A Biotic/Abiotic Three-Phase In Situ Barrier System to Treat TCE in Groundwater

摘要

A groundwater remediation pilot test (PT) consisting of three (3) in series, in situ reactive barriers was designed to evaluate treatment of dissolved phase tri-chloroethene (TCE) at concentrations up to 650 μg/L and cis-l,2-dichloroethene (cis-DCE) concentrations up to 350 μg/L at the Canadian Department of National Defense (DND) site in Valcartier, Quebec, Canada. The layout of the pilot test cell provides for the testing of biotic/abiotic treatment approach consisting of a mixture of zero valent iron and an integrated ZVI-carbon product (EHC~R from Adventus) (ZVI/EHC), hydrogen sparging, and air sparging. Geology at the PT cell consists of sand with fine sand seams from ground surface to 28 metres below ground surface (m bgs) (92 ft bgs). Depth to groundwater is 10 m bgs (33 ft bgs) and a bedrock confining unit is at 28 m bgs (92 ft bgs). The ZVI /EHC barrier was installed using a proprietary pneumatic injection method developed by ARS Technologies. A total of 44,000 kilograms (96,000 pounds) of ZVI/EHC were injected into 12 points at a ratio of 2.7 to 1 (ZVI/EHC). Hydrogen sparging is being used to supplement hydrogen concentrations needed for reductive dechlorination of TCE. Four (4) hydrogen sparging wells were installed to evaluate radius of influence and treatment benefits of hydrogen sparging. As a final treatment, air sparging/bioventing wells were installed downgradient of the hydrogen sparging wells in the event that vinyl chloride (VC) is produced and needs treatment. All barrier systems and monitoring wells were installed during July 2006 and post construction PT monitoring was initiated in August 2006. Results to date indicate that groundwater TCE and cis-DCE concentrations have declined by over 50%, primarily in the ZVI/EHC barrier. Very high flow velocities and colder then anticipated groundwater temperatures have resulted in a reduction in the rate at which in situ chemical and biological treatment occurs and has increased the acclimation period for biological degradation.