Rendering of Gross Dam current

An artists rendering of the proposed expansion to Gross Reservoir.

Denver Water can proceed with design and construction to expand Gross Reservoir in Boulder County, thanks to an order Friday by the Federal Energy Regulatory Commission.

The state's largest water utility noted that it began the federal permitting process 17 years ago and gained approvals from the Colorado Department of Public Health and Environment and U.S. Army Corps of Engineers in 2016 and 2017, respectively.

“Obtaining the Federal Energy Regulatory Commission order to move forward with the Gross Reservoir Expansion Project brings a comprehensive 17-year federal and state permitting process — one that involved nearly 35 agencies and organizations — to a close,” Denver Water CEO/Manager Jim Lochhead said in a statement. “This order directs Denver Water to move ahead with construction to meet mandated milestones and timelines.

“Expanding Gross Reservoir is a critical project to ensure a secure water supply for nearly a quarter of the state’s population. The project provides the system balance, additional storage and resiliency needed for our existing customers as well as a growing population. We are seeing extreme climate variability and that means we need more options to safeguard a reliable water supply for 1.5 million people in Denver Water’s service area,” Lochhead said.

Denver Water expects the expansion's design phase to finish by mid-next year to begin four years of construction to raising of the 340-foot-tall dam by 131 feet.

That's expected to allow the reservoir to store another 77,000 acre-feet of water. An acre foot is a measurement that essentially supplies two households for a year, about 326,000 gallons.

The new capacity would include 5,000 acre-feet for South Boulder Creek flows to be managed by the cities of Boulder and Lafayette.

“We are committed to working closely with the Boulder County community to ensure safety, be considerate neighbors and retain open, two-way communication channels during this construction project,” stated Jeff Martin, program manager for the Gross Reservoir Expansion Project. “We will continue to seek community input on topics such as traffic control plans, hauling traffic schedules, tree removal plans, and other construction-related activities.”

Denver Water has provided more than $20 million to more than 60 environmental mitigation and enhancement projects, including new habitat and flow protections to rivers and streams on both sides of the Continental Divide to provide a net benefit to Colorado's water quality, the utility said in its press release.

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