2021-09-07_REVISION - M1973021 - Laserfiche WebLink

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Aggregate Industries, Morrison Quarry Amendment No.7 to Permit M-1973-021 FN Morrison,CO Exhibit DA presents the West Quarry Haul Road final configuration. Exhibit D.2 presents the buildout configuration for Phase III in plan view. A detailed narrative for Phase III is provided below. Mining Operation Support Structures Phase III mining operations prioritize completion of support structures critical to re-establishing access to the upper quarry and maintaining surface drainage control as mining in the South and West Quarries progress. Construction of the West Quarry Haul Road, a structure necessary to re-establish access to the upper benches of the South Quarry and commence West Quarry development, is underway and is scheduled for completion in late fall 2021. The Haul Road plans were summarized in Technical Review (TR07) and approved in July 2020. TR07 included the haul road design specifications and proposed configuration, but recognized that the final road alignment was pending and would be finalized in conjunction with AM07. Since the start of the construction, fill material limitations have resulted in a change to the road alignment to maximize the use of cut material. Exhibit D.1 presents the final West Quarry Haul Road design configuration, based on work completed to date and current design plans. As mining and reclamation continues in the South and West Quarries, the haul road will be removed as benches progress eastward. Once haul road construction is complete and concurrent with the South and West Quarry upper bench reclamation activities, runoff from UD#1 will be permanently diverted to UD#2. The drainage diversion structure consists of an open culvert and two detention basins: one at the culvert inlet and one at the UD#2 culvert outlet. All drainage diversion structures were sized based on calculated 100-year peak flow rates and runoff volumes to limit impacts to downstream structures in UD#2. Both detention basins will include emergency spillways, designed to accommodate 500-year peak flow with 50% grate blockage. Detention Basin 2, the inlet basin, will be installed at approximate El. 7,040 on the north side of the South Quarry western face to intercept UD#1 along its natural flow path. Water will pass through the outlet control structure to a culvert to be installed on the existing upper western bench at El. 7,040 with a slope of 0.2% carrying water south along the bench towards UD#2. Once the culvert exits the western face bench, the slope will increase to 1.1% and pass through a control structure to enter Detention Basin #2. From there, water will discharge to UD#2. The drainage diversion will remain after mining activities are complete. The draft final Drainage design can be found in Appendix 2, and Exhibit F.3 presents its final configuration. South Quarry Development Phase III continues full development of the South Quarry. South Quarry mining activities will first focus on lowering existing benches in the southwestern corner of the quarry to El. 6,500. The 2020 Annual Report Geotechnical Addendum and visual inspections for benches completed through April 2021 in this area have identified localized instabilities and slope failures. Based on these observations, remaining bench configurations in the southwestern corner of the South Quarry will be a maximum bench height of 40 feet and a minimum bench width of 40 feet, for a maximum bench configuration of 40H:40V. Once mining in this area is completed, mining will September 2021 1 17