The behavior of radionuclides in the soils of Rocky Flats, Colorado

Radionuclide contamination of soils in Rocky Flats, Colorado, resulted from leaking drums of Pu-contaminated oil stored at an outdoor area. To evaluate the mechanisms of radionuclide transport from the contaminated soils to groundwater, an advanced monitoring system was installed across a toposequence. The impact of natural rain, snowmelt, and large-scale rain simulations on the mobility and distribution of the radionuclides in soil interstitial water was studied. The distribution of radionuclides during the monitoring period from 1993 to 1995 suggested that Pu-239 + 240 and Am241 are largely immobile in semi-arid soils. Large-scale rain simulations with a 100-year recurrence interval occasionally remobilized large fluxes of radionuclides that constitute between 1 and 3.3% of the stored Pu and Am in these soils. Fractionation of Pu-239 + 240 and Am-241 to different particle sizes in the soil interstitial water suggested that most of the radionuclides (83–97%) were associated with suspended particles, whereas the level of radionuclides associated with colloidal (0.45 μm > X > 1nm) and nonfilterable (< 1 nm) fractions ranged from 1.5 to 15%.