Feds’ approval of Gross Reservoir dam expansion violated environmental law, judge rules

Federal regulators violated environmental protection laws when they improperly issued permits allowing Denver Water to expand Gross Reservoir, a judge ruled this week — though the finding’s impact on the underway project is still unclear.

The U.S. Army Corps of Engineers violated the Clean Water Act and the National Environmental Policy Act when approving permits for the construction of the dam, U.S. District Court Judge Christine Arguello found in the ruling, issued Wednesday. The federal agency failed to sufficiently consider other options that could be less environmentally damaging than dam expansion, Arguello wrote in her order.

Arguello did not order Denver Water to stop construction on the dam, in part because the utility already plans to halt construction in November for the winter season. An abrupt halt to the project could also affect the integrity of the dam, she wrote.

The defendants and plaintiffs will now work to create a remedy for the improperly issued permits. Each side must submit briefs on proposed solutions to Arguello by Nov. 15.

In a statement, Denver Water said it still hopes “to move the project toward completion.”

The order was the latest decision in a winding six-year legal fight over the controversial dam project. A coalition of environmental groups first filed suit in 2018 to stop the expansion of the reservoir, which they say would harm the health of the Colorado River system — where the reservoir’s water is sourced.

Denver Water began the permitting process for the project in 2002 and began construction on the $531 million dam project in 2022. Already, workers have partially deconstructed the existing dam to prepare it for expansion, dumped fill material and poured concrete for the expansion.

When completed, the expanded dam will triple the reservoir’s capacity from 42,000 acre-feet to 120,000 acre-feet. An acre-foot of water can supply two Colorado families for a year, so the expanded reservoir will be able to store water for approximately 156,000 additional households.

The expanded reservoir will anchor Denver Water’s northern supply system and help protect the utility’s ability to deliver water if its much larger southern supply system is impacted by fire, mudslides or drought, according to Denver Water. The utility provides water to 1.5 million people in metro Denver — about a quarter of the state’s population.

Denver Water argued in its filings that the issues raised were moot since construction had already begun and one of the permits in question already used.

Arguello, however, dismissed that argument, as the reservoir had not yet been expanded and the 400 acres of land and 500,000 trees it would drown still remained above water.

“To the extent Denver Water disagrees, it has only itself to blame — because Denver Water chose to proceed with construction despite the obvious risk posed by pending federal litigation that could lead to vacatur of the permits authorizing said construction,” Arguello wrote, then referred to legal precedents: “Denver Water cannot ‘evade judicial review’ or ‘defeat a judgment’ through its own ‘questionable behavior.’ ”

One of the Army Corps of Engineers’ failures was its lack of analysis of how climate change could impact the project. As climate change shrinks the amount of water available in the Colorado River system, Arguello asked, is it practical and reasonable to build a reservoir to store water that doesn’t exist?

“Despite acknowledging that future climate conditions might neuter the Gross Dam’s value as a water storage solution, the Corps expressly declined to attempt to quantify the impacts of climate change — or even provide an educated guess, for purposes of discussion,” Arguello wrote.

The lack of analysis shows that the USACE did not fully analyze the practicality of the dam project, as required by law, she wrote.

The environmental groups that filed the suit will now start discussing what legal remedies they will pursue, said Gary Wockner, director of Save the Colorado, one of the lead plaintiffs.

“This is a stunning victory for the Colorado River, the people of Boulder County and the rule of law,” Wockner said. “We look forward to engaging with Denver Water to reach a good-faith agreement about how to remedy the Corps’ non-compliance.”

Denver Water officials plan to work through the legal process and address any potential solutions to move the project toward completion, the utility said in a statement Thursday. The utility is legally required by the Federal Energy Regulatory Commission to finish the project by 2027, it said.

“Throughout the permitting process, Denver Water has been driven by a singular value: the need to do this expansion the right way, by involving the community; upholding the highest environmental standards; providing a sustainable, high-quality water supply to our customers; and protecting and managing the water and landscapes that define Colorado,” according to the utility.

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