The hydraulic barrier is ensured by low hydraulic conductivities, resulting in small water fluxes and low advective velocities. Very low hydraulic conductivities indicate mass transport dominated by molecular diffusion.
This section presents direct evidence on hydraulic properties. This includes laboratory tests on drill core samples (cm – dm scale) and in-situ hydraulic packer tests (metre to decametre scale). These are discussed in relation to rock mineralogy, porosity and structural inventory, and are complemented by observations from underground laboratories and tunnels.
Note that independent evidence on the hydraulic barrier effect such as natural tracers in porewater is presented in Section 4.6.