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WSDOT admits big mistakes on 520 pontoons

Bellamy Pailthorp photo

Big mistakes were made by the State Department of Transportation in its construction of the pontoons that will hold up the new 520 bridge across Lake Washington.

The agency says it is making repairs and design modifications to ensure the bridge will last the full 75 year lifespan promised.

The announcement comes as a result of findings by an expert review panel that was convened last year, after cracks and leaks began showing up in the pontoons. State Transportation Secretary Paula Hammond says the agency has been working hard to maintain transparency.

“And as we came to understand that we had design issues with the pontoons, it was very important to me to make sure that we put to rest the notion of whether these pontoons are safe, whether they’re sound and whether they’ll serve the public for the 75-year design life,” Hammond said.

She says the good news is that the expert review panel was able to use computer modeling to fairly quickly analyze patterns in the pontoons’ cracking and identify a fix. They will add post-tensioning rebar to strengthen the concrete and close cracks or prevent new ones from forming. But Hammond says the internal review also pointed to sloppy work on the part of her agency.

‘And as we came to find out is that we as a WSDOT design team did not run a model that could have and should have shown where those stresses and flaws were in the design as it was put together.”

She says some confusion likely came from a rushed contracting process, in which WSDOT provided the designs for the pontoons, but hired an outside firm as a design-build entity. So it wasn’t always clear who was in charge of preventing flaws.

The agency says it has $200 million dollars in a contingency fund to pay for fixes. Negotiations with the contractor on the costs are underway. The repairs could take an extra six months, but the new bridge is still expected to open in 2015.

Bellamy Pailthorp covers the environment for KNKX with an emphasis on climate justice, human health and food sovereignty. She enjoys reporting about how we will power our future while maintaining healthy cultures and livable cities. Story tips can be sent to