REACTIVE TRANSPORT OF URANIUM IN SUBSURFACE: MODELING BIOGEOCHEMICAL DYNAMICS AND IMPACT OF FIELD SCALE HETEROGENEITY

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2022-11-30

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Gökçe, Selin

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The concept and role of aquifer heterogeneity have received considerable attention to understand the behavior of contaminant transport in subsurface environments. Although it has been proven that heterogeneity has significant control over quantithe fication of processes, the extent of this impact is yet to be studied. The main objective of this thesis is to investigate the impact of physical and chemical heterogeneity in understanding biogeochemical processes of contaminants, coupled with advective, dispersive transport in situ with mixing limitations. This study is particularly focused on an example of uranium behavior, where especially coupled bioreduction reactions with uranium reoxidation process in the presence of Fe (III) hydroxides are considered. Model simulation results have shown that neglecting spatial heterogeneity might lead to an overestimation of uranium bioremediation in the subsurface environment, where physical heterogeneity has observed to have a greater impact than chemical heterogeneity in the absence of adsorption reaction incorporations. On the other hand, when adsorption of uranium is included, the significance of chemical heterogeneity is more pronounced. Thus, when potential adsorption of contaminants is ignored in a chemically heterogeneous environment, the concentrations might be underestimated. The underestimation is seen to be more pronounced especially in the low hydraulic conductivity zones. The impact of the oxidation and reduction reactions are particularly enhanced in the zones with highest mixing, whereas the limited mixing within the low hydraulic conductivity zones remain with limited or no reaction potential. This mixing limitation impact is especially highly pronounced in chemically heterogeneous environments.

Subject Keywords

Heterogeneity, Reoxidation, Biogeochemical Processes, Uranium, Reactive Transport Modeling

URI

https://hdl.handle.net/11511/101291

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

S. Gökçe, “REACTIVE TRANSPORT OF URANIUM IN SUBSURFACE: MODELING BIOGEOCHEMICAL DYNAMICS AND IMPACT OF FIELD SCALE HETEROGENEITY,” M.S. - Master of Science, Middle East Technical University, 2022.