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Evaluation of Bear No. 3 Mine Landslide It has been postulated that the water now surfacing at the Edwazds portal spring saturated the toe of the slide and triggered the slide movement. Several lines of evidence refute this. If the spring triggered the slide, the first and most intense movement would be near the spring (Figures 4 and I l). Slide movement reportedly started at the west edge and progressed from west to east. Maximum movement as indicated by the arcuate scarps was some 250 fee[ west of the spring. It is highly unlikely that that small amount of water could have saturated enough of the slide to have triggered the slide. The highly permeable terrace gravel beneath the slide would act as a lazge toe drain carrying the water away from the slide. If the toe of the colluvial wedge Itad been saturated sufficiently to trigger the slide, the failure would be rotational. This would provide considerable evidence at the toe. Certainly if the toe were saturated enough to trigger the slide, the toe would still be seeping water. Not only was no seeping water seen, observers felt the slide was abnormally dry and called it a dry slide. The spring, at least on and prior to December 2 and 3, was physically sepazated from the active slide. We also found no evidence to support the theory that the spring was originally located under the slide mass and that the slide's movement redirected [he spring to its present location. There is a known source of groundwater in the slide mass. Surface precipitation from the wet spring, summer, and fall of 1997 incident on the landslide could have infiltrated through the colluvium and/or seep along tension cracks in the slide mass. The two active slides at the head of the current slide would facilitate introduction of this water into the head of the slide. Some of this water would undoubtedly reach the contact of bedrock and the colluvium. [t would not require much moisture to lubricate the bedrock-colluvial interface in the upper part of [he slide mass. Tltis moisture may be producing a small hydrostatic head on the base of the sliding mass. The moisture which saturates the soils along the failure plane results in a decreased shear strength which reduces the forces able to resist the downslope movement. Therefore, a small amount of moisture at the head of the slide could have a significant efTect on the stability of the colluvial mass even though only the upper portions of the slide were wetted. The most likely scenario is that surface water from the abnormally wet spring, summer, and early fall of 1997 entered the slide mass through tension cracks in and around the two then active small 831-032.411 Wright Water Engineers, Inc. Page 14