Snettisham Hydroelectric Project
The Snettisham Hydroelectric Project was authorized in 1962 by Congress to provide additional power to the growing population in Juneau, AK. Constructed by the Alaska District of the US Army Corps of Engineers between 1968 and 1973, it was developed in two stages.
The Long Lake Stage consists of an approximately 8,400-ft long, 13.5-ft diameter power tunnel, an 8.5-ft diameter, 900-ft long steel penstock, and an underground powerhouse housing two Francis type turbines with an installed capacity of 47 MW. The Crater Lake Stage includes an underwater lake tap into a high mountain lake, over 8,000 ft of unlined power tunnel, a 900-ft deep surge shaft, an underground machine shop, and several large underground chambers, ranging in excavated volume from 37,500 to 180,000 cubic feet.
In 1996, Lachel was retained to perform an inspection of the Long Lake power tunnel and another inspection was performed in August 2006. In each case the inspection team traversed the 8,400 ft of the power tunnel performing visual inspection of the tunnel and installed support elements. While much of the power tunnel is unsupported hard rock, some areas required additional support systems such as rock bolts, shotcrete, mine straps, or full perimeter concrete lining. Lachel also prepared a final inspection report documenting the findings of the inspection as well as recommending actions and procedures for correcting any problems found.
In 2007, Lachel was retained to perform an inspection on the second stage power tunnel at Crater Lake. Lachel performed the tunnel walk-through and inspection of the 8,000-ft tunnel while it was shut down for maintenance in early July 2007. Lachel performed a visual inspection of the tunnel facilities for any deterioration or damage and prepared a final inspection report documenting the results of the inspection as well as recommending actions and procedures for correcting any problems found.