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Storm Water - MS4 Municipal Program

Storm Water - MS4 Municipal Program

NOTICE: The U.S. Environmental Protection Agency's (U.S. EPA) Urban Waters Small Grants program is currently requesting proposals. For more information please see the U.S. EPA's Urban Waters web page (http://www2.epa.gov/urbanwaters/urban-waters-small-grants-mapping)

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MS4 Municipal Program Content


The Municipal Storm Water Permitting Program regulates storm water discharges from municipal separate storm sewer systems (MS4s). MS4 permits were issued in two phases.

  • Under Phase I, which started in 1990, the Regional Water Quality Control Boards have adopted National Pollutant Discharge Elimination System (NPDES) storm water permits for medium (serving between 100,000 and 250,000 people) and large (serving 250,000 or more people) municipalities. Most of these permits are issued to a group of Co -permittees encompassing an entire metropolitan area.

  • On April 30, 2003, as part of Phase II, the State Water Resources Control Board issued a General Permit for the Discharge of Storm Water from Small MS4s (WQ Order No. 2003-0005-DWQ) to provide permit coverage for smaller municipalities (population less than 100,000), including non-traditional Small MS4s, which are facilities such as military bases, public campuses, prisons and hospital complexes. The Phase II Small MS4 General Permit covers Phase II Permittees statewide. On February 5, 2013, the Phase II Small MS4 General Permit was renewed and became effective on July 1, 2013.

Region-wide Permit

The Central Valley Water Board is currently working with Phase I and II permittees to develop a Region-wide MS4 Permit (Region-wide Permit) that could include both Phase I and II MS4 Permittees within the Central Valley region. Currently, each Phase I MS4 Permittee is covered under an individual permit issued by the Central Valley Water Board. Phase II MS4 Permittees are currently covered under the State Water Resources Control Board's Phase II MS4 (Order No. 2013-001 DWQ). Central Valley Water Board staff is developing a single Region-wide Permit that would promote greater watershed/drainage shed coordination and water quality measure protections, and promote greater program implementation efficiencies.

  • Some of the benefits of such an approach might include:
    1. A region-wide MS4 permit approach would conceptually use municipal resources more efficiently, leveraging resources at a regional level (monitoring and outreach);
    2. Increased flexibility;
    3. Relate constituents of concern to storm water program actions;
    4. Consistent standards across Central Valley region;
    5. May provide the ability for municipalities to prioritize storm water program elements; and
    6. Assess progress at regional, local, or watershed levels.

emailsubscription  To receive information and updates on upcoming meetings for the Region-wide Permit, please visit: http://www.waterboards.ca.gov/resources/email_subscriptions/reg5_subscribe.shtml. Provide your email address and name in the spaces provided and select "Storm Water Region-wide Permit" from the list of selections.

Stakeholder Meeting Process

Phase I MS4 Municipal Program

Phase II Small MS4 Program

Other Resources

Questions or Comments about MS4 Permits or the MS4 Program?

  • You may submit your MS4 questions or comments to Program Staff.

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--Web page updated 11/18/2015