THE BEHAVIOR OF RADIONUCLIDES IN THE SOILS OF ROCKY FLATS, COLORADO

Radionuclide contamination of soils in Rocky Flats, Color ado, resulte d from leaking drums of Pu-contaminated oil stored at an outdoor area. To evaluate the mechanisms of radionuclide transport From the contami nated soils to groundwater, an advanced monitoring system was installe d across a toposequence. The impact of natural rain, snowmelt, and lar ge-scale vain simulations on the mobility and distribution of the radi onuclides in soil interstitial water was studied. The distribution of radionuclides during the monitoring period from 1993 to 1995 suggested that Pu-239 + 240 and Am-241 are largely immobile in semi-arid soils. Large-scale min simulations with a 100-year recurrence interval occas ionally remobilized large fluxes of radionuclides that constitute betw een 1 and 3.3% of the stored Pu and Am in these soils. Fractionation o f Pu-239 + 240 and Am-241 to different particle sizes in the soil inte rstitial water suggested that most of the radionuclides (83-97%) were associated with suspended particles, whereas the level of radionuclide s associated with colloidal (0.45 mu m > X > 1 nm) and nonfilterable ( < 1 nm) fractions ranged from 1.5 to 15%. (C) 1997 Elsevier Science Lt d.