I Wanna Rock!

York Soil Survey Staff Search for Bedrock

by Lance Brewington, NRCS Soil Scientist

Caleb Gulley, Bishopville Soil Scientist, maneuvers the GPR unit while NRCS Soil Scientist Lance Brewington, Wes Tuttle (from the National Soil Survey Center), and Dennis DeFranceso (retired) follow along.

During the week of December 18-21, 2006, the York Soil Survey Office invited Wes Tuttle of the USDA-NRCS National Soil Survey Center in Wilkesboro, NC, to visit South Carolina and use geophysical methods to assess depth to bedrock and soil characteristics in two areas of York County. One of the areas was south of Rock Hill, in the broad flats, where the Iredell soils are found. The Iredell series consists of moderately well drained, very slowly permeable soils often found on uplands throughout the Piedmont. The second area was in the northern parts of York County, in the Kings Mountain National Military Park.

Iredell soils were investigated after the discovery of a soft bedrock contact that occurred consistently around 20 to 40-inches deep. “We felt that it was also a good idea to pursue this bedrock study because in addition to the transect data that was recorded, the data from this study could reinforce the transect data by supporting what was found with an auger,” explained Tuttle. The Iredell series does not allow for the bedrock contact and thus, a new series to accommodate for the bedrock was born—the Brewback series. The tool that Tuttle used for exploring this area is the Electromagnetic Induction (EMI) meter. This instrument allowed him to show a bedrock contact at depths of 20 to 40-inches, which reinforces data collected with an auger.

In the study at Kings Mountain National Military Park, the Ground Penetrating Radar (GPR) was utilized. The soil scientists agree that the GPR is definitely a tool that works you to the core, especially if you’re the one dragging it up and down the mountains! The GPR unit measures depths to restrictive layers; in this case bedrock. The GPR unit was not used in the Iredell soils due to their high clay content which produced inaccurate readings with this device. The unit weighs approximately 40 pounds, so you can imagine dragging 40 pounds with no wheels up and down mountains.

According to aerial photos, the study area is very steep compared to the surrounding area, yet it is all mapped as one soil type with the same slope breaks. The results of this study showed that the bedrock depths were less than 20 inches along the ridges and 20 to 40 inches on the side slopes. Depending on the size of the ridges, the group will either map out two separate map units (one on the ridge and one on the side slope) or map them together as a complex.

As an added treat, the group managed to coerce Clemson University’s Dr. Virgil Quisenberry to give a demonstration on use of the Amoozameter. This is a tool that measures ksat—basically a measurement of how fast water can move through soil. NRCS recently purchased three of these devices, so it was helpful to receive hands-on training.

The use of the Electomagnetic Induction Meter and the Ground Penetrating Radar proved to be useful tools in measuring the depths to bedrock in two distinctly different areas of York County. They also helped verify what was previously found with the auger. The data collected will be used to make a better soils map for the citizens of York County.

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