Stochastic Analysis of Adsorbing Solute Transport in Two-Dimensional Unsaturated Soils

Adsorbing solute transport in two-dimensional heterogeneous unsaturated soil was studied by means of stochastic numerical simulations. Heterogeneities in the soil's hydraulic properties and in the adsorption isotherm were simulated using random fields having specified statistical structures. Macrodispersion was analyzed using the spatial moments of numerically generated solute plumes. Among different realizations of the heterogeneous soil, the discrepancies between second-order moments and macrodispersion coefficients were large. Macrodispersivities of unsaturated soils increased with decreasing water content. Also, heterogeneous adsorption of solute enhanced the solute spreading. When the adsorption coefficient was negatively correlated with the saturated hydraulic conductivity, solute spreading was greater than when adsorption was uncorrelated or positively correlated with the conductivity.

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