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U.S. completes repairs to unstable Pennsylvania dam

The Corps of Engineers' Pittsburgh District has completed critical repairs to stabilize a navigation dam on the Allegheny River near Clinton, Pa.

The Corps initiated an emergency repair contract in November 2008 after divers conducting an inspection of Allegheny River Lock and Dam No. 6 discovered severe scour conditions. (HNN 11/14/08) Brayman Construction Corp. placed concrete into a large void extending nearly 200 feet along the length of the dam.

Under a $2.97 million contract, Brayman crews first installed a steel wall along the toe of the dam to seal off the void. They then filled the void with 60 truckloads of concrete.

The Corps had declared the dam unstable, expressing concern ice loads on the dam or large chunks of ice slamming into the dam could knock it off its foundation and into the river. Additionally, dam failure would have inflicted severe damage to the 8.56-MW Allegheny Lock &Dam No. 6 hydro plant (No. 3494), operated by Allegheny No. 6 Hydro Partners, an affiliate of Sithe Energies Inc.

During the repairs, Sithe Energies drew as much water as possible through the hydroelectric plant to reduce flows over the dam and to facilitate lower flow conditions for construction crews, the Corps said.

Allegheny River Lock and Dam No. 6 is one of eight navigation facilities on the Allegheny River. An inspection of the other seven facilities did not reveal such severe problems. However, the Corps said, Allegheny River Lock and Dam No. 5 shows similar, less severe erosion that will require some repair work.

Pittsburgh District officials said that age, fatigue, and the deteriorating condition of the region's navigation system coupled with hundreds of millions of dollars of unfunded critical maintenance work on the Allegheny, Monongahela, and Upper Ohio rivers probably would result in additional unplanned repairs.

�We're in a fix-as-fails mode,� Col. Michael Crall, the district engineer, said.

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