1.
Introduction
1.1
Project Background
1.1.1
In
2002, the Environmental Protection Department (EPD) carried out the Outlying
Islands Sewerage Master Plan Stage 2 Review, and completed the Preliminary
Project Feasibility Study for Outlying Islands Sewerage Stage 2 (hereinafter
referred to as “PPFS”).
1.1.2
In
February 2008, Drainage Services Department (DSD) commenced the Investigation
Stage of “Upgrading of Cheung Chau and Tai O Sewage Collection, Treatment and
Disposal Facilities” under Agreement No. CE 31/2007 (DS) by commissioning a
consultant to carry out review on the conclusions and recommendations of the
PPFS report, surveys, investigations, impact
assessments, preliminary environmental review and preliminary design of the
recommended works (hereinafter referred to as “Investigation Consultancy”).
1.1.3
In
December 2010, DSD commissioned Atkins China Limited (ACL) to undertake Design
and Construction of “Upgrading of Cheung Chau and Tai O Sewage Collection,
Treatment and Disposal Facilities” under Agreement No. CE 15/2010 (DS).
1.1.4
An
Environmental Impact Assessment (EIA) Study Brief No. ESB-212/2009 was issued
to cover the Upgrading of Cheung Chau Sewage Collection, Treatment and Disposal
Facilities (hereinafter refers to as “the Project”). The EIA Study covers the following main works
elements:
Ÿ Expansion of the sewage treatment capacity
and upgrading of the treatment level of the existing Cheung Chau Sewage
Treatment Works (STW);
Ÿ Expansion of the pumping capacity of the existing
Pak She Sewage Pumping Station (SPS) and construction of a new SPS at Kwun Yam
Wan;
Ÿ Upgrading of some existing sewers and
construction of some new sewers in various necessary locations in Cheung Chau;
and
Ÿ Construction of effluent reuse facilities within
the Cheung Chau STW.
1.1.5
The
purpose of this EIA study is to assess the environmental issues arising from
the construction and operational phases of the Project, and to recommend
appropriate mitigation measures for all identified adverse environmental impacts.
2.
Project Description
2.1
Project Location and Brief Description
2.1.1
The
Cheung Chau STW is located at the western side of the Cheung Kwai Estate. It is currently a primary treatment works
with design capacity of 4,000 m3/day. Upon completion of the Project, it will be
increased to a capacity of 9,800 m3/day with secondary treatment
level. A Membrane-bioreactor (MBR) type
sewage treatment plant will be adopted.
Effluent reuse would be proposed for non-potable use within the Cheung
Chau STW including toilet flushing and process cleansing.
2.1.2
Existing
Pak She SPS was commissioned in 1984 and is located at the junction of Pak She
Praya Road and Ping Chong Road, opposite to the Cheung Chau Fire Station. The current pumping capacity of Pak She SPS
is 29,376 m3/day (340 L/s).
Upon completion of the Project, it will be increased to a capacity of
42,336 m3/day (490 L/s).
2.1.3
The
original Kwun Yam Wan SPS scheme proposed under the Investigation Consultancy
is not recommended due to potential adverse environmental impacts arising from
close proximity of the proposed SPS to the adjacent Kwun Yam Wan Beach. The land resumption required and the
operation and maintenance difficulties of the Kwun Yam Wan SPS also made it not
preferable. Therefore, the proposed Kwun
Yam Wan SPS has been eliminated under the Project. A Deep Sewer Option has been proposed to
replace the SPS scheme by constructing a 700 m long underground gravity sewer
to collect sewage from Kwun Yam Wan to the existing sewerage along Cheung Chau
Praya Street.
2.1.4
Sewers
works in Cheung Chau includes:
Ÿ Upgrading of approximately 120 m long
existing sewer of size 150 mm to 400 mm diameter;
Ÿ Rehabilitation of approximately 160 m long
existing sewer of size 525 mm diameter;
Ÿ Construction of approximately 7,500 m long
of new sewer with size 150 mm to 400 mm diameter in village areas by open cut method; and
Ÿ Construction of approximately 300 m long of
new deep sewer with size Twin 400 mm to Twin 500 mm diameter along Cheung Chau
Sports Road and Tung Wan Road by trenchless method.
2.1.5
Under
Part I, Schedule 2 of the Environmental Impact Assessment Ordinance (EIAO), the
Project consists of the following Designated Projects (DP):
(a) Upgrading of the existing Cheung
Chau STW – under Item F.2 which is Sewage
Treatment Works with an installed capacity of more than 5,000 m3/day
and a boundary less than 200 m from the boundary of a residential area;
(b) Upgrading of the existing Pak She
SPS – under Item F.3 which is Sewage
Pumping Station with an installed capacity of more than 2,000 m3/day
and a boundary less than 150 m from the boundary of a residential area; and
(c) Upgrading of the existing Cheung
Chau STW – under Item F.4 which includes an
activity for the reuse of treated sewage effluent from a treatment plant.
2.1.6
The
works for this Project in Cheung Chau are shown in Layout Plan of Figure 2.1.
2.2
Purpose and Objectives of the Project
2.2.1
Currently there are areas in
Cheung Chau not provided with public sewerage system. Sewage and greywater generated from most of these
village houses are disposed of at septic tanks that regular maintenance is
required, and in some occasions they are even discharged directly into surface
drainage system. In addition, the
existing Cheung Chau STW is a primary treatment facility which would be
inadequate to cope with the population growth and future development. In this regard, there is a need to improve
this situation.
2.2.2
The
Project is to improve the coastal water quality to the northwest of Cheung Chau
by upgrading of existing sewers and provision of new sewers where practicable
within the catchment, upgrading of the existing primary treatment plant to a
secondary STW and expand the STW to cope with the population growth and future
developments to improve the hygiene conditions at Cheung Chau.
2.3
Project Implementation Programme
2.3.1
The
tentative implementation schedule for different works packages is presented in Table 2.1 below.
Table 2.1 : Tentative
Implementation Schedule for Different Works Packages
3.
Key
Findings of the Environmental Impact Assessment
3.1
Air Quality
3.1.1
Construction
dust generating activities were identified and evaluated. Mitigation measures including proper watering
of on-site construction area and good practices on dust control measures are recommended. Model simulation results show that the
fugitive dust emissions are minimized and the dust levels are limited to
acceptable levels by implementing the recommended mitigation measures.
3.1.2
The
operation of Cheung Chau STW and Pak She SPS are the main potential odour
emission sources. The upgrading works
will include the installation of better odour control for these facilities to
avoid or minimize potential odour nuisance.
Upon completion of the upgrading works, all potential odour generating
components of the facilities will be enclosed, and odourous gas will be
ventilated to the deodorization units for further treatment before
discharge. During sludge transportation, it is
recommended that the sludge should be carried by closed container to avoid or
minimise odour nuisance.
3.1.3
With
the above measures, odour impact should be insignificant. An Environmental
Monitoring and Audit (EM&A) programme will be implemented to ensure the continuing effectiveness of
the odour control installations.
3.2
Noise
3.2.1
Concurrent
construction noise impacts from the Project, including the Cheung Chau STW and
Pak She SPS upgrading works and sewers works have been assessed. A theoretical worst case in construction
noise assessment has been undertaken with consideration of cumulative impacts
arising from other projects proposed in the vicinity of the study area.
3.2.2
Construction
noise control measures such as adopting quiet plant, use of temporary barriers
along site boundary of the Cheung Chau STW and Pak She SPS, employing movable barrier
close to construction plants and good scheduling of works, etc., have been
recommended to minimise construction noise.
3.2.3
With
the above measures, noise impact is not anticipated during the Cheung Chau STW and Pak She SPS upgrading works. However, for the sewers works, predicted noise level would exceed the noise criteria at some isolated occasions for certain NSRs that are in
close proximity to the proposed sewers works.
This residual impact is expected to be localised, temporary, reversible,
and the actual impact can be minimized through proper phasing of works and
properly managed construction schedule.
A systematic EM&A programme will be carried out to ensure proper
implementation of both construction phase mitigation measures and the
construction schedule of the sewers works.
3.2.4
Noise
impacts due to the upgraded Cheung Chau STW and Pak She SPS during the
operational phase are not anticipated as proper acoustic treatment,
including silencer and
acoustic louvre would
be provided. Basic building design such
as avoiding opening or louvres facing the nearest NSR would also be adopted. Noise commissioning test for all major fixed
noise sources is recommended and the requirements would be included in the contract documents.
3.3
Water Quality
3.3.1
Potential
water quality impacts during construction phase will be mainly associated with
land-based construction that may result from site runoff and sewage from the
construction workforce. Effluent will be
controlled to comply with the WPCO standards by implementing the mitigation
measures recommended on the basis of ProPECC Note
(PN1/94) for Construction Site Drainage.
Adverse water quality impact is not expected.
3.3.2
Improvement
in water quality of surrounding water body due to the operation of the Project
is anticipated. Assessment of water
quality impact was made using the Delft3D model. Generally, the proposed Cheung Chau STW upgrading would
result in a reduction in concentration of TIN, UIA, SS, BOD5 and E. coli. under normal operation of the
Cheung Chau STW. This is mainly
attributable to the improved treatment efficiency of upgraded facility and
better quality of the upgraded Cheung Chau STW effluent, resulting in a
reduction in pollutant loads into the marine water.
3.3.3
Upon upgrading of the Pak She SPS, emergency overflow of raw
sewage from the Pak She SPS will be diverted to Cheung Chau STW. Therefore, the potential water quality impact
on Cheung Chau receiving water body due to emergency overflow of Pak She SPS
will be eliminated.
3.3.4
The assessment of potential impacts associated with the emergency
discharge from the Cheung Chau STW was conducted although emergency discharge
is rare. The prediction results show
that the impact of
emergency discharge would be limited only to local areas. The potential impact would disappear rapidly
and sharp concentration of water quality variables such as E. coli would return to their normal levels in less than 12 hours
after the emergency discharge of 9,800 m3/day flow for 6 hours. Impact to more distant WSRs would be
extremely small and insignificant.
3.4
Waste Management
3.4.1
Waste
types generated by the construction activities include C&D materials,
general refuse from the workforce, and chemical wastes from the replacement of
construction plants and equipments.
Wastes generated during the operation activities include screenings,
silt and debris, grits
and dewatered sludge
and chemical waste. Provided that these
wastes are handled, transported and disposed of using approved methods and that
the recommended good site practices are followed, adverse environmental impacts
are not anticipated during the construction and operation phases.
3.5
Land Contamination
3.5.1
The
land contamination assessment was undertaken by reviewing historical and
current land uses and site reconnaissance.
Based on the findings of the site appraisal, there were potential
contaminated sites at the shipyard and the machinery repairing and recycling
workshops for ship along Ping Chong Road and Pak She Praya Road. However, as there are no excavation works
within the contaminated site, no potential contaminated soils would be
disturbed. The impacts of land
contamination are not expected during the construction phase of the
Project.
3.5.2
The
operation of the Project will not cause potential land contamination. No operational contamination impacts are
anticipated.
3.6
Ecology
3.6.1
No
important habitat or optimal habitats of fauna species of conservation
importance will be lost due to the Project as all works will be located within
developed land. The overall ecological
impact is ranked as minimal and the residual impact is considered acceptable
with respect to EIAO-TM.
3.6.2
Besides
good site practices, no other major mitigation measure for ecology is
required. With the regular site
inspection performed under the Environmental Monitoring and Audit Programme, no
specific ecological monitoring programme is needed.
3.7
Fisheries
3.7.1
The
fisheries baseline condition has been established within the assessment area
and assessment of potential impacts has been conducted in accordance with the
EIAO-TM requirements. All construction
works would be land-based and no works would be carried out in the marine or
intertidal environment. No significant adverse fisheries impacts are anticipated and no specific fisheries EM&A
programme would be required. Upon completion of this
Project, the water quality and hence the habitat quality for fisheries
resources is expected to be improved.
3.8
Cultural Heritage
3.8.1
No
impacts on archaeology or built heritage will occur due to the Cheung Chau STW
and Pak She SPS upgrading works. Thus,
no specific mitigation measures are required.
3.8.2
An
Archaeological Watching Brief programme
during construction
phase was recommended for the sewers works within Tung Wan Site of
Archaeological Interest.
In order to better protect the Cheung Chau Rock Carving which is a
Declared Monument, a buffer zone is required to ensure that the Declared
Monument and its environs are not infringed upon during the construction works.
3.8.3
There
are graded and non-graded historical buildings identified near the proposed
sewers works. None of the buildings will
be infringed upon during the construction works. Protective measures include condition survey,
vibration monitoring, provision of buffer zone, protective covering, and safe
public access.
3.9
Landscape and Visual
3.9.1
Landscape
and visual impact assessment has been carried out for the proposed upgrading of
the Cheung Chau STW to be constructed within the boundary of the existing Cheung
Chau STW.
3.9.2
Landscape
Resources (LRs), Landscape Character Areas (LCAs) and Visually Sensitive
Receivers (VSRs) have been identified within the study area to assess the
landscape and visual impacts arising from the proposed expansion and upgrading
of the Cheung Chau STW. After
mitigation, residual landscape and visual impacts are considered to be “Slight”
and “Insubstantial”. With reference to
the criteria defined in EIAO-TM, landscape and visual impacts in the
construction and operation phases arising from the proposed works is considered
as acceptable.
3.9.3
All
the upgrading works of Pak She SPS will be constructed within the existing
superstructure of the SPS. Landscape and
visual impact during construction and operation stage is therefore considered
to be negligible.
3.9.4
For
the sewers works, the proposed new and upgrading of sewers will mainly be laid
underground along the existing carriageway, footpaths and paved tracks. The construction works will be carried out
section by section in a local area with a short period of time, in order to
reduce the disturbance to the surrounding areas and nearby residents. The works area will be reinstated to its
original conditions. Residual landscape
and visual impact is considered to be negligible.
3.10
Environmental Monitoring and Audit
3.10.1
An
Environmental Monitoring and Audit (EM&A) Manual and an Environmental
Mitigation Implementation Schedule (EMIS) have been prepared to monitor and
audit the relevant air quality,
noise, water quality, waste management, cultural
heritage impacts, and landscape and visual impacts. Event and action plan for the potential
environmental impacts has been formulated and stated in the EM&A Manual.
4.
Key environmental outcomes of the project
4.1
Environmental
Benefits of the Project and the Environmental Protection Measures Recommended
4.1.1
The sewage treatment level of
the Cheung Chau STW will be upgraded from primary to secondary and the capacity
will be expanded to cope with the population growth and future
developments. Discharge of low quality
effluent to the receiving water body will be reduced and hence will improve the
coastal water quality of Cheung Chau.
Furthermore, hygiene problems within the catchment areas arising from
the use of septic tanks will be largely relieved with provision of public
sewers to currently unsewered villages, where practicable.
4.2
Population
and Environmentally Sensitive Area Protected
4.2.1
The marine waters near Cheung
Chau are protected by the improved treatment standard and treatment capacity of
the Cheung Chau STW and the elimination of overflow from Pak She SPS. The residential areas and village houses
which are currently unsewered are also protected by provision of new sewers
under this Project.
4.3
Environmentally
Friendly Designs Recommended
4.3.1
The Deep Sewer Option instead
of Kwun Yam Wan SPS would eliminate any potential environmental impacts arising
from the construction of a new SPS adjacent to Kwun Yam Wan Beach and the need
of private land resumption.
4.3.2
For Cheung Chau STW and Pak She
SPS, the provision of standby parts and standby power sources improve the
reliability of the sewage treatment and disposal system, while the provision of
deodorizing units could reduce the possible odour impact to adjacent sensitive
receivers. In the design of Cheung Chau
STW, non-potable reuse of treated effluent within the STW site will be proposed
to reduce the consumption of potable water.
The facilities of the upgraded Cheung Chau STW are so arranged as to
minimize disturbance to the existing trees within the STW and more trees will
be planted within the upgraded STW to enhance greenings and improve the visual
appearances.
4.4
Key
Environmental Problems Avoided
4.4.1
Potential deterioration of
effluent quality of the existing Cheung Chau STW due to ageing problem of the
facilities will be avoided by the proposed upgrading of the sewage treatment
level and increasing the existing capacity of the STW. The hygiene problems arising from the use of
septic tanks will also be largely relieved by the provision of public sewers to
currently unsewered village, where practicable.
Furthermore, potential sewage overflow to Cheung Chau receiving water
body will be eliminated by the proposed upgrading works for Pak She SPS.
5.
Conclusion
5.1.1
Upon
completion of the proposed upgrading works, there will be improvement in water
quality of the water body around Cheung Chau.
The EIA study concludes that with incorporation of the recommended
mitigation measures and proper implementation of the EM&A programme, the
Project will not impose adverse impacts on the neighbouring environment during
construction and operational phases.