The role of fault pathways for modern and deep recharge to a semi-confined aquifer: revised analysis of modern water leakage pathways in the Davis wellfield, Memphis, Tennessee, USA

Abstract

Hydrologic tracer, borehole log and geophysical data provide new insight into recharge sources and pathways to the semi-confined Memphis aquifer in the Davis wellfield, Memphis, Tennessee, U.S.A. New data and recent studies highlight the importance of faults as potential pathways for the migration of modern water into the Memphis aquifer, an important regional public, industrial, and agricultural water supply. Geochemical and environmental tracer data collected over the past 28 years, combined with hydrologic, stratigraphic, and structural data, were used to evaluate changes in water quality and different recharge pathways to the Memphis aquifer. Assessment of stratigraphic and structural relationships argue for the wellfield being bound by a fault along the bluff line (west) and another fault or faults along the eastern and southeastern margins. Modern water recharge (< 60 years old) occurs through the fault along the western boundary of the wellfield, whereas modern water and, seasonally, deep-seated (helium-bearing) fluids recharge along the fault on the southeastern margin. Each recharge source and pathway present different vulnerabilities, suggesting that the role of faults in wellfields within active tectonic regions needs to be assessed.