The Wellenberg K-Model: A Geostatistical Description of Hydraulic Conductivity Distribution in the Host Rock for Site Characterization and Performance Assessment Purposes

Abstract

The Wellenberg K-model describes the distribution of the hydraulic conductivity of the host rock at Nagra's proposed site for a LLW/ILW repository. The description takes the form of the expected value of hydraulic conductivity at a location and the uncertainty around this expected value. The development of the K-model is based on geostatistical concepts and, in particular, on kriging and conditional simulation methods. The model is built of cubes with sides of 100 m. Upscaling of the transmissivity profiles at the borehole locations to effective K-values on the 100 m scale is realised by fracture network modelling. The K-model accounts explicitly for the hydraulic conductivities estimated at each borehole. It is consistent with the hydrogeological conceptualization of the host rock and generates realistic hydraulic conductivity distributions with a degree of variability similar to that observed in the data.