• Due to a lack of deep Lloyd and Magothy aquifer observation wells in parts of the study area, a network of Lloyd and Magothy outpost wells will be installed. The approximate capital costs for this objective are shown in the attached budget, and will be administered separately through the Nassau County Department of Public Works (NCDPW) (for Kings, Queens, and Nassau County drilling) and the Suffolk County Water Authority (SCWA) for Suffolk County. Shallow to intermediate well drilling in Suffolk County may be augmented by utilizing newly acquired capabilities of the Suffolk County Department of Health Services (SCDHS). USGS cooperative drilling efforts in the recent past with the NCDPW, SCWA, and SCDHS have been very successful, and will provide the most cost effective and efficient means for installing these wells and collecting the required hydrogeologic, hydrologic, geophysical, and water quality data needed to properly delineate the hydrologic framework and saltwater-freshwater interface on Long Island.
• Complete offshore seismic-reflection survey surveys of northern Queens and Suffolk Counties. Offshore seismic-reflection surveys are a very rapid and cost effective tool to delineate major hydrogeologic features such as Pleistocene buried valleys and the Raritan Clay (Stumm, 1993; Stumm and Lange, 2002). Results of the seismic reflection surveys will be used to direct the drilling of new wells and delineate the extent of features.
• Produce a new hydrogeologic framework map for the major aquifers and confining units underlying Long Island. By integrating the seismic reflection survey, new borehole core samples, borehole geophysical logs, and pre-existing well drilling logs a higher resolution map that will build upon the last comprehensive hydrogeologic framework (Smolensky and others, 1990).
• Monitor groundwater levels, sample chloride concentrations, and collect an advanced suite of geophysical logs from the well network, which combines the current observation outpost well network with newly drilled wells as they become available.
• Determine the current location, thickness, and chloride concentration (used to assess salinity) of the freshwater-saltwater interface based on the new data and available historical information. Delineate a revised hydrogeologic framework in critical areas such as northern and central Long Island from new and available core samples and geophysical logs.
• Construct a groundwater-flow and interface model by combining pre-existing USGS models within the study area with new data as it becomes available. Preliminary simulations will be published as an extended abstract to help guide decisions about the location of new outpost-monitoring wells, interpretation of initial data, and management response to significant changes in stress such as reactivation of Queens County supply wells.
• Construct detailed scenarios of pumpage and hydrologic conditions in Kings, Queens, Nassau, and Suffolk Counties.
• Finalize groundwater-flow models and evaluate freshwater-saltwater-interface movement, including delineation of groundwater-flow pathlines at supply-well capture zones susceptible to saltwater intrusion. The model grid shall be equally spaced and extend to all natural hydrologic boundaries of Long Island.
• Evaluate changes in groundwater pathlines as a result of scenarios at inland well sites, not susceptible to saltwater intrusion, but at risk of water-quality degradation from other sources of known contamination.
• Provide a model maintenance website (defined below) to facilitate the use of models by water resource planners and managers.
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