NPDES MS4 General Permit
What is an MS4?
MS4 is short for, "Municipal 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 stormwater from built-up areas and discharge it, without treatment, into local streams and rivers. It's called a separate system because it's not connected to the sanitary sewer system which drains waste water from inside a home to a sewage treatment facility or private septic system.
The authorization that MS4 communities get fro m the DEP to legally discharge stormwater into local streams and rivers is called a "NPDES" permit which stands for National Pollution Discharge Elimination System. The NPDES Permit program addresses water pollution by regulating point sources that discharge pollutants to waters of the United States. Created in 1972 by the Clean Water Act, the NPDES Permit program is authorized to state governments by EPA to perform many permitting, administrative, and enforcement aspects of the program.
The NPDES Permit regulations require municipalities with MS4s in urbanized areas to develop and implement a stormwater management program which addresses six minimum control measures. 1. Public Education and Outreach 2. Public Involvement and Participation 3. Illicit Discharge Detection and Elimination 4. Management of Construction Site Runoff 5. Management of Post Construction Site Runoff 6. Good Housekeeping in Municipal Operations