1. 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
(713) 1 1

2. 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

3. 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:

4. 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

5. 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:

6. 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:

7. 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)

8. 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.

9. 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:

10. 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.

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

12. 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

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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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.

20. (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:

21. 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.

22. 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

23. 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

24. 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.

25. 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

26. 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

27. 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

28. 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:

29. 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

30. 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.

31. 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.

32. 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.

33. 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

34. 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:

35. Soil Gas Sample Collection: Scheme for Summa Canister

36. 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

37. 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

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

39. 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.

40. 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
PHOTO PROVIDED BY:

41. 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

42. 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

43. 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.

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

45. 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

46. 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:

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

48. 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 =
833 =
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:

49. 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.
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.

50. 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.

51. 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:

52. 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

53. 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:

54. 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:

55. 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:

56. Acknowledgements Special Thanks to:
Support provided by by the Environmental Security Technology Certification Program (ESTCP) Projects ER-0423 and ER-0707
Project Reports: (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)