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About the Project
Hensel Phelps was the general contractor on the Hazeltine Pump Station Heavy Civil (Phase One) which entailed a new 60-foot-deep reinforced concrete wet well, isolation slide gate, box culvert and intake structure with a steel trash rack, which were founded on drilled piers. The major work elements included significant excavation, dewatering and shoring; 42-inch and 48-inch buried steel discharge piping; electrical conduit routing within structural concrete; slope reconstruction; and site restoration. The structure featured a 7-foot-thick foundation, walls exceeding 5-feet-6-inches-thick and mass concrete placements totaling 3,623 cubic yards of concrete.
“Hensel Phelps has established and consistently executed a robust Quality Control Program built around a structured 6-Step QC/Safety Process. Their approach ensures clear expectations, early risk identification and continuous verification of contract compliance throughout the life of the project. Their operational discipline, attention to detail, transparent documentation and commitment to quality make them exceptionally well-suited for the rigorous requirements of large-scale water resource infrastructure.”
DANIEL BABYAK, PE, CONSTRUCTION PROJECT SENIOR MANAGER, DENVER WATER
Challenge
The recently completed first phase of the Hazeltine Pump Station was constructed within a former gravel mining operation that has been converted for use in Denver Water’s North Reservoir Complex. Positioned at the lowest point in the system, the site attracts groundwater and surface water. As excavation progressed, Hensel Phelps crews encountered groundwater migrating along the rock surface, water intrusion around the adjacent slurry wall and surface water. The project was effectively surrounded by water, creating continuous inflows that threatened excavation stability, site access and construction activities. Inflows ultimately approached 200,000 gallons per day, making groundwater management one of the project’s most significant construction challenges.
Solution
Hensel Phelps developed a management and excavation support strategy to address the site’s complex groundwater conditions. To control inflows, the team installed a dewatering network consisting of 11 dewatering wells, four localized sumps, collection trenches and perimeter drainage systems. As excavation advanced below the groundwater table and into bedrock, the system captured groundwater migrating through subsurface layers, and into the excavation from surrounding reservoirs and gravel pits.
Compounding the challenge, the pump station excavation was constructed adjacent to an existing slurry wall. Rather than relying on conventional excavation support methods, Hensel Phelps engineered a unique shoring solution that supported only two sides of the excavation while managing global slope stability to avoid impacts to the nearby slurry wall and roadway. Through the dewatering and shoring systems, construction progressed safely and efficiently despite a challenging groundwater environment.
Result
By successfully controlling groundwater, managing surface water and treating discharge before release, the team minimized environmental impacts while maintaining excavation stability and construction progress. The approach safeguarded workers onsite as well as nearby infrastructure, protected the project schedule and supported delivery of the first phase of the pump station project. The successful completion of the heavy civil phase of the Hazeltine Pump Station is a critical step in furthering Denver Water’s long-term water storage and conveyance program
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