Closure of trichloroethene and 1,1,1-trichloroethane DNAPL remediation using thermal technologies

A soil and groundwater remediation, cleaning up trichloroethene (TCE) and 1,1,1-trichlorethene (TCA) has been completed, receiving a no further remediation letter from Illinois EPA. The chlorinated aliphatic compounds were present as a dense non-aqueous phase liquid (DNAPL) measuring up to 2.4 m thick in one of the monitoring wells. A number of techniques were used to accomplish this. Initially, steam with enhanced biodegradation(1) was utilized from 1991 to 1998. This process also incorporated a "huff and puff" mode of operation to optimize removal of the TCE acid TCA by vapor extraction. Redox manipulation was also performed to provide optimum conditions for the biodegradation of the residual compounds in the groundwater. From June 1998 to the end of April 1999, six phase electrical resistive heating was used to treat the areas where the steam was being limited by subsurface man-made features. The remediation was terminated after concentrations of chlorinated aliphatic compounds were reduced below site-specific risk-based criteria, concentrations of chlorinated compounds in the groundwater declined to below detectable levels and vapor concentrations were in the low part per million levels. Post closure monitoring shows no rebound for TCE and TCA, and biodegradation of residual compounds. The remediation removed or biodegraded approximately 32,000 kg of chlorinated aliphatic compounds. Of this, it is estimated that in the order of 18,000 kg were removed through vapor or groundwater extraction, while 12,000 kg were biodegraded. Active remediation is complete, treatment equipment has been removed and redevelopment is underway as part of a movie theater complex.