2010-12-17_REVISION - C1981019 (94)

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axis results in lower dip as the axis is approached. Below the downstream toe of the spoil fill, the X -seam floor contours indicate the bedrock dips towards the NE at about 2 to 5 percent. 5.2 Landslides Aerial photo analysis indicates several features within the footprint of the proposed temporary spoil fill that appear to be landslide features. Figure 3 shows the locations and extents of these features. One landslide was mapped by Intrasearch (2005) as part of a Photogeologic study of the Colowyo property. Based on the location of these features relative to the planned spoil fill location, it appears that the features will be buried by the fill, such that the fill will act as a buttress, and the features will not be near the toe of the out - slopes. Therefore, it is our opinion that these landslide features will not affect the stability of the spoil fill. 5.3 Underground Mining Colowyo has informed us that, to their knowledge, no underground mining is located beneath the site that would affect the stability of the temporary spoil fill. 5.4 Soil and Groundwater Conditions Is Following is a discussion of soil and groundwater conditions found in our borings; in later sections we discuss our interpretation of the generalized stratigraphy and engineering properties of the soils with respect to development of our stability analysis models. In general, surficial soils consist of a relatively thin layer of colluvial /residual soils on steeper slopes, and thicker colluvial/alluvial soils in valley bottoms. The colluvial /alluvial soils consist of gravel to boulder - sized bedrock fragments within a clayey or sandy matrix. The deposits can be stratified with clay seams in areas along valley floors. Our borings were drilled in the valley near the creek and therefore reflect deeper soil deposits. Soil conditions found in borings C -101, 103 and 104 consisted of a medium stiff to hard, sandy to gravelly clay, with occasional clayey sand or gravelly layers to depths of 7 to 22 feet. At deeper depths, in borings C -101 and C -104 the clay was medium stiff to stiff down 27 to 37 feet. Further downstream, in boring C -103 the deeper clay was soft to medium stiff. Medium dense clayey gravel was found below the clay (3 to 8 feet thick). Borings C -101 and C -104 indicated a depth to bedrock of approximately 32 to 37 feet in the valley bottom; bedrock was not encountered to a depth of 45 feet in boring C -103 located further downstream. Based on our field observations and the topographic map, we expect the soil 23 -1- 01101- 400- R1.docx /wp/1kn 23 -1- 01101 -400 Exh. 23 -1 -12 Revision Date: 08/05/09 Revision No.: PR -03