Description: Top-seal thickness. Several studies define the confining unit above the lower Potomac aquifer (Trapp, 1992; Trapp and Meisler, 1992). It is generally composed of "tough" or "hard" clay and sandy clay beds. It is regionally continuous from North Carolina to New Jersey and generally ranges in thickness from 50 to 100 ft but exceeds 1,000 ft toward the mouth of Delaware Bay (Trapp, 1992). Trapp (1992) provided a map showing the thickness distribution of the lower Potomac confining unit across the area of interest, and this map was digitized.
Copyright Text: Trapp, H., Jr., 1992, Hydrogeologic framework of the northern Atlantic coastal plain in parts of North Carolina, Virginia, Maryland, Delaware, New Jersey, and New York: U.S. Geological Survey Professional Paper 1404-G, 59 p., 13 plates.
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Trapp, H., Jr., and Meisler, H., 1992, The regional aquifer underlying the northern Atlantic coastal plain in parts of North Carolina, Virginia, Maryland, Delaware, New Jersey, and New York—summary: U.S. Geological Survey, Professional Paper 1404A, 33 p., 11 plates.