Geohydrology of the northern part of the town of Brookhaven, Suffolk County, New York

In general, ground water in the area is of suitable quality for drinking and most other uses. Some constituents, however, particularly iron, chloride, and nitrogen, occur locally in unacceptable concentrations. Average hydraulic conductivity ranges from 100 to 300 feet per day (ft/d) in the upper glacial aquifer and from 50 to 70 ft/d in the Magothy aquifer. Transmissivity ranges from 25,000 to 105,000 feet squared per day (ft2/d) in the upper glacial aquifer and from 13,000 to 41 ,000 ft2/d in the Magothy aquifer. Only sparse data are available for the Lloyd aquifer; average hydraulic conductivity and transmissivity are estimated to be 40 ft/d and 10,000 ft2d, respectively. Precipitation (44.4 inches per year) is the only source of ground water in central and eastern Long Island. In the area studied, about 21.5 inches per year reaches the ground-water reservoir. The remainder is lost to over-land runoff (0.5 inch) and evapotranspiration (22.4 inches). Total public-water-supply pumpage in the area is estimated to be 23.2 million gallons per day. Of this total, 15.8 million gallons per day is withdrawn from the upper glacial aquifer and 7.4 million gallons per day from the Magothy aquifer; the Lloyd aquifer is not used for water supply in the area. (USGS)