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theses

Hydrogeologic processes of the vadose zone have important implications for many environmental issues including agricultural practices such as irrigation, water resource management, and contaminant transport, among others. Current methods for characterizing the vadose zone involve invasive and sparse data collection techniques. While geophysics has the potential to measure hydrogeologic processes non-invasively, current geophysical measurements have not been widely used to study the vadose zone. Of interest in this study is developing nuclear magnetic resonance (NMR) as a means to investigate the vadose zone. The first laboratory study in this thesis investigated the NMR relaxation time versus saturation curve of unconsolidated geologic media for samples exhibiting NMR relaxation in different diffusion regimes. Six synthetic sands were created that varied in both grain size and total iron content, in order to simulate different pore size distributions and surface relaxivities. The relative relaxation time versus saturation curve was found to be linear for fast diffusion regime samples and a power law relationship for samples outside the fast diffusion regime. This study proves that samples in different diffusion regimes have different relaxation time versus saturation relationships. The second laboratory study investigated the response in the NMR measurement due to hysteresis caused by drainage and imbibition. The water retention curves, WRC, of four synthetic sands and two loamy sand soils were measured with a porous plate experiment during both drainage and imbibition. Hysteresis was observed for the WRC’s of all samples, but not observed for NMR parameters versus water content. This study proves that NMR is insensitive to differences in the WRC as expressed during drainage and imbibition. Surface NMR is an NMR field measurement, which is capable of measuring a vertical profile of water in the subsurface, and offers a new way of studying the vadose zone. The third study investigated the ability of signal cancellation algorithms to remove the signal originating from a surface water layer present during a surface NMR measurement. An infiltration experiment resulted in a scenario in which the measurement loop was submerged in a layer of surface water. The algorithms presented in this study were capable of removing the signal originating from the surface water layer, resulting in a usable dataset for monitoring infiltration.

ETD_6958

Ph.D.

Includes bibliographical references

by Samuel O. Falzone

doi:10.7282/T3P84DZ3

ETD doctoral

The author owns the copyright to this work.