2021-11-03_REVISION - M1973021 - Laserfiche WebLink

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Aggregate Industries, Morrison Quarry Amendment No.7 to Permit M-1973-021 FYZ Morrison,CO Exhibit D — Mining Plan Rationale for Amended Mining Plan Amendment No. 05 (AM05) identified a four-phase mining approach focused on: 1) developing the quarry in a manner that will disturb only limited areas each time; 2) facilitating reclamation of mined slopes in inactive areas in a timely manner; and 3) accommodating mine operation considerations. Phases I and II were established to develop the Central and North Quarries; mining operations in these areas are complete, and reclamation activities are ongoing. Phases III and IV focus on development of the South Quarry. Phase III is underway and is the focus of this amendment. Aggregate Industries, Inc. intends to further develop the South Quarry as identified in Phase IV of the AM05 mining plan. However, limited information is currently available to define this phase. Further development will proceed via a future amendment. Since initiating Mining Plan Phase III (opening the South Quarry), local rock observations have resulted in modifications to the bench configuration identified in AM05 for work completed to date. Additionally, recently installed groundwater monitoring wells have identified water levels that will be used to inform the bottom elevation of Phase III mining. A mining plan modification is required to document completed bench geometries and to modify Phase III mining operations based on geotechnical analyses and monitoring of South Quarry work completed to date. The substantial changes proposed by this amendment are: • Documentation of completed South Quarry West Wall benches that deviate from AM05; • Clarification of how mining will be conducted in accordance with the proposed bench configuration and observational method identified in previous amendments; and • Revisions to Phase III bottom elevation to allow for mining to continue in the South and West Quarries until groundwater is encountered Other changes to the mining plan include the redesignation of the ridge west of the Central Quarry as the West Quarry, inclusion of the West Quarry Haul Road in the Mining Plan, , and inclusion of the Unnamed Drainage 1 and 2 (UD#1 and UD#2) draft final design package to satisfy outstanding permit stipulation #10 (refer to Additional Information for stipulation details). Phase III Work Completed to Date To date, Phase III mining operations have resulted in lowering the South Quarry to approximately Elevation (El.) 6,635 on the western face (referred to as the West Wall) and lowering the eastern face (referred to as the East Wall) to approximately El. 6,600. In accordance with AM05, South Quarry West Wall benches above El. 7,000 were mined at a 40-foot highwall and 60-foot bench (60H:40V) configuration and partially reclaimed to El. 7,350. Below El. 7,000, mining has advanced on the South Quarry West Wall and East Wall using various configurations within the maximum 80-foot highwall and minimum 40-foot bench October 2021 1 16