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General Storm Water Permit for Small Municipal Separate Storm Sewer Systems (MS4)

2021 MS4 Permit Renewal Notice: The MS4 Permit is in the process of being reissued. Until this permit is reissued you will continue to operate under the expiring MS4 permit. The timeframe for the renewal will most likely occur by March 2024. If you have not submitted an NOI for Renewal, please do so as soon as possible. Please note we have new Renewal & Waiver NOIs.

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Phase I of the NPDES Storm Water program began in 1990 and required medium and large municipal separate storm sewer systems (MS4s) to obtain NPDES coverage. The expanded Phase II program began in March 2003 and required small MS4s in urbanized areas with a population of at least 50,000 to obtain NPDES permits and implement six (6) minimum control measures.
An urban areas with a population of at least 50,000 as delineated by the US Census Bureau is defined as a central place or places and the adjacent densely settled surrounding area that together have a residential population of at least 50,000 people and an overall population density of at least 500 people per square mile.
The General Storm Water Permit for MS4s was reissued on February 10, 2016 with an effective date of March 1, 2016. The expiration date is February 28, 2021. Significant changes have been made in the permit based on comments received by the Agency. See IEPA's Response to Comments.

  1. The reissued permit requires consideration by permittees of incorporation of green infrastructure concepts into their storm water program. For more information see USEPA's Managing Wet Weather with Green Infrastructure.
  2. The Agency now requires, for purposes of public notification and participation, that the Notice of Intent (NOI) for your construction site projects be submitted to the Agency electronically and posted at the construction site.
  3. The Agency has also developed e-mail addresses for the electronic submission of your Notice of Intent and annual reports. Those addresses are included in the general permit.
  4. Part V.B of the reissued permit states: Permittees must post their NOI, storm water management program plan, and annual reports on the permittee’s website.  Storm sewer maps may be withheld for security reasons.

MS4 Permit Requirements

  1. Develop a storm water management program comprised of best management practices (BMPs) and measurable goals for each of the following six minimum control measures:
    • Public education and outreach on storm water impacts
    • Public involvement and participation
    • Illicit discharge detection and elimination
    • Construction site storm water runoff control
    • Post construction storm water management in new development and redevelopment
    • Pollution prevention/good housekeeping for municipal operations

    For full descriptions of each measure, including examples of BMPs and measurable goals, see link below.

    Measurable Goals Guidance for Phase II Small MS4s

  2. Submit a completed Notice of Intent. Operators can choose to share responsibilities for meeting the Phase II program requirements. Those entities choosing to do so may submit jointly with other municipalities or governmental entities. The NOI form may be submitted electronically to:
  3. The permittee must submit annual reports to the Agency by June 1 for each year that the permit is in effect. The annual report should be submitted electronically to: The report must include:
    • The status of compliance with the permit conditions, including an assessment of the BMPs and progress toward the measurable goals;
    • Results of any information collected and analyzed, including monitoring data;
    • A summary of the storm water activities planned for the next reporting cycle;
    • A change in any identified best management practices or measurable goals;
    • If applicable, notice of relying on another governmental entity to satisfy some of the permit obligations.