2023-10-31_REVISION - M1973021 (5)

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Holcim-WCR,Inc. I Morrison Quarry Drainage Report Appendix F—Hydraulics Appendix F — Hydraulics This calculation is used to determine the drainage diversion dimensions, riprap requirements, and outlet apron configuration. Phase III Drainage Report — Proposed Drainage Diversion 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. uesign 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) and included analysis of potential detention basins to mitigate peak flows leaving the site. The Phase III Design analyzed here does not require a detention basin because all flows continue to remain on site. The Phase III Drainage Diversion is proposed to be a uniform channel with a prepared subgrade consisting of existing reclaimed slope materials, an impervious liner with non-woven geotextile placed upon the subgrade, and a layer of riprap placed upon the liner material. Freeboard will be the greater of 1 foot or the hydraulic energy of the peak design flow in the channel as previously used in the Phase 11 Report in accordance with Jefferson County requirements. Proposed Drainage Diversion Drainage Diversion Location The drainage diversion is proposed to intercept flows originating from the reclaimed South Quarry slope and direct flows away from the highwall. The diversion is planned to flow north parallel to the highwall along an inactive bench at a mild slope and then travel down a steeper chute slope to outlet to the South Quarry drainage area. Model Parameters and Assumptions The hydraulics for the drainage diversion were analyzed using Manning's open channel equation and the chute design is calculated using an National Resources Conservation Service (NRCS) excel workbook based on Design of Rock Chutes by Robinson, Rice, Kadavy, ASAE, 1998. Bentley's FlowMaster software is used for performing the Manning's channel sizing calculations.