The Seoul Metropolitan Government has been conducting a purification project since 2003, but petroleum-based contaminants above the standard level have continued to be detected from water near the US base.

Upholding a lower court's decision, the Supreme Court ordered the country's environment minister to open to the public the result of its joint probe with the USFK.

The two sides agreed in June 2013 to carry out several on-the-spot probes. The first investigation was conducted in May 2015, but the authorities did not reveal the outcome to the public.

In August 2015, the Lawyers for a Democratic Society, a group of activist attorneys, filed a petition with a local administrative court seeking disclosure of the information.

The Seoul Administrative Court earlier said relevant information should be revealed for the people's right to know.

"It is hard to say the two countries' ties will be damaged even if the information is disclosed," the administrative court said, adding the concealment could lead to further distrust in the USFK and unnecessary diplomatic issues. (Yonhap)