Last Updated 07/20/2026
Arizona Stormwater Laws and Regulations
The state operates under the Arizona Pollutant Discharge Elimination System, through NPDES Permit (AZG2002-002) and state regulation Arizona Administrative Code (A.A.C.) R18-9-A905. There is a phase II MS4 general permit to address stormwater runoff from new development and redevelopment projects that “disturb greater than or equal to one acre, including projects less than one acre that are part of a larger common plan of development or sale, and discharge into the small MS4.” The standards are only applicable in regulated MS4 areas, and Indian Lands are exempted.
Excerpt- Arizona Department of Environmental Quality Stormwater Page
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.
Excerpt – ADOT Municipal Separate Storm Sewer System Permit
3.2 Maintain Adequate Legal Authority
ADOT shall utilize the powers delegated to it by the Arizona Legislature to control and enforce the release of pollutants to and discharges from the MS4 that is owned or operated by ADOT through rules and regulations regulating encroachments (e.g., A.A.C. R17-3-501 – 509), permits, contracts or similar means.
Where necessary to assist in implementing this legal authority, ADOT shall develop and/ or revise procedures, agreements, and/or memorandums of understanding with other agencies, such as the Arizona Office of the Attorney General and the Arizona Department of Public Safety. These procedures/ agreements/ memorandums shall be documented in the SWMP.
To be considered adequate, this legal authority shall, at a minimum, address the following:
- Authority to Prohibit Illicit Discharges: Prohibit and eliminate illicit connections and discharges to the MS4. Illicit connections include pipes, drains, open channels, or other conveyances that have the potential to allow an illicit discharge to enter the MS4. Illicit discharges include all non-stormwater discharges except firefighting discharges, discharges from NPDES permitted industrial sources and discharges not otherwise allowed under Part 3.2(b) of this permit.
- Allowable Non-Stormwater Discharges: Exceptions to the prohibition in Part 3.2(a) may include the allowable non-stormwater discharges described in Part 1.3, only if they are nonsignificant contributors of pollutants (i.e., do not result in the discharge of pollutants above a numeric or narrative SWQS).
- Authority to Prohibit Spills or Other Releases: Control the discharge of spills, and prohibit dumping or disposal of materials other than stormwater into the MS4.
- Authority to Require Compliance: Require compliance with conditions in ADOT’s statutes, rules, permits, contracts, or orders (i.e., hold dischargers accountable for their contributions of pollutants and flows).
- Authority to Require Installation, Implementation, and Maintenance of Control Measures: Require owners/operators of construction sites, new or redeveloped land, and industrial and commercial facilities that discharge to ADOT’s MS4 to minimize the discharge of pollutants through the installation, implementation, and maintenance of stormwater control measures.
- Authority to Receive and Collect Information: Require from operators of construction sites that discharge to ADOT’s municipal storm sewer system information such as stormwater plans, inspection reports, and monitoring results, and other information deemed necessary to assess compliance with this permit. Permit No. AZS000018 – 2015 [6] Arizona Department of Transportation AZPDES Municipal Separate Storm Sewer System Permit
- Authority to Inspect: To the extent allowable under state law, ADOT shall have authority to inspect facilities or activities that result in a discharge to its municipal storm sewer system.
- Response to Violations: Establish written procedures to promptly require that violators cease and desist illicit discharges or discharges of stormwater in violation of any ADOT-specific statute, rule, permit or other mechanisms and abate such discharges, including the ability to:
- Require the responsible person to abate the illicit discharge, spill, or pollutant release immediately and initiate remedial activities as soon as practicable;
- If a situation persists where pollutant-causing sources or activities are not abated, provide the option to order the cessation of activities until such problems are adequately addressed.
- When all parties agree that remedial activities cannot be initiated immediately, ADOT shall determine a new timeframe and notify ADEQ within 14 days of becoming aware of the illicit discharge, spill, or pollutant release.
- Interagency Agreements: As necessary, establish agreements (memorandum of agreement, etc.) with other MS4s to abate, control, or reduce the discharge of pollutants to ADOT’s municipal storm sewer system
View State Page
Frequently Asked Questions
What is AZPDES, and how does it relate to Arizona property owners?
The Arizona Pollutant Discharge Elimination System is the state’s own version of the federal NPDES program. Arizona gained authorization from the EPA in December 2002 to administer permitting at the state level, which means facilities discharging pollutants into waters of the United States, including stormwater runoff, generally seek coverage through AZPDES rather than a federal permit directly.
Does every property need an individual AZPDES permit?
No. Most stormwater discharges are covered under general permits, which apply broadly to similar types of activity. An individual permit becomes necessary only when a facility’s specific situation doesn’t fit within a general permit’s limitations of coverage, and it’s the applicant’s responsibility to determine whether that applies to their site.
What size project triggers Arizona's Phase II MS4 requirements?
Any new development or redevelopment disturbing one acre or more that discharges into a small MS4. As with the other AZPDES-covered cities, smaller projects aren’t automatically exempt. If a project under one acre is part of a larger common plan of development or sale, the same requirements still apply.
Does Arizona's stormwater program apply everywhere in the state?
No. The standards only apply within regulated MS4 areas, meaning municipalities and other entities that hold MS4 permit coverage. Indian Lands are specifically exempted from this state-level framework, which is worth knowing if a property’s exact location is near a jurisdictional boundary.
What counts as an illicit discharge under Arizona's MS4 framework?
Any non-stormwater discharge into an MS4 that isn’t specifically allowed, with limited exceptions for firefighting activity, NPDES-permitted industrial sources, and other narrowly defined allowable discharges. MS4 operators are required to hold the legal authority to prohibit and eliminate these illicit connections, which is part of why local ordinances tend to treat illicit discharge so seriously.
What happens if an illicit discharge or spill is found on a property tied to an MS4 in Arizona?
The responsible party is generally required to abate the discharge immediately and begin remedial activity as soon as practicable. If remediation genuinely can’t start right away, the MS4 operator has to set a new timeframe and notify ADEQ within 14 days of becoming aware of the issue, so a delay still comes with a formal reporting obligation attached.
How can AQUALIS help my property navigate Arizona's AZPDES requirements?
AQUALIS helps Arizona property owners determine whether their project needs individual or general permit coverage, implement the post-construction stormwater controls the state’s MS4 framework requires, and respond quickly if an illicit discharge or spill puts a property at risk of an abatement deadline.
The information on this page is provided for general informational purposes only and is not legal advice. Regulations change frequently — AQUALIS makes no warranty as to the accuracy or completeness of this content, and any reliance on it is at your own risk. Consult a qualified professional or your local regulatory authority to confirm requirements applicable to your specific property.
