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Upper Pit 6900 Access Road I Design Summary American Gypsum <br /> completed in approximately 1 year, requiring the existing road to remain operational during <br /> construction. <br /> During operation, the road will disturb approximately 4.1 acres of land. The land is controlled by <br /> the Bureau of Land Management (BLM) and is within the approved disturbance boundary from <br /> the major modification to permit M-1984-041 on file with the Colorado Division of Reclamation, <br /> Mining and Safety (CO DRMS) (2001) and BLM (2002). <br /> A single 18-inch culvert will be installed from the northeast to the southwest side of the road fill to <br /> convey upland flows under the road. The culvert will terminate in the natural stream channel with <br /> a riprap-lined erosion protection apron. Surface water runoff from the road will report to the <br /> existing sediment control pond M501, which can sufficiently contain the increased sediment load <br /> from the new road disturbance. <br /> Post-mining, the road will be regraded to 3H:1V slopes and revegetated for recreational use, <br /> changing the total disturbance area from 4.1 acres during operation to approximately 5.8 acres. <br /> The culvert will be plugged at both ends and a riprap-lined channel will be constructed on the <br /> regraded road surface to convey upland flows to the natural channel downstream. <br /> Tierra Group subcontracted SWCA Environmental Consultants (SWCA) to confirm the <br /> appropriate cultural resources surveys were performed within the anticipated road disturbance <br /> footprint. <br /> Attachment A contains construction drawings for the road, culvert, and a conceptual reclamation <br /> grading plan. Subsequent sections summarize design details, design support calculations, and <br /> analyses. <br /> 2.0 Proposed Construction <br /> The road footprint will be cleared and grubbed prior to road construction, with any topsoil <br /> stockpiled within existing disturbed areas. Estimated clearing and grubbing depth is 1 to 1.5 feet. <br /> If encountered, unsuitable foundation material (depth/extents determined by visual observations <br /> during construction)will be removed as necessary. <br /> An 18-inch culvert will be installed to convey upland flows under the road fill. The culvert will be <br /> bedded in fine-grained material meeting the Bedding Material specifications on Drawing 02 and <br /> according to the typical cross-section on Drawing 04 (Attachment A). A minimum of 4 feet of <br /> Structural Fill will be placed and compacted over the culvert prior to placing the remaining road <br /> fill. Structural Fill specifications are included on Drawing 02 (Attachment A). Erosion protection <br /> will be provided by a riprap collar for the culvert inlet and a riprap apron for the culvert outlet as <br /> shown on Drawing 04 (Attachment A). During culvert installation, temporary sediment controls <br /> such as silt fences, straw bales, or straw wattles will be installed as necessary to prevent sediment <br /> from entering natural drainages downstream of the construction area. <br /> The road will be constructed primarily in fill (about 257,000 cy of fill and 6,500 cy of cut). For the <br /> road segment constructed in fill (with the exception of Structural Fill placed over the culvert), non- <br /> economic material (intraburden) from open pit mining operations will be dumped, spread, and <br /> compacted by routing equipment over the fill. <br /> AG Upper Pit 6900 Access Rd 20181015 October 2018 Page 2 of 9 <br />