[en] An infiltration experiment to investigate potential changes in pH and redox conditions and in buffering capacity as well as the hydrogeochemical processes related to groundwater infiltration was started in late 2008 near ONKALO. The purpose of the experiment is to monitor the major infiltration flow path from ground surface into the upper part of ONKALO at a depth of about 50 to 100 m depending on the observations made during the experiment. Infiltration is activated by pumping a highly transmissive fracture zone (13-18.2 m) in drillhole OL-KR14, which is a part of the site scale hydrogeological feature. The influence of pumping is then monitored in drillholes, groundwater observation tubes and lysimeters through water, groundwater and microbiological samplings and hydrogeological measurements. Before the experiment was started, four new monitoring drillholes, nine groundwater observation tubes and nine lysimeters were installed in the test area and very detailed baseline field investigations were performed. In addition, information of existing investigation data from the area of interest was collected in together. The baseline field investigations included geological logging of the cores of new shallow drillholes, flow and transverse flow measurements in new shallow drillholes, SLUG measurements in groundwater observation tubes, head monitoring, groundwater and microbiological sampling and analysis from observation tubes, shallow drillholes and the pumping section in OL-KR14, water sampling and analysis from lysimeters and resistivity measurements of the overburden. The results of previously performed soil pit investigations and hydrogeological measurements carried out in the area of interest were also added to the investigation data. A detailed hydrogeological model of the experiment area was updated simultaneously with baseline field investigations; the previous version was presented in Pitkaenen et al. (2008). Apart from the field investigations, predictive reactive transport calculations and flow simulations were performed. The main objective of the predictive reactive transport calculations was to successfully integrate hydrodynamic processes and chemical reactions. The calculations were carried out using the TOUGHREACT code and with the EQ3/6-database implemented in the code. A detailed surface hydrological model version was also developed in order to study water balance components at the experiment area site and to evaluate the effects of the pumping of OL-KR14 on groundwater level in overburden soils and in shallow bedrock drillholes. This Report describes the objectives of the Infiltration Experiment, the experimental site and setup, and the results of the aforesaid baseline field investigations. In addition, an updated hydrogeological model of the area of interest as well as the results of predictive flow simulations and reactive transport calculations are presented. (orig.)