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Arsenic Mobilization in Central Arizona Groundwater: Impacts and Risks

This study explores arsenic concentrations in groundwater within the Verde Valley in central Arizona, revealing levels exceeding 200 ppb, well above the EPA and WHO thresholds of 10 ppb. The research indicates that arsenic mobilization is influenced by microbial processes under reducing conditions and the geochemical evolution of water from limestone aquifers into arsenic-rich areas. This has significant implications for local populations and their water supply, highlighting the need for targeted well water testing and improved groundwater management strategies to mitigate health risks.

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Arsenic Mobilization in Central Arizona Groundwater: Impacts and Risks

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  1. Arsenic and Old Lakes

  2. / ppb / ppb / ppb / ppb / ppb > 200 ppb USEPA/WHO = 10 ppb

  3. RISK = One in a million probability of death

  4. As

  5. As (V) As (III)

  6. Jeromite As(S, Se)2

  7. Plutonic Relationship

  8. 100 ppb Sinagua Peoples

  9. Ground water arsenic in the Verde Valley in central Arizona, USA. R.D. Foust Jr., et al Northern Arizona Univ. Applied Geochemistry 19 (2004) 251-255 www.elsevier.com Geology Rules!

  10. Clarkdale mine tailings / ground water trough 210 ppb 400 – 500 ppb

  11. Supai Formation – 280/300 MYA Verde Formation – 5/2 MYA Supai Formation ~ ground level near Sedona

  12. Solution Breccia Pipes

  13. Arsenopyrite FeAsS

  14. 40 Fine-grained deposits Big Chino Valley Schwab(1995), USGS 89 Open File Report 2005-1154

  15. As

  16. Oxidation Rust…………..

  17. Reduction (anaerobic) methane swamp gas

  18. Anoxic Depositional Setting high organic content

  19. Oxidation and Reduction control Arsenic transport

  20. Oxidation of Arsenopyrite: 4 FeAsS + 13 O2 + 6 H2O 4FeSO4 + 4H3AsO4 Add Oxygen and water – Lower the water table in an Arsenopyrite-rich aquifer – Arsenic will be mobilized

  21. Microbial processes mediate the release of arsenic into ground water under reducing conditions

  22. Ground Water Arsenic Concentrations INCREASED When landfill covered! Slower ground water velocity allows more time to strip the water of oxygen, resulting in geochemically reducing conditions. In reducing conditions, microbial processes release arsenic.

  23. Arsenic mobilization Geochemical evolution of ground water to high pH, alkaline conditions, can induce transport of arsenic

  24. Ground water flow from limestone (alkaline pH) into arsenic-rich aquifer, will mobilize arsenic.

  25. As (III) Reduction pH Oxidation As (V)

  26. Options: • well construction – • no method to predict • optimal design / depth • treatment dependent • on arsenic species • present – water softener • + Fe-based resin filter • geochemistry rules • test your well water

  27. Finding NEMO* in Arizona

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