1. Charge Questions for Expert Panel Modeling Vapor Attenuation Workshop Annual International Conference on Soils, Sediments, and Water October 19, 2004 Amherst, MA

2. Charge Questions – Modeling Vapor Attenuation Workshop 1: Models and Measurements Does the VI Guidance use the proper balance of model predictions and observations? Models (Predicting Exposure Pt. Conc. from GW or SG) Semi-site-specific (Figure 3) Site-specific Measurements (GW or SG; indoor air)

3. Charge Questions – Modeling Vapor Attenuation Workshop 2: VI Database Is the VI database comprehensive enough to make decisions? If not, what is missing? Topics: Data quality and extent Resistant vs. degradable compounds Precluding factors Generic alphas

4. Charge Questions – Modeling Vapor Attenuation Workshop 3:Figure 3 and Observed Alphas In cases where observed alphas plot above or well below the line in Figure 3, are there reasons that could be used to improve the VI Guidance? Topics: Values higher than Figure 3 attenuation factors Values well below Figure 3 attenuation factors

5. Charge Questions – Modeling Vapor Attenuation Workshop 4: Indoor Air Background How do background VOC concentrations in indoor air affect the reliability of observed alpha datasets? How should we screen for background influences? If we could remove “background,” what would the measured alphas look like?

6. Charge Questions – Modeling Vapor Attenuation Workshop 5: Factors Impacting Attenuation What variables influence attenuation and how do they rank in terms of impacts on alphas? How should they be considered in the VI Guidance? Variables: Chemical type (resistant, degradable) Depth to source Soil type Weather conditions Building (type, foundation, ventilation)

7. Charge Questions – Modeling Vapor Attenuation Workshop 6: Precluding Factors Are the VI Guidance Precluding Factors appropriate and adequate for generic and semi-site-specific screening? Site-specific modeling? VI Guidance Precluding Factors: Signs for immediate action: wet buildings, NAPL, … Sources of vapors above the water table, or Shallow GW (<5 ft below building foundation), or Relatively shallow groundwater sources )<15 ft) and Crawlspace homes (without liners*) Very permeable geology Significant preferential pathways Mobile gas plumes (landfill gas, vapor clouds) Very low air exchange rates or Very high (negative) pressure differentials

8. Charge Questions – Modeling Vapor Attenuation Workshop 7: Shallow Sources Is it technically justifiable to allow (for SG or GW): Semi-site-specific models within 5 ft of building base? Site-specific models within 5 ft of building base? Do you recommend we modify VI Guidance to allow it? Note: Basis for this policy in VI Guidance was largely public relations

9. Charge Questions – Modeling Vapor Attenuation Workshop 8: Q4 and Q5 Screening Do we need both Q4 and Q5? Could we combine them? Q4 = Generic (observation-based screening Q5 = Semi-site-specific (model-based screening Should we continue to use different Henry’s law constant temperatures (approximately 2x factor)? 25 C in Q4 Table 2 10 C in Q5 Table 3