MS4 Permit MS4 is short for:
Municipal Separate Storm Sewer System
“Municipal" refers to a unit of local government like a borough but may also refer to an organization responsible for the administration of a developed area
The number 4 refers to the four words that start with the letter “S": “Separate," “Storm," “Sewer," “System."
A separate storm sewer system is a collection of structures, including retention basins, ditches, roadside inlets and underground pipes, designed to gather storm water from built-up areas and discharge it, without treatment, into local streams and rivers. It is referred to as a separate system because it's not connected to the sanitary sewer system which drains wastewater from inside a home to a sewage treatment facility or a private septic system. Some communities in Pennsylvania do have combined storm and sanitary sewers. The areas served by these “combined systems" are not covered by the MS4 program.
