5.5.40 As shown in Table 5.9, the predicted peak hour traffic flow for year 2021 on SWC are the highest among other years from the year of commissioning of SWC (year 2005). Tables 5.10 to 5.12 indicated that the NOx, RSP and CO emissions for year 2021 on SWC are also the highest among the other years. However, comparison in Table 5.13 showed that the SO2 emissions from SWC would be the highest in year 2008 regardless of lower traffic flows. 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.

5.5.41 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 SWC 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 2008 and 2021. Details of the year 2021 afternoon peak hour traffic forecast are included in Appendix 5B.

Stack Emissions from other Major Air Pollution Sources

5.5.42 Other than road traffic emissions, there is currently no other major air pollution sources in the Ngau Hom Shek area. 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 5.2. 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.

5.5.43 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, 1998, and the ongoing Additional Study of Waste-to-Energy Facilities, details of the stack emissions are summarised in Table 5.14 below.

Table 5.14 Summary of Stack Emissions from Major Existing and Planned Sources

Dispersion Modelling

Traffic Emissions from Open Roads

5.5.44 The USEPA approved CALINE4 dispersion model is used to assess traffic emissions impact from existing and planned road network. In the dispersion model, meteorological conditions of Pasquill stability class D, mixing height of 500 metres, and horizontal wind direction standard deviation of 13 degrees are 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 4 degrees are adopted. Surface roughness coefficient of 20cm is taken in the CALINE4 model to represent the large portion of water surface and small portion of rolling terrain within the study area.

5.5.45 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 5A.

5.5.46 In view of the constraint 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 are 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.

5.5.47 A schematic diagram of the modelled road network is shown in Appendix 5C.

Stack Emissions from other Major Air Pollution Sources

5.5.48 The USEPA approved ISCST3 model is 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 is adopted.

Concentration Calculations

5.5.49 The worst-case 1-hour average NO2, CO, SO2 concentrations and the worst-case 24-hour average NO2, RSP and SO2 concentrations are calculated at each representative assessment point to check the compliance with the respective Air Quality Objectives (AQOs). The assessment heights are taken as 1.5m and 10m above ground. 1.5m is the average height of human breathing zone and 10m is the maximum height of elevated roads taken in the CALINE4 model. These two assessment heights covered the maximum heights of the ASRs in the Ngau Hom Shek area which are all single storey or low-rise village houses.

5.5.50 For road traffic emissions, a daily profile of road traffic prepared by the traffic engineer as shown in Table 5.15 was taken in this assessment for the calculation of predicted concentrations.

Table 5.15 Traffic Profile Relative to Afternoon Peak Hour Flow

5.5.51 The hourly average concentrations for road traffic emissions calculated by the dispersion models are based on the 2021 afternoon peak hour traffic flow (see Appendix 5B). In order to calculate the hourly average concentration for each hour of the day, the CALINE4 hourly average modelling results due to emissions from road network are multiplied by the factors listed in Table 5.15 above to produce the hourly average concentration for each hour of the day. The hourly average concentrations of NO2 are calculated using the Ozone Limiting Method. Vehicle tailpipe emissions NO2 / NOx ratio of 7.5% is adopted. The background ozone concentration is taken as 57 µgm-3 derived from EPD's monitoring data for rural and new development area.

5.5.52 For major stack emissions, the NO2/NOx ratio of 0.83 is 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/new development area derived from EPD's monitoring data.

5.5.53 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.

5.5.54 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).

5.5.55 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.

5.5.56 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.

5.5.57 Cumulative impacts are calculated by adding the predicted concentrations for each hour of the day from:

· CALINE4 modelling results of open roads traffic emissions (from SWC and other major roads in the area including DBL, 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.

5.5.58 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.

5.5.59 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.

Accuracy, Uncertainty, and Limitations of Models

5.5.60 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.

5.5.61 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.

5.5.62 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.

5.5.63 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.

5.5.64 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.

5.6 Identification of Environmental Impacts

5.6.1 The major potential air quality impacts during the construction phase of SWC would result from dust arising from construction activities including:

· Site clearance and preparation;

· Excavation and filling;

· Open site erosion;

· Concrete batching;

· Precasting of road segments; and

· Handling and transportation of construction and demolition material (C&DM).

5.6.2 During operational phase of the project, major air quality impacts would be related to the tailpipe emissions from the vehicles travelling on SWC as well as other planned and existing road networks in the area.

5.7 Prediction and Evaluation of Environmental Impacts

Construction Phase

5.7.1 The modelling results at the assessment points for the mitigated and unmitigated scenarios are presented in Table 5.16. The assessment height is 1.5m above local ground level. Since all the dust generating sources are at ground level, this assessment height would represent the height with the worst-case impact. All the results presented in the table included the background concentration. For the mitigated scenario, 50% dust reduction by twice daily watering with complete coverage is assumed for the active construction areas. It is also assumed that the construction vehicle travel speed on unpaved site areas would be limited to not more than 10 km per hour.

5.7.2 The predicted 1-hour average and 24-hour average TSP concentration contours in the Ngau Hom Shek area for the mitigated and unmitigated scenarios are shown in Figures 5.5 to 5.8 respectively.

Table 5.16 Predicted Construction Phase Dust Impacts at Assessment Points for Unmitigated and Mitigated Scenarios

Note: Modelling results that exceeded the guideline level or AQO are shown in bolded characters.

5.7.3 As shown by the modelling results, without any dust suppression measures, exceedance of the TSP 1-hour average guideline level of 500 µgm-3 and/or the 24-hour average AQO of 260 µgm-3 would be expected at some of the assessment points (assessment points 8106, 8108, 8110, 8116 and 8117) in close proximity to the works areas and access roads.

5.7.4 With the implementation of dust suppression measures, exceedance of the TSP guideline level and AQO would not be expected. The modelling results showed that the worst-case dust impacts at the assessment points are on average reduced by about 60% and 53% respectively for the 1-hour average TSP level and the 24-hour average TSP level.

5.7.5 With the implementation of proper dust control and suppression measures stipulated in the Air Pollution Control (Construction Dust) Regulation and described in Section 5.8 below, adverse dust impact from the construction activities of the Project is not expected.

5.7.6 A concrete batching plant and the associated precasting yard is proposed at Lung Kwu Sheung Tan for the SWC project. The proposed location of the concrete batching plant is rather remote with no existing or planned air sensitive receivers identified within 500m from the site (see Figure 6.3 of Section 6). The nearest air sensitive receiver to the proposed concrete batching plant is an existing village house along Lung Kwu Tan Road at about 600m away. With the implementation of the practicable dust suppression measures stipulated in EPD's "A Guidance Note on the Best Practicable Means for Cement Works (Concrete Batching Plant), BPM3/2", dust generation from the proposed concrete batching plant should be minimal. The total silo capacity of the proposed concrete batching plant is estimated to be about 1000 tonnes and is classified as a Specified Process under the Air Pollution Control (Specified Processes) Regulations (for cement works with a total silo capacity exceeds 50 tonnes). The contractor is required to obtain a Specified Process licence for the operation of the proposed concrete batching plant to ensure that any potential dust emission would be properly controlled.

Operational Phase

5.7.7 The modelling results for the operational phase cumulative impact assessment at the assessment points at assessment height of 1.5m and 10m above ground level are presented in Table 5.17. These two assessment heights covered the maximum heights of the ASRs in the Ngau Hom Shek area which are all single storey or low-rise village houses. All the modelling results included the contribution due to stack emissions from the power stations as well as the background concentration.

5.7.8 As shown by the modelling results in Table 5.17, NO2 and RSP are the two traffic air pollutants with higher predicted impacts when compared with the respective AQO. Figures 5.9 to 5.14 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 SWC in the CALINE4 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 SWC.

Table 5.17 Predicted Operational Phase Cumulative Air Quality Impacts at Assessment Points

5.7.9 As shown by the modelling results tabulated in Table 5.17 above, there is no predicted exceedance of the AQOs for the assessed air pollutants at the selected assessment points. For 1-hour average NO2, the highest concentration of 245.4 µgm-3 (82% of AQO) is predicted at assessment point 8116. Assessment point 8116 is an existing village house in Ngau Hom Shek located at about 20m to the west of the SWC alignment.

5.7.10 For 24-hour average NO2, the highest concentration of 142.7 µgm-3 (95% of AQO) is predicted at assessment point 8110. Assessment point 8110 is an existing village house in Ngau Hom Shek located at about 40m to the east of the SWC alignment.

5.7.11 The highest 24-hour average RSP concentration of 97.3 µgm-3 (54% of AQO) and the highest 1-hour average CO concentration of 7241.0 µgm-3 (24% of AQO) are both predicted at assessment point 8116.

5.7.12 For SO2, the highest 1-hour average concentration of 193.8 µgm-3 (24% of AQO) is predicted at assessment point 8128. Assessment point 8128 is an existing village houses in Ngau Hom Shek located at more than 280m to the west of the SWC alignment. The highest 1-hour average concentration is predicted with the wind blowing from the northwest. In other words, the predicted highest 1-hour average SO2 impact at assessment point 8128 is due to stack emissions from the Shenzhen Ma Wan Power Station and not traffic emissions from SWC. The highest 24-hour average SO2 concentration of 67.4 µgm-3 (19% of AQO) is predicted at assessment point 8110 which is an existing village house located at about 40m to the east of SWC alignment.

5.7.13 As tabulated in Table 5.13 above, the SO2 emissions in year 2008 could be as high as about 118% of those in year 2021. The predicted SO2 levels presented in Table 5.17 above 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.

5.7.14 As shown in Figures 5.9 to 5.12, exceedances of the 1-hour average and 24-hour average AQOs for NO2 are predicted at areas in close proximity to the main alignment of SWC. Exceedance at existing or planned ASRs are not expected.

5.8 Mitigation of Adverse Environmental Impacts

Construction Phase

5.8.1 In order to ensure that dust emission is minimised during the construction phase of the road works, 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. The specific measures recommended in this assessment include dust suppression by twice daily watering with complete coverage of all active construction areas and limit the construction vehicle travel speed on unpaved site areas to not more than 10 km per hour. Besides, the mitigation measures listed below should be adopted where applicable. With the implementation of effective dust control measures, adverse dust impacts from the construction works of the project is not expected.
Site clearance and demolition of existing structures

5.8.2 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.

5.8.3 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

5.8.4 Vehicle washing facilities including a high-pressure water jet should be provided at every discernible or designated vehicle exit point.

5.8.5 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.

5.8.6 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

5.8.7 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.

5.8.8 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

5.8.9 Immediately before leaving a construction site, every vehicle should be washed to remove any dusty materials from its body and wheels.

5.8.10 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

5.8.11 The concrete batching plant should be located away from the nearest existing air sensitive receiver at Lung Kwu Tan Road as far as practicable.

5.8.12 The total silo capacity of the proposed concrete batching plant is estimated to be about 1000 tonnes and is classified as a Specified Process under the Air Pollution Control (Specified Processes) Regulations (for cement works with a total silo capacity exceeds 50 tonnes). The contractor is required to obtain a Specified Process licence for the operation of the proposed concrete batching plant to ensure that any potential dust emission would be properly controlled.

5.8.13 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.

5.8.14 Silo used for the storage of cement should not be overfilled.

5.8.15 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.

5.8.16 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

5.8.17 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 to maintain the entire surface wet.

5.8.18 Exposed earth should 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

5.8.19 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

5.8.20 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.

Operational Phase

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

5.9 Evaluation of Residual Impacts

5.9.1 With the implementation of effective dust control measures during the construction phase of the project, adverse dust impacts from the construction activities of the project would not be expected. The modelling results showed that there would be no exceedance of the AQO and guideline level for TSP at the ASRs under the mitigated scenario.

5.9.2 Specific measures assumed in the mitigated scenario for this assessment include dust suppression by twice daily watering with complete coverage of all active construction areas and limit the construction vehicle travel speed on unpaved site areas to not more than 10 km per hour. With the implementation of these dust suppression measures, the modelling results showed that the worst-case dust impacts at the assessment points are on average reduced by about 60% and 53% respectively for the 1-hour average TSP level and the 24-hour average TSP level. The highest residual 1-hour average and 24-hour average TSP level at the assessment points are predicted to be 435 µgm-3 and 214 µgm-3 respectively and exceedance of the respective AQO and guideline level for TSP criteria is not expected.

5.9.3 During the operational phase, major air quality impact associated with this project would be related to the tailpipe emissions from SWC and the associated road network. The modelling results showed no exceedance of the AQO for all major traffic pollutants namely NO2, RSP, CO, and SO2 at the ASRs.

5.9.4 The predicted highest 1-hour average and 24-hour average NO2 level at the ASRs are 82% and 95% of the corresponding AQO. The predicted highest 24-hour average RSP level at the ASRs are 54% of the corresponding AQO. Whereas the highest predicted 1-hour average CO level, and the 1-hour average and 24-hour average SO2 levels at the ASRs are all below 28% of the corresponding AQO.

5.10 Environmental Monitoring and Audit

5.10.1 The detailed environmental monitoring and audit requirements for air quality during the construction phase of the project are prepared in accordance with the requirements stipulated in Annex 21 of the TM on EIAO Process. Together with the implementation schedule for air quality mitigation measures, all the material is included in a separate EM&A Manual prepared as part of this EIA study.

5.11 Conclusions

5.11.1 The major potential air quality impacts during the construction phase of the project would result from dust arising from site clearance and preparation, excavation and filling, open site erosion, concrete batching, precasting of road segments, and handling and transportation of C&DM. Practicable and effective dust suppression measures should be implemented to minimize the dust nuisance arising from the construction activities. In particular, the 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 adopted by the site agent while carrying out construction works. The specific measures recommended in this assessment include dust suppression by twice daily watering with complete coverage of all active construction areas and limit the construction vehicle travel speed on unpaved site areas to not more than 10 km per hour. With the implementation of effective dust control measures, adverse dust impacts from the construction works of the project is not expected.

5.11.2 Major air quality impact during the operational phase of the project would arise from the tailpipe emissions of the vehicles travelling on the proposed SWC. There might also be cumulative air quality impacts at some sensitive receivers due to traffic emissions from the proposed Deep Bay Link as well as other planned and existing roads in the area and the stack emissions from major existing and planned sources in the area.

5.11.3 Computer dispersion modelling was undertaken to assess the potential operational phase cumulative air quality impacts due to traffic emissions from the proposed SWC and the future road network in the area. The modelling results showed no exceedance of the respective Air Quality Objectives (AQO) for nitrogen dioxide, respirable suspended particulates, carbon monoxide, and sulphur dioxide at all the identified existing and future air sensitive receivers in the vicinity of the proposed SWC. Mitigation measures for operational phase air quality impacts would therefore not be required.