STRUCTURAL CONTROL OF SPRING LOCATIONS IN THE NORTHERN SHENANDOAH VALLEY, VIRGINIA AND WEST VIRGINIA: INTERPRETATION OF GEOLOGIC CONTROLS ON GROUND-WATER FLOW PATHS IN FOLDED AND FAULTED CARBONATE ROCKS

New and revised detailed geologic mapping by the U.S. Geological Survey in the Paleozoic carbonate rocks of the northern Shenandoah Valley of Virginia and West Virginia is providing a geologic framework with sufficient spatial resolution for testing correlation of ground-water flow paths to geologic setting. Thrust faults, cross faults, and major folds in the valley serve as directional controls on ground-water flow, and combined with lithologic units produce physical compartments for ground-water storage and flow. Strike-parallel ground-water flow is interrupted by compartment-bounding cross faults that may either direct water across strike or force flow towards the surface, often producing springs. Flow-paths are complex and the compartments are leaky. Support for these ideas include: 1) results of multidisciplinary hydrogeologic studies at the U.S. Geological Survey, Leetown, WV Science Center which indicate strong anisotropy in ground-water flow directions and correlation between test-well transmissivity and geologic structures, including folds and faults; 2) New geologic mapping in the Middletown, Winchester, Stephens City, Stephenson, Inwood, and White Hall 1:24,000 quadrangles suggests that spring location, magnitude, and geographic spacing is positively correlated with the location of thrust, diagonal, and cross faults; 3) the density of sinkholes and closed depressions located within large (several km scale) synclines that indicate zones of focused ground-water recharge. Two synclines of note are the Buffalo Marsh Run syncline situated in the Middletown quadrangle and the Welltown syncline situated in the Winchester, White Hall and Inwood quadrangles.