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.


Consent Decree

The Maryland Department of the Environment and the Montgomery County Department of Environmental Protection have reached tentative agreement on a consent decree to be filed in Montgomery County Circuit Court resolving issues with the county’s performance pursuant to the National Pollutant Discharge Elimination System (NPDES) Municipal Separate Storm Sewer System (MS4) permit issued February 15, 2010. The five-year permit expired in 2015.


You can view background information on each jurisdiction by clicking on the municipality's name in the chart below. Initial permits, current permits, and links to the agency responsible for administering each local permit are also accessible by clicking on the respective links below.


Initial Permit Issued Current Permit Issued Local Agency Responsible for Annual Reporting

Large Jurisdictions

Anne Arundel County



Dept. of Public Works / Watershed Protection and Restoration

Baltimore County



Dept. of Environmental Protection & Sustainability (EPS) / NPDES

Baltimore City



Dept. of Public Works

Montgomery County



Dept. of Environmental Protection

Prince George’s County



Dept. of Environment

Medium Jurisdictions

Carroll County



Land Use, Planning & Development

Charles County

05 /01/1997


Planning & Growth Management

Frederick County



Sustainable Development - Watershed Management

Harford County



Dept. of Public Works - Water Resources

Howard County



Dept. of Public Works / Stormwater Management Division

State Storm Drain Systems

State Highway Administration



Office of Environmental Design

Summary of Local Requirements

NPDES municipal stormwater permits require the jurisdictions to develop comprehensive programs to reduce storm drain system pollution to the MEP. Typical NPDES stormwater permit conditions require jurisdictions to:

  • Legal Authority: provide certification from appropriate legal counsel that adequate authority exists to control discharges from the municipal storm drain system
  • Source Identification: map storm drain pipes and best management practices (BMPs), land use, impervious cover, and watershed restoration projects in geographical information system (GIS) format
  • Management Programs: implement erosion and sediment control, stormwater management, illicit connection detection and elimination, and public education and outreach programs
  • Watershed Assessment: evaluate all urban watersheds thoroughly regarding water quality and develop goals and action plans for restoration,
  • Restoration Projects: restore 20% of uncontrolled impervious surfaces based on watershed assessments during each five-year permit cycle
  • Assessment of Control: document work toward meeting watershed restoration goals, including total maximum daily loads (TMDLs)*, using chemical, biological, and physical monitoring
  • Program Funding: provide an annual fiscal analysis of the capital, operation, and maintenance expenditures necessary to comply with permit conditions

More information on TMDLs may be found on MDE's webpage here: Introduction to TMDLs

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 ​​​