16.
Conclusion and recommendations
16.1
Introduction
16.1.1
The surface runoff falling within the northern
catchments of
16.1.2
16.1.3
The EIA report has provided an assessment of the
potential environmental impacts associated with the construction and operation
of the Project. Study has been
undertaken in accordance with EIAO-TM and the Study Brief. The Implementation Schedules of the
recommendations are present in Appendix J to this report. The principal findings of this Report
are summarised in the following sections.
16.2
Water Quality
Construction
Phase
16.2.1
During the construction phase, it was determined that
minor and short term impacts to water quality could arise directly from
land-based construction works.
These works relate to excavation of drainage tunnel and construction of
intake structures, construction of the stilling basin at the Western Portal, the
construction of a temporary pier at the Western Portal and the placement of
rock armour units on the existing seabed.
No direct construction runoff is expected. Impact may result from the surface runoff
and sewage from on-site construction workers. The impacts could be controlled to
comply with WPCO standards by implementing the recommended mitigation measures
which would provide a series of good site management options to minimise the
impact of stormwater runoff. For
the construction of stilling basin, temporary pier and armor rock panel at the
outfall of the Western Portal, adverse impact on water quality after
implementation of preventive measures is not expected.
Operation Phase
16.2.2
An assessment of water quality impact due to the
operation of the Project was made using the Delft3D-Flow and Delft3D-PART models. With these quantitative modelling tools,
impacts were assessed for different rainstorm and tide level scenarios during
the wet season. Discharge at the western
portal outfall will only occur during rainstorm events. The modelling results
indicate that the predicted concentrations of SS, E. coli and fresh water salinity would
satisfy the Water Quality Objectives (WQOs)/ambient water quality for 1 in 2
and 1 in 50 years rain storm events for all identified ecological sensitive
sites (corals) and fish culture zones.
16.2.3
The sediment plume during the operation phase is very
narrow and localized along the western coast of
16.3
Noise
16.3.1
Representative noise sensitive receivers (NSRs)
(Airborne and Structural borne) were identified. Construction noise impacts from the
construction activities including the operation of TBM were identified as key
environmental issues for this Project.
The potential noise impact arising form the Project have been assessed
and evaluated.
16.3.2
During the construction phase, the unmitigated
airborne noise level at most of the NSRs would experience noise level exceeding
noise criteria stated in the EIAO-TM.
To alleviate the noise impact, noise mitigation measures including the
adoption of good site practices, quieter equipment and restriction on the
number of equipment operating as well as other possible mitigation measures
including erecting of semi or full noise screening structure around work sites,
pre-splitting and followed by chemical blasting instead of mechanical blasting
method are recommended. The impacts
of structural borne noise due to the operation of tunnel boring machine and
drilling/blasting activities for the construction of drainage tunnel/adits have
been examined. Mitigation measures are
required at for tunnel construction near Western Portal and Eastern Portal and
the adit construction with vertical shaft W3 by restricting the operation hours
of the TBM or blasting activities at those identified NSRs.
16.3.3
With the recommended mitigation measures, the
mitigated noise levels at identified NSRs would comply with the daytime
construction noise standard as set out in the EIAO-TM. In addition, an EM&A programme would
be implemented to monitor the construction noise impact.
16.3.4
No exceedance of the noise criteria was predicted
except short-term exceedances at some of the several intake shafts. It is expected the residual impacts
would be transient and localized. By
considering that the construction of the proposed drainage tunnel is unavoidable
as it is an integral element of this Project, the short duration of the
sensitive receivers experiencing the residual impacts is considered acceptable.
16.4
Ecology
Terrestrial
16.4.1
The
proposed construction would cause a permanent loss of 0.16 ha of woodland, 0.70
ha of urbanised/disturbed, 0.04 ha of shrubland habitats and 85 m of natural
stream. The temporary habitat loss would include 0.53 ha of woodland, 1.56 ha of
urbanised/disturbed land, 0.11 ha of
shrubland, 91 m of natural stream, and 384 m of nullah.
16.4.2
Both the Western Portal and the Eastern Portal
would encroach upon urbanised/disturbed habitat but the Eastern Portal would
also affect a stand of woodland. Among
the 35 intake points, 18 would encroach only one type of land habitat,
i.e. urbanised/disturbed
habitat. 16 intake points would encroach woodland habitats which however are mainly
located along the roads. There are also 2 intake points which would encroach shrubland habitat (including one from the 16 intake points affecting
woodland, i.e. this intake point would encroach both shrubland and woodland
habitats). Impacts of loss of urbanised/disturbed
and shrubland habitat are considered insignificant due to limited ecological values of these
habitats. Due to the limited size
of woodland to be permanently lost, and the temporary nature of the impact on
most of the woodland to be affected, the construction impact on terrestrial habitats is ranked as minor. However, due to the ecological value of
woodland habitat, mitigation is required to compensate the impact of woodland
loss. Compensatory planting of about 1.5: 1 ratio would be provided.
16.4.3
The
loss of stream habitat is limited in the present project (91m temporary loss in
total and 85m permanent loss in total). The majority of the
permanent loss would come from the modification of a section of stream channel
immediately upstream to the Eastern Portal. No species of conservation
importance/concern was found at the Eastern Portal stream, given its
significant proportion in the stream habitat loss, the impact of stream habitat
loss is ranked as minor to moderate.
Notwithstanding the above, low flow channel is provided at Eastern
Portal to provide living space within the modified section of the stream
courses for aquatic communities to develop. Step chute in the form of a series of
descending water pools is also provided to avoid isolating the aquatic fauna in
the channelised section from natural habitats.
16.4.4
Other permanently lost sections of streams are scattered among various
intake locations and all are close to traffic roads, residential buildings, or
existing drainage facilities. Compensation of these scattered stream habitat losses is thus not required.
Marine
Ecology
16.4.5
The
construction and operation of the Project would cause subtidal seabed loss and
require replacement of artificial intertidal habitat by newly constructed
portal. The impact is considered minor as the affected area is small and not
colonized by coral. The identified marine benthic communities are also not of
conservation concern. The
assessment also conclude that the Project will has no significant impacts on
Chinese White Dolphin and Finless Porpoise, as their range lies in the west and
south of the project area respectively. The impacts to the marine water quality
due to change in water quality by the operation discharge are limited. None of the recognized site of marine
conservation concern would be affected. A well-planned program of site
practices should be able to maintain the impacts to acceptable level.
16.5
Fisheries
16.5.1
The construction
of the temporary berthing point, permanent outfall and stilling basin will
result in some loss of fishing ground (subtidal muddy bottom habitat). However, the size of the loss is small
and the fisheries importance of the area is low. This loss is not expected to
have a significant negative impact on the capture fisheries. Impacts on fishing ground loss are acceptable.
16.5.2
No
residual impacts on the Fish Culture Zones (FCZ) are predicted as there are no
overlaps between the area of waters affected during the operation phase and the
FCZs.
16.5.3
The
water quality assessment results indicate that the operation phase effluent
from the drainage tunnel would have only limited and localized impacts on
marine water quality. Impacts on
fisheries resources are not anticipated.
16.6
Waste Management
16.6.1
The construction work will involve site formation and
drainage tunnel excavation which will necessitate the removal of spoil. The major source of waste material will
be from the tunnelling operation, from which a total of 522,040 m³ will be
excavated. The rate of generation is
estimated to be around 500 m³ per day at each portal. Waste will be removed form the temporary
stockpile areas at both Portals, after treatment, and disposed at a designated
Government facility. Only small
quantities can be used to backfill for this Project.
16.6.2
Other waste generated by construction works would
include workforce wastes, maintenance and chemical wastes. Materials which can be reused should be
separated from those which require disposal and appropriate facilities provided
on site to maintain a clean and tidy site.
Recycling should be practiced wherever possible. Provided that the identified waste
arising are handled, transported and disposed of using approved methods and
that the recommended good site practices are adhered to, adverse environmental
impacts would not be expected during construction works.
16.6.3
The recommended mitigation measures should form the
basis of the site Waste Management Plan to be developed by the Contractor at
the commencement of the construction phase.
16.7
Air Quality
16.7.1
Potential impacts on air quality during the
construction of drainage tunnel were shown to be minimal due to excavated spoil
produced from both portals will be transported by enclosed conveyor to a
temporary stockpiling area for storage or stored at the barge (or temporary
stockpiling area) for Eastern and Western Portals respectively. Stockpiling of excavated spoil will be
regularly removed by lorry and barge.
For the construction of intakes, most of the excavated spoil will be
dropped down to the intake shafts, then collected and transport to either Portals
for removal (reverse boring method).
No adverse construction dust impact would be expected at all ASRs in the
vicinity of the study area.
16.7.2
With the implementation of mitigation measures
specified in the Air Pollution Control
(Control Dust) Regulation and inclusion of good site practices, dust
nuisance at ASRs is not expected.
An EM&A programme for the construction phase will be required to ensure
that the dust criteria are satisfied at the ASRs.
16.7.3
No unacceptable air quality impact during the
operation phase is predicted and expected.
16.8
Cultural Heritage
16.8.1
A comprehensive baseline review and site survey of the
Study Area was carried out to determine the presence of historical buildings,
potential existence of prehistoric or historic occupation on, or close, to the
drainage tunnel alignment.
16.8.2
A number of built heritage resources were identified
in the Cultural Heritage Review.
Most of them are located more than 50m from works areas and no impacts
will result. A total of 4 graded historical buildings
were found to be located within 50 m of proposed works areas associated with
the project.
16.8.3
Based
on the Literature Review, AMO files have been used as a reference guide for
interpretation and analysis of Terrestrial and Marine Archaeology. No known archaeological sites along the
proposed alignment or in the vicinity of any of the proposed works areas. For marine archaeology, no known marine
archaeological site was found in the offshore areas at Western Portal near Pok
Fu Lam.
16.8.4
The
proposed works will not directly impact any of the buildings. However, indirect
impacts may result at Haw Par Mansions, the Wall and Gate of the former Haw Par
Mansion Gardens and at the former Explosives Magazine. Recommendations have
been made to mitigate these potential impacts including condition survey to the
buildings, provision of buffer zone between the buildings and the construction
site, erection of protective fencing and screening, and conduction of monitoring
during construction works. All mitigation should be undertaken by the project
contractors and be in place before works commences.
16.8.5
No
impacts on historical buildings are predicted during operation phase of the
drainage tunnel.
16.9
Landscape and
Visual Assessment
16.9.1
In general, the Project will cause slight to moderate
adverse visual impact in the construction phase and negligible to slight
adverse visual impact in operation phase before the implementation of mitigation
measures.
16.9.2
Eastern
Tunnel Portal is proposed near the existing carpark to the north of Haw Par
Mansion. VSRs identified are
motorists and pedestrians along Tai Hang Road and the occupants in the True Light
Middle School of Hong Kong. Their
sensitivity is medium to low. Western
Tunnel Portal is proposed at the south west coastal line of Hong Kong
Island. VSRs identified are
motorists along Cyberport Road, workers in the Preliminary Treatment Works
Complex and travelers in ferry at a distance to the south of site. Their sensitivity is low.
16.9.3
There
are 35 intake structures proposed along the main drainage tunnel from
16.9.4
The
major source of visual impact is due to the permanent alienation of landscape
areas for the provision of intake structures. Since there will be no major above ground
structures proposed within boundary of the intake structure, the magnitude of
change in visual quality on the existing VSRs is generally considered small.
16.9.5
Major source of visual impact during the
construction phase of the project are due to the permanent loss of existing
vegetation and temporary construction works. During the operation phase of the
project, visual impacts are due to the change in existing visual quality (permanent
alienation of landscape areas and permanent
erection of the above ground structures).
After implementation of mitigation measures, the residual visual
impacts during the construction and operation phase will be reduced to
negligible to slight.
16.10
Hazard to Life
16.10.1
There will be no overnight
storage of explosives for this project. Transportation of explosives to site
for the
construction of adit will be undertaken on a daily basis. The contractor is required to destroy
any unused explosives before nightfall.
With the implementation of rigorous safety measures
for the blasting operation, adverse impact to the nearby sensitive receivers adjacent to the blasting locations
will not be expected.
16.11
Environmental
Monitoring and Audit (EM&A)
16.11.1
Environmental monitoring and
audit requirements for the construction phase are described in terms of the
monitoring locations, period of time, frequency and standards against which the
monitoring results should be compared to determine compliance. The monitoring programme covers aspects
on underground water levels, air, noise and water quality. Site audit
would be carried out to check its compliances of the air, noise, water quality,
waste management, ecology, fisheries, landscape and visual and cultural
heritage mitigation measures during the construction phase. During the
initial Operation phase, ground water monitoring will be carried out for a year
to confirm the steadiness of the ground water table monitoring in respect of
ground water monitoring is only required.
An Implementation Schedule of the relevant mitigation measures for the
works is included in the EIA report.
Details of the programme are presented in a separate
Environmental Monitoring and Audit Manual.
16.11.2
The use of real time reporting
of monitoring data on internet website for data record will be used during
construction phase which would facilitate the rapid and effective communication
with local residents/sensitive receivers nearby to resolve any problems in
respect of noise impact to the project.
16.12
Overall Conclusions
16.12.1
The
EIA has critically assessed the overall acceptability of any environmental
impacts likely to arise as a result of the construction and operation of the
proposed drainage tunnel. Where
necessary and practicable, the EIA has specified the conditions and
requirements for the detailed design, construction and operation of the Project
in order to mitigate environmental impacts to acceptable levels. The potential environmental impacts
would be expected to arise during the construction phase if no mitigation
measures are in place.
16.12.2
With
the recommended mitigation measures applied, the Project would be
environmentally acceptable and no unacceptable residual impacts would be
anticipated. The schedule of
implementation of the recommended mitigation measures has been provided in Appendix
J to this report – Implementation Schedule. Monitoring requirements have also been
specified in a separate EM&A Manual to ensure proper implementation of the
recommended mitigation measures.
[1] The catchment is
enclosed by the ridgelines running between Jardines Lookout in the east through