REACTIVE SOLUTE TRANSPORT MODELING IN GROUNDWATER

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The reactive solute transport with a variable exchange selectivity coefficient was investigate based on undisturbed soil column experiments and simulation results. The experimental results indicated that the selectivity coefficients for Ca-Na and Ca-Mg exchange could be considered constant, while the slectivity coefficient for Ca-K exchange increased with the equivalent fraction of K in the solid phase This relationship was approximated by an exponential regression equation, which was incorporated in the simulation model developed in this study. The use of a variable selectivity coefficient for the equivalent fraction in the solid phase resulted in an acceptable prediction of cation concentration distributions for both the liquid and the solid phases. In contrast, the use of a constant selectivity coefficient for Ca-K exchange provided a less satisfactory prediction for the spatial distribution of cation concentrations in the solid phase. Therefore, it is concluded that the model performance can be improved by using a bariable selectivity coefficient for the soil under consideration. A variety of mathematical models for the determination of the fate of reactive solutes in soild has been proposed. The reliability of these models was discussed in comparison with experimental results. It should be emphasized that the soil chemical paramenters used in these models play an important role in identifying which mechanisms control the solute transport in soils.