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
Carlton Tunnel discharge water quality, or that such water will be controlled in a fashion
that will minimize impacts to the hydrologic balance.
Response:
Flow
The flow evaluation performed as part of the TR-43 and submitted in Exhibit F, Section
4.2, and discussed at length in earlier responses to comments predicts that there will be
no "additional waters" flowing into the regional groundwater system intercepted by the
Carlton Tunnel, as a result of the development of ECME. This prediction is supported by
the observed lack of increased flow resulting from the considerably larger developments
and surface disturbances associated with the currently permitted mining project.
Water ouality
The geochemical evaluation performed for Amendment No. 8, and confirmed by
evaluation of the actual response to development of the mining projects permitted under
Amendment No. 8 and prior amendments, indicate that there will be no impact to water
quality in the flows exiting the Carlton Tunnel.
In addition, CC&V is currently monitoring flow and water quality in the Carlton Tunnel
and will continue to do so by permit requirement. If, contrary to the predictions of
Amendment No. 8 and the current TR-43, there were an identifiable impact to the water
quality and/or hydrologic balance resulting from the development of ECME, it would be
observable in the flows exiting the tunnel. Thus there is no possibility that there will be
an unobserved, or unmitigable impact, on water quality or hydrologic balance. This
provides additional assurance to the Division of environmental protection.
Appendix 1, p.3, Section 2.4 and Appendix 5, sec 2, comment 3.
Comments in these two segments do not agree. The first says that `Yhe diatreme is
dominated by vertical orsub-vertical faults, joints, and dikes oriented approximately
N20W to N50W, with a complementary minor fabric oriented N20 E to N70E. ° The
second says `The only consistent structures in these rocks (bedrock] appear to be sub-
vertica/ faults and joints, oriented approximately northeast-southwest." Both comments
ignore fhe veins, which also have a northwesterly fabric. Whether this error in the
dominant structural orientation was propagated through structural stability calculations
is not evident. Please clarify, and verify whether the existing stability calculations are
correct.
Response: The commenter identifies an error in the characterization of the structural
conditions in the diatreme: `beins" are not specifically considered. Veins are not called
out specifically in the structural description because they are relatively rare, are almost
always sub-vertical, and almost always follow (and are frequently identified as or are
associated with) major faults. Features that might be described as veins in the Cresson
rockmass are in general integral with the rock, and do not generally form zones of
weakness separate from zones of weakness associated with faults. From the point of
r- - - - --
Adrian Brown Consultants, Inc. Page 6 of 7
130 West Fourth Avenue, Denver Colorado 80223 USA 9/27/2004
Phone:[phone]Fax:[phone] Email:abrown~abch2o.com 16:29