Operable Unit #6
Stray Horse Gulch, Operable Unit 6 of the California Gulch Superfund Site, is located directly east of Leadville in the historic mining district. Additional information about the California Gulch Superfund Site is available at http://www.epa.gov/region8/superfund/co/calgulch/.
The current remedy involves managing between three and five million gallons of acidic and metal-laden water that results when water flows through several mine waste piles in Stray Horse Gulch each spring. This water is conveyed to the Bureau of Reclamation’s water treatment plant via a series of underground mine workings and the Leadville Mine Drainage Tunnel.
Recent studies conducted by EPA conclude that using the mine workings and tunnel to convey water cannot be relied on for the long-term. This is due to known blockages within the tunnel and concerns about the structural integrity and general competency of tunnel.
EPA and the Colorado Department of Public Health and Environment (CDPHE) have determined that the surface water portion of the current remedy in Stray Horse Gulch is not efficient or sustainable and must be changed.
Click for PDF
Click for PDF
Timeframe
EPA and CDPHE made the Proposed Plan for an Amendment to the 2003 Record of Decision available to the public on June 4, 2010. The public comment period will begin on June 10 and end on July 12. The public meeting on the Proposed Plan to accept public comments will be on June 24, 2010 at 6:30 p.m. at the National Mining Hall of Fame & Museum in Longyear Auditorium. Please click here for a copy of the fact sheet on the Proposed Plan and here for a copy of the Proposed Plan.
For more information about the agency’s proposed changes in Stay Horse Gulch, please click on the fact sheet: Understanding Proposed Surface Water Remedy Changes at Stray Horse Gulch.
About the Pilot Study on Capping Approaches in Stray Horse Gulch
 Photo taken before capping pilot initiated
Based on community concerns about changing the landscape of the mining district, EPA and CDPHE recently completed a study to identify potential capping approaches for use on the RAM, Mikado and Greenback mine waste piles. Specifically, EPA and CDPHE have worked with the community to explore more aesthetically-pleasing ways to cover mine waste piles using materials that might help to preserve the appearance of the mining landscape.
This study is based on input from citizens and officials in Lake County and the City of Leadville. The pilot study identified potential capping designs for addressing the spring run-off from mine waste rock piles that are contributing to surface water contamination in Stay Horse Gulch.
What is the purpose of the study?
Based on community concerns about changing the landscape of the mining district, the study has been developed to accomplish the following:
- Explore alternative and more aesthetically-pleasing ways to cover mine waste piles with materials that would help to preserve the appearance of the mining landscape; and
- Help determine possible drainage issues associated with using the alternative materials.
ALTERNATIVE 1: Natural Face with Partial Cap
 Photo after capping
Approach: Preserve natural face or slope. Place a liner on the top and back side of the mine waste pile and then
cap with non-acid generating waste rock.
Advantages:
- Face is left undisturbed for “historic” look
- Most economical and efficient alternative to complete
Disadvantages:
- Front face will continue to be susceptible to erosion and generation of acid generation.
- Retention/treatment of surface water runoff may be necessary
ALTERNATIVE 2: Shotcrete with No Liner on Slope
 Photo before capping  Photo after capping
Approach: Approximately six inches of shotcrete, a type of concrete, is applied directly on the natural face or slope. The top of the pile has a liner and is capped with non-acid generating waste rock.
Advantages:
- Shotcrete will be stained to resemble waste pile
- Shotcrete will significantly reduce infiltration
- Surface runoff is unlikely to come into contact with acid generating material
Disadvantages:
- Shotcrete may crack over time, leading to infiltration
- Inspection and maintenance higher than non-shotcrete alternatives
- May not be practical on steeper slopes
ALTERNATIVE 2A:
Shotcrete with Liner on Slope
 Photo before capping  Photo after capping
Approach: Same as Alternative 2, however a liner is added beneath the shotcrete on the front slope.
Advantages:
- Shotcrete will be stained to resemble waste pile
- Comprehensive shotcrete and liner system will significantly reduce infiltration
- Surface runoff is unlikely to come into contact with acid generating material
- Liner will help protect against infiltration even in the event that the shotcrete cracks
Disadvantages:
- Inspection and maintenance higher than non-shotcrete alternatives
- May not be practical on steeper slopes
ALTERNATIVE 3: Liner on Slope with Non-acid Generating Waste Rock
 Photo before capping  Photo after capping
Approach: The front slope, top and back is covered with a liner and capped with non-acid generating waste rock.
Advantages:
- Liner placed directly on historic waste rock pile prevents water infiltration to the acid generating material
- A minimum of 18 inches non-acid generating mine waste rock placed on liner retains historic waste pile without the acid generation potential
- Surface runoff is prevented from coming into contact with acid generating material
Disadvantages:
- Sufficient local sources of non-acid generating waste rock will need to be identified.
Minor maintenance on the front face; more in first couple years while front face stabilizes.
ALTERNATIVE 4: Cribbing/Retention Wall with
Non-acid Generating Mine Waste Rock
 Photo before capping Photo after capping & adding crib wall
Approach: Same as Alternative 3 but with cribbing.
Advantages:
- In the full scale, a liner would be placed directly on historic waste rock pile preventing water infiltration to the acid generating material
- A minimum of 18 inches non-acid generating mine waste rock would be placed on liner, which would retain historic waste pile look without the acid generation potential
- Surface runoff would be prevented from coming into contact with acid generating material
- Cribbing maintains historic look & provides more slope stability
- With a liner, surface runoff is unlikely to come into contact with acid generating material
Disadvantages:
- Sufficient local sources of non waste rock will need to be identified
- Minor maintenance on the front face; more in first couple years while front face stabilizes
For more information about this study please see the brochure About EPA’s Pilot Study on Capping Approaches in Stray Horse Gulch
EPA and CDPHE Want Your Comments
EPA and CDPHE are asking citizens for their input on the capping study and have placed a comment box at the Denver City Mine Claim study site along the Mineral Belt Trail. Please also feel free to submit comments via this website at leadville@merid.org.
Directions to the Denver City Mine Claim (Pilot Study Site):
From Harrison Avenue in Leadville, follow 7th Street east to the Jim Martin Bridge where the Mineral Belt Trail crosses 7th Street (near the Matchless Mine). Park and walk south on the Mineral Belt Trail about 200 yards. The pilot study is on the left.
|
