After fulfilling their government contracts, many companies closed down their uranium mills and left large piles of tailings at the mill sites. Because the tailings were not disposed of properly, they were spread by wind, water, and human intervention, thus contaminating properties beyond the mill sites. In some communities, the tailings were used as building materials for homes, schools, office buildings, and roads because at the time the health risks were not commonly known. The tailings and waste liquids from processing uranium ore also contaminated the groundwater. The most hazardous constituent of uranium mill tailings is radium.
Radium produces radon, a radioactive gas whose decay products can cause lung cancer.
The amount of radon released from a pile of tailings remains constant for about 80,000 years. Tailings also emit gamma radiation, which can increase the incidence of cancer and genetic risks. Other potentially hazardous substances in the tailings include arsenic, molybdenum, and selenium. DOE's cleanup authority was established by the Uranium Mill Tailings Radiation Control Act of 1978. Title I of the act governs the cleanup of uranium ore processing sites that were already inactive at the time the legislation was passed.