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

The role of degree of saturation on the coefficient of diffusion of contaminants in the aqueous phase is presented and theoretical models for predicting the coefficient of diffusion at any degree of saturation are described. Three predictive models were developed based on three different diffusion modes: diffusion in parallel and series arrangements and combination of both. Diffusion tests were conducted on a sand at various water contents ranging 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 coefficient of potassium with a decrease in degree of saturation. The functional relationship between the normalized diffusion coefficient for potassium and the degree of saturation is slightly nonlinear. The results for chloride also showed a decreasing trend, although the data were quite scattered and further verification is needed. Model verification based on the results for potassium showed that among the three models proposed, the model which combines the diffusion pathways in parallel and series arrangements provides the best fit to the experimental data.