Taum Sauk pumped storage plant

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Water stored in the upper reservoir was available for hydroelectric generation during times of peak demand.

The two generators are each capable of producing up to 225 MW of power.

The Taum Sauk pumped storage plant is located in the St. Francois mountain region of the Missouri Ozarks approximately 90 miles (145 km) south of St. Louis near Lesterville, Missouri. The pumped-storage hydroelectric plant, operated by the AmerenUE electric company, was designed to help meet peak power demands during the day. Electrical generators will again be turned by water flowing from a reservoir on top of Proffit Mountain into a lower reservoir on the East Fork of the Black River. The generators and turbines at river level are reversible, and at night the excess electricity available on the power grid was used to pump water back to the mountaintop. The plant has been out of operation ever since the upper reservoir suffered a catastrophic failure on December 14, 2005. The upper reservoir dam is being replaced with a roller-compacted concrete dam and construction is over 50% complete as of December 1, 2008.

The Taum Sauk plant is notable in that it is a pure pump-back operation – there is no natural primary flow available for generation, unlike most other pumped storage sites. It was among the largest such projects when it was built. Construction of the Taum Sauk plant began in 1960 and operation began in 1963. The two original reversible pump-turbine units were each capable of generating 175 megawatts of power. They were upgraded in 1999 to units capable of 225 megawatts each.

[edit] Size and location

The original upper reservoir had a capacity of 4,350 acre-feet (5,366,000 m³). The upper reservoir is 800 feet (244 m) above the hydroelectric plant, which gives it a greater head than that of Hoover Dam. The two are connected by a 7,000 ft (2,100 m) tunnel through the mountain.

This powerplant is 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.

The Taum Sauk reservoir (37°32'10" N, 90°49'05" W) is atop Proffit Mountain and not Taum Sauk Mountain (37°34'13" N, 90°43'40" W), which was often a source of confusion to visitors to the site when it was open to the public prior to the reservoir failure. Taum Sauk Mountain, the highest point in Missouri, is about five miles (8 km) east of Proffit Mountain and hosts a state park. The reservoir is plainly visible from the lookout tower on Taum Sauk Mountain. The upper reservoir is also visible from Route 21 north of Centerville.

Before the failure of the upper Reservoir visitors could usually drive to the top of Proffit Mountain and walk a ramp to an observation deck at the top of the reservoir. At the entrance gate Ameren also operated a museum highlighting the natural history of Missouri. The powerplant 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.

[edit] Leaks and lining

There had been minor leaks in the reservoir since it was constructed. A pumpback station had eventually been installed to collect and return leakage to the reservoir. From September 13, 2004 to November 15, 2004 Geo-Synthetics Inc. installed lining material to reduce leaks^[1].

[edit] Upper reservoir breached

A large section of the upper reservoir failed, draining over a billion gallons of water in less than half an hour.

A broad swath of dense forest was washed away and scoured to bedrock by the escaping flow. Source: FERC

Aerial photos showing upper reservoir before and after failure. Click to enlarge.

On the morning of December 14, 2005, a triangular section on the northwest side of the upper reservoir failed, releasing a billion gallons (4 million m³) of water in twelve minutes and sending a 20 foot (7m) crest of water down the Black River. According to AmerenUE, a computer software problem caused the reservoir to continue filling even though it was already at its normal level. The water overtopped the walls, leading to the failure at 5:12 a.m. In addition, preliminary indications are that minor leakage through the dam walls over a prolonged period, had carried away fine material in the walls, weakening the reservoir's holding walls. Piping ultimately creates voids in reservoir walls and causes reservoir walls to slump and fail. The failure of the reservoir occurred as the reservoir was being filled to capacity or may have possibly been overtopped.

There was no overflow spillway. A maximum fill level was reported to be 6 feet (1.8 m) below the top. If the reservoir was filled in 16 hours and is 55 acres (220,000 m²) across, that would calculate to about 1 ft (0.30 m) of water rise in 12 minutes. The reservoir would have overflowed in approximately 72 minutes, once the maximum level was exceeded. It was likely that the reservoir failed once water overflowed the reservoir as earthen levees will erode when overtopped.

The reservoir had been lined with a membrane in 2004 to minimize water leakage. It had been losing two feet of water for some time prior to the installation of the lining. The phenomenon of fine material being washed out of a reservoir structure is known as "piping". When piping occurs, the reservoir structure can settle in or slump, which means water may start flowing over its top – but that is because a weakened area in the reservoir has settled down.

Periodic surveys are necessary at a reservoir to identify if leakage and "piping" is occurring.

No fatalities were reported. Jerry Toops, his wife and three children were swept away when the wall of water obliterated their home. Toops is the superintendent of Johnson's Shut-Ins State Park and Taum Sauk State Parks. They survived with injuries and suffering from exposure. The children were transported to a hospital in St. Louis and later released. One child was treated for severe burns which resulted from heat packs applied by rescue workers as treatment for hypothermia.

Low cloud levels prevented medical helicopters from flying to aid victims. It was not until the clouds cleared up that the helicopters could retrieve victims. Three victims, all children, were first taken to Farmington, then they were transported by ambulance to SSM Cardinal Glennon Children's Hospital in St. Louis. A spokesperson for the family has informed the media that they do not want the conditions of the children to be disseminated.

The dam of the lower reservoir held, trapping much of the deluge. If it had given way then towns downstream, including Lesterville and Centerville, would have been in grave danger. A voluntary evacuation order was issued for those areas, but there was no damage. The high water was stopped at Clearwater Lake, the dam of which was not damaged by the rising waters^[2].

A memo from Richard Cooper, superintendent of Ameren’s Taum Sauk Hydroelectric Plant, indicated that the reservoir had a "Niagara Falls" style overflow on September 27 at the same spot that was breached, (caused by wave action related to winds from Hurricane Rita.) Another Cooper memo had also indicated that Cooper had warned that gauges used to monitor the water height in the reservoir were malfunctioning in October.

[edit] Litigation and Investigations

FERC has fined Ameren $15 million pursuant to a settlement for the breach at Taum Sauk. This is the highest fine ever levied by FERC.

The State of Missouri has sued Ameren for Actual and Punitive Damages alleging Ameren was reckless in its operation of the plant^[3]^[4].

The Missouri Highway Patrol delivered a report of its criminal investigation to the 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^[5]^[6].

KMOX radio in St. Louis reports that the EPA assisted by the U.S. Attorney's Office has begun an investigation into violations of the Clean Water Act and has requested the Highway Patrol's report^[7].

The Public Service Commission reopened its investigation (based on the Highway Patrol report) and subsequently found the accident to be a failure of Ameren management, stating:

...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)

Ameren has 90 days from the date of the report to answer back to the PSC how it will meet the recommendations of the report, which include a whistle blower rule, changes in safety management structure, financial accounting for the rebuild of the upper reservoir, and single point of management for the rebuild.^[8]^[9]

[edit] Rebuilding

Federal regulators approved Amerens plan to rebuild the reservoir, and construction began in late 2007. The rebuilt structure will be made entirely of concrete, unlike the rock-fill original. In addition to fill-detection instrumentation it will include a spillway to handle any overflow and a video system to monitor the water level. The $450 million cost of rebuilding the reservoir is expected to be covered mostly by insurance. The utility is prohibited from billing customers to recoup any of the cost. Construction is expected to be complete in late 2009.^[10]

[edit] Church Mountain reservoir

The lower reservoir for a Church Mountain plant would flood 400 acres (1.6 km²) of Taum Sauk Creek valley.

In June, 2001, Ameren Development Corp, a subsidiary of Ameren Corporation, announced that it had filed for a permit from the Federal Energy Regulatory Commission in order to begin evaluating the construction of a much larger pump-back plant on neighboring Church Mountain. The upper reservoir of this 770 megawatt plant would be 130 acres (0.5 km²), and the lower reservoir would flood 400 acres (1.6 km²) of the scenic and environmentally significant Taum Sauk Creek valley. Resistance from a number of environmental groups, the Missouri governor's office, and the state's attorney general caused the company to conclude it was impossible to build the plant in both an environmentally friendly and cost-effective manner, and the permit application was withdrawn in August 2001.

[edit] Gallery of Taum Sauk Destruction

Aerial view of reservoir	Aerial view of reservoir	Aerial view of reservoir	Scour path
Scour path	Scour path	Scour path	Reservoir breach
Reservoir breach	Reservoir breach	Reservoir breach	Reservoir breach
Reservoir breach	Empty reservoir	Empty reservoir	Dam of lower reservoir