With the Bülach borehole, Nagra enhanced its knowledge of the Nördlich Lägern siting region. Investigations focused on the properties of the underground rock formations – particularly those of the Opalinus Clay in which the deep geological repository will eventually be constructed. The Bülach borehole reached a depth of 1,370 metres. It was the first of nine deep boreholes that were drilled within the framework of Stage 3 of the site selection process.
The Opalinus Clay at its deepest
The Bülach, Bachs, Stadel-2 and Stadel-3 boreholes supplement the overview of the geological conditions in the region.
In the south-eastern part of the siting region, the Opalinus Clay shows quiet bedding. The Bülach borehole allowed investigating the edge of this zone. In Bülach, the Opalinus Clay is located at its deepest point in the siting region, meaning that it was possible to investigate all relevant geological layers.
Fossilised coral reef
Earlier investigations using so-called 3D seismic measurements – similar to probing the subsurface by means of ultrasound – revealed a body of rock overlying the Opalinus Clay that differs from the surrounding rock. We now know from the Bülach borehole that this layer is a fossilised coral reef. Between this reef and the Opalinus Clay is a 30-metre-thick layer of rock with a high clay content that provides a very high level of containment. The coral reef itself is almost 50 metres thick.
Earlier boreholes
Data for the Nördlich Lägern region are already available from a deep borehole previously drilled in the community of Weiach in 1983 (see photo on left). The Weiach exploratory borehole reached a final depth of 2,482 metres. As a result, for the first time, it was possible to prove beyond doubt the existence of the so-called Permo-Carboniferous Trough, which is sunk deep into the crystalline bedrock.
Investigations using so-called 3D seismic measurements – similar to probing the subsurface by means of ultrasound – revealed fault zones in the deep subsurface in the northern part of the Nördlich Lägern siting region. For a deep geological repository, the geology has to be undisturbed. Nagra therefore withdrew the other applications for boreholes in Weiach and Glattfelden that had been submitted as part of the 2019 – 2022 deep borehole campaign. No new findings were to be expected.
Find out more about the Weiach exploratory borehole in Technical Report NTB 88-08.
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Further deep boreholes
Stadel-3 borehole
Stadel-3 was the second deep borehole to be drilled in the Nördlich Lägern siting region as part of Stage 3 of the site selection process.
Stadel-2 borehole
The Stadel-2 borehole was the third deep borehole to be drilled in the Nördlich Lägern siting region as part of Stage 3 of the site selection process.
Bachs-1 borehole
The Bachs borehole was the fourth deep borehole to be drilled in the Nördlich Lägern siting region as part of Stage 3 of the site selection process.
Trüllikon-1 borehole
The Trüllikon borehole was the first deep borehole to be drilled in the Zürich Nordost siting region as part of Stage 3 of the site selection process.
Marthalen borehole
The Marthalen borehole was the second deep borehole to be drilled in the Zürich Nordost siting region as part of Stage 3 of the site selection process.
Rheinau-1 borehole
The Rheinau borehole was the third deep borehole to be drilled in the Zürich Nordost siting region as part of Stage 3 of the site selection process.
Bözberg-1 borehole
Bözberg-1 was the first deep borehole to be drilled in the Jura Ost siting region as part of Stage 3 of the site selection process.
Bözberg-2 borehole
Bözberg-2 was the second deep borehole to be drilled in the Jura Ost siting region as part of Stage 3 of the site selection process.
Work report
