ENFORCE21415 - Laserfiche WebLink

Home Browse Search

-^ Susan McCannon, Dave Berry Colorado Division of Minerals and Geology January 9, 1998 Page 2 • Beaz's alluvial monitoring well, AA1, was discussed in terms of its location and what it has shown. Beginning in July 1986, the electrical conductivity increased from 300-600 µmho/cm to 2,000-3,000 µmho/cm. The cause for this si8rtifieant rise in conductivity was not known. • Pendleton asked what the depth to water information indicates and whether the water levels in ! the well reflect river levels. W WE did not have that information available at the meeting. • Rold noted the black organic soil on top of the colluvium and mature trees, estimated by Pendleton to be 50 to 60 years old. Both of these features indicate that the colluvium has been fairly stable for a number of years. • Pendleton noted that based on the fact that the hillside was historically relatively stable, the landslide indicates that there was a significant changed condition. Also, the single episode of slide movement indicates a dry slide. The slide "tore from the top down". The slide was comprised of colluvium, no signi£cant bedrock was noted. The material is high in clay but not saturated. The slide represents translational failure, not rotational. • ]ubenville discussed potential trigger mechanisms for the slide, including: moisture, steep slope, and mine subsidence influences. On the cross-section (Figure 1), Jubenville noted that the Bear C-Seam mining apparently came within approximately 25 feet of the bedrock-colluvium interface. It was unknown if Bear robbed pillars in this area. • Pendleton noted that Bear was required to leave pillars in some areas and to monument potential slide areas to the west where mining was planned close to the outcrop. The reports did not show any large failures, the land mass basically just "sat down". ! • The discussion returned to the spring and the high salinity water in well AAI. Welt noted that Bear's old reclaim tunnel had water in it and it may have served as a French drain. When it was backfilled, the water may have found a new path (i.e., the spring). • Pendleton suggested that MCC "source" the water. Welt responded by noting the water quality and isotope analyses that are currently in progress. • Pendleton wanted to make Buie that this is not a symptom of a larger event ("toe to the elephant")_ He questioned whether the hillside has stabilized and suggested that monuments should be considered. Welt pointed out that current conditions prohibit safe access for surveying near or on the landslide and that Intraseareh has not recommended a photogrammetric flight due to the snow cover (i.e., monochrome issues). Ne noted that MCC and WWE have made the "logical observations". • Kelly asked Pendleton what MCC and W WE can or should do now, after the fact, to determine what water, if any, caused the slide. Pendleton responded that if water were emerging, you could source it; however, there is not. He further noted that after the fact it is usually just "dumb luck" if you aze able to determine the source of water in a landslide and that we may never know. The meeting concluded shortly after noon. ! C:\8~tfi321411kab112-18 Mtg.mem.doc