Dessel-5 borehole: technical aspects and hydrogeological investigations

The drilling and core-drilling of the 200 meter deep Dessel-5 borehole in the eastern part of the Kempen is part of an extensive data acquisition campaign. It aims at providing data for the various hydrogeological models that are running at SCK•CEN. This research, commissioned by ONDRAF/NIRAS, is executed 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 characterization of the Diest (lower part) and the Berchem aquifer, and the top of the Boom Clay aquitard (Boeretang member, formerly referred to as transition zone). Therefore, 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 local piezometric network of and regularly monitored by SCK•CEN.