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• Response: <br />It is possible that alkalinity is rising at the end of the reported data period. However, CC&V <br />has not taken credit for further protective neutralization in the application, so any increase <br />represents further conservatism in the evaluation. <br />CC&V believes that the principal reason for the increase in alkalinity is the reduction in <br />opportunities for rapid flow of infiltrating water through (particularly) historical <br />underground mine workings to the regional ground water table intersected by the Carlton <br />Tunnel. This bypass water may have required some further neutralization within the Carlton <br />Tunnel, resulting in a reduction of the alkalinity in the water emerging at the portal. In the <br />last decade CC&V has been diligently closing surface and subsurface openings to the <br />interconnected network of historic mine workings, covering a significant percentage of the <br />ground surface with finely divided overburden materials, and backfilling previously open <br />mines. The ensemble effect of this appears to significantly attenuate the ingress of water to the <br />diatreme, which has in turn resulted in fewer and less extreme flow peaks observed in the flow <br />of water from the Tunnel. CC&V would attribute the potential increase in alkalinity as a <br />direct positive consequence of the current mining activities performed by CC&V. <br />0. The reported carbonate contents of the diatreme below elevation of 7500-8000, based on <br />data from only three deep drill holes, is substantially greater than the reported carbonate <br />• content of shallower depths that were based on a significantly larger number of drill holes. <br />Is the carbonate content at depth real, or is it a function of the smaller sample size and good <br />fortune in hitting carbonate rich zones when drilling the deep test holes? It would be <br />beneficial to have more complete deep drill hole coverage. Lacking that, DRMS <br />recommends sensitivity analyses of the acid-generating characteristics of the deep diatreme <br />assuming a more uniform carbonate content top to bottom. <br />Response. <br />CC&V considers that the identified carbonate at depth is "real". However, the point made by <br />DRMS is well taken, as one of the holes identified a very rich carbonate mass at depth. <br />Inspection of Figure 17 of the MLE Project Application indicates that at below elevation <br />8,000 ft the carbonate content rises from about 7.5% to about 9%, if one ignores the interval <br />from 7,000 to 8,000 ft. The carbonate available for neutralization has been recalculated <br />ignoring the high carbonate hole in this elevation range, and assuming that there is a gradual <br />increase in carbonate from 8,000 ft elevation down to 5,500 ft elevation. <br />The results of this evaluation are that the available calcium carbonate is as presented in Table <br />5. <br />Table 5 - Minimum Carbonate Mass in Diatreme <br />• <br />Elevation <br />(ft msi) Diatreme Mass <br />(million tons) CaC03 <br />(%) CaC03 <br />(million tons) Total CaC03 <br />(million tons) <br />10000-10500 2206 1.0 22 22 <br />9500-10000 4511 2.2 100 122 <br />9000-9500 4570 3.4 154 276 <br />8500-9000 3902 5.3 207 482 <br />?9