The Yerington/Anaconda Mine Site is an abandoned copper mining, milling, and processing facility. It covers 3,468 acres and is located two miles north of Yerington, Nevada.
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The Anaconda Copper Company operated the mine from 1952 to 1978 as a low-grade copper mine and milling operation. During this period, a total of 350 million tons of ore and waste rock were mined form the Yerington Pit, and 189 tons of waste was generated.
In 1977 the Atlantic Richfiel Company acquired Anaconda and assumed its operations at the Site. In June 1978, Atlantic Richfield terminated operations at the Site. In or about 1982, Atlantic Richfield sold its interests in the private lands within the Site to Don Tibbals, a local resident, who subsequently sold his interests with the exception of the Weed Heights community to Arimetco, Inc. Arimetco operated a copper recovery operation from existing ore heaps within the Site from 1989 to November 1999. Arimetco terminated operations at the Site and filed for bankruptcy.
The site consists of an office/process facility, an open-pit mine, an overburden dump, sulfide and oxide stockpile dumps, leach pads, tailings and waste rock piles, and evaporation ponds. Naturally occurring radioactive materials including uranium, thorium, and radium, are present at the site and have become concentrated in some areas due to mining processes.
To date, EPA has conducted five separate removal actions at the site. An initial removal action was conducted at the site in February 2006. This removal action consisted of two phases of work. The first phase involved the removal of approximately 120 PCB-containing transformers. All transformers at the site were sampled for PCBs. Those transformers found to have greater than 50 ppm were removed and transported to the Clean Harbors facility in Coffeeville, KS for disposal. The second phase of this removal action involved addressing fugitive dust at the site. This work, which was conducted from April 5 to May 12, 2006, primarily involved placing a soil cap over approximately 75 acres of exposed sulfide tailings. The cap was constructed using onsite materials, referred to as vat leach tailings. During the capping work, the EPA Environmental Response Team (ERT) conducted air monitoring and sampling. Results of this monitoring and sampling effort indicated that airborne concentrations of metals and radioactive isotopes were either at non-detectable levels or were below levels that would cause health concerns. EPA also applied a soil sealant to other areas of the site, approximately 20 acres, that could possibly be contributing to fugitive dust.
EPA conducted a second removal action at the site from August to October 2006. This removal action addressed fluids management problems associated with the Arimetco heap leach system. These problems included insufficient fluids storage capacity and leaking pond liners. EPA conducted the following activities: construction of a 4-acre evaporation pond, construction of an 1,100 foot french drain intended to capture heap draindown before it enters the Megapond, and relining of Slot Pond #2.
EPA conducted a third removal action at the site in October 2007. This removal action addressed the Bathtub Pond of the fluids management system. The liner for this pond had been torn badly by windstorms during the spring and summer of 2007, and heap leach fluids were being released directly to the subsurface. EPA removed the sediments and liner from the pond, backfilled and compacted the pond area, and installed a french drain to collect the heap leach fluids draining down from the adjacent heap.
In August 2007, EPA also conducted two separate removal assessments. One was a radiological assessment of the Process Area and one was a subsurface assessment of the heap leach ponds.
In September 2008, EPA completed a fourth removal action. The goal of this removal action was to complete stabilization of the Arimetco heap leach fluids management system. This project included closure of the following heap leach ponds: South Slot Pond, Plant Feed Pond, Old Raffinate Pond, New Raffinate Pond and the Megapond. Pond closure consists of removing sediment from the pond, removing the liner, and in some cases backfilling the pond. In the case of the the Old Raffinate Pond, kerosene contaminated soils exist beneath the pond to a depth of more than 20 feet. These contaminated soils will were excavated and bioremediated onsite. Bioremediation of these kersosene contaminated soils was completed in June 2010. EPA also relined the Phase I/II Pond and repair the VLT Pond, as both of these ponds were still needed to capture heap leach draindown fluids. EPA will also implemented measures to reduce bird mortalities associated with these ponds, including installation of propane bird-scare cannons.
In May and June 2009, EPA conducted a fifth removal action. Asbestos containing material in the Anaconda Mine Office was removed and disposed of offsite. Following removal of the asbestos, the buidling was demolished and placed in an onsite construction debris landfill. A tire pile, consisting of more than 300 large tires, was screened for radioactive contaminants. The screening demonstrated that the tires were acceptable for free release, and the tires weres sent offsite for disposal/re-use.
On April 21, 2009, EPA and the Atlantic Richfied Company (ARC) signed an Administrative Order on Consent under which ARC agreed to conduct four removal actions: removal of electrical hazards, removal of radiological soil contamination, removal of transite pipe and capping of two areas (Thumb Pond and Sub Area A). The electrical hazards removal action was completed in advance of the other actions. From 10/20/2009-12/13/2010, all activities related to the remaining three removal actions were completed by ARC. START and EPA personnel were onsite to oversee cleanup activities. Metrics for the project include the following:
- 247 truckloads (6,097 tons) of radiological contaminated soil were transported to the U.S. Ecology facility in Grand View, ID.
- 18.3 acres were capped in the Thumb Pond (using 33,900 cubic yards of Vat Leach Tailings material.
- 8.2 acres were capped in of Sub-Area A (using 31,886 cubic yards of Vat Leach Tailings material)
- Approximately 20,799 feet of transite pipe was removed. The majority of this was landfilled onsite, with approximately 5,300 ft of pipe and 88 cubic yards of pipe fragments disposed offsite at the U.S. Ecology facility in Grand View, ID.
From September 5, 2012 to October 4, 2012, EPA conducted a sixth removal action. This removal action was being funded by the Atlantic Richfield Company and Quaterra Resources (the current owner of the property), under separate agreements with EPA. This removal action will included relining the VLT heap leach pond and making repairs to certain areas of the heap leach perimeter ditch system.