For Information

LegCo Panel on Environmental Affairs Environmental Problems of Shing Mun River

INTRODUCTION

The purpose of this paper is to inform Members of the environmental problems of Shing Mun River, the improvement measures taken and further possible measures arising from a consultancy study " Environmental Improvement of Shing Mun River Main Channel and Associated Nullahs" to tackle the problems.

POLLUTION OF SHING MUN RIVER

2. By the late 1980's the Shing Mun River had become excessively polluted due to the discharges of untreated industrial, commercial, livestock, and domestic wastes. The organic pollution load dumped into the river was estimated to contain some 9,000 kg of Biochemical Oxygen Demand (BOD) per day in 1987.

3. Since then, the government has actively been improving the environmental conditions of the river through implementation of pollution control measures such as the declaration of the Tolo Harbour and Channel Water Control Zone under the Water Pollution Control Ordinance (WPCO) and the control over the disposal of livestock waste under the Livestock Waste Control Scheme (LWCS). By the end of 1996, the pollution load discharged to the river has been reduced by 86% to 1,200 kg BOD per day. This remaining BOD loading is contributed mainly from unsewered domestic premises in the Shing Mun River catchment area. In this regard, a sewerage connection scheme is being implemented in the Shing Mun River catchment area in phases to resolve the problem. The overall pollution loading of Shing Mun River over the past 10 years is shown at Annex 1.

PRESENT STATE OF THE RIVER

4. Over the years, the water quality of Shing Mun River has improved. The improvement, expressed as a Water Quality Index (WQI)(note 1), is shown in Annex 2. Whilst the WQI has improved from a "Fair" to a "Good" grading, the water quality of Shing Mun River is still not entirely in compliance with the required standard to make Shing Mun River good enough to be a secondary contact recreation zone.

note 1: The water quality index (WQI) is a numerical value which is used to summarise, on the basis of monitoring data, the state of river water quality. The WQI ranges from 3 to 15 and corresponds to 5 gradings of water quality conditions from excellent to very bad.

5. Due to its configuration and low natural water flow, the Shing Mun River has acted as a sediment basin. It is estimated that over 400,000 m3 of contaminated sediments with high levels of organic and heavy metal contaminants have been deposited along the river channel. These organic and heavy metal contents in the sediments continuously contribute to the pollution load of the river, exerting a high oxygen demand on the overlying river water and posing also a threat to the development of the natural ecology within the river. Moreover, the sediments accumulated in the upstream stretch of the river, when exposed during low tide, are aesthetically offensive and cause a considerable odour nuisance to the local community.

THE CONSULTANCY STUDY

6. To tackle the sediment problem, Environmental Protection Department (EPD) commissioned a consultancy study on Environmental Improvement of Shing Mun River Main Channel and Associated Nullahs in August 1996, with a view to achieving the following objectives:-

  1. establish the extent of the sediments deposited on the river bed of Shing Mun River and its associated nullahs;

  2. determine the extent of contamination of the sediments and their impact on water quality, ecology and local residents;

  3. identify the scope of works necessary to improve the environmental conditions of the River;

  4. specify measures required during the works to minimise environmental impacts; and

  5. determine the cost, programme and technical specifications for implementation of the recommended works.

7. The consultant completed in February 1997 a comprehensive site investigation exercise, covering odour survey, ecology survey, geophysical survey, river water and sediment sampling and testings. Based on the investigation results, evaluation and assessment of the environmental impacts caused by the sediments to the river were made. Feasibility of various improvement techniques, including dredging, in-situ treatment and ex-situ treatment, were being evaluated. To enable the determination of the most suitable and environmentally acceptable sediment improvement measures, a second phase sampling and testing of river sediments is also underway.

8. The in-situ treatment of sediments, known as "bioremediation", is a relatively new technology and has not been conducted in Hong Kong in a scale comparable to Shing Mun River. In order to ascertain its applicability in practice, a pilot field trial will be arranged should the bioremediation technique be suggested. The recommended improvement works, which could be one or a combination of the aforementioned various techniques, will eventually be determined by their cost-effectiveness and environmental acceptability.

9. The entire Study is scheduled for completion in early September 1997.

CONCLUSION

10. EPD anticipates that, with the continuing enforcement of the WPCO and LWCS and implementation of the sewerage connection scheme and further improvement works as arising from the Study, the water quality of the Shing Mun River would be able to meet its designated water quality by the turn of the century.

Environmental Protection Department
May 1997

Last Updated on 18 August 1998