What exactly is a Municipal Separate Storm Sewer System (MS4)?
An MS4 includes the conveyance or system of conveyances designed or used for collecting or conveying storm water that is not a combined sewer or part of a publicly owned treatment works. It includes roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, or storm drains. These drainage systems typically dump their water (and any associated pollutants) directly into streams, bays, and/or the ocean.
