Investigation of Recharge Sources, Mechanisms, and Rates to the Shallow Aquifer Within Shelby County, TN, USA

Determination of recharge rates for an urban setting is a complicated process that is subject to variation based on the chosen methodology, as well as the suitability and constraints of each method. The recharge mechanism and rates to the shallow aquifer within Shelby County were assessed using multiple approaches, including the water-table fluctuations (WTF) method (using two approaches), the vadose zone pulsing method, the chemical tracer method, and the identification of areas with potential infrastructure leaks. The WTF method generated a total annual recharge rate ranging from 0.12 m/year, or 9% of precipitation (for S_y = 0.1), to 2.17 m/year, or 158% of precipitation (for S_y = 0.3), using the master recession curve (MRC) method. The large disparity in results could be due to the influence of surface-water features, additional recharge from underground water infrastructure, and high specific yield. However, the vadose zone pulsing method failed to yield any definitive outcomes, while the chemical tracer method revealed no significant presence of fluoridated municipal water flowing into the shallow aquifer. The results of WTF appeared to be more coherent and more reasonable than the other approaches. Additional regional-scale techniques and a comprehensive investigation of artificial recharge computation via leakage should be conducted to obtain more accurate estimations of recharge rate.