It looked busy on the Chimney Hollow reservoir construction site this week, as numerous vehicles and orange-clad workers moved slowly along the crest of the main dam, adding another 9-inch layer to the asphalt core or spreading rock backfill to support it.
Looking elsewhere, however, there were signs that the massive project five miles west of Loveland is winding down. South of the dam, a long row of rock-hauling trucks used to deliver the backfill sat idle because the narrowing crest can no longer accommodate them. At peak productivity, when the embankment dam was much shorter and wider, those trucks were loaded with 100 tons of rock every two minutes for up to 20 hours per day.
On the north side of the dam, the temporary concrete batch plant was similarly idle, with construction on permanent structures such as the main spillway now complete.
“We’re starting to ‘demobilize’ is the way our contractor is putting it,” said Jeff Stahla, public information officer for Northern Colorado Water Conservancy District. “As tasks get completed, then the big equipment and workers move on to the next site or the next job, or if they’re local subcontractors, go back to doing some other local work.”
Barring an act of nature or something wholly unexpected, major work on the future 90,000-acre-foot Chimney Hollow reservoir will wrap up sometime in May or June. After a few more weeks of equipment testing, water from the Colorado River will start filling it in mid-July, about three weeks ahead of the schedule mapped out when the project broke ground in August 2021, Stahla said.
The project
Lying just west of Carter Lake, Chimney Hollow reservoir will span 2.5 miles and cover 740 acres. At full capacity, it will store 90,000 acre-feet of water for use by the project’s 12 civic partners.
Though construction has been underway for nearly four years, planning for Chimney Hollow goes back decades, explained Stahla.
“This is the completion of what we call the Windy Gap project, which was built in the ’80s,” he said, referring to an infrastructure system that diverts water near Granby to communities in the Front Range. Until Chimney Hollow, the system did not have much storage capacity.
“And we knew back in the day that there would need to be a reservoir, but it wasn’t until the 2002-2003 drought,” that the need became pressing, he continued. “And it was just right after that that we started looking at sites.”
Workers walk on the asphalt core dam as crews work to finish construction at Chimney Hollow Reservoir Wednesday, April 2, 2025, west of Loveland. (Jenny Sparks/Loveland Reporter-Herald)Among those project partners is Loveland, which has acquired rights to 10,000 acre-feet of storage in the reservoir, or about 11% of its capacity.
Construction on Chimney Hollow was originally slated to start in 2019, with a budget of $480 million, but was delayed by a federal lawsuit. When it finally got underway, the budget was closer to $600 million, but has since grown to more than $700 million due to a combination of legal costs, pandemic-driven inflation and an unlucky guess about a portion of the site’s underlying geology, said Stahla.
“That valley is at the boundary between the Rocky Mountain granite and the old-fashioned sedimentary rocks, and there was a section where the rock wasn’t very high quality, and so we had to do a little bit of extra treatment,” he explained. “It was a known risk factor, but when you get those interactions between two very, very different types of geology, sometimes you don’t know what you’re going to get until you’re digging.”
To fill the budget gap, Northern Water and its partner cities last year secured a $60 million loan extension from the Colorado Water Conservation Board, a state agency that helps manage the state’s water resources.
Remaining tasks
The most visible item remaining on the to-do list is completing the main dam, now about 90% of the way to its eventual 350 feet of height, according to Stahla. For workers, that means adding the final 40 layers of asphalt core and backfill, 9 inches at a time.
“To me, it’s akin to a 3D printer,” Stahla said. “Even though it’s getting narrower on top, from north to south, it’s getting wider from east to west as the canyon opens up and so it takes a full day to do one of those lifts across the top.”
When completed, sometime in May, the dam will be the third tallest in the state and just the second asphalt core type in the U.S.
“What’s unique about Chimney Hollow is just the timing of it,” Stahla continued. “It has been easily a quarter century since there’s been a dam like this built.”
The other major items to be checked off are taking place in less visible areas of the site, including installation of the final valves inside the valve house. Crews are also finalizing the underground inlet/outlet tunnel that will convey water in or out of Chimney Hollow and should wrap up later this month.
As a final step, the contractor will regrade several access roads built to support the construction, giving the bottom of the reservoir a more natural landscape.
Stahla said that once the construction ends in the coming weeks, the contractors will begin testing infrastructure and equipment.
“We do what’s called ‘dry’ testing,” he explained. “Basically you check on the status of the valves — do they open? Do they close? How long does it take? Then we’ll do ‘wet’ testing where we put water in the pipes.”
If no problems are found, Windy Gap water will start filling the reservoir in mid-July, going slowly over the first few months.
“There are some benchmarks that we have to hit for dam safety,” Stahla said. “You don’t want to quickly fill a dam for the first time. You want to be able to do it slowly and see if there are any concerns.”
If none are identified, Northern Water will open the valves for faster flow, with hopes of getting Chimney Hollow to 50% capacity by the end of the year. However, it will take up to three years for it to reach full capacity.
What it means for Loveland
For Loveland, the 10,000 acre-feet of Chimney Hollow storage is a “critical element” in the city’s raw water portfolio. With a price tag of around $70 million, it will boost the city’s firm yield (the amount of water it can count on during a dry year) from 25,210 to nearly 30,000 acre-feet annually, enough to meet demands through at least 2056 without curtailing use, according to the city’s 2020 Raw Water Master Plan.
The stored water, Loveland Water and Power Resources Manager Todd Hanlin said, will primarily be used as a drought and emergency reserve and to support future population growth. It will be conveyed to the city’s water treatment plant through existing infrastructure, including the Colorado-Big Thompson system, the Charles Hansen Feeder Canal and Green Ridge Glade Reservoir.
Hanlin added that despite the project’s scale and cost, Loveland water customers are unlikely to see sudden changes in their bills.
“Construction of Chimney Hollow has long been planned and our long-range rate track has been well designed to spread these costs out, ensuring that there will be no short-term impacts on water rates,” he said.
Most of Loveland’s share of ongoing operations and maintenance costs have already been built into current rates, with just a one-time 1% increase projected for 2026 to cover the remaining expenses, he added.
In addition to water storage, the Chimney Hollow site will eventually offer limited day-use recreation on nearly 2,000 acres surrounding the reservoir, managed by Larimer County Natural Resources. Released late last month, the final plans for Chimney Hollow Open Space call for 10-12 miles of trails, picnic areas and access to wakeless boating on the water, slated for opening in 2027
For more information about the Chimney Hollow construction site, visit northernwater.org/CHRP. To see plans for the open space, visit larimer.gov/naturalresources/parks/chimney-hollow.
Read More Details
Finally We wish PressBee provided you with enough information of ( Finish line: Chimney Hollow reservoir construction nearing completion )
Also on site :
- Brett Baty exits with groin tightness in new Mets injury concern
- Red Sox trade Rafael Devers to Giants
- WWE Legend Ric Flair Issues Update After Cancer Diagnosis