(519e) Application of Emulsified Carbon Substrate to Soil Excavations to Enhance Biodegradation of Chlorinated Ethenes

Emulsified oil substrate was applied using an innovative application technique to enhance the reductive dechlorination of dissolved chlorinated ethenes at two RCRA sites at Seymour Johnson Air Force Base in Goldsboro, NC. A source area consisting of petroleum and chlorinated hydrocarbons as well as an associated groundwater plume extending from the source zone had been delineated during the site investigations. At both sites, the soil source area was remediated through excavation of contaminated soil for offsite disposal. Both excavations extended to groundwater. The preferred remedy for groundwater was previously determined to be monitored natural attenuation (MNA). The excavation eliminated much of the source mass including all or some of the petroleum hydrocarbons that may have been contributing to the reducing conditions at the site. The changes entailed in the soil removal may have been detrimental to the reducing conditions that are favorable to reductive dechlorination. This may slow biodegradation of the residual primary contaminants of concern, the chlorinated ethenes. Therefore, the addition of a carbon substrate to enhance reductive dechlorination was recommended. The emulsified oil was added in July 2005 as part of the soil excavation task. The diluted substrate was applied to a high permeability trench constructed at the bottom of the open excavation. The addition of the substrate while the excavation was open eliminated the need for the injection wells and pumping systems normally required for an in-situ application. Additionally, the application directly into the open excavation simplified the regulatory approval process by eliminating the need for an injection permit. The emulsified oil was determined to be the most amenable substrate for this type of application due to ease of injection, substrate longevity and material cost. The fatty acids in these oils are slowly broken down to hydrogen and acetate, providing a long-lasting source of reducing power for reductive dechlorination. The emulsion was applied and then followed with potable water containing vitamin B12. Post remedial sampling events conducted in October 2005 and February and April 2006 included monitoring well sampling and sampling using direct push technology. Post application data indicated that the carbon substrate had maintained the reductive water chemistry within the aquifer, thus providing long term treatment potential for the remaining dissolved chlorinated ethene contamination.