Thai govt fast-tracks cleanup of Kok River arsenic contamination affecting Chiang Mai and Chiang Rai

Deputy Prime Minister Prasert Jantararuangtong, in his capacity as Chair of the National Environment Board, signed an order appointing a Subcommittee for Water Quality Management in Surface Water Sources, which he will chair himself to drive tangible solutions. 

This subcommittee includes the Minister of Natural Resources and Environment and Deputy Interior Minister Theerarat Samrejvanich as vice chairs, alongside several key agencies. Their mandate is to analyze the situation and its causes in detail, devise solutions, restore contaminated water sources, alleviate public hardship, and crucially, engage in international negotiations to address cross-border pollution sources. 

To date, authorities have continuously monitored water quality, sediment, aquatic life contamination, and bioaccumulation in humans. Satellite imagery and geospatial technology are being deployed to trace pollution sources. In addition, diplomatic and military mechanisms via the Regional Border Committee (RBC) between Thailand and Myanmar are being used to tackle pollution linked to neighboring countries.

The government places high priority on solving public hardship, and this subcommittee is a step toward more proactive and closely monitored remediation. The first meeting is scheduled for May 27, at Government House, where agencies will present progress reports and consider installing sediment traps in the Kok River to reduce arsenic contamination. Discussions with Myanmar’s government will also be held to seek a sustainable joint solution.

Teerachun Boonyasit, Director-General of the Department of Water Resources, announced that his department is collaborating with relevant agencies to urgently design an underwater sediment trap weir in Chiang Rai’s section of the Kok River. This aims to reduce concentrations of arsenic and heavy metals in the Kok, Sai, and Mekong Rivers before the water flows through communities, while maintaining ecological balance. 

He explained that work began with aerial surveys of the river, conducted jointly by the Water Resources Department and the Civil Aviation Department, to collect topographical and hydrological data. This will be integrated with data from the Pollution Control Department to determine optimal trap locations—such as the number of traps, spacing, and the most effective sediment capture points.

The Director-General emphasized that this project does not involve constructing large dams or major barriers. The weirs will be specially designed for subsurface sediment filtration, capturing arsenic-rich particles before water reaches communities. Arsenic levels must meet national safety standards.

The project is currently in the design phase and is being fast-tracked for early completion. There are also plans to install CCTV cameras along the river to monitor flow and turbidity in real time.

Authorities are assessing all factors to ensure the sediment traps function efficiently without disrupting ecosystems or altering the river’s natural flow, which could otherwise cause erosion or environmental degradation.