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Humboldt Smelter Project




Contaminants of Concern (COCs): 

Concern for public safety is the reason for the work conducted for this project. Please refer to the Iron King Mine-Humboldt Smelter Superfund Site webpage for information on contaminants of concern | Visit Page >


The Humboldt Smelter portion of the Iron King Mine-Humboldt Smelter Superfund Site operated from the late 1800s until 1969. The structure that had been most visible from a distance, prior to the 2022 dismantling activities, was the tall brick smokestack (circa 1917) remaining from past smelter operations. The smokestack consisted of an attached rectilinear brick converter flue on elevated steel reinforced concrete piles. The converter flue measured approximately 140 feet long prior to its partial collapse in 2021. The large portion of the converter flue that collapsed caused destabilization of the structure and raised concern for public safety. According to a 2008 Cultural Resource and Historic Building Survey, the smokestack measured approximately 156 feet by 18 feet and was elevated 30 feet above ground level.

The surrounding area to the smokestack and flue remains contaminated with chemical hazards from formerly mined metals. The Humboldt Smelter area contains fencing and signage to warn trespassers not to enter the area. The Arizona Department of Environmental Quality (ADEQ) and the United States Environmental Protection Agency (EPA) continue to advise people to avoid the area and follow the posted warning signs.

Project Activities:

In January 2022, ADEQ, in coordination with the EPA, completed the careful dismantling of the smelter smokestack and what remained of the attached converter flue on the Humboldt Smelter portion of the Iron King Mine-Humboldt Smelter Superfund Site. Dust control measures were implemented and air quality monitoring showed no PM2.5 or PM10 exceedances during the takedown activity. This work was completed in accordance with the Humboldt Smelter Project Work Plan | View Work Plan >

Upon completion of the smelter dismantling, all brick debris was consolidated in place around the stack foundation and encapsulated utilizing sprayed concrete. Additional fencing was installed within the smelter plateau to further deter trespass. Finally, due to the overall condition of the remaining existing dust-control cover (Posi-Shell®) at the site, ADEQ repaired all of the existing Posi-Shell®  at the former Humboldt Smelter property to help minimize further weathering and degradation.

The Humboldt Smelter Project was completed in April 2022 and a Community Update was provided to stakeholders | View Community Update >

ADEQ’s Stack Demolition and Fencing Completion Report documents the activities conducted during takedown, the monitoring completed throughout the project, and presents the data collected during the project | View Report >

Tetra Tech created a time-lapse video of the dismantling of the smelter smokestack and converter flue | Watch Video >

For more information, see the project documents listed on the sidebar under SEE MORE.


The Humboldt Smelter Project is complete.

This page will be archived on October 31, 2022.  Information on the Humboldt Smelter Project will still be available for review through the ADEQ Records Center | Learn How >