Environmental groups file appeal to stop Gross Dam expansion in southern Boulder County

BOULDER COUNTY — A coalition of environmental defense groups are appealing a decision by federal agencies allowing Denver Water to expand Gross Dam to more than triple its current capacity.

The coalition includes Save The Colorado, The Environmental Group, WildEarth Guardians, Living Rivers, Waterkeeper Alliance Inc., and the Sierra Club; it filed a notice of appeal in federal court Monday morning, asking the U.S. 10th Court of Appeals in Denver to review a district court judge’s dismissal of the original complaint.

Gross Reservoir is a 440-acre reservoir just west of Eldorado Canyon State Park at the southern end of Boulder County. Denver Water received final approval last year to raise the existing dam from 340 feet to 465 feet and more than triple the reservoir’s capacity from 41,811 acre-feet to 114,000.

The environmental coalition first filed suit to stop the dam in 2018, claiming that the U.S. Army Corps of Engineers failed to fully take into account the potential downstream effects of further diversion from the river and whether Denver needs the additional water capacity at all. It also claimed that the dam’s construction would effectively cut off water flow to Forsythe Falls and place a heavy amount of construction-related pollutants into the area that would damage ecosystems.

The judge in that case dismissed the complaint last month, citing existing law that gives the federal appellate courts original jurisdiction over legal challenges that involve permits issued by the Federal Energy Regulatory Agency. FERC was one of the agencies that was required to sign off on the dam’s expansion due to the project’s hydropower component.

Save the Colorado Executive Director Gary Wockner said in a statement that the project violates multiple environmental protection laws, including the federal Clean Water Act, Endangered Species Act and National Environmental Policy Act.

“This massive dam project would further drain and destroy the Colorado River, as well as cause irrevocable damage in Boulder County, and thus we are firmly committed to defending the river and the environment to the fullest extent of the law,” he said.

The appeal comes days after several members of the environmental coalition agreed to drop its appeal of a similar lawsuit aiming to halt construction of the Chimney Hollow Reservoir west of Berthoud in exchange for $15 million to a Grand County nonprofit dedicated to Colorado River watershed protection.

At the time, Wockner said the plaintiff groups still fear the long-term environmental impacts of the Chimney Hollow project and other water-transfer plans that they collectively fight, but old water laws are hamstringing their ability to successfully fight against those projects.

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