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ASSESSMENT RESULT

The potential water quality impacts, the scale, extent and severity of potential net (i.e. unmitigated) construction, operation/restoration and aftercare impacts were evaluated, taking into account all potential cumulative effects including those of adjacent projects, with reference to the WPCO criteria.

Construction Phase

Construction Runoff		During the first year of the construction, works including site formation and construction of site office buildings, workshops, landfill gas and leachate treatment plant will be carried out. With good construction practices and appropriate mitigation measures, contamination construction runoff will be minimal and there will be no unacceptable water quality impacts to the receiving water bodies.
		There will be no wastewater generated by the demolition of existing facilities.
		The fuel and waste lubricant oil from the on-site maintenance of machinery and equipment will be collected by a licensed chemical waste collector.
		The runoff contained oil and grease will pass through the oil interceptor before being discharged off-site.
Wastewater Generated from Construction Activities		There will be no wastewater generated from tunnel excavation, except the recycle water and bentonite slurry required for the cooling of the cutter head during boring rocks and soil respectively. The recycle water will be conveyed to the sedimentation tanks for treatment and most of the treated water will be reused in the boring operations. Similarly, the bentonite slurry will be recirculated wherever practicable.
Wastewater Generated from Construction Activities		Only limited amount of excess water will be disposed to the surface drains in TKO Area 137 after proper treatment.
Sewage Generated from Workforce		Sewage will arise from the sanitary facilities provided for the on-site workforce. No sewage will be allowed to discharge directly into the surrounding water body without treatment. Therefore adverse impacts to water quality as a result of handling and disposal of sewage generated by the workforce are not expected.

Operation/Restoration Phase

Surface Water		The design of the Extension has comprehensively considered surface water management features to minimise the infiltration of surface water into the landfill and avoid seepage of leachate from the waste slopes into the surface water drainage system. A Drainage Impact Assessment (DIA) has concluded that the existing and planned surface water drainage infrastructure in TKO Area 137 and the surrounding area is adequate to convey surface water flows from the Extension and the surrounding catchments to the existing and planned discharge points.
Groundwater		With the provision of a containment facility incorporating a multi-layer composite liner system covering the entire land formation of the Extension Site, it is expected that the groundwater will be isolated from the Extension Site and therefore leachate generation from groundwater infiltration will be negligible. The result of a hydrogeological assessment indicates that the leachate seepage, in case of defeats in the basal lining system, is predicted to elevate the pollutants content in the groundwater and the coastal water by a negligible degree.
Leachate Management		The leachate management system will be considered as comprising a leachate collection system, a leachate extraction system and a leachate treatment system. Treated leachate will be disposed of to foul sewer leading to the TKO STW. The treatment effluent being disposed off will meet the discharge standards as stipulated in the Technical Memorandum and therefore will not cause adverse water quality impacts to the WSRs and the operations of the TKO STW.
Wastewater Generated from Workforce		The wastewater from the administrative office as well as laboratory and maintenance will be collected and treated together will leachate at the new Leachate Treatment Plant prior to disposal at the TKO STW. It is therefore anticipated that no adverse impacts on the surrounding aquatic environment will arise.

Aftercare Phase

Surface Water		The hydrogeological assessment concludes that whilst the cap remains intact and leachate control is maintained, there are no significant impacts on surface water quality.
Surface Water		With the implementation of mitigation measures, surface breakout is unlikely.
Groundwater		The likelihood of the leachate leakage to the groundwater system is considered to be very low.
		Since the down-gradient groundwater within the fill deposits is not generally used as a potable water supply, the severity of leachate leakage to groundwater is considered to be very low.
		The leachate leakage to the groundwater will be prevented by effective leachate management as well as full implementation of a monitoring programme.
Coastal Waters		The development of the Extension will not have adverse impact to the groundwater flow to Joss House Bay which is located to the east of the Extension Site.
Coastal Waters		The hydrogeological assessment concludes that whilst the cap remains intact and leachate control is maintained, there are no significant impacts on groundwater quality. Even in a very long term, assuming cap degradation and cessation of active leachate control, the prediction shows that the impacts on groundwater are slight, and groundwater discharges to Junk Bay would still remain within the effleunt discharge standards.

Cumulative Impact

It is not expected that there will be cumulative water quality impacts during the construction, operational/restoration and aftercare phases of the Extension.