In response to media enquiries on the suspected leakage of leachate from the West New Territories (WENT) Landfill, the spokesman for the Environmental Protection Department (EPD) today (August 31) replied as follows:
Water management at the WENT Landfill involves two independent collection and treatment systems, namely the rainwater and ground water management system and the leachate management system. This incident was caused by the contractor's improper handling of the valve for a rainwater collection facility, thus causing leakage of rainwater contaminated with pollutants into an adjacent river.
The spokesman explained that pollutants easily accumulate on the ground of the landfill, and may be washed away by the first flush of rainstorm after a period of dry days (not only the first rainstorm after the dry season). Such rainwater will be relatively turbid. To reduce such kind of pollution, rainwater management facilities are installed at particular spots surrounding the landfill to collect and intercept polluted rainwater. The rainwater retention pond mentioned in media reports is actually part of the landfill's rainwater management system. When the rainwater retained by the retention pond rises to a certain level, the water pump installed inside the pond will be activated. The rainwater with pollutants is then pumped into the leachate management system, where it will be treated together with the leachate and finally discharged into the sewers of the Drainage Services Department.
The water pump will not operate until the water level of the retention pond has reached the triggering position. Therefore, polluted rainwater will accumulate in the retention pond and some pollutants will be left at the bottom of the pond. The contractor thus needs to clean the residual polluted rainwater, silt and waste in the retention pond regularly. To facilitate the cleaning of the rainwater retention pond, a valve is installed at its bottom to enable the collection and delivery of the residual polluted rainwater to the leachate management system for proper treatment, to be followed by the cleaning of the sludge and waste left at the retention pond.
The EPD received complaints from members of the public in August this year that Tai Shui Hang River was being polluted and it was suspected that there was an illegal discharge into the river. After investigation by the Environmental Compliance Division of the EPD on August 7, it was found that wastewater was leaking from the landfill. The EPD subsequently collected evidence and will instigate prosecution against the contractor concerned if there is sufficient evidence. The Department also gave the contractor a stern warning and ordered the contractor to conduct an investigation on the incident immediately so as to rectify the problem. The contractor rectified the problem on the same day and deactivated the valve of the rainwater retention pond. Thorough inspections of similar facilities have also been conducted to ensure the incident will not happen again.
It has been reported that leakage of leachate still continues after the rectification. In fact, the suspected leachate is actually polluted rainwater which is now deposited at the bottom of the retention pond. Consequently, the polluted water in the retention pond shows a darker colour, which is normal, and it will continue to be pumped away. Since the pollutants on the ground have been washed away and accumulated at the bottom of the retention pond during the first flush of rainstorm, the rainwater that entered the retention pond at a later stage is relatively clean and will pass through the top of the retention pond and flow away crossing the top of the outer wall. As the valve of the rainwater collection facility has been deactivated, the wastewater at the bottom will not leak or be directly discharged through the valve. It can only be pumped away.
The spokesman stressed that this is an individual incident and such irregularity caused by the malfunction of the valve was detected for the first time since the WENT Landfill began operation more than 20 years ago. Despite the incident, the surrounding environment and water bodies have not been significantly affected and there are no signs of algae or fish kills.
The EPD has all along been closely monitoring the performance of the contractor. If it fails to meet contractual requirements, the EPD will demand it to conduct a thorough investigation into the cause and formulate measures to prevent such incidents from happening again. The investigation findings and proposed measures will be reviewed by the EPD and an independent consultant. The EPD will, together with the independent consultant, continue to urge the contractor to follow up on the incident and further enhance the environmental monitoring work at WENT.
If it is confirmed that the contractor breached the contract requirements by failing to treat wastewater properly or discharging it illegally, the Environmental Infrastructure Division of the EPD will follow up the case according to the contract provisions. All relevant information will be reflected in the contractor's assessment report and will directly affect the contractor's bid for a new government contract and its chances of being appointed in the future. In addition, law enforcement officers of the EPD have been closely monitoring the discharge of wastewater from landfills. Investigation will be launched if suspected violations are found. If any contractor is confirmed to have breached the Water Pollution Control Ordinance, prosecution in accordance with the law will be instigated.
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