Region 8

Central City / Clear Creek

Central City/Clear Creek site location map
Site Type: Final NPL
City: Idaho Springs
County: Clear Creek
Street Address: Near town
ZIP Code: 80452
EPA ID: COD980717557
SSID: 0813
Site Aliases: Argo Tunnel, Five Mile Tunnel, Central City Mining District, Quartz Hill Tunnel, National Tunnel, Gregory Incline, Newhouse Tunnel
Congressional District: 2

What's New?

Updated June 2014

Work will begin this spring on the Quartz Hill tailings pile in Central City. The project will entail re-grading the tailings pile to a manageable slope for run-off from rain or snow melt. The final step will be to place a vegetative cover over the pile to prevent sediment erosion into the stormwater sewer. This project will be the final remedial component for Operable Unit 4 (OU4).

The conceptual design for constructing a flow-through bulkhead in the Argo Tunnel is underway. The project will entail construction of a flow control structure to prevent large releases of contaminated water and sediment from overwhelming the Argo Tunnel water treatment plant.

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Site Description

The discovery of gold near Idaho Springs, Central City and Black Hawk in 1859 played a significant role in Colorado’s gold rush. For the next 20 years, the Black Hawk/Central City area was the leading mining center in Colorado primarily due to the construction of mills to process the gold and silver mined nearby. The silver crash in the 1890s brought a decline in mining to the area, but mining remained an important industry in Clear Creek and Gilpin Counties until about 1950. Only a limited number of mines are currently in operation.

Black Hawk Smelters and Gregory Lode
Black Hawk Smelters and Gregory Lode
(Denver Public Library Western History Images)

The Central City/Clear Creek Superfund Site consists of a 400-square mile watershed extending from the Continental Divide east to near Golden. The site is located in Gilpin and Clear Creek Counties. Popular for activities like fishing, rafting, kayaking, and gold panning, it also serves as a drinking water source for over 500,000 people in the Northwest Denver Metro area.

In September of 1983, the Central City/Clear Creek site was placed on the National Priorities List (NPL), or Superfund list. Historic gold mining and mine wastes left behind in the Clear Creek basin contaminated the watershed. Elevated levels of metals in Clear Creek were the driving factors in the listing of the site. Only a small fraction of this watershed is actually impacted by the historical mining operations making cleanup more difficult. Because mine wastes are scattered throughout the watershed, cleanup goals focus on improving water quality rather than individual tasks.

Map of the NPL site and surrounding area, January 2013

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Site Risk

Media Affected Contaminants Source of Contamination
soil, surface water, leachate, groundwater, liquid waste heavy metals like zinc, copper, manganese, cadmium, lead and arsenic mining and milling operations within a watershed

EPA and the Colorado Department of Public Health and the Environment (CDPHE) assessed potential impacts to human health and the environment from mine waste piles and tunnel discharges.

The environmental issues addressed by these projects include metals contamination in the waters of Clear Creek, particularly the North Fork, and management of mine tailings, waste rock and tunnel drainage to prevent further contamination of the Creek.

Contaminants of concern (COCs) for aquatic life include zinc, copper, cadmium and manganese. These metals are found in surface water and primarily affect trout, aquatic insects and other aquatic organisms.

The COCs for humans are arsenic and lead. Health risks could result from long-term drinking of groundwater containing high concentrations of these metals, the incidental ingestion of tailings and waste rock, and inhalation of airborne dust.

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Cleanup Progress


  • Work began on designs for the North Fork Clear Creek water treatment facility.
  • EPA and CDPHE started work on the Gold Hill tailings pile in Central City. This work entailed re-grading and partial removal of some of the tailings. After this work was completed a cap was placed over the pile.
  • Initial work began on a proposed plan to install a flow control system inside the Argo Tunnel bulkhead to help control mine water draining from the adit.


  • American Recovery and Reinvestment Act of 2009 logo
    Designs for a new active water treatment plant were undertaken at Operable Unit 4 (OU4). This plant will treat mine waste water emanating from the Gregory Incline, National Tunnel, and Gregory Gulch. Construction date for this project is anticipated to begin in 2014; funding came from the American Recovery and Reinvestment Act of 2009.
  • Recovery funds were also used to construct a pipeline to carry the mine-contaminated water coming from the National Tunnel, Gregory Incline, and Gregory Gulch.
  • Work was completed on remediation of the mine waste rock piles located in OU4.


  • The Central City/Clear Creek Superfund Site received $2.16 million from the American Recovery and Reinvestment Act of 2009 to complete the sediment reduction component and pipeline conveyance of Operable Unit 4 Remedial Action work.
  • Work began in July of 2009 on the sediment reduction and mine waste pile remediation component of OU4 Phase III. This work focused on the mine waste piles impacting the North Fork of Clear Creek. Projects included:
    • relocating and consolidating various waste rock piles at the Church Placer Repository
    • erosion-control measures at other mine waste piles
    • Some waste rock piles were left in place, slopes were re-graded and run-on control ditches or other erosion controls were constructed.
  • CDPHE, EPA, and CDOT worked jointly on a highway curve straightening project on the North Fork of Clear Creek near Black Hawk. This project used the rock generated from the curve straightening project for the rock cover at the Church Placer Repository and the Pittsburgh waste pile. This project led to stream sediment improvements and habitat restoration.
  • The city of Black Hawk consolidated two mine waste piles and used the Church Placer Repository for the mine wastes.


Church Placer property
Church Placer property before work began
  • Purchase of the Church Placer property was a major milestone for completing Phase II work for Operable Unit 4 (OU4). Upon completion of the new access road, crews worked hard preparing the property with the necessary erosion control measures to handle mine wastes brought to this location. Mine waste rock and tailings piles planned for removal in the summer of 2009 will be taken to this site.
  • Sediment detention basins, rock check dams, rock drop structures, and run-on control ditches were built to help with sediment control and slow down the flow of water. Some eroded tailings were removed from the channel and placed on a more stable site with existing mine waste piles. Other mine waste piles were re-graded with a rock cover placed over them. This work occurred primarily in Russell and Nevada Gulches and included at least six waste rock and tailings piles.


  • Phase 1 Operable Unit 4 work included the construction of two sediment detention basins and erosion control measures at five mine waste rock and tailings piles. Erosion control measures included run-on and run-off ditches, re-grading of steep or eroding slopes, and placing rock at the bottom of the pile if necessary. This work was completed in Russell Gulch, Nevada Gulch, South Willis Gulch and Gregory Gulch.
  • The State and EPA formed partnerships to complete two separate projects:
    • Working with the Colorado School of Mines, a pilot project testing various passive systems known as "sulfate-reducing bioreactors" was used to treat water from the National Tunnel.
    • Black Hawk/Central City Sanitation District along with CDPHE and EPA constructed a wetlands project to filter and remove metals from North Clear Creek water.


  • The Record of Decision for Operable Units 3 and 4 was amended to add an on-site mine waste repository.
  • In an effort to address significant sources of metals contamination to the main stem of Clear Creek, structures to pipe water from both Virginia Canyon and the Big 5 Tunnel to the Argo Water Treatment Facility were built.


Argo water treatment plant
Argo water treatment plant
  • The Argo Water Treatment Facility began using hydrated lime in its treatment process of metals-laden water from the Argo Tunnel.
  • Design work for the reclamation of the Golden Gilpin Mill was completed.
  • Construction of the cap for the Chase Gulch #2 mine waste pile was completed.
  • The State, CDOT, EPA and the city of Idaho Springs worked collaboratively to design and construct a conveyance system to take the water from the Big 5 Tunnel drainage and pond to the Argo Water Treatment Facility. As part of this project the Big 5 Pond has been drained, filled and capped.
  • A cutoff wall and sediment basins were constructed along with general storm water management maintenance the county needed in Virginia Canyon to assist with the collection of the metals-laden surface and groundwater.
  • Record of Decision for Operable Unit 4 (OU4) was signed Sept. 29, 2004 for the cleanup of North Fork of Clear Creek and its tributaries as well as Quartz Hill, Gregory Incline and National Tunnel mine discharges.


  • The five-year review and update of the Community Involvement Plan were completed.
  • A public meeting was held to discuss the proposed cleanup plan and preferred alternative for OU4. Comments were accepted from the public about the cleanup alternatives and the OU4 Record of Decision was finalized in September.
  • Work was completed in Virginia Canyon which included removing mine waste piles from the Two Brothers Mine, the Little #6, and collecting groundwater to divert to the Argo water treatment plant.
  • The Clear Creek Watershed Foundation completed cleanup of waste piles at the Leavenworth, Sydney and Dibbens mines.


  • In 2003, an amendment to the ROD for OU3 to change the remedial action at the Burleigh Tunnel to a no-action response was completed.
  • In 2000, the State and EPA began looking at locations for use as an on-site mine waste repository. Three locations were considered: the Gem/Franklin in Clear Creek County, the Glory Hole and the Druid/Church Placer, both located in Gilpin County.


  • In 1999, the State began high-flow and low-flow surface water monitoring on Clear Creek below the Burleigh Tunnel.
  • During 1998, one of the wetland components at OU 3 was decommissioned and the other component operated until 1999.
  • April 1998, the Argo Water Treatment Plant was completed and began operation, removing about 99 percent of the metals from the mine water.
  • August 1993, pursuant to the Operable Unit 3 Record of Decision: a passive treatment wetland was constructed as a pilot scale demonstration project at the portal of the Burleigh Tunnel.
  • Cleanups of numerous tailings and waste rock piles occurred during the 1990s.
  • The OU3 Record of Decision was signed Sept. 30, 1991.

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Community Involvement

Community involvement plays an important role in the Superfund process. EPA uses a number of different tools and resources to promote effective, on-going, meaningful community involvement. The goals of the Superfund community involvement program are to:

  • Keep communities affected by sites informed throughout the cleanup process
  • Provide opportunities for communities to comment and offer their input about site cleanup plans
  • Facilitate the resolution of community issues tied to a site

Team members regularly meet with local elected officials, groups like the Upper Clear Creek Watershed Association, Black Hawk Rotary Club and individuals as needed. It is important to reach out to communities to understand any concerns the community may have as work progresses.

CDPHE and EPA have provided the community with information about the work being done by using fact sheets, public notices and press releases in local papers, a community involvement plan, maintaining an information repository, public meetings, individual or small group informal meetings, and occasional emails.

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EPA places a high priority on land reuse as part of its Superfund response program mission. The agency tries to select cleanup options that encourage and support future use of a site. We use two fundamental methods to facilitate reuse of Superfund sites:

  • Exploring future uses before the cleanup remedy is implemented, an approach that gives the Agency the best chance of designing cleanup remedies to support the likely future use of a site
  • Working with landowners and communities to remove barriers not considered necessary for the protection of human health or the environment at those sites where remedies are already in place

One option for reuse is the siting of clean and renewable energy projects on contaminated (or formerly contaminated) lands. As part of this effort, EPA is evaluating the potential for energy projects on these properties and working with landowners and communities to identify ways to remove barriers to such projects.

In 1992, limited stakes gaming began in Central City and Black Hawk. As property for the casinos was developed many mine waste clean-up projects were implemented. For example, mine wastes were capped or covered when a parking lot was constructed.

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Land Use Controls and Other 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

Remediated areas where mine waste is left in place are subject to environmental covenants between CDPHE and the landowner. A number of settlements or agreements were entered into with casino developers to assure that development of gaming properties is consistent with mine waste remaining on site.

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Five-Year Reviews

EPA or the lead agency conducts five-year reviews following the start of a Superfund cleanup when contamination is left on the site. These reviews are repeated every five years. We use these reviews to determine:

  • How the remedy is working
  • If the remedy remains protective of human health and the environment

The fourth five-year review of the cleanup actions performed as part of the Superfund program at the Central City/Clear Creek site was conducted in 2009. The review concluded that cleanup alternatives remain protective of human health and the environment. Concurrently, community interviews were conducted and the Community Involvement Plan was updated.

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Site Documents

You will need Adobe Reader to view some of the files on this page. See EPA’s About PDF page to learn more.

Amendment to the OU4 ROD for the Active Treatment of the National Tunnel, Gregory Incline and Gregory Gulch, April 2010

OU4 Proposed Plan to Amend the ROD, December 2009

Update Fact Sheet, July 2009

Update Fact Sheet, September 2008

Explanation of Significant Differences in the Big Five Tunnel Discharge, May 2005

Records of Decision (RODs)

Amendments to Records of Decision (RODs)

Five-Year Reviews

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Les Sims
Remedial Project Manager
U.S Environmental Protection Agency, Region 8
1595 Wynkoop Street (8EPR-SR)
Denver, CO 80202-1129
800-227-8917 ext. 312-6224 (toll free Region 8 only)

Site Information Repositories:

Gilpin County Courthouse
203 Eureka Street
Central City, CO 80427

Clear Creek Watershed Foundation
2060 Miner Street
Idaho Springs, CO 80452
Please call for an appointment

Colorado Department of Public Health and Environment
HMWMD Records Center
4300 Cherry Creek Drive South
Denver, Colorado 80246-1530
888-569-1831 ext. 3331 (toll free)
303-759-5355 FAX
By appointment only

EPA Superfund Records Center
1595 Wynkoop Street
Denver, CO 80202-1129
To request copies of administrative record documents call:
800-227-8917 ext. 312-7273 (toll free Region 8 only)


Mary Boardman
State Project Manager
Colorado Department of Public Health and Environment
Hazardous Materials and Waste Management Division
4300 Cherry Creek Drive South B2
Denver, CO 80246-1530
FAX 303-759-5355

Warren Smith
Community Involvement Manager
Colorado Department of Public Health and Environment
Hazardous Materials and Waste Management Division
4300 Cherry Creek Drive South B2
Denver, CO 80246-1530
FAX 303-759-5355

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Photo/Video Gallery

Click on a thumbnail below to view the full size image.

Gregory Gulch, 1865(Denver Public Library Western History Images)
Water flolwing in Gregory Gulch
Water flowing in Gregory Gulch
Church Placer Mine Waste Repository 2008
Dump truck at Church Placer Mine Waste Repository 2009
North Fork Clear Creek
Hampden Mine Waste Pile
Hampden Mine Waste Pile Phase I
Hampden Mine Waste Pile Phase II
Chase Gulch Mine Waste Pile 2006
Chase Gulch Mine Waste Pile 2007

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The following links exit the site Exit

Central City/Clear Creek site at the Colorado Department of Public Health and Environment

Clear Creek Watershed Foundation

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