Combined Bioremediation and Zero-Valent Iron for In Situ Treatment of PCE(Abstract)

摘要

A pilot test was conducted to assess the overall performance of a combined approach towards in situ remediation within a chlorinated solvent (VOC) source zone. The approach involved combining the biotic reductive dechlorination of tetrachloroethene (PCE) and less-chlorinated ethenes (trichloroethene, cis-1,2-dichloroethene, and vinyl chloride) with abiotic reduction on granular zero-valent iron (ZVI). The pilot test system comprised three, large diameter groundwater extraction wells that were four inches in diameter, and completed within the center of three-foot diameter boreholes that were backfilled with ZVI to depths of approximately 50 feet. The extraction wells were con- structed with multiple, hydraulically separate depth intervals (i.e. well screens), so that flow could be isolated from 4 to5 different water-bearing zones encountered between depths of 10 and 50 feet. Extracted groundwater was amended with carbohydrate to act as an electron-donor and food source to promote biotic reductive dechlorination of VOCs. The amended water was injected at a multi-level extraction well located approximately 40 feet upgradient of the three large-diameter ZVI-filled extraction wells, and screened over similar depth intervals. The continuous extraction and injection of amended ground- water was implemented to establish a groundwater circulation zone to promote the distri- bution of carbohydrate solution for biotic reduction, and to maintain abiotic destruction with ZVI. This system was operated for approximately 6-months, and was monitored on a monthly basis with five multi-depth monitoring wells located between the injection well and three extraction wells. Effluent water quality from the extraction wells was also monitored on a monthly basis.