The Pleistocene Jameco Gravel unconformably overlies the Monmouth Group and is only present in western Long Island; its eastward extent just barely enters Nassau County. The Jameco Gravel attains thicknesses of 200 feet and is comprised of brown, fine to coarse grained sand and gravel. The Jameco Gravel may represent fluvioglacial deposits of Illinoian age associated with deposition in an ancestral Hudson River valley (Soren, 1978). The Jameco Gravel makes up the Jameco aquifer which is confined below the Gardiners Clay and displays a average horizontal hydraulic conductivity between 200 to 300 feet per day (Smolensky et al., 1989).
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