Delaware County approves design contract for Lower Big Walnut 48-inch tunnel

Delaware County commissioners voted unanimously to approve a professional services agreement with Black & Veatch Corporation to design Phase 1 of the Lower Big Walnut trunk sewer, a 48-inch tunnel intended to connect into a City of Columbus tunnel near Harlem and Smothers Road.

Tiffany Mag, director of environmental services, told commissioners the contract covers an alignment and design study that will run through 2025, with design work slated for 2026 and construction expected in 2027. “This is the contract for design services that would build our 48 inch diameter tunnel, and that's gonna connect into the city of Columbus' 702 inch diameter tunnel that they are constructing up to the corner of Harlem and Smothers Road,” Mag said. She said microtunneling is the likely construction method because of the size, depth and groundwater conditions, though open-cut alternatives will be evaluated.

Mag said the county is coordinating with township trustees on the alignment and noted the schedule anticipates finishing shortly after Columbus completes its tunnel. She told commissioners the county expects some delay in the city's schedule that could align the projects: “I think I heard of roughly a 6 month hold up, which is actually gonna work out perfectly for us.”

The resolution (25-350) passed with Commissioners Barb Lewis, Gary Merrill and Jeff Benton voting aye. Mag said the design will make the connection to developable acreage and that the ultimate extent of the county’s tunneling beyond the phase will depend on township land-use decisions and future development demands.

Commissioners and staff said they will continue stakeholder meetings with township trustees and landowners as the alignment study proceeds.

The vote advances a project the county expects to carry design into 2026 and construction into 2027, timed to link with Columbus’ regional sewer work.