P1247176262qGxwn

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Arsenic and Old Lakes
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/ ppb
/ ppb
/ ppb
/ ppb
/ ppb

200 ppb
USEPA/WHO 10 ppb
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RISK One in a million probability of death
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As
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As (V)
As (III)
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Jeromite As(S, Se)2
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Plutonic Relationship
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100 ppb
Sinagua Peoples
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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!
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Clarkdale mine tailings / ground water
trough
210 ppb
400 500 ppb
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Supai Formation 280/300 MYA Verde
Formation 5/2 MYA
Supai Formation ground level
near Sedona
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Solution Breccia Pipes
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Arsenopyrite FeAsS
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Fine-grained deposits Big
Chino Valley Schwab(1995), USGS
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Open File Report 2005-1154
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As
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Oxidation Rust..
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Reduction (anaerobic)
methane

swamp gas
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Anoxic Depositional Setting
high organic content
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Oxidation and Reduction control Arsenic transport
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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
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Microbial processes mediate the release
of arsenic into ground
water
under reducing conditions
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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.
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Arsenic mobilization
Geochemical evolution of ground water to high
pH, alkaline conditions, can induce transport of
arsenic
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Ground water flow from limestone (alkaline pH)
into arsenic-rich aquifer, will mobilize arsenic.
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As (III)
Reduction
pH
Oxidation
As (V)
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• 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

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Finding NEMO in Arizona