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Technical Report NTB 86-19

Chemistry of waters in the Böttstein, Weiach, Riniken, Schafisheim, Kaisten and Leuggern boreholes: A hydrochemically consistent date set

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Chemical analyses were made on water samples taken from many intervals of the first six Nagra deep boreholes. Wittwer (1986, NTB 85-49) gives complete results of these analyses, evaluates their purity, and where possible, corrects them for contamination. This report evaluates the geochemical consistency of these analyses with formations from which the samples were extracted.

Most samples appear to have lost CO2 during collection, leading to calculated oversaturation with respect to calcite. Such samples were adjusted to calcite saturation, and the pH values, concentrations of carbonate species, and other saturation indices are given at that state.

Saturation indices were also calculated for the minerals dolomite, anhydrite, celestite, barite, fluorite, and the silica minerals quartz and chalcedony, all of which are present in one or more of the rock type samples. With a few exceptions there is consistency between the calculated saturation indices and the presence of the respective minerals. This indicates that both the analytical data on the components of the minerals and the mineral properties included in the thermochemical data base are reliable.

Oxidation potentials were calculated from the platinum electrode potential and from analyzed concentrations of members of several redox couples. pE values based on the arsenic couple and the assumption of uraninite saturation tend to be similar. The platinum electrode potential measured in some samples is also similar.

A thermochemical data base for aqueous species and minerals was developed to support the geochemical modeling performed for this report. This data base and the sources of the data chosen are included in an appendix.

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