In place of sparsely populated farmland, imagine 20,000 Lawrence residents living south of the Wakarusa River.

That scenario will become reality by 2025, officials said, part of a boom that will raise the city’s population to 150,000. And a consultant is recommending that the city and county build a new wastewater treatment plant on the Wakarusa River to accommodate the growth.

Doing so would save the city and county as much as $9 million compared to expanding service from the city’s treatment plant on the Kansas River, the consultant said Wednesday. A new plant also would ease burdens on the existing plant.

City and county officials indicated they probably would follow the recommendation, but they’ll have to wade through five years of cultural- and environmental-impact studies so the plant could be built by 2011 — the same time an as-yet-incomplete expansion of the Kansas River plant reaches capacity.

“Some pretty hard decisions need to be made rather quickly,” Douglas County Commission Chairman Bob Johnson said.

Matthew Schultze, an engineer with Black & Veatch, said a Wakarusa River location for a wastewater treatment plant only recently had become a good possibility because of regulations from Kansas Department of Health and Environment.

“In the past, the Wakarusa wasn’t a good option because KDHE had a pretty high bar for treatment options along the river,” he said. “What has happened is that KDHE has raised the bar just as high for treatment options on the Kansas River.”

The Kansas River plant can treat 9 million gallons of waste per day and usually does, Utilities Director Roger Coffey said. The expansion, to be completed this summer, will raise that to 12.5 million.

Pipes and pumps

There are 1,567 people living south of the Wakarusa in Lawrence’s urban growth area, none with access to Lawrence sewer services. Officials expect that population to grow to 20,000 by 2025.

That population could be served by further expanding the Kansas River plant, Schultze said. But that option would cost $57 million, including the expense of building pipes and pump stations to carry waste from the southern part of town to the northeast part of town. And when 2025 arrives, Schultze said, there will be no room for further expansion at the site.

“You can’t just keep going there,” Schultze said of the Kansas River plant.

He presented two options for a new wastewater treatment plant south of the Wakarusa River: one directly south of Lawrence and the other to the southeast. The south option would cost $52 million; the southeast option would cost $48 million. A Wakarusa plant would be cheaper to operate because it would be run by remote control, Schultze said, and construction costs are lower because there’s no need to build pipes across town.

And constructing a Wakarusa River plant would be cheaper, Schultze said, because gravity would carry the flow to the plant — no need for expensive pump stations.

“That’s huge,” Johnson said.

Whether the Kansas River plant expands or a new Wakarusa River plant is built, the city would end up with the ability to treat 19 million gallons of waste per day.

Wetlands impact?

Commissioners said Schultze made a strong case.

“I haven’t heard anything that says we should expand on the Kansas River,” City Commissioner David Dunfield said.

There are concerns. Joyce Wolf, president of the Indian Hills Neighborhood Assn. in south Lawrence, said a Wakarusa plant “makes sense from a growth standpoint.”

But Wolf didn’t like the southeast option. She said it was too close to the Baker Wetlands.

“If you’re going to be dumping effluent, whether it’s clean or not, you don’t want effluent going into the wetlands,” Wolf said.

Officials said the city and county commissions would consider the matter further in upcoming meetings.