Electrically Induced Redox Barrier (e-Barrier)
-- An e-barrier consists of a panel of closely spaced permeable electrodes installed in a trench that intercepts a plume of contaminated groundwater.
-- Application of an electrical potential to the electrodes creates oxidizing conditions at the positive electrodes and reducing conditions at the negative electrodes. This drives sequential oxidation and/or reduction of contaminants with the net benefit of reducing contaminant flux.
-- The e-barrier constructed for this field demonstration consisted of 17 individual electrode panels each 0.3 x 2 square meters (m2) in area. Concentric interlocks linked the individual panels. The overall as-built dimension of the e-barrier is 9.2 x 1.9 m2. The effective cross-sectional area was 17 m2.
-- Each panel contained three Ti-mmo electrodes, four layers of Geotextile™, and six layers of Triplanar Geonet™.
-- Panels were framed in slotted 3-in inner diameter (ID) PVC pipe.
-- Each e-barrier module includes a discrete electrical connection, gas vents, and washout tubing that are conveyed to the surface via 3-in PVC riser pipes.
-- The assembled e-barrier was installed in two sections.
-- Washed granular backfill from the Crow Creek alluvium was placed around the e-barrier to an elevation of approximately 1 foot (ft) above the barrier.
-- Following installation at the site, the e-barrier was allowed to equilibrate with the contaminant in the plume for 5 months. Power was applied to the e-barrier in January 2003. Power was supplied by a 30V DC 200 amp single-phase rectifier. The rectifier was connected to a 110V AC 60 amp electrical service.
-- As of August 2004, the e-barrier had been operating continuously for approximately 19 months.
Demonstration conducted under the Department of Defense (DoD) Environmental Security Technology Certification Program (ESTCP).
ESTCP Program Manager
901 North Stuart Street, Suite 303
Arlington, VA 22203
3207 Sidney Brooks Road
Brooks AFB, TX 78235-5344
EPA - Region 8 (EPR-F)
999 18th St., Suite 300
Denver, CO 80202
Wyoming Department of Environmental Quality
122 West 25th St. 4-W
Cheyenne, WY 82002
Trichloroethene (TCE), approximately 300 mg/L
Historical missile maintenance and disposal activities.
Type/Quantity of Media Treated:
Groundwater (quantity not provided)
Purpose/Significance of Application:
The purpose of the demonstration was to demonstrate/validate a potential new efficient and cost-effective technology for managing contaminated groundwater at the Department of Defense (DoD) facilities.
Regulatory Requirements/Cleanup Goals:
Trichloroethene - 5 µg/L; cis-1,2-DCE - 70 µg/L.
The primary effect of the e-barrier was to shift thermodynamic conditions in the vicinity of the electrodes, resulting in an overall effect of oxidation followed by reduction. This facilitated oxidation and/or reduction of the TCE. The groundwater became more acidic (approximately 1 pH unit) close to the e-barrier. On day 290, the highest potential was applied. Samples of groundwater collected at this time showed a 95% reduction in TCE concentration between 0.5 meters up- and downgradient face of the e-barrier. This achieved the cleanup goal of 5µg/L.
In general, no adverse reaction intermediates were observed. An exception was the apparent formation of chloroform at the center of the e-barrier. Plausible explanations for chloroform formation include highly toxic conditions developed at the e-barrier and/or unanticipated reactions with polyvinyl chloride (PVC) pipe cement. Operation of the e-barrier had no apparent impact on the mobility of inorganic constituents in groundwater.
The total costs associated with the demonstration included capital expenditure (96.5% of total) and operation and maintenance (O&M) (3.5% of total). The capital costs consisted of e-barrier installation (29.7%), electrode materials (15.5%), and labor for panel fabrication (9%). Total observed capital and O&M costs, normalized to the cross-sectional area of the e-barrier, were $409/ft3/year and $10/ft3/year, respectively.
Research on e-barriers has been underway at Colorado State University (CSU) since September 1998. The e-barrier was designed and fabricated at CSU in May through July 2002 and was installed at F.E. Warren AFB in August 2002. Warren AFB was selected for this demonstration due to favorable geologic conditions at the site, the presence of the desired target compound, and proximity to CSU. Some primary site attributes include a background TCE concentration of approximately 300 µg/L; depth to groundwater of approximately 12 ft (below grade); and a groundwater seepage velocity of 0.37 ft/day.
F.E. Warren is a 7,000-acre facility underlain by alluvial deposits and the Ogallala Formation. Locally, the Ogallala Formation consists of interbedded gravel, sand, and silt with varying clay content and cementation. The site selected for the demonstration is a shallow alluvial plume containing approximately 300 µg/L of TCE.