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a safe and healthy environment.

Stormwater Program

Some cities across the country operate combined sewer systems. These sewers are designed to carry both stormwater runoff and wastewater from homes and businesses to a water treatment plant, where the water is treated prior to being discharged.

In the Valley, most municipalities operate two separate drain systems-a sanitary sewer, which carries wastewater to a water treatment plant, and a Municipal Separate Storm Sewer System (MS4). The MS4 conveys stormwater runoff through drains, streets and open channels, directly discharging the water into retention basins, washes, rivers, or lakes. This water does NOT go to a water treatment plant.

Did you know that stormwater runoff is one of the leading causes of water pollution in the United States? The U.S. Environmental Protection Agency has estimated that over 30% of pollutants in our nation’s waters are the result of stormwater runoff. In an effort to address this problem, revisions were made to the Clean Water Act (CWA), creating the National Pollutant Discharge Elimination System (NPDES). In Arizona, the program is administered by the Arizona Department of Environmental Quality (ADEQ) and is called the Arizona Pollutant Discharge Elimination System (AZPDES).

Construction sites that meet the criteria are required to obtain permit coverage under the Arizona Construction General Permit (AZG2013-001). Municipalities operating separate storm sewer systems within the local urbanized area which have been designated by the EPA or the Director of ADEQ must get permit coverage under Arizona’s AZPDES authority. There are two types of municipal permits: Phase I and Phase II. Phase I permits are for large and medium-sized MS4s; Phase II permits are for small MS4s. Maricopa County is designated as a small MS4 and must obtain stormwater discharge permit coverage under Phase II Small MS4 General Permit AZG2002-002.

Maricopa County’s Permit Requirements

In December 2007, Maricopa County applied for and obtained coverage under permit AZG2002-002. The County’s Stormwater Quality Program will address urban runoff to reduce and potentially eliminate pollution from entering our main water bodies (Salt and Gila River Systems). Elements of the program include a Stormwater Management Plan (SWMP) that incorporates Best Management Practices (BMPs) associated with six (6) Minimum Control Measures as outlined by the federal rule:

  1. Public Education and Outreach
  2. Public Participation and Involvement
  3. Illicit Discharge Detection and Elimination
  4. Construction Site Runoff Control
  5. Post-Construction Runoff Control
  6. Pollution Prevention/Good Housekeeping for Municipal Operations
Stormwater Management Plan (SWMP)
FY 2009 Annual Report
FY 2010 Annual Report
FY 2011 Annual Report
FY 2012 Annual Report
FY 2013 Annual Report
FY 2014 Annual Report
FY 2015 Annual Report
FY 2016 Annual Report

To meet the minimum requirements of the Phase II permit, the Maricopa County Stormwater Quality Management and Discharge Control Regulation was enacted. This regulation prohibits non-stormwater discharges and illicit connections to the County’s MS4. Runoff from construction sites, as well as long-term, permanent runoff control is also regulated by the County.

For more information on Maricopa County’s Stormwater Program, please E-mail us at or call (602) 506-5557.

For regulation related comments or questions, please e-mail us at