John Scarffe, Boulder County. On July 17, 2020, the Federal Energy Regulatory Commission (FERC) approved Denver Water proceeding with the design and construction of expanding Gross Reservoir in Boulder County. The FERC regulates the production of hydropower in the United States, and expanding Gross Reservoir required FERC’s approval of Denver Water’s application to amend its hydropower license.

Clearing its final federal hurdle with the FERC approval, the $464 million expansion involves raising Gross Dam by 131 feet to nearly triple the size of the reservoir behind it, according to Denver Water’s “On Tap” newsletter. “This approval and order carry the force of law and are the final federal authority over the reservoir project,” according to a Denver Water news release. 

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

 According to “On Tap,” Gross Dam was built in the 1950s and named after Dwight D. Gross, a former chief engineer at Denver Water. The reservoir was built to store water from the West Slope traveling through the Moffat Tunnel and from South Boulder Creek. 

“The original engineers designed the dam so that it could be raised twice, if needed,” said Jeff Martin, Gross Reservoir project manager. “Based on our water supply projections and current system shortfalls, that need is here.”

In 2003, Denver Water began the federal environmental permitting process that led to approvals by the Colorado Department of Public Health and Environment and U.S. Army Corps of Engineers in 2016 and 2017. In December 2019, Denver Water hit a stumbling block when Colorado State District Court Judge Andrew Macdonald ruled against Denver Water and required them to go through Boulder County’s review process. 

According to a release from an organization fighting against the expansion, TEG, the court stated that, based on evidence placed on the record by both sides, Denver Water versus Boulder County, Boulder County did not exceed its jurisdiction or abuse its discretion, or misinterpret or misapply the law when it asserted its permitting authority.

According to an article in The Mountain-Ear newspaper, Denver Water then needed to submit a detailed application proving that they will be able to construct the proposed dam while complying with Boulder’s requirements to conform to the Boulder County Comprehensive Plan.

On March 14, 2019, after a four-hour public hearing by the Boulder County Board of County Commissioners, the Board considered Denver Water’s appeal of the Land Use Director’s decision that the Gross Reservoir Expansion Project is not exempt from the County’s Areas and Activities of State Interest, according to House Bill 1041. 

Denver Water challenged that authority by a zoned law exemption, which excused Denver Water from having to pass through the Boulder County process because the zoning at the reservoir that existed at the time of the passage of the 1041 legislation permitted its planned activities. Macdonald ruled that Denver Water did not have a claim to an exemption based on prior zoning.

During the March 14 meeting, Boulder County Land Use Director Dale Case and Kevin Doyle, flood plain administrator, presented the case for Boulder County. The area is zoned forestry and the County did not have a dam or reservoir as listed in that zone, so it gives the County a method for getting uses required for review. Denver Water’s plans be referred back to Boulder County.

Explaining the case for the expansion, Lochhead said that the critical project will ensure a secure water supply for 1.5 million people in Denver and provides the system balance, additional storage and resiliency needed for our existing customers as well as a growing population. Due to extreme climate variability, Denver Water needs more options to safeguard a reliable water supply. 

The project involves raising the existing 340-foot-tall dam by 131 feet, which will increase the capacity of the reservoir by 77,000-acre-feet, and includes 5,000 acre-feet of storage for South Boulder Creek flows that will be managed by the cities of Boulder and Lafayette, according to the release. It will make Gross Reservoir the second-largest in Denver Water’s system, according to “On Tap.” 

“When the project is complete, Gross Reservoir will be able to hold 119,000-acre-feet, second only to Dillon Reservoir in Summit County, which is capable of holding just north of 257,000-acre-feet, according to “On Tap.” “Expanding Gross Reservoir is a major part of Denver Water’s long-term, multipronged approach to deliver safe, reliable water.

“The additional reservoir capacity will enable increased water capture in wet years to help avoid shortages during droughts. It will also help offset a current imbalance in Denver Water’s collection system that is a significant risk,” according to “On Tap.”

Jeff Martin, program manager for the Gross Reservoir Expansion Project, said: “Right now, 90 percent of our water storage is on the south end of our water collection system, but just 10 percent of our storage is on the north end. By enlarging Gross Dam, we’ll be able to store more water in the north, which will improve our flexibility in the event there’s a problem on the south side that could come from any number of operational issues or threats, like wildfires.”

Once filled, Gross will provide an additional 72,000-acre-feet of water storage, which is roughly the amount 288,000 residential households would use for one year, and 5,000 acre-feet of storage space in the expanded reservoir, known as the environmental pool, is reserved to support environmental needs as part of an agreement with the cities of Boulder and Lafayette. 

Water from the environmental pool will be used to provide beneficial stream flows along a 17-mile stretch of South Boulder Creek below the dam during dry periods to protect fish and aquatic insects. According to the release, the design phase is expected to be completed by mid-2021 and will be followed by four years of construction. 

“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,” Martin said “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.”

“The FERC order, along with the permitting conditions put in place by CDPHE and the Corps, further commits Denver Water to implement environmental improvements by putting in place measures evaluated in the environmental assessment issued in February 2018.” The project relies on the expansion of an existing footprint without the placement of a new dam, reservoir or diversion structure and benefits from an original design that anticipated eventual expansion, according to the release.  

Denver Water has committed more than $20 million to more than 60 different environmental mitigation and enhancement projects to create new habitat on both sides of the Continental Divide as a result of the Gross Reservoir Expansion Project. Denver Water will use its existing water rights to fill the reservoir when it is complete. 

Engineers estimate that it will take about five years to fill the newly expanded portion of the reservoir, depending on precipitation and water use from customers. Lochhead said Denver Water will continue working closely with communities impacted by construction to ensure safety while minimizing public inconveniences like traffic, dust and noise.

“In the end, this project won’t be judged by whether we raised the dam, but rather how we went about expanding the reservoir,” Lochhead said. “We will continue to seek community input and look forward to further conversations with Boulder County about local permits and the county’s participation in the development of various construction plans per the FERC order.”

For more information on the Gross Reservoir Expansion Project, visit grossreservoir.org.

(Originally published in the July 23, 2020, print edition of The Mountain-Ear.)