Site characteristics include fractured limestone bedrock.
Targeted Environmental Media:
 Dense Non-aqueous Phase Liquids (DNAPLs) - Fractured Bedrock
Trichloroethylene (TCE) was found at depths approximately 9 to 12 meters below ground surface.
Major Contaminants and Maximum Concentrations:
- Trichloroethene (5,000 µg/L)
No technologies selected.
- Pump and Treat
- Other (Enhanced In Situ Bioremediation)
Comments:
Enhanced in situ bioremediation was selected as a technology to replace a 15-year old pump and treat system that yielded low TCE mass despite groundwater concentrations as high as 5,000 µg/L. Initial treatment consisted of an emulsion of 1% by volume soybean oil introduced into the subsurface via five source area wells. Upon achieving anaerobic and reducing conditions, 5 liters of a Dehalococcoides culture (KB-1") was added to each well. Total chlorinated volatile organic compound (CVOC) concentrations decreased by approximately 85 percent within 6 months of culture addition. The amount of TCE estimated to be destroyed was 6.7 kilograms, though more TCE mass may have been removed due to sorption to or trapping within the rock matrix.
Not identified in the reference reviewed.
Down gradient barrier wells were installed to capture residual CVOCs that might be migrating off-site.
The cost of bioremediation was approximately equal to operating a pump and treat system for 18 months.
References: Elder, Carl R, Larson Douglas G., and Vidumsky, John E., Replacement of a Groundwater Extraction System with Bioremediation to Treat Trichloroethylene in Fractured Bedrock. Presented at the 23rd Annual International Conference on Soils, Sediment and Water. University of Massachusetts, Amherst, MA. October 15-18, 2007.
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