Taum Sauk Reservoir

The upper Taum Sauk reservoir can hold about 1.5 billion gallons of water (4,600 acre feet (5,700,000 m3)) behind a wall nearly 100 feet (30 m) tall. It sits 760 feet (230 m) above the 450 MW hydroelectric plant, which gives it a greater head than that of Hoover Dam. The two are connected by a 7,000-foot (2,100 m) tunnel bored through the mountain. The Taum Sauk upper reservoir sits atop Proffit Mountain, not Taum Sauk Mountain about 5 miles (8.0 km) to the east. It is visible from Route 21 north of Centerville and from Route N approaching Johnson's Shut-ins State Park from the south. Construction on Taum Sauk began in 1960, and it went into operation in 1963 with two reversible pump-turbine units that could each generate 175 megawatts (235,000 hp) of power. It was not licensed by the Federal Power Commission (the predecessor of the Federal Energy Regulatory Commission) because Union Electric contended that the FPC did not have jurisdiction over the non-navigable headwaters where the power station was constructed. In FPC v. Union Elec. Co., 381 U.S. 90 (1965), the United States Supreme Court held that the FPC did have jurisdiction and that Taum Sauk did require a FPC license. Although designed and built without federal supervision, a license was retroactively granted. At the time, the Taum Sauk plant was by far the largest pumped storage plant in North America in a number of measures, and was considered a major milestone in the development of pumped storage technology. In 1999, the plant was upgraded with units capable of 225 megawatts (302,000 hp) apiece. On December 14, 2005, a catastrophic failure in the upper reservoir dam put the plant out of operation until it was rebuilt, recertified, and reopened on April 21, 2010. The new upper reservoir dam, rebuilt from the ground up, is the largest roller-compacted concrete dam in North America. Before the failure of the upper reservoir, visitors could drive to the top of Proffit Mountain and walk to an observation deck above the reservoir. Ameren operated a museum at the entrance gate highlighting the geologic and natural history of Missouri. The power plant was frequently visited by geology students because of a striking example of Precambrian/Cambrian unconformity in the rock layers exposed by the plant's construction. The Taum Sauk pumped storage plant is in the St. Francois mountain region of the Missouri Ozarks about 90 miles (140 km) south of St. Louis in Lesterville Township, near Lesterville, Missouri, in Reynolds County. It is operated by the AmerenUE electric company. The pumped-storage hydroelectric plant was built to help meet peak power demands during the day. Electrical generators are turned by water flowing from a reservoir on top of Proffit Mountain into a lower reservoir on the East Fork of the Black River. At night, excess electricity on the power grid is used to pump water back to the mountaintop. The Taum Sauk plant is a pure pump-back operation; there is no natural primary flow available for generation, unlike most other pumped storage sites. It is therefore a net consumer of electricity; the laws of thermodynamics dictate that more power is consumed pumping the water up the mountain than is generated when it comes down. However, the plant is still economical to operate because the reservoir is filled at night when the electrical generation system is running at low-cost baseline capacity. As a way to store excess power until it is needed, it has been described by the utility as "the biggest battery that we have."