In late 2025, something happened in Minnesota that has never happened before – some cities and townships were released from the MS4 permitting program because of a change in their Census status.

The MS4 program here is regulated by the Minnesota Pollution Control Agency (MPCA). The determination MS4 permitting status governed by Minn. Rule 7090.1010.Subp.1.A. This state rule incorporates, by reference, Code of Federal Regulations. Title 40.Section 122.32., which reads (in part): § 122.32 As an operator of a small MS4, am I regulated under the NPDES storm water program?

(1) Your small MS4 is located in an urban area with a population of 50,000 or more people as determined by the latest Decennial Census by the Bureau of the Census. (If your small MS4 is not located entirely within an urban area with a population of 50,000 or more people, only the portion that is within this urban area is regulated)

Census status has been the determining factor for most cities in the U.S. that are permitted MS4s. There are, though, other factors in Minnesota that can be used to determine that an entity should be regulated.

In the 1999 Federal Rule that created the MS4 Phase II program, EPA included this language in the Rule preamble: "a small MS4 that is automatically designated into the NPDES program for storm water under an urbanized area calculation for any given Census year will remain regulated regardless of the results of subsequent urbanized area calculations.’’

Based on the 2020 Census, the MPCA determined that 11 MS4 permittees (cities and townships) had fallen outside of any urban area with a population of 50,000 or more people and did not fall under any of the other state factors that would cause them to require MS4 permits. The MPCA notified these entities that they could complete a petition form provided by the MPCA to seek to become unregulated.

This petition process was completed and the permittees were released from the permitting program in early 2026.

This action by the MPCA is unprecedented and in direct contradiction of the EPA guidance in the Federal Rule preamble. This presentation will provide the details and significance of all this, by a staff person for a coalition of MS4-permitted cities in Minnesota, the Minnesota Cities Stormwater Coalition. This experience may be relevant for a number of MS4-permitted cities throughout the United States and replicable in other states.

Workshop Host: Minnesota Cities Stormwater Coalition