Ground Penetrating Radar And Electromagnetic Profiling Of Bedrock Topography At The Portsmouth Gaseous Diffusion Plant, Piketon, Ohio

Low-frequency ground penetrating radar (GPR) and electromagnetic profiling (EM-3 1 and EM-34) surveys were<br>carried out at the Portsmouth Gaseous Diffusion Plant (PGDP) in Pike County, Ohio. The primary objective of the<br>surveys was to profile sedimentary bedrock topography beneath unconsolidated fluvial and lacustrine deposits. The<br>EM surveys show high conductivity (8.5-39 mS/m) values for the unconsolidated sediments and underlying bedrock,<br>presenting a hostile environment for GPR. The low-frequency GPR, however, penetrated to bedrock depths of up<br>to 10 m, which exceeds the predictions of forward modelling. The data show that low-frequency GPR is effective<br>in this lossy-dielectric environment, and is not accurately modelled using typical low-loss assumptions.<br>The site occupies a buried channel of the late-Tertiary Portsmouth River (Figure 1). The unconsolidated deposits<br>include the clay-rich Minford formation, which extends from the surface to approximately 4 m, and the gravel and<br>clay bearing sand of the Gallia formation. The Gallia deposits are part of interbraided fluvial channels which vary<br>in thickness, and are laterally heterogeneous. It is the bedrock beneath the Gallia that is the primary target of these<br>surveys. The bedrock is generally the Sunbury Shale or, where the channel is more deeply eroded, the Berea<br>Sandstone.