LCQ5 : Low risk of virus spreading through drainage system
Following is a question by the Hon Tsang Yok-sing and an oral reply by the Secretary for the Environment, Transport and Works, Dr Sarah Liao, in the Legislative Council meeting today (June 11）:
An environmentalist is reported to have stated that the underground drainage system in the area around Dundas Street in Mongkok has been misconnected, causing the inflow of sewage from commercial and domestic buildings into the stormwater drainage system and threatening the health of the residents in the vicinity. As such sewage may not have undergone any treatment before it is directly discharged into the Victoria Harbour, the marine environment may be polluted. In this connection, will the Government inform this Council:
(a) whether it has assessed the risk of virus spreading through the misconnected drainage system; if it has, of the assessment results;
(b) as the stormwater drainage system in the above area also discharges sewage and its flood relief ability is thus weakened, of the measures the authorities will take to prevent the occurrence of flooding in the area during rainstorms; and
(c) whether it has assessed if the discharge of sewage from commercial and domestic buildings into the harbour through stormwater drainage pipes will hinder the optimal use of public sewage treatment facilities, resulting in a waste of public funds?
(a) As the drainage system is laid underground, it is unlikely that members of the public will come into contact with it. Therefore, the risk of virus spreading through the drainage system is very low.
There is no misconnection with respect to the underground communal drainage system in the area around Dundas Street in Mongkok. The presence of domestic sewage and trade effluent in the communal drains there is probably caused by illegal expedient connections between individual private buildings and the communal drainage system, or by the direct discharge of wastewater into the drains at roadsides or back lanes. The Environmental Protection Department (EPD) and the Buildings Department will step up their inspection of private buildings to look for expedient connections and, if any irregularities are spotted, will request the owners of the relevant premises to rectify the situation promptly. EPD will also initiate prosecutions against illegal discharge of wastewater into the communal drainage system as part of its routine enforcement work.
To further minimise the problem caused by wastewater found in the communal drains, the Drainage Services Department had installed a dry-weather flow interceptor in the section of the underground communal drainage system around the intersection of Dundas Street and Portland Street. During dry weather, the interceptor can intercept the wastewater discharged into the communal drainage system and divert it back to the communal sewerage system. The wastewater will be conveyed to Northwest Kowloon Preliminary Treatment Works for screening, and then to the Stonecutters Island Sewage Treatment Works for treatment before discharge, and hence should neither affect public health nor pollute the marine environment. During wet weather, the flows in the communal drainage system will increase substantially, thereby dispersing and diluting any wastewater therein. After the wastewater has been discharged into the sea, most viruses in the seawater will eventually be killed by the ultraviolet radiation of sunlight and therefore public health should not be affected.
(b) The design capacity of the communal drainage system is intended for handling the surface runoff arising from rainstorms, the volume of which is much higher than the volume of wastewater being inappropriately discharged into the drainage system. Even though some wastewater may find its way into the communal drains, the drainage system which is serving a large catchment area should be able to handle it without increasing the risk of flooding.
(c) During the last ten or more years, the Government has invested some $20 billion in sewage collection and treatment facilities. These facilities are now handling some 2.5 million cubic metres of sewage daily, which accounts for 95% of the sewage produced by the population in Hong Kong. As a result of the operation of these facilities in various districts, there has been significant improvement of the water quality in many parts of our marine waters over the last decade or so.
End/Wednesday, June 11, 2003