Valley and Ridge, Piedmont, and Blue Ridge Aquifers

Fluorescent tracer injection into a sinkhole in the Leetown area, WV. Tracer tests were conducted as part of intensive investigations of the hydrogeology, water quality, and ground-water flow of the karst aquifer in the Hopewell Run Watershed, northern Shenandoah Valley, near Leetown, West Virginia. (Photo by Mark Kozar)

Streamflow tracer test on a tributary to Hopewell Run near Leetown, WV. U.S. Environmental Protection Agency scientist Malcolm Field conducts this test. It was conducted to assess potential leakage of stream water to the karst aquifer in the northern Shenandoah Valley of West Virginia. (Photo by Carol Boughton)

Karst conduit in a borehole, Cumberland County, PA. A still-frame from a video taken from a camera lowered into a borehole in karst terrane. A conduit appears in this photo as a distinctive void space, which likely transmits large volumes of water through the aquifer rapidly. (Photo by Randy Conger)

Cave along Cedar Creek, Virginia. USGS Hydrologist Bob Hirsch experiences karst terrane first hand while kayaking on Cedar Creek. He is paddling out of a cave along Cedar Creek, about 20 miles south of Winchester. Cedar Creek is a tributary of the North Fork of the Shenandoah River. (Photo by Mary Cirincione)

The carbonate aquifers of the Appalachian Valley and Ridge Province are formed within a thick Paleozoic sequence of layered carbonate and siliciclastic rocks that were highly folded and faulted during Appalachian mountain building. Fluid flow thus has been through complex geologic structures, resulting in highly variable karst aquifer characteristics with a wide range of ground-water residence times, geochemical characteristics, and aquifer compartmentalization. Cave geometries likewise are variable, ranging from small, isolated caves of limited extent to some of the longest and deepest caves known in the United States.

The Great Valley aquifer is the primary carbonate aquifer in the Valley and Ridge Province, formed within a sequence of Cambrian and Ordovician rocks over 10,000 feet (3,048 meters) thick. This aquifer is an important water resource for numerous cities and towns along the Interstate 81 corridor from Tennessee to Pennsylvania.
The northern extent of the Great Valley in Virginia, West Virginia, and Maryland has been particularly well studied, especially within the drainage basin of the Shenandoah River. Larger springs typical of the Shenandoah Valley karst aquifer are 4th and 5th magnitude (10-500 gal/min; 0.6 to 28 L/sec) artesian springs, most with relatively muted discharge variability. Geologic structure strongly influences spring locations, discharge and geochemistry. Spring discharge accounts for more than 85% of stream flow in the Shenandoah River basin. As a result, surface-water quantity and quality is highly dependent on ground-water use and management. Circulation of ground water through conduits exceeds depths of 2000 feet (610 meters) as evidenced by a small number of high-yield deep wells. Most wells are finished less than 300 feet (100 meters) below land surface and may yield between 1-150 gal/min (0.063-9.45 L/s). While the majority of springs have ambient water temperatures, many mildly thermal springs have been identified.

The Shenandoah Valley karst hosts a number of unique endemic species. Of note is the Madison Cave Isopod (Antrolana lira), a crustacean of originally marine ancestry found only caves containing fresh ground water in the Shenandoah Valley region.