2023-10-31_REVISION - M1973021 (7)

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Holcim-WCR,Inc. I Morrison Quarry Drainage Report Appendix E—Hydrology Appendix E — Hydrology This calculation is a revision to the Phase II Drainage Report Hydrology performed by Brown and Caldwell in July 2021. The "Existing Conditions Drainage Map" presented as Figure B-1 in Appendix B and the analysis performed previously have not been modified to maintain a consistent comparison. Phase III Drainage Report — Proposed Condition Revisions This calculation serves to support the design of the Morrison Quarry Drainage Diversion. The Phase 11 proposed condition analysis performed by Brown and Caldwell (2021) had identified potential diversion routes that had the potential of affecting the offsite drainages adjacent to the mine. However, during design it was determined that a diversion offsite could be difficult to construct and maintain. The HDR drainage diversion presented in this Phase III Drainage Report and supported by this calculation maintains off site drainage as-is and flows on site will continue to be managed as permitted by Colorado Department of Public Health & Environment (CDPHE) certificate number COG500320 presented in Appendix C. The flows estimated here are used for the hydraulic design and analysis of the proposed Phase I II Drainage Diversion. Design Criteria The 2021 Phase 11 Drainage Report used excel templates provided by the Mile High Flood District (MHFD) that are based on the Colorado Urban Hydrograph Procedure (CUHP). This calculation uses the latest CUHP excel templates from the MHFD to analyze the peak flow for the diversion channel and evaluates the revised drainages shown in Appendix B. Drainages are updated in this Phase III Drainage report that include the proposed diversion, surveyed haul road, and reclamation as of June 2023. Proposed Diversion Drainage Drainage Catchment Revisions The following drainage revisions were analyzed for the proposed diversion and include site changes that are typical of active mining operations. The drainage names here correspond to the names presented in the Appendix B report figures: • Drainage 02A —This area includes reclamation activity above the proposed diversion and areas above the diversion and below the installed haul road. The 90 percent Phase III diversion was previously anticipated to tie into a culvert drainage channel installed with the new haul road. The haul road was not constructed with culverts and therefore the diversion has been extended to tie into the existing mine stormwater management drainage in this report. • Drainage 02B —This drainage includes areas below the drainage diversion, the South Quarry, and the area previously identified as Drainage 04 that were altered due to ongoing mine operations.