This paper considers a mathematical model of the transport of a degrading solute in a two-zone porous medium, including active and passive zones. The model takes into account the processes of diffusion, adsorption and decay of the solute in both zones. To describe the dynamics of concentrations, a system of differential equations is used, which is solved numerically using the finite difference method. A numerical analysis of the influence of decay parameters on the behavior of concentration profiles is carried out