ANALYSIS OF DIFFUSION AND SORPTION OF ORGANIC SOLUTES IN SOIL-BENTONITE BARRIER MATERIALS

A series of laboratory studies was conducted to assess the transport o f chloride, trichloroethylene (TCE), and aniline in soil-bentonite (SB ) slurry wall materials. Column transport experiments were conducted, with a primary emphasis on the measurement of spatial contaminant mass profiles within columns after 25-50 days of transport under diffusion -dominated conditions. The advective-dispersive-reactive (ADR) equatio n was found to provide good predictions of the results of the column e xperiments with calibrated diffusion parameters that were within the r ange observed by other researchers for earthen barrier materials. Howe ver, Values of the porosity-corrected hindrance factor were higher tha n those observed in; other studies of diffusive transport in SE, and s orption coefficients calibrated from the column experiments were signi ficantly lower than values measured in batch isotherm tests conducted with unconsolidated SE. A number of factors could contribute to variab ility across experiments and investigators, including differences betw een batch and column conditions, differences in experimental apparatus and design used to study diffusive transport in SE, correlation betwe en parameters in the calibration process, and the potential influence of nonequilibrium sorption in column experiments. For the design of co nventional slurry walls, it is likely that conservative predictions of organic contaminant penetration can be obtained with the ADR equation using established correlations for effective diffusion coefficients a nd neglecting sorption to barrier materials.