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

To assess the performance of a modified slurry wall material, laboratory-sc ale 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, wi th the primary emphasis on the measurement of spatial contaminant distribut ions from columns operated for different durations. Batch experiments were also performed to assess the sorption characteristics of the modified SB. P enetration of TCE into the amended SB was significantly retarded, suggestin g that the addition of organic-rich material can be an effective strategy f or improving barrier performance. The advective-dispersive-reactive equatio n (ADRE) gave good predictions of the observed contaminant spatial distribu tions in the columns provided that nonequilibrium sorption was included in the model formulation. The calibrated TCE diffusion coefficient corresponde d to a porosity-corrected hindrance factor of 2.7, which is similar to othe r studies of barrier materials. However, the sorption distribution coeffici ent estimated from the column data was approximately one half the value mea sured 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 b atch test data. (C) 2000 Elsevier Science B.V. All rights reserved.