Using an innovative biological-based cleanup method (bioremediation), GSI is working to clean up soil and groundwater on three sites that were contaminated with dissolved chlorinated solvents.
Remediation at the three sites was necessary in order to meet EPA cleanup requirements within the agency’s 15-year allotted timeframe. The contaminants were trichloroethane (1,1,1-TCA) and trichloroethene (TCE).
GSI’s approach was to use an enhanced in situ bioremediation (EISB) system that would continue to treat contaminated groundwater as it moves naturally through the aquifer, using a process called bioaugmentation. There are several advantages to bioremediation: completely breakdown the contaminants, minimal impact on infrastructure, and relatively low cost.
EISB involves injecting emulsified soybean oil and dechlorinating bacteria into the soil where the solvents were detected. The soybean oil creates favorable geochemical conditions for the bacteria, and the bacteria break down the contaminants into relatively benign ethene and ethane.
A pilot study at the first site included nearly 20 injection points that were used to apply the soybean oil and bacteria. After eight months of bioaugmentation, contaminant concentrations decreased in four of six monitoring wells. After 18 months, concentrations were lower than EPA cleanup requirements.
Following this successful pilot study, bioaugmentation was initiated at the remaining two sites, each of which had additional challenges. At one site, hydrochloric acid had been spilled so buffering compounds were added to the soybean oil and bacteria to adjust the pH to a range amenable to bioaugmentation. At the third site, sensitive equipment was required to carefully monitor and avoid seepage of the remediation materials into subsurface structures.
Treatment is ongoing and monitoring shows that bioaugmentation is effectively reducing chlorinated solvent levels at each site.
GSI is also successfully using this technique on other projects in the Pacific Northwest and in Europe.