Small Municipal Separate Storm Sewer Systems (MS4)

What is Municipal Separate Storm Sewer Systems (MS4)?

MS4 is a general permit that authorizes the discharge of storm water from small Municipal Separate Storm Sewer Systems provided that the permittee complies with all the requirements set forth in the permit.


MS4 is a federal program required under the United States Environmental Protection Agency (EPA) National Pollutant Discharge Elimination System (NPDES) intended to eliminate storm water pollutant discharges to receiving waters of the United States.

As such, the Arizona Department of Environmental Quality (ADEQ) issues the Arizona Pollutant Discharge Elimination System (AZPDES) general permit for the discharge of storm water from Small Municipal Separate Storm Sewer Systems (MS4s) to waters within the State of Arizona, pursuant to Arizona Administrative Code (A.A.C.), Title 18, Article 9.

The current MS4 general permit number AZG2016-002 was issued to Cochise County by ADEQ for the discharge of storm water from Small Municipal Storm Sewer Systems within the required regions located inside the unincorporated areas of Sierra Vista, Douglas and Bisbee, Arizona. These regions are the urbanized fringes outside the cities. This permit was issued in September 2016 and is valid for five years.

You can check if you are a resident or a business owner within Cochise County MS4 jurisdiction on the maps:

Purpose of the MS4 Permit

The conditions in the permit are established pursuant to the Clean Water Act (CWA) Section 402(p)(3)(iii) to ensure the pollutant discharges through stormwater from the MS4s are reduced to the maximum extent practicable (MEP) through six control measures, protect water quality, and satisfy the appropriate water quality requirements of the CWA.


The six control measures:

  1. Public Education and Outreach
    1. Household Hazardous Waste Disposal Information (PDF)
    2. Clean Water & Municipal Seperate Storm Sewer System (MS4) (PDF)
  2. Public Involvement and Participation
  3. Illicit Discharge Detection and Elimination (IDDE)
  4. Construction Activity Stormwater Runoff Control
  5. Post-construction Stormwater Management in New Development and Redevelopment
    1. Review Checklist (PDF)
  6. Pollution Prevention and Good Housekeeping for Municipal Operations

Additional Requirements

Besides implementing these control measures, Cochise County is also required to keep its Stormwater Management Program (SWMP) updated, monitor stormwater discharges and send Discharge Monitoring Report (DMR) and Annual Report to ADEQ.

Impact of Storm water Discharge in Your Community

Rainfall washes pollutants (such as Motor Oil, Fertilizers, Pesticides, Pathogens, Detergents, and other Chemicals) off roads, lawns, and other surfaces and carries them into the nearest body of water. These toxic pollutants can contaminate the aquatic inhabitants including fish, sources of drinking water and waterways.

Reduce Pollutants

Steps that you can take to reduce pollutants in storm water runoff:

  • Do not dump any waste on the ground, and street.
  • Be watchful on any deliberate, illegal dischargers of prohibited items such as motor oil, radiator fluid, battery acid or other suspected hazardous waste, or accidental large spill from gasoline tanker and report to the County.
  • Volunteer in any cleanup programs in your neighborhood.
  • Keep your own property free of solid or liquid waste that may run into the storm sewer.
  • Always pick up after your pet.
  • Minimize using pesticides and use fertilizers thriftily.