HYDRO29964

• Permit No: M1980244
• IBM Index Class Name: Hydrology
• Doc Date: 4/28/1997
• Doc Name: CRESSON MINE PN M-80-244 POTENTIAL FOR ACID ROCK DRAINAGE FROM THE MINE
• From: DMG
• To: CRIPPLE CREEK & VICTOR GOLD MINING CO
• Media Type: D
• Archive: No

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1^2' • . IIi III III IiIIIII III
STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Deparlmeni of Vauiral Resources
111 ~ Sherman A., Roum 215
Denver, Colorado 80203
Phone: [phone] ~ 15 b i
~.j\ 141131 ti;'~hlllb
April 28, 1997
Mr. John Hardaway
Cripple Creek & Victor Gold Mining Company
2755 State Highway 67
P.O. Box 191
Victor, CO 80860
~~~
I)EPAIiTMENT OF
NATURAL
RESOURCES
Ruv Romer
Governor
lames 5. lochhead
Fxeculive Dueclor
nTChael B Long
Div is~nn Dueclor
RE: Cresson Mine (Permit M-80-244) Potential for acid rock drainage
from the mine
Dear Mr. Hardaway:
Division staff met with you on April 4, 1997 in regard to a number
of concerns at the Cresson Mine. Among those discussed was the
matter of the potential impacts of acid rock drainage (ARD) from
the Ironclad and Squaw Gulch overburden dumps. As a result of a
commitment made to you during that meeting, Division staff have re-
examined the 1993 and 1994 HCI reports supplied by CC&V in order to
provide you with specific concerns regarding the data considered
and conclusions reached by those studies.
It is the Division's position that the HCI reports do not
adequately consider the actual conditions at 'the mine and,
therefore, do not incorporate the most appropriate input data for
their modeling. In summary, we believe that the acid production
potential of the mine may have been underestimated as indicated
below:
1) The HCI modeling is based on htamidity cell test results
rather than on long term batch tests which means that the
amount of acid assumed to be generated is too low. Humidity
cell tests characterize water from a single pass through
"weathered" rock rather than the water that results as it
passes thru several volumes of rock.
2) The volume of sulfide rich rock considered as having
potential to generate ARD is underestimated because the model
was based on infiltration thru the surface footprint of the
Cresson Pit alone. The calculations did not consider
infiltration through the Ironclad Pit, Globe Hill Pit and
other waste dump areas. These dump areas not only increase the
areal extent but provide considerably more surface area
exposure of sulfides to infiltrating waters.