Municipal storm drain systems are referred to by the permit as, municipal separate storm sewer systems (MS4s) ultimately drain to local rivers and streams without treatment.  The EPA’s Storm Water Phase II Rule establishes an MS4 storm water management regulation that is intended to improve the Nation’s waterways by reducing pollutants that reach storm drain systems during storm and other runoff caused events.  Common pollutants automotive pollutants including oil and grease, salts and deicing materials associated with transportation.  Pesticides, fertilizers and organic debris from private and commercial landscape maintenance.  Sediment and various construction related pollutants from construction sites projects.  Also carelessly discarded trash and poor trash receptacle management, mostly paper and plastic.  When these pollutants are collected by the miles of roadway gutter and acres urban surfaces, the pollution volumes are significant and impair the waterways, affecting the beneficial use of the water body, contaminating water supplies, and damaging habitat for aquatic organisms, and land wildlife. 

In 1990, EPA promulgated rules establishing Phase I of the National Pollutant Discharge Elimination System (NPDES) storm water regulation.   The Phase I regulation for MS4s requires operators of “medium” and “large” MS4s, that is, those that generally serve populations of 100,000 or greater, implement a storm water management program as a means to control polluted runoff from these MS4s.  The Storm Water Phase II Rule extends requirement of the NPDES storm water program to other population size qualifying “small” MS4s.

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