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(YDROGEOLOGYAND%XTENTOF3ALTWATER)NTRUSION OFTHE'REAT.ECK0ENINSULA 'REAT.ECK ,ONG)SLAND .EW9ORK 53'EOLOGICAL3URVEY 7ATER 2ESOURCES)NVESTIGATIONS2EPORT 0REPAREDINCOOPERATIONWITHTHE .!33!5#/5.49$%0!24-%.4/&05",)#7/2+3 Hydrogeology and Extent of Saltwater Intrusion of the Great Neck Peninsula, Great Neck, Long Island, New York By Frederick Stumm ____________________________________________________________ U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 99-4280 Prepared in cooperation with the NASSAU COUNTY DEPARTMENT OF PUBLIC WORKS Coram, New York 2001 Hydrogeology and Extent of Saltwater Intrusion of the Great Neck Peninsula, Great Neck, Long Island, New York i U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. Geological Survey Charles G. Groat, Director The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey. ______________________________________________________________________ For additional information Copies of this report may be write to: purchased from: U.S. Geological Survey U.S. Geological Survey 2045 Route 112, Bldg. 4 Branch of Information Services Coram, NY 11727 Box 25286 Denver, CO 80225-0286 ii CONTENTS Abstract ............................................................................................................................................................................ 1 Introduction ...................................................................................................................................................................... 2 Purpose and scope .............................................................................................................................................. 2 Location of study area........................................................................................................................................ 2 Methods of study................................................................................................................................................ 2 Seismic-reflection surveys ................................................................................................................... 2 Borehole-geophysical logs................................................................................................................... 4 Water-level data ................................................................................................................................... 4 Water-quality data................................................................................................................................ 4 Previous investigations....................................................................................................................................... 6 Acknowledgments.............................................................................................................................................. 6 Hydrogeology ................................................................................................................................................................... 6 Stratigraphy ........................................................................................................................................................ 7 Bedrock................................................................................................................................................ 7 Lloyd aquifer........................................................................................................................................ 8 Raritan clay.......................................................................................................................................... 8 Magothy aquifer................................................................................................................................... 11 North Shore aquifer ............................................................................................................................. 17 North Shore confining unit .................................................................................................................. 17 Upper glacial aquifer ........................................................................................................................... 21 Seismic-reflection surveys.................................................................................................................................. 21 Borehole-geophysical logs ................................................................................................................................. 21 Precipitation ....................................................................................................................................................... 23 Ground water...................................................................................................................................................... 26 Pumpage............................................................................................................................................... 27 Water levels.......................................................................................................................................... 27 Upper glacial aquifer ............................................................................................................. 30 Magothy aquifer .................................................................................................................... 30 Lloyd and North Shore aquifers ............................................................................................ 30 Water quality........................................................................................................................................ 31 Chloride ................................................................................................................................. 31 Volatile organic compounds .................................................................................................. 32 Inorganic constituents and metals ......................................................................................... 32 Extent of saltwater intrusion............................................................................................................................................. 32 Saltwater wedges A and B ..................................................................................................... 33 Saltwater wedge C................................................................................................................. 35 Saltwater wedge D................................................................................................................. 33 Other saltwater wedges ...................................................................................................................................... 36 Summary and conclusions................................................................................................................................................ 38 References cited................................................................................................................................................................ 39 FIGURES 1. Map showing location of Great Neck and Manhasset Neck peninsulas, and of seismic-reflection profiles, Nassau County, N.Y.: A. General location map. B. Location of Great Neck study area......................................... 3 2. Map showing locations of public-supply wells, observation wells, and golf-course wells within the Great Neck Peninsula, Nassau County, N.Y.................................................................................................................................. 5 3. Map showing surface altitude of bedrock underlying Great Neck, N.Y..................................................................... 9 4. Hydrogeologic sections on Great Neck, N.Y. A. Section A-A´.......................................................................................................................................................... 10 Contents iii B. Section B-B´ ......................................................................................................................................................... 11 C. Section C-C´ ......................................................................................................................................................... 12 D. Section D-D´......................................................................................................................................................... 13 5-10. Maps of Great Neck, N.Y., showing extent and upper surface altitude of selected hydrogeologic units: 5. Lloyd aquifer ...................................................................................................................................................... 14 6. Raritan clay......................................................................................................................................................... 15 7. Magothy aquifer ................................................................................................................................................. 16 8. North Shore aquifer ............................................................................................................................................ 18 9.