Portage City, Strand Associates update wastewater plant redesign and raise cost estimate to about $55 million

Portage City officials and engineers from Strand Associates presented a final design update for the city's wastewater treatment plant and an updated project cost estimate on a facilities-plan item, saying the work is intended to meet upcoming Wisconsin DNR permit limits and to replace aging 1980s equipment. The firm and city staff said ground improvements and rising trade costs raised the planning estimate to about $55 million and that construction would likely finish in mid to late 2028.

The design replaces the plant's rotating biological contactors (RBCs) with two large oxidation ditches (with space for a future third), installs larger, deeper final clarifiers, adds a new return activated sludge (RAS) pumping building and a new electrical room, and upgrades the biosolids process with drying equipment and a dried-biosolids silo. Strand described reusing existing anaerobic digesters for a waste-activated-sludge (WASS) step, then drying cake from the belt press to roughly 90% solids to produce dried (Class A) biosolids for off-site disposal or beneficial reuse.

City staff emphasized the project responds to looming WPDES phosphorus limits in the DNR permit, aging infrastructure, and projected growth over a 20-year planning horizon. Strand representatives said the oxidation ditches provide larger process volume and operational reliability compared with the existing RBCs, and that the new…