BOULDER COUNTY, Colo. (CBS4) – Denver Water received federal approval on Friday to proceed with the Gross Reservoir Expansion Project. The process to obtain environmental permits for the project began in 2003.

Gross Reservoir (credit: Denver Water)

“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,” said Denver Water CEO/Manager Jim Lochhead. “This order directs Denver Water to move ahead with construction to meet mandated milestones and timelines.”

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The Colorado Department of Public Health and Environment approved the project in 2016, followed by the U.S. Army Corps of Engineers in 2017. Environmental groups sued to block the expansion in 2018, claiming the U.S. Army Corps of Engineers violated environmental laws when it granted a permit to increase the height of Gross Dam by 131 feet.

Copter4 flew over Gross Reservoir (credit: CBS)

Denver Water officials say the reservoir expansion project will balance water supplies, increase resiliency and enhance water security for more than 1.5 million people. The enlarged dam will increase the capacity of the reservoir by 77,000 acre-feet, and includes 5,000 acre-feet of storage dedicated to South Boulder Creek flows that will be managed by the cities of Boulder and Lafayette.

“Expanding Gross Reservoir is a critical project to ensure a secure water supply for nearly a quarter of the state’s population,” said Lochhead. “We are seeing extreme climate variability and that means we need more options to safeguard a reliable water supply.”

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In 2019, a district court judge sided with Boulder County’s request to review the project. Denver Water filed to appeal the ruling.

Officials say the design phase of the Gross Reservoir Expansion Project is expected to wrap up by mid-2021 and will be followed by four years of construction. The project is estimated to cost about $380 million.

As a result of the project, Denver Water has committed more than $20 million to 60+ environmental mitigation and enhancement projects that create new habitat and flow protections to rivers and streams on both sides of the Continental Divide.

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“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,” said 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.”