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BioVapor

BioVapor. A 1-D Vapor Intrusion Model with Oxygen-limited Aerobic Biodegradation. Application of BioVapor to Petroleum Vapor Intrusion Sites. Course Outline. n Overview of Petroleum Vapor Intrusion (60 min) n Introduction to BioVapor Model (45 min) n Break (15 min)

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BioVapor

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  1. BioVapor A 1-D Vapor Intrusion Model with Oxygen-limited Aerobic Biodegradation Application of BioVapor to Petroleum Vapor Intrusion Sites

  2. Course Outline nOverview of Petroleum Vapor Intrusion (60 min) nIntroduction to BioVapor Model (45 min) nBreak (15 min) nCase Study 1: GW Screening Values (30 min) nCase Study 1: Dissolved Hydrocarbon Plume (30 min) nCase Study 2: Gasoline Vapor Source (30 min) nQuestions (30 min)

  3. BioVapor Model Gettin’ the Goods How • Download at: www.api.org/pvi(Registration information used so we can notify users of updates. No spam.) • Roger Claff Claff@api.org • (202) 682-8399 • • Bruce Bauman Bauman@api.org (202) 682-8345 Who

  4. Introduction Meet the Trainers • GSI Environmental • Developer of BioVapor Interface Thomas McHugh • Shell Global Solutions • Developer of BioVapor Model George DeVaull • US EPA, Office of Research and Development • Petroleum Vapor Intrusion Research and Policy Jim Weaver

  5. Overview of Petroleum VI nGeneral VI Conceptual Model nVadose Zone Attenuation of Petroleum Vapors nOxygen Below Building Foundations nFramework for Evaluation of Petroleum VI

  6. Conceptual Model for Vapor Intrusion: Regulatory Framework BUILDING Building Attenuation Due to Exchange with Ambient Air 3 Air Exchange Advection and Diffusion Through Unsaturated Soil and Building Foundation Unsaturated Soil 2 Affected Soil Affected GW Partitioning Between Source and Soil Vapor 1 Groundwater-Bearing Unit Regulatory guidance focused on building impacts due to vapor migration. KEY POINT:

  7. B B B A A A Physical Barriers to Vapor Intrusion

  8. Overview of Petroleum VI nGeneral VI Conceptual Model nVadose Zone Attenuation of Petroleum Vapors nOxygen Below Building Foundations nFramework for Evaluation of Petroleum VI

  9. AerobicBiodegradationPossible Co>Comin No AerobicBiodegradation Co<Comin Petroleum Biodegradation Conceptual Model Comax CHmin  Oxygen L Hydrocarbon Comin CHmax Hydrocarbon Source Vapor Concentration Correlation between oxygen consumption and hydrocarbon attenuation. KEY POINT: From Roggemans et al., 2001, Vadose Zone Natural Attenuation of Hydrocarbon Vapors: An Empirical Assessment of Soil Gas Vertical Profile Data, API’s Soil and Groundwater Technical Task Force Bulletin No. 15.

  10. Conceptual Model: Biodegradation Rapid vapor attenuation is observed within the “clean soil” layer above top of dissolved or NAPL source. KEY POINT:

  11. O2 HC Conceptual Model What is “Clean Soil”? Soil impacted by mobile NAPL, residual NAPL, NAPL smear zone, or Groundwater fluctuation zone. Dirty Soil Clean Soil Soil with low hydrocarbon concentrations (e.g., <100 mg/kg TPH). Consider potential for shallow sources or other unexpected vadose zone impacts. Watch-out “Clean soil” means low hydrocarbons, not zero hydrocarbons. KEY POINT:

  12. Petroleum Biodegradation: Real Site Data Diesel Release Site, North Dakota VOC Concentration vs. Depth Biogenic Gases vs. Depth

  13. Oxygen Petroleum Biodegradation: Real Site Data Carbon Dioxide Benzene Beaufort, SC Coachella, CA Salina, UT Ubiquitous vadose zone attenuation of petroleum hydrocarbons. KEY POINT: Vadose zone profiles compiled by Robin Davis, UDEQ.

  14. Petroleum Soil Vapor Database: Robin Davis, Utah DEQ 2/13 ~170 sites & ~1000 Soil Vapor Sample Events United States, Canada, Australia 54/307 KEY 54 # Geographic Locations Evaluated # Subsurface paired benzene soil vapor & GW sample events 307 112/608 Perth Sydney Tasmania

  15. Robin Davis Soil Vapor Database: Observed Soil Vapor Attenuation 73 exterior/near-slab + 24 sub-slab = 97 total 199 exterior/near-slab + 37 sub-slab = 236 total For dissolved sources (<1000 ug/L benzene or <10,000 ug/L TPH), 5 ft of clean soil is sufficient for vadose zone attenuation to non-detect benzene in soil gas. KEY POINT:

  16. Robin Davis Soil Vapor Database: Observed Soil Vapor Attenuation 73 exterior/near-slab + 24 sub-slab = 97 total 199 exterior/near-slab + 37 sub-slab = 236 total For UST site NAPL sources, 10 ft of clean soil is sufficient for vadose zone attenuation. KEY POINT:

  17. Petroleum Vapor Intrusion vs Chlorinated Solvent VI KEY POINT: Increasing regulatory acceptance that petroleum releases have much lower vapor intrusion risk. Graphic from: USEPA OUST Petroleum Vapor Intrusion Workgroup, 2010, Petroleum Vapor Intrusion Information Paper, June 2010 Draft

  18. Correlation Between Groundwater Concentration and Indoor Air?? IA ?? Chlorinated Solvents Petroleum Hydrocarbons GW Indoor Air Concentration ( ug/m3) Indoor Air Concentration ( ug/m3) CORRELATION ? YES (p <0.001) CORRELATION ? NO (p = 0.11) GW Concentration (ug/L) GW Concentration (ug/L) Observable RelationshipCia vs. Cgw ? n Petroleum Hydrocarbons: No n Chlorinated Solvents: Yes - Direct Cgw = COC conc. In groundwater; Cia = COC conc. In indoor air; (p = 0.11) = Probability = 11% that slope of best-fit line = 0 (I.e., no trend).

  19. Overview of Petroleum VI nGeneral VI Conceptual Model nVadose Zone Attenuation of Petroleum Vapors nOxygen Below Building Foundations nFramework for Evaluation of Petroleum VI

  20. aerobic zone Oxygen Under Building Foundation Key Question nIs there enough oxygen below building foundations to support aerobic biodegradation? Ct anaerobic zone Cs Vapor Source

  21. Oxygen Under Foundation: Model Prediction Numerical model predicts oxygen shadow below building, but….. nVery strong vapor source (200,000,000 ug/m3) nAll flow into building is through perimeter crack nNo advective flow below building Model may not account for key oxygen transport processes. KEY POINT: From Abreu and Johnson, ES&T, 2006, Vol. 40, pp 2304 to 2315.

  22. Aerobic Biodegradation: Oxygen Mass Balance bacteria Hydrocarbon + Oxygen Carbon dioxide + Water 1 kg CxHy + 3 kg O2 3.4 kg CO2 + 0.7 kg H2O New Cells Electrons & Carbon + Petroleum Hydrocarbons Energy Electrons Electron Acceptor (e.g., O2)

  23. Aerobic Biodegradation: Oxygen Mass Balance nAtmospheric air (21% Oxygen)= 275 g/m3 oxygen> Provides capacity to degrade 92 g/m3 hydrocarbon vapors(= 92,000,000 ug/m3) Even limited migration of oxygen into subsurface is sufficient to support aerobic biodegradation. KEY POINT:

  24. Transport of Oxygen Under Foundation Bi-Directional Flow Across Foundation Wind Driven Advection +/- +/- KEY POINT: Advection drives oxygen below building foundation.

  25. Depth (m) Depth (m) 0.01 0.1 1 10 100 1000 Transport of Oxygen Under Foundation Conceptual Model Field Data 0.0 0.5 Wind-driving building ventilation isoP 1.0 CH4 CO2 Wind Loading 02 1.5 Advection of subslab soil gas into bldg. 0.0 0.5 1.0 Biodegradation Upwind-downwind advection in soil gas Diffusion from deep sub-slab soil gas 1.5 0.0 Subslab VOC source Concentration (g m-3) Conceptual model and field data indicate common presence of oxygen under building foundation. KEY POINT: From Fisher et al., 1996 Environmental Science and Technology, Vol. 30 No. 10, p. 2948.

  26. Time = 0 Low Oxygen N 0.9 0.8 1.1 0.9 0.8 0.8 0.8 0.9 0.8 0.8 0.8 1.0 garage 3 m % O2 After Flood concrete Injection wells % O2 (shallow) Soil Column Attenuation Transport of Oxygen Under Foundation Nitrogen Flooding Experiment: Purge sub-foundation soils with nitrogen gas and observe oxygen recovery Time > 0 Oxygen Recovery Below Building Data from Lundegard, Johnson, and Dahlen. “Sub-slab Nitrogen Flood-Oxygen Re-entry Test.”

  27. Injection wells % O2 (shallow) Time = 0 Time = 2 weeks High Oxygen Low Oxygen N N 0.9 15.9 0.8 1.1 0.9 15.4 16.6 14.5 0.8 0.8 0.8 0.9 14.0 16.6 16.6 13.7 0.8 0.8 0.8 12.2 15.2 18.4 1.0 19.4 garage garage 3 m 3 m concrete concrete Soil Column Attenuation Transport of Oxygen Under Foundation Nitrogen Flooding Experiment: Purge sub-foundation soils with nitrogen gas and observe oxygen recovery KEY POINT: Rapid recoveryof oxygen below building foundation supports petroleum biodegradation. % O2 After Flood Data from Lundegard, Johnson, and Dahlen. “Sub-slab Nitrogen Flood-Oxygen Re-entry Test.”

  28. Gas flow fromsubsurface into building EXAMPLES Lower building pressure High Pressure Residence in winter(chimney effect); bathroom, kitchen vents Flow in Low Pressure Gas flow frombuilding into subsurface EXAMPLES Higher building pressure Building HVAC designed to maintain positive pressure Flow out Bi-directional flow betweenbuilding and subsurface EXAMPLES Variable building pressure Reversible flow Barometric pumping; variable wind effects Advective Transport Processes LowPressure High Pressure UPWARD TRANSPORT DOWNWARD TRANSPORT

  29. Pos. Pressure (Flow out of Bldg) Neg. Pressure (Flow into Bldg) Pressure Gradient Measurements: School Building, Houston, Texas KEY POINTS: • Pressure gradient frequently switches between positive and negative within a single day. • Continuous inward flow does not occur. Differential Pressure (Pascals) Time (July 14-15, 2005)

  30. Advection Through Building Foundation: Field Evidence nVOCs from indoor air typically detected in sub-slab samples:- alpha pinene- limonene- p-dichlorobenzene nOxygen transported below foundation by same mechanism INDOOR AIR S BELOW SLAB Reversing pressure gradient drives air (and VOCs and oxygen) through building foundation. KEY POINT: S

  31. Chatterton Research Site, British Columbia, Canada (Hers, et al 2000) Building Feet Below Grade SG-BC, 10/1/97 SG-BR 5/14/97 0 <1000 10 % Fill, “crust,” sandy silt 11% <1000 80,000 8 % 10% 55,000 3% KEY 6% 25,000,000 50,000,000 Vapor sample point identifier SG-BC Fill, dredged river sand 1.0% Sub-Slab vapor sample point 50,000,000 60,000,000 5 1.0% Sub-Surface vapor sample point 50,000,000 Benzene, ug/m3 1.0% Oxygen, % 10 LNAPL, benzene-rich 0 20 Feet, horizontal Slide from Robin Davis, UDEQ

  32. Hal’s, Green River, Utah (Utah DEQ, 8/26/06) Feet Below Grade Motel Office Breezeway Café/Bar VW-7 Asphalt 0 8.4 850 Basement Basement 14% Clayey Silt 7.0 380 VW-4 VW-5 20% 51 22 10 2800 1600 7.7 9.5% 18% Silt 250 12% 87 570 12,000 70,000 260,000 4.1% 11% 33,000,000 2.5% Benzene in GW 1,000-5,000 ug/L 20 LNAPL, gasoline KEY Multi-depth vapor monitoring well VW-7 Sub-Surface vapor sample point 260,000 Benzene, ug/m3 33,000,000 0 20 TPH-gro, ug/m3 2.5% Oxygen, % Feet, horizontal Slide from Robin Davis, UDEQ

  33. Perth, Australia (B. Patterson & G. Davis, 2009) Very Large Building 410 Feet Below Grade Uncovered open ground <2 0 19,000,000 <50,000 <50,000 <50,000 <0.5% 10.7% 19.9% 18.8% Lateral Extent of Oxygen & Biodegradation Sand 35,000,000 <50,000 <50,000 <50,000 5 <0.5% 8.2% 14.5% 15.9% 35,000,000 1,200,000 <50,000 <50,000 <0.5% 8.2% 4.5% 4.6% 10 KEY LNAPL Kerosene (very low BTEX) Outdoor air sample Indoor air sample Sub-slab vapor sample 0 20 Sub-surface vapor sample 1,200,000 Total Petroleum Hydrocarbons, ug/m3 Feet, horizontal 8.2% Oxygen, % Slide from Robin Davis, UDEQ

  34. Oxygen Under Building Foundation Summary nWind and building pressure drive atmospheric air below building foundation nEven modest oxygen transport sufficient aerobic biodegradation

  35. Overview of Petroleum VI nGeneral VI Conceptual Model nVadose Zone Attenuation of Petroleum Vapors nOxygen Below Building Foundations nFramework for Evaluation of Petroleum VI

  36. 4 3 2 1 Groundwater-Bearing Unit Petroleum Vapor Intrusion: Field Experience BUILDING Preferential pathway allows vapors to enter building. NAPL directly impacts building wall or floor. Unsaturated Soil NAPL NAPL Affected GW Vapors from NAPL diffuse through vadose zone (large releases). Sump draws NAPL or dissolved hydrocarbons into building. NAPL For petroleum sites, vapor intrusion is generally associated with two factors acting together - shallow sources and preferential pathways. KEY POINT:

  37. Unsaturated Soil NAPL Affected GW GW-Bearing Unit Framework for Evaluation of Petroleum Vapor Intrusion Sites: Based on Modeling and Empirical Data (McHugh et al.1) 1 LNAPL or Dissolved Plume in Contact with Foundation: HIGHER RISK BUILDING Proposed Action: Test hydrocarbon concentrations inside structure. Mitigate as needed. 1) Adapted from McHugh, Davis, DeVaull, Hopkins, Menatti, and Peargin, 2010. Evaluation of Vapor Attenuation at Petroleum Hydrocarbon Sites: Considerations for Site Screening and Investigation, Soil and Sediment Contamination: An International Journal, November/December 2010, Vol. 19, No. 5.

  38. 2 BUILDING ? ? ? ? Unsaturated Soil 3 to 10 m LNAPL Groundwater-Bearing Unit Framework for Evaluation of Petroleum Vapor Intrusion Sites: Based on Modeling and Empirical Data (McHugh et al.1) LNAPL present 3 to 10 m (10 to 30 ft) below building foundation:MEDIUM RISK Subsurface LNAPL: Vapor intrusion observed at a few large release sites (refineries) but not at UST sites. (10 to 30 ft) Proposed Action: Test for hydrocarbons in shallow soil gas below or directly adjacent to building foundation. 1) Adapted from McHugh, Davis, DeVaull, Hopkins, Menatti, and Peargin, 2010. Evaluation of Vapor Attenuation at Petroleum Hydrocarbon Sites: Considerations for Site Screening and Investigation, Soil and Sediment Contamination: An International Journal, November/December 2010, Vol. 19, No. 5.

  39. 3 BUILDING >3 to 10 m Unsaturated Soil LNAPL Groundwater-Bearing Unit Framework for Evaluation of Petroleum Vapor Intrusion Sites: Based on Modeling and Empirical Data (McHugh et al.1) LNAPL present >10 to 30 ft below building foundation:LOWER RISK (>10 to 30 ft) Evaluate presence of preferential flow pathways or other site-specific risk factors. Testing for hydrocarbons in shallow soil gas below or directly adjacent to building foundation may be appropriate. Proposed Action: 1) Adapted from McHugh, Davis, DeVaull, Hopkins, Menatti, and Peargin, 2010. Evaluation of Vapor Attenuation at Petroleum Hydrocarbon Sites: Considerations for Site Screening and Investigation, Soil and Sediment Contamination: An International Journal, November/December 2010, Vol. 19, No. 5.

  40. 4 BUILDING >1.5 to 3 m Unsaturated Soil Affected GW Framework for Evaluation of Petroleum Vapor Intrusion Sites: Based on Modeling and Empirical Data (McHugh et al.1) Dissolved hydrocarbon plume 5 to 10 ft below building:LOWER RISK (>5 to 10 ft) Proposed Action: Evaluate presence of preferential flow pathways or other site-specific risk factors. 1) Adapted from McHugh, Davis, DeVaull, Hopkins, Menatti, and Peargin, 2010. Evaluation of Vapor Attenuation at Petroleum Hydrocarbon Sites: Considerations for Site Screening and Investigation, Soil and Sediment Contamination: An International Journal, November/December 2010, Vol. 19, No. 5.

  41. Course Outline nOverview of Petroleum Vapor Intrusion (60 min) nIntroduction to BioVapor Model (45 min) nBreak (15 min) nCase Study 1: GW Screening Values (30 min) nCase Study 2: Dissolved Hydrocarbon Plume (30 min) nCase Study 3: Gasoline Vapor Source (30 min) nQuestions (30 min)

  42. Vapor Intrusion Models Types of Vapor Intrusion Models Predictions based on observations from other sites (e.g., attenuation factors). Empirical (Tier 1) Mathematical equation based on simplification of site conditions (e.g., Johnson and Ettinger). Analytical (Tier 2) SIMPLE MATH Numerical models:- Abreu and Johnson, Bozkurt et al. Mass flux model, foundation transport model, etc. Others (Tier 3) KEY POINT: Wide range of approaches to vapor intrusion modeling, varying in complexity and specificity.

  43. Groundwater-Bearing Unit Vapor Intrusion Models Johnson and Ettinger Model (Tier 2) Building Attenuation Due to Exchange with Ambient Air 1 RESIDENTIAL BUILDING Air Exchange Advection and Diffusion Through Unsaturated Soil and Building Foundation Unsaturated Soil 2 Equilibrium Partitioning Between GW and Soil Vapor Csv = Cgw x H’ source area 3 “Site-specific” predictions based on soil type, depth to groundwater, and building characteristics. KEY POINT: H = Henry’s Law Constant

  44. Vapor Intrusion Models J&E Model: Key Assumptions Does not account for heterogeneities, preferential pathways, or temporal variation. 1-D Steady-State Model No mass balance; mass flux into building can exceed available source mass. Infinite Source soil vapor Does not account for biotransformation in the vadose zone No Bio-degradation Affected GW Plume J&E model is generally conservative, but model error can be very large (orders-of-magnitude). KEY POINT:

  45. BioVapor: 1-D VI Model w/ Bio nConceptual Model nModel Inputs nModel Outputs nExample Model Validation

  46. O2 HC Conceptual Model What is BioVapor? Version of Johnson & Ettinger vapor intrusion model modified to include aerobic biodegradation (DeVaull, 2007). 1-D Analytical Model SIMPLE MATH Oxygen Mass Balance Uses iterative calculation method to account for limited availability of oxygen in vadose zone. Simple interface intended to facilitate use by wide range of environmental professionals. User-Friendly Easy-to-use vapor intrusion model that accounts for oxygen-limited aerobic vapor intrusion.Free download at: www.api.org/vi KEY POINT:

  47. 3 Advection, diffusion, and dilution through building foundation aerobic zone 2 Diffusion & 1st order biodegradation in aerobic zone 1 Diffusion only in anaerobic zone Conceptual Model BioVapor: Conceptual Model Ct anaerobic zone Cs Vapor Source

  48. Conceptual Model BioVapor: Oxygen Mass Balance Iterative Calculation Method Calculate oxygen demand:- depth of aerobic zone- HC vapor concentration- 1st order biodegradation ?? No Increase or decrease depth of aerobic zone anaerobic interface O2 demand = supply? ?? Yes Vapor Source KEY POINT: Calculations are cheap & quick Final Model Solution

  49. Conceptual Model BioVapor: Intended Application • Obtain improved understanding of petroleum vapor intrusion. • Calculate oxygen concentration/flux required to support aerobic biodegradation. • Identify important model input parameters and evaluate model sensitivity. Yes Simplifying Assumptions • 1-D Model: Does not account for spatial variability • Steady State: Does not account for temporal variability • Single Source: Does not account for indoor sources and other background sources of petroleum VOCs

  50. BioVapor: 1-D VI Model w/ Bio nConceptual Model nModel Inputs nModel Outputs nExampleModel Validation

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