PLC Panel on Environmental Affairs
Special Meeting on 1.8.97
INFORMATION PAPER ON RECENT SEWAGE LEAKS RESULTING IN THE TEMPORARY CLOSURE OF BEACHES IN TUEN MUN & STANLEY
Introduction
This information paper presents an account of the recent beach water pollution incidents involving the temporary closure of several gazetted beaches in Tuen Mun and Stanley and the actions taken by Government in response to these incidents. It also looks into various measures which will be adopted to avoid future recurrence of these incidents and minimise any adverse impact should similar incidents occur.
Pollution arising from damaged sewage outfall
2.At about 4am on Tuesday, 8 July 1997, the contractor (Zen Pacific-Dredging International Joint Venture) employed by the Developer (River Trade Terminal Co. Ltd.) for the River Trade Terminal project in Area 38 of Tuen Mun damaged one of the existing twin sewage outfall pipes during their dredging works.
3.The outfall pipes are used for the submarine discharge of screened sewage from the Pillar Point Sewage Treatment Works in Tuen Mun. They are laid below the seabed and are protected by a rubble mound of 2.4m thickness. The damaged location was about 30m away from the shore.
4.The Drainage Services Department (DSD) was notified of the damage at about 9:30 am on 8 July and responded immediately by diverting the sewage flow to the undamaged outfall pipe. Emergency action was taken immediately among DSD staff, the Authorised Person employed by the Developer and the contractor to repair the pipe.
5.The Environmental Protection Department (EPD) was informed of the incident on 11.7.97. On this same day, the analytical results of the regular beach water samples collected on 8.7.97 revealed that the five nearby gazetted beaches [Old Cafeteria, New Cafeteria, Kadoorie, Butterfly and Golden] were seriously polluted. The pollution was most likely to have been caused by the screened sewage which leaked from the damaged outfall, however, the situation could have been exacerbated by the exceptionally heavy rainfall bringing pollutants to the beaches from the surrounding areas. All five beaches had E-coli measurements ranging from over 1 500 to 15 000 counts per 100 mL which were well beyond the normal range of a few hundred to around 1 000 E-coli counts per 100mL.
6.In light of the available E-coli measurements and the fact that the damaged outfall was still under repair the EPD advised the Regional Services Department (RSD) to temporarily close all five affected beaches in order to minimise any risk to public health. The RSD immediately issued a press statement in the late afternoon of 11.7.97 that all the 5 gazetted beaches in Tuen Mun were closed until further notice.
Latest position of the five beaches in Tuen Mun
7.The contractor has carried out urgent repair works. The major damage was repaired on 10.7.97 but some leakage was still observed in subsequent tests. It is, however, expected that the repair to the remaining leaky areas will be completed fairly soon.
8.Since the incident was reported to the EPD, more frequent monitoring of water quality has been carried out and the monitoring results, based on the samples collected on Tuesday 22.7.97, showed that the water quality of all the affected beaches had gradually improved and was back to the normal acceptable level. Upon the advice of EPD, RSD re-opened the five beaches on 25.7.97.
Malfunctioning of the Tung Tau STW affecting St. Stephen's Beach
9.The biological process of a small sewage treatment plant with a capacity of 240m3 /day serving the Tung Tau Correctional Institution failed on 7.7.97 due to ingress of chemical wastes to the sewers. The plant was quickly repaired and resumed operation on 9.7.97, but during the breakdown period discharged substandard but disinfected sewage into the vicinity of St. Stephen's Beach.
10.After a review of the latest data from the regular beach water monitoring sample collected on 8.7.97, which showed a higher than usual E-coli measurement, and as the result of further investigations of other possible sources in the Stanley Bay area on 15.7.97, EPD considered that it was prudent to immediately advise the Urban Services Department (USD) that the water quality was likely to be unacceptable for swimming. Upon receiving this advice on 16.7.97, USD immediately closed the beach on the same evening.
11.The EPD collected water samples on 15.7.97 and subsequent days, which showed that beach water quality had returned to normal. The EPD therefore advised USD that the water quality was suitable for swimming and the beach was re-opened by USD on 18.7.97.
Incident of Sewage Overflow at Stanley Main Beach
12.On 21.7.97 an overflow of sewage was observed in the Stanley Main Beach Sewage Pumping Station by DSD who then immediately advised EPD. After preliminary investigation, EPD considered the overflow might affect the beach water quality and advised USD of this condition who then closed the beach on the same evening.
13.EPD collected water samples on 21.7.97 and subsequent days, which showed that the beach water quality had not been adversely affected. Upon the advice of EPD of the water quality, the beach was re-opened by USD on 24.7.97.
14.Further investigation of this incident revealed that due to the recent rainstorm, excessive quantity of rain/stream water was collected by the dry weather flow interceptors upstream of the Stanley Main Beach Sewage Pumping Station and had exceeded the capacity of the pumping station. EPD and DSD are working together to reduce the quantity of rainwater intercepted into the sewerage system in order to avoid recurrence of overflow in the pumping station.
15.After completion of the property connections to the public sewers in the catchment area by 1999, the dry weather flow interceptors will be decommissioned and the rain/stream water infiltrating into the sewerage system during the wet season will be significantly reduced.
Proposed Action
Strengthening inter-departmental coordination
16.As a result of the above incidents, both DSD and EPD see a need to improve communications and an emergency action plan is being drawn up. Both departments have now agreed, with immediate effect, that the relevant Chief Engineer of DSD shall inform the Principal Officer in charge of the relevant EPD Local Control Office by phone and by fax regarding any malfunctioning or other problems of the sewage treatment facilities or sewage outfalls. If there is a possibility of beach water quality being adversely affected so that swimmers might be at risk, EPD will inform USD or RSD of the incident, following which EPD will conduct an investigation to assess the position before advising USD or RSD further on whether the beach water quality is suitable for swimming.
First aid and longer term improvement measures for beaches
17.EPD and DSD will jointly identify those beaches which are more susceptible to sewage pollution under unforeseen circumstances that may affect the normal functioning of sewage treatment works or sewage outfalls. Due to the urgency to assess the potential for other similar pollution incidents and to consider remedial measures, EPD will commission a study to look into possible first aid measures including private and public facilities so as to reduce the risk of pollution in case of emergency breakdown, sewage bypasses or polluted storm drains. Other short term contingency arrangements to deal with emergencies such as tankering away of untreated sewage in case of equipment breakdown will also be actively pursued.
18.Since 1992, we have been implementing a programme of Sewerage Master Plans (SMPs) to improve regional sewerage schemes in Hong Kong at a total cost of around $7.6 billion. The basic aim of the programme is to direct all sewage into the sewerage system and provide treatment facilities which will cater for future growth. Work on all the 16 SMPs are scheduled for completion by 2006. EPD and DSD will jointly review the implementation of the programme.
Law enforcement
19.EPD is actively collecting relevant documents and site drawings, and interviewing concerned parties to gather facts and evidence relating to the incidents. Upon reviewing all these and seeking advice from the Department of Justice as appropriate, EPD will initiate prosecution under the Water Pollution Control Ordinance against all the parties which are considered responsible for the incidents.
Beach monitoring and laboratory analysis
20.The routine beach monitoring programme was designed for general monitoring of the beach water quality trends in order to check for compliance with the water quality objectives. This information also allows EPD to advise the public on the latest beach water quality through the bi-weekly press releases during the bathing season. If significant pollution at beaches is suspected or detected, an immediate investigation will be carried out to search for possible sources of pollution and further water samples will be taken more frequently at beaches likely to be affected. EPD is considering the implications of increasing the monitoring frequency to enable the public to be advised more frequently on beach water quality.
21.The current laboratory analytical method for determining E-coli is a standard used worldwide for monitoring beach water quality and takes about 3 days before the result is available. EPD is currently developing a new analytical method which could provide quicker results. This would be used in the investigation of suspected pollution and other emergency incidents, but the method is not yet accepted throughout the scientific community for use in a long term monitoring programme. EPD intends to introduce the new testing regime in the near future if it is proved reliable.
Works Bureau
31 July 1997
