Contributions of rocky flats releases to the total plutonium in regional soils

Total Pu-239,Pu-240 and the Pu-240:Pu-239 atom ratio were measured in soil samples from around the Rocky Flats Environmental Technology Site (RFETS) during 1992-1994. Mass isotopic data provided a sensitive technique to resolve low levels of RFETS Pu-239,Pu-240 superimposed on plutonium from global fallout. Concentrations of Pu-239,Pu-240 within this sample set ranged from 1.1 Bq kg(-1) offsite to 57 Bq kg(-1) onsite, and the Pu-240:Pu-239 atom ratio increased from 0.055 onsite to 0.123 at approximately 19 km east of the RFETS boundary. The relationship between Pu-240:Pu-239 atom ratios and distance indicated that a measurable RFETS contribution may have extended to greater than or equal to 19 km offsite in the easterly direction. Although the RFETS contribution to total plutonium at the offsite locations ranged from 24-90%, the overall inventory was relatively small. Total inventory estimates, for one transect, based on Pu-239,Pu-240 and from Pu-240:Pu-239 atom ratio measurements were not significantly different.