Enhancement of soil-bentonite barrier performance with the addition of natural humus

To assess the performance of a modified slurry wall material, laboratory-scale contaminant transport experiments were conducted with trichloroethylene (TCE) and soil-bentonite (SB) amended with the addition of natural humus. Low-flow column studies were performed using flexible wall permeameters, with the primary emphasis on the measurement of spatial contaminant distributions from columns operated for different durations. Batch experiments were also performed to assess the sorption characteristics of the modified SB. Penetration of TCE into the amended SB was significantly retarded, suggesting that the addition of organic-rich material can be an effective strategy for improving barrier performance. The advective-dispersive-reactive equation (ADRE) gave good predictions of the observed contaminant spatial distributions in the columns provided that nonequilibrium sorption was included in the model formulation. The calibrated TCE diffusion coefficient corresponded to a porosity-corrected hindrance factor of 2.7, which is similar to other studies of barrier materials. However, the sorption distribution coefficient estimated from the column data was approximately one half the value measured in the batch isotherm test. Although the reason for this discrepancy was not identified, the results suggest that caution should be exercised in extrapolating the performance of strongly sorbing barrier materials from batch test data. (C) 2000 Elsevier Science B.V.