Advisory Council on the Environment

Review of the Strategic Sewage Disposal Scheme

(ACE Paper 07/2000)
For discussion


This paper sets out the Administration's plans for the process and expected timetable for conducting the review of the Strategic Sewage Disposal Scheme (SSDS) for Members' consideration.


2.In October 1999, taking account both of the rate of progress with the tunnelling work for Stage I of the SSDS and of continuing public questions on a number of aspects of the system, including the adequacy of the treatment to be provided and its cost effectiveness, the Administration decided that, before seeking funds for further stages, an independent review should be conducted.The review is to consider the experience with Stage I works, the present plans for later stages, and alternative proposals, so as to make recommendations on the future direction of the Strategy.A background note on the SSDS is at Annex.

3.In setting up the review, the following principles are considered to be fundamental:

  • The process should be open and participatory.The public will be given full access to all the background information prepared for the review panel.All who wish to make a submission to the review panel will be welcome to do so either in writing or verbally during a public forum.All written submissions received, including any submission which may be made by the Administration, will be forwarded to the review panel for consideration and, unless objected to by the submission proponents, will be published; and
  • The review panel will be drawn from experts of high professional standing in sewage treatment, tunnelling, economics and environmental assessment, so that it can take a comprehensive view of the current scheme and alternative proposals.

The Review Process

4.The following sets out how it is intended to take forward the review in the light of the principles described in paragraph 3:

7 April Further discussion at the LegCo Panel on Environmental Affairs.
10 April Formal commencement of the process.A digest of information about present and projected sewage loads, environmental conditions, and other information relevant to planning of sewage systems for the main urban area will be made available to the public.
10 April - 10 June Period for members of the public and the Administration to submit written views/ proposals to the review panel.
April/May First visit by overseas members of the review panel to join with the local members to get to know each other, discuss procedures, conduct site visits, make initial contacts, and to meet ACE and LegCo EA Panel.
June/July Second visit of overseas members. The review panel will conduct a public forum to receive verbal submissions.A moderator, who is not a member of the review panel or of the Administration, will preside over the forum.
August - October The review panel to consider the submissions received, review alternative options, and prepare its recommendations. Further meetings and visits if the panel members consider them necessary.
30 October and shortly thereafter The review panel to submit their recommendations to the Administration. They will be invited to brief ACE and the LegCo EA Panel.
December and January Public consultation.

Composition of the Review Panel

5.The review panel will comprise international and local experts in wastewater treatment, marine biology, tunnelling and financial analysis.Specifically, it will be made up of:

  • 3 international wastewater treatment experts including 1 expert in biological nutrient removal processes nominated by the International Water Association and 2 who participated in the review of the SSDS conducted in 1994/95
  • 1 international tunnelling expert
  • 1 local expert in marine biology nominated by The Marine Biological Association of Hong Kong
  • 1 local engineer nominated by the Hong Kong Institution of Engineers
  • 1 local expert in financial analysis

Terms of Reference of the Review

6.The terms of reference have been drafted to give the review panel full scope to consider alternative proposals.The review panel will be requested to:

  1. review proposals for further developments of SSDS based on the experience gained from Stage I;
  2. review alternative options for the sewage strategy presented by members of public or the Administration, in terms of environmental benefits, engineering feasibility, cost-effectiveness, economic and systems sustainability, and time required; and
  3. make recommendations on the most sustainable way forward for development of the sewage system for the main urban area.

In carrying out the above tasks, the review panel will attend meetings as necessary and present findings.

7.The review panel will also be asked to advise the Administration as soon as possible if, after assessing experience with Stage I, there is any strong likelihood that its recommendations may have significant impact upon the remaining Stage I works currently in progress, to the extent that it would be necessary to consider stopping or altering these works.

Secretariat for the Review Panel

8.A secretariat will be established from which the public and interested parties can seek information, and a website will be set up from which the digest of technical information can be obtained.The secretariat will also serve as the focal point to receive submissions and forward them to the review panel.

Advice sought

9.Members are invited to note and give their views on the planned process for conducting the review of the SSDS.

Environment and Foo Bureau
March 2000


An Outline of Progress with the Strategic Sewage Disposal Scheme

The Strategic Sewage Disposal Scheme was conceived in the 1980's as a means of replacing the present unacceptable discharges of sewage from the main urban area into the central harbour after receiving preliminary treatment by:

  • Collection of all discharges from the main urban areas
  • Centralized treatment
  • Discharge of the treated effluent through an outfall in oceanic waters south of Hong Kong

2.As originally projected, the scheme was to consist of two treatment plants, providing primary treatment supplemented with lime dosing.Several means for conveying the sewage from the catchment areas to the treatment plants and to the outfall were considered.Deep tunnels were selected because the greater geotechnical problems in construction were considered to be offset by reduced engineering complexity, reduced operational risks and reduced interference with other urban infrastructure.

3.The scheme was divided into four stages:

  • Stage I collecting sewage from the urban areas of Kowloon, Tsuen Wan, Tseung Kwan O and the northeastern part of Hong Kong Island for primary treatment at Stonecutters Island Sewage Treatment Works (SCISTW).
  • Stage II comprising an effluent transfer system to an outfall south of Hong Kong.
  • Stage III/IV collecting sewage from the north and south-western parts of Hong Kong for treatment at Mount Davies before adding to the oceanic outfall.

4.Following review in 1995, the scheme was revised:

  • The treatment system at SCISTW to be upgraded to a chemical process using ferric chloride
  • Stages III/IV to be diverted to convey the sewage to SCISTW
  • Stage II to undergo further EIA assessment of the outfall location and treatment level

Present Position

5.Stage I of SSDS comprises a treatment plant at Stonecutter's Island, pumping and screening stations and seven deep tunnels with a total length of 25.3 km.One tunnel, the interim outfall tunnel, 1.7 km in length, has already been completed and is now in operation.The SCISTW is also in operation and is currently treating about 320,000 cubic metres of sewage daily. This represents 25% of the total design flow from the whole SSDS Stage I catchment. Since the SCISTW was put into operation in May 1997, the performance of the chemical treatment process using ferric chloride is satisfactory. Over 80% suspended solids and 70% biochemical oxygen demand on average are removed from the raw sewage against the respective target removal rate of 75% and 35%.

6.To date, 19.4 km (82%) of the six sewage collection tunnels have been excavated. Two tunnels have been bored through and are being lined.We expect to complete excavation of the remaining 4.2 km during this year and to commission the whole sewage collection system in 2001.The progress of the tunnelling works as at 19 March 2000 is as follows:

Tunnel Length of Tunnel(m) Excavation completed up to end 12/1999 Excavation completed in this quarter Total Excavation completed to 19.3.2000
Western Tunnels
Tunnel from Kwai Chung to Tsing Yi 779 779 (100%) N/A 779 (100 %)
Tunnel from Tsing Yi to Stonecutters Island 3580 2669 (75%) 82 (2%) 2751 (77%)
Eastern Tunnels
Tunnel from Tseung Kwan O to Kwun Tong 5332 5332 (100%) N/A 5332 (100%)
Tunnel from Chai Wan to Kwun Tong 4830 2662 (55%) 745 (16%) 3407 (71%)
Tunnel from Kwun Tong to To Kwa Wan 3572 2536 (71%) 763 (21%) 3299 (92%)
Tunnel from To Kwa Wan to Stonecutters Island 5495 2857 (52%) 939 (17%) 3796 (69%)

The tunneling progress as at 19 March 2000 is shown on the attached drawing No.DSS/99/001R.

7.The EIA study for Stage II has been completed. It has recommended that the outfall be located in the southeast of Lamma Island, and that the treatment process should be further upgraded.A disinfection process should be added at the time of constructing the Stage II tunnels and land reserved should biological nutrient removal processes need to be added in future.


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Friday, 28 April, 2006