A SIMPLE METHOD OF COMPUTING PUMPING INDUCED LEAKAGE RATE AND VOLUME IN AN AQUIFER-AQUITARD SYSTEM

Many natural aquifers are semi-confined where aquitards separate them from adjacent aquifers. When groundwater is withdrawn from one aquifer, transfer of water from the adjacent aquifer to the pumped aquifer will occur, a process termed leakage. Pumping induced leakage across aquitards could be an important water budget component that must be considered in groundwater management. In this paper, we have discussed pumping induced leakage in a leaky-confined aquifer bounded by a relatively thin aquitard whose storage effect is neglected. Both constant-rate and constant-drawdown, fully penetrating vertical pumping wells are considered. We have provided closed-form analytical solutions of steady-state leakage rates and volumes within any given radial distance from the well for both the constant-rate and constant-drawdown pumping wells. For the constant-rate well, we have provided closed-form analytical solutions for total leakage rate and volume over the entire aquitard-aquifer boundary at a given time; and semi-analytical solutions for calculating leakage rate and volume within any radial distance from the pumping well at a given time. For the constant-drawdown well, we have further provided the analytical solutions of the leakage rate and volume in the Laplace domain, which are numerically inverted to yield results in the real time domain. These solutions are useful for managing multi-layer aquifers in which pumping induced water transfer across the aquitards can occur.