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Maryland State Government Maryland Department of the Environment

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.

Final Determination to Issue Stormwater Permit to Anne Arundel County (February 12, 2014)

The Maryland Department of the Environment (MDE) has reissued a National Pollutant Discharge Elimination System (NPDES) stormwater permit to Anne Arundel County, Maryland. This permit covers stormwater discharges from the storm drain system owned or operated by Anne Arundel County. Permit requirements include implementing comprehensive stormwater management programs for addressing runoff from new and redevelopment projects, restoring urban areas where there is currently little or no stormwater management, and working toward meeting stormwater waste load allocations for local water resources and Chesapeake Bay. Also included in the permit are conditions that require the County to possess the necessary legal authority to control stormwater discharges, map its storm drain system, monitor urban runoff, and eliminate illicit discharges to the storm drain system. It is MDE's final determination that this permit complies with the United States Environmental Protection Agency’s NPDES regulations to control stormwater pollutant discharges from Anne Arundel County’s storm drain system to the maximum extent practicable.

This permit and the Basis for Final Determination may be viewed here:

Final Determination to Issue Stormwater Permit to Baltimore City (December 27, 2013)

The Maryland Department of the Environment (MDE) has reissued a National Pollutant Discharge Elimination System (NPDES) stormwater permit to Baltimore City, Maryland. This permit covers stormwater discharges from the storm drain system owned or operated by Baltimore City. Permit requirements include implementing comprehensive stormwater management programs for addressing runoff from new and redevelopment projects, restoring urban areas where there is currently little or no stormwater management, and working toward meeting stormwater waste load allocations for local water resources and Chesapeake Bay. Also included in the permit are conditions that require the City to possess the necessary legal authority to control stormwater discharges, map its storm drain system, monitor urban runoff, and eliminate illicit discharges to the storm drain system. It is MDE's final determination that this permit complies with the United States Environmental Protection Agency’s NPDES regulations to control stormwater pollutant discharges from Baltimore City’s storm drain system to the maximum extent practicable.

This permit and the Basis for Final Determination may be viewed here:

Final Determination to Issue Stormwater Permit to Baltimore County (December 23, 2013)

The Maryland Department of the Environment (MDE) has reissued a National Pollutant Discharge Elimination System (NPDES) stormwater permit to Baltimore County, Maryland. This permit covers stormwater discharges from the storm drain system owned or operated by Baltimore County. Permit requirements include implementing comprehensive stormwater management programs for addressing runoff from new and redevelopment projects, restoring urban areas where there is currently little or no stormwater management, and working toward meeting stormwater waste load allocations for local water resources and Chesapeake Bay. Also included in the permit are conditions that require the County to possess the necessary legal authority to control stormwater discharges, map its storm drain system, monitor urban runoff, and eliminate illicit discharges to the storm drain system. It is MDE's final determination that this permit complies with the United States Environmental Protection Agency’s NPDES regulations to control stormwater pollutant discharges from Baltimore County’s storm drain system to the maximum extent practicable.

This permit and the Basis for Final Determination may be viewed here:

Final Determination to Issue Stormwater Permit for Carroll County (December 29, 2014)

The Maryland Department of the Environment (MDE) has reissued a National Pollutant Discharge Elimination System (NPDES) stormwater permit to Carroll County, Maryland. This permit covers stormwater discharges from the storm drain system owned or operated by Carroll County. Permit requirements include implementing comprehensive stormwater management programs for addressing runoff from new and redevelopment projects, restoring urban areas where there is currently little or no stormwater management, and working toward meeting stormwater waste load allocations for local water resources and Chesapeake Bay. Also included in the permit are conditions that require the County to possess the necessary legal authority to control stormwater discharges, map its storm drain system, monitor urban runoff, and eliminate illicit discharges to the storm drain system. It is MDE's final determination that this permit complies with the United States Environmental Protection Agency’s NPDES regulations to control stormwater pollutant discharges from Carroll County’s storm drain system to the maximum extent practicable.

This permit and the Basis for Final Determination may be viewed here:

Final Determination to Issue Stormwater Permit for Charles County (December 26, 2014)

The Maryland Department of the Environment (MDE) has reissued a National Pollutant Discharge Elimination System (NPDES) stormwater permit to Charles County, Maryland. This permit covers stormwater discharges from the storm drain system owned or operated by Charles County. Permit requirements include implementing comprehensive stormwater management programs for addressing runoff from new and redevelopment projects, restoring urban areas where there is currently little or no stormwater management, and working toward meeting stormwater waste load allocations for local water resources and Chesapeake Bay. Also included in the permit are conditions that require the County to possess the necessary legal authority to control stormwater discharges, map its storm drain system, monitor urban runoff, and eliminate illicit discharges to the storm drain system. It is MDE's final determination that this permit complies with the United States Environmental Protection Agency’s NPDES regulations to control stormwater pollutant discharges from Charles County’s storm drain system to the maximum extent practicable.

This permit and the Basis for Final Determination may be viewed here:

Final Determination to Issue Stormwater Permit for Frederick County (December 30, 2014)

The Maryland Department of the Environment (MDE) has reissued a National Pollutant Discharge Elimination System (NPDES) stormwater permit to Frederick County, Maryland. This permit covers stormwater discharges from the storm drain system owned or operated by Frederick County. Permit requirements include implementing comprehensive stormwater management programs for addressing runoff from new and redevelopment projects, restoring urban areas where there is currently little or no stormwater management, and working toward meeting stormwater waste load allocations for local water resources and Chesapeake Bay. Also included in the permit are conditions that require the County to possess the necessary legal authority to control stormwater discharges, map its storm drain system, monitor urban runoff, and eliminate illicit discharges to the storm drain system. It is MDE's final determination that this permit complies with the United States Environmental Protection Agency’s NPDES regulations to control stormwater pollutant discharges from Frederick County’s storm drain system to the maximum extent practicable.

This permit and the Basis for Final Determination may be viewed here:

Final Determination to Issue Stormwater Permit for Harford County (December 30, 2014)

The Maryland Department of the Environment (MDE) has reissued a National Pollutant Discharge Elimination System (NPDES) stormwater permit to Harford County, Maryland. This permit covers stormwater discharges from the storm drain system owned or operated by Harford County. Permit requirements include implementing comprehensive stormwater management programs for addressing runoff from new and redevelopment projects, restoring urban areas where there is currently little or no stormwater management, and working toward meeting stormwater waste load allocations for local water resources and Chesapeake Bay. Also included in the permit are conditions that require the County to possess the necessary legal authority to control stormwater discharges, map its storm drain system, monitor urban runoff, and eliminate illicit discharges to the storm drain system. It is MDE's final determination that this permit complies with the United States Environmental Protection Agency’s NPDES regulations to control stormwater pollutant discharges from Harford County’s storm drain system to the maximum extent practicable.

This permit and the Basis for Final Determination may be viewed here:

Final Determination to Issue Stormwater Permit for Howard County (December 18, 2014)

The Maryland Department of the Environment (MDE) has reissued a National Pollutant Discharge Elimination System (NPDES) stormwater permit to Howard County, Maryland. This permit covers stormwater discharges from the storm drain system owned or operated by Howard County. Permit requirements include implementing comprehensive stormwater management programs for addressing runoff from new and redevelopment projects, restoring urban areas where there is currently little or no stormwater management, and working toward meeting stormwater waste load allocations for local water resources and Chesapeake Bay. Also included in the permit are conditions that require the County to possess the necessary legal authority to control stormwater discharges, map its storm drain system, monitor urban runoff, and eliminate illicit discharges to the storm drain system. It is MDE's final determination that this permit complies with the United States Environmental Protection Agency’s NPDES regulations to control stormwater pollutant discharges from Howard County’s storm drain system to the maximum extent practicable.

This permit and the Basis for Final Determination may be viewed here:

Final Determination to Issue Stormwater Permit to Prince George's County (January 2, 2014)

The Maryland Department of the Environment (MDE) has reissued a National Pollutant Discharge Elimination System (NPDES) stormwater permit to Prince George's County, Maryland. This permit covers stormwater discharges from the storm drain system owned or operated by Prince George's County. Permit requirements include implementing comprehensive stormwater management programs for addressing runoff from new and redevelopment projects, restoring urban areas where there is currently little or no stormwater management, and working toward meeting stormwater waste load allocations for local water resources and Chesapeake Bay. Also included in the permit are conditions that require the County to possess the necessary legal authority to control stormwater discharges, map its storm drain system, monitor urban runoff, and eliminate illicit discharges to the storm drain system. It is MDE's final determination that this permit complies with the United States Environmental Protection Agency’s NPDES regulations to control stormwater pollutant discharges from Prince George's County’s storm drain system to the maximum extent practicable.

This permit and the Basis for Final Determination may be viewed here:

Final Determination to Issue Stormwater Permit for the Maryland State Highway Administration (October 9, 2015)

The Maryland Department of the Environment (MDE) has reissued a National Pollutant Discharge Elimination System (NPDES) stormwater permit to the Maryland State Highway Administration (SHA). This permit covers stormwater discharges from the storm drain system owned or operated by SHA. Permit requirements include implementing comprehensive stormwater management programs for addressing runoff from new and redevelopment projects, restoring urban areas where there is currently little or no stormwater management, and working toward meeting stormwater waste load allocations for local water resources and Chesapeake Bay. Also included in the permit are conditions that require SHA to possess the necessary legal authority to control stormwater discharges, map its storm drain system, monitor urban runoff, and eliminate illicit discharges to the storm drain system. It is MDE's final determination that this permit complies with the United States Environmental Protection Agency’s NPDES regulations to control stormwater pollutant discharges from SHA's storm drain system to the maximum extent practicable. This permit and the Basis for Final Determination may be viewed here:

NPDES Phase I Permits

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

12/02/1993

02/12/2014

Dept. of Public Works / Watershed Protection and Restoration

Baltimore County

11/17/1994

12/23/2013

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

Baltimore City

11/17/1993

12/27/2013

Dept. of Public Works

Montgomery County

03/15/1996

02/16/2010

Dept. of Environmental Protection

Prince George’s County

11/17/1993

01/02/2014

Dept. of Environment

Medium Jurisdictions

Carroll County

11/17/1993

12/30/2014

Land Use, Planning & Development

Charles County

05 /01/1997

12/26/2014

Planning & Growth Management

Frederick County

11/15/1994

12/30/2014

Sustainable Development - Watershed Management

Harford County

05/17/1994

12/30/2014

Dept. of Public Works - Water Resources

Howard County

04/17/1995

12/18/2014

Dept. of Public Works / Stormwater Management Division

State Storm Drain Systems

State Highway Administration

01/08/1999

10/09/2015

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 between 10% and 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

Additional Resources

Guidance for Maryland's NPDES Stormwater Permits

NPDES municipal separate storm sewer system permits in Maryland require the restoration of a certain percent of a jurisdiction's impervious surface area (e.g., 20%) that has little or no stormwater management. How to calculate impervious surface requirements and treatment credits has generated numerous questions. This document standardizes procedures for reporting of traditional, new, and alternative best management practices (BMPs) and the impervious area each controls. The guidance may be found here:

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 Raymond.Bahr@maryland.gov.