Multi-geophysical Field Measurements to Characterize Lithological and Hydraulic Properties of a Multi-scale Karstic and Fractured Limestone Vadose Zone: Beauce Aquifer (O-ZNS)

The deciphering of the coupled processes that govern the transfers of mass and heat within the vadose zone is recognized as a complex issue. In this context, an observatory of transfers in the vadose zone (O-ZNS) has been implemented near Orléans (France). By combining multiscale laboratory and field experiments using various monitoring techniques, this observatory will improve our knowledge regarding water flow and contaminant transport throughout the 15–19 m highly heterogeneous vadose zone. To image the lithological and hydraulic properties of its heterogeneous facies, we adopted a multi-geophysical monitoring strategy in order to overcome the limitations of each individual geophysical method. This approach includes surface, borehole, and well multi-geophysical measurements. Preliminary investigations undertaken since 2017 leads to an effective and complete characterization of the vadose zone including (i) a lithological description of the geological facies, (ii) the identification of local heterogeneities (karsts, fractures, silicified layers) whose density increases with depth, and (iii) an estimation of the water content variations within the vadose zone. This whole set of results constitutes a first base to ongoing joint inversion that should lead to a refined characterization of the petrophysical and transport properties of the vadose zone column.