Zhenxue Dai (Committee Member), David Dominic (Committee Member), Mark Goltz (Committee Member), Chao Cheng Huang (Committee Member), Robert Ritzi (Advisor), Mateen Rizki (Committee Member)
Doctor of Philosophy (PhD)
This dissertation addresses the transport of reactive solutes in groundwater. The goal is to better link reactive transport processes to what is known about sedimentary architecture. New forms of Lagrangian-based models for the processes of retardation and dispersion are derived through linking the models to hierarchical and multiscale sedimentary architecture. This allows for a fundamental understanding of how these processes arise from the hierarchical architecture of sedimentary facies, and allows for a quantitative decomposition of these processes into facies-related contributions at different scales within the hierarchy.
The main focus is on reactive transport characterized by a high Damkohler number, DN, in which the transport processes are controlled by equilibrium sorption. Reactive transport characterized by a low DN, in which transport processes are controlled by the rate of kinetic mass transfer, is also considered.
For the high DN case, the reactive plume behavior is assumed to be controlled by linear-equilibrium sorption and the heterogeneity in both the log permeability, Y=ln(k), and the log sorption distribution coefficient, Ξ=ln(Kd). Heterogeneity in Y and Ξ arises from sedimentary processes and is structured by the consequent sedimentary architecture. The spatial auto- and cross covariances for the relevant attributes are linear sums of terms corresponding to the probability of transitioning across stratal facies types defined at different scales. Unlike previous studies that used empirical relationships for the spatial covariances, here the model parameters are developed from independent measurements of physically quantifiable attributes of the stratal architecture (i.e., proportions and lengths of facies types, and univariate statistics for Y and Ξ). Nothing is assumed about Y - Ξ point correlation; it is allowed to differ by facies type. However, it is assumed that Y and Ξ variance is small but meaningful, and that pore-scale dispersion is negligible. The time-dependent retardation and dispersion are functions of the effective ranges of the cross-transition probability structures (i.e., the ranges of indicator correlation structures) for each relevant scale of stratal hierarchy. The well-documented perchloroethene (PCE) tracer test conducted at the Borden research site is used to illustrate the models. The models were parameterized with univariate statistics for Y, Ξ of (PCE), and proportions and lengths of lithologic facies types defined at two scales within a two-level hierarchical classification. The model gives a viable explanation for the observed time-dependent retardation and dispersion of the PCE plume, and thus the processes can be explained by the equilibrium sorption and the heterogeneity in permeability and sorption coefficient. The plume velocity and the effective retardation stabilized at a large-time limit after the plume centroid had traveled a distance that encompassed the effective ranges of the cross-transition probability structure. By quantitatively decomposing the retardation and dispersion into facies-related contributions, it was shown that the retardation and the time-dependent rate of spreading were mostly defined by the cross-transition probability correlation structure imparted by the proportions and sizes of the larger-scale facies types. The weak Y - Ξ cross-correlation was shown to not significantly affect the retardation, however, it did significantly impact the spreading rate.
In unconsolidated sedimentary deposits like the Borden aquifer, texturally defined facies types can be effectively used to characterize heterogeneity in both hydraulic and reactive attributes. However, in bedrock flow systems it is the type of reactive minerals and their spatial distributions which exert the strongest control on reactivity.
Department or Program
Department of Earth and Environmental Sciences
Year Degree Awarded
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