Mission accomplished: Deep borehole reached record depth at Mont Terri: GFZ

06/10/2026 3-4 Reaktive Fluide und Geomaterialien

[Translate to English:] Mission accomplished! Drilling of DEBORAH as reach its final depth of 848.58 m after more than 3 months of drilling. The last on-site team was happy to celebrate in front of the drill rig *(Photo: I. Semenov, swisstopo)*

[Translate to English:] Screenshot from the mDIS software platform, used during the DEBORAH drilling campaign for digital core documentation. The implementation was supported by the International Continental Scientific Drilling Program (ICDP), particularly by Cindy Kunkel (Section Geomechanics and Scientific Drilling). The image displays 360° scans of several recovered core runs from the Bänkerjoch Formation, representing part of the extensive core dataset acquired during the campaign. *(Photo: GFZ)*

[Translate to English:] Final Depth Poster as Headline Picture *(GFZ)*

Mission accomplished: Deep borehole reached record depth at Mont Terri

The international research project DEBORAH (DEep BOrehole to Resolve the Mont Terri Anticline Hydrogeology) has successfully completed its deep drilling campaign at the Mont Terri Underground Research Laboratory (URL) in northern Switzerland, reaching its final target depth of 848.58 meters on 10 June 2026.

The project, initiated by GFZ Helmholtz Centre for Geosciences and carried out in close collaboration with swisstopo, operator of the Mont Terri URL, the Federal Institute for Geosciences and Resources (BGR), and Nuclear Waste Services from the UK, marks the deepest drilling project ever conducted at the Mont Terri site.

Drilling operations began on 18 February 2026 from within the Mont Terri tunnel, approximately 150–200 meters below the surface, resulting in a total vertical investigation depth of nearly 1,000 meters below ground level. Over the course of the campaign, the team successfully collected more than 680 core samples, corresponding to more than 150 meters of core material, while achieving full core recovery throughout the entire borehole.

The drilling campaign was accompanied by an extensive scientific programme, including systematic core sampling, hydrogeological testing, and comprehensive geophysical logging operations. In addition, the borehole will serve as a key reference structure for an upcoming seismic characterization campaign designed to image the geological architecture of the Mont Terri anticline using an integrated surface–tunnel–borehole acquisition geometry.

DEBORAH builds on more than three decades of multidisciplinary research on Opalinus Clay at the Mont Terri URL. As the deepest scientific borehole drilled at the site to date, the project provides a unique opportunity to investigate the hydrogeology and geological structure of the folded Jura on a regional scale, extending previous research far beyond earlier local investigations.

Project coordinator Dr. Felix Kästner, who has supervised the on-site works and drill core processing emphasizes the significance of this achievement:

“Reaching the final depth of 848.58 meters marks a major milestone for the DEBORAH drilling campaign and represents the successful outcome of a remarkable team effort involving numerous national and international partners. The completion of drilling is not the end of the project, but rather the beginning of an equally important scientific phase, where we will focus on the analysis and interpretation of the extensive data and samples collected throughout the campaign. This borehole now serves as a key geological and scientific reference, not only for the Mont Terri site, but also for future deep geological investigations, including the upcoming site selection programme in Germany and other international initiatives.”

With drilling operations now successfully completed, the project enters its next scientific phase, focusing on the detailed analysis and interpretation of the extensive geological, hydrogeological, and geophysical datasets collected during the campaign. DEBORAH is an important scientific benchmark for future deep geological investigations at Mont Terri and beyond.