One issue was the disposal of nearly a million tons of rock. This came from the excavation of the underground levels of the main station building, from the construction of the tunnels, and also from the foundations for the two dams. Rock from the upper dam was placed in the reservoir, where it is permanently covered by water.
A significant issue was disposing of over a million tons of rock extracted during the construction of the station's underground levels, tunnels, and dam foundations. The rock from the upper dam was then deposited in the reservoir, which now covers it with water.