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 representative sites in the city (including a drive‑through restaurant site and a veterinary clinic). The scenarios range from maintaining current TSS standards while adding modest TP requirements up to citywide application of reach‑scale TMDL numbers. Staff said many new‑development sites already meet higher TSS targets because flood‑control design affords room for wet detention ponds, but TP reductions at the scale the TMDL asks for are typically much harder and more costly to achieve.

Boiled down: staff told the workshop that a mid‑range option (referred to in materials as “scenario 3”) best balances water‑quality progress, implementability and developer impacts. Scenario 3 keeps 80/40 TSS for new and redevelopment in some areas but raises the TSS expectation in the Sawyer Creek reach and asks for a modest TP requirement (staff noted TP removal of roughly the mid‑30s to mid‑50s percent range in many practicable designs). "There will be target reductions or target levels to meet that will be in our permit," Boehm said. "We're not going to be required to meet those numbers tomorrow or 5 years or 10 years or maybe even 50 years."

Council members and attendees pressed on enforcement, monitoring and cost. Several asked how numeric targets are measured; staff and the consultant said compliance is modeled at site plan stage (using recognized stormwater models) and that routine field monitoring of every site is not feasible because continuous sampling is costly. The consultant added that DNR and USGS sampling programs and model calibration underpin the removal credits the state uses, but that a development’s modeled performance depends on correct input and sufficient as‑built documentation. "Those models were built based on numbers and numbers and numbers of samples," Boehm said.

On enforcement and consequences, workshop participants asked whether the DNR would fine or otherwise penalize a municipality that fails to make progress. Staff responded that DNR has enforcement tools — administrative orders, fines and other mechanisms — though the city’s stormwater permit historically has emphasized showing progressive improvement rather than a single fixed deadline for full TMDL attainment.

Cost and feasibility came up repeatedly. Staff presented unitized cost estimates for common stormwater practices (wet detention ponds, sand or proprietary filters, permeable pavement, expanded catch basins), including capital, routine maintenance and periodic nonroutine maintenance over a long lifespan. Some high‑performance practices (and some proprietary filters and coagulant or iron‑amended media) can achieve stronger TP reductions but raise construction and recurring costs. Staff emphasized tradeoffs: some practices are well suited to new development (where land is available for wet ponds), while others are more practical for redevelopment (permeable pavement, sand filters), and no single approach fits every site.

The workshop also covered interagency coordination. Staff described existing cooperation with Winnebago County Land and Water Conservation and noted the city participates in broader strategies such as multi‑discharge variance programs and grant funding to support agricultural practices that reduce watershed loads. The DNR Urban Nonpoint Source grant that funded the citywide planning project (applied for in 2023, contract approved in 2024, as described at the meeting) supports planning rather than construction.

Next steps: staff asked the council for direction to refine ordinance language and recommended advancing the mid‑range scenario for further public and stakeholder review. Staff also agreed to test the selected scenario against major developments already under review so council members can see how current large projects would score under the proposed standards.

No formal ordinance changes or votes were taken at the workshop; the session produced direction to proceed with drafting code language, further analysis of large pending developments, and continued outreach to stakeholders and other municipal partners.

Ending note: staff emphasized communications and appeals processes will be part of the draft ordinance. The current appeals path for control‑authority decisions runs from the Department of Public Works review to the city manager and then to the common council, and staff said they will include clear administrative criteria and process steps in the proposed code language to reduce discretionary perception and to make exception processes administrable.