Degree

Doctor of Philosophy (PhD)

Department

Department of Civil & Environmental Engineering

Document Type

Dissertation

Abstract

The Pleistocene period significantly contributed to the formation of alluvial aquifer worldwide. These productive aquifers are crucial for domestic, industrial, and agricultural water supplies. The Mississippi River Valley alluvial aquifer (MRVA), a principal aquifer in the U.S., is crucial for national food security and global agricultural supply. This study aims to characterize the subsurface architecture of the MRVA, thereby enhancing fundamental understanding of sedimentological processes involved in the genesis of glacio-fluvial aquifers worldwide. The research objectives are threefold: (1) to provide a detailed characterization of the MRVA; (2) to develop 3D geostatistical methods for geological modeling; and (3) to develop a data fusion workflow that integrates airborne electromagnetic (AEM) data and well logs for enhanced alluvial characterization.

Firstly, the MRVA is characterized using 73,000 boreholes to distinguish three lithofacies: fine-grains, fine-medium sands, and graveliferous sands. The MRVA basal configuration is influenced by bedrock formations and geodynamic processes, such as faulting, salt dome intrusion, and contemporary earthquakes. The top of graveliferous sands reveals complex surface processes during Pleistocene-Holocene transition in the Lower Mississippi Valley (LMV). The impact of geologic controls on groundwater resources of the MRVA are evaluated from the aspects of groundwater quantity and quality, hydrologic connectivity with other aquifers and surface waters, and lithological heterogeneity.

Secondly, two geostatistical methods—indicator interval kriging and ordinary interval kriging—are developed to efficiently conduct 3D borehole-based lithological modeling and AEM resistivity interpolation. Both methods consider 3D anisotropies between two orthogonal components—a horizontal plane and a vertical axis—with a minimized smoothing effect. A new 3D interval semivariogram is developed. The comparison of geostatistical methods—including interval kriging, 2.5D kriging, 3D kriging, and SNESIM—is facilitated.

Thirdly, a novel resistivity-to-multi-lithofacies (R2ML) workflow incorporates geologic constraints from well logs and geological observations, enabling a multi-lithofacies alluvial characterization and effectively addressing the complexities associated with AEM utilization. This workflow is applied to a case study in Shellmound, Mississippi.

Overall, by serving as a comprehensive study, the MRVA provides a rich dataset and conceptual framework that can be applied to glaciofluvial aquifers worldwide, enhancing the fundamental understanding of these complex and vital groundwater resources.

Date

3-27-2025

Committee Chair

Tsai, Frank T.-C.

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