LAKE STEVENS — Costco is considering a new store on a piece of property at Highway 9 and 20th Street, according to the Lake Stevens mayor.

The Issaquah-based chain is doing due diligence on the property, which is mostly owned by the city, Mayor John Spencer said. The area is 15 to 18 acres; part of the land isn’t able to be developed because wetlands, topography and geology, he said.

“I’m very optimistic that we’ll have an opportunity to have a Costco here,” Spencer said. “To go any further than that is not possible because the feasibility studies aren’t done and we’re not sure what we’ll learn.”

Costco has a policy not to talk about future locations until three or four months before development, said Muriel Cooper, a Costco spokeswoman. The average size of a Costco warehouse store is 144,500 square feet. The number of employees varies from store to store, she wrote.

Costco started studying the property this spring and the studies could take up to a year, Spencer said. But he said the city could have a better idea about the likelihood of the project by this summer.

The City Council would need to make the final decision on whether to sell the property to Costco and what conditions need to be met for development.

County records show the city owns a little more than 13 acres at the intersection. The city took possession of the property about a year ago when it swapped land on Grade Road for the property along Highway 9.

Another developer wants to build senior housing on the land at Grade Road, Spencer said. The area Costco is studying along Highway 9 of Lake Stevens is aimed for commercial development.

Costco has been rumored for months on social media to be considering a Lake Stevens store, but nothing previously had been confirmed, Spencer acknowledged.

“They’re such a large corporation it’s hard for them to keep a secret,” he said.

There are currently four Costco Wholesale stores in Snohomish County — one each in Smokey Point, Everett, Lynnwood and North Creek. There’s also a smaller Costco Business Center in Lynnwood.

Costco would boost sales tax revenues for the city, Spencer said. And many residents already travel outside of Lake Stevens to get to the wholesaler.

Costco building along Highway 9 could spur more economic development, Spencer said.

A store of that size would also draw a lot of traffic. Spencer said that’s part of the studies being conducted, to determine the amount of traffic and what improvements would need to be done. He said the city would confer with the Washington State Department of Transportation.

“I doubt the morning commute would be affected much by Costco,” Spencer said. “The afternoon commute could be impacted. We’ll have to work with WSDOT on how to deal with that on Highway 9.”

Costco isn’t the only big-box store eyeing development along the Highway 9 corridor. Lowes Home Improvement is looking to build a 121,000-square-foot store in southeast Marysville at Highway 9 and Soper Hill Road.

Jim Davis: 425-339-3097; jdavis@heraldnet.com. Twitter: @HBJnews.