Chimney Hollow project mostly on schedule for 2025 completion

LOVELAND — The Chimney Hollow Reservoir project west of Berthoud is mostly on schedule for completion in 2025, but it may require a couple of additional months beyond the project schedule.

Joe Donnelly, principal project manager for Northern Water, reviewed the status of the project at the Northern Water Conservation District Fall Water Symposium Wednesday.

He said the project, because of pre-construction litigation delays and other factors, may require about $65 million above the $650 million project budget. 

The project will be paid for by 12 participating entities, which include cities and water districts that are part of the Windy Gap water project. 

The project has reached the midway point of its four-year construction cycle. When done, it will be the tallest new dam — 350 feet — built in the United States during the past 20 years and will hold back a reservoir 2.5 miles long. The dam was 142 feet tall as of Monday and rising 4.5 feet on average each week.

Donnelly said crews are working around the clock and “spending about a million dollars per day” on the project.

Other notable numbers:

• About 62,000 tons of rock is quarried on site per day. 
• If the rock were hauled in highway-rated dump trucks, about 4,500 truck loads would be dumped on the dam each day. The project uses much larger trucks, including 12 100-ton trucks.
• Crews are placing 100-ton loads of rockfill every two minutes, 20 hours per day, and will for two and a half years.
• The grouting crews, who inject a concrete-like slurry mixture into the structure to shore up any leaks, are drilling 30 miles of holes into the foundation.

The valve house is largely done, Donnelly said, with about 50 valves to be placed there to control flow and pressures.

The 2,000-foot inlet and outlet tunnel boring is complete with crews now coating the tunnel surfaces with a concrete mixture. The tunnel will be complete in February next year, Donnelly said.

The reservoir will take about three years to fill, depending on snowfall and weather conditions.Additional information can be found at chimneyhollow.com.

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