ational ollutant ischarge limination ystem

A federal permit authorized by the Clean Water Act which is required for discharge of pollutants to navigable waters of the United States which includes any discharge to surface waters - lakes, streams, rivers, bays, the ocean, wetlands, and storm sewer tributary to any surface water body.

National Pollution Discharge Elimination System

a provision of the Clean Water Act which prohibits discharge of pollutants into waters of the United States unless a special permit is issued by EPA, a State, or (where delegated) a tribal government on an Indian reservation.