On this page:
- What Is Being Done to Clean Up the Site?
- What Is the Current Site Status?
- EPA’s Involvement at the Site
- Activity and Use Limitations
- Emergency Response and Removal
- Operable Units (opens new page)
- Cleanup Progress (opens new page)
The Eagle Mine Superfund site is located in the Rocky Mountains, approximately 8,000 feet above sea level, bordered to the south and west by the White River National Forest. The roughly 235-acre site sits 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 heavily impacted by heavy metal contamination as a result of 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 of arsenic, cadmium, copper, lead and zinc in the soils, structures, surface water, sediments, and groundwater across the site.
EPA divided the Eagle Mine Superfund site into three Operable Units (OUs). Operable Unit 1 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.
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, later a subsidiary of New Jersey Zinc Company, began consolidating individual mining claims into what is now known as the Eagle Mine. In 1929, a mill was constructed underground within the mine workings and the tailings were slurried 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, the pipeline was extended 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, then-owner 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 and 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 years that followed. EPA and the state of Colorado identified CBS Operations, Inc. (CBS) as the party responsible for the cleanup of the site. CBS had acquired Viacom International, Inc., the successor in interest to New Jersey Zinc Company.
What Is Being Done to Clean Up the Site?
The Eagle Mine closed in 1984, forcing the last of the miners to move on. However, elevated levels of arsenic, cadmium, copper, lead and zinc in soil, surface water and groundwater stayed behind. The contaminants 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 is 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 Gilman would make redevelopment difficult.
To address threats to human health, precautions were taken such as constructing upstream water wells for Minturn residents, removing metals from the Maloit Park wetlands, monitoring air and drinking water and consolidating and capping mine waste. These actions and others also alleviated the extremely serious ecological risks at the site, particularly risks to water quality and aquatic life from heavy metals.
After a decades-long Superfund environmental investigation and cleanup process (see EPA’s Involvement at this Site for more details), EPA declared construction completion of all cleanup necessary to protect human health and the environment at the Eagle Mine Superfund site in 2001. The site is in Operation and Maintenance status today, which includes periodic site inspection and maintenance activities, as well as continual operation of the water treatment plant and land use controls to ensure that the remedy remains protective. In addition, EPA conducts a review of the site every five years, which includes on-site inspections, to ensure the remedy remains protective of human health and the environment.
Recently EPA and the State of Colorado have been working at the site planning additional cleanup work at OU1 to meet revised water quality standards to protect human health and the environment. Also, the agencies have been working with the property owner of OU3, or the North Property, so that that all necessary investigation and cleanup steps occur to prepare the property for potential residential use. (See What is the current site status? and Redevelopment Activity for more information on these efforts.)
What Is the Current Site Status?
The Eagle Mine Superfund site has been in a post-remedy Operation and Maintenance phase (O&M) from 2001 through the present. O&M at the site consists primarily of maintaining the water treatment plant, periodic water quality monitoring and ensuring the required site access restrictions.
However, there is a new cleanup effort developing for Operable Unit 1 (OU1) – Sitewide contamination. 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. To comply, EPA and the Colorado Department of Public Health and Environment (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.
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 was released to the public in 2013. Additional data was collected in 2014 and 2015 related to arsenic sources and arsenic in the Eagle River. A Focused Feasibility Study Addendum for arsenic was finalized 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, EPA and the state finalized a proposed cleanup plan for OU1, referred to as a proposed plan. The proposed plan identifies the agencies’ preferred cleanup alternative from those described in the 2013 Feasibility Study and 2016 Addendum. The public is to comment on the proposed plan before a final decision in made.
EPA’s Involvement at the Site
The state of Colorado filed a natural resource damage (NRD) lawsuit in 1983 against Gulf + Western for impacts to the Eagle River and surrounding areas from activities at the Eagle Mine site. EPA listed the site on the National Priorities List, known as the list of Superfund sites, in 1986 because of the mine metals discharge, uncontrolled mine waste piles, and the close proximity of people living, working and going to school near the mine and its associated features (the closest town, Minturn, is located less than two miles downstream along the Eagle River. Other Eagle County towns further downstream along the Eagle River include Eagle and Avon. The town of Red Cliff sits just upstream of the site).
A state-mandated remedy was detailed in a 1988 consent decree and a remedial action plan known as the CD/RAP. Per the CD/RAP, the responsible party, Viacom (today, CBS Operations, Inc.) implemented a cleanup plan in 1988. 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 working 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. This mine flooding was allowed so the rock would not be exposed to oxygen, thereby reducing acid generation and the amount of metals dissolved from the mine workings. 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. 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. The oldest tailings pile, 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 on site, 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 form the Eagle Mine.
In 1989, EPA became more involved in the project, resulting in additional efforts such as:
- Assessing 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.
- Ordering 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.
- Removing hazardous materials from the mine site: A large quantity of hazardous materials, including chemicals, PCBs, and dynamite caps were removed from the site, particularly in the Belden and Gilman areas.
In 1993, EPA issued a Record of Decision for the majority of the site, referred to as Operable Unit 1 (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 second Record of Decision for Operable Unit 2 (OU2). OU2 was established to evaluate health risks at Maloit Park Wetlands, the Minturn Middle School and the abandoned company town of Gilman. As the wetlands have been remediated and the school proved to not be a risk, OU2 today focuses on contaminated soils at Gilman only The OU2 Record of Decision identified institutional controls, or restricted access, as a sufficient remedy.
In September 2001, EPA declared that construction of the 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.
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
Institutional controls are an important aspect of the Eagle Mine Superfund site remedy. At OU1, which encompasses sitewide contamination, 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 institutional controls that limit site access. In addition, ICs dictate that EPA and the state of Colorado 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 the state of Colorado must review any developer-generated plans to assure they are protective of human health and the environment.
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 cancer-causing polychlorinated biphenyls (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 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 and some of the waste rock is becoming unstable. There was concern that 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.
During cleanup, a site can be divided into a number of distinct areas depending on its complexity. These areas, called operable units (OUs), may address geographic areas, specific problems, or areas where a specific action is required. Examples of typical operable units include construction of a groundwater pump and treatment system or construction of a cap over a landfill.