EFFECTS OF NITRATE ON ARSENOPYRITE OXIDATION DURING AQUIFER STORAGE AND RECOVERY CONDITIONS

An increasing number of regions are tasked with combatting groundwater availability and quality issues. A growing reliance on groundwater due to population growth and climatic changes have motivated the onset of groundwater enhancement techniques such as aquifer storage and recovery (ASR). ASR often involves injection of treated wastewater and later retrieval from a dual-purpose well. One the most observed issues with this technique is contaminant mobilization, namely the release of arsenic species via oxidative dissolution of arsenic-bearing minerals. Consequently, previous research has focused on how oxygen, and other electron acceptors facilitate this reaction. However, few studies have thoroughly investigated the specific role nitrate has on arsenic release within ASR conditions. Appreciable amounts of nitrate can be introduced into groundwater via injection during ASR, and other anthropogenic sources. Thus, this research aims to characterize the geochemical changes occurring from nitrate induced oxidation of arsenopyrite during ASR conditions. To simulate ASR conditions, triplicate microcosms were created that contain arsenopyrite, partially treated municipal wastewater, and local Florida groundwater. Microcosms were then sparged with nitrogen gas and sealed to create an anoxic environment. Nitrogen gas bags were attached through tubing to maintain anoxic conditions, along with secondary tubing for sampling. Four additional microcosm triplicates were created as controls for this experiment. Changes in chemical species within the microcosms are being determined using ion chromatography. Preliminary data suggests that non-nitrogen species may preferentially facilitate arsenopyrite oxidation under ASR conditions. Samples are continuing to be analyzed to fully understand the temporal geochemical changes. Further results and analyses will be presented at the 2023 Geological Society of America Connects Meeting. This research will provide improved understanding of arsenopyrite oxidation during ASR that should be considered to assist in minimizing arsenic mobilization in groundwater. The findings of this study will have important implications for protecting human health, enhancing environmental engineering practices, and guiding future research.