What is the MS4 Annual Report?Every year, the District submits an Annual Municipal Separate Storm Sewer System (MS4) Report to the U.S. Environmental Protection Agency (EPA), documenting the activities that fulfill the requirements of the District’s National Pollutant Discharge Elimination System (NPDES) MS4 permit. The NPDES permit program, authorized by the federal Clean Water Act and managed by the EPA, addresses water pollution by regulating point sources that discharge pollutants to waters of the United States. Activities under the permit include, for example, implementation of stormwater management practices and water quality monitoring. This story map summarizes these activities and is a regulatory requirement under the permit.What is the MS4? MS4 is an acronym that stands for Municipal Separate Storm Sewer System. The MS4 collects and conveys stormwater from streets, sidewalks, and rooftops to nearby waterways through stormwater sewers and outfalls. In the District of Columbia, the MS4 area is located along the outer edges of the city and surrounds the combined sewer system (CSS) area that serves the inner portions of the city. The MS4 area is different from the CSS area in that it does not convey sanitary sewage. Stormwater from the CSS area is either conveyed to the Blue Plains Wastewater Treatment Plant or discharged at combined sewer outfalls. DC Water’s Clean Rivers Program is dedicated to reducing combined sewer overflows into the District’s waterways.Several areas in the District are not part of either the MS4 or CSS. Most District parkland falls within this “Direct Drainage” category, and stormwater from these areas naturally drain to nearby waterways following the local topography. Learn more about why the MS4 is important to the District's waterways in this Story Map collection.