The Memphis Sand ("500-foot" sand) supplies about 95 percent of the water used in the Memphis area for municipal and industrial purposes. In general, pumpage has increased at an irregular rate since the completion of the first well to this aquifer in 1886. These withdrawals are responsible for an almost continuous decline of water levels in wells throughout the Memphis area. Water-level data indicate that over the years a broad, regional cone of depression has developed in the potentiometric surface of the Memphis Sand and is centered near downtown Memphis. Areally smaller, subsidiary cones are superimposed upon this regional cone in areas heavily pumped by municipal and industrial wells. Pumpage from the Memphis Sand in Shelby County, Tenn., was 188 Mgal/d (million gallons per day) or 712 Ml/d (million litres per day) in 1975, although a maximum of 190 Mgal/d (719 Ml/d) was reached in 1974.
Pumpage from the Fort Pillow Sand ("1,400-foot" sand) began in 1924 and increased at a yearly rate of about 0.6 Mgal/d (2.3 Ml/d) until 1942. From 1943 to 1962, pumpage averaged about 11.5 Mgal/d (43.5 Ml/d), then was reduced as MLGW (Memphis Light, Gas and Water Division) discontinued wells that became unserviceable. MLGW ceased pumping from the aquifer in 1974, and pumpage from the remaining industrial wells in Shelby County in 1975 was 4.4 Mgal/d (16.6 Ml/d). Water levels in the Fort Pillow Sand generally have risen since 1963. Water l evels in the aquifers in the Memphis area fluctuate inversely with changes in pumping. Analysis of observation-well and pumpage data indicates that local water levels can be altered by changing the pumping rates or by varying the areal distribution of pumping.
