Provisional Legislative Council
Panel on Environmental Affairs



The Strategic Sewage Disposal Scheme (SSDS) is planned to comprise a series of deep tunnels which will transfer sewage to Stonecutters Island for treatment prior to discharge through a long tunnelled outfall into the waters south of Lamma island. An environmental impact assessment is currently being carried out to enable us to select the final outfall location and level of treatment. As the fieldwork for the EIA has been completed this is a suitable juncture at which to brief members on the progress of the study and outline the planned future schedule.


2. The SSDS was conceived in the 1980s. As originally conceived, the first stage involved the transfer of mainly urban Kowloon sewage to Stonecutters Island for primary treatment prior to discharge through an interim outfall in the Western Anchorage. Stage II called for the subsequent transfer of that effluent through a long tunnelled outfall to a discharge point south of Hong Kong, in the Lema Channel.

3. Following considerable public debate, in 1994 we commissioned a review of the options for Stage II, focussing particularly on alternatives for the long term level of treatment, and possible locations of treatment works and outfalls. An independent International Review Panel (IRP) comprising three internationally acclaimed experts in wastewater treatment and disposal, was appointed to oversee the work of the consultants.

4. The IRP considered that chemically enhanced primary treatment (CEPT) would be an appropriate solution and should be used permanently at Stonecutters Island Sewage Treatment Works. This option not only saves space for the treatment of sewage from later stages of the SSDS scheme at Stonecutters Island, but also gives flexibility with respect to the choice of long term treatment and disposal options. The IRP also recommended that a comprehensive EIA Study should be carried out to determine the preferred arrangement for Stage II of the scheme, i.e. the preferred long term treatment level and outfall location.

5. Following the recommendations made by the IRP, we commissioned the SSDS EIA Study in May 1996. The main objectives of the study are to evaluate and confirm, based on the recommendations of the previous studies, a preferred long term treatment and disposal option for the SSDS to protect Hong Kong and the surrounding Mainland waters; and to carry out a detailed EIA of, and recommend measures to mitigate any likely adverse impacts arising from, the construction and operation of the preferred option.

6. The study, undertaken by a joint venture of Hong Kong and Mainland Consultants, is being carried out in two phases:

  1. Phase 1 - in this phase, the Consultants are required to carry out field surveys to characterize the sewage effluent and the existing environmental conditions (including hydrodynamics, water quality, sediment quality and ecological characteristics) for the development of water quality and ecological and human health risk assessment models. A set of environmental, engineering and social-economic criteria will also be established. Based on this set of criteria and the modelling results, a preferred long term treatment and disposal option will be selected.

  2. Phase 2 - following the completion of the Phase 1 Study, the Consultants will prepare a schematic design and carry out a detailed EIA on the preferred option, which will address particularly the construction and operation impacts, and propose mitigation measures if necessary.


7. Up to now the consultants have completed the following survey work:

  1. Wet season and dry season marine surveys - these surveys covered extensive areas of Hong Kong and Mainland waters as shown in Figure 1. In the surveys, a large amount of hydrodynamic, water quality and sediment quality data was obtained for the development of the water quality models and evaluation of options.

  2. Marine ecological surveys for spring, summer, autumn and winter - these ecological surveys aimed at identifying and quantifying the fish, shrimp, plankton and other swimming communities in the sea as well as bottom-dwelling communities on the seashores and seabed.

  3. Sewage characterization - these tests characterized the chemical composition of the sewage and CEPT-treated effluent. Results showed that the heavy metal concentration in the effluent is low and almost all the organophosphorus and organochlorine pesticides are below detection limits.

  4. Whole effluent toxicity tests - these tests used both local and United States Environmental Protection Agency standard species to determine the toxicity of the sewage and treated effluent. This information will be used to ensure the discharge will not cause any toxic effect to the marine life.

8. Apart from the survey work, the consultants have recommended a set of options selection criteria relating to the marine environment (including water quality, whole effluent toxicity, sediment quality, mixing zone size, and biological and human health risk assessment), the onshore environment (including air, noise, and terrestrial ecology), and engineering, economic and social aspects. These criteria will be used:

  1. to establish which potential project components (i.e. treatment works and sewage outfalls) are feasible;

  2. to compare the various options and select the preferred option;

  3. as basic criteria for the detailed Environmental Impact Assessment.

9. Based on this set of criteria, findings of the previous studies and the IRP's recommendations, a shortlist of options including CEPT, disinfection and biological treatment processes as well as outfall locations at Stonecutters Island, Lamma Island west, Lamma Island east and Lema Channel were developed for further investigation and preferred option selection. The locations of these sites are shown in Figure 2.

10. To ensure that the most appropriate option is selected, it is important that the criteria should be adequate, comprehensive and realistic. The Consultants have initiated a community consultation programme to seek technical and professional inputs from the tertiary education institutes, green groups, and professional bodies. A list of consultees is at Annex A.

11. Comments were received from a total of 13 interest groups. The issues raised included:

  1. the need to establish bacterial criteria to protect the marine mammals (currently, there is no bacterial water quality objective for general marine waters);

  2. the need to include additional criteria for toxic substances, including mercury and trace organics; and

  3. the methodology in determining the size of the "mixing zone".

12. To follow up these issues, the Consultants have attended meetings with the interest groups to discuss their comments and explain the draft criteria and development of options in more detail. The Consultants are now carrying out further studies on the issue of setting additional toxic substances and bacterial criteria.


13. Analysis of data collected in the above surveys and testing programmes is now in progress. The Consultants have also started the development of the risk assessment model and the full 3-dimensional water quality model. Once set up, the models will be used to project environmental conditions. This work will form the basis of the impact assessment which in turn will drive the selection of the preferred option.

14. We now envisage that the modelling and impact assessment work should be completed by mid June. There will then be a period of public consultation lasting approximately six weeks. A recommendation on the preferred option would then be made in August. Assuming it is endorsed, the detailed EIA of construction and operational impacts (Phase II) would proceed immediately for completion by the end of 1998.

Environmental Protection Department
February 1998