Abstract

Leakage of water into the semi-confined Memphis aquifer near the Sheahan well field in Memphis, Tennessee, has been suggested by many studies extending back to the 1960s. A leakage pathway from Nonconnah Creek to the Sheahan well field was investigated over a 1-year period using multiple approaches: (1) stream discharge data, (2) hydraulic head data, (3) geochemical and environmental tracer (3H/3He and chlorofluorocarbon) studies, and (4) geochemical modeling. The stream loss data strongly support the conclusion that losses from the creek contribute at least 2,600 m3/d to the shallow aquifer, and hydraulic head data consistently indicate the majority of this infiltrated surface water flows within the shallow aquifer toward the Sheahan well field. Tritium-3He data from shallow aquifer monitoring wells within the Sheahan well field are composed of modern water with ages that generally increase with distance from the creek toward the well field. The leakage pathway from the creek to the well field is interpreted to involve seepage of creek waters into the shallow aquifer, mixing with other water sources and chemical reactions as the infiltrated waters flow in the shallow aquifer along a paleovalley toward the Sheahan well field, as well as leakage from the shallow to the Memphis aquifer through a hydrologic window in the upper Claiborne confining unit. The results of this work emphasize the utility of multiple investigative approaches in studies of groundwater flow to well fields, but they also illustrate the complexity of groundwater flow and groundwater vulnerability in a stressed water-supply aquifer system.

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