ADEQ Hosts Hermosa Mine Air Permit Meeting
South32 seeks changes to natural gas generator and backup engine limits at its Patagonia Mountains project.
Updated on Nov. 13, 2026 in Asthma
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The Arizona Department of Environmental Quality will hold a public meeting on December 10, 2026, on proposed changes to South32 Hermosa's air quality permit. South32 has requested reducing permitted natural gas generators from 58 to 40 and adding four backup engines.
Why it matters
The permit changes would alter how emissions are controlled at the planned Hermosa mine in southeastern Arizona, a project the company says will produce critical minerals. Residents and stakeholders can weigh in before the state decides on the revised permit.
South32 requested reducing permitted 2.6 megawatt natural gas generators from 58 to 40 and adding 4 backup engines. Whether the revision will lower actual emissions over time remains unconfirmed, since the company's projection depends on reduced load bank use and fewer startups and shutdowns.
The players
South32
South32 is a global diversified mining and metals company that acquired the Hermosa project in 2013 through its purchase of Arizona Minerals.
Arizona Department of Environmental Quality
The Arizona Department of Environmental Quality is the state agency that regulates air quality permits and holds the public meeting on the Hermosa permit changes.
The details
South32 says removing the interlock requirement would let engines keep running while people or materials are hoisted underground, eliminating the need to run load banks solely to maintain 75% load. The public can comment on the permit changes and the associated technical documents through December 14.
Timeline
November 13, 2026: Public comment period on permit changes opens.
December 10, 2026: ADEQ public meeting in Patagonia at 6 p.m. at Patagonia Elementary and High School.
December 14, 2026: Public comment period on permit changes closes.
Mineral Supply Context
The Hermosa mine is expected to produce five federally designated critical minerals, including zinc, silver and manganese. Its permit revision therefore arrives as domestic supply of those minerals is a national priority.
Residents near the Hermosa project can submit comments on the proposed generator and backup engine changes through December 14, 2026. The outcome could affect local air quality for people living in Patagonia and nearby communities.
The takeaway
Residents who want a say in the Hermosa air permit can attend the December 10 meeting or submit written comments by December 14, 2026.
What happens next
The public comment period closes December 14, 2026, and the ADEQ public meeting is scheduled for December 10, 2026, in Patagonia.
Further reading
Learn more about air quality and respiratory health in Asthma coverage across Arizona.
Source note: This article includes information reported by Tucson Sentinel.
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