Laserfiche WebLink
The sedimentation and drainage control system used in the Refuse Disposal Area are slightly different <br />• as shown on Maps 76, 77, 77A, 78, 79, 80 and 80A. The watershed of a sub-area is progressively <br />disturbed as the sub-area is filled with refuse. During this process, runoff from undisturbed areas is <br />diverted away from disturbed areas by temporary ditches. The purpose of these temporary ditches is to <br />prevent excessive erosion of the refuse and not to prevent mixing of runoff from disturbed areas. Both <br />runoffs are carried by the perimeter diversion ditches into the sedimentation ponds. Both types of runoff <br />are mixed. This is not considered detrimental as the watersheds are small and the ponds are designed <br />for the worst expected situations (i.e., when most of the watershed is disturbed). Sediment design and <br />diversion ditch calculations are given in Illustrations I~ for refuse area 1, I-5 for refuse area 2/3, I-6 for <br />refuse area 4 and I-6A for refuse area SA. With the approval of TR42 to combine refuse area RP-2/3 <br />and RP-4 into RP2/3/4, the sedimentation design and ditch calculations are given in Illustration 44. In <br />order to maintain a 10-year runoff storage volume after a major storm event, the water level in Pond RP- <br />2/3 will be dewatered 1.6 feet, the water level in Pond RP-4 will be dewatered 2.0 feet and the water in <br />Pond RP-5 will be dewatered 1.65 feet below the primary spillway. <br />The DP-1 Pond decant hole will be controlled by a valve. Since DP-1 discharges frequently, the valve <br />will normally be kept open. The valve will be closed if a need arises to provide more settling time for <br />solids in the water. See Map 80A. ,t <br />In accordance with Rule 4.05.2(4) runoff from the haul and access roads will not pass through <br />sedimentation ponds unless within the portal or refuse disposal areas. Check dams to slow the velocity <br />• of water collected in ditches alongside the roads were installed during the construction phase. All <br />ditches have been revegetated and check dams inside ditches are no longer used. Water relief bars <br />divert water out of the ditches into natural drainages at appropriate points. <br />IV.J.2 Installation Diversion ditches and dikes which intercept runoff from undisturbed areas and direct <br />it away from disturbed areas and into the natural drainage system were installed prior to grading <br />activities in an area. Ditches within disturbed areas were constructed during grading activities in an <br />area. Sediment ponds in the Refuse Disposal area were installed prior to grading activities. <br />The sediment pond for the D Portal Area could not be constructed prior to grading activities since it was <br />located on top of the Scullion Gulch stream diversion pipe and it could not collect runoff from all of the <br />"D" Portal Area until most of the 2,750-foot-long diversion pipe was in place. Construction of the Scullion <br />Gulch diversion had to be completed concurrently with the "D" Portal Area grading since it was covered <br />with fill material cut from the bench areas above the bottom of the Gulch. Construction of the Scullion <br />Gulch diversion pipe started at the lower end of the "D" Portal Area. <br />Mine Permit Renewal #3 (Rev. 3/00) IV-39 <br />