Technischer Bericht NTB 85-49

As part of the Nagra geological investigation programme in northern Switzerland, numerous water samples were taken in the Böttstein, Wleiach, Riniken, Schafisheim, Kaisten and Leuggern boreholes to obtain information on the chemistry and residence times of deep groundwaters.

This report contains a compilation of hydrochemical data, comments on the individual water sampling actions and an evaluation of sample quality with respect to admixing of drilling fluids.

The samples were taken from separate test intervals in the sediments and the crystalline rock. After removal of various types of drilling fluids such as mud as well as fresh water or deionised water during a cleaning phase, the samples were taken at the surface or at depth using pressure vessels.

The tracers added to the drilling fluids (uranine, m-TFMBA) as well as the tritium content were used for a quantitative estimation of the content of drilling fluid in the samples (contamination). With a view to further geochemical modelling, the samples were assessed with reference to the effect of contamination on the results of the chemical analyses.

A total of 68 water samples were taken from 53 different intervals:

• 27 samples had problem-free cleaning phases and were taken with negligible contamination.

• 23 samples were taken under difficult conditions. Problems with hydraulic communication around packers, uncertain origin, inaccuracy as to extent of contamination, presence of cement, possible traces of salt from drilling fluid etc. meant that the analyses could only be used with extreme caution or after additional data-processing.

The analysis results from 18 samples will be disregarded due to significant drilling fluid content or because more reliable data are available for the same test interval.