sentences:  Both of these fires resulted in this radioactive material being released into the atmosphere, with the then-secret 1957 fire being the more serious of the two.The contamination of the Denver area by plutonium from these fires and other sources was not reported until the 1970s, and as of 2011 the U.S. Government continues to withhold data on post-Superfund cleanup contamination levels.Elevated levels of plutonium have been found in the remains of cancer victims living near the Rocky Flats site, and breathable plutonium outside the former boundaries of the plant was found in August 2010.