City updates design and $36.75M estimate for wastewater plant primary treatment and UV upgrade

City staff and the design-build team told the commission the wastewater treatment plant primary-treatment and ultraviolet (UV) upgrade project is over 90% through design and moving toward trade-package bidding.

Art Krieger, the city's director of municipal utilities, said the project replaces obsolete primary settling tanks and screening and improves grit removal, pumping and UV disinfection. The upgrades respond to hydraulic and treatment requirements in the facility’s administrative consent order, staff said; they are intended to improve reliability and treatment efficiency, not to expand the plant’s permitted capacity.

Doug Urquhart, the owner’s representative from the design-build team, updated the commission on scope and schedule. The 90% cost estimate is $36,748,000 (the estimate includes a 2% contingency; the EGLE State Revolving Fund program allows up to 6% contingency). The progressive design-build process will bid subcontract trade packages in April, assemble a guaranteed maximum price (GMP), and a tentative award resolution is tentatively scheduled for the May 19 commission meeting. Loan closing under EGLE’s SRF program is expected in the third quarter of 2025 (July 2025), with construction commencing in fall 2025 and continuing through 2028.

Commissioners asked whether the project increases treatment capacity; staff replied it does not. Staff provided operational figures: typical dry-season flow is about 4 million gallons per day (mgd), typical sanitary peak flows about 8 mgd, and storm events have produced short-duration peaks above 17 mgd. The upgrade focuses on the front-end processes (headworks, grit removal, primary treatment) and UV disinfection to meet permit/Agr administrative requirements and improve reliability.

Financing: staff said the city’s financial advisors modeled a 20-year amortization for a roughly $41 million bond ceiling previously authorized; a 20-year SRF-type loan at current assumptions would produce annual debt service in the ballpark of $2.65 million after initial interest-only draw periods. Staff noted SRF financing permits drawing funds as construction progresses, reducing immediate interest costs compared with a full bond draw.

Separately, commissioners and staff noted ongoing work to reduce infiltration and inflow (I&I) in city sewers; a lining project budget of up to $1.2 million for prioritized pipe lining on the west trunk line was scheduled to come before the commission at a future meeting.

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