Reg. the creation of a mesh file for the reactive domain

[lurpi]

I have no direct experience. Check

Set permeability with uniform gradient distribution

I think it is easier to do it in python. With VTUinterface you need to basically adapt this example: https://github.com/joergbuchwald/VTUinterface/blob/master/examples/vtu_create_field.py With less confusing code as in the notebook before;-)

as well as the publication https://www.sciencedirect.com/science/article/pii/S136516092100263X

I suggest you to open a different question, related to the definition of random fields: OGS: [case] RandomFieldMeshElementParameter