Pumping-induced Well Hydraulics and Groundwater Budget in a Leaky Aquifer System with Vertical Heterogeneity in Aquitard Hydraulic Properties

Abstract

In groundwater hydrology, aquitard heterogeneity is often less considered compared to aquifers, despite its significant impact on groundwater hydraulics and groundwater resources evaluation. A semi-analytical solution is derived for pumping-induced well hydraulics and groundwater budget with consideration of vertical heterogeneity in aquitard hydraulic conductivity (K) and specific storage (S_s). The proposed new solution is innovative in its partitioning of the aquitard into multiple homogeneous sub-layers to enable consideration of various forms of vertically heterogeneous K or S_s. Two scenarios of analytical investigations are explored: one is the presence of aquitard interlayers with distinct K or S_s values, a common field-scale occurrence; another is an exponentially depth-decaying aquitard S_s, a regional-scale phenomenon supported by statistical analysis. Analytical investigations reveal that a low-K interlayer can significantly increase aquifer drawdown and enhance aquifer/aquitard depletion; a high-S_s interlayer can noticeably reduce aquifer drawdown and increase aquitard depletion. Locations of low-K or high-S_s interlayers also significantly impact well hydraulics and groundwater budget. In the context of an exponentially depth-decaying aquitard S_s, a larger decay exponent can enhance aquifer drawdown. When using current models with a vertically homogeneous aquitard, half the sum of the geometric and harmonic means of exponentially depth-decaying aquitard S_s should be used to calculate aquitard depletion and unconfined aquifer leakage.

Keywords

hydrogeology / aquitard / vertical heterogeneity / semi-analytical solution / well hydraulics / groundwater budget

RIGHTS & PERMISSIONS

2023 Geological Society of China