Interdisciplinary cooperative geologic mapping and ground-water resource 
analyses of Frederick County, Virginia by the U.S. Geological Survey

By David J. Weary, George Harlow, Randall C. Orndorff, and Wilma Alemán-González

As a bedroom community for the Washington, D.C. metropolitan area, the northern 
Shenandoah Valley of Virginia is facing increased potential human impacts on ground-
water resources. Expansion of industrial and housing development combined with low 
water tables experienced during recent drought years have prompted local governments 
to support scientific studies of the karst aquifers of the northern Shenandoah Valley. The 
aquifer comprises Lower Paleozoic carbonate rocks that have been extensively folded, 
faulted, and fractured. In many places the fractures have been solutionally enlarged into 
caves and conduits for ground water. In cooperation with the Frederick County Water 
Authority, U.S. Geological Survey (USGS) geologists and hydrologists are studying the 
detailed geology and ground-water resource in the area around Winchester, VA. The 
effort, supported by the National Cooperative Geologic Mapping Program (NCGMP), 
includes new 1:24000 scale geologic mapping in quadrangles containing the valley karst 
aquifer. Special emphasis is put on identifying faults and other structures that may affect 
the partitioning and movement of ground water on a regional scale. Fracture 
measurement and analysis are being performed in an attempt to characterize the 
anisotropy of the bedrock in respect to ground-water flow at local and regional scales. 
Preliminary results indicate that ground water moves preferentially along strike in the 
folded and faulted rocks of this area, and many conduits develop along the intersection of 
joints and bedding plane fractures. The effort also includes installation and monitoring of 
stream gauges for base-flow data as well as an extensive well monitoring and aquifer test 
regime. 

© Copyright 2004 The Geological Society of America (GSA), all rights reserved. 
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Weary, D.J., Harlow, G.E., Jr., Orndorff, R.C., and Alemán-González, Wilma, 2004, 
Interdisciplinary cooperative geologic mapping and ground-water resource analyses 
of Frederick County, Virginia by the U.S. Geological Survey [abs.]: Geological Society 
of America Abstracts with Programs, v. 36, no. 5, p. 578.

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