OFF SITE AND BOUNDARY EXTERNAL RADIATION EXPOSURES FROM THE COTTER URANIUM MILL LOCATED IN CAÑON CITY, COLORADO Although many of the uranium mills in the United States have been decommissioned, the mill tailings remain and can pose health threats to those living nearby. Many studies have been done showing the relationship between radon exposure and lung cancer development for those living near a uranium mill, but it seems that little attention has been paid to the possible threat posed by

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... re to gamma radiation from these tailings piles. Since 1979 the Cotter Uranium Mill in Cañon City, Colorado has been measuring external gamma exposure rates at the fence line, and at several offsite locations including the closest residence and the Shadow Hills Golf Course. These exposure rate measurements were tested against background and it has been shown that exposure rates above background exist at all locations except for the nearest residence. Assuming full time occupancy, the excess dose received by members of the public from these exposure rates do not exceed regulatory limits of 100 mrem/yr except at the entrance road of the mill, which was remediated in 2009. For a hypothetical person living in the area of highest exposure rate above background, their risk of developing a fatal cancer is only increased by 0.43%. These exposure