Groundwater Services, Inc.

Long-Term Sustainability of Reductive Dechlorination Reactions at Chlorinated Solvents Sites

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Courtesy of Groundwater Services, Inc.

The sustainability of biodegradation reactions is of interest at Type 1 chlorinated solvent sites where monitored natural attenuation is being considered as a remedial alternative. Type 1 chlorinated solvent sites are sites where anthropogenic electron donors (such as landfill leachate or fermentable organics in the waste materials) exist with dissolved chlorinated solvents, resulting in biological reductive dechlorination. A framework is provided that classifies Type 1 chlorinated solvent sites based on the relative amounts and the depletion rates of the electron donors and the electron acceptors (i.e., chlorinated solvents). Expressions are presented for estimating the total electron donor demand due to the presence of solvents and competing electron acceptors such as dissolved oxygen, nitrate, and sulfate. Finally, a database of 13 chlorinated solvent plumes was analyzed to estimate the median and maximum mass discharge rate for dissolved oxygen, nitrate, and sulfate flowing into chlorinated solvent plumes. These values were then used to calculate the amount of hydrogen equivalents and potential for lost perchloroethylene (PCE) biodegradation represented by the inflow of these competing electron acceptors. The median and maximum mass of PCE biodegradation lost due to competing electron acceptors, assuming 100% efficiency, was 226 kg/yr and 4621 kg/yr, respectively.

KEY WORDS: chlorinated solvents, natural attenuation, biodegradation, reductive dechlorination, electron acceptors, sustainability

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