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The purpose of this project was to investigate the potential applications of stable isotope ratio measurements in characterization of the source terms, the transport, and the fate of chlorinated solvents in groundwater aquifers. The approach to this research was threefold: to develop methods for the sampling and isotopic analysis of chlorinated solvents in groundwaters; to perform laboratory experiments to measure equilibrium and kinetic isotope effects associated with biological and physical transformation processes of chlorinated solvents; and to perform field investigations at well-characterized, contaminated aquifer sites to demonstrate the applicability of the isotopic approach in real-world situations. New methods were developed for the extraction and isotopic analysis of chlorinated solvents in water samples. The new methods were applied to a series of laboratory experiments assessing the isotope effects associated with biological and physical transformation processes. The authors found that a large kinetic isotope effect was caused by microbial degradation of chlorinated solvents, under both aerobic and anaerobic conditions. The evaporation of chlorinated solvents also caused a large isotope effect, but in that case the carbon isotopic fractionation was in the reverse sense. Isotopic fractionation associated with adsorption and chemical exchange of chlorinated solvents was negligible. The authors performed field investigations at five present and former industrial sites undergoing various stages of remediation. These investigations were collaborative with Lockeed-Martin Energy Systems, Inc., and ENSR, Inc., the companies responsible for the remedial work at these sites. Application of the new sampling and analytical methods at these sites showed that stable isotopic measurements yield powerful insights into underground processes. In particular, they found positive evidence for in-situ microbial degradation of chlorinated solvents at all five sites, evidence for volatilization of chlorinated solvents at three sites, and evidence for multiple sources of chlorinated solvents at two sites. At a site where six-phase heating was applied, they found evidence for increased solubilization of pure phase chlorinated solvents during heating. The general conclusion of the field investigations is that stable isotope measurements should become an essential component in site characterization and remediation of sites contaminated with chlorinated solvents

Stable isotopic investigations of in-situ bioremediation of chlorinated organic solvents