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File No. M-2001-046 Owens Brothers <br />5/9!02 <br />-2- <br />Soils Information <br />No soils report has been prepared for the Nix property, thus no speck soils properties <br />are known. For this reason, soil properties have been assumed based on research and <br />guidance from the DMG. To be conservative, the following values for the relevant soil <br />properties (Total Weight, Effective Cohesion, Effective Friction Angle) have been used to <br />simulate a "worst case scenario": <br />Conservative Soil Pro erties <br />Soil <br />Type Total Weight <br />(pcf) Effective Cohesion, C <br />(psf) Effective Friction <br />An le, (de ree) <br />Overburden 115 50 24 <br />Sand and Gravel 126 0 35 <br />Weathered Shale 125 0 14 <br />Note: assumed soil properties are consistent for materials represented by the drilling logs and are <br />ical for this area. <br />Although no specific soils report has been prepared, soil bore logs were evaluated to <br />classify the overburden. This information indicates that the overburden material consists <br />of silty sand and silty fine sand. <br />Slope Stability Analysis <br />A slope stability analysis (SSA) has been performed for an excavation, approximately <br />650 feet in length, parallel to Weld County Road 28 (WCR 28) in the southeast corner of <br />the site. This analysis is referred to herein as South SSA. A second location was also <br />evaluated representing approximately 700 feet of excavation parallel to Weld Gounty <br />Road 17 (WCR 17) on the west portion of the site, referred to herein as West SSA. <br />Relevant soil borings, taken for reserve estimates on the property, have been used to <br />establish depth of overburden, extent of sand and gravel, and depth to weathered shale <br />in the areas of the necessary SSA. Along WCR 28, two soil borings in the vicinity of the <br />SSA ident~ed an overburden depth of 12 feet and 15 feet with a depth to weathered <br />shale of 56 feet and 43 feet, respectively. Along WCR 17, one soil boring identified an <br />overburden depth of 7 feet with a depth to weathered shale of 50 feet in the vicinity of <br />the SSA. Given this information, a SSA was evaluated and setbacks are recommended <br />based on the resultant factors of safety. <br />The software used in the analysis is GSLOPE from MITRE Software Corporation. The <br />reserves at the Nix site are to be excavated by wet mining methods; thus, the water in <br />the pit is included in the analysis, as is the piezometric surface in the overburden. The <br />piezometric surface simulates a saturated soil condition with groundwater approximately <br />3 feet below the ground surface. <br />SSA Results <br />The scenarios and the results for several scenarios are included with this submittal and <br />described below. <br />The first scenario, identified as West-1 and South-1, represents the previously proposed <br />mined slope of 2:1, the proposed setback of 25 feet, and the expected water conditions <br />of the pit water surface elevation equal to the piezometric water surface elevation. The <br />