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• SUMMARY <br />1) The subsurface conditions in the area of the proposed dam were investigated by conducting a <br />field exploration program. <br />2) The subsurface conditions encountered in the azea of the proposed dam were variable and <br />generally consisted of interbedded layers of sand, clay, and sand and clay overlying competent <br />bedrock to the maximum depth investigated, 54 feet. The depth to competent bedrock ranged <br />from 9 fee[ in test hole H to a depth of 46 feet in test hole E. <br />3) Based on the results of the field and laboratory investigations, our review of the project <br />documents and our experience with similar projects, we believe that the factor of safety of a <br />dam built on a pervious foundation, with an appropriate key trench and toe drain, will be <br />greater than 2. Embankment factor of safety is a result of using SB-Slope, simplified bishop <br />slope stability analysis. <br />PURPOSE AND SCOPE OF STUDY <br />This report presents the results of the geotechnical investigation for the proposed earthfill dam for <br />Sediment Pond 005 and associated haul road at the Seneca Ii-W Mine in Routt County, Colorado. A <br />site plan is shown in Appendix A. <br />Afield exploration program was conducted to obtain information on subsurface conditions. Material <br />samples obtained during the subsurface investigation were tested in the laboratory to provide data on <br />the classification and engineering characteristics of the on-site soil and rock. The results of the field <br />and laboratory investigations are presented herein. <br />This repon'has been prepared to summarize the data obtained and to present our conclusions and <br />recommendations based on the subsurface conditions encountered and the site conditions and <br />constraints. Design pazameters and a discussion of geotechnical engineering considerations related to <br />the stability analysis, embankment drainage and construction considerations are included. <br />SITE CONDITIONS <br />The project site is located at the Proposed Pond 005 at the Seneca II-W Coal Mine, Routt County, <br />Colorado. <br />• <br />Job No. 91-562 <br />Ground Engineering Consultants, Int. <br />Page 1 <br />