Analysis of processes controlling fluoride and phosphate release during managed aquifer recharge

The release of geogenic contaminants from ubiquitous apatite minerals following the injection of low ionic strength water into aquifers was investigated using experimental, analytical and modelling approaches. Batch-type laboratory experiments were performed to study the mechanisms controlling the field-observed release of fluoride and phosphate that occurred during a four-year long field experiment. Preferential removal of divalent calcium ions onto sediment exchange sites under low ionic strength conditions was found to be the trigger for fluoride and phosphate release from carbonate-rich fluorapatite. Geochemical and reactive transport modelling was used to both interpret laboratory and field-scale observations and to assess mitigation strategies.