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<br /> <br />• <br />H2.0 Characterization of Landslide <br />This section is an update of Section 2.0 of the "1997/98 Landslide Corrective Measures Report". This <br />section provides new information on [he character of the landslide, based on 1998 and 1999 engineering <br />analysis and study of the slide that was performed. <br />Geology: The West Elk Mine surface facilities occupy the area of a reactivated landslide. The slide is <br />located on the south side of the North Fork of the Gunnison River, just east of the mouth of Sylvester <br />Gulch. The landslide occurs as an elongated arch about 600 feet wide at its head near Elevation 6,500 and <br />1,800 feet wide at its toe near Elevation 6,250. Figure H 1 shows a plan of the existing 1999 facilities, the <br />present identified limit of the slide, and the estimated location of a buried rock terrace wall. Previous work <br />by Barr, Harding-Lawson and Associates, Mountain Coal Company, and others have assisted with <br />mapping and characterization of the landslide. <br />The landslide occurs in overburden that buries a bedrock terrace scoured by the ancestral North Fork <br />River. The buried terrace is a meander carved into the Cretaceous Mesaverde Formation. The meander <br />opens to the river valley on the north, but a buried rock wall borders the meander on the east, south, and <br />west. The rock boundary of the meander appears to contain, or limit, the slide on the west. On the south, <br />however, the slide extends well into overburden material above the buried rock bluff The east boundary <br />of the slide and rock meander is not well defined and an estimate of the location of this terrace has been <br />made. Figure HS (lunge, 1978) places the slide azea in the regional geology and identifies it to be the <br />youngest of three alluvial-filled terrace remnants. Figure H3 shows an interpretation of a cross section <br />through the landslide. <br />Materials in and Under the Landslide. Previous work at the site classified the materials in and under the <br />landslide (from top [o bottom) as Upper Colluvium, Lower Colluvium, Granite Cobbles, and Bedrock. <br />The Upper and Lower Colluvium are clays with embedded angular sand, gravel, and cobbles created <br />primarily from local sedimentary rocks. Beds, lenses, and stringers of clayey sand occur throughout the <br />Colluvium. Color is the distinguishing visual difference between the Upper and Lower Colluvium. The <br />Upper Colluvium is oxidized to shades of brown and yellow brown, and the Lower Colluvium is generally <br />Barr Engineering Company <br />PCDOCS1209220/CAK <br />July 31, 7999 <br />Appendix H <br />1999 Addendum to <br />1997198 Landslide Corteetive Measures Report <br />