A realistic resaturation of the seal is an essential element of the "proof of concept" of the "engineered gas transport system" (EGTS). The combination of the geological/hydrogeological conditions at the GTS, the technical infrastructure and the possibility to establish hydraulic/gas pressures similar to those in a future L/ILW repository provides ideal conditions for the GAST experiment. Particularly important for a realistic simulation of the resaturation process is the high water injection pressure of more than 5 MPa. While this can be implemented at the GTS, it could not, for example, be applied at the Mont Terri rock laboratory without impairing the integrity of the surrounding rock.

Several potential sites at the GTS fulfill the requirement of having practically no excavation induced fracturing of the tunnel walls. Eventually, the rock conditions in the WT tunnel section were found to be most favourable.

gast site selectionMap of the GTS tunnel system with the GAST experiment site at the end of the WT tunnel  

Gas-Permeable Seal Test (GAST)