Source area bioremediation of chlorinated solvents with edible oils emulsion


Groundwater in a sand and gravel aquifer beneath this active manufacturing facility was contaminated with high concentrations of 1,1,1- Trichloroethane (1TCA) and cis-1,2-dichloroethene (cDCE), and their degradation products including ethene and ethane. An acclimated anaerobic microbial population was present at the site, but was limited by the availability of carbon. Emulsified edible oil was injected into six points from 7.6 to 15.2 m below ground surface. The radius of migration of the substrate was as much as 7.6 m from the point of injection. Decreases in the parent compounds and increases in the daughter products including ethene and ethane were observed within the first month and a half after substrate addition. After 16 months, the average concentration of the total volatile contaminants had been reduced by 66%. However, substrate levels had fallen below the desired levels of 50 mg/L TOC in several wells. A second application of the emulsified substrate was injected into twelve 2.5 cm injection wells. Elevated total organic carbon levels were then observed throughout the treatment zone and stimulated further dechlorination. Degradation rates for the total volatile contaminants over the 762 day treatment period were as high as 268 mg/L-day in a source zone well. 1TCA concentrations in this well have been reduced from 1,334 micromolar (mM) to 42.4 mM, a reduction of 97%. The overall average of total volatiles has declined by 82% over the 25 months since the emulsion was first injected.

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