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Engineering briefing: McMahon tells Harrison board TMDLs will require enhanced treatment and long-term CIP
Summary
McMahon engineer Phil Clayman told the board that state DNR TMDL targets for Garner's Creek and Lake Winnebago require phosphorus reductions beyond what typical wet ponds achieve and suggested enhanced settling systems (chemical treatment) and long-term capital investment shared across jurisdictions; a draft ordinance and CIP were presented.
Phil Clayman of McMahon told the Village of Harrison board that the municipal stormwater permit and recent TMDL (total maximum daily load) requirements will force stricter phosphorus and sediment reductions than the village currently achieves. “Garner's Creek carries a 69% phosphorus and a 60% sediment [reduction requirement],” he said, adding that Lake Winnebago’s phosphorus target can be as high as 83%.
Clayman explained typical wet-detention ponds commonly used in the Fox Valley generally achieve about 80% sediment reduction but only about 60% phosphorus removal — short of the TMDL targets for some subwatersheds. “To meet these strict phosphorus requirements...we are going to chemically treat stormwater now,” he said, presenting an enhanced settling system that literature suggests could remove 90–95% of phosphorus in pilot reports.
He outlined a village-wide plan of action and preliminary cost estimates: converting or retrofitting regional ponds in Garner's Creek was estimated at roughly $3.2 million in 2018 dollars, with cost-sharing among the Garner's Creek cooperative members (village plus neighboring communities). Lake Winnebago subwatershed obligations would fall primarily on the village’s own utility.
Clayman recommended updating village ordinances to require a reasonable phosphorus reduction requirement for new development (he suggested a 60% phosphorus standard to balance feasibility and growth) and discussed design implications such as reserving small building footprints at pond sites for future chemical-feed equipment.
Why it matters: The DNR/EPA-backed TMDL requirements are now written into the municipal permit; meeting them will require a mix of regulatory updates, capital projects, and possibly developer contributions. Board questions focused on model baselines, enforcement scope, and shared costs with neighboring communities.
Next steps: Staff and McMahon presented a draft ordinance and capital improvement plan to be reviewed by the board and referred to Ehlers for financing analysis.
Quotes drawn from the hearing are on the record and used with attributions to Phil Clayman.
