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strength properties for the underlying mine spoil materials. The standard Proctor and classification test results <br />conducted on the sample of the proposed embankment fill materials are shown in the attached Figure #1. It should be <br />noted that an unconfined compressive strength value of 7,300 psf was obtained on a sample of the clays remolded to <br />95% of the maximum standard Proctor value. <br />For this evaluation a unit weight (soil density) of 120 pcf, a cohesion value of 0 psf and a phi angle of 28 were used for <br />the underlying spoil materials. A unit weight (soil density) of 120 pcf, a cohesion value of 1000 psf and an effective <br />phi angle of 0 were used for the remolded clays to be used in construction of the embankment and compacted to at least <br />95% of the maximum standard Proctor density determined in accordance with ASTM D698. <br />Slone Stability Analyses Results: Based on our calculations and analyses, the minimum calculated theoretical factor <br />of safety for a failure of the maximum embankment downstream section will be 2.84 under static conditions. The <br />minimum calculated theoretical factor of safety for the maximum embankment upstream section under a rapid <br />drawdown condition will be 3.19 under static conditions. <br />Based on these results, we believe that the embankments that are properly constructed to the above configurations and <br />are filled to the primary spillway elevation should be stable and perform adequately. We strongly recommend that a <br />representative of NWCC observe the embankment construction to observe the foundation and groundwater conditions <br />during construction, as well as be present to test the compaction of the fill materials as they are placed in the <br />embankment. <br />We appreciate the oppo i ` to be of professional service to you in this matter. If you have any questions regarding <br />this report, or if we can t <br />e f further service, please contact this othce. <br />Sincerely, .0. R <br />NWCC,IN ?'• PI•D,`?•? a <br />Brian D. L, P'E <br />xc: Jay Jame•;'? <br />• <br />Job Number: 07-7600 NWCC, Inc. Page 2