Purpose and
Objective of the Project
2.1
2.2
Over the past few decades, the
water quality of
2.3
While improvements have been
made, these gains, due to the continuous growth of our population and economy,
will be eroded in the future unless sustained efforts to clean up the harbour
are maintained. To this end, Government
is committed to proceeding with Stage 2 of HATS in two phases. Notably, HATS Stage
2.4
The purposes of Stage
· To deal with the remaining sewage that now discharges into the Harbour virtually untreated
· To provide additional treatment to all sewage from the whole HATS service area to protect our beaches from bacterial pollution
· Consequently, to restore the Harbour to a more natural, healthier condition
2.5
Specifically, the prime objectives of HATS Stage
·
To intercept and treat the
sewage generated from the populated areas in the northern and southwestern
parts of
· To increase the SCISTW treatment capacity to cope with the anticipated population and economic growth in the harbour area
·
To provide an adequate level of
treatment for all HATS flows to
2.6 The best way to improve Victoria Harbour’s water quality in the long term is to ensure all the sewage, including the extra flows anticipated to arise in future as a result of population and economic growths, is collected and treated properly.
2.7
Stage 1 of HATS was
commissioned fully in the end of 2001.
It collects sewage from Tsuen Wan, Kwai Tsing, Tseung Kwan O, the urban areas of
2.8 On average, levels of oxygen in the water, necessary for fish to live, increased by 10% overall, compared with the situation immediately before full commissioning; the concentration of ammonia, which can be toxic to marine organisms, was reduced by 25% overall; and the levels of E. coli, which is a measure of disease-causing organisms, fell by 50% overall.
2.9
While HATS Stage 1 has brought
about remarkable improvements, the situation in some areas remains
unsatisfactory. Stage 1 collects only 1.4 million m3/d of sewage output and its treatment levels are not thorough enough
to remove all pollutants. The remaining 450,000 m3/d generated by a population of approximately one million people
living on the northern and western shores of
2.10
Provision of HATS Stage 2 would
address all of these concerns and provide a sustainable programme for
maintaining clean waters throughout
·
Under HATS Stage
·
Stage 2B, that is to provide
biological treatment to all HATS flows, is needed after completion of Stage
2.11
While the ADF (as part of Stage
· Prevent another 190 to 500 tonnes of sewage sludge (depending on sewage quantity) from being dumped into the harbour each day
· Reduce toxic ammonia by 10% on average
· Reduce total inorganic nitrogen and phosphorus by 5% and 8% respectively
· Increase dissolved oxygen levels by 5%
2.12
The HATS programme is a major
sewerage infrastructure for
2.13 In summary, there is a clear need to proceed with the remaining stages of HATS, not only to restore the Harbour to a more natural and healthier condition, but also to protect harbour water quality from future decline due to the anticipated population increase and economic activities. 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.
Outline of Proposed
Scheme and Project Elements
2.14
The operational philosophy of
HATS Stage
· Firstly, screened and de-gritted at the preliminary treatment works (PTWs) to remove large solid objects and sediments, so as to protect the downstream sewer tunnels from blockage or excessive sedimentation
·
Then, discharged into the
sewage conveyance system (
· Finally, treated (and disinfected) at SCISTW, to a level suitable for discharge via a submarine outfall system into the sea (off the western anchorage area)
2.15 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.
2.16
The key elements of HATS Stage
· Upgrading of eight existing PTWs on northern and western Hong Kong Island, i.e., North Point (NP), Wan Chai East (WCE), Central, Sandy Bay (SB), Cyberport (CP), Aberdeen, Wa Fu (WF), and Ap Lei Chau (ALC), to meet design treatment and flow requirements
·
Construction of a
· Augmentation of the existing SCISTW to meet design flow and treatment performance requirements, including:
· Construction of a new influent pump station to cater for additional flows
· Expansion of the existing chemically enhanced primary treatment (CEPT) facilities to cater for the additional flows
· 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
· Expansion of the existing sludge processing facilities to cater for additional sludge volumes associated with the additional sewage flows
· Construction of a new effluent tunnel to convey treated (and disinfected) effluent to the existing outfall system
· Ancillary facilities, including an electrical substation
2.17
In developing the HATS Stage
2.18 Notwithstanding the above, environmental benefits and dis-benefits of feasible alternatives with respect to treatment methods, construction methods, and sequence of works have also been considered with a view to reducing any adverse environmental impacts. These considerations are outlined in the Section under “Consideration of Alternatives” below.
2.19
The following paragraphs
outline the proposed HATS Stage
2.20
The overall approach to sewage
flow and load management for HATS Stage
Exhibit 2.1 Diagrammatic
Illustration of HATS Stage
1.7
2.21
As for HATS Stage 1, the design
of HATS Stage
2.22 For HATS Stage 1, the SCISTW CEPT treatment facilities have been sized at 2.0 times ADWF (average dry weather flow), while the Stage 1 deep tunnel system was at between 2.0 and 2.2 times ADWF, depending on the projected population of the catchment. The Stage 1 PTWs were sized at higher peaking factors, depending on the size of the contributing catchment, i.e., smaller catchments having higher design peaking factors.
2.23
For HATS Stage
2.24 In summary, a considered approach to flow and load management that balances cost and environmental benefits is proposed, recognising that it would be extremely costly to provide full treatment capacity for the very high rates of flow that would occur only very rarely. A view is taken that in such extreme circumstances, the environmental (i.e., receiving water quality) impacts of any discharge of untreated or partially treated effluent is expected to be acceptable, given the infrequent nature and relatively short duration of such discharges. The impact of sewage overflows is addressed in Section 6 of this EIA report dealing with water quality.
2.25
As for HATS Stage 1, two levels
of sewage treatment are proposed for HATS Stage
2.26
At the PTWs, the objective of
preliminary-level treatment is to remove large debris and grits (inorganic
particles) from the incoming raw sewage.
Debris removal is by mechanical screens, which is to prevent as much as
possible large solids, floating refuse or alike from entering the downstream
2.27
Grit removal at the PTWs will
be by sedimentation, the purpose of which is to avoid progressive accumulation
of sediments in the downstream
2.28 At SCISTW, the objective is to provide additional primary-level sewage treatment capacity at SCISTW to cater for the projected design flows under the ultimate development scenario in the HATS service area. Primary-level treatment refers to the use of sedimentation principles to remove “settle-able” pollutants from the influent sewage. To enhance pollutant removal efficiency, primary treatment may include addition of chemical substance(s) to serve as a coagulant in the sedimentation process. For example, the existing SCISTW is a CEPT plant, using ferric chloride solution as the coagulant.
2.29
As for HATS Stage 1, the
proposed quality requirements for the treated effluent from the expanded SCISTW
under HATS Stage
Table 2.1 Proposed Effluent
Quality Limits for Expanded SCISTW Under HATS Stage
|
Parameter |
Units |
Monthly Geometric Mean |
95th percentile |
Maximum |
|
Total Suspended Solids ( |
mg/L |
- |
55 |
110 |
|
Biochemical Oxygen Demand (BOD5) |
mg/L |
- |
75 |
150 |
|
E.
coli |
counts per 100mL |
20,000 |
300,000 |
- |
2.30
Based on the latest population
and employment growth projections for the HATS catchments, and the adopted flow
management philosophy, a set of design flows for the various elements of HATS
Stage
Table
2.2 Design Flows for HATS Stage
|
Element |
|
Design Flow |
|
Upgrading of Preliminary
Treatment Works (PTW) |
||
|
Upgraded North
Point (NP) PTW |
|
|
|
Upgraded Wanchai
East (WCE) PTW |
|
|
|
Upgraded |
|
|
|
Upgraded |
|
|
|
Upgraded Cyberport
(CP) PTW |
|
|
|
Upgraded |
|
|
|
Upgraded Wa Fu
(WF) PTW |
|
|
|
Upgraded Ap Lei
Chau (ALC) PTW |
|
|
|
Sewage Conveyance System -Tunnel Sections |
||
|
Tunnel J: NP to WCE |
|
|
|
Tunnel K: WCE to Central to Sai Ying Pun (SYP) |
|
|
|
Tunnel Q: ALC to |
|
|
|
Tunnel P: |
|
|
|
Tunnel N: CP to SB |
|
|
|
Tunnel M: SB to SYP |
|
|
|
Tunnel L: SYP to
SCISTW |
|
|
|
Sewage Conveyance System - Ancillary Pumping Stations (PS) |
|
|
|
NP Seawater PS
(located within existing NP PTW site) |
|
|
|
WCE Sewage
Transfer PS (located within existing WCE PTW site) |
|
|
|
SB Sewage
Transfer PS (located adjacent to existing SB PTW site)* |
|
|
|
CP Sewage
Transfer PS (located within existing CP PTW)* |
|
|
|
Aberdeen
Seawater PS (located with existing Aberdeen PTW site) |
|
|
|
ALC Sewage
Transfer PS (located within existing ALC PTW site) |
|
|
|
Augmentation of |
||
|
Upgraded/Expanded
Influent Pump Stations |
|
|
|
Upgraded/Expanded
Primary Treatment Facilities |
||
|
Upgraded/Expanded
Disinfection Plant |
||
Note *: The sewage
transfer PS will be constructed in either
2.31
It is anticipated that
construction of the various elements of the Project will commence
progressively, with the first construction contract to be awarded in early 2009
and others to follow within two years.
The construction (including testing and commissioning) of the whole of
HATS Stage
2.32
Relevant concurrent projects in
the vicinity of the HATS
Table
2.3 Concurrent Projects in
relation to Construction of HATS Stage
|
Concurrent Projects |
Project Proponent |
Tentative Construction Programme |
Project Conflicts |
|
Wan Chai Development Phase II
(WDII) and |
Civil Engineering and
Development Department (CEDD) |
2009 to 2016 |
·
WDII is competing the southern one third of Site
Portion WCE-I for re-provision of a salt water pumping station. ·
Construction of Tunnel K and Wan Chai East
production shaft would be interfaced with WDII. |
|
Shatin to Central Link (SCL) |
Kowloon-Canton
Railway Corporation (KCRC) |
No programme
available |
·
No direct conflict between SCS and SCL
proposed alignments. ·
Works area (WCE-i) may be required by SCL. |
|
(WIL) |
Mass Transit Railway
Corporation Limited (MTRCL) |
2007 to
2012 |
·
No direct conflict between SCS and WIL
proposed alignments due to different elevations. ·
Partly or whole alignment of WIL & SCS
could be constructed by drill & blast. Discussion with Mines Department
of CEDD for the explosives issue is on-going. |
|
(SIL) |
Mass Transit Railway
Corporation Limited (MTRCL) |
2009 to
2014 |
·
SIL could be close to the works areas of SCS
at Ap Lei Chau, Wah Fu and Cyberport. ·
Alignment selection for SIL is still under
consideration (Information is not available). |
|
Reprovisioning of Central
District Headquarters and Central Divisional Police Station at |
Architectural
Services Department (ASD) |
2007 to
2010 |
·
Central District Headquarters and Divisional
Police Station will be built on the site at |
|
Laying of |
Water
Services Department (WSD) |
2008 to 2011 |
·
EIA Report (EIA-131/2007) was approved by EPD
on ·
Works area required by the WSD project is
located at the eastern side of Site Portion SYP-I for SCS. ·
Water main along |
|
|
Architectural Services Department (ASD) |
2008 to
2011 |
·
Site Portions SYP-SCC and SYP-I for SCS are
located only about |
|
Drainage Improvement in Northern
|
Drainage Services Department (DSD) |
2008 to
2011 |
·
SCS and HKWDT would use the parcels of land south
of the Cyberport PTW as works area. Sharing of access road within the PTW to
access the works areas is required. |
|
Consultancy to develop a
conceptual design for the Aberdeen Tourism Project |
Tourism Commission |
2009 to 2014 |
·
Two of SCS proposed workshop and storage sites at (a) the eastern end of |
2.33 The overall objective of the upgrading works is to achieve that the PTWs will be able to meet designated design performance (i.e., screening and degritting) and flow (under ultimate development conditions) requirements.
2.34 Preliminary-level treatment of sewage at the PTWs is achieved by mechanical screening and physical sedimentation (settling) processes without the use of any process chemicals. Major plant and equipment in proposed upgraded PTW include:
· Mechanical screens of various sizes
· Pumps
· Grit traps (sedimentation tanks)
· Compactors (for solid residues processing)
· Deodorising units (e.g., bio-filters and/or activated carbon filters)
2.35 Depending on the capacity and condition of the existing facilities, the upgrading works may involve relatively straightforward equipment replacement or in some cases, relatively elaborate reconstruction works.
2.36
Based on the recommendations of
a preliminary design undertaken as part of this EIA study, the PTW upgrading
works under HATS Stage
2.37
A typical “process flow
diagram” for the proposed upgrading works at North Point, Central,
2.38 Figures 2.1 to 2.8 show the existing and proposed layouts of the eight PTWs. In addition to the screening and de-gritting facilities, these also show:
· The proposed drop shaft location inside or adjacent to each PTW site
·
Location of a possible seawater
pumping station in each of NP and Aberdeen PTW, which might be needed for the
operation of the Stage
· Location of a possible sewage transfer pumping station inside or adjacent to each of WCE, SB, CP, and ALC PTW
2.39
These drop shafts and ancillary
seawater or sewage transfer pumping stations are part of the Stage
2.40 At WCE PTW, only equipment replacement and minor building construction works (i.e. transformer room and switch room) are proposed. No demolition works are required. Similarly, no upgrading works is proposed for the existing SB and CP PTWs. Nevertheless, a sewage transfer pumping station might be constructed inside or adjacent to each of these sites.
2.41
All of the upgraded PTW will
use the similar types of mechanical plant and equipment for screening and
de-gritting. At NP, Central,
· Demolition of existing buildings
· Generally shallow excavation (less than 5m) for the main plant building, except for manholes/pits and the grit traps where excavation at these locations could be down to depths of about 8m below ground level
· Piling (non-percussive piling method only)
· Construction of new buildings & structures
· Installation of electrical and mechanical equipment
· Reconstruction of a section (~53m) of seawall (only at Aberdeen PTW)
· Laying of sewers, drainage pipes, and other utility lines
2.42 Conventional construction plant and equipment (e.g. dozers, backhoes, dump trucks, hydraulic breakers, cranes, etc) will be used to upgrade the PTWs.
2.43 The overall duration of upgrading works at each of the above PTW site would be up to about 3.5 years. This is because the existing PTW operation must be maintained at all times during the upgrading works, necessitating a phased approach whereby a new replacement treatment train must be installed before an old one may be decommissioned and removed.
2.44
At the same time, working space
is also needed for the construction of the
2.45
After commissioning of HATS
Stage
2.46 Sewage will continue to enter the PTW via the existing sewer system, and it will flow through the various treatment units in the PTW. The solid residues (screened debris and grits) will be removed by trucks to landfill for disposal.
2.47
During high inflow periods
(e.g., caused by high intensity storms), which would be rare or infrequent,
diluted sewage in excess of the capacity of the downstream
2.48 The number of PTW operators in each of the upgraded PTW would be similar to current conditions.
Exhibit 2.2 Typical
Process
2.49
The
2.50
As shown in Exhibit 2.3, the HATS Stage
2.51
The proposed
2.52
Extensive ground investigations
using modern technology have been conducted to identify any potentially
difficult geological or subsurface conditions and to provide input to the
design of the tunnel alignments (both vertically and horizontally). The alignments of the
2.53 Generally, the horizontal alignment has been carefully selected such that it avoids passing under private land as far as possible, thereby eliminating interfaces with private properties.
2.54
In addition, to ensure that future
development of the surface land would not be constrained, the tunnels are
designed to be located at least
Exhibit 2.3 Diagrammatic
Representation of HATS Stage
Sewage
transfer and seawater pumping stations in the
Not to Scale
2.55
For the purposes of discussion,
the
Table
2.4 Summary of
|
|
Location |
Horizontal Length (km) |
Approx. Level (mPD) |
Cross Section Area of Finished Pipe(s) |
Approx. Tunnel Excavated Diameter (m) |
|
Tunnel J |
North Point (NP) to Wan Chai East (WCE) |
3.2 |
-163.4 to -157.0 |
Twin oval pipes, one with: 1.73m2, one with: 2.26m2 |
4.5 |
|
Tunnel K |
Wan Chai East (WCE) to Central |
3.4 |
-157.0 to -150.2 |
Twin oval pipes, one with: 3.90m2, one with: 2.26m2 |
5.1 |
|
Central
to Sai Ying Pun (SYP) |
0.9 |
-150.2 to -148.4 |
Twin oval pipes, one with 5.65m2, one with 2.26m2 |
5.5 |
|
|
Tunnel Q |
Ap Lei
Chau (ALC) to |
1.3 |
-76.0 to +1.0 |
0.64m2, circular |
1.3 |
|
Tunnel P |
|
1.1 |
-80.18 to -78.0 |
1.77m2, circular |
3.5 |
|
Wah Fu
(WF) to Cyberport
(CP) |
1.5 |
-78.0 to -75.0 |
2.14m2, circular |
3.5 |
|
|
Tunnel N |
Cyberport
(CP) to |
1.2 |
-75.0 to -72.6 |
2.14m2, circular |
3.5 |
|
Tunnel M |
to Sai
Ying Pun (SYP) |
3.7 |
-123.0 to -115.6 |
2.14m2, circular |
3.5 |
|
Tunnel L |
Sai
Ying Pun (SYP) to SCISTW |
4.6 |
-148.4 to -139.3 |
7.07m2, circular |
3.9 |
2.56
The longest section is Tunnel L
(SYP to SCISTW), which measures about
2.57
The deepest
2.58 In all tunnel sections, except Tunnels J and K as well as the southern sections of the SCS, a single sewer pipeline (of carrying size or diameter) would be constructed.
2.59 Two main types of shafts (vertical tunnels or deep wells) would be involved:
· Temporary production shafts
· Permanent drop and/or riser shafts
2.60 “Production shafts” are formed for the purposes of gaining access to the main tunnel level from ground surface, and they will be decommissioned (backfilled) after completion of the main tunnelling works.
2.61
A production shaft is excavated in a vertical direction and the
main tunnel is excavated along a horizontal direction. The depth of the
production shaft is corresponding to the level of the main tunnel.
Through the production shafts, the excavated material (tunnel spoil) is removed
to the ground surface, and construction equipment and materials are brought
in. Hence, production shafts are temporary in nature. However, in the
cases of SYP, SB and CP, the production shafts would remain open to allow flow
of sewage instead of being backfilled at the end of the construction period
(i.e. converted from productions shafts to drop and/or riser shafts). It is
expected there would be a maximum of 9 temporary production shafts (with
diameters from 10 to
2.62
“Drop shafts” are constructed
primarily for the purposes of allowing screened/de-gritted sewage from the PTWs
to enter the main tunnel system. A
“riser shaft”, on the other hand, allows sewage to be lifted (via pumping) to
ground surface from the deep tunnels.
Drop/riser shafts are an integral part of the
|
Location |
Details of Shaft |
|
|
North Point |
PTW |
1 Drop Shaft |
|
|
Temporary Works
Area |
1 Production
Shaft (backfilling required) |
|
Wan Chai East |
PTW |
1 Drop/Riser
Shaft |
|
|
Temporary Works
Area |
1 Production
Shaft (backfilling required) |
|
Central |
PTW |
1 Drop Shaft |
|
Sai Ying Pun |
Works Areas |
2 Production
Shafts; which will be converted to a “Drop Shaft” and a “Riser Shaft” after completion of tunnel construction |
|
|
Works Areas |
2 Production
Shafts; one of which will be converted to “Drop/Riser Shaft” after completion
of tunnel construction and another one will be backfilled. |
|
Cyberport |
PTW |
1 Production
Shaft; which will be converted to “Drop/Riser Shaft” after completion of
tunnel construction |
|
Wah Fu |
PTW |
1 Drop Shaft |
|
|
PTW |
1 Drop Shaft |
|
|
Works Area |
1 Production Shaft
(backfilling required) |
|
Ap Lei Chau |
PTW |
1 Drop Shaft |
|
|
SCISTW |
1 Riser Shaft 1 Production
Shaft (backfilling required) |
2.63 Taking into account the latest development of the Project, there are 20 temporary/permanent works areas required which are listed in Table 2.6. The locations are shown in Figure 2.9. Most of the works areas will be used temporarily for shaft construction or as supporting areas for temporary stockpile/storage during construction stage.
2.64
There are 2 permanent works
areas required for construction of the drop and riser shafts in Sai Ying Pun,
as well as the drop/riser shaft and transfer pumping station in
Table 2.6 Summary of Works Areas
Location
|
Site Details
|
Approximate Area (m2) |
Occupation
|
Main Usage
|
|
North
Point |
NP-viii |
4,000 |
Temporary |
- Production
shaft for tunnel construction (backfilling required) |
|
Wan
Chai East |
WCE-i |
2,600 |
Temporary |
- Production shaft for
tunnel
construction (backfilling required) |
|
|
WCE-v |
1,000 |
Temporary |
- Storage/Stockpiling area |
|
|
WCE-vi |
1,000 |
Temporary |
- Storage/Stockpiling area |
|
Central |
CTL-ii |
700 |
Temporary |
- Supporting works area for PTW and drop shaft construction |
|
|
CTL-iii |
2,010 |
Temporary |
- Back-up works area |
|
|
CTL-iv |
1,000 |
Temporary |
- Storage/ Stockpiling area |
|
Sai
Ying Pun |
SYP-I |
4,130 |
Temporary |
-
Stockpiling area |
|
|
SYP-ii |
1,130 |
Temporary |
- Storage/Stockpiling area - Site Office |
|
|
SYP-SCC |
620 |
Permanent |
- Production
shaft/riser shaft and production
shaft/drop shaft for tunnel construction |
|
|
SB-PS |
695 |
Permanent |
- Production shaft/ drop/riser shaft construction -
Construction of
ancillary facilities for PTW upgrading |
|
|
SB-i |
3,600 |
Temporary |
-
Production
shaft for tunnel construction (backfilling required) |
|
Cyberport |
CP-iv |
2,300 |
Temporary |
- Storage/Stockpiling area - Supporting works area for tunnel construction |
|
|
Abd-i |
1,520 |
Temporary |
-
Supporting works area for tunnel construction by HDD |
|
|
Abd-iii |
4,140 |
Temporary |
-
Production
shaft for tunnel construction (backfilling required) |
|
Ap
Lei Chau |
ALC-i |
1,400 |
Temporary |
- Supporting works area for HDD construction |
|
|
ALC-iii |
1,200 |
Temporary |
- Storage/Stockpiling area |
|
|
ALC-iv |
1,000 |
Temporary |
- Storage/Stockpiling area - Site Office |
|
|
SCI-i |
3,910 |
Temporary |
- Storage/Stockpiling area |
|
|
SCI-ii |
2,550 |
Temporary |
- Storage/Stockpiling area |
2.65
A new Influent Pump Station at
SCISTW will “lift” the sewage up into the treatment trains on SCI. However,
depending on the final Stage
2.66 The purpose of these STPS would be to lift progressively the sewage up as it travels towards SCI so that the pumping energy required at the terminal pumping station at SCISTW could be reduced, with a view to optimising the overall energy requirements of the scheme in light of cost and other considerations (e.g., land availability, construction risks, etc).
2.67
At this stage, the hydraulic
design of the
2.68
In addition, it is proposed to
construct two seawater-pumping stations, one to be located at each of the
northern and western section of the Stage
2.69 At this stage, for the purposes of the EIA study, it is assumed that the seawater pumping stations would be located inside the NP and Aberdeen PTWs, where land is available.
2.70 The production/drop/riser shaft construction works would involve typically two phases:
· Mechanical excavation of the softer material near ground surface using diaphragm-walling techniques
· Excavation of harder (rock) materials at greater depths using mechanical or blasting techniques
2.71 For the temporary production shafts, they will be backfilled with concrete and granular fill after completion of tunnel construction except at SYP, SB and CP where the production shafts would be converted to drop shaft, permanent shaft or junction shaft after tunnelling. In the case of the permanent drop/riser shafts, they will be lined or with pipes installed. For drop shafts, a hydraulic energy dissipating structure (e.g., vortex chamber) will also be constructed except the drop shaft at ALC.
2.72 It is anticipated that conventional construction plant and equipment (e.g., cranes, hydraulic breakers, trucks, backhoes, excavators etc) would be used.
2.73 As construction activities are confined to the shaft sites, disturbance to the public and local communities can be reduced to a minimum, e.g. hoarding will be erected to minimize visual impacts, and noisy construction equipment will be housed to minimise noise impacts to the residents.
2.74
For HATS Stage
2.75
Generally, mechanical boring
methods refer to use of specialised drilling/boring machines to excavate the
tunnel sections. For large diameter
tunnels, “Tunnel Boring Machines” (TBMs), which are a group of highly
specialised tunnelling equipment, would be an option for HATS Stage
2.76 “Drill & Blast”, on the other hand, refers to the controlled placement of explosives in carefully located pre-drilled holes in the tunnel face, followed by ignition of the explosives (blasting) to form the desired tunnel void.
2.77 Given that the construction method has not yet been determined by the Engineer at the time of preparing this EIA, both drill and blast and mechanical boring methods therefore remain feasible construction method and are considered in the EIA study.
2.78 Irrespective of whether mechanical boring or drill & blast method is used, the principal consideration would be effective control of water ingress into the excavated tunnel sections. Since the tunnels are deep, groundwater would tend to enter the tunnel under high-pressure through any joints in the rock during excavation. Uncontrolled ingress of groundwater may cause undue settlement of the surrounding ground. To overcome this, probe holes would be drilled ahead of the tunnel excavation face to investigate the ground condition. If groundwater is detected, the ground ahead of the tunnel face will first be grouted with cement materials to seal up the joints in the rock. This will form a solid core to stop ingress of ground water before tunnel excavation advances to that region. Once the excavation is completed, one or more sewer pipelines of the required sizes (as shown in Table 2.4) will be laid or constructed in-situ inside the excavated tunnel void.
2.79 Besides, effective control of vibration would be considered by using drill and blast or mechanical boring means (e.g. TBM). Since the tunnels are proposed deep underground, with careful control of quantity of explosives by blasting assessment, the vibration can be restrained to within acceptable level during drill and blast. Vibration impact induced by mechanical boring method can also be controlled by speed of boring. Therefore, mechanical boring method would also be considered feasible for tunnel construction from vibration point of view.
2.80 Groundborne noise impact would also be considered in the selection of construction methods. In principle, vibration would be transmitted from tunnelling via bedrock or soil to the nearby foundations of the noise sensitive receivers (NSR), and it would then be transmitted primarily through the structural elements of the buildings, resulting in groundborne noise to the NSR. Since the duration of blasting is very short and infrequent, groundborne noise impact induced by drill and blast would not be a concern with respect to noise annoyance. For mechanical boring methods, as discussed in Section 5 of the groundborne noise assessment, there would not be any adverse groundborne noise impact anticipated on the NSR along the proposed tunnel alignments during construction of the Project.
2.81 The pumping station construction method would be conventional, and would involve principally:
· Piling (non-percussive piling method only)
·
Excavations to depths of up to
· Construction of new buildings & structures
· Installation of electrical and mechanical equipment
· Laying of sewers, drainage pipes, and other utility lines
2.82 It is anticipated that conventional construction plant and equipment (e.g. dozers, backhoes, dump trucks, hydraulic breakers, cranes, etc) will be used.
2.83
The
2.84 The existing SCISTW is designed to cater for 1.7million m3/day under design average dry weather flow condition. It is now proposed to increase the overall treatment capacity of SCISTW to about 2.45 million m3/day under design average dry weather flow condition, which is based on the updated flow and load projections conducted under this EIA. The SCISTW effluent flow rate of 2.8 M m3/d as stated in the EIA Study Brief for this Project is no longer applicable.
2.85 The proposed augmentation works will be integrated with the existing facilities, as illustrated in the process flow diagram in Exhibit 2.4.
2.86 Construction of the upgrading works will be conducted while the existing SCISTW maintains essentially uninterrupted operation at all times. To achieve this, it is proposed to phase the construction works packages over an overall construction period of about 3.5 to 4 years. Phased construction also reduces the peak magnitudes of constructional stage impacts such as noise, dust, etc. so that the relevant environmental criteria can be met at all times.
2.87
The proposed augmentation works
under Stage
·
A new Influent Pumping Station (
· Additional sedimentation (i.e., CEPT) facilities, to be located adjacent to the existing CEPT tanks
·
Upgraded effluent disinfection facilities (over and above the Advance Disinfection Facilities being
implemented ahead of HATS Stage
· A new Effluent Conveyance System (ECS) and associated chamber, consisting of a deep sewer tunnel connecting the CEPT tanks and the new chlorine contact tank, and the discharge culvert to Chamber 15. A new Chamber 15A and an extension of the existing Chamber 15 would be added to the effluent conveyance system.
· Additional sludge processing (dewatering) facilities, located adjacent to the existing sludge building
· A new odour treatment system, based on use of bio-filtration and activated carbon filtration technologies
· Ancillary facilities, including high-voltage electrical substation (transformer station)
2.88 These are elaborated in more details as follows:
Exhibit 2.4 HATS Stage
2.89
It is proposed to construct a
new
2.90
As shown in Figure 2.10, the new
2.91
The
2.92
Construction of the
· Deep excavation using diaphragm-walling technique
· Concreting to form substructure and superstructure using conventional reinforced concrete building techniques
· Equipment installation
· Testing and commissioning
2.93 Similarly, construction of the interconnection pipe/culvert would follow conventional practice, i.e., trench excavation (e.g. laying of precast concrete pipes or in-situ construction of the reinforced concrete box culvert, and backfilling), or trenchless methods (e.g. micro-tunnelling).
2.94
According to the current schematic
design, it is proposed to construct additional CEPT facilities (consisting of
mixing chambers, flocculation tanks, and double-deck sedimentation tanks)
adjacent to the existing CEPT facilities, as shown in Figure 2.10. The new CEPT facilities would measure about
2.95
Construction of the CEPT tanks
would follow similar practices as for HATS Stage 1. Piles have already been sunk under HATS Stage
1 at where the new CEPT facilities are to be located. Subject to confirmation during the detailed
design stage that these pre-sunk piles are adequate for the purposes of HATS
Stage
2.96
The upgraded effluent
disinfection facilities would be located at a site off
·
A chlorine contact tank of
reinforced concrete construction, about
·
A dechlorination plant
(measuring about
· Two new sodium hypochlorite storage tanks, with the size of 8m diameter and 13m height (4 of which to be constructed under ADF)
2.97 Construction of the chlorine contact tank and dechlorination facilities would follow conventional practices, including piling (bored piles) to form foundations, concreting, and installation of storage tanks and electrical and mechanical equipment. The ADF dechlorination plant constructed under ADF (near proposed Chamber 15A) would be demolished.
2.98
The proposed ECS comprises a
large-diameter (
2.99 Construction of the effluent tunnel would be by either mechanical boring or “drill and blast”. The riser shaft would be constructed using conventional techniques, i.e., mechanical excavation of the near surface softer materials by diaphragm-walling techniques, and blasting for the deeper harder (rock) materials.
2.100 The flow distribution chamber and Chamber 15A would be a conventional reinforced-concrete structure. Typically, this would involve excavation (e.g., by backhoe), piling (non-percussive type) and subsequent placement of reinforced concrete to form the chamber.
2.101 The proposed sludge processing facilities would include about 12 new centrifuges housed in an enclosed reinforced concrete building located adjacent to the existing sludge building. Also in the new building will be a control room, an electrical panel room, and a chemical (polymer) storage room. Up to three new sludge silos will also be constructed next to the new sludge building.
2.102 Construction of the new sludge facilities will follow conventional practices, involving piling (bored piles) to form foundations, building construction, and then equipment installation.
2.103 For the purpose of this assessment, two stages odour treatment with 97% odour removal efficiency (e.g. bio-trickling filters followed by activated carbon filters) would be adopted for SCISTW (except Chamber 15A), and the Chlorine Contact Tank. For the drop shaft, upgraded facilities of PTWs and the SCISTW Chamber 15A, only one stage deodorization system (e.g. biofilter) with 90% odour removal efficiency would be installed. Subject to future detailed design, the Engineer should design the deodorization system to achieve the odour removal efficiency.
2.104 At present, as a worst case scenario for the purpose of the EIA study, it is assumed that odour treatment will be centralised, i.e., the foul air collected from all parts of SCISTW will be pumped to a centralised Odour Treatment Plant for treatment. Subject to future detailed design, a decentralised approach (involving multiple, smaller odour treatment plants located at strategic positions in SCISTW) may be adopted.
2.105
Under the EIA study, the
current layout is for a centralised odour treatment plant located on the
southeastern part of the SCISTW site next to the IPS. There would be about thirty-two
2.106 Construction of the odour treatment plant would follow conventional practices, involving piling (bored piles) to form foundations, building construction, and then equipment installation.
2.107 The key ancillary facilities would include a switchgear building and a high-voltage electrical substation. These are proposed to be located to the northwest of the IPS.
Consideration
of Alternatives
2.108
Two major alternatives for the
· Option 1, the initial scheme presented in the EIAO Study Brief, which was developed based on the schematic design produced under the EEFS commissioned by EPD in 2001.
·
Option 2, an updated alignment developed
for the
2.109
Both
· Onshore vs. offshore alignment: A majority of the alignments under Option 2 are running offshore or close to the shoreline (e.g. Tunnels K, M, and Q). This would avoid passing through public facilities/amenities and reclaimed lands with sensitive structures/old built-up areas at which built heritage resources may be of concern. It is also considered that the offshore scheme would impose least impacts on inland environmental sensitive receivers when comparing with the alignment of Option 1.
·
Straight vs. curve alignment: The
alternative scheme under Option 2 shows more curvature over the entire
alignment. This can avoid encroaching
into the private lots as
far as possible thus minimise programming risk during
the gazetting period under the Sewage Tunnels Ordinance (Statutory
Easement). In particular, the alignment
of Tunnel L under Option 1 is a straight section from Sheung Wan passing
through the People Liberation Army’s Barrack to the SCISTW. In order to avoid vibration impacts imposed
on the built heritage resources on
·
Sheung Wan vs. Sai Ying Pun for the meeting point of flow from
south-western section and northern section: The
location of the flow meeting point is at the ex-Gala Point in Sheung Wan under
Option 1. However, taking into account
the proposed shaft locations which would be near the proposed amenity park
development at the ex-Gala Point, a detailed study was then carried out to
pursue another suitable site for relocation of the shafts and associated
structures. The
·
Tunnels P and R: Based on the scheme under Option 1, sewage at
Wah Fu PTW would be conveyed by gravity to Aberdeen PTW via Tunnel R. The
sewage would then be combined with that at Aberdeen PTW and then pumped to
Central via Tunnels P, N and M. For this section of Tunnel R, it runs beneath
the path in the proximity of
·
Length of tunnel alignment: The total
length of tunnels and pipes for Option 1 is
2.110
In all, 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 be
resulting in the reduction of programming risk and hence duration of
environmental impacts to the public. Although the volume of waste generation is
increased for Option 2 owing to the length of the tunnels which is 0.5km
longer, it is offset by elimination of pipe-jacking and intermediate pits which
would cause social disturbance. On considering the relative environmental
impacts of the tunnel alignments, Option 2 is preferred from an environmental
perspective and is proposed for HATS
2.111 A summary of the environmental benefits and dis-benefits of the above options is provided in Table 2.7.
Table 2.7 Summary of Environmental Benefits and Disbenefits for SCS Alignment Options
|
Option |
Environmental Benefits |
Environmental Dis-benefits |
|
Option 1, the initial scheme presented in the EIAO Study
Brief, developed based on the schematic design produced under the EEFS
commissioned by EPD in 2001. |
§ Less volume of
waste generation |
§ Potentially significant noise, dust,
visual and other amenity impacts to local communities along the sections
using cut and cover methods § Higher
programming risk with encroachment to private lots. (i.e. duration of
environmental impacts to the public could be extended) § Potentially
higher and more direct vibration impact to the sensitive structures /heritage
resources |
|
Option 2, an updated alignment developed for the |
§ Minimisation
of environmental impacts (e.g. dust, noise, visual and other amenity impacts) to inland sensitive
receivers due to offshore alignment § Reduction of
vibration impacts to old-built-up areas and heritage resources § Enhancement of
the landscape and visual scene for early public enjoyment at Sheung Wan by
proposing the flow meeting point at Sai Ying Pun instead of the ex-Gala Point
site § Avoid social disturbance by elimination of pipe-jacking and
intermediate pits for Tunnel R |
§
Slightly higher volume of spoil to be generated |
2.112
The objective of the PTWs is to
protect the downstream
· Different types of screens (e.g., bar vs. perforated screens)
· Different configurations of sedimentation devices (e.g., aerated grit channel vs. vortex units
2.113 The key environmental impacts during PTW operation would be air quality (odour) and noise. Contemporary good practice is for all treatment units to be enclosed, and having the exhaust air treated to remove odour emissions to an acceptable level. The enclosed nature of the PTWs also mitigates against any unacceptable noise impacts.
2.114 Therefore, the odour and noise impacts of a PTW are not sensitive to the choice of preliminary treatment methods (i.e., type of screen or grit removal device). As such, alternative preliminary treatment methods are not considered further.
2.115
The
2.116 Three types of unit treatment process are relevant here: (a) alternative primary treatment methods, (b) alternative disinfection methods and (c) alternative sludge treatment processes. These are elaborate below.
2.117 Consistent with the phased implementation approach for HATS Stage 2, it is proposed to increase the capacity of the CEPT facilities at SCISTW to cater for the projected flows from the whole of HATS service area. Later, HATS Stage 2B will provide biological treatment of all HATS flows to improve effluent quality further.
2.118
As demonstrated in Section 6 of
this EIA Report (Water Quality Impact Assessment), provision of CEPT under HATS
Stage
2.119 With respect to UIA:
·
Water quality modelling
conducted as part of this EIA study (see Section 6) has confirmed that
implementation of HATS Stage
· A non-biological treatment approach to reducing the level of ammonia in the CEPT effluent would involve treatment by chemical means. However, ammonia level in the CEPT effluent is generally too low and effluent volume too large for cost-effective treatment by such methods. Instead, international best practice is to focus on the small quantity of high ammonia “centrate” stream in the total effluent. Centrate is the liquid residue from the sludge centrifuges, and this typically has an elevated concentration of ammonia that can be treated cost-effectively.
· In the case of SCISTW, however, the centrate stream has been found to contribute to only about 2% of the total ammonia load. This means that separate treatment of centrate will be ineffective in reducing the total ammonia load in the effluent.
· In addition, if centrate treatment were to be pursued, a separate treatment plant for centrate will have to be constructed and operated on SCISTW. This would not only need additional land, but also result in additional operational stage environmental impacts (e.g., odour, noise, etc).
·
As centrate treatment would
have little water quality benefit, but it could increase the potential for
significant land based environmental impacts such as odour and noise, treatment
of centrate under Stage
2.120 With respect to TIN and P:
· The Stage 2A implementation would reduce the inorganic nutrients including both TIN (N) & PO4 (P) in the whole study area as compared to the Stage 1 condition. Hence, the Stage 2A implementation would not increase the risk of red tide (since phytoplankton requires both N & P for algal growth).
· Implementation of Stage 2B would cause a further reduction of P level in the receiving water as compared to the Stage 2A condition. Further increase in N caused by the nitrification process of Stage 2B would not increase the risk of algal bloom because their growth would be limited by the reduced P in the water.
·
Nutrient removal has been
considered as an alternative treatment method for HATS Stage 2A to minimize the
TIN levels in the marine water. As the background source (
· Water quality modelling assessment was conducted under this EIA to assess the effectiveness of the enhanced P removal for HATS. Although the enhanced P removal generally has an advantage of further reducing the P level in the water environment, it was predicted that there would be no substantial improvement in the extent of P levels at the semi-enclosed bays (which are vulnerable to algal bloom) resulting from the adoption of the enhanced P removal (details refer to Section 6). Furthermore, adopting the enhanced P removal by adding higher dose of ferric chloride at SCISTW will warrant environmental dis-benefits in collecting, handling and disposal of increased quantities of sludge produced in the sewage treatment process. Therefore, enhanced P removal is not considered as an effective treatment option for HATS Stage 2A. To ensure acceptability of the Project discharge, a Post Project Monitoring (PPM) programme, based on requirements outlined in the EM&A Manual of this EIA, is recommended to confirm the model predictions made in this EIA and to review the need for upgrading or improvements to the HATS operation based on actual measurement data.
2.121 Under the ADF EIA[1], a comprehensive evaluation has been conducted to select the most appropriate disinfection technology for HATS (and the ADF), considering environmental as well as non-environmental factors. The evaluation process included long-listing and short-listing of technology options, along with multi-criteria assessments with increasing levels of sophistication.
2.122 In summary, it was found that the only feasible sewage disinfection options for HATS are chlorination (with dechlorinatin) and UV radiation. Further, both chlorination/dechlorination (purchase of sodium hypochlorite and soudium bisulphite) and UV radiation were found to be environmentally acceptable for HATS. Water quality and ecological impacts can be controlled to well within established criteria (contained in the Technical Memorandum of EIA Process) for either option.
2.123 Although both disinfection options would be environmentally acceptable, there are relative environmental benefits and dis-benefits, as summarised in Table 2.8.
Table 2.8 Summary of Environmental Benefits and Dis-benefits of Disinfection Options
|
Disinfection Option |
Environmental Benefits |
Environmental Dis-benefits |
|
Chlorination with dechlorination |
§
Reduction of pathogen discharge from un-disinfected
effluent and the associated potential health and safety problems. §
Improvement to beach water quality. §
Can be installed at the earliest opportunity
(i.e. end 2009). |
§
Potential discharge of chlorine residues, which are toxic to aquatic
life, but the residues can be controlled by the proposed dechlorination
system to meet the TRC discharge limits (0.2 mg/l at 95 percentile and 0.4
mg/l at maximum as proposed in the ADF EIA Report). §
Formation of potentially harmful chlorinated organic compounds, but the
short- and long-term residual risks to human and ecological health have been
found to be well within acceptable limits. §
Potential hazard to life due to handling and
storage of disinfection chemicals, but this can be eliminated/minimized upfront with
precautionary design measures and the residual risk level is well within
acceptable criteria. |
|
UV radiation |
§
Reduction of pathogen discharge from
un-disinfected effluent and the associated potential health and safety
problems. §
Improvement to beach water quality. |
§
Generation of spent UV lamps which contain
mercury (which is a hazardous waste), but this will be controlled by recycle and re-processing by the UV equipment
suppliers. §
Possible mercury release into the effluent when UV
lamps break during operation and maintenance activities, but this is unlikely
given proper operation procedures will be in place. §
Formation of potentially harmful compounds (e.g., aldehydes and other
oxidation by-products) , but the residual risks to human and ecological
health have been found to be well within acceptable limits. §
Generation of additional waste sludge from the
CEPT process due to the need
to use alum instead of ferric chloride as coagulant at SCISTW but the
increase in sludge volume is slight (about 100 wet tpd). |
2.124 It is evident from the above table that either chlorination or UV radiation has relative environmental benefits and dis-benefits over the other. Neither is superior to the other on all environmental aspects.
2.125 However, the chlorination option would be preferred in terms of cost, reliability (in terms of scale up risk), flexibility to cater for uncertainties, and ease of implementation. Overall, the ADF EIA has recommended that chlorination be adopted as the preferred disinfection technology for HATS.
2.126
Review on various sludge
treatment methods for the sludge generated from sewage treatment works in
2.127 Under the Study, a number of proven and developing technologies for sludge treatment including thickening, stabilization, dewatering, thermal reduction and heat drying processes were reviewed. A comprehensive list on sludge treatment options including a combination of anaerobic digestion and incineration or heat drying was evaluated. For all options with anaerobic digestion, transportation of liquid sludge from SCISTW to a site with separate sludge treatment facilities (STF) would be necessary due to land constraints at SCISTW.
2.128 The following list of plans, including those with anaerobic digestion of liquid sludge prior to dewatering, for the sewage treated at SCISTW and the STF site located in the vicinity of WENT Landfill have been considered. An economic assessment was conducted to short-list the promising plans for treatment of the SCISTW sludge.
·
Marine
transfer of sludge cake from SCISTW to WENT – dry – landfill
·
Road
transfer of sludge cake from SCISTW to WENT – dry – landfill
·
Relocate centrifuges to WENT – pump liquid sludge
from SCISTW to WENT – anaerobic digestion – dewater – dry – landfill
·
Relocate centrifuges to WENT – tanker liquid sludge from
SCISTW to WENT by sea – anaerobic digestion – dewater – dry – landfill
·
Relocate centrifuges to WENT – tanker liquid sludge
from SCISTW to WENT by road – anaerobic digestion – dewater – dry – landfill
·
Marine transfer to sludge cake from SCISTW to WENT –
incinerate - landfill
·
Road transfer to sludge cake from SCISTW to WENT –
incinerate - landfill
·
Relocate centrifuges to WENT – pump liquid sludge
from SCISTW to WENT – anaerobic digestion – dewater – incinerate – landfill
·
Relocate centrifuges to WENT – tanker liquid sludge
from SCISTW to WENT by sea – anaerobic digestion – dewater – incinerate –
landfill
·
Relocate centrifuges to WENT – tanker liquid sludge
from SCISTW to WENT by road – anaerobic digestion – dewater – incinerate –
landfill
2.129 The shortlisted sludge treatment plans were then further evaluated in terms of environmental, flexibility, security and reliability factors. After evaluation, it concluded that development of the STF for centralized treatment of sewage sludge, including that generated from the SCISTW, at the site in the vicinity of WENT Landfill was the preferred option for sludge treatment in Hong Kong in the long run.
2.130 The STF project has been recognised as one of the top priority government projects under the current government plan. A separate EIA is being carried out by EPD for the development of STF which is targeted to be completed by mid-2008. The first phase STF with design capacity of 1,600 tpd dewatered sludge is scheduled for commissioning by end 2012, according to EPD’s latest schedule. Upon commissioning of the HATS 2A in 2014, the dewatered sludge from SCISTW would be transported to the proposed STF for centralised treatment.
2.131 The PTW upgrading works would involve typically:
· Demolition of existing buildings
·
Generally shallow excavation
(less than 5m) for the main plant building, except for manholes/pits and the
grit traps where excavation at these locations could be down to depths of about
· Piling to form foundations for the heavy mechanical equipment (e.g., pumps)
· Construction of new buildings & structures
· Installation of electrical and mechanical equipment
· Reconstruction of a section of existing seawall (only at Aberdeen PTW)
· Laying of sewers, drainage pipes, and other utility lines
2.132 The key construction stage environmental impact would be related to noise, which in turn would be dictated by the method of piling (percussive vs. bored pile). All other elements would be constructed using conventional construction plant and equipment (e.g. dozers, backhoes, dump trucks, hydraulic breakers, cranes, etc), for which the choice of equipment would unlikely lead to significantly different noise impacts.
2.133
On considering the relative
environmental impacts of the alternative piling methods, bored piling is
proposed for HATS
2.134
The key alternatives for
construction of the
· Option 1 - Shallow sewer pipes, involving many kilometres of open trench excavation
· Option 2 - Deep tunnelling (which is a trenchless or “no dig” technology)
2.135 For Option 1, shallow sewer pipes laid in open trenches, there would be significant environmental impacts in dense urban areas during the construction stage, e.g., dust, noise, visual, spoil handling, etc, as well as traffic and other adverse impacts on local amenities.
2.136 On the other hand, Option 2 (deep tunnelling) would have a much lower level of construction stage environmental impacts, as activities on the surface would be restricted to a relatively small number of production shafts. Further, at these shaft locations, environmental noise, dust, and visual impacts can be effectively mitigated with a carefully designed enclosure. Deep tunnelling is therefore preferred from an environmental perspective.
2.137 With respect to alternative tunnel construction methods, the principal options are (a) mechanical boring and (b) drill & blast. Both options would be environmentally acceptable, as demonstrated in relevant chapters of the EIA Report. The final selection will be designed by the Engineer and specified in the tender document.
2.138
Based on the reference design,
the new
2.139 The method for constructing the additional CEPT tanks would likely follow standard practices for similar situations (i.e., HATS Stage 1), i.e., construction of piled foundations, followed by reinforced concrete tanks, and equipment installation.
2.140 Piles have already been sunk at locations where the proposed new CEPT tanks would be placed. If new piles were needed, it is proposed that bored piles would be used rather than percussive piles. As noted above, bored piles would have lesser vibration and noise impacts compared to the percussive piling method.
2.141 With respect to the reinforced concrete CEPT tanks, there are not alternative construction methods that would give rise to significantly different construction stage environmental impacts.
2.142 The upgraded disinfection facilities would involve additional chemical storage tanks, a new chlorine contact chamber, and associated piping and pumping equipment.
2.143 The method for constructing the additional facilities would likely follow standard practices, i.e., construction of piled foundations, followed by the reinforced concrete chlorine contact chamber and steel/GRP chemical storage tanks, and equipment installation.
2.144 It is proposed that bored piles would be used rather than percussive piles. As noted above, bored piles would have lesser vibration and noise impacts compared to the percussive piling method. Other than choice of piling methods, there are not alternative construction methods that would give rise to significantly different construction stage environmental impacts.
2.145
The ECS will involve a
conveyance conduit about
2.146 The key alternatives for construction of the ECS are: (a) a shallow pipeline, involving open trench excavation, (b) a deep tunnel, and (c) a discharge culvert.
2.147
Similar to the
2.148 The method of construction would follow standard conventional practices, where the piled foundations will first be constructed, followed by the new (reinforced concrete) building and then installation of the electrical and mechanical equipment (i.e., centrifuges).
2.149 As mentioned before, it is proposed to use bored piles rather than percussive piles. Bored piles would have lesser noise and vibration impacts, and this is preferred from an environmental perspective.
2.150 With respect to the building and equipment installation works, there are not alternative construction methods that would give rise to significantly different construction stage environmental impacts.
2.151
Table 2.9 summarises the relative
environmental benefits and dis-benefits of the alternative construction methods
for HATS Stage
Table 2.9 Environmental Benefits and Dis-benefits of Alternative Construction Methods
|
Construction Method |
Environmental Benefits |
Environmental Dis-benefits |
|
Piling Methods for
Foundations of PTWs and SCISTW Upgrading Works |
||
|
Percussive piles |
|
§
Potentially significant noise and vibration
impacts |
|
Non-percussive (bored) piles |
§
Significantly reduced noise and vibration impacts
compared to percussive piling methods §
Impacts can be effectively mitigated to within
acceptable environmental criteria |
|
|
Sewage Conveyance System
(SCS) and Effluent Conveyance system (ECS) Construction Methods |
||
|
Shallow sewer pipeline by open-cut trenching method |
|
§
Potentially significant noise, dust, traffic,
visual and other amenity impacts to local communities along whole of sewer
pipeline alignment |
|
Deep tunnelling (“no dig” or trenchless technologies) |
§
Noise, dust, visual impacts are restricted to
isolated shaft locations and these can be effectively mitigated and managed
by enclosing the works areas to within acceptable environmental criteria |
|
2.152 Owing to the limited space available in each PTW and the need to maintain continuous operation of the PTWs, it is essential that the PTW upgrading works should be conducted in phases. That is, new treatment trains will be constructed and commissioned to replace the existing trains, one at a time, rather than the alternative of constructing all the new treatment trains at the same time. This arrangement will reduce the intensity of construction activities on site at any time.
2.153
A further consideration is the
timing for the construction of the
2.154 With respect to sequence of construction works, the alternatives are:
· Option 1 - Constructing the drop shafts at the same time as the main PTW upgrading works
· Option 2 - Phased construction of the drop shaft and PTW upgrading works
2.155 Option 2 (phased construction of drop shaft and the PTW upgrading works) would have less construction activities on site at a given time, e.g. the SCS Contractor will construct the upper portion of the shaft (involving diaphragm-walling techniques) within a specified period, then part of the works area would be handed over to the PTW Contractor, while the SCS Contractor would still continue the construction of lower portion of the shaft. Subject to the programme, the construction works would be arranged to allow phased implementation such that construction works would be avoided to be undertaken concurrently above ground. This sequence of work would achieve compliance with relevant environmental criteria (e.g., construction noise) and therefore is preferred from an environmental perspective.
2.156
The above discussion on phased
construction of the
2.157
Similar to the PTW upgrading
works, it will be necessary to maintain continuous operation of the SCISTW at
all times during the implementation of the Stage
2.158 The sequence of construction would be standard, i.e., construction of substructure followed by superstructure and equipment installation. There are not alternative sequences of construction that would give rise to significantly different construction stage environmental impacts.
2.159 The sequence of construction would be standard, i.e., construction of substructure followed by superstructure and equipment installation. There are not alternative sequences of construction that would give rise to significantly different construction stage environmental impacts.
2.160 The sequence of construction would be standard, i.e., construction of substructure followed by superstructure and equipment installation. There are not alternative sequences of construction that would give rise to significantly different construction stage environmental impacts.
2.161 There are not alternative sequences of constructing the effluent tunnel that would give rise to significantly different construction stage environmental impacts.
2.162 The sequence of construction would be standard, i.e., construction of piled foundation followed by superstructure and equipment installation. There are not alternative sequences of construction that would give rise to significantly different construction stage environmental impacts.
2.163
Table 2.10 summarises the relative
environmental benefits and dis-benefits of key alternative sequences of
construction for HATS Stage
Table 2.10 Environmental Benefits and Dis-benefits of Key Alternative Construction Sequences
|
Construction Sequence |
Environmental Benefits |
Environmental Dis-benefits |
|
PTWs and SCS Shaft
Interfacing |
||
|
Concurrent
construction of PTW upgrading works and SCS drop shafts inside PTWs |
§
Potentially
shorter duration (but with higher noise intensity) of disturbance to the
public due to construction works |
§
Potentially
significant construction noise, dust, traffic impacts to local communities |
|
Phased construction
of part of PTW upgrading works and SCS drop shaft construction |
§
Significantly
reduced magnitude of construction stage impacts (e.g., noise, dust, traffic,
etc) compared to the alternative of concurrent construction such that these
construction stage impacts can be effectively mitigated to within acceptable
environmental criteria |
§
Potentially
longer duration (but with much lower noise intensity) of disturbance to the
public due to construction works |
|
SCISTW Upgrading Works |
||
|
Concurrent
construction of the new and upgrading works elements (e.g., IPS, new
sedimentation tanks, chlorination facilities, sludge processing facilities,
ECS, etc) on the SCISTW site |
§
Potentially
shorter duration (but with higher noise intensity) of disturbance to the
public due to construction works |
§
Potentially
significant construction noise, dust, traffic impacts to local communities |
|
Phased
construction of the new and upgrading works elements (e.g., IPS, new
sedimentation tanks, chlorination facilities, sludge processing facilities,
ECS, etc) on the SCISTW site |
§
Significantly
reduced magnitude of construction stage impacts (e.g., noise, dust, traffic,
etc) compared to the alternative of concurrent construction such that these
construction stage impacts can be effectively mitigated to within acceptable
environmental criteria |
§
Potentially
longer duration (but with much lower noise intensity) of disturbance to the
public due to construction works |
2.164 Consistent with the Government’s proposed phased implementation approach for HATS Stage 2, it is proposed to increase the capacity of the CEPT facilities at SCISTW to cater for the projected flows from the whole of HATS service area under Stage 2A.
2.165
Implementation of HATS Stage
2.166 On UIA,
· An investigation into the feasibility of reducing ammonia concentration in the CEPT effluent of Stage 2A by methods other than biological treatment has been made. The investigation focussed on treatment of centrate in the total CEPT effluent, but this had found that centrate treatment would not be effective in reducing effluent ammonia in the SCISTW CEPT effluent. In any case, centrate treatment would require the construction and operation of a separate treatment plant on SCI, with potentially significant odour and noise impacts.
· As centrate treatment would not be effective in reducing CEPT effluent ammonia levels, but would result in additional land based noise and odour impacts, centrate treatment is not preferred from an environmental perspective.
·
At the same time, the
environmental impacts of HATS Stage
2.167 On TIN and P,
· As compared to the Stage 1 condition, implementation of Stage 2A would reduce the inorganic nutrients, including both TIN (N) & PO4 (P) which are one of the factors to cause algae blooms, in the whole study area. With implementation of Stage 2B, it would cause a further reduction of P level in the receiving water.
· Nevertheless, assessment was conducted to evaluate whether nutrient removal for HATS Stage 2A would be effective to minimize the chance of algal bloom.
· Further enhancement in P removal from the Stage 2A effluent was considered a more effective option (as compared to N removal) in further minimizing the chance of algal bloom.
· The water quality modelling results, however, indicated that there would be no substantial improvement in the extent of P levels at the semi-enclosed bays (which are vulnerable to algal bloom) resulting from the adoption of the enhanced P removal for HATS. Besides, adoption of enhanced P removal would increase quantities of sludge generation. Therefore, enhanced P removal as an alternative treatment option would not be recommended for HATS Stage 2A.
2.168 As reported in the ADF EIA Report, the only feasible sewage disinfection options for HATS are chlorination and UV radiation, and both chlorination (purchase of sodium hypochlorite) and UV radiation would be environmentally acceptable for HATS. Water quality and ecological impacts can be controlled to well within established criteria (contained in the Technical Memorandum of EIA Process) for either option.
2.169 The relative environmental benefits and dis-benefits of both disinfection methods have been considered. This has found that while either method would be environmentally acceptable, neither would be superior to the other on all environmental aspects, as discussed in the sub-section “Alternative Disinfection Technologies”.
2.170 Overall, chlorination is preferred to UV radiation, as the former would be better in terms of total life cycle cost, flexibility to cater for uncertainties, ease of implementation, and scale-up factor.
2.171
It is proposed that all piling
works under HATS Stage
2.172
For the HATS Stage
2.173
For HATS Stage
2.174 Two rounds of public consultation were conducted with green groups, academics and professional institutions for the Project. In February 2007, the first round public consultation was conducted during early stage of the EIA process to introduce the EIA Study and brief the latest progress of the Project. The second round public consultation was conducted in January 2008 to present the EIA findings and solicit views and comments for finalisation of the EIA Study.
2.175 The list of green groups, professional bodies and academics institutions that were invited to the consultation exercises is presented in Table 2.11.
Table 2.11 Green Groups, Professional Bodies, and Academics Institutions Invited For Consultation Exercises
|
Green Groups |
Attendance |
Academics
Bodies / Professional Institutions |
Attendance |
||
|
Feb 07 |
Jan 08 |
Feb 07 |
Jan 08 |
||
|
Conservancy
Association |
No |
Yes |
|
No |
No |
|
Earthcare |
No |
No |
|
No |
Yes |
|
Friends of the
Earth (HK) |
No |
No |
Chartered
Institution of Water and Environmental Management |
Yes |
Yes |
|
Green Power |
Yes |
Yes |
|
Yes |
No |
|
Green Student
Council |
Yes |
No |
|
No |
No |
|
Greenpeace |
No |
No |
|
No |
No |
|
|
Yes |
No |
|
No |
No |
|
World Wide
Fund for Nature |
Yes |
Yes |
Open |
No |
Yes |
|
|
|
|
|
No |
No |
|
|
|
|
|
No |
No |
|
|
|
|
Marine
Biological Association of |
Yes |
No |
|
|
|
|
Hong Kong
Institute of Planners |
No |
No |
|
|
|
|
Hong Kong
Institute of Architects |
No |
No |
|
|
|
|
Hong Kong
Institute of Surveyors |
No |
No |
|
|
|
|
Association of
Engineering Professionals in Society Ltd |
No |
No |
|
|
|
|
Hong Kong
Project Management Exchange Centre |
Yes |
Yes |
|
|
|
|
Veolia Water |
Yes |
No |
|
|
|
|
ATAL
Engineering Limited |
Yes |
No |
2.176 Key comments and views received from the first round public consultation forum are summarized in Table 2.12.
Table 2.12 Summary of Key Comments/Views from the Public – February 2007
|
Concerned Parties |
Key
Comments / Views |
Consultant’s Response |
|
Green |
1. Sewage Conveyance System |
|
|
Groups |
·
Alternative construction
methods |
·
A deep sewage tunnel would be constructed mainly by either tunnel
boring machine (TMB) or drill & blast (D&B). Given that the construction
method has not yet been determined by the Engineer at the time of preparing
this EIA, both drill and blast and TBM methods would remain feasible
construction method and are considered in the EIA study. Other than the
above, horizontal directional drilling would also be used at Tunnel Q from Ap
Lei Chau to |
|
|
·
Concerns with dredging |
·
No dredging work was proposed, therefore no assessment on dredging was
carried out under this EIA. |
|
|
·
Concerns with maximum treatment capacity |
·
The sewage flow of 2.45m3/day for the ultimate design of the
treatment system is calculated based on the projected population from 2030
and beyond by Planning Department with safety factor included. This flow rate
has been adopted in this EIA study. |
|
|
·
Concerns with land subsidence especially at crowded areas |
·
To deal with ground settlement issue, it would be mainly to i) control
the groundwater inflow into the SCS system which is a major design consideration
of the SCS and ii) adopt a comprehensive settlement monitoring system during
construction stage. With the experience gained from HATS Stage 1, a model for
the underground hydrogeological condition for HATS Stage 2A has already been
built up to assess the potential water ingress at different locations along
the tunnel. ·
The Engineer has also studied the technology available in the market
under Agreement No. CE 34/2005(DS) “Harbour Area Treatment Scheme Stage |
|
|
2. Concerns with disinfection |
|
|
|
·
Consider the long-term effect on the marine environment |
·
The risk levels of all assessment parameters and the effects on
representative marine animals at different trophic levels were fully covered in
the Whole Effluent Toxicity Test (WETT). Monitoring data from other similar
scale of sewage treatment works overseas, especially Deer Island Sewage
Treatment Works in |
|
|
·
Consider alternative programme of disinfection to let the natural
cleansing capability of the harbour to be built up and marine lives to be
progressively established |
·
Natural cleansing ability of the sea may not be that effective to have
strong dilution effect taking into account the large volume of sewage being
discharged to the harbour every day. |
|
|
·
The worthiness of the Project for the whole community to bear long-term
financial commitment |
·
Providing disinfection to the HATS effluent is not solely for
re-opening of the Tsuen Wan beaches for swimming, it also gives long-term
water quality improvement (in particular E.coli) in the Victoria Harbour.
Details of water quality assessment results can be referred to Chapter 6 of
the EIA. |
|
|
·
Consider implementation of biological treatment without interim
disinfection process |
·
After implementation of HATS Stage 1, the level of E.coli has found
increasing at certain locations. It would be necessary to protect the public
health and the environment by putting in more effective pathogen control
mechanism i.e. disinfection process. ·
Through the studies in the ADF EIA and the HATS Stage 2A EIA, both
possible short-term and long-term impacts on the environment due to
disinfection have been investigated. No unacceptable adverse impacts to
human, ecological resources and the environment would be expected. |
|
|
3. Impacts on fisheries |
|
|
|
·
Will fisheries impact assessment be included in EIA? |
·
Assessed in Chapter 12 of the EIA. No adverse fisheries impacts from
the proposed disinfection or discharge of effluent would be expected. |
|
|
·
Consider cumulative impacts of contaminated mud on fisheries culture
zones |
·
Since all tunnels would be constructed deep underground (in bedrock
layer) and no dredging work would be carried out at seabed level, cumulative
impacts of contaminated mud would not be an issue in this EIA. |
|
|
4. Concerns with waste management |
|
|
|
·
Ways of waste materials disposal |
·
The ways for waste disposal have been studied under Agreement No. CE
34/2005(DS) “Harbour Area Treatment Scheme Stage |
|
|
·
Control measures of waste transportation |
·
Disposal of construction waste will be controlled through a trip-ticket
system established by the Government. Recommendations on waste control have
been included in Chapter 9 of the EIA. |
|
Academic |
1. Ecological concerns in the Project |
|
|
Bodies/ Professional Institutions |
·
Mitigation measures for marine ecological impacts during construction
and operation of the SCS |
·
The impacts from construction works under HATS Stage 2A have been
assessed. Since deep sewage tunnel is
proposed to be constructed in the rock layer, marine ecological impact would
not be anticipated. The only potential impact of concern would be the
reconstruction of seawall at Aberdeen PTW where three small colonies of
Oulastrea crispate (zebra coral) were found within the survey area.
Mitigation measures have been proposed to translocate these colonies of coral
to the eastern part of the treatment plant (approximately 50m away from the
affected seawall). Post translocation monitoring has also been proposed to
minimise the adverse impacts on these corals
(Chapter 11 of the EIA Report refers). |
|
|
·
Impacts on Chinese White Dolphins |
·
Based on risk assessment on marine mammals conducted under the ADF EIA
and HATS 2A EIA (Chapter 8), adverse ecological impact on Chinese White
Dolphins would not be expected. |
|
|
2. Concerns with Stage 2B biological treatment |
|
|
|
·
Any contingency plan if Stage 2B will not be implemented. |
·
After completion of the Environmental and Engineering Feasibility
Studies (EEFS) and the 5-month public consultation on the way forward for
HATS Stage 2 in 2004, the government confirmed that biological treatment is
needed to improve water quality in the Harbour in the long term. The
programme of Stage 2B implementation would be reviewed at 2010/11. |
|
Individual person |
1. Concerns with design of SCS |
|
|
·
Environmental benefits of using deep underground tunnel especially the
tunnel from Ap Lei Chau to |
·
Different forms of construction methods/options of the SCS design have
been evaluated under Agreement No. CE 34/2005(DS) “Harbour Area Treatment
Scheme Stage |
|
2.177 Key comments and views received from the second round public consultation forum are summarized in Table 2.13.
Table 2.13 Summary of Key Comments/Views from the Public – January 2008
|
Concerned
Parties |
Key Comments / Views |
Consultant’s Response |
|
Green Groups |
·
Concerns with noise impacts due to above-ground construction activities
which would cause disturbance to the nearby residential areas especially
those areas with quiet noise background e.g. ·
Recommended to present drawings to show how many residents are affected
by noise impact at each work site. ·
Recommended to assess the marginal increase of noise level instead of
comparison solely with noise criteria under EIAO-TM. |
·
Under the EIA report, drawings are available to show identified Noise
Sensitive Receivers (NSRs) which are mostly affected near the PTWs and SCISTW
(See Chapter 4 of the EIA). ·
As the tunnel construction works are mainly undertaken underground,
only the construction activities at the shaft sites and the PTWs which are
exposed to the ground surface would have concerns with noise impacts. In
order to minimize the impacts to the public, night time construction works
will be avoided and quieter construction plant/equipment will be adopted as
far as possible. ·
Detailed calculation has been included in the construction noise
assessment in Chapter 4 of the EIA. With implementation of proposed
mitigation measures e.g. noise barrier and enclosure which are effective to
block the line of sight to NSRs as demonstrated in the HATS Stage 1 project,
the noise levels at all representative NSRs except a school at North Point
during the examination period would comply with the construction noise
standards stipulated in the EIAO-TM. For the school with residual impact,
noisy construction activities have been recommended to be scheduled during
the summer vacation period as far as practicable to further ameliorate the
noise impacts. ·
It would not be able to assess the marginal noise increase using noise
modelling or construction noise calculation. An environmental monitoring and
audit (EM&A) mechanism would be available to control the marginal
increase of noise level during construction stage. Both baseline monitoring
and impact monitoring would be carried out to check compliance of the noise
criteria. Details would be shown in the stand-alone EM&A Manual. |
|
|
·
Concerns with odour assessment |
·
Odour modeling in the EIA already considered one year of hourly meteorological
data, including wind speed, wind direction, temperature etc., in order to
predict the odour level at the Air Sensitive Receivers (ASRs). The modeling
results as showed in Chapter 3 indicated that the predicted odour levels at
all identified ASRs would be within the odour criterion under EIAO-TM. |
|
|
·
Measures to control spoil transportation to designated place for
disposal ·
Concerns with sites identified for storage of surplus spoil |
·
Disposal of construction wastes by road transport will be controlled
through a mandatory trip-ticket system established by the Hong Kong
Government. The type, quantity and
disposal designation of waste will be clearly recorded. This control
mechanism would also be applied to this Project to avoid illegal dumping.
Besides, satellite monitoring system for barges is also being considered. ·
Most of the wastes generated in this Project would be inert materials
with commercial value. These materials will be crushed into aggregates in
appropriate size for on-site reuse and surplus materials will be delivered to
fill bank/quarry for temporary storage (e.g. Lam Tei Quarry) until re-use
opportunities are identified. ·
Currently, a Construction & Demolition Material Management Plan
(C&DMMP) is being prepared to work out a whole plan for management of
disposal of the C&D materials under Agreement No. CE 34/2005(DS) “Harbour
Area Treatment Scheme Stage |
|
|
·
Suggestion of having education centre at some of the PTWs where are
convenient for public access |
·
A 3–dimensional EIA webpage prepared under this Project would help the
general public to understand the HATS Stage 2A project and various aspects of
the environmental impacts to the nearby sensitive receivers. ·
As the site area of the PTWs is relatively small and the facilities
were not designed to accommodate large number of public for site visit,
safety would be a matter of concern if the PTWs are allowed for public
access. Currently, DSD have been using
the SCISTW as a major visitor centre for public access. Open days are
normally held every year at SCISTW to show the public how sewage is treated
and how water quality is protected through sewage improvement projects. DSD
also have a plan to further enhance the facility of the visitor centre at
SCISTW. |
|
Academic Bodies/ Professional Institutions |
·
Concerns with marine ecological impact assessment when sewage loading
be increased after implementation of HATS Stage 2A. |
·
Assessment of the ecological impacts at the SCISTW outfall location was
conducted at the HATS Stage 1 project. For HATS Stage 2A, the existing
outfall would still be used but only the discharge of treated effluent would
be increased. The water quality modelling results (Chapter 6 refers) already
indicated that implementation of HATS Stage 2A would improve the overall
water quality and reduce suspended solids loading and sediment deposition by
CEPT treatment at SCISTW, adverse impacts to the marine communities
(including benthic organisms) would not be expected. Besides, the existing SCISTW outfall
location was chosen in an area with low ecological resources, no adverse
ecological impacts are therefore anticipated from the Project. Details can be
found in Chapter 11. |
[1] The ADF EIA
Report is available at http://www.epd.gov.hk/eia/register/report/eiareport/eia_1342007/index.htm