The upper part of the penstock is a concreted, sloping section of pipe 7.9 m in diameter. The lower part of the penstock is horizontal, steel-lined and only 6.1 m in diameter. This was done bottom to top, to make it easier to remove the excavated material. Swedish-made Alimak raises were used. These consist basically of a platform suspended from a rail.
Miners drill and charge blasting holes and perform other excavation work from the platforms.
As the work progresses, additional sections of rail are added to reach the tunnel face. When the pilot tunnel for the penstock reaches the intake site, the excavation is completed from top to bottom using drills, and the rock is removed from the tunnel.