Calling All Desert Storm-Chasers! The New Arizona Multi-Sector General Permit Has Arrived!

The Arizona Department of Environmental Quality (ADEQ) Water Quality Division (WQD) has issued the Arizona Pollutant Discharge Elimination System (AZPDES) 2024 Industrial Multi-Sector General Permit (MSGP) for Stormwater Discharges Associated with Non-Mining and Mining Industries. Following collaboration with stakeholders during the public comment period, ADEQ signed the final versions of the MSGPs on January 13, 2025. The permits replace the expired 2019 AZPDES MSGPs and are effective as of January 16, 2025.

Summary of changes to the 2024 Mining and Non-Mining MSGPs:

• Consideration of Major Storm Events – ADEQ has added new requirements for Mining and Non-Mining permittees to consider enhanced and more resilient pollution prevention measures during major storm events. The MSGPs include several control measures to review including improvements to infrastructure and elevated storage locations during flooding. Similar requirements have been added to the United States Environmental Protection Agency (U.S. EPA) MSGP and other state MSGPs in recent years; for more information about resiliency planning in stormwater permitting, check out our 2025 lookahead article.
• ADEQ added Additional Implementation Measures (AIM) to the Non-Mining MSGP, which includes a three-level response approach to action level exceedances. The response requirements become more rigorous with each level in effort to bring the facility back to baseline status. There are exceptions to the AIM requirements, including if the action level exceedance can be attributed to background pollutant levels, run-on from a neighboring source, an abnormal event, or demonstrated not to result in an exceedance of a surface water quality standard. It should be noted that regardless of if an exemption applies, the permit holder must still review the control measures, the stormwater pollution prevention plan (SWPPP), and on-site activities to determine if other modifications are necessary.
• ADEQ updated the action level formulas for hardness-dependent metals to include the default metal translator factors from U.S. EPA The Metals Translator: Guidance for Calculating a Total Recoverable Permit Limit from a Dissolved Criterion. The metal translator converts the dissolved metal criteria to a total recoverable basis to create action levels.
• ADEQ added action levels for metal parameters in the Mining MSGP. These action levels are protected surface water dependent (PSWD) and must be included in the Notice of Intent for coverage (NOI) process based on the surface water’s lowest applicable designated use.
• ADEQ updated Part 7.2 of the Mining MSGP that requires the permittee to submit a Control Measure Assessment Report following receipt of an action level exceedance.
• A 30-calendar day period has been established for the submittal of a corrective action report following a corrective action trigger in Part 3.1.1. of the MSGP. This is in response to public comments regarding the vague “as soon as possible” in previous permits.
• ADEQ clarified the coordinates listed in the NOI must be the central location of the facility in Footnote 2 of Table 1-2 in the MSGPs. It is important to check the historical coordinates before submitting a new NOI, as a discharge is not authorized if the NOI is incorrect.
• ADEQ removed the action level for Total Suspended Solids (TSS) for Sector G and J (metal mining and non-metallic mineral mining and dressing, respectively) in the Mining MSGP. These sectors are still required to monitor and report the results.

Summary of items NOT changing in the 2024 Mining and Non-Mining MSGPs:

• Monitoring Frequency – ADEQ believes that sampling twice per year (once per rainy season) provides the best dataset and will not be implementing more frequent sampling.
• Emerging Contaminant Research – ADEQ has decided to not include per- and polyfluoroalkyl substances (PFAS) or microplastic monitoring in the 2024 MSGPs. ADEQ has stated they are paying close attention to U.S. EPA recommendations regarding approved monitoring methods for microplastics and are partnering with wastewater treatment facilities to screen for PFAS.
• AIM for the Mining MSGP – ADEQ has decided not to include AIM requirements in the Mining MSGP, as ADEQ will give permittees time to understand if existing control measures are sufficient to meeting the action levels.

What are my next steps?

To seek coverage under the new MSGP, each facility must submit an NOI and updated SWPPP through the MyDEQ online portal by April 16, 2025. If you have any questions regarding the updates to the AZPDES 2024 MSGP or what actions your facility needs to take to get coverage, please don’t hesitate to reach out to me at akelley@all4inc.com.