6.1.1. This section presents a water quality impact assessment, which identifies water quality impacts, assesses the potential impacts and recommends mitigation measures where required, for the construction and operation of the proposed Project.
General
6.2.1. The water quality impact assessment is carried out with reference to the following:
· Environmental Impact Assessment Ordinance (Cap. 499);
· EIA Study Brief No. ESB-267/2014, particularly clause 3.4.6 and Appendix D1 and D2;
· Environmental Impact Assessment Ordinance Technical Memorandum (EIAO-TM), particularly Annex 6 and 14; and
· Water Pollution Control Ordinance (Cap. 358).
6.2.2. Other relevant guidelines include:
·
Water Supplies Department (WSD)
Water Quality Criteria;
·
Technical Memorandum on
Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland
and Coastal Waters (WPCO-TM);
·
Practice Note for Professional
Persons on Construction Site Drainage (ProPECC PN 1/94);
·
Practice Note for Professional
Persons on Drainage Plans subject to Comment by the Environmental Protection
Department (ProPECC PN 5/93); and
·
Sewerage Manual (SM) and the
Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning
(GESF).
Water Pollution Control Ordinance (Cap. 358)
6.2.3.
The Water Pollution Control
Ordinance (WPCO) is the principal legislation to protect the water quality in
Hong Kong. Under this Ordinance, Hong Kong’s waters are classified into 10
Water Control Zones (WCZs) with specific Water Quality Objectives (WQOs)
stipulated for each WCZ. The Project area is adjacent to the Eastern Buffer WCZ
and the respective WQOs are summarised in Table 6.1.
Table 6.1 Summary of WQO for Eastern Buffer Water Control Zone
|
Parameters |
WQOs |
Sub-zone |
|
Offensive Odour, Tints |
Not to be present |
Whole zone |
|
Visible foam, oil scum, litter |
Not to be present |
Whole zone |
|
E. coli |
Not exceed 610 per 100mL, calculated as the geometric mean of all samples collected in one calendar year |
Fish culture subzones |
|
Less than 1 per 100mL, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days |
Water gathering ground subzones |
|
|
Not exceed 1000 per 100mL, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days |
Other inland waters |
|
|
Colour |
Change due to human activity not to exceed 30 Hazen units |
Water gathering ground |
|
Change due to human activity not to exceed 50 Hazen units |
Other inland waters |
|
|
Dissolved oxygen (DO) within 2m of seabed |
Not less than 2 mg/L for 90% of the sampling occasions during the whole year |
Marine waters and Fish culture subzones |
|
Depth-averaged DO |
Not less than 4 mg/L for 90% of the sampling occasion during the whole year |
Marine waters except Fish culture subzones |
|
Not less than 5 mg/L for 90% of the sampling occasion during the year |
Fish culture subzones |
|
|
Not less than 4 mg/L |
Water gathering ground subzone and other inland waters |
|
|
pH |
To be in the range of 6.5 – 8.5, change due to human activity not to exceed 0.2 |
Marine waters |
|
To be in the range of 6.5 – 8.5 |
Water gathering ground subzones |
|
|
To be in the range of 6.0 – 9.0 |
Other inland waters |
|
|
Temperature |
Change due to human activity not to exceed 2ºC |
Whole zone |
|
Salinity |
Change due to human activity not to exceed 10% of ambient |
Whole zone |
|
Suspended Solids (SS) |
Not to raise the ambient level by 30% caused by human activity and shall not accumulate to affect aquatic communities |
Marine waters |
|
Change due to human activity not to exceed 20 mg/L of annual median |
Water gathering ground subzones |
|
|
Change due to human activity not to exceed 25 mg/L of annual median |
Other inland waters |
|
|
Unionised Ammonia (UIA) |
Annual average (arithmetic mean) not to exceed 0.021 mg/L as unionised form |
Whole zone |
|
Nutrients |
Shall not cause excessive algal growth |
Marine waters |
|
Annual mean depth-averaged inorganic nitrogen not to exceed 0.4 mg/L |
Marine waters |
|
|
5-day Biochemical oxygen demand (BOD5) |
Not to exceed 3 mg/L |
Water gathering ground subzones |
|
Not to exceed 5 mg/L |
Other inland waters |
|
|
Chemical oxygen demand (COD) |
Not to exceed 15 mg/L |
Water gathering ground subzones |
|
Not to exceed 30 mg/L |
Other inland waters |
|
|
Toxic substances |
Should not attain such levels as to produce significant toxic, carcinogenic, mutagenic or teratogenic effects in humans, fish or any other aquatic organisms |
Whole zone |
|
Human activity should not cause a risk to any beneficial use of the aquatic environment |
Whole zone |
WSD Water Quality Criteria
6.2.4. Besides the WQOs set under the WPCO, WSD has also specified a set of water quality objectives for water quality at flushing water intakes as show in Table 6.2.
Table 6.2 WSD Water Quality Standards at Flushing Water Intakes
|
Parameter (in mg/L unless otherwise stated) |
Target Limit |
|
Colour (Hazen Unit) |
< 20 |
|
Turbidity (NTU) |
< 10 |
|
Threshold Odour Number (odour unit) |
< 100 |
|
Ammonia Nitrogen |
< 1 |
|
Suspended Solids (SS) |
< 10 |
|
Dissolved Oxygen |
> 2 |
|
5-day Biochemical Oxygen Demand (BOD5) |
< 10 |
|
Synthetic Detergents |
< 5 |
|
E. coli (no. per 100 mL) |
< 20,000 |
Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters
6.2.5. Discharges of effluents into WCZs are controlled by the WPCO through a licensing system. The Technical Memorandum on Standards for Effluents Discharged into Drainage Sewerage Systems, Inland and Coastal Waters set limits for effluent discharge, covering the physical, chemical, and microbial quality of effluents. Any effluent from the construction and operation of the proposed Project must comply with the standards for effluents discharged into the foul sewers, inland/inshore/marine waters of the Eastern Buffer WCZ.
Practice Note for Professional Persons on Construction Site Drainage
6.2.6. The EPD has issued the Practice Note for Professional Persons on Construction Site Drainage (ProPECC PN 1/94) that controls site runoff and wastewater generated during construction phase of the proposed Project. It provides guidelines for handling and disposal of construction discharges. Practices given in the ProPECC PN 1/94 shall be followed as far as possible during construction phase to minimise potential water quality impacts due to construction site drainage. Other ProPECC Notes including ProPECC PN 5/93 Drainage Plan would also be considered.
6.3.1. A desktop study was conducted to collect and review background information on the water systems, the respective catchments and sensitive receivers that may be affected by the potential water quality impact from the proposed Project.
6.3.2. The Project site is located adjacent to the Chai Wan Eastern Buffer Water Control Zone with Chai Wan Preliminary Treatment Works located in the vicinity. The Stonecutter Island Sewage Treatment Works (SCISTW) was commissioned under Harbour Area Treatment Scheme (HATS) Stage 1 in 2002 to collect the sewage generated from eight Preliminary Treatment Works (PTW), including Chai Wan PTW, for treatment. Since its implementation, the pollution load (in terms of organic pollutants) into the harbour has reduced by 70%. In 2012, the Eastern Buffer WCZ has achieved full compliance (100%) with the WQO according to the “Marine Water Quality in Hong Kong in 2012”.
6.3.3. There are five representative EPD’s marine water quality monitoring stations within Eastern Buffer WCZ that are in vicinity of the Project site, namely EM1, EM2, EM3, ET1 (Chai Wan Cargo Handling Basin) and ET2 (Aldrich Bay Typhoon Shelter). The locations of the monitoring stations are shown in Figure 6.1. The monitoring data at these stations are summarised in Table 6.3 upon the latest available information.
6.3.4. Based on the best available information at the time of the EIA study, no major change in the existing environmental condition is anticipated in the future in the absence of the proposed Project.
Table 6.3 Marine Water Quality for Eastern Buffer WCZ in 2012
|
Parameters |
EPD’s Monitoring Stations |
||||
|
EM1 |
EM2 |
EM3 |
ET1 |
ET2 |
|
|
Temperature (ºC) |
23.0 (15.0 – 28.4) |
22.9 (14.9 – 28.7) |
22.8 (14.9 – 28.1) |
22.9 (15.2 – 28.6) |
22.7 (15.1 – 28.1) |
|
Salinity (ppt) |
31.7 (30.3 – 32.9) |
31.8 (30.3 – 33.0) |
32.1 (31.0 – 33.1) |
30.8 (29.7 – 32.3) |
30.8 (30.1 – 32.3) |
|
Dissolved Oxygen (mg/L) |
6.7 (4.5 – 9.7) |
7.0 (4.2 – 9.7) |
7.0 (4.5 – 9.7) |
6.8 (4.6 – 9.1) |
5.9 (3.2 – 8.7) |
|
Bottom Dissolved Oxygen (mg/L) |
6.7 (4.3 – 9.6) |
6.8 (3.5 – 9.7) |
6.6 (3.2 – 9.7) |
6.7 (4.7 – 9.1) |
5.7 (2.3 – 8.8) |
|
SS (mg/L) |
2.9 (0.8 – 6.8) |
3.0 (1.2 – 7.8) |
2.3 (1.3 – 3.9) |
2.1 (1.1 – 3.9) |
1.8 (1.3 – 2.6) |
|
BOD5 (mg/L) |
0.5 (0.2 – 0.9) |
0.5 (0.2 – 1.0) |
0.4 (0.2 – 0.8) |
0.7 (0.4 – 1.1) |
0.4 (0.1 – 0.6) |
|
Unionised Ammonia (mg/L) |
0.002 (<0.001 – 0.006) |
0.002 (<0.001 – 0.005) |
0.001 (<0.001 – 0.005) |
0.003 (<0.001 – 0.008) |
0.003 (0.001 – 0.009) |
|
Total Inorganic Nitrogen (mg/L) |
0.23 (0.14 – 0.32) |
0.19 (0.09 – 0.31) |
0.17 (0.06 – 0.28) |
0.30 (0.20 – 0.37) |
0.38 (0.23 – 0.46) |
|
Chlorophyll-a (µg/L) |
1.6 (0.4 – 4.8) |
1.8 (0.5 – 5.6) |
1.6 (0.5 – 4.3) |
3.2 (0.5 – 9.3) |
1.2 |
|
E. coli (count/100mL) |
57 (1 – 550) |
18 (1 – 140) |
4 (1 – 35) |
380 (140 – 1100) |
710 (110 – 2300) |
Notes:
[1] Data presented are depth averaged (except as specified) and are the annual arithmetic mean except for E. coli (geometric mean);
[2] Data in brackets indicate the ranges;
[3] Underlined indicates occurrence of non-compliance with that parameter of WQO.
6.4.1. The water quality impact assessment identified and analysed the existing and planned future activities, beneficial uses and water sensitive receivers (WSRs) within 500 m from the boundary of the Project site and Eastern Buffer Water Control Zone in accordance with clause 3.4.6.2 of the EIA Study Brief and evaluates the potential water quality impact from the proposed Project. The review was made with reference to the latest best available information at the time of preparation of this study, which include those earmarked on the approved Chai Wan OZP (No. S/H20/21), Development Permission Area Plans, Outline Development Plans and Layout Plans, and other relevant published land use plans, including plans and drawings published by Lands Department and any lands use and development applications approved by the Town Planning Board.
6.4.2. Due to the highly urbanised nature of the area, no natural streams or rivers are located within 500 m from the Project site. Also, there are no marine biological sensitive receivers, such as shellfish culture grounds, marine park/reserves or commercial fishing rounds, identified within the assessment area. However, a cargo handling basin and seawater abstraction points for flushing and cooling are identified within the assessment area. The details of the key WSRs that may potentially be affected by the proposed Project are provided in Table 6.4 and shown in Figure 6.1.
Table 6.4 Water Sensitive Receivers in Eastern Buffer WCZ
|
WSR No. |
Descriptions |
|
WSR 1 |
WSD Water Flushing Intake – Sai Wan Ho |
|
WSR 2 |
Shau Kei Wan Typhoon Shelter |
|
WSR 3 |
Cooling Water Intake – Pamela Youde Nethersole Eastern Hospital |
|
WSR 4 |
Chai Wan Cargo Handling Basin |
|
WSR 5 |
WSD Water Flushing Intake – Siu Sai Wan |
|
WSR 6 |
Cape Collinson – Corals |
|
WSR 7 |
Joss House Bay – Corals |
|
WSR 8 |
Tung Lung Chau West – Corals |
|
WSR 9 |
Tung Lung Chau Fish Culture Zone |
|
WSR 10 |
Tung Lung Chau North – Corals |
|
WSR 11 |
Tung Lung Chau South – Corals |
6.5.1. The water quality impact assessment follows the criteria and guidelines as stated in Annexes 6 and 14 of the EIAO-TM.
6.5.2. The assessment reviews specific construction methods and operational activities of the proposed Project to identify potential pollution sources, including pollutants from point discharges and non-point sources to surface water run-off, sewage from workforce and polluted discharge generated from the proposed Project.
6.5.3. The identified pollution sources have been evaluated to determine the significance of the physical, chemical and biological disruptions to the adjacent water system and sensitive receivers.
6.5.4. The potential cumulative impacts due to other related concurrent and planned projects or pollution sources within assessment area have been assessed with proposed mitigation measures where required to ensure that any water quality impacts would be controlled to acceptable levels.
6.6.1. As described in Section 3 of this EIA Report, the proposed Project comprises mainly the construction of land-based structures with foundation piling. Upon site clearance, site formation will be carried out in limited scale as the site is relatively flat, followed by construction of foundation work by piling. As marine construction works are not required, potential water pollution sources during construction phase would originate from the land-based works activities including excavation works, piling, footing, concrete slab, utilities work, etc.
6.6.2. Major potential sources of water quality impacts during construction phase of the proposed Project are identified, which include:
· Construction site run-off;
· Accidental spillage of chemicals; and
· Sewage generated from on-site construction workers.
6.6.3. Construction site run-off may increase the loads of sediment and other contaminants. The discharge of uncontrolled site run-off may cause potential blockage of drainage channel and increase of SS level and turbidity in the Eastern Buffer WCZ. The pH of the water system may be altered from the release of contaminants and result in toxic effects to the water biota. However, these potential impacts are considered as temporary and reversible.
6.6.4. Major construction site run-off comprises:
· Contaminated surface run-off and erosion from site surfaces, exposed bare soil and earth, drainage channels, earth working areas and stockpiles;
· Effluents from dewatering associated with piling, grouting and cement washing;
· Wastewater from dust suppression sprays and vehicle wheel washing; and
· Contaminated surface run-off by fuel, oil, solvents and lubricants from maintenance area for construction equipment and vehicle.
6.6.5. The potential release of high levels of pollutants into the stormwater drainage system and coastal marine water can be minimised by the adoption of good site practices and relevant guidelines for construction run-off. Adequate site drainage with sedimentation tank and perimeter drain along Site boundary will be provided on Site. With the implementation of mitigation measures and good site practices outlined in Section 6.9, the effluent discharge quality will meet the requirements specified on the discharge licence and the WPCO-TM. Therefore, unacceptable water quality impacts on the water system including nearby WSRs are not anticipated.
6.6.6. Surface soils may be contaminated by the accidental spillage of trace of chemicals used in general construction works, e.g. lubricant oil, paints, diesel and solvents, etc. The contaminated soil may be washed away by construction site run-off and enter nearby stormwater drainage channels, thus resulting in adverse water quality impacts. These potential impacts are considered as temporary and reversible.
6.6.7. Implementation of good construction and site management practices, such as perimeter drain along site boundary and sediment trap, will ensure the generation of accidental chemical spillage is minimised. As such, spillage of chemicals shall not enter nearby stormwater drains and adverse water quality impacts on the water system including nearby WSRs will be avoided.
6.6.8. There will be sewage generation from eating areas, temporary sanitary facilities and waste disposal area for on-site construction workforce and staff. The characteristics of the sewage may include high levels of BOD5, ammonia and E. coli. However, adverse water quality impacts on the water system including nearby WSRs are not anticipated by adequate control of construction phase sewage through provision of sewage collection and disposal facilities, such as on-site chemical toilets.
6.7.1. According to the current design as shown in Figure 3.1, the entire Project site, except the landscape area on Level 1 and the roof floor, is enclosed by the building envelop that is impermeable to water. With reference to the operational activities as described in Section 3, major potential sources of water quality impacts during operation phase of the proposed Project are identified, which include:
· Sewage generated from vehicle washing and maintenance;
· Spillage from use and storage of chemical; and
· Sewage generated from staffs at office and depot.
6.7.2. The proposed Project will be constructed in the form of a six-storey building comprising various facilities for vehicle washing and repair / testing operation, vehicles parking as well as offices. An automatic vehicle washing machine will be provided for the FEHD while a vehicle washing bay for manual vehicle washing will be provided for each of the FEHD and the EMSD Depots.
6.7.3. A desktop study was carried out to identify the existing sewerage networks, sewage treatment and disposal facilities and the characteristics of the concerned sewerage catchments within and in the vicinity of the proposed Project.
6.7.4. An assessment of the DSD sewerage record drawings has concluded that there are existing sewerage networks in the vicinity of the proposed Project for serving the concerned sewerage catchments. The existing public sewers have pipe diameters ranging from 225mm to 600mm running along Sheung On Street and Sheung Ping Street. These sewers are then connected into the 2100mm trunk sewer for discharging into the DSD Chai Wan PTW at the downstream end, which is located approximately 400m to the southeast of the proposed Project.
6.7.5. Apart from the above existing sewers, no committed or planned sewerage networks, sewage treatment or disposal facilities was identified in the vicinity of the proposed Project.
6.7.6. Potential contaminated wastewater may be generated from vehicle washing activities that contain high levels of oil and grease and suspended solids. The estimated quantity of water use for vehicle washing is shown in Appendix 6.1. Limited amount of oil and grease run-off may also be generated from vehicle examination and maintenance areas, repair / testing areas, brake testing areas, parking area and parking spaces.
6.7.7. Proper drainage channels with wastewater treatment facilities will be provided at these areas to confine the potential contaminated wastewater and run-off within the Site area. The collected wastewater will be treated by the wastewater treatment facilities, including sedimentation tank and petrol interceptor, and discharged to public sewerage system[1]. Therefore, no potential contaminated wastewater is anticipated to be washed out to the uncovered portions of the Project site. A preliminary layout of drainage system is provided in Figure 6.3 for indicative purpose and subject to review and confirm during detail design stage.
6.7.8. Since the potential contaminated wastewater will be properly treated to comply with WPCO-TM standards prior to discharge to prevent the potential contaminated wastewater from entering public sewerage system, adverse water quality impact on the water system including nearby WSRs is not anticipated.
6.7.9. Chemical spillage may contaminate surface run-off during the storage, transfer and trans-shipment of operation chemicals, such as oil, fuel and disinfectant fluid, at workshops, stores, battery charging room, dangerous goods stores, lubricant storage area, fire services facilities, air compressor room and waste oil tank if handled improperly.
6.7.10. By implementation of appropriate practices with suitable facilities, such as provision of drip tray underneath each chemical container for retention of potential chemical spill and appointment of licenced collector, contamination of surface run-off would be prevented and spillage shall not enter the public stormwater drainage system and the public sewerage system. As such, adverse water quality impact on the water system including nearby WSRs would be avoided.
6.7.11. Sewage from the operation of the proposed Project would be generated mainly from toilet and shower facilities in workshop and office, including sanitary wastewater and showering facilities and floor drainage, while potentially contaminated run-off is anticipated to be generated from the cleaning activities at vehicle washing bays and maintenance area within the proposed Project.
6.7.12. According to the GESF, the average dry weather flows (ADWF) from the proposed Project is estimated to be 210 m3/d based on the estimated sewage generation in Appendix 6.1. A peaking factor of 8 and a catchment inflow factor of 1.10 have then been applied to the ADWF to establish the peak wet weather flow (PWWF) of 0.0214 m3/s, which includes the stormwater allowances in accordance with the GESF, in order to provide a conservative basis for the performance assessment of the sewerage facilities.
6.7.13. No maintenance activity will be carried out on roof floor except for access to plant rooms. Proper drainage will be provided in each plant room on roof floor to ensure no wastewater or run-off from plant room will enter the uncovered portion of the roof. Contamination of rainwater from plant room is not anticipated.
6.7.14. No fertilisers or pesticides will be routinely used for vegetation management in landscape area in accordance with the General Specification for Building (2012 edition) by Architectural Services Department (ASD). During heavy rainfall, trace of pollutants may be wash-off and is often bound or adsorbed onto particles (i.e. loose soil or litter). The stormwater drainage system will be equipped with silt trap to remove the particles and associated pollutants prior to discharging into the public stormwater drainage system. The stormwater discharge will satisfy the effluent standards and requirements stipulated in the WPCO-TM, notably, with respect to prohibited substances as stated in clauses 8.4 and 9.1, as the case may be. The detailed design of silt traps will be reviewed and confirmed during detailed design stage so that WPCO-TM, in particular, the aforesaid requirements pertaining to prohibited substances, will be complied with.
6.7.15. Two existing public stormwater drainage systems, i.e. along Sheung Mau Street and along Sheung On Street North, were identified nearby the Project site according to the drainage record plans from DSD. As shown in Figure 6.1, the collected stormwater will be discharged to the stormwater drainage system along Sheung On Street North with outfall located near the entrance/exit of the cargo handling basin, which is anticipated to have relatively non-stagnant water due to the frequent travelling of vessels as compared to the stormwater drainage system along Sheung Mau Street with outfall located near the end of the basin (i.e. on the south-western boundary of the basin), to minimise the potential impact on the cargo handling basin. The discharge is clear from the remaining sensitive receivers.
6.7.16. Since the stormwater will be properly treated to satisfy the effluent standards prior to discharge and complies with the clearance requirements as listed in the WPCO and its TM, no adverse water quality impact on the public stormwater drainage system and nearby water bodies and WSRs is anticipated during operation of the Project.
6.7.17. With the provision of the stormwater drainage system as shown in Figure 6.3, no rainwater would enter public sewerage system during operation phase in accordance with ProPECC PN 5/93.
6.7.18. The collected sewage flows from the proposed Project will be connected and discharged into the existing 225 mm diameter gravity sewer along Sheung On Street. The PWWF to be discharged into the existing sewer is estimated to be 0.0214 m3/s (with peaking factor of 8 taken into account).
6.7.19. A hydraulic assessment, which has taken into account of the sewage discharge from the surrounding development listed in Table 6.5, is conducted for the existing sewerage system as shown in Appendix 6.1. Comparing the PWWF of 0.0214 m3/s from the proposed Project with the capacities of the existing 225 mm diameter gravity sewer and the downstream 400 mm, 600 mm and 2100 mm diameter gravity sewers, no significant impact to the receiving sewerage networks and the associated sewage treatment and disposal facilities arising from the proposed Project is anticipated. Mitigation works for the sewerage networks, sewage treatment and disposal facilities are not required.
6.7.20. The proposed sewerage layout plans for the proposed Project for connection into the public sewerage system as shown in Figure 6.2 shall be submitted to the Government authorities (including DSD and EPD) for approval in the detailed design stage of the proposed Project. Agreement from the authorities should be sought prior to the commencement of the proposed sewerage connection work.
6.7.21. As there would be discharge of treated effluent from the proposed Project, application for a discharge licence pursuant to the WPCO should be submitted to EPD for approval.
6.8.1. The known concurrent projects to the proposed Project, as described in Section 3 of this EIA Report, would include the following:
Table 6.5 List of Potential Concurrent Projects
|
Concurrent Projects |
Potential Cumulative Water Quality Impacts |
|
|
Construction Phase |
Operation Phase |
|
|
Planned THEi New Campus (construction tentatively between the third
quarter of 2013 and the third quarter of 2016; operation phase from the third
quarter of 2016) |
O |
O |
|
Existing EMSD Hong Kong Workshop at Chai Wan (EP-442/2012) |
O |
O |
|
Existing New World First Bus
Permanent Depot at Chai Wan (EP-052/2000) |
O |
O |
|
Existing Headquarter and Bus Maintenance
Depot in Chai Wan (EP-107/2001) |
O |
O |
|
Government Logistics Centre |
O |
O |
6.8.2. The construction phase of the planned THEi New Campus will be nearly completed when the construction of the proposed Project commences in mid-2016. Therefore, the interfacing construction of the two projects is limited. In view of the works practices and the associated environmental measures to be implemented, it is anticipated that no adverse cumulative water quality impact would be arisen during construction phase.
6.8.3. The operation phase of the proposed Project will interface with the operation of four projects as listed in Table 6.5, where the EMSD Workshop will be shut down. It should be noted that the sewage from the operation phase of the planned THEi New Campus is discharged to another sewerage system along Shing Tai Road. Given that individual water quality mitigation measures, such as provision of stormwater drainage system, petrol interceptor, etc., would be implemented by each project to ensure that the discharge complies with WPCO-TM standards, unacceptable cumulative water quality impact is not anticipated during operation phase.
6.9.1. In accordance with ProPECC PN 1/94, potential water quality impact shall be minimised by the implementation of construction phase mitigation measures and general good practices including the following:
· At the establishment of works site, perimeter cut-off drains to direct off-site water around the Site should be constructed with internal drainage works and erosion and sedimentation control facilities implemented. Channels (both temporary and permanent drainage pipes and culverts), earth bunds or sand bag barriers should be provided to divert the stormwater to silt removal facilities. The design of the temporary on-site drainage system will be undertaken by the Contractor prior to the commencement of construction, followed by proper maintenance and management practices throughout the construction phase;
· Dikes or embankments for flood protection should be implemented around the boundaries of earthwork areas. Temporary ditches should be provided to facilitate the run-off discharge into an appropriate watercourse, through a silt/sediment trap. Silt/sediment traps should also be incorporated in the permanent drainage channels to enhance deposition rates;
· The design of efficient silt removal facilities should be based on the guidelines in Appendix A1 of ProPECC PN 1/94, which states that the retention time for silt/sand traps should be 5 minutes under maximum flow conditions. The sizes may vary depending upon the flow rate, but for a flow rate of 0.1 m3/s, a sedimentation basin of 30 m3 would be required and for a flow rate of 0.5 m3/s the basin would be 150 m3. The detailed design of the sand/silt raps should be undertaken by the Contractor prior to the commencement of construction;
· The construction works should be programmed to minimise surface excavation works during rainy seasons (April to September), as possible. All exposed earth areas should be completed and vegetated as soon as possible after completion of the earthwork, or alternatively, within 14 days of the cessation of earthworks where practicable. If excavation of soil cannot be avoided during the rainy season, or at any time of year when rainstorms are likely, exposed slope surfaces should be covered by tarpaulin or other means;
· The overall slope of works sites should be kept to a minimum to reduce the erosive potential of surface water flows, and all trafficked areas and access roads should be protected by coarse stone ballast. An additional advantage accruing from the use of crushed stone is the positive traction gained during the prolonged periods of inclement weather and the reduction of surface sheet flows;
· All drainage facilities and erosion and sediment control structures should be regularly inspected and maintained to ensure their proper and efficient operation at all times particularly following rainstorms. Deposited silts and grits should be removed regularly and disposed of by spreading evenly over stable, vegetated areas;
· Measures should be taken to minimise the ingress of site drainage into excavations. If the excavation of trenches in wet season is inevitable, they should be dug and backfilled in short sections wherever practicable. The water pumped out from trenches or foundation excavations should be discharged into storm drains via silt removal facilities;
· All open stockpiles of construction materials (for example, aggregates, sand and fill materials) should be covered with tarpaulin or similar fabric during rainstorms. Measures should be taken to prevent the washing away of construction materials, soil, silt or debris into any drainage system;
· Manholes (including newly constructed ones) should always be adequately covered and temporarily sealed so as to prevent silt, construction materials or debris being washed into the drainage system and storm run-off being directed into foul sewers;
· Precautions to be taken at any time of the year when rainstorms are likely, actions to be taken when a rainstorm is imminent or forecasted and during or after rainstorms, are summarised in Appendix A2 of ProPECC PN 1/94. Particular attention should be paid to the control of silty surface run-off during storm events;
· All vehicles and plants should be cleaned before leaving the Project site to ensure no earth, mud, debris and the like is deposited by them on roads. An adequately designed and sited wheel washing bay should be provided at the exit of Project site where practicable. Wash-water should have sand and silt settled out and removed at least on a weekly basis to ensure the continued efficiency of the process. The section of access road leading to, and exiting from, the wheel-washing bay to public roads should be paved with sufficient backfall toward the wheel-washing bay to prevent vehicle tracking of soil and silty water to public roads and drains;
· Oil interceptors should be provided in the drainage system downstream of any oil/fuel pollution sources. Oil interceptors should be emptied and cleaned regularly to prevent the release of oil and grease into the storm water drainage system after accidental spillage. A bypass should be provided for oil interceptors to prevent flushing during heavy rain. Any drainage channels connecting storm drains via designed sand/silt removal facilities should be disconnected/removed after completion of construction stage to prevent any direct discharge to the stormwater system;
· The construction solid waste, debris and rubbish on-site should be collected, handled and disposed of properly to avoid causing any water quality impacts. The requirements for solid waste management are detailed in Section 8 of this EIA Report; and
· All fuel tanks and storage areas should be provided with locks and sited on sealed areas, within bunds of a capacity equal to 110% of the storage capacity of the largest tank to prevent spilled fuel oils from reaching the nearby WSRs.
6.9.2. By adopting the above mitigation measures with best management practices, it is anticipated that the impacts of construction site run-off will be reduced to an acceptable level.
6.9.3. There is a need to apply to the EPD for a discharge licence for discharge of effluent from the construction site under the WPCO. The discharge quality must meet the requirements as specified in the discharge licence. All the run-off and wastewater generated from the works areas should be treated so that it satisfies all the standards listed in the Technical Memorandum. Minimum distances of 100 m should be maintained between the discharge points of construction site effluent and the existing seawater intakes. Incorporation of these requirements in the contract document of the proposed Project shall be considered. In addition, no new effluent discharges in nearby typhoon shelters should be allowed. The beneficial uses of the treated effluent for other on-site activities such as dust suppression, wheel washing and general cleaning etc., would minimise water consumption and reduce the effluent discharge volume.
6.9.4. Portable chemical toilets and sewage holding tanks are recommended for the handling of the construction sewage generated by the workforce. A licenced contractor should be employed to provide appropriate and adequate portable toilets and be responsible for appropriate disposal and maintenance.
6.9.5. The Contractor must register as a chemical waste producer if chemical wastes would be produced from the construction activities. The Waste Disposal Ordinance (Cap. 354) and its subsidiary regulations in particular the Waste Disposal (Chemical Waste) (General) Regulation should be observed and complied with for control of chemical wastes.
6.9.6. Any maintenance facilities should be located on hard standings within a bunded area, and sumps and oil interceptors should be provided. Maintenance of vehicles and equipment involving activities with potential for leakage and spillage should be undertaken within the areas appropriately equipped to control these discharges.
6.9.7. All sewage arising from the proposed Project should be collected and diverted to the public sewerage system via proper connections to minimise water quality impact from the operation of the proposed Project and ensure compliance with WPCO-TM.
6.9.8. Run-offs from the covered areas including vehicle washing bays and vehicle examination / maintenance / repair / testing area would be properly treated prior to discharge into the sewerage system. The wastewater treatment facilities for the proposed Project, which comprised of petrol interceptor and sedimentation tank, would be designed using sedimentation process with adequate treatment capacity. Oily waste collected by petrol interceptors is considered and disposed of as chemical waste. The wastewater treatment facilities for the proposed Project will be designed during the detailed design stage and the treated effluent for discharging into the public sewerage system should comply with the effluent standards as stated in the WPCO-TM.
6.9.9. Best practices with appropriate management should be implemented during transfer of operation chemicals. Each chemical container should be provided with drip trays at storage. In case of chemical spillage, licenced collector would be appointed for waste collection.
6.9.10. There is a need to apply to the EPD for a discharge licence for discharge of the operational effluent from the proposed Project, i.e. the effluents as mentioned in Section 6.7.1, under the WPCO. The discharge quality must meet the requirements as specified in the discharge licence.
6.10.1. With the implementation of the above mitigation measures, the proposed Project is not anticipated to result in adverse residual impacts on the water system including nearby WSRs, with regards to the standards and guidelines as listed in Section 6.2, during the construction and operation phases.
6.11.1. The implementation of good construction works practices as well as the various specific mitigation measures recommended above will be important to prevent pollution of marine water during the construction phase. It is, therefore, recommended that construction activities should be subject to a routine audit programme throughout the construction period. Further details on the scope of this audit are provided in the EM&A Manual.
6.11.2. With the full implementation of the recommended mitigation measures during operation phase, no adverse water quality impact is anticipated. Therefore, no operation phase EM&A for water quality is considered required.
6.12.1. Potential water pollution sources have been identified as construction site run-off, sewage from workforce, and potential risk of chemical spillage. Mitigation measures including the implementation of the construction site practices in accordance with the EPD’s ProPECC PN 1/94 Construction Site Drainage, provision and management of portable chemical toilets on-site as well as preventive measures for avoiding accidental chemical spillages are recommended to mitigate any adverse water quality impacts. With the implementation of these measures, adverse residual impacts would not be anticipated. Furthermore, there would be insignificant sewerage and sewage treatment implications during the operation of the proposed Project, and adverse water quality impact would not be anticipated with the implementation of the recommended mitigation measures based on the findings of this EIA study.