MAPPING SAND LAYERS IN CLAYEY TILL USING CROSSHOLE GROUND-PENETRATING RADAR

Fluid transport through clayey tills governs the quantity and quality of groundwater resources in the Northern hemisphere. This transport is often controlled by a three-dimensional network of macropores (biopores, fractures and sand lenses) within the clayey till. At present, a non-destructive technique that can map and characterize the sand-lens-network does not exist, and full excavation or extensive drilling is therefore the only solution. Acquisition and modeling of crosshole ground penetrating radar (GPR) may provide the answer to this problem. We collected one- and two-dimensional crosshole GPR data at a field site in Denmark between four 8-m-deep boreholes with horizontal distances varying between 2.64–5.05 m. We show that the depth, thickness, and tilt of a coherent sand layer within the clayey till (approximately 0.4–0.6 m thick), as well as the underlying sand formation, can be mapped accurately using the GPR data. We efficiently identify the sand as a highly resistive section with high electrom...