Preserving Water Quality Arsenic and Chromium Threats Scott Fendorf Stanford University Surface WaterSediment Ratio 10001 GroundwaterSediment Ratio 11000 Water Quality Problems ID: 1021788
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1. A Challenge with Groundwater ManagementPreserving Water Quality: Arsenic and Chromium ThreatsScott FendorfStanford University
2. Surface Water:Sediment Ratio, 1000:1Groundwater:Sediment Ratio, 1:1000 Water Quality ProblemsGroundwater Quality Challenge
3. Appreciating Geogenic ThreatsFeCr2O4(s)UO2(s)As2S3(s)MnO2(s)
4. Arsenic Mobilization ProcessesPersistence of anaerobic conditionsAlkaline pH (greater than 8.5)Competing anions (e.g., phosphateKnown processesEmerging processesChange in ionic composition Aquifer compression with pumping
5. Orange County Water DistrictNon-oxidative Release of Low-Arsenic Strata
6. Modes of Recharge
7. Post-Treatment Infiltration
8. YearMonitoring Well Arsenic
9. Cation bridging is key to arsenic retentionCa2+HAsO42-
10. Destabilized Arsenic with Purified WaterFakhreddine et al., EST 2015
11. Direct Injection to Confined AquifersFakhreddine, 2018
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13. Direct Injection to Confined AquifersFakhreddine, 2018
14. Pumping and Aquifer Compression
15. Arsenic Release From Clay Pore-Water with Aquifer Compression
16. Tulare Basin SubsidenceSmith, Knight, Fendorf, Nature Com. 2018
17. As (mg/L)10>100Arsenic Release with Groundwater Pumping
18. Groundwater Cr(VI) Concentrations
19. Industrial SourcedGroundwaterCr(VI)Geogenic Cr(VI)Cr(VI) Contamination of California Groundwater
20. 50 micronschromite grains(Fe0.46Mg0.52)(Cr0.61Al0.29Fe0.10)2O4FeCr2O4(s) + 7/2MnO2(s) + 5H+ = 2HCrO4-(aq) + Fe(OH)3(am) + 7/2Mn2+(aq) Chromite OxidationOze et al., PNAS 2007
21. CONTRIBUTORS and COLLABORATORS Sarah Fakhreddine Debra Hausladen Ryan Smith Chris Oze Laura Erban Jason Dadakis, OCWD Steve Gorelick Rosemary Knight
22.
23. Cr(VI) Generation from Native Cr(III) Minerals
24.
25. 50 micronschromite grains(Fe0.46Mg0.52)(Cr0.61Al0.29Fe0.10)2O4FeCr2O4(s) + 7/2MnO2(s) + 5H+ = 2HCrO4-(aq) + Fe(OH)3(am) + 7/2Mn2+(aq) Chromite OxidationOze et al., PNAS 2007
26.
27. Cr(OH)3MnO2Cr – Mn Separation Distance is Key to Cr(VI)
28. Deposition of MnO2 Proximal to Cr(OH)3
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30.
31. Cr(III) Oxidation: Mn-oxide DependentCr(OH)3 (s)+ 2H+ Cr(OH)2+ + 2H2O DissolutionOxidationCr(OH)2+ + 2MnO2 + 3H+ HCrO4- + 2Mn2++ 2H2O Oze et al., PNAS 2007
32. California Groundwater Chromium(VI)
33. Arsenic in Lower Mekong Delta -- VietnamErban et al. PNAS 2013
34. Shallow vs Deep Aquifer Arsenic
35. Erban et al. EST 2014Shallow vs Deep Aquifer Arsenic
36. Deep Aquifer Arsenic and Pumping Erban et al., PNAS 2013
37. Pumping Induced Land Subsidence
38. Release PathwaysOxidation-ReductionCr(III) (s) Cr(VI) (aq)Se(0)/S(-II) (s) Se(VI) (aq)U(IV) (s) U(VI) (aq)Oxidative (Aerobic) ReleaseAs(V) (s) As(III) (aq)Reductive (Anaerobic) Release