Reactive Transport Modeling to Support Long-Term Monitoring Strategy: Ion Exchange Induced Contaminant Remobilization at Subsurface Contaminated Sites Influenced by Abrupt Changes in Geochemical Conditions

This study presents a long-term monitoring strategy for early risk warning of the remobilization of contaminants, mainly attenuated through an ion exchange reaction, induced by abrupt changes in geochemical conditions.The strategy aims to utilize readily in-situ measurable groundwater quality parameters in the prediction of near-future contaminant remobilization caused by cation exchange reactions.The proposed approach was demonstrated using historical monitoring data from the Department of Energy (DOE) Savanna River Site (SRS) F Area, which experienced abrupt geochemical disturbance during the pump-treat-reinjection remedy, and a reactive transport model developed through this study to understand 90 Sr migration behavior in the subsurface of the SRS F Area.The historical monitoring data analysis and reactive transport modeling results suggested that in-situ specific conductance sensors can be used for an early warning system to detect contaminant remobilization associated with cation exchange species.This strategy is expected to benefit the long-term management of the contaminated site for elements with cation exchange reactions by providing the means to detect the remobilization of contaminants before the remobilization occurs.