MS4 PERMIT

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Phase I MS4 NPDES Permit 

📘 What Is an MS4?

A Municipal Separate Storm Sewer System (MS4) is:

  • A conveyance system (e.g., streets, curbs, gutters, storm drains, ditches) designed to collect or convey stormwater.

  • Owned or operated by a public entity such as a city, county, state, or federal facility.

  • Separate from sanitary sewers (does not carry sewage).

🌧️ What Is the NPDES MS4 Program?

Under the Clean Water Act, the NPDES MS4 program aims to reduce the discharge of pollutants from stormwater systems to surface waters, thereby protecting water quality and aquatic ecosystems.

🔍 What Is a Phase I MS4?

Phase I MS4 refers to:

  • Large (population over 250,000) and medium (population between 100,000 and 250,000) cities or counties.

  • Required to obtain NPDES permits since 1990.

  • Include state departments of transportation, airports, military bases, and public universities.

📋 Permit Requirements for Phase I MS4

Phase I MS4s must develop and implement a comprehensive stormwater management program (SWMP), including:

  1. Public Education and Outreach

    • Inform citizens about stormwater impacts.

    • Encourage public involvement.

  2. Illicit Discharge Detection and Elimination (IDDE)

    • Locate and remove unauthorized non-stormwater discharges.

  3. Construction Site Stormwater Runoff Control

    • Require erosion and sediment control at sites >1 acre.

  4. Post-Construction Stormwater Management

    • Reduce long-term stormwater impacts from new developments.

  5. Pollution Prevention/Good Housekeeping

    • Minimize pollution from municipal operations (e.g., street sweeping, salt storage).

  6. Monitoring and Reporting

    • Conduct water quality sampling.

    • Submit annual compliance reports to the permitting authority.

🧪 What Pollutants Are of Concern?

Stormwater can carry:

  • Sediment from construction sites

  • Nutrients (nitrogen, phosphorus) from fertilizers

  • Heavy metals from roads and roofs

  • Oil and grease from vehicles

  • Bacteria from pet waste and leaking sewers

🏛️ Enforcement and Oversight

  • The California State Water Resources Control Board enforce compliance.

  • Violations may result in civil penalties or corrective actions.

🌎 Why It Matters

  • Helps protect rivers, lakes, and coastal waters.

  • Improves community resilience to flooding and pollution.

  • Supports clean drinking water and healthy ecosystems.

📚 Learn More