The mineralogical composition of the Opalinus Clay host rock is relevant for the sorption of radionuclides and the buffering of the porewater chemistry. Unaltered host rock also ensures, for example, unaltered diffusion properties (Section 5.8) and hydraulic conductivity (Section 5.6).

A number of studies show that the mineralogical composition of the Opalinus Clay is only altered if the overburden thickness is less than a few decametres (Hekel 1994, Mäder & Mazurek 1998, Mazurek et al. 2023b; Fig. 6‑46).

Given the expected erosion and the remaining overburden thickness (Fig. 6‑44), these processes are not relevant during the period under consideration. The host rock provides a stable and predictable system regarding porewater chemistry, sorption, diffusion properties and hydraulic conductivity.