Sustainability Board recommends updated Chapter 14 standards to address stormwater pollutants

The Oshkosh Sustainability Board voted unanimously June 2 to recommend a set of updated post-construction stormwater water-quality standards for Municipal Code Chapter 14 aimed at reducing sediment and phosphorus in local waterways.

The vote followed a consultant presentation on options tied to the Wisconsin Department of Natural Resources's total maximum daily load (TMDL) work for the Fox and Wolf watersheds and a citywide analysis of how different practices and numeric targets would affect new development and redevelopment across the city.

Board members said the recommendation seeks a balance between achievable on-site practices and the city's responsibility to make measurable progress under state watershed goals.

Consultant Chuck Behm, who led the analysis on behalf of the city, described how the TMDL sets reduction targets for total suspended solids (TSS) and total phosphorus (TP) and how technology and land availability affect those targets. "We do expect that the target reductions from this TMDL study will be rolled into that [the next municipal permit]," Behm said, referring to the city's stormwater permit. He stressed that phosphorus is harder to remove than sediment because a larger share is dissolved in runoff rather than bound to particles.

City Department of Public Works staff told the board the technical threshold that typically triggers on-site water-quality requirements is either one acre of land disturbance or 20,000 square feet of new impervious surface on a parcel. "Your typical single-family home will not be triggering those requirements," James Robbie of the Department of Public Works said; "however, if the home is being built in a subdivision that was recently platted, the subdivision does have to provide management for the subdivision."

Why it matters: the Upper Fox–Wolf TMDL (studied by DNR and completed in 2020) establishes load-reduction goals for phosphorus and sediment that the city must show progress toward in its municipal stormwater permit. Board members and staff said the city cannot immediately meet the highest modeled TP reductions with current, widely available on-site technologies, so the board focused on achievable near-term targets while preserving the Maximum Extent Practicable (MEP) review for sites that cannot meet the standards.

Key points from the discussion

- The consultant presented five scenarios that mix different percent reductions for TSS and TP for new development and redevelopment. Several participants said the highest phosphorus reductions modeled in the TMDL (above 80%) are not broadly achievable with ordinary on-site practices and would require costly, wastewater-style treatment or large on-site ponds. Behm said such measures would likely trigger many MEP exceptions.

- The board compared sample redevelopment and new-development sites under each scenario. Behm said many newer or greenfield projects already include wet detention basins and other measures that perform well for both peak-flow control and water quality; redevelopment sites often have less space for large wet basins.

- Several members argued TP should be a central focus because it drives algal growth and lake impairments. Others urged caution about creating requirements that would be impractical and could impose disproportionate costs or review burdens.

Board action and next steps

The board voted 8'2 to recommend that the city adopt the numeric reductions in Scenario 1 for Chapter 14 updates (the recommendation was recorded as a single-board position to forward to the Plan Commission and Common Council for their consideration). The board asked staff to continue refining ordinance language and cost/feasibility details before final council action and to include the recommendation in the city's code update timeline tied to grant funding that expires in 2025.

What the recommendation includes (summary)

- Apply the Scenario 1 percent-reduction targets (TSS and TP) from the study for both new development and redevelopment, with a continued MEP/engineering review process for sites that cannot meet numeric targets.

- Ask planning and engineering staff to prepare draft code language for Chapter 14 consistent with Scenario 1, and return to the Plan Commission and Common Council for hearings and adoption.

Additional context and clarifications from the meeting

- The consultant and staff emphasized that the TMDL analysis is incorporated into the city's next WPDES (municipal stormwater) permit as an expectation to make progress, not an immediate retrofit mandate for all existing facilities.

- Sawyer Creek, one of Oshkosh's watersheds, carries a higher sediment-reduction target in the TMDL; the study considered whether to apply watershed-specific requirements or a citywide standard.

- The board requested that staff collect and present cost estimates and implementation plans as part of any ordinance change so councilmembers understand tradeoffs before voting.

Supporting quote

"Phosphorus has a much higher solubility portion to it'so some of it will settle out as particulates with the sediment. A lot of it though is dissolved in that water and gets much, much more challenging to pull out," consultant Chuck Behm said during the presentation.

Ending

The board's recommendation moves the city into a formal code-update process that will proceed to the Plan Commission and then to Common Council consideration. Staff and the consultant will continue drafting ordinance language, assessing implementation costs for typical sites, and preparing materials for forthcoming public hearings.