Vapor Intrusion: Investigation of Buildings Migration of VOCs through the building foundation and lessons learned from the detailed field investigation of the vapour intrusion process at Altus and Hill Air Force Bases Vingsted Center Monday, March 9, 2009 source area Air Exchange SITE BUILDING GSI ENVIRONMENTAL INC. Houston, Texas www.gsi-net.com (713) 522-6300 temchugh@gsi-net.com 1 1

Vapor Intrusion: Investigation of Buildings l United States Regulatory Framework l Spatial and Temporal Variability l Impact of Indoor Sources on VI Investigations Air Flow and VOC Migration Around Buildings l Controlled Investigation of Vapor Intrusion in Buildings l Conclusions and Recommendations

Groundwater-Bearing Unit Overview of USEPA VI Guidance Conceptual Model for Vapor Intrusion: BUILDING Building Attenuation Due to Exchange with Ambient Air 3 Air Exchange Advection and Diffusion Through Unsaturated Soil and Building Foundation Unsaturated Soil Affected Soil 2 Affected GW Partitioning Between Source and Soil Vapor Slide Topic: Conceptual model for vapor intrusion The standard conceptual model of vapor intrusion has the following key elements: Partitioning between the source and soil vapors. An infinite source of VOCs is assumed (i.e., no mass flux or mass balance considerations) Diffusion and advection (but not biodegradation) through unsaturated soils and the building foundation Attenuation in the building due to exchange with ambient air. This conceptual model is based on the J&E model. The U.S. EPA VI guidance was developed using this conceptual model of vapor intrusion. Slide Presentation: Describe the conventional conceptual model for vapor intrusion. Key Points: This conceptual model does not distinguish between petroleum and chlorinated VOCs. The model assumes an infinite source of VOCs The model does not account for biodegradation in the vadose zone. The model does not reflect industry experience with petroleum vapor intrusion impacts (see next slide). Groundwater-Bearing Unit 1 Standard conceptual model for vapor intrusion does not account for variable air flow in buildings. KEY POINT:

DOWNWARD VOC TRANSPORT Effect of Building Pressure on VOC Transport Gas flow from subsurface into building Low Pressure High Pressure EXAMPLES Lower building pressure Residence in winter (chimney effect); bathroom, kitchen vents Flow in Gas flow from building into subsurface UPWARD VOC TRANSPORT EXAMPLES Higher building pressure Building HVAC designed to maintain positive pressure Flow out High Pressure Low Pressure Bi-directional flow between building and subsurface EXAMPLES Variable building pressure Reversible flow Barometric pumping; variable wind effects DOWNWARD VOC TRANSPORT

Effect of Weather on Building Pressure COLD WEATHER WIND + + + wind - - soil subslab fill soil subslab fill Stack Effect: Warm air leaks through roof creating negative building pressure Wind on Building creates pressure gradient that results in air flow. Slide Topic: Conceptual model for vapor intrusion The standard conceptual model of vapor intrusion has the following key elements: Partitioning between the source and soil vapors. An infinite source of VOCs is assumed (i.e., no mass flux or mass balance considerations) Diffusion and advection (but not biodegradation) through unsaturated soils and the building foundation Attenuation in the building due to exchange with ambient air. This conceptual model is based on the J&E model. The U.S. EPA VI guidance was developed using this conceptual model of vapor intrusion. Slide Presentation: Describe the conventional conceptual model for vapor intrusion. Key Points: This conceptual model does not distinguish between petroleum and chlorinated VOCs. The model assumes an infinite source of VOCs The model does not account for biodegradation in the vadose zone. The model does not reflect industry experience with petroleum vapor intrusion impacts (see next slide). Temperature and wind create pressure gradients that influence air movement in and around buildings. KEY POINT:

Effect of Mechanical Ventilation Examples in Houses: - HVAC system - Exhaust fans (kitchen, bath) - Furnace - Other combustion appliances (water heater, cloths dryer, etc) MECHANICAL VENTILATION Slide Topic: Conceptual model for vapor intrusion The standard conceptual model of vapor intrusion has the following key elements: Partitioning between the source and soil vapors. An infinite source of VOCs is assumed (i.e., no mass flux or mass balance considerations) Diffusion and advection (but not biodegradation) through unsaturated soils and the building foundation Attenuation in the building due to exchange with ambient air. This conceptual model is based on the J&E model. The U.S. EPA VI guidance was developed using this conceptual model of vapor intrusion. Slide Presentation: Describe the conventional conceptual model for vapor intrusion. Key Points: This conceptual model does not distinguish between petroleum and chlorinated VOCs. The model assumes an infinite source of VOCs The model does not account for biodegradation in the vadose zone. The model does not reflect industry experience with petroleum vapor intrusion impacts (see next slide). Mechanical ventilation can create localized or building-wide pressure differences that drive air flow. KEY POINT:

Differential Pressure (Pascals) Pressure Gradient Measurements: School Building, Houston, Texas Neg. Pressure Pos. Pressure Pressure Transducer Differential Pressure (Pascals) KEY POINT: Pressure gradient frequently switches between positive and negative within a single day. Time (July 14-15, 2005)

Positive pressure: HVAC High north wind & low atmospheric pressure Pressure Gradient Measurements: Tropical Storm Cindy Positive pressure: HVAC High south wind Pressure Transducer Differential Pressure (Pascasl) Pos. Pressure Neg. Pressure High north wind & low atmospheric pressure Test Site Storm Track: TS Cindy Time (July 5-6, 2005) KEY POINT: Pressure gradients potentially influenced by wide variety of factors. Measurements document non-representative sampling conditions.

INTERPRETATION OF VOC DATA Interpretation of VOC Measurements PRESSURE CONDITION INTERPRETATION OF VOC DATA Negative Pressure “ Worst Case” VI conditions. No current VOC transport from subsurface. Indoor VOCs due to background sources. Positive Pressure Bi-directional VOC transport. Carefully consider potential sources of measured indoor and sub-slab VOCs. Pressure Reversal Pressure gradients drive VOC transport. Multiple indoor VOC sampling events may be needed to measure VI. KEY POINT:

Typical Building VI Investigation: Outdoor, Indoor, and Sub-Slab Sampling Sub-Slab Sampling Data at Apartment Complex KEY POINT: Concurrent sampling of sub-slab, indoor air, and outdoor air.

Vapor Sampling: No Vapor Intrusion VOC Concentration (ug/m3) at Residence in Illinois INDOOR AIR AMBIENT AIR BELOW SLAB S

Common indoor sources of VOCs Used as air freshener and indoor pesticide for moths and carpet beetles. p-Dichloro-benzene Petroleum-based solvents, paints, glues, gasoline from attached garages. BTEX Emitted from molded plastic objects (e.g., toys, Christmas decorations). 1,2-DCA Even at sites with no subsurface source, these chemicals will commonly be detected in indoor air and sub-slab samples. KEY POINT: 1,2-DCA = 1,2-dichloroethane

VOC Transport Model: Bidirectional Flow Model simulates advective transport of chemicals between building air and subsurface soil through building slab. Positive Pressure Negative Pressure

BIDIRECTIONAL VOC TRANSPORT Model Results: Transient Indoor VOC Source VOC Conc. vs. Time: Transient Source Indoor PRESSURE Sub-Slab BIDIRECTIONAL VOC TRANSPORT KEY POINT: VOCs from building can be trapped below slab. Vapors trapped below slab

Vapor Intrusion: Investigation of Buildings l United States Regulatory Framework l Spatial and Temporal Variability l Impact of Indoor Sources on VI Investigations l Air Flow and VOC Migration Around Buildings Controlled Investigation of Vapor Intrusion in Buildings l Conclusions and Recommendations

Study Design: Sampling Program MEASUREMENT PROGRAM: Measure VOC concentrations in and around building under baseline and induced negative pressure conditions. Samples per Building SF6 MEDIUM Analyses Ambient Air VOCs, Radon 1 - 3 s Slide Topic: Conceptual model for vapor intrusion The standard conceptual model of vapor intrusion has the following key elements: Partitioning between the source and soil vapors. An infinite source of VOCs is assumed (i.e., no mass flux or mass balance considerations) Diffusion and advection (but not biodegradation) through unsaturated soils and the building foundation Attenuation in the building due to exchange with ambient air. This conceptual model is based on the J&E model. The U.S. EPA VI guidance was developed using this conceptual model of vapor intrusion. Slide Presentation: Describe the conventional conceptual model for vapor intrusion. Key Points: This conceptual model does not distinguish between petroleum and chlorinated VOCs. The model assumes an infinite source of VOCs The model does not account for biodegradation in the vadose zone. The model does not reflect industry experience with petroleum vapor intrusion impacts (see next slide). s 1.5 s Indoor Air VOCs, Radon, SF6 3 - 5 Radon VOCs, Radon, SF6 Sub-slab 3 - 5

Study Design: Building Pressure Sample Event 1: Baseline Conditions Sample Event 2: Induced Negative Pressure TIME Building Pressure 0.5 -2.5 Slide Topic: Conceptual model for vapor intrusion The standard conceptual model of vapor intrusion has the following key elements: Partitioning between the source and soil vapors. An infinite source of VOCs is assumed (i.e., no mass flux or mass balance considerations) Diffusion and advection (but not biodegradation) through unsaturated soils and the building foundation Attenuation in the building due to exchange with ambient air. This conceptual model is based on the J&E model. The U.S. EPA VI guidance was developed using this conceptual model of vapor intrusion. Slide Presentation: Describe the conventional conceptual model for vapor intrusion. Key Points: This conceptual model does not distinguish between petroleum and chlorinated VOCs. The model assumes an infinite source of VOCs The model does not account for biodegradation in the vadose zone. The model does not reflect industry experience with petroleum vapor intrusion impacts (see next slide). subslab fill soil soil

Study Design: Test Site Slide Topic: Conceptual model for vapor intrusion The standard conceptual model of vapor intrusion has the following key elements: Partitioning between the source and soil vapors. An infinite source of VOCs is assumed (i.e., no mass flux or mass balance considerations) Diffusion and advection (but not biodegradation) through unsaturated soils and the building foundation Attenuation in the building due to exchange with ambient air. This conceptual model is based on the J&E model. The U.S. EPA VI guidance was developed using this conceptual model of vapor intrusion. Slide Presentation: Describe the conventional conceptual model for vapor intrusion. Key Points: This conceptual model does not distinguish between petroleum and chlorinated VOCs. The model assumes an infinite source of VOCs The model does not account for biodegradation in the vadose zone. The model does not reflect industry experience with petroleum vapor intrusion impacts (see next slide). TEST SITE: Three single-family residences over a TCE plume near Hill AFB in Utah

Cross-Foundation Pressure Gradient Change in Air Exchange Rate (AER) Study Results: Impact of Depressurization on Air Flow Cross-Foundation Pressure Gradient Change in Air Exchange Rate (AER) Baseline Depressure AER Ratio (Depressure/ Baseline) 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 Res. #1 Res. #2 Res. #3 Gradient (Pa) Slide Topic: Conceptual model for vapor intrusion The standard conceptual model of vapor intrusion has the following key elements: Partitioning between the source and soil vapors. An infinite source of VOCs is assumed (i.e., no mass flux or mass balance considerations) Diffusion and advection (but not biodegradation) through unsaturated soils and the building foundation Attenuation in the building due to exchange with ambient air. This conceptual model is based on the J&E model. The U.S. EPA VI guidance was developed using this conceptual model of vapor intrusion. Slide Presentation: Describe the conventional conceptual model for vapor intrusion. Key Points: This conceptual model does not distinguish between petroleum and chlorinated VOCs. The model assumes an infinite source of VOCs The model does not account for biodegradation in the vadose zone. The model does not reflect industry experience with petroleum vapor intrusion impacts (see next slide). soil subslab fill KEY POINT: Induction of negative building pressure resulted in 3 to 6-fold increase in air exchange rate.

(Sub-slab/Indoor air) (Sub-slab/Indoor air) Study Results: Chemical Concentration Ratios Baseline Samples Depressurization Samples SS Source Indoor Source SS Source Indoor Source Concentration Ratio (Sub-slab/Indoor air) Concentration Ratio (Sub-slab/Indoor air) Slide Topic: Conceptual model for vapor intrusion The standard conceptual model of vapor intrusion has the following key elements: Partitioning between the source and soil vapors. An infinite source of VOCs is assumed (i.e., no mass flux or mass balance considerations) Diffusion and advection (but not biodegradation) through unsaturated soils and the building foundation Attenuation in the building due to exchange with ambient air. This conceptual model is based on the J&E model. The U.S. EPA VI guidance was developed using this conceptual model of vapor intrusion. Slide Presentation: Describe the conventional conceptual model for vapor intrusion. Key Points: This conceptual model does not distinguish between petroleum and chlorinated VOCs. The model assumes an infinite source of VOCs The model does not account for biodegradation in the vadose zone. The model does not reflect industry experience with petroleum vapor intrusion impacts (see next slide). Residence #1 Residence #2 Residence #3 Sub-slab to indoor air concentration ratio provides an indication of the likely source of the chemical. However, multiple sources may contribute to indoor air impact. KEY POINT:

Study Results: Volatile Chemical Detection Frequency Indoor Air Samples Sub-slab Gas Samples Detection Frequency Detection Frequency Slide Topic: Conceptual model for vapor intrusion The standard conceptual model of vapor intrusion has the following key elements: Partitioning between the source and soil vapors. An infinite source of VOCs is assumed (i.e., no mass flux or mass balance considerations) Diffusion and advection (but not biodegradation) through unsaturated soils and the building foundation Attenuation in the building due to exchange with ambient air. This conceptual model is based on the J&E model. The U.S. EPA VI guidance was developed using this conceptual model of vapor intrusion. Slide Presentation: Describe the conventional conceptual model for vapor intrusion. Key Points: This conceptual model does not distinguish between petroleum and chlorinated VOCs. The model assumes an infinite source of VOCs The model does not account for biodegradation in the vadose zone. The model does not reflect industry experience with petroleum vapor intrusion impacts (see next slide). Baseline Samples Depressurization Samples KEY POINT: All chemicals commonly detected in indoor air samples. Chemicals w/ subsurface sources (Radon and TCE) more commonly detected in sub-slab samples. Note: Detection frequency is for combined sample set from all three residences.

VOC Conc. in sub-slab gas Study Results: Impact of Depressurization on VOC Concentration Subsurface Source Indoor Source Concentration Ratio (Depressurization/ Baseline) 10 10 Radon TCE 1,2-DCA PCE VOC Conc. in indoor air Concentration Ratio 1 1 Baseline) (Depressurization/ 0.1 0.1 Res. #1 Res. #2 Res. #3 Res. #1 Res. #2 Res. #3 Location Location 0.1 1 10 Res. #1 Res. #2 Res. #3 Location Concentration Ratio (Depressurization/ Baseline) 10 Slide Topic: Conceptual model for vapor intrusion The standard conceptual model of vapor intrusion has the following key elements: Partitioning between the source and soil vapors. An infinite source of VOCs is assumed (i.e., no mass flux or mass balance considerations) Diffusion and advection (but not biodegradation) through unsaturated soils and the building foundation Attenuation in the building due to exchange with ambient air. This conceptual model is based on the J&E model. The U.S. EPA VI guidance was developed using this conceptual model of vapor intrusion. Slide Presentation: Describe the conventional conceptual model for vapor intrusion. Key Points: This conceptual model does not distinguish between petroleum and chlorinated VOCs. The model assumes an infinite source of VOCs The model does not account for biodegradation in the vadose zone. The model does not reflect industry experience with petroleum vapor intrusion impacts (see next slide). Radon TCE SF6 Benzene VOC Conc. in sub-slab gas Concentration Ratio (Depressurization/ 1 Baseline) 0.1 Res. #1 Res. #2 Res. #3 Location

Study Results: Impact on VOC Conc. BUILDING Air Exchange VOCs from subsurface source VOCs from indoor source (DCA, PCE, SF6, Benzene) (TCE, Radon) VOC conc. in indoor air Slide Topic: Conceptual model for vapor intrusion The standard conceptual model of vapor intrusion has the following key elements: Partitioning between the source and soil vapors. An infinite source of VOCs is assumed (i.e., no mass flux or mass balance considerations) Diffusion and advection (but not biodegradation) through unsaturated soils and the building foundation Attenuation in the building due to exchange with ambient air. This conceptual model is based on the J&E model. The U.S. EPA VI guidance was developed using this conceptual model of vapor intrusion. Slide Presentation: Describe the conventional conceptual model for vapor intrusion. Key Points: This conceptual model does not distinguish between petroleum and chlorinated VOCs. The model assumes an infinite source of VOCs The model does not account for biodegradation in the vadose zone. The model does not reflect industry experience with petroleum vapor intrusion impacts (see next slide). VOC conc. in sub-slab gas

Impact of Building Pressure on Evaluation of Vapor Intrusion Building Depressurization: Project Findings Cia Low Pressure High Pressure “Worst Case” Vapor Intrusion n Building depressurization does NOT appear to increase the magnitude of vapor intrusion. Impact of Building Pressure on Evaluation of Vapor Intrusion n Building depressurization improves ability to detect vapor intrusion by increasing the contrast between VOCs from indoor vs. subsurface sources. KEY POINT: Use building depressurization to increase contrast between indoor and subsurface sources of VOCs.

Vapor Intrusion: Investigation of Buildings l United States Regulatory Framework l Spatial and Temporal Variability l Impact of Indoor Sources on VI Investigations l Air Flow and VOC Migration Around Buildings l Controlled Investigation of Vapor Intrusion in Buildings Recommendations

Vapor Intrusion: Recommendations l General Strategy l Groundwater Sampling l Soil Gas Sampling l Indoor Air Sampling l Non-VOC Measurements l Typical Building Sampling Program

It’s Background, Stupid Cartridges are Funky, Summas are Re-Used VOCs: Practical Tips from the Field n VOCs are pervasive. You will always find hits in indoor air. n Use radon as a tracer to control for background. It’s Background, Stupid For Petroleum, Run Full VOC Scan n Run full Method T0-15 scan to be able to distinguish petroleum hydrocarbon composition of soil vapor vs. indoor air. n Sorbent cartridges affected by moisture, less repeatable. n Summa canister preferable, but have individually-certified clean. Summa Canister Cartridges are Funky, Summas are Re-Used

Accounting for Variability Understand variability in VOC concentration: Single sample can accurately characterize well-mixed space. 1) Indoor Air: Consider multiple measurement locations and sample events: Separate sample events by months Evaluate uncertainly based on observed variability 2) Subsurface: Skip samples to don’t increase knowledge: (e.g., multiple indoor samples; daily resamples.) KEY POINT:

Vapor Intrusion: Recommendations l General Strategy l Groundwater Sampling l Soil Gas Sampling l Indoor Air Sampling l Non-VOC Measurements l Typical Building Sampling Program

Key Physical Processes at GW Interface Groundwater Interface Key Physical Processes at GW Interface Evapotranspiration Exxon has developed Best Practice guides for collection of indoor air and soil gas samples (discussed in more detail in following slides) to ensure that sampling is conducted in a consistent manner across Exxon sites.

Distribution of TCE in Shallow Groundwater Based on >150 water table samples Exxon has developed Best Practice guides for collection of indoor air and soil gas samples (discussed in more detail in following slides) to ensure that sampling is conducted in a consistent manner across Exxon sites. KEY POINT: VOC distribution at water table is difficult to predict and may be very different from deeper GW plume. Graphic from presentation by Bill Wertz (NYSDEC) made at ESTCP-SERDP Conference, December 2008.

Groundwater Sampling: Key Considerations Exxon has developed Best Practice guides for collection of indoor air and soil gas samples (discussed in more detail in following slides) to ensure that sampling is conducted in a consistent manner across Exxon sites. KEY POINT: - Understand physical processes at water table. - For vapor intrusion, collect water samples from top of water table.

Vapor Intrusion: Recommendations l General Strategy l Groundwater Sampling l Soil Gas Sampling l Indoor Air Sampling l Non-VOC Measurements l Typical Building Sampling Program

Soil Gas Sampling: Considerations Where Does Your Sample Come From? Goal: Minimize the flow of gas in subsurface due to sample collection Sample Volume: Lab often needs only 50 mL of sample. Use ≤1L sample vessel (not 6L Summa), if available. Purge Volume: Use small diameter sample lines to minimize purge volume. Sample Rate: Use lower flow rate in fine grain soils to minimize induced vacuum. Flexibility required to allow use of newly validated sample collection and analysis methods. KEY POINT:

Soil Gas Sample Collection: Scheme for Summa Canister

Shallower Sample Point Soil Gas Sampling: Sample Collection Pressure gauge Flow controller Example of temp point installed w/ geoprobe Shallower Sample Point Deeper Sample Point

Soil Gas Sampling: Leak Tracers Photo from Blayne Hartman Apply to towel and place in enclosure or wrap around fittings. Liquid Tracer • Examples: DFA, isopropyl alcohol, pentane • High concentrations in samples may cause elevated detection limits for target analytes (Check w/ lab before using) Photo from Todd McAlary Inject periodically or continuously into enclosure around fittings and sample point: Gas Tracer • Examples: Helium, SF6 • On-site analysis (helium) Potentially more quantitative DFA = 1,1-difluoroethane, SF6 = sulfur hexafluoride

Field Meter for Leak Tracer Soil Gas Sampling: Gas Phase Leak Tracer Leak Tracer Gas Sample Point Shroud Field Meter for Leak Tracer

Soil Gas Sampling: Summas vs. Sorbent Tubes Most accepted in U.S. Simple to use Less available outside U.S. Canisters are re-used, subject to carry-over contamination Summa Canisters More available world wide Better for SVOCs* Use is more complex - pump calibration - backpressure - breakthrough of COC - selection of sorbent Sorbent Tubes * = Analysis for SVOCs not typically required, but sometimes requested by regulators.

Summa vs Sorbent: Side-by-Side Results Comparison: Summa / Sorbent (ug/m3) SG-04 SG-02 SG-03 TCE 20.5 / 10.5 292 / 149 <2.7 / <1.7 PCE 3070 / 1357 22,200 / 5917 187 / 225 Even skilled practitioners see up to 4x difference between Summa and sorbet tube results. KEY POINT: Reference: Odencrantz et al., 2008, Canister v. Sorbent Tubes: Vapor Intrusion Test Method Comparison, Proceedings of the Sixth International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, California, May 2008. beacon-usa.com 1-800-878-5510 PHOTO PROVIDED BY:

Vapor Intrusion: Recommendations l General Strategy l Groundwater Sampling l Soil Gas Sampling l Indoor Air Sampling l Non-VOC Measurements l Typical Building Sampling Program

Indoor Sampling: Overview Sample Location Considerations Recommend sampling in lowest level and consider sampling next highest level Investigate COC patterns Consider sampling near potential indoor sources or preferential pathways Attached garage, industrial source Basement sump, bathroom pipes Collect at least one outdoor sample Compare indoor and outdoor Consider collection subslab samples (concurrent with indoor air samples) Compare indoor and subslab or near-slab

Indoor Sampling: Sample Locations Placement of samplers Place at breathing-level height Avoid registers, drafts Remember to sample for appropriate length of time Typically 24 hours for residential Typically 8-24 hours for occupational Collect indoor and subslab samples concurrently QA Samples: Collect greater of one duplicate per day or one per 20 samples. (Collect additional QA samples if required by regs.) NOTE: Little value to collect multiple samples in a single building zone (e.g. same room), unless collecting QA duplicates.

Sample Collection Sub-Slab Sampling Outdoor Air Sampling Measure VOC concentration below building foundation Document ambient conditions

Vapor Intrusion: Recommendations l General Strategy l Groundwater Sampling l Soil Gas Sampling l Indoor Air Sampling l Non-VOC Measurements l Typical Building Sampling Program

VI Investigation Methods: Non-VOC Measurements Naturally occurring tracer gas measures attenuation through building foundation. Radon Magnitude and duration of building pressure fluctuations: negative vs. positive building pressure. Building Pressure Rate of ambient air entry into building. Supports mass flux evaluations. Air Exchange Non-VOC measurements can be used to evaluate vapor intrusion while avoiding background VOC issues. KEY POINT:

Radon: Measurement Options Cost/ Sample $10-50 $100 $25-50 n Home Test Methods: Charcoal Canister, electret, alpha detector n Air Samples: Radon concentration measured at off-site lab * Indoor Air n Air Sample: Radon concentration measured at off-site lab * n Electret: Placed over hole in foundation (questionable accuracy) Sub-Foundation Key Point: n Radon analysis less expensive than VOC analysis ($200-250/sample for VOCs by TO-15). * Off-site analysis provided by Dr. Doug Hammond, University of Southern California

Radon (Ra) as Tracer for Foundation Attenuation Indoor Ra = 0.9 pCi/L Sub-slab Ra = 833 pCi/L Test Results AF Calculation AFss-ia = 0.9 - 0.3 833 = 0.00048 Ambient Ra = 0.3 pCi/L No common indoor sources of radon. Lower analytical costs compared to VOCs. Less bias caused by non-detect results indoors. Can be used for long-term testing (up to 6 months). BENEFITS:

Ventilation Standards Air Exchange: What ‘n How Air Exchange BUILDING Rate at which indoor air is replaced by ambient (fresh) air. What ESTIMATION METHODS Recommended ventilation rates for commercial building. Ventilation Standards ASHRAE Std. 62.1-2004 SF 6 Measure dilution of tracer gas to determine air exchange rate Tracer Gas WHY: n Better understand observed VOC attenuation. n Use value model or mass flux calculation. J&E = Johnson and Ettinger model.

Recommended Building Ventilation Rates ANSI / ASHRAE Standard 62.1 – 2004 Ventilation for Acceptable Indoor Air Quality Building Type Air Exchanges (per day) USEPA Default (Residential) 6 Office Space 12 Supermarket 17 Classroom 68 High Building Ventilation Restaurant 102 KEY POINT: Buildings designed for high density use will have high air exchange rates.

Air Exchange: Measured Values How: Test Building n Release tracer gas (SF6 or helium) into building at constant rate. n Measure steady-state concentration of gas in building. n Calculate air exchange based on release rate, concentration, and building volume. Site-specific measurement provides most accurate measure of air exchange under current operating conditions. KEY POINT:

Vapor Intrusion: Recommendations l General Strategy l Groundwater Sampling l Soil Gas Sampling l Indoor Air Sampling l Non-VOC Measurements l Typical Building Sampling Program

Residential Building Investigation: Recommended Sampling Program GAS MEASUREMENTS: Samples per Building MEDIUM Analyses Ambient Air VOCs, Radon 1 s s 1.5 s 1 - 2 (lowest level) Indoor Air VOCs, Radon Radon Sub-slab Gas Slide Topic: Conceptual model for vapor intrusion The standard conceptual model of vapor intrusion has the following key elements: Partitioning between the source and soil vapors. An infinite source of VOCs is assumed (i.e., no mass flux or mass balance considerations) Diffusion and advection (but not biodegradation) through unsaturated soils and the building foundation Attenuation in the building due to exchange with ambient air. This conceptual model is based on the J&E model. The U.S. EPA VI guidance was developed using this conceptual model of vapor intrusion. Slide Presentation: Describe the conventional conceptual model for vapor intrusion. Key Points: This conceptual model does not distinguish between petroleum and chlorinated VOCs. The model assumes an infinite source of VOCs The model does not account for biodegradation in the vadose zone. The model does not reflect industry experience with petroleum vapor intrusion impacts (see next slide). VOCs, Radon 3 - 5 For more definitive results, conduct sampling program under induced negative pressure and positive pressure building conditions. BUILDING PRESSURE:

Identifying Sites Needing VI Mitigation Guidelines for Vapor Intrusion Evaluation Identifying Sites Needing VI Mitigation Indoor Air > Risk Limit? > Std? 1 Indoor air conc’s. > applicable limits. Subslab Vapors > Risk Limit S 2 Subslab vapors > applicable limits. >Std? air Building Pressure Supports VI 3 Pressure gradient supports soil gas flow into building SG Swell ! Step-wise approach can help distinguish VI sources from indoor sources. KEY POINT:

Identifying Sites Needing VI Mitigation Guidelines for Vapor Intrusion Evaluation Identifying Sites Needing VI Mitigation Indoor Air > Risk Limit? Cause = Indoor/Ambient Source? > Std? 1 6 5 4 Indoor air conc’s. > applicable limits. Data set shows clear indoor/ambient source. Subslab Vapors > Risk Limit Radon Data Suggest Actual VI? S 2 Rn S Rn Subslab vapors > applicable limits. Rn attenuation factor suggests VOCs may enter house, too. >Std? Rn air Building Pressure Supports VI Pressurization shows Actual VI ? air 3 Pressure gradient supports soil gas flow into building Pressurization and depressurization of bldg. show VI through slab. P SG Swell ! Step-wise approach can help distinguish VI sources from indoor sources. KEY POINT:

Acknowledgements Special Thanks to: Support provided by by the Environmental Security Technology Certification Program (ESTCP) Projects ER-0423 and ER-0707 Project Reports: www.estcp.org (Search “0423” & “0707”) Special Thanks to: Tim Nickels and Danny Bailey (GSI) Sam Brock (AFCEE) Kyle Gorder (Hill AFB) Blayne Hartman David Folks (Envirogroup), Todd McAlary (Geosyntec)