The Taum Sauk pumped storage plant is a power station in the St. Francois mountain region of Missouri, United States about south of St. Louis near Lesterville, Missouri, in Reynolds County. It is operated by Southeastern Ameren Missouri.

The pumped-storage hydroelectric plant was constructed from 1960–1962 and was designed to help meet daytime peak electric power demand. It began operation in 1963. 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 an open-loop pure pumped operation: unlike some other pumped storage sites, there is no natural primary flow into the upper reservoir available for generation. It is therefore a net consumer of electricity; the laws of thermodynamics dictate that more power is used to pump the water up the mountain than is generated when it comes down. However, the plant is still economical to operate because the upper reservoir is refilled at night, when the electrical generation system is running at low-cost baseline capacity. This ability to store huge amounts of energy led its operator to call Taum Sauk "the biggest battery that we have". An unusual feature is the upper reservoir which is constructed on a flat surface, requiring a dam around the entire perimeter.

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.

Size and location

The upper reservoir can hold about of water behind a wall nearly tall. It sits above the 450 MW hydroelectric plant, which gives it a greater head than that of Hoover Dam. The two are connected by a tunnel bored through the mountain.

The Taum Sauk upper reservoir sits on a ridge just below the summit of Proffit Mountain, not Taum Sauk Mountain, which is about 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.

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.

History

Site selection

In 1953, the Union Electric Company began to look for a site on which to build a new pumped storage plant. By 1958, company officials had decided to focus on sites with at least of vertical head, which would allow them to use a smaller storage reservoir. Union Electric hired Sverdrup-Parcel & Associates to evaluate potential sites in the St. Francois Mountains, which were chosen for their relative proximity to St. Louis (where Union Electric was based) and the favorably large elevation differentials (some approaching ).

Sverdrup-Parcel & Associates intended to recommend Taum Sauk Mountain as the site, in part because it was the highest point in Missouri at , but strong political opposition to development of the scenic mountain (which was later incorporated into a state park) ruled it out. The nearby Proffit Mountain ended up being an excellent alternative thanks to its comparable elevation (, the 6th-highest point in Missouri), its close proximity to the East Fork of the Black River, and the reasonably short distance of to the existing power transmission grid.

At its completion, 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. Its pump-turbines were the largest ever produced at the time of construction, it had an unusually high head (the highest in the US at the time, far surpassing all previous US pumped storage projects), a large storage capacity (it has been described as "the first of the large capacity pumped-storage stations to begin operation in the United States"), black start capability, and had the unique ability to be operated either remotely by remote human operators in off-site facilities located 90–120 miles away (at St. Louis or Osage Power Plant/Bagnell Dam) or even fully automatically with zero human intervention.

From 1998–1999, the turbine runners for both units were upgraded, resulting in improved flow rates and another power uprate to 225 MW per unit (450 MW total).

The plant was named an IEEE Milestone in October 2005, just months before the upper reservoir failed. It was subsequently rededicated as an IEEE Milestone in 2010 after the new upper reservoir dam was completed.

Litigation and investigations

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The US Federal Energy Regulatory Commission (FERC) fined Ameren US$15 million pursuant to a settlement for the breach at Taum Sauk—a US$10 million civil penalty combined with the requirement to pay US$5 million into interest-bearing escrow in order to fund a variety of "project enhancements at or near the Taum Sauk project". The US$15 million fine was the largest fine in FERC's history, 30 times larger than the previous record fine of US$500,000.

In 2006, Ameren settled with the Toops family, stating it would pay restitution to the injured family while withholding the terms of the settlement.

The Missouri Highway Patrol delivered a report of its criminal investigation to the Missouri Attorney General in June 2007 which "did not name any suspect" and the attorney general made a statement that there would be no criminal charges. According to press reports, the report states that Ameren failed to provide the identity of the person who raised the gauges meant to prevent overtopping and also states that the gauges were moved before investigators were on the scene.

KMOX radio in St. Louis reported that the US Environmental Protection Agency assisted by the US Attorney's Office for the Eastern District of Missouri had begun an investigation into violations of the Clean Water Act and has requested the Missouri Highway Patrol's report.

The Missouri Public Service Commission (PSC) reopened its investigation and subsequently found the accident to be a failure of Ameren management, stating:

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...the Commission can only conclude that the loss of the Taum Sauk plant was due to imprudence on the part of UE (Ameren's AmerenUE Subsidiary). UE was well aware of the catastrophic results likely to occur if the UR (Upper Reservoir) was overtopped by over-pumping. UE knew, or should have known, that storing water against the parapet wall of a rockfill dam was 'unprecedented'. UE knew, or should have known, that operating with a freeboard of only one or two feet left no margin for error and required particularly accurate control of the UR water level. Given that circumstance, UE's decision to continue operating Taum Sauk after the discovery of the failure of the gauge piping anchoring system and the consequent unreliability of the piezometers upon which the UR control system was based is frankly beyond imprudent – it is reckless. UE also knew or should have known that the upper Warrick probes had been reset above the lowest point at the top of the UR." (PSC Report page 71, definitions of Acronyms added)

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Ameren had 90 days from the date of the report to tell the PSC how it will meet the recommendations of the report, which include a whistleblower rule, changes in safety management structure, financial accounting for the rebuild of the upper reservoir, and single point of management for the rebuild.

Ameren was reported to have paid a total of close to US$200 million in settlements related to the 2005 breach.

Reconstruction

thumb|Aerial photo shows reconstruction progress in late November 2009

thumb|The completed replacement reservoir, viewed from the scour created by the collapse of the original

Water was pumped into the rebuilt reservoir for the first time on February 27, 2010, and engineers monitored the response of the new structure as the water level was repeatedly raised and lowered. The final approval required from the FERC for "return to normal project operations" was received on April 1, 2010. The utility met the Missouri Public Service Commission’s in-service criteria for operations on April 15, and electricity was first generated from the new structure on April 21, 2010.

See also

  • List of hydroelectric power station failures

References

General references

  • Southeast Missourian (Cape Girardeau, Missouri): Taum Sauk Reservoir fails
  • Ameren Press Releases: Media Release Detail, Media Release Detail
  • Daily Journal (Park Hills, Missouri): Taum Sauk Dam Fails
  • National Weather Service, St. Louis Office: Taum Sauk Dam Failure
  • Photos from the USGS Mid-Continent Geographic Science Center
  • Johnson's Shut-Ins State Park damage update page
  • Ameren web pages on Taum Sauk and Johnson's Shut-ins restoration
  • FERC Independent Panel of Consultants (IPOC) Report, May 25, 2006
  • Ameren Missouri Taum Sauk Water Management Website