Sioux City, IA Environmental Rules: Stormwater Management (2026)

Sioux City sits at the confluence of the Missouri and Big Sioux rivers and discharges urban runoff into receiving waters that the Iowa DNR regulates for pollutants under the federal Clean Water Act. The city is on the published Iowa DNR list of regulated MS4s, which obligates Sioux City to develop and enforce a stormwater management program addressing the six minimum control measures required by 40 CFR 122.34: public education and outreach, public involvement/participation, illicit discharge detection and elimination, construction site stormwater runoff control, post-construction stormwater management for new development and redevelopment, and pollution prevention/good housekeeping for municipal operations. The state authority sits in Iowa Code section 455B.197, which empowers the Iowa DNR to issue NPDES permits including stormwater permits authorized under section 455B.103A. The rules implementing that authority are in IAC 567 chapter 60 (Title IV Wastewater Treatment and Disposal). For construction activity, IAC 567-60.11 incorporates the federal stormwater rules and requires NPDES coverage for any disturbance of one or more acres - in practice Iowa DNR General Permit No. 2 (Storm Water Discharge Associated with Industrial Activity for Construction). Sioux City's Environmental Services Division conducts on-site inspections of every General Permit No. 2 site within city limits as required by the city's MS4 permit. Local implementation appears across multiple titles of the Sioux City Municipal Code: Title 20 chapter 20.30 (Grading Ordinance) controls earth disturbance and erosion, and Title 25 (Zoning) addresses post-construction runoff treatment in new development. Illicit-discharge prohibitions (pool water with chlorine, used motor oil, paint, soapy wash water, sediment-laden runoff) flow from the MS4 permit and IAC 567-60.11.