4                    WATER QUALITY

4.1              Introduction

4.1.1        The potential water quality impacts arising from the proposed construction works for the CWB & IECL have been assessed and are presented in the EIA Report.  As no reclamation will be undertaken directly for the CWB & IECL, the primary concern with regard to water quality will be the control of runoff during construction.  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 is therefore not considered necessary.

4.1.2        During the site inspections as described in Section 6 of this Manual, the ET Leader 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.

4.1.3        The following is a summary of the recommended water quality mitigation measures.  The implementation schedule for water pollution control is given in Appendix A.

4.2              Construction Phase

Site Runoff

4.2.1        All site construction runoff should be controlled and treated to prevent high levels of SS entering nearby water bodies.  The site practices outlined in ProPECC PN 1/94 “Construction Site Drainage” should be followed as far as practicable in order to minimise surface runoff and the chance of erosion, and also to retain and reduce any SS prior to discharge.  In particular:

·        temporary ditches should be provided to facilitate runoff discharge into the appropriate watercourses, via sedimentation traps / silt retention ponds;

·        permanent drainage channels should also incorporate sediment basins or traps, and baffles to enhance deposition rates;

·        sand / silt removal facilities such as sand traps, silt traps and sediment basins should be provided to remove sand / silt particles from run-off.  These facilities should be regularly cleaned and maintained by the Contractor.  The design of silt removal facilities shall be based on the guidelines in Appendix A1 of ProPECC PN 1/94;

·        collection of spent bentonite / other grouts in a separate slurry collection system for either cleaning and reuse or disposal to landfill should be implemented;

·        maintenance and plant areas should be bunded and constructed on a hard standing with the provision of sediment traps and petrol interceptors;

·        all drainage facilities must be adequate for the controlled release of storm flows;

·        careful programming of the works to minimise surface excavation works during the rainy season;

·        exposed soil areas should be minimised to reduce the potential for increased siltation and contamination of runoff;

·        all fuel tanks and storage areas shall be contained (bunded) such that spills are not allowed to gain access to water bodies;

·        open drainage channels and culverts adjacent to the site shall be kept safe and free from any debris and excavated materials arising from the works;

·        open stockpiles of construction materials (for examples, aggregates, sand and fill material) of more than 50 m3 should be covered with tarpaulin or similar fabric during rainstorms; and

·        as and when necessary, installation and regular maintenance of silt screen at seawater intakes in the vicinity of the site.

4.2.2    Precautions to be taken at any time of year when rainstorms are likely, actions to be taken when a rainstorm is imminent or forecast, and actions to be taken during or after rainstorms are summarised in Appendix A2 of ProPECC PN 1/94. 

Debris and Litter

4.2.3    In order to maintain water quality of an aesthetically acceptable condition, contractors should be required, under conditions of contract, to ensure that site management is optimised and that disposal of any solid materials, litter or wastes to marine waters does not occur.  Entrapment boom should be installed to avoid loss of floating refuse from construction site.  Regular scavenging shall be provided to collect both the trapped and escaped refuse.

Oils and Solvents

4.2.4    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.  All maintenance and plant areas together with chemical and chemical waste storage areas shall be provided with cover to avoid ingress of rainwater.  Waste chemical should be handled, treated and disposed of in accordance with the legislative requirements.

Sewage Effluent

4.2.5        Temporary sanitary facilities, such as portable chemical toilets, shall be provided on-site by a licensed contractor.  A licensed contractor shall be responsible for appropriate disposal and maintenance of these facilities.  There will be no new sewage outfall during construction and operation of the CWB & IECL.

4.3              Operational Phase

4.3.1    A surface water drainage system shall be provided to collect road runoff.  The following operation stage mitigation measures are recommended to ensure road runoff would comply with the Technical Memorandum, Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters under the Water Pollution Control Ordinance (WPCO):

·           The drainage from tunnel sections should be directed through petrol interceptors to remove oil and grease before being discharged to the nearby foul water manholes.

·           Petrol interceptors should be regularly cleaned and maintained in good working condition.

·           Road drainage should be provided with adequately designed silt trap so as to minimise discharge of silt runoff.

·           Oily contents of the petrol interceptors should be collected and transferred to an appropriate disposal facility.

4.3.1        Sewage arising from ancillary facilities of CWB & IECL (for example, car park, control room, ventilation and administration buildings and tunnel portals) shall be connected to public sewerage system.  Sufficient capacity in public sewerage shall be made available to the proposed facilities to avoid overflow.

4.3.2        The design of the operational stage mitigation measures should take into account the guidelines published in ProPECC PN 5/93 “Drainage Plans Subject to Comment by the EPD.”  All discharges into drainage or sewerage systems during the operation phase shall be licensed by the EPD under the WPCO.