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According to the 1994 mine permit, the clay seam that was discussed as a potential failure zone <br />was removed by mining activity by 2000, "reducing the risk of sliding into the hole." CTL refers <br />to unidentified clay layers in the limestone as likely being the failure surface, yet there are no <br />drill logs or surface observations that would support this being a more likely scenario than other <br />potential failure mechanisms. The CTL stability analysis does not take into account any clay- <br />filled discontinuities or clay seams for modeling. <br />The CTL report indicates that investigative core logging had been completed, and states, <br />"Although all that exists of those borings are the descriptive drill logs, they are sufficient to <br />construct this picture of the mountainside structure." These boring logs are not included in the <br />CTL report. It is hard to judge the material properties used by CTL in their stability analyses <br />without some indication of the quality of the rock. During the December field visit, CGS noted <br />many instances of shear zones, fractures, and gouge in the rock-mass that would affect the <br />RQD and strength parameters of the rock-mass. Additionally, these borings would help give <br />insight into the clay seams and valuable information as to their depth, structure, and continuity <br />through the formation. <br />The connection with higher precipitation in the preceding months as the trigger for failure is <br />tenuous at best. There has historically been far larger and longer wetting periods (1995, 1997, <br />and 1998) when failures did not occur. CGS did not observe any evidence during our <br />December 11, 2008 site visit following the failure, which would point to dramatically increased <br />groundwater conditions in the slide mass. It is unclear whether there was any groundwater level <br />monitoring being done at the site that might have provided better data as to the actual <br />groundwater levels at the site. In our earlier memorandum, CGS did mention groundwater as a <br />minor potential causal agent to slope instability, but we consider the field evidence not indicative <br />of groundwater being the major cause of the rockslide. It is questionable that the "steam plume" <br />mentioned in the CTL report that was observed by quarry personnel rising from the landslide <br />debris in any way relates to high groundwater levels. It is more likely a result of direct <br />sublimation of the snow to vapor as the surface rock warms, or condensation of moist warmer <br />air rising from the broken ground when encountering the drier colder-temperature air above. If <br />the slide was truly driven by high groundwater levels, we would expect 1) seeps or springs to <br />have appeared in the quarry wall in the area of failure prior to the rockslide, and 2) that <br />significant water would have decanted from the rubble at the landslide toe. We have seen no <br />reports to the former and no water or mud flow from the toe of the landslide was observed <br />ponding on the floor of Area H (the hole) during our inspection, which would support the latter. <br />(See Figure 1 taken by CGS on December 11, 2008.) <br />2