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The Chevron Questa Mine site is located near the Village of Questa in Taos County, New Mexico. The Site includes a former molybdenum mine and milling facility on 3 square miles of land and tailing impoundments on about 1.5 square miles of land. A pipeline running along State Highway 38 connects the milling facility to the tailings impoundments.

The Chevron Questa Mine, previously known as the Molycorp Mine, operated intermittently from 1920 until 2014, when Chevron Mining Inc. (CMI) permanently closed the mine. Open pit mining took place from 1965 to 1983. Mining operations and waste disposal contaminated soil, sediment, surface water and groundwater. While the mine was operating, about 328 million tons of acid-generating waste rock were excavated and deposited in nine large waste rock piles. After molybdenum was extracted from ore, the tailing was transported by pipeline to a tailing facility where it was deposited in tailing impoundments.


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What Is Being Done to Clean Up the Site?

Cleanup has included removal actions, or short-term cleanups, to address immediate threats to human health and the environment. Removal actions include removal and off-site treatment and disposal of PCB-contaminated soil, removal of historic tailing spill deposits along the Red River riparian corridor, removal of contaminated sediment at Eagle Rock Lake, installation of a stormwater control structure for the lake inlet, and piping of unused irrigation water.
The site is being addressed through federal, state and potentially responsible party (PRP) actions

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EPA’s Involvement at the Site

EPA re-proposed the Molycorp, Inc. site to the National Priorities List (NPL) of Superfund Sites in March 2011. The site was placed on the NPL on September 16, 2011. As part of the listing, EPA changed the name of the site to the Chevron Questa Mine Superfund site based on comments received during the public comment period. EPA selected the remedy in a December 20, 2010 Record of Decision (ROD).

The ROD identified the following cleanup actions for five areas of the site:

Mill Area: excavation and off-site disposal of contaminated soil, construction of a cover, and revegetation

Mine Site Area:  removal and regrading of waste rock piles, construction of a cover, revegetation, operation of seepage interceptinos and groundwater extraction systems, dewatering of the underground mine, treatment of water, provision of a temporary alternate water supply, and temporary well drilling restrictions.

Tailing Facility Area: covering and revegetation of tailing impoundments; upgrading existing seepage collection drains and wells; piping of irrigatrion water in eastern diversion channel; extracting and treating groundwater; access controls; provision of temporary alternate water supplies; and temporary well drilling restrictions.

Red River, Riparian and South of Tailing Facility Area: removal and on-site disposal of molybdenum-contaminated soil and tailing spill deposits.

Eagle Rock Lake:  installation of inlet stormwater controls, dredging, and disposal of sediment at Tailing Facility


Prior Investigations and Clean-up Activities: CMI conducted a Remedial Investigation/Feasibility Study (RI/FS) at the Site and EPA conducted a baseline human health risk assessment and baseline ecological risk assessment for the Site concurrently with CMI's RI/FS.

Following completion of these efforts, EPA selected a Remedy for the Site, which is presented in the Record of Decision (“ROD”), dated December 20, 2010.

Removal Actions

On March 7, 2012, EPA and CMI entered into an Administrative Settlement Agreement and Order on Consent for Removal Actions (Removal AOC). Under the Removal AOC CMI undertook the following removal actions:

  • Excavate PCB contaminated soil at the mill area
  • Remove tailing spill deposits along the Red River riparian corridor.
  • Pipe of unused irrigation water in the Eastern Diversion Channel at the Tailing Facility
  • Remove sediment at Eagle Rock Lake

Early Design Actions

On September 26, 2012, EPA and CMI entered into a second Administrative Settlement Agreement and Order on Consent for Early Design Actions (Early Design AOC). Under the Early Design AOC, CMI is undertaking Early Actions that will be used to implement portions of the selected remedy for the Site. On September 30, 2014, EPA and CMI entered into the First Amendment to the Early Design AOC (“First Amendment”). The First Amendment expanded the scope of the Early Design AOC to include three additional early design projects: 1) design of a groundwater extraction system to collect drainage from one of the roadside waste rock piles, 2) design of groundwater extraction systems to enhance existing seepage barriers at the tailings facility, and 3) design and construction of a pilot surface-based mine dewatering system. On November 13, 2014, EPA and CMI entered into the Second Amendment to the Early Design AOC (“Second Amendment”).  The Second Amendment further expands the scope of the Early Design AOC to include two more early design projects: 1) design of the grading plan for the tailing facility and 2) design and construction of field trials of waste rock cover material. CMI and EPA entered into a Third Amendment to the  Early Design AOC on August 15, 2016 to conduct Tailing Facility vegetation and wildlife studies.

Partial Consent Decree

On August 9, 2016, the Department of Justice (DOJ) lodged a First Partial Remedial Design/ Remedial Action (RD/RA) Consent Decree (Consent Decree) with the United States District Court for the District of New Mexico. The Court formally entered the Consent Decree on May 1, 2017. The Consent Decree is a settlement agreement between CMI, EPA and the State of New Mexico. Under the Consent Decree, CMI will perform the following cleanup work at the site:

  • Tailing Facility Cover Demonstration Pilot Project: CMI will regrade, cover and revegetate approximately 275 acres of the tailing facility with 2 feet of cover material. The pilot project will test whether 2 feet of cover will be protective of human health and the environment.
  • Surface-based Mine Dewatering System: CMI will install a pumping system to keep the water level in the underground mine workings below the level of the Red River.
  • Mine Site Groundwater Extraction System: CMI will install an additional extraction system to capture impacted groundwater before it reaches the Red River.
  • Mine Site Area Water Treatment Plant: CMI is constructing a new water treatment plant at the site that will be used to treat contaminated water prior to its discharge to the Red River.
  • Excavation of Soil at Dry/Maintenance Area: CMI will excavate an area of soil where molybdenum levels in the soil are over 41 parts per million.
  • Seepage Barrier Upgrade: Two seepage interception systems at the tailing faci8lity have been operating since 1975 to limit contaminated groundwater from reaching the Red River. The seepage interceptor systems will be upgrade to improve capture of contaminated groundwater
  • Tailing Facility Groundwater Extraction System: Under the Removal ACO, CMI began piping irrigation water into a diversino channel to keep it from becoming contaminated and seeping into groundwater. If this system does not result in a decrease of contamination in groundwater, CMI will install an extraction system to remove the contaminated groundwater



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Sampling and Monitoring

Molycorp conducted the RI/FS from 2001 to 2009 under the direction and oversight of EPA, as supported by NMED and MMD. As part of the RI/FS, EPA performed the baseline human health risk assessment (HHRA) and baseline ecological risk assessment (BERA) for the Site from 2003 to 2009.

Environmental media were initially sampled from August 2002 through 2004, including soil, sediment, surface water, ground water and air. Terrestrial biota and aquatic biota were also sampled for risk assessment. As the initial environmental data were collected and evaluated, additional work plans were developed to characterize areas of the Site further. Several RI/FS work plan addendums were prepared in 2004 and 2005 to collect additional data, including focus sampling at seeps and springs along the mine site reach of the Red River and characterization of the roadside waste rock piles. Additional monitoring wells were installed at the tailing facility in 2005 and 2008.

The Final RI Report (RI Report) was submitted to EPA on July 3, 2009, and revised on November 24, 2009. The HHRA Final Report and BERA Final Report were completed in May 2009. EPA completed a re-evaluation of the risk assessment for the tailing facility as an addendum to the BERA in November 2009. The Final FS Report was submitted in August 2009 and a revised Final FS Report (FS Report) was submitted on November 16, 2009.

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