Macro and micro scale simulations of TCE diffusion in organic matter and two sediments

The remediation of volatile organic chemical (VOC) contaminated sites has proven to be very difficult, especially with the passage of time from the point of release. Times estimated for the reduction of VOC concentrations below regulatory limits are often underestimated using currently available mass transport models. The underestimations may be a result of not accounting for the hindered diffusion of VOCs in microporous regimes that are thought to exist in the organic and mineral fractions of soils. The goal of the research presented here is to examine the role of aging (length of time a soil or sediment is exposed to a contaminant) on trichloroethylene (TCE) diffusion in soil organic matter and the applicability of macro- and micro-scale simulations to model the observed behavior.; The coupled convection and diffusive mass transfer of TCE from Pahokee Muck (PM)—used as a model for soil organic matter—was measured as a function of three aging periods (i.e., 1 hour, 1 day, and 21.7 days). The results suggest that the uptake of WE continued as a function of time after adsorption breakthrough, even though additional sorption after the 24-hour aging interval could not be resolved.; A multi-pore regime mass transport (MPRMT) model was successfully used to estimate the experimental WE mass transfer rates in PM. The model accounts for the potential existence of hindered diffusional regimes and aging intervals. The fitted parameters—hindered diffusivities and associated contaminant mass fractions—suggested that there might have been a redistribution of mass rather than a continued uptake of TCE with time. The redistribution of mass may have occurred due to the macromolecular composition of PM.; MPRMT model input parameters (i.e., TCE isotherm parameters, micropore pore volume, skeletal density, and diffusivity) were estimated for PM using molecular simulations. The simulation-based estimates were accomplished using a virtual humic acid complex that was created as a surrogate for humic acid complexes in soil organic matter. The estimated parameters compared favorably with literature-based and measured (this research) values. MPRMT model estimates of mass transfer based on the virtual inputs were better than estimates made using a local equilibrium assumption.