The leaking tank was built in the 1940s and was stabilized in February 1995, when all pump-able liquids were removed by agreement with the state.
The specific cause of the liquid level decrease in Tank T-111 has not been determined, the DOE said.
Monitoring wells in the T Tank Farm, where Tank T-111 is located, have not identified significant changes in concentrations of chemicals or radionuclides in the soil, the DOE said.
“DOE is continuing to monitor its network of monitoring wells in the area of T Tank Farm and is evaluating possible next steps,” the department said.
In Olympia, Gov. Jay Inslee said, “I am alarmed and deeply concerned by this news. This was a problem we thought was under control years ago, when the liquids were pumped from the tanks and the sludge was stabilized. We can’t just leave 149 single-shell tanks with high-level radioactive liquid and sludge siting in the ground for decades after their design life.
“Let me be clear: Washington state has a zero tolerance policy on radioactive leakage. We will not tolerate any leaks of this material to the environment.
“Fortunately, there is no immediate public health risk,” Inslee said. “The newly discovered leak may not hit the groundwater for many years, and we have a groundwater treatment system in place that provides a last defense for the river. However, the fact that this tank is one of the farthest from the river is not an excuse for delay. It is a call to act now.”
The DOE said this tank was classified as an assumed leaker in 1979. In February 1995, interim stabilization was completed for this tank. In order to achieve interim stabilization, the pumpable liquids were removed in accordance with agreements with the state of Washington. The tank currently contains about 447,000 gallons of sludge, a mixture of solids and liquids with a mud-like consistency, it said.
This is the first tank that has been documented to be losing liquids since interim stabilization was completed in 2005. There are a total of 177 tanks at the Hanford site, 149 of which are single shell tanks.