Gas Migration in EBS and Geosphere (GMT) - Site Characterisation
The silo cavern was positioned such that the southern boundary of the VE-shear zone intersects the silo at the centre of the cavern floor. The southern part of the cavern is dominated by a weakly to moderately deformed Granodiorite with an increasing intensity towards the boundary of the shear zone.
Before excavating the GMT access drift, the hydraulic head distribution in the shear zone was studied by introducing mutipacker systems into pre-existing boreholes. The measurements showed a distinct pressure gradient across the site. In the upper part of the target area (i.e. roof of the silo cavern) hydraulic pressures up to 9 bar were measured, whereas the observation in the lower part (i.e. below the bottom of the silo cavern) indicated pressures between 0.5 and 2 bar. This implies that the groundwater flow is preferentially directed downward.