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PG&E Exchequer-Yosemite 70kV Reliability Project

Yosemite National Park » PG&E Exchequer-Yosemite 70kV Reliability Project » Document List

Pacific Gas and Electric Company (PG&E) is requesting authorization from the National Park Service (NPS) to conduct maintenance activities on the electrical transmission line that PG&E owns and operates within lands administered by Yosemite National Park (YNP). The project's goal is to improve the reliability of electrical transmission in Mariposa County. In addition, PG&E is addressing known conductor height discrepancies to meet standards set by California Public Utilities Commission General Order (GO) 95 and North American Electric Reliability Corporation (NERC), which is part of the Federal Energy Regulatory Commission. This maintenance work is required to bring existing lines into compliance. Project actions include the replacement of four existing lattice-steel towers with new lattice-steel poles (LSPs), maintenance activities on eleven existing towers, and the replacement of approximately two miles of electrical transmission wire (conductor) with new conductor.

Tower Replacement: Each of the four tower replacements will require site preparation work within a 50-x-50-foot area at both the new structure locations and around the existing towers to be replaced. Site preparation may include activities such as vegetation trimming and removal, and limited surface blading, grading, and filling to create a stable and level work pad for equipment and vehicle staging. Work areas will be returned to original surface contours at the completion of work.

The new LSPs require micropile foundations that consist of up to 12 composite piles within a 5 to 6-foot diameter square array. Individual piles are cylindrical and less than 1 foot in diameter and will be embedded up to 30 feet below ground. The resulting array will project a minimum of approximately 1-foot above ground. Following the installation of foundations, the new LSP will be assembled at a nearby landing zone, and a helicopter will fly the new LSP to the work site and set it on the foundation. The new structures will be approximately 75 to 90-foot-tall structures, approximately 20 feet to 30 feet taller than the existing towers.

Once the conductor has been transferred to the new structure, the existing tower will be dismantled and removed from the site by helicopter. Remaining tower foundations will be chipped and removed to approximately 2-3 feet below grade then capped with native soil to match existing surface contours.

Vegetation Management: A work area approximately 50-foot by 50-foot will be cleared of vegetation at each of the four new LSP sites in order to employ proper and safe construction methods. The size of the work area provides a defensible work area for construction crew safety in the event of a potential wildfire in the area. In addition, the clearing will also bring the new LSP location in compliance with vegetation management safety standards with the removal of any tree and woody or vine material 10 feet around each planned LSP and the removal of any dead, dying, or leaning tree that poses a safety hazard to the planned LSP or new conductor. Sixteen trees and 4 brush units have been identified for removal. Every effort will be made to retain any healthy tree that does not pose a safety hazard and that does not interfere with the safe and proper installation of the micropile foundations.

Maintenance Activities: Routine maintenance activities proposed at eleven towers include installation of structural reinforcements and or cross arm replacement, replacement of existing insulators with new ceramic insulators made of glass or porcelain, installation of anti-climb guards, and installation of bird spikes to deter nesting activities on the towers. No ground disturbance is associated with the maintenance work, it is to be accomplished above-ground on the towers. Crew and equipment will be transported to each tower location by helicopter.

Conductor Replacement: The existing conductor will be replaced (reconductored) between towers 037/219 - 039/236. Reconductoring will occur after all tower replacements, described above, are complete. To replace the conductor, the existing conductor will be detached from its support structure and temporarily lifted. Rollers will then be installed at the conductor's attachment point, and the conductor will be placed onto the rollers. The rollers will allow the new conductor to be pulled through each structure. Installing rollers and detaching the existing conductor will be completed by construction crews accessing each structure by helicopter. Once the rollers are in place for an entire section of conductor being replaced, the existing conductor will be pulled out of place, and the new conductor pulled in.

Equipment at pull site E will feed the conductor along the previously installed rollers while maintaining tension on the line so that it does not sag to the ground. Once the new conductor is in place, a helicopter will then be used to remove the rollers and clip the conductor to new insulators on the tower. Pull site E is 295 feet by 85 feet encompassing approximately 0.68 acres.

Access Routes: Project construction and access to towers will be accomplished primarily using helicopter operations. Construction vehicles are anticipated to access work areas using a combination of existing paved, unpaved roads that are currently used for ongoing transmission line operations and maintenance, and overland travel off existing roads.

Portions of some of the access road may need to be reestablished and maintained through tree trimming, vegetation clearing, the addition of substrate, and some minor grading/blading. Typical construction equipment required for road repairs includes a grader, bulldozer, compactor, and haul trucks. No new roads will be constructed as part of the project.

Overland access from existing access roads or along the existing easement is required at pull site E, tower 037/221 and tower 039/232. The terrain in these areas is relatively flat and grassy. These overland routes are not expected to require grading or filling; however, mowing and trimming of vegetation may be required.

Helicopter Landing Zones: Two helicopter landing zones (HLZ) have been identified for the project. HLZ #11 is located in a previously disturbed, graded area used for aggregate storage between the Merced River and Highway 140 on NPS land in the vicinity of the NPS warehouse and El Portal. HLZ #11 is 200 feet by 200 feet encompassing approximately 0.7 acres. HLZ D is 350 feet by 250 feet encompassing approximately 2 acres. It is located in Foresta.

Both helicopter landing zones will be used to support helicopter operations (e.g., transport crew and materials to and from the tower), as well as facilitate other project activities, including but not limited to, staging and storing construction materials and equipment, refueling, and assembling construction materials. Site preparation, including grading is not expected to be required at the landing zones. The sites are previously disturbed, flat areas that has been rough graded and/or graveled and used for equipment staging and helicopter landing previously. Ground access to the helicopter landing zones will occur over existing roads. Large matting can be placed on the ground to minimize disturbance if needed.