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National Pollutant Discharge Elimination System (NPDES)

Stormwater Discharges from Municipal Sources

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Quick links to relevant information on stormwater discharges from municipal sources: 

Polluted stormwater runoff is commonly transported through municipal separate storm sewer systems (MS4s), and then often discharged, untreated, into local water bodies.

An MS4 is a conveyance or system of conveyances that is:
  • owned by a state, city, town, village, or other public entity that discharges to waters of the U.S.,
  • designed or used to collect or convey stormwater (e.g., storm drains, pipes, ditches),
  • not a combined sewer, and
  • not part of a sewage treatment plant, or publicly owned treatment works (POTW).

To prevent harmful pollutants from being washed or dumped into MS4s, certain operators are required to obtain NPDES permits and develop stormwater management programs (SWMPs). The SWMP describes the stormwater control practices that will be implemented consistent with permit requirements to minimize the discharge of pollutants from the sewer system.

Phase I MS4s
Phase II MS4s

The 1990 Phase I regulation requires medium and large cities or certain counties with populations of 100,000 or more to obtain NPDES permit coverage for their stormwater discharges.

There are approximately 855 Phase I MS4s covered by 250 Individual Permits

The 1999 Phase II regulation requires small MS4s in U.S. Census Bureau defined urbanized areas, as well as MS4s designated by the permitting authority, to obtain NPDES permit coverage for their stormwater discharges. Phase II also includes non-traditional MS4s such as public universities, departments of transportation, hospitals and prisons.

Most of the 6,695 Phase II MS4s are covered by statewide General Permits, however some states use individual permits. There are three Watershed Permits that cover 3 Phase I and 40 Phase II MS4s.

Urbanized Area Maps for NPDES MS4 Phase II Stormwater Permits

Developing an MS4 Program

Owners/operators of regulated municipal separate storm sewer systems (MS4s) are required to develop, implement, and enforce a stormwater management program (SWMP). The focus of the SWMP is to describe how the MS4 will reduce the discharge of pollutants from its sewer system and addresses these program areas:

Use the guidance and references on this page to help you develop your SWMP.


Long-Term Stormwater Planning

  • Community Solutions for Stormwater Management: A Guide for Voluntary Long-Term Planning - Guide to assist states and local governments in developing and implementing effective long-term stormwater plans. This document describes how to develop a comprehensive long-term community stormwater plan that integrates stormwater management with communities' broader plans for economic development, infrastructure investment and environmental compliance. 

Permit Resources

Fees and Funding

Federal Government and Stormwater Fees

  • Federal Government Obligations to Pay Stormwater Fees — On January 4, 2011, President Obama signed into law "An Act to Amend the Federal Water Pollution Control Act to clarify Federal responsibility for stormwater pollution," Pub. L. No. 111-378, 124 Stat 4128 (2011) to clarify that reasonable service charges payable by federal agencies, as described in section 313(a), include certain stormwater assessments.
  • Memorandum Clarifying that New Legislation Provides for Stormwater Fees to be Paid from Current Lump-sum Appropriations — On March 18, 2011, the Department of Justice/Office of Legal Counsel released a memorandum to clarify that language in section 313(c)(2)(B) of the Clean Water Act contained in new legislation obligating federal agencies to pay stormwater managements fees does not impose a specific appropriation requirement. Stormwater assessments are payable from annual—including current—lump-sum appropriations.

Funding Sources and Resources

  • Clean Water State Revolving Fund (CWSRF) — This page describes funding options for a wide variety of water quality projects.
  • Green Infrastructure Funding Opportunities — Learn about federal funding sources and comprehensive guides, case studies, and training materials that government and nonprofit organizations have developed as well as spreadsheet tools designed to help assess program costs and funding sources.
  • Water Infrastructure and Resiliency Finance Center — This page serves as a resource to communities for improving their wastewater, drinking water, and stormwater systems, particularly through innovative financing and increased resiliency to climate change.
  • Nonpoint Source (319) Grant Program — This page describes grant money that is available under section 319 of the Clean Water Act to states, territories, and Indian Tribes to support activities as part of an approved nonpoint source management program.

Fact Sheets and Guidance

  • Funding Stormwater Programs — This fact sheet for municipalities provides information on alternatives for funding their stormwater programs.
  • Guidance for Municipal Stormwater Funding — This document was developed in January 2006 by the National Association of Flood and Stormwater Management Agencies (NAFSMA) under a grant provided by EPA to provide funding guidance for stormwater utilities.

Training and Webcasts

EPA provides webcasts for stormwater professionals on the minimum control measures as well as joint EPA-Federal Highway Administration (FHWA) webcasts on transportation stormwater management.

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