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Geotechnical Stability Exhibit <br />Exhibit 6.5 <br />• Install inside road ditch with appropriately sized rip rap or check dams; <br />• Install catch basin and culvert inlet structure; <br />• Stabilize cut and fill areas per the construction specifications using approved planting <br />guidelines outlined in Exhibit E; <br />• Construct berms and guard rails per CDOT_design specifications; <br />• Grade and prepare road base to recommended specifications; <br />• Prepare as built drawings and engineering QA/QC construction reports; <br />• Grade the access road base (3 inch rock); and <br />• Construct entrance from CR -124 to the mine complex in accordance with adopted BMPs <br />and La Plata County Public Works approved permit. <br />Road fill in -place densities will be measured to demonstrate road stability. There are no <br />potential road construction geologic hazards or erosion and sedimentation controls impacts that <br />have been identified that have not been mitigated. <br />Embankments: These are discussed with respect to the Augmentation Pond (Attachment D -5). <br />Highwall: Road cuts will be reclaimed to slopes that are less steep than 0.7(H):1(V) whereas <br />portal highwall will be reclaimed to a slope equal to or less than 2(H):1(V). Potential slope <br />geologic hazards will be evaluated once site access is granted and a final determination will be <br />provided to the DRMS. (See geotechnical study work plans for details). <br />Bench Stability <br />Bench stability, including potential rock storage areas at May Day No. 1, May Day No. 2, May <br />Day No. 3, and the Idaho will be evaluated. Severe instability has not been noted based on the <br />fact that the Idaho, Lamb and May Day mine benches and rock storage areas were constructed in <br />the early 1900s, and have remained intact to date. No major geologic hazards have been <br />identified that would affect any potential rock storage locations. Future bench and storage areas <br />will be limited to current bench configurations and in any event no out slopes will be steeper <br />than 1.5(H):1(V) without additional geotechnical analysis. Drainage (surface and subsurface) <br />control design will be incorporated into all structures and appropriate BMPs will be adopted to <br />mitigate offsite erosion and sedimentation including diversion ditches, sedimentation traps, rock <br />drains and rock berms to minimize any potential impacts as discussed in the Storm Water <br />Management Plan (Attachment U -3). Future benches and rock storage areas will be located <br />where ponds or material saturation are minimized or nonexistent. <br />Geotechnical slope stability assessments will be conducted on the May Day No. 1, May Day No. <br />2, May Day No.3 and the Idaho Augmentation pond. Mine benches that were created in the <br />early 1900s currently show no signs of deep slope failure planes or instability. In the future, <br />stable rock storage areas will be constructed where the backfilled material will be placed without <br />compaction. The angle of repose of the benches outslope will range from 30 to 35 degrees where <br />the natural slopes range from 1.5 to 2 (horizontal) to 1 (vertical). Approximately 3,500 cubic <br />yards will be used from May Day No. 1 bench and portal collapse area to repair the mine area. <br />Wildcat Mining Corporation <br />May Day Idaho Mine Complex — 112d Permit Application <br />Revised August 2011 <br />Geotechnical Stability Exhibit 6.5 <br />Page 6 of 11 <br />