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The Memphis area as described in this report comprises about 1,300 square miles of the Mississippi embayment part of the Gulf Coastal Plain. The area is underlain by as much as 3,000 feet of sediments ranging in age from Cretaceous through Quaternary. In 1960, 150 mgd (million gallons per day) of water was pumped from the principal aquifers. Municipal pumpage accounted for almost half of this amount, and industrial pumpage a little more than half. About 90 percent of the water used in the area is derived from the "500-foot" sand, and most of the remainder is from the "1,400-foot" sand; both sands are of Eocene age. A small amount of water for domestic use is pumped from the terrace deposits of Pliocene and Pleistocene age. Both the "500-foot" and the "1,400-foot" sands are artesian aquifers except in the southeastern part of the area; there the water level in wells in the "500foot" sand is now below the overlying confining clay. Water levels in both aquifers have declined almost continuously since pumping began, but the rate of decline has increased rapidly since 1940. Water-level decline in the "1,400foot" sand has been less pronounced since 1956. The cones of depression in both aquifers have expanded and deepened as a result of the annual increases in pumping, and an increase in hydraulic gradients has induced a greater flow of water into the area. Approximately 135 mgd entered the Memphis area through the "500-foot" sand aquifer in 1960, and, of this amount, 60 mgd originated as inflow from the east and about 75 mgd was derived from leakage from the terrace deposits, from the north, south, and west and from other sources. Of the water entering the "1,400-foot" sand, about 5 mgd was inflow from the east, and about half that amount was from each of the north, south, and west directions. The average rate of movement of water outside the area of heavy withdrawals is about 70 feet per year in the "500foot" sand and about 40 feet per year in the "1,400-foot" sand. The average rate of depletion of storage in each aquifer since pumping began is about 1 mgd. Most of the recharge to the "500-foot" and "1,400-foot" sands occurs in outcrop areas about 30-80 miles east of Memphis. Also, water leaks from the terrace deposits to the "500-foot" sand in some places, and there may be some leakage from streams where the confining clay is thin or is breached by faults or streams. 01 02 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES The quality of water from both the principal aquifers is very good. Iron, carbon dioxide, and hydrogen sulfide are the only constituents found in undesirable quantities. 'Vater from the terrace deposits is hard but generally contains less iron and carbon dioxide than water from either of the principal aquifers. The hydraulic characteristics of both aquifers were determined by• pumping tests and by applying the knowledge of the geology o.f the area ; these characteristics indicate that the aquifers are capable of producing more water than is currently being pumped from them. The "500-foot" sand wil...

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 o f 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 evel s 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 chang ing the pumping rat es or by varying the areal distribution of pumping.

Springs constitute an important source of water in east Tennessee, and many individual springs are capable of supplying the large quantities needed for municipal and industrial supplies.Most of the springs in east Tennessee issue from solution openings and fractured and faulted zones in limestone and dolomite of the Knox Group, Chickamauga Limestone, and Conasauga Group. The ability of these rocks to yield a sustained flow of water to springs is dependent on a system of interconnected openings through which water can infiltrate from the land surface and move to points of natural discharge.Ninety springs were selected for detailed study, and 84 of these are analyzed in terms of magnitude and variability of discharge. Of the 84 springs analyzed, 4 flow at an average rate of 10 to 100 cfs (cubic feet per second), 62 at an average rate of 1 to 10 cfs, and 18 at an average rate of 1 cfs or less. Of the 90 springs, 75 are variable in their discharge; that is, the ratio of their fluctuations to their average discharges exceeds 100 percent.Mathematical analysis of the flow recession curve of Mill Spring near Jefferson City shows that the hydrologic system contributing to the flow of the spring has an effective capacity of about 70 million cubic feet of water. The rate of depletion of this volume of water, in the absence of significant precipitation, averages 0.0056 cfs per day between the time when the hydrologic system is full and the time when the spring ceases to flow. From such a curve it is possible to determine at any time the residual volume of water remaining in the system and the expected rate of decrease in discharge from that time to cessation of flow.Correlation of discharge measurements of 22 springs with those of Mill Spring shows that rough approximations of discharge can be projected for springs for which few measurements are available. Seventeen of the springs analyzed in this manner show good correlation with Mill Spring: that is, their coefficients of correlation were 0.70 or better as compared with a perfect correlation factor of 1.00

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