2025-06-23_REVISION - M1980244 (96)

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Docusign Envelope ID:45B9721C-FDE2-4821-B686-80BBC79CA6DD 62. Please revise detail X/A029 on Drawing A029 Infiltration Gallery Sections & Details to include the distance or range of distances from the bottom of the 125' well to the PSSA • geomembrane. The ranges of well depth and distance from the bottom of the well have been added to Section X. 63. Appendix B Laboratory Testing contains Table B.1 which shows lab data for 16 of the 19 test pits. Please add a note to the table to explain why Test Pits 3, 12, and 13 were not sampled. A note has been added to Table B.1. Test Pits 3 and 13 were located on a topsoil stockpile, which will be removed before construction; therefore, sampling was not conducted. Test Pit 12 was positioned at the base of a 35-foot exposed cut slope, which was logged as a test pit. Due to exposed pipes on the ground, an excavator could not access the area, and no surface sample was collected. 64. Appendix C.4 Hydrogeological Evaluation of VLF Leachate Injection System into VLF2 , Section 4,describes solution will express, pool, and then run down the crest of the 9550 ft bench beyond 24 hours or depending on the starting level in the PSSA.At the end of this section, it states that if the starting level is 55',the solution mound will reach the surface within 24 hours of infiltration. The Operator will need to thoroughly expanded this section or the designs to include, but not limited to, providing more details on the controls in place to prevent surface expression, commitments from the Operator for how long the infiltration gallery can run while ADR2 does not receive VLF2 Phase 4 solution, commitments from the Operator to notify the Division regarding exceedances of timeframes or surface expression, how solution will be safely conveyed down to the ADR2 platform if solution pools and crests the 9550 ft bench, a time graph which shows when surface expression will occur based on different starting PSSA pool elevations, demonstration to assure the normal operating conditions and an overflowing injection system does not compromise the geotechnical stability of the VLF2 facility, etc. • An analysis of the phreatic surface elevation over time at a point in the middle of the well field, where build up is highest at 24 hours, was completed and is charted in Figure 64-1. One-dimensional numerical modeling in HYDRUS of a single infiltration well was performed and the resulting rise in the PSSA phreatic surface elevation due to the cumulative effects of the entire infiltration well field was evaluated at 5, 10, 15, 20, and 24 hours in order demonstrate the transient rise from static. The rise over time was then plotted as a function of the duration of operation, with each series representing the phreatic surface elevation over time for a given starting PSSA level. The curves range from 9370 to 9430 ft above mean sea level(amsl), which covers the full range of observed values. For starting PSSA phreatic surface elevations of 9410, 9420, and 9430 ft amsl the land surface at the 9550'bench will be breached before 24 hours(at approximately 20.5, 22, and 23 hours, respectively). For all starting PSSA elevations below 9400 ft amsl, the system can effectively operate for longer than the 24-hours that it is designed to. In the event that the 9550'bench is breached, or the slope between the ADR2 foundation and the 9550' bench, the operator will notify the appropriate authorities or agency as outlined in the EPP. However, this is not anticipated to occur if the system utilization stays within the design parameters. To safely guide solution from the 9550-bench to the ADR2 platform, containment berms will be established in the area surrounding the infiltration wells to direct flow to a drop structure. Final design of containment berms and drop structure will be included in final engineering designs. 65. Please confirm and demonstrate that injected solution will not"daylight" out the slope between the 9450' ADR2 pad and the 9550' bench. Please also discuss and demonstrate if the injection wells will impact the nearby PSSA pond level compliance piezometer. • In order to demonstrate that infiltrated solution will not daylight out of the slope between the ADR2 foundation and the 9550' bench, a grid was applied to the well field and surrounding area to provide control points at which the phreatic surface elevation rise from the cumulative effects of the infiltration SSR Mining Inc. PAGE 16/19