[en] The construction of ONKALO, the underground rock characterisation facility at Olkiluoto, started in summer 2004. The potential disturbances due to construction of ONKALO, which were assessed prior to construction, have been reassessed in this report. The reassessment is based on observations and experiences from construction work, in situ and surface based monitoring, and numerical flow modelling. The implications of the construction of ONKALO and the repository on hydrogeochemical disturbances and the technical development of grouts are considered. Based on the new assessment, the recommendations of the practises to be adapted after the penetration of RH19B at the depth between 70 and 170 m are presented. The identified disturbances due to the construction of ONKALO were the drawdown of the groundwater table, and intrusion of surface water and upcoming of deep saline groundwater. The intrusion of surface water would lead to reduced pH and redox buffering capacity of the rock. The latter would lead to locally high salinity levels that may negatively impact the performance of the buffer bentonite and backfill. If the rock were sealed with ordinary cementitious grout, the formation of a high-pH plume originating from cement would affect transport processes in the geosphere and the performance of the Engineered Barrier System, especially of the bentonite buffer around the canisters. This report comprises the observations for the first 670 m of access tunnel (reached in September 2005). The measured water inflow (1.7 l/min/100 m of tunnel) has remained well within the set target (1 - 2 l/min/100 m of tunnel). Grouting has been used as a measure to minimize water inflow. So far, the use of cement has been about the same as the amount estimated prior to construction. No significant changes in hydrogeochemistry have been observed, except for the highpH plume due to the effect of cement in the monitoring of some of the boreholes. The numerical flow model used to analyse the impact of several grouting alternatives is based on two different geometries and transmissivity values for certain geohydrological features (flow model 2005 and flow model 2005 alt). The results showed that independent of the hydrogeological model used, the water inflow rate to ONKALO would be far too high if no grouting were used. The performance of the currently used ordinary cementitious grout and of the proposed new grouting materials (low-pH cementitious grouts and colloidal silica) has been evaluated. It is recommended that the use of the current grouts be continued while grouts based on low-pH cements and non-cementitious materials are being developed and tested. Clear acceptance criteria and peer review of new materials performance need to be adopted before adopting new materials. (orig.)