Mercury recovered from a soil sample taken at the Y-12 National Security Complex. (ORNL)

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By Frank Munger of the Knoxville News Sentinel

OAK RIDGE — The cleanup of mercury contamination at the Y-12 nuclear weapons plant could ultimately cost up to $3 billion, according to a U.S. Department of Energy report.

The report, dated February 2016 but only recently released, states the estimated cost for mercury remediation at Y-12 is between $1 billion and $3 billion.

The report was prepared to outline the technology plans for mercury cleanup at Y-12, as well as the DOE's Savannah River Site in South Carolina.

Enormous quantities of mercury were used at Y-12 for lithium-separation processes during the Cold War development of hydrogen bombs.

During peak years — 1950 to 1963 — about 11 million kilograms of mercury were used at the plant. About 3 percent of this total was released into the environment, according to DOE estimates, with mercury seeping into soils and leaking into local waterways. Pockets of mercury are found in the structures of old process buildings at the plant.

"The overarching challenges at Oak Ridge include remediation of the large quantity of residual elemental mercury still present in shallow source zones adjacent to and beneath former mercury use facilities," the report stated.

The report also noted the potential for mercury to mobilize during efforts to deactivate and decommission the old buildings at Y-12 and further spread the mercury and other contaminants.

Another concern is the continuing presence of methylmercury, the most toxic form of the metal, in East Fork Poplar Creek — which has been posted as a hazard since 1982.

Environmental scientists at Oak Ridge and Savannah River are working together to address common issues and resolve key technical issues.

The two sites, however, have had different experiences with mercury.

Savannah River used mercury for decades as a catalyst for dissolving the aluminum cladding during nuclear separation processes at the site near Aiken, S.C.

Unlike Oak Ridger, the mercury at Savannah River has not been released into the environment.

"Rather, an estimated 60,000 kilograms of mercury is in high-level (radioactive) waste tanks and throughout the liquid waste system," the report stated.

In Oak Ridge, various technology plans are already underway, with design in the works for a new $148 million mercury-treatment facility at Y-12. The facility will be located near Outfall 200, where residual mercury in the storm sewer system at the plant continues to leak into the upper stretches of East Fork Poplar Creek.

The DOE is also looking to locate a research laboratory alongside the East Fork's lower stretches so that field studies can be conducted on how mercury is transformed in the environment to become methylmercury and other mercury-related issues. Methylmercury is a bigger issue downstream than it is in the upper parts of the creek inside Y-12, where it originates.

The report said mercury contamination "poses a unique, high-priority challenge" to the DOE's cleanup missions at the two sites.

DOE officials said research and technology development are "critical" to the future cleanup efforts.

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