Science Inventory

CSIA of TCE and Daughter Products with Multiple Sources, Multiple Attenuation Mechanisms and Low Ethene

Citation:

McLoughlin, P., A. Peacock, R. Pirkle, J. Wilson, AND R. McCracken. CSIA of TCE and Daughter Products with Multiple Sources, Multiple Attenuation Mechanisms and Low Ethene. Remediation Journal. John Wiley & Sons, Inc., Hoboken, NJ, 25(1):11-21, (2014). https://doi.org/10.1002/rem.21411

Impact/Purpose:

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Description:

Monitored Natural Attenuation (MNA) was the selected remediation strategy at the former 23 England AFB (fEAFB). Previously declining concentrations of TCE, cDCE and VC recently 24 increased in selected wells. Less ethene was observed than expected on the basis of mass 25 balance. Reductive dechlorination, partial or otherwise, could not explain observed trends, so 26 the questions at fEAFB become: 1)is there a mechanism for complete TCE detoxification (i.e. 27 complete degradation to innocuous end products)? and 2)are VC and cDCE degrading? 28 Compound specific isotope analysis (CSIA) was used to investigate these questions at fEAFB. A 29 previously developed formalism was adapted to interpret the CSIA data to answer the first 30 question. Standard interpretation assuming only reductive dechlorination demonstrated 31 detoxification in 9 of the 15 contaminated wells, the interpretation developed here did so in 14. Since the active mechanisms needn’t be purely reductive, VC and cDCE may be persistent by-33 products, not degrading intermediates. For TCE, abiotic degradation (i.e. biogeochemical 34 transformation) uses 12C more preferentially than reductive dechlorination. When acting 35 together, abiotic degradation produces 12C rich chloroacetylene while reductive dechlorination 36 produces cDCE depleted in 12C that eventually accumulates to form cDCE more depleted than 37 the undegraded TCE. CSIA data interpretation assuming only reductive dechlorination does not 38 consider this. That assumption could lead to the false conclusion cDCE and/or VC was 39 degrading. Criteria are established to identify cDCE and VC degradation at sites where it is not 40 appropriate to rule out abiotic degradation.