Neil Smith puts a trained eye on the pressure and flow of a food grade compound being injected into an underground plume of hazardous waste near the X-720 Maintenance Facility at the DOE Piketon Site. The sodium lactate compound promotes bacterial growth in the groundwater that turns hazardous waste into harmless end-products.
John Collins of Fluor- B&W Portsmouth Environmental Remediation discusses a report with Subject Matter Expert Neil Smith of CDM in the Operations Center for the 7 Unit Enhanced Anaerobic Bioremediation project.
PIKETON, Ohio – The U.S. Department of Energy (DOE) Office of Environmental Management’s Portsmouth site is using an environmentally friendly approach to reduce hazardous waste in a groundwater plume.
EM and specialists with the environmental remediation operations of decontamination and decommissioning (D&D) contractor, Fluor-B&W Portsmouth, are injecting food-grade organic compounds into contaminated groundwater to promote the growth of a special strain of anaerobic bacteria known as Dehalococcoides (DHC). The remedial technology is known as enhanced anaerobic bioremediation.
“The bacteria is consuming hazardous solvents and turning them into harmless end products,” said Neil Smith, a subject matter expert with CDM, a company subcontracted by Fluor to complete the project.
The first DHC species was described in 1997 and its potential for use in anaerobic bioremediation of chlorinated solvents quickly became apparent. A growing technology in the remediation industry, DHC biodegradation has been used at EM’s Savannah River and Idaho sites. At the Idaho site, for example, the treatment resulted in significant removal of the solvent, trichloroethylene (TCE), from the contamination source area. Anaerobic bioremediation is energy efficient and less expensive than the traditional pump-and-treat approach.
“It’s an example of EM’s strategy to shift from expensive, energy-intensive remediation methods to those that are more economical and based on natural processes,” said Kurt Gerdes, Director of EM’s Office of Soil and Groundwater Remediation.
A large plume of groundwater containing TCE exists in a band of soil between 15 and 30 feet below the ground surface. TCE was formerly used to degrease equipment several decades ago. The plume originated from two sources, one adjacent to the X-720 Maintenance Facility and the other near the X-700 Cleaning Facility. Those buildings supported operations at the Portsmouth Gaseous Diffusion Plant, a federal facility of more than 400 buildings and systems that was built on a 3,700-acre reservation during the height of the Cold War to enrich uranium under the nation’s nuclear weapons complex for national defense. Production ended in 2001 after nearly 50 years of operations, and the facility is now part of one of the world’s largest cleanup programs.
The molasses-like substance largely composed of sodium lactate is injected into the groundwater using a series of 35 wells. Each injection event costs about $250,000. Another 20 wells are used to monitor the progress of the remedy.
“It takes six weeks to inject, then we wait for another six weeks (before further injection),” Smith said. “The plume is monitored monthly and samples are drawn from the monitoring wells. The compound we inject ferments in the ground and gives off hydrogen, which nourishes the natural bacteria in the ground.”
The goal is to promote the growth of DHC, which will metabolize the TCE similar to how humans metabolize oxygen.
“We’re using an inedible food-grade compound here, which is soybean based,” Fluor Superintendent John Collins said. “We’re using the soybean compound on that plume because of the nature of the soil and the level of contamination.” The soil in the treatment area is a mix of clay and silt, sand and fine gravel, above a layer of shale.
Smith said samples taken as part of the project are being used to study the DNA of the bacteria in the groundwater to help determine if DHC is present in a significant amount.
“It’s a very exciting project and a very interesting type of work because it involves biology, chemistry, geology, engineering — many areas of science,” Smith said.
The project began in January. The impact of the treatment on TCE levels has yet to be determined.
“We’re still in the early stage with this project,” Smith said.