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
changes will occur. However, this notion is not supported by the hydrology or
geochemistry described in Amendment 8 and augmented in this TR.
Response: The commenter is correct in stating that changes in infiltration of
precipitation or chemistry as a result of the development of the ECME are in general
quantifiable. The quantification is illustrated below for the infiltration and the
geochemistry.
Influence on Infiltration
The amount of additional precipitation entering the diatreme through the ECME is
quantifiable and predictable, and measurable by monitoring the water exiting the Carlton
Tunnel, which integrates all the infiltration to the diatreme. The prediction of the
additional precipitation entering the diatreme as infiltration due to the proposed ECME
project is presented in TR-43 Exhibit F, Section 4.2, based on infiltration parameters
calibrated on the current project, as presented in Amendment No. 8.
This quantification indicates that there will be increased infiltration through the
approximately 50 acre footprint of the ECME during its operation (with an approximately
corresponding reduced diatremal infiltration due to the storage of the overburden from
the mine elsewhere) then no infiltration from the backfill for approximately 12 years due
to incident moisture uptake in the backfill, after which time the infiltration rate will return
to the pre-ECME level (due to reclamation of the surface of the ECME). This
quantification of the effect of the ECME on groundwater infiltration is refined from
Amendment No. 8, which (conservatively) did not take account of moisture uptake in the
stored overburden to return it to field moisture content.
The refinement has been adopted because there has been no observed increase in the
rate of water exiting the Carlton Tunnel as a result of CC&V mining on the 9,342-acre
diatreme to date, despite the prediction in earlier Amendments that there would be an
increase. The current evaluation was refined by including the effect of the moisture
uptake of the overburden produced by mining, which improves the accuracy of the
prediction of infiltration.
Influence on Water Quality
The evaluation of impact of infiltrating water from mine backfill in the Cresson Project
mines has been presented in Amendment No. 8, and that evaluation is applied in the
ECME TR-43 (Section 3.2). It states that any sulfide oxidation that may take place in the
backfill material will be neutralized by the Cresson Project-wide net neutralizing capacity
of the overburden rock. To the extent that any un-neutralized acidic water infiltrates the
underlying bedrock from the backfill, it will be neutralized by contact with the net
neutralizing rock along the flow pathways, and/or by mixing with the neutralizing water
in the regional groundwater system, prior to exiting the diatreme. Based on the analyses
presented in Amendment No. 8> the infiltrating water will also become locally saturated
with calcium sulfate and zinc species in transit through the rockmass. This process has
been observed since before the current mining by CC&V, and has limited the transport
of dissolved species to the regional ground water system both before and during the
CC&V mining period. Thus the acidity and concentration of species in the water exiting
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