Revised On: Sept. 11, 2023 - 8:14 p.m.

2023: EPA issued the Proposed Plan in March, public comment period was open from March to May, and the Public Hearing for the Proposed Plan was held on March 29, 2023. EPA issued the Record of Decision in October. 

2022: EPA issued the feasibility study in September, providing alternatives for cleanup options. 

2021: EPA drafted the feasibility study, which is a study of options to clean up the contamination at the former Iron King Mine property and the former Humboldt Smelter property.

2020: EPA issued a Reuse Assessment of the Former Smelter Property.  The reuse assessment summarizes information gathered during interviews, public input and background research in order to help inform the evaluation of the Superfund cleanup approaches. 

2019 – 2020: EPA placed many additional warning signs on or near the former Iron King Mine property and the former Humboldt Smelter property. These signs warn of toxic hazards and some also warn of unstable structures.

2019: In order to control dust at the smelter property, EPA applied a stabilizing cover material called Posi-Shell® on top of the contaminated dross material at the north end of the smelter property. 

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.

2016: EPA completed the Final Remedial Investigation Report in September.

2014 – 2015: EPA completed the evaluation and investigation of over 600 residential properties.

2013: Field activities for the RI addendum included emergency response action sampling for future remediation of several residential properties and extensive sampling for background study and dispersion of contaminants from the smelter. A site-wide sampling plan to address all areas of tailing deposits, smelter materials and gulch sediments was implemented with preliminary field investigations. The installation and sampling of new groundwater wells are planned to determine the conditions and overall stability of the main tailings pile.

2012: The ATSDR and ADHS offered blood lead screening events to the Dewey-Humboldt community on April 19 and May 21. The screening was conducted in response to concerns expressed by parents about potential toxins related to the Iron King and Humboldt Smelter Superfund site. Children younger than 6 and pregnant women were especially encouraged to get the screenings. No children under the age of 6 included in the recent Dewey-Humboldt community testing exceeded the 5 micrograms per deciliter (ug/dl) recommended blood lead level. The Centers for Disease Control & Prevention (CDC) recently adopted a new reference value for children under 6 years old, which decreased to 5 micrograms per deciliter (µg/dl) from 10 µg/dl. Additional data was collected to evaluate the stability of the Iron King Mine Main tailings pile. Preliminary results indicated the tailings pile volume as approximately 3.2 million cubic yards (instead of the original estimate of 6.4 million cubic yards). The results and analysis will be included in the RI addendum. The EPA began evaluating naturally occurring metals in the area. In-situ x-ray fluorescence (XRF) level results were measured and shallow soil samples were collected throughout the Dewey-Humboldt area. The assessment area extended approximately 20 square miles (5 miles east to west and 4 miles north to south). The XRF and soil data analysis results will assist in determining contaminant (metals) background concentrations at the site. Once the soil data has completed validation, results will be provided to the residents whose properties were sampled. The sampling event analytical results will be part of the RI addendum. The EPA installed four additional groundwater wells at the Iron King Mine tailings pile and two wells down-gradient of the mine. These groundwater wells will provide more information on the groundwater arsenic concentrations at, and down-gradient, from the Iron King Mine main tailings pile. The sampling event analytical results will be part of the RI addendum.

2011: The EPA completed interim removal, control and improvement actions. Three primary objectives were completed between September and November: Eleven residential yards were stripped of soil, received up to two feet of clean soil backfill and restored to their original condition. These residential yards contained elevated levels of arsenic and lead. The removed soil was placed on the Iron King Mine’s Main tailings pile. Hydro-seed was added on top of the soil to encourage vegetation growth and to act as a temporary dust suppressant. The small tailings pile, located adjacent to the Chaparral Gulch, was relocated to a designated area on top of the Iron King Main tailings pile. More than 20,000 cubic yards were moved. Upon placement of the small tailings pile in the storage area, Gorilla Snot®, a temporary soil sealant was applied to the relocated material to act as a temporary dust suppressant. The former small tailings pile location area was restored to a natural drainage pathway. A soil sealant was applied to the ash piles at the Humboldt Smelter. The final report documenting the removal action is available in the information repository, as well as on EPA website.

2010: By March, the RI was completed. EPA identified five areas of interest (AOI): Iron King Mine (includes the Iron King Mine proper area, Iron King Mine operations area, former fertilizer plant area, salvage yard and ancillary associated properties), Humboldt Smelter (includes several abandoned buildings, a smelter stack, a tailings pile, a smelter ash pile and a slag pile), Waterways (includes the Chaparral Gulch, Galena Gulch, Agua Fria River and adjoining drainage channels and outfalls), In-Town Soil (includes residential, background and ancillary properties), Groundwater (includes shallow alluvium and deep bedrock groundwater). A remedial alternatives evaluation and a closure cover alternatives evaluation for the Iron King Mine main tailings pile were also completed.

2009: Additional RI sampling was conducted during April. Technical documents completed in 2009 included a reuse assessment, a cultural resource and historical buildings survey, a biological evaluation, and a riparian evaluation/jurisdictional determination of the lower Chaparral Gulch. A data validation report for sample analysis results was also completed.

2008: On September 3, the EPA listed the site on the National Priorities List (NPL). A community site kick-off meeting was held in Dewey-Humboldt on August 20th, and the first remedial investigation (RI) sampling round began. The primary RI objectives included assessing the nature and extent of contamination and to gather sufficient information so that EPA could select a remedy that eliminates, reduces, or controls risks to public health. Sampling included soil, sediment, groundwater, surface water and air.

2006 – 2007: North American Industries performed removal action of tailings impacted soil from four residential properties in the vicinity of the Ironite property and Chaparral Gulch under an Administrative Settlement Agreement and Order on Consent with EPA effective in May. Work was started in July and completed in May 2007. An expanded site inspection report was completed on October 31, for the Iron King Mine and Humboldt Smelter area by the ADEQ site assessment unit. Samples were collected at 12 drinking water wells including the main and backup wells for the Humboldt Water System as well as 10 private domestic wells. Arsenic concentrations were found to be above the EPA maximum contaminant level of 10 parts per billion (ppb) in a majority of the samples collected.  

2005: The Superfund Technical Assessment and Response Team (START) performed a removal assessment of 16 residential properties and one horse pasture along the Chaparral Gulch at the request of ADEQ. The assessment objective was to determine the level of arsenic and lead in soils due to erosion from tailings. There were 153 surface locations and 17 subsurface locations that were evaluated. Sample results were compared to the previously established background arsenic and lead concentrations.

2004: A PA/SI report was completed at the Humboldt Smelter and other areas by ADEQ. Samples were collected at the ore pile, evaporation pond, assay lab discharge pipe, large ash pile, gray ash, large tailings pile, retention basis, school yard and two private residences. Samples were analyzed for semi-volatile organic compounds (SVOCs), metals and cyanide. No SVOCs were detected, but elevated levels of arsenic and other metals were present.

2003 – 2005: Aquatec operated a permitted septage treatment facility on the former fertilizer plant site, previously operated by Ironite Products Company and located within the boundary of the former Iron King Mine.

2003: Greenfields Enterprises purchased the Humboldt Smelter property. Previous tenants included an aluminum recycling facility, wooden shed manufacturer, sawmill and Humboldt Precast. No operations are currently active at the smelter property. Ironite Products Company entered into the ADEQ voluntary remediation plan (VRP) as a result of the 2002 PA/SI which found that additional investigation of the site was needed.

2002: A Preliminary Assessment/Site Inspection (PA/SI) report was completed for the Iron King Mine and tailings by the ADEQ Site Assessment Unit. Surface and subsurface soil samples were collected at 21 locations including the large tailings pile, ponds, Ironite plant area, former assay laboratory, former mill site, former fertilizer plant and nearby school. The conclusions were that heavy metals, including antimony, arsenic, cadmium, lead and mercury met observed release criteria and exceeded EPA and state benchmarks as documented sources of contamination and have been released to sediments in the Chaparral Gulch. Further study and evaluation was recommended. Kuhles Capital acquired the Iron King Operations property including the laboratory and Glory Hole. Kuhles received a solid waste permit to operate a waste reduction and recycling facility at the former Glory Hole.

1974: Ironite Products Company (now North American Industries) purchased 85 acres of the former Iron King Mine consisting mainly of the tailings area and included an administrative building, a warehouse and process facilities. Ironite Products Company mixed mine tailings with sulfuric acid, urea and water to produce a fertilizer marketed as Ironite.

Late 1800s – 1969: The Humboldt Smelter operated from the late 1800s until 1969. The original smelter burned down in 1904 and was rebuilt in 1906. Ore from the Iron King Mine may have been processed at the Humboldt Smelter during this time period.

The Iron King Mine operated from the late 1800s until the early 1960s and was a periodically active mine for gold, silver, copper, lead and zinc. The mine was expanded in 1936 to remove metals from underground. In 1938, a 140-ton mill was erected to crush ore and expanded to 225-ton capacity. In 1940, a cyanide processing plant was added to the site to treat the mill tailings and enhance precious metal recovery.