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A 100-year 24-hour rain event will produce 4.6 inches of rain located near Walsenburg, <br /> Colorado. The available storage volume in the western sump that captures the entire processing <br /> area is 3.5 acres x 9 feet= 31.5 acre-feet. The calculated peak discharge potential for the <br /> processing area is 5.27 cfs and the calculated maximum runoff volume in a 24-hour 100-year <br /> event is 10.33 acre-feet. <br /> Since the required storage volume of 10.3 acre-feet is so much less than the available storage <br /> volume of 31.5 acre-feet, the western sump volume is more than adequate to contain stormwater <br /> runoff from the processing area. There is no threat of discharge from the processing area during a <br /> 100-yer 24-hour flood event,the anticipated worst case scenario. <br /> During various stages of dump development, a windrow will be maintained on the edge of the <br /> top to keep surface mining flows from overtopping and draining down the dump face. Final <br /> reclamation of dump lifts will include catch ditches to control surface flows along the dump. <br /> Therefore, the available storage volume in the dump sump that captures the dump slope area is <br /> 1.5 acres x 9 feet= 13.5 acre-feet. The calculated peak discharge potential for the dump slope <br /> area is 3.9 cfs and the calculated maximum runoff volume in a 24-hour 100-year event is 7.8 <br /> acre-feet. <br /> Since the required storage volume of 7.8 acre-feet is so much less than the available storage <br /> volume of 13.5 acre-feet, the dump sump area is more than adequate to contain stormwater <br /> runoff from the dump slope area. There is no threat of discharge from the dump area during a <br /> 100-yer 24-hour flood event, the anticipated worst case scenario. <br /> The site will not affect existing water rights. The pit will not expose groundwater and will not <br /> store stormwater for more than 72 hours. After reclamation, stormwater encountered in the <br /> mining area will continue to infiltrate or evaporate. <br /> Two principal ways that gravel pit mining could affect the water quality of the area downstream <br /> are through poor sediment controls within the site causing increased sedimentation downstream <br /> and by fuel leakage from a ruptured tank. Water encountered in the pit will not be released from <br /> the site. The only water that will be found within the disturbed area is stormwater runoff and <br /> currently held Edmundson Ranch water that will be used for processing and for dust control. <br /> Brad ford Mesa Quarry <br /> August 2019 G-2 <br />