Arbeitsbericht NAB 09-16

Introduction

In the years 2007–2008, the French National Agency for Radioactive Waste Disposal, Andra, conducted a comprehensive drilling campaign for the characterisation of the Callovo-Oxfordian and surrounding stratigraphic units on a regional scale within and around the so-called "zone de transposition" (FZT). Fourteen deep drillholes were drilled from six different sites ("platform") to depth between 400 m and 2000 m (e.g. Linard et al., 2011). Each five of these borehole aimed for a detailed geological, hydrological and hydrochemical characterisation of the Oxfordian units (5 boreholes), the Callovo-Oxfordian (3), the Dogger units (5) and the entire Mesozoic sediment pile down to the Trias (1).

Within the bilateral agreement between Andra and Nagra, the Rock-Water Interaction Group of the Institute of Geological Sciences, University of Bern, was invited to participate on the geochemical program conducted on drillcore material of the 2000 m deep borehole EST433, drilled from the surface down to the Triassic base conglomerate.

From borehole EST433, 84 samples for porewater chemistry and porewater gas investigations were collected on site by the RWI-team greatly supported by the field geology team between March and June 2008. After the appropriate on site conditioning the samples were transported to the Institute of Geological Sciences in Bern and further examined and analysed in the laboratory. The focus of the investigations was firstly the derivation of multi-tracer profiles in the porewater across a) the Callovo-Oxfordian and b) the underlying sediment pile from the Dogger to the Trias in order to investigate solute transport processes across the entire Paris Basin in the Bure area. The investigated tracers included dissolved chloride, d¹⁸O and d²H of the porewater and dissolved noble and reactive gases. A second focus of the investigations was the comparison of porewater data derived by the same protocols on a regional scale, i.e. between the Transposition Zone (borehole EST433) and data elaborated earlier on boreholes from the Bure URL Site (EST207, EST210, EST211, EST212; Bigler et al., 2005; Waber 2005).

The present report describes the complete porewater data gathered from drillcore samples from borehole EST433, except for the reactive gas data, which will be reported elsewhere. The report includes a detailed description of the sampling, analytical and experimental protocols conducted on the samples and evaluation of the raw data and their conversion to porewater concentrations. It further includes a short comparison with the porewater data produced by the same techniques earlier on the Bure URL Site. A detailed interpretation of the data is not subject of this report and will be given elsewhere.

Excerpts of the present data and findings have been reported earlier on different occasions (Vinsot et al., 2011; Waber & Vinsot, 2010, 2011).