T59 A Showcase of Undergraduate Research in Hydrogeology (Posters)

Sunday, 10 October 2021
2:30 PM - 6:30 PM
Exhibit Hall A

EFFECTS OF NITRATE ON ARSENIC MOBILIZATION FROM ARSENOPYRITE DURING SIMULATED AQUIFER STORAGE AND RECOVERY CONDITIONS

Paper number: T59-21
Program: Technical Sessions
Time: 2:30 PM – 6:30 PM

Authors

Abstract

Aquifer storage and recovery (ASR) includes the injection (storage) and withdrawal (recovery) of water into and from aquifer systems during the wet and dry seasons to provide a constant supply of water year-round. ASR offers a multitude of benefits; however, when applied to karst limestone aquifers containing arsenic-bearing minerals such as arsenopyrite, arsenic can be mobilized at alarming levels within the withdrawn water. The World Health Organization has classified arsenic as toxic and carcinogenic, and the federal limit in the United States for publicly supplied drinking water has been set at 10 µg/L. In water withdrawn from ASR systems in Florida, arsenic concentrations of up to 130 µg/L have been found, raising extreme concern. Arsenic mobilization is already known to be induced by the presence of dissolved oxygen in the aqueous phase; however, it is not yet known if nitrate is similarly able to oxidize arsenopyrite and mobilize arsenic. The objective of this experiment is to determine how nitrate affects mobilization of arsenic from arsenopyrite under simulated ASR conditions. Microcosm experiments have been conducted to simulate ASR conditions and to quantify the mobilization of arsenic as a function of (a) the nitrate concentration, and (b) the presence or absence of Thiobacillus denitrificans bacteria. Arsenic and iron concentrations in the aqueous phase are measured over time via Graphite Furnace Atomic Absorption (GFAA), and Ion Chromatography is used for analysis of aqueous concentrations of nitrate, nitrite, sulfate, and ammonium. Preliminary results suggest that nitrate does mobilize arsenic from arsenopyrite under simulated ASR conditions in the absence of dissolved oxygen. Experiments are still underway and more complete results will be available at a later date. Continued research in this field is critical in order to continue supplying safe drinking water at an increased demand amidst the rising scarcity of water worldwide.

Geological Society of America Abstracts with Programs. Vol. 53, No. 6

doi: 10.1130/abs/2021AM-369310

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