Most groundwater contaminants present at Department of Defense facilities are sensitive to oxidation-reduction (redox) conditions. In many instances, in situ redox conditions result in natural attenuation of contaminant plumes over short distances; however, in situ redox conditions are not always favorable for natural attenuation of contaminant plumes. The objective of this project was to demonstrate and validate a promising new technology for modifying in situ redox conditions to treat contaminated groundwater.
The technology’s premise is that closely spaced permeable electrodes can be installed through a groundwater contaminant plume in the format of a permeable reactive barrier (e-barrier). Application of low voltage direct current (DC) drives sequential oxidation and/or reduction of contaminants with the net benefit of reducing contaminant flux.
The site selected for the demonstration was a shallow alluvial plume containing approximately 300 µg/L of trichloroethene (TCE) at F. E. Warren Air Force Base, Wyoming. As of January 2005, the e-barrier had been operating continuously for 24 months. TCE flux reduction was sustained over this period. At the highest imposed potential (6.5 volts), bulk TCE flux reduction of 90% was demonstrated. Data from the primary transect through the center of the e-barrier indicated TCE flux reduction of 95%. In general, no adverse reaction intermediates were observed. An exception was the apparent formation of chloroform at the center of the e-barrier at 6.5 volts. Cost components associated with the demonstration e-barrier included (1) capital expenses of $409/ft2 of intercepted plume and (2) operation and maintenance (O&M) expenses of $10/ft2/year. Taking into account opportunities for cost reduction and economies of scale, the costs for full-scale systems are anticipated to be 25 to 50% lower than the demonstration cost. Using this assumption, a typical full-scale e-barrier would have capital and O&M costs similar to those of current proven technologies for treating TCE (i.e., pump-and-treat and zero-valent iron permeable reactive barriers).
On a site- or contaminant-specific basis, the e-barrier technology may have advantages over existing technologies. One of the most promising is application to energetic compounds. Complementary studies involving energetic compounds in groundwater have been funded by the Strategic Environmental Research and Development Program (SERDP) and the U.S. Army Corps of Engineers. This research has led to an e-barrier demonstration at Pueblo Chemical Depot, Colorado, for treatment of RDX in groundwater under ESTCP project ER-200519. (Project Completed - 2006)