An Evaluation of Limiting Parameters of an In Situ Trichloroethene Bioremediation Project Based on Seven TCE Field Bioremediation Studies

Abstract

Seven aerobic field trichloroethene (TCE) bioremediation projects were evaluated to determine key parameters leading to in situ TCE bioremediation effectiveness. Key parameters identified were: 1) presence of other contaminants, 2) efficacy of the cometabolic inducer, 3) technology design, and 4) site soils and hydraulics. These four parameters were then used to evaluate the pilot bioremediation operation at Air Force Plant #44 in Tucson, Arizona. The pilot operation was poorly designed. Site characterization appeared insufficient; laboratory studies were not representative of site conditions; 1, 1-dichloroethene appeared to inhibit TCE degradation; the purpose of the injected methanol ( cometabolic inducer) was unclear. Well design, specifically screen interval location, also contributed to technology deficiency. Soil type appeared to be the most limiting component; hydraulic conductivity (K) representative of the contaminated clay at the APP #44 site was estimated at 1.5 x 10-5 cm/sec. Over the course of the trial, spatially averaged TCE concentrations decreased by 41 %. Well chloride data calculations indicated that a 27% reduction may be attributable to dilution, thereby suggesting that only a 14% decrease in concentrations may be attributable to biological degradation.