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 column s are presented and simulated with the Distributed Dual Diffusion Mode l (DDDM) presented in the first of this two-paper series. Elution prof iles 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 San ta Clara sediment, and/or a Norwood soil, all at 100% relative humidit y. Advection and dispersion control TCE transport through the vapor ph ase of purged columns. Diffusion controls TCE transport through the va por phase of unswept columns. For both purged and unswept columns a fa st and a slow desorbing fraction of TCE were observed. The DDDM effect ively simulated both of these fractions. For the fast fraction the DDD M predicted desorption with no fitting parameters. For the slow fracti on the DDDM was not predictive but it simulated desorption using eithe r a single (for silica gel) or a gamma distribution (for soil and sedi ments) of micropore diffusion rate constant(s) and a micropore capacit y factor. Micropore capacity factors obtained by fitting the DDDM to p urged column results were used to predict the onset of slow desorption in unswept columns of the same solid.