Isotopic characterization of chlorinated solvents—laboratory and field results

Abstract

Pure-phase chlorinated solvent δ 13C and δ 37Cl values of tetrachloroethylene (PCE), trichloroethylene (TCE), and 1,1,1-trichloroethane (TCA) from a new solvent batch from Dow and PPG were analyzed and compared to values obtained from a previous chlorinated solvent batch. These analyses were performed to determine if each chlorinated solvent had a distinct δ 13C and/or δ 37Cl value associated with each manufacturer. Results indicate that the δ 13C and the δ 37Cl values of TCA do not remain consistent from batch to batch. However, the δ 37Cl values for PCE and TCE did remain consistent from batch to batch. Furthermore, these tests show a consistent and significant δ 13C difference between PPG and DOW PCE that could allow the use of 13C/ 12C in conjunction with 37Cl/ 36Cl ratios for fingerprinting applications. Chlorinated solvent/water solutions having known δ 13C and δ 37Cl values were used to test a purge-and-trap unit to extract chlorinated solvents for isotope analyses. These results show that the purge-and-trap unit produces both accurate and reproducible results for dissolved chlorinated solvent δ 13C and δ 37Cl analyses. The δ 13C and δ 37Cl reproducibility of the purge-and-trap unit was better than 0.9‰ and 0.4‰, respectively. The purge-and-trap unit was tested at a field site that has a well-defined plume of dissolved PCE emanating from a dry cleaner located in Angus, Ontario. The δ 13C and δ 37Cl data suggest that the PCE forming the core of the groundwater plume is related to one manufacturer. The results of this study along with results from a chlorinated solvent contaminated site affected by biodegradation show the potential of 13C/ 12C and 37Cl/ 36Cl ratios for isotopic fingerprinting applications on the field of organic contaminant hydrogeology.