YAKIMA, Wash. — Workers cleaning up the nation's most contaminated nuclear site have discovered an area of soil so radioactive it exceeds lethal limits tenfold, the U.S. Department of Energy announced Wednesday with its cleanup contractor.
The finding represents some of the worst contamination at south-central Washington's Hanford nuclear reservation and highlights the difficulty and danger in cleaning up a site where records about Cold War-era weapons production either weren't kept or were incomplete.
Even though it's highly radioactive, the contaminated soil does not pose an immediate risk to health or safety of workers or the environment, said Todd Nelson, spokesman for Washington Closure, the contractor hired to clean up this area of Hanford for the DOE.
The federal government created Hanford in the 1940s as part of the top-secret Manhattan Project to build the atomic bomb. The site produced plutonium for nuclear weapons through the Cold War, but the work left hundreds of radioactive buildings, including nuclear reactors, debris and waste.
Workers found this soil contamination under a building that was used from 1966 to 1996 to explore methods to treat radioactive waste. The workers discovered a cracked steel liner under a drain in a radioactive hot cell, where the research years ago could be conducted safely, then used remote equipment to conduct soil samples under the building to determine if there may have been a leak.
The samples showed radiation levels thousands of times greater than allowable levels for exposure over one hour, and 10 times the lethal limit.
Nelson said the three biggest concerns when such a high level of radioactivity is located are direct exposure to workers, the contamination becoming airborne, and the contamination migrating to groundwater. Because the soil sits under a building and workers are shielded from the radiation, he said, the first two are not an immediate risk.
There also is no evidence the contamination has affected groundwater, said Mark French, project coordinator for the DOE's Columbia River corridor cleanup.
The building in question sits about a quarter-mile from the Columbia River, which is the largest waterway in the Pacific Northwest and creates the northern and eastern boundaries of the Hanford site.
French said the level of contamination was a surprise, though it had obviously been there some period of time.
"This is part of the business," he said. "We don't have good historical records in many cases, and even when we do, there's always things that happened that weren't documented. Things come up that we don't expect."
A 1993 report detailed a large spill of radioactive cesium and strontium in the cell in question, Nelson said, and it's possible the contamination is a result of that spill.
French said workers would redouble groundwater sampling efforts in the area and continue to work to characterize the extent of the contamination as they develop a new plan for cleaning up the area and demolishing the building.
The building, in Hanford's 300 Area where research was conducted, is considered one of the area's most difficult to decontaminate and demolish. Under a cleanup compact between the state and federal governments, the building is to be demolished by the end of 2012.