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TETRA TECH <br />Ms. Anne Best Johnson A1CP <br />October 27, 2010 <br />Page 2 <br />¦ A Noble Energy gas storage tank <br />• A gas well operations access road <br />¦ A communications tower and associated facilities and access road, owned by TowerCo <br />¦ Facilities associated with the communications tower <br />¦ A private residence and associated out buildings <br />• The Poudre River Trail owned by Weld County <br />¦ The Boyd Freeman irrigation ditch, owned by the Boyd Irrigation Company <br />• Various fences surrounding the properly. <br />STA&MI- AMLYSES <br />Stability analyses were performed in order to evaluate potential for damage to existing permanent structures due to <br />mine highwall slope failures. Analyses were performed with the Slope/W 2007 v7.17 computer program. For <br />each case we analyzed the most critical soil profile(s) based on exploratory boring data (i.e. the tallest highwall, <br />thickest overburden layer, etc). <br />The stability analyses were run in accordance with accepted geotechnical standards and DBMS requirements for <br />temporary pit slopes summarized as follows: <br />• Mine highwalls modeled as vertical slopes <br />• Residual soil strength parameters used for the upper 2.5 feet of weathered bedrock <br />• factor of Safety must be greater than 1.0 <br />Groundwater levels on the profiles were input to portray site dewatering. <br />Laboratory strength tests were not performed on soils from the site. The soil strength parameters used were based <br />on typical values for the anticipated soils and our experience working with DRMS at other sites in the area. The <br />input strength parameters were: <br />Table 1 <br />Q a.. U111A.. A....l..etn QLrnw.efh Z7.rs mare <br /> Moist Unit Saturated Unit Efreetive Cohesion EffeedveFrkdon <br />Material Weight (c Weight e (Nfi Angle (dees <br />Overburden clay 1 14 126 150 28 <br />Sand and gravel 130 137 0 37 <br />Clay Lease 116 119 200 22 <br />Weathered Residual 124 134 0 14 <br />Strength Bedrock <br />aCla tone Bedrock 124 134 500 22 <br />The scenarios were modeled with a general section developed from the most conservative conditions encountered <br />at the site including 6 feet of overburden overlying 33 feet of sand and gravel. Beneath the alluvium, the section <br />was modeled with 25 feet of residual strength bedrock on top of claystone bedrock. <br />The structures within 200 feet of the mine limit are shown in Table 2.