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I i I I I I I I I I I I I I I I I I I I lifts. The final lift will be compacted, then scarified and dressed to match surrounding topography and finally reseeded with native grasses. Section C-C', as presented in Figure 6.4 is typical of pipeline construction in the area from Station 762+ 10to Station 764+05. This section presents a conceptual detail of the pipeline at 1-70 and Colorado River crossings. Construction of the pipeline under 1-70 will entail specialty work. In an effort to limit construction outside of the R.O.W. of 1-70, a steel carrier pipe will be jacked under the highway embankment. Based on our conversations with the Colorado Department of Highways personnel, the embankment material used in construction and the subsurface material at 1-70 pipeline crossing locations may encounter large size material (cobbles and boulders). This subsurface condition may present difficulty during jacking of the carrier pipe. Prior to the actual jacking, a jacking pit and receiving pit will be constructed on either side of the highway. The pit dimensions will be specified in the actual design; the minimum jacking pit dimensions should accommodate the jacking machine, a section of pipe and personnel, while the minimum dimensions of the receiving pit should accommodate one length of pipe and space for construction personnel to move unhindered. The excavation of the jacking pits will require de-watering and excavation support provisions. Once the carrier pipe is jacked into place, the pipeline construction under the highway would continue. The pipes under the highway will be welded in the pit previously used for the jacking. Redwood skids (recommend three, minimum) will be banded to the pipeline prior to pushing the pipeline through the carrier pipe. Upon completion of the pipeline placement under the highway, the section of pipe should be tested according to the specifications. Once the pipeline has passed the testing, the annular space between the carrier pipe and the pipeline will be filled with sand or as specified. Construction of the pipeline under the Colorado River is anticipated to proceed as follows. By using a dredge, a backhoe or by other means, the contractor will excavate a trench along the proposed alignment for only half of the river. The soil and muck excavated from the river bottom will be placed and compacted around the area opened to form a cofferdam. The trenched area will be de-watered to maintain a stable, workable trench bottom. As indicated in section 6.1 the subsurface material at this location consists mainly of coarse grained soils with inter-layering of sandy silts to a depth of 40 feet below the river bed. The coarse grained material will not be suitable for construction of a cofferdam system. If this type of subsurface material is present at the river crossing, which will be confirmed during our design phase, then use of foreign material suitable for cofferdam construction will be 38