Numerous sources of VOCs in urban areas are a likely explanation for the high frequency of detections in the urban subunit. In the urban area, ground water contaminated with VOCs flows from springs that feed coldwater streams known for their trout populations.
EXPLANATION SUBUNIT 1 - Piedmont crystalline agricultural 2 - Piedmont limestone agricultural 3 - Great Valley limestone agricultural 4 - Great Valley limestone urban 5 - Appalachian Mountain limestone agricultural 6 - Appalachian Mountain sandstone and shale agricultural 7 - Appalachian Mountain sandstone and shale forested |