Yosemite AT&T Microwave Radio Upgrade
AT&T proposes to increase the bandwidth capacity of its existing microwave radio service. This microwave system provides phone and internet service to Yosemite National Park, the Hetch Hetchy Water and Power O'Shaughnessy Dam complex, and the communities of El Portal, Foresta, Wawona and Yosemite West. Yosemite National Park and its residential communities are currently experiencing capacity issues with the existing service, limiting the internet bandwidth available to the park, its concession operations and residents.
AT&T proposes to replace their existing radios and microwave dishes at their El Portal, Wawona and Yosemite Village central offices and their Henness Ridge, Sentinel Dome and Turtleback Dome communication sites. They also propose at their Henness Ridge communication site to replace their existing 30 foot monopole with a 125 foot steel lattice tower.
The new, taller tower at the Henness Ridge communication site will allow AT&T to send microwave signals directly to Fremont Peak outside of Mariposa. Additionally, the existing microwave connection rearrangement will better distribute the upgraded capacity brought to the park and the surrounding communities.
Design of the foundation for the proposed Henness Ridge tower AT&T will require geotechnical investigations consisting of three subsurface borings to determine the soil conditions at the site. These investigations will inform the design of the tower's foundation. A triangular tower with 17' between the three legs is proposed, each leg base will be 6 feet square. The disturbed area excavated to build a foundation for such a tower is estimated to be 20 to 25 feet on a side, creating a possible disturbed and excavated area of 400 to 625 square feet. An additional excavation will need to occur to bury a grounding loop just beyond the foundation. Its size is unknown at this time, but it is expected to not be much more than the size of the excavation for the tower foundation. Trenching to connect to the building is estimated to be 5 feet long, 2 feet wide and 3 feet deep.
AT&T will create a GIS view shed analysis to aid in identifying which areas the proposed tower could be viewed. AT&T will also develop photo simulations of the proposed tower. Finally, AT&T will conduct a balloon test, tethering a 10 foot balloon to a crane at the 125 foot height to simulate the location of the proposed tower. AT&T and park staff will then visit sites that the GIS analysis identifies as possible viewing points of the tower and will evaluate its potential scenic impact. At the existing Sentinel Dome communications site AT&T will need to remove 5 White fir (Abies concolor) trees to maintain the existing and proposed microwave radio transmission paths to the existing Turtleback Dome communications site.