Results of monitoring at Olkiluoto in 2004. Geochemistry

Olkiluoto at autumn 2004. ONKALO will be an important part of the site investigations during next few years, because the suitability of the bedrock at Olkiluoto for final repository is tried to shown by investigations done in ONKALO and by ONKALO itself. The construction of ONKALO will inevitably affect the rock mass and the groundwater flow system. It will also affect the chemical environment both on the surface and at depth. In order to determine the magnitude and extent of such effects monitoring programme was established. In 2004 geochemical monitoring has been focusing on changes that are possibly noticed in groundwater. Groundwater samples have been taken both from overburden and deep bedrock by different methods. All groundwater samples have been taken from the surface because the ONKALO construction started in the autumn 2004 and it was not possible to take samples from ONKALO yet. The chemical properties of water used in ONKALO during exvation (process water) has been analysed and also some chemical analysis has been done for the water pumped up to the surface from ONKALO. Some changes in main ions can be noticed in groundwater samples taken from surface as a function of date. All noticed changes are mainly minor and cannot be caused by ONKALO construction because most of the samples have been taken before ONKALO construction started. Analysis results from surface water and shallow depths from year 2001 are presented in this report. The results from deep boreholes are even from year 1990. In addition the results of Gefinex 400 S measurements are presented here. Possible movements of the saline waters are trying to be studied by Gefinex measurements, but the results from year 2004 are still baseline information for the further years. (orig.)