Design, financing are next steps for Chimney Hollow |

Design, financing are next steps for Chimney Hollow

The future site of the Northern Water's yet-to-be-constructed Chimney Hollow Reservoir is located in Larimer County slighty west of Carter Lake. Here the diminutive Flatiron Reservoir is seen slightly northwest of Carter Lake with the future site of Chimney Hollow in the valley above.
Courtesy photo |

After 13 years working through the federal government’s permitting process Northern Water’s Chimney Hollow Reservoir is set to move forward with construction.

The new reservoir will be located in Larimer County just west of Carter Lake and will store up to 90,000 acre feet of water. Construction on the reservoir is set to begin in 2019. At this stage the project’s process is divided up into two main areas: construction and financing.

“We have dotted all the i’s and crossed all the t’s,” Brian Werner, Northern Water’s spokesman said. “We crossed the last hurdle.” According to Werner Northern Water will now focus on finishing the design work for Chimney Hollow and noted the water utility provider is already, “well into that”, adding design work has been underway for approximately six months.

Engineering and consulting firm Stantec is handling the design duties. Stantec has been busy recently taking core samples from the site of the future reservoir. Werner said Northern hopes to hire a contractor sometime next year.

“We are going to be refining the design to get the project to the point we can issue construction specs,” Werner said. “We are really looking at numbers so that when we issue bids we know exactly what we need.”

When construction of the reservoir begins the new dam built for Chimney Hollow will be something new in the U.S. The Chimney Hollow Dam will be an asphalt core dam, and depending on when construction is completed officials from Northern said they believe it will be the first asphalt core dam built in the country.

“There is another project is process, so we will either be first or second,” Werner said. “The technology has been used all over the world except here. There are asphalt core dams in Canada, Scandinavia and Germany. The technology is 50 to 60 years old.”

The new dam will be roughly 3,000 feet in length, just over half a mile, and will be roughly 150 feet wide at its base and 20 feet wide at the top. The physical construction will entail digging down the area where the future dam will be located, to anchor the structure into the bedrock.

While no construction on the new reservoir will happen this summer Northern will be looking to the Western Area Power Authority to relocate one power line that will be impacted by the new reservoir. Northern will also be constructing access roads and other infrastructure to make the project possible.

The other major aspect of the project is the financing component. According to Werner the total cost of the project is estimated at about $420 million. Northern is looking to secure a $90 million low interest loan from the Colorado Water Conservation Board and is discussing specifics for the remainder of financing needs. Werner noted roughly $16 million has already been spent on the Chimney Hollow permitting process.

Each of the 12 participants in the Windy Gap Firming Project, including two water districts, nine towns and the Platte River Power Authority, will be contributing varying amounts to cover the remainder of outstanding costs. The 12 contributing entities do not include Grand County or any entities based in Grand County.

Each entity’s finance requirement for the project is prorated based upon that entity’s share of the overall 90,000 acre feet of reservoir storage. Broomfield has the largest storage share at 26,000 acre feet and as such will have the largest individual cost share among the 12 entities.

Because the project has been in the works since 2003 many of the participating entities have funds in reserve specifically for the construction of Chimney Hollow.

The new project will mean more diversions out of Grand County. Werner said the overall impact is estimated on the order of 8,000 to 9,000 acre feet of additional diversions.

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