Application of Numerical Groundwater Model to Determine Spatial Configuration of Confining Unit Breaches near a Municipal Well Field in Memphis, Tennessee

Abstract

Thinning or localized absence (a breach) of an aquitard warrant concern because this limits the protection it affords water-supply aquifers beneath. The objective of this study was to assess potential spatial configurations of breaches within the aquitard overlying a water-supply aquifer in an urban well field. A three-dimensional groundwater flow model was utilized to investigate leakage pathways through the aquitard and simulate five potential breach configurations with three different hydraulic conductivity values. Through particle tracking analysis , estimates for the modern water percentage and apparent age of the modern water extracted by the production wells at the well field were obtained and compared to published age-dating data. Breach configurations resembling a broad paleochannel, which could originate through erosion of clay and silt within the aquitard, match the extent and proportion of modern water in the water-supply aquifer at the well field. This methodology has utility in evaluating the vulnerability of water-supply aquifers that are partially confined and susceptible to contamination, while assessing the likelihood of potential zones of increased vulnerability and offering targets for further investigations. DOI: 10.1061/ (ASCE)HE.1943-5584.0002117. This work is made available under the terms of the Creative Commons Attribution 4.0 International license , https://creativecommons.org/licenses/by/4.0/.