PROJECT DATE: September 2000 to present
BACKGROUND: Groundwater in a sand and gravel aquifer beneath this active manufacturing facility was contaminated with 1,1,1-TCA (concentrations up to 480 mg/L), PCE, and their degradation products. The site owner, faced with a long term (in excess of 100 years) and expensive pump and treat system, selected Terra Systems, Inc. to conduct an anaerobic bioremediation field pilot test at the site. The analytical data for the past 10 years indicates that an acclimated microbial population capable of completely biodegrading the 1,1,1-TCA and PCE to ethane and ethene is present at the site.
ACTION TAKEN: A grid of 6 injection points for emplacement of the emulsified substrate was installed using a Geoprobeâ direct push unit. Emulsified substrate was injected in a zone from 25 to 50 feet below ground surface. A second application of the emulsified substrate was conducted after 16 months to maintain reducing conditions and further promote reductive dechlorination in a somewhat larger treatment area.
EFFECTIVENESS: The formation accepted the emulsified substrate easily. The emulsion appeared in several monitoring wells suggesting that the radius of migration of the substrate was as much as 30 feet from the point of injection. Degradation of the contaminants is being monitored over time. We have observed decreases in the parent compounds and increases in the daughter products including ethene and ethane 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%. Degradation rates for the total volatile contaminants over the 495 day treatment period were as high as 394 mg/L-day in a well with greater than 100,000 mg/L total volatiles. In areas with lower concentrations, total VOC degradation rates were lower, in the range of 2.8 to 24 mg/L-day. A second application of the soybean emulsion was performed in February 2002.