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<br />- 9- <br /> <br />The discussion about the relation between paste pH, NNP, depth, and sources of acidity is not <br />everywhere supported. <br />(a) Paste pH, which is dominantly a soil test, can provide information on hydrogen ion activity that <br />would result immediately by saturation of a previously unsaturated media. That a paste pH <br />measurement of unoxidized or slightly oxidized rock is an appropriate utility for predictions of <br />long-term ARD potential is not unambiguous. <br />(b) The text indicates, last paragraph, page 25, that less than one third of the 578 samples tested <br />show signs of acidification from sulfide, and refers to figure 4-4, yet clear support for this <br />statement based on figure 4-4 is not apparent. (This discussion is re-visited on p 36-37.) The <br />figure depicts approximately ] l3 samples, not 578 as slated. The figure shows that 7090 of the <br />samples have a net negative NNP. <br />Please address the apparent discrepancies between figure 4-4 and the text. <br />Please re-visit the presumptions about paste pH, lack of oxidation at depth, evidence far lack of <br />acid production in the shallow sections, and the use of paste pH as a predictor of NNP. <br />Please provide adequate figures to support the statements in the test or remove the statements <br />altogether. <br />5. Page 36-37, Vol. II <br />The text states: <br />"Taken together, the NNP and paste pH trends with depth [Figure 5-4] indicate there was a <br />higher sulfide to carbonate ratio originally present in the diatreme at elevations above about <br />9000 ft. Otherwise, the paste pH values in the oxidized zone would be expected to be entirely <br />alkaline, as they are at lower elevations, where the NNP values increase to large positive <br />va]ues." <br />While the utility of this presumption is not evident, the statement nonetheless is unsupported. <br />Please explain this conclusion. <br />6. Pale 38, 2"a par. <br />It appears from discussions in the amendment and site knowledge that overburden from the East <br />Cresson and North Cresson pits, which were determined to have net negative neutralization <br />potential, are deposited in part in the SGOSA. Acid venerated by this rock may be neutralized <br />by reaction with carbonate in the lower pan of [he diatreme. Absent precipitation or adsorption, <br />zinc that may be dissolved from waste rock in the mining zone and carried into the groundwater <br />system could increase the overall concentration of zinc in [he diatreme and in the Carlton <br />discharge. <br />The text indicates that carbonate which precipitates in the diatreme derives from "increased <br />interaction of the wound water with carbonate minerals" in the diatreme. It is not evident how r <br />solution that becomes carbonate-saturated due to water-rock interactions along a flow path can <br />then precipitate carbonate without a chance in some other extrinsic property such as a change in <br />temperature, pH, salinity, Ca'' or CO;-concentration, or pC0- decrease. Because the only <br />