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Superfund Site | Iron King Mine - Humboldt Smelter

Superfund Site

Iron King Mine - Humboldt Smelter

Revised on: May 22, 2023 - 1:22 p.m.

EPA#: AZ0000309013

Superfund National Priority List (NPL) Placement: Sept. 3, 2008


The former Iron King Mine and Humboldt Smelter are located in the town of Dewey-Humboldt, Yavapai County, Arizona.

Bordered by Chaparral Gulch to the north and Galena Gulch to the south, the former Iron King Mine encompasses approximately 153 acres west of State Route 69. The former Humboldt Smelter area occupies approximately 182 acres east of State Route 69, including an area along Chaparral Gulch and the property at the east end of Main Street in the town of Dewey-Humboldt | View Site Map >

Contaminants of Concern

Soil I Arsenic, Lead, and other heavy metals

Groundwater | Arsenic, lead, and other heavy metals

  • We encourage you to test the well water if you have a private well near the exceedance.
  • Not sure what to test for? | Learn More >

COCs at the site may change as new data become available.

Action Taken

In 2008, the U.S. Environmental Protection Agency (EPA) initiated a remedial investigation (RI) with the primary objectives of determining the nature and extent of contamination and gathering information to select a remedy that eliminates, reduces or control risks to public health. EPA collected soil, sediment, surface water, groundwater and air samples from the Iron King Mine, Humboldt Smelter, residential and commercial areas, and waterways (Chaparral Gulch, Galena Gulch and Agua Fria River). The results from the RI indicated a need for cleanup actions to protect public health and the environment.

Between 2011 and 2012, EPA completed a removal action that included the cleanup of a subset of residential yards, the removal of the Iron King Mine small tailing pile adjacent to the Chaparral Gulch, and application of a soil sealant to the Humboldt Smelter dross piles. EPA also evaluated background levels of arsenic and lead in the area and continues to evaluate groundwater at the site.

Between 2013 and 2014, EPA continued investigations on and near the mine and smelter, and within residential yards to better understand contamination at the source areas. 

Between April and July in 2017, EPA cleaned up surface soils in 31 residential yards in Dewey-Humboldt that had soils contaminated with lead and/or arsenic from the former mine and smelter activities after investigating, sampling and evaluating over 600 properties. For further information, please refer to EPA's fact sheet dated August 2017.

Between November 2021 and June 2022, ADEQ conducted a project, in coordination with EPA, to take down the Humboldt Smelter Stack, install fencing on the Humboldt Smelter area, and mitigate dust by application of soil sealant to the Humboldt Smelter dross. For more information on the Humboldt Smelter Project I | Visit Page >


EPA has completed the feasibility study and proposed a plan that presents the alternatives or options feasible to cleanup the site. As part of the proposed plan process, EPA held a public hearing on March 29, 2023, and an open public comment period for 60 days from March 15 to May 13, 2023.  ADEQ will be supporting EPA by assisting in field work activities that will help EPA design the cleanup action.  ADEQ will have crews in the area assessing land conditions, collecting soil samples, and visually inspecting various areas near the mine and smelter and surrounding properties.  Workers may be intermittently on the site or in town until the end of 2023. Any noise and/or dust issues are expected to be minimal. Permission to access private properties has been given by respective landowners.

If necessary, ADEQ will use dust suppression during these activities.  In addition, ADEQ will repair any damage it may cause to the protective covering (called Posi-Shell) that has been placed on top of the dross waste at the smelter, to make sure it remains effective.  The cover forms a hard crust that keeps the waste from entering the air on an interim basis until the final cleanup is performed.

After EPA considers the information submitted during the public comment period, they will select the cleanup option for the site. That cleanup option selected will be documented in the next process step of the Record of Decision, which details the remedial action they will conduct to remediate the site. EPA is working to complete the Record of Decision by the end of 2023.