The National Pollutant Discharge Elimination System (NPDES) Stormwater Program regulates stormwater discharges from three potential sources: municipal separate storm sewer systems (MS4s), construction activities, and industrial activities. Most stormwater discharges are considered point sources, and operators of these sources may be required to receive an NPDES permit before they can discharge. This permitting mechanism is designed to prevent stormwater runoff from washing harmful pollutants into local surface waters such as streams, rivers, lakes or coastal waters. The NPDES Stormwater Program covers the following types of stormwater discharges:
- MS4s – Operators of large, medium and regulated small MS4s may be required to obtain authorization to discharge stormwater.
- Construction Activities – Operators of construction sites that are one acre or larger (including smaller sites that are part of a larger common plan of development) may be required to obtain authorization to discharge stormwater under an NPDES construction stormwater permit. Where EPA is the permitting authority, operators must meet the requirements of EPA’s Construction General Permit (CGP).
- Industrial Activities – Industrial sectors may require authorization under an NPDES industrial stormwater permit for stormwater discharges. Where EPA is the permitting authority, operators must meet the requirements of EPA’s Multi-Sector General Permit (MSGP).