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Mr. Richard Atkinson <br />May 5, 1981 <br />Page Three <br />2. For a given set of soi I properties, the effect can further be evaluated by <br />comparing the safety factors of the "Colowyo" and the "OSM" configurations. <br />The "OSM" configuration consisted of 30-foot wide benches at 50-foot <br />vertical intervals between the toe and EI. 7100 and slopes between the <br />benches of 3 horizontal on 1 vertical. The "OSM" configuration is not <br />significantly different from the proposed revision of the "Colowyo" con- <br />figuration. It is believed that proposed revision would result in a slightly <br />lower safety factor than the "OSM" configuration for a given set of soi I <br />properties but would exceed the minimum value of 1.5. <br />3. For Water Table No. 4 and colluvium having an angle of friction (~d) of <br />either 26 degrees or 40 degrees, it is believed that in either case the <br />proposed revision would result in slightly lower safety factor than the <br />"Colowyo" configuration but would exceed the minimum value of 1.5. <br />For the reasons discussed above and as stated in the meeting of 30 April 1981, it is <br />our opinion that the proposed change in configuration would have a minimal effect on the <br />stability of the spoil fill in Streeter Gulch. <br />Very truly yours, <br />TIPTON AND KALMBACH, INC. <br />:, <br />C. W. Mehring <br />CWM:mh <br />Enclosure <br />