A Municipal Separate Storm Sewer System (MS4) is a network of drainage systems, including pipes, ditches, and other conveyances, designed to carry stormwater runoff directly to nearby streams, rivers, and other bodies of water. MS4s are distinct from sanitary sewers, which carry sewage and industrial wastewater to treatment facilities. The MS4 program is a regulatory framework established by EPA, under the authority of the Clean Water Act National Pollutant Discharge Elimination System (NPDES), to treat these stormwater conveyance systems as a point source discharge. DEQ has been delegated as a permitting authority by EPA to implement the NPDES program in Virginia as the Virginia Pollutant Discharge Elimination System  permit program. MS4 discharges are regulated under the Virginia Stormwater Management Act, and the Virginia Stormwater Management Program (VSMP) Permit Regulation. The MS4 permit program is designed to address the unique challenges associated with urban and suburban areas, where stormwater can pick up pollutants from various sources and ultimately discharge into local water bodies.  

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