at the time, far surpassing all previous US pumped storage projects), a large storage capacity (it has been described as "the first of the large capacity pumped-storage stations to begin operation in the United States"), black start capability, and had the unique ability to be operated either remotely by remote human operators in off-site facilities located 90–120 miles away (at St. Louis or Osage Power Plant/Bagnell Dam) or even fully automatically with zero human intervention. Taum Sauk was also the first pure pumped storage plant in the United States. Upgrades The pump-turbine units were uprated in July 1972 from their initial rating of 175 MW each to 204 MW each, increasing the plant's overall rating from 350 MW to 408 MW. From 1998–1999, the turbine runners for both units were upgraded, resulting in improved flow rates and another power uprate to 225 MW per unit (450 MW total). Minor leaks in the reservoir led to the construction of a collection pond and pumpback station to collect and return leaked water to the reservoir. Later, to reduce leakage, Geo-Synthetics installed lining material in the reservoir itself from September 13 to November 15, 2004. The plant was named an IEEE Milestone in October 2005, just months before the upper reservoir failed. It was subsequently rededicated as an IEEE Milestone in 2010 after the new upper reservoir dam was completed. 2005 upper reservoir failure At 5:12 a.m. on December 14, 2005, the northwest side of the upper reservoir was overtopped when water continued to be pumped from the lower reservoir after the upper was full. This led to the catastrophic failure of a triangular section of the reservoir wall and the release of of water in 12 minutes. The sudden release sent a crest of water northwest of the reservoir about 1.75 miles down the ridge to the East Fork of the Black River inside the north upstream side of Johnson's Shut-Ins State Park. The river at the park is normally very shallow with rapids running over granite boulders. The flood destroyed many of the structures in the park and forced the closing of the trail connecting it to Taum Sauk Mountain. A combination of design and construction flaws, continuing to operate the dam when the primary system for gauging the water level was known to be inaccurate (gauge pipes had become detached), moving the "failsafe" secondary gauging system above the actual height