CONCEPTUALIZING LITHOLOGIC AND STRUCTURAL CONTROLS ON A CARBONATE AQUIFER IN THE GREAT VALLEY, WEST VIRGINIA

Underlying the Great Valley of West Virginia, fractured carbonate-rock aquifers of Cambro-Ordivician age display high degrees of folding, faulting, and jointing. As a result, wells typically yield 100 gpm or more if located with some knowledge of the subsurface fracture system or secondary permeability of the aquifers. In part, well yields can be explained with detailed geologic mapping, yet order of magnitude ranges in yields over only tens of feet of distance lends evidence to the extreme heterogeneity of the subsurface system, and makes adequate conceptualization of the fractured carbonate-rock aquifer in the Great Valley difficult.

Subsurface conduits, as great as 8 ft in width, identified in outcrops along the Potomac River have no surficial expression and are vertically elongate in the direction of bedding. Preferential enlargement of caves and sinkholes along bedding planes and joints parallel to strike suggests that conduit development can be attributed to restriction of flow along lithologic boundaries. Conversely, lesser degrees of solutional enlargement have occurred along cross-strike features and structural boundaries that are conducive to high yielding wells.

Much has been cited in the literature about using surficial expressions of subsurface fracture zones as a tool for groundwater exploration in the area. Yet, less attention has focused on the relationship between the spatial distribution of sinkholes and the occurrence of high yielding wells. The role and importance of surficial karst features in regional hydrology and usefulness in studies of groundwater exploration is examined in this study. Aquifer test data is incorporated with sinkhole and high yielding well distributions into a conceptual model to further define structural and lithologic boundaries and prevailing flow conditions (radial, linear, etc.).