Tom Sauk Reservoir owned by Ameren UE was operational in 1963 and was the largest pumped storage plant in North America. The $50 million dollar engineering feat is built atop 1,900 foot Proffit Mountain. When electric demands are low (nightime) water is pumped from the lower reservoir to the upper reservoir. At peak enregy time water is then released back down to the lower reservoir creating power through turbines (hydroelectric). The Reservoir is 55 acres and is 92 feet deep with 1.5 billion gallons of water. One week before Christmas, the upper reservoir broke. Reports state that one of the high level sensors failed causing the upper reservoir to overfill causing its 1.5 billion gallons of water to drain in minutes.