The Lower Baker Unit 4 Powerhouse is a design-build, 55-foot, below-grade powerhouse located along the Baker River, 400 feet south of the existing Powerhouse Unit #3 near Concrete, Washington. The project includes the design and construction of a new steel-lined tunnel from the existing surge tank connection to the new powerhouse, a steel penstock and bifurcation, a synchronous bypass and turbine shutoff valves, a Francis turbine/generator with all controls, instrumentation, SCADA communications, a governor and excitation system, a GSU transformer, a tailrace, and site access improvements.
The new powerhouse is located on a relatively flat bench located on the Baker River’s east bank. The powerhouse is a subterranean, reinforced, concrete structure housing a single 30 MW+/- Francis turbine/generator and associated accessory and auxiliary equipment. The facility has a hydraulic capacity of 1,800 cfs, providing the ability to generate power while meeting license-mandated minimum in-stream flows. The project was completed in four phases.
The design-build project delivery method allowed the client to start construction ahead of design completion. Phase 1 excavation commenced in December 2010, well in advance of the completion of final design packages for the remaining phases of work. This phased approach allowed the owner to qualify for federal incentives. Commercial operation was achieved in mid-2013, fewer than three years from construction start.