Abstract The Hanford Site is a 560-square-mile (1,450-km2) complex established by the U.S. government in 1943 to produce plutonium for nuclear weapons, ultimately bringing an end to World War II. Plutonium production activities continued after the war through 1991, at which point the site's mission changed from plutonium production to environmental cleanup and restoration. Production activities at the site resulted in a broad range of contaminated materials and facilities, including 57 million gallons of high-level (i.e., highly radioactive) nuclear waste in liquid and solid forms. The high-level waste was stored as it was created, first in single-shell tanks built between 1943 and 1964, then in more robust double-shell tanks constructed between 1968 and 1986. Due to waste leakage in a small number of single-shell tanks and the potential for additional single-shell tank failures, all single-shell tanks were removed from service by 1980. All pumpable liquid has been transferred to sound double-shell tanks....