Construction Underway at Chimney Hollow

Northern Water's Municipal Subdistrict has 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 being contracted at $485.4 million.

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:

Aug. 12 – Quarry and Chimney Hollow Conduit, 4-5 p.m. 
Aug. 15  – Downstream Tunnel, 7-9 a.m., Quarry, 4-5 p.m.
Aug. 16  – Downstream Tunnel, 7-9 a.m.
Aug. 17  – Downstream Tunnel, 7-9 a.m.
Aug. 18 – Downstream Tunnel, 7-9 a.m., Quarry and Chimney Hollow Conduit, 4-5 p.m. 
Aug. 19 – Quarry, 4-5 p.m. 

Subcontracting Opportunities

To inquire about subcontracting opportunities with Barnard, please email