RICHLAND, Wash. (AP) — Three radioactively contaminated structures are at high risk of collapsing on a former nuclear weapons production site, but could be stabilized by filling them with a concrete-like grout within the next year, the federal government said.

Otherwise, the U.S. Department of Energy has concluded the structures on the Hanford Nuclear Reservation could fail and release radioactive contamination, the Tri-City Herald reported Tuesday.

“A number of structures are over-stressed and at risk of age-related failure, which could result in a release of contamination with impacts to human health and the environment,” DOE said in a letter last week to the Environmental Protection Agency, which regulates nuclear waste at Hanford.

The Hanford site, located near Richland, Washington, for decades made plutonium for nuclear weapons. The sprawling site for the past 30 years has been engaged in cleaning up a massive amount of radioactive waste left over from making plutonium.

Two of the underground structures, a trench and a tank, are estimated to be contaminated with a combined 170 to 255 pounds (116 kilograms) of plutonium.

DOE could award a contract for grouting as soon as March, according to the letter.

After the partial collapse of a waste storage tunnel at Hanford’s PUREX plant in 2017, DOE and its contractor CH2M Hill Plateau Remediation Co. analyzed other old and contaminated structures to determine if they were at risk of collapsing.

They determined that the three below-ground structures at the Plutonium Finishing Plant presented the highest risk.

Hanford Challenge, a Seattle-based Hanford watchdog group, does not object to the grouting as a short-term solution, but it should not be a substitute for complete cleanup, said Tom Carpenter, executive director.