Groundwater injection process filters out contaminants
July 20, 1998
RICHLAND, Wash. –
A new technique developed at the Department of Energy's Pacific Northwest National Laboratory may be able to remove deadly contaminants from groundwater more easily and less expensively.
Pacific Northwest researchers have created In-Situ Redox Manipulation, or ISRM, to remediate contaminated groundwater at up to 60 percent savings over 10 years when compared to current remediation methods. Potential application sites include military bases, petroleum and chemical plants and weapon production facilities.
ISRM could address the growing concern surrounding chromate -- a contaminant found near metal-plating production sites, automobile production plants and military bases. Chromate can be toxic to fish and humans above certain levels.
In one example, chromate has leaked into the groundwater and aquifer at the Hanford Site in Washington state, where plutonium was produced from 1943 to 1989 for use in building America's nuclear weapons. DOE and its predecessor agencies used chromate to inhibit corrosion of aluminum fuel elements in nuclear reactors. It has been detected at Hanford along the rivershore and in groundwater headed toward the Columbia River.
Field tests conducted at Hanford indicate ISRM can remove chromate from the groundwater to levels below drinking water standards and water quality standards for aquatic life.
"After testing, chromate levels dropped below detection near the testing wells and we expect to see the same results in the river," said John Fruchter, Pacific Northwest's principal investigator. Researchers also expect ISRM to be effective in removing technetium and chlorinated solvents, such as trichloroethylene and uranium.
R&D Magazine recently honored the ISRM technology as one of the 100 most significant innovations of 1997. DOE has supported the project with about $4 million since its initial development in 1993. The project could receive an additional $100,000 in 1999 to continue monitoring results at Hanford.
ISRM is an improvement upon current remediation techniques. In the widely used pump and treat method, contaminated water is withdrawn through wells, treated at water treatment plants then injected back into the ground. But it is costly to drill wells, build a special treatment facility and perform long-term operation and maintenance. And, in many cases, pump and treat remediation is ineffective.
Another remediation method, called a trench and fill permeable barrier, involves digging trenches to act as barriers. The trenches are filled with iron particles that react with and filter contaminants. But trenches cannot be dug deep enough to reach groundwater in many locations, including the Hanford Site.
ISRM uses a standard 6-inch groundwater well and does not require building permanent structures. It also is conducted below the surface, therefore decreasing risk of exposure to workers. Additional benefits include its one-time installation an improvement over methods such as pump and treat that are conducted over long periods of time.
In testing at Hanford, Pacific Northwest researchers positioned five groundwater wells about 500 feet from the Columbia River in a known chromate plume. There, they injected the chemical sodium dithionite diluted in water and buffered with potassium carbonate and potassium bicarbonate into a well for about 10 hours. Once it reached the groundwater, the sodium dithionite reacted with iron in the ground and spread out into a circle about 50 feet in diameter.
The five wells have created a large barrier about 150 feet wide for groundwater to pass through as it flows toward the river. As the groundwater crosses the barrier, targeted contaminants are destroyed or immobilized.
After about 30 hours, sodium sulfate, a nontoxic byproduct, is removed over a one-week period. Unlike pump and treat methods of remediation, the barrier remains effective for up to 30 years.
"Monitoring of test results at Hanford will continue because groundwater moves slowly, and the remediated groundwater won't reach the river for about another two years," Fruchter said.
ISRM also has been field tested at the H-reactor on the Hanford Site. It is scheduled to be field tested this year at an Army base in Ft. Lewis, Wash., and a Navy base, Moffitt Field in Mountain View, Calif., to remediate chlorinated hydrocarbons. Chlorinated solvents have been used as degreasers and super cleaners in military maintenance operations.
Tags: Operations, Facilities