What is an MS4?
MS4 stands for “Municipal Separate Storm Sewer System.” It is a municipality’s system of stormwater conveyances, including all roads, catch basins, gutters, man made channels, leaching basins, ditches, outfall structures and storm drains. They are separate from traditional wastewater sewers in that they only convey and do not treat stormwater. Municipalities covered under Phase II are sometimes referred to as MS4s.
