The 30-site network was designed to represent a subarea of the Allegheny and Monongahela River Basin in the Appalachian Plateau Physiographic Province. The subarea is limited to areas underlain by the Pittsburgh Series rocks of upper Pennsylvanian and lower Permian Age. The Pittsburgh Series is comprised of the Monongahela, Conemaugh, and Allegheny formations. The network is located in the central and lower parts of the Allegheny and Monongahela River Basin and includes twelve counties in Pennsylvania, eight counties in West Virginia and one county in Maryland. The 30 sites were randomly selected from privately owned wells used to supply water to homes and businesses. The wells were sampled to assess the ground-water quality across the region. This sampling is termed a Study-Unit Survey for the NAWQA Program. Field constituents were measured and water samples collected for laboratory analysis of nutrients, major ions, trace elements, pesticides and volatile organic compounds (VOC's).
The shaded part of the figure below shows the sampling subarea in the fractured rock of the Pittsburgh Series of the Appalachian Plateau Physiographic Province and the location of the 30 well sites: