Utilizing Electrical Conductivity for Characterizing Hydrogeologic Properties - Appendix

A variety of methods utilizing geophysical tools have been developed to characterize fundamental subsurface material properties. Relationships between measured values and material properties are often defined through empirical equations. Mapping fluid distribution and movement within an aquifer can help to identify changes in porosity and permeability and to define preferential flow paths. I relate changes in fluid type and properties within pore spaces to changes in measured electrical properties, specifically electrical conductivity. In synthetic and field experiments, ground-penetrating radar (GPR) is used to map the location and movement of conductive salt tracers introduced into high porosity sand layers. Conductivity increases the attenuation of the GPR signal. Using a novel surface-based time-lapse tomographic approach, increases in GPR attenuation can be mapped to areas of increased conductivity. Electrical conductivity can also be used with low frequency methods. In a laboratory experiment, I use converted electric to elastic energy in a method called electroseismics to image fluid boundaries between water and a NAPL (non-aqueous phase liquid) with acoustic energy. Acoustic energy originates from the top and bottom of the introduced NAPL layer allowing for the imaging of very thin contaminant layers. Both methods show that time-lapse data collection can reveal subtle changes in the concentration and location of fluids within the pore space that may otherwise be missed