Clear Creek originates in the mountains near Colorado's Continental Divide and runs 60 miles east and several thousand feet lower in elevation to Golden, Colorado, a western suburb of Denver, Colorado and then discharges to the South Platte River north of Denver. The drainage basin encompasses approximately 400 square miles, including a portion of the Colorado Mineral Belt, which includes several mining districts in Clear Creek and Gilpin Counties. Due to the rich mineralization, these two counties became some of the most heavily mined areas of Colorado, with gold and silver accounting for the vast majority of the mining. As part of ore extraction activities, the miners constructed tunnels. Acidic, metal-rich water from these mine tunnels has continued to enter Clear Creek and its tributaries at many locations. The Argo Tunnel and Big Five Tunnel, located in Idaho Springs, Colorado, are two of the tunnels that EPA and CDPHE have focused on to reduce acid and metals loading to Clear Creek.

• Remediation System Evaluation, Central City/Clear Creek Superfund Site Argo Tunnel Water Treatment Plant (PDF)(37 pp, 2 MB, 2007, 542-R-07-019)