Replace 5.1 Miles of the Park's Primary Electrical Transmission Line

Yosemite National Park » Replace 5.1 Miles of the Park's Primary Electrical Transmission Line » Document List

This project will repair/replace 5.1 miles of 70 kV transmission line and associated infrastructure along the utility line corridor in the Merced River Canyon, between El Portal and the Cascades substation. The transmission line serves Yosemite Valley and Glacier Point.

This project involves the Exchequer electrical transmission line located within the Merced River Canyon that extends from the park boundary in El Portal to the Cascades Substation located adjacent to the El Portal Road. This line was constructed between 1929 and 1934 and includes multiple steel towers and associated foundation pads. The line has been modified multiple times in the modern era for repairs after fires and rockfall events. Current repairs are needed because the current overhead electrical system does not meet current code requirements and contains components that are past their service life. The replacement will decrease the likelihood of future emergency repair efforts and will provide for a reliable energy utility for Yosemite Valley.

The proposed repair/replacement efforts will include the following activities:

• 9 towers would undergo structural modifications/repairs (no ground disturbance)

• 4 poles would be replaced with new towers in the same locations, and 8 towers will be replaced with new towers located adjacent to the existing towers (within 50-feet of each existing tower). The overall alignment of the overhead transmission line will remain largely unchanged; towers will be placed along the existing alignment at a location facilitating construction)
o Each new tower would 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).
o Existing poles and towers would be removed using helicopter assistance, as poles are not accessible by road. Removal of the existing poles would require minimal digging (soil disturbance would be limited to the area disturbed during their initial installation).

• Insulator counter weights would be installed at 16 towers to mitigate conductor clearance to the towers (no ground disturbance)

• Bird spikes would be installed at all structures (no ground disturbance)

• The existing conductor line will be replaced (no ground disturbance)

All repairs and improvements shall be completed in accordance with the California Public Utilities Commission General Order 95, Rules for Overhead Electric Line Construction ((https://www.cpuc.ca.gov/gos/GO95/go_95_startup_page.html).

The subsurface vertical soil disturbance will not exceed 15-feet in depth and is associated with installing the new towers. Penetration 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.

Equipment and materials staging for this work 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 Waste Water 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. Helicopter landing areas have not been fully identified; all landing areas will be on existing paved areas. Potential landing areas include the Crane Flat Helibase (fully paved) and a private parking area just west of the park entrance on Highway 140 (fully paved). These areas will be used to stage the helicopter and tower components, drill equipment, and conductors.

A previous project (PEPC 86795) proposed the removal of brush along the power lines 6 feet in either direction of the electrical towers for 5.1 miles. This work was planned to occur between September 2019 and Feb 2020. This project also included the subsequent identification of potential hazard trees that threaten to impact the transmission line if they fall, as many trees in the corridor perished in the 2018 Ferguson Fire and pose an increased risk of toppling onto the line. The tree removal phase would begin in July 2020 and be completed by August 2020, ahead if implemented the proposed project.