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Jared Ebert <br /> September 16,2019 <br /> Page 10 of 11 <br /> Al Response: The overhead electric parallel to Highway 7 was selected as the critical structure for <br /> analysis at Cross Section H. The analysis showed the 35 foot offset from the overhead electric met the <br /> requirements. The noted 106-foot offset is applicable to Cross Section N. Cross Section H and Cross <br /> Section N are intended to represent the conditions north of Highway 7, west and east of Tucson Street, <br /> respectively. <br /> 6(1). The Applicant modeled the Figure J analysis which produced a minimum FOS located 44 feet <br /> from the edge of the Brighton Return Ditch. The Exhibit C-3 Map indicates the Applicant modeled a 77 <br /> feet offset. Please explain this discrepancy and revise the Figure J models and/or the Exhibit C-3 Map <br /> accordingly. <br /> Al Response: The Slope/W cross section and analysis summary table was revised to reflect an offset <br /> of 51' from the Brighton Return Ditch easement boundary, which is located closer to the limit of mining <br /> excavation than the actual ditch. <br /> 6(2). The Division duplicated the Figure J models with the 77 feet offset from the edge of the Brighton <br /> Return Ditch. The models produced factors of safety of 1.07—Static and 0.89— Pseudostatic, which do <br /> not meet the required FOS. Please review the Applicant's and Division's models and reevaluate the <br /> proposed offset distance from the Brighton Return Ditch to conform to the FOS requirement of the <br /> MLRB. <br /> Al Response: We examined the DRMS analysis and noted that the failure surface and subsequent <br /> FOS is located approximately 20 feet from the limit of mining excavation. The DRMS analysis should <br /> be revised to reflect a failure surface at the easement boundary, approximately 51 feet from the limit of <br /> mining excavation. This will result in a different FOS which may satisfy the requirements. <br /> 7. Please note there are numerous inconsistency in the geometry: offset from top of slope, offset from <br /> easements, offset from structures and offset from the slurry wall location between the Stability Analysis <br /> Models, the Figures 3 through 7 cross-sections provided in the Stability Analysis, the Mine Plan Map <br /> and the Actual Offset from the Mining Excavation Limits listed on the Structures List on the Exhibit C-2 <br /> Map. The Division will consider the enforceable offset as the offset distance listed on the"Actual Offset <br /> from Mining Excavation Limits" listed on the Structures List on the Exhibit C-2 and C-3 Map if the permit <br /> is approved and issued by the Division. <br /> Al Response: We have reviewed the cross sections, analysis summary table, and stability analysis <br /> cross sections and made edits for consistency. While having the drawings and stability analysis cross <br /> sections match exactly is ideal, the iterative process needed to develop both makes an exact match <br /> impractical and unnecessary. The stability analysis is used to set the maximum limit of mining <br /> excavation based on the geotechnical analysis only. Other factors that influence the limit of mining <br /> excavation, include, but are not limited to, required County setbacks, UDFCD setbacks, agreements <br /> with structure owners, and slurry wall constructability concerns. When we determined the limit of <br /> mining excavation, we consider all these factors, but review the limits to verify that we do not exceed <br /> the limits set within the geotechnical analysis. It is also not necessary to update the geotechnical <br /> Aggregate Industries—WCR,Inc <br /> 1687 Cole Blvd Suite 300 <br /> Golden,CO 80401 <br />