2023-10-31_REVISION - M1973021 (2)

Home Browse Search

3. Drainage Facility Design For operational purposes, Holcim plans to divert stormwater from the reclaimed slope of the south quarry highwall above elevation 7,110 ft. in a proposed diversion channel. The diversion channel will 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 along the installed west quarry haul road. The reclaimed south quarry slope above and below the diversion channel, and the portion of the diversion channel constructed on the reclaimed South Quarry bench are permanent features that will remain during mine operations and post-closure. The portion of the diversion channel constructed along the existing topography below the current West Quarry Haul Road, referred to herein as the diversion channel chute, is a temporary feature that will be removed or modified as the West Quarry mine plan progresses. The updated design will be completed at a later date. This report documents the design of the diversion channel. 3.1 Proposed Sub-Drainage Basins There are 10 proposed sub-basins on Site, of which only three, 02A, 0213, and 03, are impacted by the diversion channel design, as shown on the Proposed Drainage Map in Appendix B and summarized in Table 3-1. Table 3-1. Proposed Sub-basin Characteristics Summary Drainage Area Description Drainage Runoff Outfall Area acres 01A and 01B UD2 58 Off-Site 02A Reclaimed portion of the 15 Conveyed to Outfall 003 or south quarry highwall above detained in south quarry and the proposed diversion pumped to Outfall 006b channel and areas above the diversion channel and below the installed west quarry haul road. 02B The South Quarry below the 55 Conveyed and detained in south diversion channel, inclusive of quarry and pumped to Outfall 006b the area previously identified as Drainage 04 in the South Quarry that were altered due to ongoing mine operations. 03 UD1, the installed west 87 Detained in central quarry and quarry haul road, and the pumped to central quarry. The hydrologic boundary is Outfall 003 or 005b updated to reflect the installed west quarry haul road and proposed diversion channel. 1670 Broadway,Suite 3400,Denver,CO 80202-4824 hdrinc.com (303)764-1520 13