3.1.1
Potential
environmental impacts associated with the construction and operation phases of
the proposed Project have been assessed in the EIA Report and are summarized in
the following sections.
3.2.1
Impacts
arising from the construction of the Project would primarily relate to dust
nuisance from excavation works, material handling and gaseous emissions from
the construction plant. With the
implementation of mitigation measures as stipulated in the Air Pollution
Control (Construction Dust) Regulation, no adverse air quality impact arising
from construction works of the Project would be expected.
3.3.1
Noise arising
from the construction activities of the proposed Project would have potential
impacts on the Noise Sensitive Receivers (NSRs) located in the vicinity of the
proposed work areas. Unmitigated
construction noise levels at representative NSRs were predicted to exceed the
EIAO-TM daytime construction noise criteria.
3.3.2
Sufficient
noise control measures would be required to mitigate the potential construction
noise impacts, such as adopting quiet construction plant, using
movable/temporary noise barriers, and implementing good site practices.
3.3.3
With the
recommended mitigation measures in place, the mitigated noise levels at most of
the NSRs would comply with the EIAO-TM noise criteria. A NSR located in very close proximity to the
works site of the proposed retaining wall at Pak Ngau Heung River outlet would
still be exposed to noise levels in exceedance of the EIAO-TM noise criterion,
despite all practicable direct noise mitigation measures exhaustively
employed. However, it is expected that
the residual impacts would be short-term and localized, and hence these
residual impacts were considered surmountable.
3.4.1
The key issue
in terms of water quality would be related to excavation works during the
construction stage. To minimize
potential impacts on water quality during the channel construction, special
working method controls and pollution control measures have been
recommended. In particular, excavation
works at each river channel would be carried out in dry condition using
containment measures within the channel.
The recommended water quality mitigation measures should be enforced by
the provision of specifications of pollution control measures into works
contracts.
3.4.2
Other
potential sources of water quality impact would comprise construction site
runoff and drainage; debris, refuse and liquid spillages from general
construction activities; and sewage effluents from the construction
workforce. Minimization of water
quality deterioration could be achieved through implementing adequate
mitigation measures, such as control measures on the runoff and drainage from
the works areas to minimize construction run-off. Proper site management and good housekeeping practices would also
be required to ensure that construction wastes and materials would not enter
the adjacent waterbodies or stormwater drains.
Sewage effluent arising from the construction workforce would also
require appropriate treatment through provision of portable toilets.
3.4.3
With the implementation of these recommended mitigation
measures, the construction works for the proposed drainage improvements
to the river channels in Mui Wo would not be anticipated to result in
unacceptable impacts on water quality.
Site inspections should be undertaken routinely to inspect the
construction activities and works areas in order to ensure the recommended
mitigation measures are properly implemented.
In addition, given that Pak Ngan Heung River, Tai Tei Tong River and Luk
Tei Tong River discharge to the three-river confluence at the head of the
Silver River, which ultimately discharges to Silver Mine Bay, monitoring of
downstream water quality within the rivers was recommended during the
construction phase.
3.5.1
The main
waste arising during the construction phase would be excavated material from
the river improvements works at Pak Ngan Heung River, Tai Tei Tong River, Luk
Tei Tong River and Luk Tei Tong Bypass Channel. The excavated material would
comprise soil, gravel and small rocks.
Excavated material with suitable characteristics should be be reused
on-site as far as practicable, e.g. fill material for backfilling of temporary
drainage channels or construction of river embankments. Surplus excavated material would require
disposal to a public filling area.
3.5.2
Other wastes
generated by the construction activities are likely to include general refuse
from the workforce, chemical wastes from plant and vehicle maintenance, as well
as construction and demolition material material from the demolition of
existing structures and site clearance.
Provided that these identified waste arisings are to be handled,
transported and disposed of using the recommended methods and good site
practices are to be strictly followed, adverse environmental impacts would not
be expected during the construction works.
The recommended mitigation measures should form the basis of the Waste
Management Plan to be developed by the Contractor.
3.6.1
A literature
review and ecological surveys covering the wet and dry seasons were undertaken
to establish the ecological profile of the assessment area.
3.6.2
Habitats
considered of low-moderate/moderate/moderate-high ecological value included Pak
Ngan Heung River, Tai Tei Tong River, Luk Tei Tong River and Luk Tei Tong (2)
River. Secondary woodland was found on the hillsides surrounding Mui Wo Valley
and Butterfly Hill, and Luk Tei Tong Marsh. Other habitats recorded such as
active agricultural land and villages were considered of lower ecological
value.
3.6.3
Several
faunal species of conservation interest were recorded in the assessment area,
comprising two fishes, one amphibian, and 16 birds. Of particular interest were
the fish species Flagtail (Kuhlia marginata) and Predaceous Chub (Parazacco spilurus). Avifauna of conservation interest
included White-shouldered Starling (Sturnus
sinensis), which have been recorded breeding adjacent to
the proposed Luk Tei Tong works area near the confluence, and various species
of avifauna recorded feeding at the lower reaches of the three rivers, and to a
lesser extent, Luk Tei Tong Marsh. The locally uncommon and declining Chinese Bullfrog
(Rana rugulosa) has been recorded from the Mui Wo area during
previous surveys, and was again recorded from the Assessment Area during
surveys conducted for this Study. Previous records of the locally protected Romer’s Tree
Frog (Philautus romeri) have also been
noted in the Mui Wo Area. Although not recorded during recent surveys, it is
possible this species still occurs in the assessment area.
3.6.4
The key
ecological impact resulting from the Project would be the direct impacts to
175m of Pak Ngan Heung River, 160m of Tai Tei Tong River, and 225m of Luk Tei
Tong River. The Project would also directly impact approximately 0.13ha of
moderate-high value secondary woodland, and 0.8ha of Luk Tei Tong Marsh.
Although the Marsh as a whole was considered of moderate-high ecological value,
areas directly affected by the proposed works were observed to be relatively
dry, dominated by weedy species, and not to be of particular conservation
interest.
3.6.5
Measures to
avoid, minimise and compensate for identified ecological impacts have been
recommended. These included measures to control sedimentation, the adoption of
ecological design for the drainage channels (such as the use of natural lining
for channel beds, rock-filled gabion to line the channel banks, and
compensatory planting along the channel banks), the provision of compensatory
marsh habitat in the design of Luk Tei Tong By-pass Channel, avoidance of works
close to White-shouldered Starlings (Sternus sinensis) during the main
breeding season of the Starling, and translocation of fish and amphibian
species of conservation interest
3.6.6
With the
implementation of the recommended mitigation measures, residual impacts from
the proposed drainage improvement works are expected to be ecologically
acceptable.
3.7.1
Based on
cultural heritage field surveys undertaken, key potential archaeological
impacts would be limited to small areas of minor excavation works associated
with the proposed 0.75m U-channel at Ling Tsui Tau Tsuen within the Chung Hau
Archaeological Site. Further investigation and a watching brief are recommended
before the construction work takes place.
3.7.2
There may be
potential vibration impact to the existing retaining wall and associated
structures of the Yuen Compound during the construction of rubble seawall and
retaining wall at the Luk Tei Tong River, requiring careful construction and
vibration monitoring.
3.8.1
An
environmental monitoring and audit programme for the Project will be
implemented to monitor construction noise, water quality, ecology and cultural
heritage. Details of the programme are
presented in a separate Environmental Monitoring and Audit Manual.