NATURAL ATTENUATION OF A TRICHLOROTRIFLUOROETHANE PLUME IN GROUNDWATER SUPPORTED BY CO-MINGLED ACETONE

摘要

Subsurface investigations conducted at an integrated circuits research and manufacturing facility in Southern California detected a variety of chlorinated solvents and other compounds in soil and groundwater. Releases of process wastewater in a former metals coating application area and releases from a neutralization clarifier resulted in impacted soil and groundwater. Additional releases had occurred from an exterior drum storage area. The predominant dissolved contaminants were identified to be 1,1,2-trichlorotrifluoroethane (Freon-113) and acetone. Other contaminants identified in soil and groundwater at the facility included 1,2-dichlorobenzene, trichloroethene, toluene, and xylenes. Sampling data indicated that the dissolved plume of Freon-113 was attenuating downgradient from the suspected identified sources. In addition, acetone was not detected in significant concentrations in groundwater as compared to the concentrations remaining in soil, indicating that potential degradation/sorption was occurring. A conceptual model of natural attenuation at the facility was developed based on the observed data that included: shallow groundwater at the facility was impacted by volatile organic compounds; attenuation of Freon-113 in shallow groundwater; probable biodegradation of Freon-113 driven/supported by an exogenous carbon source, acetone; deeper groundwater to approximately 75 feet below ground surface was not impacted and was most likely protected by discontinuous clay/silt layers; source removal was conducted to the extent possible; and results of a bench-scale study indicated that indigenous microbial populations existed in soil and groundwater at the facility. The information presented herein was conducted as part of a feasibility analysis for the dissolved constituents in groundwater at the facility.