Actinide Migration from Contaminated Soil to Surface Water at the Rocky Flats Environmental Technology Site

Abstract

:Surficial soils of the Rocky Flats Environmental Technology Site (RFETS) contain elevated levels of 239,240Pu and 241Am due to wind dispersal of soil particles, contaminated in the 1960's by leaking drums stored on the 903 Pad. Over the past 4 years, actinide mobility in the surface environment at RFETS, Golden, Colorado, USA, was examined through field and laboratory experiments. From measurements of total 239,240Pu and 241Am concentrations in storm runoff and pond discharge samples, collected during spring and summer times, it was established that most of the actinide transport from contaminated soils to streams occurred in the particulate (0.45μm) and colloidal (3kDa – 0.45μm) phases. Controlled laboratory investigations of soil resuspension, indicated that remobilization of colloid-bound Pu during soil erosion events can be enhanced by humic acidsl).2-D Polyacrylamide Gel electrophoresis (PAGE) experiments of radiolabeled colloidal organic and inorganic matter, extracted from RFETS soils, suggested that colloidal Pu, which was focused at pHIEP p of 4.5, is mainly associated with organic (humic acids) colloids of 10-15 kDa molecular weight. Pu(IV) oxide and inorganic colloids such as iron and aluminum oxides have pHIEP of 8-10. While some clay minerals also have pHIEP of 3-5, no Al was found coincident with Pu. This finding has important ramifications for possible remediation, erosion controls, and land-management strategies.