Permanganate injection is increasingly applied for in situ destruction of chlorinated ethenes in groundwater. This laboratory and field study demonstrates the roles that carbon isotope analysis can play in the assessment of oxidation of trichloroethene (TCE) by permanganate. In laboratory experiments a strong carbon isotope fractionation was observed during oxidation of TCE with similar isotopic enrichment factors (-25.1 to -26.8 per thousand) for initial KMnO{sub}4 concentrations between 67 and 1250 mg/L. At the field site, a single permanganate injection episode was conducted in a sandy aquifer contaminated with TCE as dense nonaqueous liquid (DNAPL). After injection, enriched δ 13{sup left}C values of up to +204 and elevated Cl{sup}- concentrations were observed at distances of up to 4 m from the injection point. Farther away, the Cl{sup}- increased without any change in δ 13{sup left}C of TCE suggesting that Cl{sup}3- was not produced locally but migrated to the sampling point. Except for the closest sampling location to the injection point, the δ 13{sup left}C rebounded to the initial δ 13{sup left}C again, likely due to dissolution of DNAPL. Isotope mass balance calculations made it possible to identify zones where TCE oxidation continued to occur during the rebound phase. The study indicates thatδ 13{sup left}C values can be used to assess the dynamics between TCE oxidation and dissolution and to locate zones of oxidation of chlorinated ethenes that cannot be identified from the Cl{sup}- distribution alone.
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