Bellevue is investing nearly $10 million in sewer capacity upgrades to accommodate development growth in the Wilburton neighborhood, with larger pipelines projected to handle the next century of change.

The Bellevue City Council rezoned the Wilburton subarea to allow increased height limits and densities in 2008, the neighborhood expected to be a transition zone between residential development on the east side and the downtown area west of Interstate 405.

“The sewage infrastructure out there was designed for a low level of development; historically, it has been car dealerships,” said Paul Bucich, Bellevue’s assistant director of engineering. “The systems out there were undersized for the rezone that the city has implemented.”

The two years of engineering work for replacing 4,300 feet of various sized sewer pipes that started in 2013 anticipates the city council’s follow-through with another rezone for mixed-use development in the near future, Bucich said.

The city council on Monday approved an ordinance granting low bidder MidMountain Contractors, Inc., a $7.9 million contract for the Wilburton sewer capacity project, with the expectation the cost will rise to $9.85 million before completion. Bucich said the contract was signed Tuesday to begin preconstruction discussions ahead of a potential September start time.

“A lot of the work is being done outside the road right-of-way, except out on 114th (Avenue Northeast),” said Bucich, adding traffic coordination will be necessary. “We can’t shut off the road. That is the access for many (hotel) businesses to get their goods.”

The project will take about a year to complete, and comes with a number of challenges, such as having to use auger cast piles to support a pipeline that will run through a wetland area to prevent the line from sinking, removing and replacing a pipe crossing under I-405 and 20-foot excavations in certain areas to mitigate groundwater impacts.

The Wilburton sewer project is one of three undertakings by the city — all amounting to about $19 million — to increase sewer capacity. Discussions are ongoing about mitigating traffic when the East Central Business District trunkline improvement project — 1,850 feet of 30-inch and 42-inch sewer lines within 112th Avenue Southeast —  starts in mid-August.

“They’re already feeling traffic jams from the Bellefields Pump Station project,” Bucich said, which is being replaced in order to continue being served by the ECBD line.