Oshkosh Sustainability Board backs updating Chapter 14 stormwater code; recommends scenario 1

The Oshkosh Sustainability Board voted unanimously on June 2 to recommend the city pursue the Chapter 14 post‑construction stormwater management update labeled “scenario 1” after hearing technical briefings from City of Oshkosh staff and consultants on TMDL targets, treatment feasibility and site‑specific tradeoffs.

James Robbie of the City of Oshkosh Department of Public Works told the board the code applies at thresholds of “either an acre of disturbance or 20,000 square feet of impervious surface on a parcel,” and typically new development is held to a higher water‑quality reduction requirement than redevelopment. “Your typical single family residential home will not be triggering those requirements,” Robbie said, but larger subdivisions or developments do.

Consultant Chuck Behm summarized the watershed targets coming from Wisconsin Department of Natural Resources (DNR) TMDL studies for the Upper Fox and Wolf watershed. He said the TMDL establishes substantial phosphorus goals — roughly an 85.5% reduction target in the study — that will be difficult to attain with common on‑site practices, and therefore the city must balance ambition with technologies that developers can practically implement. “Phosphorus has a much higher solubility portion to it … it gets much, much more challenging to pull out,” Behm said.

The staff presented five regulatory scenarios combining different total suspended solids (TSS) and total phosphorus (TP) requirements for new development and redevelopment. Existing city code requires 80% TSS reduction for new development and 40% for redevelopment; the scenarios adjusted those TSS percentages and added TP targets in varying combinations and, in some scenarios, a higher TSS requirement inside the more impaired Sawyer Creek watershed.

Staff tested the scenarios against a set of recent new‑development and redevelopment sites. For redevelopment, several scenarios would be challenging; for new development, wet‑detention basins often met higher removal targets because the basin design used for peak‑flow control produces additional water‑quality volume. Staff said some on‑site changes and proprietary filters can increase phosphorus removal but at significant cost, and maximum‑extent‑practicable (MEP) evaluations would be needed in borderline cases.

After discussion the board debated options, focused on TP because of its regulatory weight in the TMDL, and voted to recommend scenario 1. The motion passed 8–0 (Margie Davie, Lisa Moore, Jacob Claymeier, Alyssa Reinke, Vic Oliver, Jaden Zern, Paul Trader and Brad Spannbauer voted yes). The recommendation asks staff to draft code language consistent with scenario 1 for Plan Commission consideration; staff said they will bring revised ordinance language to Plan Commission and onward to Common Council as part of the city’s grant‑funded update process with an aim to complete the project by the end of 2025.

Board members noted tradeoffs: higher TP requirements reduce long‑term pollutant loads but can raise construction and land‑use costs, especially for redevelopment in built‑out areas where space for wet ponds is limited. Several board members recommended prioritizing practical, technology‑available targets that reduce phosphorus while limiting MEP appeals by applicants. Staff cautioned that the city’s next WPDES/MS4 permit will incorporate TMDL targets and that the city is expected to make progress toward TMDL goals over future permit cycles rather than meet the study’s full numeric reductions immediately.

The board’s vote is advisory; the Plan Commission will consider the ordinance amendment on its next agenda and will forward a recommendation to Common Council, which must adopt any changes to the city code.

Sources and attribution: summary and quotations from James Robbie (City of Oshkosh Department of Public Works), consultant Chuck Behm, and recorded board discussion at the June 2, 2025 Sustainability Board meeting.