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Comments pertaining to the Kleinfelder Highwall and Rockslope Engineering <br /> Analysis (Attachment A) <br /> 5. In section 5 and subsequent stability cross sections, the faults identified in <br /> figure 4.1 are not included, and presumably not included in the stability <br /> evaluation. Faults can convey moisture and contain weak material that <br /> can lead to slope failure, similar to that of the Pikeview Quarry in El Paso <br /> County. <br /> o Faults identified at the site should be evaluated for stability <br /> considerations. <br /> Response: <br /> The features shown on Figure 4.1 are interpreted as contacts between <br /> the intruded dacite and the adjacent sedimentary parent rock. The <br /> features are assumed to be more associated with intrusion of the dacite <br /> sill than fault movement. This interpretation is discussed in more detail <br /> below. However, these features were still evaluated as reduced shear <br /> strength materials for the stability analyses. <br /> The Lyons Geologic Quadrangle Map (Braddock, et al, 1988) shows a <br /> fault mapped to the northwest of the site that is trending N30W with an <br /> 80 degree dip to the southwest. This mapped fault trace terminates at <br /> the north edge of the site. Just to the south of the fault termination, the <br /> mapping at the quarry shows the intruded dacite sill, which generally <br /> follows the bedding of the sedimentary strata, has a thicker section with <br /> two vertical contacts in the area exposed along the highwall face. The <br /> contact on the east side of the sill strikes N2OW dipping 80 to 90 degrees <br /> to the southwest, very similar in orientation to the mapped fault. <br /> Additionally, the vertical offset across the contact at the top of the dacite <br /> is about 80 feet and this large offset combined with the similar orientation <br /> to the mapped fault trace has been interpreted by others as a fault. <br /> However, the site mapping identified continuous sandstone units across <br /> the top and on either side of the sill, suggesting that the sedimentary <br /> units are not faulted to the surface in this area. So, based on the site <br /> mapping, the features shown on Figure 4.1 are described as an inferred <br /> contact. The geotechnical report also states that a study of topography <br /> and stereo aerial photography indicates that the mapped fault, if present <br /> across the site, would extend across the site to the east of the features <br /> shown on Figure 4.1. <br /> 7 <br /> hdrinc.com <br /> 1670 Broadway,Suite 3400, Denver,CO 80202-4824 <br /> (303)764-1520 <br />