Reactive transport modeling of ⁹⁰Sr sorption in reactive sandpacks

Strontium-90 (⁹⁰Sr) is one of the most problematic radioactive contaminants in groundwater at nuclear sites. Although ⁹⁰Sr is retarded relative to groundwater flow, it is sufficiently mobile and long-lived to require treatment in many hydrogeological settings. A detailed study was performed on the practicality of using granular clinoptilolite as a sandpack around groundwater wells where groundwater is contaminated with ⁹⁰Sr and the water table must be lowered. The effectiveness of the reactive sandpack concept and the mechanisms controlling ⁹⁰Sr attenuation was investigated by numerical analysis of data obtained from four in situ column experiments. The experiments spanned the range of pore-water velocities that would occur during radial flow through granular clinoptilolite sandpacks. A kinetic sorption model was required to adequately reproduce the experimentally observed ⁹⁰Sr behavior. Calibrated first-order kinetic rates were correlated with pore-water velocities. After calibration, three sorption models were used to simulate ⁹⁰Sr attenuation for four hypothetical pumping scenarios. Results show that a velocity-dependent kinetic model accurately simulates the observed early breakthrough for high pore-water velocities. The results indicate (1) that reactive sandpacks have good potential for in situ remediation and construction dewatering and (2) that quantitative modeling can aid in the design and application of this novel technique.