CHARACTERIZATION OF GROUNDWATER FLOW FROM KARST SINKHOLE AT SURFACE INTO THE GRAND CAVERNS CAVE SYSTEM IN GROTTOES, VA. USING RESISTIVITY

Grand Caverns, located in Grottoes, VA., is a large commercial cave system and the oldest show cave in the United States. The cave system lies within the Conococheague (carbonate) formation beneath Cave Hill. Beginning in 2013, the USGS began to monitor stable isotope values of rain water in a sinkhole located some 60m above the Curtain Room in the caverns below, as well as of cave drip within the Curtain Room. Differences between the isotope values at the surface and within the cave itself could be explained by a perched aquifer somewhere between the sinkhole and the cave. In this study, we present an electrical resistivity survey that will aim to characterize the hyrological pathways between the sinkhole and cave, with an express interest in locating any perched aquifers.

Six lines of shallow (~17 m) resisitivity readings have been acquired at the sinkhole using an AGI Supersting R-1 Resisitivity meter during/after a period of moderate to heavy rainfall. Preliminary results show the infiltration paths of the water into the bedrock to those depths, but does not allow us to see deeply enough to fully characterize the flow paths. We will be collecting several more lines of resisitivity data, including some that should give penetration depths all of the way to the top of the Grand Caverns system itself. This should enable us to detect (or preclude the existence of) any perched aquifer as well as to characterize the entire flow path of water from the surface to the cave system. This investigation combined with the work being done by the USGS will help us to better understand groundwater flow into the Grand Caverns system and more generally into any karstic cave system.