Crews successfully blasted out the last 12 feet of rock in the tunnel dug into the side of the lake, allowing the tunnel to fill with water for the first time.
Construction at Lake Dorothy, about four miles up Taku Inlet, started in 2006. The 14-megawatt hydropower generating station is scheduled to come on line in the fall of 2009, adding to Juneau's supply of clean energy.
"This is an important milestone in the construction of the Lake Dorothy Project," said Tim McLeod, president and general manager of Alaska Electric Light and Power Company. "We're pleased that the actual lake tap went so smoothly."
The Lake Dorothy tap consisted of drilling an 870-foot-long tunnel to within about 12 feet of the lake. The tunnel entrance is about 150 feet below the water line at the lake.
In preparation for the Aug. 19 blast, a large valve was placed at the downstream end of the tunnel and explosive charges were set to clear out the final 12 feet of rock. The valve was closed and the tunnel was pressurized with water and air to cushion the impact of the blast. The tunnel filled with water up to the closed valve, which will be opened when the entire system is ready for water flow.
"With completion of the lake tap, we can focus on the remaining work to bring the project on line," McLeod said.
More than 50 workers are on the job each day, mostly contractors, completing the 8,200-foot steel pipeline that will direct Lake Dorothy water to the power plant, a 20-foot-high dam on Bart Lake.
"The Lake Dorothy Project will allow us to meet future electric demand with affordable, clean, renewable hydro power," McLeod said. "It also makes us less dependent on our back-up diesel generation in case of a problem with Snettisham."