Jan. 8, 2025

Chimney Hollow 2024 Year In Review

With the final full year of scheduled construction at Chimney Hollow in the rearview, many project components are finished or nearing completion. In 2024, crews safely worked almost 1 million hours with safety incident rates of about one-third of the national average.  

Dams

Significant progress on the dams was made this year. The main dam reached just over 300 feet tall, which leaves only about 50 feet to go to the final height of 350 feet. Crews have placed about 5.7 million cubic yards of rockfill and 30,000 cubic yards of asphalt. The embankment of the 40-foot-tall saddle dam began in May and was completed in mid-November. About 45,000 cubic yards of clay was sourced on-site and placed on the dam, along with nearly 110,000 cubic yards of rockfill.  

Grouting

The grouting program, which began in May 2022, wrapped up in fall 2024. The grouting team completed 32 miles of drilling and grouting, providing a double-row grout curtain to prevent seepage through the foundation that extends as deep as 230 feet below the bedrock surface. 

Inlet/Outlet Works

The entire inlet/outlet works are nearing completion. In 2024, the Chimney Hollow Conduit was finished, the valve house was fully enclosed, the inlet/outlet tunnel was completed, and the inlet/outlet tower will be completed in early 2025. Crews continue to install conduit from the valve house through the tunnel and are working on electrical and fiber connections to remotely operate and monitor the project. As work areas are completed, crews are constructing the final grade for the project, including removing temporary construction roads.  Disturbed areas are covered with topsoil and vegetated with native seed mix for a successful establishment next spring. 

Spillway

All of the reinforced concrete for the spillway was completed in 2024, with the final backfill wrapping up in early 2025. Additionally, the Carter Lake interconnect is now complete and will allow Northern Water to send water to Carter Lake from Chimney Hollow or Pinewood reservoirs.

Quality Control

The quality control program performed almost 3,400 earthworks tests and about 2,000 concrete tests, maintaining quality measures required on site.  

Despite some setbacks in 2024, including six adverse weather delays and four days lost to mandatory evacuations from nearby wildfires, the project is still a couple of weeks ahead of schedule. As construction wraps up in summer 2025, project managers plan to begin filling the reservoir, which is expected to take about three years. Larimer County will manage the reservoir’s recreation and is expected to begin construction of trails and parking lots after the reservoir construction is complete.