Determination of diffusion and adsorption coefficients for volatile organics in an organophilic clay-sand-bentonite liner

In the design of barriers for containment of petroleum products it is essen tial to know the conditions for contaminant transport. In this work, a batc h test method was used to determine the adsorption coefficients (K-d) of be nzene, toluene, and 2-fluorotoluene (a tracer for toluene) on three soils. For Ottawa sand using soil to water ratios of 0.10-0.30 g/mL, K-d values we re 2.5-1.2 mL/g (benzene), 11.3-3.6 mL/g (toluene), and 10.9-3.7 mL/g (2-fl uorotoluene), respectively. Using organophilic clay at similar soil to wate r ratios, the K-d values were 40.9-50.0 mL/g (benzene), 154-129 mL/g (tolue ne), and 157-114 mL/g (2-fluorotoluene), respectively. K-d values for bento nite were 37.6-0.14 mL/g (benzene), 60.3-16.5 mL/g (toluene), and 51.2-33.6 mL/g (2-fluorotoluene) using soil to water ratios in the range 0.01-0.05. In general, for a given mixture, toluene was two to five times more adsorpt ive than benzene, indicating that hydrophobicity was an important factor in their adsorption. The diffusion coefficients in material comprised of 3% o rganophilic clay, 12% bentonite, and 85% Ottawa sand ranged from 0.48 x 10( -6) to 2.5 x 10(-6) cm(2)/s at 20 degreesC. These values are lower than tho se measured for natural clay with low organic carbon content.