A key question for the Otway Fault Project is what happens to the CO2 when it reaches the upper clay layer after migrating up Brumbys Fault? The Hesse Clay sits as a 2m thick blanket over the Port Campbell Limestone and Brumbys Fault. Permeability tests on clay core suggests the clay has very low permeability. Further, groundwater monitoring wells Brumbys 1 and Brumbys 2 are artesian (i.e. the ground water level in the wells is above the ground surface) during the high rainfall wintertime, suggesting a level of confinement. 

Shallow groundwater monitoring over a 4-year period has provided further insight into the permeability of the clay. Evidence from groundwater level response times after rainfall events and barometric response functions suggest the clay is semi-permeable. This suggests that if the controlled release experiment is conducted during dry conditions, it is likely that the CO2 gas will find leakage pathways through the clay and reach the surface above the fault zone. Surface soil flux monitoring will be employed during the experiment to assess this anticipated CO2 migration behaviour.