Legislative Council

LC Paper No. CB(1)659/98-99
(These minutes have been
seen by the Administration)

Ref: CB1/PL/EA

LegCo Panel on Environmental Affairs

Minutes of special meeting
held on Monday, 26 October 1998, at 8:30 am
in Conference Room A of the Legislative Council Building

Members present :

Hon Christine LOH (Chairman)
Hon HUI Cheung-ching (Deputy Chairman)
Dr Hon Raymond HO Chung-tai, JP
Hon Bernard CHAN
Hon CHAN Wing-chan
Hon Mrs Sophie LEUNG LAU Yau-fun, JP
Hon WONG Yung-kan
Hon YEUNG Yiu-chung
Hon LAU Kong-wah
Hon Mrs Miriam LAU Kin-yee, JP
Hon CHOY So-yuk
Hon LAW Chi-kwong, JP

Members absent :

Prof Hon NG Ching-fai
Dr Hon LEONG Che-hung, JP

Public officers attending :

Mr Kim SALKELD
Deputy Secretary for Planning, Environment and Lands (Environment)

Mr Danny TSUI
Principal Assistant Secretary for Planning, Environment and Lands (Environment)

Dr Malcolm BROOM
Principal Environment Protection Officer
(Water Policy and Planning)
Environmental Protection Department

Dr Samuel CHUI
Senior Environment Protection Officer
(Water Policy and Planning)
Environmental Protection Department

Mr C K HON
Chief Engineer / Strategic Sewage Disposal Scheme
Drainage Services Department

Mr Philip HATTERSLEY
Consultant
Montgomery Watson

Mr Keith BARLETT
Consultant
Montgomery Watson

Mr Douglas McLEARIE
Consultant
Montgomery Watson

Mr Alan KWOK
Consultant
Montgomery Watson

Professor HUANG Ming-rong
Consultant
Binhai Wastewater Treatment & Disposal
(HK) Consultants Ltd.

By invitation :

Department of Civil Engineering, The University of Hong Kong

Professor C F LEE
Professor of Civil Engineering

Professor Herbert H P FANG
Professor of Civil Engineering

Dr Albert KOENIG
Associate Professor of Civil Engineering

Clerk in attendance :

Miss Odelia LEUNG
Chief Assistant Secretary (1)1

Staff in attendance :

Mrs Mary TANG
Senior Assistant Secretary (1)2


I Discussion on Phase I of Environment Impact Assessment for Stage II of the Strategic Sewage Disposal Scheme
(LC Paper Nos. CB(1)354, 358 and 365/98-99)

Meeting with the Department of Civil Engineering, The University of Hong Kong

At the invitation of the Chairman, Dr A KOENIG briefed members on some of technical issues in respect of centralised treatment of sewage and deep sea tunnels by highlighting the salient points of the submission which was circulated to members vide LC Paper No. CB(1)365/98-99.

Engineering feasibility of deep sea tunnels

2. Some members were concerned about the engineering feasibility of constructing and operating deep sea tunnels given the difficulties encountered in Stage I works of the Strategic Sewage Disposal Scheme (SSDS). In response, Professor C F LEE said that the geological conditions of Hong Kong were well understood. Its rock structure composed mainly of a hard and stable type of granite. Experience showed that construction of deep sea tunnels through this type of rock, whether using the explosive method or the boring machine method, would be technically feasible because the stable nature of the rock should not present a serious engineering problem. Intersecting faults were not uncommon but these could be detected through advanced tunnel boring surveys along with a number of horizontal boreholes. For best results, pre-probing works should be undertaken as part of geophysical survey. Referring to the difficulties experienced by the original contractor of SSDS Stage I tunnelling works, Professor LEE said that due to some technical limitations, the original contractors were unable to control the ground water intrusion problem and had since withdrawn from the contract. The problem had been subsequently resolved by the new contractor. With the existing improvements in tunnel boring machines, problems with ground water intrusion could be controlled. Longer and larger sea tunnels had been built under geological conditions much worse than those encountered in Hong Kong. With the state-of-the-art site investigation, rock excavation and ground water control methods, it was technically feasible to complete tunnel projects such as those planned for SSDS. There had been many successful examples of deep sea tunnels, such as the long railroad tunnel connecting the Japanese islands of Honshu and Hokkaido.

3. Comparing the geological conditions of the three outfall locations, viz the East, West and South East Lamma, Professor LEE said that there was not much difference among the three locations as far as geological conditions were concerned. He explained that basically there were two types of rocks encountered, namely the harder and more stable granite and volcanic rocks, and the softer and more pliable shale. Both kinds of geological environment presented different advantages. Granite and volcanic rocks had a high degree of stability and would unlikely collapse. However, fissures and faults were common and water intrusion problems would occur. Unlike granite, shale was of a much softer texture and had self-healing capability. This quality would prevent water from intruding but at the same time did not have a high degree of stability.

4. Elaborating on the difference between granite and volcanic rocks, Professor LEE said that these two types of rocks were both stable and there were not much difference as far as tunnelling aspects were concerned. Granite tended to be harder than volcanic rocks but fissures were common in both. Granite was commonly found in Hong Kong North while volcanic rocks in Hong Kong South. Sedimentary rocks were found in Peng Chau but these were confined to a small number of areas. There had been little geological changes over the years. Experience showed that underground geological conditions were more stable than on-shore conditions.

5. As regards geological surveys, Professor LEE stated that surveys for tunnelling works were carried out in two stages. The first stage involved the boring of holes within the tunnelling area. However, given the distance between boreholes, it was not possible to detect the in-between geological variations. Hence the first stage surveying works could only provide a general understanding of the geological environment but might not identify the exact location of fissures. The second stage involved dredging works which would reveal the natural composition of the tunnelling area. Suitable materials would be added and grouting works applied to ensure a firm rock support system. Provisions for building a rock support system could be stipulated in the contract.

6. Providing further details on grouting works for deep sea tunnels, Professor LEE advised that these would involve a special technology which was different from normal grouting works. A special kind of chemical grout would have to be applied to prevent water intrusion. These chemical grouts would solidify quickly, thereby instantly sealing cracks and fissures. Cement grouts would then be applied. These procedures would be applied in stages until all fissures were sealed. The form of application to be adopted and the type of grouting materials to be used could be specified in the contract.

7. Given the unforeseeable ground conditions which might delay the tunnelling works, members sought Professor LEE's views on how this could be addressed. Professor LEE suggested that consideration could be given to awarding a lump sum contract which would bring the cost under control. Since contractors involved with tunnelling works were dealing with unforeseen ground conditions entailing a high degree of uncertainty, flexibility would need to be built in the contract. It was not uncommon for contractors and project proponents to agree on sharing contract risks to cater for the need to do extra works to take account of unforeseen circumstances. In fact, most tunnelling contracts were signed on a contract risk sharing basis.

8. Responding to a member's enquiry on the certainty of the successful implementation of the SSDS Stage II works, Professor LEE said that as a civil engineer, he was only able to give advice on the engineering feasibility of deep sea tunnels. He was not in a position to give any undertaking on the successful implementation of SSDS Stage II works as this would depend on a number of factors. Although a few tunnels had been successfully completed in Hong Kong in the past, these were built either above the ground or using caisson technology. Hong Kong attempted to construct deep sea tunnels for the first time under the SSDS. Whilst fissures were common and geological environment could be quite unpredictable, if suitable geological surveys were performed using tunnel boring machines, coupled with pre-grouting works, the water intrusion problems could be kept under control. With the latest tunnelling technology, it was feasible to construct deep sea tunnel under the geological conditions of Hong Kong.

Centralised versus distributed sewage treatment system

9. Comparing the centralised and distributed sewage treatment system, Dr KOENIG said that the centralised treatment system was more effective as it allowed for efficient control of treatment processes and higher operational flexibility. A number of safeguards could be built into the centralised system to ensure its smooth operation. A large centralised sewage treatment plant was not inherently more at risk of failure than a series of smaller sewage plants. Professor Herbert FANG supplemented that there were a series of parallel treatment systems in a centralised treatment plant such that when one system failed, the remaining systems could still continue to operate.

10. As regards any incident of total failure of centralised treatment plants, Dr KOENIG said that he was not aware of any such incident. A large treatment plant consisted of many units operating in parallel and was not inherently more complicated than a small treatment plant. Both would need to have its own auxiliary power supply to safeguard against power failure. In fact, the overall risk of failure of one large plant was less than the combined risk of a series of small plants. Professor FANG added that flooding and other natural disasters would affect the operation of sewage plants, but these would not have anything to do with the size of the plant.

11. Dr Hon Raymond HO pointed out that if Hong Kong was to build several distributed plants, these would not be of a small scale as each would be expected to serve over a million people. He was concerned about the failure of the pumping system of a centralized treatment plant which might lead to the suspension of the entire treatment system. In response, Dr KOENIG explained that it would be more preferable to build one centralised plant than several distributed plants because the latter would require more equipment and would incur higher redundancy. As regards the concern about failure of the pumping system, Dr KOENIG said that back up facilities should be made available in case of failure and efforts should be made to ensure that operators were well trained in maintaining the system. Dr HO remarked that the size of a treatment plant should have no bearing on maintenance.

Peak factors and cost implications

12. Dr KOENIG explained to members the relationship between the size of a plant and its peak factors. The peak factor of a sewage plant was the ratio of the maximum flow over the average flow. The peak factor would decrease with the increasing size of the population in the catchment area. It also determined the design capacity of the plant. The peak factor of a large centralised plant was relatively lower and would require less spare capacity to handle the maximum flow. Professor FANG added that if Hong Kong was to construct three distributed plants instead of one large centralised one, a much higher peak factor would be involved in each of these plants to deal with the peak flow which was usually around 6:00 pm to 9:00 pm. Owing to the high variation of flow, there was a need to increase the overall design capacity of each of the three plants to cater for the maximum flow. Experience showed that it was more cost effective to build a large centralised plant because the peak load factor would be relatively lower, resulting in a lower design capacity. Moreover, the time lapse in conveying the sewage to a centralised plant would also help in lowering the variation of flow. Professor FANG illustrated that sewage effluent from Tseung Kwan O would take several hours to reach Stonecutters Island and this would effectively spread out the flow. In this way, less spare capacity would be required in respect of a centralised plant.

13. As regards the cost implications of peak factors, Professor FANG said that the construction cost would depend on the size of the plant but it would be difficult to estimate the cost implications or price differentials for different sizes of treatment plants.

14. For members' reference, Dr KOENIG cited a few overseas cases in which the same issue of centralisation versus decentralisation of sewage treatment had been addressed. The Boston Harbour Clean-up Plan recommended a single centralised plant with secondary treatment and a single outfall as a result of which a second plant was closed and its sewage conveyed by a deep underground tunnel to the centralised plant. The city of Zurich in Switzerland decided to replace the extension of the second, smaller sewage treatment plant by constructing a 7-kilometre long sewer to the first, large treatment plant despite incurring much higher investment costs on the ground that this would generate considerable savings on operation cost. The main driving force in these two cases was cost savings. As for Hong Kong, since the population density was higher and the volume of sewage larger, the centralised treatment plant would need to be larger. However, it would still be cheaper to build and maintain one centralised treatment than a few smaller distributed plants. Moreover, there were other factors such as land requirements, manpower and operation costs which needed to be taken into account. Since Hong Kong was densely populated, it would be difficult to identify sites to accommodate several decentralised treatment plants.

Land requirements of sewage treatment plants

15. As regards the optimum size of a sewage plant, Dr KOENIG said that the size of a plant should be proportional to the catchment area, and there was no optimum size of a treatment plant. The catchment area normally did not exceed 200 square kilometres. Since Hong Kong had a much higher population density, more sewage would be treated for a catchment area of a comparable size in other countries. Professor FANG said that a decentralised system was simply not possible in Hong Kong because of land constraints. A compact sewage treatment plant would require a minimum of 40 hectares of plant area together with 68 hectares of buffer zone which was roughly eight times the area of the Happy Valley Racecourse. Such a vast area of land could hardly be made available for building a sewage plant along the shoreline of the Victoria Harbour.

16. With the aid of a visualizer, Dr KOENIG showed some photographs of conventional and newer compact sewage treatment plants to illustrate the land requirements. He said that sewage plants built along the shoreline of Victoria Harbour would definitely require secondary treatment. It would be up to the Administration to decide whether a centralised system or decentralised system would be a more cost effective and viable option.

17. The Chairman thanked Professor LEE, Professor FANG and Dr KOENIG for providing expert advice to the Panel for reference.

Meeting with the Administration
(LC Paper No. CB(1)354/98-99)

Centralized versus distributed sewage treatment system

18. At the invitation of the Chairman, the Deputy Secretary for Planning, Environment and Lands (DS/PEL) said that over the years the Administration had looked at various options for providing sewage treatment in Hong Kong and quite a number of sites had been identified for building sewage plants. The Administration was mindful of the need to keep costs down such that the sewage charges could be kept at a reasonable level. Careful consideration was required to select an option which would be both cost effective as well as environmentally acceptable. All the available options, whether under centralised or decentralised treatment, required a collection system to convey sewage from catchment areas. Since a distributed system would require higher operation costs and entail a higher degree of redundancy, the Administration thus decided that it would be more cost effective in terms of capital and recurrent costs to build and maintain a centralised system. Admin.

19. Hon CHOY So-yuk was of the view that a detailed comparison on the pros and cons of a centralized and distributed sewage treatment system was of utmost importance in considering the future strategy of sewage disposal. DS/SPEL responded that such information had been provided to members (LC Paper No. CB(1)262/98-99(03)) but he would give an update as far as practicable.

Provision of land for sewage treatment

20. As to whether any land in Kwun Tong and Tseung Kwan O had been reserved for building sewage treatment plants, DS/PEL clarified that although there had been indications on where sewage plants could be located, the Administration would have to weigh the different land use options before arriving at a decision. The Principal Environmental Protection Officer (PEPO) added that the site in Kwun Tong was occupied by a preliminary treatment works. It had some scope for upgrading to provide primary treatment for some industrial flows only. It could not accommodate a secondary treatment works. Similarly the site in Tseung Kwan O was occupied by a preliminary treatment works. There was some scope for expansion but the site was not large enough to provide secondary treatment for the Tseung Kwan O population. PEPO further advised that when the sewage strategy was developed in the 1980s, the Administration had looked into the possibility of providing a distributed system of treatment utilising Tseung Kwan O (among other places). This would have involved a sewage discharge to the east of Hong Kong. The idea was dropped because there was a need to give maximum protection to the eastern waters of Hong Kong. Any discharge to the east, even if it had undergone a high level of treatment, would run the risk of injecting additional nutrients to the semi-enclosed bays around Port Shelter and Mirs Bay. Owing to the nature of semi-enclosed bays, they were more susceptible to nutrient pollution and consequential formation of red tides and algae blooms. To by-pass these semi-enclosed bays, a long sea outfall to the south east of Hong Kong possibly stretching into Mainland waters would need to be built. This was considered not a good option in environmental planning terms and would not be any better than the proposed centralised treatment system with a long sea outfall. In response to members, the Administration agreed to provide further information on the two sites and the projected flows. Admin.

Environmental impact at discharge location

21. On members' concern about the ecological impact on mariculture at the discharge location, PEPO advised that based on the results of the modelling exercises, sewage would be diluted and dispersed very quickly once it was distributed from the diffusers. After the initial dilution process, any toxic contaminants in the sewage would be at a level which would have no toxic effect. The initial dilution process took place within a hundred metres of the diffusers. After that there would be some further diffusion of sewage and the organic contents of the sewage would start to affect the water quality. The main effect of this would be on the level of dissolved oxygen which was a main criterion in assessing acceptability of water quality. There might be a small decrease of dissolved oxygen in an area a few kilometres away from the discharge point but the prediction was that the water quality criteria would still be met. All the options identified met the criteria despite the decrease of dissolved oxygen. The only likely impact on mariculture was a small increase of nutrient level in the water at the discharge location. However, the increase was minimal and was not expected to have any ecological effect. The conclusion reached was that the proposed options would have no impact on marine life.

22. PEPO further advised that the data collected in the modelling exercise were contained in the Working Paper Number 2 which had been deposited with the Legislative Council Secretariat for members' reference. These results were endorsed by the Hong Kong - Mainland Expert Group. The Mainland side agreed that the work done by the consultants were conducted in a thorough and professional manner and that the conclusions reached were scientifically sound and reliable. They had indicated a preference for chemically enhanced treatment with an outfall location at East of Lamma Island as a first step. The Mainland side also agreed that this option would be able to meet the criteria identified and that there would be no environmental impact.

23. Members were concerned about whether the Administration had had any discussions with the Mainland on the ecological impact of discharge on mariculture. PEPO said that the subject of mariculture had not been specifically raised by the Mainland side. However, the conclusion that there would be no impact on marine fish culture, fisheries and plankton was mentioned in page 21 of the briefing document which was made available to the Mainland side. (The said document was circulated to members for discussion at the Panel meeting on 11 September 1998 under LC Paper No. CB(1)161/98-99(03)).

24. Regarding the subject of ecotoxicological assessment which was raised by the Friends of the Earth (FOE) at the Panel meeting on 5 October 1998, PEPO explained that the consultants had taken into account the worst case scenarios. The established criteria had taken natural variations into consideration. Referring to the de-oxygenation incident in Mirs Bay cited by FOE, PEPO said that this was caused by some deep oceanic waters intruding into Mirs Bay, an area where the circulation was very limited. A discharge of treated sewage at the proposed outfall locations would not cause recurrence of such an incident because it would be in an area with strong currents and good water exchange where the treated sewage would be better diluted and dispersed.

Outcome of consultation with the Advisory Council on the Environment (ACE)

25. Regarding the outcome of consultation with the ACE on the SSDS Stage II options, DS/PEL advised that a number of green groups including FOE, Conservancy Association, World Wide Fund for Nature, and Green Power were represented on the ACE. At the last meeting held on 22 October 1998, the ACE members indicated that they would prefer option 2, i.e. chemically enhanced primary treatment (CEPT) plus disinfection with outfall at South East Lamma. They however recognised the potential problem with the option and would accept a fall back on option 1, i.e. CEPT plus disinfection with outfall at East or West Lamma. The ACE stressed the need for retaining flexibility to develop the system in future. They felt strongly that a proper sewage system should be put in place as soon as practicable.

Minutes of meeting of the Expert Group

26. Responding to Hon CHOY SO-YUK's request for releasing the minutes of meetings of the Expert Group at which SSDS had been discussed, DS/PEL said that it was not a usual practice to make public the minutes of these meeting. A press release was normally made by the Expert Group each time after a meeting was held. The Administration would consult the Mainland side on the matter. Admin.

Environment Impact Assessment (EIA) studies

27. As regards the EIA studies on the various options, DS/PEL said that full information on the environmental impact of the various options had been contained in the briefing document provided to members. The Administration would take into consideration the concerns raised by members in deciding on the option. Funding application for SSDS stage II would be made in the year 2000. PEPO said that a site specific EIA would be conducted for the construction and operation phases of the selected option. The whole EIA process was expected to be completed in May 1999 and a report would be made available for public comments under the provisions of EIA Ordinance, Cap 499.

(The Chairman left the meeting at this juncture. The Deputy Chairman took over the chair.)

Sewage charges

28. Hon CHAN Wing-chan expressed concern about possible increase in sewage charges upon implementation of the SSDS Stage II in the year 2009/10. DS/PEL advised that the Administration had only worked out the costs but had not made any decision on the sewage charges. Whether these costs were met by sewage charges or tax revenue would be a price to be paid by the people of Hong Kong for a proper sewage system. The Administration would try to keep down the sewage costs by using the most cost effective means so that the sewage charges would still be comparatively lower than most countries. Currently an average domestic customer paid 30 cents a day for sewage treatment. A two-to-three time increase would not mean a lot to an average person in actual cash terms. Admin.

29. The Principal Assistant Secretary for Planning, Environment and Lands referred members to Table 2 of the information paper on the recurrent costs of sewage treatment (LC Paper No. CB(1)354/98-99(01)(b)) which illustrated the effects of different approaches to meeting sewage costs. He emphasized that any proposal to adjust sewage charges would need to be approved by the Legislative Council.

30. As to how sewage costs would be apportioned between the Administration and polluters, DS/PEL said that since these charges would only be imposed in 10 years' time, it would be difficult at the present stage to make any realistic forecast on the apportionment of charges which were subject to changes in inflation , productivity and population growth. In response to a member, the Administration agreed to provide information on the plan to put into effect the pledge made by the Secretary for the Treasury at the Provisional Legislative Council meeting on 19 November 1997 that the operation and maintenance costs of sewage services were to be borne equally by the Administration and polluters in 2000-2001.

Way forward

31. On the way forward, DS/PEL said that the Administration would consider the advice of the Legislative Council and the ACE and the public comments received. It would have further discussions with the Mainland counterparts. The Panel would be informed of the decision on the choice of option which would be made by the end of the year. There would be a final round of discussion on the EIA report upon its completion in May 1999.

32. Hon CHOY So-yuk suggested setting up a Subcommittee under the Panel to further study the SSDS Stage II options. The Deputy Chairman suggested that the matter be discussed at the next regular Panel meeting.

II Any other business

33. There being no other business, the meeting ended at 10:50 am.


Legislative Council Secretariat
17 December 1998