 From 1953 to 1989 , the Rocky Flats Plant , a DOE nuclear weapon facility formerly located about 15 miles from Denver , produced fissile plutonium " pits " for nuclear warheads . A major fire at the facility in 1957 , as well as leakage from nuclear waste stored at the site between 1958 and 1968 , resulted in the contamination of some parts of Denver , to varying degrees , with plutonium @-@ 239 , a harmful radioactive substance with a half @-@ life of 24 @,@ 200 years . A study by the Jefferson County health director , Dr. Carl Johnson , in 1981 linked the contamination to an increase in birth defects and cancer incidence in central Denver and nearer Rocky Flats . Later studies confirmed many of his findings . Plutonium contamination was still present outside the former plant site as of August 2010 , and presents risks to building the envisioned Jefferson Parkway , which would complete Denver 's automotive beltway . 
