3D Gpr Imaging Of A Sand-Gravel/Clay Boundary At Hill Air Force Base, Utah

3D Ground Penetrating Radar survey (GPR) defines the boundary between a sand/gravel unit and an<br>underlying clay aquitard at Hill Air Force Base, Utah, Despite attenuation due to an artificial clay cap<br>approximately 2 ft thick, a strong reflection from a depth of 20-30 ft occurs. Lateral and vertical resolution along<br>the boundary are approximately 2 ft and 1 ft, respectively. There is abrupt topographic variation of 5 ft over<br>distances of 20 ft or less in the surface of the clay layer. This variation may have a major influence on ground<br>water movement and on the local accumulation of chlorinated organic pollutants.<br>This study shows that a three-dimensional GPR image provides far better definition of geologic<br>boundaries than does projection of soil boring logs into two-dimensional profiles. In the present case this highresolution<br>image provides a detailed estimate of target depths for future soil borings and will facilitate the choice<br>of the location of cells to be used for testing new remediation techniques.