2023-07-19_REVISION - M2021052 (16)

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Rifle Gravel Pit#1 July 2023 6.2.3.1 Mining Methods and Earthmoving This phase of the project will include mining, stockpiling of material for screening, washing and crushing processes. • The working surface of the mine will consist of the alluvial gravel surface that is exposed after removal of the overburden. A long-reach excavator stationed on the edge of the pit will excavate material to a depth of approximately 20 feet. The pit will fill with water as excavation proceeds, forming a pond that expands as the excavator continues to remove material. The pond water will be in direct contact with the water table of the Colorado River via lateral migration through the underlying permeable gravels. Excavated material will be piled on the edge of the pond to allow drainage of free water from the material back into the pond. • Sideload dump trucks will travel to the pond edge and will be loaded with the dried material. The dump trucks will transport the dried material from the active excavation area to the processing facility (800 feet to1,500 feet depending upon the mining location), where the material will be stockpiled for washing, processing, and subsequent sale. • Any agricultural return flows in the tailwater ditch, which are estimated at<2 cubic feet per second (cfs) during peak irrigation season, will be discharged into the pond, mixed with the alluvial aquifer, and migrate laterally through the permeable gravels into the larger Colorado River water table. Given the minimal flows in the ditch, the large size of the pond (estimated at approximately 6 acres within one year), and the highly permeable nature of the gravel, the agricultural return flows will have a negligible effect on water levels in the pond. As excavation proceeds, the tailwater ditch will be subsumed into the expanding pond boundaries, until under final conditions (Figure 11, Exhibit C6) the confluence of the ditch and the pond will be located where the ditch enters the eastern boundary of the property. • A six-foot wide greenbelt area with a 5:1 slope will be constructed at the inner edge of the perimeter berm, and planted with wetland reclamation species as mining activity progresses subject to operational requirements and seasonal constraints. The intention is for the six-foot wide greenbelt area to be nearly inundated during high-water periods as the water table rises, and then to be progressively exposed as the water table drops during the growing season. The remainder of the pit slope to the bottom of the pond will not exceed 3:1 slope. These slopes will be verified using GPS equipment. It should be noted that the existing topography is variable between the distance of the toe of the 3:1 to 5:1 transition slope across the site, hence creating an estimated 3.57 acres that will need to be reclaimed throughout Phase 3 and potentially during Phase 4 (noted as the Berm Area or Berm to Greenbelt Area on Figure 14, Exhibit E1). • The greenbelt area slope of 5:1 will be visually apparent due to the shallow water covering the fringe. The deeper slopes will be maintained at no steeper than 3:1, and verified using GPS equipment. During mining operations, Scott will utilize the GPS receiver in the excavator to see the excavated profile and make sure that the requirements of the permit are being met, including the 3:1 maximum slope. Scott will also use a handheld rover and check the slopes as excavation occurs to ensure that all requirements of the mining permit are being met, including the 3:1 maximum slope. 30