The Pollution Control Department (PCD) has sought help from the Natural Resources and Environmental Crime Suppression Division (NED) to find out who was responsible for illegally dumping 1,000 tonnes of hazardous waste in Ayutthaya.
This is not the first occasion illegal waste disposals have been made in the area, and local officials suspect the same company may be responsible.
Pitthaya Pramotevoraphan, deputy chief of the PCD, said local villagers had complained regarding the latest dump in Phachi district.
Staff worked with local authorities to explore the site and found six big holes containing hazardous waste on 70 rai of private land.
Initial tests showed the waste had enough acidity to legally rank as a hazardous substance. According to the law, anyone in possession of such substances must have a permit.
"The local authority also collected samples from small canals connected to Phachi River to identify whether there is any toxic contamination," Mr Pitthaya said.
He said the latest dump could be linked to a previous case that saw 4,000 tonnes of hazardous waste found in a warehouse in the district.
Police found trucks from a company that manages hazardous waste at the site. The company rented a warehouse there to store its industrial waste temporarily, even though it lacked a permit to do so. Legal action was taken against the company, Mr Pitthaya said.
"We have been asking police from the NED to investigate the latest case, and previous cases, to see if they are linked to that company," he said.