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Mountain Coal Company <br />West Elk Mine <br />Exhibit 51 <br />Lower Refuse Pile <br />63 Design of Sediment Control Pond <br />The sedimentation pond was designed to collect the sc <br />of the lower refuse pile and to meet the discharge req <br />ttng sedimentation basin storage vs. volume curve <br />Appendix L. The current sedimentation basin em <br />~ approximate 6111 et with a pond bottom el ati <br />< < ~ ~ I I A 24-inch C op spillway pipe structure is ocate <br />12-inch drain valve located approximately a elevatic <br />The 10-year, 24-hour storm peak <br />maximum runoff is shown in Table <br />water diverted into the sedimentati~ <br />TABLE 10. 10-Year, 24-Hour Peak Discharge <br />me t runoff from each phase <br />ents of the CMLRB. The <br />shown in Figure LWP-014 in <br />ment has a top a on of / <br />of approximately 6104 et. 111/// <br />at elevation 6109'feerwtth a <br />6107 feet. <br />barge for each phase and the calculated <br />Also shown on this table is the amount of <br />.sin from underdrains and seeps. <br />Ma~dmum Runoff <br /> Peak / Total Total Runoff Total <br />Phase Discharge Storm Runoff from Underdrains Design Runoff <br /> (cfs) ~ (ft') (ft') (ft') <br />I 3.7 9,369 NA 9,369 <br />II 4.4 ~ 11,264 NA 11,264 <br />lil 5.3 14,106 770' 14,876 <br />IV 15.24 / 50,094: 4,2602 54,354 ~. <br />'Assume 4 gpm now [or 24 hou~4 Gom roeC drains. <br />2 Assume 4 gpm now fmm rock drarro aad 20 gpm now from seep collector drains for a 1A-hour period. <br />The sedimentation basin is designed to handle the precipitation and sediment from <br />a 10-year; 24-hour storm without discharge. The sediment yield was determined using <br />the Universal Soil Loss Equation. The sediment soil loss equation is as follows: <br />A = (R)(C)(LS)(P), where <br />R =Rainfall <br />A =Soil Erodability <br />LS =Slope Length Factor <br />C =Vegetative Cover <br />P =Erosion Practice <br />25 <br />