In 1978, Congress passed the Uranium Mill Tailings Radiation Control Act (UMTRCA), a measure designed to assist in the cleanup of 22 inactive ore-processing sites throughout the southwest. This also included constructing 19 disposal sites for the tailings, which contain a total of 40 million cubic yards of low-level radioactive material.[55] The Environmental Protection Agency estimates that there are 4000 mines with documented uranium production, and another 15,000 locations with uranium occurrences in 14 western states,[56] most found in the Four Corners area and Wyoming.[57]