NPDES MS4 Permits

Maryland’s NPDES Municipal Separate Storm Sewer System (MS4) Permits

The Environmental Protection Agency’s (EPA) National Pollutant Discharge Elimination System (NPDES) stormwater regulations were published in 1990. Phase I of these regulations require large urban jurisdictions to control pollution in stormwater to the maximum extent practicable (MEP). For permitting purposes,municipalities with populations of greater than 250,000 are considered “large” and those with populations of between 100,000 and 250,000 as “medium.” Municipalities with less than 100,000 are handled separately under Phase II NPDES stormwater rules discussed here ( click here to learn more about Phase II ). After receiving applications from Phase I municipalities in 1991 and 1992, MDE began issuing NPDES municipal stormwater permits in 1993. These permits are updated every five years. The following provides information on the most current activities on the Phase I permits.

Contact Info

Questions about NPDES municipal permits may be directed to the Sediment, Stormwater, and Dam Safety Program at 410-537-3543 or emailed to Mr. Raymond Bahr at