Properties at the meshes laying on the interface
 

As Finite Element-Finite Volume discretization method consider a control volume around a node, I wonder how the properties are treated when a mesh lies on an interface, particularly when we have a subregion of porous media beside an open region. Does it means that half of that control volume have the source term associated with it but not the other half? if yes? how is that treated? Any comment would be appreciated.

Amir