1. Assessing Variability in Petroleum Vapor Intrusion Jim Weaver United States Environmental Protection Agency Office of Research and Development National Risk Management Research Laboratory Ground Water and Ecosystem Restoration Division Ada, Oklahoma

2. Outline Vapor Intrusion and Petroleum Vapor Intrusion Characteristics of Environmental Models PVIScreen model Examples –Cumulative Frequency Curves –Screen Shots Availability and Peer Reviews 9/4/20152

3. Vapor Intrusion and Petroleum Vapor Intrusion 9/4/20153 Chlorinated Solvent (left) petroleum (right) are distinguished by prospects for biodegradation

4. Why vapor intrusion and models? Technical Challenges –ambient air contamination, internal sources/sinks, temporal changes Social –RP or homeowner reluctance to sample In some cases—redeveloping a site—no building exists for testing, so models are relied upon 9/4/20154

5. Vapor Intrusion and Models Series of articles in the Denver Post in 2000 –The vapor intrusion model (Johnson-Ettinger) over-predicted indoor air concentrations sometimes and under-predicted indoor air concentrations sometimes –(Model used with defaults and very few site specific values) 9/4/20155

6. Environmental Transport and Fate Models Environmental transport models have an inherently empirical two-part basis: –relationships between physical, chemical and biological quantities –Experimentation to determine the values of coefficients 9/4/20156

7. Example: Darcy’s Law Darcy flux q = -K dh/dl –Relationship from Darcy’s sand tank experiments –Empirical coefficient, the hydraulic conductivity (K), from experiment: measuring the flow (q) MaterialValue (m/d) Gravel10 2 to 10 4 Sand10 -1 to 10 3 Clay10 -8 to 10 -3 Sandstone10 -5 to 10 Basalt10 -6 to 10 -2 9/4/20157

8. Limits to Predictability Note the work of N. Oreskes on ideal applications for models: –Classical physics experiments –Planetary motion Planets are observed to check model predictions –Weather forecasting Forecast given and received with uncertainties Oreskes, Naomi, 2003, The role of quantitative models in science, in Models in Ecosystem Science, C.D. Canham and W.K. Lauenroth, eds. Princeton University Press, 13-31 9/4/20158

9. Calibrated and Uncalibrated The planetary motion models can be calibrated, while the weather forecast can only be calibrated after the fact. –The forecasts of the uncalibrated models need uncertainty analysis. Vapor Intrusion models are being used in a partially/wholly uncalibrated fashion. 9/4/20159

10. PVIScreen PVIScreen includes: –A petroleum hydrocarbon lens as a source (can be omitted to create ground water source) –BioVapor equations, recoded in Java Johnson-Ettinger model if no biodegradation –Automated Monte Carlo uncertainty analysis –Flexible and customizable unit choices –User Interface –Automated Report Primary raison d’ ê tre –To make uncertainty analysis practical 9/4/201510

11. 11 0.0 1.0 0.0 1.0 0.0 1.0 0.0 1.0 0.0 1.0 0.0 1.0 frequency parameter value frequency parameter value A constant Uniform distribution: min, max Data-driven empirical distribution 0.0 1.0 Results: indoor air concentration frequency Multiple Model Runs Inputs Results All other inputs, Other distributions can be used: Triangular, truncated normal Log normal 9/4/2015

12. Example Problem Definition Reformulated Gasoline, BTEX + TPH Groups Some of the variable parameters –Air Exchange Rate 0.1 to 1.5 hr -1 –Moisture content 0.05 to 0.2 –Porosity 0.3 to 0.5 –Fraction Organic Carbon 0.00075 to 0.00125 –“Q soil ” 1 to 10 L/min –Crack width 0.5 to 5 mm 9/4/201512

13. Example Problem Schematic 9/4/201513

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21. Model Output – all parameter values saved with results Method to display parameter values which exceed risk levels is being developed 9/4/201521

22. Availability and Peer Review Command Line or “DOS” version –Input and output from Excel spreadsheet –Flexible input, but requires exactitude in entering required quantities User Interface – being completed –Available for review Email: weaver.jim@epa.govweaver.jim@epa.gov The views expressed in this presentation are those of the author and do not necessarily represent the views or policies of the U.S. Environmental Protection Agency 9/4/201522