THE RE-BUILD OF THE UPPER RESERVOIR TAUM SAUK PUMPED STORAGE PROJECT

PERSPECTIVES OF THE OWNER, REGULATOR, AND DESIGNER/CONSTRUCTION MANAGER

(REV 6)

ROBERT L. POWERS Vice President, Technical Services, AmerenUE, St. Louis Missouri, USA

CONSTANTINE G. TJOUMAS

Director (Retired), Division of Dam Safety and Inspections, Office of Energy Projects, Federal Energy Regulatory Commission, Washington, DC, USA

PAUL C. RIZZO

President, Paul C. Rizzo Associates, Inc., Monroeville, PA, USA

INTRODUCTION On December 14, 2005, the dumped rockfill Dike surrounding the Upper Reservoir for the Taum Sauk Pumped Storage Project failed catastrophically, releasing about 1.4 billion gallons of water through a 700 feet wide Breach Area on the northwest corner of the Reservoir as indicated on Figures 1 and 2.

Figure 1 - Aerial View of the Upper Reservoir before the Breach

Figure 2 - Aerial View of Upper Reservoir after the Breach Damage caused by the Breach was confined to the flow path down the west side of Proffit Mountain and to the Johnson’s Shut-in State Park at the base of the Mountain as shown on Figure 3. As the incident occurred during the winter, no campers or tourists were visiting the Park at the time of the incident. However, the Park Ranger’s home was destroyed and his family sustained serious injuries. No fatalities occurred as a result of the Breach.

J o h n s o n ’s S h u t-In C a m p g ro u n d

R o u te N

B la c k R iv e rS ite o f T o o p ’s h o m e

Figure 3 – Aerial View of the Damage at Johnson’s Shut-in State Park

The Taum Sauk Upper Reservoir Failure has been the subject of numerous formal and informal inquiries and is a significant event in the history of the design of reservoirs for pumped storage projects. Key issues addressed during the inquiries included the nature of the dumped rockfill dike comprising the Upper Reservoir, the foundation preparation work performed during the original construction, and the instrumentation used to control the level of water in the Upper Reservoir. Much has been learned about the behavior of dumped rockfill dikes and the evolving technology of dams for pumped storage projects. As a result of this incident, the design, construction, and operation characteristics of pumped storage projects in the United States are being reviewed, and it is likely to result in changes at existing and new projects around the world. This paper discusses the many issues faced by the Owner, Regulator and Designer/Construction Manager immediately after the Breach and during efforts to re-build the Upper Reservoir place it back in operation.

THE OWNER’S PERSPECTIVE The Lead Author, acting as the lead spokesman for the Owner, the Ameren Corporation based in St Louis, Missouri, USA, was initially faced with a large number of difficult questions concern the failure of the Upper Reservoir Dike. The corporate crisis management program was immediately implemented and maintained well after the event occurred. The overall integrity of the Corporation was challenged in the local media and the local politicians have focused on the incident during a political campaign. Ameren Corporation is a major US utility in the Mid-western United States with three hydroelectric projects, a nuclear plant and numerous coal-fired and gas-fired generation units. They service several million customers in three States. The major issues addressed by the Owner included the following:

• Implementation of the Emergency Action Plan • The immediate cleanup of the damaged environment. • The stabilization of the remnant Dike. • Interaction with the National and State Regulators • Development of a Plan to Re-Build the Project

Implementation of the Emergency Action Plan Immediately following the Breach when it was clear to the Plant Operators that a failure had occurred, Ameren’s Emergency Action Plan (EAP) was implemented by the Plant Operators. EAP’s are a requirement of the Federal Energy Regulatory Commission (FERC) for all hydroelectric projects in the USA. These are reviewed annually, tested with “table top” and “functional” exercises and maintained in a current status by the dam owners. Each plan includes a flow chart of agencies to be notified of an incident and what should be done by the Plant Operators to mitigate the emergency.

For this incident, the EAP was implemented in a highly successful manner. The Plan functioned as intended and no post-incident panic or consequential incident occurred. Local police and emergency management personnel were rapidly informed and were able to implement the EAP efficiently. After it had been established that no loss of life occurred and that injured people had been rescued, the emergency management personnel re-established traffic patterns and other services impaired by the incident. The immediate cleanup of the damaged environment Within hours of the incident and once it became clear that the public health and safety issues associated with the Breach were being handled with the EAP, Ameren proceeded to assess the environmental impact and engaged an emergency response contractor to support the corporate efforts. The immediate clean-up involved restoration of roads, removal of excessive debris from natural drainage ways and restoration of impaired services. Subsequent efforts, which are still in process 18 months after the Breach, involved removal of sediment from the stream beds, Black River and the Lower Reservoir, restoration of vegetation, re-construction of the Johnson’s Shut-ins Park facilities and restoration of water quality. The stabilization of the remnant Dike. About 90% of the original rockfill Dike, as shown on Figure 2, remained in place after the Breach in the northwest corner. The Forensic Investigation as discussed below questioned the safety of the remnant Dike because of the revelation that the Dike was supported on a poor foundation and that the material comprising the Dike itself was not a true rock fill as considered in modern dam design as illustrated on Figure 4.

Figure 4 – View of the North Side of the Breach

The slopes at Breach were at their natural angle of repose, indicating a factor of safety less than one against subsequent sliding. Also, the Parapet Wall on the crest of the remnant Dike was undermined in a number of locations as shown on Figure 5.

Figure 5 – View of the Undermined Parapet Wall at the Southeast Corner

Consequently, Ameren, with the concurrence of the Regulators, proceeded as soon as practical with a Stabilization Program implemented by the Designer/Construction Manager. This initial Program occurred over a period of about six months after the Breach, but during the course of the work, it had to be extended to include additional slope stabilization and removal of the concrete face panels which were found to be undermined at a number of locations as shown on Figure 6.

Figure 6 – Undermined Concrete Facing Panel Interaction with the National and State Regulators In the United States, all non-federal dams used for hydroelectric generation are regulated by the FERC. This includes dam safety, environmental, and all other issues of project development. In addition, the State of Missouri has regulatory authority over water quality and local environmental impacts. Therefore, Ameren has to comply with the regulations at two levels of regulators which are manifested in approximately ten different offices and agencies. The FERC, being the lead agency and the grantor of the Federal license for the Taum Sauk Project, immediately undertook an independent investigation of the project to supplement a Forensic Investigation conducted by Ameren through the DCM as mentioned below. The FERC also is the lead Agency for regulating the re-build of the Project, but the local and State agencies, plus Non-Government Organizations (NGO’) investigate and deal with impacts associated air emissions, water quality, noise, socio-environmental impacts and the like. One of the most significant outcomes of the Agency Interaction was the re-structuring the Dam Safety Program at Ameren. Ameren developed and implemented a model dam safety program, as illustrated in Figure 7, that is now the model that can be used by others in the USA and is being adopted in similar formats at other utilities. The program is independent of power generation

activities and includes a reporting system as high as the corporate Board of Directors and an independent auditing function.

Figure 7 - Ameren dam safety program Development of a Plan to Re-Build the Project After a comprehensive evaluation period, Ameren elected to re-build the Project if, and only if, the Project could be re-built with a safe dam and if the project economics are favorable. The Re-Build Plan had to consider a large number of parameters, many of which required in excess of one year to fully resolve. These parameters and issues include the following:

• The Re-built Dam encompassing the Upper Reservoiu must be safe, meet modern day safety standards, both at the Federal and at the State level.

• The Re-built Dam must meet all Federal and State environmental standards and

regulations, and recognize the concerns of the local inhabitants and State environmental regulators.

• The Re-Built Dam must address issues and concerns raised by Ameren’s insurance

carriers.

• The Project must be re-built as rapidly as possible with the constraints of dam safety and environmental regulations with an eye toward being back in commercial operation by June 2009.

Working together with the DCM, the FERC and State Regulators, a plan evolved over a period of six months from the date of the Breach. Construction Bids, based on 90% drawings, were received within one year of the Breach and preliminary site preparation and early construction activities are underway as of this writing. Full scale construction is expected to begin in August after the FERC completes its environmental assessment.

THE REGULATOR’S PERSPECTIVE

The Regulator at the Federal level considered major issues including the cause of the Breach, the Owner’s Dam Safety Program, the implementation and overall success of the Project’s Emergency Action Plan, the original design versus modern dam design and construction standards, and a relatively rapid and responsive investigation program and design review process.

The Taum Sauk project is under the Federal regulatory authority of the FERC and maintains a license under the Federal Power Act of the United States. FERC immediately dispatched engineering staff and an independent consultant to begin investigating the incident. The investigation began the evening of the day of the breach of the embankment dam. During the ensuing weeks investigations including interviewing Ameren staff continued.

All aspects of Ameren’s regulatory responsibilities were reviewed in accordance with

the Federal Power Act, the dam safety regulations (Part 12 of the Code of Federal Regulations), and the FERC Engineering Guidelines. The breach of the Upper Reservoir did not result in any loss of life, but did result in significant environmental damage. The Lower Dam did not suffer any damage, but on the other hand stored the majority of the water discharged from the Upper Reservoir. The Lower Reservoir is a concrete gravity overflow structure and passed water to a depth of about two feet over the uncontrolled Ogee section. This flow is less than what occurs during each spring season.

There are several dam safety requirements that pertain to any license issued by the

FERC. Periodic inspections for dam safety and for operation and maintenance are required. In addition to inspection and instrumentation surveillance an appropriate Emergency Action Plan (EAP) as mentioned above is required in order to be prepared for any unexpected condition or emergency.

The EAP development follows the FERC requirements in content, format,

coordination with emergency response personnel, and periodic testing. The process begins with the development of inundation maps covering a range of breach possibilities and sensitivity of breach parameters considering sunny day as well as potential flood scenarios (the latter for the Taum Sauk Project mainly applied to the Lower Dam and Reservoir). The FERC provides for the review of the EAP and, once finalized, the plan is reviewed annually, redone every five years, and undergoes periodic testing as required by FERC. The Test includes a “table-top” Exercise in which an emergency scenario is developed and tested

under a non-stressful situation with no concern for timeliness of actions. With what is learned from this exercise, a Functional Exercise with a more detailed emergency scenario is tested under stressful conditions with time being an important parameter. Normally these two tests are done back-to-back with the Functional Exercise occurring the next day or next week. In this manner both the dam owner and the emergency response personnel are tested for their knowledge and ability to fulfill each of their responsibilities should an emergency develop. The dam owner has the responsibility for notification and the emergency response personnel have the responsibility for responding to the emergency and for evacuation if required.

Having a good and well tested EAP is a major reason why no loss of life occurred as a

result of the Breach of the Upper Reservoir. The Emergency Response personnel attributed this due to the periodic testing of the EAP (one within the year prior to the Breach) and thoroughly understanding what to expect and what they would have to do during an emergency to save lives.

Post Investigation Requirements The Taum Sauk Pump Storage Project was constructed during an era when the design of rockfill dams with impervious membranes was evolving. A main conclusion of FERC was that if the Upper Reservoir would be re-built, the remnant dam would need to be completely removed and any design of a new dam would need to substantially address the foundation conditions and an appropriately designed new dam would include an adequately prepared and treated foundation consistent with the new dam design. Current state-of –knowledge and state-of-practice would need to be incorporated in the design of the dam and dam foundation. By necessity, adequate conservative measures need to be included in the final design. In addition, Ameren is taking adequate precautions to allay any concerns of the public. Ameren’s Dam Safety Program Another consideration of the FERC concerned Ameren’s dam safety organization and dam safety decision-making processes. A review of causes of all types of failures has found that inadequate organization and the lack of clear lines of communications and responsibilities have led to failure incidents. A review of Ameren’s organization demonstrated that over the years, changes in management, organization, and the loss of institutional memory perhaps played a role in leading up to the over-pumping situation, resulting in the Breach. If this did indeed play a role in the overtopping incident occurring, FERC required Ameren to develop a clear dam safety program and establishing a dam safety officer position that would have an independent role and the sole responsibility for dam safety. Ameren has developed a detailed dam safety program that satisfies the FERC requirements and has been very meticulous in the content, staffing, authorities (including independent lines of communications and responsibilities), training, and periodic program auditing. The dam safety program developed by Ameren will be used as a model for dam owners to follow.

THE DESIGNER/CONSTRUCTION MANAGER’S PERSPECTIVE The Designer/Construction Manager (DCM) had to deal with the root cause of the Breach, the original design versus modern dam design and construction issues, and an intense schedule to return the project to operation. As regards the original dike design and

construction, the dike was constructed by simply “slicing off” the top of a domal-shaped mountain and moving the excavated rock to the edges of the dome to form a perimeter dike. The rockfill was placed by dumping on a foundation surface consisting of residual soil and weathered rock. The rock was dumped, sluiced with water jets to remove some of the fines, but was not compacted. The foundation preparation work was minimal and judged inadequate by modern standards of dam construction. The DCM has dealt with the following major issues from a design and construction perspective:

• Why did the original Dike fail? • Can a new Dike be constructed at the same location without fear of a second failure? • How should the new Dike be constructed in the shortest period of time? • What measures can be taken to minimize the impact on the environment during the re-

build process?

Why did the original Dike Fail? The cause of failure was the subject of several independent groups, but the DCM published the first and most comprehensive report, including the results of test borings, laboratory testing, stability analysis, and hydraulic/hydrologic analysis. The DCM concluded that the Breach of the Rockfill Dike caused a “rapid release of water from the Upper Reservoir,” which was a consequence of a stability failure caused by the following:

(1) A rapid rise in the phreatic surface and the associated pore pressure at the Dike/foundation interface caused by the flow overtopping the Parapet Wall.

(2) Weak foundation conditions attributed to the

original design and construction specifications. (3) Inadequate shear strength of the material comprising

the rockfill attributed to the original design and construction practices.

(4) Poor construction practices and failure to meet the

intended design criteria. The consultants retained by FERC to perform an independent study concluded that:

(1) The embankment had a long history of settlement and high leakage.

(2) The steep rockfill embankment was possibly marginally stable for the “dirty” dumped rockfill and the seepage conditions previously experienced (prior to geomembrane liner installed in 2004).

(3) There was no margin for accepting the additional pore pressures and erosive effects of overtopping the parapet, as was the case with the failure.

(4) Factors which caused the overtopping to occur included instrumentation problems, inadequate freeboard, and insufficient visual monitoring.

(5) Contributing factors which combined to make the embankment more vulnerable to failure by overtopping.

Can a new Dike be constructed at the same location without fear of a second failure? The DCM concluded emphatically in the affirmative as the location of the Dike was not a factor in the failure of the original Dike. How should the new Dike be constructed in the shortest period of time? The failure of the original Dike resulted in a loss in generation of 440 Mw of capacity to the Owner, capacity that is sorely needed during summer months when air conditioning loads significantly increase demand. In addition, the economy of the nearby towns is highly dependent on the project being in an operating condition. Therefore, a primary objective of the re-build effort is to re-build the project as soon as practical, specifically by June 1, 2009 to allow for use of the plant during the summer of 2009. The DCM recommended and the FERC and Owner concurred that the new dam should be safe, robust and consistent with modern technology. Also, it is recalled that the foundation material, once the weathered rock and residual soil is removed, is a sound granitic rock or ryolite, lending the site suitable for a gravity type of dam. In addition, the rock comprising the original Dike is a suitable aggregate for a Roller Compacted Concrete (RCC) mix design. After several iterations, all concerned parties agreed that a RCC, symmetrical Dam is highly suitable for the new Dam. In addition, the DCM and the Regulator had worked together on a large RCC Dam and had worked out many details related to drainage, foundation preparation, test programs, water stops, and the like that will be incorporated in the new Dam for Taum Sauk. The final design and construction details will satisfy the specific site conditions and foundation treatment required and is conservative. The progress and detail of investigation and analyses of foundation conditions and the cross-section of the dam are continuously being reviewed and evaluated by the FERC dam safety staff along with their consultants and the Independent Board of Consultants retained by the Owner. RCC construction is very rapid compared to conventional concrete construction, especially when the aggregate is readily available without the need for an off-site rock quarry. Combining the rapid construction opportunities with RCC and the fact that many design and construction details of this type of construction had recently been discussed and analyzed with the FERC in the prior months for a similar sized project, all parties agreed that an RCC

Dam is the best approach for re-building the Dam as soon as practical. The typical design Section is shown below in Figure 8 below. One of the primary features of the new Dam is an Overflow Release Structure (ORS) which is designed to respond to the pressing “What if” question of what is the consequence if the new, modern water level instrumentation does not function as intended. The ORS is a depressed section of the new Dam on the southwest side of Upper Reservoir as shown on Figure 8. Figures 9 and 10 show the location, length (about 700 feet) and the stepped spillway design for dissipating energy. The ORS will have a stilling basin at the toe to further dissipate energy of the cascading water. It is emphatically emphasized that it is highly unlikely that the ORS will ever function because of the redundancy of the water level monitoring instrumentation system, which include video surveillance, and the new Ameren Dam Safety Program and its associated monitoring and system checks (instrumentation and inspection) and balances.

Figure 8 – Typical Sectio for the New RCC Dam

n

Figure 9 – Upper Reservoir Re-Constructed with RCC

(Note location of new Overflow Release Structure)

Figure 10 – Close-up View of Overflow Release Structure

(Note Depressed Crest Level and Stepped Spillway Surface) What measures can be taken to minimize the impact on the environment during the re-build process?

The environmental impacts of new construction activities is a particularly important issue as the site is immediately adjacent a State Park that heavily populated during the summer construction season. Therefore, DCM adopted the following measures during the re-build process:

• Confine as much of the new construction activity as possible to the area with the confines of the old Dike. In this manner, minimal new land is disturbed and noise is confined by the remnant Dike and the new Dam.

• Utilize the rock comprising the original Dike as aggregate for the new RCC Dike,

thus eliminating the need for a quarry. • Assure that all local and State Permits applicable to air emissions, noise, water supply,

traffic control and dust are obtained on a timely basis. • Employ on site a full time environmental compliance officer on the site to guard

against permit violations by all contractors working on the site. All of the above measures were implemented, and except for the initial permitting process, environmental issues have not been an impediment to the Project. The Authors may be reached at the following addresses. It is noted that the Paper was submitted to the Conference Officials for consideration while Mr. Tjoumas was the Director at the Federal Energy Regulatory Commission. He has since retired from the Commission and may be reached at the address indicated below. Robert L. Powers AmerenUE One Ameren Plaza 1901 Chouteau Avenue P.O. Box 66149 MC 600 St. Louis, MO 63166-6149 RLPowers@ameren.com (314) 554-6101 Fax: (314) 554-4406 . Constantine G. Tjoumas gus.tjoumas1@verizon.net (410) 715 1170 Paul C. Rizzo Paul C. Rizzo Associates, Inc. 105 Mall Boulevard Suite 270E Monroeville, PA 15146 paul.rizzo@rizzoassoc.com (412) 856-9700 Fax: (412) 856-9749