What’s the Problem: The Vapor Intrusion Issue Brownfields 2008 Heavy Starch: Cleaning the Dry Cleaners Detroit, MI May 5, 2008 Presented by: Henry Schuver, DrPH, US EPA – OSW* *A personal perspective, does not represent Agency positions See:

Overview of the VI Pathway Chemicals with evidence of toxicity PCE, TCE, DCE, VC, … Carcinogenicity, developmental neuro- & immuno- … Evidence of migration to receptors Exposure point concen. > acceptable Inhalation is relatively unavoidable Uninvited guest

Conceptual model of the vapor intrusion exposure pathway Dissolved contamination LTLT Diffusion Vadose zone Building zone of influence Wind effects Enclosed space Cracks Q soil Air streamlines Convection Top of capillary zone Water Table Stack effects Mixing in indoor air and inhalation Convection Diffusion Phase partitioning C gw to C soil gas Slide by M. Bolas, Ohio EPA, presented Jan Vapor Source Term

Migration Potential Vertical Depth Horizontal Distance Conductivity (gas) Geologic Factors Barriers (with lateral continuity) Preferential pathways Natural Anthropogenic Building Factors Design, construction, conditions Pressure differential (lower indoors = driving force)

Storm Sewer Map DC/MD Dry Cleaner vapor plume mapped using TAGA unit. Plume follows (leaky) sewer line

Assessment Challenges Indoor air samples confounded by: Background (unless real-time measurements) Indoor sources Outdoor sources External samples confounded by: Uncertainty (lack of knowledge) of migration Variability (now well documented) - multiple orders Space Time Data collection techniques vary Interpretation of data is immature field

Background* Indoor Air Concentrations vs Indoor Air Concentrations at Vapor Intrusion Sites [*Residential] Presented by H. Dawson see http//:iavi.rti.org

The VI Assessment Trap Requires characterization of: 1 Source of vapors (x time) 2 Attenuation (x time) 3 Toxicity (x time, + interactions) No health benefits unless & until actions No reductions in liabilities until actions Decreasing probability of showing no problem

3-D Modeling [& Exterior samples] by L. Abreu & P. Johnson, EST, 2005 In NY state 5 out of 11 sample pairs shows conc. > under slab than nearby soil-gas implants – Bill Wertz of NYS 2/7/06 w/ Westside soil gas vs subslab.xls [up to 30 x higher under slab] Not representative of the sub-slab Goal of soil-gas sampling is to represent the concentration under the slab. (Use SS alpha.) Soil-gas wells Note: SS can be 60% of source conc. (In Sandbox Geology) AF = 0.1 AF = AF = Some of what we have learned since 2002 – effect of building

Observations: Exterior Soil Gas vs. Subslab H. Dawson Presented by H. Dawson see http//:iavi.rti.org

Attenuation: Summary & Conclusions Data Set 2 Presented by H. Dawson see http//:iavi.rti.org

Groundwater-to-Indoor Air Attenuation Individual Site Box Whisker Plots Presented by H. Dawson see http//:iavi.rti.org

Subslab-to-Indoor Air Attenuation Individual Site Box Whisker Plots Presented by H. Dawson see http//:iavi.rti.org

A pivotal time for VI approaches Some observations by Paul Johnson: “conventional point sampling … not adequate” “We should … increase confidence and efficiency.” MLE = Multiple Lines of …?

Spatial and temporal indoor radon variations (Alavanja, et al., 2000) “Substantial year-to-year variability in radon concentrations has been routinely observed in homes [Steck, 1992], making it clear that a radon measurement made at a single point in time, even if measurement continued for an entire year, can result in increased exposure misclassification.”

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Three main Brownfields messages Early consideration of VI is good Pre-construction cost savings VI need not prevent re-development