Risk-Based Clean-Up in Georgia Under the VRP Vapor Intrusion

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1 Risk-Based Clean-Up in Georgia Under the VRP Vapor Intrusion Presented by: Genesis Project, Inc. in conjunction with Atlas Geo-Sampling

2 Presentation Topics 1. Regulatory Implications 2. Vapor Intrusion Pathways Analysis and Risk Assessment 3. Tools EPAs Final Guidance for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Sources to Indoor Air ( ) Vapor Intrusion Screening Level (VISL) Calculator (2012c) 4. Attenuation Factors Calculation: Default/Empirical 5. Natural Attenuation Sampling Strategies 6. Empirical Calculation of site-specific attenuation factor 7. Summary

3 Regulatory Implications State of Georgia Voluntary Remediation Program VI assessment and mitigation incorporated into VRP Additional exposure pathway to consider Some Future Site Cleanup may be based solely on VI Key Challenges Variability in vapor migration Physical Characteristics Low Acceptable Risk Criteria

4 Pathway Courtesy of Ohio EPA

5 Pathways Analysis Three Conditions must exist for completed pathway: Source of Hazardous Vapors in subsurface Vapors must have pathway to migrate to building Entry routes (cracks, seams, penetrations in foundation) and driving forces (pressure gradient) must be present for vapors to enter building. Complicated by volatiles present in air (not related to release) Background Collecting indoor air is problematic

6 Acceptable Risk in Indoor Air Acceptable Risk Criteria = very low concentrations Comparison to OSHA Exposure Guidelines Tetrachloroethene OSHA PEL \1 670,000 ug/m 3 \1 Permissible Exposure Limit (8- hour weighted average) EPA VISL 180 ug/m 3 (commercial non-carcinogen THQ=1) Target Indoor Air Concentration in Parts Per Trillion

7 Vapor Intrusion Screening Level (VISL) Calculator Screening Tool to identify areas or buildings that may warrant further investigation of the vapor intrusion pathway, including screening levels for: Indoor air Sub-slab soil gas Near-source soil gas Groundwater sampling results Key Issues Exposure Scenario (residential/commercial/sensitive population commercial) Target Risk for Carcinogens Target Hazard Quotient for Non-Carcinogens Attenuation Factors Limitations Conservative attenuation factors

8 Attenuation Factor AFVI = CIA VI CSV AF VI Attenuation Factor (vapor intrusion) C IA-VI Concentration in Indoor Air C SV Concentration in subslab soil vapor

9 Attenuation Factor Factors That May Influence Attenuation Factors Spatial and Temporal Variability Building Specific building construction, foundation type, condition of foundation) Air Exchange Rate Background sources in indoor air concentrations

10 Attenuation Factor VISL Default Attenuation Factor 0.1: Sub-slab and Exterior Soil Gas Groundwater Conservative Values EPA s Vapor Intrusion Database Evaluation of Attenuation Factors for chlorinated compounds in residential buildings Sites where sub slab > 50 times background) Tetrachloroethene min. 2.5E-05 Max. 3.5E-01 Mean 8.6E-03

11 Attenuation Factor Characterization EPA 530-R

12 Attenuation Factor Calculation of a Site-Specific Attenuation Factor Accomplished by Measuring Naturally Occurring Non Reactive Analytes (i.e. Radon) In Georgia, Radon exists in measureable levels throughout the Piedmont Noble Gas Inert to most chemical reactions Used to Calculate a Site Specific (or Slab Specific) Attenuation Factor

13 Attenuation Factor Sampling Protocols Site-Specific Attenuation Factor may be used as an Additional Line of Evidence of Incomplete Pathway. Two Sampling Approaches for developing the Radon Site Specific Attenuation Factors (RSSAF) 1) Collect Paired (subslab and indoor air) radon samples from one location every hour for 8 or 10 hours (Temporal) 2) Collect Paired (subslab and indoor air) radon samples from several location within the building to make sure that variation if concrete slab thickness, slab penetrations and construction are not causing a bias in the RSSAF (Spatial)

14 Attenuation Factor Sampling Protocols Temporal Sampling Method Significant number of paired samples from one location over time Potentially biased data since it is based on one location within a Building Does not reflect spatial variability in foundation/local penetrations and Variability in air exchange rates over sampling period Recent data in GA (10-hour sampling period) showed some variation in concentration of radon but no significant change in calculated attenuation factor Spatial Sampling Method Paired samples in variety of locations based on space usage. More likely to identify variability on attenuation factors based on variables Looking for consistency of both indoor air results and sub-slab sample results across space. SPATIAL SAMPLING PROTOCOLS PREFERRED TO TEMPORAL

15 Attenuation Factor AFVI = CIA VI CSV AF VI Attenuation Factor (vapor intrusion) C IA-VI Concentration in Indoor Air C SV Concentration in subslab soil vapor

16 Empirical Attenuation Factor Calculation Radon Levels are measured in the Sub-Slab and above the Slab. Results from recent investigation: Radon in Indoor Air =.073 pci/l Radon in the Subslab Soil Gas = 268 pci/l The Calculated Attenuation Factor is or 3 x 10-4 ~3 Orders of Magnitude smaller than the Default AF of 0.1

17 Empirical Attenuation Factor Calculation Impact on Site-Specific Target Sub-Slab Concentration Tetrachloroethene IA Screening Level 180 ug/m 3 (1E-5 cancer risk) Attenuation Factor of Target Sub-Slab Gas Concentration = 600,000 ug/m 3

18 Summary Vapor Intrusion evaluations will become routine May become the driving force in many remedial efforts Collection of Indoor Air samples problematic Don t Do It (unless absolutely necessary) Default Attenuation Factors Very Conservative Calculation of Site-Specific Attenuation Factor best method to get realistic values