The greatest thickness of the containment-providing rock zone is one of the central arguments for selecting Nördlich Lägern as the site for a deep geological repository (Explanatory Report on the General Licence Applications, NTB 24-12, Chapter 6).
The argument is explained in the report Begründung der Standortwahl (“Justification of the Site Selection” (in German), NTB 24-03, Section 5.2.1). At over 300 metres, Nördlich Lägern has the thickest vertical extent of the containment-providing rock zone. This is favourable for both the HLW and the L/ILW repository in terms of the retention capacity of the geological barrier.
The reference report Qualitative Bewertung der 13 Kriterien gemäss Sachplan geologische Tiefenlager (“Qualitative Assessment of the 13 Criteria according to the Sectoral Plan for Deep Geological Repositories” (in German), NAB 24-23, Section 4.1.1) defines the spatial extent of the three siting regions and shows how the argument is substantiated by means of a qualitative assessment of the respective containment-providing rock zones based on pre-defined criteria relating to safety.
The supporting geological information for the qualitative assessment of the containment-providing rock zone, which is composed of the host rock and the confining geological units, is documented in detail in the reference report Geosynthesis of Northern Switzerland (NTB 24-17, Section 4.2.3 and Section 4.9). The key statements are presented below: Nördlich Lägern has the greatest distance between the centre of the host rock and the nearest overlying aquifer, while this distance is smallest in Jura Ost. In Nördlich Lägern and Zürich Nordost, the upper confining geological units are demarcated by the Malm aquifer, in Jura Ost by the Hauptrogenstein aquifer. The distance from the centre of the host rock to the nearest underlying aquifer (the Keuper aquifer) is similar in all siting regions. However, the Keuper aquifer differs in the three regions: in Zürich Nordost and Jura Ost, the aquifer appears to be continuous, whereas in Nördlich Lägern the permeable layers are bound to locally occurring drainage channels filled with sandstone. The spatial occurrence of the Keuper aquifer in Nördlich Lägern is thus heterogeneous, and water circulation is limited. Where the Keuper aquifer is not present in Nördlich Lägern, the thickness of the containment-providing rock zone is significantly greater, reaching down to the Muschelkalk aquifer.
