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MTCA Science Advisory Board Presentation

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

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MTCA Science Advisory Board Presentation

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  1. MTCA Science Advisory Board Presentation Establishing Moderate Soil Levels for Arsenic October 23, 2006

  2. Tacoma Smelter

  3. Pesticide Applications

  4. Yakima County Historic Orchards

  5. 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)

  6. Arsenate Column Experiment

  7. Arsenite Column Experiment

  8. Field Data as an Indicator of Arsenic and Lead Mobility

  9. Soil Profiles Near the Tacoma Smelter Lead Arsenic

  10. Soil Profiles – Central, WA

  11. Old Yakima Orchard Concentrations w/ Depth

  12. 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

  13. WDOH Database

  14. Equilibrium Partitioning Model 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)

  15. Kd - Distribution Coefficient Container Soil (mg/kg) Kd = = L/kg Water (mg/L) Water (mg/L) Soil (mg/kg)

  16. Kd - Arsenic Examples of Kd values reported in literature reviews

  17. Kd - Lead Examples of Kd values reported in literature reviews

  18. Equilibrium Partitioning Model Arsenic (CS =25 mg/kg) CW (Kd of 29, MTCA) = 43 μg/L CW(Kdof 2512, EPA median) = 0.50 μg/L CW(Kdof 1585, EPA mean) = 0.79 μg/L CW(Kd of 1825, Sauve median) = 0.68 μg/L CW(Kd of 13119, Sauve mean) = 0.10 μg/L

  19. Equilibrium Partitioning Model Arsenic (CS = 251 mg/kg) CW (Kd of 2,510) = 5 μg/L

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