The hydrogeologic framework of the Valley and Ridge Physiographic Province in Maryland, New Jersey, and Pennsylvania was analyzed by the U.S. Geological Survey as part of the Appalachian Valleys— Piedmont Regional Aquifer-System Analysis project. Local differences in lithology, structure, and weathering result in large variation in the water-yielding properties of the rock that underlies the area, Selected rock types, however, can account for a substantial part of this variation because of the unique way in which these rock types deform and weather to produce secondary openings. On the basis of the relations among rock type and water-yielding openings and properties, the regolith and consolidated rock were classified and mapped as five hydrogeologic terranes—alluvium, dolomite. limestone, argillaceous carbonate rock, and siliciclastic rock.

Specific-capacity data for homogeneous data sets, which consist of all wells that have the same characteristics in regard to casing diameter, primary use of the water, and topographic setting, revealed significant differences in water-yielding properties among the five hydrogeologic terranes. According to results of Tukey tests at a probability (alpha level) of 0.10, eight out of ten pairs of hydrogeologic terranes had significantly different median specific-capacity values. Estimates of potential yields to public- and industrial-supply wells were calculated from specific-capacity data for most-productive wells—wells with casing diameter of 7 inches or more, used primarily for public or industrial supply, and in a valley—using median drawdowns for each hydrogeologic terrane, Estimated interquartile ranges in potential yields to most-productive wells in the hydrogeologic terranes, in gallons per minute, were 170 to 600 in alluvium; 280 to 1,700 in dolomite, 80 to 520 in limestone; fish to 550 in argillaceous carbonate rock; and 60 to 24s) in siliciclustic rock.