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~~ Banks and Gesso, LLC <br />~~ <br />February 28, 2002 <br />Mr. Allen Sorenson <br />Division of Minerals and Geology <br />1313 Sherman St., Room 215 <br />Denver, CO 80203 <br />Re: Slope Stability Analysis for Existing Structures <br />Owens Bros. Concrete -Nix Sand and Gravel Mine <br />Dear Mr. Sorenson, <br />720 Kipling St.,Suite117 <br />Lakewood, Colorado 80215 <br />{303)274-4277 <br />Fax (303)274-8329 <br />www. banksandgesso.com <br />Enclosed you will find the analysis and relevant material that support mining within the 200 foot <br />setback, per DMG Rule 6.4.19(b), for the above referenced site. The evaluation will establish <br />mining setback limits, in the vicinity of the west and south property lines, to protect existing <br />structures from damage during mining activities. The existing structures in question are utility <br />poles/overhead power lines as indicated on Exhibit C-3 of the Regular 112 Permit. Two <br />underground gas mains also exist in the vicinity of this analysis, but agreements have been <br />attained which allow for mining at the indicated setbacks. <br />No soils report has been prepared for the Nix property, thus no specific soils properties are <br />known. For this reason, soil properties have been assumed based on research and guidance <br />from the DMG. To be conservative, the following values for the relevant soil properties (Total <br />Weight, Effective Cohesion, Effective Friction Angle) have been used to simulate a "worst case <br />scenario': <br />Conservative Soil Properties <br />Soil <br />Type Total Weight <br />(pcf) Effective Cohesion, C <br />(psf) Effective Friction <br />Angle, (degree) <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 />typical for this area. <br />A slope stability analysis (SSA) has been performed for approximately 650 feet of excavation <br />parallel to Weld County Road 28 (WCR 28) in the southeast corner of the site (South SSA) and <br />approximately 700 feet of excavation parallel to Wefd County Road 17 (WCR 17) on the west <br />portion of the site (West SSA). Relevant soil borings, taken for reserve estimates on the <br />property, have been used to establish depth of overburden, extent of sand and gravel, and <br />