Design of Embankments

Structural Stability Measures

In 2008 and 2014 structural failures of surface impoundments at two energy centers in the southeastern United States resulted in the release of large quantities of coal ash slurry into adjacent rivers. In one of those instances, the failure was largely the result of stacking coal ash well above the top of the basin embankment while the other was the result of a collapsed drainage pipe located beneath the basin. Following both incidents, Ameren voluntarily took steps to evaluate the physical condition of its facilities and to ensure ongoing safe operation. That assessment reflects that the various practices that contributed to the failure, including inappropriate storage and stacking of CCRs and inadequate foundations, were and are not present at Ameren's facilities.

A key to safe and secure management of CCR is by ensuring the integrity of landfills and ash basins. The CCR Rule creates an evaluation process for existing CCR units and design standards for the construction of new units. Plant operations staff inspect ash basins embankments weekly. In addition, on an annual basis, we perform evaluations of all critical areas of the ash impoundments including embankment crest, interior and exterior slope, downstream toe area, and inlet/outlet works, etc. Ameren's Dam Safety Program team regularly performs vegetation control, routine maintenance and erosion protection measures. As part of its CCR Rule compliance and to guard against the risk of structural failures, third-party engineering firms also perform specialized assessments at each of the energy centers, including hazard potential classification, structural stability, hydrologic and hydraulic capacity and safety factor determinations. We also added video cameras to our inspection protocols to observe subsurface features such as piping and outlets.

Ameren's basins and landfills are all protected by berms designed and maintained to withstand extreme weather events. Third party engineers have performed modeling assessments to verify that the basins have sufficient retention capacity to hold a 100 year, 24 hour rainfall event. In addition, perimeter berms surrounding CCR landfills at our Sioux and Labadie Energy Centers are built to withstand a 500 year flood event.