The Seoul Metropolitan Government is speeding up its investigation into alleged water contamination near the Yongsan Garrison, the U.S. military base in central Seoul.

The city’s inspectors plan to request approval from the United States Forces Korea next month to obtain a sample of underground water from the base for further research after completing a preliminary investigation last month.

About 10 city officials accessed the site last month to begin inspecting the ground water tube wells, the city said Monday.

The city government has been carrying out purification activities since 2001 after oil leaks were detected around Noksapyeong Station, near the U.S. base.

Local environment activists have argued that the clean-up efforts must be carried out on base as well.

The city estimates that 1,870 tons of polluted water have been emitted near the base up to last year, with toxic substances including xylene and toluene found in the underground water system.

By Claire Lee (dyc@heraldcorp.com)