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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 water <br />containing significant amounts of coal fines as the water might have characteristics more objection- <br />able 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 slot <br />area into SS -1. Diversion ditches direct runoff from a disturbed laydown area on the west side of <br />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 and 80A. The watershed of a sub -area is <br />progressively disturbed as the sub -area is filled with refuse. During this process, runoff from <br />undisturbed areas is diverted away from disturbed areas by temporary ditches. The purpose of <br />these temporary ditches is to prevent excessive erosion of the refuse and not to prevent mixing of <br />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 TR42 to combine refuse area <br />RP -2/3 and RP-4 into RP2/3/4, the .sedimentation design and ditch calculations are given in <br />Illustration 44. In order to maintain a 10 -year runoff storage volume after a major storm event, the <br />water level in Pond RP -2/3 will be dewatered 1.6 feet, the water level in Pond RP-4 will be <br />dewatered 2.0 feet and the water in Pond RP -5 will be dewatered 1.65 feet below the primary <br />spillway. <br />The DP -1 Pond decant hole will be controlled by a valve (Map 80B). This valve will remain open <br />under normal operations maintaining the pond level near or below this level. If an incident occurs, <br />such as a diesel spill, this valve will be closed as needed to appropriately address the situation. It is <br />. Technical Revision #68 (01/2011) IV -3 9 <br />