Key points:

•  Deep flow systems are affected by large changes in morphology and / or by high sub- glacial water pressure. This may affect deep aquifer exfiltration paths, water fluxes and residence times, notably in the aquifers above the host rock (Malm, Hauptrogenstein).
• Robust and efficient self-sealing of reactivated faults in Opalinus Clay are maintained as long as the overburden remains > 200 m. This is the case for all sites over the next one million years in the most likely erosion scenario. For certain less likely evolutions in JO these conditions are not met. A substantial increase of hydraulic conductivity only occurs for overburden lower than ca. 30 – 50 m, this is very unlikely at all sites.
• Changes in porewater chemistry and diffusion properties of Opalinus Clay will be small during the period under consideration.
• The loading and unloading of the host rock with a few hundred metres of ice will result in only a minor change in host-rock porosity. Associated changes in pore pressure will result in a short-term increase in hydraulic gradient from the host rock towards the aquifers. The effect can be constrained and shown to be not relevant for overall tracer transport.
• Dissolution processes are unlikely to affect properties and long-term stability of the host rock and confining units because of small driving forces, low hydraulic