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installation of the tunnel. <br /> Will the portal sediment pond system capacity be sufficient to accommodate this <br /> increased flow rate? <br /> RESPONSE. Yes. Please see response to question on Section 3.4.1 above. <br /> Will maintenance of the pond system continue post-mining? <br /> RESPONSE: Yes. <br /> Will monitoring of the water exiting the portal continue post-mining? <br /> RESPONSE: Yes. <br /> 4.2.3 Static Evaluation of Performance of the Groundwater Neutralizing System <br /> • Page 24: Under Item#1 -Plate 24—Neutralizing Capacity—All Mined Material,the text <br /> states"when the remaining acid enters the saturated zone in Cell 3,no acid is added because <br /> the cell is saturated, and sulfide oxidation cannot occur. However,the remaining acid is <br /> neutralized by the carbonate in the cell."This statement might be considered accurate as long <br /> as the diatreme water table remains at the level of the Carlton Tunnel (-7,000 feet elevation). <br /> However,throughout the mining operation,the Carlton Tunnel flow rate appears to show an <br /> overall decreasing trend(except for during the high precipitation events of 2014-2015; see <br /> Plate 8—Carlton Tunnel Flow),which may be attributed to less infiltration to the diatreme <br /> due to construction of VLFs, large overburden stockpiles, etc. If the diatreme water table <br /> lowers,there could be a substantial loss of Acid Neutralizing Potential in the mining district. <br /> For example,on Plate 24,the Acid-Base Accounting Flowsheet assumes that vadose zone <br /> rock is not oxidized(not mined)and saturated rock remains saturated(offering <br /> neutralization), giving a net 0 million tons CaCO3 acid equivalent(exiting the Carlton <br /> Tunnel). However, if the diatreme water table were to drop,thereby losing the neutralization <br /> potential of previously saturated bedrock,this would change the flowsheet results. The <br /> estimated 35 million tons CaCO3 acid equivalent from the mined rock would pass through <br /> both the vadose zone and the previously saturated zone with no net change, leaving 35 <br /> million tons CaCO3 acid equivalent. Because the Carlton Tunnel only drains diatreme <br /> groundwater at approximately 7,000 feet elevation, a reduced water table may not drain to <br /> this tunnel. In this case,there could potentially be acidic groundwater sitting below the <br /> tunnel elevation,which only exits the portal during high infiltration events(as experienced in <br /> 2015).Do you have a plan in place to mitigate impact to Fourmile Creek in case of loss of <br /> Acid Neutralization Potential in the diatreme due to lowering of the water table? <br /> RESPONSE:In the unexpected event that infiltration reduces to the point where it would <br /> create a lowering of the water table in the diatreme, exposing more sulfide for oxidation <br /> and reducing the saturated carbonate, the water level in the diatreme can be raised back <br /> to or above the current level by emplacing a plug in the Carlton Tunnel and raising the <br /> exit elevation to any desired level. <br /> 4.2.3 Static Evaluation of Performance of the Groundwater Neutralizing System <br /> • On Plate 25—Neutralizing Capacity—All Vadose Material, some of the data listed appears <br /> to be inconsistent with what was listed elsewhere. In the Acid Generation Computation <br /> table, for Cell 2: Vadose Zone Rock, under the column Vadose Zone Acid Generation <br /> (million tons CaCO3), the first four values listed are"13,45, 194, 303". However, on Plate <br /> 19—Acid Generating Potential,the values associated with these elevations are listed as <br /> Page 11 of 28 <br />