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Staff Accomplishments

In-Situ Redox Manipulation - Technology solving groundwater contamination in the Pacific Northwest

April 2004
In-situ Redox Manipulation is recognized by regulators and clients alike as a valuable technology for protecting groundwater from hazardous contamination in industrial settings. Following an October 2002 field test of the In-situ Redox Manipulation technology at the Frontier Hard Chrome (FHC) Superfund site in Vancouver, Wash., Environmental Protection Agency officials, with PNNL's support, are deploying a full-scale barrier to remediate chromium-polluted groundwater. Hexavalent chromium, which is generally produced by industrial processes and is the chromium species of primary environmental concern, is hazardous to both human and aquatic life. Groundwater contamination at the now-defunct FHC site, located approximately one-half mile north of the Columbia River, occurred decades ago when an electroplating plant discharged chromium-tainted wastewater into a dry well. Detailed characterization of the Frontier Hard Chrome site indicated that the majority of contamination is contained in the upper portion of the aquifer, approximately 25 to 35 feet below ground surface. Based on the size of the contamination source area, which is about the size of a football field, and the predominant groundwater flow direction at the site, researchers determined that a 200-ft long barrier would be sufficient to meet the remedial objectives. As a result of the effective deployment of the In-situ Redox Manipulation technology at FHC, the technology may be applied at another nearby Superfund site. The In-Situ Redox Manipulation technology is based on injecting a solution of sodium dithionite into standard groundwater wells. Once injected, the solution reacts with iron in the soil to form a permeable reactive barrier capable of destroying or immobilizing targeted contaminants. Researchers in PNNL's Environmental Technology Division estimate that In-Situ Redox Manipulation barriers can, depending on site conditions, remain effective for up to 30 years. If necessary, the barrier can be easily rejuvenated using the existing well network. An important advantage of the In-situ Redox Manipulation technology is its long-term effectiveness requiring minimal monitoring and maintenance costs. The ability of In-situ Redox Manipulation to treat deeper and larger contaminant plumes opens remediation options once thought technically and fiscally impossible. Large-scale demonstrations at the Hanford site in south-central Washington State show the groundwater barrier technology to be more cost-effective than conventional remediation techniques. A cost benefit analysis of the In-situ Redox Manipulation technology showed it was approximately 62% less costly than a comparably sized pump and treat system for treating chromium contaminated groundwater. The primary cost reduction resulted from reduced operations and maintenance. "In-Situ Redox Manipulation was developed in Pacific Northwest National Laboratory's Environmental Technology Directorate and is showing promise to be a major groundwater remediation technology at industrial and government sites alike," said John Fruchter, PNNL Staff Scientist. Winners of an R&D 100 award, the In-situ Redox Manipulation technology inventors were recognized for developing one of the top technologically significant products in 1997. Encouraged by the remediation results with chromium contaminated plumes, In-situ Redox Manipulation technology scientists are exploring applications with a variety of contaminants including solvents and explosive compounds. Funding for the Frontier Hard Chrome project came from the Environmental Protection Agency, Region 10.

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Energy and Environment

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