AEROBIC COMETABOLIC DEGRADATION OF CHLOROETHENES: PILOT TEST AND FULL-SCALE DESIGN

摘要

Engineered in situ aerobic cometabolic degradation was selected to remediate groundwater beneath an Indiana industrial facility contaminated with trichloroethene (TCE) and cz's-l,2-dichloroethene (cDCE). Achieving groundwater concentrations equivalent to drinking water standards at the facility property line is required as part of the state-approved remedy for the site. Site characterization suggested a low rate of reductive dechlorination under the existing site conditions. Microcosm studies using aquifer solids and groundwater indicated that anaerobic reductive dechlorination could be stimulated by adding electron donors. However, several microcosms amended with methane and oxygen produced greater degradation rates than the anaerobic trials. An in-field pilot test was completed to evaluate the in situ degradation of chloroethenes and the mechanics of adding methane and oxygen to the aquifer. A two-well injection and extraction well couplet oriented transverse to the groundwater flow direction was selected for chemical injections. Numerical simulations of the pilot test area were used to establish well spacings, pumping rates, and monitoring well placement. Bromide injection was applied first to verify chemical spreading patterns within the aquifer. Methane and oxygen were introduced in two 5-day periods with subsequent groundwater monitoring. The estimated TCE degradation rate observed in the pilot test was 25 X10~(-9) kg/L/d. Also degraded in the aquifer was cDCE; chloroethene (CE) was not detected. The pilot test results were applied to a facility-wide numerical model to design an overall remedy. A conceptual model of the remedy suggests that the engineered bioremediation solution may require as little as 15 years to achieve the remediation goals compared to over 100 years for hydraulic containment by pumping and treating at the facility property line.