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Statistical Evaluation of Attenuation Factors at Lowry Air Force Base, CO

Statistical Evaluation of Attenuation Factors at Lowry Air Force Base, CO. Helen E. Dawson, PHD Regional Superfund Hydrogeologist US EPA Region VIII Denver, CO 303-312-7841 dawson.helen@epa.gov AEHS VI Workshop October 2004. LAFB TCE Plume. Study Area. LAFB Cross-Section.

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Statistical Evaluation of Attenuation Factors at Lowry Air Force Base, CO

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  1. Statistical Evaluation of Attenuation Factors at Lowry Air Force Base, CO Helen E. Dawson, PHD Regional Superfund Hydrogeologist US EPA Region VIII Denver, CO 303-312-7841 dawson.helen@epa.gov AEHS VI Workshop October 2004

  2. LAFB TCE Plume Study Area

  3. LAFB Cross-Section • Depth to groundwater: 6 m • Vadose zone: fining upwards sequence; sand and gravels to sandy silts. • Saturated zone: sands and gravels Base Residential Area

  4. LAFB Soil Gas Study Area

  5. LAFBIndoor Air & Foundation Vapor

  6. TCE Concentrations Background Regulatory Levels Lowry Air Force Residences ½ Basement½ Crawlspace Full Basement Slab

  7. Sampling Methods • Indoor and ambient air: • 24-hour Summa; TO15S • Subslab: • Summa after 2 L purge; TO15S • Groundwater: • Bailer; 8260S

  8. 11DCA 1,1-Dichloroethane 12DCA 1,2-Dichloroethane 11DCE 1,1-Dichloroethene C12DCE cis-1,2-Dichloroethene T12DCE trans-1,2-Dichloroethene PCE Tetrachloroethene 111TCA 1,1,1-Trichloroethane 112TCA 1,1,2-Trichloroethane TCE Trichloroethene VC Vinyl Chloride Chemicals

  9. Attenuation Factors Calculated • Groundwater to indoor air (GW-IA) • Groundwater to subslab (GW-SS) • Subslab to indoor air (SS-IA)

  10. Data Quality Filters • Data excluded if: • GW, SS, or IA value < detection limit • IA conc. > subslab conc. • IA conc. < OA conc. • (IA – OA)/IA < 20% • Chemicals filtered out: • 12DCA, T12DCE, 112TCA

  11. Groundwater to Subslab Attenuation Factors

  12. Groundwater to Subslab Attenuation Factors

  13. Subslab to Indoor Air Attenuation Factors

  14. Subslab to Indoor Air Attenuation Factors

  15. Groundwater to Indoor AirAttenuation Factors

  16. Groundwater to Indoor AirAttenuation Factors Q4 Generic Alpha Q5 Alpha

  17. Comparison with Figure 3(b)of EPA’s VI Guidance

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