The in-situ GAM tests involve the injection of different tracers into a dipole flow field established in a shear zone. The location of the GAM site at the GTS can be seen below.

The GAM site is focused on a shear zone intercepted by 20 boreholes. All the boreholes are equipped with triple packer systems, which allow the shear zone to be hydraulically isolated and minimise the internal volume of the test. The site was extensively characterised both geologically and hydraulically before any tracer tests took place.

The boreholes used for the geophysical investigation have a "fan-like" distribution parallel to the shear zone. This was aimed at monitoring transport processes in the plane of the shear zone by radar reflection methods.

The site of the in situ test was subject to a series of site characterisation techniques. The image above shows the geological map of the tunnel section and the photograph was taken down a borehole to provide images of the geology of the site. The photograph above shows a section of the shear zone. The extracted core is also shown.