ANALYTICAL SOLUTIONS FOR PRESSURE PERTURBATION AND LEAKAGE THROUGH AQUITARDS AND WELLS IN MULTILAYERED AQUIFER SYSTEMS

Large-scale groundwater pumping or deep fluid injection in a multilayered subsurface system may generate pressure perturbation not only in the target formation(s), but also in over- and underlying units. Hydraulic communication in the vertical direction may occur via diffuse leakage through aquitards and/or via focused leakage through leaky wells. Existing analytical solutions for pressure perturbation and fluid flow in such systems consider either diffuse leakage or focused leakage, but never in combination with each other. This study presents generalized analytical solutions for pressure buildup and leakage rates in a multilayered aquifer-aquitard system consisting of any number of aquifers, alternating aquitards, injection wells, and leaky wells. The equations of horizontal groundwater flow in the aquifers are coupled by the vertical flow equations in the aquitards and by the continuity equations in the leaky wells. The general solutions were obtained by applying the Laplace Transform method and eigenvalue analysis to the governing equations. Accuracy of the solutions was demonstrated by comparison with other analytical solutions as well as with detailed numerical predictions. Application to an eight-aquifer system with leaky aquitards and one leaky well demonstrates the usefulness and efficiency of the approach, and illustrates the pressure behavior over a spectrum of leakage scenarios and parameters.