The deposition hole was closed on the 1st February 2005 signifying the start of the hydration
phase. Groundwater inflow through a number of conductive discrete fractures resulted in
elevated porewater pressures leading to the formation of conductive channels (piping), the
extrusion of bentonite from the hole and the discharge of groundwater to the gallery floor. This
problem was addressed by drilling two pressure-relief holes in the surrounding rock mass.
Artificial hydration began on the 18th May 2005 after 106 days of testing. Initial attempts to raise
porewater pressure in the artificial hydration arrays often resulted in the formation of preferential
pathways. These pressure dependent features were not focused in one location but occurred at
multiple sites at different times in the test history. These pathways appear to be relatively short
lived, closing when water pressure is reduced.
It was determined that both pressure relief holes should remain open until the bentonite had
generated sufficient swelling pressure to withstand the high water pressure in the system when
these holes are closed. Packers were installed into the pressure relief holes on 23rd March 2006
and sections in them closed off over the period to 5th July 2006. There was no repeat of the
formation of piping through discrete channels so, on 20th November 2006, pressures to the
artificial hydration filters on the canister were increased to 2350 kPa
