2 PROJECT DESCRIPTION Purpose and Objective of the Project · 2001 after full commissioning of HATS...

Agreement No. CE 43/2005 (EP) Harbour Area Treatment Scheme (HATS) Stage 2A EIA Study – Investigation Final EIA Report

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2 PROJECT DESCRIPTION

Purpose and Objective of the Project

2.1 Victoria Harbour is well recognised as one of Hong Kong’s most precious natural assets. Apart from its significant social value, the Harbour has brought, and continues to bring, inestimable economic benefits to Hong Kong directly, and indirectly through our tourism industry.

2.2 Over the past few decades, the water quality of Victoria Harbour deteriorated because of

rapid urbanisation and development of the areas surrounding the harbour. Until the end of 2001 after full commissioning of HATS Stage 1, 75% of sewage generated around Victoria Harbour was collected and treated before discharge. Water quality in the eastern part of Victoria Harbour has improved significantly since then.

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 2A is a precursor to HATS Stage 2B, as set out in the phased implementation programme for further stages on HATS.

2.4 The purposes of Stage 2A of HATS (which is the Project being considered in this EIA Report)

are:

• 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 2A are:

• To intercept and treat the sewage generated from the populated areas in the northern and southwestern parts of Hong Kong Island (which is currently only subject to preliminary screening and de-gritting before being discharged into the harbour)

• 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 Victoria Harbour, in the context of the phased implementation plan for HATS Stage 2

Need for the Project

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 Kowloon and northeastern Hong Kong Island, for treatment at the existing Stonecutters Island Sewage Treatment Works (SCISTW). At present, about 1.4 million cubic metres of wastewater each day is treated at SCISTW (which has a design capacity of 1.7million m3/day).

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.


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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 m

3/d generated by a population of approximately one million people living on the northern and

western shores of Hong Kong Island, still receives only rudimentary treatment prior to discharge into Victoria Harbour, where it exerts a significant negative effect on water quality.

2.10 Provision of HATS Stage 2 would address all of these concerns and provide a sustainable

programme for maintaining clean waters throughout Victoria Harbour:

• Under HATS Stage 2A (the Project), the remaining 450,000 m3/d untreated sewage flows,

as well as future flows would be collected and treated in the SCISTW. The treatment capacity of SCISTW would be expanded and disinfection added, as discussed in Section 1 under “Phased Implementation” of this EIA Report.

• Stage 2B, that is to provide biological treatment to all HATS flows, is needed after completion of Stage 2A in order to sustain the above gains. While this phase is an integral part of HATS Stage 2 programme, its timing would depend on trends in water quality, projected increases in population and sewage flow and consensus within the community on how it could be implemented. A review is planned for 2010/11 to determine a timetable for its implementation.

2.11 While the ADF (as part of Stage 2A works) is to be introduced in advance, the overall water

quality should be further improved in order to achieve the targeted water quality in Victoria Harbour. Through the remaining works of Stage 2A, sewage would be collected from eight upgraded preliminary treatment works (PTWs) at the north and west of Hong Kong Island and conveyed, through over 20 km of deep sewage tunnel system, to the expanded SCISTW for centralized treatment. This would provide the following major benefits to the pollution loading discharged into the Habour further to those achieved in Stage 1:

• 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 Hong Kong. It is planned to

advance the construction of part of the disinfection facility at SCISTW for completion by the end of 2009 to facilitate the early re-opening of the Tsuen Wan beaches. As for the Stage 2A main works, construction is planned to start in 2009 and the whole of Stage 2A should be completed and commissioned by 2014, according to the current programme. The 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 and would target to provide a much-improved environment for marine life and a possibility of staging water events.

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.


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Outline of Proposed Scheme and Project Elements

Overview of Proposed Scheme for HATS Stage 2A

2.14 The operational philosophy of HATS Stage 2A is similar to HATS Stage 1. That is, sewage from the catchments will be:

• 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 (SCS), consisting of sewer tunnels or pipelines, which conveys the screened/de-gritted sewage to SCISTW

• 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 2A include:

• 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 SCS to bring sewage flows from northern and western Hong Kong Island to SCISTW. The SCS includes seven main tunnel sections, 16 shafts (6 temporary and 10 permanent), and up to three sewage transfer pumping stations and two ancillary seawater pumping stations at strategic locations in the SCS

• 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 2A scheme, environmental factors have been fully taken into account in the design of SCS, PTWs and SCISTW. For instances, in order to minimise odour impact which is regarded as one of the key environmental concerns, the facilities with major odour emission have been designed to be enclosed in the PTWs and SCISTW and the foul air will be ventilated to deodorizer for treatment before discharging to the atmosphere. Nothing that tree preservation is important to the environment, the footprints of PTW buildings/structures have been designed to minimise conflict with the existing trees as far as possible. Besides, selection of works areas has been restricted mainly to developed land or wasteland. Construction works have been avoided on woodland area or other area of conservation interest (e.g. Country Park). In terms of landscape and aesthetic considerations, both have been incorporated to the PTW/SCISTW design so as to minimise the potential visual impacts as well as to beautify the landscape of the local environs. Hard and soft landscape techniques e.g. vegetations, green roof, colour treatment for aesthetic improvement have been integrated to the design, especially for those PTWs located along the harbour-front (notably Central and WCE). For SCS, the tunnel alignment has been refined to


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be running offshore which would impose less impact on inland environmental sensitive receivers. Furthermore, the curved alignment design also minimises the possibility of passing through private lots/existing underground structures. This would be resulting in reduction of programming risk and hence duration of environmental impacts to the public.

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 2A scheme in terms of flow

management philosophy, treatment level, design parameters, project schedule, and interfaces with other projects.

Flow Management (Operation) Philosophy

2.20 The overall approach to sewage flow and load management for HATS Stage 2A is illustrated diagrammatically in Exhibit 2.1.

Exhibit 2.1 Diagrammatic Illustration of HATS Stage 2A Flow Management Approach

PTWs

Sewage Conveyance

System

SCI STW

Sewage Inflow /

Infiltration

Treated Effluent

via Submarine Outfall

SEA

Emergency discharge

of untreated or partially

treated effluent

Excess flow

or emergency

bypass

SEA

Hydraulic Capacity = 2.0 ADWF

Hydraulic Capacity = 2.0 ADWF

Treatment Capacity = 1.7 ADWF

2.21 As for HATS Stage 1, the design of HATS Stage 2A takes into account not only the sewage

flows under average conditions, but also the higher rates of flow that will occur from time to time due to diurnal, seasonal, or other factors (e.g., rainwater inflow, groundwater infiltration, etc). The intention is that an adequate degree of protection to public health and the environment will be provided under most situations.

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 2A, with the benefits of having the opportunity to analyse the actual flow data

collected from SCISTW and the actual performance of the HATS Stage 1 system, it is considered appropriate to adopt a lower peaking factor for the SCS and the SCISTW treatment processes, with a view to enhancing the cost-effectiveness of the overall system

1.7


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without jeopardising its environmental performance. The HATS Stage 2A SCS and the SCISTW treatment units will be sized at 1.7 times of ADWF (rather than at 2.0 times ADWF as in the case of HATS Stage 1). As a result of changing the peaking factor for the Stage 2 tunnels from 2.0 times ADWF to 1.7 times ADWF, the percentage of time when the inflow exceeds the allowable flow of the tunnels will be changed from 0.07% (1 - 99.93%) to 0.3% (1 - 99.7%), based on detailed analysis of historical flow records for HATS Stage 1. The water quality impact arising from such overflow has been assessed in Section 6 of this EIA report and the assessment results indicated that the impact associated with the overflow would be acceptable.

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.

Treatment Level

2.25 As for HATS Stage 1, two levels of sewage treatment are proposed for HATS Stage 2A:

preliminary treatment at the PTWs and primary treatment at SCISTW. 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 SCS (which aims to be a maintenance free system). Screening will minimise also the visual impact of any sewage overflows from the PTWs in case of excessive inflow or emergencies. Typically, mechanically raked bar screens with bar spacing of 4mm to 6mm will be used.

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 SCS. The new grit removal facilities for HATS Stage 2A will be designed to achieve the highest current achievable performance standards in the industry.

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 2A will be based on Total Suspended Solids (TSS) and 5-Day Biochemical Oxygen Demand (BOD5). In addition, as disinfection is proposed, the effluent standard will refer to E.coli counts. Table 2.1 summarises the proposed effluent quality requirements.

Table 2.1 Proposed Effluent Quality Limits for Expanded SCISTW Under HATS Stage 2A

Parameter Units Monthly Geometric

Mean 95

th percentile Maximum

Total Suspended Solids (TSS) mg/L - 55 110

Biochemical Oxygen Demand (BOD5)

mg/L - 75 150

E. coli counts

per 100mL

20,000 300,000 -


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Design Flows

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 2A has been estimated. These are summarised in Table 2.2 below.

Table 2.2 Design Flows for HATS Stage 2A

Element Design Flow

Upgrading of Preliminary Treatment Works (PTW)

Upgraded North Point (NP) PTW 3.72 m3/s

Upgraded Wanchai East (WCE) PTW 5.40 m3/s

Upgraded Central PTW 4.16 m3/s

Upgraded Sandy Bay (CB) PTW 0.40 m3/s

Upgraded Cyberport (CP) PTW 0.35 m3/s

Upgraded Aberdeen PTW 2.93 m3/s

Upgraded Wa Fu (WF) PTW 0.37 m3/s

Upgraded Ap Lei Chau (ALC) PTW 1.30 m3/s

Sewage Conveyance System -Tunnel Sections

Tunnel J: NP to WCE 2.84 m3/s

Tunnel K: WCE to Central to Sai Ying Pun (SYP)

7.07 m3/s (WCE to

Central) 10.27 m

3/s (Central to

SYP)

Tunnel Q: ALC to Aberdeen 1.11 m3/s

Tunnel P: Aberdeen to WF to CP 3.12 m

3/s (Aberdeen

to WF) 3.37 m

3/s (WF to CP)

Tunnel N: CP to SB 3.60 m3/s

Tunnel M: SB to SYP 3.86 m3/s

Tunnel L: SYP to SCISTW 14.13 m3/s

Sewage Conveyance System - Ancillary Pumping Stations (PS)

NP Seawater PS (located within existing NP PTW site) 0.24m3/s

WCE Sewage Transfer PS (located within existing WCE PTW site)

2.84 m3/s

SB Sewage Transfer PS (located adjacent to existing SB PTW site)*

3.60 m3/s

CP Sewage Transfer PS (located within existing CP PTW)* 3.37 m3/s

Aberdeen Seawater PS (located with existing Aberdeen PTW site)

0.22m3/s

ALC Sewage Transfer PS (located within existing ALC PTW site)

1.11 m3/s

Augmentation of Stonecutters Island Sewage Treatment Works (SCISTW)

Upgraded/Expanded Influent Pump Stations

Upgraded/Expanded Primary Treatment Facilities

Upgraded/Expanded Disinfection Plant

2,450,000 m

3/day

(average) 56.71 m

3/s (peak)

Note *: The sewage transfer PS will be constructed in either Sandy Bay or Cyberport.

Project Schedule

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


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of HATS Stage 2A is scheduled to complete by 2014. The tentative construction programme is given in Figure 2.12.

Interfaces with Other Projects

2.32 Relevant concurrent projects in the vicinity of the HATS 2A project boundary which could have cumulative environmental impacts during its construction period are shown in Table 2.3. Cumulative impacts from the concurrent projects, if any, have been assessed in the individual section of this EIA Report.

Table 2.3 Concurrent Projects in relation to Construction of HATS Stage 2A

Concurrent Projects Project Proponent

Tentative Construction Programme

Project Conflicts

Wan Chai Development Phase II (WDII) and Central Wanchai Bypass & Island Eastern Corridor Link (CWB & IECL)

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.

West Island Line (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.

South Island Line (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 Chung Kong Road, Sheung Wan

Architectural Services Department (ASD)

2007 to 2010 • Central District Headquarters and Divisional Police Station will be built on the site at Chung Kong Road adjacent to the Waterfront Police Station which is close to the Central PTW.

Laying of Western Cross Harbour Main and Associated Land Mains from West Kowloon to Sai Ying

Water Services Department (WSD)

2008 to 2011 • EIA Report (EIA-131/2007) was approved by EPD on 31 July 2007.

• Works area required by the WSD project is located at the


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Concurrent Projects Project Proponent

Tentative Construction Programme

Project Conflicts

Pun eastern side of Site Portion SYP-I for SCS.

• Water main along Fung Mat Road would impact on the access to Site Portions SYP-I and SYP-SCC for SCS.

Sun Yat Sen Memorial Park, Phase 2 at Waterfront of Sheung Wan

Architectural Services Department (ASD)

2008 to 2011 • Site Portions SYP-SCC and SYP-I for SCS are located only about 300m to the west of the Sun Yat Sen Memorial Park.

Drainage Improvement in Northern Hong Kong Island - Hong Kong West Drainage Tunnel (HKWDT)

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 Lee Nam Road (Site Portion ACL-iii) and (b) Ap Lei Chau Praya Road near Sham Wan Towers (Site Portion ALC-iv) lie within the area being studied under the Aberdeen Tourism Project.

Preliminary Treatment Works Upgrading

Overview

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,


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the PTW upgrading works under HATS Stage 2A would include principally the replacement of screening and de-gritting facilities (and reconstruction of associated buildings, roadways, pipelines, etc).

2.37 A typical “process flow diagram” for the proposed upgrading works at North Point, Central,

Aberdeen, Ap Lei Chau, and Wah Fu PTWs is presented in Exhibit 2.2. 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 2A SCS

• 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 2A SCS, which are discussed in the sub-section “Stage 2A Sewage Conveyance System”.

PTW Construction Method

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, Aberdeen, ALC, and WF PTWs, the PTW upgrading works would involve principally:

• 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 SCS drop shaft,

which means that this must be phased rather than conducted simultaneously with the main PTW upgrading works.


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PTW Operation 2.45 After commissioning of HATS Stage 2A, the primary function of PTWs will remain the same,

except that the preliminarily-treated (screened and de-gritted) sewage will be discharged into the deep tunnel system rather than the sea, thereby preventing discharge of sewage to the marine water environment under normal operating conditions.

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 SCS will need to be discharged into the sea after screening and de-gritting. The water quality impacts of sewage overflows are discussed in Section 6 of the EIA Report.

2.48 The number of PTW operators in each of the upgraded PTW would be similar to current

conditions.

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Agreement No. CE 43/2005 (EP) Harbour Area Treatment Works (HATS) Stage 2A EIA Study – Investigation Final EIA Report

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Stage2A Sewage Conveyance System

Overview

2.49 The SCS is consisted of a network of sewage tunnels, shafts (vertical tunnels or deep wells), and ancillary sewage transfer and seawater pumping stations.

2.50 As shown in Exhibit 2.3, the HATS Stage 2A SCS includes drop shafts that pick up sewage

from the PTWs in North Point, Wan Chai East, Central, Sandy Bay, Cyberport, Wah Fu, Aberdeen, and Ap Lei Chau. Sewage from the PTWs is discharged via the drop shafts in the deep tunnels (total length about 21 km) and then conveyed to the SCISTW.

2.51 The proposed SCS alignment, tunnel sizes, depths, and lengths, shafts, works areas and

ancillary pumping stations are outlined below.

I. SCS Alignments

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 SCS are shown in Figure 2.9.

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 30m below bedrock in general except at a few locations in the sea. As a result, the depths of the tunnels would vary from about 70m to 160m below sea level.

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II. Tunnel Sizes, Depths, and Lengths

2.55 For the purposes of discussion, the SCS is divided into seven sections: J, K, Q, P, N, M, and L. Based on hydraulic design requirements, the required sizes (diameters) of each section of the SCS have been calculated, as shown in Table 2.4.

Table 2.4 Summary of SCS Tunnel Depths, Sizes, and Lengths

SCS

Section 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

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

Tunnel K

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 Aberdeen 1.3

-76.0

to

+1.0

0.64m2, circular 1.3

Aberdeen to Wah

Fu (WF) 1.1

-80.18

to

-78.0


Tunnel P

Wah Fu (WF) to

Cyberport (CP) 1.5

-78.0

to

-75.0


Tunnel N Cyberport (CP) to

Sandy Bay (SB) 1.2

-75.0

to

-72.6


Tunnel M

Sandy Bay (SB)

to Sai Ying Pun

(SYP)

3.7

-123.0

to

-115.6


Tunnel L Sai Ying Pun

(SYP) to SCISTW 4.6

-148.4

to

-139.3


2.56 The longest section is Tunnel L (SYP to SCISTW), which measures about 4.5km. The

shortest section is Tunnel N (Cyberport to Sandy Bay), which measures about 1.2km. 2.57 The deepest SCS section is Tunnel J, with the deepest end at about -163mPD. The

shallowest section is Tunnel Q, with the highest point at +1.0mPD (which would be several metres below ground surface).

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.

III. Shafts

2.59 Two main types of shafts (vertical tunnels or deep wells) would be involved:

• Temporary production shafts

• Permanent drop and/or riser shafts


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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 12m) for the construction of the SCS. Their locations are shown in Table 2.5 and Figure 2.9.

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 SCS operation and therefore are permanent structures. In all, there are 11 permanent shafts for the SCS. Their details and locations are shown in Table 2.5 and Figure 2.9 respectively.

Table 2.5 Summary of Shafts

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

Sandy Bay 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

Aberdeen PTW 1 Drop Shaft

Works Area 1 Production Shaft (backfilling required)

Ap Lei Chau PTW 1 Drop Shaft

Stonecutters Island

SCISTW 1 Riser Shaft 1 Production Shaft (backfilling required)

IV. Works Areas

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 Sandy Bay.


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Table 2.6 Summary of Works Areas

Location Site Details

Approximate Area (m

2)

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

Sandy Bay SB-PS

695 Permanent - Production shaft/ drop/riser shaft construction - Construction of ancillary facilities for PTW upgrading

SB-i


Cyberport CP-iv

2,300 Temporary - Storage/Stockpiling area - Supporting works area for tunnel construction

Aberdeen Abd-i

1,520 Temporary - Supporting works area for tunnel construction by HDD

Abd-iii


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

Stonecutters Island

SCI-i 3,910 Temporary - Storage/Stockpiling area

SCI-ii 2,550 Temporary - Storage/Stockpiling area

V. Sewage Transfer Pumping Stations

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 2A SCS hydraulic design, one or more “sewage


Version 3 2-17

transfer pumping stations” (STPS) (or intermediate pumping stations) may be also constructed as part of the SCS.

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 SCS has not been finalised, and it is not confirmed if

and how many STPS will be required eventually, except at ALC where a STPS is confirmed to be required (Figure 2.8). As such, for the purposes of the EIA study, it is assumed that, other than the one at ALC, STPS could also be located inside or adjacent to each of the existing PTWs at WCE and SB/CP, where land is available, as shown in layout plans for these PTWs (see Figures 2.2, 2.4 & 2.5).

VI. Seawater Pumping Station

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 2A SCS, to pump seawater into the SCS to flush the tunnels for the purposes of operation or maintenance.

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.

SCS Construction Methods

I. Shafts

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.

II. Main Tunnels

2.74 For HATS Stage 2A SCS, either mechanical boring or “drill and blast” could 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). In either case, the excavated spoil would be moved to the ground surface via the production shafts.

2.75 Generally, mechanical boring methods refer to use of specialised drilling/boring machines to


Version 3 2-18

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 2A SCS. Typically, TBMs would produce excavated sections about 3.5m to 5m in diameter. For the smaller diameter tunnel sections, other mechanical methods involving smaller boring equipment may be used (e.g., horizontal directional drilling).

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.

III. Sewage Transfer and Seawater Pumping Stations

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 11m below ground level




2.82 It is anticipated that conventional construction plant and equipment (e.g. dozers, backhoes,


Version 3 2-19

dump trucks, hydraulic breakers, cranes, etc) will be used.

SCS Operation

2.83 The SCS serves to convey sewage to SCISTW. Flow management is achieved by adjusting the pumping rates at the influent pumping station(s) at SCISTW, as well as at the proposed STPS and SWPS.

Stonecutters Island Sewage Treatment Works Augmentation

Overview

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 m

3/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 2A (see Exhibit 2.5) would include:

• A new Influent Pumping Station (IPS), which will be interconnected with the existing SCISTW Main Pumping Station (constructed in HATS Stage 1)

• 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 2A), consisting of two new sodium hypochlorite storage tanks, a new chlorine contact tank, and dechlorination facility.

• 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)

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Version 3 2-22

New Influent Pump Station (IPS)

2.89 It is proposed to construct a new IPS to cater for the ultimate HATS Stage 2A sewage flow and the projected additional flows from the HATS Stage 1 catchment under the ultimate development scenario, as well as any overflows from the existing Northwest Kowloon PTW.

2.90 As shown in Figure 2.10, the new IPS would be located on the south side of the SCISTW site.

According to the current schematic design, it would be configured as a partially buried, cylindrical reinforced-concrete structure, with a diameter of about 45m and depth of about 62m (18m and 44m above and below ground, respectively). Inside the reinforced concrete structure will be the pump sets, pipe works, and associated electrical and mechanical equipment.

2.91 The IPS would be connected hydraulically to the existing Main Pumping Station (on the

eastern side of the Main Pumping Station) via a reinforced box culvert or pipe. 2.92 Construction of the IPS would follow standard practices for similar situations:

• 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). Additional Sedimentation Tanks

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 140m by 42m in plan overall, and be about 10m above ground level.

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 2A CEPT facilities, the outstanding works would be construction of the new reinforced concrete tanks, followed by installation of electrical and mechanical equipment.

Upgraded Effluent Disinfection Facilities

2.96 The upgraded effluent disinfection facilities would be located at a site off Container Port Road (see Figure 2.10 for a preliminary layout of the proposed facilities), and would include:

• A chlorine contact tank of reinforced concrete construction, about 174m by 34m in plan, and partially buried (with a height of about 6m above ground surface level)

• A dechlorination plant (measuring about 15m by 21m in plan), consisting of a tank farm (containing two sodium-bisulphite storage tanks) and associated pumping and control equipment housed in separate rooms

• Two new sodium hypochlorite storage tanks, with the size of 8m diameter and 13m height (4 of which to be constructed under ADF)


Version 3 2-23

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.

New Effluent Conveyance System (ECS)

2.98 The proposed ECS comprises a large-diameter (7m), short (430m in length), deep (about 80m below ground level) sewer tunnel, a flow distribution chamber at its upstream end to receive the CEPT effluent, a riser shaft at its downstream end to convey the effluent to the disinfection facilities, the existing Chamber 15 modification and extension, and the proposed Chamber 15A.

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.

Additional Sludge Processing Facilities

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.

Odour Control System

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 8.5m-tall bio-trickling filters arranged in four rows. Next to the bio-trickling filters is a two-storey building, in which the activated carbon filters and other associated systems (e.g., water tanks, blowers, etc) are located.

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.


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Ancillary Facilities

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

Alternative SCS Alignment

2.108 Two major alternatives for the SCS alignment have been considered:

• 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 SCS under Agreement No. CE 34/2005(DS), Harbour Area Treatment Scheme Stage 2A Sewage Conveyance System – Investigation, Design, and Construction

2.109 Both SCS alignment options are shown in Figure 2.11. The major differences between the 2 alignment options are highlighted below:

• 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 Stonecutters Island, the alignment of Tunnel L has been reviewed to run north-east from Sai Ying Pun towards the eastern cape of the Stonecutters Island before reaching the SCISTW. This alternative scheme would therefore allow minimal impact on the historical buildings during tunnelling. Further, the alignment Under Option 2 would not pass underneath the Western Harbour Crossing, which could minimize the risks of affecting existing facilities during construction. Construction risk reduction would enable smooth project delivery in which duration with potential environmental impacts to the public would be shortened i.e. overall environmental benefits would be gained.

• 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 Fung Mat Road site is therefore proposed under Option 2. It is located at the parcel of land along the shoreline between Fung Mat Road and the Western Wholesale Food Market. Since this site is located away from the busy Central District, the existing congested pedestrian and vehicular traffic in Central would not be aggravated by the construction works. Moreover, from landscape and visual point of view, DSD would complete the temporary landscape works for the whole ex-Gala Point site in late 2009 for the public use after completion of another project at the Sheung Wan Stormwater Pumping Station (SWSPS). As a result, the open space at the ex-Gala Point would be landscaped for public enjoyment earlier without having to wait until the completion of the HATS Stage 2A project by 2014, and it would be in harmony with the


Version 3 2-25

proposed Sun Yat Sen Memorial Park Phase II Development targeted to complete by 2011.

• 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 Ka Lung Court and Tin Wan Praya Road towards Aberdeen, which enables cut and cover method to be adopted for the tunnel construction. However, under Option 2, an alternative alignment by combining Tunnel P with Tunnel R alignment (also denoted as Tunnel P) allows that the sewage would flow by gravity from Aberdeen to Cyberport, with connection from Wah Fu PTW. This tunnel forming an S –curve alignment would be constructed by drill and blast and hence environmental impacts would be minimised without using the originally proposed cut and cover method. Besides, this alignment would avoid encroachment into private lots / structures (e.g. the lot boundary of Ka Ping House (AL416 NNG)) which would minimise programming risk. Further, hydraulic design also revealed that sewage could flow from Aberdeen to Cyberport without the need for immediate pumping station. This would also minimize potential air and noise impacts during construction and/or operation stage of the Project.

• Length of tunnel alignment: The total length of tunnels and pipes for Option 1 is 21.4 km, including 20.3 km of deep tunnels and 1.1 km of pipeline (Tunnel R). The total length of tunnels for Option 2 is 20.8 km. Option 2 results in an overall shorter sewer line but the length of deep tunnels is 0.5 km longer. Although the volume of waste generation is increased for Option 2, it is offset by elimination of pipe-jacking and intermediate pits which would cause social disturbance.

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 2A.

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


Version 3 2-26

Option Environmental Benefits Environmental Dis-benefits

Option 2, an updated 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

� 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

Alternative Sewage Treatment Methods

PTW Upgrading

2.112 The objective of the PTWs is to protect the downstream SCS by providing preliminary treatment (i.e., removing large debris and grits from sewage). Alternative (Preliminary) treatment methods include:

• 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.

Sewage Conveyance System

2.115 The SCS is a conveyance, not treatment, system. Consideration of alternative treatment methods is therefore not applicable to the SCS.

SCISTW Augmentation

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.


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These are elaborate below.

I. Alternative Sewage Treatment Methods

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 2A will improve water quality in the harbour compared to existing baseline conditions.

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 2A will significantly improve harbour water quality in this respect compared to the scenario of “no HATS Stage 2A”. This notwithstanding, alternative treatment methods (other than biological treatment proposed for Stage 2B) has been considered for achieving further improvement in the UIA level.

• 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 2A is not preferred from an environmental perspective.

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 (Pearl River discharge) contains high N relative to P, the N loading from HATS would only have a relatively minor contribution to the N level in the marine water. On the other hand, given that the background source (Pearl River discharge) contains low P content and as indicated from past monitoring records, the marine water in the Study Area generally had abundant N relative to P all year round, further enhancement in P removal from the Stage


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2A effluent was considered a more effective option (as compared to N removal) in further minimizing the chance of algal bloom.

• 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.

II. Alternative Disinfection Technologies

2.121 Under the ADF EIA1, 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.

1 The ADF EIA Report is available at http://www.epd.gov.hk/eia/register/report/eiareport/eia_1342007/index.htm


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Disinfection Option


� 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.

III. Alternative Sludge Treatment Methods

2.126 Review on various sludge treatment methods for the sludge generated from sewage treatment works in Hong Kong including SCISTW was conducted under the Sludge Treatment Disposal Strategy Study, which was completed in 1999, by EPD.

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


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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.

Alternative Construction Methods

PTW Upgrading

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 5m to 8m below ground level. If sewage transfer pumping stations are present, the excavation could be down to 10m to 11m deep.

• Piling to form foundations for the heavy mechanical equipment (e.g., pumps)



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• Reconstruction of a section of existing seawall (only at Aberdeen PTW)


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 2A. As it would have lesser noise and vibration impacts compared to percussive piling, bored piling is preferred from an environmental perspective.


2.134 The key alternatives for construction of the SCS are:

• 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.

Stonecutters Island Sewage Treatment Works Augmentation

I. Influent Pumping Station

2.138 Based on the reference design, the new IPS would involve construction of a superstructure (i.e., enclosed reinforced concrete building) and a substructure (i.e., reinforced concrete structure in a deep excavation). The methods for constructing the IPS would likely follow standard practices for similar situations, i.e., diaphragm walling for the substructure and conventional building structures and equipment installation. There are not alternative construction methods that would give rise to significantly different construction stage environmental impacts.

II. CEPT Facilities

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


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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.

III. Upgraded Disinfection Facilities

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.

IV. Effluent Conveyance System (ECS)

2.145 The ECS will involve a conveyance conduit about 7m diameter, 430m long extending from the flow distribution chamber at the downstream end of the CEPT tanks to the new chlorine contact chamber at a site off Container Port Road.

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 SCS, it is proposed to construct the effluent conduit as a deep tunnel. This

option would have lesser environmental, community, and traffic impacts compared to the alternative of a shallow pipeline involving open trench excavation.

V. Sludge Processing Plant

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.

Summary of Environmental Benefits and Dis-benefits of Key Alternative Construction Methods

2.151 Table 2.9 summarises the relative environmental benefits and dis-benefits of the alternative construction methods for HATS Stage 2A.


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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

Alternative Sequences of Construction

PTW Upgrading

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 SCS drop shafts inside the

existing PTW sites. The drop shaft construction works will involve two phases: (a) mechanical excavation of the softer material near ground surface using diaphragm-walling techniques and (b) excavation of harder materials at greater depths using mechanical or blasting techniques.

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


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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 SCS drop shafts in conjunction with the PTW upgrading works is relevant. Phased construction is preferred from an environmental perspective.

Stonecutters Island Treatment Works Augmentation

VI. Overview

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 2A upgrading works. As the existing SCISTW has only limited spare room or land, the upgrading works must be carefully conducted in phases so that the existing operation is not jeopardised, and sufficient working areas for the different construction packages is allowed. This also means that the intensity of construction works at any single point in time on site will necessarily be restricted with a generally lowered level of environmental impacts (e.g., construction noise, dust, etc).

VII. New IPS

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.

VIII. Additional CEPT Facilities


IX. Upgraded Disinfection Facilities


X. Effluent Tunnel

2.161 There are not alternative sequences of constructing the effluent tunnel that would give rise to significantly different construction stage environmental impacts.

XI. Sludge Processing Plant

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.


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Summary of Environmental Benefits and Dis-benefits of Key Alternative Sequences of Construction

2.163 Table 2.10 summarises the relative environmental benefits and dis-benefits of key alternative sequences of construction for HATS Stage 2A work elements.

Table 2.10 Environmental Benefits and Dis-benefits of Key Alternative Construction Sequences

Construction Sequence


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


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Selection of Preferred Scenario / Scheme

Preferred Sewage Treatment Method 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 2A will significantly improve baseline water-quality conditions

compared to the scenario of “no HATS Stage 2A”. Later, HATS Stage 2B will provide biological treatment of all HATS flows to improve effluent quality further.

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 2A CEPT effluent has been assessed under this EIA and found not to lead to adverse human and ecological health impacts. Therefore, there appears no strong justifications from an environmental perspective to pursue further ammonia reduction in the CEPT effluent.

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.

Preferred Disinfection Method

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.


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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.

Preferred Construction Method and Sequence of Works

2.171 It is proposed that all piling works under HATS Stage 2A be conducted using non-percussive bored pile techniques. This is preferred to percussive piling from an environmental perspective, due to lower noise and vibration impacts.

2.172 For the HATS Stage 2A SCS and ECS, it is proposed to adopt deep tunnelling techniques (i.e.,

trenchless or no dig technologies) rather than open cut trenching. The former is preferred from an environmental perspective, due to its much lower construction stage dust, traffic, visual, and amenities impacts.

2.173 For HATS Stage 2A, the construction works or packages would be phased to allow continuous

operation of the existing facilities. For example, the upgrading of the PTWs will be partly phased with the construction of the SCS drop shafts located inside the PTWs. Also, the construction of the various new elements on SCISTW (i.e., new IPS, additional sedimentation facilities, upgraded disinfection facilities, additional sludge processing facilities, ECS, etc) will be phased. Phasing of the construction works will minimise the magnitude of the construction stage impacts (e.g., noise, dust, etc), and this is preferred from an environmental perspective.

Continuous Public Involvement

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

Attendance Attendance Green Groups

Feb 07

Jan 08

Academics Bodies / Professional Institutions

Feb 07

Jan 08

Conservancy Association

No Yes Hong Kong Institution of Engineers

No No

Earthcare No No

Hong Kong Institution of Environmental Impact Assessment

No Yes

Friends of the Earth (HK) No No

Chartered Institution of Water and Environmental Management

Yes Yes

Green Power Yes Yes

University of Hong Kong

Yes No

Green Student Council

Yes No Chinese University of Hong Kong

No No

Greenpeace China No No Hong Kong University of No No


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Attendance Attendance Green Groups

Feb 07

Jan 08

Academics Bodies / Professional Institutions

Feb 07

Jan 08

Science and Technology Hong Kong Marine Conservation Society

Yes No City University of Hong Kong No No

World Wide Fund for Nature Hong Kong

Yes Yes Open University of Hong Kong

No Yes

Hong Kong Polytechnic University

No No

Hong Kong Baptist University

No No

Marine Biological Association of Hong Kong

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 South China Limite

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 Aberdeen.

• 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


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Concerned Parties


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 2A Sewage Conveyance System

(SCS) – Investigation, Design, and

Construction”. Considering the size of

all tunnels, except Tunnel Q, the

currently commercially available

construction methods would be either

drill and blast or tunnel boring machine

(TBM). Horizontal directional drilling is

only suitable for Tunnel Q, taking into

account of its length and excavated

size. Other method such as pipe

jacking would cause significant impacts

to the society including traffic, social,

dust, noise and hence would not be

considered.

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 Boston,

have been reviewed. The assessment

results as presented in Chapter 8 of the

EIA indicated that chlorination by-

products present in the HATS effluent

would not induce unacceptable

ecological risk.


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Concerned Parties


• 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 2A Sewage

Conveyance System – Investigation,

Design, and Construction” and

assessed in Chapter 9 of this EIA.

Most of the waste generated would be

inert material from tunneling. They will


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Concerned Parties


be re-used on site as far as possible

and surplus materials will be taken to

the public fill/quarry for temporary

storage until re-use opportunities are

identified.

• 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.

1. Concerns with design of SCS Individual person • Environmental benefits of • Different forms of construction


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Concerned Parties


using deep underground

tunnel especially the

tunnel from Ap Lei Chau

to Aberdeen across the

harbour

methods/options of the SCS design

have been evaluated under Agreement

No. CE 34/2005(DS) “Harbour Area

Treatment Scheme Stage 2A Sewage

Conveyance System – Investigation,

Design, and Construction”. Deep tunnel

adopted in most parts of the SCS

design is mainly due to the land issue

and minimization of environmental

impacts. Use of deep tunnel

underground would limit aboveground

construction works only at shaft sites

and the rest of the activities would be

conducted underground which can

largely reduce the scale of disturbance

to the public. More details can be

referred to Chapter 2 – Consideration

of Alternatives.

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


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. Sandy

Bay and Cyberport.

• 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


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Concerned Parties


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


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Concerned Parties


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 2A Sewage Conveyance

System (SCS) – Investigation, Design,

and Construction”. Liaison with relevant

departments to identify designated sites

(e.g. fill bank, quarry etc.) for C&D

materials disposal is underway.

• 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


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Concerned Parties


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.

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2 PROJECT DESCRIPTION Purpose and Objective of the Project · 2001 after full commissioning of HATS...

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