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Municipal Separate Storm Sewer System (MS4) Discharges: Am I Regulated?

Explains which MS4s are required to obtain permit coverage for their stormwater discharges.

Municipal Separate Storm Sewer System (MS4) permit requirements were implemented in two phases: Phase I for large and medium MS4s and Phase II for regulated small MS4s.

• Click here for information from EPA about stormwater discharges from municipal sources

Phase I MS4 Requirements

If you operate an MS4 which serves or is located in an incorporated place or county with a population of 100,000 or greater (based on the 1990 U.S. Census), then you operate a regulated Phase I MS4 and you must apply for an individual permit*.

*Please note that all Phase I MS4s are already permitted and there are no new Phase I designations.

Phase II MS4 Requirements

If you operate a small MS4:

  • located in an urbanized area (UA), as defined by the Bureau of the Census (note that MS4s may be regulated based on the 2000 or the 2010 Census UAs), or

  • located outside of a UA and are brought into the program on a case-by-case basis (i.e., “designated”) by the TCEQ,

then you operate a regulated small MS4 and must obtain authorization or apply for a waiver.

To determine if you are located in a UA, you can visit the Environmental Protection Agency's (EPA's) Urbanized Area Map Web page and find maps of urbanized areas in a city near you.

Contact us if you have any questions about this general permit.