Empirical Attenuation Factors Predictions & Observational Data

1. Empirical Attenuation FactorsPredictions & Observational Data Ian Hers, Ph.D. Golder Associates Vancouver, BC, Canada Robert Truesdale RTI International RTP, North Carolina Helen Dawson, Ph.D. US EPA Region VIII Denver, CO

2. Empirical Attenuation Factors • 2001-2002 Evaluations (Helen Dawson) • 2004 Evaluations (Ian Hers) • Future Evaluations (Robert Truesdale)

3. Measured Attenuation Factors2001-2002 Database Summary • 15 sites, 15 VOCs, 274 total residence/chemical combinations • 35 BTEX; 239 CHC residence/chemical combinations • 99 sites with IA > 10-6 IA RBC(84 CHC, 14 BTEX) • 68 sites with IA > 10-5 IA RBC

4. 2001 – 2002 Empirical Attenuation FactorsGroundwater-to-Indoor Air All residences and chemicals with concentrations above MDLs

5. Factors evaluated (2001 – 2002) • Chemical type • Foundation type • Soil type • Depth to source

6. 2001 – 2002 Empirical Attenuation FactorsChlorinated Hydrocarbons vs. BTEX

7. 2001 – 2002 Empirical Attenuation FactorsInfluence of Foundation Structure? Groundwater

8. 2001 – 2002 Empirical Attenuation FactorsInfluence of Foundation Structure?

9. 2001 – 2002 Empirical Attenuation FactorsInfluence of Soil Type?

10. 2001 – 2002 Empirical Attenuation FactorsDepth to Groundwater?

11. 2001 – 2002 Empirical Attenuation FactorsConclusions • Measured attenuation factors range from 10-2 to 10-7 with median values around 10-4. • Influence of foundation type, soil type, and depth to water on the empirical attenuation factors is unclear. • Higher ranges of attenuation factors are observed for BTEX compounds; median value is around 10-5.