AMP - BWG-5 : Mont Terri Project - Geochemistry of Water in the Opalinus Clay Formation at the Mont Terri Rock Laboratory
This report presents the integrated geochemical investigations conducted at the Mont Terri Rock Laboratory (Canton Jura, Switzerland), focusing on the Opalinus Clay formation of Middle Jurassic age.
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Abstract
Complementary analyses of solutes, stable isotopes and gases were performed, yielding a comprehensive dataset on pore water chemistry. The results were assessed through geochemical modelling, enabling interpretation of the most probable in situ chemical conditions and their long-term evolution. The study highlights the crucial role of water–rock interactions, ion exchange and diffusion-controlled transport in shaping the geochemical environment of Opalinus Clay. Findings also underline the sensitivity of measurements to perturbations, especially oxidation, and stress the importance of minimising such artefacts. Overall, the project improves understanding of chemical and transport processes in claystone systems, with implications for hydrogeology, natural geochemical evolution, and potential safety assessments for underground waste disposal.