2025-06-23_REVISION - M1980244 (96)

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Docusign Envelope ID:45B9721C-FDE2-4821-B686-80BBC79CA6DD well field could be calculated. The calculated phreatic elevation at 24 hours from a starting level of 9400 ft amsl (or 50 ft above the liner surface at the observation well) was then subtracted from the land • surface elevation, yielding the unsaturated thickness remaining between the phreatic surface and land surface. This information is displayed as a raster in Figure 65-1. It is evident that there is remaining unsaturated material along the bench face and along the 9550'bench top. The extent of the raster also corresponds to the calculated extent of the infiltration well field on the phreatic surface (outside of it there is no calculated effect). The current observation well lies outside of the calculated area of effect. 66. Please inform the Division how the results of the testing program and any necessary revisions to the design discussed in Section 6 and 7 of Appendix C.4 Hydrogeological Evaluation of VLF Leachate Injection System will be provided to the Division prior to construction of the full injection system. Data for test well flow rates and measured solution levels in the subsurface via the accompanying observation wells, will be provided in excel format following the testing. Any necessary revisions to the system will be documented and explained in a subsequent Technical Memorandum. 67. Within Appendix C.5, Drawing 810-30-01 Rich Solution Plan & Profile, a 28" pipeline is drawn along the same alignment as the four VLF2 Phase 4 solution pipes, but bypasses the collection tank and continues along the toe of the 9650 ft bench's slope. Please provide additional details of this line. Drawing 810-30-01, Rich Solution Plan & Profile, has been updated to Revision B to remove the 28" pipe in question, which was included in error. The Drawing now aligns with Drawing 810-20-01 Revision A, accurately reflecting the pipes in the area 68. Within Appendix C.5, Drawing 810-60-01 Collection Tank Layout,there are four 24" inlet flanges to receive solution from the four VLF2 Phase 4 solution pipes, however based on details provided within Appendix 1-Valley Leach Facility Expansion Design Report only • two of these pipes are 24" in size with the other two being 28". Please explain this discrepancy. The inlet flange size has been updated on Drawing 810-60-01 Revision B with two 24" and two 28" flanges to match the connecting pipes. 69. In Appendix E,the cases described through the geotechnical analysis assume a case where little to no solution is present within the ore except for residual solution near the liner. Please provide additional information regarding the choice to rely on this set of conditions, as well as an additional case that better represents conditions closer to those present during active leaching operations. The geotechnical analysis models phreatic conditions within the HLP at approximately two feet above the HDPE liner (0.5 feet above the liner was an error in the original submittal), representing a fully drained heap with minimal solution accumulation along the base geomembrane within the drain cover fill(DCF)layer. Without prescriptive criteria that define the maximum head allowed on the liner, industry practice is to keep head on the liner within the DCF layer. The calculations that were provided in Appendix C demonstrate that the average head on the liner will remain below 1.5 feet with a maximum of 1.9 feet.All four scenarios maintain the head within the 2-foot DCF layer.A system of 4-inch diameter collection pipes placed at a maximum spacing of 65-feet on center will provide sufficient drainage capacity to minimize the head on the liner. Additionally, the pads are free draining, so there will not be a constant head on the liner at the downstream toe of the facility. In response to this comment, an additional case has been modelled for each section to be more representative of active leaching operations. The additional case considers a higher phreatic surface within the heap, accounting for transient solution levels during leach cycles. The leach solution • application rate to the heap is 0.0055 gallons per minute per foot squared (gpm/sf). The hydraulic conductivity of the DCF is approximately 1.1E-01 centimeters/second (cm/s). The lower bound SSR Mining Inc. PAGE 17/19