Stormwater Management Program

Municipal Separate Storm Sewer System (MS4)

Stormwater runoff is generated from rain and snowmelt that flows over land or impervious surfaces (e.g., paved streets, parking lots, building rooftops) and does not soak into the ground. The runoff picks up pollutants such as trash, chemicals, oils and dirt/sediment that can harm our rivers, streams, lakes and coastal waters. To protect these resources, communities, construction companies, industries and others use stormwater controls, known as best management practices (BMPs). These BMPs filter pollutants and/or prevent pollution by controlling it at its source.

To reduce the discharge of pollutants to the maximum extent practicable, to protect water quality, and to satisfy the requirements of the Clean Water Act and A.R.S. 49-255.04, the following 6 Minimum Control Measures (MCMs) have been implemented:

  1. Public Education and Outreach
  2. Public Involvement and Participation
  3. Illicit Discharge Detection and Elimination (IDDE) Program
  4. Construction Site Stormwater Runoff Control
  5. Post-Construction Stormwater Management
  6. Pollution Prevention and Good Housekeeping.


NPDES Permit Program

The Environmental Protection Agency (EPA) has estimated that about 30 percent of known pollution to our nation's waters can be attributed to stormwater runoff. In 1987, Congress directed the EPA to develop a regulatory program to address the stormwater problem and, in 1990, issued regulations authorizing the creation of a National Pollutant Discharge Elimination System (NPDES) permitting program. The NPDES stormwater program regulates some stormwater discharges from three potential sources: municipal separate storm sewer systems (MS4s), construction activities, and industrial activities. Operators of these sources might be required to obtain an NPDES permit before they can discharge stormwater.


AZPDES Permits

On December 5, 2002, Arizona became one of 45 states authorized by the EPA to operate the NPDES Permit Program (Clean Water Act, sect 402) at the state level under the Arizona Pollutant Discharge Elimination System (AZPDES) Permit Program. All activities that discharge pollutants from any point source into waters of the United States (WOTUS) or non-WOTUS protected surface waters are required to obtain or seek coverage under an AZPDES permit. Pollutants can enter WOTUS or non_WOTUS protected surface waters via a variety of pathways, including agricultural, domestic, and industrial sources. For regulatory purposes, these sources are generally categorized as either point source or nonpoint source.

Arizona is authorized to issue Notices of Intent (NOIs) for construction and industrial activities under AZPDES. An AZPDES permit is required for any point source discharge of pollutants to a water of the United States. Because stormwater runoff can transport pollutants to either a municipal separate storm sewer system or to a WOTUS or non-WOTUS protected surface water, permits are required for those discharges. Most stormwater discharges are permitted under one of more general permits. However, an individual permit is required when the general permit requirements do not accurately represent the activity at a facility, so a permit is custom tailored to the site. An individual permit may be necessary if the Limitations of Coverage section of a general permit does not allow the facility's discharge to be covered by the general permit. It is the responsibility of every applicant to determine if any of the Limitations of Coverage apply to the facility seeking a general permit.

ADEQ AZPDES Why have an MS4 General Permit?