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<br />I <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />1.2 Tunnel Alternative <br /> <br />The overall project area can be characterized as a steep, cliff-like or canyon-type topography. The <br />new tunnel is proposed to be located on the west wall of the Plateau Creek Canyon. Elevations in <br />the vicinity of the proposed tunnel range from 4,760 feet to 6,000 feet, MSL. <br /> <br />The regional geological units in the general project area consist of a thin layer of alluvial, eolian and <br />colluvial deposits of Quaternary age overlaying sandstone and shale units of Hunter Canyon <br />Formation of Cretaceous age. These units provide geologic conditions that are generally very good <br />for tunnel construction. The existing bedrock is quite stable and it is anticipated that the tunnel can <br />be excavated with only a minor amount of temporary support. Two general alignments were <br />evaluated as part of this report. Alignment "A" is situated at a point approximately 850 feet down <br />the ridge from the existing plateau tunnel portal. The alignment will proceed from this point <br />southwest upgrade approximately 1.5 percent to the west portal of the existing plateau tunnel. <br />Alignment "a" will start on the east side at the same point as Alignment A and will run <br />approximately 3,050 feet at a grade of approximately -1.6 percent to a west portal which is located <br />approximately 650 feet northwest of the existing plateau tunnel portal. <br /> <br />The proposed tunnels will be seven feet wide and eight feet in height. Three pipeline alternatives <br />through the tunnel have been evaluated including 42 inch diameter steel exposed pipe, a 60 inch <br />diameter buried pipe, and a 42 inch diameter buried steel pipe. <br /> <br />1.3 Pi peline Alternati ve <br /> <br />The subsurface conditions expected along the proposed bypass pipeline alternative alignment are <br />fairly variable. The subsurface conditions along Plateau Creek and the Colorado River consist of <br />unconsolidated, soft, saturated, flood plain alluvial deposits. These conditions are expected to <br />require the use of dewatering and excavation support methods during construction. Furthermore, <br />the foundation material exposed at the bottom of the trench may be too soft or loose to provide <br />adequate support for the water pipe. Under these conditions some densification and stabilization <br />of foundation soils would be required. <br /> <br />Based on our discussion with regulatory agencies which will be involved in permitting this project, <br />permitting considerations do not represent a fatal flaw for the proposed bypass pipeline alternative <br />at its currently proposed alignment. However, due to sensitivity of the area involved, a minimalistic <br />approach to the permitting effort is not recommended as it could be unsuccessful and <br />counterproductive. The number of agencies and required permits in conjunction with the sensitive <br /> <br />2 <br />