New Process Filters Water Contaminants - Brief Article

USA Today (Society for the Advancement of Education), June, 1999

A technique developed at the Department of Energy's Pacific Northwest National Laboratory, Richland, Wash., may be able to remove deadly contaminants from groundwater more easily and less expensively. In-Situ Redox Manipulation (ISRM) treats contaminated groundwater at up to 60% savings over 10 years when compared to current 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.

The process is an improvement upon current remediation techniques. In the widely used pump-and-treat method, contaminated water is withdrawn through wells, purified at water treatment plants, then injected back into the ground. However, it is costly to drill wells, build a special treatment facility, and perform long-term operation and maintenance.

Another method involves digging trenches to act as barriers. The trenches are filled with iron particles that react with and filter contaminants, but cannot be dug deep enough to reach groundwater in many locations.

ISRM uses a standard six-inch groundwater well and does not require building permanent structures. It 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, Wash., where chromate was used to inhibit corrosion of aluminum fuel elements in nuclear reactors, the contaminant has been detected along the shore and in groundwater headed toward the Columbia River. Pacific Northwest researchers positioned five groundwater wells about 500 feet from the river in a known chromate plume. 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 in 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 by-product, is removed over a one-week period. Unlike pump-and-treat methods, the barrier remains effective for up to 30 years.