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.
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., the current owner. Arimetco operated a copper recovery operation from existing ore heaps within the Site from 1989 to November 1999. Arimetco has terminated operations at the Site and is currently managed under the protection of the United States Bankruptcy Court in Tucson, Arizona.
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.
5/24-5/29. EPA-1, START-2, RAC-1, ERRS-6. Site operations continued through the week. Asbestos abatement activities in the mine office building were completed by the asbestos subcontractor. Final asbestos clearance samples were collected, and the building was cleared for demolition by an asbestos consultant. Demolition of building began on 5/27, with debris being hauled to an onsite construction debris landfill in the suflide tailings area. START collected GPS data marking the location of this landfill. START continued to collect perimeter asbestos monitoring in the vicinity of the mine office building and also collected PM10 samples in the vicinity of the landfill during demolition activities.
ERRS completed repairs to the leak in the perimeter ditch in the vicinity of Slot Pond #1. There were actually three layers of liner in this area, and it appeared that fluid was accumulating between and below the liners. A sump was constructed beneath the liners. Piping was run from this sump to the nearby leak detector. Fluid drains from the sump, to the leak detector, and is then pumped to the nearby slot sediment pond. The repairs appears to be functioning effectively.
The RAC contractor and START conducted a Marsame Class III radiological survey of the tires. The tires were cleared for free release.
EPA plans to conduct the following removal activities:
Asbestos removal of the Anaconda Mine office, offsite disposal of the asbestos containing material, demolition of the mine office, onsite landfilling of the demolition debris,
Removal and radiological screening of more than 300 large truck tires. The tires will be sent for offsite disposal/re-use.
Maintenance of the Arimetco heap leach fluids management system. Including performance of an evaporation pilot test and conducting repairs to a leaking area of the perimeter ditch.
EPA removal operations will continue next week, with the following activities:
Complete demolition and landfilling of mine office building,
Install fencing in area of demolished building,
Continue evaporation pilot test. A second vendor is coming to demonstrate their equipment.
Begin trucking tires for offsite re-use.
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