When Batavia finishes constructing a new headquarters building for its sewage-treatment plant, the Fox River Trail will again curve in front of it.

But the "trail" will be on the Flinn Street pavement, with bicyclists and runners sharing the space with cars. And while that option is the easiest and least expensive option, aldermen dream of a prettier idea: Build a concrete retaining wall for the west bank of the river and put the path on top of it.

That, however, would likely cost $4 million to $5 million, according to an engineering consultant's report. And that is if the Illinois Department of Natural Resources and the Army Corps of Engineers would approve the idea.

"When you start to do the engineering, the slope, stabilization, regulatory issues, future construction, it gets a lot more complicated than maybe you might realize," public works director Gary Holm told aldermen at a committee meeting Tuesday.

The regional trail goes around the west side of the treatment plant. It used to then curve through the front yard, back to the riverside. The new building is taking that space, and Flinn Street is being rebuilt. Riders and runners this summer were detoured on to Union Street, to Water Street to First Street.

Members of the Batavia Bicycle Commission worry about the safety of bicyclists and pedestrians sharing Flinn with vehicles visiting the treatment plant, nearby businesses and the Batavia Interfaith Food Pantry. They prefer the riverside idea.

Three commission and city workers also looked at building a bridge from the trail on the south side of the plant to Clark Island Park on the east bank of the river. Bicyclists could then continue on the east side of the river, or they could use two bridges to islands to return to the west side, north of the plant. They recommended against that option, because it is convoluted and because the bridges would be closed when the river floods.

The potential riverside path would be combined with shoreline stabilization and erosion repair recommended by engineers several years ago. The city has not done any of the recommended work.

Alderman Scott Salvati exhorted councilmates to think big. The city needs to develop a master plan, he said, for what it wants the riverfront to look like through town. "This is a jewel that we have running through our town, it absolutely is," he said.

Alderman Mark Uher agreed about having an overall plan, including how to pay for the work, and said he would not want anything done "piecemeal."

Alderman Dave Brown suggested establishing a community commission to work on the idea, including cost and whether residents would be willing to pay for improvements.

Holm said the pathwork near the treatment plant may be eligible for some state funding. Aldermen gave him and city engineer Rahat Bari permission to pursue that funding, and to start talking to regulatory agencies about the idea.

Work on the first phase of the plant expansion began in May. Overall, the project, estimated at $60 million, will expand its capacity, replace equipment, and install equipment to reduce phosphorus discharged in to the river.