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• material and are more readily flushed and mobilized than are the products of more <br />refectory sulfides that are present in the un-oxidized material? Please comment on this in <br />terms of how much of this material might be present and what effect it might have on water <br />quality? <br />Response. <br />Humidity cell testing of the materials that would be mined as part of the MLE Project shows <br />consistently that there is very little sulfate present in the samples at the start of testing, and <br />almost no constituents are mobilized from the material in the initial leach (MLE Project <br />Application, Appendix 1, Attachment 4). In addition, the limited material that is mobilized <br />by the initial leach is considered in the overall test analysis, and is included in the analysis <br />results. Thus, any initial leach would have no incremental effect on the water quality. <br />M. Vol. II PG. 15 states that sulfate and zinc releases will not result in loading increases as <br />calculated, because of factors such as the slow transport of the constituents and water <br />sequestration. This reasoning is not entirely clear and requires further explanation. <br />Additionally, this analysis begs the question that after the plug of newly released sulfate <br />and zinc have been migrating downward for some years, is it reasonable to assume that the <br />condition of chemical steady state can be attained through the vertical section of the <br />diatreme in which those calculated concentrations (22,000 mg/l for sulfate, and 159 mg/1 <br />for zinc) may actually be sustained? <br />• Response. <br />The principal reason that the zinc and sulfate loading that may be generated in overburden <br />will have no incremental increase in concentrations in the regional ground water table <br />intersected by the Carlton Tunnel is that the seepage carrying the constituents would be <br />neutralized in transit by the abundant carbonate in the diatreme. Neutralization changes the <br />geochemical condition of the leachate, causing the sulfate and zinc to precipitate. The slow <br />transport allows time for the full neutralization reaction to occur, including diffusion of <br />acidic fluids into rock particles to access disseminated carbonate. These are processes that are <br />naturally occurring as the diatreme slowly oxidizes. Proposed mining by CC&V may affect <br />the rate of that oxidation, but with abundant carbonates in the deep diatreme, this would not <br />affect the quality of the regional ground water that is intersected by the Carlton Tunnel. <br />For the chemical steady state envisioned by the DBMS to occur, the entire inventory of <br />carbonate in the diatreme would have to be consumed, and neutralization of the transporting <br />liquor would have to cease. CC&V has demonstrated that this would not happen as a result of <br />the oxidation of sulfides in the overburden materials contemplated to be exposed in the entire <br />Cresson Project, inclusive of the MLE Project. <br />N. A statement is made that the alkalinity has leveled off in the Carlton Tunnel Discharge. In <br />fact, the three highest alkalinity values ever measured have been collected in the past 5 <br />sampling events shown on Figure 18, suggesting the alkalinity values are on the rise again. <br />• It may be beneficial from a modeling standpoint to quantify why alkalinity has been <br />increasing in recent years. If future overburden leachate turns out not to be as predicted, <br />better knowledge of the factors controlling alkalinity generation could greatly help in the <br />future mitigation. <br />RR