SORPTION OF LOW-MOLECULAR-WEIGHT ORGANIC CONTAMINANTS BY FLY-ASH - CONSIDERATIONS FOR THE ENHANCEMENT OF CUTOFF BARRIER PERFORMANCE

Experimental measurements indicate that class F fly ashes have significant capacity for sorption of low molecular weight organic contaminants from aqueous solution, the capacity being related to the carbon content and to other properties specific to the fly ashes tested. Correlations of Freundlich sorption capacity parameters with the respective octanol-water partition coefficients and the aqueous solubilities of the organic contaminants were highly significant. Transient diffusion experiments verified that incorporation of fly ash into soil-bentonite cutoff barriers can impart significant capacity for contaminant retardation in these barriers. Analysis of the experimental data suggests that the sorption process is rate limited and that assumptions of local equilibrium are not appropriate in the diffusive regime of a soil-bentonite cutoff barrier. Simulations of the performance of a hypothetical soil-bentonite cutoff barrier amended with high-carbon fly ash suggest that such amendments can provide significant improvement in performance with respect to retardation of contaminant breakthrough.