Technischer Bericht NTB 88-10

In 1980, Nagra (the National Cooperative for the Storage of Radioactive Waste) launched an extensive geological investigation programme covering an area of some 1'200 km² in Northern Switzerland. The aim of the programme was to collect 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 performed can be divided logically into a deep drilling programme, geophysical reconnaissance of the rock formations and structures in the region, a hydrogeology programme for investigating water flow paths deep in the bedrock and a neotectonic programme for identification of active crustal movements in the area.

The Leuggern borehole was the sixth in the deep drilling programme. The drill-site (coordinates 657.664/271.208; 358.8 m a.s.l.) is located within the community of Leuggern in Canton Aargau, some 13 kilometres to the north of Brugg. The borehole reached a final depth of 1'689 m.

The aim of the Leuggern borehole was to penetrate through the sedimentary overburden and around 1'500 metres deep into the underlying crystalline bedrock. A wide range of investigations was carried out in the borehole itself, as well as on drill-cores and water samples, and state-of-the-art techniques were used to compile a detailed picture of the geology of the basement and the deep groundwater regime.

Drilling began on 9^th July 1984 and continued, with regular interruptions for scientific investigations, until 19^th February 1985. Further tests were then carried out during the course of the following months up till 22^nd May 1985. A temporary multipacker system was installed for long-term monitoring of the hydraulic conditions in the crystalline formations. Fluid logging tests designed specifically to identify water inflow points were carried out in August and September 1987. The temporary monitoring system also had to be dismantled and replaced with a definitive multipacker system which came into operation on 1^st October 1987. The investigation programme was carried out more or less completely according to plan and with a considerable degree of success.

The drilling and investigation programmes were conceived and managed by Nagra scientists with the assistance of external advisers. More than 40 technical colleges, outside contractors and service companies from Switzerland, Germany, France, Great Britain, the Netherlands, Canada and the USA participated in the programmes, bringing the total number of scientists and technicians involved to over 150.

This report takes the form of a summary of the most significant results obtained in Leuggern during the course of the investigation programme. The series of reports for the deep boreholes (Böttstein, Weiach, Riniken, Leuggern, Schafisheim, Kaisten and Siblingen) is structured in such a way as to allow cross-comparisons to be made between results and data-sets for the different sites. Presentation of the actual conclusions to be drawn from the data will be reserved for a final synthesis report. Detailed documentation of individual experiments can be found in Nagra's Technical Report (NTB) series (see list at the end of this report).

Komplette Zusammenfassung / Résumé complet / Full abstract: NTB 88-10 Zusammenfassung – Résumé – Summary.pdf