TABLE OF CONTENTS
List of Tables
Table 4.1 USEPA Guidelines for Water Reuse (Unrestricted Access).......................................................... 8
Table 6.1 Summary of Potential Environmental Impacts and Mitigation Measures....................................... 14
List of Figures
1.1 Rainwater and Greywater Recycling in Tseung Kwan O (TKO) Area 86 Property Development, also known as TKO Town Lot 70.
Tseung Kwan O (TKO) Area 86
property development has a site area of about 33 hectares. The development is expected to house
21,500 flats in 50 residential towers, and will be home to a population of
58,000 people. It will also provide
a retail accommodation of about 50,000 m2 and comprehensive GIC
facilities including educational institutes, nurseries, and a community hall,
etc. The development site will be
split into 8 – 13 development packages from 2005 to 2014 of which design works
for Package 1 has started and is targeted for construction early 2006. The total landscaped area in the
development site will be about 55,000 m2, which includes the
In view of the extensive landscaping
planned in TKO Area 86, there will be significant water demand for landscaping
irrigation. Based on the current
planning, the total landscaping areas and corresponding daily irrigated water
demand are estimated to be 8 ha
and 400 m3/day1, respectively. The most significant demand for
irrigation water is the
1.4 Water sources in TKO Area 86 that can be recycled include grey water, rainwater and condensate from air-conditioning systems. Of these, grey water recycle is considered to be the most promising and can provide a steady source of treated effluent.
1.5 The recycled rainwater and greywater will be for beneficial uses such as landscape irrigation, street cleaning and water features. The recycle applications will undoubtedly enhance the image of TKO Area 86 development as an environmentally friendly community.
1.6 Mass Transit Railway Corporation Limited (MTRCL)
1.7 The proposed rainwater and greywater recycling system will serve the whole TKO Area 86 Property Development and the system consists of:
(i) A greywater collection system from four residential towers to the Greywater Treatment Plant;
(ii) A rainwater collection system from the selected landscaped areas or podium of the Development;
(iii) A condensate water collection system from the Main Shopping Mall air conditioning system;
(iv) A grey water treatment plant capable of treating greywater to a standard acceptable to Government;
(v) A storage tank for treated effluent; and
(vi) A pressurized distribution system for distributing the treated effluent to all development packages in TKO Town Lot 70 for irrigation, street cleaning and topping up of water features.
1.8 A separate sewerage system is recommended to convey the greywater from 4 residential towers of TKO Area 86 Property Development to the greywater treatment plant. The size of the proposed sewer will be designed to cater for the peak flows of the grey water collection system. The proposed layout of the greywater collection system is shown in . The greywater pipeline will be routed across the proposed Estate Road R6 and directed to the proposed equalization tank and then to the greywater treatment plant.
The proposed greywater treatment
plant will be located near the roundabout of the proposed Estate Road R6, R1
and R2. All the treatment
facilities of the grey water treatment plant will be enclosed by the proposed
car park underneath the
1.10 The internal dimension of the proposed greywater treatment plant is approximately 17.6m (W) x 19.3m(L) x 7.2m(H) and its preliminary layout is shown in . This will be subject to review to suit the detail design.
1.11 The grey water treatment plant will consist of one equalization tank, two mechanical raked bar screens, an aerobic bioreactor system, a sludge holding tank, a chlorination system, an effluent storage tank, and associated pipeworks, fitting and valves for grey water treatment system. The major process flow instrumentation is indicated in . This will be subject to review to suit the detail design. The whole plant operation will be fully automatic under a continuous control and monitoring scheme.
1.12 Since the suspended solids level and organic level of condensate collected from air-conditioning units at shopping center and rainwater from the landscape areas or podium are expected to low, the condensate collected from air-conditioning units at shopping centre and rainwater from the landscape areas or podium will therefore be diverted to the chlorination tank of the treatment plant. The disinfected effluent including treated grey water, condensate from air conditioning systems and rainwater from the landscape areas or podium will be mixed and stored in the effluent storage tank. The disinfected effluent will be used for landscape irrigation, street cleaning and water features in whole TKO Area 86.
1.13 The total design flow for the system is estimated to be about 440 m3/day1, Based on the predictions for annual consumption, the components of the water sources would consist of 85%1 of grey water, 5%1 from condensate, 4%1 from rainwater and 10%1 from fresh water. .
1.14 The project involves the reuse of treated sewage effluent from a treatment plant and therefore is classified as a Designated Project (DP) under Schedule 2 Part I – Category F.4 of the Environmental Impact Assessment Ordinance (EIAO) Cap. 499. An Environmental Permit is required during construction and operation of the Project.
1.15 The contact person for this Project is shown below:
Mr. Willie Tse
MTR Corporation Limited
MTR Tower, Telford Plaza, 33 Wai Yip Street, Kowloon Bay, Hong Kong.
Tel: 2993 3260
2.1 Maunsell Consultant Asia Ltd. will carry out preliminary design of the proposed rainwater and greywater recycling system and MTRCL will maintain the system. Most equipment to be used at the greywater treatment plant would be pre-fabricated at factory, only installation assembly would be carried on-site. Major construction activities would be pipeline laying for collection system and effluent distribution system. shows the layout of the treated effluent distribution system. Contractors will be commissioned by MTRCL to construct the Project in accordance with both the statutory standards and other guidelines under the supervision of MTRCL staff. The construction works for the Project will be planned and constructed under environmental friendly manner to minimize construction nuisance.
2.2 Key target dates for the Project are:
Finalise Design Requirement – 1st Quarter 2006
Award Contract – 1st Quarter 2007
Project Construction Commencement – 1st Quarter 2007
Completion of the Project and operation – 1st Quarter 2009
2.3 The construction of this Project is scheduled to commence in the 1st Quarter 2007 for completion in the 1st Quarter 2009. Construction activities for MTRC Area 86 Property Development Package 1, 2 & 3 would also be carried out concurrently within this period. Given that limited works of this Project, it is not expected to generate significant cumulative construction impact.
3.1 TKO Area 86 is just north of the TKO Industrial Estate. It will be developed by the MTRCL as a comprehensive development area to include the depot and a station for the MTR Tseung Kwan O Extension (TKE). The TKO Industrial Estate is more than 1km away from the proposed site.
3.2 During construction phase of the Project, there is no air and noise sensitive receivers identified within 300m of the proposed rainwater and greywater recycle system. During operation phase of the Project, the nearest air & noise sensitive receivers (NSR) identified in the vicinity of the proposed greywater treatment system would be residential blocks of Package 1 & 3 of TKO Area 86 Property Development.
The nearest water quality
sensitive receiver will be
3.4 No ecological sensitive receivers are identified within the Project site.
4.1 The major potential air quality impact during the construction phase of the Project would be dust emission from excavation and filling activities for pipe laying works. Temporary stockpiling of excavated material on site would generate dust especially during dry season but minor localised air quality nuisance is expected. Most of the equipment to be used at greywater treatment plant would be pre-fabricated at factory, only installation and assembly would be carried out on site. Given that the small scale of construction works and limited area for excavation, minimal dust impacts would be expected.
4.2 Good site practices are recommended in Section 5.1 to further minimise the dust impact.
4.3 Construction noise would be generated mainly by activities including excavation, pipe installation and filling works. All major equipment for greywater treatment plant would be skid mounted and pre-fabricated. Due to limited scale of the above construction works, adverse construction noise impact would not be anticipated and also there was no NSR identified in the vicinity of the Project site during construction period.
4.4 Water quality impacts of the Project would be associated with site runoff and wastewater and sewage generated from construction activities. With the implementation of good site practices and recommended mitigation measures in Section 5, adverse water quality impact during the construction phase would not be anticipated.
4.5 Wastes that would likely be generated during the construction phase include general refuse such as packaging and container wastes, workforce waste, construction wastes such as excavated material and chemical wastes including oil and lubricant from construction plant.
4.6 With the implementation of good site practices and recommended mitigation measures in Section 5, the potential environmental impacts resulting from the storage, handling and transportation of general site wastes would be minimal.
4.7 No habitat with ecological values was identified within the site for the grey water treatment facilities and the associated pipeline. No adverse ecological impact is therefore anticipated for the Project.
4.8 No tree removal activities are anticipated under this Project.
4.9 The implementation of the rainwater and greywater recycling system would reduce the use of potable water. It is anticipated that approximately 400 m3/day would be saved each day due to the proposed system.
The collected grey water will
further undergo treatment and disinfection by the treatment plant at the
proposed site. The nearest air sensitive
receiver would be a residential block of Package 3 which would be located at
the height of +29.9 mPD and
4.11 The greywater treatment facilities would be an accommodated in a fully enclosed compartment under a podium, therefore no adverse noise impact would be anticipated during the operational stage.
The recycling treatment plant
would be constructed with a design capacity of 440m3/d. The treated
effluent would then be used for landscape irrigation (including
4.13 The rainwater collected from landscape areas or podium will initially be disinfected and filtered off to get rid of impurities. In addition to solid removal and disinfection, organic removal would be required in some situations. High efficiency of organic removal could be achieved in the aerobic bioreactor system biologically. The prevention of the potential Legionnaires’ disease from recycling condensate is being addressed in Section 5. In case of high infection disease (such as SARS and Avian Flu) outbreaks, the recycling system would be halted during that period.
There are specific water
quality standards for landscape irrigation applications in
4.15 The recycled rainwater and grey water will be used for landscape irrigation, street cleaning and water features, of which direct human contact is possible. The water reuse system is design on the basis of USEPA Guidelines for Water Reuse (2004) and will be in compliance with Class 1 reliability requirement. As per USEPA Guidelines, recycled water that meets that standard provided will not cause any hazard to the health of the public and staff. Regular sampling program on the effluent of water recycling system would also be set up for closely monitoring the quality of recycled water and determine whether it is comply with the standards. The measures to prevent Legionnaires’ disease will also be adopted (described in Section 5), the impacts to human health and hygiene are considered minimal.
Type of Use
Water Quality Standard
(1) pH: 6-9
(2) BOD: 10mg/l
(3) Turbidity: 2NTU
(4) No detectable Total coliform/100ml
(5) Cl2 residual: 1mg/l
4.16 Negligible amount of sludge would be produced from the aerobic bioreactor process. The licensed desludging contractor will regularly collect the sludge by desludging tanker and deliver the sludge to nearby sewage treatment plant for further treatment.
4.17 No ecological impact would be expected during operation of the Project.
The only chemicals that would be
stored on site are sodium hypochlorite solution required for the chlorination
process. Sodium hypochlorite solution is a poisonous substance classified as
Category 4 dangerous goods item. The solution can be transported to the site in
liquid and would be stored in tanks fabricated from fiberglass or rubber lined
steel. Fire Services Department’s requirements for bulk storage would be
properly observed. Under the current design, about 15 –
5.1 In order to minimise the air quality impact during the construction of the Project, the dust mitigation measures stipulated in the Air Pollution Control (Construction Dust) Regulation should be implemented. Major control measures relevant to this Project are listed below:
Installation of temporary fencing board;
Frequent watering for particularly dust static construction areas;
Dusty materials stockpiled on site should be covered;
Tarpaulin covering the load of dusty materials carried by vehicle transported to, from and between site location;
Where feasible, routing of vehicles and positioning of construction plant should be at the maximum possible separation distance from air quality sensitive receivers.
5.2 No adverse noise impact during the construction phase would be anticipated from the greywater treatment plant with the implementation of good site practices described in .
5.3 The practices outlined in ProPECC PN 1/94 Construction Site Drainage will be adopted during the construction of the Project where appropriate. Water quality impact would be minimised during construction stage with the adoption of good site arrangement and management practices. Clauses will be incorporated into the contract document requiring the contractor to comply with the WPCO and its subsidiary regulations and the relevant measures recommended in the ProPECC PN 1/94. In view of the small scale of this Project, adverse water quality impact during the construction phase would not be anticipated. The major water pollution control measures are listed as followed.
Construction Site Runoff and Drainage
Sand/silt removal facilities such as sand traps, silt traps and sediment basins shall be provided to remove sand/silt particles from runoff to meet the requirements of the Technical Memorandum standard under the Water Pollution Control Ordinance. The design of silt removal facilities shall be based on the guidelines provided in ProPECC PN 1/94. All facilities shall be inspected monthly and maintained to ensure proper and efficient operation at all times and particularly during rainstorms.
Water pumped out from foundation excavations shall be discharged into silt removal facilities.
Open stockpiles of construction materials or construction wastes on-site of more than 50m3 shall be covered with tarpaulin or similar fabric during rainstorms.
General Construction Activities
Debris and rubbish generated on-site shall be collected, handled and disposed of properly to avoid entering the nearby watercourses and storm water drains. Stockpiles of cement and other construction materials shall be kept covered when not being used.
Oils and fuels shall only be used and stored in designated areas which have pollution prevention facilities. All fuel tanks and storage areas shall 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 shall be drained of rainwater after a rain event.
Sewage from Construction Workforce
Temporary sanitary facilities, such as portable chemical toilets, shall be employed on-site. A licensed contractor shall be responsible for appropriate disposal and maintenance of these facilities.
5.4 Most of the excavated material generated from the Project could be reused/backfilled on-site. It is anticipated that only a small amount of excavated spoil will require off-site disposal. In order to monitor the disposal of construction material and solid wastes at public filling areas and landfills, and to control fly-tipping, a trip-ticket system as described in WBTC No. 5/99 and 5/99A should be included as one of the contractual requirements and implemented by the contractor. Pollution control clauses as described in will be incorporated into the contract documents requiring the contractors to comply with Waste Control Ordinance and its subsidiary regulations as well as good waste management practices. In view of the small scale of the Project, no adverse waste impact is anticipated.
5.5 No adverse ecological impact was identified during the construction stage and no ecological mitigation measure is therefore required.
5.6 No adverse water quality impact would be anticipated from the Project. The Project has in fact advantage of decreasing wastewater discharges and thus reducing pollution loading to the environment, and reducing fresh water demand for water-featured activities in TKO Area 86.
5.7 As Legionnaires’ disease is a concern from recycling condensate, specific preventive steps to avoid water conditions that allow the organism to grow to high levels include the following:
Regularly maintain and clean the treated effluent storage tank to prevent growth of Legionella. This should include twice-yearly cleaning and periodic use of sodium hypochlorite or other effective biocide, such as chloramines.
Avoid conditions that allow water to stagnate. Frequent flushing of unused water lines will help alleviate stagnation.
5.8 In TKO Area 86, condensate from shopping centre will be conveyed to storage tanks via pipelines. The water in the storage tanks would not be stored longer than one week. Chlorine disinfectant would be dosed in the storage tanks for maintaining the chlorine residual as required in USEPA Guidelines. Therefore, the recycled water to be used, which may be in direct contact with human, will be disinfected. The Legionnaires’ disease would be inhibited under this application.
In order to ensure the
performance of disinfection process, a monitoring programme will be implemented
in the operation phase. Sampling
and subsequent laboratory analyses will be carried out at a monthly basis for
the recycled water stored in the storage tank. In addition, measures will be
implemented to prevent cross contamination with Water Supplies Department’s
potable water distribution system.
For example, smaller pipe size or different pipe type would be applied
for reclaimed water distribution system.
This measure is commonly adopted to avoid cross connection of fresh
water and salt water mains in
5.10 To minimize human contact with the recycled water, signage of “Recycled Water – Do Not Drink” shall be provided and generation of aerosols of recycled water would be minimized. If spray irrigation were employed, suitable precautionary measures would be applied to prevent the public from making direct contact with the spray. This can be achieved either by spraying at odd hours only and/or fencing off/excluding the public from entering the irrigation spot during spraying. Spray irrigation would also be located to avoid getting contact with air conditioners, fan intake points and area where food or drink is processed for consumption. Water features using treated effluent will not be restricted by provision of adequate buffer or barriers.
In case there are any other
unexpected emergency situations for the greywater treatment plant or high
infection diseases (SARS and Avian Flu) out-break in
5.12 Chlorination tank will be constructed in the grey water treatment plant. A deodorization system will be provided for the greywater treatment plant. An odour filter / activated carbon adsorption filter will be connected to the exhaust fan of the system. The discharge location will be designed in such way as not to cause any nuisance to the nearby residents / passers-by.
5.13 No mitigation measure would be required during the operation phase.
5.14 Sewage sludge generated from the greywater treatment plant will follow the current general practice of mechanically dewatered at individual treatment works and taken to landfills for final disposal.
5.15 No adverse ecological impact would be identified during the operational stage and no mitigation measure is therefore required.
5.16 No hazard impact was identified during the operational stage and no mitigation measure is therefore required.
5.17 The duration of construction of the Project is expected to be completed in two years. In view of the small scale of construction work, no residual impacts on air quality, noise, water quality, waste and ecology would be predicted during construction phase with the implementation of mitigation measures described above.
5.18 During operation of the Project, no unacceptable environmental impacts including air quality, noise, water quality, wastes, ecology and hazard to life are identified.
6.1 The potential environmental impacts and the proposed mitigation measures to be incorporated into the design and construction contract of the proposed rainwater and greywater recycling system are summarised in Table 6.1.
Potential Environmental Impact
Minor dust nuisance
Control by contract specifications
Minor noise impact
Control by contract specifications
Minor waste impact
Control by contract specifications
No adverse impact is identified; no mitigation measure is required
Impact on natural resources
Beneficial impact; no mitigation is required.
Negligible odour impact from grey water treatment plant
A deodorization system provided, and the grey water
treatment plant and chlorination tank will be enclosed by the proposed car
park underneath the
Negligible operation noise impact from grey water treatment plant
No adverse noise impact is identified, mitigation measure is not required.
Impact on water quality
Unexpected emergency situation in recycling system
or high infection diseases outbreaks in
Mitigation measures to avoid Legionnaires’ disease
Mitigation measures to minimize human direct contact to the recycled water
No adverse impact is identified; no mitigation measure is required.
No adverse impact is identified
No adverse impact is identified; no mitigation measure is required.
6.2 With proper implementation of the recommended environmental mitigation measures that will be incorporated into the design and construction contracts of the proposed Works, insurmountable environmental impact during the construction and operational stages of the proposed Project is not expected. An implementation schedule of recommended environmental protection measures is shown in .
6.3 To conclude, rainwater and greywater recycling has the advantage of having beneficial uses of the treated effluent, decreasing wastewater discharges and thereby reducing pollution loading to the environment and reducing the demand on fresh water.
 The exact demand would be refined in conjunction with the landscape design at the detailed design stage.
 Grey water is defined as the water and solids from household fixtures and water-using appliances excluding the water and solids from toilets. The grey water sources include automatic clothes washer, automatic dishwasher, bath and shower and sinks (including kitchen).
 The public will not be accessible to the water features. Workers maintaining the water features will be aware of the water source and will apply necessary precautionary measures (e.g. all workers should be informed about the recycled water which is not designed for drinking).
 Table in Regulation 92 of Dangerous Goods (General) Regulations refers.