Oshkosh workshop considers tougher stormwater rules to meet TMDL pollutant targets

Oshkosh City staff and consultants briefed a council workshop on proposed updates to Chapter 14 of the municipal code intended to help the city meet pollution‑reduction targets in the Upper Fox‑Wolf watershed TMDL and to comply with its Municipal Separate Storm Sewer System (MS4) permit.

Consultant Chuck Boehm of Brown and Caldwell told the workshop that the city’s MS4 permit, issued through the Wisconsin DNR, requires municipalities to “show continued progress towards meeting those TMDL reductions.” He said the permit is reviewed on five‑year cycles and that the Upper Fox‑Wolf TMDL was adopted by DNR in 2020.

The discussion centered on two measured pollutants: total suspended solids (TSS, the sediment load) and total phosphorus (TP, the nutrient that drives algal blooms). Under the city’s current code, new development must achieve 80 percent TSS removal and redevelopment 40 percent; Oshkosh’s code contains no explicit TP reduction percent. The TMDL framework the city must work within includes much higher TP reduction targets (the plan the consultant showed lists an 85.6 percent TP target for some reaches).

Why it matters: higher removal targets would reduce sediment and nutrient loads draining to Lake Winnebago and connected waterways but also change site design, land reserved for stormwater features, and construction and long‑term maintenance costs for developers and for city projects.

Workshop material reviewed five draft ordinance scenarios and modelled performance on five…