A Bioavailable Ferric Iron Assay and Relevance to Reductive Dechlorination

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Untitled Document ABSTRACT: Reductive dechlorination of chlorinated organic compounds can be promoted through the addition of electron donors to the subsurface. The presence of ferric iron that is bioavailable can affect reductive dechlorination by supporting the growth of iron-reducing bacteria. These bacteria can maintain sufficiently low dissolved hydrogen concentrations to prevent reductive dechlorination of cisdichloroethene (cDCE) for example. Evaluation of data from 13 sites that have undergone pilot testing with Regenesis Hydrogen Release Compound (HRC) were evaluated for reductive dechlorination of chlorinated ethenes and production of dissolved ferrous iron. Data from nine of the sites supported the hypothesis that bioavailable ferric iron can prevent the reductive dechlorination of cDCE to vinyl chloride. Data from one of the sites were to the contrary and data from three of the sites were inconclusive. The hypothesis that this “cDCE stall” is mediated by bioavailable ferric iron and that it can be a transient phenomenon is supported by the data. This is important from the standpoint that there is some regulatory concern for the accumulation of cDCE when parent compounds are actively dechlorinated. An assay was developed that is capable of measuring bioavailable ferric iron in soil. Such an assay may be used to determine the potential for cDCE accumulation and subsequently engineer total cleanup strategies. These strategies may include sequential reductive-oxidative treatments in which reductively dechlorinated compounds are subsequently oxidized though natural attenuation or engineered methods.

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