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HYDRO30973
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HYDRO30973
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Last modified
8/24/2016 8:54:44 PM
Creation date
11/21/2007 1:05:37 AM
Metadata
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Template:
DRMS Permit Index
Permit No
M1980244
IBM Index Class Name
Hydrology
Doc Date
4/14/1997
Doc Name
INTERNAL MEMO HCI REPORTS CRESSON OPERATION
From
HARRY POSEY
To
JIM STEVENS
Media Type
D
Archive
No
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<br />The HCI (1994) report elaborates on the HCI (1993) report and <br />presents modeling results that include Zn in the acid solution <br />mixture. (Zn is of interest because it occurs in elevated <br />concentrations in some of CC&V's leach tests.) The conclusions of <br />the 1994 report indicate that the researchers were unable to <br />predict the Zn content of the two-fluid mixtures because they did <br />not have sufficient data. I disagree, again, with some of their <br />input assumptions. I do agree, however, that they did not have <br />enough data to make valid predictions. <br />II. PROBLEMS <br />1. Underestimation of acid production potential. <br />It appears that HCI's calculations may underestimate the amount of <br />acid that will be generated by the waste rock for several reasons: <br />a. The models are based on the humidity cell (HC) test <br />results rather than on long term batch (LTB) tests. HC tests <br />are not adequate to determine the amount of acid that will be <br />generated because they characterize water from a single pass <br />of water through a "weathered" rock sample rather than the <br />cumulative water that results as it passes through several <br />volumes of rock. <br />b. The mining area that will be affected by acid water <br />infiltration is lower than what is real because the model <br />results were based on infiltration in the Cresson pit only. <br />The models did not predict infiltration through the Iron Clad <br />Pit, the Globe Hill pit, or through any other waste rock <br />areas. <br />c. The mining area that will be affected by acid water <br />infiltration is lower than what is real because the model <br />results assume that the diatreme outcrop is continuous <br />downward, with minor narrowing, at least to the Carlton Tunnel <br />level [See Figure, attached]. However, only part of the <br />diatreme outcrop is continuous to the Carlton level; part of <br />the diatreme - a part that is unmineralized and thereby is <br />assumed to be a net acid neutralizer - is only a veneer above <br />Precambrian rock. This unmineralized veneer comprises a <br />greater percentage of so-called acid-neutralizing rock at the <br />surface than it does at depth, because it is not present at <br />depth. <br />Neutralizing capacity of the system depends on mixing the sulfuric <br />acid generated from pyrite weathering with the alkaline water <br />currently flowing from the Carlton Tunnel. Current calculations <br />may overestimate the contribution to the Carlton flow from the <br />diatreme (conservative) but underestimate the amount of acid that <br />will be generated (due to the use of inadequate bench test and <br />underestimation of the surface area of the waste rock). <br />
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