The Washington Transportation Department expects construction to start as soon as next month in Aberdeen on the facility that will build pontoons for the new Highway 520 floating bridge at Seattle.

The department says the Aberdeen site won federal approval this week. Kiewit-General Joint Venture still needs other permits to start construction on the pontoons, each up to 360 feet long.

The pontoons will support the new six-lane bridge to replace the existing Lake Washington bridge, built in 1963.

Tolling starts on the bridge this year to help pay for construction. The new bridge is scheduled to open by the end of 2014.