As the Chimney Hollow Reservoir Project reaches 30 months of construction in February, Northern Water’s Municipal Subdistrict staff, along with key project contractors, anticipate completion of the reservoir in late summer 2025. While this date may adjust slightly for weather throughout the next year-and-a-half, Principal Project Manager Joe Donnelly remains optimistic about achieving that deadline.
“Our schedule is certainly trending where we like it to be,” he said. “We are only about three weeks behind schedule right now, which for a project of this size, that is quite a feat.”
However, two additional winter and summer seasons remain in the construction timeline to complete the project’s components. The slight delays that have been incurred are attributed to several factors: First, rock from the on-site quarry is being placed more densely in the embankment, ultimately providing a stronger dam, but requiring crews to mine more rock. An estimated additional 2 million tons of rock will need to be mined to complete the rockfill on the main dam embankment. Second, a long, cold winter in 2023 followed by an extremely wet spring slowed the project’s progress.
Alongside adjustments to the construction timeline, Donnelly said the project has seen an increase in overall costs. When crews broke ground in August 2021, the project had a $556 million price tag. Now the project is anticipated to cost approximately $584 million.
“Heavy civil projects always have risk, and we’ve been able to manage those well alongside our contractor,” Donnelly said.
Overall, the construction project cost is trending around $6,500 per acre-foot of water storage, which is a tremendous value to the 12 project participants who are funding the 90,000 acre-foot reservoir.
