Central City-Clear Creek

This is a National Priorities List (NPL), or "Superfund," hazardous waste site. While we’re the lead agency for remediation of the site, the EPA Superfund Program provides technical support and input on all remediation-related activities to ensure the objectives of the Superfund program are met.

Site summary


  • Central City and Idaho Springs, Mining District/Argo Tunnel.
  • In Clear Creek and Gilpin counties, approximately 30 miles west of Denver.
  • Covers a 400-square mile area of the Clear Creek drainage basin.


  • Gold was discovered in 1859.
  • This area was a leading mining center in Colorado with the construction of ore processing mills. Mining in the area has been limited since 1950.
  • The site was placed on the list of Superfund sites in September 1983.
  • Limited-stakes gaming began in Central City and Black Hawk in 1992.
  • Many mine waste cleanup projects were implemented as property was developed.

Environmental concerns

  • The human health hazard from this site involves potential exposure to heavy metals, primarily lead, arsenic and cadmium.
  • Acidic mine water containing heavy metals drains from many mines, impacting aquatic life and habitats.
  • Soil from the tailings piles and waste rock also contains heavy metals.
  • Clear Creek is a drinking water source for more than a quarter-million people living in the Denver area.
  • The creek is also a favored place for kayaking, rafting, fishing, wildlife watching and gold panning.

Site remediation

  • Cleanup involves treatment of contaminated water, capping of tailings and waste rock piles, further investigation of groundwater and identification of contaminated domestic drinking water wells.
  • The Argo Tunnel, in Idaho Springs, is the largest single source of metals contamination to Clear Creek.
    • A 700-gallon-per-minute water treatment facility was completed in 1998 to remove approximately 1,200 pounds of metals each day from Argo Tunnel water.
    • The removed metals are pressed into a solid waste and disposed of in a solid waste landfill.
    • The treated water is discharged into Clear Creek.
  • Several waste piles were remediated near Dumont, Idaho Springs and the Black Hawk/Central City area.
  • A study was conducted to determine whether individual homeowners might be drinking contaminated water from domestic wells.
    • Owners whose well water contained levels of metals that exceeded drinking water standards were supplied with an alternate source of water.
    • Only a small percentage of the wells tested required an alternate source of drinking water.

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