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<br />• In evaluating the analysis, it should be understood the report (24)* does
<br />not stand alone and requires additional supportive data from the referenced
<br />reports (19, 20, 21, 22, 23) to evaluate the assumptions. it should be fur-
<br />ther realized that the assumptions, particularly the water table assumptions,
<br />are quite conservative, Based on our experience, the probabil',ty of a water
<br />table deveicping in the spoil material is relatively low. This assumption is
<br />CrltiCal t0 the OerTOrr~iance Of `he Slgpe, We SUCg°St a System OT ground
<br />water monitoring ~;+eils be developed at several levels t•+ithin the `ill and that
<br />a continual monitoring program be established. If ~•rater develops ti+ithin
<br />the fill, the fill can be drained using horizontal drainage galleries or
<br />similar systems to stabilize the slope.
<br />In evaluating the stability of the fill, two additional factors should be
<br />considered. First, the construction of the fill was begun approximately
<br />January i977 and the `til is currently up to 400 feet in height. After three
<br />years of experience, there are no sions to indicate potential stability pro-
<br />blems. Observations made by OSM, ML,48, and CTL/Thempson, Inc. personnel on
<br />June 13, 1979, indicate the fill is dry and stable. While this is no guarantee
<br />or' long-term stability, the data and observations do cony"irm short-term stability.
<br />If the colluvium were the controlling factor, the most likely failure would be
<br />shortly after application of load ,prier to consolidation of the colluvium.
<br />In the long-term case, the weight of the fill will consolidate and strengthen
<br />the colluvium and fill. Secondly, the fill has been constructed in a reverse
<br />"'/" r cn '*.:~°t '.s, -?,~ ^nuth 'r" tl-_ can+;on is narro:+ anc he ~.vidt.': o. the
<br />canyon^increased upstream). This effectively increases the stability of the
<br />fill by "blocking" the mouth of the canyon and limiting the area of potential
<br />slip failures. To the best of our knowledge, there is no way to quantify
<br />this effect, but it ~rriil increase the overall stability of the fill.
<br />it should be noted that the scope of our ~.vork was limited to the analysis of
<br />the existing available data. h1r. Pendleton's comments concerning the lack
<br />of testing may be some~•+hat appropriate, however. there were no contract pro-
<br />visions for obtaining and independently testing the nature of the materials.
<br />In our opinion, there were sufficient data available from previously pub-
<br />lished reports (19, 20, 21, 22, 23) to allow reasonable estimates of the
<br />necessary parameters. The only data which could have been improved are the
<br />density and support characteristics of the colluvium.
<br />In paragraph 2, the letter states "The slope configuration was assumed by the
<br />consultant...". This is incorrect. In the meeting of June 13, 1979, Colowyo
<br />personnel stated that the spoil pile a+as to be constructed in accordance with
<br />their ;otter of .August 29, i977 (19). The meeting •:+as attended by representa-
<br />tives or OSi•1. CTL/Thompson, Colowyo, Tipton and Kalmbach, Golder Associates,
<br />and t4LRB. In the course of the meeting, the construction of the fill o-ras
<br />observed and all participants agreed,that at that point in time,the fill was
<br />in general conformance with the Colo~.vyo plan. If subsequent to that meeting,
<br />plans have changed and the fill has been substantially altered, then the
<br />existing analysis may not be appropriate and additional analytical work should
<br />be performed. _
<br />•
<br />*Numbers in parentheses indicate references
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