Limitations and advances in site investigation techniques

The particular knowledge required to select and to characterise sites for ultimate repositories of high level radioactive wastes have lead to further development and improvement of the investigation techniques. This is demonstrated by a number of examples from a Swiss programme destined to evaluate deep lying crystalline formations covered with several hundred meters of sediments. They relate to two areas: firstly, the quantitative determination of water movements in formation of extremely low permeability, i.e. 10 exp. - 12 m/s and possibly one to two orders of magnitudes lower. Data on permeability, storability, hydraulic heads, flow patterns, chemistry and age of groundwaters are used to construct a hydrodynamical model of an area of several thousand square kilometers in which a repository could be placed at a depth of about 1500 m; secondly, neotectonic studies have been initiated based on a geohistorical analysis and involving a high accuracy level measurement showing movements of 0,1 to 0,3 millimeters per year as well as continuous detection of microearthquakes, down to the magnitude of 0,8 over years. These data are collected with a view to facilitate forecasting of future tectonic changes which might influence the hydrodynamics in the repository region