High levels of harmful organic chemicals were detected in a well in the vicinity of Yokota Air Base, and Japanese authorities suspect the contamination may be due to activity at the U.S. military facility in western Tokyo.

The Tokyo metropolitan government noted that the contamination was about 19 times the level set by a U.S. drinking water health advisory.

Officials asked the Defense Ministry to contact U.S. military authorities to ascertain the levels of such chemicals in groundwater within the air base, but as yet has received no response.

Checks for the presence of Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoic Acid (PFOA) were conducted after Jon Mitchell, a British journalist working in Japan, filed a report in December 2018 about the leakage of firefighting foam from a storage tank at Yokota Air Base in 2012.

Mitchell used the U.S. Freedom of Information Act to obtain documents that included reports of past leakages of various chemicals not only at Yokota, but also at U.S. facilities in Okinawa Prefecture and elsewhere.

Four wells in the vicinity of Yokota Air Base were monitored for levels of PFOS and PFOA. Japan has banned the production, importation and use of PFOS since 2010. The decision came a year after PFOS was included in the Stockholm Convention on Persistent Organic Pollutants. The convention added PFOA to its list in 2019, and the government is seeking to extend its ban to PFOA this year.

Metropolitan government officials said they were unable to conclude that the well water outside the Yokota facility was contaminated by chemicals in the base, given the complicated nature of the underground structure.

Their efforts to get U.S. military officials to divulge the state of water quality within the base as well as explain the use of firefighting foam went nowhere as U.S. authorities have not cooperated with such requests.

The metropolitan government detected the high levels of PFOS and PFOA in January 2019. The Asahi Shimbun asked the metropolitan government to release information related to the monitoring of the wells.

According to metropolitan government officials, the well with high levels of organic chemicals was not being used as a source for drinking water at the time of the detection.

A drinking water health advisory issued by the U.S. Environmental Protection Agency limits the combined presence of PFOS and PFOA to 70 nanograms per liter of water.

The advisory states that no health effects would arise if an individual drank two liters a day of water with that level of chemicals for 70 years.

The Environment Ministry is planning to establish its own guidelines for the two organic chemical groups this spring.

Of the four wells checked, one in Tachikawa, also in western Tokyo, had a combined total of 1,340 nanograms of the two chemicals.

A well in Musashi-Murayama, which is also in western Tokyo, was found to contain a total of 143 nanograms of PFOS and PFOA.

A spokesperson for Yokota Air Base said no assessment of the results obtained by the metropolitan government was made because the monitoring was done while the official at the base in charge of such matters was absent.

Similar levels of contamination involving the two chemicals were found at the U.S. Kadena Air Base in Okinawa during tests conducted between fiscal 2013 and fiscal 2018. The maximum combined totals of PFOS and PFOA detected ranged between 498 and 1,379 nanograms.

Because rivers in the vicinity of Kadena Air Base supply drinking water, prefectural authorities there spent about 170 million yen ($1.6 million) in fiscal 2016 to strengthen the capability of a water purification system to lower the levels of the two chemicals to meet the health advisory level set by U.S. safety standards.

The documents obtained by Mitchell not only included information about the leakage of firefighting foam at Yokota, but also a report that 90,000 nanograms of PFOS were detected in a pond within Kadena Air Base in June 2014.

Other documents included reports about the leakage of chemicals at the U.S. Marine Corps Air Station Futenma, also in Okinawa, as well as the U.S. Naval Air Facility Atsugi in Kanagawa Prefecture and Tokyo, U.S. Misawa Air Base in northern Aomori Prefecture and the U.S. Marine Corps Air Station Iwakuni in Yamaguchi Prefcture, western Japan.

Mitchell called for studies into the level of contamination in all the areas outside of Okinawa.

(This article was written by Yuji Moronaga, Kei Fujiyama and Ayako Suzuki.)