FERC approves reconstruction of breached 408-MW Taum Sauk

The Federal Energy Regulatory Commission has authorized utility AmerenUE to begin reconstruction of the breached upper reservoir of the 408-MW Taum Sauk pumped-storage project in eastern Missouri.

Taum Sauk has not operated since the reservoir’s ring dam breached Dec. 14, 2005, releasing 1.4 billion gallons of water down the Black River, injuring nine people, and damaging property.

J. Mark Robinson, director of FERC’s Office of Energy Projects, said authorization for reconstruction of the upper reservoir is based on a record developed by FERC staff, AmerenUE, independent consultants, and various entities that either have been consulted or have provided comments.

The utility submitted plans to regulators earlier this year, proposing to begin reconstruction in 2007, and return Taum Sauk (No. 2277) to service in 2009. (HNN 2/6/07) In those plans, AmerenUE stressed the failed mountaintop reservoir would be rebuilt using roller-compacted concrete, and follow criteria used in current dam design and construction practice.

FERC said Aug. 15 that AmerenUE must submit final design plans and specifications for approval, and a plan and schedule for refilling of the reservoir, prior to reconstruction. AmerenUE must implement mitigation measures to minimize the effects of rebuilding the reservoir. The measures are consistent with a final environmental assessment, issued by FERC staff Aug. 14.

The final EA recommends the licensee, in consultation with resource agencies, develop a plan for commission approval to provide limited recreational opportunities at the project’s lower reservoir during construction. Since the 2005 dam breach, all recreational access to the project has been closed.

The reservoir was overtopped when pumps failed to shut off. Once overtopping began, erosion undercut the rockfill dam and soon formed a breach about 656 feet wide at the top of the dam and 496 feet at the base. The reservoir was emptied within 25 minutes, rendering the project inoperable.

AmerenUE’s reconstruction plans included safety features such as a crest elevation in excess of the highest anticipated water surface, including rain events or high water levels. It also proposed an overflow release structure to protect against damage to the dam in the unlikely event that redundant control systems fail and the upper reservoir overflows.

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