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Rifle Gravel Pit #1 PJaiu11 2021 <br /> 8.6.2 Water Lost with Mined Aggregate <br /> Scott estimated for the entire property they could meet a production rate of 200,000 tons of <br /> aggregate per year, or 16,667 tons per month assuming a year-round operation. DWR-SEO <br /> uses a standard assumption that aggregate production water depletions are four percent of <br /> the production rate when washed and mined below the groundwater table, which results in <br /> total annual demand of 5.89 acre-feet(AF)for 200,000 tons of aggregate. <br /> 8.6.3 Water Used for Dust Control <br /> Dust control water will be captured from the dewatering well. Scott estimates that the active <br /> mining operations will use 50,000 gallons per day for dust suppression. Based on 20 <br /> operational days per month, this results in an annual demand of 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 B 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 does not anticipate using water from the site for indoor water demands. Because <br /> potable water is not available from City of Rifle or Town of Silt and because drilling a well for <br /> potable water on the property is not feasible given the mining plan, Scott is planning to truck <br /> potable water onto the site to supply 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 /> distribution for elevations below 6,500 feet The evaporation was then reduced to account <br /> for periods when the pit is expected to be frozen over when the average temperature is <br /> below freezing, typically December through February for Rifle. <br /> The completed size of the gravel pit pond is not yet known, however for this preliminary <br /> analysis 53 acres is estimated, which includes all of the property area within the 25-foot <br /> setback. The 53 acres of surface evaporation is estimated to have 179.87 AF of depletions <br /> annually (note Sheet C8 of the drawings depicts an 18.4-acre pond, but the conservative 53- <br /> acre area is being used for evaporation estimating). Table 4 presents the post-mining <br /> phase water use demand. <br /> 32 <br />