Present study is motivated by problems of admixture transport in geothermal systems. Numerical simulations of stochastic haline convection in an inhomogeneous domain consisting of a homogeneous isotropic porous medium divided by a horizontal layer at different porosity and permeability are performed. Convection is driven by more dense brine near the upper boundary which is fed by a dissolved admixture diffusing from the boundary. An influence of interior layer on convective flows and mass transfer in all domain is investigated. As obtained, dynamic behavior of fluid in the layer is forced or natural mode of convection depending on properties of this layer. There is the intermediate case when forced convection arisen initially is transformed into natural convection with time. In this case, the layer can order convective flows above itself so that the roughly periodic structure of "brine balls" is formed. (C) 2018 Elsevier Ltd. All rights reserved.