The plan calls for use of hydroseeding, a buffer and silt fencing to stabilize those areas of the reservoir's exposed sediment that are not subject to immediate excavation. All removed material will be transported to an approved upland location. Work will begin as soon as possible and is expected to be completed within 14 to 20 weeks.
This initiative is part of an on-going company and state effort to restore the river and the Johnson's Shut-Ins State Park, following the Dec. 14 failure of AmerenUE's Taum Sauk Hydroelectric Plant Upper Reservoir. The plan has been carefully reviewed and approved by the Missouri Department of Natural Resources, the Missouri Department of Conservation and the Federal Energy Regulatory Commission.
On Jan. 25, AmerenUE administered a one-time treatment of the lower reservoir with flocculates\-alums that helped settle suspended particles out of water and allowed a portion of the clay to be removed from the Black River. After the treatment of the Lower Reservoir, the water level was lowered to approximately 736 feet in an attempt to remove in-stream sediments. The 736- foot level represents a 13-foot drop from the normal high pool level of 749 feet. However, evaporation, continued draining for keeping flow in the river, and lack of rainfall have dropped the reservoir to a current level of 733 feet.
Over the past few months, wave action and other factors caused some solids---particularly clay---to become re- suspended in the reservoir water. Analysis has shown that water quality upstream of the reservoir has improved more quickly than the water in the Lower Reservoir.
"Our intent is to permanently remove sediments that are affecting water clarity in the Black River," said Mike Menne, Ameren Vice President of Environmental, Safety & Health.
Menne added that Ameren and its contractors will take all practical measures to prevent further degradation of the river, but releasing some additional sediments downstream will be unavoidable from time to time.
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On Dec. 14, 2005 the AmerenUE Taum Sauk Plant experienced a breach in the northwest corner of its upper reservoir that caused flooding in the Johnson Shut-ins and resulted in the closing of one road. The rupture caused 1.5- billion-gallons of water to flow downward. The company implemented its emergency plan and assembled a multi-disciplinary team of experts, company officials and consultants to analyze the event and determine next steps; 281 of the park's 2,490 acres or 11% of the total park was affected by the Dec. 14 event.
Built in 1963, AmerenUE's Taum Sauk is a "pumped-storage" hydroelectric plant. It stored water from the Black River in the upper reservoir, built atop the 1,590-foot-high Proffit Mountain, and released the water to generate electricity when power is needed. The water flowed down a mile-long tunnel inside the mountain, turning turbine-generators to produce electricity. When power demand was low, the same turbines ran in reverse to pump water back to the upper reservoir.
AmerenUE is a subsidiary of St. Louis-based Ameren Corporation. Ameren companies serve 2.4 million electric customers and nearly one million natural gas customers in a 64,000-square-mile area of Missouri and Illinois.