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Please provide adequate figures to support the statements in the text or remove the <br />statements altogether. <br />Page 36-37. <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 <br />entirely alkaline, as they are at lower elevations, where the NNP values increase to large <br />positive values." <br />While the utility of this presumption is not evident, the statement nonetheless is unsupported. <br />Please erplairr this conclusion. <br />Page 38, 2nd 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 generated by this rock may be neutralized <br />by reaction with carbonate in the lower part of the 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 the 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 ground water with carbonate minerals" in the diatreme. It is not evident how a <br />solution that becomes cazbonate-saturated due to water-rock interactions along a Flow path can <br />then precipitate carbonate without a change in some other extrinsic property such as a change in <br />temperature, pH, salinity, Ca.z or C03- concentration, or pCOz decrease. Because the only <br />documented control over removal of dissolved Zn is Zn adsorption via cazbonate precipitation, it <br />seems important that the mechanism of carbonate precipitation be understood. <br />Please explain in more specific geochemica! terms how carbonate cun•ently forms in the <br />diatreme. <br />Please explain l:ow the diatreme solutions car? simultaneously dissolve and precipitate <br />carbonate to sorb Zrr. <br />GENERAL COMMENTS <br />1. The geology section indicates that most of the water derived from surface infiltration moves <br />downward through the diatreme via discrete fracture tlow rather than by more homogeneous <br />porous media flow. The model for acid neutralization by cazbonates in the deeper part of the <br />diatreme however appeazs to rely on rather diffuse water movement through a somewhat <br />homogeneous porous media. <br />3 <br />