An integrated approach to site characterisation: experience from the crosshole project

Site characterization for a nuclear waste repository aims at producing information on which to base a reasonably accurate nuclide transport model. The model contains information on geometry, hydrogeology and solute transport. Within the Crosshole Project, the techniques of radar and seismics were developed with respect to fractured crystalline rock. The resulting interpretations were then used to focus the hydraulic characterization efforts. It was found that the radar could be used effectively in both single borehole reflection mode and tomographically-interpreted crosshole mode. The seismics were best in the crosshole mode also. Geometric models of the 3 million m3 of the site derived from the two techniques agreed closely. Features thus identified mainly fracture zones were tested specifically hydraulically using the sinusoidal pressure technique. It was found that all the major hydrogeological features were easily identified but that they were by no means planar. The combined approach resulted in improved confidence in the resulting overall hydrogeological model of the site