Supplementary Information for the LegCo EA Panel
Follow-up to the Panel Meeting on 5 February 1999

Monitoring of the uncontaminated mud disposal sites at
east of Tung Lung Chau, south of Tsing Yi and north of Lantau

This paper aims at addressing key concerns raised by Members of the LegCo Environmental Affairs Panel at its meeting on 5 February 1999. Due to the pressing time at the meeting, the Chairman suggested and the Administration agreed to provide written response to address the concerns and questions raised by the Members. Also the Administration had taken the Chairman's suggestion of submitting a separate funding application for the monitoring of uncontaminated mud disposal at north of Lantau and south of Tsing Yi, to which Members have no objection.

2. This supplementary information is based largely on the Environmental Impact Assessment reports endorsed by the Advisory Council on the Environment at its meetings on 9 February 1996 and 23 March 1998.

Additional Background Information at East of Tung Lung Chau

3. The disposal site at east of Tung Lung Chau (ETLC) was first gazetted under the Foreshore and Sea-bed (Reclamations) Ordinance (Chapter 127) on 14 September 1990 (Gazette No. 3233). The gazetted activities included dredging of the sea-bed for materials and backfilling to a level not higher than the original sea-bed. Authorisation was given under section 7 of the Ordinance on 22 November 1990 (Gazette No. 4295).

4. Sand dredging at ETLC site was carried out between November 1991 and June 1994 for the West Kowloon Reclamation project and between September 1994 and July 1995 for Tseung Kwan O Development. A total of about 55 Mm3 of sand was extracted from the site.

5. Ex-gratia allowance of HK$ 45,785,303.00 had been paid to 863 eligible fishermen between 19.4.1993 and 22.4.1997. Ex-gratia allowance of HK$9,355,759.99 had also been paid between 15.12.1992 and 14.12.1996 to 55 mariculturists affected by the dredging operation. 6. An Environmental Impact Assessment (EIA) study was carried out to determine the environmental acceptability of backfilling at the site. The detailed assessment included effect of backfilling at the ETLC site on water quality, marine ecology, air quality and noise level. The study indicated that there are unlikely to be any insurmountable or unacceptable residual environmental impacts. The Environmental Monitoring and Audit programme (EM&A) recommended as part of the EIA provides guidelines on the management of the disposal site. The Operations Plan is summarised in Annex A. The EM&A also suggested mitigation measures to be employed should unacceptable impacts arise, thereby ensuring the environmental acceptability of the project. These include reduction of disposal volume and even ceasing the disposal operation should water quality drops below the pre-set levels. The EIA report was endorsed by the Advisory Council on the Environment on 23 March 1998. The Aquaculture Subcommittee and Capture Fisheries Subcommittees of the Advisory Committee on Agriculture and Fisheries did not raise any objection to this project.

7. Some members of the Sai Kung Provisional District Board (SKPDB) expressed concern about the potential environmental impacts resulting from the proposed backfilling. To demonstrate the feasibility of this project, a trial disposal was carried out on 25 March 1999 using two barges. Forty persons including the Hon. Ng Leung-sing, the Hon. Wong Yung-kan, representatives from SKPDB, Aquaculture Fisheries Sub-Committee, Capture Fisheries Sub-Committee, EPD, AFD, MD and fishermen attended the trial. The trial indicated that there was no measurable rise in suspended solid in less than an hour after each disposal and the water quality had not been adversely affected.

8. The project was presented to the Sai Kung fishermen representatives on 8 April 1999 and to Mr Christopher Chung (Urban Councillor and Eastern Provisional District Board Member) and a group of fishermen from the Eastern district on 12 April 1999. Separate discussion was held with the Hon. Wong Yung-kan and Mr Christopher Chung on 24 April 1999.

9. The project was then presented in the Environment Improvement Committee meeting of SKPDB on 6 May 1999. Despite the demonstrated outcome of the trial disposal, the Committee was not prepared to support backfilling of the ETLC site. However, we would continue to try to address their concern.

What are the benefits of backfilling and the losses for not backfilling the empty pits at ETLC?

10. The uneven seabed due to empty pits is not suitable for bottom trawling. Backfilling the empty pits would restore about 900 hectares of sea bed to its previous level which will once again be suitable for bottom trawling.

11. Benthic organisms that dwell on the seabed are an important chain in the food web. The area around ETLC is currently in a transient hydrodynamic state due to the large depressions left by sand dredging. Erosion and deposition are taking place inside and around the pits, particularly at the northern pit where the pit-bottom is about 18 m (about 59 ft) below the surrounding seabed level. The unstable condition hinders recovery of the benthic communities because organisms that start to occupy the pit-floor are smothered and buried by the continuous sediment deposition inside the pits. The pit-floor is therefore ineffective in feeding the fish population in the area. This situation will continue for many years until a state of equilibrium is attained.

12. Sequential bathymetric surveys in July 1994, April 1997 and February 1999 confirm active erosion and deposition at ETLC. This suggested that the current pit environment is not conducive to full recovery of the benthic communities.

13. A recent seabed ecology study at Tathong Channel (Seabed Ecology Studies: Tathong Channel by ERM, 30 October 1997) found that the presence of fluid mud in the pit bottom has resulted in lower species diversity and abundance inside the pits than in the surrounding areas. The ETLC site is similar in setting and dredging history to the Tathong Channel site, this phenomenon probably also exists at ETLC.

14. If the empty pits at East Tung Lung Chau are not available for backfilling, then we might have to continue disposal on open seafloor disposal. This is environmentally less favourable than mud disposal at the empty pits because pits can provide much better containment of disposed mud. After sand dredging ceased at the ETLC marine borrow area, the marine environment has gradually improved as shown by new fish species caught in the area for the past year. Why renew activities that affect fishery?

15. Higher fisheries production was reported in recent years in the ETLC area. This may be due to more fishing activity or higher fishery resources. The latter may have been brought about by a slight increase in sea water temperature. Such (i.e., higher fishery resources due to warmer sea water) has been reported along the California coast over the last two years.

16. The EIA study had assessed the impact of backfilling on fisheries resources at ETLC. It predicted that it would not cause any long-term adverse impacts to the fisheries resources and the impacts to capture fisheries would be localised and temporary. It further predicted that less than 0.4% of the spawning ground of the southern waters would be disturbed by backfilling and would only happen during the disposal events. Our recent disposal trial indicated that the suspended sediment level in the water column had returned to the ambient level in less than an hour.

17. For mariculture fisheries, the EIA study predicted that there would be no elevation of suspended sediment levels at the nearby mariculture sites at Tung Lung Chau, Po Toi O and Po Toi Islands.

18. During backfilling, the environmental acceptability will be verified by a comprehensive Environmental Monitoring and Audit programme which comprises water quality, marine ecology and bathymetric monitoring. The monitoring programme will provide an early indication of any environmental degradation and will enable immediate implementation of mitigation measures. All monitoring results will be reviewed by a Working Group comprising representatives of the Environmental Protection Department, the Agriculture and Fisheries Department and the Civil Engineering Department. We also welcome fishermen representatives to join the Working Group.

The EIA study for South Tsing Yi and North Lantau was completed in 1996. Are the conclusions of the study still valid?

19. Yes. The feasibility of South Tsing Yi and North Lantau disposal sites have been demonstrated by a pilot scheme to assess whether environmental impacts associated with backfilling operations were in accordance with predictions made in the EIA study. The scheme involved the following:

  1. In 1996 to 1997, disposal at South Tsing Yi of about 1.5 million cubic metres of grab-dredged uncontaminated mud generated from the Hei Ling Chau Typhoon Shelter project.

  2. In 1997-1998, disposal at North Lantau of about 1 million cubic metres of grab-dredged uncontaminated mud generated from the Tuen Mun River Trade Terminal project.

20. During the full scale trial, monitoring results at the above two sites were reviewed to assess the effectiveness of the operations plan and the monitoring programme. No water quality impacts were detected at the perimeter and sensitive receivers during the backfilling operations.

What is the content of the EIA study for the proposed backfilling at ETLC?

21. The EIA study for backfilling the empty sand borrow pits at ETLC included the following:

  1. Water quality impacts were evaluated under different disposal rates and seasonal conditions using sediment transport and hydrodynamic models.

    For backfilling following the proposed operations plan, the EIA study predicted that suspended sediment (SS) concentrations, dissolved oxygen and nutrients would comply with the adopted standard and the Water Quality Objectives (WQO).

  2. Marine Ecology studies assessed possible impacts on soft bottom benthic organisms, corals, fish and invertebrates (e.g. squid) and examines the effect on fishery resources.

    The EIA study predicted that the impacts of the proposed backfilling operations are very localised. The soft bottom benthic communities in and around the disposal site, which may be temporarily and locally affected by the disposal activity, do not contain rare species. Water quality at nearby coral sites such as Ninepins Islands and Tung Lung Chau would not be adversely affected and would comply with the adopted SS standard and the WQOs. The Finless Porpoise present in the eastern waters would not be affected because water quality would be within the WQOs.

    Fisheries impact assessments at ETLC predicted that there would be no SS elevation at nearby mariculture zones at Tung Lung Chau and Po Toi O. The effects on the spawning ground would be very small and temporary. The impacts to capture fisheries would be localised and temporary.

  3. Impacts on air quality and noise levels were assessed respectively against the Air Quality Objectives and criteria set by the Noise Control Ordinance.

    The EIA study predicted that the proposed backfilling operations would not cause any unacceptable air quality or noise impacts.

How could you ensure that only uncontaminated mud would be disposed of at the uncontaminated mud disposal site?

22. Before an allocation is given to the project proponent to dispose of any volume of dredged mud, the project office is required to undertake an extensive sediment sampling and testing programme in accordance with Works Branch Technical Circular No. 22/92 and Environmental Protection Department Technical Circular No. 1-1-92. The Environmental Protection Department will examine the sediment quality reports and confirm the extent of uncontaminated mud that needs to be dredged and disposed of. Contaminated mud has to be disposal of at East Sha Chau.

23. During dredging, the resident engineer at the dredging site will ensure that only uncontaminated mud is loaded on barges heading for the allocated uncontaminated mud disposal site. In addition, the dumping permit issued under the Dumping at Sea Ordinance (Cap. 466) by the Director of Environmental Protection also stipulates, among others, the installation of an Automatic Self-Monitoring System on all disposal vessels which records their draught, navigation route and disposal location and time. This equipment enables the Environmental Protection Department to effectively monitor the entire disposal operation of the disposal vessels. The Environmental Protection Department also maintains a spot-check programme to guard against non-compliance with the permit conditions.

Did you employ experts in the marine ecology and fisheries assessments at ETLC?

24. Yes. The following local and international experts were engaged in the marine ecology and fisheries assessments of ETLC EIA study:

  1. Ms Shelley Clarke, Technical Director with ERM Hong Kong - an expert in marine ecology and fisheries and in managing dredged materials;

  2. Dr. Robin Kennish, Senior Consultant with ERM Hong Kong - an expert in marine ecology and fisheries;

  3. Professor Rudolf S. S. Wu, Professor of City University of Hong Kong & Director of Centre for Coastal Pollution and Conservation - an expert in fisheries and marine pollution;

  4. Professor Z.R. Chen, Professor of South China Institute of Oceanology in Guangzhou, China - an expert in fisheries in South China Sea.

  5. Professor Tony Pitcher, Professor of University of British Columbia, Canada - an expert in fisheries management; and

  6. Professor Daniel Pauly, Professor of University of British Columbia, Canada and Associate at International Centre for Living Aquatic Resources Management, The Philippines - an expert in tropical and sub-tropical fisheries.

25. All the results of the marine ecology and fisheries assessments have been thoroughly reviewed by experts of the Environmental Protection Department and the Agriculture and Fisheries Department.

What would you do when unacceptable impacts occur at ETLC?

26. The detailed EIA study at ETLC predicted no unacceptable impacts resulting from the disposal operation. The backfilling activities will be subject to stringent environmental monitoring and control, following the requirements laid down in the EM&A Manual. The monitoring programme allows early detection of any unfavourable impacts and enables immediate implementation of mitigation measures. The prime mitigation measure in the event of the water quality alarming targets being exceeded is a reduction in the daily disposal rate, down to zero where necessary. If such situation occurs, the ETLC site will be abandoned.


27. There is an on-going need in the Hong Kong Special Administrative Region for disposal of dredged uncontaminated mud. Marine disposal in empty sand borrow pits is the most practical and environmentally acceptable option. The detailed EIA study at ETLC predicted no unacceptable impacts resulting from the disposal operation. The backfilling activities will be subject to stringent environmental monitoring and control, following the requirements laid down in the EM&A Manual. Backfilling the pits restores the seabed to its original profile. The restored seabed will be suitable for bottom trawling again and the benthic organisms, an important food source for fish, will thrive on it.

Fill Management Committee Secretariat
Geotechnical Engineering Office,
Civil Engineering Department,
3 June 1999