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Knight Piesold <br /> CONSULTING <br /> Jared Rhea November 3, 2017 <br /> American Gypsum Company <br /> pit or mined and stockpile mine waste, in both cases a derivative of anhydrite soil/rock. Below are the <br /> assumed material parameters used as slope stability inputs. <br /> Property Fill material Intact native material <br /> Gamma(pcf) 120 180 <br /> Phi' 28 33 <br /> c' (psf) 0 10,000 <br /> acceleration 0.072g <br /> For the SLOPE/W inputs, the intact rock layer(s)were assigned the properties of inpenetrable bedrock to <br /> aid in obtaining realistic slip surface configurations. <br /> For the pseudostatic analyses, the peak ground acceleration input was obtained from the United States <br /> Geological Service (USGS) Earthquake Hazards Program website: <br /> https://earthquake usgs.gov/hazards/interactive/ <br /> Based on a Site Class B/C and using a Time Horizon of 475 years, a site-specific acceleration value of <br /> 0.072g was obtained. <br /> Analysis Results <br /> Employing the cross sections generated for the proposed backfilled and reclaimed West Pit area and the <br /> material parameters and site acceleration summarized above, the SLOPE/W results thus obtained are <br /> provided below. <br /> Cross section Static FoS Pseudostatic FoS <br /> 1.7 1.3 <br /> J 1.6 1.3 <br /> For cross section I, the slope is situated within the backfilled mine pit and therefore has virtually no <br /> opportunity to impact any area beyond the pit perimeter even if slope movement occurred during a more <br /> severe earthquake event. For cross section J, it is anticipated that the proposed regrading may remove <br /> virtually all fill from this area, leaving just the native profile. If this proves to be the case,the resulting terrain <br /> will revert to native conditions,and reflect similar slope stability conditions to the natural surroundings. Both <br /> analyses are assumed to present conservative conditions. We believe these results satisfy the <br /> requirements of the DRMS 2016 Memo. <br /> We trust this meets the objectives of your request and this document can be used to support your response <br /> to DRMS on this matter. <br /> Sincerely, <br /> Knight Piesold and Co. <br /> Richard F echette, P.E. <br /> Senior Vice President <br /> Enclosures: <br /> Figure 1 <br /> Attachment 1 <br /> M\Denver\Projects\101\00100 04\Deliverables\Letters\SlopeStabLetter docx <br /> 2 <br />