Background to the Study
The existing Siu Ho Wan Water
Treatment Works (WTW) and the associated raw water and treated water transfer
and distribution systems were commissioned in 1997 to provide treated water
capacity of 150,000 m3/day.
It provided treated water to the Hong Kong International Airport at Chek
Lap Kok and the initial phases of North Lantau New Town and Discovery Bay.
In order to cope with the water
demands of the developments in North Lantau New Town, northshore &
north-east Lantau area and Discovery Bay, Water Supplies Department (WSD)
conducted a Preliminary Project Feasibility Study (PPFS) in respect of the
project “Siu Ho Wan Water Treatment Works Extension” (hereinafter referred to
as the Project) in January 1999. The
PPFS identified the requirements of the Project, describing the studies
undertaken and the new works required, together with the outline design for
principal elements of the Project, cost estimate, land requirements and
implementation programme. Following the
PPFS, WSD commissioned Metcalf & Eddy Ltd. to undertake the Extension of Siu Ho Wan Water Treatment Works - Investigation (the
Assignment) that comprises the uprating of Siu Ho Wan WTW and the associated
raw water and treated water transmission systems.
As the capacity of the Siu Ho Wan WTW is more than 100,000
m3 per day, the Project is a designated project under Schedule
2, Part I, Category E.2 of the Environmental Impact Assessment Ordinance (EIAO) (Cap. 499). An environmental permit is required under the EIAO.
As part of the Assignment, an Environmental Impact Assessment
(EIA) tudy was undertaken
to provide information on the nature and extent of potential environmental
impacts arising from the construction and operation of the proposed Project,
and to contribute to decisions on the overall environmental acceptability
of the Project.
The EIA provided an assessment of the
potential environmental impacts associated with the Project, in relation to the
issues specified in the EIA Study Brief No. ESB-046/2000, including noise, air quality,
water quality, waste management, ecology, cultural heritage, landscape and
visual, and hazard to life.
The proposed Siu Ho Wan WTW extension is within the existing
WTW site boundary (location refers to Figure 2.1), located at the foot of
the Tai Che Tung hill in a area, with
a Sewage Treatment Plant to the west, North Lantau Service Road to the north
and North Lantau Highway about 100 m away.
The layout plan of the Siu Ho Wan WTW is shown in Figure 2.2. A Siu Ho Wan Raw Water Booster Pumping Station is also proposed
and its location is shown in Figure 2.1.
The existing Pui O Raw Water Pumping
Station and Pui O No. 2 Raw Water Pumping Station are located next to South
Lantau Road. The demolition and
reprovisioning of the Pui O Raw Water Pumping Station and uprating of the Pui O
No. 2 Raw Water Pumping Station would take place within its existing
boundary. A proposed alignment for the
duplication of two sections of the existing raw water mains (about 2 km in length)
at Pui O is mainly along the existing South Lantau Road, as shown in Figure
The scope of this Project covered in
the EIA comprises:
of the existing Siu Ho Wan WTW within the existing Siu Ho Wan WTW compound from
a capacity of 150,000 m3/day to 300,000 m3/day;
Uprating of treated/fresh water pumping
capacity in the existing Siu Ho Wan Raw Water and Fresh Water Pumping Station
within the existing Siu Ho Wan WTW compound from a capacity of 150,000 m3/day
to 300,000 m3/day;
Construction of the proposed Siu Ho Wan Raw
Water Booster Pumping Station together with the associated raw water mains,
E&M plants and access road to increase the raw water transfer capacity from
Tai Lam Chung Reservoir to Siu Ho Wan Water Treatment Works;
Demolition and reprovisioning of the Pui O Raw
Water Pumping Station;
Uprating of the Pui O No. 2 Raw Water Pumping
Laying of two sections, approximately 2 km
long, of 1200 mm diameter raw water mains at Pui O; and
All other associated civil, building,
structural, pipeworks, mechanical and electrical works, plant and equipment
including pumping plant, power supply plant, and water treatment plant and
equipment, site formation, geotechnical, landscaping, environmental assessment,
surge protection facilities, control and monitoring works, Supervisory Control
and Data Acquisition System, Distributed Control System, energy management
system, permanent and temporary land issues necessary for completion and
commissioning of the works element as listed in the above.
The construction of the Project is
scheduled for commencement in late 2007 for completion and commissioning in
Potential environmental impacts associated with the construction and operation
phases of the proposed Project are summarized below.
Air quality impacts from the
construction works for the proposed extension of Siu Ho Wan WTW, Siu Ho Wan Raw
Water Booster Pumping Station, Pui O raw water pumping stations and laying of
raw water mains at Pui O would mainly be related to construction dust from
excavation, demolition, materials handling and wind erosion. With the implementation of mitigation
measures specified in the Air Pollution Control (Construction Dust)
Regulation and Environmental Monitoring and Audit (EM&A) programme,
dust impact on air sensitive receivers would be limited during the construction
No operation air quality impact would
Construction noise impacts from the laying of raw water mains,
demolition and reprovisioning of Pui O Raw Water Pumping Station, if unmitigated,
may exceed daytime noise criterion at noise sensitive receivers (NSRs).
The use of silenced Powered Mechanical Equipment
and movable noise barriers during the raw water mains construction at Pui
O would be required to ensure compliance with the noise criterion and no adverse
noise impact on the NSRs.
No construction noise impact would be expected in the
area of the Project at Siu Ho Wan as no NSR is identified in that area.
With the implementation of the
recommended mitigation measures, potential noise impacts associated with the
operation of the Pui O raw water pumping stations would be limited and within
the noise criteria under the Noise Control Ordinance.
Potential key water quality impact would be related to construction
phase earthworks for the proposed extension of Siu Ho Wan WTW
Siu Ho Wan Raw Water Booster Pumping Station and trench excavation
for the mainlaying works at Pui O, and demolition works for Pui O Raw Water
Pumping Station. The nearest identified
water bodies to the works areas at Siu Ho Wan and Pui O are the existing streams
at Pui O and the drainage channel to the north of the Siu Ho Wan WTW.
Potential sources of water quality impact comprise construction site
runoff and drainage; debris, refuse and liquid spillages from general construction
activities; and sewage effluents from the construction workforce.
Minimisation 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 minimise 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 nearby watercourses. Sewage effluent arising from the construction workforce would also
require appropriate treatment through provision of portable toilets. With the implementation of appropriate mitigation
measures, the construction works for the proposed Project would not be anticipated
to result in impacts on water quality.
After careful alignments selection, construction of the proposed
raw water mains at Pui O would mainly be confined to the existing South Lantau
Road. However at either end of the
proposed alignment, these would unavoidably have direct impact on small areas
of woodland habitat. Excavation of the proposed 2.5m wide trench
would affect approximately 0.1ha of woodland habitat. This trench excavation
would occur inside a 10m wide temporary works area encompassing approximately
0.4ha of woodland habitat. This reserved 10m wide temporary works area is
primarily to allow minor adjustments of the raw water mains alignment
subject to site conditions in the subsequent detailed design and construction
During ecological field surveys, it
was found that individuals of two locally common plant species of conservation
interest (the protected shrub/tree Pavetta
hongkongensis and International Union for Conservation of Nature and
Natural Resources (IUCN) listed tree Aquilaria
sinensis) were scattered throughout the woodland habitat in the Pui O
area. Mitigation measures were
recommended to minimise disturbance to the plant as much as practicable and
where unavoidable, transplantation of affected individual plants would be
undertaken. In addition, tree felling
would also be minimised and replanting and landscaping would reinstate the
With good site practice and
implementation of environmental mitigation measures, other impacts, such as
indirect impacts on stream water quality due to site runoff and indirect
disturbance to wildlife would be very minor.
It is anticipated that the Project would have no long-term residual
impact on ecology of the Pui O Assessment Area.
Works at Siu Ho Wan would be mainly
confined to existing site boundary and the proposed Siu Ho Wan Raw Water
Booster Pumping Station would be built on very low ecological value
developed/abandoned land, and therefore minimal ecological impact is
The landscape and visual impact
assessment identified potential impacts of the proposed works to the existing
landscape and visual character of the study areas which would be mainly in
terms of removal of existing vegetation and proximity of proposed structures to
villagers. As the scale of
proposed works in terms of number of affected trees and dimension of structures
are limited, landscape and visual impacts could be effectively mitigated eg. by
compensatory planting to an acceptable level.
The assessment found that there was no
archaeological sites or areas of archaeological potential along the proposed
raw water mains alignment under the Project.
Therefore there would be no cultural heritage impacts associated with
the construction works. However, as a
good practice, mitigation measures in the form of a temporary fenced off buffer zone in
proximity to a shrine at Pui O Lo Wai Tsuen with allowance for public access
should be provided as far as practicable as the demolition and reprovisioning works for
the Pui O Raw Water Pumping Station may restrict access or affect the
structure. In case of site constraint, the existing perimeter fence at Pui O Raw Water Pumping Station
could be incorporated to protect the shrine and should form the limit of the
and Operability (HAZOP) study was conducted to identify
additional chlorine hazards initiated by construction activities within the Siu
Ho Wan WTW compound for the extension of Siu Ho Wan WTW. A number of mitigation measures, such as monitoring and inspection of chlorine dosing
facilities, management of materials and personnel, investigation and training,
were identified to be included in the Contract document, as well as in the
Safety Plan and Emergency Plan for the extension of Siu Ho Wan WTW, to avoid
occurrence of deviations.
As there will be no increase of
storage and on-site transport of chlorine to that of the allowable storage
capacity for the Siu Ho Wan WTW, the hazard assessment
of the operation phase is not required
in the EIA.
Wastes generated by the construction
activities are likely to include construction & demolition (C&D)
material from the earthworks for the extension of the Siu Ho Wan WTW, Siu Ho
Wan Raw Water Booster Pumping Station and the mainlaying works along South
Lantau Road at Pui O, demolition works for the Pui O Raw Water Pumping Station,
general refuse from the workforce and chemical wastes from plant and equipment
maintenance. Provided that these identified waste arisings are to be handled,
transported and disposed of using the recommended methods and that good site
practices are to be strictly followed, adverse environmental impacts would not
be anticipated during the construction works.
Waste management will be the
contractor’s responsibility to ensure that all wastes produced during the
construction of the Project are handled, stored and disposed of in accordance
with good waste management practices and EPD’s regulations and requirements.
The recommended mitigation measures will form the basis of the site Waste
Management Plan to be developed by the Contractor at the commencement of the
An environmental monitoring and audit
programme was recommended for dust, noise, ecology and landscape and visual
during construction phase. Site
inspection/audit was also recommended to check the implementation of the water
quality, waste management and cultural heritage mitigation measures during the construction
phase. Details of the programme are
presented in a stand-alone Environmental Monitoring and Audit Manual.
The findings of the EIA have provided
information on the nature and extent of environmental impacts arising from the
construction and operation of the Project.
The EIA Report has predicted that, the Project would be environmentally
acceptable in compliance with environmental standards and legislation with the
implementation of the construction and operation stage mitigation measures, as
well as environmental monitoring and audit programme.