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

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

3. Measured Attenuation Factors 2001-2002 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 Factors Groundwater-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 Factors Chlorinated Hydrocarbons vs
2001 – 2002 Empirical Attenuation Factors Chlorinated Hydrocarbons vs. BTEX

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

8. 2001 – 2002 Empirical Attenuation Factors Influence of Foundation Structure?

9. 2001 – 2002 Empirical Attenuation Factors Influence of Soil Type?

10. 2001 – 2002 Empirical Attenuation Factors Depth to Groundwater?

11. 2001 – 2002 Empirical Attenuation Factors Conclusions
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.