An assessment of uranium in surface air within the continental US

Historical trends and regional variations of uranium in surface air within the continental United States from the late 1970s to the present was assessed using results from DOEʹs Argonne National Laboratoryʹs (ANL) East Environmental Monitoring program, and from 25 monitoring stations from EPAʹs Environmental Radiation Ambient Monitoring System (ERAMS) surveillance program. The historical total uranium activity levels for these databases fall within the range of concentration levels that have been observed in Europe. The ERAMS stations located in the northern and midsection of the country show a decrease in total uranium levels of ˜40% over this time period. No other long-term trends were observed. Excluding three EPA ERAMS stations, due to likely local source-term effects, the mean average 234U/238U activity ratios within the US was determined to be 1.1 (0.31 SD). There was no evidence of any historical trend, seasonal changes, large regional effect or coastal variation for these ratios. Results from a simple mixing model show that the range of 234U/238U and 235U/238U activity ratios for the EPA ERAMS Lynchburg surface air monitoring station database reflect a mixing of natural uranium with a maximum of 1% high-enriched uranium from a local source.