Effects of grain-scale mass transfer on the transport of volatile organics through sediments .2. Column results

Trichloroethylene (TCE) elution profiles for purged and unswept columns are presented and simulated with the Distributed Dual Diffusion Model (DDDM) presented in the first of this two-paper series. Elution profiles were measured at 15, 22, 30, and/or 60 degrees C for a silica gel, a Livermore sand fraction, a Livermore clay and silt fraction, a Santa Clara sediment, and/or a Norwood soil, all at 100% relative humidity. Advection and dispersion control TCE transport through the vapor phase of purged columns. Diffusion controls TCE transport through the vapor phase of unswept columns. For both purged and unswept columns a fast and a slow desorbing fraction of TCE were observed. The DDDM effectively simulated both of these fractions. For the fast fraction the DDDM predicted desorption with no fitting parameters. For the slow fraction the DDDM was not predictive but it simulated desorption using either a single (for silica gel) or a gamma distribution (for soil and sediments) of micropore diffusion rate constant(s) and a micropore capacity factor. Micropore capacity factors obtained by fitting the DDDM to purged column results were used to predict the onset of slow desorption in unswept columns of the same solid.