Laboratory determination of diffusion and distribution coefficients of contaminants using undisturbed clayey soil

This paper describes a technique for determining the diffusion coefficient and the distribution coefficient for contaminants using saturated, intact (undisturbed) clayey soil samples. The technique is illustrated with reference to a number of laboratory tests involving advective-diffusive migration of potential contaminants through an intact clayey soil from Sarnia, Ontario. An important aspect of the proposed technique is that the mass of contaminant in the system is kept constant and so significant decrease in source leachate concentration occurs during each test. A simple theoretical model is used to analyze this case and it is shown that this phenomenon can be used to deduce both the diffusion coefficient and the distribution/partitioning coefficient from a single test. Parameters are deduced for a number of salt solutions passing through the clay from the Sarnia area. On the basis of these tests it is suggested that for the Sarnia soil and advective velocities up to the maximum examined (0.035 m/a), mechanical dispersion does not measurably affect the magnitude of the "coefficient of hydrodynamic dispersion" (i.e., there is no significant dispersion). It is also suggested that the effective porosity corresponds to that deduced from the water content of the soil. Key words: contaminant migration, soil, laboratory study, experimental, analysis, diffusion, advection, clays, groundwater.