On September 10, 2025, the U.S. Environmental Protection Agency (EPA) announced a major regulatory shift, granting the State of Arizona primary enforcement authority, or "primacy," over all classes of underground injection wells within its borders. This decision transfers regulatory power for the federal Underground Injection Control (UIC) program from the EPA to the Arizona Department of Environmental Quality (ADEQ). While UIC primacy is usually focused on Class VI wells for carbon capture and storage (CCS), this ruling is most critical for Arizona’s long-term water management and resource protection.