Publications—Open-File Report

Hydrogeology of the Lloyd Aquifer on Long Island, New York—A Brief Summary of USGS Investigations

By Anthony Chu

U.S. Geological Survey Open-File Report 2006–1341

The body of the report is available in PDF Format (13,772 KB)


The four counties of Long Island (fig. 1) are underlain by a wedge-shaped sequence of unconsolidated deposits of Late Cretaceous and Pleistocene age that lie unconformably on crystalline bedrock (fig. 2). A saprolitic (weathered bedrock) zone 20 to 100 ft thick overlies the bedrock in most areas. The sequence of unconsolidated deposits thickens to the south and southeast by about 65 to 100 feet per mile and contains Long Island’s fresh ground water.

Long Island’s ground-water system consists of four main aquifers–the upper glacial, the Jameco, the Magothy, and the Lloyd. The Lloyd aquifer underlies nearly all of Long Island (fig. 3), but pumpage from the Lloyd has been limited to the northern and southern coastal areas of the island by the New York State Department of Environmental Conservation since about 1955 (Garber, 1986). Coastal areas are exempt where the Lloyd is the only source of potable water. The former Jamaica Water Supply Corporation (now owned by New York City) is a noted exception withdrawing as much as 6 million gallons per day (Mgal/d) since the mid-1930s from the Lloyd in central Queens County.

This paper: (1) provides a brief history of U.S. Geological Survey (USGS) studies that provided significant data on the Lloyd, (2) summarizes the hydraulic characteristics of the Lloyd as reported in those studies, and (3) describes present-day monitoring of the Lloyd by the USGS.

Suggested Citation:

Chu, Anthony, Hydrogeology of the Lloyd Aquifer on Long Island, New York—A Brief Summary of USGS Investigations: U.S. Geological Survey Open-File Report 20061341, 12 p.

If you have Adobe® Acrobat® or Adobe® Acrobat® Reader® installed on your computer, you may view and print the PDF version of this report. Acrobat Reader, is a free download from Adobe Systems, Inc. Users with disabilities can view information concerning accessibility at .

For further information, contact:

U.S. Geological Survey
New York Water Science Center
425 Jordan Road
Troy, NY 12180


or visit our Web site at:

U.S. Department of the Interior, U.S. Geological Survey
Persistent URL:
Page Contact Information: Contact USGS
Last modified: Saturday, January 12 2013, 10:27:06 PM
FirstGov button  Take Pride in America button