2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 215-2
Presentation Time: 9:15 AM

A TEST OF COMBINING TIME-LAPSE ELECTRICAL RESISTIVITY IMAGING AND SALT INJECTION FOR LOCATING KARST CONDUITS


ATCHER, Clay D., Earth and Environmental Science, University of Kentucky, 280 Swigert Ave, Lexington, KY 40505, SAWYER, Audrey H., School of Earth Sciences, The Ohio State University, 12, Columbus, OH 43210, ZHU, Junfeng, Kentucky Geological Survey, University of Kentucky, Lexington, KY 40506 and CURRENS, James C., Kentucky Geological Survey, Univ of Kentucky, 228 Mining and Minerals Building, Lexington, KY 40506-0107, clayatcher@mac.com

The use of electrical resistivity imaging to locate karst conduits has traditionally shown mixed success. However, time-lapse electrical resistivity imaging combined with a salt injection may improve conduit detection by elucidating regions where electrical conductivity changes due to salt passage. We tested the approach above a known karst conduit in the Kentucky Horse Park (Lexington, Kentucky). A salt tracer solution was injected into a karst window over a 45-minute interval, and repeat resistivity surveys were collected approximately one kilometer away along a 125-meter transect every 20 minutes. The resistivity transect was located near a well that penetrates the conduit, where a conductivity sensor was deployed. The in-situ conductivity data are essential for verifying the results of the electrical resistivity method. Conductivity in the well peaked at approximately 125% of the initial value ~3 hours after salt injection. Preliminary pseudo-sections show areas of increasing conductance that correlate to conductivity changes recorded in the well. If this imaging method proves viable after inversion of the resistivity data, time-lapse electrical resistivity imaging could allow for more reliable identification of karst conduits in the subsurface.