The Taum Sauk Pumped Storage Project opened in 1963, after three years of construction by its owners and operators, Ameren, Missouri’s largest utility company. The project consists of a 55-acre upper reservoir on Proffit Mountain, connected by a 7,000 foot long tunnel to a power plant, located on a dammed creek, 760 feet lower in elevation. The upper reservoir was unique, as it was created by building a 120-foot-tall continuous earth-fill dam, resembling a giant above ground pool, which its operators often kept filled to the brim, sometimes just a few feet from the top of the dam. Early on a December morning in 2005, the reservoir overflowed, and, without a spillway, its wall eroded and collapsed. 1.5 billion gallons of water spewed down the hill, scouring the ground of all trees and soil, down to bedrock. Ameren was declared liable for the accident, fined $15 million by the federal government, and have paid more than $200 million in settlements. In 2010 a rebuilt reservoir atop Proffit Mountain went online. Instead of an earth-filled dam, this one was made by the more sturdy roller compaction method, and includes a spillway. It cost $500 million, much of which was covered by insurance.
