AN ASSESSMENT OF URANIUM IN SURFACE AIR WITHIN THE CONTINENTAL US

Historical trends and regional variations of uranium in surface air wi thin the continental United States from the late 1970s to the present was assessed using results from DOE's Argonne National Laboratory's (A NL) East Environmental Monitoring program, and from 25 monitoring stat ions from EPA's Environmental Radiation Ambient Monitoring System (ERA MS) surveillance program. The historical total uranium activity levels for these databases fall within the range of concentration levels tha t have been observed in Europe. The ERAMS stations located in the nort hern and mid-section of the country show a decrease in total uranium l evels of similar to 40% over this time period. No other long-term tren ds were observed. Excluding three EPA ERAMS stations, due to likely lo cal source-term effects, the mean average U-234/U-238 activity ratios within the US was determined to be 1.1 (0.31 SD). There was no evidenc e 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 U-234/U-238 and U-235/U-238 activity ratios fo r the EPA ERAMS Lynchburg surface air monitoring station database refl ect a mixing of natural uranium with a maximum of 1% high-enriched ura nium from a local source. 1996 Published by Elsevier Science Limited