Factors Controlling Solute Dilution in Heterogeneous Formations

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9522651 Kitanidis The objective of the proposed research is to quantify the interaction of heterogeneity in soil hydraulic conductivity, local dispersion, and other factors in controlling the temporal behavior of dilution in porous media. Although the effect of heterogeneity on the spreading of plumes of dissolved chemicals has been studied extensively, the effect of heterogeneity on dilution of contaminants remains to be determined, especially at "early" times, which are relevant in tracer tests and remediation projects. Dilution is quantified by measures such as the peak concentration and the volume occupied by solute. Spreading is quantified by the spatial second moment of the concentration distribution. In assessing environmental impacts of groundwater contamination, if is important to be able to anticipate peak concentration in addition to the spatial extent of contamination. In this work, we will conduct theoretical analysis, detailed numerical experiments, and comparisons with field data. Contaminant dilution measures will be related to the porous media constitutive parameters and, primarily, the variability of hydraulic conductivity. Predictions of dilution will be made via analytical approximations or "closures" which lead to deterministic equations and through variational analysis. The performance of the approximations will be numerically assessed and the results will be evaluated by comparison with results from field experiments. The contribution of this work will be a better understanding of the time-evolution of contaminant concentration levels in heterogeneous porous media, and guidance to the practitioner to assess dilution of contaminants in the subsurface environment.