MASS FLUX STATISTICS OF KINETICALLY SORBING SOLUTE IN HETEROGENEOUS AQUIFERS - ANALYTICAL SOLUTION AND COMPARISON WITH SIMULATIONS

Variability in hydraulic properties and various mechanisms resulting i n rate-limited mass transfer influence field scale solute transport in aquifers. In this study analytical expressions are presented for the expected value and variance of the mass Aux for a solute undergoing a nonequilibrium sorption reaction controlled by first-order kinetics. T he uncertainty in the mass flux, expressed through the variance, stems from finite solute injection volumes compared to the hydraulic conduc tivity integral scale. Two-dimensional numerical simulations are perfo rmed under statistically identical conditions to the ones assumed in t he derivation of the analytical results. Two cases of variability in t he log hydraulic conductivity are considered (sigma(Y)(2) = 0.1 and si gma(Y)(2) = 1.0). The analytical model and the numerical simulations y ield comparable predictions of the mass flux statistics for both varia bility cases. Comparing conservative and kinetically sorbing solute an apparent effect of sorption kinetics is to lower the discrepancy betw een the analytical model and the simulations due to increased spreadin g of the solute resulting from rate-limiting mass transfer.