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You are here: Home / Permitting / Stormwater Permits / Municipal Separate Storm Sewer System (MS4) Discharges: Am I Regulated?

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

Explains which MS4s are required to obtain permit coverage for their storm water 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.

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 areaExit the TCEQ (UA), as defined by the Bureau of the Census (Note that additional MS4s may be regulated based on 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 Texas Commission on Environmental Quality (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 Results for TexasExit the TCEQ web page and find maps to urbanized areas in a city near you.

new_tiny.gifProposed EPA Rulemaking

On December 29, 2009, the U.S. EPA proposed a new regulation to establish a program to reduce storm water discharges from new development and redevelopment and make other regulatory improvements to strengthen its storm water program. EPA sought input on the following preliminary regulatory considerations:

  1. Expand the physical area subject to federal storm water regulations.

  2. Establish specific requirements to control storm water discharges from new development and redevelopment

  3. Develop a single set of consistent storm water requirements for all MS4s (i.e., Phase I and Phase II).

  4. Require MS4s to address storm water discharges in areas of existing development through retrofitting the sewer system or drainage area with improved storm water control measures.

  5. Explore specific storm water provisions to protect sensitive areas.

TCEQ will follow the development of this rulemaking and will incorporate elements into the TPDES permitting program as required following adoption of any new rules.

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