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Rifle Gravel Pit#1 May 2023 <br /> 8.5 Surface Water <br /> The Colorado River is generally located north of the mining area and comes as close as <br /> approximately 0.25-mile northwest of the mining area. The Last Chance Ditch is located <br /> south of the property on the south side of Interstate 70 and irrigates lands adjacent to the <br /> Rifle Pit property. An existing irrigation tailwater ditch, known as the Last Change Tailwater <br /> Channel, runs across the Rifle Pit property east to west and ultimately discharges into the <br /> Colorado River. Any agricultural return flows in the Last Chance Tailwater Channel are <br /> estimated at less than 2 cfs during peak irrigation season, will be incorporated into the pond, <br /> mix with the alluvial aquifer, and eventually migrate laterally through the underlying <br /> permeable gravels into the larger Colorado River water table. Given the minimal flows in the <br /> ditch, the large size of the pond (estimated at 6 acres within the first year of operation), and <br /> the highly-permeable nature of the gravel, the agricultural return flows will have a negligible <br /> effect on water levels in the pond. As excavation proceeds, the tailwater ditch will be <br /> subsumed into the expanding pond boundaries, until under final conditions the discharge <br /> point will be where the ditch enters the eastern boundary of the property. <br /> 8.6 Water Management <br /> Incidental runoff moving away from pits and working areas will be controlled using standard <br /> stormwater BMPs. A Colorado Discharge Permit System (CDPS) Construction Stormwater <br /> Permit will be acquired from the CDPHE-WQCD prior to any discharge. There will be a <br /> permanent berm around the entire mining footprint that will be revegetated, and remain in <br /> place for the duration of the project. This will control off-site runoff. There will also be wattles <br /> at the toe of the stockpiles and the toes of the outside slope of the berms. <br /> See previous water handling discussions in this document. <br /> 8.7 Project Water Requirements <br /> Rule 6.4.7 requires the operator/applicant shall provide an estimate of the project water <br /> requirements including flow rates and annual volumes for the development, mining and <br /> reclamation phases of the project. The following subsections outline the estimated project <br /> water requirements estimating methods with a summary of the annual active mining and <br /> post-mining demands shown in Table 3 and Table 4, respectively. This information reflects <br /> full development of the property for pending future development of the full site. <br /> 8.7.1 Water Requirements During Mining Phase <br /> During active mining, depletions to the Colorado River will occur from water lost with <br /> evaporation from exposed groundwater, mined aggregate (trucked offsite with mined <br /> aggregate) and water used for dust control. Gravel pit operations also typically include <br /> domestic or commercial indoor uses; however, Scott expects to provide trucked water from <br /> offsite for indoor water use. <br /> 8.7.2 Water Lost with Mined Aggregate <br /> Scott estimated for the entire property they could meet a production rate of 105,000 tons of <br /> aggregate per year, or 13,125 tons per month assuming operations 8 months of the year. <br /> DWR-SEO uses a standard assumption that aggregate production water depletions are four <br /> percent of the production rate when washed and mined below the groundwater table, which <br /> results in total annual demand of 3.09 acre-feet (AF)for 105,000 tons of aggregate. <br /> 47 <br />