Underground water near the US military base in central Seoul still contains much higher levels of pollutants than the legal limits, the Seoul city government said Monday.

According to an internal inspection by the Seoul Metropolitan Government, the average concentration of benzene in groundwater near the US military base around Noksapyeong Station was 0.532 milligrams per liter.

It went as high as 8.811 miligrams per liter, which is roughly 587 times more than the environmental standard of 0.015 mg/L.

The amount of petroleum hydrocarbons near Camp Kim close to Namyeong Station averaged 20.4 mg/L and reached up to 768.7, some 587 times higher than the government standard of 1.5 mg/L.

The readings mean the level of toxic pollutants in the groundwater has decreased by 70 percent near Noksapyeong Station and by 92 percent near Camp Kim since 2015, but it is still a lot higher than sewage laws allow.

As the relocation of key military bases in central Seoul to Pyeongtaek, Gyeonggi Province, is set to be completed by the end of 2017, the Seoul government has been clearing the contaminated soil since 2001.

However, the source and full extent of the toxic contamination of the soil and ground water near the Yongsan base is not known, with the US military refusing to disclose the details of its cleanup efforts.

The Environment Ministry carried out on-site inspections on soil and ground water in the Yongsan base on three occasions from May to August, but has declined to release its results, citing “possible diplomatic clashes.”

The refusal is in line with the Status of Forces Agreement signed between Korea and the US, which defines areas of legal responsibility for the US soldiers here. According to the SOFA, the US military is only responsible for the contamination within its camp.

A high court ordered on Dec. 14 that the Environment Ministry disclose its inspection result about the level of pollution inside the US military base, ruling in favor of environmental groups.

The environmental civic groups have criticized the US military for dodging responsibility for the pollution and the Korean government for overlooking its citizens’ health and safety.

The activists have urged the Korean government to figure out the source of the pollutants and effectively remove it to prevent the spread of the contamination. As the Korean government is covering the costs of tackling the pollution, they also have demanded the US Army pay a share of the cleanup costs.

Since 1988, there have been 14 reported cases of environmental contamination involving US bases here.

In 2000, the US 8th Army Command was found to have dumped untreated toxic waste into the Han River, a major source of drinking water for Seoul residents. In 2001 and 2006, oil was spilled from the US Army Garrison and Camp Kim in Yongsan, contaminating underground water systems in the neighborhood.

By Ock Hyun-ju(laeticia.ock@heraldcorp.com)