Transient model of the confined aquifers below the Boom Clay: 2011 update: Regional Hydrogeological Modelling of the Mol Site

For more than 35 years, SCK•CEN has been investigating the possibility of high-level radioactive waste disposal in the Boom Clay in north-eastern Belgium. This research, defined in the long term management programme for high and medium long-lived waste of ONDRAF/NIRAS, includes the regional hydrogeological modelling of the aquifer systems surrounding the Boom Clay. In this paper, the most recent update of the Deep Aquifer Pumping model (DAP) is described, which was developed to characterize and quantify the regional groundwater flow in the complex confined aquifers lying below the Boom Clay in NE-Belgium. Several conceptual improvements to the model were performed. The DAP-model was successfully calibrated using an automated inverse optimization algorithm and is able to reproduce satisfactorily the general trends in the observed groundwater heads. A detailed parameter and conceptual model sensitivity analysis were conducted. This regional model has proven its importance in gaining insight in the processes and parameters that are important in the considered confined aquifer system. These insights are of great value for planning future characterization efforts and reducing the predictive model uncertainty.