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1 1__1 1 _ Brighton Water Storage Project - Slope Stability Calculations - Adams CounTy; Colorado The Contractor should keep the lateral extent of exposed back cut slope. open at any one rime to a minimum. Wider extents of open slope will entail an increased risk of erosion and local slope failures, and associated increased slope maintenance during construction, Similarly, the temporary slope which will be created as the clay liner is brought up appears to have an acceptable factor of safety for a temporary condition when placed at a 1'/,:1 {horizontal vertical) slope angle and properly moisture-conditioned and compacted. The suggested 15-foot width for the clay liner appeazs acceptable, as well, in this regard. Again, the factors of safety estimated for this study assumed a drained condition. GROUND'S analyses indicated a factor of safety on the order of 1,6 against deep seated failure for the proposed 2'/x:l (horizontal :vertical) permanent slope configuration. Factors of safety were estimated for a statio and de-watered (empty reservoir) condition, such as would exist upon completion of project earthworks. A factor of-safety of 1.6 is considered adequate for a permanent slope configuration. Surficial erosion and local sloughing-which likely will require periodic maintenance shotild be anticipated, particularly in more granular $il materials. Project plans should allow for periodic maintenance of the reservoir slopes. It should be noted, again, that the material properties used for the `miscellaneous fill' were assumed. We recommend that the materials actually proposed for use as the `miscellaneous fill' be tested, and the conclusions and recommendations herein updated, once those soils are identified. Project Earthworks Site soils free of deleterious materials are, in general, suitable for placement as compacted fill. Caze should be taken, however, with regazd to achieving and maintaining proper moisture contents during placement and compaction. Prior to earthwork construction, existing structures, vegetation, topsoil and other deleterious materials should be removed and disposed of off-site. Relic underground utilities should be abaridoned in accordance with applicable regulations, removed as necessary, and capped at the marginsof the property. If it is necessary to import material to. the site as common fill, the imported soils should be free of ' organic material, and other deleterious materials, Imported material should have less than 50 percent passing the No. 200 sieve and should have a plasticity index of.less than between 5 and ' 30. All soils proposed for import should be. tested and approved by the Geotechnical Engineer prior to transport to the site. Job No. 02-0065 Ground Engineering Consultants, Inc. Page'?