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Rifle Gravel Pit#1 June 2021 <br /> Pit Mining -Dewatering <br /> Figure 9, Exhibit D1, depicts a typical cross-section during mining, including the use of a <br /> dewatering floor trench and dewatering pump to remove water from the pit floor during <br /> mining. Water pumped from the pit floor will be discharged to the dewatering pipeline. <br /> Dewatering Wells - Dewatering <br /> Scott will support the mining dewatering needs using 3 wells (plus temporary drains and <br /> pumps to capture incidental inflows). The rate of groundwater discharge (pumping) <br /> associated with dewatering is expected to approach about 7 cfs. Mr. Bill Hahn (Hahn Water <br /> Resources, LLC) predicted the anticipated dewatering operations (through modeling); <br /> however, this is an estimate based upon borings and groundwater level data. Mr. Hahn <br /> presented one possible dewatering configuration that might be employed for dewatering <br /> associated with the initial stages of mining. Figure 122 shows the estimated drawdown <br /> following one-year of dewatering using 3 wells in the vicinity of the Stage 1 and Stage 2 <br /> mining limits and the approximate locations of the dewatering wells. <br /> The number and size of the dewatering pump(s)will be determined once mining <br /> commences, however, Mr. Hahn assumed the wells would be drilled to a depth of 30 feet, <br /> constructed with nominal 8-inch to 12-inch diameter casing and screen, equipped with 10 <br /> horsepower pumps and motors to pump 400 to 700 gallons per minute (gpm) and 2 to 4 <br /> centrifugal ditch pumps capable of pumping up to several hundred gpm of incidental pit <br /> inflows. <br /> Scott will apply for coverage under Permit No. COG603000 (Discharges Associated with <br /> Subterranean Dewatering or Well Development) or Permit No. COG608000 (Discharges to <br /> Surface Water from Well Development and Pumping Test Activities)to manage dewatered <br /> water. The specific permit will be determined once the water is sampled and analyzed. <br /> 5.2.2 Mining Preparation (Phase 2) <br /> This phase of the project will include mobilization of the heavy equipment, work trailer, <br /> screening and wash equipment, and major site grading to prepare the site for mining <br /> activities. <br /> 5.2.2.1 Topsoil and Overburden Handling <br /> This phase of the project will include additional minor site grading and vegetation removal, <br /> as needed. Equipment for this phase will include, but not be limited to, a bulldozer, track- <br /> hoe, and a 35-ton haul truck. <br /> 5.2.2.2 Water Handling and Dewatering <br /> Phase 1 dewatering activities will continue throughout this phase. No additional water <br /> diversions nor impoundments will be required during this phase. Figure 122 shows the <br /> estimated drawdown following one-year of dewatering using 3 wells in the vicinity of the <br /> Stage 1 and Stage 2 mining limits and the approximate locations of the dewatering wells. <br /> 21 <br />