8.1
The water
quality impact assessment in the EIA Report identified that no adverse impact would occur during the
construction and operation of the Project provided the
recommended mitigation measures were correctly implemented. It is recommended that regular site inspections (at least weekly) be
undertaken to inspect the construction activities and works areas in order to
ensure the recommended mitigation measures are properly implemented.
8.2
The site
inspection should be conducted at least weekly to inspect the construction
activities and works areas in order to ensure the recommended mitigation
measures are properly implemented.
Construction Phase
Construction Site Run-off and
Drainage
8.3 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. The following measures are recommended to protect water quality and sensitive uses of the coastal area (including coral sites identified in Section 5 of the EIA report), and when properly implemented should be sufficient to adequately control site discharges so as to avoid water quality impacts:
§
Before
commencing any site formation work, all sewer and drainage connections should
be sealed to prevent debris, soil, sand etc. from entering public
sewers/drains.
§
Temporary
ditches should be provided to facilitate run-off discharge into appropriate
watercourses, via appropriately sized/ designed silt retention pond or similar
structure. No site run-off should enter
artificial ponds. Cut-off ditches
should be provided for all major site clearance/ excavation works where soils
would be exposed so that instances of uncontrolled run-off from exposed areas
would be minimized. As well as
channels, earth/ concrete bunds and/ or sand bags, as appropriate, should be
deployed to direct surface run-off towards channels. Catchpits and perimeter channels should be constructed in advance
of relevant site formation works.
§
Boundaries
of earthworks should be marked and surrounded by dykes or embankments for flood
protection, as necessary.
§
Sand/silt
removal facilities such as sand/silt traps and sediment basins should 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 should be based on the guidelines provided in ProPECC PN 1/94. All drainage facilities and erosion and
sediment control structures should be inspected monthly and maintained to
ensure proper and efficient operation at all times and particularly during
rainstorms.
§
Silt removal
facilities, channels and manholes should be maintained and the deposited silt
and grit should be regularly removed, at the onset of and after each rainstorm
to ensure that these facilities are functioning properly at all times.
§
exposed soil
surfaces should be covered,
§
Water pumped
out from foundation excavations should be discharged into silt removal
facilities.
§
If
excavation cannot be avoided during rainy seasons, temporarily exposed
slope/soil surfaces should be covered by a tarpaulin or other means, as far as
practicable, and temporary access roads should be protected by crushed stone or
gravel, as excavation proceeds. Interceptiong channels should be provided (e.g.
along the crest/ edge of the excavation) to prevent storm runoff from washing
across exposed soil surfaces.
Arrangements should always be in place to ensure that adequate surface protection
measures can be safely carried out well before the arrival of a
rainstorm.. Other measures that need to
be implemented before, during and after rainstorms are summarized in ProPECC PN
1/94.
§
Exposed soil
areas should be minimized to reduce potential for increased siltation and
contamination of runoff.
§
Earthwork
final surfaces should be well compacted and subsequent permanent work or
surface protection should be immediately performed. Appropriate intercepting channels should be provided where
necessary. Rainwater pumped out from
trenches or excavations should be directed to silt removal facilities before
discharge.
§
Open
stockpiles of construction materials or construction wastes on-site of more
than 50m3 should be covered with tarpaulin or similar fabric during
rainstorms
8.4 In addition to the above measures, further precautionary measures for controlling potential water quality impact due to major excavation works at the Summit are required in order to safeguard the known coral sites of value at the headland during the construction phase, particularly during the rainy season as there is a risk that intense rainfall events may result in discharge of turbid drainage water. The contractor should implement the following mitigation measures:
§
Locate
the construction phase discharge point at the outlet of
the existing 1000 mm diameter storm water pipe at Tai Shue Wan.
§
Sand/ silt removal facilities with enhanced performance
should be employed for treatment of runoff from the major excavation at the
Summit. The performance of these
facilities would be enhanced with the use of flocculants to improve the
coagulation and sedimentation process for the treatment of wastewater.
§
To minimize the water quality impact during rainy seasons, a
silt curtain system should be used to enclose the construction phase discharge
point at Tai Shue Wan.
§
The contractor should set out and agree with EPD the
specific measures, and any additional measures, in a site run-off management
plan, before commencement of construction activities during the wet season.
General Construction Activities
·
Debris and
refuse generated on-site should be collected, handled and disposed of properly
to avoid entering any nearby water bodies and public drainage system. Stockpiles of cement and other construction
materials should be kept covered when not being used.
·
Oils and
fuels should only be used and stored in designated areas which have pollution
prevention facilities. To prevent
spillage of fuels and solvents to nearby water bodies and public drains, all
fuel tanks and storage areas should 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 should be
drained of rainwater after a rain event
Sewage from Construction Workforce
·
Temporary
sanitary facilities, such as portable chemical toilets, should be employed
on-site where necessary to handle sewage from the workforce. A licensed contractor would be responsible
for appropriate disposal of waste matter and maintenance of these facilities
Operation Phase
8.5 The following measures will be adopted to reduce potential water quality impacts:
· Ozone would be the primary disinfectant used in the marine life pools and aquariums. Chlorine would only be used as a back-up. When chlorine is used in pool water subject to discharge direct to sea, the discharge shall be less than 6,000 m3/ day and the total residual chlorine level in the effluent shall be less than 1 mg/L
· Mechanical cleaning of pools will be used to reduce the need to drain the pools for manual cleaning
· Filter backwash water will be discharged only to foul sewer after passing through an effluent holding tank.
· Sludge accumulating in effluent holding tanks will be pumped out and removed from site by a licensed contractor
· Discharges to public sewer or to the sea would need to comply with the requirements of the relevant effluent discharge license
· There will be no discharge of sewage or cooling water to sea
8.6 For the control of non-point source discharges, including run-off from landscaped areas that could contain residual pesticides, fertiliser or other such chemicals, the following measures will be adopted:
· Where possible, surface run-off will be collected into artificial ponds at the Park, to be re-used for irrigation water on landscaped areas
· Potentially toxic chemicals including pesticides would not be applied during heavy rainfall, or if heavy rainfall were to be forecast imminently
· Surface run-off will not be discharged direct to sea but will pass through trenches or catch pits containing loose soil or other porous media to act as a delay to the “first-flush” run-off and to provide a certain amount of additional adsorption capacity
·
Environmental friendly
fertilisers and pesticides would be selected where available in the market,
either consisting of natural products and/ or having a rapid degradation half
life of three days or less; chemicals would be selected that have a low
toxicity to non-target animals
8.7
Ocean Park already carried out routine
monitoring as part of normal operations.
Additional water quality impact
auditing and monitoring during operational phase would
not be necessary
8.8
The
implementation schedule for the recommended water quality mitigation measures
is presented in Appendix
B.