UTILIZING COMPOUND SPECIFIC STABLE ISOTOPES IN EVALUATING DIFFUSION AND STORAGE OF TRICHLOROETHELENE IN LOW-PERMEABILITY ZONES

In the last two centuries, the negative impact of human activities on nature has been growing dramatically. Groundwater contamination by hazardous compounds such as chlorinated solvents has become a serious widespread problem that represents a substantial liability. Chlorinated solvents are immiscible in water and have densities greater than water. Upon disposal or accidental spills, these compounds migrate downward as a separate non-aqueous phase to aquifers to form one or more source zones. From these source zones aqueous phase plumes are formed through various mechanisms such as advection, diffusion and dispersion. In heterogeneous aquifers where both high and low-permeability zones exist, aqueous phase plumes tend to flow through these different zones at different rates. In heterogeneous aquifers or fractured rocks, contaminants enter the low-permeability zones through diffusion. Once in the low-permeability zones, contaminant transport could be retarded though sorption. The low-permeability zones become secondary storage areas that act as long-term sources of chlorinated solvent plumes that are persistent and very challenging to treat. Compound specific stable isotope analyses (CSIA) have been increasingly used as a toll to assess the fate of chlorinated solvents and other organic compounds in the subsurface. In this study compound-specific stable isotopes (¹³C and ²H) are utilized to better understand the behaviour of trichloroethelene during diffusion into low-permeability zones as well as the sorption on various materials.