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2011-06-29_PERMIT FILE - C1981019A (16)
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2011-06-29_PERMIT FILE - C1981019A (16)
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Last modified
5/17/2021 5:50:57 PM
Creation date
8/23/2011 10:21:17 AM
Metadata
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Template:
DRMS Permit Index
Permit No
C1981019A
IBM Index Class Name
Permit File
Doc Date
6/29/2011
Doc Name
Section 21 Sedimentation Pond
Section_Exhibit Name
Exhibit 07 Item 20 Part B -ST
Media Type
D
Archive
Yes
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EXHIBIT 7, ITEM 20, PART B <br />SECTION 21 SEDIMENTATION POND <br />Due to the reduction in the South Taylor Disturbance limits and the revisions to <br />the post- mining topography described in TR -81, and the consequent extended <br />service life of the Section 16 Sedimentation Pond, the Section 21 Sedimentation <br />Pond is no longer required. As of the approval date of TR -81 there are no plans <br />to construct the Section 21 Sediment Pond. The most recent design submitted <br />with PR -02 (Rev. Date 3/29/07) is nevertheless retained intact here to provide for <br />the possibility that future mine plan revisions may once again require this facility. <br />All pages of the approved PR -02 design remain unchanged except this first page <br />introductory text. The original introductory text unchanged from PR -02 follows <br />below. <br />The location of the Section 21 Sedimentation Pond is presented on Map 41A. The profiles of the <br />associated permanent ditches (Section 21 East Tributary Ditch and Section 21 West Tributary <br />Ditch) are presented on Map 33B. Channel design of these permanent drainage channels is <br />provided in Exhibit 7, Item 20, Part E. Exhibit 7, Item 20, Figure 113 shows the breakdown of <br />drainage areas and hydrologic conditions for this sediment pond, and Figure 1B -2 provides a <br />diagram of the structures and networking. A design drawing for the impoundment is presented <br />on Figure 1 B -3. <br />To minimize the size of the structure needed, a variety of control features will be utilized. Three <br />short-term sediment traps will be utilized along the edge of the topsoil replacement limit. It is <br />expected that these sediment traps will be relocated as the topsoil replacement progresses. Thus <br />the life of these structures will generally be less than one year. These sediment traps will be <br />subgrade (excavated by dozing) and will have a maximum capacity of 2.0 acre -feet. The <br />sediment traps will typically be rectangular in shape with a maximum depth of 10 feet and a <br />maximum of 2H:1 V side slopes. They will be evacuated by pumping when needed. The design <br />also includes the construction of a permanent stock pond in this drainage basin as shown. This <br />will have a maximum capacity of 0.50 acre -feet and will be similar in nature to those currently <br />constructed. <br />The following pages present the results of three SEDCAD runs for the worst case hydrologic <br />conditions. The first run provides the results of the 10 year, 24 hour design storm. This design <br />event generated about 50 cfs of peak runoff and a total runoff volume of about 4.7 acre -feet <br />under these conditions. Further information regarding the design assumptions and the model <br />inputs are documented in the introductory text of Exhibit 7, Item 20. Note that these design <br />assumptions are identical to the assumptions provided in at the front of Volume 2D (Introductory <br />text) for the 10 existing sediment ponds at the Colowyo Mine. The second model run documents <br />the results of the 100 year, 24 hour design event, and the final model run shows a maximum <br />event (50% of Probable Maximum Precipitation) for adequacy of spillway design. <br />Table 4 of the introductory text of Exhibit 7, Item 20 provides a summary of the design <br />parameters for this sediment pond. <br />Exh. 7 -20B -1 Revision Date: 12/31/10 <br />Revision No.: TR -81 <br />
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