REV02378

• Permit No: M1980244
• IBM Index Class Name: Revision
• Doc Date: 6/14/2000
• Doc Name: ADEQUACY COMMENTS PN M-1980-244 CRESSON PROJECT AM-108
• From: DMG
• To: CRIPPLE CREEK&VICTOR GOLD MINING CO
• Type & Sequence: AM8
• Media Type: D
• Archive: No

•
DIVISION OF MINERALS AND GEOLOGY
Departmem of natural Resources
1313 Sherman 51.. Room ?t>
Denver, Colorado 80?03
Phone: 130] 1 866 ~ 3>6,'
fAX: [phone]?8106
June 14,2000
~ iii iiiiiiiiniii iii
STATE OF CCLORr~DO
fOR YOUR CORRESPONDENCE FILE
Mr. Scott Lewis, Manager of Environmental Affairs
Cripple Creek & Victor Gold Mining Co.
P.O. Box 191
Victor, CO 80860
RE: Adequacy comments, Permit No. bI-1980-244, Cresson Project, AM-08
Dear Mr. Lewis:
The Division has reviewed your Amendment Application and has the following comments:
GENERAL
DIVISION OF
MINERAL S
GEOLOGY
R E C L A M A T I O N
MINING•SAFETY
Bill Owens
Governor
Greg E. watcher
E ~ecuove Dmecmr
Michael B. Long
Dwisian Direao~
The application appeared [o be well prepared and all the required information under the Rules and the Act is
provided. However, since [he Amendment relied a great deal on materials covered under AM-07, it would have
been helpful if the operator had provided the permit areas approved under AM-07 to give the reader a
comparison of the changes requested under AM-08. Also, it would have been helpful if the contour intervals
were placed in the maps legend.
Each of three separate mine pit wall slope stability reports addresses the potentially destabilizing effects of
water. Water can destabilize the mine pit walls by reducing effective stress on potentially skidding surfaces, and
by increasing the driving pressure on the potentially failing rock mass. As Adrian Brown Consultants observed,
"The combing[ion of these two effects is that mine wall stability is a strong function of ground water condition."
Mines excavated beneath a standing ground water table can result in seepage from saturated bedrock into the
mine pit. The presence of ground water can, therefore, result in less stable mine walls.
Historically [he Cripple Creek and Victor areas were mined largely by underground mining techniques. Ground
water seepage into underground workings necessitated dewatering and caused roof and rib instability. As in
many historic mining areas, dewa[ering tunnels were driven beneath the ground mass being mined to dewater
the ore body and eliminate ground water problems. In the case o the Cripple Creek and Victor mining area three
tunnels were driven. Each subsequent tunnel was a thousand feet deeper than the previous one to allow mining
to progress deeper in the diatreme. The Moffat tunnel was installed at 9,000 feet above sea level in 1900. The
Roosevelt tunnel was installed at 8,000 feet above sea level in the 1920's. The Carlton tunnel was installed at
7,000 feet above sea level in the 1940's. These tunnels appear to have been relatively effective in dewaterino the
overlying rock mass.
Each of [he three separate mine pit wall slope stability evaluations concluded that because the rock mass is
dewatered ;round water will not destabilize the pit walls. The past decade's experience in the Main Cresson
Mine has verified [he analyst's assumption. However, the Main Cresson pit immediately' surrounds the Cresson
underground workings, known to connect directh to the Carlton Tunnel. The possibility exists that mine pits
excavated farther from the dewaterins tunnels may encounter eround water conditions. If ground water is
encountered b}' any of the Cresson mine pits, the stability of the effected pit walls will need to be re-eculuated
by CCSV in a timely fashion.