Denver Water must temporarily pause construction on its costly Gross Reservoir dam project and is permanently barred from expanding the reservoir, a federal district court judge ruled Thursday.
Judge Christine M. Arguello of the U.S. District Court of Colorado also ruled that the U.S. Army Corps of Engineers must reconsider two key environmental documents and a project permit after making what she called several “serious” mistakes when approving the expansion.
The ruling throws another wrench into the project, which broke ground in 2022 outside Boulder and was already on track to build a new “arch dam” over 100 feet taller than the existing structure.
Denver Water sought an expansion that would triple the reservoir’s capacity and require flooding more than half a square mile of forest while destroying 500,000 trees. The reservoir currently stores 13.6 billion gallons of water bound for use on the Front Range.
For decades, Denver Water said it needed to enlarge Gross Reservoir for two main reasons: The utility may one day run out of water and storing more water would protect the southern and northern reaches of its system from emergencies like megadroughts.
Environmental groups first challenged the expansion in 2018, and said it would permanently damage waterways and ecosystems. Gary Wockner, executive director of Save the Colorado and one of the plaintiffs suing to stop the construction, applauded the ruling.
“We are pleased with the judge's ruling and will continue to defend it if Denver Water appeals,” Wockner wrote in a statement.
The ruling also permanently prevents Denver Water from expanding the reservoir by clearing trees or diverting water, which could impact wildlife. The permanent injunction says the reservoir expansion would cause “irreparable” harm and came as Arguello rebuked the utility for its “impatience with the project” in the order. The company started building the dam even as legal challenges threatened to halt or completely derail it.
“Because she also enjoined the proposed new diversion of water, this ruling is also a shot across the bow for all the proposed future new dam and diversion projects in the Colorado River Basin,” Wockner told CPR News.
Arguello will consider permanently barring dam construction at the site after a hearing in late April or May. That hearing will likely feature expert testimony on how to make the structure safe if it’s not fully complete.
Denver Water said it would review the order and appeal.
“We have grave concerns regarding the ruling,” a company spokesperson wrote in an email.
“We are prepared to appeal the decision so that we can continue to meet the water supply needs of the 1.5 million people we serve.”
Order builds on October Ruling
In October 2024, Judge Arguello ruled that the Corps violated multiple federal laws when it issued a permit allowing Denver Water to expand the reservoir.
At the time, the judge did not halt construction because Denver Water said that could harm the dam’s structural integrity, and because construction was about to pause for the winter. The judge ordered Wockner’s group, the Corps, Denver Water and other groups to try to hash out an agreement.
But those negotiations stalled around four months ago.
In her rulings, Judge Arguello found that the Corps violated three federal laws when approving a “dredge-and-fill” permit for the project, including the Clean Water Act and the National Environmental Policy Act. That permit allows the utility to dig up dirt and rock and dump it onto wetlands, which may cause permanent damage.
NEPA and the Clean Water Act require the Corps to analyze a range of construction options that could meet Denver Water’s goals. The laws then direct the Corps to pick an option that causes the least environmental damage.
Arguello wrote in an April ruling that the Corps’ mistakes during that process are so widespread that it needs to essentially start over.
The Corps must now redefine the entire project’s purpose, consider more alternatives outside of expanding the reservoir, better consider the costs of every alternative and “seriously consider” climate change data. In theory, that could lead the Corps to pick a completely different option for Denver Water.
“The deficiencies found by the Court are extensive and serious,” Arguello wrote. “They are not of the type that can simply be supported by better reasoning.”
- Judge rules Denver Water’s permit for Gross Reservoir expansion violates federal laws, orders alternative to flooding wetlands and forest
- Some Environmental Groups In Colorado Still Hope To Stop The Gross Reservoir Expansion
- Boulder County’s Gross Reservoir Can Proceed With Expansion Following Lawsuit
