Hydrogeology and ground-water quality of the northern part of the Town of Oyster Bay, Nassau County, New York, in 1980

This report presents geohydrologic and water quality data from the northern part of the Town of Oyster Bay, in the north-shore area of Long Island. The groundwater reservoir underlying the area consists of clay, silt, sand, and gravel layers that form six geohydrologic units; from bottom to top: the Lloyd aquifer, Raritan clay, Magothy aquifer, Port Washington aquifer, Port Washington confining unit, and the upper glacial aquifer. Crystalline bedrock underlies the Lloyd aquifer and forms the base of the groundwater system. The regional drought of 1962-67 caused groundwater levels to decline as much as 16 feet, but the water table altitude in 1980 equaled or exceeded predrought levels. Water levels measured in wells screened in the lower part of the Magothy aquifer and in the Lloyd aquifer throughout much of the area are still below those measured before the drought but are recovering. Groundwater in some areas contains nitrates, volatile organic compounds, and chloride in concentrations that exceed New York State drinking-water standards. Contamination is limited largely to the upper glacial aquifer and upper part of the Magothy aquifer. Saltwater has been reported in some wells along the shore but probably represents a natural condition rather than saltwater encroachment due to excessive pumping. (Author 's abstract)