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Cresson Pro'ect H dro • eochemist AdrianBrown <br />from the start of surface mining to the end of MLE2 based on current production rates is determined as <br />follows: <br />• Carbonate required to neutralize mined rock oxidation products < 38 million tons ( §3.3.2 above) <br />• Carbonate available for neutralization = 2,055 million tons ( §3.3.3 above) <br />• Proportion of carbonate to neutralization overburden acid products < 1.8% <br />The calcium carbonate available in the Diatreme is more than 50 times the mass required to neutralize <br />all products of complete sulfide oxidation in all rock surface mined up to the end of MLE2. <br />Neutralization of water infiltrating from the surface of the Diatreme requires contact with the <br />neutralizing material. This contact could be avoided by flow down preferential pathways in the <br />Diatreme, in particular fractures, faults, or mined underground openings (such as stopes). In the <br />Diatreme this is not expected to be a significant factor, for the following reasons: <br />1. There is a great excess of calcite over requirements, so contact with calcite is inevitable in a <br />flowpath length of between 3,000 feet and 12,000 feet. <br />2. A significant portion of the flowpath for all ground water movement to Carlton Tunnel will take <br />place in the saturated portion of the Diatreme, where there is relatively high calcite <br />concentration, very slow flow, and flow generally not along major natural or mined conduits. All <br />of these factors encourage contact with neutralizing material within the rockmass. <br />3. Neutralization of the products of sulfide oxidation by natural calcite creates gypsum, as shown in <br />the neutralization equation below (for high concentrations): <br />CaCO3 + H2SO4 = CaSO4 + H2O + CO2 <br />Accordingly, locally neutralization causes the replacement of the dissolved calcite by gypsum, <br />resulting in little if any decrease in solid phase volume. Thus formation of preferential pathways <br />by dissolution of carbonate is not expected to be significant in this system'. <br />Accordingly it has been determined that there will be no detrimental change in the water quality in the <br />Diatreme, or in the flow of water from the regional ground water system at the Carlton Tunnel as a <br />result of the proposed MLE2. <br />3.3.5 Carlton Tunnel Water Quality Verification <br />Verification that the protective geochemical process of neutralization is occurring and will continue to <br />occur in the Diatreme is available by reference to the quality of the regional ground water flow from the <br />Carlton Tunnel This tunnel collects essentially all of the ground water entering the Diatreme and the <br />immediately contiguous rocks, and forms a single location for monitoring and evaluating the <br />geochemical processes occurring in the Diatreme and contiguous areas. <br />The water quality data from the Carlton Tunnel provides three verification opportunities, as follows. <br />' In the natural system, massive gypsum and/or selenite are present as joint and fault fillings in considerable quantity at depth in the <br />Diatreme, apparently as a result of neutralization of naturally- produced products of sulfide oxidation. <br />1385L.20120125 19 <br />