PLUTONIUM-239+240 AND AM-241 IN SOILS EAST OF ROCKY-FLATS, COLORADO

Soils east of the Rocky Flats (RF) near Golden, CO, were contaminated with Pu-239 + 240 and Am-241 as a result of past waste-storage practices. The physicochemical parameters that govern the actinides distribution in the soil are poorly understood. Twenty-six soil pits at various distances and directions from a contaminated site at RF were excavated, sampled, and analyzed for actinide activities as well as selected physical, chemical, and mineralogical attributes. Plutonium-239 + 240 and Am-241 activities in the soils ranged from 164 280 Bq/kg to 0.0037 Bq/kg, decreasing with distance from the source. More than 90% of the Pu-239 + 240 and Am-241 activities were confined to the upper 12 cm of the soil, regardless of the soil characteristics, or distance and direction from the source. Evidence of preferential transport in macropores formed along decayed root channels was observed in four soil pits and had translocated Pu-239 + 240 to a depth of 90 cm. This transport mechanism increased by a factor of 30 the level of Pu-239 + 240 activity at this depth. Earthworm activity is probably important in the redistribution of actinides in the upper 40 cm of many of the soils investigated. Planning of future remedial activities at RF should consider the findings of this contaminant-transport study.