Radium is the contaminant of most concern.
Radium, thorium and uranium are all radioactive elements and can potentially cause cancer. In addition, radon gas emitted from the decay of radium has been known to cause lung cancer. However, radon is only a health risk if the gas is concentrated in enclosed spaces where people can be exposed for long periods of time. The site consists of 44 separate properties combined into 11 Operable Units in central Denver. Radium extracted from ore mined on the Colorado Plateau was used for cancer therapy, research and a variety of commercial purposes in the early 1900s.