EVIDENCE FOR RADIONUCLIDE TRANSPORT AND MOBILIZATION IN A SHALLOW, SANDY AQUIFER

Evidence is reported for the movement of plutonium, americium, thorium , and radium in a shallow, sandy aquifer after the forced injection of colloidal and macromolecular natural organic materials (humic and ful vic acids). Ultrafiltration was used to size-fractionate the materials smaller than 0.45 mum in the injection water. Characterization of the se organic materials showed the most mobile to be primarily fulvic aci ds with a high carboxylate content. Fallout-derived plutonium and amer icium in the injected materials were transported in the aquifer with t he smaller organic fractions. Americium was shown to move from the les s mobile colloidal materials to the smaller more mobile fulvics during transport. Thorium, uranium, and radium levels all increased upon inj ection of the organics into the aquifer, demonstrating the ability of low molecular weight, high carboxylic content fulvic acids to dissolve and mobilize radionuclides from the aquifer's mineral matrices. This effect also increased with decreasing flow rate in the aquifer. The im plications of these observations for the interactions of low-level rad ioactive waste with natural organics are discussed.