Environmental

The Hancock Creek and Calligan Creek Hydroelectric projects coincided to create two, run-of-the-river hydroelectric facilities that now provide a renewable energy supply source for Snohomish County. Situated in the middle of 89,500 acres of timber forest lands, these projects required thorough pre-planning and coordination to accommodate the extremely remote location, environmentally sensitive work areas, and steep terrain with varying ground conditions.

The project began with the construction of diversion structures in Hancock and Calligan creeks to direct flow from the creeks to sluice-way channels. With the streams diverted, crews constructed concrete cast-in-place weir systems that would direct excess water flow from the streams into a pipeline (penstock), that would flow into the powerhouses containing the energy-producing turbines. Construction of the penstock lines required major clear-and-grub for a contractor-designed haul road that ran through the steep terrain, requiring constant communication for tight deliveries and workers to safely construct the pipeline in the limited easement work area. Penstock construction required installation of 5,900 feet of butt fusion welded HDPE pipe and 7,900 feet of 39-45” welded steel pipe in deep trenches requiring specialized shoring and dewatering with sump pumps. Tying it together, crews constructed a concrete and masonry building containing the turbines that required over 2,800 cubic yards of concrete poured. Each turbine installed is rated to produce 6000 KW of power.