Modeling contaminant transport in a two-aquifer system with an intervening aquitard

This study deals with the issue of one-dimensional solute transport in a two-aquifer system, where an aquitard lies between two aquifers. Different from previous studies on analysis of the contaminant transport affected by the presence of an aquitard, we developed a mathematical transport model in an aquifer-aquitard-aquifer system with considering transport of solutes in the aquitard governed by both advection and diffusion. The Laplace-domain solution of the model for concentration distributions is obtained by the Laplace transform technique and its corresponding time-domain results are computed numerically by using Laplace numerical inversion. An explicit finite difference model is also developed to simulate two-dimensional contaminant transport process in the system. The simulated depth-averaged concentrations in the lower and upper aquifers slightly differ from those predicted by the present solution. The results show that the movement of contaminant in the upper aquifer is slowed down considerably due to the advective transport in aquitard. When neglecting the aquitard advection (a zero Peclet number), the concentration level in the lower aquifer will be underestimated, especially at late times. In addition, the contaminant concentration in the lower aquifer increases significantly with aquitard's Peclet number.