A group of local villagers from the Kham Tanod community in Prachin Buri province on Tuesday filed a petition with the Department of Primary Industries and Mines in Bangkok against a mining concession held by a private company.
They reasoned the concession is near their village in an agricultural area connected to Khao Yai National Park. They also questioned the transparency of the second public hearing.
Sumet Rienpongnam, an advisor to the "Kham Tanod Says 'No' to Sand Mining" group, said local villagers are unhappy with the way in which the company conducted the process in May.
Mr Sumet said the group found at least 35 newcomers had moved in just before the public hearing was organised, and their votes were all cast in support of the mine.
Of the 190 eligible voters, 91 agreed with the project, 82 disagreed, seven abstained and 10 votes were bad ballots, he said.
"The result can't reflect the real opinion of the locals. This is the second public hearing, and the first ended with equal votes. The company may have deployed a tactic to win unfairly," he added.
Mr Sumet said local people had aired their grievances with the governor but had not heard any feedback.
"We will file a complaint with the Central Administrative Court claiming unfair practice by a state official in dereliction of his duty to protect and preserve the rights of the local community," he added.
He said the mining company had asked the Department of Primary Industries and Mines for a 30-year sand mining concession on a 300-rai site that is just 300 metres away from the community.
Residents fear chemicals from the mining activity will contaminate their soil and underground water supplies, the main source of their farming and other daily living activities.
Moreover, it could exacerbate drought and dust pollution in the dry season, Mr Sumet said.
Aditad Vasinonta, deputy chief of the Department of Primary Industries and Mines, said the department is willing to listen to all complaints raised by locals and will then examine them all thoroughly.
He said the current mining law allows for local participation, adding the project will likely not be approved if it looks set to cause harm to nearby communities.