Phasing in the construction of a new wastewater treatment plant in Oak Harbor will have little effect on the estimated rate increases facing residents who pay monthly sewer fees.

City officials, however, are still hoping to find ways to ease the burden.

“There are many different funding options that we are exploring,” City Engineer Joe Stowell said. “That may be grants or low or on-interest loans.”

Brian Matson, of Carollo Engineers, presented the Oak Harbor City Council with the treatment plant facilities plan, proposed project phasing and updated user-rate estimates during a council workshop Wednesday, which followed a public open house with sparse participation.

Estimated total cost of the facility, which is supposed to go online at the end of 2017, is $93.5 million. That number includes $7.6 million for a conveyance system to bring wastewater from the Navy base to the proposed treatment plant.

Matson said the Navy would be responsible for paying for the conveyance system, plus a percentage of the cost of building and operating the new facility, if officials decide to partner with the city on the project.

Currently about 20 percent of the wastewater comes from Navy property.

Joe Stowell, the city engineer, said he asked Navy officials to make a decision on whether they want the city to continue to treat wastewater from base property by July 1.

He admits it’s a quick turnaround on such a big decision for the Navy, but he’s hopeful he’ll get an answer.

Matson said the project can be phased so that all the equipment won’t be purchased immediately.

Under one scenario, the first phase will cost an estimated $82.6 million if the Navy is involved. Of that, the city’s share will be $60 million.

Under a second scenario, the project will cost $67.7 million if the Navy is not involved. The city will bear the entire amount.

The phasing, however, won’t have much of an impact on the rates homeowners will pay.

Last fall, an expert from HDR Engineering presented estimated sewer service rate increases that will be necessary to fund the project. He said the current rate of just under $36 a month could skyrocket in the next eight years. Depending on the variables, he estimates from $86 to $116 a month.

Wednesday, Matson said his firm was able to come up with more accurate estimates now that more information is known about the project.

Under the new estimates, the monthly rate in the year 2018 could range from $85 to $115. The plan is to gradually increase rates over the years until the necessary amount is reached.

City council members had few questions about the financing, but expressed concerns about the siting of the facility. The council previously voted to build the facility somewhere in the “vicinity of Windjammer Park,” which Matson describes as a 50-to 60-acre area that includes the park and a section of Pioneer Way. The city’s focus has been on commercial property on the south side of the road.

“The objective is to keep the footprint as small as possible,” Matson said.

Councilman Rick Almberg urged Stowell to work with property owners to identify the best site as soon as possible. Under the timeline, the final location will be selected in the fall, following more meetings and workshops.