1. Dungeons, Dragons, Pica Houses and the Need for Alternative, Vapor Intrusion Screening Tools Roger Brewer, Josh Nagashima, Mark Rigby, Martin Schmidt, Harry O’Neill February 10, 2015 contact: roger.brewer@doh.hawaii.gov

2. Reference Roger Brewer & Josh Nagashima: Hawai’i Dept of Health State vapor intrusion guidance Mark Rigby: Parsons Corporation, UC Santa Barbara Toxicology, risk assessment, vapor intrusion Martin Schmidt: Cox-Colvin and Associates, Inc. Vapor intrusion field investigations, Vapor Pins Harry O’Neill: Beacon Environmental Services, Inc. Vapor intrusion field investigations, passive soil gas Brewer, R., Nagashima, J., Rigby, M., Schmidt, M. and O'Neill, H. (2014), Estimation of Generic Subslab Attenuation Factors for Vapor Intrusion Investigations. Groundwater Monitoring & Remediation, 34: 79–92. http://onlinelibrary.wiley.com/doi/10.1111/gwmr.12086/full

3. Estimation of Generic Subslab Attenuation Factors for Vapor Intrusion Investigations Reviews two USEPA methods for estimation of default soil gas-to-indoor air attenuation factors. Two years preparing manuscript; Discussions with vapor intrusion experts across the mainland, including USEPA and various state agencies; Presentation at national conference prior to final paper; Informal review of draft manuscripts by regulators and private consultants; Eight months peer review by Groundwater Monitoring & Remediation; Published December 2014.

4. Vapor Attenuation slab contaminated soil or groundwater subslab vapors Subslab Soil Gas Attenuation Factor Attenuation of intruding vapors in indoor air; Critical parameter for vapor intrusion screening; Two primary methods for estimation of default AFs. Vapor Intrusion Subslab Attenuation Factor (negative ΔP)

5. Vapor Attenuation slab contaminated soil or groundwater subslab vapors Method #1: Ratio of Vapor Entry to Indoor Air Exchange Indoor Air Exchange Rate (L/minute) Vapor Entry Rate (L/minute) Subslab AF = Vapor Entry Rate IAER

6. Subslab Soil Gas Attenuation Factors Subslab AF = 1 Vapor Entry Rate (5 L/min) 2 IAER (2,000 L/min) VI Model Default AF: 1/400 (0.0025) California (DTSC 2011, rounded): Method #1 Examples: Subslab AF = 1 Vapor Entry Rate (4 L/min) 2 IAER (4,000 L/min) VI Model Default AF: 1/1,000 (0.001) Hawai’i (HDOH 2012): 1.Vapor entry rate per 100m 2 2.Default house volume = 244 m 3

7. Subslab Soil Gas Attenuation Factors Method #1: Divide estimated Vapor Entry Rate by estimated Indoor Air Exchange Rate Used as basis of 2004 USEPA vapor intrusion guidance; Well studied by building radon experts and ventilation engineers; Models based on field studies and empirical data; Used in “site-specific” USEPA and DTSC vapor intrusion models.

8. slab contaminated soil or groundwater Method #2: Indoor Air and Subslab Soil Vapor Database Subslab AF = Conc. Indoor Air Conc. Soil Vapor Indoor Air Sample (µg/m 3 ) X X Subslab Vapor Sample (µg/m 3 )

9. Method #2: Divide measured concentration in indoor air by measured concentration in subslab soil gas Intuitively more direct and accurate; USEPA database for hundreds of homes and buildings; Compiled in the early 2000s; Calculate generic AFs based on statistical evaluation of database; Draft document published 2012 (subsequent extensive public comment received). SubSlab Soil Gas Attenuation Factors

10. Basis of USEPA VI Subslab “Attenuation Factors” Subslab Attenuation Factor 0.10.01 0.001 1.0 0.0001 Less Conservative More Conservative Frequency 95% UCL= 0.03 (1/33) Median = 0.003 (1/333) CalDTSC Default SSAF = 0.05

11. Method #2: Draft default subslab AF = 0.03 (95% UCL) proposed; Currently favored by some USEPA regulators; Resulting subslab soil vapor (and groundwater) screening levels 20-30 + times lower than published by some states based on Method #1 approach; Significantly larger number of sites flagged for potentially vapor intrusion risks; Many left in bureaucratic or technical limbo (low priority, irresolvable source of VOCs in indoor air, etc.); Imposes a significant legal and financial burden on property owners and responsible parties; Default attenuation factors seem excessively conservative for much/most of US based on more detailed field data. Subslab Soil Gas Attenuation Factors

12. Headaches, High blood pressure, Heart problems, Diabetes, Dermatitis, Asthma, Arthritis, Depression, Anxiety. Additional Health Risk? TCE? Stress

13. Problem #1: One Size Does Not Fit All… USEPA Database: Most data from cold areas of country; Application to Hawai’i questionable; Majority of indoor air samples from basements, poor ventilation (dungeon); Indoor air data within potential background for 80% of buildings; Most data not useable to calculate AFs; Worst-case scenario assumes heating & high vapor flux year round (dragon); Use of combined minimum indoor air exchange rate and maximum vapor intrusion rate questionable (pica house); Rates positively correlated (IAER increases as vapor entry rate increases).

14. CalEPA 2011 (among others): “The default attenuation factors assume [that] …the subsurface is reasonably homogeneous (uniform). Still an understandable approach when starting out… But…

15. Second and Bigger Database Problem… Reliance on SINGLE SUBSLAB SAMPLE to calculate a subslab AF for 85+% of individual structures included in database (max 3 samples for other structures?); 1,000s of potential one-liter, vapor samples under a single slab; Representativeness of sample collected questionable; Increasing number of samples typically reveals increasing spatial heterogeneity (e.g., high-density Vapor Pin and passive sampler data); Spatial variability due to source area heterogeneity, soil type, moisture, preferential pathways, air movement, etc. Subslab AF = Conc. Indoor Air Conc. Soil Vapor

16. Subsurface Vapor Plume Heterogeneity VOC concentrations in vapor plumes can vary by orders of magnitude; Calculated subslab AF depends on where sample taken; Vapor entry point(s) likewise usually unknown; Additional uncertainty due to temporal variability for both soil gas and indoor air; Potential error in estimated AF for a building not quantifiable. Example petroleum vapor plume under building (Luo 2009). X X X X Subslab AF = Conc. Indoor Air Conc. Soil Vapor

17. Accuracy of individual subslab AFs unknown; Error in extrapolated, generic attenuation factors not quantifiable; Database not technically defensible for development of generic attenuation factors; Can’t be “fixed” by statistical analysis; Median AF similar to Method 1 but error unknown. Recommended Reading (Silver 2012): The Signal and the Noise: Why So Many Predictions Fail - but Some Don't Frequency IA:Random Subslab Noise? 95% UCL Median Implications for Database

18. Statisticians Can’t Fix the Problem for You 1.8156302,3008737 0.71156331011045 0.946.34804209350 2.416622,00021041 1.5142108,4009634 0.180.247.4269.9980 0.150.169.4594.8600 0.180.733.512181,100 0.320.461624426,100 0.0470.321637200370 0.370.143.6141636 0.600.181.7181.926 1.90.24.6164033 0.240.263.6121629 0.090.343.6224736 0.051.232275.27.7 0.110.4326158.26.0 0.0541.05.5407.591 0.0368.1160391.514 0.0610.3319521.84.9 Imagine if… Survey of ages and weight but unknown number of people lied; Field data but PID found to be malfunctioning and error unknown; Lab data but equipment malfunctioned and error unknown… Collecting more data of unknown reliability doesn’t help; Start over…

19. Vapor Attenuation slab contaminated soil or groundwater subslab vapors Back to Method #1: More Technically Defensible Indoor Air Exchange Rate (L/minute) Vapor Entry Rate (L/minute) Subslab AF = Vapor Entry Rate IAER

20. Song et al (2014): Quantifying the influence of stack and wind effects on vapor intrusion (HERA, Vol 20). Used well-established “building leakage” models to estimate daily change in indoor air pressure (ΔP), based on building design and climate data; Feed into USEPA vapor intrusion model, generate daily vapor entry rate; Model calculates daily subslab AFs. slab contaminated soil or groundwater Vapor Intrusion Model Method #1: New and Improved ΔPΔP Building Leakage Model

21. Daily, Seasonal & Annual Average Vapor Flux Rates Based on Building Leakage Models (after Song et al 2014) Vapor entry rate and IAER positively correlated and vary with climate/season (but not exactly linear); Maximum similar to USEPA default (5 L/minute per 100m 2 ); Near zero vapor intrusion if no wind and open windows (no ΔP); Air conditioning can over pressure building and force indoor air into subslab space (“vapor extrusion”). Day of Year *Lower Vapor Flux When Home Cooled Higher Vapor Flux When Home Heated 1801306090120150210240270300330360 0 2 4 6 8 Modeled Vapor Entry Rate (L/min) *Assumes open windows and home under negative pressure due to wind effects winterspringsummerfallwinter

22. Expanded Method #1 Develop climate-specific, annual-average vapor entry rates per 100m 2 bottom floor area based on number of days below and above mean temperature of 65ºF (55ºF for Mediterranean climates); Combine with published estimates of annual average indoor air exchange rates. Assume “Heating Day” vs “Cooling Day” default Vapor Entry Rates: “Heating Days” (mean temp <65ºF): 5 L/minute “Cooling Days” (mean temp >65ºF): 2 L/minute Average Vapor Entry Rate AF (L/min) = (# 65ºF Days x 2 L/min) 365

23. Region A (cold, +Alaska) Region B 1 (warm) Region C (Med) Region B 2 (Coastal) Region D (tropical) Region A (cold): Average 303 days 65ºF Region B (warm/hot summers): Average 243 days 65ºF Region C (Mediterranean): Average 166 days 55ºF Region D (tropical): Average 0 days 65ºF Published Climate Data overlain on *CBECS Climate Zone Map: *Climate Zones and Daily Average Temperatures *Modified from Commercial Buildings Energy Consumption Survey (ICC 2012) Region D (tropical) +Hawai’i

24. Climate Zone 1 Average Number of Heating Days per Year (VER = 5 L/min) 2 Average Number of Cooling Days per Year (VER = 5 L/min) 4 Weighted Annual Average Vapor Entry Rate Region A (Cold) 303624.5 L/min Region B (Warm) 2431224.0 L/min 2 Region C (Med) 1661993.4 L/min Region D (Tropical) 03652.0 L/min Example Region-Specific Annual-Average Vapor Entry Rates (VER) 1.Heating (Non-Cooling) Day = Mean daily temperature <65ºF. 2.Mediterranean Heating Day = Mean daily temperature <55ºF. 3.Cooling Day = Mean daily temperature Heating Day temperature. 4.Vapor flux per 100m 2 lower floor space area.

25. Published Regional Indoor Air Exchange Rates (residential homes) Climate Zone 1,2 Example Default Indoor Air Exchange Rate Region A (Cold)0.35/hour1,423 L/min Region B (Warm)0.50/hour2,033 L/min Region C (Med)1.0/hour4,067 L/min Region D (Tropical)1.0/hour4,067 L/min 1.Based on review of published information for residential homes each climate region. 2.Default 100m 2 floor area and 244m 3 total volume (USEPA 2004).

26. Example Estimation of Region Specific, Annual Average Subslab Attenuation Factors Climate Zone Default Annual Average Subslab Attenuation Factor Vapor Entry Rate Indoor Air Exchange Rate 1 Region A (Cold) 4.5 L/min1,423 L/min0.003 Region B (Warm) 4.0 L/min2,033 L/min0.002 Region C (Med) 3.4 L/min4,067 L/min0.0008 Region D (Tropical) 2.0 L/min4,067 L/min0.0005 AF = Ave Vapor Entry Rate Ave IAER 1.Database method got the subslab AF right much of the time (median = 0.003)? Tells us something about vapor plume variability.

27. Example Vapor Intrusion Risk Regions VIR Region A(cold, +Alaska) Highest Risk VIR Region B 2 (warm) Moderate Risk VIR Region C (Med) Lower Risk VIR Region B 1 (Coastal) Moderate Risk VIR Region D (tropical) Lowest Risk Region A: High Vapor Flux, Low Indoor Air Exchange (SSAF = 0.003) Region B: Mod Vapor Flux, Mod Indoor Air Exchange (SSAF = 0.002) Region C: Lower Vapor Flux, High Indoor Air Exchange (SSAF = 0.0008) Region D: Low Vapor Flux, High Indoor Air Exchange (SSAF = 0.0005) VIR Region D (tropical) +Hawai’i

28. Summary USEPA vapor intrusion database worthwhile to compile but not technically defensible due to growing evidence of vapor plume heterogeneity; Comparison of estimated vapor flux rate to IAER most defensible method for estimation of subslab AFs; “Vapor Intrusion Risk” regions can be designated using a combination of: Estimated vapor entry rates based on building leakage models, vapor flux models and climate data; Published indoor air exchange rate data; Calculation of annual-average subslab attenuation factors; More accurate identification of high-risk vapor intrusion sites; More expedited clearance of low-risk vapor intrusion sites based on groundwater and soil gas data; Use soil gas data from center of slab, slab area closest to source and downwind slab area for worst-case screening.

29. Indoor Air 1.2 µg/ m 3 slab Groundwater: 610 µg/L SS Soil Gas:1,200 µg/m 3 Current HDOH Vapor Intrusion Action Levels (e.g., TCE residential chronic exposure) Average Vapor Entry Rate: 4L/minute (too high); Average IAER (1/hr): 4,000 L/minute; Subslab Soil Gas AF: 0.001 (1/1,000). >3m (10ft) TCE TCE in soil gas >3m (10ft) from the water table not expected to exceed 1,200 µg/m 3 if TCE in groundwater <610 µg/L. Based on combined models and field observations

30. HDOH Vapor Intrusion Guidance Vapor intrusion action levels overly conservative by at least 2X (assumed vapor flux rate too high); Subslab soil gas ALs adequately conservative (assumed vapor flux rate too high); Groundwater vapor intrusion action levels adequately protective (no exceedences of shallow soil gas action levels reported); Collect soil gas samples if VOC-contaminated soil suspected or known; Unexpectedly high, shallow soil gas VOCs related to previously unidentified soil source, inadequate groundwater data, etc.; A/C probably negates significant vapor intrusion risk for most buildings (over-pressured buildings could force indoor air into subslab space); Refer to expanded vapor intrusion discussion in Section 13 of HDOH TGM; No updates currently planned.

31. Other Vapor Intrusion Guidance Approach presented in paper under consideration in several states; Reviewing data for paired, groundwater and shallow soil gas data to confirm adequacy of groundwater vapor intrusion screening levels in different areas.

32. Are discrete soil gas samples too small to be reliable? It’s a bird! Nest Step: Bigger and/or More Soil Vapor Samples (sound familiar?)

33. 100L 50L 50ml 1L 6L Example subslab areas covered by different volumes of subslab soil gas samples (assuming sample collected from first 15cm of fill under slab and 20% air-filled porosity); Total volume of air-filled pore space in first 15cm of subslab fill approximately 2,250 liters per 100m 2 area; Collection of large-volume samples more challenging in tight soils (increase # of samples). Smaller is NOT Better Subslab Vapor Sample Volume vs Approximate Area of Influence 200cm For example only

34. Objective: Estimate Mean VOC concentration in subslab soil vapors for designated Decision Units (e.g., refer to HDOH and ITRC guidance on Incremental Sampling); Develop sampling method to achieve this goal (i.e., larger and/or more soil vapor samples) Designate Subslab Vapor Sample Decision Units For example only X X X X X X X X X

35. Next HEER Webinar When:March 11 th, 2015 (11am-12pm HI Time) Who:Martin Schmidt (Cox-Colvin, Inc.) and Harry O’Neil (Beacon Environmental, Inc.) What:Use of Active and Passive Soil Gas Samples to Support Vapor Intrusion Investigations TCEPCE