Isotopic characterization of chlorinated solvents—laboratory and field results

Pure-phase chlorinated solvent δ13C and δ37Cl 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 δ13C and/or δ37Cl value associated with each manufacturer. Results indicate that the δ13C and the δ37Cl values of TCA do not remain consistent from batch to batch. However, the δ37Cl values for PCE and TCE did remain consistent from batch to batch. Furthermore, these tests show a consistent and significant δ13C 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 δ13C and δ37Cl 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 δ13C and δ37Cl analyses. The δ13C and δ37Cl 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 δ13C and δ37Cl 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.