Valley and Ridge, Piedmont, and Blue Ridge Aquifers
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 groundwater 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 groundwater use and management. Circulation of groundwater 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 groundwater in the Shenandoah Valley region.
Photos of Karst Features
Karst produces distinctive topographic features that can be prominent and distinctive. There are photographs available of the following karst features in karst aquifers of the Valley and Ridge, Piedmont, and Blue Ridge province:
- Caves Along Creek
- Sinking Streams
- Doctor, D.H., Weary, D.J., Orndorff, R.C., Harlow, G.E., Jr., Kozar, M.D., and Nelms, D.L. (2008) Bedrock structural controls on the occurrence of sinkholes and springs in the northern Great Valley karst, Virginia and West Virginia: in Yuhr, L.B., Alexander, E.C., Jr., and Beck, B.F. (eds.), Sinkholes and the Engineering and Environmental Impacts of Karst, Geotechnical Special Publication, 183, p. 12-22.
- McCoy, K.J., and Kozar, M.D. (2008) Use of sinkhole and specific capacity distributions to assess vertical gradients in a karst aquifer: Environmental Geology, v. 54, p. 921-935.
- McCoy, K.J., and Kozar, M.D. (2006) Relation of chlorofluorocarbon ground-water age dates to water quality in the aquifers of West Virginia: USGS Scientific Investigations Report 2006-5221, 37 p.
Featured Studies and Datasets
Aquifer-scale studies and the datasets they produce are a key component to understanding how karst aquifers behave, and the quality of water within them.
- Assessment of the Northern Shenandoah Valley karst aquifer — Hydrogeologic assessment and simulation of groundwater flow.
There are 5 USGS scientists you can contact for more information about this aquifer.
The following websites are additional sources of information about this aquifer: