Ground Penetrating Radar Investigations In Soils Containing Plinthite In the Coastal Plain Region of South Carolina, Southeastern USA.

Ground Penetrating Radar (GPR) records were collected across representative landscapes of the Upper and Middle Coastal Plain of South Carolina. GPR was used to assess the presence, concentration and varying depths to plinthite along with an underlying dense subsoil layer usually associated with the presence of plinthite. GPR was also used to help determine the within map unit variability of plinthite. Radar records obtained were generally of good to excellent interpretative quality. Observation depths were often greater than 3 meters. GPR interpretative depths to plinthite were verified with soil borings. On the Upper Coastal Plain, depths to plinthite and concentrations of plinthite were quite variable across the varying landscapes and within the same soil map units.  Inclusions of fine-loamy, kaolinitic, thermic Typic Kanhapludults (Cowarts and Barnwell soils) were often observed within soil map units classified as fine-loamy, kaolinitic, thermic Plinthic Kandiudults (Dothan soils).  On the Middle Coastal Plain, plinthite was generally observed at greater depths, but within the range of the soil map units.  An abrupt discontinuity was often observed below the plinthic layer and was readily observable in GPR records.  The abrupt discontinuity was associated with an underlying layer referred to as the “brick layer”. Gradational boundaries to the plinthic layer complicated GPR interpretations and precise depths to the contact/interface were more difficult to predict. Typically, where plinthite and iron stone were present, a more chaotic “shotgun” pattern was observed in radar records. Pebble-size iron stone concretions were normally observed in soil profiles where plinthite was observed.  Plinthite bodies and iron stone concretions were usually observed as small point reflective objects resulting in a higher amplitude signal in the radar records. The upper boundary of plinthic layers was often gradational, obscure, irregular and interpreted based on the concentration and amplitude of the plinthite. A more concise and distinct boundary was also observed in multiple radar records at numerous locations. GPR appears to be an excellent interpretative tool for soils investigations in the coastal plain region of South Carolina and areas with similar soil characteristics across the southeast USA.