2021-09-07_REVISION - M1973021 (4)

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Aggregate Industries, Morrison Quarry Amendment No.7 to Permit M-1973-021 FN Morrison,CO Additional variability of benching is planned along the proposed elevation interface between Phases III and IV, where the shoreline for a potential reservoir in the South Quarry is planned. Equipment used for backfilling will include a D-9-sized dozer, a 988 B-sized loader, and a 50-ton haul truck, or equivalent machinery. The vegetation, wildlife habitat structures, rockpiles, and other components of reclamation (detailed in Exhibit F.5) will then be placed on the benched or sloping surface. An access road will be located on the steep upper reclamation benches to allow for hydroseeding and to assist in monitoring revegetation programs in these difficult-to-access areas. Reclamation of Phase IV South Quarry As discussed in Exhibit D— Mining Plan, Phase IV— South Quarry Deepening, Phase IV finalizes expansion of the South Quarry by lowering the bottom of the South Quarry to El. 5,840. Mining operations in Phase IV are anticipated to occur within the water table, requiring dewatering and water management throughout the mining process. Additionally, end uses of the South Quarry are still under consideration. Until such time that the hydrogeologic and geotechnical investigations are complete and end use decisions are made, Phase IV is considered conceptual, and work pursuant to Phase IV will not begin until the investigation results and final end use decisions are documented in a future Permit Amendment. To allow for flexibility regarding the final layout and end use of a possible reservoir, the South Quarry will maintain a slope no steeper than 3:1 to be configured 5 feet above and 10 feet below the estimated elevation of groundwater. Based on piezometer (MW-2019-02 and MW-2019-03) data in the South Quarry from 2020 to 2021, it is assumed the groundwater would be encountered and reach a hydrostatic equilibrium between El. 6,495 and El. 6,500. Habitat management and creation along the slopes within the South Quarry will provide suitable wildlife habitat. As the South Quarry reaches the end of mine life and final reclamation efforts begin, the operator will work with Colorado Parks and Wildlife and/or federal agencies with wildlife responsibilities to see if any unique opportunities are available to enhance habitat and/or benefit wildlife that could be accomplished within the framework of the Reclamation Plan and costs. Some potential options for enhancing habitat are provided in the Revegetation section below. Because the slope configuration of Phase IV will be highly dependent on the results of further geotechnical and hydrogeologic investigations and revisions to the mining plan, the costs for reclamation of the 91.5 acres of Phases III and IV (shown in Exhibit F.3) are based on an assumed 10HAV fill slope below El. 7,000. This 10HAV slope assumes average variations between the 1H:1V and 20HAV slope configurations that were approved in AM05. Based on the estimated 91.5 acres for the South Quarry below El. 7,000, a total of 492,067 cubic yards will be needed for fill material. The majority of this volume is included in Table E-1 for the South Quarry Phase III work between EL. 7,000 and El. 6,500, totaling 414,089 cubic yards. Stormwater and Erosion Control Features With the proposed changes to the site grading plan, corresponding revisions to the approved AM05 plan for channeling stormwater runoff and controlling erosion will be necessary. As with the original plan, slopes equal to or less than 1H:1V will be stabilized as needed with September 2021 1 28