Geotechnical Applications of the Self-Potential (SP) Method. Report 2. The Use of Self Potential to Detect Ground-Water Flow in Karst

Self potential is a geophysical method that measures naturally occurring voltage in the earth. Negative anomalies arise from electrokinetic, or streaming potential, effects resulting from the flow of groundwater. SP was monitored at sites in karst terrain in Virginia. Results were evaluated for effectiveness in detecting and mapping groundwater flow paths and flow rates. The ability of SP to distinguish between shallow flow in soil and regolith and deeper flow through bedrock conduits was examined. It was demonstrated that soil temperaturemoisture and precipitation are major variables influencing SP data. An automated data collection system was used for 1 long-term monitoring of SP changes and environmental variables and 2 measuring SP changes induced by the rapid artificial recharge of water into a sinkhole. SP results were compared with geological observations, electrical resistivity and electromagnetic terrain conductivity surveys, streamflow measurements, and speleological surveys. Results indicate that SP can effectively locate and track shallow 20 m groundwater flow paths in karst. A relationship was observed between SP and changes in flow rate where the flow was through porous material, but SP could not be directly related to flow through solutional channels and conduits. Presence of conduits may be indicated by SP anomalies where surface soil moisture is drawn into fractures that supply water to conduits at greater depths. Influence of geologic structures on groundwater flow must be considered in interpreting SP results in karst. Surfacesubsurface drainage.