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Fate and Transport of Plutonium-239 + 240 and Americium-241 in the Soil of Rocky Flats, Colorado

University of Colorado, Dep. of Civil, Environ., and Architectural Eng., Boulder CO 80309-0428.

^* Corresponding author.

ABSTRACT

Actinides contamination of soils around Rocky Flats, CO, resulted from leaking drums of Pu-contaminated oil stored at an outdoor site. The transport of these actinides through the soil to groundwater was studied using an advanced monitoring system (MS). The fully automated, remotely controlled MS gathered real-time data on soil water content, groundwater level, and timing of gravitationally flowing water. Controlled rain simulations coupled with measurements of volume flux and actinide activities provided essential information about the fate and transport of Pu-239 + 240 and Am-241. Volume fluxes at most sampling locations were similar, regardless of the antecedent moisture or the duration, frequency, and intensity of the simulated rain. Actinide activities were not correlated with the measured volume flux, or the duration, frequency, and intensity of the simulated rain. Flow was facilitated primarily via macropore channeling. The relatively short residence time precluded a continuous interaction between the soil and the flowing water, which minimized the movement of actinides in the soil. Actinide activities in the interstitial water collected from the upper 20 cm of the soil were significantly higher (P > 0.001) than water collected at deeper sampling depths (20–70 cm). Actinide activity in water samples from the deepest sampling depth (40–70 cm) did not exceed 0.4 Bq/L. These results suggest that, under the experimental conditions, the movement of actinides was restricted to the top 20 cm. A transport mechanism involving discrete Pu oxide particles, coupled with macropore channeling is proposed to explain the observed actinide activities in the soil.

M.I. Litaor, present address: Tel-Hai College, Upper Galilee 12210, Israel.

Received for publication August 7, 1995.