Chemical character of ground water in the shallow water-table aquifer at selected localities in the Memphis area, Tennessee

Abstract

The City of Memphis depends solely on ground water for its water supply. About 97 percent of inventoried pumpage in the Memphis area, which totaled about 194 Mgal/d in 1979, is from the Memphis Sand. This aquifer generally has been believed to be separated from the shallow water-table aquifer (alluvium and fluvial deposits) by a relatively thick and wide-spread confining bed consisting chiefly of clay. Studies by the Geological Survey in recent decades, however, have indicated that part of the recharge to the Memphis Sand probably is derived by vertical leakage from the shallow water-table aquifer through the confining bed and that locally "windows" of sand exist in the confining bed through which any contaminants in the shallow water-table aquifer could enter the Memphis Sand (See Criner and others, 1964, p. 30; Bell and Nyman, 1968, p. 7-8; Parks and Lounsbury, 1976, p. 26-27). More recently, additional evidence of vertical leakage being a component of recharge to the Memphis Sand was provided during the calibration of a digital computer model of the aquifers in the Memphis area. For this calibration a leakage factor, averaging about 20 percent over the Memphis area, had to be applied to the model in order to simulate known historic water levels in the Memphis Sand (J. V. Brahana, 1980, oral commun. ). This discovery has heightened concern about the possibility of contaminants being in the shallow water table aquifer, and thus, the potentiality for any contaminants to enter the Memphis Sand. Areas where the shallow water-table aquifer is most susceptible to contamination are those that have been or are being used for waste disposal. Historically, Memphis and Shelby County along with private concerns and industries have used dumps and landfills in two geologically and topographically different areas -- the flood plains of nearby streams and abandoned gravel pits in upland areas. These dumps and landfills have received a large variety of wastes including ashes, construction and demolition materials, garbage, rubbish, street refuse, and chemical and industrial wastes. Most of these dumps and landfills were closed in the early 1970's at the beginning of state regulation of waste disposal practices. Nevertheless, leachates from these waste disposal facilities presumably have been and are entering the shallow water-table aquifer.