8.                    water quality 

Introduction

8.1               This section presents the assessment of the potential water quality impacts associated with the proposed Project.  The key water quality issues and concerns arising from the Project have been identified and assessed.  Recommendations for possible mitigation measures have been made, where necessary, to reduce the identified water quality impacts to an acceptable level.

Environmental Legislation, Policies, Plans, Standards and Criteria

Water Pollution Control Ordinance (WPCO)

8.2               The Water Pollution Control Ordinance (Cap. 358), in existence since 1980, is the major legislation relating to 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 (WCZ).  Corresponding statements of Water Quality Objectives (WQO) are stipulated for different water regimes (marine waters, inland waters, bathing beaches subzones, secondary contact recreation subzones and fish culture subzones) in each of the WCZ based on their beneficial uses.  The study area is located within the Eastern Buffer WCZ and the corresponding WQOs are listed in Table 8.1.

Table 8.1       Summary of Water Quality Objectives for the Eastern Buffer WCZ

Parameters

Objectives

Sub-Zone

Offensive odour, tints

Not to be present

Whole zone

Visible foam, oil scum, litter

Not to be present

Whole zone

Dissolved oxygen (DO) within 2 m of the seabed

Not less than 2.0 mg/l for 90% of samples

Marine waters

Depth-averaged DO

Not less than 4.0 mg/l for 90% of samples

Marine waters excepting fish culture subzones

Not less than 5.0 mg/l for 90% of samples

Fish culture subzones

Not less than 4.0 mg/l

Water gathering ground subzone and other Inland waters

5-Bay biochemical oxygen demand (BOD5)

Change due to waste discharges not to exceed 3 mg/l

Water gathering ground subzones

Change due to waste discharges not to exceed 5 mg/l

Inland waters

Chemical oxygen demand (COD)

Change due to waste discharges not to exceed 15 mg/l

Water gathering ground subzones

Change due to waste discharges not to exceed 30 mg/l

Inland waters

pH

To be in the range of 6.5 – 8.5, change due to waste discharges 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

Inland waters

Salinity

Change due to waste discharges not to exceed 10% of ambient

 

Whole zone

Temperature

Change due to waste discharges not to exceed 2 oC

Whole zone

Suspended solids (SS)

Not to raise the ambient level by 30% caused by waste discharges and shall not affect aquatic communities

Marine waters

Change due to waste discharges not to exceed 20 mg/l of annual median

Water gathering ground subzones

Change due to waste discharges not to exceed 25 mg/l of annual median

Inland waters

Unionized ammonia (UIA)

Annual mean not to exceed 0.021 mg(N)/l as unionized 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 0.4 mg(N)/l

Marine waters

Dangerous substances

Should not attain such levels as to produce significant toxic effects in humans, fish or any other aquatic organisms

Whole zone

Waste discharges should not cause a risk to any beneficial use of the aquatic environment

Whole zone

E.coli

Not exceed 610 per 100 ml, calculated as the geometric mean of all samples collected in one calendar year

Fish culture subzones

Less than 1 per 100 ml, 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 100 ml, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days

Inland waters

Colour

Change due to waste discharges not to exceed 30 Hazen units

Water gathering ground

Change due to waste discharges not to exceed 50 Hazen units

Inland waters

 

Source:  Statement of Water Quality Objectives (Eastern Buffer Water Control Zone).

 

Technical Memorandum

8.3               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, storm water 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 quality of effluents. Any effluent discharge during the construction works should comply with the standards specified in the TM-DSS.

Practice Notes

8.4               A practice note (PN) for professional persons was issued by the EPD to provide environmental guidelines for handling and disposal of construction site discharges. The ProPECC PN 1/94 “Construction Site Drainage” 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.

Water Sensitive Receivers

8.5               There are no natural streams or rivers within or in close proximity to the proposed land-based works areas. The water or stream courses identified closest to the Project site are at least 100 m away from the Project site boundary. No other existing or planned water sensitive receiver (WSR) was identified.

Assessment Methodology

8.6               Potential sources of water quality impact that may arise during the Project works were described.  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.

Identification of Environmental Impacts

Construction Phase

Demolition and Construction Works

8.7               All the proposed Project works will be land-based and would include demolition of the existing cremators and construction of new cremators and ancillary facilities. The key concern from demolition/construction works will be surface runoff and site effluent.

 

8.8               Surface runoff may cause potential water quality impact during the demolition and construction activities. Precipitation that falls on unpaved lands and areas with the topsoil exposed during the demolition would wash away soil particles. Potential sources of water pollution from site runoff may also come from the release of bentonite slurries and other grouting materials with construction run-off or stormwater. Such surface runoff and stormwater overflows with high levels of suspended solids if directly discharged into the water bodies or via the drainage channel could lead to a water quality impact.

 

8.9               Effluent discharge from temporary site facilities will be controlled to prevent direct discharge to the neighbouring marine waters and storm drains. Such wastewater may include wastewater resulting from wheel washing of site vehicles at site entrances.

Sewage from Workforce

8.10            Sewage will arise from the on-site workforce.  It is characterized by high level of BOD, NH3-N and E.coli counts and may adversely affect the water quality, if not proper controlled.

Accumulation of Solid Waste and Accidental Spillage

8.11            Accumulation of solid waste (such as debris, rubbish and demolition materials), and spillage of oil, diesel or solvents by vessels and vehicles involved with the construction works, if uncontrolled, could also lead to deterioration in water quality.

Operation Phase

 

8.12            Potential water pollution sources during operation of the Project include sewage from visitors and workers as well as other site effluent generated from the Project, which may affect the water quality, if not proper controlled.

Prediction and Evaluation of Environmental Impacts

Construction Phase

Demolition and Construction Works

8.13            As a good site practice, mitigation measures should be implemented to control site runoff and drainage and site effluent from the works areas, and to prevent runoff and drainage water with high levels of suspended solids from entering the adjacent watercourses.  With the implementation of adequate site drainage and provision of sediment removal facilities as described in Sections 8.20 to 8.46 below, it is anticipated that unacceptable water quality impacts will not arise. Surface runoff will be collected by the temporary drainage system and then treated or desilted on-site before discharging to the storm water drain.  Effluent from wheel washing will also be treated or desilted on-site before discharged. A license should be obtained from EPD for discharge to the public drainage system.

Sewage from Workforce

8.14            Domestic sewage will be generated from the workforce during the construction works.  Portable chemical toilets can be installed within the site. The chemical toilets should be properly maintained, and licensed contractors should be employed to collect and dispose of the waste off-site at approved locations.  Therefore, adverse water quality impacts associated with sewage from workforce would not be expected.

Accumulation of Solid Waste and Accidental Spillage

8.15            On-site construction and demolition activities may cause water pollution from the following:

l             Uncontrolled discharge of debris and rubbish such as demolition materials and refuse

l             Spillages of liquids stored on-site, such as oil, diesel and solvents etc.

8.16            Good construction and site management practices should be observed, as detailed in Sections 8.20 to 8.46 below, to ensure that litter, fuels and solvents do not enter into the adjacent water system.

 

Operation Phase

Wastewater from Air Pollution Control Equipment

8.17            No effluent will be discharged from the Air Pollution Control equipment in the new crematorium as “dry” process will be adopted. Hence, adverse water quality impact is not expected.

Sewage from Public and General Cleaning Activities

8.18            Only small amount of sewage will be generated by visitors and workers, as well as wastewater from cleaning activities, at the new crematorium.

 

Sewage from Visitors and Workers

 

8.19            The sewage from visitors and workers generated within the Project site during the operational phase was estimated based on the guideline set out in the DSM, Sewerage Manual (SM) Part 1 (DSD, 1995) and the design information as given below.

 

(a)               Population (visitors and workers):

(i)       Services Halls -        256 persons

(ii)      Office -                    41 persons

 

(b)               Sewage flow factors:

(i)       Services Halls -        0.025m3/person/day

(ii)      Office -                    0.290m3/person/day

 

(c)               Daily Discharge Flow:

            Qd1        = 256*0.025 + 41*0.290

                                                            = 18.29m3/d

 

Wastewater from Cleaning Activities

 

8.20            Wastewater would also be generated from the general floor cleaning and sand filter cleaning activities.  Locations of these wastewater generating activities are given below:

 

General Cleaning

·     Potable and flushing room, water pumps & tank room

·     FS pump room

·     Cremator plant room

·     Filtration plant room

·     Cleaner’s store

·     A/C room

·     Gardener’s room

           

Sand Filter Cleaning

·     Potable and flushing room, water pumps & tank room

·     Water feature plant room

 

8.21            The designed wastewater discharge quantity generated from the Project site was estimated based on the following design information:

 

(a)               General Floor Cleaning:

(i)       no. of cleansing points                                  -           9 nos.

(ii)      water flow rate of each cleansing point           -           0.3 l/s

(iii)    duration of use                                             -           5 mins

(iv)     frequency of use/day                                    -           2/day

(v)      Daily Discharge Flow:

Qd2  = 9*(0.3/1000)*(5*60)*2

                  = 1.62m3/d

 

(b)               Sand Filter Cleaning:

(vi)     no. of sand filter                                           -           3 nos.

(vii)   water flow rate for filter cleaning                     -           3 l/s

(viii)  duration of filter cleaning                               -           5 mins

(ix)    frequency of use/day                                    -           1/day

(x)     Daily Discharge Flow:

Qd3  = 3*(3/1000)*(5*60)*1

                        = 2.70m3/d

 

Total Sewage / Wastewater Flow

 

8.22            The designed wastewater discharge quantity generated from the Project site was estimated as follows.

 

Total estimated quantity of sewerage discharge, Q average   = Qd1+ Qd2+Qd3

                                                                                                =18.29+1.62+2.70

                                                                                                = 22.61m3/d

8.23            Based on a peaking factor of 6 and operational period of 8 hours per day, the discharge peak flow, Q p, from the Project was estimated to be:

 

 Discharge flow, Q p       =  Q average x 6 / (8*3600)

                                   =  0.0047 m3/s (or 4.7 L/s)

 

8.1               All wastewater generated from the Project site will be collected and discharged to the public foul sewer through connection to the existing government foul water manhole, namely FMH7025323, as shown in Appendix 8.1.

 

Sewerage Impact Assessment

 

8.2               It is proposed that the Project effluent would be connected to the existing government sewers serving the existing Cape Collinson Crematorium and ultimately discharged to the Chai Wan Preliminary Treatment Works (PTW) under Stage 1 of Harbour Area Treatment Scheme (HATS).

 

8.3               Appendix 8.2 presents the capacity performance of the existing sewers downstream of the Project site under the ultimate conditions with and without the Project discharge. The existing sewers under assessment are shown in Appendix 8.3. The baseline sewage flow in the government sewers (without the Project discharge) is based on the latest flow projection available from the “Review of Hong Kong Island Sewerage Master Plans”, which has taken account of the cumulative effects of any potential future developments in catchment of the concerned sewer system.  As shown in Appendix 8.2, no sewers are identified as hydraulic inadequate in the existing sewers assessed.

 

8.4               With regard to the capacity performance of the existing Chai Wan PTW, reference is made to the latest flow projection available from the “Environmental Impact Assessment Study for HATS Stage 2”, where the projected ultimate peak flow for Chai Wan PTW was estimated to be 2.07m3/s as compared to its existing design capacity of 2.61m3/s.  Therefore, the Chai Wan PTW is capable of handling the Project effluent flow of only about 0.0047m3/s.

 

8.5               Based on the sewerage impact assessment, the Project effluent would not cause any adverse impacts to the existing sewers as well as the sewage treatment facilities, and therefore mitigation measures would not be required.

Mitigation of Adverse Environmental Impacts

Construction Phase

Demolition and Construction Works

8.6               The following measures as outlined in the ProPECC PN 1/94 should be followed where applicable.

 

Surface Run-off

8.7               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 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.

 

8.8               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.  Any practical options for the diversion and re-alignment of drainage should comply with both engineering and environmental requirements in order to provide adequate hydraulic capacity of all drains.

8.9               Construction works should be programmed to minimize soil excavation works in rainy seasons (April to September).  If excavation in soil could not 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.

 

8.10            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.

 

8.11            Measures should be taken to minimize the ingress of rainwater into trenches. If excavation of trenches in wet seasons is necessary, they should be dug and backfilled in short sections.  Rainwater pumped out from trenches or foundation excavations should be discharged into storm drains via silt removal facilities.

 

8.12            Open stockpiles of construction materials (e.g. aggregates, sand and fill material) on sites should be covered with tarpaulin or similar fabric during rainstorms. 

 

8.13            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.

 

Groundwater

8.14            Groundwater pumped out of wells, etc. for the lowering of ground water level in basement or foundation construction should be discharged into storm drains after the removal of silt in silt removal facilities.

 

Boring and Drilling Water

8.15            Water used in ground boring and drilling for site investigation or rock / soil anchoring should as far as practicable be recirculated after sedimentation.  When there is a need for final disposal, the wastewater should be discharged into storm drains via silt removal facilities.

 

Wastewater from Concrete Batching and Precast Concrete Casting

8.16            Wastewater generated from the washing down of mixing trucks and drum mixers and similar equipment should whenever practicable be used for other site activities.  The discharge of wastewater should be kept to a minimum and should be treated to meet the appropriate standard as specified in the TM-DSS (refer to Section 8.3) before discharging.

 

8.17            To prevent pollution from wastewater overflow, the pump sump of any wastewater system should be provided with an on-line standby pump of adequate capacity and with automatic alternating devices.

 

8.18            Under normal circumstances, surplus wastewater may be discharged into foul sewers after treatment in silt removal and pH adjustment facilities (to within the pH range of 6 to 10).  Disposal of wastewater into storm drains will require more elaborate treatment.

 

Wheel Washing Water

8.19            All vehicles and plant should be cleaned before they leave a construction site to minimize the deposition of earth, mud, debris on roads.  A wheel washing bay should be provided at every site exit if practicable and wash-water should have sand and silt settled out or removed before discharging into storm drains.  The section of construction road between the wheel washing bay and the public road should be paved with backfall to reduce vehicle tracking of soil and to prevent site run-off from entering public road drains.

 

Bentonite Slurries

8.20            Bentonite slurries used in construction works should be reconditioned and used again wherever practicable.  If the disposal of a certain residual quantity cannot be avoided, the used slurry may be disposed of at the marine spoil grounds subject to obtaining a marine dumping licence from EPD on a case-by-case basis.

 

8.21            If the used bentonite slurry is intended to be disposed of through the public drainage system, it should be treated to the respective effluent standards applicable to foul sewer, storm drains or the receiving waters as set out in the TM-DSS (refer to Section 8.3).

 

Water for Testing & Sterilization of Water Retaining Structures and Water Pipes

8.22            Water used in water testing to check leakage of structures and pipes should be used for other purposes as far as practicable. Surplus unpolluted water could be discharged into storm drains.

 

8.23            Sterilization is commonly accomplished by chlorination.  Specific advice from EPD should be sought during the design stage of the works with regard to the disposal of the sterilizing water.  The sterilizing water should be used again wherever practicable.

 

Wastewater from Building Construction

8.24            Before commencing any demolition works, all sewer and drainage connections should be sealed to prevent building debris, soil, sand etc. from entering public sewers/drains.

 

8.25            Wastewater generated from building construction activities including concreting, plastering, internal decoration, cleaning of works and similar activities should not be discharged into the stormwater drainage system.  If the wastewater is to be discharged into foul sewers, it should undergo the removal of settleable solids in a silt removal facility, and pH adjustment as necessary.

 

Acid Cleaning, Etching and Pickling Wastewater

8.26            Acidic wastewater generated from acid cleaning, etching, pickling and similar activities should be neutralized to within the pH range of 6 to 10 before discharging into foul sewers.  If there is no public foul sewer in the vicinity, the neutralized wastewater should be tinkered off site for disposal into foul sewers or treated to a standard acceptable to storm drains and the receiving waters.

 

Wastewater from Site Facilities

8.27            Wastewater collected from canteen kitchens, including that from basins, sinks and floor drains, should be discharged into foul sewer via grease traps capable of providing at least 20 minutes retention during peak flow.

 

8.28            Drainage serving an open oil filling point should be connected to storm drains via a petrol interceptors with peak storm bypass.

 

8.29            Vehicle and plant servicing areas, vehicle wash bays and lubrication bays should as far as possible be located within roofed areas.  The drainage in these covered areas should be connected to foul sewers via a petrol interceptor.  Waste oil should be collected and stored for recycling or disposal in accordance with the Waste Disposal Ordinance.

Effluent Discharge

8.30            There is a need to apply to EPD for a discharge licence under the WPCO for discharging effluent from the construction site. The discharge quality is required to meet the requirements specified in the discharge licence. All the runoff, wastewater or extracted groundwater generated from the works areas should be treated as necessary so that it satisfies all the standards listed in the TM-DSS (see Section 8.3).  It is anticipated that the wastewater generated from the works areas would be of small quantity. Monitoring of the construction site effluent quality should be carried out in accordance with the WPCO license which is under the ambit of regional office (RO) of EPD. 

Sewage from Workforce

8.31            Temporary sanitary facilities, such as portable chemical toilets, should be employed on-site where necessary to handle sewage from the workforce. A licensed contractor would be responsible for appropriate disposal of waste matter and maintenance of these facilities.

Accumulation of Solid Waste and Accidental Spillage

8.32            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. Stockpiles of cement and other construction materials should be kept covered when not being used.

 

8.33            Oils and fuels should only be used and stored in designated areas which have pollution prevention facilities.  To prevent spillage of fuels and solvents to the nearby watercourse, all fuel tanks and storage areas should be provided with locks and be sited on sealed areas, within bunds of a capacity equal to 110% of the storage capacity of the largest tank.  The bund should be drained of rainwater after a rain event. Oil leakage or spillage should be contained and cleaned up immediately.

 

Operation Phase

 

8.34            Sewerage impact assessment has been conducted for the Project. Assessment results indicated that the additional sewage / wastewater generated from the Project would not cause any adverse impacts to the existing sewerage systems, and therefore mitigation measures would not be required. For handling and disposal of other operation stage effluent (such as for the storm drainage), the practices outlined in ProPECC PN 5/93 should be adopted where applicable.  

Evaluation of Residual Impacts

8.35            Provided that all the recommended mitigation measures are implemented properly, no unacceptable residual water quality impacts would be expected.

Environmental Monitoring and Audit

8.36            No off-site water quality impact will be expected from the proposed construction and demolition activities, marine water quality monitoring is not considered necessary.  It is recommended that regular site inspections be undertaken to inspect the construction activities and works areas in order to ensure that the recommended mitigation measures are properly implemented.  Monitoring of the construction site effluent should be carried out in accordance with the WPCO license which is under the ambit of regional office (RO) of EPD.

Conclusion

Construction Phase

8.37            Water quality impacts from the land-based construction and demolition works can be controlled to acceptable levels by implementing the recommended mitigation measures.  No unacceptable water quality impacts would be expected from the land-based construction and demolition activities. Site inspections should be undertaken routinely to inspect the works areas in order to ensure the recommended mitigation measures are properly implemented.

Operation Phase

8.38            No effluent will be discharged from the Air Pollution Control equipment in the new crematorium as “dry” process will be adopted. Sewage generated by visitors and workers, as well as wastewater from cleaning activities will be connected to the sewerage system.  Sewerage impact assessment has been conducted for the Project. Assessment results indicated that the additional sewage / wastewater generated from the Project would not cause any adverse impacts to the existing sewerage systems.  Hence, adverse water quality impact is not expected.