The Lloyd aquifer contains only about 9% of the water stored in Long Island 's groundwater system but is the only source of potable water for several communities near the north and south shores. The Lloyd aquifer is virtually untapped throughout most of central Long Island because current legal restrictions permit its use only in coastal areas. The upper surface of the Lloyd aquifer ranges in depth from 100 ft below land surface on the north shore to more than 1,500 ft on the south shore. Aquifer thickness increases southward from 50 ft to about 500 ft. Transmissivity ranges from 1,500 to 19,000 sq ft/day. All recharge (35 to 40 mil gal/day) and nearly all discharge is through the overlying confining unit. Nearly all of the pumpage (approximately 20 mil gal/day) is in Queens and along the north and south shores of Nassau County. Potable water can be obtained on most of Long Island in larger quantities and at shallower depths from other aquifers than from the Lloyd. Local contamination of these other aquifers, however, may require at least temporary withdrawals from the Lloyd in noncoastal areas. Significant withdrawals from the Lloyd aquifer may lower the potentiometric surface and thereby induce landward movement of sea water into the aquifer in coastal areas.
