2015-09-09_PERMIT FILE - C1981019A (11)

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EXHIBIT 7, ITEM 20, PART E PERMANENT CHANNEL DESIGN There are two permanent primary channels and eight permanent secondary channels associated with the South Taylor Mine Plan. The primary and secondary channels are permanent channels that convey runoff from the areas near the watershed divide near the southernmost extension of the mining activity. The primary channels are associated with drainage from the face of the permanent fill in Section 17. Their purpose is to convey water to the north from the head of the watershed in Sections 19 and 20 toward the West Taylor Sedimentation Pond as shown on Map 41A. The secondary channels drain reclaimed pit areas near the watershed divide in Sections 16, 20 and 21 to the southeast toward Section 16 Sedimentation Pond and Section 28 Sedimentation Pond. The secondary ditches rely on several temporary ditches to convey the runoff to the respective sedimentation ponds until reclamation is complete and the ponds are no longer needed. These temporary ditches are described in other exhibits. Two of these temporary ditches, described in Exhibit 7, Item 20, Part D are the Section 29 Collector Ditch and the Section 28 Collector Ditch. However, the designs of these ditches did not require modification for TR -105. Another temporary ditch, the Section 16 Pond Ditch also receives flow from some of the secondary channels. It is described in Volume 2C, Exh 7-14B, but also requires no modification pursuant to TR -105. The remaining temporary ditch that collects flow from the secondary channels described in this Part E is the Section Sixteen Pond Ditch Extension. This temporary ditch was also not modified pursuant to TR -105 and is described in Volume 2C, Exh. 7-140. All of these ditches are shown on Map 41A. Channel profiles for these channels are presented on Map 33B. Watershed details are also shown in Exhibit 7-20C. Primary Channels The two primary channels are the following: • West Taylor, East Tributary Ditch • West Taylor, West Tributary Ditch There were two other channels that were previously approved but have now been removed as result of TR -105. These were the East Taylor, East Tributary Ditch and the East Taylor, West Tributary. The design basis for each ditch is identified on the following Table 1. By inspection, the area contributory to each ditch is less than one square mile, making the appropriate design storm the 10 year, 24 hour event as specified in Rule 4.05.3. However, portions of these ditches pass over permanent fills, so the design event required by Rule 4.09.2 becomes the 100 year, 24 hour event. For simplicity of design, the entire channel for each ditch is designed to this larger event. Exhibit 7, Item 14 as modified pursuant to TR -105 describes the hydrologic design methodology used at the mine. For channels protected by a riprap liner, selection of minimum rip rap size is Exh. 7-20E-1 Revision Date: 07/20/15 Revision No.: TR -105