New Technology Tackles Groundwater Cleanup Problems

An innovative groundwater cleanup technology developed in the early 1990s at the Battelle-operated Pacific Northwest National Laboratory (PNNL) is delivering positive results for the U.S. Department of Energy’s Hanford Site and soon may be dispatched to another location in Washington State.

In Situ Redox Manipulation (ISRM) treats contaminated groundwater in place by creating, within an aquifer, a permeable chemical barrier that immobilizes or destroys contaminants. Military bases, petroleum and chemical plants, and weapon production facilities are potential sites where the technology may be useful.

At Hanford, a former plutonium production complex, ISRM field tests began in 1995. Approximately four years later, a 150-foot-long ISRM barrier was installed on site to intercept and immobilize chromate—a corrosion inhibitor—as it migrates through the groundwater toward the Columbia River, about 500 feet away. The technology works, and the site’s environmental restoration contractor, Bechtel Hanford Inc., is in the process of expanding the barrier to 2,300 feet. ISRM has also shown significant promise for treating groundwater contaminated with other heavy metals and volatile organic compounds, such as trichloroethylene.

To create a successful barrier treatment zone, iron must be present in the subsurface. Wells are drilled, and sodium dithionite and pH buffers are injected through the wells into the groundwater, where the chemicals react with the iron and other sediments to create a permeable chemical “curtain” or barrier. As groundwater passes through the barrier zone, subsequent chemical interactions destroy, immobilize, or convert contaminants into benign products.

The barriers do not create additional environmental problems and typically will remain effective for 15 to 25 years, reducing the long-term operations and maintenance costs associated with other cleanup methods, such as “pump and treat” (pumping polluted water out of the ground, cleaning it, and returning it to the aquifer). ISRM also reduces worker exposure to contaminants.

The technology is currently in the remedial design phase of deployment at a former chrome-plating business in Vancouver, Washington, near the Columbia River. Chromate is present in groundwater at the site, and the Environmental Protection Agency has called on PNNL scientists to participate in a field test. The ISRM technology will be used in conjunction with a separate source term remediation technology that essentially mixes chemical reductants with contaminated sediments. The Vancouver project, which involves only a few acres, is significantly smaller in scope than ISRM’s application at Hanford. The field test, initiated in June, will continue through September, when the effectiveness of ISRM at this site will be evaluated.

PNNL researchers also continue to support ISRM activities at Hanford, and are currently discussing with several organizations, including government agencies, the viability of applying ISRM technology at other contaminated sites.

For more information, contact Kathryn Lang at (509) 375-3837, kathryn.lang@pnl.gov.