A LABORATORY ESTIMATION OF DIFFUSION AND ADSORPTION COEFFICIENTS FOR SEVERAL VOLATILE ORGANICS IN A NATURAL CLAYEY SOIL

A laboratory diffusion-test estimation of the diffusion coefficient (D) and the adsorption coefficient (K(d)) for several volatile organic species in a saturated, relatively undisturbed, clayey soil is presented. The species considered were acetone, 1,4-dioxane, aniline, chloroform and toluene, at maximum concentrations ranging from 200 to 300 mg L-1. In addition to the diffusion tests, batch tests were performed for aniline, chloroform and toluene, and the resulting K(d)-values were compared with those estimated from the diffusion tests. For the more soluble species (acetone, 1,4-dioxane and aniline) D- and K(d)-values were readily inferred from the diffusion-test results and are considered to accurately represent diffusion through the soil and adsorption onto the soil solids under the conditions imposed. For the hydrophobic species (chloroform and toluene), the inferred D- and K(d)-values from the diffusion test are significantly influenced by adsorption of the species onto the diffusion cell materials, resulting in unreasonably high D- and K(d)-values. However, it is shown that by combining the results of both batch tests and diffusion tests, an upper and lower bound estimate of D and K(d) may be obtained.