Modeling flow within a fractured rock aquifer using electrical conductivity measured through ground penetrating radar

Solving transport problems in fractured rock has proved ambiguous and unreliable, partly since the groundwater flow field in a fracture is highly heterogeneous. Surface Ground Penetrating Radar (GPR) was used to image heterogeneous flow in a bedding plane fracture. Electromagnetic wave amplitudes were reflected from the fracture due to the contrast in electrical properties of the rock and the water in the fracture. Flow paths were imaged by injecting NaCl as a tracer, which increased the reflection amplitudes of the water in the fracture. An experimental relationship was established between radar amplitude and the electrical conductivity of the water in the fracture. Using this relationship, maps of the electrical conductivity of the water in the fracture were created. Imaging of both the NaCl tracer and native groundwater in the fracture was found to be repeatable. The reflection amplitude was a predictable function of both fracture aperture and saline concentration.