EPA Finalizes Arizona SO2 Attainment Plan for Hayden Area
The agency approved Arizona's state plan for cutting sulfur dioxide pollution around the Hayden smelter area, effective September 21, 2026.
The Environmental Protection Agency finalized approval of Arizona's state implementation plan for bringing the Hayden sulfur dioxide nonattainment area into compliance with the 1971 and 2010 SO2 national air quality standards. The plan covers the Clean Air Act elements required for nonattainment areas: an attainment demonstration, reasonable further progress toward the standards, reasonably available control measures and technology, base-year and projection-year emissions inventories, new source review requirements, emissions limits needed to reach attainment, and contingency measures.
The approval closes out a lengthy state rulemaking process tied to the plan. Arizona's regulatory review council approved the underlying Hayden lead and SO2 rules on December 2, 2025, and the state submitted the finalized package to its Secretary of State on December 9, 2025. Those rules were published in the Arizona Administrative Register on January 2, 2026, with a state effective date of February 7, 2026, though the codified version had not yet appeared in the Arizona Administrative Code.
The plan also folds in earlier amendments to standards governing existing primary copper smelters, which sunset once a related site-specific rule takes effect. Those amendments were submitted to EPA in 2017, and the agency found them administratively complete that same year.
Public comment on the proposal ran from March 4, 2026, to April 3, 2026, drawing one submission from a member of the public and a supportive letter from Asarco, which operates the Hayden smelter. Because Asarco's comment backed the proposed approval, EPA did not need to respond to it substantively.
The rule takes effect on September 21, 2026. Parties seeking judicial review must file a petition with the appropriate U.S. Court of Appeals by October 19, 2026.
Source: Federal Register, EPA final rule, published 2026-08-20.