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West Sediment Control System and Section 26 Pond <br />Throughout this haul -back operation the area reporting to the northern crest of the spoil pile in <br />the Bear Draw drainage will increase until ultimately the entire pit area in that drainage and <br />watershed areas above it, as well as the entire footprint of the now exhausted spoil pile, are <br />reporting to the northern crest of the remaining spoil pile. The location of this northern crest will <br />gradually move north above the valley floor in Bear Draw. Concurrently, the northern crest of <br />this western lobe of the spoil pile will also drop in elevation. However, throughout this time <br />period the northern crest of the remaining spoil pile will always act as a plug that prevents any <br />runoff from directly proceeding further downstream to the Section 26 Pond. Eventually, once <br />the final lifts are removed from Bear Draw (again, refer to the profile presented on Exh. 7-23, <br />Figure I1), the entire watershed will be reporting to the Section 26 Pond. Also, as the temporary <br />spoil pile is removed, the face area of the spoil pile that is directly tributary to Section Pond 26 <br />will be gradually shrinking, thereby slightly lightening the pond's service load temporarily, until <br />the final lift is removed (refer to profile Exh. 7-23, Figure I1). At this point, the entire western <br />watershed will be tributary to the Section 26 Pond. <br />To retain the full use of the Sidehill Sediment Pond for sediment control as the final spoil pile lift <br />is removed from the Bear Draw bottoms, a diversion ditch will be employed to route the majority <br />of the watershed runoff through the Sidehill Sediment Pond. When the temporary spoil pile <br />surface has been lowered to just above the 7200 contour, which is at about the elevation of the <br />Sidehill Sediment Pond, a contour ditch will be constructed across the valley bottoms to direct all <br />runoff from the nearly complete watershed toward the Sidehill Pond before release to the Section <br />26 Pond via D-1 Lower Ditch. This "Side Hill Contour Ditch" appears on Map 41C (Volume <br />22). <br />In the West System, use of the Side Hill Contour Ditch as described above will allow the full <br />capacity of the Sidehill Sediment Pond to be used to pre -condition the runoff before release to <br />the Section 26 Pond. Ultimately, when the final lift of the spoil pile is removed from the pile's <br />footprint below this El 7200 contour ditch, thereby removing the plug above Section 26 Pond, <br />the area below the contour ditch will report directly to Section 26 Pond. However, the majority <br />of the watershed will still continue to report to Section 26 Pond only after having passed through <br />the Sidehill Sediment Pond via the Side Hill Contour Ditch. <br />Above Sta. 37+00, the D-1 Upper Ditch will be removed when the top of the remaining spoil pile <br />has dropped below the ditch invert, which is the condition addressed in this time frame. This <br />ditch is modeled in Part C and described in detail in Part B. It is a vegetated trapezoidal channel <br />with an average slope of 5%, a bottom width of 12 feet, and 2H:1 V sideslopes. It formerly <br />extended from Sta. 0+00 at the Sidehill Sediment Pond to Sta. 57+74 near the center of the south <br />face of the temporary spoil pile (refer to Part D of this exhibit). <br />The remaining portions of this ditch, from Sta. 37+00 northerly to Sta. 0+00 at the Sidehill <br />Sediment Pond, will continue in service. The lower 3,700 feet of the D-1 Upper Ditch is <br />therefore incorporated into this model (as SEDCAD Structure No's 10 and 8). <br />Exh. 7-23I-2 Revision Date: 2/15/16 <br />Revision No.: PR -04 <br />