1D reactive transport model for the Opalinus Clay at Mont Terri underground laboratory

摘要

The geochemical characterisation of argillaceous rocks and their pore waters is of crucial importance for the performance assessment of nuclear waste repositories hosted in this type of formations. It is hence essential to obtain a methodology suitable to analyse the pore water composition in clay rocks. For this reason underground laboratories, like the one at Mont Terri (Switzerland) excavated in the Opalinus Clay, can be used to test different analytical techniques and to evaluate the analytical data by means of geochemical modelling. A reactive transport model has been constructed to explain the geochemical evolution of pore waters and evaluate the obtained analytical data. The modelling results show a reasonable agreement with the measured chemical data. This is true for all constituents except for carbonate concentration and pH, a possible explanation for this disagreement could be related to a CO_2 loss of pore water samples during sampling. The original carbonate and alkalinity content has been reconstructed by geochemical modelling with reasonable results. The results of this exercise indicate that there is much to gain from combined analytical and modelling techniques to achieve a reliable characterisation of clay pore water.