Read this - http://en.wikipedia.org/wiki/Hanford_Site
A huge volume of water from the Columbia River was required to dissipate the heat produced by Hanford's nuclear reactors. From 1944 to 1971, pump systems drew cooling water from the river and, after treating this water for use by the reactors, returned it to the river. Before being released back into the river, the used water was held in large tanks known as retention basins for up to six hours. Longer-lived isotopes were not affected by this retention, and several terabecquerels entered the river every day. These releases were kept secret by the federal government.[4] Radiation was later measured downstream as far west as the Washington and Oregon coasts.[45]
The plutonium separation process also resulted in the release of radioactive isotopes into the air, which were carried by the wind throughout southeastern Washington and into parts of Idaho, Montana, Oregon, and British Columbia.[4] Downwinders were exposed to radionuclides, particularly iodine-131, with the heaviest releases during the period from 1945 to 1951. These radionuclides filtered into the food chain via contaminated fields where dairy cows grazed; hazardous fallout was ingested by communities who consumed the radioactive food and drank the milk. Most of these airborne releases were a part of Hanford's routine operations, while a few of the larger releases occurred in isolated incidents. In 1949, an intentional release known as the "Green Run" released 8,000 curies of iodine-131 over two days.[46] Another source of contaminated food came from Columbia River fish, an impact felt disproportionately by Native American communities who depended on the river for their customary diets.[4] A U.S. government report released in 1992 estimated that 685,000 curies of radioactive iodine-131 had been released into the river and air from the Hanford site between 1944 and 1947.[47]
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