On September 10, 2025, the U.S. Environmental Protection Agency (EPA) announced a final rule granting Arizona primacy to administer all classes of underground injection wells under the Safe Drinking Water Act (SDWA). This decision transfers authority for permitting and oversight of the Underground Injection Control (UIC) program from EPA to the Arizona Department of Environmental Quality (ADEQ).
The UIC program safeguards underground drinking water sources by regulating six classes of wells, from hazardous waste disposal (Class I) to carbon capture and storage (Class VI). States may obtain primacy if they demonstrate their program meets federal requirements.
EPA’s approval followed a detailed technical and legal review of Arizona’s application and determined that ADEQ has the resources and statutory authority to implement the program consistent with SDWA.
Comprehensive Authority: ADEQ now regulates permitting, compliance, and enforcement for all six well classes in Arizona. EPA will retain oversight for wells on Indian lands, except for Class II wells on Navajo Nation lands, where primacy already exists.
Carbon Capture and Storage: Arizona gains authority over Class VI wells, enabling the state to support carbon capture and storage projects that are central to climate and energy strategies.
Hazardous Waste Disposal: Oversight of Class I wells underscores Arizona’s responsibility to manage hazardous waste operations safely and protect groundwater.
In a news release, EPA Administrator Lee Zeldin called the decision a win for “efficient and effective permitting,” balancing groundwater protection with energy development. Governor Katie Hobbs noted that this authority would allow Arizona “to safeguard the integrity of our groundwater, while also supporting responsible economic growth and clean energy development.” Governor Hobbs further observed that EPA’s grant of primacy provides Arizona with “the tools to lead on sustainable environmental management and innovation for years to come.”
Describing it as a “major milestone,” ADEQ Water Quality Division Director Trevor Baggiore commented that with primacy, Arizona “can make decisions faster and tailor oversight to Arizona’s unique groundwater conditions to better protect our water resources.”
Arizona’s congressional delegation praised the move as well, citing faster permitting timelines, greater flexibility, and increased investment certainty for industries considering carbon capture, energy, and manufacturing projects.
Implications for Regulated Entities
Streamlined Permitting: Localized oversight may reduce delays tied to federal processes.
Tailored Oversight: ADEQ can adapt requirements to Arizona’s specific hydrogeology and industry needs.
Federal Backstop: EPA will continue supervisory oversight to ensure compliance with SDWA.
Arizona is now the fifth state since 2018 to secure primacy for Class VI wells, signaling a broader trend toward state-led oversight of underground injection. With primacy in place, Arizona is positioned to play a leading role in balancing groundwater protection with energy development and carbon management.
Companies considering projects involving underground injection should monitor ADEQ’s forthcoming guidance on implementation and be prepared to align compliance strategies with new state-level oversight.
