What is an MS4?

Deputy Project Manager Ryan Lefler describes municipal separate storm sewer systems, also known as MS4, in about 120 seconds.

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Hello, my name is Ryan and today I'm going to discuss “what is an MS4?” MS4 stands for municipal separate storm sewer system. An MS4 conveys or moves stormwater through pipes, channels, and culverts; and is owned by a city or county, designed to collect and convey stormwater runoff, and is not part of a sewage treatment plant. Stormwater runoff contains a mixture of pollutants from both human and natural activities. These pollutants are commonly transported through pipes, culverts, and channels, and are often discharged untreated into local rivers, streams, and lakes. Under the Clean Water Act, the Environmental Protection Agency created the first National Pollution Discharge Elimination System regulation in 1973. This regulation led to the development of permits and MS4 programs, which are mandated under the federal Clean Water Act, and authorize public entities to discharge stormwater collected by storm sewer systems into waters of the United States. The permits are intended to prevent harmful pollutants from being washed into the MS4s and require cities and counties to develop stormwater management programs. A stormwater management program describes the stormwater control practices that will be implemented and are consistent with permit requirements to minimize the discharge of pollutants. Every community stormwater management program is unique, but they're all based on the same six requirements. Each state develops its own program to adhere to these regulations, which are enforced nationally, and you can find a copy of your local stormwater management program on your city or county's website. There are over 7,000 MS4s permitted throughout the U.S., and this number is growing annually with the intent of increasing the awareness of stormwater effects, promoting best practices, and investing in the community. Thank you.