Assessing environmental drivers of fluoride mobilization in groundwater under increased loading of dissolved organic matter from managed aquifer recharge (MAR) Item

Geogenic fluoride contamination of groundwater is common in many semi-arid regions, and the impact of managed aquifer recharge (MAR) on increased mobilization of fluoride to the water in these regions is a concern. This work used saturated column experiments to explore the aqueous and mineralogical environmental drivers of fluoride mobilization and how they interact with increased loading of dissolved organic matter (DOM) from infiltrated runoff collected by MAR structures. Groundwater alkalinity was identified as the dominating driver of fluoride mobilization, resulting in increased dissolution of fluorite under all mineral matrix compositions. The influx of a 20 mg/L load of DOM somewhat reduced the mobilization of fluoride from the solid matrix under alkaline conditions, but otherwise did not influence fluorite dissolution compared to unloaded conditions. Environmental drivers were therefore identified as important predictors of fluoride mobilization at groundwater extraction sites, whereas the additional load of DOM to the groundwater resulting from MAR structures does not appear to increase fluoride concentration in the groundwater.