Overview of Industrial Stormwater TMDL Updates
Under Wisconsin Administrative Code Chapter NR 216 and WPDES Industrial Stormwater General Permits (including Tier 1, Tier 2, and industry-specific permits), the Wisconsin Department of Natural Resources (WDNR) requires industrial permittees to complete an annual review of their receiving waterbody conditions by February 15 of each calendar year. This requirement directs facilities to evaluate whether their stormwater outfalls discharge directly to a waterbody listed on Wisconsin’s 303(d) Impaired Waters List or covered under an EPA-approved Total Maximum Daily Load (TMDL) restoration plan.
As WDNR continues to update its statewide Water Condition Lists and to establish new TMDL watershed allocations (such as in the Rock River, Milwaukee River, Upper Fox/Wolf Rivers, and Wisconsin River basins), receiving water classifications frequently change. If a facility’s receiving waterbody is newly identified as impaired or subject to an approved TMDL for a Pollutant of Concern (POC) that is discharged by the facility, mandatory updates to its Storm Water Pollution Prevention Plan (SWPPP) and ongoing sampling protocols are required.
The 2026 Water Condition List Update
WDNR released its draft 2026 Water Condition Lists for public comment from February 16 through March 18, 2026. The draft lists identify 92 new waterbodies or segments as impaired. Of the 100 new listings, 10 are being added directly to the Waters in Restoration List because they fall under an existing TMDL. Those additions affect:
- Milwaukee River Basin TMDL (4 listings)
- Upper Fox-Wolf Basins TMDL (4 listings)
- Northeast Lakeshore TMDL (1 listing)
- Rock River Basin TMDL (1 listing)
At the same time, 15 impairment listings are being removed from the list , with 8 of 15 being delisted for phosphorous.
Important to note, the 2026 Water Condition List is draft, and must be approved by the United States Environmental Protection Agency (USEPA). Until the USEPA approves the 2026 lists, the 2024 Water Condition Lists remain the current, official reference for permit compliance purposes. Facilities should continue using the 2024 lists for their annual receiving water checks until WDNR announces EPA approval of the 2026 update.
What This Means for Permittees
If a facility’s receiving waterbody is newly identified as impaired, or is added to an EPA-approved TMDL for a Pollutant of Concern tied to that site’s industrial activities, the facility may need to update its SWPPP and sampling protocols once the update becomes final. Common pollutants of concern in these basins include Total Phosphorus (TP), Total Suspended Solids (TSS), and bacteria such as E. coli. More waters are being listed as impaired due to per- and poly-fluoroalkyl substances (PFAS) in either the perfluorooctane sulfonate (PFOS) or perfluoro-n-octanoic acid (PFOA) varieties. This family of chemicals is ubiquitous, and facilities may not be aware of potential stormwater contamination due to very low levels of PFAS in raw materials, below the previous de minimis levels on Safety Data Sheets (SDSs), or due to contamination of feedwater. Facilities should be aware of the potential inclusion of PFAS and investigate stormwater discharge if discharging to a TMDL for PFAS.
Facilities with discharges to newly listed impaired waters or TMDL restoration waterbodies should be prepared for:
- Evaluation of facility outfalls against updated WDNR Water Condition Lists and receiving waterbody identification codes (WBICs).
- Updating the SWPPP as soon as practicable to identify designated Pollutants of Concern.
- Conduct routine benchmark monitoring or numeric effluent sampling as follows:).
- Tier 1 facilities: Sample for designated Pollutants of Concern (POCs) identified in the applicable TMDL Waste Load Allocation (WLA).
- Tier 2 facilities: Sample for pollutants identified in the applicable TMDL WLA only when monitoring is specifically required by the TMDL; otherwise, sampling is not required.
- Installing, upgrading, or re-evaluating site Best Management Practices (BMPs) and structural controls if stormwater sampling results exceed benchmark levels or allocated discharge limits.
- Enhanced annual reporting and documentation retention within SWPPP records to demonstrate ongoing compliance during WDNR inspections.
These requirements affect a wide range of industrial operations across Wisconsin, including heavy manufacturing, chemical production, metal fabrication, scrap recycling, salvage yards, and nonmetallic mining operations operating under WPDES industrial stormwater coverage.
For many facilities, a change in receiving water status is a significant operational shift. Baseline permit coverage typically requires quarterly visual inspections and annual site assessments. Depending on the applicable Tier 1, Tier 2, or sector-specific general permit, a new impairment or TMDL listing may also trigger additional monitoring, sampling, or reporting obligations tied to the identified pollutant of concern. Failure to conduct the annual check or update SWPPPs accordingly can expose facilities to compliance notices and enforcement under Chapter NR 216.
What Facilities Should Do
Permittees should conduct their annual water conditions evaluation using WDNR’s online Surface Water Data Viewer and the currently official Water Condition Lists (2024, pending EPA approval of the 2026 update). If an outfall matches a listed waterbody for an applicable pollutant, facilities must update their SWPPP, establish required monitoring points, and evaluate current stormwater controls. Reviewing stormwater outfalls early and watching for WDNR’s announcement of final 2026 list approval will help facilities stay compliant ahead of annual deadlines and reporting windows.
Additional Resources
If you have any questions about the annual TMDL review process or how updated impaired water lists may impact your facility’s SWPPP, please contact the Wisconsin office at 262.200.0200. Our team is available to assist you in understanding these changes and how they apply to your facility.
