4.2.1
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.
4.3.1
The mitigation measures
recommended for the construction phase of the Project are summarised
below. The implementation schedule
of the recommended water quality mitigation measures is presented in Appendix
A.
Measures for Tuen Mun
River Channel
4.3.2
Mitigation measures
would be implemented to minimise the direct impacts to the nearby Tuen Mun
River Channel by controlling construction site runoff and drainage from the
proposed works area, thus, prevent any runoff and drainage water with high
levels of suspended solids from entering the River Channel. Site runoff would be directed towards
regularly cleaned and maintained sand traps, silt traps and where appropriate,
oil/grease separators to minimize risk of sedimentation and pollution to the
River Channel. Debris and rubbish
generated on-site would be collected, handled and disposed of properly. The stockpile or temporary storage area
and chemical waste storage area shall be located at least 30m away from Tuen Mun River Channel.
Construction Site
Run-off and Drainage
4.3.3
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, and also to retain and reduce any suspended solids prior to discharge.
These practices include, inter alia, the following items:
Ÿ
Sand/silt removal
facilities such as sand/silt traps or sediment basins should be provided to
remove sand/silt particles from runoff to meet the requirements of the TM
standard under the Water Pollution Control Ordinance (WPCO). The design of efficient silt removal
facilities should be based on the guidelines in Appendix A1 of ProPECC PN 1/94,
which states that the retention time for silt/sand traps should be 5 minutes
under maximum flow conditions. The
detailed design of the sand/silt traps shall be undertaken by the contractor
prior to the commencement of construction. 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;
Ÿ
Measures should be taken
to minimize the ingress of site drainage into excavations. Water pumped out
from foundation excavations should be discharged into storm drains via silt
removal facilities;
Ÿ
Careful programming of
the works to minimize surface excavations during the rainy season. If surface excavation works cannot be
avoided during the wet season (April to September), 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. Interception
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 summarised in ProPECC PN 1/94;
Ÿ
Exposed soil surface
shall be protected by paving as soon as possible to reduce the potential of
soil erosion; and
Ÿ
Open stockpiles of
construction materials or construction wastes on-site should be covered with
tarpaulin or similar fabric during rainstorms.
General Construction
Activities
4.3.4
Debris and refuse
generated on-site should be collected, handled and disposed of properly to
avoid entering any nearby storm water drain. Stockpiles of cement and other
construction materials should be kept covered when not being used.
4.3.5
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 any nearby storm water drain, 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 Effluent
4.3.6
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.