For Information
Provisional LegCo Panel on Environmental Affairs
Water Pollution at Shing Mun River
INTRODUCTION
This paper provides the current environmental conditions of Shing Mun River and the proposed improvement measures identified in a Study conducted between August 1996 and December 1997 with a view to fulfilling the river's designated use for secondary contact recreation purposes.
ENVIRONMENTAL CONDITIONS OF THE RIVER
2. The river was heavily polluted in the 1980s due to indiscriminate discharges from industrial, commercial, livestock and domestic sources. The organic pollution load discharged into the river in 1987 was around 9,000 kg Biochemical Oxygen Demand (BOD) per day.
3. The pollution load has since substantially reduced following the declaration of the Tolo Harbour and Channel Water Control Zone under the Water Pollution Control Ordinance (WPCO) and the implementation of the Livestock Waste Control Scheme (LWCS). By the end of 1997, the pollution load discharging into the river has dropped by nearly 90% to some 1,050 kg BOD per day. Annex 1 provides the pollution load reduction achievement over the past 11 years.
4. Water quality in Hong Kong is graded into Excellent; Good; Fair; Bad and Very Bad. From late 1980s to 1992, the average water quality of the main Shing Mun River channel was graded "Fair". It turned to "Good" in 1993 and remained in this grading over the past 5 years as shown at Annex 2.
AREAS FOR IMPROVEMENT
5. The reduction of remaining pollution load and improvement of the contaminated sediments at the bottom of the river are the areas for further upgrading of the river water quality. More than 95% of the 1,050 kg pollution load originate from untreated domestic sewage discharged from unsewered villages. Accumulated on the river bed are contaminated sediments containing organic materials and heavy metals which are capable of releasing obnoxious odour and suppressing the development of a balanced natural ecology within the river system.
ACTIONS TO REDUCE POLLUTION LOAD
6. To reduce the pollution load in the catchment of Shing Mun River, a sewerage connection programme for many unsewered villages is being implemented to intercept untreated domestic sewage. There were resistance to the programme initially on technical and land matters. Successful connections have given confidence to the villagers, e.g. Tai Wai Village, and the programme is now progressing satisfactorily. So far, out of the 500 houses in 4 villages in Sha Tin served with new sewers, some 55 % have completed the house connection works and a further 28 % will complete in the near further. By 2001/02, a further amount of some 600 kg BOD per day reduction will be achieved.
7. Equally important, the Environmental Protection Department (EPD) is maintaining stringent enforcement in the Sha Tin area to curb any illegal discharges into the river catchment. At present, almost all industrial and commercial discharges made into the stormwater drainage system have been eliminated. In 1997, some 700 inspections together with a total of 20 prosecution actions were undertaken.
ACTIONS TO IMPROVE CONDITION OF SEDIMENT
8. EPD commissioned a study to formulate the most cost-effective and environmentally acceptable methods to tackle the contaminated sediments. The applicability of various improvement techniques, including aeration, in-situ bioremediation, chemical treatment, ex-situ treatment, dredging, engineering methods, etc are evaluated under the study. As bioremediation is a relatively new technology that has not been practised in Hong Kong at a scale comparable to Shing Mun River, a pilot field trial was conducted to ascertain the applicability and effectiveness of the technique. The results of the 3-month pilot trial indicated that there was a reduction in the organic contaminant content in the treated sediment and the emission of obnoxious odour was also suppressed.
9. The study recommends an improvement strategy combining bioremediation and dredging methods. This strategy will start off with bioremediation of the river by phases plus an option to dredging triggered off by findings of a rigorous monitoring programme running from the outset of bioremediation.
TENTATIVE PROGRAMME
10. According to the necessary public work funding/approval arrangements, it is anticipated that improvement works for the sediments will commence in 2000/01 for completion in 2002/03. As a flood control dredging programme at the Shing Mun River is being planned by the Drainage Services Department and Civil Engineering Department, EPD will take that programme into consideration for completion of environmental improvement works at an earlier stage. Local consultation with members of the Sha Tin Provisional District Board (STPDB) and a number of interested parties have been undertaken during the whole course of the study. This includes 3 briefings together with a visit to the pilot trial site between Janurary 1997 and the recent months. Further liaison with the STPDB members and local residents will also be arranged during implemenation of the works.
OTHER IMPROVEMENT OPTIONS SUGGESTED
11. People have high expectations of the use of Shing Mun River. A proposal of converting Shing Mun River into an artificial lake was suggested by a member of the STPDB. The proposal requires construction of dams which will likely impede the natural flow of water. The proposal was commented by relevant government departments
12. The Shing Mun River was designed as a drainage channel for flood control of the whole Sha Tin New Town during heavy rainfall. As recently reported by the Drainage Services Department, the flow capacity of the river has already reached its limit for preventing flooding. The construction of dams for an artificial lake will inevitably impede the existing flow capacity and substantially increase the risk of large scale flooding within the area. Provision of dams within the river will also restrain the natural tidal flushing and cleaning effect within the river, thus leading to deterioration of the river water quality. The stagnant water contained by dams will enhance sedimentation and will create adverse impacts affecting the natural ecology within the confined area.
LONG TERM IMPROVEMENT
13. Long term improvement and maintenance of Shing Mun River rely on the successful implementation of a suite of activities, which include pollution source control by sewerage connection, stringent enforcement actions to curb illegal discharges, implementation of the recommended sediment improvement works, and continuous environmental monitoring as well as auditing of the about to be launched improvement actions.
14. EPD anticipates that, with the implementation of the suite of activities aforementioned, the designated water quality of Shing Mun River will ultimately be achieved and the beneficial use as secondary contact recreation zone satisfied after the turn of the next century.
Environmental Protection Department
March 1998
