ABSTRACT

Three-dimensional characterization of subsurface hydrogeologic properties is critical for understanding groundwater flow and has implications in water resources development, and engineering and/or environmental studies. Major cities rely on fractured anisotropic carbonate aquifers, such as the Edwards aquifer in Texas. In order to predict flow in these aquifers, fracture network and rock matrix hydraulic properties must be characterized accurately.

Overlapping ground-penetrating radar (GPR) surveys, consisting of one high-resolution three-dimensional data volume, and four two-dimensional lines, were collected over a fractured Silurian dolomite aquifer in Door County, Wisconsin. 100 MHz and 200 MHz center frequency surveys provided a depth of investigation of 20 m and 12 m, respectively, and vertical resolution in the order of decimeters. The data successfully imaged varying carbonate lithofacies, lithologic discontinuities, bedforms, and fractures in both the unsaturated and saturated sections of the aquifer. Prominent flow conduits had been identified previously by a dense network of monitoring wells, pump tests and tracer tests, making this an excellent site to test the GPR system. These conduits were clearly identifiable in the ground-penetrating radar data volumes and delineated in three-dimensions by distinct continuous reflections.