Pacific Southwest, Region 9: Superfund
Serving Arizona, California, Hawaii, Nevada, the Pacific Islands, and Tribal Nations
Iron King Mine And Humboldt Smelter
EPA #: AZ0000309013
Congressional District: 01
A fact sheet is now available describing the results of the 2014 sampling of residential yards in Dewey-Humboldt. IKHS Residential Sampling Results 4-15.pdf
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Description and History
NPL Listing History
NPL Status: Final
Proposed Date: 03/19/08
Final Date: 08/03/08
The Site is a combination of sources and releases from two areas: the Iron King Mine and the Humboldt Smelter. A portion of the Town of Dewey-Humboldt is situated between the mine and the smelter. Three waterways (Chaparral Gulch, Galena Gulch, and Agua Fria River) also transect the Site.
The Iron King Mine area covers approximately 153 acres. The majority of this area is covered by tailings and waste rock piles. There are five retention ponds, at least five mine shafts, a collapsed mine shaft (glory hole), and areas of stained soil. The Iron King Mine was an active mine from 1904 until 1969. The mine was expanded in 1936 to remove lead, gold, silver, zinc, and copper from underground. A 140-ton mill was erected to crush ore and was expanded to 225-ton capacity in 1938. A cyanide processing plant was added to the site in 1940 to treat the mill tailings to enhance precious metal recovery. Waste rock and tailings were deposited in large piles adjacent to actual mine property boundaries. More recently, the mine tailings from the site have been used to create fertilizer.
The Humboldt Smelter occupies approximately 182 acres. This area is covered in approximately 763,800 square feet of yellow-orange tailings, over 1 million square feet of grey smelter ash, and 456,000 square feet of slag. The Humboldt Smelter operated from the late 1800s until the early 1960s. The original smelter burned down in 1904 and a smelter that processed 1,000-tons of ore per day was rebuilt in 1906. This smelter operated until 1918 and then intermittently between 1922 and 1927. The smelter reopened in 1930.
Contaminants and Risks
- Surface Water
- Soil and Sludges
The contaminants of concern at this site are arsenic, lead, and sulfate. The primary sources of contamination are:
• Iron King Mine Main Tailings Pile and Impoundment/Ponds
• Iron King Mine Small Tailings Pile
• Humboldt Smelter Ash Pile
• Humboldt Smelter Impoundment/Pond
• Humboldt Smelter Tailings Pile
• Lower Chaparral Gulch
The locations of these source areas are shown on the map titled "Site Map" below. These sources contain average arsenic and lead levels from one to two orders of magnitude greater than average background arsenic and lead levels. Exposure to these metals could present a health risk if a person is in contact with them over a long period of time. EPA recommends that residents, especially children and the elderly, limit or avoid contact with soils and any water in these areas and obey EPA caution signs until these areas can be addressed through cleanup actions. Residents should limit or avoid spending time in Chaparral Gulch as tailings have been deposited along most of its length.
Human Health and Ecological Risk Assessments
EPA conducted a human health risk assessment to evaluate the potential harm to residents posed by site contaminants. The risk assessment indicates that contamination at the site could pose health risks (cancer risks and noncancer hazards) if no cleanup action is taken.
EPA conducted an ecological risk assessment to evaluate whether potential exposure to contaminants could harm plants or animals. The assessment found that contamination poses risks to many plant and animal groups (for example: mammals, birds, reptiles, and aquatic organisms).
The results of the RI indicate a need to take cleanup actions to protect human health and the environment. The next phase in the Superfund process is the Feasibility Study, which focuses on developing cleanup options that will reduce the health risks posed by the site to people, animals, and plants.
A potentially responsible party (PRP)-lead removal action by Ironite was conducted in 2006 to remove contaminated soil from four residential properties. Staff from EPA’s Office of Emergency Response supervised the sampling and removal of the contaminated soil conducted by the PRP’s contractor, Brown and Caldwell.
Portions of this Site were regulated under the Arizona Department of Environmental Quality (ADEQ)’s Voluntary Remediation Program. In September 2007, EPA received a response from Arizona Governor Napolitano consenting to the placement of the Site on the National Priorities List (NPL). On 19 March 2008, EPA formally proposed the Site to the NPL, commonly called the Superfund List.
Placing the site on the NPL allows EPA to use federal resources to conduct cleanup activities at the site, including investigating the sources of contamination and determining what measures may be necessary to protect human health and the environment.
EPA received comments from the community on EPA’s NPL proposal for this Site. EPA reviewed and considered each comment and placed the site on the NPL on September 3, 2008.
During summer 2008, EPA initiated the Remedial Investigation or "RI". The primary objectives of the RI are to determine the nature and extent of contamination and to gather sufficient information so that EPA can select a remedy that eliminates, reduces, or controls risks to human health.
During the course of the RI, 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
- Ground Water – Includes shallow alluvium and deep bedrock ground water
EPA conducted the following tasks as part of the RI:
- Collected over a thousand soil samples in the mine and smelter areas, residential yards, and the Humboldt Elementary School
- Collected background data for site contaminants
- Conducted water quality monitoring at six new groundwater monitoring wells and over 50 private well and tap water locations
- Conducted a storm water evaluation
- Developed volume estimates for waste and tailings piles
- Collected surface water samples along the Agua Fria River, the Galena Gulch, and the Chaparral Gulch
- Conducted air monitoring at ten air monitoring stations for 11 months
- Conducted an Ecological Habitat Survey
- Conducted a Cultural Resource and Historic Building Survey
- Conducted a Wetlands Assessment
- Collaborated with the University of Arizona on three site research projects
- Initiated a Reuse Assessment
The results of the RI are compiled in the RI Report, which is an in-depth document that identifies source areas, defines the nature and extent of contamination, and presents a summary of human health and ecological risks. A copy of the RI Report is available at the Dewey-Humboldt Library and EPA Superfund Records Center and can also be found electronically below. A summary of the RI results is presented in the factsheet dated April 5, 2010, which can also be found below.
Please send any questions or comments on the RI Report to Jeff Dhont, contact information provided below.
Data collected during the RI influences the development of cleanup options for the Site. The detailed development and analysis of cleanup options is called the Feasibility Study. During the Feasibility Study, the advantages and disadvantages of each cleanup method are explored. EPA, working in conjunction with ADEQ, will propose a recommended cleanup option for the Site in the Proposed Plan, which is accompanied with a public comment period. The Feasibility Study is currently underway.
EPA continued investigations in 2013 and 2014 on and near the mine and smelter, as well as in residential yards. These investigations have allowed EPA to better understand contamination at the source area, as well as determine whether levels of metals in soils in residential yards are elevated as a result of past mine and smelter activities. These investigations supplement RI activities conducted by EPA in previous years and will help EPA evaluate cleanup options.
Field work on and near the mine and smelter -
EPA conducted an extensive field investigation at the mine tailings pile, the Chaparral Gulch, smelter, smelter flood plain, and dam in 2014. This field work included installing and sampling from hundreds of new borings, thousands of soils and tailings samples, and installing new groundwater monitoring wells.
Field work in residential yards –
In 2009 and 2010, EPA conducted sampling of soils in almost 200 residential yards near the mine and smelter. In 2014, EPA conducted sampling at a few hundred remaining yards that may have been impacted by the Site in order to complete our investigation of residential yards. EPA has reached out to residents with results from this investigation.
Potentially Responsible Parties
Potentially responsible parties (PRPs) refers to companies that are potentially responsible for generating, transporting, or disposing of the hazardous waste found at the site.
PRPs also include current owners and operators of the site and parties who were owners or operators during a time of disposal.
- As part of the Superfund process, EPA identifies those parties that are "potentially responsible parties" who fall into one or more of the above categories of PRPs, and then may negotiate with the PRPs to perform cleanup activities under EPA oversight and/or help pay EPA's response costs. EPA has conducted a search for parties associated with the Iron King Mine-Humboldt Smelter Superfund Site and on November 19, 2009, issued a General Notice Letter to 14 parties advising them of their status as PRPs under CERCLA.
Documents and Reports
Public Meetings: The EPA recognizes that Americans have the right to be involved in the decisions that affect their lives. EPA’s experience has been that when the public is involved in EPA’s work, the cleanup process results in a better outcome and a more robust remedy.
At the Iron King Mine – Humboldt Smelter Superfund Site, EPA’s Community Involvement Program helps citizens participate throughout the cleanup process, including the investigation phase and the remedy selection phase. The goals of EPA’s Community Involvement Program are to:
1. Provide opportunities for the public to become actively involved
2. Meet the community’s information needs
3. Incorporate issues and concerns into cleanup decisions
4. Give feedback to the public on how their issues and concerns were incorporated into the cleanup work
EPA and ADEQ have a number of ways for the community to become more knowledgeable about and involved with the Iron King Mine – Humboldt Smelter Superfund Site.
Community Involvement Plan
The Iron King Mine – Humboldt Smelter Superfund Site Community Involvement Plan provides a detailed explanation of how EPA and ADEQ will encourage public participation in the cleanup decision-making process. It is a flexible plan that organizes both EPA’s and ADEQ’s efforts but can change based on new community needs. A copy is located at the Dewey-Humboldt Town Library and is also available above.
Community Advisory Group
A Community Advisory Group is stakeholder forum where individuals or those representing groups meet together to learn more about the Superfund cleanup process, and to provide information, issues and concerns to EPA and ADEQ. Membership in the group does not require a technical background.
The CAG is a self-forming and voluntary group. Although EPA and ADEQ do not manage the group, EPA can provide limited support, such as making copies, providing documents, renting meeting rooms, paying for meeting notices, etc. The biggest advantage of a CAG is that it meets regularly and at intervals that are usually far more frequent than EPA’s event-driven meetings. In this way, attendees can get the latest information and can talk directly to EPA and ADEQ representatives.
If you are interested in participating in a CAG, please send an email with your contact information to firstname.lastname@example.org (Note: This e-mail address is managed independently by a Dewey-Humboldt resident and is not associated with EPA).
Technical Assistance Grant Available
EPA awarded a Technical Assistance Grant to the Community Coalition of Dewey-Humboldt, a local non-profit group. The purpose of the Technical Assistance Grant is to promote public participation by providing financial assistance to a community group so it can obtain independent technical assistance. After the independent technical advisor reviews Site related documents, the advisor can help the community formulate its issues and concerns, and communicate them effectively to EPA. On behalf of the community, the Community Coalition of Dewey-Humboldt hired Brian Beck to help the community interpret and comment on Site related cleanup information and decisions.
If you would like to be added to the site mailing list or email list, please contact Amanda Pease (contact information below) or call the toll free hot-line (800) 231-3075 and leave a message with your name and address.
Public Information Repositories
The public information repositories for the site are at the following locations:
Dewey-Humboldt Town Library
2735 N. Corral Street
EPA Site Manager
Mail Code SFD
75 Hawthorne Street
San Francisco, CA 94105
EPA Community Involvement Coordinator
Mail Code SFD
75 Hawthorne Street
San Francisco, CA 94105
EPA Public Information Center
Phoenix, AZ 85007
After Hours (Emergency Response)