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2. Surface Water <br /> 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 maximum runoff volume in a 24-hour <br /> 100-year event is 10.33 acre-feet. <br /> c=runoff coefficient;NRCS Soil Survey, <br /> shown in Appendix 1 <br /> i =rainfall intensity (inches/day); <br /> Runoff _ ( i(A x c) NOAA Atlas 14 Point Precipitation <br /> Volume 12 Frequency Estimate:Walsenburg,CO <br /> A=drainage area(acres);measured Map C-2 <br /> Runoff 4.6(30.28 x 0.89) _ 10.33 acre-feet <br /> Volume 12 <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-year 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 equipment and surface mining flows from overtopping and draining down the dump <br /> face. It should be noted that the MSHA required safety berms at the crest of the dump slope— <br /> through each lift of development—effectively precluded stormwater which falls on the dump <br /> surface from running down the sloped surface of the dump. Instead,precipitation on the <br /> horizontal dump surface is directed west towards the active mining area and/or the processing <br /> area. Final reclamation of dump lifts will include catch ditches to control surface flows along the <br /> dump. Therefore, the available storage volume in the dump sump that captures the dump slope <br /> area is 1.5 acres x 9 feet= 13.5 acre-feet. The calculated maximum runoff volume in a 24-hour <br /> 100-year event is 7.8 acre-feet. <br /> Brad ford Mesa Quarry ` <br /> January 2020 G-2 <br />