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U.S. irrigation districts study 880-MW Don Pedro pumped-storage

Modesto and Turlock irrigation districts are studying the feasibility of building a 440-MW or 880-MW Don Pedro pumped-storage project at Don Pedro Reservoir, south of Sonora in Tuolumne County, Calif.

The districts filed a preliminary permit application with the Federal Energy Regulatory Commission in October, seeking to secure priority for the site while they study whether to seek a license. FERC issued notice of the application Nov. 16, and set Jan. 15, 2007, as the deadline for filing of comments, protests, and motions to intervene.

Modesto Irrigation District has authorized Turlock Irrigation District to serve as project manager.

The districts are co-licensees of an existing project, 168.015-MW Don Pedro (No. 2299), which includes Don Pedro Reservoir. The reservoir, impounding more than 2 million acre-feet, would serve as the lower pool for the pumped-storage project.

The new project would include a new upper reservoir, conveyance tunnel, powerhouse, transmission lines, and other appurtenant facilities. Based on preliminary engineering studies, the districts have identified two possible upper reservoir configurations.

Alternative A would feature a site near Moccasin Peak, about one-half mile north of Don Pedro Reservoir, for the upper reservoir of an 880-MW project. It would include a 465-foot-tall, 1,700-foot-long dam across a ravine, creating a small reservoir with a surface area of about 240 acres and 25,000 acre-feet of storage.

Alternative B would feature another site north of Don Pedro Reservoir for the upper reservoir of a 440-MW project. It would have a surface area of about 166 acres and about 13,000 acre-feet of storage. Alternative B would include a 285-foot-tall, 2,700-foot-long dam.

The applicants said they would refine the two alternatives over the 36-month term of the permit to select an optimal configuration for the project (No. 12745).

A powerhouse is expected to be built on the shore of Don Pedro Reservoir, or underground, depending on the results of engineering studies, the districts said.

Don Pedro Dam and Reservoir were built in 1971 by a partnership of the two irrigation districts, along with Hetch Hetchy Water and Power, and the Corps of Engineers. The reservoir is the sixth largest body of water in California, providing energy production, flood control, agricultural and municipal water supply, and recreation.

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