What is Stormwater?

Revised on: April 28, 2022 - 4:07pm

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 | View Flow Diagram > 

NPDES Permit Program

The Enivronmental Protection Agency (EPA) has estimated that about 30 percent of known pollution to our nation's waters is attributable to stormwater runoff. In 1987, Congress directed EPA to develop a regulatory program to address the stormwater problem and issued regulations in 1990 authorizing the creation of a National Pollutant Discharge Elimination System (NPDES) permitting system. 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 05, 2002, Arizona became one of 45 states with authorization from EPA to operate the NPDES Permit Program (Section 402 of the Clean Water Act) on the state level under the Arizona Pollutant Discharge Elimination System (AZPDES) Permit Program. All facilities that discharge pollutants from any point source into waters of the United States (navigable waters) are required to obtain or seek coverage under an AZPDES permit. Pollutants can enter waters of the United States from a variety of pathways, including agricultural, domestic and industrial sources. For regulatory purposes these sources are generally categorized as either point source or nonpoint sources.

Arizona is authorized to issue 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 water of the United States, permits are required for those discharges. Most stormwater discharges are permitted under various general permits. However, an individual permit is required when the general permit requirements do not accurately represent the activity at a facility and a permit is customized 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 within 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.

What are Impaired Waters?

The following waterbodies (commonly referred to as the 303(d) list) were assessed by ADEQ as having impaired uses that require more than existing technology and permit controls to achieve or maintain water quality standards.

What are Outstanding Arizona Waters (OAW)?

The following surface waters have been classified as outstanding Arizona waters1 | View OAW Listing > 

 

For more information on stormwater permitting on Tribal land2 within Arizona, visit EPA Region 9 NPDES Stormwater Program | Learn More > 

1 Under Arizona Administrative Code R18-11-112
2Tribal land is defined as Indian Country as recognized by the EPA and defined at 18 U.S.C. § 1151 and 40 C.F.R. § 171.3