GROUNDWATER POTENTIAL IN THE HELDERBERG-TONOLOWAY LIMESTONE, KNOBLEY MOUNTAIN, WILLS CREEK ANTICLINE, WEST VIRGINIA

Doubly-plunging anticlines in the Valley and Ridge province of West Virginia, such as Knobley Mountain, expose the Helderberg (Lower Devonian) and Tonoloway (Upper Silurian) limestone of potential for groundwater supply. These folds are flanked by overlying Oriskany sandstone and surrounded by younger shale-rich Devonian lithologies of low aquifer potential and less desirable water quality. Initial groundwater exploration in 1988-1997 yielded three successful wells of 160-220 L/min and excellent chemical quality, although the shallowest had to be decommissioned due to turbidity following storms. From 2001-2004, all well tests but one were unsuccessful due to selection of drillsites of inappropriate geology and/or too far from the anticline. From 2009-2017, we investigated hydrogeology and fracture trace patterns along Knobly Mountain. The Helderberg and Tonoloway showed fewer springs than other formations, but of much higher discharge. Both abruptly gaining and abruptly losing minor streams were observed. Fracture traces mapped using DRG hillshades show a prominent orientation of 115^o to 121^o, more or less perpendicular to strike; lineament density from 0.7 to 3.2/km; and lognormal distribution of fracture lengths. Most springs are associated with these fractures, but not all mapped fractures have springs. A strategy of test well drilling was devised to locate wells as close as possible to fractures without springs, at sufficiently high elevation to optimize drilling depths yet avoid shallow contamination. 4 successful test wells drilled since 2011 yield from 350-650 L/min at depths from 128-243 m. The deepest was at the crest of a high wind gap. Only one of the four was further than 10 m from a fracture trace, and this well had only one evident yield zone. Borehole video shows the producing zones appear as solution-widened bedding planes dipping about 45^o. Aquifer test data indicate either confined or slightly-leaky response and extensive continuity. Appropriately-sited wells in this montane karst aquifer appear to have potential for moderate yields of excellent chemical quality for public supply. Here the Lattman and Parizek (1964) method seems to work in a montane setting where compressive stresses have evidently been applied parallel to strike.