Photo/Illutration The U.S. Marine Corps Camp Hansen is located in the northern part of Okinawa's main island. This photo was taken in Kin, Okinawa Prefecture, on July 15. (Asahi Shimbun file photo)

KIN, Okinawa Prefecture--A suspected carcinogen and other substances exceeding government-set levels were detected in tap water in this town that co-hosts the U.S. Marine Corps Camp Hansen, officials said.

Even though the town learned in July last year that perfluorooctane sulfonic acid (PFOS) and other organic fluorine compounds were present in local tap water, it held off making an announcement until Oct. 1.

“We were initially planning to explain it to residents in fiscal 2022, when water quality checks are due to end,” said an official of the town’s water and sewage division.

The town checked tap water quality at two locations on June 22, 2020, and detected 70 nanograms of PFOS and other organic fluorine compounds per liter of water at one site and 50 nanograms per liter at the other, according to officials.

In its water quality guidelines for drinking and river water, as well as groundwater, the central government sets a provisional target for restricting the combined presence of PFOS and other substances to no more than 50 nanograms per liter of water.

Town officials said reservoirs that supply water to the two locations cover about 2,300 residents. They noted that no one has complained of health problems after drinking or using the water.

The town’s tap water is a mixture of water from a dam managed by Okinawa Prefecture and groundwater.

In June last year, the town also carried out checks of water quality at nine wells where groundwater is drawn. They found the level of organic fluorine compounds exceeded the government target at four of the sites with a maximum of 410 nanograms per liter detected in one well.

All four wells are located within 100 meters from Camp Hansen, which is situated in the northern part of Okinawa’s main island. However, the town has not confirmed whether the presence of the organic fluorine compounds has anything to do with the U.S. base, officials said.

The town began increasing the ratio of water drawn from the dam in tap water in July 2020 to dilute PFOS and other substances.

In checks of water quality levels conducted at the two locations on July 27 this year, the level of organic fluorine compounds detected was 15 nanograms per liter and 4 nanograms per liter, respectively.

The town plans to stop mixing groundwater into all water supplies.

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