The Federal Energy Regulatory Commission’s Office of Energy Projects has reviewed Baker County, Oregon’s application for a license to construct its proposed Mason Dam Hydroelectric Project, and has prepared an Environmental Assessment (EA).
The proposed 3.4-MW project would be located on the Powder River, at the existing U.S. Bureau of Reclamation Mason Dam, near Baker City in Baker County, Oregon. The project would occupy federal land managed by Reclamation and the U.S. Forest Service.
The EA, which as of Oct. 27 is out for comment for 45 days, contains commission staff’s analysis of the potential environmental impacts of the proposed hydroelectric project. The EA concludes that licensing the project, with appropriate environmental protective measures, would not constitute a major federal action that would significantly affect the quality of the human environment.
On April 30, 2014, Baker County applied to the commission for an original license to construct, operate, and maintain this project. It would be located on the Powder River at Reclamation’s existing 173-foot-tall, 895-foot-long Mason Dam at river mile (RM) 131. Mason Dam creates a 2,235‑surface‑acre impoundment (Phillips Reservoir) with a normal maximum water surface elevation of 4,070.5 feet mean sea level.
The project would use Reclamation’s existing reservoir outlet works and would require modification of its discharge conduit with a bifurcation to a new 105-foot-long, 72-inch-diameter penstock. The penstock would deliver flows to a new 40-foot by 28-foot powerhouse that would house a single 3.4-MW horizontal shaft Francis Turbine/generator unit. The project would require the modification of the existing stilling basin to add a tailrace, and the construction of a new 0.8-mile-long, 12.47-kV overhead transmission line, a new substation, and appurtenant facilities.
The proposed project boundary would be limited to the footprint of the bifurcation, penstock, powerhouse, tailrace, transmission line, and the substation needed to connect to an existing Idaho Power 138-kV distribution line.
Mason Dam was built by Reclamation to provide for irrigation and flood control. Flow releases for irrigation typically begin around April 15 and last until Sept. 30. During the irrigation season (April to October), flow released generally remains between 100 and 200 cubic feet per second (cfs) but may be as high as 350 cfs. During the non-irrigation season (November to January), a flow release of about 10 cfs is maintained to protect downstream aquatic habitat in the Powder River, with flow releases increasing to about 20-50 cfs in February and March to increase the flood storage capacity within Phillips Reservoir.
The proposed project would operate in a run-of-release mode using flows made available by Reclamation and/or Baker Valley Irrigation District, with no proposed change to Reclamations’ operation or the current flow regime of the Powder River.
Baker County proposes to install a synchronous bypass in the project’s penstock and dam’s outlet works. If the powerhouse unexpectedly goes offline, the existing slide gates on Reclamation’s outlet works would automatically open to bypass flows away from the turbine until the powerhouse is brought back online.