Superfund Information Systems: Site Profile

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The Bonita Peak Mining District site consists of 48 historic mines or mining-related sources where ongoing releases of metal-laden water and sediments are occurring within the Mineral Creek, Cement Creek and Upper Animas River drainages in San Juan County, Colorado. Historic mining operations have contaminated soil, groundwater and surface water with heavy metals. A remedial investigation to determine the nature and extent of contamination is underway.

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What Is Being Done to Clean Up the Site?

All Superfund sites include an evaluation of potential threats to human health. This does not necessarily mean that exposures are occurring. While the community of Silverton is not included in the Superfund site, people do use the mining district for recreation. EPA has begun to collect data to evaluate possible exposures for a variety of recreational uses—ATV use, camping, hiking, guiding, fishing as well as traditional practices.

The Interim Water Treatment Plant (IWTP), installed at Gladstone as part of the emergency removal action at the Gold King Mine (GKM) in October 2015, is treating ongoing acid mine drainage being discharged from the GKM.

As EPA continues to treat discharge from the GKM, it conducted an evaluation for continuing operations of the IWTP beyond this year. The public comment period for the Engineering Evaluation and Cost Analysis (EE/CA) for the Gold King Mine IWTP ended on Dec. 14, 2016. EPA’s preferred response action alternative is to continue operations of the IWTP as currently configured while it evaluates longer-term options to manage water quality in Cement Creek as part of the Bonita Peak Mining District Superfund site remedial action. However, before making a final decision regarding continued operations of the IWTP, EPA will consider all comments received during the public comment period.

In October 2016, the U.S. Forest Service and EPA completed an early action at the Brooklyn Mine in the Mineral Creek Drainage. An existing pipeline that drains mining impacted water from the mine adit to a passive treatment trench was cleaned and repaired. Due to a blockage in the pipe, 15 gallons per minute of drainage had been flowing across the mine tailings and bypassing the passive treatment system. By cleaning out and repairing the pipeline, the flow of drainage across the tailings pile was reduced significantly. Additional work inside the adit is planned for a later date.

Under the Superfund Removal program, an engineered concrete bulkhead was installed in the adit of the Red and Bonita Mine during summer 2015. The bulkhead will help control the flow of the ongoing release of contaminated water coming out of the adit.

EPA is evaluating plans to close the bulkhead valve and incrementally increasing the water level behind the bulkhead. These include various monitoring procedures such as pressure measurements behind the bulkhead and flow measurements at the Gold King and other mines.

The objectives for closing the bulkhead would be to: 1) reduce the rate at which water can move through underground mine workings and discharge from mine adits, and 2) reduce the oxygen available for chemical reactions in the mountain that lead to the formation of acid mine drainage. The ultimate goal would be to return the hydrologic system to something closer to natural conditions. Based on the monitoring results and as part of the long-term remedy planning, EPA would determine if the bulkhead would remain closed.

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What Is the Current Site Status?

The site team is conducting a Remedial Investigation/Feasibility Study RI/FS at the site. During 2016, a number of sampling activities that support the Remedial Investigation of the BPMD were successfully completed. These include:

  • High-flow and low-flow sampling focused on the 48 source areas of the site, including major confluences and sentinel locations, such as existing gauging stations;
  • Sampling of waste rock, campground soil and road material;
  • A benthic macroinvertebrate study;
  • A fish habitat study in the Upper Animas River drainages;
  • Measurement of flows from all draining adits identified as source areas in the BPMD; and
  • Identification of seeps and springs in the Cement Creek drainage.

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EPA’s Involvement at the Site


EPA and the Colorado Department of Public Health and Environment (CDPHE) conducted a Superfund Site Assessment of the area in the 1990s. This assessment identified the severe impacts to aquatic life in the Upper Animas River and its tributaries from naturally occurring and mining-related heavy metals. It also acknowledged the community-based collaborative effort that was under way at that time to address those impacts. In recognition of the community-based collaborative effort, EPA agreed to postpone listing of a site to the Superfund National Priorities List (NPL), as long as progress was being made to improve the water quality of the Animas River.


Until approximately 2005, water quality in the Animas River was improving. However, since 2005, water quality in the Animas River has not improved, and for at least 20 miles below the confluence with Cement Creek, has declined significantly.

In 2008, because of this declining water quality in the Animas River, EPA’s Superfund Site Assessment program began investigations in upper Cement Creek focused on evaluating whether the upper Cement Creek area alone would qualify for inclusion on the NPL. This evaluation indicated that the area would qualify, although after receiving additional community input, EPA again postponed efforts to include the area on the NPL and continued to participate in the community-based collaborative efforts.

In support of the collaborative effort, EPA’s Superfund Remedial program contributed resources for water quality sampling, ecological risk assessment and data analysis. In addition, the Superfund Removal program contributed resources for the investigation and closure (bulkheading) of the Red and Bonita Mine tunnel.

EPA, through its Ecosystem Protection program, also provides the Colorado Water Quality Control Division of CDPHE with Nonpoint Source Management program (Section 319) grant funds. The Animas River Stakeholders Group (ARSG) and others have received grants under that program, as well as contributing other resources, for investigation and cleanup efforts in the Upper Animas watershed.

Sunnyside Gold Corporation (SGC), the U.S. Bureau of Land Management and the State of Colorado also have conducted reclamation activities in the Upper Animas watershed. These efforts have included diverting runoff away from and capping mine waste piles, moving mine waste piles away from drainages, consolidating mine waste piles, placing bulkheads in draining adits and re-vegetating mine waste piles.


Under the Superfund Removal program, an engineered concrete bulkhead was installed in the adit of the Red and Bonita Mine during summer 2015.

On August 5, 2015, EPA’s Superfund Removal program was conducting an investigation and assessment of the Gold King Mine to:

  • assess the on-going water releases from the mine,
  • treat mine water, and
  • assess the feasibility of further mine remediation.

While investigating the adit, pressurized water began leaking above the mine tunnel, spilling about three million gallons of water stored behind the collapsed material into Cement Creek. Since October 2015, EPA has been treating the discharge from the Gold King Mine at the Interim Water Treatment Plant (IWTP) at Gladstone, Colorado.

This event prompted renewed interest in addressing the long-term, mining-related impacts to water quality in the Animas River. On February 29, 2016, EPA received a letter from Colorado Governor John Hickenlooper expressing support for the addition of the BPMD to the NPL. In his letter, he noted that the Town of Silverton, San Juan County, City of Durango, La Plata County, local tribes and other interested stakeholders requested that the site be added to the NPL.

EPA proposed the BPMD for addition to the NPL on April 7, 2016. A 68-day public comment period, during which EPA accepted comments from the public on the NPL proposal, closed on June 13, 2016. After carefully considering and responding to all comments in a responsiveness summary, EPA officially added the BPMD to the NPL on September 9, 2016.

In 2016, EPA awarded a $100,000 Environmental Education Grant to MSI. With the funding, MSI proposes to collaborate with the EPA to build awareness and understanding of the Animas River watershed for residents, recreationalists and visitors.

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Sampling and Monitoring

Water sampling has shown that there was a marked increase in the levels of several heavy metals in the Animas River below the confluence with Cement Creek after active and passive treatment ceased in the Cement Creek drainage late in 2004.

Modeling conducted by U.S. Geological Survey (USGS) using the One-Dimensional Transport with Equilibrium Chemistry (OTEQ) model identified the need for additional information about pollutant loads from sources other than Cement Creek to the Upper Animas River.

Sampling activities conducted by EPA in 2015 are reported in the Sampling Activities Report, 2015 Sampling Events (PDF) (SAR) (638 pp, 189 MB, About PDF). The SAR presents mapped and tabular results from field activities conducted by EPA and its state and federal partners under the Final Revision 0, Sampling Analysis Plan/Quality Assurance Project Plan Upper Animas Mining District – 2015 Sampling Events (SAP/QAPP) (EPA, 2015). The SAR includes results from the high-flow sampling event conducted on June 9–10, 2015; the August 4–6, 2015 soil-sampling event; and the low-flow sampling event conducted on September 28–October 1, 2015. Detailed interpretation of the data presented in the SAR will be completed as part of the planned remedial investigation (RI) at the Bonita Peak Mining District Superfund site.

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Emergency Response and Removal

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Operable Units

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.

View a list of all of the operable units at this site.

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Cleanup Progress

View the schedule for cleaning up this site.

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