Technical Approach

In recent years, compound-specific stable isotope analyses (CSIA) have been increasingly used as an indicator of chemical and biological degradations of chlorinated solvents in groundwater and as a tool to distinguish different plumes (i.e., fingerprinting) and trace them back to the release source point. Most previous studies that used CSIA (mainly ¹³C) assumed that isotopic fractionations associated with physical processes such as sorption and diffusion are negligible. These assumptions were based on studies that concluded that sorption does not cause significant isotopic (¹³C) fractionation. However, recent studies concluded that diffusion might cause significant isotopic (¹³C) enrichments and depletion during transport of organic compounds in groundwater. The impacts of sorption and diffusion on compound-specific hydrogen and chlorine stable isotopes of chlorinated solvents have not been studied previously. Recent availability of new methodologies to analyze these isotopes will facilitate this investigation. Furthermore, hydrogen isotopes tend to fractionate more than other isotopes due to the larger mass difference ratio of the two stable isotopes of hydrogen in comparison to other isotopes. Therefore, it has become necessary to develop accurate characterization techniques to quantify critical parameters such as isotopic behaviours (³⁷Cl and ²H) that govern chlorinated solvent diffusion into low permeability zones and sorption within them in the subsurface.