Assessment of a cryogenic coring method to preserve depth-discrete distributions of trichloroethylene and volatile reaction products in a low-permeability aquitard
Back diffusion of trichloroethylene (TCE) from low permeability zones (LPZs), such as clay aquitards, presents a challenge in attainment of site cleanup goals. There is not a clear understanding of the extent by which naturally occurring reactions can attenuate TCE and its daughter products within the LPZs. In this study, a soil coring method that freezes the soil in-situ (a.k.a., cryogenic coring) was utilized to measure depth-discrete distributions of TCE and its volatile reaction products through a TCE-impacted silty clay aquitard. The results were compared with those from adjacent soil cores taken using a conventional coring approach, and found the two coring methods recovered statistically equivalent concentrations of select volatiles across most depths. Biotic reductive dechlorination was found to be the dominant TCE reaction pathway at the site, and concentrations of TCE, cis-1,2-dichloroethylene (DCE), vinyl chloride (VC), ethane, and methane were all compared between the two coring methods. Benefits of the cryogenic coring were better recovery of dispersed sand layers and more variable concentration profiles for TCE, DCE, and VC.