Korrelationer mellan meteorologiska händelser och hydrologiska responser i djupt berg

This thesis presents a closer look at correlations between major meteorological events and groundwater level responses observed in deep boreholes drilled in the bedrock at Forsmark, which is situated ca. 120 km north of Stockholm in the Fennoscandian Shield, Sweden. Understanding how large geological structures are hydraulically connected to the surface is of great importance as a repository for spent nuclear fuel is intended to be built in Forsmark. Understanding monitoring data under natural conditions gives greater knowledge of how the hydrogeological system near the surface might be affected during the construction, operation and closing phases of the repository.The hydrological monitoring of each borehole is performed in intervals (sections), i.e., the ground-water levels in the bedrock are measured at different depths. At the different depths, changes in pressure from different meteorological events is measured. A major precipitation event was recorded during a few hours between 21 and 22 September 2014. Groundwater level responses in four deep drill holes show different reaction rates and magnitudes depending on borehole location, the structures they inter-sect, and depth in the bedrock. Furthermore, the properties of the deformation zones determine how the groundwater levels respond to meteorological events. Previous work reveals that gently dipping defor-mation zones have higher hydraulic diffusivity than the steeply dipping deformation zones.Two major air pressure events combined with groundwater level reactions in two deep bedrock bore-holes were also analysed. A lowering of the air pressure resulted in a higher sea level, which is seen in the boreholes as an increase in the groundwater level and vice versa.Clear responses from meteorological events are seen where boreholes intersect gently dipping deformation zones that leads all the way up to the ground surface.