New estimates of construction costs for a sewage treatment plant in downtown Oak Harbor show the price tag has decreased.

Yet the numbers are still well above the original estimate for the large-scale project being built on City Beach Street.

City Engineer Joe Stowell presented the newest estimates for the “60-percent design” milestone during a City Council workshop Wednesday. The city’s consultant engineer and general contractor/construction management developed estimates separately.

Carollo Engineers pegged the number at $91.3 million, which is down from the company’s $98-million estimate set during the 30-percent design phase.

Hoffman Construction’s estimate is significantly higher at $110.2 million, but it is down from its previous estimate of $113 million.

The numbers are for construction and don’t include costs for design, engineering, property acquisition or any amenities.

They do include the significant costs of a large community room and a sewage dryer system; the council hasn’t yet decided if the project will include these items.

The council will look at the numbers more in depth during a workshop from 12 to 4 p.m., Wednesday, Sept. 30 at the Elks Club.

The public is welcome to attend, but no action will be taken.

Stowell emphasized that the numbers are still preliminary — only at the 60 percent phase — and they should continue to go down as the project is refined. He said the numbers are “opinions of costs” and not bids.

A city consultant explained that estimates tend to be high since the national standard for engineers is to peg them at a range from 5 percent below to 15 percent above actual cost.

“The entire time we’ve been working on this our focus, as a team, has been on the impact to the ratepayers,” Stowell said.

That impact is still unclear. The bulk of the cost of the project will be funded through sewage utility rates.

The city has $38 million in grants and low-interest loans which will help keep the rates down.

After the meeting, interim City Administrator Doug Merriman said the city is continuing to apply for grants and low-interest loans and will hopefully receive more from the state.

Merriman explained that the city has been gradually increasing rates to build up cash for the project. He said there’s currently $8 million in the account after $2.6 million was spent on buying the Whidbey Island Bank building in Pioneer Way.

The plant is being built in the parking lot behind the building.

Nearly three years ago, Carollo estimated that the construction project would cost about $78.9 million. Under that estimate, a consultant calculated that rates should gradually increase to $97 a month in 2021.

Early this year, Hoffman caught city leaders off guard when it released skyrocketed construction estimate of about $116 million, including the $2 million cost of the outfall project — which is currently being built at the end of City Beach Street.

Given the new estimates, the city will look at sewage rate projections again in the next few months, Merriman said.