Water flow in the Oxfordian and Dogger limestone around the Meuse/Haute-Marne Underground Research Laboratory

Abstract Within its scientific program devoted to the feasibility of a high level radioactive waste facility in the Callovo-Oxfordian argillaceous rock (COx) of the eastern Paris Basin, Andra has conducted an extensive characterization of the Oxfordian and Dogger limestone formations above and below the COx. More than 25 wells were dedicated to the hydrogeological and geochemical characterization of the Oxfordian and Dogger limestones over a 400 km 2 sector. An original strategy was developed to obtain field hydrogeological measurements and representative formation water samples in these wells. An extensive 3D set of field data and water compositions were obtained over 15 years. The geochemical and isotopic data indicate a meteoric origin for the Oxfordian and Dogger limestone waters. The geological observations revealed a clay rich level horizontally dividing the Oxfordian limestones into two parts in the NE zone of the study area. In the lower Oxfordian, water inflows come mainly from the outcrop in the south-eastern part of the study area. Three meteoric water inflows were identified in the upper Oxfordian in the study area: the first one covers the eastern and southeastern part of the area, the second one covers the diffuse fracturation zone (DFZ) south of the area, and the third one is located in the north eastern part of the area. The two first inflows consist of fresh water, while the last one consists of Mg 2+ , SO 4 2 - and Na + rich waters coming from the erosion of the Purbeckian lithological type facies. Fresh waters from the outcrops flow slowly towards the North West. They equilibrate with the limestone dolomite formations and are enriched by a Na + and Cl − diffusive flux coming from the Dogger through the Callovo-Oxfordian argillaceous rock. These waters mix with the water coming from the North East upper Oxfordian. The Dogger limestone is characterized by sodium chloride groundwaters with higher salinity values than the Oxfordian limestone. North–northwest flows in the Dogger limestone are slower than flows in the Oxfordian formation. In both formations, the DFZ must be considered to be an apart hydrological system.