At least a dozen inside the base were highly contaminated with benzene, a cancerous substance, one of which recorded a level 672 times the limit in the August survey. The wells also showed high levels of toluene and ethylbenzene pollution, according to the report.

The joint Korea-US committee said they will continue to have a constructive discussion over the matter.

South Korea and US forces have conducted three joint environmental surveys near the Yonsan base. But they had refused to reveal the findings citing the Status of Forces Agreement by which they say they are bound to keep any documents of such kind confidential.

Civic groups filed a series of suits demanding the reports be released, scoring a win from the top court for the first survey and the latest victory from the appeals court for the other two. The government revealed the first one in April.

Concerns have grown over the possible chemical contamination of soil and water worsening in and near the US military base. The Seoul city government has spent 7 billion won ($6.3 million) on its own environmental survey near the surrounding areas, which found high levels of harmful chemicals in the soil and water.

Based on SOFA, South Korea is forbidden from accessing the inside of the US base for an environmental test, while calls are rising that such clauses need to be revised. (Yonhap)