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C. Sedimentation ponds hold runoff from disturbed areas a required length of time <br /> (theoretical detention time) to allow most of the solids to settle out and release the <br /> supernatant back into the natural drainage system. <br /> d. Rock check dams in areas otherwise hard to control. <br /> e. Rip-rap lined ditches. <br /> f. Use of a chemical flocculent such as Nalco Enact 7888 or equivalent for decreasing <br /> settling time in sediment ponds. <br /> In the "D" Portal Area, special washdown facilities in and around the preparation plant are provided <br /> for areas where significant amounts of fine coal dust might accumulate. Water from plant <br /> operations which gets into these areas is collected in sumps and pumped to the process water <br /> settling pond. This water is then used in the makeup water cycle. Special attention is given to <br /> water containing significant amounts of coal fines as the water might have characteristics more <br /> objectionable and more difficult to treat than would runoff from other disturbed areas. <br /> Sediment control systems along the conveyor consist of ditches and berms to return runoff to a <br /> natural drainage area. Culverts are also used for controlling drainage. Two ponds are used at the <br /> slot storage area (SS-1 and SS-2). Ditches, berms, and culverts direct runoff from the top of the <br /> slot area into SS-1. Diversion ditches direct runoff from a disturbed laydown area on the west side <br /> of the slot storage area to SS-2. <br /> The sedimentation and drainage control system used in the Refuse Disposal Area are slightly <br /> different as shown on Maps 76, 77, 77A, 78, 79, 80, 80A, 162, and 165. The watershed of a <br /> sub-area is progressively disturbed as the sub-area is filled with refuse. During this process, runoff <br /> from undisturbed areas is diverted away from disturbed areas by temporary ditches. The purpose <br /> of these temporary ditches is to prevent excessive erosion of the refuse and not to prevent mixing <br /> of runoff from disturbed areas. The perimeter diversion ditches into the sedimentation ponds carry <br /> both runoffs. Both types of runoff are mixed. This is not considered detrimental as the watersheds <br /> are small and the ponds are designed for the worst expected situations (i.e., when most of the <br /> watershed is disturbed). Sediment design and diversion ditch calculations are given in Illustrations <br /> 1-4 for refuse area 1 and I-6A for refuse area 5A. With the approval of TR74 to combine refuse area <br /> RP-2/3/4 and RP-5A into RP2/3/4/5, the sedimentation design and ditch calculations are given in <br /> Illustration 61. The sedimentation and discharge design and ditch calculations for RP-A are <br /> included in Illustration 59. Red Wash Pond will be utilized for water quality compliance. <br /> Calculations are provided in Illustration 60. <br /> TR-74 (4/2022) IV-41 <br />