Arsenic-Containing Water Leaked at Hokkaido Geothermal Site

Yomiuri Shimbun file photo
Steam erupts from a geothermal energy research site in Rankoshi, Hokkaido, on July 1.

RANKOSHI, Hokkaido — Mitsui Oil Exploration Co.’s geothermal energy research site in Hokkaido continues to experience problems, such as copious steam erupting and high concentrations of arsenic detected in on-site water.

The Tokyo-based firm announced Sunday that approximately 10,000 liters of water containing arsenic, an extremely toxic element, had overflowed a water reservoir at the site and spread to the nearby Hokkaido government-owned forest.

Around 11:50 p.m. Friday an alarm sounded indicating an abnormal level of water in the reservoir. Upon investigation, workers found that the valve of a steel pipeline used to transfer water to another well was nearly fully closed. The workers promptly opened the valve, but it is estimated that the water overflowed over an about 10-minute period.

The company is currently investigating the cause of the valve closure.

On July 20, there was also a leak of approximately 2,000 liters due to a valve switching mistake at the site.

Beyond the Hokkaido-owned forest lies the tourist spot of Oyunuma, a hot spring pond near the famed Noboribetsu Onsen hot spring resort. As of Saturday, no increase in arsenic concentration has been confirmed in Oyunuma.