City commissioners are set to take their biggest step yet in building a new $76 million sewer plant along the Wakarusa River that could open up vast new areas for development.

Commissioners at their Tuesday meeting will be asked to approve a recommendation to begin negotiating with the engineering firm of Black & Veatch to select a site for the plant.

The project is expected to be among the larger and more pressing issues the city commission will undertake in the near future.

“Basically, without it, we won’t be able to grow much more,” City Commissioner David Schauner said.

The plant is the key piece of infrastructure that would allow the city limits to jump south of the Wakarusa River for the first time. It could also play a major role in serving new development in the city’s southeast.

The plant would be built somewhere along the Wakarusa River and is scheduled to be completed by 2011. That is when consultants have said the city’s current sewer plant won’t be able to meet the city’s projected growth needs.

Determining exactly where the plant should be located is what Black & Veatch engineers will study. Debbie Van Saun, assistant city manager, said city staff members were recommending Black & Veatch over three other companies because of the engineering firm’s extensive knowledge of the city’s sewer and water systems.

Van Saun said that should allow Black & Veatch – which has designed much of the city’s existing sewer system – to hit the ground running. She said completing the wastewater plant on time was critical.

“If you don’t stay on schedule with projects like this, you end up with people not getting the service they expect, and that is exactly what we don’t want to have happen,” Van Saun said.

Van Saun said Black & Veatch would look for sites where the Wakarusa River runs relatively close to the city. She said sites north and south of the river could be examined.

She also said the city study would determine how big a site the city needs for the new sewer plant. The city’s existing plant, which will remain in operation, occupies 117 acres.

The proposed plant is expected to be about half the size of the existing plant. Studies have shown the plant is needed to allow the city to reach its projected population growth of about 150,000 people by 2025.

The plant has an estimated cost of $76 million. Beginning in January, sewer bills rose by about 15 percent, on average, to help begin paying for the new plant.

City staff members interviewed three other firms to serve as site selection consultants. They were Burns & McDonnell/PEC; Carollo Engineers; and Camp, Dresser & McKee/BG Consultants.

A final fee for the site selection company has not been determined, but will be negotiated by staff members and brought back to commissioners for final approval.

Commissioners meet at 6:35 p.m. on Tuesday at City Hall, Sixth and Massachusetts streets.