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Memo to Dan Mathews <br />Deserado Pond RP-4 Analysis <br />page 2 <br />swelled in response. However, the subsoils heaved to a greater extent than the <br />embankment soils, resulting in a relative extension of the embankment. <br />Because soils have little tensile strength this extension resulted in the <br />observed cracking. They further conclude that because the pond will probably <br />maintain this saturation level the cracking should not increase in magnitude. <br />Finally, they theorize that if the pond were to maintain a maximum head for an <br />extended period of time, piping might degrade the embankment. Because the <br />mine is required to dewater the pond in order to maintain required storage <br />volume, maximum head should not occur for extended periods of time. <br />The approach taken by Lincoln-DeVore in completing its investigation and <br />analysis appears appropriate. In my opinion the conclusions appear plausible <br />and supported by the analyses completed. Further, the relatively low risk <br />exposure of the structure makes the approach plausible. <br />I recommend that the Division accept the analysis and Western Fuel's-Utah, <br />Inc.'s proposal to monitor the embankment for signs of future distress, with one <br />condition. I believe it would be appropriate to install a pair of monuments in <br />the area of the cracking. For construction of these two simple survey <br />monuments, a 5' roof bolt driven into the embankment at centerline and collared <br />18 inches deep in concrete should suffice. The monuments should be surveyed <br />immediately after installation this fall. They should then be surveyed quarterly <br />for one year in connection with the required embankment visual inspections. If <br />no significant movement has been documented in one year's time the surveying <br />can be discontinued. The monuments, however, should be maintained for <br />resurveying in the future if any significant movement were to be suspected <br />during future inspections. <br />If you require any additional assistance, please don't hesitate to contact me. <br />Cc: Larry Routten <br />Doc: C:\WP51\COAL\RP4GEOT.WPS <br />JP/jp <br />