Oscillatory Hydraulic Tomography: Numerical Experiments and Laboratory Studies

Oscillatory hydraulic tomography (OHT) has been proposed to be an effective methodology for aquifer heterogeneity characterization. In this approach, sinusoidal or periodic signals are generated at pumping locations and pressure response data are collected at observation locations for tomographic analysis. In this study, I implemented both numerical modeling and laboratory sandbox experiments to evaluate the performance of OHT.;In the first part of my study, sandbox experiments are conducted and analyzed tomographically to evaluate the performance of OHT on imaging aquifer heterogeneity. In this section, both homogeneous and heterogeneous sandbox aquifers were packed for tomographic study. By collecting oscillatory data due to multi-frequency OHT simulation, a much more detailed description of aquifer heterogeneity can be obtained when compared to the single frequency case. Different pumping and observation location combinations are also explored with the goal of providing guidelines for potential field OHT application. The OHT approach was able to successfully characterize both homogenous and heterogeneous aquifers, though the ability to detect small, low-contrast micro-scale heterogeneity may be limited.;In the second part of my study, the OHT approach was further investigated for use in mapping NAPL spreading within an aquifer. This investigation is based upon the fact that aquifer measured effective hydraulic conductivity (K) changes with the fluid properties (e.g., density and viscosity). Aquifer heterogeneity before and after NAPL spreading were compared and NAPL source zone distributions throughout time were obtained by inverting for differences in effective K heterogeneity, comparing snapshots before and after the NAPL has spread.;In the third part of my study, I used sandbox experimental data to evaluate a phenomenon observed in the field in which effective hydraulic parameters appear to be dependent on the oscillatory testing period. Numerical experiments on OHT are also conducted to study the frequency-dependence of estimating effective hydraulic conductivity in between a single pumping and observation location. Results generated from numerical and laboratory experiments are not entirely consistent with those from field studies. I propose an alternative hypothesis for explaining these observations and suggest potential directions for future research.;This dissertation provides a solid experimental evaluation of the effectiveness of Oscillatory Hydraulic Tomography under various conditions. With the high-resolution imaging reported in this dissertation, this technique could be one of the most reliable tools for detailed field investigation of aquifer heterogeneity.