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Rifle Gravel Pit 41 August 2021 <br /> 8.6.1 Water Requirements During Mining Phase <br /> During active mining, depletions to the Colorado River will occur from water lost with mined <br /> aggregate (trucked offsite with mined aggregate) and water used for dust control. Depletions <br /> are not expected from evaporation associated with dewatering efforts; Scott Contracting, <br /> Inc. plans to intercept any groundwater with perforated pipe and pump it to the dewatering <br /> pipeline without evaporation. Gravel pit operations also typically include domestic or <br /> commercial indoor uses; however, Scott Contracting, Inc. expects to provide trucked water <br /> from offsite for indoor water use. <br /> 8.6.2 Water Lost with Mined Aggregate <br /> Scott Contracting, Inc. estimated for the entire property they could meet a production rate of <br /> 200,000 tons of aggregate per year, or 16,667 tons per month assuming a year-round <br /> operation. DWR-SEO uses a standard assumption that aggregate production water <br /> depletions are four percent of the production rate when washed and mined below the <br /> groundwater table, which results in total annual demand of 5.89 acre-feet (AF) for 200,000 <br /> tons of aggregate. <br /> 8.6.3 Water Used for Dust Control <br /> Dust control water will be captured from the dewatering well. Scott Contracting, Inc. <br /> estimates that the active mining operations will use 50,000 gallons per day for dust <br /> suppression. Based on 20 operational days per month, this results in an annual demand of <br /> 36.83 AF. <br /> 8.6.4 Water Lost Due to Evaporation During Dewatering <br /> Evaporation from exposed groundwater during active mining is expected to be minimal. A <br /> series of dewatering wells (exact number unknown at this time but modeled and <br /> documented in Attachment C reports) will lower the local groundwater table at the site and <br /> allow for dry mining operations. In the instance mining exposes groundwater not pumped by <br /> the dewatering well, a perforated pipe will be buried in a trench at least 3 feet below the <br /> mining floor, allowing this water to be intercepted and directed to the dewatering well. <br /> Hence, it is assumed that no water is lost to evaporation during active mining. <br /> 8.6.5 Water Used Indoors (Domestic and Commercial) <br /> Scott Contracting, Inc. does not anticipate using water from the site for indoor water <br /> demands. Because potable water is not available from City of Rifle or Town of Silt and <br /> because drilling a well for potable water on the property is not feasible given the mining <br /> plan, Scott Contracting, Inc. is planning to truck potable water onto the site to supply <br /> employees with potable water. <br /> 8.6.6 Water Requirements During Reclamation Phase (Post Mining) <br /> After mining is completed, water depletions from the site will be solely from evaporation of <br /> the exposed groundwater in the finished gravel pit pond. Annual gross evaporation for the <br /> Rifle area is estimated at 45 inches based on the contours from National Oceanic and <br /> Atmospheric Administration Technical Report NWS 33 dated June 1982, Map No. 3. Annual <br /> evaporation was distributed annually using the DWR General Guidelines for Substitute <br /> Water Supply Plans for Sand and Gravel Pits (DWR Gravel Pit Guidelines) annual <br /> 45 <br />