Constructional and environmental aspects. Exploratory boreholes Wellenberg SB1, SB2, SB3, SB4, SB4a7v, SB4a7s und SB6. Appendices

The Valanginian Marls at Wellenberg have a number of properties which make them suitable as a host formation, namely their sorption properties, their plastic behaviour under mechanical loading and, in particular, their low water permeability. In 1987, Nagra submitted an application for permission to carry out an extensive exploration programme at Wellenberg, with a view to assessing the suitability of the site for construction of a repository for low- and intermediate-level waste. The decision of the Federal Council granted permission to carry out investigations which would not disturb the potential disposal zone. The first five exploratory boreholes formed the focal point of Phase I investigations. The programme started in November 1989 and was completed in summer 1993. Building on the results from Phase I, a second stage was initiated in summer 94. Phase II included a further surface seismic campaign, several piezometer boreholes and shallow cored boreholes. The first chapter of this report discusses regional geology, the aims of the investigation programme and the timetable which was followed. Licensing and environmental issues are discussed in chapter 2, which deals both with general aspects of construction and operation and with the specific measures taken for noise protection. Chapter 3 describes the drilling techniques used and chapter 4 to 10 each discuss one borehole in detail. Chapter 11 addresses supervisory bodies and documentation of the programme. (author) figs., tabs