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Long Island Water Supply Sustainability Study

Plan Updates:

January - June, 2018, Long Island Groundwater Sustainability Study Progress Report (PDF, 804KB)

The Study Purpose:

The purpose of the Long Island Water Supply Sustainability Study is to create an updated and enhanced regional groundwater-flow modeling tool for use by the United States Geological Survey (USGS), DEC, Nassau County, Suffolk County, and other key water-resources management partners in the region. This tool will enable us to collaboratively manage the region's groundwater resources and address concerns of over-pumping, saltwater intrusion, plume migration, changes in groundwater outflow to surface waters, and determination of sustainable yield for changing hydrologic stress conditions. In addition, the study will provide:

  1. An updated and improved understanding of the hydrogeologic framework of Long Island;
  2. An expanded network of deep observations wells to augment the current monitoring well network for the Magothy and Lloyd aquifers; and
  3. Information on the current and projected future extents of saltwater intrusion and saltwater upconing.

This study aligns with the goals of the Long Island Nitrogen Action Plan, the Long Island Commission on Aquifer Protection, and the Suffolk County Comprehensive Water Resources Management Plan.

Visit USGS's website (link found on the right side of this page) regularly to view up to date information on this study.

Overview of the Proposed Work Plan:

The project will be comprised of a series of well installations, groundwater monitoring, offshore and subsurface geophysical surveys conducted at strategic locations throughout Long Island (including Kings and Queens counties) and will include the following:

  • Offshore marine seismic surveys will be conducted in northern Queens and Suffolk County to enhance the delineation of major hydrogeologic features in that area.
  • Deep Magothy and Lloyd aquifer observation wells will be installed at approximately 25 selected locations where no nearby wells currently exist. Additional shallow wells may be drilled to augment the existing monitoring well network.
  • Borehole geophysical logging will be conducted at the newly installed wells initially and intermittently throughout the study period to determine the presence and rate of saltwater intrusion. Monitoring wells will periodically be sampled for groundwater levels and chloride concentrations.
  • The current location and thickness of the freshwater-saltwater interface will be delineated and an island-wide dataset of historical chloride date will be assembled.
  • A new island-wide groundwater-flow model will be developed to simulate various scenarios of groundwater pumpage and aquifer recharge to determine changes in groundwater-surface interactions, movement of the freshwater-saltwater interface, and the migration of major plumes.
  • Public-supply sustainable yield will be determined at both local and regional scales.

The information mentioned above will be used to create updated hydrogeologic framework maps of the major aquifers and confining units underlying Long Island, and delineate the current location of the freshwater-saltwater interface. The groundwater-flow model will be developed with new hydrogeological data as it becomes available. The model will be used to predict effects of pumping under various hydrologic conditions, and evaluate the potential risk for wells susceptible to saltwater intrusion, saltwater upconing, and water-quality degradation from anthropogenic sources.


Over-pumping: When water is pumped from an aquifer at an unsustainable rate.

Safe or Sustainable Yield: The amount of groundwater that can be withdrawn from an aquifer on a sustained basis without impairing native groundwater quality or creating undesirable environmental effects. (Fetter, 2001)

Saltwater Intrusion: The movement of saline water into a freshwater aquifer either due to lateral encroachment or vertical upconing. Saltwater intrusion may occur naturally or due to human processes.

Saltwater Upconing: The vertical movement of saltwater through a freshwater aquifer, typically occurring near or at pumping wells.