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The 235-acre Eagle Mine Superfund site is located in the Rocky Mountains approximately 8,000 feet above sea level, one mile south of the town of Minturn in Eagle County, Colorado. The Eagle River and a number of its tributaries flow through the site, which is an area impacted by heavy metal contamination from past mining activities. The site includes an estimated 70 miles of underground mine tunnels; underground mill workings; the abandoned company town of Gilman; and various mine waste features such as former roaster pile areas; waste rock piles; tailings piles; a tailings slurry line and trestle, and the Belden Mill and load out area. Contaminants include arsenic, cadmium, copper, lead and zinc in the soils, structures, surface water, sediments, and groundwater across the site.

Miners began mining for gold and silver in the Battle Mountain area between the towns of Minturn and Red Cliff as early as the 1880s. In 1912, the Empire Zinc Company began consolidating individual mining claims into what is now known as the Eagle Mine. In 1929, miners constructed a mill underground within the mine workings and slurried the tailings through a pipeline/trestle system to a location downstream, known as the Old Tailings Pile. In the mid-1940s, the Old Tailings Pile reached capacity. Tailings were then deposited across the Eagle River from the Old Tailings Pile in an area known as Rex Flats. In 1942, they extended the pipeline to a location near Cross Creek using an elevated wooden trestle to cross Rex Flats, and the New Tailings Pile (now known as the Consolidated Tailings Pile) was constructed. The New Tailings Pile also included a 1.5-acre water retention pond known as the Historic Pond. Tailings were again deposited in Rex Flats in the 1950s.

In December 1977, the previous owner of the mine site, Gulf + Western Industries, Inc. closed the mill and most mining activities ceased. Some copper and silver production continued until the mine workings were allowed to flood when the mine closed in 1984. Remaining workers vacated the company town of Gilman immediately after the mine closed. Portions of the site were bought and sold numerous times in the years that followed.

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What Has Been Done to Clean Up the Site?

In 1983, the state of Colorado filed a natural resource damage (NRD) lawsuit against Gulf + Western for impacts to the Eagle River and surrounding areas from activities at the Eagle Mine site. In 1988, the state and the corporate successor to Gulf + Western signed a consent decree and a remedial action plan known as the CD/RAP to implement cleanup activities at the site. Some of the main actions included:

  • Plug mine portals to flood the mine workings: From 1986 through 1990, six openings, or adits, to the Eagle Mine workings were permanently plugged to prevent the direct flow of mine water into the Eagle River. Because the mine adits were plugged and pumping of the mine water was discontinued, the mine filled with water. The theory behind mine flooding was to limit the rocks’ exposure to oxygen, thereby reducing acid generation and the amount of metals dissolved from the mine workings. However, after a certain elevation, the pool of water impounded within the mine began to seep out of fractures in the mountain. Currently, the water from the mine, as well as the surface and groundwater from the tailings pile areas, is being collected and transported to the water treatment plant.
  • Collect and treat mine water and groundwater: The water treatment plant has been in place since 1990. It treats water collected from the mine, groundwater beneath the Consolidated Tailings Pile, and contaminated surface and groundwater collected from multiple locations across the site.
  • Consolidate, cap and/or revegetate tailings piles: A primary component of the cleanup has been the relocation, or consolidation, of scattered onsite tailings to one location. The New Tailings Pile was the largest pile onsite, so it was determined that the other piles would be relocated and consolidated at the New Tailings Pile, renamed the Consolidated Tailings Pile. The oldest tailings pile, called the Old Tailings Pile, was relocated to the Consolidated Tailings Pile. Nearly one million tons of tailings were relocated, and the former location of the Old Tailings Pile was covered with clean fill material and revegetated with native grasses. Tailings from the approximately 20-acre Rex Flats tailings pile, another significantly-sized tailings pile onsite, were relocated to the Consolidated Tailings Pile and the area was revegetated. Additionally, material from five roaster piles (roasting was an early smelting process to separate metals from rock) was also relocated to the Consolidated Tailings Pile. This relocation included the 38,000-ton roaster pile in Belden and the 100,000-ton roaster pile across the Eagle River from the Eagle Mine. To isolate millions of tons of tailings material consolidated at this area from precipitation, air and direct human contact, the Consolidated Tailings Pile was covered with a multi-layered engineered cap and seeded with natural grasses.

In 1986, EPA added the Eagle Mine Superfund site to the National Priorities List of Superfund sites due to continued uncontrolled metals discharges into the environment. Heavy metals at the site reduced fish populations and other aquatic life in the Eagle River downstream from the mine and its waste piles. The contaminants also posed a threat to two drinking water wells used by the town of Minturn, which had a population at that time of about 1,500 people, just north of the site. Airborne particles from the Consolidated Tailings Pile were also of concern, because the pile was adjacent to the Minturn Middle School. Contamination was destroying the nearby Maloit Park wetlands area, and elevated concentrations of heavy metals in soils adjacent to houses in the abandoned company town of Gilman would make redevelopment difficult.

EPA divided the Eagle Mine Superfund site into three operable units (OUs). OU1 was established to control the transport of heavy metals from the principal sources of mine waste (such as the Eagle Mine itself and various tailings and roaster piles) that were impacting the Eagle River. OU2 was established to evaluate health risks at Maloit Park Wetlands, the Minturn Middle School and the abandoned company town of Gilman. Because the wetlands have been remediated and the school proved not to be a risk, OU2 today focuses on contaminated soils at Gilman only. OU3 (also referred to as the North Property) was established in the early 2000s to mirror the boundaries of a private residential development proposed for the area at that time.

The definitions of the operable units have evolved over time. Now, OU1 is primarily media-based, focusing on protecting surface water at the site by reducing metals loading to the Eagle River. On-going remediation within OU1 includes active engineered remedial features designed to capture and treat mine waste in surface and groundwater. OU2 is geographically based to focus on evaluating potential human health risks in the historic town of Gilman. OU3 is media-based and focuses on protection of human health for residential use through reduction of exposures to surface soil. Geographically, OU1 and OU3 overlap except for the area of Belden, which is in OU1 only.

EPA’s involvement resulted in additional efforts such as:

  • Assessed health risks at the Minturn Middle School and the Minturn area: An extensive risk assessment and sampling program found no elevated metals levels on school area soils. Constant air sampling did not reveal any violation of air quality standards at the Minturn Middle School during construction of the Consolidated Tailings Pile cap.
  • Ordered the cleanup and reconstruction of the wetlands area: Maloit Park Wetlands, adjacent to the Minturn Middle School, was once visibly contaminated with heavy metals such as lead, cadmium and chromium. It was virtually lifeless. Today, the area has been reclaimed, contaminants removed, and a vegetative community has been regenerating. Minturn town wells located near the wetlands area have been moved upstream.
  • Removed hazardous materials from the mine site: A large quantity of hazardous materials, including chemicals polychlorinated biphenyls (PCBs), and dynamite caps were removed from the site, particularly in the Belden and Gilman areas.

In 1993, EPA issued a Record of Decision, which detailed the cleanup plans for OU1. The Record of Decision required further action than had already been taken. The goal of the remedial activities required by the Record of Decision was to control the transport of metals from various sources on the Eagle Mine Superfund site to the Eagle River and to groundwater.

In 1998, EPA issued a Record of Decision for OU2. The OU2 Record of Decision identified land use controls, referred to as institutional controls, that restricted access, at the abandoned company town of Gilman as a sufficient remedy.

In September 2001, EPA declared that construction of all required elements of the remedy as described in the OU1 and OU2 Records of Decision was complete. The site moved into the operations and maintenance (O&M) phase.

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What Is the Current Site Status?

The Eagle Mine Superfund site was in a post-remedy operation and maintenance phase from 2001 through 2017, which included maintaining the water treatment plant, periodic water quality monitoring and ensuring the required site access restrictions. In 2009, the Colorado Water Quality Control Commission modified the standards for the amount of zinc, cadmium and copper allowed in the Eagle River. As a result of previous cleanup efforts at the Eagle Mine site, the Eagle River typically meets the new water quality standards as it flows through the site, except in March and April, when metals concentrations can be elevated. The violation of water quality standards in March and April necessitated amending the OU1 Record of Decision so that the OU1 remedy was protective of human health and the environment. EPA and CDPHE began working on a study to identify remedial actions capable of further reducing the amount of metals impacting the site and entering the Eagle River. In order to gather more data on the sources of metals loading from the site, pilot tests were conducted in 2012 that involved pumping groundwater in specific locations and evaluating the effect on the water level inside the mine workings.

EPA and CDPHE released a Focused Feasibility Study Report for OU1 presenting possible additional remedial actions necessary to further reduce metals loading from the site into the Eagle River to the public in 2013. Additional data was collected in 2014 and 2015 related to arsenic sources and arsenic in the Eagle River. EPA and CDPHE finalized a Focused Feasibility Study Report Addendum for arsenic in 2016. The addendum presented possible additional remedial actions necessary to further reduce arsenic concentrations in the Eagle River in addition to other metals. In June 2017, CDPHE and EPA finalized a proposed cleanup plan (proposed plan) for OU1. The proposed plan identified the Agencies’ preferred cleanup alternative from those described in the 2013 Focused Feasibility Study Report and 2016 addendum. The Agencies took public comment on the proposed plan for 45 days and extended the public comment period by another 30 days upon request. After considering all public comment, EPA issued the OU1 Record of Decision Amendment in September 2017. The Record of Decision Amendment details the alternatives that will be implemented. The Record of Decision Amendment for OU1 defines the scope of the operable units; modifies the cleanup levels in surface water for cadmium, copper, and zinc; adopts a site-specific arsenic remedial goal; expands the current groundwater collection system to meet the new cleanup levels and goal; and incorporates land use controls to protect engineered remedial features at the site such as the water treatment plant and waste pile caps.

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Activity and Use Limitations

At this site, activity and use limitations that EPA calls institutional controls are in place. Institutional controls play an important role in site remedies because they reduce exposure to contamination by limiting land or resource use. They also guide human behavior. For instance, zoning restrictions prevent land uses – such as residential uses – that are not consistent with the level of cleanup.

For more background, see Institutional Controls.

Land use controls are the most common type of institutional control (IC). ICs are administrative or legal controls that help reduce the likelihood for human exposure to contamination. ICs can also help protect the integrity of the remedy. Examples of ICs are:

  • Zoning ordinances
  • Environmental covenants
  • Deed notices
  • Well-drilling restrictions
  • Building permits
  • Informational advisories

ICs are an aspect of the Eagle Mine Superfund site remedy. For instance, groundwater is restricted from being used at many areas of the site due to remaining heavy metal contamination, including Rex Flats, the Old Tailings Pile and the Maloit Park areas. The remedy for OU2, which includes the abandoned company town of Gilman and surrounding areas, consists entirely of ICs that limit site access. In addition, ICs dictate that EPA and CDPHE be informed of any proposed change in land use at the Eagle Mine Superfund site. If land use changes, the Agencies must determine if additional remediation would be required. EPA and CDPHE must review any land use change plans to assure they are protective of human health and the environment. New ICs described in the 2017 OU1 Record of Decision Amendment are intended to protect engineered remedial features at the site such as the water treatment plant and waste pile caps. New ICs described in the 2017 Record of Decision for OU3 are intended to restrict access and eliminate potential exposure to contaminants on site.

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Emergency Response and Removal

Electrical transformer removal action: When the Eagle Mine was first abandoned by its owner in 1984, EPA conducted an emergency action to remove electrical transformers from the flooding mine. Much of the equipment in the mine contained PCBs. Because of extremely hazardous conditions, including a partially collapsed tunnel and an ongoing mine fire, three transformers were not removed, though most of the PCBs from these transformers were drained and recovered.

Belden Cribbings removal: The Belden Cribbings are a series of old timber retaining walls placed up the steep slopes of Battle Mountain in Belden Canyon. The Belden Cribbings area is directly upstream from the Eagle Mine Superfund site and outside of the boundary included in the NPL listing. The cribbings were built at the turn of the last century to stabilize about eight million tons of waste rock deposited on the mountainside as part of past mining activity at Eagle Mine. The cribbings appear old, worn and decayed. Should the cribbings fail, tons of fine, acidic, metallic waste rock would avalanche down the steep slope, directly onto the tracks of the former Denver and Rio Grande Western Railroad and into the Eagle River below. This failure could be catastrophic to the Eagle River recovery, reversing the water quality improvements achieved through the Eagle Mine Superfund site cleanup. Such a failure could also cause significant flooding upstream in the town of Red Cliff.

EPA conducted a removal action in 2008 to address the Belden Cribbings, though the cribbings proved too unstable, the slope too steep, and a suitable repository location for the cribbings too difficult to actually remove the cribbings. Instead, crews built two earthen and concrete block retaining walls at their base. The walls are approximately 600 feet long and 17 feet tall. Groundwater filtering through the cribbings is passively treated by a neutralizing agent placed behind the walls and collected by a perforated pipe running along the lower retaining wall. The water is then released to the Eagle River. EPA maintains the condition of the cribbings walls and has returned to the Belden Cribbings area to conduct repairs as needed.

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Enforcement Information

In 1983, the state of Colorado filed a natural resource damage (NRD) lawsuit against Gulf + Western, the owner and operator of the site at that time, for impacts to the Eagle River and surrounding areas from activities at the Eagle Mine site.

In 1988, the state of Colorado and a corporate successor to Gulf + Western entered into a consent decree/remedial action plan to conduct cleanup activities at the Eagle Mine site.

In 1990, the 1988 consent decree/remedial action plan was amended to include the construction of a water treatment plant at the Eagle Mine site.

In 1996, EPA, the state of Colorado, and the corporate successor to Gulf + Western signed a consent decree to conduct additional remediation at the Eagle Mine site requires by the OU1 Record of Decision.

In 2004, a developer called Ginn Battle North purchased parts of the site and approached EPA and CDPHE with a proposal to develop parts of the site into a private, residential golf course community. Because the existing OU1 remedy addressed soil contamination based upon trespasser and recreational use, an analysis was required to determine if additional actions were needed to ensure that future residents and workers at the North Property would be protected. When Battle North, LLC took over the property from Ginn Battle North, Battle North, LLC continued working with EPA as a Bona Fide Prospective Purchaser (BFPP).

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