The geology at the site consists of reddish-brown, moderately plastic, sandy clay to a depth of roughly 4.6 meters below ground surface (bgs) underlain by fractured clayey shale with occasional gypsum layers. The depth to groundwater is 2.4 to 3.1 meters below ground surface. Most groundwater flow and contaminant transport appear to occur through a series of weathered shale fractures located immediately beneath the surficial clay and within a thick gypsum layer approximately 10.7 meters bgs.
Targeted Environmental Media:
 Fractured Bedrock
Historical solvent releases of degreasing agents at the site have resulted in a 1,520-meter-long plume of chlorinated solvents.
Major Contaminants and Maximum Concentrations:
- Sulfate (1,623,000 µg/L)
- Methane (1,500 µg/L)
- Trichloroethene (1,656 µg/L)
- 1,2-Dichloroethene (0 µg/L)
- Vinyl chloride (0 µg/L)
- Acetylene (0 µg/L)
- Other (Not Documented)
- Bioremediation (In Situ)
- Reductive Dechlorination (In Situ Bioremediation)
Comments:
An emulsion of soybean oil, surfactant, yeast extract, and lactate was prepared and injected into six injection wells spaced 1.5 meters apart. The wells were placed in a barrier configuration to intercept the groundwater plume at the SS-17 site, approximately 76 meters downgradient from the source area. The wells were screened from 2.4 to 5.5 meters below ground surface to achieve maximum distribution of the treatment mixture in the upper weathered fractured zone. The project was started in November 2001 and was completed in January 2003. Samples were collected in July 2002 from three cores near the injection area; groundwater contamination was monitored through various monitoring wells and injection wells situated around the area.
The pilot-scale project was conducted to evaluate the potential for an emulsion of soybean oil to promote reductive dechlorination and abiotic transformation of trichloroethene (TCE) in groundwater.
After only 9 months, significant decreases in TCE were observed with associated by-product increases in cis-1,2-dichloroethene, vinyl chloride, and ethene observed in several monitoring wells downgradient of the permeable reactive barrier. Biological reduction of iron and sulfate resulted in the accumulation of ferric sulfide and ferric disulfide within the treatment zone compared with an untreated location. Still, the abiotic transformation mechanism appeared to be a minor contributor to the removal of TCE within this area of the aquifer.
Degradation of TCE can be stimulated by biological and abiotic process in areas with high levels of sulfate and iron. Injection of a soluble or long-lasting substrate can promote reductive dechlorination of TCE and stimulate the reduction of sulfate and iron that can then abiotically react with TCE.
References:
Pilots to Enhance Trichloroethene Reductive Dechlorination and Ferrous Sulfide Abiotic Transformation, Paper K-14, in: V.V. Magar and M.E. Kelly (Eds.), In Situ and On-Site Bioremediation 2003. Proceedings of the Seventh International In Situ and On-Site Bioremediation Symposium (Orlando, Florida). June 2003. ISBN 1-57477-139-6, published by Battelle Press, Columbus, Ohio; http:www.battelle.orgbookstore#
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