The biodetritic and oolitic limestones of the Hauptrogenstein constitute a fractured and partly karstic aquifer in the Jura Mountains (Jäckli & Kempf 1972). The facies transition towards the clay-mineral-rich Klingnau Formation in the east occurs within the JO siting region (Section 4.2.6), i.e. the Hauptrogenstein is a relevant aquifer only in JO.

A comparatively small dataset is available on the hydrogeological properties (Fig. 4‑86). The highest transmissivities in the range of 10^-5 m²/s relate to test depths < 270 m. In the BOZ2 borehole, fluid losses occurred related to a fracture at around 350 m depth (Nagra (ed.) 2022b). The transmissivity of 4 × 10^-7 m²/s allowed groundwater to be sampled (Section 4.5.5.3). This transmissive zone is also nicely expressed in the profiles of the natural tracers in porewater (Section 4.6). In the BOZ1 borehole, only a minor inflow zone was detected by fluid logging (2 × 10^-9 m²/s) which is without expression in the tracer profiles. In the easternmost Riniken (RIN) borehole, the Hauptrogenstein is characterised by a low hydraulic conductivity and a reduced thickness (Fig. 4‑85).

Overall, the hydraulic properties mirror the facies change from west to east. The eastern limit of the Hauptrogenstein aquifer is only vaguely defined.