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Municipal Separate Storm Sewer System (MS4)

Presents the definition of municipal separate storm water sewer system (MS4) as taken from federal rules.

"Municipal separate storm sewer system" is specifically defined in the federal rules (Title 40 Code of Federal Regulations Part 122.2 ), but the term is easier to understand if we break it down.

First, "separate storm sewer system" includes ditches, curbs, gutters, storm sewers, and similar means of collecting or conveying runoff that do not connect with a wastewater collection system or treatment plant.

And to be a "municipal separate storm sewer system" (MS4), the system must be owned or operated by a public agency—for example:

  • a city or town

  • a municipal utility district, flood control district, or other special district

  • a county

  • a state or federal agency

If you have any questions as to whether you own or operate an MS4, contact us.