Technischer Bericht NTB 88-08

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.

The Weiach borehole was the second in the deep drilling programme. The drill-site (coordinates 676'744/268'618; 368.7 m a.s.l.) lies within the community of Weiach in Canton Zurich some 3 km west of Glattfelden. The final depth of the borehole was 2'482m.

It was intended that the Weiach borehole should penetrate through the sedimentary overburden and around 1'000 m into the crystalline basement. A wide range of investigations was carried out in the borehole itself, as well as on drill cores and water samples. The most up-to-date methods were used to draw up a detailed picture of the geology of the basement and of the deep groundwater regime.

Drilling began on 10th January 1983 and continued, with numerous interruptions for scientific investigations, until mid-November 1983. Further tests were then carried out during the months up to the end of March 1985. Finally, a multiple packer system was installed between 30.3. and 3.4.1985 with a view to earring out long-term observations of the hydraulic conditions in the upper Muschelkalk, the Buntsandstein, the Rotliegendes and the Crystalline. The planned programme was carried out more or less in full and with a considerable degree of success.

The drilling and investigation programmes were planned and managed by Nagra employees with the assistance of external advisers. In total, more than 40 universities, contractors and service companies from Switzerland, the Federal Republic of Germany, France, Great Britain, Denmark, Canada and the USA were involved in the investigations, with a total manpower of over 150 scientists and technicians.

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 (Böttstein, 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 end of this report).

Komplette Zusammenfassung / Résumé complet / Full abstract:

NTB 88-08 Zusammenfassung – Résumé – Summary.pdf