Application of Compound-Specific Carbon and Chlorine Stable Isotope for Fingerprinting Sources of Chlorinated Compounds in Groundwater

Groundwater contamination by hazardous substances including chlorinated solvents has become a serious widespread problem, representing a substantial liability. Evaluation of contaminant sources in groundwater plumes, which has significant relevance for assignment of responsabilities for groundwater remediation, is one of the key aspects that consultants and environmental agencies have to deal with in contaminated groundwater. In recent years, compound-specific stable isotope analysis have become a valuable methodology that is employed as an indicator of chemical and biological degradations of chlorinated solvents in groundwater and as a tool to distinguish different plumes (fingerprinting) and trace them back to the release source point. In this study, chlorine and carbon stable isotopes were used to identify the origin of trichloroethene (TCE) in a co-mingled plume that can be associated to a primary in-site source and an off-site TCE source link to biodegradation of perchloroethene (PCE). The stable isotope data showed a very distinct and significantly different isotopic fingerprint for the primary source of TCE compared to the off-site source. This difference can be observed in the co-mingled TCE plume downgradient from the two TCE sources clearly showing that the off-site TCE source is contributing to the in-site TCE plume. These results showed the great potential of the combined use of 37Cl and 13C for fingerprinting organic contaminant sources in groundwater.