Simulation of Variable-Density Ground-Water Flow and Saltwater Intrusion beneath Manhasset Neck, Nassau County, New York, 1905-2005

• DOI: 10.3133/sir20085166
• Publication Date: 2020-05-28T16:25:29Z
• Authors: Jack Monti; Paul E. Misut; Ronald J. Busciolano
• Keywords: Saltwater intrusion

The coastal-aquifer system of Manhasset Neck, Nassau County, New York, has been stressed by pumping, which led to saltwater intrusion and the abandonment one public-supply well in 1944. Measurements chloride concentrations water levels 2004 from deep, confined aquifers indicate active response pumping. A numerical model capable simulating three-dimensional variable-density ground-water flow solute transport heterogeneous, anisotropic was developed using U.S. Geological Survey finite-element, variable-density, solute-transport simulator SUTRA, investigate extent beneath Neck. is composed eight layers representing hydrogeologic Four modifications area?s previously described framework were made (1) bedrock-surface altitude at N12191 corrected a reported value, (2) part Raritan confining unit shifted, (3) North Shore (4) clay layer upper glacial aquifer added central southern parts Neck peninsula. Ground-water location freshwater-saltwater interface simulated for three conditions (time periods) steady-state (predevelopment) simulation no pumping prior about 1905, 40-year transient based on 1939 pumpage 1905-1944 period gradual intrusion, 60-year 1995 1945-2005 stabilized withdrawals. rate (12.1 million gallons per day (Mgal/d)) applied caused modeled average water-level declines 2 4 feet (ft) shallow deep systems predevelopment conditions, respectively, net decrease 5.2 Mgal/d freshwater discharge offshore areas increase 6.9 entering eastern, western, lateral boundaries. (43.3 Mgal/d) 5 8 ft 13.2 30.1 two under Saline ground third due absence near Sands Point. Simulated greater than 250 milligrams liter (mg/L) used represent interface, movement this concentration evaluated simulations. advance landward more 1,700 its position vicinity Baxter Estates Village, Long Island, York. different area 600 approximately 1 mile south Village. However, underestimates determined water-quality samples collected wells N12508 N12793, where measured increased 625 18 mg/L 1997 t