Development of a Ground-Water Flow Model for the Manhasset Neck Peninsula, Nassau County, New York

Problem  

The ground-water flow system underlying the Manhasset Neck Peninsula, which provides potable water to the local population, consists of a complex assemblage of Pleistocene- and Cretaceous-age sediments that form five aquifers and at least two confining units. Recent hydrogeologic mapping in Manhasset Neck indicates significant glacial erosion of the Magothy aquifer, Raritan Clay, and Lloyd aquifer, and several gaps in the confining units that overlie the North Shore and Lloyd aquifers. Five areas of salt-water intrusion have been delineated, two of which are considered active. Several public-supply wells on the Manhasset Neck Peninsula have been shut down in the past as a result of saltwater intrusion. Documented increases in chloride concentrations and decreases in hydraulic head indicate that several pumping centers in the Port Washington and Sand's Point Water Districts are vulnerable to contamination from saltwater intrusion. Contamination from pesticides and volatile organic compounds (VOC's) is also a concern on the Manhasset Neck Peninsula.

Objectives 

There are two principal objectives of the study: (1) Collect additional data to characterize the hydrogeologic framework, including geologic cores and geophysical logs at three locations where the hydrogeologic framework is currently unknown; and (2) use a numerical model of density-dependent ground-water flow and solute transport to simulate saltwater intrusion.

The development of a numerical model of density-dependent ground-water flow and solute transport model for the Manhasset Neck Peninsula will provide ground-water managers and suppliers with the information needed for proper management of the underling aquifer system. The model will (1) delineate the current position of the five known saltwater wedges on the peninsula; (2) define areas with a potential for new intrusion and estimate rates of intrusion; and (3) indicate the extent of aquifer interconnection and water-level response to several pumpage scenarios.

Related Publications

• Misut, Paul, Aphale, Omkar, 2013, Simulation of Groundwater Flow Pathlines and Freshwater/Saltwater Transition Zone Movement, Manhasset Neck, Nassau County, New York: U.S. Geological Survey Scientific Investigations Report 2013–5201, 44 p.
• Busciolano, Ronald, 2002, Water-table and potentiometric-surface altitudes of the Upper Glacial, Magothy, and Lloyd aquifers on Long Island, New York, in March-April 2000, with a summary of hydrogeologic conditions: U.S. Geological Survey Water-Resources Investigations Report 01-4165,17 p., 6 sheets
• Busciolano, Ronald, 2005, Statistical analysis of long-term hydrologic records for selection of drought-monitoring sites on Long Island, New York: U.S. Geological Survey Scientific Investigations Report 2004-5152, 47 p., online only.
• Busciolano, Ronald, Monti, Jack, Jr., and Chu, Anthony, 1998, Water-table and potentiometric-surface altitudes of the Upper Glacial, Magothy, and Lloyd aquifers on Long Island, New York, in March-April 1997, with a summary of hydrogeologic conditions: U.S. Geological Survey Water-Resources Investigations Report 98-4019, 17 p., 3 pls. (6 sheets)