Change in potentiometric head in the Lloyd Aquifer, Long Island, N.Y

The potentiometric surface of the Lloyd aquifer in 1970 locally was as much as 40 feet lower than in 1900. During this period, withdrawal of water from wells was estimated to exceed 300 billion gallons, and the amount of water released from aquifer storage by compressive forces was estimated to be 1.6 billion gallons (about 0.5 percent of the withdrawal). The remainder of the withdrawal was derived from downward leakage through overlying aquifers and confining layers and by the displacement of fresh water in the aquifer by landward movement of salty ground water