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
Phase II MS4 Requirements

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.