Oct. 11, 2022

Colorado-Big Thompson Project Tie-In Started at the Bald Mountain Interconnect

One of the most time-sensitive aspects of the Chimney Hollow Reservoir Project is currently in progress – the Bald Mountain Interconnect. To complete this portion of construction, a shutdown of the Colorado-Big Thompson (C-BT) Project is in place as crews cut into the existing infrastructure to tie in a 126-inch steel pipe with a 72-inch steel offtake (known as a wye) to add ability to deliver water into Chimney Hollow Reservoir from the C-BT Project. This interconnect requires coordination, planning and communication between the U.S. Bureau of Reclamation, Northern Water, Barnard Construction and on-site subcontractors. 

To keep water from flowing to Flatiron Reservoir, the first step was to install a bulkhead at the outlet of Pinewood Reservoir. The U.S. Bureau of Reclamation then partially refilled Pinewood Reservoir. Once the bulkhead was in place, crews cut into the existing concrete-encased tunnel connecting the two reservoirs to place the wye. This was the first time the tunnel has been excavated and exposed since it was cast 70 years ago. 

Once at the site, the 25,000-pound, steel wye was loaded onto a flatbed trailer and pulled up the hill by a D-10 bulldozer, the largest on site. The intricate process took nearly four hours before the wye was lifted in place by a crane and sealed into the existing C-BT infrastructure. 

Crews will continue to work double shifts to complete this project phase by the end of November. Additionally, the U.S. Bureau of Reclamation is conducting maintenance during this time at the Adams Tunnel’s East Portal before C-BT Project water resumes flowing in mid-December.  

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