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• when measured 72 days after the drilling was completed. It should be noted that the test holes that were <br />not cased collapsed or caved off at depths of 3 to 4'/z feet beneath the ground surface when measured 72 to <br />73 days after the drilling was completed. In addition, the test pits were backfilled immediately after they <br />were excavated due to the caving of the fill materials. The groundwater conditions were highly variable <br />and can be expected to fluctuate significantly with changes in precipitation and runoff at the site. <br />As mentioned previously, the 2-inch diameter PVC casing was also installed in several of the test holes to <br />monitor the water levels and soil movement in the slope failure. However, we did not observe any <br />apparent downslope movement or displacement in the casings at the time of our last site visit on September <br />11, 2008. <br />Slope Failure Analysis <br />Based on the results of the field and laboratory investigations and our experience with similar types of <br />slope failures, we believe the slope failure that has occurred above Pond 12 can be characterized as a <br />moderately sized rotational slump failure that appears to have occurred in the natural overburden soils and <br />weathered claystone materials. The original failure surface appears to be located near the toe of the <br />• original natural slope, which was undercut by the excavation for the pond in this area. The removal of the <br />soils from this area most likely initiated the failure by removing support from the toe of the slope. Based <br />on our review of the photographs taken in 1999 during the construction of the pond, it appears that the <br />slope started to fail during or shortly after the pond excavation had been completed as evidenced by an <br />obvious tension crack in the cut slope. <br />The failure of these overburden soils and weathered claystone materials can probably be attributed to the <br />presence of relatively shallow groundwater levels present in the overburden soils and the presence of a <br />marginally stable natural slope prior to excavation for the pond at the toe of the slope. It appears that the <br />overburden clays represent materials redeposited by older landslides or debris flows that may have <br />occurred along the drainage that is situated just south of the slide. In addition, the placement of fill <br />materials over the marginally stable/failed natural soils, as a result of the haul road construction, increased <br />the loading on the slope thus increasing the size and rate of failure in this area. Loss of support created by <br />the formation of the head scarp and downslope movement of the debris flow has contributed to the uphill <br />propagation of the failure. <br />We have not yet observed any movement or displacement in the PVC test hole casings that were installed <br />at this site in July 2008. However, we anticipate that the failure plane is probably located within the upper <br />15 to 35 feet of overburden soils and weathered claystone materials. Based on the subsurface conditions <br />Job Number: 07-7600 NWCC, Inc. Page 6 <br />