vapor intrusion: investigation of buildings
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Vapor Intrusion: Investigation of Buildings. SITE BUILDING. Air Exchange. source area. 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 - PowerPoint PPT PresentationTRANSCRIPT
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 CenterMonday, March 9, 2009
GSI ENVIRONMENTAL INC.Houston, Texaswww.gsi-net.com (713) 522-6300 [email protected]
source area
Air Exchange
SITE BUILDING
2
Vapor Intrusion: Investigation of BuildingsVapor Intrusion: Investigation of Buildings
United States Regulatory Framework
Spatial and Temporal Variability
Impact of Indoor Sources on VI Investigations
Air Flow and VOC Migration Around Buildings
Controlled Investigation of Vapor Intrusion in Buildings
Conclusions and Recommendations
United States Regulatory Framework
Spatial and Temporal Variability
Impact of Indoor Sources on VI Investigations
Air Flow and VOC Migration Around Buildings
Controlled Investigation of Vapor Intrusion in Buildings
Conclusions and Recommendations
4
Effect of Building Pressure on VOC Transport
Lower building pressure
Residence in winter(chimney effect); bathroom, kitchen vents
Flow in
EXAMPLES
Gas flow from subsurface into building
High Pressure
Low Pressure
DOWNWARD VOC TRANSPORT
LowPressure
High Pressure
UPWARD VOC TRANSPORT
Higher building pressure
Building HVAC designed to maintain positive pressure
Flow out
EXAMPLES
Gas flow from building into subsurface
Variable building pressure
Barometric pumping; variable wind effects
Reversible flow
EXAMPLES
Bi-directional flow between building and subsurface
5
Effect of Weather on Building Pressure
COLD WEATHERCOLD WEATHER
Temperature and wind create pressure gradients that influence air movement in and around buildings.
Stack Effect: Warm airleaks through roof creating negative building pressure
Stack Effect: Warm airleaks through roof creating negative building pressure
soilsoil subslab fill
+ +
- -
WINDWIND
Wind on Building creates pressure gradient that results in air flow.
Wind on Building creates pressure gradient that results in air flow.
soilsoil
wind
++
++
subslab fill
KEY POINT:
6
Effect of Mechanical Ventilation
Mechanical ventilation can create localized or building-wide pressure differences that drive air flow.
KEY POINT:
MECHANICAL VENTILATION
Examples in Houses:- HVAC system
- Exhaust fans (kitchen, bath)- Furnace- Other combustion appliances (water heater, cloths dryer, etc)
7
Pressure Gradient Measurements:School Building, Houston, Texas
Dif
fere
nti
al P
ress
ure
(P
asca
ls)
Time (July 14-15, 2005)
-40
-30
-20
-10
0
10
20
30
40
6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 9:00 12:00 15:00
Neg. Pressure
Pos. Pressure
Pressure gradient frequently switches between positive and negative within a single day.
KEY POINT:
Pressure Transducer
8
Pressure gradients potentially influenced by wide variety of factors. Measurements document non-representative sampling conditions.
Pressure Gradient Measurements:Tropical Storm Cindy
KEY POINT:
Pressure Transducer
Dif
fere
nti
al
Pre
ssu
re
(Pas
casl
)
-80
-60
-40
-20
0
20
40
60
80
13:00 17:48 22:36 3:24 8:12 13:00 17:48
Time (July 5-6, 2005)
High south wind
High north wind & low
atmospheric pressure
Positive pressure:
HVAC
Neg. Pressure
Pos. Pressure
Test Site
Storm Track: TS Cindy
9
Negative PressureNegative Pressure
Positive PressurePositive Pressure
“ Worst Case” VI conditions.
No current VOC transport from subsurface. Indoor VOCs due to background sources.
Bi-directional VOC transport. Carefully consider potential sources of measured indoor and sub-slab VOCs.
Pressure ReversalPressure Reversal
-8
-6
-4
-2
0
2
4
6
0.00 10.00 20.00
-6
-4
-2
0
2
4
6
0.00 10.00 20.00
-6
-4
-2
0
2
4
6
0.00 10.00 20.00
Interpretation of VOC Measurements
PRESSURE CONDITION
INTERPRETATION OF VOC DATA
Pressure gradients drive VOC transport. Multiple indoor VOC sampling events may be needed to measure VI.
KEYPOINT:KEYPOINT:
10
Typical Building VI Investigation: Outdoor, Indoor, and Sub-Slab SamplingTypical Building VI Investigation: Outdoor, Indoor, and Sub-Slab Sampling
Sub-Slab Sampling Dataat Apartment Complex
Concurrent sampling of sub-slab, indoor air, and outdoor air.
KEY POINT:
11
0.1
1
10
100
1000
10000
Vapor Sampling: No Vapor IntrusionVapor Sampling: No Vapor Intrusion
INDOOR AIR
VOC Concentration (ug/m3) at Residence in Illinois
S
BELOW SLAB
AMBIENT AIR
12
KEY POINT:
Common indoor sources of VOCs
p-Dichloro-benzene
Used as air freshener and indoor pesticide for moths and carpet beetles.
Petroleum-based solvents, paints, glues, gasoline from attached garages.
BTEX
Even at sites with no subsurface source, these chemicals will commonly be detected in indoor air and sub-slab samples.
Emitted from molded plastic objects (e.g., toys, Christmas decorations).
1,2-DCA
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 PressurePositive Pressure
Negative PressureNegative Pressure
14
Model Results: Transient Indoor VOC SourceModel Results: Transient Indoor VOC Source
VOCs from building can be trapped below slab.
KEY POINT:
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
1.E+03
0 1 2 3 4 5
Time (days)
Predicted VOC
Concentration (ug/m3)
Indoor Air
Subsurface
Detection limit
Phase 1 Phase 2 Phase 3
Phase 4
VOC Conc. vs. Time: Transient SourceIndoor
Sub-Slab
BIDIRECTIONAL VOC TRANSPORT
Vapors trapped below slab
PRESSURE
15
Vapor Intrusion: Investigation of BuildingsVapor Intrusion: Investigation of Buildings
United States Regulatory Framework
Spatial and Temporal Variability
Impact of Indoor Sources on VI Investigations
Air Flow and VOC Migration Around Buildings
Controlled Investigation of Vapor Intrusion in Buildings
Conclusions and Recommendations
United States Regulatory Framework
Spatial and Temporal Variability
Impact of Indoor Sources on VI Investigations
Air Flow and VOC Migration Around Buildings
Controlled Investigation of Vapor Intrusion in Buildings
Conclusions and Recommendations
16
Study Design: Sampling Program
MEASUREMENT PROGRAM:
Measure VOC concentrations in and around building under baseline and induced negative pressure conditions.
1.5ss ss ss
SF6SF6
RadonRadon
VOCs, Radon
VOCs, Radon, SF6
VOCs, Radon,
SF6
Analyses
Ambient Air
Indoor Air
Sub-slab
MEDIUMSamples
per Building
1 - 3
3 - 5
3 - 5
17
Study Design: Building Pressure
Sample Event 1: Baseline ConditionsSample Event 1: Baseline Conditions
Sample Event 2: Induced Negative PressureSample Event 2: Induced Negative Pressure
soilsoilsubslab fill
-2.50.5
TIME
Bu
ild
ing
Pre
ssu
re
TIME
Bu
ild
ing
Pre
ssu
re
18
Study Design: Test Site
TEST SITE:
Three single-family residences over a TCE plume near Hill AFB in Utah
19
Study Results: Impact of Depressurization on Air Flow
soilsoil
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
Res. #1
Res. #2
Res. #3
AE
R R
atio
(Dep
res
sure
/B
asel
ine)
subslab fill
Cross-Foundation Pressure GradientCross-Foundation Pressure Gradient
-1.5
-1
-0.5
0
0.5
1
1.5
4/30/2007
12:00
4/30/2007
18:00
5/1/2007
0:00
5/1/2007
6:00
5/1/2007
12:00
5/1/2007
18:00
5/2/2007
0:00
5/2/2007
6:00
5/2/2007
12:00
5/2/2007
18:00
5/3/2007
0:00
Time
Gra
die
nt
(Pa)
Baseline Depressure
Change in Air Exchange
Rate (AER)
Induction of negative building pressure resulted in 3 to 6-fold increase in air exchange rate.
KEYPOINT:KEYPOINT:
20
Study Results: Chemical Concentration Ratios
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.
KEYPOINT:KEYPOINT:
Co
nce
ntr
atio
n R
atio
(Su
b-s
lab
/In
do
or
air)
Baseline Samples Depressurization Samples
Residence #1 Residence #2
0.01
0.1
1
10
100
1000
RadonTCE SF6
1,2-DCA
PCE
Benzene
SS Source Indoor Source
0.01
0.1
1
10
100
1000
RadonTCE SF6
1,2-DCA
PCE
Benzene
Co
nce
ntr
atio
n R
atio
(Su
b-s
lab
/In
do
or
air) SS Source Indoor Source
Residence #3
21
Study Results: Volatile Chemical Detection Frequency
All chemicals commonly detected in indoor air samples. Chemicals w/ subsurface sources (Radon and TCE) more commonly detected in sub-slab samples.
KEYPOINT:KEYPOINT:
0%10%20%30%40%50%60%70%80%90%
100%
RadonTCE SF6
1,2-DCA
PCE
Benzene
0%10%20%30%40%50%60%70%80%90%
100%
RadonTCE SF6
1,2-DCA
PCE
Benzene
Det
ecti
on
Fre
qu
ency
Det
ecti
on
Fre
qu
ency
Indoor Air Samples Sub-slab Gas Samples
Baseline Samples Depressurization Samples
Note: Detection frequency is for combined sample set from all three residences.
22
Study Results: Impact of Depressurization on VOC Concentration
Res. #1 Res. #2 Res. #3
Location
0.1
1
10
Co
nc
en
tra
tio
n
Ra
tio
(De
pre
ss
uri
zati
on
/B
as
eli
ne
)
Location
0.1
1
10
Res. #1 Res. #2 Res. #3
Co
nc
en
tra
tio
n R
ati
o
(De
pre
ss
uri
zati
on
/B
as
eli
ne
)0.1
1
10
Res. #1 Res. #2 Res. #3
Location
Co
nc
en
tra
tio
n
Ra
tio
(De
pre
ss
uri
zati
on
/B
ase
lin
e)
0.1
1
10
Res. #1 Res. #2 Res. #3
Location
Co
nc
en
tra
tio
n R
ati
o
(De
pre
ss
uri
zati
on
/B
as
eli
ne
)
1,2-DCAPCE
SF6
Benzene
RadonTCE
RadonTCE
Subsurface Source Indoor Source
VOCConc.
in sub-slab gas
VOCConc.
in indoor
air
23
BUILDING
Air Exchange
Study Results: Impact on VOC Conc.
VOCconc. in sub-slab
gas
VOCconc. in indoor
air
VOCs from indoor source
VOCs from subsurface
source(DCA, PCE, SF6,
Benzene)(TCE, Radon)
24
Building depressurization does NOT appear to increase the magnitude of vapor intrusion.
Building depressurization improves ability to detect vapor intrusion by increasing the contrast between VOCs from indoor vs. subsurface sources.
Impact of Building
Pressure on Evaluation of Vapor Intrusion
Building Depressurization: Project Findings
“Worst Case”Vapor
Intrusion
CiaCia
LowPressure
High Pressure
Use building depressurization to increase contrast between indoor and subsurface sources of VOCs.
KEYPOINT:KEYPOINT:
25
Vapor Intrusion: Investigation of BuildingsVapor Intrusion: Investigation of Buildings
United States Regulatory Framework
Spatial and Temporal Variability
Impact of Indoor Sources on VI Investigations
Air Flow and VOC Migration Around Buildings
Controlled Investigation of Vapor Intrusion in Buildings
Recommendations
United States Regulatory Framework
Spatial and Temporal Variability
Impact of Indoor Sources on VI Investigations
Air Flow and VOC Migration Around Buildings
Controlled Investigation of Vapor Intrusion in Buildings
Recommendations
26
Vapor Intrusion: RecommendationsVapor Intrusion: Recommendations
General Strategy
Groundwater Sampling
Soil Gas Sampling
Indoor Air Sampling
Non-VOC Measurements
Typical Building Sampling Program
General Strategy
Groundwater Sampling
Soil Gas Sampling
Indoor Air Sampling
Non-VOC Measurements
Typical Building Sampling Program
27
VOCs: Practical Tips from the Field
VOCs are pervasive. You will always find hits in indoor air.
Use radon as a tracer to control for background.
It’s Background,
Stupid
Cartridges are Funky,
Summas are Re-Used
Run full Method T0-15 scan to be able to distinguish petroleum hydrocarbon composition of soil vapor vs. indoor air.
For Petroleum,Run Full VOC Scan
Sorbent cartridges affected by moisture, less repeatable.
Summa canister preferable, but have individually-certified clean. Summa
CanisterSumma Canister
Understand variability in VOC concentration:
1) Indoor Air:
2) Subsurface:
Single sample can accurately characterize well-mixed space.
Consider multiple measurement locations and sample events:
- Separate sample events by months
- Evaluate uncertainly based on observed variability
Accounting for Variability
Skip samples to don’t increase knowledge: (e.g., multiple indoor samples; daily resamples.)
KEY POINT:
29
Vapor Intrusion: RecommendationsVapor Intrusion: Recommendations
General Strategy
Groundwater Sampling
Soil Gas Sampling
Indoor Air Sampling
Non-VOC Measurements
Typical Building Sampling Program
General Strategy
Groundwater Sampling
Soil Gas Sampling
Indoor Air Sampling
Non-VOC Measurements
Typical Building Sampling Program
30
Key Physical Processes at GW InterfaceGroundwater InterfaceGroundwater Interface
Aquifer
SourceArea
SourceArea
Clean waterlense
Aquifer
Evapotranspiration
31
Distribution of TCE in Shallow Groundwater
Based on >150 water table samples
VOC distribution at water table is difficult to predict and may be very different from deeper GW plume.
KEY POINT:
Graphic from presentation by Bill Wertz (NYSDEC) made at ESTCP-SERDP Conference, December 2008.
32
Groundwater Sampling: Key Considerations
Aquifer
SourceArea
SourceArea
Clean waterlense
Aquifer
- Understand physical processes at water table.- For vapor intrusion, collect water samples
from top of water table.
KEY POINT:
33
Vapor Intrusion: RecommendationsVapor Intrusion: Recommendations
General Strategy
Groundwater Sampling
Soil Gas Sampling
Indoor Air Sampling
Non-VOC Measurements
Typical Building Sampling Program
General Strategy
Groundwater Sampling
Soil Gas Sampling
Indoor Air Sampling
Non-VOC Measurements
Typical Building Sampling Program
34
Soil Gas Sampling: Considerations
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.
Goal: Minimize the flow of gas in subsurface due to sample collection
Where Does Your Sample Come From?
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
Soil Gas Sampling: Sample Collection
Shallower Sample Point
Pressure gauge
Flow controller
Deeper Sample Point
37
Liquid Tracer
Apply to towel and place in enclosure or wrap around fittings.
• Examples: DFA, isopropyl alcohol, pentane
• High concentrations in samples may cause elevated detection limits for target analytes(Check w/ lab before using)
Gas Tracer
Inject periodically or continuously into enclosure around fittings and sample point:
• Examples: Helium, SF6
• On-site analysis (helium)• Potentially more quantitative
DFA = 1,1-difluoroethane, SF6 = sulfur hexafluoride Photo from Todd McAlary
Photo from Blayne Hartman
Soil Gas Sampling: Leak Tracers
38
Sample Point Shroud
Leak Tracer Gas
Field Meter for Leak Tracer
Soil Gas Sampling: Gas Phase Leak Tracer
39
Summa Canisters
Soil Gas Sampling: Summas vs. Sorbent Tubes
Sorbent Tubes
Most accepted in U.S. Simple to use
Less available outside U.S. Canisters are re-used,
subject to carry-over contamination
More available world wide Better for SVOCs*
Use is more complex- pump calibration- backpressure - breakthrough of COC- selection of sorbent
* = Analysis for SVOCs not typically required, but sometimes requested by regulators.
40
Results Comparison: Summa / Sorbent (ug/m3)
Summa vs Sorbent: Side-by-Side
beacon-usa.com1-800-878-5510
PHOTO PROVIDED BY: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.
TCE
PCE
SG-02 SG-03
20.5 / 10.5 292 / 149
3070 / 1357 22,200 / 5917
<2.7 / <1.7
187 / 225
SG-04
KEYPOINT:
Even skilled practitioners see up to 4x difference between Summa and sorbettube results.
41
Vapor Intrusion: RecommendationsVapor Intrusion: Recommendations
General Strategy
Groundwater Sampling
Soil Gas Sampling
Indoor Air Sampling
Non-VOC Measurements
Typical Building Sampling Program
General Strategy
Groundwater Sampling
Soil Gas Sampling
Indoor Air Sampling
Non-VOC Measurements
Typical Building Sampling Program
42
Sample Location ConsiderationsSample Location Considerations
■ Collect at least one outdoor sampleCollect at least one outdoor sample► Compare indoor and outdoorCompare indoor and outdoor
■ Consider collection subslab samples Consider collection subslab samples (concurrent with indoor air samples)(concurrent with indoor air samples)
► Compare indoor and subslab or near-slabCompare indoor and subslab or near-slab
■ Recommend sampling in lowest level and consider Recommend sampling in lowest level and consider sampling next highest levelsampling next highest level
► Investigate COC patternsInvestigate COC patterns
■ Consider sampling near potential indoor sources Consider sampling near potential indoor sources or preferential pathwaysor preferential pathways
► Attached garage, industrial sourceAttached garage, industrial source► Basement sump, bathroom pipesBasement sump, bathroom pipes
Indoor Sampling: Overview
43
■ Placement of samplersPlacement of samplers
NOTE:Little value to collect multiple samples in a single building zone (e.g. same room), unless collecting QA duplicates.
■ Place at breathing-level heightPlace at breathing-level height■ Avoid registers, draftsAvoid registers, drafts■ Remember to sample for appropriate Remember to sample for appropriate
length of timelength of time► Typically 24 hours for residentialTypically 24 hours for residential► Typically 8-24 hours for occupationalTypically 8-24 hours for occupational
Collect indoor and subslab samples Collect indoor and subslab samples concurrentlyconcurrently
QA SamplesQA Samples: : Collect greater of one Collect greater of one duplicate per day or one per 20 samples. duplicate per day or one per 20 samples. (Collect additional QA samples if required by regs.)(Collect additional QA samples if required by regs.)
Indoor Sampling: Sample Locations
44
Sub-Slab Sampling
Sample CollectionSample Collection
Measure VOC concentration below building foundation
Outdoor Air Sampling
Document ambient conditions
45
Vapor Intrusion: RecommendationsVapor Intrusion: Recommendations
General Strategy
Groundwater Sampling
Soil Gas Sampling
Indoor Air Sampling
Non-VOC Measurements
Typical Building Sampling Program
General Strategy
Groundwater Sampling
Soil Gas Sampling
Indoor Air Sampling
Non-VOC Measurements
Typical Building Sampling Program
46
VI Investigation Methods: VI Investigation Methods: Non-VOC MeasurementsNon-VOC Measurements
Non-VOC measurements can be used to evaluate vapor intrusion while avoiding background VOC issues.
Non-VOC measurements can be used to evaluate vapor intrusion while avoiding background VOC issues.
KEY POINT:KEY POINT:
RadonRadon
Building PressureBuilding Pressure
Naturally occurring tracer gas measures attenuation through building foundation.
Magnitude and duration of building pressure fluctuations: negative vs. positive building pressure.
Air ExchangeAir Exchange
Rate of ambient air entry into building. Supports mass flux evaluations.
47
Home Test Methods:Charcoal Canister, electret, alpha detector
Air Samples:Radon concentration measured at off-site lab *
Sub-Foundation
Indoor Air
Air Sample:Radon concentration measured at off-site lab *
Electret:Placed over hole in foundation (questionable accuracy)
* Off-site analysis provided by Dr. Doug Hammond, University of Southern California
Radon: Measurement OptionsRadon: Measurement Options
Cost/Sample
$10-50
$100
$100
$25-50
Key Point:Key Point:
Radon analysis less expensive than VOC analysis ($200-250/sample for VOCs by TO-15).
Radon analysis less expensive than VOC analysis ($200-250/sample for VOCs by TO-15).
48
BENEFITS:BENEFITS:
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).
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
49
Rate at which indoor air is replaced by ambient (fresh) air.
What
ASHRAEStd.
62.1-2004
SF 6SF 6
Air Exchange: What ‘n How
WHY: Better understand observed VOC attenuation. Use value model or mass flux calculation.
Recommended ventilation rates for commercial building.
Ventilation Standards
Tracer Gas
Measure dilution of tracer gas to determine air exchange rate
ESTIMATION METHODS
J&E = Johnson and Ettinger model.
Air Exchange
BUILDING
50
Recommended Building Ventilation Rates
KEYPOINT:
Buildings designed for high density use will have high air exchange rates.
ANSI / ASHRAE Standard 62.1 – 2004Ventilation for Acceptable Indoor Air Quality
Building Type
Building Type
Air Exchanges(per day)
Air Exchanges(per day)
USEPA Default (Residential)
Office Space
Supermarket
Classroom
Restaurant
6
12
17
68
102
High Building Ventilation
51
KEY POINT:
Site-specific measurement provides most accurate measure of air exchange under current operating conditions.
Test Building
How:
Release tracer gas (SF6 or helium) into building at constant rate.
Measure steady-state concentration of gas in building.
Calculate air exchange based on release rate, concentration, and building volume.
Air Exchange: Measured Values
52
Vapor Intrusion: RecommendationsVapor Intrusion: Recommendations
General Strategy
Groundwater Sampling
Soil Gas Sampling
Indoor Air Sampling
Non-VOC Measurements
Typical Building Sampling Program
General Strategy
Groundwater Sampling
Soil Gas Sampling
Indoor Air Sampling
Non-VOC Measurements
Typical Building Sampling Program
53
Residential Building Investigation: Recommended Sampling Program
BUILDING PRESSURE:
For more definitive results, conduct sampling program under induced negative pressure and positive pressure building conditions.
1.5ss ss ss
RadonRadon
VOCs, Radon
VOCs, Radon
VOCs, Radon
Analyses
Ambient Air
Indoor Air
Sub-slab Gas
MEDIUMSamples
per Building
1
1 - 2 (lowest level)
3 - 5
GAS MEASUREMENTS:
54
Guidelines for Vapor Intrusion Evaluation
Identifying Sites Needing VI Mitigation
KEY POINT:
Step-wise approach can help distinguish VI sources from indoor sources.
Swell !
Indoor Air > Risk Limit?
> Std?Indoor air conc’s. > applicable limits.
Subslab Vapors > Risk LimitSubslab vapors > applicable limits. >Std?
Pressure gradient supports soil gas flow into building
Building Pressure Supports VI
S
3
2
1
SG
air
55
Guidelines for Vapor Intrusion Evaluation
Identifying Sites Needing VI Mitigation
KEY POINT:
Step-wise approach can help distinguish VI sources from indoor sources.
Cause = Indoor/Ambient Source?Data set shows clear indoor/ambient source.Radon Data Suggest Actual VI?Rn attenuation factor suggests VOCs may enter house, too.
Pressurization and depressurization of bldg. show VI through slab.
Pressurization shows Actual VI ?
SRn
Rn
airP
Rn
Swell !
6
5
4Indoor Air > Risk Limit?
> Std?Indoor air conc’s. > applicable limits.
Subslab Vapors > Risk LimitSubslab vapors > applicable limits. >Std?
Pressure gradient supports soil gas flow into building
Building Pressure Supports VI
S
3
2
1
SG
air
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:
Acknowledgements
Tim Nickels and Danny Bailey (GSI)Sam Brock (AFCEE)Kyle Gorder (Hill AFB)Blayne HartmanDavid Folks (Envirogroup), Todd McAlary (Geosyntec)