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Union Electric Company
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Union Electric Company
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The Union Electric Company of Missouri (formerly NYSE: UEP) was an electric power utility that was organized in 1902 and grew to be one of the large U.S. companies listed among the S&P 500. In 1997, its holding company merged with a smaller neighboring utility, Central Illinois Public Service Company through its holding company, CIPSCO Inc. (formerly NYSE: CIP), to form Ameren Corporation (NYSE: AEE) based in St. Louis, Missouri.[1]

History

[edit]
Ashley Street Light and Power building

The company's first incarnation, the Union Company, was organized in 1902 in St. Louis. Two years later, the renamed Union Electric Company built the 36 MW coal-fired Ashley Street Plant in the city's Near North Riverfront region to provide steam heat to downtown St. Louis. The plant was for years the city's main source of electricity. It powered The Palace of Electricity's electric lights at the 1904 World's Fair in St. Louis.[2] The plant was converted to oil in 1972 and from oil to natural gas in 1996. Today, the plant functions as a district steam plant for the city of St. Louis and is owned by Ashley Energy.

By 1906, Union Electric Company was a publicly traded stock and began to pay a cash dividend to shareholders, which it paid every year until the 1997 merger.[2][3]

In 1909, Union Electric began selling electric cars, and became the St. Louis agent for Studebaker and Rauch & Lang automobiles.[2]

In 1919, the Shubert-Jefferson Theatre in the Union Electric building hosted a post-war national caucus in which the American Legion was born.[2]

In 1927, a tornado struck St. Louis, destroying more than US$10 million worth of property, including Union Electric's electricity lines to the city.[2]

By 1929, Union Electric Company became a subsidiary holding company of North American Company, one of the original stocks in the Dow Jones Industrial Average.[4] Union Electric subsidiaries at the time included Union Electric Light and Power (Missouri) and Union Electric Light and Power of Illinois.

In 1929, UE completed Bagnell Dam on the Osage River, creating the Lake of the Ozarks with 1,400 miles of shoreline and a power station that generated almost 175 megawatts of hydroelectricity.[2] The associated Union Electric Administration Building-Lakeside was constructed in 1930; it was added to the National Register of Historic Places in 1998, with a boundary increase in 2011.[5][6]

In 1937 the company acquired the shares of the Union Colliery Company,[7][8][9]

By 1940, Union Electric Company was one of three holding companies and also one of the ten major direct subsidiaries in the US$2.3 billion North American Company pyramid of 80 companies. At that time, North American owned more than 79% of Union Electric stock.[10]

North American Company was broken up by the Securities and Exchange Commission after the United States Supreme Court decision of April 1, 1946.[10] Union Electric Company was then divested from North American. Until the 1997 merger, Union Electric Company traded publicly as an independent company on the New York Stock Exchange under the ticker symbol UEP.[3]

By the 1950s, Union Electric owned gas operations in and around Alton, Illinois, and acquired other utilities to become the third largest distributor of natural gas in Missouri.[2]

In 1952, Union Electric joined with its future Ameren mate, the Central Illinois Public Service Company; and also with another later Ameren subsidiary, the Illinois Power Company, to form the Midwest Power Pool system.[2]

In 1963 Union Electric completed construction of one of the largest pumped storage plants at that time, the then-350-megawatt Taum Sauk Plant, in Reynolds County, Missouri.[2] In December 2005, a large section of the dam containing the plant's upper reservoir failed, draining over a billion gallons of water in less than half an hour.

In 1984, Union Electric's first nuclear energy plant, the Callaway Nuclear Generating Station, began providing 1,143 megawatts of power from Callaway County, Missouri.[2]

In 1993, Union Electric battled a 500-year flood in the St. Louis metropolitan area from the swollen Missouri and Mississippi Rivers. In 1994, Union Electric shared the industry's Edison Award with Midwest Power Systems, Inc., of Des Moines, Iowa, for their work providing electric service to customers during the 1993 flood disaster.[2]

In 1995, shareholders of both Union Electric Company and CIPSCO Inc. approved the companies' merger.[2] The merger was completed on December 31, 1997, forming Ameren Corporation.[2] At the time of the merger, Union Electric had assets of nearly US$600 million, but still carried nearly US$1.8 billion in long-term debt, down from US$2.5 billion which it had accumulated by the 1980s.[3]

The former Union Electric Company is now a subsidiary of the Ameren Corporation holding company, initially d/b/a AmerenUE, later becoming Ameren Missouri in 2010.[1] Ameren is now also a holding company for several other power companies and energy companies as well.

Ameren Missouri continues to own Bagnell Dam. Ameren Missouri is responsible for managing water levels on the Lake of the Ozarks according to federal regulations; if levels are not appropriate, the lake must be closed until Ameren can solve the problem.

Today, with nine power plants, Ameren Missouri serves 1.2 million power customers and 110,000 gas customers, primarily in Missouri, where more than half of its customers reside in the St. Louis metropolitan area. It formerly served Iowa as well through the mid-1990s. The former AmerenUE also served adjoining parts of Illinois; that portion would be transferred to Ameren Illinois in 2010.

References

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[edit]
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Union Electric Company

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Union Electric Company was an American based in , , founded on May 20, 1902, that grew to become the state's largest and a major provider of services, serving approximately 1.1 million electric customers and 120,000 customers before merging into Corporation in 1997. Originally organized with a small staff and about 2,000 customers, the company experienced rapid expansion following the 1904 , which boosted demand and infrastructure development in the region. By the early , Union Electric had incorporated as Union Electric Light and Power Company in 1922, succeeding earlier entities, and focused on generating, transmitting, and distributing power across central and eastern . A pivotal achievement came in 1931 with the completion of the on the Osage River, creating the and establishing one of the largest hydroelectric facilities in the U.S. at the time to meet growing industrial and residential needs. The company also operated the Callaway Nuclear Plant, which began commercial operation in 1984 and remains a key asset under its successor. Throughout the mid-20th century, Union Electric expanded through interconnections like the 1965 Mid-Continent Area Power Planners pooling agreement with other utilities, enhancing reliability and efficiency across the Midwest. By the 1990s, facing trends in the sector, it pursued strategic growth, culminating in a merger with CIPSCO Incorporated on December 31, 1997, to form Corporation, a that integrated Union Electric's operations with utilities. Today, Union Electric operates as a known as , continuing to deliver regulated electric generation, transmission, distribution, and services to communities.

History

Founding and Early Operations

The Union Electric Light and Power Company was incorporated on May 20, 1902, in , Missouri, through the merger of several smaller local electric utilities, including the Imperial Electric Light, Heat and Power Company, the Citizens Electric Lighting and Power Company, and the Missouri Edison Electric Company. At its inception, the company operated with a small staff and served approximately 2,000 customers, primarily in the urban core of . To meet rising demand, the company quickly invested in new infrastructure, constructing the Ashley Street coal-fired power plant in 1904 with an initial capacity of 12 megawatts. This facility, located in the Near North Riverfront district, became the primary source of electricity for the city and notably powered the lighting and exhibits at the 1904 , highlighting the reliability of electric service to millions of visitors. During the ensuing years, Union Electric expanded through the acquisition of additional local utilities and the development of transmission lines across eastern , particularly amid heightened industrial needs during . By 1920, the company's customer base had grown substantially, encompassing both industrial operations and residential users throughout the St. Louis metropolitan area, solidifying its role as a key provider in the region.

Major Infrastructure Projects

In 1925, Union Electric Company acquired a in the Keokuk Dam on the , adding significant hydroelectric capacity to its portfolio. The facility, originally developed by the Keokuk and Hamilton Water Power Company, featured 15 turbines with a combined capacity of approximately 130 MW, marking one of the largest low-head hydroelectric projects of its era and enabling power distribution across the company's growing service area. The company's most ambitious hydroelectric endeavor was the construction of on the Osage River, completed in 1931 after starting in August 1929. This 2,543-foot-long concrete created , a spanning 93 square miles with over 1,150 miles of shoreline, which boosted regional tourism through recreational development and provided flood control benefits by regulating Osage River flows. The project added 175 MW of generating capacity via eight turbines at the adjacent Osage Power Plant, diversifying Union Electric's generation beyond early coal-fired facilities. Building presented substantial engineering challenges amid the , including the need to excavate bedrock foundations in a narrow and pour over 500,000 cubic yards of under tight timelines. The total cost reached $30 million, funded by Union Electric after acquiring the stalled project from prior developers, while labor demands peaked at around 10,000 workers, offering critical employment in an economically devastated region. Environmental considerations involved inundating fertile Osage River valley lands, displacing rural communities and altering local ecosystems, though the dam's design incorporated spillways to manage water levels and mitigate downstream flooding risks. By the , Union Electric expanded its infrastructure through the absorption of its parent holding company, the North American Company, in February 1955, which integrated additional generating properties and enhanced transmission networks across , , and . Complementing this, the company initiated a program of intercompany transmission lines and power pools starting in the early , interconnecting facilities to improve regional reliability by allowing shared resource access during peak demands or outages. These developments laid the foundation for later innovations, such as the Taum Sauk pumped-storage project in the 1960s.

Post-War Expansion and Nuclear Development

Following World War II, Union Electric Company pursued significant expansion to meet growing electricity demands in its Missouri service territory, shifting toward advanced technologies like pumped-storage hydroelectricity. The company's most notable project in this era was the Taum Sauk Pumped Storage Plant, constructed between 1960 and 1963 in Reynolds County, Missouri. This facility featured two reversible pump-turbine units with a combined capacity of 350 megawatts, designed to store energy by pumping water from a lower reservoir to an upper one during off-peak hours and generate power during peak demand by releasing it through turbines. The upper reservoir, engineered on Proffit Mountain with a substantial hydraulic head of approximately 444 feet, utilized a kidney-shaped rock-fill rim dike structure to create a 4,350-acre-foot storage capacity, enabling efficient peak-load balancing for the regional grid. Operational by December 1963, Taum Sauk represented a pioneering application of pumped-storage technology in the United States, enhancing Union Electric's ability to integrate with its existing hydroelectric assets like the Bagnell Dam. The development of Taum Sauk faced regulatory challenges that underscored federal oversight of interstate energy infrastructure. In 1959, Union Electric sought approval from the Federal Power Commission (FPC) without a full license, arguing the project on a non-navigable tributary of the Black River fell outside federal jurisdiction. The FPC disagreed, requiring a license under Section 23(b) of the Federal Power Act due to the plant's use of water power for interstate electricity transmission and its potential effects on downstream navigable waters. The Eighth Circuit Court of Appeals initially reversed this, but in the landmark 1965 Supreme Court case Federal Power Commission v. Union Electric Co., the ruling affirmed the FPC's authority, emphasizing that projects affecting interstate commerce in electricity warranted licensing regardless of direct navigation impacts. This decision not only validated Taum Sauk's operation but also established broader precedents for federal regulation of non-navigable water projects tied to the electric grid. Amid the 1970s energy crises triggered by oil embargoes and supply disruptions, Union Electric responded by diversifying its fuel sources and expanding capacity to reduce reliance on imported oil and enhance reliability. The company accelerated construction of coal-fired plants, with the Labadie Energy Center in , becoming its flagship addition. Initiated in 1970, Labadie's four subcritical coal units came online sequentially through 1973—each rated at approximately 600 megawatts—yielding a total capacity of 2,400 megawatts and making it Union Electric's largest generating facility. This expansion burned locally sourced , supporting fuel diversification efforts, while efficiency improvements in and designs minimized energy losses compared to older plants. These measures helped stabilize supply during the crises, allowing Union Electric to meet surging demand without excessive rate hikes, though they also increased coal consumption and emissions scrutiny. Union Electric's post-war strategy culminated in nuclear power adoption to further secure baseload generation. The Callaway Nuclear Generating Station, located near Fulton, Missouri, began construction in 1975 as a (PWR) designed by Westinghouse. With a net electrical capacity of 1,143 megawatts, the single-unit plant incorporated advanced safety features, including a robust structure, redundant emergency core cooling systems, and multiple fission product barriers to prevent radiological releases. Initial licensing by the was granted on October 18, 1984, after extensive reviews addressing seismic and environmental concerns, with commercial operation commencing in December 1984 at a total construction cost exceeding $3 billion. Callaway's completion marked Missouri's entry into nuclear energy, providing carbon-free power that complemented the company's hydro and coal portfolio amid ongoing diversification needs.

Merger into Ameren and Modern Era

On December 31, 1997, Union Electric Company merged with CIPSCO Incorporated, the parent company of Public Service Company (CIPS), to form Corporation, a with combined assets of approximately $9 billion and service territory spanning and . This merger expanded Union Electric's operations into central and , integrating CIPS's electric and gas assets, including approximately 1,000 megawatts of capacity and service to over 300,000 customers. The transaction occurred amid U.S. deregulation efforts in the late 1990s, particularly in , where the 1997 Customer Choice Act introduced retail competition, rate freezes until 2007, and requirements for utilities to divest or separate from transmission and distribution to foster market-based pricing. These changes prompted to restructure operations, separating competitive activities while retaining regulated transmission and distribution under subsidiaries like AmerenUE (Union Electric's successor) and AmerenCIPS. In 2010, rebranded to , aligning with the consolidation of its three utilities into and emphasizing its role as 's primary operating subsidiary. This rebranding supported streamlined customer service and regulatory compliance across states, with inheriting Union Electric's legacy assets, including the Callaway Nuclear Plant, while adapting to post-deregulation market dynamics in that included stranded cost recovery and unbundled services. In the modern era, has focused on , retiring older coal-fired units such as the 343-megawatt Venice plant in in 2002 to reduce emissions and operational costs amid tightening environmental regulations. By the , the company integrated significant renewables, adding over 700 megawatts of capacity through projects like the Atchison Renewable Energy Center (a 299 MW ) and fulfilling 's Renewable Energy Standard with a mix of solar, , and energy efficiency programs, aiming for net-zero carbon emissions by 2045. In March 2025, Ameren Missouri's Integrated Resource Plan was approved, outlining a $16.2 billion investment to achieve a balanced —one-third each nuclear, renewables, and —by 2045 while enhancing reliability. As of 2025, Union Electric operates as a legacy legal entity under , serving approximately 1.3 million electric customers in central and eastern through this evolved structure.

Operations and Service Territory

Geographic Coverage

Union Electric Company, now operating as Ameren Missouri, provides electric service primarily in eastern and central Missouri, encompassing approximately 24,000 square miles across about 60 counties and more than 500 communities, extending from the area to the region. This territory includes diverse landscapes, from urban centers to rural farmlands, and supports around 1.3 million electric customers. The company's infrastructure network features a 2,970-mile high-voltage operating at 138 kV to 345 kV, interconnected with over 33,000 circuit miles of distribution lines, linking major urban hubs like and other urban centers in central to remote rural areas. These lines facilitate reliable power delivery across the service area, with key interconnections to neighboring utilities such as Evergy for seamless regional coverage. The geographic scope incorporates vital river basins, including the Osage River basin for hydroelectric generation at facilities like and the basin supporting operations such as the Keokuk Energy Center, enhancing resource integration within the and riverine areas. Historically, Union Electric began with a core service area around and expanded significantly through acquisitions, notably purchasing Missouri Power & Light Company in 1950 and Missouri Edison Company in 1954, which extended coverage to much of central and eastern by the mid-1950s. Following the 1997 merger forming Corporation, the territory gained interstate transmission connections to , while maintaining boundary overlaps with other Missouri providers to avoid service gaps.

Customer Base and Services

As of 2025, Ameren Missouri, the successor to Union Electric Company, serves approximately 1.3 million electric customers and 135,000 customers across its service territory. The customer base is predominantly residential, accounting for the majority of electric accounts at around 1.1 million, followed by commercial users at approximately 156,000 and a smaller industrial segment. This composition reflects steady growth in residential and commercial classes, with annual increases of 0.5% to 1% in recent years, driven by population and economic expansion in central and eastern . Ameren Missouri provides essential services in electricity distribution and delivery, with the latter expanded through acquisitions in the 1950s that integrated gas operations in areas around , establishing Union Electric as a major regional distributor. In addition to core utility operations, the company offers energy efficiency programs such as Pay As You Save (PAYS), which provides free energy-saving products and rebates for home upgrades, and BizSavers® for businesses seeking incentives on equipment efficiency improvements. These initiatives, including Peak Time Savings for , help customers reduce usage during high-demand periods and promote . Peak demand management is closely linked to the industrial sector's growth, particularly in St. Louis manufacturing, where economic development efforts support increased energy needs from sectors like automotive and production. Missouri's strategies, including demand-side resources identified in its 2023 DSM Market Potential Study, address these patterns by encouraging efficiency and shifting loads to maintain grid reliability amid projected 0.5% annual peak growth. Rates for electric and services are structured with a fixed charge—such as $9 per month for residential electric—and variable energy charges based on usage tiers, designed to recover costs for delivery and supply while incentivizing conservation. All rate adjustments and service offerings fall under regulatory oversight by the Commission (MPSC), which approves changes through formal rate cases, as seen in the 2025 electric rate agreement increasing revenues by $355 million while capping residential impacts. The evolution of services traces from early 20th-century origins in street lighting and basic in to advanced implementations in the , including full of distribution circuits and deployment of advanced metering infrastructure as part of the Smart Energy Plan. These modern enhancements enable real-time monitoring, outage management, and integration of renewable sources to support reliable supply for the diverse customer base.

Power Generation Assets

Hydroelectric Facilities

Union Electric Company's hydroelectric facilities, now operated by Missouri, form a key component of its portfolio, harnessing the power of major rivers in the Midwest for . The primary assets include the on the Osage River and the Keokuk Dam on the , both developed or acquired during the company's early expansion in the 1920s and . These run-of-the-river plants provide baseload and peaking power while supporting regional water management. The total run-of-the-river hydroelectric capacity is 383 MW as of 2025. The , constructed between 1929 and 1931 by Union Electric Company, is a 2,543-foot-long structure with a maximum height of 148 feet above , impounding the spanning 54,000 acres. It features eight main vertical Francis turbines in the adjacent Osage Hydroelectric Plant, each with a hydraulic capacity of approximately 4,210 to 5,000 cubic feet per second, operating under an average head of 90 feet, alongside two auxiliary units. The facility has an operating capacity of 235 MW as of 2025 and generates an average of 636 gigawatt-hours (GWh) annually, contributing to flood control through regulated releases and fostering recreation on the lake, which attracts millions of visitors yearly. The Keokuk Dam, originally built in 1913 as on the , was acquired by Union Electric Company in 1925 and integrated into its system, spanning the Iowa-Illinois border with associated locks for navigation. This facility includes 15 main turbine-generator units and operates as part of a lock-and-dam complex that facilitates barge traffic and river flow management. With a capacity of 148 MW, it supports hydroelectric generation while coordinating with upstream Iowa-based infrastructure for efficient power dispatch. Ongoing maintenance efforts in the 2020s have focused on enhancing reliability and at these sites. At the Osage Energy Center (), replaced the fish protection barrier net in 2023 to minimize entrainment of aquatic species through the turbines, aligning with the Lower Osage River Protection and Enhancement Plan that promotes mussel restoration, such as for the pink mucket pearly mussel. Similarly, the Keokuk Energy Center underwent comprehensive turbine upgrades completed in 2022, modernizing all 15 units to improve efficiency and operational safety while ensuring compliance with federal and state environmental regulations. These initiatives reflect Union Electric's legacy commitment to sustainable operations, coordinated with agencies like the (FERC) and the Department of Conservation. Collectively, these hydroelectric assets contribute approximately 5% to Missouri's total generation mix as of 2025, with 383 MW of capacity amid a system-wide portfolio exceeding 9,300 MW, underscoring their role in diversifying energy sources and reducing reliance on .

Fossil Fuel Plants

Union Electric Company's generation portfolio historically centered on coal-fired power stations, which formed the backbone of its electricity production to meet the demands of St. Louis's expanding urban in the early . The Ashley Street Power House, constructed in 1902 along the , served as the company's inaugural large-scale facility, initially equipped with coal boilers to generate electricity and later repurposed for steam distribution after power generation ceased amid the shift to more efficient plants in the mid-. By the late , Union Electric had developed several major that dominated its capacity, with fossil fuels accounting for over 70% of its generation resources prior to 2000, supplemented by emerging nuclear facilities for baseload stability. The Labadie Energy Center, located in , exemplifies this expansion; comprising four -fired units with a combined capacity of 2,400 megawatts (MW), it began operations in 1970 and remains the state's largest power plant. Efforts to control emissions at Labadie have included compliance with federal regulations, though full installation of advanced has been subject to ongoing litigation into the . The Energy Center in St. Charles County, with two units totaling approximately 1,000 MW, entered service in the late and features installed in 2010 to reduce emissions. The Rush Island Energy Center in Jefferson County, featuring two 600 MW coal units for a total of 1,200 MW, operated from 1976 until its full retirement in October 2024, driven by regulatory pressures and the broader shift toward cleaner energy sources. Following the 1997 merger forming Ameren, the successor entity has accelerated the phase-out of these assets, targeting net-zero carbon emissions by 2045 through retirements like Rush Island and investments in renewables, reducing reliance on fossil fuels from historical highs to under 50% of capacity today.

Nuclear Facilities

The Callaway Nuclear Generating Station, operated by Union Electric Company (dba Ameren Missouri), serves as the company's primary nuclear asset and Missouri's sole commercial nuclear power facility. Located in Callaway County near Fulton, Missouri, approximately 25 miles northeast of Jefferson City, the plant features a single-unit pressurized water reactor (PWR) designed by Westinghouse with a four-loop configuration. It has a net generating capacity of 1,190 megawatts and operates on an 18-month fuel cycle, during which the reactor is refueled approximately every 30-45 days while offline. Construction began in August 1975 and concluded with commercial operation on December 19, 1984, at an initial cost of approximately $3 billion. The plant's annual electricity output averages 9.2 million megawatt-hours (MWh), accounting for about 15% of Missouri's in-state generation and providing baseload power that supports the state's energy needs with low-carbon emissions. Its (NRC) operating license, initially issued in 1984, was renewed in 2015 to extend operations through October 18, 2044. The facility employs a turbine-generator and relies on robust infrastructure, including a and steel containment building (205 feet tall and 150 feet in diameter) and a 553-foot-tall , to ensure reliable performance. Safety features at Callaway include an emergency core cooling system (ECCS) designed to inject borated water into the reactor core during loss-of-coolant accidents, preventing core damage, along with multiple redundant systems for containment integrity and radiation monitoring. Following the 2011 Fukushima Daiichi accident, the plant implemented NRC-mandated enhancements, such as improved flooding protection, seismic monitoring upgrades, and additional emergency diesel generator capabilities to bolster resilience against extreme events. These measures, combined with routine NRC inspections confirming no critical safety issues, have maintained Callaway's strong operational safety record since startup. For long-term management, Callaway maintains an NRC-approved decommissioning fund, with recent analyses estimating prompt decommissioning costs at approximately $1.1 billion (in 2023 dollars) under a DECON post-2044, covering license termination, , and site restoration. is managed on-site in a and an adjacent system, providing sufficient capacity through the current period, with plans for transfer to a federal repository once available. Low-level is processed and disposed of off-site at licensed facilities, ensuring compliance with federal regulations.

Notable Events and Controversies

Taum Sauk Pumped Storage Incident

The Taum Sauk Pumped Storage Project, operated by AmerenUE (formerly Union Electric Company), suffered a catastrophic failure of its upper reservoir on December 14, 2005, when overfilling led to overtopping and a breach around 5:15 a.m. The reservoir, which had been filling overnight via pumps drawing water from the lower reservoir, exceeded its safe capacity due to undetected level increases, initiating erosion at the parapet wall and releasing approximately 1.42 billion gallons (4,350 acre-feet) of water over about 25 minutes. This sudden discharge created a peak flow of around 273,000 cubic feet per second through a breach roughly 656 feet wide at the top, transforming the structured rockfill embankment into a debris field and rendering the 440-megawatt facility inoperable until its reconstruction. The failure stemmed from multiple interconnected causes, including faulty instrumentation that misread water levels. Pressure transducers and conductivity probes, installed in protective high-density polyethylene (HDPE) pipes, provided inaccurate readings because the pipes bowed upward by about 2.5 feet, underestimating the reservoir elevation by roughly 4 feet—the actual peak reached 1,597.7 feet, while sensors reported only 1,593.72 feet. High-level alarms (set at 1,597.4 feet for "HI" and 1,597.66 feet for "HI-HI") were positioned above the lowest parapet wall elevation of 1,596.99 feet, allowing overtopping to occur before triggering an emergency pump shutdown, which required both sensors to activate for redundancy. Compounding these issues was the absence of on-site staffing during the overnight pumping cycle, eliminating visual monitoring, and a lack of response to prior warnings, such as overtopping events on September 25 and 27, 2005, attributed to storm effects rather than systemic flaws. Additionally, programmable logic controller (PLC) programming errors, including incorrect message tags and no formal configuration controls or testing, prevented automated shutdown of Unit 2, while abnormal pumping rates (115 minutes per foot of rise versus the typical 7-8 minutes) went unnoticed. Immediate impacts were severe, with the floodwaters surging down the East Fork of the Black River, inundating approximately 317 acres in Johnson's Shut-Ins State Park and causing extensive erosion that stripped soil and vegetation across the path. The discharge destroyed the residence of the park superintendent at Johnson's Shut-Ins State Park, flooded Missouri Highway N, and inflicted heavy damage to the park's infrastructure, including campgrounds and trails, though the lower reservoir contained most of the inflow with only minor overtopping of 1.1 feet. Five individuals sustained injuries, primarily the superintendent's family during their evacuation, but no fatalities occurred as the incident happened before dawn when the nearby campground was unoccupied. The plant itself suffered irreparable damage to its upper structures, leading to an estimated $60 million in initial repair and mitigation costs, with the facility remaining offline until its reconstruction and return to service in 2010. AmerenUE initiated its Emergency Action Plan (EAP) promptly upon detecting the breach around 5:40 a.m., when the Osage operator notified the Taum Sauk superintendent of anomalous readings from reports by the Lesterville Fire Department and Reynolds County Sheriff. By 6:00 a.m., the superintendent confirmed the failure and activated notifications to the Federal Energy Regulatory Commission (FERC), local authorities, and state agencies, while coordinating voluntary evacuations downstream of the lower reservoir and warning boaters and campers in the area. The Lesterville School served as an emergency shelter, supported by the American Red Cross and Salvation Army for immediate aid to affected residents. Federal assistance followed, with the Federal Emergency Management Agency (FEMA) declaring the event a disaster and providing relief funding for recovery efforts in the impacted region. The facility's original 1963 design, constructed by Union Electric as the first large-scale pumped-storage plant in the United States, featured a concrete-faced rockfill dam without a spillway, relying on a 2-foot freeboard above the 1,596-foot operating level, later reduced to 1 foot after a 2004 geomembrane liner installation. The upper reservoir dam measured 6,562 feet in length with a crest elevation of 1,599 feet and a structural height of approximately 90 feet, enclosing a 55-acre surface area capable of holding 4,350 acre-feet at full capacity. Power generation utilized two reversible pump-turbine units with a total initial rating of 350 megawatts, upgraded to 440 megawatts total by 1999, enabling the system to pump water uphill during off-peak hours for release during peak demand. The facility was rebuilt using roller-compacted concrete and returned to full operation in April 2010, continuing to provide peaking power to the regional grid as of 2025. Prior to 2005, the plant had operated reliably since its 1963 commissioning. In 1965, the U.S. Supreme Court ruled in Federal Power Commission v. Union Electric Co. that the (now the , or FERC) held jurisdiction over the Taum Sauk Pumped Storage Project, even though it was located on non-navigable waters, because the project utilized water power for the interstate transmission and sale of electricity, thereby affecting interstate commerce and requiring a license under Section 23(b) of the Federal Power Act. The 2005 Taum Sauk reservoir failure triggered extensive regulatory scrutiny of Union Electric (operating as AmerenUE). A 2007 report by the Commission (PSC) concluded that the breach resulted from the company's imprudent and reckless operations, including failure to repair known faulty water level sensors since October 2005, improper calibration of backup sensors above safe levels, and inadequate safety margins that allowed overtopping of the reservoir wall. In response, FERC imposed a record $15 million penalty in 2006, comprising a $10 million civil fine for 15 violations of license conditions and regulations, plus $5 million for local improvements near the site. Additionally, in 2009, the U.S. Army Corps of Engineers filed a against AmerenUE, alleging in the project's operation led to sediment and debris contamination of Clearwater Lake downstream, reducing its storage capacity and lifespan; the suit sought unspecified damages for remediation. The (NRC) has maintained strict oversight of the Callaway Nuclear Plant, owned by Union Electric. In 2011, AmerenUE applied for a 20-year extension, prompting battles in over environmental impacts and , including public hearings where activists cited post-Fukushima seismic risks and urged enhanced scrutiny of the plant's vulnerability in Missouri's Central Ia-2 . The NRC approved the extension in 2015, extending operations to 2044, but required ongoing seismic upgrades, such as reinforced restraints on equipment like the equipment hatch missile shield to withstand potential earthquakes. During the , Union Electric faced significant challenges from efforts to the industry, which threatened traditional rate structures and prompted the company's merger with Central Illinois Public Service Company in 1997 to form Corporation as an adaptation to regulatory pressures. regulators rejected full deregulation, leading to protracted rate case disputes with the Missouri PSC; for instance, in 1996, the company sought a rate increase to recover merger and operational costs, but faced opposition over stranded costs and competitive transitions, resulting in partial approvals and ongoing litigation. In the 2010s, Union Electric encountered environmental lawsuits concerning coal ash disposal at its Labadie Energy Center. In 2014, the Labadie Environmental Organization challenged AmerenUE's proposed new coal ash before the PSC and Department of Natural Resources, arguing it failed to comply with the EPA's 2015 Coal Combustion Residuals Rule by lacking adequate liners and groundwater monitoring to prevent leaching of toxins like into the . Further litigation ensued, including a 2020 citizen suit under the alleging unpermitted discharges and inadequate closure plans at Labadie's ash s, which was resolved through EPA-mandated compliance plans requiring pond closures by 2025, which were completed as of early 2025, including conversion to dry handling and enhanced monitoring to mitigate contamination risks.

References

  1. https://dynamic.stlouis-mo.gov/history/peopledetail.cfm?Master_ID=1991
  2. https://www.govinfo.gov/content/pkg/FR-1997-02-24/pdf/97-4444.pdf
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  5. https://www.ameren.com/-/media/files/our-company/generation/callaway-2024-fact-sheet.ashx
  6. https://www.govinfo.gov/content/pkg/FR-1997-10-22/pdf/97-28001.pdf
  7. https://www.stlouis-mo.gov/government/departments/planning/cultural-resources/preservation-plan/Part-III-The-Worlds-Fair-City-Utilities-Structures.cfm
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  17. https://www.nrc.gov/docs/ML2003/ML20030A226.pdf
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  20. https://www.gem.wiki/Labadie_power_station
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