The state Transportation Department said the damage was discovered May 11 after steel cables were stretched through one of the 350-foot long pontoons for strength. There wasn't enough rebar in place to hold.
"Any time we have concrete delaminating like this in a structure like this we want to identify and fix the problem so it doesn't occur again," said project engineer Dave Ziegler.
After all, millions of cars will go across the bridge and a concrete fault could be the start of something bad.
"It will definitely require more rebar," Ziegler said. "We've got to the point where we've got to excavate about a 3-foot wide section of concrete and put more rebar to restrain that force."
The big question is what will this cost, and who will pay. The answer: no one knows.
"We have to figure out why the force wasn't restrained by the existing rebar in the slab," Ziegler said. "Could it be a design problem or a build problem? ... It could be both."
The work on the fixing the problem will begin even as engineers try to figure out what went wrong. The department plans to add more rebar to four large pontoons, causing a 4 to 6 week delay until July or August for the first six pontoons.
The department had hoped to make the 260-mile tow Aberdeen to Seattle in June. Floating the pontoons out of there requires certain tide levels, and the best tide levels are in the next six weeks
The pontoon problem will not necessarily delay the entire 520 replacement program -- engineers explain there will be many opportunities to make up the lost time.
Work continues on other pontoons under construction in Tacoma, on bridge anchors in Tacoma and on bridge supports on the east side of Lake Washington.