Moffat Expansion


The Boulder Waterkeeper position is the Moffat Expansion Project and the raising of Gross Dam should be stopped. 

Problem Statement
Denver Water is proposing a massive expansion of Gross Dam and Reservoir that would have huge negative impacts on many citizens in Boulder County and on Boulder Country’s and the Colorado River’s environment.

Denver Water is proposing to increase the height of Gross Dam from 340 feet to 465 feet, nearly tripling the reservoir’s storage capacity from 41,811 to 114,000 acre-feet.  Denver Water claims that the $140M+ expansion, called the Moffat Collection System Project, would help resolve three major water supply challenges: the risk of a near-term water supply shortfall; the risk of running out of water in the north end of Denver Water’s system during a single dry year; and a serious imbalance in Denver Water’s water collection system.

Gross Reservoir was completed in 1954 and named for Denver Water former Chief Engineer Dwight D. Gross. It was built for water storage for municipalities in the Greater Denver area.  Denver Water diverts a significant portion of the headwaters of the Colorado River, west of the Continental Divide, through the Moffat Tunnel to be stored in Gross Reservoir over 20 miles away, east of the Divide.  During the summer months, when municipal water usage is significantly higher due to landscaping (over 50% of Denver Water’s total water consumption goes to this purpose), Gross Reservoir feeds into Denver Water’s supply system, contributing roughly 5% of the overall quota.  During the fall, winter and spring seasons, Gross Reservoir is shut down for recharging.

The following are just some of the environmental impacts (see

Denver Water asserts that total water supply will equal demand in 2022. No numeric data has been given to support this. The purpose and need for the Moffat Project/Gross Reservoir is based on projections of water supply and demand that cannot be validated. 

Denver Water assets that Gross Reservoir must be expanded to address an imbalance between the north / south system. The entire supply system is immense, has built in flexibility and is reliable as has been demonstrated during the drought of 2002-2004. Reservoir capacity does not tell the entire story. The critical pinch point is the capacity of the Moffat Treatment Plant. Additional storage in Gross Reservoir does not change that capacity.

Tree removal: Destruction of over 200,000 trees is obviously environmentally damaging and the method of cutting and disposal of the trees is not clear.  If burned on site, the air pollution will be significant.  If hauled out, the steepness of the terrain and the lack of accessibility to the areas is only via steep, curvy dirt roads so safety is a prime concern.

Quarry: Destruction of land for the in-site quarry cannot be mitigated.  The sound and dust pollution from operation of the quarry will have significant impacts on residents, visitors and wildlife alike.

Loss of habitat: 465 acres of inundated land affect the human residents and will eradicate critical habitat for the deer, elk, moose, coyote, bobcat, mountain lion and innumerable bird species that inhabit the area.

Road safety: Impacts to residential traffic along Highway 72 will be significant.  Denver Water has not addressed the traffic hazards in any meaningful manner.  Even if one ignores the impact of up to 50 truck trips a day in terms of noise and slowing of traffic, the hazards to drivers, pedestrians, motorcyclists and bicyclists is extreme.

Lack of water: There is simply not enough water available from involved Western Slope drainages to fill an expanded reservoir most years. Residents and recreationalists will see a barren shoreline with the reservoir less than half full at least half the time. The effects of climate change on the water supply available from the Western Slopes is not even considered. Acres of wetlands on the Western Slope will suffer, streams will run dry and ultimately the Colorado River, already the most endangered river in the United States, will be affected.

Recreation: Visitor numbers to Gross Reservoir are significant. The disruption of recreation activities due to construction, years of blasting, tree removal, and traffic interruptions will be huge.  The loss of scenic areas, the drowning of Forsythe Falls, and closures to boating, fishing, hiking, picnicking and other visitor activities have not been addressed.

Water quality; Since Gross is a bottom discharge dam, excessively cold temperature water is likely to be discharged into South Boulder Creek exceeding State of Colorado water quality standards.

NEPA Environmental Impact Statement (EIS): The stated purpose and need statement is flawed. The Environmental Impact Statement is so narrow that it precludes all alternatives other than the expansion of Gross Reservoir plus additional trans-basin diversions from the Upper Colorado Basin.

Lack of Sustainability: 48% of Denver Water’s total retail treated water is used by single-family homes. The average single-family residential customer uses 50 percent of their water for lawn irrigation use. This totals roughly 60,000 acre-feet annually. That’s 333% the volume of water that the Moffat Collection System would potentially yield.

Climate Change: The EIS fails to adequately address climate change impacts; The runoff reductions for the Colorado River in particular are expected to be on the order of 10-30% by the year 2050. There will be limited to no water available to supply Gross Reservoir.

Status of the Project

The project is still awaiting a permit decision from Federal Energy Regulatory Commission (FERC) to proceed with the design and construction project.

Due to public engagement the Boulder County Commissioners decided to oppose the overall project.

A final ruling should be provided by FERC sometime around October, 2018.

Denver Water expects to start construction in October, 2018.

TEG is expected to continue to fight the project is the FERC permit is approved.

Talking Points

When speaking on the project in general:

“Undergoing this project is bad for business and bad for Boulder County. It’s not just the money we’re spending to complete the project, but it’s literally trying to dig our way out of a hole. We can’t build our way out of a water crisis on the backs of Boulder County residents without first exhausting all of our sustainable solutions.”

“Boulder County is known around the nation as a beacon for responsible ecological awareness and action. The environmental devastation which will be caused by this construction directly conflicts with Boulder County’s core values, blemishing the County’s legacy as an environmental leader and steward of pristine wilderness. We believe instead that nature-loving Coloradans can invest in solutions inspired by conservation, not further destruction.”

When talking about how this will affect the environment:

“Stopping this reservoir is one of the most important ecological issues facing Boulder County right now. Not only will the environment be harmed by the trucks and chemicals, but developers will clear cut more than 200,000 trees, destroying a huge portion of our ecosystem. It’s time to find sustainable water supply solutions that benefit the people and the places here in Boulder County.”

When talking about whether or not this is a done deal:

“Denver Water has yet to secure the necessary permits to start construction. In fact, they have yet to release critical details to Boulder County such as how they plan to clear-cut hundreds of thousands of trees before flooding by the expanded reservoir or how it will manage inevitable pollution caused by the use of explosives, heavy machinery, diesel fuel, coal fly ash and other toxic project materials.”

What You Can Do

Contact TEG and get on the mailing list for upcoming updates and donate (

Be prepared to contact Boulder County Commissioners if the FERC decision is to approved the Gross Dam construction.

Contact Annie Hodges (TEG Coordinator) at 408-420-5600 to donate or volunteer your time.

Participate in a volunteer training day in August (date TBD) to coordinate and educate all of those interested in stopping the project.

Participating Organizations



Friends of the Canyon