Taum Sauk
Taum Sauk is a pure pumped-storage hydroelectric plant in the St. Francois Mountains of Reynolds County, Missouri, near Lesterville, about 100 miles south of St. Louis. Built by Union Electric (now Ameren Missouri) and in service since December 1963, it uses two reversible pump-turbine units with a combined EIA-rated nameplate of 408 MW to shuttle water between a lower reservoir on the East Fork Black River and an upper reservoir atop Proffit Mountain, generating during peak demand and pumping back overnight. On December 14, 2005, a catastrophic breach of the original rockfill upper reservoir dike drained the reservoir in minutes, flooding Johnson's Shut-Ins State Park; the plant was rebuilt with a new roller-compacted-concrete upper dam and returned to service on April 21, 2010. The rebuild followed a FERC finding of imprudent operation and a $15 million FERC fine, on top of roughly $200 million in related settlements paid by Ameren. FERC issued Union Electric (d/b/a Ameren Missouri) a new long-term operating license for the project in July 2014, authorizing 442.5 MW of capacity. The plant remains fully operational today with no whole-plant retirement scheduled and sells into the MISO market, settling near price nodes such as AMMO.RUSHIS1/2 and AMMO.MERAMEC4.