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Vantage to Pomona Heights Chapter 2 <br />230 kV Transmission Line Project FEIS Proposed Action and Alternatives <br /> PAGE 2-42 <br />FIGURE 2-10 TYPICAL DUCT BANK AND ACCESS ROAD SECTION <br /> <br />Construction Procedures <br />The first step in the underground construction process would be to deploy appropriate erosion and <br />sedimentation controls (e.g., catch basin protection, silt fence or straw bales) at locations where soils <br />would be disturbed. <br />Open Cut Trenching <br />To install the duct bank, a trench would be excavated approximately 6 to 10 feet deep and approximately <br />5 to 10 feet wide (for trench depths requiring shoring to stabilize the sidewalls). Excavated material (e.g., <br />subsoil) would be placed directly into dump trucks and hauled away to a designated suitable disposal site <br />or hauled to a temporary storage site for screening/testing prior to final disposal or re-used in the <br />excavations for backfill. If groundwater is encountered, dewatering would be performed in accordance <br />with authorizations from applicable regulatory agencies and may involve discharge to catch basins, <br />temporary settling basins, temporary holding tanks, or vacuum trucks. When bedrock or subsoils <br />primarily consisting of large boulders are encountered, blasting may be required. See Figures 2-7 and 2-8 <br />for photographs of open cut trenching. <br />Duct Bank Installation <br />The duct bank system would consist of 6 to 8 inch polyvinyl chloride (PVC) conduits for the XLPE <br />cables; two-inch PVC conduits for the ground continuity conductors; and four-inch PVC conduits for the <br />fiber optic relaying cables and the temperature sensing fiber cables. The conduit would be installed in <br />sections, each of which would be about 10 to 20 feet long and would have a bell and spigot connection. <br />Conduit sections would be joined by swabbing the bell and spigot with glue then pushing the sections <br />together. After installation in the trench, the conduits would be placed into spacers that hold the conduit in <br />the desired configuration and then encased in high strength concrete. If required, the trench would then be <br />backfilled with a low-strength fluidized thermal backfill with sufficient thermal characteristics to help <br />dissipate the heat generated by the cables.