A project to replace Washington state's Route 520 floating bridge across Lake Washington has begun. The $586.5 million bridge will have six lanes and be 115 feet wide. Dozens of concrete pontoons are needed to support the bridge and act as its foundation -- some will be as large as 360 feet long, 75 feet wide and 28 feet deep. Work has started at the $367 million pontoon casting site that will include on-site water treatment, a concrete batch plant and a 4-acre casting basin.

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