REV88066

• Permit No: M1980244
• IBM Index Class Name: Revision
• Doc Date: 9/29/2004
• Doc Name: Dr. Adrian Browns Responses
• From: CC&V
• To: DMG
• Media Type: D
• Archive: No

Memorandum Adrianr®~
Date: September 27, 2004
To: Phil Bames, Manager, Environmental Affairs, CC&V
From: Adrian Brown, P.E., Adrian Brown Consultants, Inc.
Subject: Responses to "Review of TR-43, CC&V, Cresson Project, East
Cresson Extension" by Dr. Harry Posey, Colorado Department of
Natural Resources, Division of Minerals and Geology, dated July 20,
2004.
Exhibit F and Exhibit T
See Drawing F-1a: "Post-Mining Topography with ECME Added" and related text.
See Adrian Brown report, pp 18-19 discussion of acid-base accounting.
Comment 1 a. It appears that the ECME will be reclaimed using waste rock fill. Based
on analyses in AM-08, fortified with discussions and data reductions in Appendix I
"Hydrochemistry of the East Cresson Mine Extension," the East Cresson Project waste
rock is potentially acid generating. Tables 4 and 5 in Appendix 1 (p. T 8) show the rock
to have a net negative neutralizing potential for both the total sulfur and pyritic sulfur
assessments. This indicates that, unless amended with alkali or placed or capped in a
way to adequately manage infiltration into and discharge of precipitation from the waste
rock fill, then drainage passing through the waste rock would pass through rock with a
net positive acid generating potential and thereby discharge acidic water.
Response: The backfilling of the East Cresson Mine Extension (ECME) will be
conducted with material from other mining location(s) within the Cresson Project. The
mining and overburden storage that will produce the ECME backfill material has already
been permitted and approved. The overburden storage facilities in Amendment No. 8
are not required to include measures to minimize infiltration of precipitation into the
overburden material as Amendment No. 8 analyses and subsequent approvals
determined such measures were not necessary to be protective of the environment. The
approved overburden storage strategy is protective of the environment as a result of
three factors: 1) The net acid neutralizing potential of the overburden generated for the
Cresson Project as a whole is positive (2.8 tons CaCO3/ton), so any acid that may be
generated is expected to be neutralized within the overburden storage facility; 2) Any
acidity that might leave the overburden storage facilities would proceed vertically into
the Cripple Creek Diatreme, and would be neutralized by the calcium carbonate that is
abundant in the underlying diatreme material above the Carlton Tunnel level; and 3)
Any residual acidity that was not neutralized in the overburden storage facility or in
transit through the Cripple Creek Diatreme would be neutralized by alkalinity of the
Adrian Brown Consultants, Inc. Page 1 of 7
130 West Fourlh Avenue, Denver Colorado 80223 USA 9/27/2004
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