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The Washington Transportation Department admits mistakes have been made in the construction of pontoons for the new Highway 520 floating bridge across Lake Washington between Seattle and Bellevue.

The results of our internal review show that we did not follow standards of good practice to validate the pontoon design elements, and as an engineer, that is particularly frustrating, Washington Transportation Secretary Paula Hammond said. We also did not strictly follow some of our protocols for oversight and administration of the contract on the construction site.

The department announced Tuesday that it is making repairs and design modifications to ensure a 75-year life of the bridge.

The changes are the result of findings by an expert review panel that was convened last year to review cracking in the first pontoons built in Aberdeen.

Underwater inspections revealed the pontoons' worst cracks grew over the winter. The most serious cracks begin in the end walls, and wrap around the upper and lower edges to continue along the top and bottoms.

An untreated underwater crack can let in water at rates of 1 cubic foot per hour, according to a technical report on the bridge.

John Reilly, chair of the expert review panel, said the structural capacity of the pontoons is sound, and more than adequate for all anticipated loads.

Hammond said disciplinary action will be taken against state bridge division staff who signed off on the design without running models that might have foreseen the cracking.

A total of 77 pontoons will make the world's longest floating bridge.

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