The first six concrete pontoons to support a replacement State Route 520 bridge were floated out of a construction facility in Tacoma Monday, marking a major milestone toward replacing the aging and vulnerable floating bridge. Crews will continue to tow pairs of pontoons out of Concrete Technology Corporation on high tides Tuesday and Wednesday evening.

The completed pontoons are the first of 77 of various sizes needed for a new six-lane floating bridge. A total of 44 pontoons will be built in Tacoma and 33 in Aberdeen. As each cycle ends, crews prepare the pontoons for assembly in the new floating bridge just north of the existing bridge. Crews in Tacoma worked for about six months to build this batch of six supplemental stability pontoons. These smaller pontoons will attach to the sides of larger new pontoons to provide additional floatation for the bridge structure. The 44 smaller pontoons each weigh 2,500 to 2,820 tons and measure 100 feet long, 50 to 60 feet wide and about 28 feet tall. In June, there were 155 workers at the Tacoma jobsite, including 100 craft workers, such as carpenters, ironworkers, concrete workers and equipment operators. Employment levels are expected to rise to meet construction demand as future pontoon construction cycles get under way. Construction is expected to continue into 2014.