Municipal Separate Storm Sewer Systems (MS4)

Stormwater that lands on impervious surfaces are conveyed through a system of manmade inlets, pipes, and structures designed to drain off surfaces quickly to reduce the potential of flooding. This system of structures that conveys this stormwater is referred to as a “MS4.”

MS4 is short for Municipal Separate Storm Sewer System. This system is identified as “separate” because the system conveying stormwater is separate from the system conveying wastewater referred to as the “sanitary sewer system.” The sanitary sewer leads to a wastewater treatment plant where the water is treated while stormwater is discharged to natural waterbodies or stormwater ponds untreated.

Some large cities throughout the country have “combined sewer systems” where both the wastewater and stormwater are conveyed to a wastewater treatment plant. In the State of Florida, these systems are always separate making it vital that we keep watch of what goes into or could go into the MS4

 Structures that are part of the MS4 include:

  • Catch Basins
  • Ditches
  • Inlets
  • Outfalls
  • Underground pipes
  • Stormwater ponds
  • Roadside Curbs
  • Exfiltration trenches
  • Baffle boxes
  • Culverts
Wet stormwater drain