Abstract:
Chlorinated aliphatic hydrocarbons (CAHs) such as vinyl chloride (VC) and 1,-2 dichioroethane (DCA), are wide-spread groundwater pollutants found at many contaminated field sites around the world. Quantitative tools are needed to determine the in situ rates of VC and DCA transformation to ethene in contaminated groundwater. The objective of this study was to evaluate the potential of E-/Z-chlorofluoroethene (E-/Z-CFE) and DCA-d₄ as surrogates for VC and DCA, respectively. Laboratory microcosm and batch reactors experiments were performed to determine the kinetics and products of VC and E-/Z-CFE transformation to ethene and fluoroethene (FE), respectively. In addition, the products and pathway of DCA and DCA-d₄ also were determined. In all microcosms and batch reactors, E-CFE was preferentially transformed over Z-CFE. For the three experimental systems, the rate of E-CFE transformation to FE was within a factor of 2.7 of that for VC to ethene, which indicates that E-CFE is suitable for use as a surrogate for VC. CFE was later used in a separate field study as a surrogate to model in situ rates of VC reductive dechlorination. The rates of DCA and DCA-d₄ were statistically similar according to a t-test at the 95% confidence level, which also indicates that DCA-d₄ is an excellent surrogate for DCA. Based on this conclusion, DCA-d₄ is now ready to be used in a field test as a surrogate for DCA. This work establishes the precedence for the use of CFE and DCA-d₄ as surrogates for VC and DCA, respectively.
