From 1953 to 1989, the Rocky Flats Plant, a DOE nuclear weapon facility that was 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 1981 study by the Jefferson County health director, Dr. Carl Johnson 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 . It presents risks to building the envisioned Jefferson Parkway, which would complete Denver's automotive beltway.