The Department of Pollution Control has asked THH Molyprocessing Company, a chemical plant in Chachoengsao, to pay 1.8 billion baht to clean up the Nam Jon reservoir.
Attapol Charoenchansa, chief of the Department of Pollution Control, said the department has written to the company concerning heavy pollution in areas close to the plant for which the company is being held responsible.
He said the company needs to pay 1.854 billion baht to rehabilitate the reservoir and its breaches of the Environment Promotion and Preservation Act, which says polluters must bear the cost of the damage they cause.
The department, acting on locals' complaints, received a report collating data from its environment protection centre, the Department of Groundwater Resources, the Department of Royal Irrigation, the 13th Regional Environment Office based in Chon Buri province and Office of Natural Resources and Environment in Chachoengsao.
The report found the THH Molyprocessing company in Phanom Salakham district has caused chemical damage in the area.
Chemical leakages from the plant leached into groundwater linking to the Nam Jon reservoir, the study found.
The conclusion was made based on laboratory evidence, showing a link between the components of chemical found in the contaminated reservoir and the plant's chemical waste, Mr Attapol said.
"We need the company to contact us within 30 days to strike a deal to clean up the polluted water source.
"If not, we will take legal action," he said.
The department calculated the cost of environmental rehabilitation would likely be in the region of 1.854 billion baht to clean the pond, clean an underground water supply of a further 1.55 million cubic metres and process a further 1.97 million cu/m in the reservoir.
Local had complained that they can't use the water for a living, thanks to its polluted state.
The officials came to collect the water samples and found heavy metals such as lead, copper and manganese were above acceptable limits.