Using chlorine stable isotopes to characterize sources and monitor attenuation of groundwater pollu

Using chlorine stable isotopes to characterize sources and monitor attenuation of
groundwater pollutantsPresented by:Dr. Max Coleman
Jet Propulsion Laboratory
California Institute of Technology
Pasadena, CAAbstractChlorine has two stable (non-radioactive) isotopes, atomic masses 35 and 37. Disappointingly for geochemists there is generally very little variation in the abundance ratio of the two isotopes in natural sedimentary rocks and waters. There are exceptions to this rule. Fortunately, manufactured chemicals occurring in soils and groundwaters show a range of values and may be characterized isotopically to trace sources of pollution. However, the microbial processes of perchlorate reduction and dechlorination of chlorinated aliphatic hydrocarbon solvents produce large changes in isotope compositions of both the pollutant and the harmless chloride produced. These changes are systematic and depend on the extent of completion of the process. Thus, they can be used to monitor natural attenuation of pollution but would seem to deny the possibility of characterizing the source. Our recent work has shown that analysis of the isotopic compositions of two elements in a pollutant (e.g. Cl and O in perchlorate and Cl and C in solvents) may allow simultaneous characterization and attenuation monitoring.

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