Solution Exercise 3
a) The permeability distribution across a fault varies considerably, as described in the text. The highest permeability will be in the damage zone that flanks both sides of the fault core, due to the abundant fractures in this zone. The fault core typically has a low permeability from crushing and smearing of fine-grained sediment (e.g., shales).
b) The permeability variations may have significant influence on the flow system. Major preferential flow pathways can occur on either side of the fault within the damage zone because the permeability there is typically much higher than that of the undamaged host rock. The fault core typically has a very low permeability and thus can act as a barrier to flow. This can compartmentalize the flow system into distinct hydrogeological units across the fault. If this were at a contaminated site, the mass flux of contaminants (i.e., the amount of contaminant being transported by the flowing water) could be significantly higher in the damage zone. In contrast, the low-permeability fault core may serve as a barrier to contaminant migration (across the fault). Thus, it is critical to characterize the physical and hydraulic character of faults as part of a hydrogeological investigation in fractured rock.