Accidental leakages of radioactive waste from underground tanks located at the U.S. Department of Energy’s Hanford Site, have created contaminated plumes that contain a mixture of contaminants with a variety of associated negative health impacts. This study specifically focuses on the co-mingled contaminants: iodine-129 (<sup>129</sup>I) as iodate and hexavalent chromium Cr(VI) as chromate which persist in the subsurface within the Central Plateau. Once active remediation is completed, a transition to more passive approaches, such as monitored natural attenuation (MNA), is required. Effective MNA necessitates a thorough understanding of the contaminant attenuation processes that affect their mobility in the vadose zone sediment. This study evaluates the competitive adsorption of the contaminants onto Hanford Formation sediments when they are present separately or blended together at maximum concentrations present in Hanford groundwater and porewater. This will be accomplished via batch competitive adsorption experiments and solid characterization studies. Preliminary results indicate significant (nearly quantitative) removal of both contaminants present together and separately from artificial groundwater over a 7-day period. The separation of the contaminants from the aqueous solution is primarily driven by the adsorption of <sup>129</sup>I and Cr(VI) onto the sediment. This indicates low mobility of contaminants in the vadose zone after active remediation is complete and is promising for effective MNA. Future work will further elucidate the mechanisms of transport associated with more contaminants found at the Hanford Site present separately and blended together at maximum concentrations.

Evaluation of competing attenuation processes for mobile contaminants in Hanford sediments

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.