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Slope Stability — Western Sugar Reclamation Land Development Project <br />Page 2 <br />June 17, 2011 <br />for the parameters for which Terracon provided measured values and values recommended by <br />DRMS/DMG in the response reference. <br />Item 2(c) (or second Item 2(b)) — The response provided is adequate. <br />Item 3 — The response provided is adequate. <br />Item 4 — The response provided is adequate. <br />Item 4(a) — The response provided is adequate. <br />Item 4(b) — The response provided is adequate. <br />Item 4(c) — The response provided is adequate. <br />Item 5 — The response provided is adequate. <br />Additional Comments: <br />Item 6 — The DRMS engineering staff uses the Galena Slope Stability Analysis software <br />(Version 5.02 to analyze slope stability. The staff used the parameters recommended in the <br />attached Table 1 and the Spencer - Wright method to analyze the two cases presented: 1) "Pit <br />Side Flood ", and 2) the dewatered condition. The staff found all analyzed failure surfaces for the <br />Pit Side Flood to have a Factor of Safety (FoS) very near or greater than 1.1. However, when the <br />staff analyzed the dewatered condition, several failure surfaces were found to have a FoS below <br />1.0 and some surfaces originating as far as 26 feet from the slope crest with a FoS less than 1.1. <br />Given the uncertainty in the soil properties and the water table, the proposed 25 -foot setback <br />must have a FoS of at least 1.1 in critical areas such as the gas wells. Please revise the mine plan <br />and provide slope stability analyses to demonstrate the revised mine plan will result in a FoS of <br />at least 1.1 in critical areas. <br />d: \documents and settings\mac\local settings \temporary interne <br />files \ content. outlook \wa1v5626 \stabilitycomments2nd meml6jun 1 l.docx <br />