Municipal Storm Sewer Systems (MS4s)
Municipal Separate Storm Sewer Stormwater (MS4)

Stormwaters, such as rain and snow melt, which run over impervious surfaces in urbanized areas – roadways, sidewalks, parking lots, roof tops, etc. – are often unintentionally, or unknowingly, mixed with potential sources of pollutants. Waters travel quickly over these impervious areas and can carry large quantities of materials.