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'(?? 1G..? ?I t ? 61t)Nd21 <br />On December 24, 2008, we received an e-mail from Tom Stefansky with an addendum <br />to the drill rig recovery plan developed by Yenter, dated December 23, 2008. On <br />January 5, 2009, we sent an e-mail to Mr. Crelly indicating that we found the plan <br />satisfactory, but recommended that the mine operator provide evidence that the pit <br />slopes have stabilized prior to removing the drill rig from the pit. <br />On January 6, 2009, Mr. Donahue spoke with Mr. Shafer regarding earlier reports of <br />additional slides at the pit slopes. Mr. Shafer stated that there were toppling failures of <br />rock blocks up to 20 feet wide along the southern portion of the main slide scarp. These <br />blocks were caught by the large rift in this location and did not reach the pit floor. <br />Additionally, on a particularly cold morning, a considerable amount of condensed <br />vapor "steam" was emitted from the fissure on the south side of the slide. This could be <br />indicative of significant features such as relatively warm springs or seeps in this fissure <br />or possible air circulation from limestone solution openings uncovered by the fissure. It <br />could also be a result of a particular meteorological condition and not significant. <br />Mr. Shafer also stated that he had sent additional photos and monitoring information to <br />Pittsburgh Technical Support for our review. These materials will be reviewed and <br />evaluated in a separate report. <br />CONCLUSIONS <br />Based on the information collected during and after the investigation, we conclude that <br />the large mass slope failure most likely occurred along a discontinuity in the limestone <br />bedding or the contact between the limestone and the underlying sandstone or granite. <br />These discontinuities likely exhibit an average dip and dip direction very close to that of <br />the pit slope. The current pit mining operation was likely removing material that had <br />provided a buttress to the rock material above the critical discontinuity, ultimately <br />triggering the slope failure. The previously blasted, then filled, "hole" in the pit slope, <br />may have been a contributing factor in the instability of the slope. The CGS geologic <br />map and report describe limestone solution features and caves in exposures of the <br />Manitou Limestone 3 to 5 miles southwest of the quarry, so the presence of solution <br />ion <br />wew athering cannot bP e ?l„mod as another possible contributing factor. <br />Rough distance measurements suggest a slide area of about 9 to 10 acres. The thickness <br />of the slide mass is uncertain, but based on a visual estimate of estimate sulting scarp and <br />fissure, the slide mass was, very roughly, about 100 feet thick. The estimated slide <br />volume would be about 1.5 to 1.6 million cubic yards. <br />In addition to the main slide mass, the secondary cracks and scarps at the south peak <br />area suggests that a large part of the pit slope to the southwest of the main slide mass is <br />at a critical stability condition (safety factor at or nearly equal to unity), and a'second