The influence of degree of saturation on the coefficient of aqueous diffusion

The role of degree of saturation on the coefficient of diffusion of contami nants in the aqueous phase is presented and theoretical models for predicti ng the coefficient of diffusion at any degree of saturation are described. Three predictive models were developed based on three different diffusion m odes: diffusion in parallel and series arrangements and combination of both . Diffusion tests were conducted on a sand at various water contents rangin g from saturation to the residual degree of saturation using potassium and chloride ions as tracers to verify the applicability of the models. Results from the diffusion tests showed a decrease in effective diffusion coeffici ent of potassium with a decrease in degree of saturation. The functional re lationship between the normalized diffusion coefficient for potassium and t he degree of saturation is slightly nonlinear. The results for chloride als o showed a decreasing trend, although the data were quite scattered and fur ther verification is needed. Model verification based on the results for po tassium showed that among the three models proposed, the model which combin es the diffusion pathways in parallel and series arrangements provides the best fit to the experimental data.