Replace Wooden Pole 59 with Metal Lattice Pole near Cascades Substation

Yosemite National Park » Replace Wooden Pole 59 with Metal Lattice Pole near Cascades Substation » Document List

The proposed action is to replace an existing wooden utility pole (#59) that poses structural and safety issues. Pole 59 has been previously replaced but, continues to be structurally inadequate. Various options were examined as alternatives to replacement. These options included rerouting of the line, removal of the pole with no replacement, and measures to strengthen the existing pole. None of these alternatives were structurally acceptable.
The project area is on a boulder bar within the Merced River corridor near the Cascades electrical substation along El Portal Road (CA highway 140). It is above the Ordinary High-Water Mark (OHWM). The new structure will be placed approximately 30 to 50-feet to the east of the existing wooden pole location. The existing pole is 70.7-feet. The new lattice structure will be approximately 105-feet high. The overall alignment of the overhead transmission line will remain largely unchanged. The new lattice tower will require the installation of 4 micropiles (each 6-inch diameter) and 2 grounding rods (5/8-inch grounding rods set 6 feet apart, extending 8 feet in deep). Micropiles will be drilled using helicopter assistance for the placement of a temporary drilling platform (approximately 12 by 15 feet in size) on top of the ground. Each micropile will be set into bedrock (the exact depth of penetration will be determined in the field, but engineers anticipate that bedrock is shallow at the proposed project sites). Penetration of the subsoil for the micropile installation is not expected to exceed 15-feet as engineers anticipate that bedrock is located at 3-4 feet in this area. The existing pole would be removed using helicopter assistance. Removal of the existing pole will require minimal digging. Equipment and materials staging for this work will be temporary. It is anticipated to occur in multiple locations. The large existing staging area along the east bank of the Merced River between the Rancheria Flat housing complex and the El Portal wastewater treatment plant may be used as will an empty lot associated with the privately-owned lodge immediately west of the park. Improvements to the staging areas are not anticipated. Potential landing areas will be on existing paved areas and include the Crane Flat Helibase and a private parking area just west of the park entrance on Highway 140. These areas will be used to stage the helicopter and tower components, drill equipment, and conductors. Some traffic delays may occur during helicopter operations. Short term traffic control for safety will be in place sporadically as needed.