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• <br />`1 <br />• <br />~~ <br />the proposed waste bank. Cuts made for the railroad track alignment expose the Rollins <br />Sandstone Member of the Mesa Verde Formation. This formation is described as 'brown to <br />gray, fine- to medium-grained sandstone and grey shale; commercially important coal beds in <br />lower part; Rollins Sandstone Member at bass' (USGS, 1978). Mining operations at the <br />Sanborn Credo Mine occur within the coal beds of the Mesa Verde Formation. The toe of the <br />proposed coal mine waste bank will be }ourded on the Rollins Sandstone Member of the Mess <br />Verde Fomlation. Mapping of the Rollins Sandstone at these outcrops showed various degrees <br />of weathering, most of which occurs near the top of the outcrop. The weathered sandstone <br />breach easily with a hand pick along bedding pWnes. Below the highly weathered upper <br />sandstone a hard, competent sandstone that is very difficult to break with a pick. Within the <br />highly weathered sandstone, there is a seam of red clayey material that was very soh and <br />easy to break with a pick. This seam was an average thickness of 2 inches. <br />According to geobgic maps for the area (USGS, 1978b1, rockfalls are the only hazard at this <br />site. This was evident in the vertical rock outcrops above the proposed coal mine waste bank, <br />and the collwial material found on the hillside. Rockfalls are not expected to be a factor in <br />design, but may prove to be a maintenance issue, i.e., removing fallen rock fragments from <br />the waste bank during the lifetime of the project. No remedial activities need to be conducted <br />to prevent rockfalls in the area. <br />2.2 SUBSURFACE CONDITIONS <br />Due to steep terain and vehicle access problems, one geotechnical borehole was completed <br />at the end of the West Yard storage arcs. This bcation was optimal in that rig access was <br />available and the tue of the railroad right-ot way could be avoided. This borehole was drilled <br />to confirm depths of colluvium/alluvium; obtain material strengths; and confirm the continuity <br />of the Rollins Sandstone with the bedrock outaops mapped near the toe of the proposed <br />waste banlt as weR as moderately deep groundwater condkions. The bcation of this borehole <br />is shown on Figure 2.1. <br />96256/1424.tiPT Cul Mkr Waata Bank L)•aipn for tMa 9antxxn Gaak Mir <br />Octotrr lase WE9TEC.Ine. s <br />