10.1
Justification and Benefits
of the Project
10.1.1
The need for the Project has evolved from the requirement to
provide a secure water supply to Cheung Chau. Specifically, it has been
determined that the existing water main serving as emergency backup is
approaching its design life of 50 years. There will be increasing risk of
having one water main under maintenance while another main has to be taken out
of service without warning.
10.1.2
Being the only water supply to Cheung Chau, it is necessary
to lay a new submarine water main from Lantau to Cheung Chau to maintain the
reliability of water supply to Cheung Chau. The consequences of not proceeding
with the Project will be serious interruption of water supply to Cheung Chau in
the event the current water main is taken out of service unexpectedly.
10.1.3
The estimated population expected to be directly benefited by
the Project will be the residents of Cheung Chau of about 23,000 as well as the
tourists visiting Cheung Chau.
10.2
Population and Environmental
Sensitive Areas Protected
10.2.1
With the adoption of Horizontal Directional
Drilling (HDD) and forward reaming, the main staging area of the Project will be located in Cheung
Chau which has less ecological impact. Equipment and works area in Lantau is
significantly minimized thereby avoiding impacts to
10.2.2
No marine works will be required with the use of HDD
in laying the water main. The seabed of Adamasta Channel will not be disturbed.
As such, impacts to Cheung Sha Wan Fish Culture Zone, fish spawning / nursery
grounds, as well as fishing activities in the area will be avoided. Likewise,
marine traffic along Adamasta Channel will not be affected during construction
phase.
10.2.3
By adopting HDD, no marine sediment will need to be dredged
and disposed thus reducing the burden on marine dumping sites. The associated
water quality impacts from dredging and disposal of marine sediment can be
avoided, thus avoiding adverse impacts to the marine environment.
10.2.4
The works site at Cheung Chau will utilize the
existing works compound at Tai Kwai Wan, thereby minimising the need to secure
additional land. The need for site formation can also be greatly reduced by using
the already formed works compound. The works site will avoid the nearby sandy
and rocky shores within the Coastal Protection Area zone.
10.2.5
A number of trees in the works area at Cheung Chau will be
preserved in-situ by adjusting the works boundary. No trees will be affected in
Lantau.
10.2.6
With the use of quiet plant and temporary noise barrier,
residents near the works area at Cheung Chau will be protected from excessive
construction noise.
10.2.7
Ultimately, all the residents of Cheung Chau will be directly
benefited as a result of the Project in terms of a more secure and reliable
water supply.
10.3
Environmental Friendly
Designs Recommended
10.3.1
The principle of using HDD instead of conventional dredging
technique in laying the submarine water main is to avoid environmental impacts
while at the same time to provide cost effective, maintenance free solution for
a secure and reliable water supply to Cheung Chau. Views and comments from the
Green Groups, District Council members and fishermen association obtained
during public consultation have also been taken into consideration in the
design.
10.3.2
When considering environmental impacts, minimization will be
the key design principle only when avoidance is not possible. The following
environmental friendly designs have been incorporated into the Project.
·
A small temporary working platform using steel decking or
wooden scaffolding will be erected in Lantau to provide a suitable working area
for retrieving the water pipe and connection. Such platform can minimize the need
for site formation, thereby avoiding adverse impact to the nearby natural
coast.
·
The length of the exposed main at Lantau will be redcued as
much as possible. The exposed main at Lantau will be shielded with nearby rocks
and boulders in order to blend in with the surrounding coastal environment. The
use of concrete structure will be minimized as far as practicable.
·
The launching site at Cheung Chau has been located on site
currently being used by other project and on disturbed or developed land. The site
can be set-up with minimal site formation.
·
By using HDD, marine sediment dredging and removal works can
be avoided thus minimizing impacts to water quality and ecological sensitive
receivers.
·
The site boundary at Cheung Chau has been modified to retain
as much trees as possible.
·
Water instead of bentonite will be used as drilling fluid in
the final bore stage at Lantau landfall to minimize potential water quality
impact.
·
Several tiers of site drainage system will be adopted to
totally confine the launching site works area. Adequate numbers of tank, pumps
and treatment facilities will be stipulated in the contract document to ensure
no site effluent is discharged untreated.
10.4
Key Environmental Problems
Avoided
10.4.1
The key environmental problems involve water quality,
ecological and noise impacts during the construction phase. Minor impact from
waste is expected. No operational phase impact is expected from the Project.
10.4.2
The EIA study has critically assessed the overall
acceptability of environmental impacts which are likely to arise as a result of
the construction of the Project. Where necessary and practicable, the EIA study
has specified the conditions and requirements for the detailed design and
construction of the Project in order to mitigate environmental impacts to an
acceptable level.
10.4.3
In order to avoid or minimize the environmental
impacts of the Project, a number of mitigation measures have been recommended
in the EIA report. The key environmental measures and problems avoided are
highlighted below.
·
The adoption of HDD will avoid impacts to the marine
environment and marine ecological sensitive receivers.
·
Works within
·
Properly designed site drainage measures,
wastewater treatment systems and good site working practices will be
implemented to ensure no adverse water quality impact to the marine waters.
·
During construction, surplus excavated materials will be
reused on-site to minimize the amount of off-site disposal to public filling
facilities.
·
With the implementation of quiet plant, temporary noise
barriers and good site practices, construction noise from construction activities
will be reduced to acceptable level. No adverse construction noise
impact on the nearby noise sensitive receivers is expected.
·
A comprehensive EM&A programme will be setup
to ensure effective implementation of mitigation measures recommended in the
EIA report, to assess the effectiveness of the mitigation measures, and to
identify any further need for additional measures or remedial actions.
10.4.4
The EIA study has demonstrated the acceptability
of any residual impacts from the Project and the protection of the
10.5
Compensation Areas Included
10.5.1
No off-site compensation area will be required for this
Project.
10.6
Environmental Benefits of
Environmental Protection Measures Recommended
10.6.1
The environmental benefits of implementing the recommended
mitigation measures can be summarized as follows:
·
The water quality and noise impacts at the sensitive
receivers will all be minimized or mitigated to within the acceptable criteria
and standards.
·
The amount of construction and demolition materials requiring
off-site disposal will be minimized through reduction, reuse and/or recycling.
·
The landscape impact from the exposed main will be mitigated
through careful selection of landfall location, minimize the use of concrete
and use of nearby natural materials such as rocks and boulders to shield and
blend in with the surrounding coastal environment.
·
By avoiding dredging or other marine works, marine sediment
will not be disturbed, impact on the marine habitat will be avoided.
10.6.1
With the implementation of the recommended mitigation
measures, no unacceptable residual environmental impacts are expected. Details
of the implementation schedule of the recommended mitigation measures are
summarized in Appendix 10.