Exploratory borehole Weiach: investigation report

In 1980, Nagra (National Cooperative for the Storage of Radioactive Waste) carried out an extensive geological investigation programme covering an area of some 1'200 km2 in Northern Switzerland. The aim of the programme was to obtain the geological information necessary for assessing the suitability of the crystalline basement as a disposal medium for high-level radioactive waste. The wide range of investigations carried out can be divided into a deep drilling programme, geophysical reconnaissance of the regional petrophysical and structural conditions, a hydrogeological programme for investigation of water flowpaths deep in the bedrock and a neotectonic programme for identification of active crustal movements in the area. This report is a summary of the most important results obtained during the course of the programme. Similar information and datasets are presented for each of the boreholes (Boettstein, Weiach, Leuggern, Schafisheim, Kaisten and Siblingen) in a series of investigation reports, thus allowing intercomparisons to be made between the different sets of results. Conclusions to be drawn from the data will be reserved for a final synthesis report. Detailed reporting of the individual investigations is provided in Nagra's series of Technical Reports (see NTB-list at the end of this report). (author) 3 figs., 9 tabs., 191 refs