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The Moccasin Penstock conveys Hetch Hetchy water from Moccasin Tunnel to the Moccasin Powerhouse. This project enhances the reliability of the penstock system through the repair and replacement of the more than 96 year-old sections of the penstock, replacement of cracked concrete anchors and saddles, and upgrades to make the pipes easier to maintain in the future.
The Moccasin Penstock conveys Hetch Hetchy water nearly one mile from Moccasin Tunnel to the Moccasin Powerhouse. The lower 1,084-foot section of welded steel pipe replaced the original penstocks when the new Moccasin Powerhouse was completed in the 1960s. The upper 4,000 feet of penstock dates back to 1924 and has been in service for more than 96 years.
Condition assessments based on external inspection and imaging have identified a number of deficiencies along the original pipe. This rehabilitation project is intended to enhance the reliability of the penstock system and will include: repair or replacement of some sections of corroded pipe; repair or replacement of four badly cracked concrete anchors and damaged penstock saddles; installation of new manways and a rollout pipe section to provide better access for inspection and maintenance; and recoating the outside pipe, where needed, to reduce future corrosion.
The project scope was expanded to include: 1) the installation of additional penstock pipe between the valve house and the first downstream anchor; 2) the replacement of the butterfly valve pneumatic actuator with an electronic actuator, which will include new controls with SCADA connectivity; and 3) a new backup generator.
The project is part of a larger Hetchy Capital Improvement Program (HCIP), a multi-year capital program to upgrade or improve water conveyance, water storage, and power generation facilities in the Sierra Nevada portion of the Hetch Hetchy Regional Water System.