Hydrogeology of East site: a conceptual model derived from ANDRA investigations

The site envisaged for a deep laboratory in the east of France, at the boundary between the Haute-Marne and Meuse Departments, is characterized by a simple geology in an extensive tabular structure with a shallow westward dip of 1 deg C - 2 deg C. The lithostratigraphic succession in this area, from top to bottom, is: Tithonian: karstic and lithographic limestones with marly intervals; Kimmeridgian: dominant marl (low permeability); Upper and Middle Oxfordian: succession of limestone and marl beds; Callovian-Oxfordian (host formation for the laboratory): clays (very low permeability); Dogger Limestone: thick, dominantly limestone unit comprising the basal Callovian (thin limestones with silty clay intervals), the Bathonian (oolitic limestones with some marly intervals) and the Bajocian-Aalenian (alternating clayey bioclastic limestone and marl). ANDRA first of all synthesised current knowledge regarding each of these formations, and then extended it through further geological investigations (mapping, core drilling, well logging, 2-D seismic lines, etc) and hydrogeological studies (hydraulic pulse and slug tests between obturators, continuous piezometric monitoring, well logging of conductivity, temperature and flow rate, etc). The results of the studies carried out by ANDRA confirm the very favourable character of the Callovian-Oxfordian argilites and their enclosing formations for a deep storage site. (authors)