Geology and ground-water resources of the Fort Pillow Sand in western Tennessee

To Fort Pillow Sand of the Wilcox Group of Tertiary age underlies approximately 7,700 sq mi in western Tennessee. The formation consists primarily of very fine to very coarse sand that locally contains minor lenses or beds of clay or silt. The Fort Pillow Sand ranges from 0 to 350 ft in thickness. Recharge to the Fort Pillow aquifer generally is from precipitation on the outcrop and by downward infiltration of water from the overlying fluvial deposits of Tertiary and Quaternary age and alluvium of Quaternary age. Long-term data indicate that water levels in the Fort Pillow aquifer in areas affected by pumping have declined at average rates ranging from 0.4 to 0.9 ft/year during the period 1945-83. The water generally is a sodium bicarbonate type that contains low concentrations of most major constituents and generally is suitable for most uses. Dissolved solids concentrations ranged from 20 to 143 mg/L. Twenty-four aquifer tests made during the period 1932-61 indicate that transmissivities average about 13,100 sq ft/day at Memphis and about 10,000 sq ft/day at Jackson. Storage coefficients at these locations average about 0.0002 and 0.0015, respectively. The Fort Pillow aquifer presently provides moderate to large quantities of water to several public and industrial well fields and small quantities to numerous domestic and farm wells. Withdrawal for public and industrial supplies in 1983 averaged about 10.6 million gal/day. The Fort Pillow aquifer is widespread and virtually untapped and has much potential for future use. (USGS)