One of the host rocks considered for disposing high-level, long-lived and heat-emitting radioactive waste arefine-grained detritic rocks. In Belgium, most research on the storage of nuclear waste is focused on poorly-lithifiedclayey host rock, i.e. the Oligocene Boom and Eocene Yper clays present in the subsurface of northern Flanders.Beside clay also pelitic shaly and slaty formations have favourable characteristics to consider as potential hostrock in Belgium (cf. 1979 European Catalogue).In this contribution a screening assignment is performed on the identification of Palaeozoic pelitic hostrock formations for their suitability to store nuclear waste. Four exclusion criteria are used to eliminate thoseformations that are less suitable as a host. The criteria are: host rock lithology (only pelitic rock is considered),minimum thickness of the formation (> 100 m), minimum depth (a minimum 100 m-thick formation needs to bepresent below 200 m depth), and maximum depth (at least 100 m above 1500 m). The screening approach allowedto retain seven low-grade metamorphic shaly and slaty formations of the Lower Palaeozoic Brabant Massif and theUpper Palaeozoic Ardenne Allochton that have favourable thicknesses and a suitable fine-grained lithology. Theirgeological extent is known to be sufficient, either in subcrop or in outcrop. Currently, a detailed mineralogicaland petrophysical research is performed to investigate complementary properties linked to the long-term safetyof a repository. For each formation, long (> 100 m) continuous drill cores were sampled at low resolution (2 m)to investigate the variation in mineralogical content (with QXRD) and thermal conductivity with depth. To decidehow to cut the cores, their internal geological structure was investigated using micro-CT scanning. The results ofour analyses are compared to published values taken from other (inter)national pelitic host rock investigations.Other formations were not selected because of less optimal characteristics or insufficient material to allowfurther investigations. However, none of the formations should be considered as definitely excluded.
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Persistent Scatterer Interferometry (PSI) is a valuable technique for studying ground deformation in Belgium and providing more information on their spatial and temporal patterns. In this work, about 700 SAR images of different tracks from the European satellites ERS (1992-2001), ENVISAT (2003-2010), SENTINEL 1 (2014-2018) were processed. TerraSAR-X data covering the time span 2012-2014 and the area of Brussels were processed as well. A mapping of the annual average velocity of the PS of the entire period highlighted already known ground movements discovered during country scale levelling campaigns. But thanks to its millimetre precision, it permitted to highlight new movements that were not identified before. Seven large subsidence or uplifting areas can be spotted from the velocity map. From north to south, the regions facing ground movements are: The West-Coast, Antwerp and along the Schelde river and estuary, the Limburg Campine coal mines basin, Merchtem Londerzeel, the cities of Brussels and Liège as well as a large area related to the Tournai Mons-Charleroi coal mines basin. The purpose of this work is to make an overview of the situation (observations, first interpretations) of these ground movements. The highest positive (uplift), 20 to 25 mm/year and negative (subsidence) -17 to -20 mm/year velocity values are recorded around the former Limburg coal mines areas. The movements are closely linked to the groundwater extraction needed during the exploitation time and the recharge of the mining aquifer occurring at the end of the pumping. Among the seven highlighted zones, in Merchtem 25 Km NW of Brussels, a ground subsidence (-3 mm/year on average) is occurring since the beginning of the ERS acquisitions in 1992. Through the time (ERS, ENVISAT, TerraSAR-X and SENTINEL 1) the subsidence pattern reduces his extent and is replaced by an uplift due to the raise of the water table. Piezometers located in the deep Cambro-Silurian aquifer show a clear recharge of this aquifer since the late 1990’s. The subsidence is finally reduced to a zone where three breweries are very active and pumping groundwater for the production in the Ledo-Paniselian aquifer and in the Cambro-Silurian as process water. The Stella Artois brewery located in Leuven 30 Km E of Brussels is facing a ground subsidence as well clearly visible with the PSI data.
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