|Lower Potomac Group, Eastern Coastal Plain of Maryland, Delaware, and New Jersey
Several authors characterized regional ground-water flow in the lower Potomac interval (Trapp and Meisler, 1992; Leahy and Martin, 1993; Trapp and Horn, 1997; Pope and Gordon, 1999). However, these studies focus on measuring and/or modeling hydraulic head in areas where the lower Potomac aquifer is shallow and contains fresh water, and their maps cover only areas that are inland (up dip) of the area of interest in this study. Meisler and others (1984) analyzed the effect of Pleistocene sea-level change on the saltwater/fresh-water interface in deep aquifers below the coastal plain. They concluded that the saltwater/fresh-water interface moves very little with major sea-level changes, which implies that the fluid residence times in these deep aquifers is very long and undoubtedly exceeds the age of the last major sea-level low, which was about 18,000 yr BP. Hence, in the GIS, we represent fluid residence times across eastern New Jersey, Delaware, and Maryland as more than 18,000 yr.
Leahy, P. P., and Martin, Mary, 1993, Geohydrology and simulation of ground-water flow in the Northern Atlantic Coastal Plain aquifer system: U.S. Geological Survey Professional Paper 1404-K, 81 p.
Meisler, H., Leahy, P. P., and Knobel, L. L., 1984, Effect of eustatic sea-level changes on salt-water-freshwater in the northern Atlantic coastal plain: U.S. Geological Survey Water-Supply Paper 2255, 28 p.
Pope, D. A., and Gordon, A. D., 1999, Simulation of ground-water flow and movement of the freshwater-saltwater interface in the New Jersey coastal plain: U.S. Geological Survey Water-Resources Investigations Report 98-4216, 159 p.
Trapp, H., Jr., and Horn, M. A., 1997, Ground water atlas of the United States-segment 11, Delaware, Maryland, New Jersey, North Carolina, Pennsylvania, Virginia, West Virginia: U.S. Geological Survey Hydrologic Investigations, Atlas No. HA-730-L, 30 p.