Superfund Information Systems: Site Profile

Superfund Site:

HOMESTAKE MINING CO.
MILAN, NM

Cleanup Activities

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Background

The Homestake Mining Co. (HMC) site is located in Cibola County, New Mexico, about 5.5 miles north of the village of Milan. The site includes a former uranium mill and the impacted portions of the underlying groundwater aquifers. Uranium milling operations began at the site in 1958 under a license issued by the Atomic Energy Commission. The mill was decommissioned and demolished from 1993 to 1995. Site operations and seepage from two tailings impoundments contaminated soil and groundwater with hazardous chemicals. Cleanup at the site is ongoing.

Current Status

EPA is currently performing a groundwater re-assessment at the Site.  The purpose of this re-assessment is to verify if the approved groundwater cleanup standards for the Site based on background is still appropriate.  In 2006, EPA, the Nuclear Regulatory Agency (NRC) and the New Mexico Environment Department (NMED) have approved groundwater cleanup levels for the Site that are higher than safe drinking water standards.  Based on additional information from the work that EPA has completed in the San Mateo basin in the past few years and historic information provided by the community, the EPA is performing this assessment.  Data from this groundwater assessment efforts will help EPA understand the nature of contamination; and provide additional lines of evidence to determine if the background levels of uranium is natural or impacted by milling operation.  EPA has engaged the United States Geological Service (USGS) to perform the investigation related to this work. USGS has published the data on the USGS ScienceBase webpage and plans to publish the findings in a technical journal.  EPA will use this technical report and also seek comments from stakeholders before making any decision regarding the background and cleanup standard at the Site.

Background
Homestake Mining Company (HMC) is located in Cibola County, New Mexico, approximately 5.5 miles north of the Village of Milan, at the intersection of Highway 605 and Country Road 63I. The Site includes the uranium mill site and the impacted portions of the underlying ground water aquifers, known locally as the San Mateo alluvial aquifer and the Upper, Middle and Lower Chinle aquifers.

Uranium milling operations at the Site began in 1958 under a license issued by the Atomic Energy Commission. Operations were originally conducted by two distinct partnerships, the Homestake- Sapin Partners and the Homestake-New Mexico. The Homestake-New Mexico Partnership dissolved in 1961, and the property was ultimately acquired by the Homestake-Sapin Partners. The name of the partnership was changed in 1968 to United Nuclear-Homestake Partners. In 1981, Homestake Mining Company purchased United Nuclear Corporation’s interest, and the name changed to Homestake Mining Company - Grants. On December 4, 2001, HMC merged with Barrick Gold Corporation, and is a wholly owned subsidiary of the Barrick Gold Corporation (NRC 2002).

The large tailings impoundment covers an area of about 200 acres and is approximately 85 - 100 feet high. It contains an estimated 21 million tons of mill tailings. The small tailings impoundment covers an area of about 40 acres and is 20 - 25 feet high. It contains approximately 1.2 million tons of mill tailings. Seepage from the two tailings impoundments has resulted in the contamination of the underlying ground water aquifers.

The current remediation system consists of a groundwater collection and injection system, a 1200 gallons per minute (gpm)reverse osmosis (RO) water treatment facility, a 1500 gpm zeolite water treatment systems, two lined collection ponds, three lined evaporation ponds, a groundwater collection system for areas outside the facility’s licensed boundary and associated equipment and structures.

The primary contaminants and constituents of concern that are present in the ground water at the Site are uranium, selenium, radium-226 + radium-228, thorium-230, chromium, molybdenum, vanadium, sulfate, chloride, nitrate, and total dissolved solids (TDS) (Hydro-Engineering 2006). Radium-226 was the primary contaminant of concern present in the soil.

The major land use immediately proximal to the Site consists of residential development. There are five residential subdivisions located south and southwest of the mill site: Felice Acres, Broadview Acres, Murray Acres, Pleasant Valley Estates, and Valle Verde. Land near the Site is also used for agricultural and livestock purposes. Much of the land immediately surrounding the mill site to the north, east and west has been acquired over the years by HMC, and this property has not been put into use, except for installation of some infiltration trenches as a part of the ground water restoration program.

The Site consists of three operable units (OUs). OU1 addresses groundwater restoration; OU2 addresses long-term tailings stabilization, surface reclamation and site closure; and OU3 addresses radon concentrations in the neighboring subdivisions. EPA issued a No Action ROD for OU3 in 1989 and is currently performing a CERCLA equivalency for OU1 and OU2. EPA planst to issue a ROD for OU1 and OU2 after it completes the CERCLA equivalency.

Homestake is performing remediation under the NRC's authority for license terminaion and concurrently with CERCLA oversight from EPA. EPA has signed a Memorandum of Understanding with NRC to perform CERCLA oversight.

Benefits
The initial action to connect the nearby residences to the municipal water supply provided a safe drinking water supply. In addition, the study on indoor radon levels showed that site contamination was not contributing to elevated indoor radon levels found in some area homes.
The contaminant plume has receded back almost 3/4 mile into the site boundaries of HMC by injecting fresh water down-gradient of the site. Nearly 4.5 billion gallons of contaminated water have been removed and 540 million gallons of treated water has been injected into the aquifer. The NRC is requiring that the Corrective Action Plan include clean-up of off-site contamination and require that the license be amended accordingly as well.
Reverse gradient injection has assured that contaminants in the ground water would not expand into the shallow aquifer, thus making the shallow water potentially usable in the down gradient areas. Once the tailings piles have been closed, the site will be transferred to DOE under general license.

NPL LISTING HISTORY
Site HRS Score: 35.21
Proposed Date: 12/30/82
Final Date: 9/08/83
NPL Update: Original

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What Has Been Done to Clean Up the Site?

The site is being addressed through federal, state and potentially responsible party (PRP) actions. The U.S. Nuclear Regulatory Commission (NRC) is the lead agency for the site.

The initial action to connect nearby residences to the municipal water supply provided a safe drinking water supply. In addition, the study on indoor radon levels showed that contamination was not contributing to elevated indoor radon levels found in some area homes.

The contaminant plume has receded back almost three-quarters of a mile into the site boundaries of HMC by injecting fresh water downgradient of the site. Nearly 4.5 billion gallons of contaminated water have been removed and 540 million gallons of treated water have been injected into the aquifer.

The NRC is requiring that the Corrective Action Plan include cleanup of off-site contamination and that the license be amended accordingly. Reverse gradient injection has ensured that contaminants in the groundwater will not expand into the shallow aquifer, thus making the shallow water potentially usable in the downgradient areas. Once the tailings piles have been closed, the site will be transferred to the Department of Energy (DOE) under general license.

EPA has conducted five-year reviews at the site. These reviews ensure that the remedies put in place protect public health and the environment, and function as intended by site decision documents. The most recent review concluded that response actions at the site are in accordance with the remedy selected by EPA and that the remedy, exclusive of OU-3, continues to be protective of human health and the environment. The protectiveness determination for OU-3 was deferred pending completion of EPA’s ongoing risk assessment. The five-year review also identified a number of issues and recommendations for each of the OUs at the site.

 

Uranium milling operations began in 1958 under a license issued by the Atomic Energy Commission. Operations were originally conducted by two distinct partnerships, the Homestake-Sapin Partners and the Homestake-New Mexico partnerships. The Homestake-New Mexico Partnership dissolved in 1961; the property was ultimately acquired by the Homestake-Sapin Partners. The name of the partnership was changed in 1968 to United Nuclear-Homestake Partners. In 1981, Homestake Mining Company purchased United Nuclear Corporation’s interest, and the name changed to Homestake Mining Company-Grants. In December 2001, HMC merged with Barrick Gold Corporation, and is a wholly-owned subsidiary of the Barrick Gold Corporation.

The mill was decommissioned and demolished from 1993 to 1995. The large tailings impoundment covered an area of about 200 acres and was about 85 to 100 feet high. It contained an estimated 21 million tons of mill tailings. The small tailings impoundment covered an area of about 40 acres and was 20 to 25 feet high. It contained about 1.2 million tons of mill tailings. Seepage from the two tailings impoundments has resulted in the contamination of the underlying groundwater aquifers.

Uranium milling operations began in 1958 under a license issued by the Atomic Energy Commission. Operations were originally conducted by two distinct partnerships, the Homestake-Sapin Partners and the Homestake-New Mexico partnerships. The Homestake-New Mexico Partnership dissolved in 1961; the property was ultimately acquired by the Homestake-Sapin Partners. The name of the partnership was changed in 1968 to United Nuclear-Homestake Partners. In 1981, Homestake Mining Company purchased United Nuclear Corporation’s interest, and the name changed to Homestake Mining Company-Grants. In December 2001, HMC merged with Barrick Gold Corporation, and is a wholly-owned subsidiary of the Barrick Gold Corporation.

The mill was decommissioned and demolished from 1993 to 1995. The large tailings impoundment covered an area of about 200 acres and was about 85 to 100 feet high. It contained an estimated 21 million tons of mill tailings. The small tailings impoundment covered an area of about 40 acres and was 20 to 25 feet high. It contained about 1.2 million tons of mill tailings. Seepage from the two tailings impoundments has resulted in the contamination of the underlying groundwater aquifers.

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What Is the Current Site Status?

The site consists of three areas, referred to by EPA as operable units (OUs). OU-1 addresses the restoration of groundwater contaminated by tailings seepage. OU-2 consists of the long-term stabilization of the tailings, surface reclamation, and decommissioning and closure of the mill. OU-3 addresses indoor and outdoor radon concentrations in residential areas next to the mill site.

The long-term remedy consists of a groundwater collection/injection system for the San Mateo Alluvial aquifer and the Upper and Middle Chinle aquifers, tailings collection wells within the tailings impoundment, a tailings impoundment toe drain, a 1200 gpm reverse osmosis (RO) treatment plant, a zeolite treatment system and three evaporation ponds. Remedy construction finished in 1996. The collection wells, tailings wells and the toe drains have recovered over four billion gallons of contaminated groundwater since 1977.

An average of two feet of contaminated soil was removed from the mill area and placed in the tailings impoundments. The completion of the final radon barrier and all other reclamation activities to secure the large tailings impoundment is scheduled for 2014. The completion of the final radon barrier and all other reclamation activities for containment of the small tailings impoundment are scheduled for September 2017

EPA is currently performing a groundwater assessment at the Site. The purpose of this assessment is to verify if the approved groundwater cleanup standards for the Site, based on historical levels, are still appropriate. In 2006, EPA, the Nuclear Regulatory Commission (NRC) and the New Mexico Environment Department (NMED) approved groundwater cleanup levels for the Site that are higher than safe drinking water standards. Based on additional information from the work that EPA has completed in the San Mateo basin in the past few years and historic information provided by the community, the EPA is performing this assessment. Data from this groundwater assessment efforts will help EPA understand the nature of contamination and provide additional lines of evidence to determine if the background levels of uranium is natural or impacted by milling operation. EPA has engaged the United States geological Survey (USGS) to perform the investigation related to this work.

EPA is also working with the Bluewater Valley Downstream Alliance (BVDA), a community organization, and providing assistance through the Technical Assistance for Superfund Communities (TASC) and Technical Assistance Grant (TAG) programs. The TASC and TAG programs will provide technical assistance to the community in reviewing technical reports.

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Emergency Response and Removal

Cleanup has also included removal actions, or short-term cleanups, to address immediate threats to human health and the environment. In 1985 and 2009, HMC provided an alternative water supply to nearby residents. EPA also installed radon mitigation systems in homes where indoor radon exceeded the EPA guidance level. The source of radon is still unknown.

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