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(FHWA) HY-8computer software (FHWA, 2015)8nd corrugated steel pipe manufacturer's design <br /> manual (Contech, 2018). Based on manufacturer's recommendations, the maximum cover height <br /> ia124 feet for both the 3O-inchculvert(anticipated road height for the extended culvert is 80feeU <br /> and 24'inch culvert (anticipated road height for the culvert is 20fSEd). Culverts were also sized for <br /> the anticipated service life, which increased the wall thickness from 18-gagetO 1O-g8ge for the <br /> 24-inch culvert (Contech, 2018). A minimum of 4 feet of structural fill will be placed over the pipe <br /> prior to trafficking with mine haulage equipment for intraburden/overburden placement. <br /> The west culvert would U* into the culvert for the Upper Pit 6800 Access Rood /BLM, 2019; CO <br /> [)RIVIS. 2019a\ on the downstream side and the existing 3O-inch culvert on the upstream side. <br /> The ooet culvert would terminate in u ripnap apron/splash pad constructed in the natural dry creek <br /> bed (ripnapvvuu|d have o D.socf8inuheo). Drawing 14 shows the upland drainage basin areas <br /> used in the HEC-HMS modeling. Drawing 10 shows typical culvert installation details. <br /> During culvert inmta!|ation, temporary sediment controls such as silt fences, straw be|ee' or etnavv <br /> vx3t1|8S vvOu|d be installed GS necessary to prevent sediment from entering natural drainages <br /> downstream Of the construction area. <br /> 4'3-4 Reclamation <br /> When the 3ooass roads are no longer required, the road fill would be excavated to expose and <br /> remove the two new culverts described in GeCtion4.3.2 to re-establish the natural drainage <br /> channels at pre-construction grades and Side slopes. Remaining fill outside the natural drainage <br /> channels would be graded at 2.5H:1Vor shallower. Re-established natural drainage channels <br /> and remaining fill would be track-walked and rewaget8hed using an approved seed mixture. If <br /> native e|Opea are steeper than 2H:1V, additional surface preparation may be required. This may <br /> include placing juniper and pinion slash from clearing and grubbing activities and ripnap or nook <br /> vortex weirs in areas that may be susceptible to erosion. Depending on conditions encountered <br /> during cnnstruction, natural drainage channels may require erosion protection. Erosion protection <br /> would mimic natural conditions to the greatest extent proct|oab|e, including rock vortex weirs or <br /> isolated sections ofhprap lining as necessary. Designs for nook vortex weirs or riprap lining would <br /> need to be completed during reclamation, as the designs will depend on the excavated channel <br /> geometry and final re-established channel conditions. [)navving11 shows the conceptual road <br /> reclamation grading and Drawing 12 shows a typical cross-section for the East Pit Access Road. <br /> 42 <br />