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There are two visions for the Basalt Creek Planning Area, that stretch of about 800 acres between Wilsonville and Tualatin.

Wilsonville city leaders want to see industrial uses, while their counterparts in Tualatin have long envisioned residential development in the area.

On Dec. 2, councilors for both cities got a glimpse of how development might unfold in the area in the coming years.

The Base Case Scenario, a report created by consulting firm Fregonese Associates, includes a mix of industrial, residential and other uses, along with a framework for installing sewer, water and stormwater infrastructure.

“It’s just a place to start,” consultant John Fregonese said during the presentation. “We’re doing scenarios and building a model and understanding what’s going on. And that gives us a platform so we can ask more sophisticated questions.”

About 400 acres of the Basalt Creek Planning Area, replete with riparian areas and other natural obstacles, are considered suitable for development.

The Base Case Scenario breaks down the developable land as follows:

• 36 percent as light industrial and warehouse use, much of it in the portion of the planning area likely become a part of Wilsonville.

• 27 percent as office park and flex space, which is office space usable for a variety of things.

• 23 percent as residential; the type of residential development has yet to be determined.

• 14 percent neighborhood commercial use, which could include things such as convenience stores, coffee shops and other business that serve nearby residents.

Those percentages are subject to change as planning progresses. But the overall pattern of development put forth in the Base Case Scenario is likely to remain consistent.

The Base Case Scenario also identifies a potential new border between the two cities along a planned east-west arterial road that likely will follow the footprint of S.W. 124th Avenue and extend east across Interstate 5.

One of the challenges facing Tualatin is determining the mix of residential and commercial development it desires, Wilsonville Mayor Tim Knapp said.

“... It is not as complicated for Wilsonville as it is for Tualatin,” he said. “We’re just extending incrementally and building on an industrial area where we already have basic concepts, but Tualatin is juggling commercial services and residential.”

An even bigger chore will be creating the infrastructure needed to support new development in the planning area.

One of the biggest decisions councilors face is how to divide responsibility for new sewer, water and stormwater systems. Because of geography, all stormwater generated by new development will flow south toward Wilsonville. Both cities are projected to have enough wastewater treatment capacity to take responsibility for sewer on their respective portions of Basalt Creek. Finally, both cities are expected to supply the same respective areas with water from existing supplies.

But it won’t come cheaply. Projected sewer construction costs included in the Base Case Scenario would be approximately $25.1 million for Tualatin and $18.7 million for Wilsonville. Stormwater costs would be an estimated $9.1 million for Tualatin and $4.6 million for Wilsonville, while extending each city’s respective water system into Basalt Creek would cost Wilsonville around $9.1 million and Tualatin $10.4 million.

Those costs could fluctuate significantly, Fregonese said, depending on the types of development ultimately agreed upon. And when it comes to roads, he added, it’s likely that developers will pay for non-arterial streets through systems development charges as development takes place.

From here, consultants will work with both cities for more precise development ideas. They will identify a range of development options in advance of the next joint council meeting in February. In March, a public open house will likely be held based on the results of that February meeting, while the spring and summer will be used to finalize a preferred scenario.

“We have actually a very short time frame to develop the next alternative scenarios,” Fregonese said. “We have about three weeks to do that to be able to wrap things up and get ready for the meeting in February, where you’ll have three scenarios.”

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