Construction Underway at Chimney Hollow

Northern Water's Municipal Subdistrict selected Barnard Construction Company, Inc. as the General Contractor for the new Chimney Hollow Dam and reservoir appurtenances located in Larimer County. Barnard and the Municipal Subdistrict entered into a contract in December 2019. Primary components for Chimney Hollow Dam and Reservoir include:

  • Chimney Hollow Dam will be a rockfill structure with a hydraulic asphaltic concrete (HAC) core approximately 350 feet tall. The main dam will contain approximately 12 million cubic yards of rockfill and 75,000 cubic yards of asphaltic concrete. Rockfill and aggregates will be sourced from within the reservoir footprint. A two-row grout curtain and consolidation grouting will be required for foundation preparation.
  • A combined reservoir inlet and outlet consisting of a submerged single-level inlet, a 2,000-foot tunnel under the right (east) abutment of the dam with a 72-inch diameter steel-lined, concrete-encased conduit with access to the centrally located valve chamber from downstream.
  • A 5,000-foot-long concrete spillway on the left (west) abutment with stilling basin to convey a peak discharge of about 850 cubic feet per second peak. The spillway contains approximately 7,000 cubic yards of concrete.
  • A 36-foot-high saddle dam to close the southern end of the reservoir. It will be a clay core rockfill dam. The saddle dam contains approximately 100,000 cubic yards of rockfill and 30,000 cubic yards of clay.
  • Water conveyance facilities include new buried pipelines connecting the Chimney Hollow Reservoir's inlet/outlet to the Bald Mountain Tunnel and Carter Lake Pressure Conduit (approximately 7,500 feet of 72-inch steel pipe) and a valve house consisting of energy dissipation facilities to control flow and pressure into and out of the reservoir.

Onsite construction started in August 2021 after the formal Notice to Proceed was given to Barnard Construction. Construction is expected to last four years. The construction cost is budgeted for $535 million.

Subcontracting Opportunities

To inquire about subcontracting opportunities with Barnard, please email  

Construction Site Blasting Schedule

An updated construction site blasting schedule will be posted weekly but is subject to change and this page will be updated as needed.

Blasting schedule:

March 17 – Quarry, 12-5 p.m. 
March 20 – Quarry, 12-5 p.m. 
March 21 – Quarry, 12-5 p.m. 
March 23 – Quarry, 12-5 p.m. 
March 24 – Quarry, 12-5 p.m. 

Construction Site Night Work

Chimney Hollow never sleeps. Neighbors will notice lights and dust as work continues through the night to keep our schedule on track. Multiple crews work in two, 10-hour shifts, with the remaining four hours dedicated to equipment maintenance.

Current night work includes:
  • Crushing operations until midnight
  • Tunnel operations through the night
  • Main Dam operations through the night

Even with night operations, rest assured that there are no blasts scheduled during nighttime hours and we continue to monitor noise levels at multiple locations 24 hours a day. 

View weekly images of construction progress

Construction Time-Lapse

The safety of our workers and guests on-site at Chimney Hollow is the highest priority.  

Learn More About Site Safety Commitments

Construction Teams

In a typical day on site, about 350 personnel come in and out of the security gate at Chimney Hollow Reservoir, which includes all the office and field staff. Northern Water is the project owner and has four employees on site daily, along with many others working on the project offsite. To complete the project, Northern Water has partnered with the following companies:  

  1. Barnard Construction, based in Bozeman, Montana, is the general contractor. It employees the largest number of personnel on site and hired many subcontractors to help during construction, including many local hires.  
  2. Black & Veatch, based in Overland Park, Kansas, is the construction manager. Approximately 12 employees are on site, with others working on the project remotely or from area offices. Black & Veatch subcontracted Kleinfelder, based in San Diego, California, to help with the on-site materials testing labs. Kleinfelder has about 5 personnel on site, with others working remotely.   
  3. Stantec, based in Edmonton, Canada, is the design engineer. The on-site team consists of about six employees, with others working on the project remotely or from area offices.