IN SITU AEROBIC BIOREMEDIATION OF METHYLENE CHLORIDE IN LOW-PERMEABILITY BEDROCK

摘要

Enhanced biodegradation was evaluated as an alternative to groundwater pump and treat for remediation of contaminated groundwater at a Colorado Department of Transportation (CDOT) facility in Denver, Colorado (Site). A pilot-scale test for enhanced in situ aerobic bioremediation of methylene chloride (MeCl) and higher chlorinated volatile organic compounds (VOCs) was performed at the Site over a 12-month period. The pilot-scale test followed a successful bench-scale study that indicated aerobic biodegradation of MeCl and higher chlorinated VOCs was possible if the naturally occurring conditions for biodegradation in the formation could be enhanced and maintained. Concentrations of MeCl in groundwater that exceed 2,000,000 micrograms per liter (μg/L), low-permeability bedrock, and complex hydrogeology presented unique challenges for the system design and implementation. The pilot-scale test included low-flow injection of nutrients and oxygen into low permeability bedrock sandstones. Methane was added to the injection stream to stimulate the potential cometabolic degradation of low concentrations of tetrachloroethene (PCE), trichloroethene (TCE), and 1,1-dichloroethene (1,1-DCE). The concentrations of MeCl and the higher chlorinated VOCs in the source area have decreased significantly over the 12-month test period.