Microorganisms recruited for Hanford cleanup
June 07, 1995
RICHLAND, Wash. –
Deep underground at the Hanford Site in southeastern Washington, an army of microorganisms has been drafted by the Department of Energy's Pacific Northwest Laboratory. The microorganisms mission: To clean soils and groundwater tainted with nitrate and carbon tetrachloride, an industrial solvent that is a suspected carcinogen.
The microorganisms are part of DOE's first large-scale test of in situ or underground bioremediation at Hanford. Researchers will demonstrate the ability of microorganisms to potentially clean up a groundwater plume containing as much as one trillion liters (300 billion gallons) of groundwater contaminated with carbon tetrachloride, a residual of past plutonium processing practices. Approximately 1.5 million liters (320,000 gallons) of groundwater will be treated at the test site as part of this pilot project.
In this bioremediation process, native bacteria, which can be coaxed into degrading contaminants, are energized. A food source, in this case vinegar, spurs the microbes to "eat" carbon tetrachloride and other contaminants. The demonstration at Hanford involves injecting several hundred gallons of a vinegar-like solution into the ground. "We're finding that the natural organisms often have the ability to destroy contamination if they're stimulated properly by an extra nutrient or by slightly changing their environment," says Tom Brouns, PNL Volatile Organic Compounds product line manager for DOE's Plume Focus Area. "Otherwise it may take hundreds or even thousands of years for the degradation to occur."
The demonstration site consists of six wells 91 meters (300 feet) deep, which are used to recirculate and monitor the groundwater, and a trailer, which is the command center for the operation. The test site is about the area of a football field and is located in Hanford's 200 West Area. Housed in the trailer are computers controlling the nutrient injection and sampling process and injection equipment. At specific times, a precise amount of nutrient is injected into a well. "We're using a precise methodology to get the maximum performance out of the microbes," said PNL Project Manager Dan Anderson. "If we get it wrong, we could potentially grow a lot of biomass around a well, and plug the well."
The demonstration consists of four phases. During the first phase, researchers recirculated the groundwater to establish baseline conditions. This included measuring the demonstration site's contaminant concentration, determining the number of native microorganisms and testing the design of the recirculation/injection system. The demonstration is in the second phase of operation. Researchers are injecting nutrients into the wells to increase the number of microorganisms to begin destruction of the contamination. Scientists will use the findings to refine the bioremediation process and increase the performance of the microorganisms. The third phase will run in production mode. Finally, in the fourth phase, researchers will conduct long- term monitoring of the water quality at the test site to ensure it is clean and safe.
Bioremediation is expected to cost less than other methods in which groundwater is pumped to the surface and treated above ground. "By attacking the contamination underground, it eliminates the expense of removing contaminated soil or water and treating it elsewhere," Anderson says. "In addition, in situ bioremediation has the advantage of providing ultimate destruction of the contaminant, requires half the time for remediation and reduces worker exposure."
The demonstration will provide researchers with data to eventually take the bioremediation to a large scale for cleanup of carbon tetrachloride and nitrate contamination. "People often lose sight of the chemical contamination problems at Hanford," said Philip Long, PNL's Deep Microbiology Project co-manager. "People consider it secondary to radioactive waste but non-radioactive, chemical pollution also is a serious problem, both here and across the country."
At Hanford, a minimum of 573 metric tons (637 tons) of carbon tetrachloride was discharged -- primarily between 1955 and 1973 -- to soil disposal facilities which include trenches and drain fields. The disposal area covers about an acre. Carbon tetrachloride contamination of the groundwater is extensive, covering a seven-square-mile area. Samples of the groundwater show carbon tetrachloride contamination up to 1,000 times the Environmental Protection Agency drinking water standard and nitrate concentrations up to 10 times the EPA drinking water standard.
PNL is using the demonstration to develop a detailed engineering "design tool," a computer-based system that provides the blueprint for future bioremediation projects. "The design tool will take you through the whole process step-by-step," Anderson says, "and allows you to simulate what will happen deep underground." The design tool can be used to devise bioremediation systems that treat groundwater contaminants such as chlorinated solvents and highly explosive compounds, or design placement of biological barriers.
The demonstration is funded through DOE's Office of Technology Development's Plume Focus Area and involves researchers from PNL, Bechtel Hanford Inc., Washington State University, Oregon State University, Montana State and Stanford University.
PNL is seeking industrial partners to commercialize the design tool.
Tags: Energy, Environment, Fundamental Science, Operations, Biomass, Biology, Facilities