The nation’s largest hydroelectric facility is about to get an upgrade. As its 75th anniversary approaches, aging transmission lines at Washington’s Grand Coulee Dam will be removed and replaced with safer, more reliable lines.

New 500-kilovolt (kV) overhead transmission lines will replace six existing underground lines that consist of 18 aging, oil-filled cables between Grand Coulee’s third power plant and a 500-kV spreading yard. In the current configuration, the cables are susceptible to threats such as fire, which could likely lead to multiple line failures in the future. In fact, temporary overhead cables had to be constructed in 1981 when a fire damaged some of the lines.

The proposed overhead solution is less likely to experience multiple line failures. The new lines will transfer power across the Columbia River, over the visitor center area, and then continue uphill to connect to existing lines that transfer power into the regional power grid. The project will include the construction of new towers and access roads.

The Bonneville Power Administration (BPA) will fund and construct the multi-million dollar project for the Bureau of Reclamation, which operates Grand Coulee. BPA also assisted the bureau with the design of the project.

The decision to move forward follows BPA’s completion of the final environmental assessment and the release of separate Findings of No Significant Impact (FONSI) by BPA and the bureau.

Constructed in 1942, Grand Coulee Dam has a capacity of 6,809 megawatts. Construction of the new 500-kV overhead transmission lines will begin this month and continue through the winter, as weather permits.