Annex A

Measures to Mitigate Water Quality Impacts from Site Run-off and Drainage During Construction

To mitigate the water quality impacts from site run-off and drainage during construction, the following shall be implemented:

1. Open stockpiles of construction materials (e.g. aggregates, sand and fill material) of more than 50 cu.m. shall be covered with tarpaulin or similar fabric during rainstorms. Measures shall be taken to prevent the washing away of construction materials, soil, silt or debris into any drainage system.

2. Manholes, including newly constructed ones, shall always be covered and sealed so as to prevent silt, construction materials or debris being washed into the drainage system and storm runoff being directed into foul sewers during the construction period. Discharge of surface runoff into foul sewers shall be prevented to avoid overloading the foul sewerage system.

3. Precautions/actions relating to rainstorms as follows:
   1. Precautions to be taken at any time of year when rainstorms are likely
      1. Silt removal facilities, channels and manholes should be maintained and the deposited silt and grit should be removed regularly.

      2. Temporarily exposed slope surfaces should be covered. eg. by tarpaulin.

      3. Temporary access roads should be protected by crushed stone or gravel.

      4. Intercepting channels should be provided (eg. along the crest/edge of excavation) to prevent storm runoff from washing across exposed soil surfaces.

      5. Trenches should be dug and backfilled in short sections. Measures should be taken to minimise the ingress of rainwater into trenches.

   2. Actions to be taken when a rainstorm is imminent or forecast
      1. Silt removal facilities, channels and manholes should be checked to ensure that they can function properly.

      2. Open stockpiles of construction materials (eg. aggregates, sand and fill materials) on site should be covered with tarpaulin or similar fabric.

      3. All temporary covers to slopes and stockpiles should be secured.

   3. Actions to be taken during or after rainstorms
      1. Silt removal facilities, channels and manholes should be checked and maintained to ensure satisfactory working conditions.

4. All vehicles and plant shall be cleaned before leaving a construction site to ensure no earth, mud, debris and the like is deposited by them on roads during the construction period. Wash-water arising from wheel washing bay provided at every site exit shall have sand and silt settled out and removed at least on a weekly basis to ensure the continued efficiency of the process.

5. If construction associated with the Project impinges upon any of the small watercourses between Yau Tong and Tiu Keng Leng, the water body shall be protected from site activities through screening or covering/culverting, and waste management procedures and drainage facilities.

6. At the start of site establishment, perimeter cut-off drains around the site and internal drainage works shall be constructed. All stormwater should be directed to silt removal facilities complying with the guidelines in Appendix A1 of the ProPECC PN 1/94 issued by the Director.

7. Construction works shall be programmed to minimize surface excavation works during the rainy season (April to September). All exposed earth shall be stabilized as soon as practicable after earthworks have been completed.

8. The overall slope of the site shall be kept to a minimum to reduce the erosive potential of surface water flows and all trafficked areas and access roads protected by coarse stone ballast.

9. Sediment tanks of sufficient capacity constructed from pre-formed individual cells of approximately 6 to 8 cubic metre capacity shall be used for settling wastewater prior to disposal during the construction period. Physical and chemical filters shall be added if refinement of the sedimentation process is required.

10. Silt contained in ground water and drilling water collected from tunneling operations shall be removed with properly designed silt removal facilities, such as the specified portable sedimentation tanks, prior to the discharge of waters into storm drains.

11. All drainage facilities and erosion and sediment control structures shall be regularly inspected and maintained to ensure proper and efficient operation at all times and particularly following rainstorms.

12. Measures shall be taken to minimise the ingress of site drainage into excavations. If the excavation of trenches in wet periods is necessary, they should be dug and backfilled in short sections. Water pumped out from trenches or foundation excavations shall be discharged into storm drains via silt removal facilities.

13. All fuel tanks and storage areas shall be provided with locks and sited on sealed areas within bunds of a capacity equal to 110% of the storage capacity of the largest tank.

14. Sewage shall be controlled by the use of portable chemical toilets or sewage holding tanks and regularly collected by reputable sewage collector for disposal.

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