Essen-1 borehole of the hydro/05neb campaign: technical aspects and hydrogeological investigations

The drilling and core-drilling of the 508 metre deep Essen-1 borehole in the northern part of the Kempen (NE Belgium) is part of a data acquisition campaign called hydro/05neb. It aims at providing data for the various hydrogeological models that are running at SCK•CEN. This research, commissioned by ONDRAF/NIRAS, was executed for the performance assessments studies with regard to the possible disposal of high-level and long-lived radioactive waste in the Boom Clay. The investigations mainly focused on the hydraulic characterisation of the Lower-Rupelian and the Lede-Brussel aquifer. Numerous analyses were performed in the borehole as well as in the laboratory. A detailed geological description of the borehole is given, based on cuttings, cores, and geophysical measurements. Hydraulic properties of the investigated units were determined from in situ pumping tests and laboratory experiments and compared to indirect (soft) data. Hydro geochemical analyses are also provided for both aquifers and the well is nowadays integrated in the regional piezometric network of and regularly monitored by SCK•CEN. Finally, the transferability aspects of the migration and geochemical properties of the Boom Clay are assessed, because up to now they were essentially studied at the Mol site.