HR: 17:00h
AN: H44A-05    [Abstracts]
TI: Relating GPR Signal Response to Fracture Fluid Salinity
AU: * Tsoflias, G P
EM: tsoflias@ku.edu
AF: The University of Kansas, 1475 Jayhawk Blvd., Room 120, Lawrence, KS 66045, United States
AU: Becker, M W
AF: University at Buffalo, 876 Natural Science Complex, Buffalo, NY 14260, United States
AU: Bourque, S R
AF: University at Buffalo, 876 Natural Science Complex, Buffalo, NY 14260, United States
AB: Predicting flow and transport in fractured bedrock remains a challenging problem. The spatial heterogeneity of flow (channeling) is commonly observed at seepage faces, but in-situ behavior is poorly understood. Time-lapse GPR amplitude differencing has been used to detect saline tracers in fractures and to identify groundwater flowpaths qualitatively. However, GPR observations of saline tracers in fractures have not been correlated quantitatively to meaningful hydrologic parameters, such as fracture aperture and fluid electrical conductivity. We investigate the relationships between GPR signal amplitude, phase, and frequency with fracture aperture and fluid salinity. Our research shows characteristic and quantifiable GPR responses that can be correlated to fracture properties. We use analytical modeling, numerical simulations, and field observations at a fractured sandstone aquifer in order to examine these relationships. We monitor the response of multifrequency GPR reflected signals from a water-saturated horizontal fracture at 7 m depth that we inject with saline tracers of increasing electrical conductivity. GPR response is simulated analytically and numerically. Although the fracture is a thin layer with millimeter scale aperture, increasing fluid conductivity results in greater EM signal wavenumber magnitude, which in turn decreases the signal wavelength and improves its thin layer resolution capabilities. These GPR signal responses from a thin layer are more pronounced in lower frequency signals. As shown by modeling, field data exhibit increasing signal amplitude and increasing phase lag as a function of increasing fluid electrical conductivity. The GPR amplitude and phase responses are detectable in the field and predictable by EM theory and modeling, therefore, they can be related to fracture aperture and fluid salinity for hydrologic investigations of fractured rock flow and transport properties.
DE: 1828 Groundwater hydraulics
DE: 1829 Groundwater hydrology
DE: 1835 Hydrogeophysics
DE: 1895 Instruments and techniques: monitoring
DE: 5104 Fracture and flow
SC: Hydrology [H]
MN: 2007 Fall Meeting