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REMEDIATION OF CHLORINATED ETHENES IN FRACTURED SANDSTONE BY NATURAL AND ENHANCED BIOTIC AND ABIOTIC PROCESSES: A CRUSHED ROCK MICROCOSM STUDY
Yu, R., R.G. Andrachek, L.G. Lehmicke, and D.L. Freedman.
Science of the Total Environment 626:497-506(2018)

Most of the mass of TCE and cis-DCE at a fractured sandstone aquifer resides within the rock matrix. Strategies to restore groundwater to pre-existing conditions are severely limited by back diffusion. A microcosm study using crushed rock and groundwater from the site was performed to assess biostimulation and natural attenuation. Lactate, hydrogen release compound® (HRC), and emulsified vegetable oil (EVO) significantly increased the rate of TCE reduction to cis-DCE. Lactate also stimulated dechlorination of cis-DCE to VC and ethene, suggesting the presence of indigenous Dehalococcoides. Illumina sequencing and qPCR analyses suggest that reductive dechlorination of TCE to cis-DCE is mediated by Geobacter spp. while Dehalococcoides spp. perform reduction of cis-DCE to VC and ethene. The rate of VC reduction to ethene was much slower than the reduction of TCE to cis-DCE and cis-DCE to VC, indicating the indigenous Dehalococcoides perform the final step cometabolically and confirmed in enrichment cultures fed with only VC. Abiotic transformation of TCE and cis-DCE was observed based on accumulation of 14C-labeled products from 14C-TCE and 14C-cis-DCE. Based on accumulation rates for 14C-products in unamended microcosms, pseudo-first-order rates for abiotic transformation were 0.038/yr for TCE and 0.044/yr for cis-DCE, rates potentially sufficient to support natural attenuation in this diffusion-controlled system. See more on this study in R. Yu's dissertation at https://tigerprints.clemson.edu/all_dissertations/2019/.



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