6. Water Quality and Sewerage Impact Assessment

6.1 Introduction

6.1.1 This section presents a water quality impact assessment for the construction and operation of the Project and assessing the potential impacts and recommending mitigation measures, where necessary, to minimise the identified water quality impacts to an acceptable level.

6.2 Environmental Legislation and Guidelines

General

6.2.1 The EIAO-TM specifies the assessment method and criteria that need to be followed in the EIA study. It also provides the details of the assessment criteria and guidelines that are relevant to the water quality impact assessment, including:

· Annex 6 Criteria for Evaluating Water Pollution; and

· Annex 14 Guidelines for Assessment of Water Pollution

Furthermore, the Water Pollution Control Ordinance (Cap 358) (WPCO) is also applicable to the water quality impact assessment of this Project:

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;

· Practice Note for Professional Persons on Construction Site Drainage (ProPECC PN 1/94); and

· Sewerage Manual (SM) and the Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning (GESF).

Water Pollution Control Ordinance

6.2.3 The WPCO is the principal legislation to protect and control the water quality in Hong Kong. Under the ordinance, Hong Kong waters are classified into 10 Water Control Zones (WCZs), in which the corresponding statements of Water Quality Objectives (WQOs) are stipulated. The Project area is adjacent to the Victoria Harbour (Phase Two) WCZ (as indicated in Figure 6-1) and the corresponding WQOs are summarised in Table 6-1.

Table 6‑1 Summary of WQOs for Victoria Harbour (Phase Two) WCZ

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 to exceed 1,000 per 100mL, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals between 7 and 21 days	Inland waters
Colour	Change due to human activity not to exceed 50 Hazen units	Inland waters
Depth-Averaged Dissolved Oxygen (DO)	Not less than 4.0mg/L for 90% of samples	Marine waters
DO within 2m of the Seabed	Not less than 2.0mg/L for 90% of samples at a year	Marine waters
DO	Not less than 4.0mg/L	Inland waters
pH	To be in the range of 6.5 to 8.5, change due to human activity not to exceed 0.2	Marine waters
pH	Not to exceed the range of 6.0 to 9.0 due to human activity	Inland waters
Temperature	Change due to human activity not to exceed 2.0°C	Whole zone
Salinity	Change due to human activity not to exceed 10%	Whole zone
Suspended Solids (SS)	Not to raise the ambient level by 30% due to caused by human activity and shall not affect aquatic communities	Marine waters
	Annual median not to exceed 25mg/l due to human activity	Inland waters
Unionised Ammonia (UIA)	Annual mean not to exceed 0.021mg/L as unionised form	Whole zone
Nutrients	Shall not cause excessive algal growth	Marine waters
Total Inorganic Nitrogen (TIN)	Annual mean depth-averaged inorganic nitrogen not to exceed 0.4mg/L	Marine waters
5-day Biochemical Oxygen Demand (BOD₅)	Not to exceed 5mg/L	Inland waters
Chemical Oxygen Demand (COD)	Not to exceed 30mg/L	Inland waters
Toxic substances	Should not attain such levels as to produce significant toxic effects in humans, fish or any other aquatic organisms	Whole zone
Toxic substances	Human activity should not cause a risk to any beneficial use of the aquatic environment	Whole zone

Water Supplies Department (WSD) Water Quality Criteria

6.2.4 Besides the WQOs set under the WPCO, the WSD specifies a set of water quality objectives at flushing water intakes as shown in Table 6-2.

Table 6‑2 WSD Standards at Flushing Water Intakes

Parameter (in mg/l unless otherwise stated)	WSD Target Limit
Colour (Hazen Unit)	< 20
Turbidity (NTU)	< 10
Threshold Odour Number (odour unit)	< 100
Ammoniacal Nitrogen	< 1
Suspended Solids	< 10
Dissolved Oxygen	> 2
Biochemical Oxygen Demand	< 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 Besides setting the WQOs, the WPCO controls effluent discharge into the WCZs through a licensing system. The Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters provides guidance on permissible effluent discharges based on the type of receiving waters (foul sewers, inland / coastal / inshore / marine waters). The limits control the physical, chemical and microbial quality of effluents. Any sewage from the proposed construction and operation activities should comply with the standards for effluents discharged into the inshore waters of the Victoria Harbour (Phase Two) WCZ.

ProPECC Notes

6.2.6 The Practice Note for Professional Persons on Construction Site Drainage (ProPECC PN 1/94) was issued by the EPD to provide environmental guidelines for handling and disposal of construction site discharges. It provides good practice guidelines for dealing with various types of discharge from a construction site. Practices given in the ProPECC PN 1/94 should be followed during the construction phase in order to minimise the water quality impact due to construction site drainage. Other ProPECC Notes including the ProPECC PN 5/93 Drainage Plan subject to Comment by the EPD would also be considered.

6.3 Existing Environment

6.3.1 According to the “Marine Water Quality in Hong Kong” in 2010 and 2011, which is the latest available information from EPD at the moment of preparing this Report, since the full commissioning of the Advance Disinfection Facilities (ADF) at the Stonecutters Island Sewage Treatment Works (SCISTW) in March 2010, the E. coli level in the western Victoria Harbour area significantly decreased by about 60%. In the Victoria Harbour WCZ, the 2010 WQO compliance rate was 77% as compared with 50% in 2011. The lower WQO compliance rate was mainly due to non-compliance with the DO WQO and increase in TIN levels. Based on EPD’s monitoring data, non-compliance with the DO objective was observed at 8 stations in Victoria Harbour during the hot and wet summer months in 2011. The increase in TIN levels would be due to a higher background TIN level under the influence of Pearl River discharge, the year-to-year normal range of fluctuation of the discharge from the Tolo Harbour Effluent Export Scheme and surface run-off, as well as the gradual increase in the amount of effluent discharged from the 4 preliminary treatment plants located in Hong Kong Island during the period.

6.3.2 The representative EPD’s marine water quality monitoring stations within the Victoria Harbour (Phase Two) WCZ that are in vicinity of the Project area, including VM7 (West of Victoria Harbour), VM15 (Stonecutters Island), VT12 (Government Dockyard Typhoon Shelter) and VT10 (Yau Ma Tei Typhoon Shelter). The location of these stations is shown in Figure 6-1 and the recent monitoring data are summarised in Table 6-3. Further to description of marine water environment in Section 6.3.1, the water quality of Victoria Harbour has been on an improving trend during the last decade after implementation of the Harbour Area Treatment Scheme (HATS) Stage 1 in end 2001, in particular shown by consistent decreasing pattern of ammonia-nitrogen and BOD₅.

Table 6‑3 Marine Water Quality for Victoria Harbour (Phase Two) WCZ in 2011 at VM7, VM15, VT12 and VT10

Parameters

EPD’s Monitoring Station

VM7

VM15

VT12

VT10

Temperature (°C)

23.2

(15.0 - 26.7)

23.1

(16.5 - 28.0)

23.4

(16.9 - 26.9)

23.2

(16.8 - 27.3)

Salinity (ppt)

31.7

(29.6 - 32.7)

31.3

(26.8 - 33.0)

31.4

(29.6 - 32.1)

31.1

(27.9 - 32.4)

Dissolved Oxygen (mg/L)

5.0

(3.2 - 6.6)

5.2

(3.9 - 6.8)

3.6

(2.2 - 4.6)

3.5

(1.5 - 5.2)

Bottom Dissolved Oxygen (mg/L)

4.7

(3.0 - 6.7)

4.9

(3.1 - 6.9)

3.6

(2.2 - 4.7)

3.5

(1.3 - 5.4)

BOD₅ (mg/L)

1.2

(0.2 - 2.2)

0.9

(0.4 - 1.6)

1.6

(0.8 - 3.4)

1.3

(0.9 - 2.2)

SS (mg/L)

4.4

(1.7 - 7.6)

4.8

(1.5 - 10.2)

8.1

(2.2 - 17.0)

4.9

(1.7 - 10.0)

TIN (mg/L)

0.47

(0.29 - 0.62)

0.45

(0.28 - 0.62)

0.53

(0.29 - 0.66)

0.57

(0.37 - 0.71)

NH₃-N (mg/L)

0.251

(0.140 - 0.387)

0.222

(0.093 - 0.297)

0.349

(0.125 - 0.465)

0.367

(0.068 - 0.503)

Unionised Ammonia (mg/L)

0.006

(0.002 - 0.010)

0.006

(0.002 - 0.011)

0.006

(0.002 - 0.011)

0.006

(0.004 - 0.008)

Chlorophyll-a (µg/L)

2.6

(0.3 - 15.7)

1.9

(0.4 - 9.8)

8.6

(1.3 - 38.0)

4.3

(0.5 - 20.7)

E.coli (count/100mL)

1,700

(230 - 12,000)

180

(10 - 2,000)

390

(49 - 1,600)

1,700

(160 - 17,000)

Notes:

[1] Data presented are depth averaged (except as specified) and annual arithmetic means except for E. coli (geometric mean)

[2] Data in brackets indicate ranges

[3] Underlined indicates occurrence of non-compliance with that parameter of WQO.

6.3.3 To further improve the water quality of Victoria Harbour, the construction of HATS Stage 2A has proceeded with a view to commissioning by end 2014. Upon commissioning, the sewage tunnels will collect the remaining 25% of the sewage currently generated daily from Hong Kong Island region, and convey the sewage to the SCISTW for treatment. Therefore, it is anticipated that the marine water environment would be further improved.

6.4 Identification of Water Sensitive Receivers

6.4.1 To evaluate the potential water quality impacts from the Project, areas within 500m from the proposed Project site, and the adjacent water sensitive receivers within the Victoria Harbour (Phase Two) Water Control Zone are considered. Due to the highly urbanised nature of the area, there is no inland watercourse such as river or natural stream located within 500m from the Project site. Also, no marine biological sensitive receivers, such as fish culture zone, shellfish culture grounds, marine park / reserve or commercial fishing grounds are identified within the Victoria Harbour (Phase Two) WCZ. However, a seawater abstraction point for flushing (Cheung Sha Wan) has been identified adjacent to the Project site as shown in Figure 6-1.

6.5 Potential Sources of Impacts

Construction Phase

6.5.1 As described in Section 3 of this EIA report, the Project comprises mainly the construction of structures with foundation piling. Since the Site is relatively flat, limited site formation works will be required. Upon site clearance, foundation work would be constructed by piling. Since no marine construction works are required, potential water pollution sources during the construction phase would be those generated from the land-based works activities including foundation piling, footings, concrete slab, utilities work, etc.

6.5.2 Major potential sources of water quality impact associated with the land-based construction of the Project have been identified and described as follow:

· Construction site run-off during foundation piling;

· Accidental chemical spillage; and

· Sewage effluent produced by on-site workforce.

Construction Site Run-off

6.5.3 Construction site run-off may contain increased loads of sediments, other suspended solids and contaminants. Release of uncontrolled site run-off would increase the suspended solid levels and turbidity in the nearby water environment.

6.5.4 Potential pollution sources of site run-off comprise:

· Run-off and erosion from bare soil and earth, drainage channels, earth working areas and stockpiles;

· Wastewater from dust suppression sprays and wheel washing facilities at site entrances;

· Fuel, oil, solvents and lubricants from maintenance of construction machinery and equipment.

Accidental Chemical Spillage

6.5.5 The on-site general construction activities may cause contamination the surface soils due to accidental spillage of chemicals used in construction works, which includes spent lubrication oil, diesel and solvents, etc. The contaminated soil particles may be washed away by construction site run-off or stormwater drainage which in turn causes water pollution.

Sewage Effluent

6.5.6 Potential impacts may arise from wastewater generated from eating areas, temporary sanitary facilities and waste disposal areas provided for the on-site construction workforce. The characteristics of the wastewater may include high levels of organics (ie. BOD₅), ammonia and E. coli.

Operation Phase

6.5.7 The proposed development will be constructed in the form of a five-storey building for the purpose of offices, stores, vehicle maintenance, vehicle washing, parking for the FEHD vehicle fleet of West Kowloon region.

6.5.8 Potential water pollution sources during the operational phase mainly include:

· Sewage generated from vehicle washing;

· Sewage / chemicals from vehicle repairing;

· Sewage generated from the staff of the offices and depot; and

· Accidental spillage of stored chemicals.

Sewage Generated from Vehicle Washing

6.5.9 Sewage would be generated during vehicle washing in the vehicle washing bays. Such sewage would contain contaminants, such as debris and residual in the vehicles, and limited amount of diluted detergents.

Sewage from Vehicle Repairing

6.5.10 The repairing activities in the vehicle repair bays may release limited amount oil and grease run-off.

Sewage generated from the Staff of the Depot and Offices

6.5.11 During operation phase of the Project, the sewage generated by the staff of the offices and depot has the potential to cause adverse water quality impacts if not managed properly. Sources of sewage would include sanitary wastewater from toilets and showering facilities and floor drainage.

Accidental Spillage of Chemicals Storage

6.5.12 The soil of Site area may be potentially contaminated by accidental spillage from the storage and transfer of the operation chemicals such as lubrication / hydraulic oil and disinfectants, if not handled properly.

6.6 Assessment Methodology

6.6.1 The criteria and guidelines for assessing water quality impacts as stated in Annexes 6 and 14 of the EIAO-TM have been followed.

6.6.2 The specific construction methods and operational activities of the Project have been reviewed and the 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 Project have been identified.

6.6.3 The identified pollution sources have been evaluated to determine the significance of impact to the adjacent water system and their representative sensitive receivers.

6.6.4 The potential cumulative impacts due to other related concurrent and planned projects activities or pollution sources within the assessment area have been assessed and mitigation measures proposed where required to ensure that any water quality impacts would be controlled to acceptable levels.

6.7 Construction Phase Impact Assessment

6.7.1 Potential sources of water quality impacts associated with the construction phase of the Project include:

· Construction site run-off;

· General construction activities and accidental spillage of chemicals; and

· Sewage generated from on-site construction workers.

Construction Site Run-off

6.7.2 Site run-off and drainage from the Site may contain suspended solids and other contaminants. Potential sources of water pollution from site run-off would comprise:

· Run-off from exposed bare soil and earth, drainage channels and stockpiles;

· Release of grouting and cement materials with rain wash;

· Wash water from dust suppression sprays and vehicle wheel washing; and

· Fuel, oil and lubricant from maintenance of construction vehicles and mechanical equipment.

6.7.3 Topography of the Site is generally flat and perimeter cut-off drains could be applied along the Site boundary to collect any site run-off reaching any surrounding water bodies.

6.7.4 However, mitigation measures of good site practice shall be implemented to control construction site run-off, and to minimise the chance of introducing silt and other pollutants into the stormwater drainage system and also nearby coastal marine water. With the implementation of adequate site drainage and provision of silt removal facilities, no unacceptable water quality impacts are anticipated.

General Construction Activities and Accidental Spillage of Chemicals

6.7.5 General construction activities have the potential to cause water pollution as a result of stockpiling, accumulation of debris and rubbish, concrete dust, etc. Spillage of chemicals, such as oil and diesel from construction plant and equipment and paints, could also result in water quality impacts.

6.7.6 Nevertheless, it is considered that the impact of these activities to nearby water bodies will be minimal provided that the site boundaries are well maintained with the aforesaid perimeter drains. Good construction and site management practices, such as sediment barriers, site drainage and waste disposal, will also limit the sediment and pollutants to acceptable levels.

Sewage Generated from On-Site Construction Workers

6.7.7 Sewage is characterised by high levels of BOD, ammonia and E. coli bacteria. Water quality impacts from sewage generated by the on-site workforce will be avoided if adequate sewage collection and disposal facilities, such as portable chemical toilets, are properly installed and maintained.

6.8 Operation Phase Impact Assessment

Existing, Committed and Planned Sewerage Facilities

6.8.1 The proposed development will be constructed in the form of a five-storey building for the purpose of offices, stores, vehicle maintenance, vehicle washing, parking for the FEHD vehicle fleet of West Kowloon region as shown in Figure 3-1. Regarding vehicle washing, an automatic vehicle washing machine is to be provided. The machine would be equipped with simple filtration and disinfection before reuse by the machine. Catalogue of possible automatic vehicle washing machine is provided in Appendix 6-1. Other type of machine with similar capability and performance might be selected in the later design stage.

6.8.2 A desk study was carried out to identify the existing sewerage facilities and the characteristics of the concerned sewerage catchments within and in the vicinity of the proposed development.

6.8.3 An assessment of the Drainage Services Department (DSD) sewerage record drawings has concluded that there are existing sewerage networks in the vicinity of the proposed development for serving the concerned sewerage catchments. The existing public sewers have pipe diameters ranging from 225mm to 600mm running along Yen Ming Road, Hoi Fan Road and underneath Nam Cheong Park.

6.8.4 These sewers are then connected into the 2,100mm diameter trunk sewer for discharging into the DSD West Kowloon No.1 Pumping Station at the downstream end, which is located approximately 150m to the northeast of the Site.

6.8.5 Apart from the above existing sewers, no committed or planned sewerage facility was identified in the vicinity of the proposed development.

Proposed Sewage Discharge from the Development

6.8.6 Based on the preliminary design arrangement, sewage from the proposed development is anticipated to be generated mainly from the toilet and shower facilities in the workshop and office, while potentially contaminated run-off is anticipated to be generated from the cleaning activities of the vehicle washing bays and maintenance areas to be provided within the proposed development. These areas will be provided with proper drainage channels and collected run-off will be discharged to public sewerage system via petrol interceptors. Preliminary layout and schematic for foul water drainage system are shown in Appendix 6-2.

6.8.7 With reference to the estimate of sewage generation in Appendix 6-3, the Average Dry Weather Flows (ADWF) from the proposed development has been estimated to be 262m³/d in accordance with the Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning (GESF).

6.8.8 The Peak Wet Weather Flows (PWWF) of 24.3L/s has been used in the assessment of the hydraulic adequacy of the sewerage systems. Peaking factor of 8, including storm water allowances in accordance with the GESF, has been applied to the ADWF to establish the peak flows, in order to provide a conservative basis for the performance assessment of the sewerage facilities.

Potential Sewerage Impact on Public Sewers and Sewerage Facilities

6.8.9 The preliminary layout of the proposed sewerage works for the proposed development is shown in Figure 6-2.

6.8.10 In order to avoid surface run-off due to rainfall for entering the public sewerage system, separated system (i.e. stormwater drainage system) will be provided for serving the uncovered areas of the proposed development. With the provision of this adequate stormwater drainage system for serving the uncovered areas of the proposed development, it is anticipated that no surface run-off due to rainfall arising within the uncovered areas of the site would enter the public sewerage system during the operational phase.

6.8.11 The collected sewage flows from the proposed development will be connected and discharged into the existing 225mm diameter gravity sewer along Yen Ming Road. The sewage flows (PWWF) to be discharged into the existing sewer is estimated to be 24.3L/s (with peaking factor of 8 taken into account).

6.8.12 Comparing the PWWF of 24.3L/s from the proposed development with the capacities of the existing 225mm diameter gravity sewer and the downstream 375mm and 600mm diameter gravity sewers, no significant impact to the receiving sewerage networks arising from the proposed development is anticipated. The hydraulic assessment for the existing sewerage systems is included in Appendix 6-3.

6.8.13 In addition, the downstream DSD West Kowloon No.1 Pumping Station currently receives about 11,500m³ sewage daily (in average in 2011), with design capacity of over 70,000m³/d. Comparing the estimated PWWF from the proposed development with the said existing and design capacity of receiving pumping station, significant impact to the downstream sewerage facilities is not anticipated.

Agreement with Government Authorities for Proposed Sewerage Discharge

6.8.14 The proposed sewerage layout plans for connection into the public sewerage system for the proposed development will be submitted to the government authorities (including DSD and EPD) for approval in the detailed design phase of this Project. Agreement from the authorities should be sought prior to the commencement of the proposed sewerage connection work.

6.8.15 As there would be potential contaminated discharge from the proposed vehicle washing bays in the workshop, application for a discharge license pursuant to the WPCO should be submitted to the EPD’s approval.

6.9 Cumulative Impacts

6.9.1 The known concurrent projects to the Project, as described in Section 3 of this EIA Report, as listed in the following, would not contribute significant cumulative impact on water quality perspective during both construction and operation phases.

Table 6‑4 List of Potential Concurrent Projects

Concurrent Projects	Potential Cumulative Water Quality Impacts
Concurrent Projects	Construction Phase	Operation Phase
Planned ffootbridge across the junction of Sham Mong Road/Tonkin Street West (construction works are scheduled to commence in late 2014 and to complete in 2018)	X ¹	X ¹
Planned Hong Kong section of the Guangzhou-Shenzhen-Hong Kong Express Rail Link along Sham Mong Road (several works area within our study area are under construction in between our project implementation programme)	X ²	X ²
Nam Cheong Station Property Development (construction has been commenced currently and to complete from 2017 to 2019 by phases)	X ²	X ³

Rationales:

1. In view of works scale, works practice and associated environmental measures

2. In view of works practice and associated environmental measures

3. Sewage discharged via separate sewers to Sham Shui Po Screening Plant

6.10 Mitigation Measures

Construction

6.10.1 General good site practice as described in the following is to be implemented as measures to minimise potential water quality impact during construction phase.

Construction Site Run-off and General Construction Activities

6.10.2 In accordance with the ProPECC PN 1/94, construction phase mitigation measures should include 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;

· 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 0.1m³/s, a sedimentation basin of 30m³ would be required and for a flow rate of 0.5m³/s the basin would be 150m³. The detailed design of the sand / silt traps 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 the earthworks have been completed, 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 material) 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 plant should be cleaned before leaving the Site to ensure no earth, mud, debris and the like is deposited by them on roads. An adequately designed and sited wheel washing facilities / bay should be provided at the exit of the 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;

· 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 Chapter 7 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.

6.10.3 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.

6.10.4 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 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 100m should be maintained between the discharge points of construction site effluent and the existing seawater intakes. 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.

Sewage Generated from On-Site Construction Workers

6.10.5 Portable chemical toilets and sewage holding tanks are recommended for the handling of the construction sewage generated by the workforce. A licensed contractor should be employed to provide appropriate and adequate portable toilets and be responsible for appropriate disposal and maintenance.

Accidental Spillage of Chemicals

6.10.6 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.

6.10.7 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 only be undertaken within the areas appropriately equipped to control these discharges.

Operation

6.10.8 All sewage arising from the Project should be collected and diverted to the public sewerage system via proper connections to minimise water quality impact from the operation of the Project and ensure compliance with Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters under the WPCO.

6.10.9 In order to prevent the potential contaminated wastewater from the proposed workshop from entering the existing public sewerage systems, run-offs from the covered areas including the vehicle washing bays and vehicle parking space will be properly treated prior to the discharge into the sewerage system. The wastewater treatment facilities for the proposed development which comprised of petrol interceptor and sedimentation tank would be designed using sedimentation process with adequately treatment capacity. The treatment facilities treat run-offs from the covered areas prior to discharging into the sewerage system. Oily waste collected by petrol interceptors is considered and disposed of as chemical waste.

6.10.10 The treated effluent for discharging into the public sewerage system should comply with the effluent standards as stated in the Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters under the WPCO. The wastewater treatment facilities for the development will be designed to comply with the effluent discharge standards and will be carried out in the detailed design stage of the Project.

6.10.11 There is a need to apply to the EPD for a discharge licence for discharge of the operational effluent from the Project under the WPCO. The discharge quality must meet the requirements specified in the discharge licence.

6.11 Residual Impacts

6.11.1 Adverse residual impacts during the construction and operation phases of this Project would not be anticipated, provided that the above mitigation measures are implemented.

6.12 Environmental Monitoring and Audit

6.12.1 The implementation of good construction works practices as well as the various specific mitigation measures recommended above will be important to prevent the pollution of Hong Kong waters 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.

6.12.2 With the full implementation of the recommended mitigation measures during operation phase, no adverse water quality impact is anticipated. Therefore, no operational phase EM&A for water quality is considered required.

6.13 Conclusions

6.13.1 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 toilets on-site, and preventive measures to avoid accidental chemical spillages are recommended to mitigate any adverse water quality impacts, based on which adverse residual impacts would not be anticipated. Furthermore, there would be insignificant sewerage and sewage treatment implications during the operation of this 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.