The price tag for flushing a toilet in Oak Harbor may be much higher than anyone anticipated.

The newest projections from two firms working on the new sewage treatment plant show that the cost may balloon by $40 million,  or nearly 50 percent.

In the latest projections by the construction management and project design firms, the plant may cost more than $116 million. The original estimate for constructing the plant without the Navy base partnership was less than $79 million, according to the capital facilities plan.

And the projection doesn’t include the cost of reconstructing the RV park, which will be destroyed during the project, or planned improvements to adjacent Windjammer Park.

Oak Harbor Mayor Scott Dudley said he’s frustrated that his own staff seems to be in the dark as to why this has happened.

“My main concern is that no one seems to be focused on keeping this under budget,” he said.

Dudley said he heard about the new price tag a couple of weeks ago and asked staff members to figure out what’s happening and to get back to him this week. After the meeting Tuesday, he said his questions still weren’t answered.

Dudley said staff members involved in the project were supposed to give a presentation about the status of the project at a workshop Wednesday, but they canceled it because there were too many questions they could not answer.

Councilman Rick Almberg said Thursday that he heard from city staff that there wasn’t a finalized estimate yet. He speculated that there might be a lot of reasons for an early number to be inflated, including nonessential add-ons and large contingency funds. He also pointed out that the project is going to be built in phases.

Dudley, however, said he worries that sewer rates may go through the roof; the project is funded by the sewer rates residents pay each month. Under the original estimate, rates are scheduled to gradually climb from the current $57.50 a month for residential customers to $97 a month in 2021.

“We’re about to build the most expensive per capita wastewater treatment plant in the state,” he said.

The firm Carollo Engineers has been working with the city since nearly the beginning of the project. The firm helped identify six possible sites for a treatment plant to replace the aging plant in Windjammer Park and the treatment lagoons on the Navy Seaplane Base.

In the end, officials chose between sites on the north side of Crescent Harbor Road or at Windjammer Park. The firm estimated that construction costs would be about the same at the two sites with the membrane bioreactor technology.

Dudley broke a tie vote in favor of the Windjammer site because operating costs would be higher at Crescent Harbor, while Almberg warned about unforeseen geotechnical and archaeological costs.

The City Council decided to construct the treatment plant through a general contractor/construction manager process in order to increase efficiency and control costs by having the construction company involved during earlier phases of the project.

Over the years, a lot of different numbers have been discussed.

The project is currently at the 30 percent design phase.

Two years ago, Carollo estimated that the project would cost $78.9 million if the Navy doesn’t partner on the project. The city and the Navy currently partner on sewage treatment, but Navy officials decided not to work with the city on the new plant because of concerns over the cost.

In its request for proposal for the construction manager last summer, the city estimated the project would cost $67.7 million.

Then on Feb. 6, the city received a cash-flow projections from the construction management firm, Hoffman Construction Company, stating that it was estimating the project to cost $116 million and that Carollo had increased its estimate to $95 million.

Then in an email to City Engineer Joe Stowell, Brian Matson of Carollo wrote that the firm’s current estimate matches Hoffman’s at $116.5 million.

Matson wrote that increase all comes from construction, not from “soft costs.”

He outlined possible reasons for the increase. Among the reasons he cited are the complexity of the geotechnical issues, archaeological concerns, increased costs of materials and labor, and additions to the project itself — such as a proposed 200-seat training facility, the extension of Bayshore Drive along the southern frontage of the site and improved solids handling technology.