OAK RIDGE, Tenn.—The U.S. Department of Energy is preparing a study that could help determine how to treat contaminated groundwater at the East Tennessee Technology Park (ETTP), the former site of uranium enrichment for nuclear weapons and nuclear power reactors.
The feasibility study is expected to evaluate technologies that could be used to treat the contaminated groundwater for the main plant area. It could be issued as a draft report in November to the U.S. Environmental Protection Agency and the Tennessee Department of Environment and Conservation, a federal official told the Oak Ridge Site Specific Advisory Board (ORSSAB) on Wednesday.
A proposed plan due in April 2021 could propose remedies, and DOE could then accept public comment before issuing a record of decision formalizing the cleanup approach. That could arrive in January 2022, said David Adler, director of the Quality and Mission Support Division for DOE’s Oak Ridge Office of Environmental Management (OREM).
Remediation could begin 18 months to two years after the record of decision is published in the Federal Register, Adler said. The Energy Department expects to have more information later about how much the work might cost and how long it might take, he said.
Then known as the K-25 site, the 2,200-acre ETTP was built to enrich uranium for the world’s first nuclear weapons as part of the Manhattan Project during World War II. The site shut down in the mid-1980s and is being remediated ahead of use as a private industrial park. All of the buildings that conducted or supported enriched uranium operations have been demolished.
Now there is the question of what to do about the groundwater contamination, Adler told the ORSSAB. Decisions will be required soon, he said.
The feasibility study focuses on the main plant area, where most of the contaminated water is found, according to Adler. The main plant area covers about 700 acres, and roughly 30 percent of it has contaminated groundwater, Adler said. Most of ETTP’s groundwater monitoring wells, 355 of 471, are in that area.
The main plant includes the area where three of the five large gaseous diffusion buildings at Oak Ridge once stood, along with an area where technetium-99 leaked. Technetium-99 is a mobile, slow-decaying radioactive metal, and there is a plume of it under the east side of the former K-25 building, Adler said.
The main plant area also includes former machine shops where large amounts of solvents were used, and a burial ground where solvents were dumped. The solvents, common materials available to the public, were used for degreasing and machining operations at K-25, including for the gaseous diffusion operations and other support equipment.
The solvents are volatile organic compounds, or VOCs, which represent more than 90 percent of groundwater contamination at ETTP, Adler said. That is typical of industrial facilities, he added. The VOC contamination is more widely dispersed across the main plant area than the technetium-99, according to information Adler provided to the ORSSAB.
The Energy Department has a large amount of information on the concentration of the contaminants found in the groundwater, but it does not have a total mass estimate, Adler said.
Adler explained some of the potential remediation technologies that could be used to treat the water, which is probably generally within 100 feet of the surface. One technology, pumping and treating, could pull water and associated material out of the ground and run them through a conventional treatment system to remove the contaminants. Another technology, bioremediation, would introduce a food source into the groundwater and stimulate the growth of bacteria to consume and degrade contaminants. A third technology, funnel and gate, would manipulate groundwater flow through a treatment system. A fourth technology, monitored natural attenuation, would monitor the groundwater and allow natural degradation. Other approaches are being considered as well.
The treatment approach could vary depending upon whether DOE is treating volatile organic compounds that can be destroyed or metals that cannot, whether the contamination remains at its origin source or is in a plume where it has spread via groundwater, and whether the contamination is in bedrock or in shallower soils, Adler said. The Energy Department could “mix and match” the remedies, he noted: “It’s a complicated site with multiple plumes.”
He said treating the contamination in bedrock will be more challenging than treating the contamination in shallower areas. The shallower contamination will be easier to retrieve and treat, while materials in cracks in bedrock will be more difficult to delineate and treat. Rocks at the surface are weathered and have more cracks, while bedrock is more solid, Adler said.
Remediation will aim to restore the groundwater as close as possible to drinking water standards, but it’s possible that groundwater use could always be prohibited at the site, according to Adler.
The main plant area being evaluated in the feasibility study does not include the area where the K-31 and K-33 gaseous diffusion buildings were on the northwest side of ETTP. The contamination is not as severe there, Adler said. The Energy Department completed one additional round of sampling at K-31 and K-33 in July and might conduct another round in a few months. The contamination in that area is so minimal and limited that DOE hopes simple groundwater use restrictions and continued monitoring in limited areas will be adequate, although those decisions will be made in consultation with the EPA and TDEC, environmental regulators for the site, Adler said.
An area known as Zone 1 at ETTP, the outlying areas that had less industrial use, might also not require treatment, assuming the EPA and TDEC agree, according to Adler.
The Energy Department has been evaluating groundwater at ETTP for between 20 and 30 years. Adler said the Energy Department has spent millions of dollars over the past several years collecting additional groundwater data, and OREM “has a vast monitoring network that provides an immense amount of data.” Crews have installed all of the wells requested by the EPA and TDEC, and DOE thinks it has collected enough information to work with the regulators to make final decisions about groundwater remediation, Adler said.
He said a final site-wide record of decision that would address ETTP surface water, sediments, and groundwater could be issued sometime in the 2020s.
