INVESTIGATING GEOLOGIC INFLUENCES ON KARST SPRINGS IN THE HANGING ROCK VALLEY, VIRGINIA

The State Fish Hatchery in Paint Bank, Virginia, relies solely on water from three karst springs. Understanding the source and flow paths to each of the springs helps the fish hatchery and local landowners make resource management decisions to maintain fish health. The fish hatchery lies within the Hanging Rock Valley, a breached NW-vergent, NE-SW striking anticline comprised of Ordovician carbonates exposed in its core that form the valley floor and Ordovician to Silurian siliciclastics forming its resistant limbs. The springs resurge in proximity (<215m) of a NE-SW trending NW-directed thrust fault within the Ordovician carbonates along the subvertical forelimb. Although new 1:24,000-scale bedrock mapping has brought greater detail to the placement of lithologic unit contacts and geologic structures in the area, their relation to karst features and hydrologic flow paths have not been extensively studied. Previous research on Shires Cave has shown that cave development follows fold-axis-parallel (NE) and perpendicular (SE) joint sets. We aimed to understand the effects of faulting and fracturing on the karst hydrology of the valley by conducting a new detailed karst hydrogeologic inventory. We hypothesize that the fault influences groundwater flow paths and possibly partitions the northernmost spring in the footwall from the two springs in the hanging wall. To test this hypothesis, we identified surface-to-subsurface connections using lidar and verified them in the field. Dye traps were set at each of the springs, the confluence of the springs along a gaining reach, and the Valley Branch: a surficial drainage divide east from the fish hatchery. Rhodamine WT and Fluorescein were injected into two sinking streams on the northern and southern ends of the valley, respectively. The dye trace results show that rhodamine WT was found only in the northernmost spring, while fluorescein was found only in the southernmost spring. The strong recovery of rhodamine WT in the northernmost spring could be explained by groundwater conduits that cut across the fault. Future research should aim to perform further traditional mapping of the fault to identify the existence of potential structures that allow groundwater conduit systems to cut across the NW-SE trending fault.