Pump Storage: a Case Study

By Dave Cooper

Recent articles in The Highlands Voiceabout the proposed Big Run Pump Storage project in Tucker County written by Kent Karriker and Randy Kesling have been both interesting and informative.

Here is a little more background and history about pump storage for those wanting more information.

In 2005, in the midst of the fight against the huge coal slurry impoundment above the Marsh Fork Elementary School near Whitesville, we learned of a major dam failure at a facility called Taum Sauk.  This was important news to those fighting the Shumate’s Branch impoundment and dam, because regulators were reassuring local area residents that dam failures could not occur with all of the modern technology being used to monitor the dams.

Taum Sauk, in the Ozark Mountains in southeast Missouri, is a pump storage facility originally built between 1960 and 1962.  It went into operation in 1963.  Built to hold about 1.5 billion gallons of water, it was – by far – the largest pump storage project in America at the time it was built.  It was constructed on top of Proffit Mountain, elevation about 1,700 feet.  Water flows through underground tunnels from the upper reservoir into the lower reservoir during times of high electric demand.  Taum Sauk has 760 feet of head (the difference in height between the upper and lower reservoirs) and the facility is capable of generating a little more than 400 MW of power.  The upper reservoir is refilled during periods of lower electric demand, i.e. at night.  It is operated by Ameren.

The original upper reservoir was contained by a rock-filled earthen embankment.  The upper reservoir was routinely filled within a few feet of the top of the rock-filled wall, but lacked a spillway to release excess water in the event of overfilling.  In September of 2005, Hurricane Rita caused some damage to the controls system which regulated the level of water in the upper reservoir, and improper measures were taken to correct the problem.

At 5 am on December 14, 2005, water overtopped the earthen wall of the upper impoundment and the wall failed, leading to a sudden and catastrophic release of water.  About one billion gallons of water flowed down the mountain – but not through the tunnels or penstocks.  The home of a superintendent at a nearby state park was washed away at the bottom of the mountain.  The inhabitants survived, with injuries.

A 2007 Associated Press article stated “probes were designed to stop the automatic filling if water got too close to the top of the reservoir walls and threatened to overflow.  The probes were set so high that water never touched them the morning the reservoir overflowed and collapsed.”

The Missouri Public Service Commission’s investigation of the incident concluded:

“…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.”

Ameren paid out about $200 million in damages.  There is a much more detailed explanation of the exact cause of the failure on the Lessons Learned webpage of damfailures.org;   https://damfailures.org/case-study/taum-sauk-dam-missouri-2005/

The Taum Sauk reservoir was rebuilt in 2010 with concrete walls 100 feet high, and photographs of the project give an idea of the scale of this huge project.  It is breathtaking.

One would think that after the Buffalo Creek tragedy and the Martin County, Kentucky coal slurry disaster in October, 2000 that regulators would be extremely careful monitoring dams, but the Taum Sauk failure and the huge coal ash spill at the TVA Kingston plant in Tennessee in December 2008 are enough to make any reasonable person wonder whether the human factors can ever been completely eliminated.  There is always pressure from upper management in corporations to delay maintenance and major repairs – they are expensive.  TVA knew there was seepage into the earthen wall that surrounded their Kingston coal ash – yet they continued to operate the impoundment without fixing the problem immediately.

Another piece of information on pump storage which may be of interest: In Michigan’s Upper Peninsula, researchers are investigating the feasibility of using old abandoned underground mines for pump storage: water would be pumped up to the surface at night, and released back into underground iron mines during periods of high electric demand.