2012-04-10_REVISION - M1981185 (43)

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Additionally, the Geotechnical Reconnaissance Report concluded that the road could be used for the purposes intended as long as the following recommendations were met: • The upper 30 inches of road should be compacted to at least 90% relative compaction per ASTM D1557 -02. • In areas where less than 30 inches of fill will be placed to complete the road, over - excavate, scarify to a depth of 6 inches, moisture condition and compact to at least 95% relative compaction per ASTM D1557 -02. • Construct new fill slopes no steeper than 1.5:1 and, if this could not be achieved, the use of retaining walls will be required. Cut slopes could be constructed as steep as 3 /4:1 if they were horizontally reinforced. • Repair or reconstruct the retaining walls along the down slope side of the road. Finally, the Geotechnical Reconnaissance Report recommended that a monitoring program be implemented to measure the movement (if any) of key access road locations and retaining wall components. The monitoring points would consist of surface monuments and inclinometers located at key locations as designated by the Geotechnical Engineer. Scope of Work Construction documents have been prepared showing the scope of work and detailing the construction required to bring the New Access Road into compliance with DRMS requirements (see Appendix A). The road will be re- graded from County Road 124 to the La Plata River to meet the requirements of the Rule 6.5 Geotechnical Stability Report, prepared by J. Erich Rauber and David McLay and dated April 2, 2012. The Rule 6.5 Geotechnical Stability Report supersedes the Geotechnical Reconnaissance Investigation performed in May 2010 and is included in Appendix B. The New Access Road will have a typical section of a 12 -foot wide drivable surface with a 1 -foot deep roadside swale for drainage run -off and a 1 -foot bench along the edge of the road opposite the swale. The roadside swale will have 2:1 (maximum) side slopes for a typical roadway width of 17 feet. Six inches of gravel will be placed on the drivable portion of the road to provide an all- weather surface for vehicular traffic. A typical section (sheet C2.00) has been shown in the Construction Drawings detailing the dimensions, depth of gravel and roadway compaction requirements. The drainage ditch will convey stormwater run -off to a low point at approximately the midpoint of the reconstructed portion of the road, where it will be captured, detained and released down slope. Wildcat is proposing that run -off be detained and settled, through the use of a three -stage outlet structure before it is released to protect the water quality of the river and wetlands that have been identified near the detention pond outfall. Detailed calculations for the drainage run -off, depth of stormwater run -off in the swale and the three -stage outlet structure can be found in Appendix C. The existing timber retaining walls will be removed and hauled off -site to be disposed of properly. In order to maintain the slopes recommended in the Rule 6.5 Geotechnical Stability Report, a retaining wall will be constructed on the down slope side of the proposed road. The proposed retaining wall will be a single mechanically stabilized (MSE) wall with a maximum height of 10 feet. This wall will transition to a concrete headwall needed for the detention pond outlet pipe. The headwall will be constructed to meet CDOT standards and specifications and will have a maximum height of 12 feet. The Rule 6.5 Geotechnical Stability Report recommends that the retaining wall should bear on bedrock. To accommodate this recommendation, the top of the retaining wall will be placed 10 feet from centerline of road to allow room for installation of a guardrail, but still have a foundation that is placed on bedrock. The 10 foot dimension from centerline also allows for a typical batter of the wall without reducing the typical section of the road. Details for the retaining wall are provided in the construction documents found in Appendix A. Page 4