EOS, or emulsified oil substrate, was used to stimulate anaerobic biodegradation of trichloroethene (TCE) and tetrachloroethene (PCE) at a former Army-owned manufacturing facility located in the Piedmont area of North Carolina. Previous use of chlorinated solvents at the facility resulted in soil and groundwater impacts. Ten years of active remediation utilizing soil vacuum extraction and air sparging (SVE/AS) were largely ineffective in reducing the TCE/PCE plume. In 2002, the Army authorized preparation of an amended Remedial Action Plan (RAP) to evaluate in situ bioremediation methods to remediate TCE in groundwater. The RAP evaluated eight groundwater remediation technologies and recommended EOS as the preferred bioremediation alternative for the site. Eight wells were drilled within the WOx WO feet area believed to be the primary source area for the TCE plume. In a first injection phase, dilute EOS emulsion was injected into half of the wells. Distribution of the carbon substrate through the treatment zone was enhanced by pumping the four wells that were not injected and recirculating the extracted water through the injection wells. The process was repeated in a second phase that reversed the injection/extraction well pairs. Overall, 18,480 pounds of EOS were injected and 163,000 gallons of water were recirculated through the source area. Anaerobic groundwater conditions were observed shortly after injection with a corresponding decrease in both PCE and TCE concentrations. Dissolved oxygen, oxidation-reduction potential, and sulfate concentrations also decreased after injection, while TCE-degradation products, ferrous iron, and methane concentrations increased. The reduction in TCE allowed the Army to meet the groundwater remediation goals for the site. Approximately 18 months after injection, eight wells were innoculated with a commercially prepared dechlorinating culture (KB-1) in an attempt to address lingering cis-7,2-dichloroethene (c\s-DCE) and vinyl chloride (VC) that continued to be observed in some wells. Dehalococcoides populations increased slightly post-bioaugmentation. Both cis-DCE and VC continue to slowly decrease. ©2007 Wiley Periodicals, Inc.
An Interstate Technology and Regulatory Council (ITRC) case study document focused on six bioremediation case studies involving contaminants commonly present as dense nonaqueous phase liquids (DNAPLs) were bioremediated. The objective of the case studies was to demonstrate that there is credible evidence for bioremediation as a viable environmental remediation technology for addressing DNAPL conditions. Three case studies have been previously published; this fourth case study involves a pilot-scale demonstration of the effects of emulsified oil substrate (EOS) used to remediate a trichloroethene (TCE) source area at the Tarheel Army Missile Plant (TAMP) in Burlington, North Carolina. Releases from manufacturing operations and underground storage tanks (USTs) had impacted soils and groundwater with petroleum hydrocarbons and chlorinated volatile organic compounds (CVOCs). Ten years of groundwater pump-and-treat combined with soil vacuum extraction and air sparging (SVE/AS) effectively reduced concentrations of the petroleum constituents. However, there was relatively little effect on the dissolved-phase TCE groundwater plume.
Solutions-IES Inc. conducted the pilot-scale study to test the ability of EOS to enhance the biological reduction of CVOCs in groundwater in a 100-foot by 100-foot area believed to be the primary source area for the TCE plume (Solutions-IES, 2005). EOS is an effective, low-cost substrate for enhancing anaerobic bioremediation of a variety of contaminants, including chlorinated solvents, perchlorate, nitrate, chromate, acid mine drainage, and explosives. EOS consists of food-grade soybean oil, surfactants, macro- and micronutrients, and vitamins blended to form a stable microemulsion with small, uniformly sized oil droplets. Once injected into the subsurface, the oil droplets attach to the sediment surfaces, providing a residual oil phase. The oil provides a slow-release carbon source for cell growth and electron donor for energy generation, supporting long-term anaerobic biodegradation of the target contaminants. This approach provides good contact between the slowly biodegradable organic substrate (oil) and the contaminants.
The noncoalescing EOS emulsion is stable for extended time periods; has small, uniform droplets to allow transport in most aquifers; and has a negative surface charge to reduce droplet capture by the solid surfaces. Laboratory permeameter studies demonstrated that emulsions can be effectively distributed with a low residual saturation in sands and clayey sands with only modest reductions in aquifer permeability (Coulibaly & Borden, 2004). Field pilot studies have demonstrated that emulsified oils can be effectively distributed over 20 feet away from the injection point and provide a long-lasting carbon source to support reductive dechlorination (Borden et al., 2001; Lee etal., 2001; Leeetal., 2003).