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o's~ ,~ <br />,. ~' <br />Memo to Erica Crosby <br />Stavbility Analysis of CRDA #1 <br />page 2 <br />~n~ s4.~~~q~ <br />potentially elevated piezometric levels might drive the structure <br />below the required static slope safety factor of 1.5. <br />Based on their thorough investigation of the pile's hydrology, and <br />their understanding and interpretation of the comprehensive <br />stability analyses, Western Engineers has recommended the <br />imposition of monitoring safe guards. They have indicated"the <br />"critical" piezometric water levels for the isolated piezometers <br />and recommended the conduct of quarterly monitoring to verify that <br />none of these hydrostatic levels are exceeded. They recommend <br />reanalysis of the pile in the event any of the critical levels are <br />exceeded. <br />Powderhorn Coal Company, in turn, included the imposition of the <br />quarterly piezometer monitoring, as a commitment within it's <br />proposed revision to the permit. I recommend acceptance of the <br />analysis and proposed technical revision to the permit with two <br />conditions: (1) Powderhorn Coal Company should be required to <br />report any piezometer levels determined to equal or exceed the <br />stipulated "critical" elevations to the Division within 2 working <br />days; and, (2) in the event any piezometer levels in excess of the <br />stipulated "critical" elevations are encountered, Powderhorn Coal <br />Company shall reevaluate the stability of pile CRDA #1 and propose <br />and implement remedial treatments to assure that the pile's static <br />slope safety factor will be expeditiously returned to 1.5 or <br />higher. <br />Please convey my compliments to both Powderhorn Coal Company and <br />Western Engineers of Grand Junction. This comprehensive technical <br />analysis, and the operator's forthright recognition of its <br />operational recommendations, exemplify the optimum conduct of the <br />permitting process. I have retained the copy of the report you <br />forwarded for my review in my personal Powderhorn file. I would <br />like to keep it in my office collection for referral to other <br />practitioners and permittees as an example of the proper method for <br />completion and implementation of a stability analysis. <br />cc: Larry Routten <br />Susan McCannon <br />Doc: M:\COAL\JAP\CRDA#1.ANL <br />JP/]P <br />