Anaconda Copper Mine, Lyon County, Nevada

On February 5, 2018, the EPA deferred listing the Anaconda Copper Mine Site (Site) on the EPA National Priorities List.  Going forward, NDEP will directly oversee Site investigation and response actions.  The complete Deferral Agreement document between the EPA and NDEP is attached below.  In addition to executing the Deferral Agreement, the NDEP and Atlantic Richfield Company (ARC) also entered into a legally binding agreement on February 5, 2018 called the Interim Administrative Settlement Agreement and Order on Consent (IAOC).  The IAOC requires ARC, under NDEP regulatory oversight, to complete interim fluid management and complete construction of a long-term remedy for the former Arimetco portion of the Site. The IAOC also requires ARC to complete a site-wide remedial investigation/feasibility study to evaluate options for long-term management of the Site.  The complete IAOC document is also attached below.

Complete Deferral Agreement

Interim Administrative Settlement Agreement and Order on Consent (IAOC)

IAOC Appendix A:  Site Map Depicting the Closure Management Units (CMUs)

IAOC Appendix B: Statement of Work for Site-Wide Remedial Investigation and Feasibility Study

IAOC Appendix C: Statement of Work for Remedial Design/Remedial Action of CMUs 2, 4, 5, 6, & 7

IAOC Appendix D: Arimetco Heap Leach Fluid Management System Operations and Maintenance Work Plan

IAOC Appendix E:  Interim Record of Decision, July 2017 - Arimetco Facilities Operable Unit 8

IAOC Appendix F:  Insurance Policy Approved for Financial Assurance


The following is a history of this site:

What is the Anaconda Copper Mine Site?

The approximately 3,400 acre Anaconda Copper Mine Site (Site) is a former copper mine located west of the City of Yerington, in Lyon County, Nevada. The Site includes both private and public lands managed by the Bureau of Land Management. Since the Site was abandoned in 2000, EPA and NDEP have been addressing environmental concerns and working toward long-term closure.

Brief chronology of Site ownership and operations:

1800s: Copper discovered in Yerington District

Early 1900s: Large-Scale exploration of Copper system by Empire-Nevada Copper

1941: Anaconda Copper Mining Company acquired property

1952: Anaconda Copper Company (Anaconda) initiates mining and milling operations at the Site, producing 1.7 billion pounds of Copper

1978: Anaconda was acquired by Atlantic Richfield Company (ARC), now a subsidiary of BP.

1982: Don Tibbals, a local resident, acquires the private property.

1989: Arimetco acquires the private property and conducts re-mining using Anaconda tailings and new ore. Five heap leach pads and an electro winning plant are constructed and operated.

1999: Arimetco files for bankruptcy and ceased mining operations at the Site.

2000: NDEP begins management of fluid management system (FMS) associated with the heap leach pads.

2004: NDEP recognized lack of resources to manage the FMS and requested EPA take the lead role.

2011: Singatse Peak Services (SPS), a subsidiary of Quaterra Resources, acquires the private property and initiates exploration activity

2016: Governor Sandoval signed conditional letter for EPA to replace site on National Priorities List (NPL).

2017: NDEP continues to work with EPA, BLM and ARC to secure private funding as an alternative to federal Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) funding.

Who is responsible?

Site environmental issues are being addressed under the oversight of EPA and NDEP. EPA is currently the lead agency with BLM, the co-lead agency responsible for overseeing investigation and remediation of environmental issues, using CERCLA (Superfund) authority. NDEP is in a support role. As a former owner, Atlantic Richfield Company/BP (ARC) has been determined to be a Potentially Responsible Party under CERCLA related to releases of contaminants from the former Anaconda operations. EPA has not determined that ARC is responsible for the Arimetco portion of the Site, consequently identifying a funding source to address permanent closure of the 260 acre Arimetco portion has been an issue since the Arimetco bankruptcy.

What is the problem at the Site?

The Anaconda operations occurred before modern environmental regulations were put in place, so many operational practices would not meet current standards and the Site was not required to be reclaimed upon closure. The Anaconda Site has many area of potential concern and risk and the highest priorities are HLP/FMS, groundwater evaporation ponds, Wabuska Drain and the process areas.  Use of unlined evaporation ponds has resulted in contamination of ground water with metal-bearing solutions. High concentrations of metals, including arsenic and uranium occur at the north end of the mine in the area of the former ponds. These contaminants have also migrated off-site in the area immediately north of the mine site. The extent and magnitude of this contamination has been extensively studied with over 350 monitoring wells installed. Atlantic Richfield Company (ARC) remains responsible for addressing issues related to the Anaconda operations, including groundwater contamination.

When Arimetco abandoned its operations in 2000, the immediate concern was management of the process fluids since the heap leach pads were fully charged with sulfuric acid process solution. The heap leach pads were all constructed on synthetic liners and the fluids are collected in lined ditches, pipes and lined pond systems. As the heaps have drained down naturally over time, the fluid flow rates have declined from over 3,000 gallons per minute in 2000 to about 10 gallons per minute currently, but the fluids, which are acidic and high in total dissolved solids, require continued management. With voluntary financial support from ARC and SPS, NDEP constructed two new evaporation ponds in 2013 to contain the drain down fluids as a stop-gap measure, but the ponds will continue to fill with evaporative salts over time, which will ultimately exceed capacity. A long term remedy is to cap and close the heaps to reduce infiltration of rainwater.

Is the water safe?

ARC provided funding to the City of Yerington to construct additional connections to the city water system minimizing the public use of groundwater and the ARC have been providing bottled water to the Yerington Paiute Tribe.  The City of Yerington water supply is safe and has never been impacted by the Anaconda Site. There are no City water supply wells located in the vicinity of the mine. City water is regularly tested and complies with state and federal drinking water requirements. Additional information on City of Yerington drinking water quality can be obtained at the City of Yerington Public Utilities Website or by contacting the NDEP Bureau of Safe Drinking Water.

Since 2004, domestic well owners north of the mine site have been provided with bottled water if uranium concentrations in their well water exceed 25 micrograms per liter (µg/l); The drinking water standard for uranium is 30 µg/l. 

Uranium occurs naturally in area ground water and there was no attempt to distinguish naturally occurring uranium from mine impacted water for purposes of the bottled water program. As a result of settlement of a class action lawsuit in 2015, brought by area residents against Atlantic Richfield Company, the City of Yerington water system is being extended to the area of groundwater impact and residents that choose to participate are being connected to the municipal system at no charge. Long-term remedies for mine impacted ground water will be evaluated as Site evaluation proceeds.

With regard to surface water, there is currently no information that indicates any impact from the Site to the Walker River, although the Wabuska Drain is being investigated as a potential historical pathway for Site contaminants. Access to the pit lake is controlled, but the quality of the water is fairly good, largely reflecting mineralized natural groundwater conditions, with elevated levels of copper and selenium but a neutral pH.

Has the Site affected agricultural products?

Agricultural products grown in the area have been tested and there is no evidence that the Anaconda Site has had any impact on agricultural production. Most fields in the area are located far south and east of the Anaconda Site, either hydrologically upgradient or not hydrologically connected to the Site at all.

What about NPL listing?

While Atlantic Richfield Company (ARC) remains responsible for the majority of Site issues, including groundwater, there is a funding gap related to closure of the Arimetco heaps and ongoing fluid management. EPA first requested to list this Site on the Superfund program’s National Priority List (NPL) in December of 2000 and Nevada rejected this request in January 2001. At that time, little was known about the extent of Site issues or the costs for closure of the Arimetco portion. Since then, extensive work has been done to investigate environmental issues and take interim actions to mitigate exposure risk. The Arimetco fluid management system has been operated and maintained by ARC under an agreement with EPA. In addition, the costs for permanent closure of the Arimetco heaps have been identified, these costs are estimated at $36 million.

As a matter of policy, NDEP views NPL listing as an option of last resort and instead strives to work with responsible parties and others to address environmental cleanups around the State. Cleanups at Superfund NPL sites tend to be very slow, expensive and process-laden. NDEP has had success with many cleanups working with private parties outside of the NPL process. In addition, the State is expected to contribute a 10% cost share to NPL site remedies financed with federal funds and then to pay any ongoing O&M costs.

In late 2015 and early 2016, NDEP attempted to negotiate a public-private funding agreement for the Arimetco work. Although discussions are ongoing, no agreement has been reached. EPA has again proposed to list the Site on the NPL to make the Site eligible for federal funding to address the Arimetco portion. EPA sent a letter to Governor Sandoval on December 22, 2015 requesting the State’s concurrence with proposed NPL listing of the Site. In follow-up correspondence, EPA requested a response by March 29, 2016. Governor Sandoval sent a reply to EPA on March 29, 2016 indicating his concurrence with initiating the process of listing the site on the NPL, subject to a number of conditions that are outlined in his letter.

Since then, NDEP has been working with ARC to provide a private funding alternative for the orphan, unfunded portion of the Site.  NDEP is also working with the EPA and BLM on a NPL deferral agreement.  NDEP is communicating frequently with SPS, the Tribes, Lyon County, The City of Yerington, and other stakeholders during this process.

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