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Based on the subsurface conditions encountered across the site, the assumed traffic loadings and our experience with similar projects, we recommend that the Intake Shaft access roadway be constnrcted with a gravel section consisting of 3 inches of base course gravels and a minimum of 8 inches of subbase (pit run) gravels. An alternate section would consist of 6 inches of pit run gravels and 4 inches of base cotttse gravels. These gravel sections should be placed on the natural clays or properly compacted subgrade fill materials. We have assumed that all of the topsoil and organic materials will be removed prior to placing the gravels or embankment fill materials, If the client elects to leave the topsoil and organic materials in- place and place the gravel section over a geotextile/stabilization fabric, such as Mirafi 600X or equivalent product, then the subbase gravel sections should be increased by 12 inches. This would result in a total subbase gravel thickness of 18 to 20 inches. Site Grading Recommendations: We recommend that roadway and pad cut and fill slopes be conswcted [o a 2 (Horizontal) to I (Vertical) or flatter slope configuration. Flatter slopes aze often desirable in that they allow for easier revegetadon of disturbed areas and reduce erosion and siltation, which often occurs with newly conswcted cuts and 511s. If groundwater seepage is encountered in any finished cut slope, we should be notified to evaluate these areas to determine if additional stabilization measures are required. The roadway subgrade should be prepared by stripping of all topsoil and organic materials. Based on the limited amount of topsoil and organic materials across [he site, it appeazs that the removal of the topsoil and organic materials will be more economically feasible than leaving the topsoil and organic materials in ~l place and using a geotextile/stabilization fabric. The exposed subgrade surface should be scarified to a depth of approximately 12 inches, moisture conditioned to near optimum moisture content and then be recompacted to at least 95% of the maximum standard Proctor density {SPD), as determined by ASTM D698. Suitable subgrade fill materials will consist of the on-site clays and should be uniformly placed and compacted in 8 to 12-inch layers to at least 95% SPD, near the optimum moisture content. The final subgrade surface should be proof rolled t~ith a heavily loaded wck prior to placing the subbase and base course gravels. Areas that deform or pump excessively under the wheel loads should be stabilized prior to placement of subbase gravels. A layer of stabilization fabric may be required on the finished subgrade surface, below the gravel materials to help stabilize and separate the gravels from the subgrade soils. The soils engineer should make this determination after the subgrade surface has been properly prepared. The base course and subbase gravels should also be compaced to at least 95% of the maximum modified Proctor density, near the optimum moisture content, as determined by ASTM D1557. We recommend that the subbase gravels meet the requirements for Class I base course aggregates in accordance with the Colorado Department of Transportation (CDOT) Specifications, 1999. The base course gravels should meet the requirements for Class V or VI base course aggregates in accordance with CDOT Specifications. r We recommend [hat the subbase gravels and base course gravels be tested for compaction and the Job Number: 03-5838 NWCC, lnc. Page 3