Technical Report NTB 94-22

Wellenberg (Gemeinde Wolfenschiessen, NW) has been chosen by Nagra as a repository site for short lived low- and medium-level radioactive waste. In certain regions of this Palfris marl formation, foreseen as actual locations for the repository, the water flow rates are so low that reliable water samples for chemical analysis were not obtainable. A sample of Palfris marl (SB1-535.83) was provided from such a region and a physico-chemical characterisation technique, developed and tested in previous work, was applied. The measurements, coupled with a geochemical modelling study, yielded a NaCI type porewater with an ionic strength of ~ 0.12 M. In addition, a matrix marl porosity of ~ 1.5 % was deduced using the chloride concentrations in the calculated porewater and measurements on the chloride content of marl.