1 INTRODUCTION

7.	WATER QUALITY
7.1	INTRODUCTION
7.1.1	The potential water quality impacts arising from the construction works for the proposed road developments have been assessed and are presented in the EIA Report. The majority of the construction works will be land-based, on existing reclamation, and thus direct impacts on marine water quality will not arise. Marine based construction works will only be required for the pile foundation works for the elevated section of Road D10 across the Eastern Drainage Channel. The EIA concluded that the identified water quality impacts could be controlled and reduced to within acceptable levels through effective mitigation. Monitoring of marine water quality during the construction phase was therefore not considered necessary.

7.1.2.

During the site inspections as described in Section 8 of this Manual, the ET shall pay special attention to the issues relating to water quality, and check whether the Contractor has followed the relevant contract specifications and the procedures specified under the laws of Hong Kong. Stringent control and audit will be necessary to ensure that effective water pollution control measures are being implemented. Site inspection should include regular checking of the proposed measures and records of maintenance services to ensure their proper functioning.

7.1.3

The following is a summary of the recommended water quality mitigation measures. The implementation schedule of mitigation measures is presented in Appendix C4.

7.2	MITIGATION MEASURES

	Construction run-off and drainage

7.2.1	The site practices outlined in ProPECC PN 1/94 "Construction Site Drainage" shall be followed as far as practicable in order to minimise surface runoff and the chance of erosion, and also to retain and reduce any suspended solids prior to discharge. These practices include the following items :

Provision of perimeter channels to intercept storm-runoff from outside the site. These shall be constructed in advance of site formation works and earthworks.

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. These facilities shall be properly and regularly maintained.

Careful programming of the works to minimise soil excavation works during rainy seasons.

Exposed soil surface shall be protected by paving as soon as possible to reduce the potential of soil erosion.

Temporary access roads shall be protected by crushed gravel and exposed slope surfaces shall be protected when rainstorms are likely.

Trench excavation shall be avoided in the wet season as far as practicable, and if necessary, these shall be excavated and backfilled in short sections.

Open stockpiles of construction materials on site shall be covered with tarpaulin or similar fabric during rainstorms.

7.2.2

All stormwater and slurry water discharge locations from the works site shall be located at a distance of over 100 m from the intake point for the TKO Bay WSD saltwater pumping station. Silt screens should be provided around the intake as a precautionary measure during construction works in the vicinity for Road D10. The disposal of slurry water will need to comply with the TM standards under the WPCO. During the construction works for the Road D10 crossing over the Eastern Drainage Channel, no waste nor wastewater should be permitted to be discharged into the Eastern Drainage Channel nor the waters of inner TKO Bay.

General Construction Activities

7.2.3

Debris and rubbish generated on-site shall be collected, handled and disposed of properly to avoid entering the nearby stormwater drains and open drainage channels. 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. Open storm water drains and culverts near the works areas shall be covered to block the entrance of large debris and refuse.

Sewage Effluent

7.2.4

Temporary sanitary facilities, such as portable chemical toilets, shall be employed on-site. A licensed contractor would be responsible for appropriate disposal and maintenance of these facilities

Remedial Measures for Road D10 Construction Adjacent to TKO Stage 1 Landfill at Area 77

7.2.5

Groundwater pumped out during foundation works for the construction of Road D10 shall not be permitted to be directly discharged into the Eastern Drainage Channel or into the coastal waters of TKO Bay. The groundwater may potentially be contaminated by leachate seepage from the TKO Stage 1 landfill and shall therefore be held in storage tanks at the works site. As EPD have advised that the leachate pre-treatment works at TKO Stage II/III landfill site does not have any spare capacity to treat contaminated groundwater from other sources, an identified option for the treatment and disposal of the collected groundwater is tankering of the groundwater to the TKO Preliminary Treatment Works (PTW) at Area 85. DSD have indicated that they have no objection to this proposed option of disposal of the collected groundwater to the TKOPTW provided that samples of groundwater are analyzed and the results submitted to DSD for approval and that the TKOPTW shall not be overloaded. The site investigation works at the detailed design stage of the Project will therefore include groundwater sampling and analysis to determine the composition of groundwater. The monitoring results of groundwater quality would be submitted to DSD for their approval.

7.2.6

A leachate monitoring and contingency plan should be developed and agreed with EPD before commencement of the construction phase. This plan should cover construction works at the Eastern Drainage Channel and the fringes of the TKO Stage 1 landfill. A copy of the plan should be submitted to EPD for approval together with the results of the detailed site investigation in respect of groundwater quality and leachate seepage potential at work sites. A tentative framework of the leachate monitoring and contingency plan is given below:

Procedures for collection and storage of groundwater pumped out during foundation works;

Monitoring of groundwater quality;

Review of monitoring data;

Proposal of suitable treatment and disposal method(s) of contaminated groundwater (should the groundwater quality be found to exceed the TM standard for discharge into foul sewers);

Site inspections of works areas;

Recommended remedial measures in event of groundwater spillage (see below).

7.2.7	During the foundation works for the construction of Road D10, the pumped out groundwater would be stored temporarily on site as the volume is anticipated to be small. Samples of groundwater would be taken from the storage tanks for laboratory measurement to determine the quality of the groundwater before tankering to the TKO PTW for treatment and disposal. The monitoring data would then be reviewed to determine if pre-treatment of the collected groundwater would be required to meet the TM on Effluent Discharge Standards prior to the groundwater being discharged to the TKO PTW. It is proposed that a packaged treatment unit be installed at the site should pre-treatment be required. All the required on-site pre-treatment of the collected groundwater should be implemented to the satisfaction of the Director of Environmental Protection prior to its discharge to the TKO PTW. It is recommended that daily inspections of the works areas be undertaken during the piling works to identify any contaminated groundwater seepage or ponding at the surface.
7.2.8	Remedial measures shall be implemented in the event of any contaminated groundwater spillage at the surface during the piling works. Spilled groundwater ponded on the surface shall be collected and held in the storage tanks at the site. The collected groundwater shall be disposed as described above. If the spill is small, it may be possible to cover the spillage using soil or sand as an adsorbent, and this waste material would then need to be properly disposed of to landfill.
7.2.9	Careful control shall be exercised during the construction phase to protect the existing facilities at the landfill from any damages resulting from construction activities, such as passive vent trench and monitoring wells DG5 and DG6.