Constructed in the 1960’s the Taum Sauk Hydro facility in St. Louis, MO features both an upper and lower reservoir designed to help meet daytime peak electrical power demand. It went into operation in 1963 with two reversible pump-turbine units – the largest ever produced at the time of construction – each capable of generating 175 megawatts of power. At its completion, the Taum Sauk plant was by far the largest pumped storage plant in North America and was considered a major milestone in the development of pumped storage technology. In December 2005, a catastrophic failure in the upper reservoir dam put the plan out of operation until it was reconstructed and recertified in April 2010. Capable of holding 1.5B gallons of water behind a nearly 100-foot wall, the new upper reservoir dam, rebuilt from the ground up, is the largest roller-compacted concrete dam in North America.