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Rifle Gravel Pit#1 May 2023 <br /> o Estimated area mined and processed between 30% and 60% = 2.05 acres <br /> Cumulative volume of material mined and processed at 60% = 140,000 CY <br /> o Estimated volume of material mined and processed between 30% and 60% = 52,000 <br /> CY <br /> Size of Area Worked at 100% <br /> The total estimated area to be mined (processed and stockpiled) at 100% is approximately <br /> 10.43 acres (depicted in Figure 11, Exhibit C6) and amounts to approximately 292,810 CY <br /> of mined (processed and stockpiled) material. <br /> • Cumulative area estimated at 100% = 10.43 acres <br /> o Estimated area mined and processed between 60% and 100% = 3.60 acres <br /> • Cumulative volume of material mined and processed at 100% = 292,810 CY <br /> o Estimated volume of material mined and processed between 60% and 100% _ <br /> 152,810 CY <br /> Equipment <br /> This phase will use conventional mining equipment for this phase, including but not limited <br /> to a long-reach excavator, a bulldozer, track-hoe, screening plant, wash plant, crusher, and <br /> a 35-ton haul truck. <br /> 5.2.3.1 Mining Methods and Earthmoving <br /> This phase of the project will include mining, stockpiling of material for screening, washing <br /> and crushing processes. <br /> • The working surface of the mine will consist of the alluvial gravel surface that is exposed <br /> after removal of the overburden. A long-reach excavator stationed on the edge of the pit <br /> will excavate material to a depth of approximately 20 feet. The pit will fill with water as <br /> excavation proceeds, forming a pond that expands as the excavator continues to <br /> remove material. The pond water will be in direct contact with the water table of the <br /> Colorado River via lateral migration through the underlying permeable gravels. <br /> Excavated material will be piled on the edge of the pond to allow drainage of free water <br /> from the material back into the pond. <br /> • Sideload dump trucks will travel to the pond edge and will be loaded with the dried <br /> material. The dump trucks will transport the dried material from the active excavation <br /> area to the processing facility (800 feet to1,500 feet depending upon the mining <br /> location), where the material will be stockpiled for washing, processing, and subsequent <br /> sale. <br /> • Any agricultural return flows in the tailwater ditch, which are estimated at<2 cubic feet <br /> per second (cfs) during peak irrigation season, will be discharged into the pond, mixed <br /> with the alluvial aquifer, and migrate laterally through the permeable gravels into the <br /> larger Colorado River water table. Given the minimal flows in the ditch, the large size of <br /> the pond (estimated at approximately 6 acres within one year), and the highly permeable <br /> nature of the gravel, the agricultural return flows will have a negligible effect on water <br /> levels in the pond. As excavation proceeds, the tailwater ditch will be subsumed into the <br /> expanding pond boundaries, until under final conditions (Figure 11, Exhibit C6)the <br /> 28 <br />