NONEQUILIBRIUM DESORPTION OF TCE: A FIELD-SCALE INVESTIGATION

摘要

The purpose of this work is to study the desorption of dense, nonaqueousphase liquids (DNAPLs), TCE in particular, from solid particles in field scale heterogeneous aquifers upon their remediation. A computer program, capable of simulating the fate and transport of NAPLs in porous media, has been developed to work under nonequilibrium sorption conditions. The model has been applied to a field site at Hill Air Force Base, Utah, which has been contaminated by DNAPLs. The simulated domain was 155 ft long, 60 ft wide, and 15.5 ft thick. This thickness represents only the saturated zone of the aquifer. Changes in permeability, grain-size distribution, and sorptive properties throughout the site have been obtained experimentally and incorporated into the model. Immediately after the aquifer cleanup, the DNAPL concentration in the aqueous phase was assumed to be zero, and this was considered to be the zero time for the simulation. Results show that, with an increase in time, the TCE diffused out of the solid particles, forming a plume. The rate of contaminant diffusion was observed to be very fast at the start and followed by a very slow stage, with a number of years required for substantial desorption of the contaminant from the solid particles. There were local variations in contaminant concentration in the fluid phase across the site due to aquifer heterogeneity.