AmerenUE plans rebuild for breached pumped storage dam

ST. LOUIS—AmerenUE, the Missouri utility operating company of Ameren Corporation, engaged Ozark Constructors LLC to rebuild the company’s Taum Sauk pumped storage hydroelectric plant upper reservoir, assuming successful resolution of outstanding issues with Missouri state authorities and of a recent lawsuit. Ozark Constructors is a venture partnership formed by ASI Constructors, Inc., and St. Louis-based Fred Weber, Inc. AmerenUE also selected Paul Rizzo Associates, Inc., engineer of record and project manager.

The selection of engineers and contractors comes almost two years after the Dec. 14, 2005, breach in the plant’s upper reservoir that caused significant flooding in the Johnson’s Shut-Ins State Park (see CE News, February 2006, page 12). Built in 1963, AmerenUE’s Taum Sauk pumped-storage hydroelectric plant stored water from the Black River in the upper reservoir on top of a mountain and released the water to generate electricity when power was needed.

In February 2007, AmerenUE submitted plans and an environmental report to the Federal Energy Regulatory Commission (FERC) to rebuild the upper reservoir of the plant. In August 2007, AmerenUE received approval from FERC to rebuild the upper reservoir. If the Taum Sauk plant is rebuilt, AmerenUE expects it to be out of service through at least the fall of 2009, if not longer.

However, the Associated Press reported in early December 2007 that a group representing state parks supporters sued to stop reconstruction. The lawsuit claims that FERC failed to study adequately the environmental effect of reopening the hydroelectric plant or alternatives to rebuilding it.

Since the company first announced its intent to rebuild in early 2007, AmerenUE has stressed that the reservoir would be rebuilt following criteria used in current dam design and construction practice. The upper reservoir would be constructed with roller compacted concrete (RCC) based on Paul Rizzo & Associates’s design, which received FERC’s approval.

According to AmerenUE, the RCC design uses the latest in overflow structures, monitoring and control systems, seismic design criteria, and other safety features. Continuous video camera monitoring of the upper reservoir water levels is expected to ensure that proper water levels are maintained in both the upper and lower reservoirs. Separate instrumentation and control systems will be dedicated to dam safety. In addition, the rebuilt project is designed to withstand potential ground shaking from both near-field and far-field earthquake events up to a 2,500-year return period.

AmerenUE and Paul Rizzo & Associates worked with FERC to develop a new dam safety program and a design-review process. AmerenUE created an organization of professionals who are independent of daily operators. The chief dam safety engineer leads this multi-disciplinary team of engineers dedicated to engineering and managing ongoing upgrades, conducting safety and other operational inspections, and implementing safety improvements.

The chief dam safety engineer is also responsible for communicating policies and expectations regarding dam safety and regulatory compliance and for monitoring compliance with FERC dam safety-related requirements, including using sound and prudent engineering practices and notifying FERC about any condition affecting the safety of a project or any modification to a project.

The chief dam safety engineer is also charged with implementing quality management initiatives such as documenting dam inspections and establishing qualification standards for dam inspection personnel. According to AmerenUE, the chief dam safety engineer has the authority to conduct unannounced facility inspections and take corrective actions, including shutdown, if dam safety is threatened.

"AmerenUE would not consider returning this plant to service if company officials were not absolutely certain that the new design met, or exceeded, all safety criteria required by the Federal Energy Regulatory Commission," said Thomas R. Voss, AmerenUE president and chief executive officer. "After much analysis, we are now confident that this plant can be returned to service and operated safely to restore a critical source of reliable power to our customers."