What is NPDES?

Authorized by the Clean Water Act, the National Pollutant Discharge Elimination System (NPDES) permit program controls water pollution by regulating point sources that discharge pollutants into waters of the United States.

The NPDES Municipal Storm Water Permitting Program regulates storm water discharges from municipal separate storm sewer systems (MS4s). NPDES Municipal Permits were issued in two phases.

Phase I, which started in 1990, permit coverage for medium (serving between 100,000 and 250,000 people) and large (serving 250,000 people) municipalities.

Phase II requires General Permit coverage for the discharge of stormwater from small MS4s, including non-traditional Small MS4s such as governmental facilities like military bases, public campuses, prisons and hospitals.

The MS4 General Permit requires the discharger to develop and implement a Storm Water Management Plan/Program (SWMP) with the goal of reducing the discharge of pollutants to the maximum extent practicable.