Hydrogeochemical site investigations by Teollisuuden Voima Oy, Finland

Groundwater samples collected from cored boreholes (500-1000 m), borehole wells and multilevel piezometers in crystalline bedrock have been characterized and classified. The reference data for local hydrogeochemical characterization was collected by sampling domestic wells, springs, brooks and lakes from a larger surrounding area. Monthly precipitation during at least one year was collected at each site, too. Freshwaters down to the depth of 1000 m were found at three of the five sites studied. Brackish waters changing to saline waters at depths below 600 m and 750 m occurred at two sites. Freshwaters were mainly Ca-Na-(Mg)-HCO3 type whereas brackish and saline waters were mainly Ca-Na-Cl or Na-Cl type. Most of the borehole waters were reducing indicated by field measurements (Eh, O2), sulphide analyses and the occurrence of hydrogen and methane in evacuated gases. The H-2 and O-18 isotopes indicate mainly meteoric origin of the waters. Both altitude and latitude effects were observed. The generally reducing character and low sulphide content of the groundwaters indicate very low corrosion risks for the spent fuel copper canisters