Investigation & Rehabilitation of Seattle's Tolt Pipeline

Seattle Water Department's Tolt Pipeline brings water 24 miles from storage in the Cascade Mountains into city and suburban distribution systems. Twenty-three miles of this pipeline originally consisted of pretensioned concrete cylinder pipe with sizes of 54 inches, 60 inches, and 66 inches. The gravity pressure is as high as 325 psi static. In November 1987, the pipeline burst during routine shutdown. A pressure reducing station was installed in place of an existing line valve, and a study was begun to determine the pipe's condition.