Oak Harbor city leaders purchased a parking lot with a bank on the side Tuesday night.

Following a due diligence investigation, the Oak Harbor City Council voted unanimously to move forward with the $2.6 million purchase of the Whidbey Island Bank property on Pioneer Way.

City officials want the parking lot in the back of the building, which is adjacent to Windjammer Park, for the future sewage treatment plant.

The 35,000-square-foot building came as a extra in the deal.

“At this point we are looking at the building as an addition, as a bonus,” Oak Harbor Mayor Scott Dudley said.

The decision of where to build the treatment facility was the last obstacle in moving forward with the multi-million-dollar project.

Dudley said the city administrator, city engineer and representatives from Carollo Engineers were already at the site this week to discuss how to configure the plant.

It will be up to the community to decide what to do with the two-story building, but loads of ideas are already popping up, Dudley said.

City officials discussed moving the crowded library into the building, or even City Hall; in fact, there’s room for both.

“Something tells me you have a prime location downtown with a lot of options,” he said.

The only potential problem, he said, is that any public use of the building would require a seismic retrofit. He said he didn’t know how expensive that might be.

Kathy Reed, director of the Oak Harbor Chamber of Commerce, agrees the possibilities are endless and that just about any use would be a boon to the downtown area. She suggested the site could even be used as a “business incubator.”

“It’s fun that the city has some real estate to work with,” she said.

Whidbey Island Bank currently uses a fraction of the building as offices for its compliance services. Under the contract, the bank will lease the building for a year, with two six-month options for extension.

The Daily Grind coffee shop is located in the rear of the building.

After a lengthy public process, the City Council voted in 2012 to site the new sewage treatment plant, which will likely be the most expensive project in city history, in the Windjammer Park vicinity downtown. City leaders investigated several potential properties on Pioneer Way.

In December, the city entered into a sales and purchase agreement with Whidbey Island Bank for the parking lot and accompanying bank building, which once housed JC Penney and later InterWest Bank.

The city hired several firms to investigate the property over the last few months. An archaeological firm dug pits in the parking lot in search of cultural remains. A geotechnical firm bored into the soil. And a real estate expert looked at the structural integrity of the building.

The parking lot has a clean bill of health, Dudley said.

The building, however, has some concerns. Dudley said officials knew ahead of time that there are problems with the roof and windows that need to be fixed, so those issues were not surprises.

But the seismic issues identified by the inspector could throw a potential wrench in the works.