6. WATER QUALITY IMPACT

6.1 Introduction

6.1.1 This chapter presents an assessment of the potential water quality impact from the construction and operation of the Project. Recommendations for mitigation measures have been provided to minimize the identified water quality impacts.

6.2 Environmental Legislation, Policies, Plans, Standards and Criteria

Environmental Impact Assessment Ordinance (EIAO) (Cap. 499)

6.2.1 The Environmental Impact Assessment Ordinance (EIAO) provides a legislative framework to safeguard the environment by reducing and minimizing adverse environmental impacts from designated projects. The Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) was issued by Environmental Protection Department (EPD) under Section 16 of the EIAO. Annexes 6 and 14 of EIAO-TM specify the criteria and guidelines for water quality impact assessment.

Water Quality Objectives

6.2.2 The Water Pollution Control Ordinance (WPCO) provides major statutory framework for the protection and control of water quality in Hong Kong. According to the Ordinance and its subsidiary legislation, Hong Kong waters are divided into ten Water Control Zones (WCZs). Corresponding statements of Water Quality Objectives (WQOs) are stipulated for different water regimes (marine waters, inland waters, bathing beaches subzones, secondary contact recreation subzones and fish culture subzones) in the WCZs based on their beneficial uses. The study area for this water quality impact assessment covers the Southern WCZ. The corresponding WQOs are listed in Table 6.1.

Table 6.1 Summary of Water Quality Objectives for Southern Water Control Zone

Water Quality Objectives	Sub-Zone
AESTHETIC APPEARANCE
(a) Waste discharges shall cause no objectionable odours or discolouration of the water.	Whole zone
(b) Tarry residues, floating wood, articles made of glass, plastic, rubber or of any other substance should be absent.	Whole zone
(c) Mineral oil should not be visible on the surface. Surfactants should not give rise to a lasting foam.	Whole zone
(d) There should be no recognisable sewage-derived debris.	Whole zone
(e) Floating, submerged and semi-submerged objects of a size likely to interfere with the free movement of vessels, or cause damage to vessels, should be absent.	Whole zone
(f) Waste discharges shall not cause the water to contain substances which settle to form objectionable deposits.	Whole zone
BACTERIA
(a) The level of Escherichia coli should not exceed 610 per 1000 mL, calculated as the geometric mean of all samples collected in one calendar year.	Secondary Contact Recreation Subzones and Fish Culture Subzones
(b) The level of Escherichia coli should not exceed 180 per 100 mL, calculated as the geometric mean of all samples collected from March to October inclusive in one calendar year. Samples should be taken at least 3 times in a calendar month at intervals of between 3 and 14 days.	Bathing Beach Subzones
DISSOLVED OXYGEN
(a) Waste discharges shall not cause the level of dissolved oxygen to fall below 4 milligrams per litre for 90% of the sampling occasions during the year; values should be calculated as the water column average (arithmetic mean of at least 3 measurements at 1 metre below surface, mid-depth, and 1 metre above seabed). In addition, the concentration of dissolved oxygen should not be less than 2 milligrams per litre within 2 metres of the seabed for 90% of the sampling occasions during the year.	Marine waters excepting Fish Culture Subzones
(b) The dissolved oxygen level should not be less than 5 milligrams per litre for 90% of the sampling occasions during the year; values should be calculated as water column average (arithmetic mean of at least 3 measurements at 1 metre below surface, mid-depth and 1 metre above seabed). In addition, the concentration of dissolved oxygen should not be less than 2 milligrams per litre within 2 metres of the seabed for 90% of the sampling occasions during the year.	Fish Culture Subzones
(c) Waste discharges shall not cause the level of dissolved oxygen to be less than 4 milligrams per litre.	Inland waters of the Zone
pH
(a) The pH of the water should be within the range of 6.5-8.5 units. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.2 units.	Marine waters excepting Bathing Beach Subzones; Mui Wo (A), Mui Wo (B), Miu Wo (C), Mui Wo (E) and Mui Wo (F) Subzones.
(b) The pH of the water should be within the range of 6.0-9.0 units.	Mui Wo (D) Sub-zone and other inland waters.
(c) The pH of the water should be within the range of 6.0-9.0 units for 95% of samples. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.5 units.	Bathing Beach Subzones
TEMPERATURE
Waste discharges shall not cause the natural daily temperature range to change by more than 2.0 degrees Celsius.	Whole zone
SALINITY
Waste discharges shall not cause the natural ambient salinity level to change by more than 10%.	Whole zone
SUSPENDED SOLIDS
(a) Waste discharges shall neither cause the natural ambient level to be raised by 30% nor give rise to accumulation of suspended solids which may adversely affect aquatic communities.	Marine waters
(b) Waste discharges shall not cause the annual median of suspended solids to exceed 20 milligrams per litre.	Mui Wo (A), Mui Wo (B), Mui Wo (C), Mui Wo (E) and Mui Wo (F) Subzones.
(c) Waste discharges shall not cause the annual median of suspended solids to exceed 25 milligrams per litre.	Mui Wo (D) Subzone and other inland waters.
AMMONIA
The ammonia nitrogen level should not be more than 0.021 milligram per litre, calculated as the annual average (arithmetic mean), as unionised form.	Whole zone
NUTRIENTS
(a) Nutrients shall not be present in quantities sufficient to cause excessive or nuisance growth of algae or other aquatic plants.	Marine waters
(b) Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.1 milligram per litre, expressed as annual water column average (arithmetic mean of at least 3 measurements at 1 metre below surface, mid-depth and 1 metre above seabed).	Marine waters
5-DAY BIOCHEMICAL OXYGEN DEMAND
Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 5 milligrams per litre.	Inland waters of the Zone
CHEMICAL OXYGEN DEMAND
Waste discharges shall not cause the chemical oxygen demand to exceed 30 milligrams per litre.	Inland waters of the Zone
DANGEROUS SUBSTANCES
(a) Waste discharges shall not cause the concentrations of dangerous substances in marine waters to attain such levels as to produce significant toxic effects in humans, fish or any other aquatic organisms, with due regard to biologically cumulative effects in food chains and to toxicant interactions with each other.	Whole zone
(b) Waste discharges of dangerous substances shall not put a risk to any beneficial uses of the aquatic environment.	Whole zone

Technical Memorandum on Effluent Discharge Standard

6.2.3 Besides setting the WQOs, the WPCO controls effluent discharging into the WCZs through a licensing system. Guidance on the permissible effluent discharges based on the type of receiving waters (foul sewers, stormwater drains, inland and coastal waters) is provided in the Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS). The limits given in the TM-DSS cover the physical, chemical and microbial qualities of the effluents. Any effluent discharge during the construction and operational stages should comply with the relevant standards as stipulated in the TM-DSS.

Practice Notes

6.2.4 The Practice Note (PN) for Professional Persons on Construction Site Drainage (ProPECC PN 1/94) issued by EPD provides good practice guidelines for dealing with various types of discharge from a construction site. Practices outlined in the PN should be followed as far as possible during construction to minimize the water quality impact due to construction site drainage.

6.3 Water Sensitive Receivers

6.3.1 A stream course located at about 250m from the project site was identified. This stream course originates from a small hill to the southeast of the Silver Mine Bay Water Treatment Works and runs through the Lai Chi Yuen Tsuen, crosses South Lantau Road via an underground culvert, continues via a concrete channel, and finally joins the Luk Tei Tong Stream which is one of the three major branches of the Mui Wo River going into Silver Mine Bay. There were also several minor stream courses located more than 90m from the project site boundary. These stream courses are generally flowing in south direction and eventually joining together before ends at Chi Ma Wan. Locations of the identified stream courses are shown in Figure 6.1.

6.4 Description of the Environment and Baseline Conditions

6.4.1 The Luk Tei Tong Stream as part of Mui Wo River is continuously monitored by EPD at MW4 downstream of the Project. Mui Wo River flows down the south-eastern slopes of Lantau and drains into Silver Mine Bay in the Southern WCZ. According to EPD’s Annual River Water Quality Report (2014), Mui Wo River generally displayed satisfactory water quality and achieved full compliance rates of WQO. The 2014 river water quality at EPD monitoring station MW4 is presented in Table 6.2.

Table 6.2 Summary of Water Quality Monitoring Data for Mui Wo River in 2014

Parameters	Unit	Sampling Station
		MW4
Dissolved oxygen	mg/L	7.5 (5.2 – 10.0)
pH	-	7.1 (6.5 – 7.5)
Suspended solids	mg/L	5 (1 – 24)
5-day Biochemical Oxygen Demand (BOD5)	mg/L	<1 (<1 – 2)
Chemical Oxygen Demand (COD)	mg/L	9 (3 – 12)
Oil & grease	mg/L	<0.5 (<0.5 – 0.8)
Faecal coliforms	cfu/100mL	1,900 (200 – 11,000)
E. coli	cfu/100mL	560 (34 – 2,100)
Ammonia-nitrogen	mg/L	0.22 (0.06 – 1.60)
Nitrate-nitrogen	mg/L	0.23 (0.13 – 0.54)
Total Kjeldahl nitrogen	mg/L	0.46 0.19 – 2.00)
Ortho-phosphate	mg/L	0.04 (0.02 – 0.17)
Total phosphorus	mg/L	0.10 (0.05 – 0.28)
Total sulphide	mg/L	<0.02 (<0.02 – <0.02)
Flow	L/s	45 (10 – 140)

Notes:

(1) Data presented are in annual medians of monthly samples; except those for faecal coliforms and E. coli which are in annual geometric means.

(2) Figures in brackets are annual ranges.

(3) cfu - colony forming unit.

(4) Values at or below laboratory reporting limits are presented as laboratory reporting limits.

(5) Equal values for annual medians (or geometric means) and ranges indicate that all data are the same as or below laboratory reporting limits

6.5 Assessment Methodology

6.5.1 The study area for the water quality impact assessment covers the Southern WCZ as designated under the WPCO and the water quality sensitive receivers in the vicinity of the Project.

6.5.2 The Water Sensitive Receivers (WSRs) that may be affected by the Project have been identified. Potential sources of water quality impact that may arise during the construction and operational stages of the Project were described. This task included identifying pollutants from point discharges and non-point sources that could affect the quality of surface water bodies. All the identified sources of potential water quality impact were then evaluated and their impact significance determined. The need for mitigation measures to reduce any identified adverse impacts on water quality to acceptable levels was determined.

6.6 Identification of Potential Impacts

Construction Phase

6.6.1 Potential sources of key water quality impact associated with the construction phase of the Project have been identified and include:

• Construction site runoff;

• Wastewater generated from general construction activities;

• Accidental spillage of chemicals; and

• Sewage effluent produced by on-site workforce.

6.6.2 No other major concurrent project related to water quality impact is identified within the study area. All the project works would be land-based and the water quality impact generated from the projects would be localized and would be controlled with proper mitigation measures in place.

Operational Phase

6.6.3 The potential source of water quality impact during operation of the new niches would be the sewage generated from staff and visitors as well as other site runoff (e.g. storm drainage) from the Project, which may affect the water quality, if not proper controlled.

6.7 Prediction and Evaluation of Environmental Impacts

Construction Phase

Construction Site Runoff

6.7.1 Runoff from the construction works may increase sediment loads and contaminants to the nearby WSRs. Potential sources of pollutants arising from the construction site include:

• Runoff and erosion from exposed soil surfaces, earthwork areas and dusty stockpiles;

• Release of cement materials during rain wash;

• Wash water from dust suppression sprays; and

• Fuel and lubricants from construction vehicles and mechanical equipment maintenance area.

6.7.2 Site runoff may carry pollutants and be washed into the nearby streams. Associated effects which may arise include increased suspended solids concentrations and contaminants in the receiving water bodies. It is important that proper site practice and good site management (as specified in the ProPECC PN 1/94 “Construction Site Drainage”) to be followed to prevent run-off with high level of SS from entering the surrounding waters. With the implementation of appropriate measures to control run-off and drainage from the construction site, disturbance of water bodies would be avoided and deterioration in water quality would be minimal. Thus, unacceptable impacts on the water quality are not expected, provided that the relevant mitigation measures as specified in the ProPECC PN 1/94 “Construction Site Drainage” are properly implemented.

General Construction Activities

6.7.3 Effluent discharged from temporary site facilities should be controlled to prevent direct discharge to the neighbouring water bodies. Such effluent may include wastewater resulting from wheel washing of site vehicles at site entrances. Debris and rubbish such as packaging, construction materials and refuse generated from the construction activities should also be properly managed and controlled to avoid accidental release to the local storm system and inland waters. Adoption of the guidelines and good site practices for handling and disposal of construction discharges as specified in Section 6.8 would minimize the potential impacts.

Accidental Spillage of Chemicals

6.7.4 The use of engine oil and lubricants, and their storage as waste materials has the potential to create impacts on the water quality if spillage occurs and enters adjacent water environment. Waste oil may infiltrate into the surface soil layer, or run-off into the nearby water environment, increasing hydrocarbon levels. The potential impacts could however be mitigated by practical mitigation measures and good site practices (as given in Section 6.8).

Sewage Arising from Workforces

6.7.5 Domestic sewage generated from the workforce during the construction phase would be forbidden to be directly discharge into public drainage systems or adjacent waterbodies. Temporary sanitary facilities, such as portable toilets, should be provided on-site where necessary to handle sewage from the workforce. Contractual desludging service would be responsible for appropriate disposal of waste matter and maintenance of these facilities.

Operational Phase

6.7.6 The identified potential source of impact on water quality during the operational phase of the Project would be the sewage generated from the visitors as well as other site runoff from the Project. It is expected that the amount of sewage to be generated by the visitors and staff and site effluent as well as runoff of the new niches would be limited in view of the small scale of the Project. With adoption of proper control measures as specified in Section 6.8, no adverse water quality impact is anticipated.

6.8 Mitigation of Environmental Impacts

Construction Phase

Construction Site Runoff

6.8.1 The practices outlined in ProPECC PN 1/94 Construction Site Drainage should be adopted to minimize the potential water quality impacts from site runoff and other construction activities. The following measures are recommended to protect water quality sensitive uses, and when properly implemented should be sufficient to adequately control site discharges so as to avoid water quality impact:

• Surface run-off from construction sites should be discharged into storm drains via adequately designed sand/silt removal facilities such as sand traps, silt traps and sedimentation basins. Channels or earth bunds or sand bag barriers should be provided on site to properly direct stormwater to such silt removal facilities. Perimeter channels at site boundaries should be provided on site boundaries where necessary to intercept storm run-off from outside the site so that it will not wash across the site. Catchpits and perimeter channels should be constructed in advance of site formation works and earthworks.

• Silt removal facilities, channels and manholes should be maintained and the deposited silt and grit should be removed regularly, at the onset of and after each rainstorm to ensure that these facilities are functioning properly at all times.

• Construction works should be programmed to minimize soil excavation works in rainy seasons (April to September). If excavation in soil cannot be avoided in these months or at any time of year when rainstorms are likely, for the purpose of preventing soil erosion, temporary exposed slope surfaces should be covered e.g. by tarpaulin, and temporary access roads should be protected by crushed stone or gravel, as excavation proceeds. Intercepting channels should be provided (e.g. along the crest / edge of excavation) to prevent storm runoff from washing across exposed soil surfaces. Arrangements should always be in place in such a way that adequate surface protection measures can be safely carried out well before the arrival of a rainstorm.

• Earthworks final surfaces should be well compacted and the subsequent permanent work or surface protection should be carried out immediately after the final surfaces are formed to prevent erosion caused by rainstorms. Appropriate drainage like intercepting channels should be provided where necessary.

• Construction materials (e.g. aggregates, sand and fill material) on sites should be covered with tarpaulin or similar fabric during rainstorms.

• Manholes (including newly constructed ones) should always be adequately covered and temporarily sealed so as to prevent silt, construction materials or debris from getting into the drainage system, and to prevent storm run-off from getting into foul sewers. Discharge of surface run-off into foul sewers must always be prevented in order not to unduly overload the foul sewerage system.

General Construction Activities

6.8.2 Good site practices should be adopted to remove rubbish and litter from construction sites so as to prevent the rubbish and litter from spreading from the site area. It is recommended to clean the construction sites on a regular basis.

Site Effluent

6.8.3 There is a need to apply to 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 runoff and wastewater generated from the works areas should be treated so that it satisfies all the standards listed in the TM-DSS. The beneficial uses of the treated effluent for other on-site activities such as dust suppression, wheel washing and general cleaning etc., can minimise water consumption and reduce the effluent discharge volume. If monitoring of the treated effluent quality from the sites is required during the construction phase of the Project, the monitoring should be carried out in accordance with the relevant WPCO licence which is under the ambit of regional office (RO) of EPD.

Accidental Spillage of Chemicals

6.8.4 Contractor must register as a chemical waste producer if chemical wastes would be produced from the construction activities. The Waste Disposal Ordinance (Cap 354) (WDO) and its subsidiary regulations in particular the Waste Disposal (Chemical Waste) (General) Regulation, should be observed and complied with for control of chemical wastes.

6.8.5 Any service shop and 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.

6.8.6 Disposal of chemical wastes should be carried out in compliance with the Waste Disposal Ordinance. The Code of Practice on the Packaging, Labelling and Storage of Chemical Wastes published under the WDO details the requirements to deal with chemical wastes. General requirements are given as follows:

• Suitable containers should be used to hold the chemical wastes to avoid leakage or spillage during storage, handling and transport;

• Chemical waste containers should be suitably labelled, to notify and warn the personnel who are handling the wastes, to avoid accidents; and

• Storage area should be selected at a safe location on site and adequate space should be allocated to the storage area.

Sewage Arising from Workforces

6.8.7 The construction workforce on site will generate sewage. It is recommended to provide sufficient portable toilets in the works areas. Contractual desludging service should be deployed to clean the portable toilets on a regular basis.

6.8.8 Notices should be posted at conspicuous locations to remind the workers not to discharge any sewage or wastewater into the surrounding environment. Regular environmental audit of the construction site will provide an effective control of any malpractices and can encourage continual improvement of environmental performance on site. It is anticipated that sewage generation during the construction phase of the project would not cause water pollution problem after undertaking all required measures.

Operation Phase

6.8.9 Following the current practice of the existing Lai Chi Yuen Cemetery, sanitary facilities such as portable toilets should be provided for the visitors and staff during operation of the Project. Sewage generated from the sanitary facilities should be collected and disposed of to a sewage treatment works for proper treatment by contractual desludging service employed by FEHD for handling sewage from the existing sanitary facilities.

6.8.10 Best Management Practices (BMPs) to reduce storm water and non-point source pollution have been proposed for the Project as follows:

Design Measures

• Exposed surface shall be avoided within the Project site to minimize soil erosion. The development site shall be either hard paved or covered by landscaping area where appropriate.

• The streams and channelized nullahs near the Project site should be retained to maintain the original flow path. The drainage system should be designed to avoid flooding.

• Evergreen trees species, which in general generate relatively smaller amount of fallen leaves, should be selected where possible.

Devices/ Facilities to Control Pollution

• Screening facilities such as standard gully grating and trash grille, with spacing which is capable of screening off large substances such as fallen leaves and rubbish should be provided at the inlet of drainage system.

• Road gullies with standard design and silt traps and oil interceptors should be incorporated during the detailed design to remove particles present in stormwater runoff, where appropriate.

Administrative Measures

• Good management measures such as regular cleaning and sweeping of road surface/ open areas are suggested. The open area cleaning should also be carried out prior to occurrence rainstorm.

• Manholes, as well as stormwater gullies, ditches provided at the Project site should be regularly inspected and cleaned (e.g. monthly). Additional inspection and cleansing should be carried out before forecast heavy rainfall.

6.9 Evaluation of Residual Impacts

6.9.1 With effective controls through good site and management practices, no residual impact on water quality is anticipated during the construction and operational phases of the Project.

6.10 Environmental Monitoring and Audit

6.10.1 No specific water quality monitoring is deemed necessary. It is recommended that regular site inspections during the construction phase should be undertaken to inspect the construction activities and works areas in order to ensure the recommended mitigation measures are properly implemented. No EM&A requirement is considered necessary during the operational phase.

6.11 Conclusion

Construction Phase

6.11.1 The key issue from the construction activities of the Project would be the potential for release of wastewater from surface works areas and open cut excavation. Minimization of water quality deterioration could be achieved through implementing adequate mitigation measures, such as control of site run-off of different general construction activities. Regular site inspections should be undertaken routinely to inspect the construction activities and works areas in order to ensure the recommended mitigation measures are properly implemented.

Operational Phase

6.11.2 The potential source of water quality impact during operation of the new niches would be the sewage generated from staff and visitors as well as runoff from the Project. It is anticipated that the water quality impact associated with the operational phase would be minimal and acceptable, provided that the recommended mitigation measures and best management practices are properly implemented.