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Response to CDRMS Comments Mr. Robert Noren, P.E. <br /> Disposal of Alluvial Fill Cotter Corporation(N.SL) <br /> The regrading proposed on Figure B-2 results in 104,800 cubic yards (cy) of additional <br /> storage capacity from the current waste rock pile configurations. The reclaimed slopes have a <br /> maximum interbench slope of 2H:1 V. EA completed slope stability analyses for the new <br /> configurations of the north and south waste rock piles shown on Figure B-2. The results are <br /> included in Attachment B. The number of benches along with cross-sections showing the <br /> benching is also included on Figure B-3 of Attachment B. <br /> 3. Adequacy Review #2, Comment # 6: "The Division views the waste rock piles as critical <br /> structures as they are designed to keep waste rock out of Ralston Creek. Plates 12 and 13 <br /> prepared by McDermid Engr. Assoc. Inc. in February 1983 summarize slope stability <br /> analyses results. It appears only the cover stability and the contact with the native ground <br /> were analyzed as potential failure surfaces. The various strength parameters used for <br /> bedrock, alluvial soils and colluvial soils were obtained from simple soil testing and/or <br /> literature data. It does not appear that slope failure surfaces thought (SIC) the waste rock <br /> itself were considered as is the current general practice for slope stability. As such it does <br /> not appear any strength parameters of the waste rock itself are discussed. Please revisit the <br /> slope stability of the waste rock piles and consider potential circular failures that may extend <br /> through the waste rock, using the Division's factors of safety in Table 1. " <br /> DRMS Table 1.Minimum Factors of Safety for Sl Stability Analyses(1 <br /> Type of Structure/Consequence Generalized,Assumed,or Single Strength Measurements <br /> of Failure TestStrengthMe_asurements i R.1thaz from Multiple T.1911) <br /> (e g. 1.3 LZS <br /> fences)/M. <br /> imminent danger to <br /> human life,minor environmental <br /> impact,and minor repair costs if <br /> slope fails <br /> Critical Structures(e.g., 1.5 L3 <br /> residences,utilities)/Potential (1.3)111 (L1S)R) <br /> human safety risk,major <br /> environmental impact,and <br /> maLor repair costs if slo a Mb: <br /> (1) The number of tests required to provide a high degree of confidence in the strength parameters used <br /> depends on the variability of the material being tested and the extent of the highwall disturbance. <br /> (2) Numbers without parentheses apply for analyses using static conditions and those within <br /> parentheses apply to analyses using seismic acceleration conditions <br /> Note: 1)Table provided in Adequacy Review#2 <br /> Response: As discussed above, a field investigation and laboratory testing have been <br /> completed for use in slope stability analyses. EA has completed stability analyses for the <br /> future configurations,of the waste rock piles. The results of these analyses are provided in <br /> Attachment B. Three failure surfaces are included for each cross-section through both the <br /> north and south waste rock piles. The cover stability and the contact with the native ground <br /> were analyzed as the surficial and deep failures. In addition, EA analyzed an optimized <br /> intermediate failure through the waste rock. The results indicate that the factor of safety <br /> meets the minimum 1.5 criteria for static analyses and the minimum 1.3 criteria for <br /> pseudo-static analyses. <br /> Limitations <br /> This report has been prepared based upon review of the field investigation, laboratory testing, <br /> and our experience. No warranty is made, express or implied. The conclusions presented <br /> represent our best judgment based on the information available. Should additional information <br /> become available we should be allowed to review that information and modify our conclusions <br /> accordingly. <br /> October 26, 2016 3 Engineering Analytics, Inc. <br />