Hi Brian and Jia
I come across an issue and would appreciate if you would help out , and maybe suggest how to go with my model.
Conceptually, I am trying to test an operational methodology that has shown promised in attenuating the geogenic arsenic contamination during aquifer storage and recovery. Basically, I am running two model scenarios: the first one (ASR_Buffer Zone) aims in creating a buffer zone by promoting an oxidizing environment around the ASR well during all cycle tests (3 cycles in this case). The second (ASR_No Buffer_Zone) corresponds to over-recovery that usually results in releases of arsenic up to levels higher than their maximum contaminant level (10 µg/L) in the groundwater. While the first scenario promotes formation of Fe oxyhydroxide with high sorption capacity of trace elements (hence arsenic attenuation around the ASR well), the second scenario tends to deplete oxygen around the ASR well; with oxygen depletion, arsenic would tend to remobilize following Fe oxyhydroxide reduction dissolution.
I am working with the thermos database developed by Lazareva et al. (2013) called (Thermo_GKD.tdat, see attached) and the two-layer surface complexation database (FeOH+.sdat).
As you can see on the ppt attached, the oxygen concentration in the first scenario is quite higher than in the second scenario, meaning that ideally the first scenario would promote more arsenic attenuation with formation of Fe oxyhydroxide (most of them, if not all, being weak HFO forms in my case). However, as seen on the 2nd slide, both scenarios seem to form almost the same amount of Hydrous ferric oxides by the end of the simulation time (954 days buffer zone scenario versus 884 days in the case of no buffer zone).
I have tried to go with kinetic model scenarios of arsenopyrite, but it didn’t improve the results.
Any advice to improve my model?