Hydraulic conductivity variability of the Boom Clay in north-east Belgium based on four core drilled boreholes

The hydraulic conductivity of the Boom Clay, is investigated since many years in Belgium in the framework of the performance assessment of potential geological disposal of high-level radioactive in this formation. Although a substantial part of the investigation have been performed at the reference site of Mol-Dessel, many efforts have been also done to characterise the Boom Clay over its depositional area. This paper presents the results of numerous vertical and horizontal hydraulic conductivity values (Kv and Kh) determined in the laboratory, on clay cores from four distant boreholes i.e. Doel-2b, Zoersel, Mol-1 and Weelde 1. These boreholes have increasing depths and thicknesses and are spread over the north-east of Belgium in an area of about 1100km². The results are interpreted according to depth and possible hydrostratigraphic subdivisions. Complementary analyses, as grain-size, are used to interpolate the vertical profile of hydraulic conductivity and to increase our confidence in the global value of the parameter at the scale of the formation thickness. The global values of Kv and Kh are calculated using harmonic means of the lower scale values. This study financed by SCK•CEN is mainly based on various projects supported by ONDRAF/NIRAS and by some additional work supported by SCK•CEN.