Short Communication Abiotic dechlorination in rock matrices impacted by long-term exposure to TCE Charles E. Schaefer a,⇑ , Rachael M. Towne a , David R. Lippincott a , Pierre J. Lacombe b , Michael E. Bishop c , Hailiang Dong c a CB&I Federal Services, LLC, 17 Princess Road, Lawrenceville, NJ 08648, United States b U.S. Geological Survey, 3450 Princeton Pike, Suite 110, Lawrenceville, NJ 08648, United States c Department of Geology and Environmental Earth Science, Miami University, Oxford, OH 45056, United States highlights  TCE abiotic dechlorination reactions were measured in rock matrices.  Abiotic dechlorination of TCE occurred in rock matrices exposed to TCE for decades.  Reaction rate constants were similar to those observed in rock not exposed to TCE.  Abiotic reactions are expected to have an impact on TCE transport in rock matrices. article info Article history: Received 15 April 2014 Received in revised form 29 July 2014 Accepted 3 August 2014 Handling Editor: Klaus Kümmerer Keywords: TCE Bedrock Matrix Diffusion Dechlorination abstract Field and laboratory tests were performed to evaluate the abiotic reaction of trichloroethene (TCE) in sed- imentary rock matrices. Hydraulically conductive fractures, and the rock directly adjacent to the hydrau- lically conductive fractures, within a historically contaminated TCE bedrock aquifer were used as the basis for this study. These results were compared to previous work using rock that had not been exposed to TCE (Schaefer et al., 2013) to assess the impact of long-term TCE exposure on the abiotic dechlorination reaction, as the longevity of these reactions after long-term exposure to TCE was hitherto unknown. Results showed that potential abiotic TCE degradation products, including ethane, ethene, and acetylene, were present in the conductive fractures. Using minimally disturbed slices of rock core at and near the fracture faces, laboratory testing on the rocks confirmed that abiotic dechlorination reactions between the rock matrix and TCE were occurring. Abiotic daughter products measured in the laboratory under controlled conditions were consistent with those measured in the conductive fractures, except that pro- pane also was observed as a daughter product. TCE degradation measured in the laboratory was well described by a first order rate constant through the 118-d study. Observed bulk first-order TCE degrada- tion rate constants within the rock matrix were 1.3  10 8 s 1 . These results clearly show that abiotic dechlorination of TCE is occurring within the rock matrix, despite decades of exposure to TCE. Further- more, these observed rates of TCE dechlorination are expected to have a substantial impact on TCE migra- tion and uptake/release from rock matrices. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The importance of contaminant diffusion from hydraulically conductive fractures into rock matrices, and the subsequent back-diffusion of contaminant from the rock matrix into conduc- tive fractures after source depletion, has been identified and dis- cussed by several researchers (Feenstra et al., 1984; Mutch et al., 1993; Fomin et al., 2010; Haddad et al., 2012; Rodríguez and Kueper, 2013). Studies have suggested that back-diffusion of con- taminants from rock matrices to water-bearing fractures will likely inhibit attainment of remedial goals at many bedrock sites (Lipson et al., 2005; Seyedabbasi et al., 2012). However, as noted by West and Kueper (2010), even relatively slow contaminant degradation within the rock matrix can have a substantial mitigating effect on the impacts of back-diffusion on the contaminant plume. Abiotic reactions between chlorinated solvents such as trichloro- ethene (TCE) and ferrous minerals have been reported (Butler and http://dx.doi.org/10.1016/j.chemosphere.2014.08.005 0045-6535/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +1 (609) 895 5372; fax: +1 609 895 1858. E-mail address: charles.schaefer@cbifederalservices.com (C.E. Schaefer). Chemosphere 119 (2015) 744–749 Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere