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Oklahoma City webinar: how industrial stormwater permits must address TMDLs under the OKR5
Summary
In a City of Oklahoma City webinar, Nathan Collier of WSP explained how Oklahoma's OKR5 multisector general permit treats impaired waters and TMDLs, highlighting stricter requirements for new dischargers, annual monitoring expectations, the one-mile applicability rule, and the need to document SWIP controls.
Nathan Collier, assistant vice president of environmental science at WSP, told a City of Oklahoma City webinar audience that total maximum daily loads, or TMDLs, are the regulatory calculation that sets the maximum pollutant load a water body can receive and still meet water quality standards. "TMDLs are a regulatory calculation that in plain language is essentially the maximum amount of pollutant that a water body can receive and still meet the water quality standards that apply to it," he said.
Collier framed the guidance around Oklahoma's OKR5 multisector general permit (MSGP), administered by the Oklahoma Department of Environmental Quality (DEEQ). He said the permit follows familiar NPDES principles: facilities typically must file a notice of intent, develop and maintain a storm water pollution prevention plan (SWIP), implement best management practices (BMPs), perform inspections and complete monitoring. Collier highlighted that OKR5 part 1.9.6 places stricter obligations on new sources: exposure of the pollutant of impairment must be prevented or the applicant must document technical evidence the pollutant is not present on site.
Why this matters: a TMDL or watershed plan that predates an NOI can impose a waste-load allocation that a permitted discharge must meet. Collier noted a facility is treated as discharging to an impaired water if it lies within one mile of a listed receiving water (or if the facility's discharge reaches an impaired water through an MS4 and the MS4 outfall to that impaired water is within one mile). He urged facilities to check the DEEQ TMDL reports by basin and to confirm whether a pollutant-specific TMDL or surrogate indicator applies.
Collier described monitoring expectations in OKR5 (part 4.2.3) for impaired waters: annual monitoring of the pollutant of concern or an agreed surrogate/indicator is typical (for example, E. coli as a bacterial indicator or TSS for turbidity), but monitoring may not be required where impairments are based on fish bioassessments or hydrology rather than a measurable pollutant. He recommended early consultation with DEEQ for surrogate selection and warned that persistent issues detected in monitoring can trigger escalated enforcement or a requirement to obtain an individual permit.
On procedural timing, Collier said he did not have a single regulatory deadline to cite during the session and recommended checking the OKR5 permit language for any SWIP update timeframes; if multiple timeframes apply, he advised using the strictest applicable schedule. He also pointed attendees to DEEQ's 2024 integrated report, approved May 27, 2026, as a resource for identifying newly listed impairments.
The session closed with a short Q&A and reminders that recordings and materials will be posted on the City of Oklahoma City's website and YouTube channel.
