Municipal Separate Storm Sewer System 

What is MS4?


M = Municipal

S4 = Separate Storm Sewer System


An MS4 is a surface water drainage system or system of drainage conveyances (ditches, pipes, culverts, etc.) that is:


  •  owned by a state, city, town, village, or other public entity that discharges to waters of the U.S.,

  • designed or used to collect or convey stormwater (e.g., storm drains, pipes, ditches),

  • not a combined sewer, and

  • not part of a sewage treatment plant, or publicly owned treatment works (POTW). 


To prevent harmful pollutants from being washed or dumped into specific types of MS4s, operators might be required to obtain NPDES permits and develop stormwater management programs (SWMPs).



In September of 2012, the Town of Raymond was notified by the U.S. Environmnental Protection Agency that it was "considered a regulated small Municipal Separate Storm Sewer System (MS4) in accordance with 40 CFR § 122.32(a)(l). Being a regulated small MS4 makes your municipality subject to the permitting requirements of Phase II storm water program which was promulgated in 1999." 


Click Here to Read Official Notice