Site History

• Background
• What Has Been Done to Clean Up the Site?
  • 1990s
  • 2005–2014
  • 2015–2016
  • 2017- present

The Bonita Peak Mining District site includes 48 historic mines or mining-related sources where ongoing releases of water and sediments containing metals  occur at  historic mining source areas. The mining source areas directly impact Mineral Creek, Cement Creek and Upper Animas River drainages in San Juan County, Colorado.  Some metals contamination migrates into the Animas River.  EPA is investigating the contamination and cleaning up the site.

• Maps of source area locations

What Has Been Done to Clean Up the Site?

1990s

EPA and the Colorado Department of Public Health and Environment (CDPHE) assessed the area in the 1990s, finding severe impacts to aquatic life in the Upper Animas River and its tributaries from naturally occurring and mining-related heavy metals. The assessment also acknowledged a community-based collaborative effort, called the Animas River Stakeholders Group (ARSG), 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 the area to the Superfund National Priorities List (NPL), if progress was being made to improve the water quality of the Animas River.

2005–2014

Until approximately 2005, water quality in the Animas River was improving. Sunnyside Gold had been operating a water treatment plant at the Gladstone area, but shut down after they installed engineered “bulkheads” (concrete plugs) into the American Tunnel and other mine tunnels. However, since 2005, water quality in the Animas River had not improved, and for at least 20 miles below the confluence with Cement Creek, water quality was declining.

Due to the Animas River declining water quality, EPA reevaluated the site in 2008, focusing on whether the upper Cement Creek area alone would qualify for the NPL and become eligible for federal Superfund cleanup. 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.

Many stakeholders supported this collaborative effort:

• EPA’s Superfund Remedial program contributed resources for water quality sampling, ecological risk assessment and data analysis.
• Sunnyside Gold Corporation (SGC), the U.S. Bureau of Land Management, U.S. Forest Service, and the State of Colorado also conducted reclamation activities in the Upper Animas watershed. These efforts include diverting runoff away from mine waste, consolidating and capping mine wastes to prevent leaching of metals into surface and groundwater, and installing engineered bulkheads (concrete plugs) into draining mine tunnels. 
• The Animas River Stakeholders Group (ARSG) had received grants through the Nonpoint Source Management program (Section 319) which is funded by EPA and managed through the Colorado Water Quality Control Division of CDPHE. ARSG used these grants along with other funding sources , for investigation and cleanup efforts in the Upper Animas watershed for many years prior to the NPL listing.

2015–2016

EPA continued to support community-based efforts and provided assistance through the Superfund Removal Program. Under the Superfund Removal program, an engineered concrete bulkhead was installed in the Red & Bonita Mine tunnel during summer 2015.
On August 5, 2015, EPA’s Superfund Removal program was investigating 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 water stored behind the collapsed material into Cement Creek.

Under EPA’s Removal Program, a water treatment facility was quickly constructed to treat discharged water from the Gold King Mine. Since October 2015, EPA has been treating this water 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.

2017-Present

The site team, including EPA, U.S. Forest Service, Bureau of Land Management and Colorado Department of Public Health and Environment is conducting a Remedial Investigation/Feasibility Study (RI/FS) at the site. This includes a Human Health Risk Assessment, Ecological Risk Assessment and a hydrologic study of the Bonita Peak groundwater system. These investigations provide information that will be used in determining cleanup options for the site.

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, 2016 and 2017 are reported in the yearly Sampling Activities Reports.

Risk Assessment  

• EPA completed the Aquatic Baseline Ecological Risk Assessment which evaluated how fish and bug populations are impacted by high metals and low pH from source areas.
  • Aquatic Baseline Ecological Risk Assessment Factsheet (BERA)(pdf) (2pp, 948KB)
  • Aquatic Baseline Ecological Risk Assessment (pdf) (2,132 pp, 79.6 MB
• EPA completed the Terrestrial Baseline Ecological Risk Assessment  which evaluates how terrestrial animals living in the mining district are impacted by mining-related contamination.
  • Terrestrial Baseline Ecological Risk Assessment Factsheet (BERA)(pdf) (2pp, 973KB)
  • Terrestrial Baseline Ecological Risk Assessment (pdf) (726 pp, 34.7 MB)
• EPA finalized the Human Health Risk Assessment which found that no occupational exposures (road workers and ATV tour guides) exceeded levels of concern. During this process, four dispersed camping areas were identified with health concerns which will be addressed under IROD actions or other remedial investigations.
  • Human Health Risk Assessment Factsheet(HHRA)(pdf) (4pp, 1.3MB)
  • Human Health Risk Assessment (pdf) (618 pp, 32 MB)

Site Strategy

With community, State, USFS, and BLM input, EPA established three goals and prioritized the stream/river areas to allow for an Adaptive Management Strategy to address this large complex site with many dispersed mine source areas.  The Goals and Priorities are described in detail in our March 2019 Factsheet (pdf)(2pp, 1MB) and they are as follows:  

• Achieve water quality improvement, with a focus on mine drainage.  
• Stabilize source areas, with a focus on solid media.  
• Minimize unplanned releases. 

EPAs site strategy was developed with input from partner agencies and the local community. The site strategy focuses EPA resources on further investigating and cleanup actions in the Bonita Peak Groundwater System (Operable Unit 3) and Upper Animas reaches. These areas contain sources that contribute significant amounts of metals to the watershed. The site strategy also includes continued operation of the interim water treatment plant (IWTP), siting and construction of a sitewide repository, design and construction of the remedial actions specified in the 2019 IROD, and continued enforcement actions. 

• Fact Sheet: BPMD Selected Site Strategy, February 2020 (pdf) (2 pp, 2.1 MB) 

As part of EPA’s Adaptive Management Strategy, while investigation and remedy evaluation efforts continue for the site in the RI/FS process, EPA had sufficient data in several areas to select interim cleanup actions. EPA has issued two Interim Record of Decisions at the site that select cleanup actions.  These cleanup actions are underway:

• 2019 Interim Record of Decision: 23 Source Areas
  • The 2019 Interim Record of Decision (IROD) was finalized in May 2019 and includes 23 source areas where EPA will conduct cleanup actions, focused on stabilizing source areas and diverting runoff away from mine wastes. For more information about cleanup progress at each of these sites, please visit the BPMD Storymap.
    • Fact Sheet: Interim Record of Decision for the Bonita Peak Mining District Superfund Site, May 2019 (pdf) (2pp, 238KB)
• 2021 Interim Record of Decision: Bonita Peak Repository
  • The 2021 IROD was finalized in 2021 and includes construction of a sitewide mine waste repository to safely store mine waste and treatment generated solids from the Gladstone Interim Water Treatment Plant

The Interim Water Treatment Plant (IWTP) at Gladstone continues to treat ongoing acid mine drainage being discharged from the Gold King Mine. EPA is currently evaluating additional cleanup actions of the Cement Creek drainage which will be presented for public comment in a proposed plan and then documented in a Record of Decision. 

The Site’s first Five-Year Review documents(pdf)(91 pp, 66.14 MB) and evaluates the progress on the selected remedies.