Superfund Information Systems: Site Profile

Superfund Site:


Health & Environment

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What Are the Risks at the Site?

The potential risks at the site include, contaminated groundwater and contaminated fugitive dust that could impact human health and surface water. Additional concerns include on-site contaminated surface water (which could impact wildlife), and physical hazards associated with abandoned buildings, debris, and unstable materials such as the waste rock, heap leach and tailings piles, and pit lake slopes. 

Groundwater: In the late 1970’s, the U.S. Geological Survey (USGS) described a groundwater plume of arsenic, cadmium, cobalt, copper, iron, lead, manganese, mercury, molybdenum, selenium, and zinc below the site and migrating northward. The shallow aquifer is contaminated with acidic process waters and metals potentially from the process areas, evaporation ponds, and leaking heap leach pads and tailings piles. Intermediate and deep aquifers may be degraded, and the aquifers may be interconnected.  

Also, research conducted by the BLM in 2003 showed knowledge of technologically enhanced naturally occurring uranium (TENORM) on the site. Testing in 2004 by ARC confirmed the presence of uranium in off-site domestic wells located north and west of the mine and in soil samples from the process area. The uranium in the off-site domestic wells may be due to either contaminant migration from the site or due to naturally occurring uranium in the area. A series of groundwater monitoring wells have been installed to better determine the source of the uranium.  

During EPA's September 2009 public meeting in Yerington, Nevada, and in subsequent public meetings, EPA provided information on groundwater conditions near the former mine site. Our current information shows that shallow groundwater contamination from the mine has migrated past the of the northern boundary of the property.  This contamination does not impact the City of Yerington Water System or the Yerington Paiute Water System, which are tested regularly and are in compliance with federal drinking water standards. Domestic wells north and west of the mine site that exceed the federal drinking water standard for uranium where provided bottled water by ARC until the City extended their water service to serve those locations. The Groundwater Remedial Investigation examined and differentiated the mine-related contamination from naturally occurring contamination and contamination from other sources. The groundwater studies have now been completed.   

Fugitive Dust: High wind events combined with a semi-arid environment contribute to occasional erosion of the mine tailings piles, creating potentially contaminated fugitive dust blowing off of the site. In 2004, ARC installed ambient air monitoring equipment to evaluate fugitive dust concerns. ARC sampled particulate matter with an aerodynamic diameter less than 10 microns (PM10), total suspended particulates (TSP), metals, and radionuclides at the site perimeter from 2005 to 2008. The air monitoring program evaluated air quality impacts from fugitive dust using EPA-approved sampling methods. In an effort to reduce fugitive dust from blowing off of the site, EPA capped and sealed approximately 125 acres of potentially contaminated soil in 2006. During the capping, additional air monitoring was conducted to ensure that capping procedures did not produce additional fugitive dust. In early 2007, ARC upgraded the ambient air monitoring equipment to better characterize the high wind events and associated air pollutant concentrations. The air monitoring program was temporarily discontinued on April 1, 2008 and ARC has submitted the results to EPA for review. ARC conducted a baseline human health risk assessment in 2010 to determine, under current conditions, how potential for adverse health effects from the inhalation of dust at the boundary of the mine site compares to regulatory guidelines and to evaluate risk associated with natural background.  

In April 2009, ARC signed an agreement with EPA to minimize the migration of dust from the lined and unlined evaporation ponds. ARC submitted a Dust Suppression Plan to EPA, proposing the application of a dust suppressant to the ponds to reduce the emission of dust. EPA approved the Dust Suppression Plan, Revision 1, in June 2011. ARC completed the application of the dust suppressant to an area within the Process Area to minimize the emission of dust from the area where a removal action was completed in late 2010. In addition, ARC began applying the dust suppressant to the unlined evaporation pond in July 2011. The dust suppression work will be completed by the end of 2011. The dust suppressant application to the lined and unlined evaporation ponds is a temporary measure being implemented until EPA and ARC agree on an interim cover design for these areas.  

Surface Water: There are several areas of surface water on the site that could pose a threat to wildlife and potentially groundwater resources. These areas include the Pit Lake, four Arimetco heap leach drainage fluids collection ponds, three ARC pumpback collection ponds, water collecting in low lying areas of Anaconda lined and unlined evaporation ponds, and parts of the sulfide tailings area during rain events. These areas are primarily contaminated with heavy metals and low pH levels. ARC completed initial characterization of the lined and unlined evaporation ponds in October 2008 and took interim measures to provide a cover for these areas as described above. ARC has also been monitoring wildlife since March 2007 and operating bird deterrent systems at the site's evaporation ponds and the Arimetco ponds since September 2008.  

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Contaminant Information

Primary Contaminants of Potential Concern 

Metals: Aluminum, Arsenic, Beryllium, Boron, Cadmium, Chromium, Copper, Iron, Lead, Manganese, Mercury, Molybdenum, Nickel, Selenium, Uranium, Zinc 

Radioisotopes: Uranium-234, Uranium-235, Uranium-238, Thorium-230, Thorium-232, Radium-226, Radium-228 

Others: Chloride, Sulfate, low pH (acidic) conditions, and particulate matter 

View a full list of contaminants of concern for this site.

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Performance Measures

EPA uses performance measures to track environmental results at Superfund sites. If you have any questions or concerns about the measures at this site, please contact the site team members listed under Site Contacts.

Read more about Superfund Remedial Performance Measures.

Status at this
Superfund Site
What does this mean?
Human Exposure Under Control Insufficient Data Yes means assessments indicate that across the entire site:
  1. There are currently no unacceptable human exposure pathways; and
  2. EPA has determined the site is under control for human exposure.

No means an unsafe level of contamination has been detected at the site and a reasonable expectation exists that people could be exposed.

Insufficient data means that, due to uncertainty regarding exposures, one cannot draw conclusions as to whether human exposures are controlled, typically because:
  1. Response to the contamination has not begun; or
  2. The response has begun, but it has not yet generated information sufficiently reliable to evaluate whether there are currently any unacceptable human exposure pathways at the site.
Groundwater Migration Under Control Insufficient Data

Yes means EPA reviewed all information on known and reasonably expected groundwater contamination. EPA concluded the migration of contaminated groundwater is stabilized and there is no unacceptable discharge to surface water. EPA will conduct monitoring to confirm that affected groundwater remains in the original area of contamination.

No means EPA has reviewed all information on known and reasonably expected groundwater contamination, and the migration of contaminated groundwater is not stabilized.

Insufficient data means that due to uncertainty regarding contaminated groundwater migration, EPA cannot draw conclusions as to whether the migration of contaminated groundwater is stabilized.

Construction Complete No

Yes means the physical construction of the cleanup is complete for the entire site.

No means either physical construction is not complete or actions are still needed to address contamination.

Sitewide Ready for Anticipated Use No Yes means:
  1. All cleanup goals affecting current and reasonably anticipated future land uses of the entire site have been achieved, so there are no unacceptable risks;
  2. All required land-use restrictions or other controls have been put in place; and
  3. The site has achieved Construction Complete status.

No means that one or more of these three criteria have not been met. However, a site listed as no may still have redevelopment occurring on portions of the site and may be eligible for additional redevelopment.

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