The assumption is that most brine is in the salt and anhydrite, but most transport will be in the anhydrite beds. The anhydrite beds have measured properties about one million times that of the salt. Salt has low permeability in the laboratory, but in the field, salt has six orders of magnitude more permeability. The Salado, as a whole, has more horizontal permeability than vertical permeability. Salt does not have perfectly plastic flow.
Salt can also be brittle.
If the stress is at a higher rate, the salt will be brittle and will fracture as it has done in some of the ceilings in the WIPP site. This example demonstrates DOE's lack of understanding of core. There is little intact core in the WIPP Core Library. Most of the core is rubble so there is a lot of debate about the true origin of the claylike features recovered. The Rustler characterization problem is compounded by the exploration difficulty.