The general conclusions follow up on the questions posed in Section 6.1.2 for the relevant climatic and erosive processes and their impact on the hydrogeology and geochemistry of the host rock and confining units.

Tectonic evolution

• Tectonic deformation rates in Northern Switzerland are small and are expected to continue to remain small over the next one million years.

• The spatial uplift pattern in Northern Switzerland over the next one million years will continue to be dominated by Alpine uplift. Uplift rates are expected to be < 0.36 mm/yr, most likely ~ 0.15 mm/yr, with relatively small differences between the NL and ZNO siting regions and slightly lower rates near JO.

• Baselevel drop due to subsidence of the Upper Rhine Graben might increase the incision potential of the Hochrhein River and the Aare River. It is expected that sediment supply and ongoing uplift of the Rhenish Massif will compensate for subsidence and work against baselevel drop.

• Inherited faults will localise strain and future deformation. Mainly the regional fault zones will be preferentially reactivated. The location of larger faults is taken into account when planning the locations of the disposal areas.

• If new faults develop in the host rock, they are expected to be segmented and small in length and offset (scaling relationships; see fault architecture in Section 5.5.4).

Climate evolution

• According to different anthropogenic CO₂ scenarios, 3 to 5 large glaciations (LGM-size or larger) are expected that might reach the external Alpine Foreland in the next one million years. The climate conditions during future glacial periods are expected to be similar to those during past cycles.

• Considering present anthropogenic climate change and the longevity of increasing CO₂ levels within the atmosphere, inception of the next glaciation is expected to be significantly delayed, and the next large glaciation may only occur in ~ 200'000 years.

• Each glacial period is expected to be associated with permafrost conditions during the phases of coldest temperatures. Permafrost is expected to reach maximum depths of 100 – 200 m.

• Ice thicknesses and the duration of the ice occupation at the sites varied during past glacial cycles because of the different distances to the Alps and different topography (ZNO > NL > JO). The same pattern will most likely be seen during future glaciations with ice thicknesses between 200 and 400 m and durations of ice occupation between 1'000 and 3'000 years.

• After a glacial state, the climate warms, and climate conditions change from a polar climate (Switzerland largely covered by ice and/or permafrost conditions) towards a continental or temperate climate. Also, a warmer-drier climate cannot be excluded, at least in the high-emission scenarios.

Erosion

• Future erosion processes (glacial and non-glacial) are expected to continue as observed in the Quaternary period, but at lower rates with no major drainage reorganisation, smaller glaciers, delay in glacial inception, and harder-to-erode rocks below the Molasse units.

• The main river system affecting erosion in the siting regions over the next one million years remains the Aare – Rhine River system. The Rhine is further growing at the expense of the Danube with a very limited impact on the incision potential.

• A residual overburden thickness of 200 m classified as reliable for maintaining self-sealing behaviour can be shown for the most likely scenarios in all the siting regions for the period under consideration. Using the 5 – 95% range as a reference, JO shows more limitation for such a 200-m criterion at the location of the provisional disposal area. This site thus depends on the preservation of the local topography (see Fig. 6‑47).

• Excavation of the repository by erosion within the next one million years is extremely unlikely at all three sites. The NL site is most robust in this regard because of the greater repository depth and the expected rates of erosive processes (see Fig. 6‑47).

Fig. 6‑47:Synthesis profiles for visualising future non-glacial erosion in the three siting regions

The profile shows ranges of future evolution of the local erosion base and local topography for selected scenarios and selected parameter combinations (see corresponding map repre­sentations in Fig. 6‑35 for the present-day drainage network scenarios and Fig. 6‑37 for the JO alternative drainage scenario Rinikerfeld). The profile location is the same as in Fig. 6‑27. Note that the formation of glacial overdeepenings is not illustrated in this plot. Vertical exaggeration is ~ 20-fold. For the provisional disposal area at JO (lateral position corresponds to the location of lithological column in the plot), the remaining overburden thickness with respect to the coloured and dashed bands of future terrain shown here contributes to the green curve ("Local Topography"; output Model B) in Fig. 6‑44.

Hydrogeology and hydrochemistry

• Deep groundwater flow systems are affected by processes of long-term geological evolution such as large changes in morphology, changing climate or by glaciations inducing high sub­glacial water pressure. This affects discharge paths, water fluxes and residence times in the aquifers. Discharge areas will be progressively located closer to the repository locations.

• Loading and unloading with a few hundred metres of ice will result in minor changes in porosity because of the pre-consolidation of the Opalinus Clay during maximum burial. At the same time, the loading and unloading induces transient over- and underpressures, respectively. The overpressures related to ice loading are of limited magnitude and duration. The overall effect on advective flux in the host rock is thus small to negligible.

• The low hydraulic conductivity of the Opalinus Clay will be maintained over the period under consideration at all sites. This is explained by the remaining overburden thickness of at least 200 m. Depending on the river network evolution, the remaining overburden thickness may be less in JO towards the end of the period under consideration (see above).

• Erosion and decreasing porewater salinity pose minor changes to diffusion properties during the next one million years.

• Dissolution processes are not expected to affect the barrier properties of the host rock and confining units in a significant way.

• Overall, the host rock and confining units provide a stable and predictable environment for hosting the repository. The deepest site, NL, is most robust in this regard.