MTCA Science Advisory Board Presentation
Establishing Moderate Soil Levels for Arsenic
October 23, 2006
Tacoma Smelter
Pesticide Applications
Yakima County Historic Orchards
Arsenic and Lead Mobility
• Metal concentration
• Metal speciation
• Soil redox and pH conditions
• Precipitation
• Soil composition and permeability
• Other (i.e., application of phosphate fertilizers)
Arsenate Column Experiment
Arsenite Column Experiment
Field Data as an Indicator of Arsenic and Lead Mobility
Soil Profiles Near the Tacoma Smelter
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Concentration (mg/kg)
Dep
th (
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es)
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Concentration (mg/kg)
Dep
th (
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Lead Arsenic
Soil Profiles – Central, WA
Arsenic vs. DepthFelker Orchard
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0 6 12 18 24
Depth (inches)
Conc
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tion
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Arsenic
Lead
Old Yakima Orchard Concentrations w/ Depth
Kissel Park
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Sample Depth - Top of Sample Interval (ft)
Ars
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Arsenic
Lead
Costco
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0 12 24 36 48 60 72 84 96
Depth (inches)
Conc
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Arsenic
Lead
Groundwater Data
• No Specific combined GW/Soil study
• However on Vashon – lots of soil data and lots of GW Data
• 22 Group A systems
• 137 Group B systems
• 50 to 75 % of Group A and B systems receive water from 25 ft or less
• DOH and King County Databases
WDOH Database
Equilibrium Partitioning Model
b
wdws KDFUCFCC
)(
Where:Cs = Soil Concentration (mg/kg)Cw = Groundwater concentration or cleanup level (μg/L)USF = Unit conversion factor (1 mg/1,000 μg)DF = Dilution factor (dimensionless: 20 for unsaturated
zone soil)Kd = Distribution coefficient (L/kg)
θw = Water-filled soil porosity (mL water/mL soil: 0.3 for unsaturated soil)
Pb = Dry soil bulk density (1.5 kg/L)
sCsC
Kd - Distribution Coefficient
Soil (mg/kg)
Water (mg/L)
Container
Kd =Water (mg/L)
Soil (mg/kg)= L/kg
Table 3. Kd Values for Arsenic and Lead
Sauve et. al (2000) Allison & Allison (2005) MTCA
Arsenic (L/kg) 29
Minimum 1.60 1.99
Median 1,830 2,510
Mean 13,100 1,580
Maximum 530,000 20,000
Lead (L/kg) 10,000
Minimum 60.6 5.01
Median 102,000 15,800
Mean 171,000 5,010
Maximum 2,300,000 100,000
Kd - As
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EPAmin
EPAmedian
EPAmean
EPAmax
Sauvemin
Sauvemedian
Sauvemean
Sauvemax
MTCA
log
KdKd - Arsenic
Examples of Kd values reported in literature reviews
Kd - Pb
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EPAmin
EPAmedian
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Sauvemax
MTCA
log
Kd
Kd - LeadExamples of Kd values reported in literature reviews
Equilibrium Partitioning Model
b
wdws KDFUCFCC
)(
CW (Kd of 29, MTCA) = 43 μg/L
CW (Kd of 2512, EPA median) = 0.50 μg/LCW (Kd of 1585, EPA mean) = 0.79 μg/L
CW (Kd of 1825, Sauve median) = 0.68 μg/LCW (Kd of 13119, Sauve mean) = 0.10 μg/L
Arsenic (CS = 25 mg/kg)
Equilibrium Partitioning Model
b
wdws KDFUCFCC
)(
CW (Kd of 2,510) = 5 μg/L
Arsenic (CS = 251 mg/kg)
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