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The $20 million Boeckman Road extension in Wilsonville has been sinking since it opened in 2008, and now the city may need to close the bridge for as long as a year while construction crews fix engineering flaws.

The city of Wilsonville in 2010 filed a lawsuit against the firm that led the project, Nebraska-based , after claiming the company was negligent. In September, the city settled for nearly $1 million, which officials hope will pay for design and construction work to fix the road extension this year.

A new study of the bridge is expected to come out next week, according to community development director Mike Bowers. The timeline for repairs is still uncertain, although he said the city will look to hire a design firm in the next 30 to 45 days.

鈥淥ne thing we know for sure is we’ll have to close road for substantial period of time,鈥� Bowers said.

The 400-foot bridge, which crosses Coffee Lake Creek Basin wetlands, is safe from settlement because it rests on pilings pounded into lower bedrock. But the ramps leading onto the bridge will continue to drop if the city doesn’t take action, according to Steve Adams, interim city engineer for Wilsonville.

鈥淭he ramp on the east side of the bridge is fairly steep now, and it will just keep getting steeper,鈥� he said.

The city attempted to slow the sinking by reducing the speed limit on the bridge from 35 mph to 20 mph, but permanent fixes are necessary.

Portions of the east ramp have already dipped 14 inches in elevation and could continue to fall another 16 inches, according to preliminary studies conducted by Seattle-based . The city hired the firm to study the sinking ramps, which trace back to an engineer who misread soil compression data, Adams said.

Studies conducted prior to the initial road construction revealed that peat deposits in the area could lead to extensive soil compression, according to Adams. To mitigate that problem, crews stacked rock soil on top of the roadbed area before beginning construction so that geotechnical engineers could study how fast the soil consolidated over a period of several months.

Soon after the bridge opened, however, the steep incline where the bridge met the road raised red flags. In the lawsuit, the city alleged that the designs by HDR Engineering and subconsultant miscalculated the amount of soil compression that would occur.

The city initially sought $2.68 million from HDR for civil negligence. The engineering firm also filed a $250,000 counterclaim for unpaid design work, which was dropped in the $1 million settlement.

鈥淏ased on the estimates made by the engineering firms during the settlement, we believe ($1 million) will be sufficient for construction,鈥� Bowers said. 鈥淎nd (we) hope the settlement funds will also include the design work.鈥�

Initial construction costs were between $16 million and $17 million, and design work, environmental permitting and geotechnical work added $4 million to the price tag, according to Bowers.

The Boeckman Road extension was built to provide an east-west connection to roadways on either side of wetlands, but drivers will need to use alternate routes during construction. The repair work could take as long as a year, Bowers said, although the exact timeline will depend upon the length of the design process as well as the complexity of the plans.