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Geologic Manning <br /> During investigation of the East Highwall in the Central Quarry, bedrock structural mapping was <br /> performed to evaluate slope instabilities and design a slope remediation scheme for the slope failure area. <br /> A set of north-south trending, west dipping, daylighting joints in that area were the primary reason for <br /> the slope instability problems that occurred. The slope remediation design became part of permit <br /> Amendment No. 3. Joint mapping data from that effort is presented in detail in Appendix A of that <br /> document. <br /> Amendments No. 3 and No. 4 include the methodology for the Observational Method of slope design at <br /> the quarry and, hence, the permit now requires additional geologic mapping and slope stability re- <br /> evaluations where steeper than 1H:1V slopes are planned. During operation year 1994, steeper slopes <br /> were planned and constructed in only one location in the West Highwall of The Central Quarry. An 80 <br /> ft x 80 ft bench with the bench elevation at approximately El. 6,560 ft was trimmed to a 0.5H:1 V <br /> configuration (40 ft bench x 80 ft highwall). This was done after detailed geologic mapping of <br /> approximately 800 LF of the 80 ft x 80 ft configuration highwall and reconsideration of slope stability <br /> by Haley & Aldrich. <br /> Attachment C, Geologic Mapping Information, includes five field highwall sketch maps portraying the <br /> results of the geologic mapping associated with this decision. The maps show foliation joint and other <br /> joint set strike and dip data, dike and shear zone nature and location information, and other relevant <br /> geotechnical data on rock type, joint characteristics and ground water seeps. The joint set data is also <br /> summarized in stereonet format in Attachment C. The relationship of the mapping data to the re- <br /> evaluation of slope stability and the decision to begin mining 80 ft x 40 ft benches at the West Highwall <br /> are discussed further, below. <br /> GEOTECHNICAL DATA ANALYSIS <br /> Update on Slope Stability <br /> During 1994, the Western and Southern highwalls of the Central Quarry were worked. The following <br /> discussion presents slope stability evaluations for the Western Highwall to document the decision to <br /> construct a 40 foot wide bench in conjunction with an 80 foot highwall. Along the southern end of the <br /> Central Quarry, the overall slope is not steeper than 1H:1V and specific slope stability update reporting <br /> is not required. <br /> Along the western side of the Central Quarry, the bench at El. 6,560 ft was trimmed from 80 ft to 40 <br /> ft wide in accordance with the previously approved Observational Method approach to slope design. The <br /> bench at El. 6560 ft is the only bench along the western side of the quarry presently less than 80 ft wide <br /> and it is the first bench above the present quarry floor which is presently at approximately El. 6480 ft. <br /> Slope stability evaluations followed the Observational Method presented in Permit Amendments No.3 and <br /> No. 4. As applied to the slopes in Cooley's Morrison Quarry, this approach establishes a baseline of <br /> expected rock mass conditions and corresponding evaluations of slope stability based on information <br /> available at that time. As the rock mass is further exposed by additional excavation, the newly exposed <br /> RP08267.200 6 <br />