2009-09-25_PERMIT FILE - M2009076 ‎(41)‎

• Permit No: M2009076
• IBM Index Class Name: PERMIT FILE
• Doc Date: 9/25/2009
• Doc Name: Big Five Tunnel Discharge
• From: Venture Resources
• To: DRMS
• Media Type: D
• Archive: No

• For additional information contact:
Mike Holmes, USEPA Region VIII„ [phone]
Jim Lewis, CDPHE, [phone]
SITE ffiSTORY, CUNTANMATfON. AND SELECTED REMEDY
The SITE is located on the east slope of Colorado's Front Range, approximately 30 miles west of
Denver. The water quality of Clear Creek and its tributaries is impaired by a legacy of historic
mining activities including the persistent drainage of low pH metals-laden water from numerous
mine tunnels. The Colorado Water Quality Control Commission classified Clear Creek as a Class I
cold water stream capable of protecting and maintaining a diversity of cold water biota. Clear Creek
has been out of compliance with stream standards set for this classification as a result of persistent
drainage from mine tunnels, mine waste piles, and tailings. These impacts have also reduced the
abundance and diversity of aquatic biota in the watershed. Table *1 attached to this ESD summarizes
the metals concentrations detected in discharge samples collected from the Big Five Tunnel during
the Phase I and Phase H Remedial Investigations, by CDPHE in 2001, and by UOS, an EPA START
Program contractor, in 2005. Discharge from the Big Five Tunnel is estimated to add 11,000 pounds
of metals per year to Clear Creek The table also includes State Drinking Water Standards for metals
and aquatic life standards for metals for comparison with the metals concentrations from the Big
Five discharge. Overall, the concentration of metals in the Big Five discharge exceeds the human
• health and aquatic life standards.
The SITE was selected for addition to the National Priorities List in September 1983 due to the
release of heavy metals to the environment. Since that time, EPA and CDPHE have conducted
investigations and made decisions regarding the implementation of response actions at specific
locations within the 400 square mile SITE boundary. Four RODS have been signed for the SITE.
The OU 1 ROD was signed September 30,1987, and called for passive treatment or a combination
of active and passive treatment for acid water draining from five mine tunnels. The five tunnels
include the Big Five and ARGO Tunnels in Idaho Springs, the Gregory Incline and National Tunnel
in Black Hawk, and the Quartz Hill Tunnel in Central City.
OU 2 was designated to address the mine waste piles in the immediate proximity to the five
discharging tunnels referenced above. The OU 2 ROD was signed on March 31, 1988. OU 4 was
designated to address the sources of contamination on the North Fork of Clear Creek. The OU 4
ROD was signed September 29, 2004.
OU 3 was originally designated to address control of surge events of acid mine drainage from the
ARGO Tunnel. The signing of the OU 3 ROD was delayedpendingthe outcome of additional Phase
II investigations. In 1988, a Phase II Remedial Investigation (RI) was initiated to take a
comprehensive view of the approximately 400 square mile Clear Creek drainage basin. The OU 3
ROD was signed on September 30,1991, and addressed the problems identified in the Phase 11 RI.
The OU 3 ROD superseded the original OU 1 ROD. The OU 2 ROD remained unchanged by the
• OU 3 ROD. The OU 3 ROD selected a combination of active treatment for the ARGO Tunnel,
passive treatment for the Burleigh Tunnel, collection of Virginia Canyon Ground Water for
treatment, provision of an alternate drinking water supply for users of contaminated ground water,
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