A model of the process of the contaminant convective diffusion with nonlinear sorption in one-layered aquifer and multi-layered, consisting of basic aquifers with an aquifer dividing them by, is considered here. A three-dimensional formulation of the problem with a special averaging is reduced to a two-dimensional one, allowing to investigate the interaction of aquifers taking into account the aquitard of arbitrary thickness, and its absence as well.