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Rifle Gravel Pit#1 Project No.21-010R-C2 <br /> Garfield County,Colorado <br /> feet of gravel underlain by claystone/siltstone bedrock to the maximum explored depths of 25 to <br /> 30 feet. The approximate elevations used in our analysis are presented in the table below. <br /> Boring 3 Boring 4 <br /> Subsurface Conditions Appx. Appx. <br /> Elevation Elevation <br /> (ft) (ft) I <br /> Ground Surface at Boring Location 5388 5385 <br /> Gravel Surface 5381 5384 <br /> Bedrock Surface 5361 5363 <br /> Bottom of Boring 5358 5360 <br /> SLOPE STABILITY ANALYSES — PROPOSED CONDITIONS <br /> Slope stability modeling was conducted to evaluate the factor of safety with respect to slope <br /> geometry and subsurface conditions to address potential damage to all structures listed in <br /> Section 1.1 above. We were provided with development plans for the Rifle Gravel Pit#1 <br /> prepared by SGM. Based on our review of the plans, we believe the Phase 1 conditions with <br /> the berm in place would be the more conservative condition and will reflect the mining through <br /> Phase 4 (final reclamation). The addition of the berm to the top of the slope will increase driving <br /> forces, which would be present during mining operations, and reduce the global factor of safety <br /> for the slope. <br /> We selected three locations along the south and north side of the project to conduct slope <br /> stability evaluations. The section locations are presented on the attached sheet. The section <br /> geometry and water surface elevation were based on proposed grading from the SGM plans. <br /> The stability was modeled using limit equilibrium (LE) method of slices using the shear strength <br /> methodology. The configuration and assumptions for each section is as follows: <br /> Section High Wall Slope Groundwater <br /> Height Gradient <br /> Section A 22 feet 3H:1V Analysis assumed a wet mining operation and <br /> West Section (18.4 degrees) water will be maintained at about elevation 5380.5 <br /> Section B 3H:1V Analysis assumed a wet mining operation and <br /> East Section 22 feet (18.4 degrees) water will be maintained at about elevation 5380.5 <br /> Section C 21 feet 3H:1V Analysis assumed a wet mining operation and <br /> North Section (18.4 degrees) water will be maintained at about elevation 5380.5 , <br /> 2 <br />