Flow and transport phenomena in porous media are the governing processes in many natural and industrial systems. Not only do these flow and transport phenomena occur on different space and time scales, but it is also the porous medium itself which is heterogeneous where the heterogeneities are present on all spatial scales. We consider a large domain with randomly distributed heterogeneities where complex two-phase--two-component processes are relevant only in a small (local) subdomain. This subdomain...