1.1
Commissioned
in the end of 2001, Stage 1 of Harbour Area Treatment Scheme (HATS) is
currently collecting and
treating 1.4 million m3/d
of sewage generated from Tsuen Wan, Kwai Tsing, Tseung Kwan O, the urban areas
of Kowloon and northeastern Hong Kong Island. Water quality in the eastern and middle
parts of Victoria
Harbour has since
improved considerably.
1.2
The
remaining sewage from northern and western Hong Kong
Island, which currently amounts to
450,000 m3/d, however receives only screening and de-gritting prior
to discharging into Victoria
Harbour, exerting a
negative effect on water quality.
With the anticipated growth in population and business activities in the
harbour area, water quality would deteriorate in the future unless the
remainder of untreated sewage is also intercepted and treated, and the overall
treatment level at Stonecutters Island to be raised by completing HATS Stage 2.
1.3
After taking into account the public’s views collected through a
five-month consultation in 2004, the Government is committed to proceeding with
Stage 2 of HATS in two phases, namely Stage 2A and Stage 2B.
l
Under Stage 2A, deep tunnels will be built to bring sewage
from eight preliminary treatment works (PTW) in the northern and western areas
of Hong Kong Island to Stonecutters Island Sewage
Treatment Works (SCISTW). The eight existing preliminary treatment works (PTW)
(at North Point, Wan Chai East, Central, Sandy
Bay, Cyberport, Wah Fu, Aberdeen, and Ap Lei Chau respectively) on Hong Kong Island will be upgraded. The treatment
works of the SCISTW will be expanded to provide centralized chemically enhanced
primary treatment (CEPT) and disinfection for all sewage from the whole of the
HATS catchment. Part of the Stage
2A disinfection facilities will be fast-tracked for completion in 2009 to
achieve early improvement to the beach water quality in Tsuen Wan. This proposal is referred to as the
“Advance Disinfection Facilities” (referred as ADF), and has been covered in a
separate EIA study[1].
l
Under Stage 2B, a new biological treatment plant on a site
adjacent to SCISTW is proposed to treat all HATS flow. Planning for Stage 2B is in hand, with a
view to completing it in time to suit actual sewage flow build up and water
quality conditions.
1.4
This
Environmental Impact Assessment (EIA) Study is concerned with HATS Stage 2A
(the Project). The objectives of HATS Stage 2A are:
l
To deal with the remaining sewage from Hong Kong Island
which is discharged into the harbour virtually untreated
l
To provide disinfection to all sewage from the whole HATS service
area to protect our beaches from bacterial pollution
l
To restore the Harbour to a healthier condition
1.5
On
27 February 2006, ENSR Asia (HK) Ltd. (formerly Maunsell Environmental
Management Consultants Ltd.) was commissioned by the Drainage Services Department
of the Hong Kong SAR Government to undertake the EIA Study of the Project. The
purpose of the EIA Study is to provide information on the nature and extent of
environmental impacts arising from the construction and operation of the
Project and related activities that take place concurrently.
1.6
Victoria Harbour is a precious natural asset of Hong Kong with tremendous socio-economic value. Rapid
population growth in the past decades on both shores of Victoria Harbour
resulted in water quality deterioration from the discharge of untreated sewage
into the Harbour. Stage 1 of HATS
has brought about noticeable improvement to the water quality of the Victoria Harbour.
Yet, sewage from the densely populated parts of Hong Kong Island
(i.e., northern and southwestern districts) is only subject to preliminary
treatment (i.e., screening and de-gritting) before discharging into the
harbour. This preliminary treated
sewage, coupled with the un-disinfected effluent from the SCISTW, is a source
of the current water quality problems, particularly in the western part of the
harbour including bathing beaches in the Tsuen Wan area.
1.7
HATS
Stage 2A is needed to further improve the water quality of the Harbour, beyond
those achieved in Stage 1. Generally,
the benefits include:
l
Prevent another 190 to 500 tonnes of sewage sludge (at
commissioning and ultimate flow conditions respectively) from being dumped into
the harbour each day
l
Reduce toxic ammonia by 10% on average
l
Reduce total inorganic nitrogen and phosphorus by 5% and 8%
respectively
l
Increase dissolved oxygen levels by 5%
l
Facilitate the re-opening of the closed Tsuen Wan beaches
1.8
HATS
Stage 2A will substantially improve the water quality conditions compared to
the scenario of ‘no HATS Stage 2A’. Improved harbour water quality will benefit
society in many different ways, including for example, enhanced recreational
opportunities, scenic quality, aesthetics, public health and safety, and
ecological and fishery resources, as well as commercial activities. Besides, completion of Stage 2A,
together with other sewerage programmes in the area, should enable the closed
Tsuen Wan beaches to be re-opened at the earliest opportunity. Completion of
Stage 2A would also provide a much-improved environment for marine life and
possibility of staging water events.
1.9
The
Harbour with improved water quality after Stage 2A will inevitably bring
economic benefits to Hong Kong directly, and
indirectly through the tourism industry.
If HATS Stage 2A does not proceed, the water quality would resume a
deteriorating trend in the near future as the population grows and development
on both sides of the harbour continues. Hence, there is a need for maintaining
sustained efforts to clean up the harbour through implementation of the
remaining stage of HATS.
1.10
The
scope of work for HATS Stage 2A includes:
l
Upgrading of eight existing preliminary treatment works
(PTWs) on Hong Kong
Island
l
Extension of the deep sewage conveyance system (SCS) to
collect and transfer sewage from the eight PTWs to SCISTW for treatment and
disposal
l
Augmentation of the existing Chemical Enhanced Primary
Treatment (CEPT) capacity at SCISTW from the present design capacity of
1.7million m3/d to the ultimate design capacity (which is estimated at about
2.45million m3/d based on the latest available planning information)
l
Provision of disinfection to all HATS effluent before
discharging into the harbour
1.11
Figure 1 shows the general layout plan of HATS Stage 2A.
1.12
In developing the HATS Stage 2A
scheme, relative environmental benefits and dis-benefits of alternatives of SCS alignment, construction
methods, treatment methods and sequence of works of the Project were evaluated.
Alternative SCS Alignment
1.13
Two
major alternatives for the SCS alignment (Figure 2 refers) were considered,
including:
l
Option 1, the initial scheme presented
in the EIAO Study Brief, which was developed based on the schematic design
produced under the “Environmental and Engineering Feasibility Assessment
Studies in relation to the Way Forward of the HATS (EEFS)” commissioned by EPD
in 2001.
l
Option 2, a revised alignment
developed for the SCS under Agreement No. CE 34/2005(DS), Harbour Area
Treatment Scheme Stage 2A Sewage Conveyance System – Investigation, Design, and
Construction.
1.14
The
alignment under Option 2 could minimise impacts to the inland environmental
sensitive receivers/historic structures by going offshore. It also minimises encroachment on
private lots and thereby eliminates interfaces with private properties. This
would result in the reduction of programming risk and hence duration of
environmental impacts to the public. Since the tunnel alignment under Option 2
is only 0.5 km longer than the alignment of Option 1, increase of waste
generation would not be a significant concern. On considering the relative
environmental impacts of the tunnel alignments, Option 2 is preferred from an
environmental perspective and is proposed for the Project.
Alternative Disinfection
Technologies
1.15
The
feasible sewage disinfection options for HATS are chlorination (with
dechlorination) and UV radiation.
Both chlorination/dechlorination (purchase of sodium hypochlorite and
sodium bisulphite) and UV radiation were found to be environmentally acceptable
for HATS. Water quality and
ecological impacts could be controlled to well within established criteria in
the Technical Memorandum of EIA Process for either option.
1.16
Although
both disinfection options would be environmentally acceptable, it has been
shown that neither is superior to the other on all environmental aspects.
However, the chlorination option would be preferred in terms of cost,
reliability, flexibility to cater for uncertainties, and ease of
implementation. The detailed
evaluation conducted under the HATS EIA Study for the Provision of
Disinfection Facilities at Stonecutters
Island Sewage Treatment
Works – Investigation (ADF EIA) has concluded the adoption of chlorination
with dechlorination as the disinfection technology for HATS.
Alternative Construction Methods
i) Sewage Conveyance System (SCS) and Effluent Conveyance system (ECS)
at SCISTW
1.17
The
key alternatives for construction of the SCS and ECS are:
·
Option
1 - Shallow sewer pipes (open trench excavation)
·
Option
2 - Deep tunnelling (trenchless method or “no dig”
technology)
1.18
Deep
tunnelling under Option 2 would be preferred from an environmental perspective
because activities on the surface would be restricted to a relatively small
number of production shafts and hence construction stage environmental impacts
would be much lower than Option 1.
Further, at these shaft locations, environmental noise, dust, and visual
impacts could be effectively mitigated with a carefully designed
enclosure.
1.19
With
respect to alternative tunnel construction methods, the principal options are
i) mechanical boring and ii) drill & blast. Both options would be environmentally
acceptable, as demonstrated in relevant chapters of the EIA Report. The final selection will be made by the
design-build contractor.
ii) PTW Upgrading and SCISTW Augmentation
1.20
There
are a number of proposed facilities for the PTW upgrading and expansion of
SCISTW which would require piling works, such as location for heavy mechanical
equipment (e.g. pumps) in PTWs as well as new sedimentation tanks, sludge
processing plant and upgraded disinfection facilities in SCISTW. The relative
environmental impacts of the alternative piling methods (i.e. percussive vs.
bored pile) were considered. From an environmental perspective, bored piling is
preferred as it would have lesser noise and vibration impacts compared to
percussive piling.
Alternative Sequences of Construction
1.21
With
respect to sequence of construction works for PTW and SCISTW, the alternatives
are:
·
Option
1 - Constructing the SCS drop shafts at the same time as
the main PTW upgrading works and the new and upgrading works elements on the
SCISTW site
·
Option
2 - Phased construction of the SCS drop shaft and PTW
upgrading works, and phased
construction of the new and upgrading works elements on the SCISTW site
1.22
Option
2 (phased construction) would have lower noise and dust impacts as it would
have less construction activities on site at a given time. This would achieve compliance with the
relevant environmental criteria (e.g., construction noise) and therefore it is
preferred from an environmental perspective.
2.1
The
operational philosophy of HATS Stage 2A is similar to HATS Stage 1 with the addition of disinfection.
That is, sewage from the catchments will be:
l
Firstly, screened and de-gritted at the PTWs to remove large
solid objects and sediments, so as to protect the downstream sewer tunnels from
blockage or excessive sedimentation
l
Then, discharged into the SCS, which consists of sewer
tunnels or pipelines to convey the screened/de-gritted sewage to SCISTW
l
Finally, treated and disinfected at SCISTW, to a level
suitable for discharge via a submarine outfall system into the sea
2.2
Sludge drawn from the
sedimentation process will be dewatered in SCISTW, and then transported offsite
for final treatment and/or disposal in accordance with Government’s strategy
for sewage sludge management. The solid residues (screened debris and grits)
from the PTW will be removed by trucks to landfill for disposal.
2.3
Eight existing PTWs on northern
and western Hong Kong Island (Figure 1 refers), including North Point, Wan
Chai East, Central, Sandy Bay, Cyberport, Aberdeen, Wah Fu, and Ap Lei Chau would
be upgraded/modified to meet design treatment and flow requirements. Principally, the major upgrading works
at most of the PTWs would include replacement or installation of the following:
l
Mechanical screens of various sizes
l
Pumps
l
Grit traps
l
Compactors
l
Deodorising units
l
Control system and expert system
2.4
Construction works would be
carried out in phases in order to minimize environmental impacts and provide
space for SCS construction and normal PTW operation. Conventional construction plant and
equipment would be used for the PTW upgrading works.
2.5
SCS would be constructed to
bring sewage discharged from the PTWs via drop shaft into the deep
tunnels and then conveyed to the SCISTW. The proposed alignment is about 21 km long and at a depth of about 70m to 160m below sea level. The longitudinal-section of the
SCS is shown in Figure 3. In general, the SCS includes 7
main tunnel sections (J, K, L, M, N, P and Q), 16 vertical shafts (6 temporary
production shaft and 10 permanent drop/riser shafts), and up to 3 sewage
transfer pumping stations and two ancillary seawater pumping stations at
strategic locations in the SCS. To facilitate the SCS construction, 20 temporary/permanent
sites are required for shaft construction or as supporting areas for temporary
stockpile/storage during construction stage.
2.6
Either mechanical boring or
“drill and blast” would be used to excavate the main tunnel sections, depending
on the anticipated ground conditions and other site-specific considerations
(e.g., construction logistics, proximity to sensitive receivers, etc). The shafts would be constructed using
conventional techniques, i.e., mechanical excavation of the near surface softer
materials and blasting/mechanical boring for the deeper harder rock
materials. For construction of
sewage transfer/seawater pumping stations, conventional construction plant and
equipment would be used.
Non-percussive piling method would be used if piling is required.
2.7
Augmentation
of the existing SCISTW (Figure 4 refers) to meet design flow and
treatment performance requirements includes:
l
Construction of a new influent pump station to lift the
sewage from the SCS to surface
l
Expansion of the existing chemically enhanced primary
treatment (CEPT) facilities to cater for the additional flows, increase present
design capacity of 1.7 million m3/d to the ultimate design capacity (which is
estimated at about 2.45 million m3/d based on latest available planning
information)
l
Upgrading of the interim disinfection facilities (also known
as the Advance Disinfection Facilities (ADF), which are scheduled to complete
by end of 2009) to cater for the ultimate design flows and the disinfection
requirements
l
Expansion of the existing sludge processing facilities to
cater for additional sludge volumes associated with the additional sewage flows
l
Construction of a new effluent tunnel to convey treated and
disinfected effluent to the existing outfall system
l
Construction of a new odour treatment system
l
Ancillary facilities
2.8
Construction of the effluent
tunnel would be by either mechanical boring or “drill and blast”. Other elements would be constructed
largely using conventional construction plant and equipment, for which the
choice of equipment would aim to reduce environmental impacts.
2.9
Noting
that the discharge of un-disinfected sewage effluent from SCISTW is
contributing to unsatisfactory beach water quality at the Tsuen Wan beaches,
the Government has proposed to advance the provision of part of the permanent
disinfection facilities under HATS Stage 2A. The construction works for ADF
have been scheduled to commence in April 2008 for completion in end 2009.
2.10
Construction of the remaining
works of Stage 2A (i.e. excluding ADF) is planned to start in 2009 and the
whole of Stage 2A should be completed and commissioned by 2014.
Construction Phase
3.1
Major
construction activities that are potential sources of construction dust in the
study area include soil excavation activities at work sites, construction of shafts
and wind erosion of open sites. Construction dust levels were assessed at 53
representative air sensitive receivers (ASR) near the 8 PTWs and the
SCISTW. These ASRs included
residential and commercial buildings, clinics, schools, institutions, community
and recreational facilities and open space. With the implementation of mitigation
measures specified in the Air Pollution Control (Construction Dust) Regulation,
dust nuisance at these ASRs would not be expected. An EM&A programme was recommended for
the construction phase to verify that the dust criteria would be satisfied at
the ASRs.
Operational Phase
3.2
Odour
emission from the PTWs and SCISTW would be the main concern during the
operation phase. Air dispersion
modelling was conducted to simulate the potential odour impacts of the SCISTW
and the PTWs on the representative ASRs.
Odour sources in the SCISTW include the distribution channel,
flocculation tanks, primary sedimentation tanks, drop shafts of the
sedimentation tanks, effluent weirs, overflow chamber, flow distribution
chamber and dewatered sludge. Odour
sources at the PTWs include the solids handling areas. Based on modelling results, the
recommendation was to properly enclose or cover all the identified odour
sources in the PTWs and SCISTW, with the foul air drawn through deodorization
units and discharged after treatment.
Good house keeping (regular cleansing schedule) should be conducted to
minimize odour generation from the PTWs and SCISTW. With the proposed mitigation, the residual
odour levels at the ASRs were predicted to comply well with the odour
criterion. Odour monitoring in the
form of odour patrol was also recommended to be carried out during the
operation phase to verify that the odour criterion is met at the ASRs.
Construction Phase
3.3
The
EIA has predicted the cumulative construction noise impacts of the Project
during normal daytime working hours. The predicted unmitigated noise levels
would range from 56 to 89 dB(A) at the 29 representative Noise Sensitive
Receivers (NSRs). These NSRs
included residential and commercial buildings, clinics, schools, institutions,
and community and recreational facilities near the 8 PTWs and SCISTW. With the use of quiet power mechanical
equipment, movable barriers and acoustic mats for construction tasks under the
Project, the noise levels at all representative NSRs except N1 (i.e. Madam Chan
Wai Chow Memorial School) during the examination periods would comply with the
construction noise standards.
3.4
Assessing
against the noise standard of 65 dB(A) during examination periods, the
predicted noise level at NSR N1 would exceed the noise standard by up to 5
dB(A). However, the school has been noise insulated with air conditioners and,
by keeping the windows closed during construction activities, noise impacts at
the indoor environment could be avoided. Notwithstanding this, particularly
noisy construction activities were recommended to be scheduled during the summer
vacation period as far as practicable.
3.5
An
indicative assessment was undertaken for possible construction activities
within the tunnel and bottom of shaft during restricted hours. The predicted construction
noise levels at representative NSRs during restricted hours would comply with
the corresponding noise limits, provided that the ventilation fans and motors
of gantry at the production shafts of Sandy Bay PTW would be properly housed
and the silencers would be installed at outlet and inlet of the enclosure for
ventilation fans. It should be noted that the results of the construction noise
impact assessment for restricted hours are for indicative purposes, the Noise
Control Authority will process any Construction Noise Permit (CNP) application
based on the Noise Control Ordinance (NCO) and the relevant technical memoranda
in addition to considering the contemporary situations / conditions.
3.6
A
construction noise EM&A programme was recommended to check the compliance
of the noise criteria during normal daytime working hours.
Operation Phase
3.7
The
noise impact associated with the operation of the Project was assessed. For
newly proposed equipment without any mitigation, the predicted noise levels at
all 29 representative NSRs except 5 near the Sandy Bay PTW (N12, N13, N14,
N15a, N15b), 2 near the Cyberport PTW (N16, N17) and one near the Wah Fu PTW
(N20) would comply with the night-time planning noise criteria. The noise
levels at these affected NSRs would exceed the planning noise criterion by 1 to
13 dB(A). For cumulative noise impact, the predicted
noise levels at all representative NSRs except N13, N15a and N15b would comply
with the night-time ANL. The cumulative noise level at N13, N15a and N15b would
exceed the night-time ANL of 50 dB(A) by up to 8 dB(A).
3.8
To mitigate the noise impact at
the affected NSRs, acoustic louvers have been proposed for air supply
fans/extraction fans of transfer pumping stations and ventilation fans of deodourization unit at
Sandy Bay PTW, Cyberport PTW and Wah Fu PTW. Besides,
it is recommended that the maximum allowable sound power level (SWL) of each
new transformer at Sandy Bay PTW shall be limited to 89 dB(A) during the
detailed design stage. With such proper designs, the predicted noise levels at
all representative NSRs would comply with both the night-time ANL and
night-time planning noise criteria. No residual operation noise impact arising
from the Project is anticipated.
3.9
Proper
designs of PTWs, SCISTW and disinfection facilities would control the potential
noise impact at noise sensitive receivers within acceptable levels, operational
noise monitoring would not be necessary.
Construction Phase
3.10
Potential groundborne noise impacts would arise mainly from rock
breaking activities and tunnel boring by Tunnel Boring Machine (TBM) during
tunnel/shaft construction of this Project.
Eleven sensitive receivers were identified, consisting of residential and
institutional buildings, school, hospital and community facilities ranging from
86 m to 343 m in slant distance from the nearest tunnel. The Le Meridien Hotel
in Cyberport would have the shortest slant distance to the nearest tunnel and
was selected as the worst affected sensitive receiver to groundborne noise
impact. The assessment results indicated that the predicted impacts at the Le
Meridien Hotel would be within the statutory requirements and no mitigation
measure would therefore be required.
Operation Phase
3.11 No groundborne noise generating
activity was anticipated during the operation phase of the Project.
Construction Phase
3.12
General
construction works for the Project would be land-based except seawall
re-construction at the Aberdeen PTW. No dredging would be required for the
Project. The fine content in the
fill material during seawall re-construction at the Aberdeen PTW should be
negligible. Key water quality issues associated with land-based construction
would include the impacts from site run-off, sewage from workforce, accidental
spillage and discharges of wastewater from various construction activities.
With well maintained site drainage and the implementation of good site
practices, impacts would be controlled to comply with the Water Pollution
Control Ordinance (WPCO) standards. No unacceptable water quality impact would
therefore be expected.
3.13
Temporary
bypass of screened sewage via seawall or submarine outfalls of individual PTWs would be
required during the construction stage.
The associated water quality impact would be short-term and the water
quality would return to the normal condition after the sewage bypass period. No
insurmountable water quality impact would be expected.
Operation Phase
3.14
The water quality impacts during
operation of the Project were assessed using the Delft3D model. Impacts
were assessed over a series of one-year simulation periods. The
assessment area included the Victoria Harbour, Western Buffer, Eastern Buffer, Junk Bay,
Northwestern, and Southern Water Control Zones. Sensitive receivers within the
assessment area identified for water quality impact assessment included cooling
water intakes, flushing water intakes, fish culture zones, beaches, sites of
special scientific interest, marine parks, marine reserves, seagrass beds,
artificial reefs, corals, the Chinese White Dolphin and Green Turtle nesting
grounds.
3.15
The
water quality modelling results showed that the Project would not cause any
adverse impact on the marine water quality and on the identified sensitive
receivers during normal operations of the SCISTW. The total residual chlorine
from the chlorination/dechlorination disinfection process would meet the
criterion set for the edge of the zone of initial dilution, with a large safety
margin. Whole effluent toxicity
tests showed that the chlorination/dechlorination disinfection process did not
introduce additional toxic effects to the test organisms. The model predicted that implementation of Stage 2A would improve
the water quality in the receiving water (including the area close to the
SCISTW outfall) for all the selected water quality parameters as compared to
the baseline (without Stage 2A) condition.
A Post Project Monitoring (PPM) programme was
proposed to confirm the model predictions made in this EIA.
3.16
Overflow
at PTW may occasionally occur only during heavy storm events and the extent of
impact was considered minor. Mitigation measures, including dual power
supply, standby pumps, treatment units and equipment, would be provided at
SCISTW and PTWs to minimize the occurrence of emergency discharge. In case of
power outage of the dechlorination plant, the uninterruptible power supply
(UPS) system to be provided would switch the power supply of the sodium
bisulphite dosing pump to a backup battery almost instantaneously, allowing
continuous dosage of sodium bisulphite for at least half an hour so that
sufficient time can be provided for shutting down the chlorination plant to
avoid the possibility of discharge of chlorinated effluent. An emergency contingency
plan has been formulated to minimise the impact of emergency discharges and
facilitate subsequent management of the emergency. An event and action
plan and a detailed EM&A programme are recommended to collect water quality
information and to mitigate the potential impact due to emergency discharge.
The monitoring results shall be employed to identify areas for any further
necessary mitigation measures to avoid, rectify and eliminate environmental
damage associated with the Project. No insurmountable water quality impact
would be expected from the temporary sewage discharges.
3.17
Risk assessments were conducted to assess potential
adverse human health and ecological effects that may result from exposure to
toxic substances from the HATS effluent.
The findings were summarized in three categories: risk to human health,
risk to aquatic life and risk to marine mammals.
Risk to Human Health
3.18
Results of Human Health Risk Assessment revealed that potential
risk/hazard impact due to chlorination by-products (CBPs) and
other contaminants present in the chlorinated/dechlorinated (C/D) HATS effluent
would be negligible and acceptable under established assessment criteria in all
Project Scenarios.
Risk to Aquatic Life
3.19
According
to the findings of Ecological Risk Assessment – Aquatic Life, the potential
risk to aquatic life due to CBPs present in C/D HATS effluent would be lower
than the risk screening value.
Since the calculated risk is below the screening value, it would
indicate that use of chlorination would not present an unacceptable risk and no
further investigation would be required.
For cumulative risk assessment, which included both CBPs and other
pollutants present in the C/D HATS effluent, the results showed a potential
hazard that was in the same order as that of the ambient marine water,
indicating that the effluent would not cause significant additional toxicity to
the ambient condition.
3.20
Results of whole effluent toxicity test on C/D effluent
were used to supplement the ecological risk assessment and to determine whether
the C/D effluent would induce adverse effects to aquatic life. The results complied with the
established toxicity criteria at the edge of both the zone of initial dilution
(ZID) and the mixing zone in all Project Scenarios. Therefore, the potential risk of C/D
effluent on aquatic life would be minimal and acceptable.
Risk to Marine
Mammals
3.21
Results of Ecological Risk Assessment – Marine Mammals
showed that the calculated risk to marine mammals due to CBPs and other
pollutants present in C/D HATS effluent were lower than the risk screening
value. This indicated that the
Project would not pose an unacceptable risk and no further investigation would
be required. Cumulative risk
assessment revealed that CBPs and other pollutants present in the C/D HATS
effluent would also pose negligible and acceptable risk in all Project
Scenarios.
3.22
According to the risk assessment results, the Project
would not cause unacceptable risk to human health and ecological
resources. Therefore, the Project
was considered environmentally acceptable in terms of risks/impacts to human
health and marine ecological resources.
Construction Phase
3.23
Wastes generated during construction of the Project
would include construction and demolition (C&D) materials from the tunnel
excavation and shaft sinking for the SCS, expansion works at SCISTW as well as
upgrading works of the PTWs (including seawall
demolishing and re-construction works at Aberdeen) and demolition of the CEPT complex next to the
Cyberport PTW after commissioning of HATS Stage 2A. Construction of the SCS would produce by
far the largest quantity of C&D materials compared to other activities,
estimated to be 791,600 m3.
Since approximately 84% of this material is rock, 78,000 m3 would
be recycled in form of aggregate for backfilling and 366,600 m3
would be delivered to the Lam Tei Quarry. Approximately 336,200 m3
of inert C&D materials would be
disposed of to public
fill reception facilities. The
remaining C&D waste would be disposed of to landfill.
3.24
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, 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 construction phase.
Operation Phase
3.25 Wastes generated during the
operation phase would comprise of approximately 61 m3/day of
screenings and grit from the upgraded PTWs and approximately 1,078 tons/day of
sludge from the expanded SCISTW.
The screenings and grit would be disposed of at landfill as is the
current practice. The sludge would
be taken to the centralized sludge treatment facility, planned for
commissioning in 2012, two years before the commissioning of this Project. To minimize potential odour impact
during the transport of sludge, marine transport was recommended as the
preferred option. However,
transport by trucks would be necessary during inclement weather. The sludge tanks on these trucks would
be required to install rubber seals to maintain air tightness and steel plates
at the bottom of the unloading to prevent leakage, which should mitigate
potential odour impact during road transport.
3.26
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. No unacceptable
environmental impacts would be anticipated during the construction and
operation of the Project.
3.27
Ecological surveys conducted under this Project
identified seven types of terrestrial habitats within the Assessment Areas,
including developed area, wasteland, woodland, plantation, shrubland, grassland
and watercourse. All the identified habitats were found to have generally low
ecological values (ranging from very low to low), except the natural woodland
habitat which is of moderate / moderate to high
ecological value. These natural woodlands were located at
North Point, Sandy Bay, Cyberport, Wah Fu, Aberdeen,
Ap Lei Chau and Stonecutters
Island. There were two
sites of conservation importance, the Pok Fu Lam Country Park and the coincided Pok Fu Lam Reservoir Catchment Area Site of Special Scientific Interest (SSSI), falling partly within the Assessment Area recorded. However, the Country Park / SSSI and most of the natural
woodlands were located on upland area and far away from the proposed project
works, potential ecological impact on these habitats and the associated
wildlife should be minimal.
3.28
Three
faunal species of conservation interest, including Black Kite, Common Buzzard
and Pallas’s Squirrel, were recorded in the Assessment Areas during recent
surveys. All were recorded outside the project boundary and therefore no direct
impact resulting from construction works would be expected.
3.29
The
key direct impacts on terrestrial ecological resources from the Project would
be habitat loss on 18.6 ha of
developed area and 4.5 ha of
wasteland. These habitats were ranked as very low in ecological value and
supported no floral or faunal species of conservation importance. Only removal
of individual trees located within the
footprint of the proposed development would result and most of the
affected trees were common species of low ecological value. No protected
species or other flora of conservation interest would be directly affected
under this Project. Tree transplantation and compensatory planting would mitigate such impact and no adverse
direct ecological impacts would result.
3.30
Other
indirect disturbance to the nearby habitats and associated wildlife during the
construction phase of the Project would be temporary and minimised with the
proposed mitigation measures in place, including noise mitigation measures and
good site practice. No direct or indirect ecological impact would occur during
the operation of the project..
3.31
A
literature review of previous studies and EIA reports was initially conducted
to establish the baseline conditions of the Assessment Area. In areas that were
identified to be directly impacted by the project, i.e. Aberdeen PTW,
ecological surveys (intertidal and dive surveys) were conducted to gather up to
date, detailed information on the baseline condition of the affected site. The
assessment of potential impacts was then conducted in accordance with the EIAO
TM requirements.
3.32
Indirect
impacts on water quality may result from site run-off, sewage from workforce,
accidental spillage and discharges of wastewater associated with land based
construction activities. If all the recommended good site practice and
mitigation measures are implemented properly then no significant adverse impact
on water quality would be expected.
3.33
A
small area of seawall (approx.50m)
would be demolished and reconstructed at the Aberdeen PTW site to complete the
construction works. As confirmed by dive surveys, the subject site supported
very limited marine life. Only 3 colonies of a common hard coral species (Oulastrea
crispata), all in small size (3 to 5cm)
and of low coverage were found in the potentially affected areas. All were
attached to moveable boulders < 50cm
diameter and thus feasible for translocation. Coral translocation and post
translocation monitoring is proposed to minimise the adverse impacts on these
corals.
3.34
Water
quality impact modelling results indicated that the potential impact zone would
be restricted to the Victoria
Harbour and Western
Buffer Water Control Zones (WCZs).
No significant impacts on ecological resources outside these two WCZs
are expected.
3.35
The
existing SCISTW outfall location was chosen in an area with low ecological
value. No significant adverse
impacts on marine ecological communities would be anticipated, considering
that:
l
Improvement in water quality with reduction in E. coli
levels in Western Buffer WCZ and Western Victoria Harbour WCZ;
l
Only localized and small changes in total residual chlorine
(TRC), chlorination by-products (CBPs) and Dissolved Oxygen (DO) around the
existing SCISTW outfall;
l
No unacceptable ecological risk on marine mammal and marine
life in relation to acute and chronic effects;
l
Water quality criteria for unionized ammonia would be met at
the edge of the zone of initial dilution (ZID) and would be out of the normal
distribution range of dolphins, porpoises and green turtles;
l
Unionized ammonia levels would be improved in the
Northwestern, Western Buffer and Victoria Harbour WCZ;
l
Oxygen depletion would be minimal and highly localized
around the SCISTW outfall;
l
Improved DO levels in the Victoria Harbour,
Eastern Buffer and Junk Bay WCZs;
l
Highly localised salinity and temperature changes would not
have adverse impacts on the ecological habitats identified;
l
Increases in the levels of Total Inorganic Nitrogen (TIN)
and Orthophosphate predicted would not be significant enough to have direct
impacts on identified ecological communities;
l
There was no documented data on the specific conditions
leading to harmful algal blooms (HABs) and they have been documented in
polluted and un-polluted water. Increases in nutrient levels during discharge
of CEPT effluent would be unlikely to trigger HAB events;
l
TIN and Orthophosphate levels have increased in the
Assessment Area since the implementation of HATS Stage 1, but no increase in
the number of HAB events has been observed;
l
Water quality modelling predicted little difference in
levels of TIN and Orthophosphate with or without the implementation of the
project. Additionally, with the implementation of HATS Stage 2B, phosphate
discharge would be reduced; and
l
Western Buffer WCZ and western Victoria Harbour WCZ, the
areas affected by the effluent, generally support low to moderate ecological
resources.
3.36
Emergency
discharge of sewage effluent at PTW and SCISTW may occur during periods of
heavy rain when inflow exceeds the capacity of the system or as a result of power/equipment
failure. This would result in a rise in the level of E. coli in the receiving
water body and thus a subsequent deterioration in water quality which would
potentially cause adverse impacts to marine ecological resources. Water quality
modelling predicted no adverse impact on water quality parameters such as
nutrients and DO by emergency discharges. In addition, it was predicted that
increases in the level of suspended sediment resulting from emergency
discharges would not exceed the assessment criteria at coral sites. Water
quality was also predicted to return to normal condition 1 to 2 days after
emergency discharges. Due to the highly transient nature of potential emergency
discharges and the ability of marine organisms to naturally resist pathogenic
strains of E. coli as documented in literature, no insurmountable impact on
water quality is predicted to result from emergency discharges.
3.37
The
existing SCISTW outfall location was chosen in an area where fisheries
resources were considered to be of low value. No adverse impact on fisheries resources
would be anticipated, considering that:
l
The project would result in improvement in water quality
with reduction in E. coli levels in Western Buffer WCZ and western Victoria
Harbour WCZ;
l
Only localized and small changes in TRC, CBPs and DO around
the existing SCISTW outfall would occur.
l
No exceedance of unionized ammonia levels, which could be
toxic to fish, were predicted.
l
Oxygen depletion would be minimal and highly localized.
l
Water quality modelling predicted little difference in
levels of TIN and Orthophosphate with or without the implementation of the
project.
l
TIN and Orthophosphate levels have increased in the
Assessment Area since the implementation of HATS Stage 1, but no increase in
the number of HAB events has been observed.
l
There was no documented data on the specific conditions
leading to HABs and they have been documented in polluted and un-polluted
water. Increases in nutrient levels during discharge of sewage effluent would be
unlikely to trigger HAB events.
l
Water quality objectives would be met at Ma Wan FCZ
3.38
As
there would be no adverse impacts on fisheries resources from the proposed
disinfection or discharge of effluent, no specific mitigation measure for fisheries
would be required.
3.39
The
proposed scheme and associated works under this Project are mainly located in
the areas zoned as Other Specified Use (OU) and Government, Institution or
Community (GIC) while the sites for the proposed PTW upgrading works are mainly
within OU zone. Mitigation measures would be applied to avoid the adverse
landscape and visual impacts in consideration with the surrounding environment.
3.40
Based
on the tree survey carried out under this Project, approximately 376 trees
would be affected due to the proposed construction works of the Project. No potential LCSD Champion Trees or
Registered Old and Valuable Trees were found either in existing PTWs/SCISTW or
temporary works areas. There were no rare species or endangered specie but
common species identified only. All the trees with high amenity value which are
unavoidably affected by the works would be transplanted. Based on the proposed works, trees would
be planted within the site and works areas to compensate for the loss of the
existing trees. Roof greening and
vertical greening would be adopted where possible for the provision of more
greening to enhance the landscape quality. In the landscape impact assessment,
with the proposed mitigation measures to be implemented, the overall residual
impacts on existing trees would be considered as slight in Wan Chai East PTW
and Aberdeen PTW. The impacts on the rest of the PTWs remain insubstantial.
3.41
For
the visual impact assessment in the construction phase, there would still be
some moderate adverse visual impact on the Visual Sensitive Receivers (VSRs)
adjacent or close to the Project sites after implementation of the proposed
mitigation measures. Residual impacts on VSRs further away from the PTWs and
works areas would become slight to insubstantial. During the operation stage,
with mitigation measures in place, there would still be slight adverse visual
impact at day 1 after commissioning of the Project except some VSRs at North
Point, Wan Chai, Central, Sandy Bay, Ap Lei Chau and Stonecutters Island
which would experience moderate visual impacts. With the implementation of
mitigation measures after 10 years during operation, the residual impacts on
most of the VSRs would become insignificant except the VSRs at the above
mentioned areas which would experience slight residual visual impact.
3.42
Overall,
the residual landscape and visual impacts of the proposed development were
considered to be acceptable with mitigation measures implemented during
construction and operation phases.
Assessment for Potential Hazardous Installations (PHIs)
3.43
A
hazard assessment was carried out for the proposed work sites at Aberdeen and
Ap Lei Chau which are located within the consultation zone of two respective
Potential Hazardous Installations (PHI), namely the Hong Kong & China Gas
Company’s Gas Holder (PHI No. H4) and the Shell LPG Transit Depot/Bulk Domestic
Supply (PHI No. H5).
3.44
The
potential hazards associated with all aspects of the construction and operation
of the Project were assessed. The overall risks posed by the activities of the
Project were considered acceptable with the implementation of all safety
measures recommended.
Construction Phase
3.45
The
construction activities of the tunnels and PTWs upgrading works were identified
and assessed. No significant increased risk level from works at both Aberdeen and Ap Lei Chau
sites would be introduced in the vicinity of gas holder and gas pipework with
the implementation of safety measures and close monitoring procedures for
construction activities which may cause vibration and ground settlement during
construction phase.
3.46
In
addition, the requirements of the Gas Safety Ordinance Cap.51 and subsidiary
regulations and the Electrical and Mechanical Services Department (EMSD)’s Code
of practice on Avoiding Danger from Gas Pipe would be followed to ensure safety
of works in the vicinity of gas pipework.
Operation Phase
3.47
The
operational activities of the upgraded PTWs would be very similar to the
existing one and both Aberdeen
and Ap Lei Chau treatment works would not introduce addition risk factor to the
nearby PHIs. Hence, the operations of Project would not increase the PHI risk
level during operation phase.
Assessment for Overnight Explosives Storage
3.48
There
would be no overnight explosives storage proposed for the Project. No hazard
assessment for overnight storage of explosives was required in this Study.
Assessment for Disinfection Facilities
3.49
Hazard
to life impact associated with the proposed disinfection facilities at SCISTW
was quantitatively assessed, with consideration of identified precautionary
measures / operation procedures that would minimize the risks associated with
the chemicals related operations.
The individual risk and societal risk associated with the chemicals used
during operations were found to be acceptable in accordance with the risk
guidelines stipulated in the Annex 4 of the EIAO TM. Hence, the hazard to life impact due to
the Project would be acceptable.
Marine Archaeology
3.50 No marine works would be required under this Project, except
reconstruction of small part of the seawall near the Aberdeen PTW to facilitate the PTW
upgrading works. As indicated in the old as-constructed drawings, the Aberdeen seawall area was dredged in 1970s and the seabed was already
disturbed at that time. The current proposed construction works would only
disturb the artificial seawall structure but not down to the level of the
existing undisturbed seabed. Further, tunnel construction works would also not
disturb the seabed as elevation of the tunnels would be deep underground below
rockhead with average depth of ~100m below ground . Hence, potential
impact on marine archaeological deposits from this Project would not be
anticipated and no marine
archaeology impact assessment on the seabed was therefore required.
Built Heritage
3.51
Built
heritage impact assessment identified heritage buildings and structures on Stonecutters Island
and also on Hong Kong
Island that may be
affected by groundborne vibration during the construction phase of the Project.
It was determined that the maximum vibration level should be limited to 25 mm/s
and monitoring of vibration levels should be undertaken during blasting for
tunnel, shafts, effluent conveyance system and disinfection facilities in the
vicinity of the buildings/structures to confirm compliance with the vibration
limits. There would be no impact to built heritage resources during the
operation phase.
3.52 Environmental monitoring and audit
(EM&A) requirements for the Project have been specified in an EM&A
Manual. The EM&A Manual contains
details of proposed baseline and compliance monitoring programmes,
implementation schedule of the environmental protection / mitigation measures,
EM&A reporting procedures and complaint handling procedures.
4.1
The
findings of this EIA Study have determined the likely nature and extent of
environmental impacts predicted to arise from the construction and operation
phases of the Project. The EIA has,
where appropriate, identified precautionary design and mitigation measures to
achieve compliance with environmental legislation and standards.
4.2
Overall,
the EIA Study for the proposed HATS Stage 2A predicted that the Project, with
the implementation of the proposed precautionary design and mitigation measures
for construction and operation phases, would comply with all applicable
environmental standards and legislation.
This EIA has also demonstrated the acceptability of the residual impacts
from the Project. EM&A
mechanisms have been recommended, where necessary, to verify the accuracy of
the EIA predictions and the effectiveness of recommended precautionary design
and mitigation measures.
