_INSPECTION - C1992080 (6) - Laserfiche WebLink

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A *130, 2013 C-1992-080/Carbon Junction Mine MLT tributary to Carbon Junction Canyon, and then traveled down the tributary to its intersection with Carbon Junction Canyon, and explored the canyon a short distance downstream of the confluence. Reclaimed Sediment Pond #2 was observed. The team then retraced its steps, collecting measurements of the permanent diversion channel throughout its length. These measurements consisted of channel gradient, channel width, and size of riprap used. As we proceeded upstream from the permanent diversion, we noted the erosion that has occurred on the southern side of the drainage. (This issue has been addressed in previous Division inspection reports, beginning with March 29, 2013.) We continued to move upstream, along the diversion berm which parallels the original channel on the south, passed beneath the toe of the reclaimed North Pit, and eventually reached the undisturbed, native channel. Designs for reconstruction of the Carbon Junction Canyon drainage were approved with TR-I I in October 2002. Details may be found in pages 5-8 thru 5-17 of Section 2.05 (Operation and Reclamation Plan). The approved design plan, profile, and cross section views of the Carbon Junction channel and its environs appear on the following permit maps, also approved under TR- 11: Mine Plan Map, Site Cross Sections, Mine Hydrology Map, and Post Mining Topography Map. (Note: the location of the shared permit boundary with the adjacent gravel pit, Ewing Mesa Pit No. 1, was subsequently revised in July 2004 under TR-12.) Permanent Diversion The permanent diversion channel was stable; however, certain field measurements indicate that the channel was not constructed as designed: • The gradients of Segments 1 through 6 differed from what was shown on the Site Cross Sections Map, with Segment 1 being steeper and the other five segments being generally flatter than was specified, as seen in the table below. Channel Segment* % Grade %Gradient (Measured) (Design) 1 14.0 7.30 2 1.4 2.19 3 4.0 5.31 4 15.0 16.14 5 9.0 to 10.0 9.78 6 (lower) 1.0 2.15 6 (upper, to curve) 1.4 2.15 *As shown on Site Cross Sections Map, approved with TR-I I • The riprap size was frequently coarser than what was required. • For the culvert crossing of the permanent haul road (Segment 4), the design called for a single pipe arch culvert, whereas twin 66" CMPs were installed. An as-built design for the twin culverts was submitted in May 2007; however, the design was not revised in the permit. Number of Partial Inspection this Fiscal Year: 2 Number of Complete Inspections this Fiscal Year: 3 Page 3 of 7