This paper addresses the achievements in understanding the hydrogeological conditions in the low permeability claystone formation of the Opalinus Clay at the Mont Terri Rock Laboratory. The synthesis work consisted of (i) an assessment of clay-specific artifacts which may affect the interpretation of hydraulic tests, (ii) a survey of hydraulic rock properties such as hydraulic conductivity and storage coefficient, and (iii) an assessment of the governing flow laws and definition of hydrogeological units and flow boundaries on the site scale. Drawing on the broad hydrogeological data base, confidence is gained in the hydraulic barrier function of the Opalinus Clay, which effectively prevents groundwater flow between the over- and underlying aquifer systems.
a Colenco Power Engineering Ltd, Täfernstrasse 26, Baden CH-5405, Switzerland
b NAGRA: Natl.Coop.DisposalRadioactive, Hardstrasse 73, Wettingen CH-5430, Switzerland
c IRSN: Inst.Radioprotect./SureteNucl., 60-68 Ave. du Genéral Leclerc, Fontenay Aux Roses Cedex F-92 262, France
d BGR: Bundesanstalt fur Geowiss., Stilleweg 2, Hannover D-30655, Germany
e Obayashi Corporation, 2-15-2 Konan, Minato-ku, Tokyo 108-8502, Japan