2012-08-31_PERMIT FILE - C1981012

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Exhibit 19(24) TR -66 RDA Haul Road, RDA Conveyor Area RDA Conveyor Area, Miscellaneous Culverts: 1. The current drainage configuration networks undisturbed runoff west of the RDA, through a culvert under HWY 12 into C14 and then into C14A. In the proposed drainage configuration, D19 will be extended, C14 will be removed and C14a will not be installed. (C14A was approved with TR -60). The previous flow shown for C14 in Table 21 was 44.4 cfs. Based on drainage areas and SedCad Calculations, that number was not correct. The flow derived for D19, as discussed below, is based on the drainage areas that previously flowed into C14 and are assumed to be correct based on most recent topography and flow patterns. 2. The flow in D19 will increase by 1.7 cfs due to the rerouting of the flow from under State Hwy. 12. Therefore, the flow in C30 will increase by approximately 1.7 cfs based on the extension of D19. Existing culvert C30 is a 36" CMP. [twill be removed and replaced with a 48" CMP. Downstream C26 is a 60" and therefore has adequate capacity. C26 at some point was removed from Table 21. It will be put back in the table, and the peak flow used is based on C30 + localized drainage area for D11 on the outlet end of C30 (63.2 +2.62). The flow in Ditch 11 has not been revised. Re- routed flow from D19 is conveyed through C30 and will end up in D11. 3. Culverts 26, 30, have been sized with use of Figure 4 -18, Inlet Control Nomograph, from the "Handbook of Steel Drainage & Highway Construction Products ", as shown on permit page 2.05.15. 4. Culverts 77, 77A ** & 78 were sized using the flow from D5. These culverts will be placed in Ditch 5 and will create access to a new employee parking area. Culverts were sized using the aforementioned nomograph. 5. C1 7C will be placed in an area where Ditch 22 is eroding under the footings of the raw coal conveyor. Culvert 17C was sized based on the size of culverts C17A & B and will be a 36" CMP. RDA Haul Road: 1. Ditches 56, 62, 63, 64, and 67, are assumed to be cut in rock, and therefore rip rap is not required. However, if they are not cut in rock, and the SedCad analysis determined rip rap is required, the appropriate rip rap has been sized and is shown on the applicable SedCad design page. Necessity of rip rap will be determined during construction. 2. Ditches 56, 57, 61 and 62 are routed to flow into culverts 40, 39 and 45 respectively. It is assumed the cut slope leading into the culvert is rock, and therefore no rip rap is required. If conditions during construction demonstrate that the cut is not in rock, rip rap will be required and the design will be revised. The 'dual ditch' configuration is required due to the steep cut and the culverts being placed at the toe of the cut. Ditches 56, 57, 61 and 62 are existing ditches and will not be reconstructed, but simply assigned a name as they became part of the network for the haul road drainage plan. 3. Ditch 55 is an upland diversion ditch, and therefore was designed using the 100 -year 24 -hour event. The remainder of the ditches and culverts were sized to safely pass the peak flow from the 10 -year 24 -hour event. 4. Ditch 55 is assumed to be constructed in rock. If it is not, 3" riprap will be required. Culvert 81 is a currently unnamed 48" in -place culvert. A design is attached. 5. Ditches associated with the haul road are not in the disturbed area as defined by Rule 4.05.2(4) and are therefore not routed to a Sediment Pond. Curve Number Selection: 1. A curve number of 74 was used for the undisturbed oak shrub based on a C soil type and poor cover (Table 2.2d - Runoff curve numbers for and and semiarid rangelands, Oak - aspen). 2. A curve number of 87 was used for the disturbed area. The calculations and were prepared by me knowledge and belie) 43402 State pages EXH. 19(24) -1 through 19(24) -31 with a date of 05/25/12 end the information presented is true and correct to the best of my -25- I Z_ Date TR -66 Page EXH. 19(24) -1 05/25/2012