2024-02-01_REVISION - M1973021 (2)

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AR9 On page 5, the text states that Figure 1 shows the site location, drainage paths, drainage features, outfalls, and the surrounding major drainage ways. However, Figure 1 is primarily a site vicinity map. Please provide a figure (or figures) that clearly identifies all the items listed above in the text. No new figures created. Text on page five updated as follows: Figure 1 shows the Site location. Figure 2 the Bear Creek Drainage Basin major drainageways. Appendix B, Drawing B-1 shows existing site drainage features and outfalls. Appendix B, p. 5. AR10 The text on page 7 states that Turkey Creek flows south into Bear Creek. This appears to be incorrect and should be revised. No change. Text states that Turkey Creek flows south into Bear Creek Lake. This statement is correct. AR11 Figure 2 on page 7 shows the site location as north of the Turkey Creek drainage basin, but this appears to conflict with text provided in the report. Please modify the text and/or the map for accuracy and consistency. Site location dot enlarged to show coverage in both Bear Creek and Turkey Creek drainage basins. Appendix B, p. 7. AR12 On page 11, the 100-year design storm (2.22 inches) appears to be a one-hour duration storm. Section 5.3 of the Jefferson County Storm Drainage Design and Technical Criteria suggests that a two-hour storm is more appropriate for this site, and the total rainfall should be 2.86 inches. Please either explain why the provided design storm of 2.22 inches is appropriate, or revise the design to use the value of 2.86 inches. As was stated in Section 2.1 of the drainage report, the diversion structure updated in this report provides for on-site management of drainage before it is conveyed to existing outfalls (in accordance with the site's SWMP). Given the on- site water management strategy and industrial nature of the facility, the 1-hour duration storm (2.22 inches) was considered an appropriate design criteria for the drainage structures. No changes made to the document. AR13 Site Conditions: Please have Holcim provide a map detailing the name and location of each borehole that was discussed and used within HDR’s Report for the Division’s review. Adding Boring Location Map at beginning of Appendix A and referenced in text within Section 3 - Field Evaluations. Appendix A, Section 3 p. 8, Document Appendix A. AR14 Site Conditions: Please have HDR provide discussion regarding the potential of groundwater, or lack thereof, to ensure the impacts of groundwater are accurately taken into account within the slope stability analysis if necessary. While there is groundwater below the current pit floor at El. 6600, the fractured nature of the rock is such that hydrostatic pressure is unlikely to build up significantly behind cut faces. Dewatering will occur during mining operations and the rock mass has a very high secondary permeability, which will therefore drain efficiently alleviating hydrostatic forces from saturated conditions of the ADEQUACY REVIEW (AR) Letter #2 November 8, 2023 - Final Drainage Report ADEQUACY REVIEW (AR) Letter #3 January 12, 2024 - Geotechnical Stability Exhibit 1