Piezometric levels from 1948 through 1950 for wells screened in the Lloyd sand member of the Raritan formation on Long Island, New York

Since 1932, the United States Geological Survey, in cooperation with the New York Water Power and Control Commission, the Nassau County Department of Public Works, the Suffolk County Board of Supervisors, and later also with the Suffolk County Water Authority, has been making both general and detailed studied dealing with the occurrence, movement, quantity, quality, and temperature of ground water found in the several water-bearing formations on Long Island. In the first years most of the emphasis was placed on studying the shallow water-table beds of Pleistocene age, although geologic and hydrologic information was obtained for the Lloyd sand member of the Raritan formation of upper Cretaceous age, the deepest water-bearing beds on Long Island, as well as for other artesian formations above the Lloyd.