We used ground penetrating radar (GPR) data to help determine the spatial distribution and the subsurface geometry of clastic dikes at the Hanford Site. This information will help to improve the understanding of the hydrological role of these ubiquitous clastic dikes at the Hanford Site. We collected 100 MHz ground penetrating radar (GPR) 3-D surface reflection data at two sites, the 216-S-16 (S-16) Pond and the Army Loop Road sites, and 2-D reflection data along a 6.9 km linear transect (Traverse site) near the Army Loop Road site. The dikes are distinguished in the GPR data by a strongly attenuated...