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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Lead Arsenic

Soil Profiles – Central, WA

Arsenic vs. DepthFelker Orchard

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Old Yakima Orchard Concentrations w/ Depth

Kissel Park

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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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MTCA

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KdKd - Arsenic

Examples of Kd values reported in literature reviews

Kd - Pb

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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)