Sewage Treatment Works Expansion and Upgrading

2.6.0.14 The San Wai Sewage Treatment Works is located in Government Land Allocation GLA-TYL 214 assigned to Drainage Services Department. It is proposed to upgrade and expand the San Wai Sewage Treatment Works and the Ha Tsuen Pumping Station to cope with the population increase in the North West New Territories (NWNT). Localised dust impact during construction phase would be expected. However, all existing and future sensitive receivers are located at considerable distance from the sewage treatment works. With the implementation of proper dust suppression measures, adverse cumulative dust impacts at sensitive receivers are not expected.

2.6.1 Operational Phase

2.6.1.1 The worst-case cumulative concentrations for 1-hour and 24-hour average NO2, 24-hour average RSP, 1-hour average CO, and 1-hour and 24-hour average SO2 at the assessment points are shown in Appendix 2C. As shown by the modelling results in Appendix 2C, NO2 and RSP are the two traffic air pollutants with higher predicted impacts when compared with the respective AQO. Figures 2.2 to 2.7 show respectively the concentration contours for the predicted worst-case 1-hour average NO2, 24-hour average NO2, and 24-hour average RSP at 1.5m and 10m above ground level. In view of the modelling constraint in CALINE4 model, the road level of DBL in the CALINE 4 model was taken as no more than 10m above ground. The air pollutant concentration contours at 1.5m and 10m above ground should thus best represent the air quality impacts at the road level of DBL.

2.6.1.2 As shown by the modelling results tabulated in Appendix 2C, there is no predicted exceedance of AQOs for the assessed air pollutants at the selected assessment points. Predicted concentrations that exceeded 90% of the respective AQO are highlighted in Appendix 2C for easy reference.

2.6.1.3 For 1-hour average NO2, the highest concentration of 245.4 mgm-3 (81.8% of AQO) is predicted at 1.5m level of assessment point 8116. Assessment point 8116 is an existing village house in Ngau Hom Shek located at about 20m from the DBL alignment.

2.6.1.4 For 24-hour average NO2, the highest concentration of 148.7 mgm-3 (99.1% of AQO) is predicted at 1.5m level of assessment point 9206. Assessment point 9206 is the site boundary of a planned residential development in Fuk Hang Tsuen adjacent to Yuen Long Highway.

2.6.1.5 There are about 80 existing and future ASRs exceeded 90% of the 24-hour average AQO for NO2. Most of these ASRs are existing and future sensitive receivers located within 100m from the alignment of DBL or the widened Yuen Long Highway or their slip roads. Some of the assessment points are subjected to the cumulative impacts from more than one road section. Although elevated pollutant levels are predicted at about 80 existing and future ASRs, it should be noted this assessment had taken into account a very conservation assumption that all vehicles travelling on the entire road network would be fuelled with Mainland fuels and thus with higher tailpipe emissions. Besides, the predicted pollutant concentrations are the predicted highest impacts under worst-case meteorological conditions coincide with peak hour traffic flow. The chance of occurrence of these worst-case conditions is anticipated to be low.

2.6.1.6 As shown in Appendix 2C, the highest 24-hour average RSP concentration of 132.2 mgm-3 (73.4% of AQO) is predicted at 1.5m level of assessment point 8815. Assessment point 8815 is an existing village house in close proximity to a proposed slip road connecting Yuen Long Highway westbound and DBL.

2.6.1.7 For CO, the predicted highest 1-hour average concentration is 7362.6 mgm-3. This is only about 24.5% of the 1-hour average AQO for CO and is about 73.6% of the 8-hour average AQO for CO. So exceedance of both 1-hour and 8-hour average AQOs for CO at the assessment points is not expected. The highest 1-hour average CO concentration is predicted at 1.5m level of assessment point 8302 which is an existing village house located to the north of Tsing Chuen Wai.

2.6.1.8 For SO2, the highest 1-hour average concentration of 193.8 µgm-3 (24.2% of AQO) is predicted at assessment point 8128 which is an existing village house in Ngau Hom Shek. Whereas the highest 24-hour average SO2 concentration of 72.1 µgm-3 (20.6% of AQO) is predicted at 1.5m level of assessment point 8327 which is an existing village house in Tsing Chuen Wai in close proximity to the DBL alignment.

2.6.1.9 As tabulated in Table 2.13 above, the SO2 emissions in year 2007 and 2008 could be as high as about 260% of those in year 2021. The predicted SO2 levels presented in Appendix C are based on year 2021 SO2 emissions from major roads. Nevertheless, the predicted highest 1-hour and 24-hour average SO2 concentrations at the assessment points are all less than one-fourth of the corresponding AQO. Thus, even with the conservative assumption that the sulphur content of Mainland diesel would not be lower than 0.2% till year 2009, the worst-case SO2 impact before year 2009 would still be within the AQOs.

2.6.1.10 As shown in Figures 2.2 to 2.7, the areas with predicted exceedance of the 1-hour average and 24-hour average AQOs for NO2 and 24-hour average AQO for RSP are predicted at areas crossed by or in close proximity to the main alignment of DBL and the widened Yuen Long Highway. Exceedance at any existing or planned ASRs are not expected.

2.6.1.11 With reference to Figures 2.2, 2.3, 2.6 and 2.7, the areas with predicted exceedance of the 1-hour average AQO for NO2 and the 24-hour average AQO for RSP are all located within the works limit / land resumption limit of the DBL project. There will be no future ASRs planned within the works limit / land resumption limit and all existing ASRs within the works limit / land resumption limit will also be resumed for the construction of DBL. Exceedance of the 1-hour average AQO for NO2 and the 24-hour average AQO for RSP is therefore not expected at all existing and future ASRs due to the operation of DBL.

2.6.1.12 As shown in Figures 2.4 and 2.5, there are areas with predicted exceedance of the 24-hour average AQO for NO2 located outside the works limit / land resumption limit of DBL project. These are highlighted as shaded areas in Figures 2.4 and 2.5.

2.6.1.13 As shown in Figures 2.4A and 2.4B, Area A and Area B are two small areas outside the works limit / land resumption limit with predicted exceedance of the 24-hour average AQO for NO2 at 1.5m above ground. These two areas are rather remote and no existing ASR is currently identified within these two areas. These two areas are currently zoned as "green belt" under the latest Ha Tsuen Outline Zoning Plan and future development of these two remote areas into air sensitive uses is not anticipated.

2.6.1.14 Further to the south along the DBL alignment, Areas C, D, E, and F shown in Figures 2.4B and C and Areas L and M shown in Figures 2.5B, D and E are within the future road reserve, amenity areas, green belt, or non-sensitive land uses of the proposed HSKNDA planned adjacent to the DBL. Whereas Areas I, J and K shown in Figure 2.4E are within the future road reserve, amenity areas, green belt, or non-sensitive land uses of the proposed HSKNDA planned adjacent to the widened Yuen Long Highway. Exceedance of the 24-hour average AQO for NO2 at future ASRs planned within the HSKNDA is not expected.

2.6.1.15 Having said that, the proposed DBL will be in operation prior to the development of HSKNDA with anticipated programme of 2004 to 2010. The actual implementation programme of HSKNDA will be subject to a separate study. Although no existing ASR is identified within Areas C to F and I to M that are fall within the future HSKNDA, some of these areas are currently allowable for development into air sensitive uses prior to the development of HSKNDA.

2.6.1.16 A sensitivity test was undertaken to examine the possible air quality impacts at those areas prior to the development of HSKNDA. The 24-hour average NO2 contours presented in Figures 2.4 and 2.5 refer to the worst-case impacts in year 2021. With reference to Table 2.10, the peak hour total NOX emissions on or before year 2011 (on or before the development of HSKNDA) from all the major roads considered in this assessment are all less than 83% of the corresponding peak hour total NOX emissions in year 2021. This percentage difference is mainly due to a lower predicted peak hour traffic before year 2021. With consideration of solely the percentage difference in NOX emissions between year 2021 and the anticipated development year of HSKNDA, the predicted 24-hour average NO2 level in Figures 2.4 and 2.5 for year 2021 would refer to a lower NO2 level for years on or before the development of HSKNDA.

2.6.1.17 Taking a location close to the road network namely assessment point 9211 as an example. The predicted worst-case 24-hour average NO2 level at 1.5m above ground at assessment point 9211 is 148.0 µgm-3 in year 2021 (see Appendix 2C). The 148 µgm-3 in year 2021 is equal to the sum of 63.4µgm-3 from traffic emissions, 16.7 µgm-3 from major stack emissions and background NO2 concentration of 67.9 µgm-3. Simply considering the difference in traffic emissions between 2021 and the years on or before the development of HSKNDA, the worst-case 24-hour average NO2 level at assessment point 9211 on or before the development of HSKNDA is estimated to be about 137.2 µgm-3. The 137.2 µgm-3 is calculated as (63.4 µgm-3 x 83% + 16.7 µgm-3 from major stack emissions + background level of 67.9 µgm-3).

2.6.1.18 A difference of about 10 µgm-3 in the predicted 24-hour average NO2 level is noted between year 2021 and the years on or before the development of HSKNDA for locations close to the road network. After taking into account the finding of this sensitivity test, it is not anticipated that there would be any area of predicted exceedance of the 24-hour average AQO for NO2 located outside the DBL works limit on or before the development of HSKNDA. Exceedance of the 24-hour average AQO for NO2 is therefore not expected at all existing and future ASRs due to the operation of DBL.

2.6.1.19 There are two other areas namely Areas G and H shown in Figures 2.4D, E, and F with predicted AQO exceedance outside the works limit. These two areas are within the existing Castle Peak Road with no ASR.

2.6.1.20 The proposed HSKNDA is the major future ASR in the area. Representative assessment points, namely 9113 to 9177, are positioned at the site boundaries of future sensitive land uses within the proposed HSKNDA for the operational phase air quality impact assessment. The locations of these assessment points are also shown in Figures 2.1C and 2.1D.

2.6.1.21 As shown in Appendix 2C, the highest predicted 1-hour average and 24-hour average NO2 concentrations among the assessment points within HSKNDA are 217.3 mgm-3 (72.4% of AQO) and 147.3 mgm-3 (98.2% of AQO) respectively. These highest concentrations are predicted at 10m level of assessment point 9172 and 1.5m level of assessment point 9173. The predicted elevated impact is mainly due to the cumulative impact of traffic emissions from DBL, Castle Peak Road, and the Route 10 portal emission.

2.6.1.22 The highest predicted 24-hour average RSP concentration among the assessment points within HSKNDA is 101.3 mgm-3 (56.3% of AQO) at 1.5m level of assessment point 9143. Assessment point 9143 is located at the site boundary of Area 2D of HSKNDA next to a planned road in HSKNDA.

2.6.1.23 With reference to the air pollutant concentration contours presented in Figures 2.2 to 2.7, exceedances of the AQOs are not expected within the future sensitive land uses of the proposed HSKNDA.

2.6.1.24 In addition to the layout of HSKNDA shown in Figures 2.2 to 2.7, the potential operational phase air quality impacts over an alternative layout of HSKNDA were examined. The predicted air pollutant concentrations contours over the alternative HSKNDA layout are presented in Figures 2.8 to 2.13. As shown in the figures, exceedances of the AQOs are not expected within the future sensitive landuses of the alternative HSKNDA layout.

2.6.1.25 For existing and/or planned ASRs located within the area encircled by the Lam Tei Interchange but outside the DBL works limit / land resumption limit, the air pollutant concentration contours in Figures 2.2F, 2.3F, 2.4F, 2.5F, 2.6F, and 2.7F showed that there would be no AQO exceedance in year 2021 under the worst-case scenario. As discussed in Sections 2.5.1.19 and 2.5.1.20, year 2021 is the worst-case year for the major air pollutants of concern namely NOx and RSP. So, given that there is no predicted AQO exceedance in year 2021, AQO exceedance in the area encircled by Lam Tei Interchange during the interim period after commissioning of DBL and prior to the completion of land resumption exercise for the Route 10 Northern Section project is therefore not expected.

2.7 Mitigation of Adverse Impacts

2.7.0 Construction Phase

2.7.0.1 In order to ensure that dust emission is minimised during the construction phase of DBL, relevant dust control requirements set out in Parts I, III and IV of Schedule 1 of the Air Pollution Control (Construction Dust) Regulation should be met. The site agent is required to adopt dust reduction measures while carrying out construction works.

2.7.0.2 Apart from the construction of DBL, there are a number of major projects planned in the vicinity of the study area which might cause cumulative construction phase impacts to the environment. These planned projects include Shenzhen Western Corridor, Yuen Long Highway Widening, Hung Shui Kiu New Development Area, Route 10 Northern Section, and San Wai Sewage Treatment Works Expansion and Upgrading.

2.7.0.3 With the implementation of effective dust control measures stipulated in the Air Pollution (Construction Dust) Regulation during the construction phase of these projects, adverse dust impacts are not expected. In particular, the mitigation measures listed below should be adopted where applicable. To further reduce the dust emissions from the construction sites, it is also recommended to undertake dust suppression by twice daily watering with complete coverage of all active construction areas.

Site clearance and demolition of existing structures

• The working area for the uprooting of trees, shrubs, or vegetation or for the removal of boulders, poles, pillars or temporary or permanent structures should be sprayed with water or a dust suppression chemical immediately before, during and immediately after the operation so as to maintain the entire surface wet;
• All demolished items (including trees, shrubs, vegetation, boulders, poles, pillars, structures, debris, rubbish and other items arising from site clearance) that may dislodge dust particles should be covered entirely by impervious sheeting or placed in an area sheltered on the top and the 3 sides within a day of demolition;

Site boundary and entrance

• Vehicle washing facilities including a high pressure water jet should be provided at every discernible or designated vehicle exit point;
• The area where vehicle washing takes place and the section of the road between the washing facilities and the exit point should be paved with concrete, bituminous materials or hardcores;
• Where a site boundary adjoins a road, street, service and or other area accessible to the public, hoarding of not less than 2.4m from ground level should be provided along the entire length of that portion of the site boundary except for a site entrance or exit;

Access road

• Every main haul road (i.e. any course inside a construction site having a vehicle passing rate of higher than 4 in any 30 minutes) should be paved with concrete, bituminous materials, hardcores or metal plates, and kept clear of dusty materials; or sprayed with water or a dust suppression chemical so as to maintain the entire road surface wet;
• The portion of any road leading only to a construction site that is within 30m of a discernible or designated vehicle entrance or exit should be kept clear of dusty materials;

Use of vehicle

• Immediately before leaving a construction site, every vehicle should be washed to remove any dusty materials from its body and wheels;
• Where a vehicle leaving a construction site is carrying a load of dusty materials, the load should be covered entirely by clean impervious sheeting to ensure that the dusty materials do not leak from the vehicle;

Concrete production

• The concrete batching plant should be located away from any air sensitive receiver as far as practicable;
• If the total silo capacity of the concrete batching plant exceed 50 tonnes, the project proponent is required to obtain a Specified Process licence to ensure that any potential dust emission would be properly controlled;
• Cement delivered in bulk should be stored in a closed silo fitted with an audible high level alarm which is interlocked with the material filling line such that, in the event of the silo approaching an overfilling condition, an audible alarm is triggered and the material filling stops within one minute;
• Silo used for the storage of cement should not be overfilled;
•  The loading, unloading, transfer, handling or storage of any cement should be carried out in a totally enclosed system or facility, and any vent or exhaust should be fitted with an effective fabric filter or equivalent air pollution control system or equipment;
• Cement collected by fabric filters or other pollution control system or equipment should be disposed of in a totally enclosed containers;

Excavation and earth moving

•  The working area of any excavation or earth moving operation should be sprayed with water or a dusty suppression chemical immediately before, during and immediately after the operation so as the maintain the entire surface wet;
• Exposed earth shall be properly treated by compaction, turfing, hydroseeding, vegetation planting or sealing with latex, vinyl, bitumen, shotcrete or other suitable surface stabilizer within 6 months after the last construction activity on the construction site or part of the construction site where the exposed earth lies;

Stockpiling of dusty materials

• Any stockpile of dusty material should be either covered entirely by impervious sheeting; placed in an area sheltered on the top and the 3 sides; or sprayed with water or a dust suppression chemical so as to maintain the entire surface wet;

Site cleanliness and tidiness

• The requirements stipulated in the Works Bureau Technical Circular No. 6/2002 "Enhanced Specification for Site Cleanliness and Tidiness" should be followed to enhance cleanliness and tidiness on construction sites.

2.7.1 Operational Phase

2.7.1.1 The modelling results showed that no exceedance of the AQOs would be expected at the existing and planned sensitive receivers. Mitigation measures for operational phase air quality impacts would therefore not be required.

2.8 Environmental Monitoring and Audit

2.8.0.1 Due to the potential construction dust impact to the nearby residential developments, it is recommended that EM&A for construction dust be carried out throughout the construction period of the project. The details are described in Chapter 11 and in the EM&A Manual.