Raccoon Mountain Pumped-Storage Plant

Raccoon Mountain Pumped-Storage Plant is a pumped-storage hydroelectric underground power station in Marion County, just west of Chattanooga in the U.S. state of Tennessee.
The facility is owned and operated by the Tennessee Valley Authority (TVA). Construction was started in 1970 and was completed in 1978.
Water is pumped from Nickajack Lake on the Tennessee River at the base of Raccoon Mountain to a storage reservoir built at the top of the mountain. The reservoir at the top of the mountain covers , with a dam that is high and long, the largest rock-fill dam ever built by TVA. It takes 28 hours to fill the upper reservoir. During periods of high electric demand, water can be released from the reservoir through a tunnel drilled through the center of the mountain, driving electric generators in an underground hydroelectric plant. The plant has a maximum power output of and can generate for up to 22 hours. The plant is used most days and serves as an important element for peak power generation and grid balancing in the TVA system.
The plant was idled in March 2012 due to cracks in the generators' rotors. The plant came entirely back on line in April 2014.
Recreation.
The facility is a popular recreation spot for hiking, walking, running, road and mountain biking, and is the home of the Raccoon Mountain Marathon, Half Marathon, Double Half and Relay, which attracts runners from all over North America. Raccoon Mountain also hosts the Raccoon Mountain 5K and 10K races held each year.