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Hazeltine/Road Runners Rest IllBrinkmann•Woodward Gravel Pits Lining Project -Design Technical Memorandum <br />Denver Water <br />August 2003 <br />2. Normal pool level of the reservoir will be at EI. 5017, which provides about 3 feet of <br />freeboard below the lowest crest elevation (north part of Road Runners Rest II pit) <br />along the perimeter of the combined reservoir. <br />3. Slopes along the Bull Seep and South Platte River will be protected against erosion and <br />long-term topography will be consistent with that shown on the topographic map <br />provided by Denver Water. <br />4. Except for unmined areas, a FOS of 1.3 was used for interior slopes, which is typical <br />for temporary conditions. A permanent design for [he side slopes of the reservoir will <br />be conducted later by Denver Water. <br />5. A FOS of 1.5 was used for interior slopes in unmined areas, which is appropriate for a <br />permanent condition. It is our understanding that future mining will result in 3H:1 V <br />side slopes and that the material in the slopes will consist of native undisturbed <br />materials. <br />6. A FOS of I.5 was used for exterior slopes, which is typical for a permanent condition. <br />7. Drained strength parameters with steady state seepage conditions were considered. <br />8. No rapid drawdown analyses were conducted because it is our understanding that rapid <br />draining of the reservoir will not occur prior to reconstruction of the slopes. <br />3.3 Representative Cross Sections <br />Based on our understanding of previous mining operations, subsurface stratigraphy identified <br />in current (GEI, 2003) and earlier (GEI, 2000) investigations, and the base topographic map <br />provided by Denver Water, we developed two idealized cross sections to represent two typical <br />depths to bedrock along the perimeter of the reservoir, 35 and 55 feet. The alignment of the <br />soil-bentonite wall and stationing are shown on Figure 3.2. The locations where the sections <br />are applicable are listed in Table 3.1 and shown on Figure 3.2. <br />The representative cross sections were comprised of four material types (overburden, sand and <br />gravel, soil-bentonite cutoff wall, and bedrock). The geometry and thickness of each layer was <br />generally based on the subsurface information obtained from the borings, and the anticipated <br />width of the cutoff wall. In areas where temporary stabilization of the side slopes will be <br />required, a fifth material type, stabilization fill, was included in the cross sections. The <br />required width of the stabilization fill was selected based on the results of the stability analyses <br />such that the minimum FOS criteria are met, and based on a 2.SH:1 V slope. All cross sections <br />generated for the analyses included asoil-bentonite cutoff wall, which was modeled as a 2.5- <br />GEI Consultants, Inc. 9 O:OSO@-OJ-3I IA-Hazeltine Design TM <br />