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Figure 6-32 (Attachment 8). However, CNI considers this case to be highly conservative <br /> and unlikely under actual field conditions. Experience at CCV has shown that water <br /> from precipitation is transient and is transmitted downward below the proposed mining <br /> levels to the extensive network of historic underground workings. <br /> To confirm the assumption of depressurized conditions, CNI recommended that a <br /> piezometer be installed in the central portion of the Globe Hill pipe prior to mining in <br /> order to verb that there are no pore pressures within the fractured pipe. The <br /> recommended piezometer installation location is shown on Figure 1-2 (Attachment 8). <br /> • The Division will likely consider the stormwater diversion(a.k.a. "bypass") a critical <br /> structure, thereby necessitating an appropriate FOS from DRMS Table 1. Please <br /> consider the FOS requirements when evaluating the stability in this area. CC&V's <br /> response to Comment No. 56 may have impacts to this comment. <br /> RESPONSE: Cross section GH-6 has a minimum FOS value of 2.22 for depressurized <br /> conditions. This FOS value meets the critical structure design criteria of 1.5. <br /> 40. Appendix 6, Paragraph 2.0, Overburden Storage Area Stability Evaluation. The stated <br /> factor of Safety goals are 1.3 and 1.15 for static and pseudo-static conditions, respectively. <br /> • Given the proximity of the ECOSA to both Grassy Creek and Teller Co Rd 81 SW of <br /> the Grassy Creek crossing,the Division considers the ECOSA a critical structure and <br /> the higher FOS (second row of DRMS Table 1) applies. <br /> RESPONSE:NewFields agrees with the assessment and has adjusted the evaluation <br /> and reporting accordingly (see Attachment 10). <br /> • These FOS values are based on DRMS Table 1 strength measurements resulting from <br /> multiple tests. However, it appears from the narrative for overburden and colluvium that <br /> these values may be based on assumptions (Overburden: "it is NewFields' opinion that <br /> the referenced strength is reasonable for the material", p. 4 in the text) and empirical <br /> relationships(Colluvium: "friction angle ((p) of 29 degrees were developed from an <br /> empirical relationship between shear strength, liquid limit and clay fraction of the <br /> material", p. 4 in the text)and not on laboratory tests. Please provide strength test <br /> results to justify the use of lower FOS or commit to meeting the Division's higher FOS <br /> for assumed, etc. strength parameters. <br /> RESPONSE: Overburden material in the ECOSA is essentially rock fill from the pits <br /> with no economic value. As such, the engineering properties are similar to that of the <br /> ore that has been studied throughout the project history. As summary of historic <br /> characterization of ore and overburden material is as follows: <br /> Material Facility Y(pcf) (deg) C(psf) Citation <br /> Ore AGVLF ** 40 0 Golder, 1996' <br /> Ore AGVLF 106 39 160 Golder, 1998' <br /> Ore AGVLF 110 40 0 SWC,20083 <br /> Golder Associates(1996). "Shear strength testing results for Cresson Ore", January 9. <br /> z Golder Associates(1998). "Final Report, Direct Shear Testing, East Cresson Ore Material, Golder Project No. 983- <br /> 2348.121", July 31. <br /> 3 Smith Williams Consultants, Inc. (2008). "Cripple Creek& Victor Gold Mining Company Cresson Project, Valley <br /> Leach Facility, Phase 5 Extension", March 3. <br /> Page 18 of 30 <br />