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4.6.4.4 Constructed West Ridge Sediment Pond <br />The actual constructed pond is 33.23 acre-feet as is located on Exhibit 4.6-17. A plan <br />view of the pond can be seen on Exhibit 4.6-19. The plan view exhibit denoted the actual size of <br />the pond and the locations and sizes of the primary spillway and the emergency spillway. <br />Calculations for the emergency spillway can be found in Table 4.6-30. <br />Exhibit 4.6-19b denotes the French drain design, the reconstructed slopes in the slump <br />area to a 3:1, redirection of the ditch into the existing drainage inlet, and the regrading of the <br />previous ditch location to prevent standing water. <br />4.6.4.5 West Ridge Diversion Ditch <br />The West Ridge diversion ditch was designed to route inflow due to a 10-year, 24-hour <br />storm and pumping from the pits from West Ridge drainage area into the sediment pond. The <br />ditch is constructed as shown on Exhibit 4.6-17 and will be extended as mining progresses as <br />shown on the exhibit. A profile of the existing ditch can be seen on Exhibit 4.6-20. Calculations <br />for the existing ditch in its two forms and the projected triangular ditch to be constructed can be <br />seen in Table 4.6-31 and 4.6-32, respectively. The West Ridge diversion ditch will be <br />permanently retained. <br />4.6.4.6 West Ridge Impoundment Permanent Design and Retention <br />Justification <br />The West Ridge impoundment will be permanently retained. Designs, supporting <br />documentation, PE certification and an evaluation of this impoundment's ability to support the <br />postmining land use are contained in Appendix 4.6-N. SEDCAD+3.1 was used to predict flow <br />volumes. Soil Conservation Service (SCS) Handbook #590 criteria was used to evaluate the <br />pond. A combined watershed map is located in Exhibit 4.6-28. <br />4.6.5 Sedimentation Control Summary for Tipple Area (Ponds reclaimed <br />2003, TR-41) <br />The Tipple Sediment Ponds were designed before the permanent regulatory program to <br />control runoff from the eastern slope of East Ridge. At that time, three ponds were proposed for <br />the drainage area. A fourth pond was added in agreement with the MLRB due to the small area <br />in which to locate the ponds. Consequently, four ponds were built to provide sedimentation <br />control for the area. The design of the ponds submitted under permanent program status is as <br />follows. <br />The ponds are permanent pool ponds with limited sediment storage volume of 0.2757 <br />acre-feet. The estimated yearly yield of sediment for the drainage area is 1.42 acre-feet. Since <br />the ponds will not provide the estimated yearly sediment delivery, they will be cleaned when the <br />sediment accumulates to this amount. The four ponds have a permanent pool volume excluding <br />the sediment storage volume of 0.2090 acre-feet. The combination open channel principal and <br />emergency spillways of the ponds were designed fora 25-year, 24-hour storm event. By inflow <br />outflow routing of storm events through the ponds, required and available volumes of the ponds <br />during the 10-year, 24-hour storm event and required and available discharge rates for the ponds <br />during the 25-year, 24-hour storm event are as follows: <br />MR-53 4.6-96 11/2007 <br />