vapor intrusion: investigation of buildings
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Vapor Intrusion: Investigation of Buildings
Overview of the US vapour intrusion framework, empirical attenuation factors, and the conceptual understanding of soil gas and
building dynamics
Vingsted CenterMonday, March 9, 2009
GSI ENVIRONMENTAL INC.Houston, Texaswww.gsi-net.com (713) 522-6300 temchugh@gsi-net.com
source area
Air Exchange
SITE BUILDING
2
Vapor Intrusion: Wazzat?
KEY POINT:
Vapor intrusion is the movement of volatile chemicals into buildings from below ground.
BUILDING
GW source area
Soil source
areaVapors in
subsurface
Effect on indoor air quality?
3
Indoor SourcesIndoor Sources
False PositivesFalse Positives
Difficulty separating vapor intrusion from indoor sources of VOCs:- Affects indoor and sub-slab samples
Low levels of VOCs often detected in soil gas and indoor air samples:- Summa carry over contamination- Lab contamination- Unexpected minor sources
High VariabilityHigh Variability
LIMITATION DETAILS
VOC measurements alone often provide a confusing picture of vapor intrusion.
KEYPOINT:KEYPOINT:
Limitations of VOC Measurements
Gas
ss
ssssss
High spatial and temporal variability:- Conservative assumptions OR- Large number of samples
Summa
Canister
Summa
Canister
IntroductionIntroduction
4
Physical Barriers to Vapor Intrusion
KEY POINT:
Non-VOC measurements can provide improved understanding of vapor intrusion.
IntroductionIntroduction
A B
A B
A BGroundwater Interface:(A) Clean water lens;(B) Saturated confining layer
Vadose Zone(A) High moisture contentfine-grained soil layer
(B) Aerobic Biodegradation
Aquifer
SourceArea
UnsaturatedSoil
5
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
6
Vapor Intrusion: Regulatory FrameworkVapor Intrusion: Regulatory Framework
USEPA Framework
State Regulations
Petroleum vs. Chlorinated VOCs
Site-Specific Screening
Mass Flux Evaluations
USEPA Framework
State Regulations
Petroleum vs. Chlorinated VOCs
Site-Specific Screening
Mass Flux Evaluations
7
Conceptual Model for Vapor Intrusion:
KEY POINT:
Regulatory guidance assumes vapor migration through soils and building foundation based on conservative assumptions.
Building Attenuation Due to Exchange with Ambient Air
Advection and Diffusion Through Unsaturated Soil and Building Foundation
Partitioning Between Source and Soil Vapor
Groundwater-Bearing
Unit
Air Exchange
BUILDING
Unsaturated Soil
3
2
1
Affected SoilAffected Soil
Affected GWAffected GW
Overview of USEPA VI GuidanceOverview of USEPA VI Guidance
8
NFA NFA NFA NFA NFA
Mitigation/Remediation
Typical Vapor Intrusion Screening Process
Step-wise VI investigation process recommended by most VI regulatory guidance.
KEY POINT
Chemicals could cause VI impact based on volatility and toxicity
CHEMICAL CRITERIA
GW conc. > VI screening levels
GW SCREENING
Soil gas/sub-slab conc. > VI screening levels
SOIL GAS/SUB-SLAB SCREENING
indoor air concentrations other measurements indicate vapor intrusion impact
INDOOR AIR TESTNG
No No No No
Yes Yes Yes Yes
Yes
No
Screening Steps Field Measurements
Current or future buildings within 10 - 30 m of edge of impact.
DISTANCE CRITERIA
9
Benzene
Ethylbenzene
USEPA VI Screening Values: Key COCs
Indoor Air (ug/m3)
Sub-slab (ug/m3)
0.31 3.1
2.2 22
3000MTBE 30000
Groundwater(mg/L)
Vinyl Chloride
Lindane
0.022TCE 0.22
0.28 2.8
0.0066 0.066
0.81PCE 8.1
* = Value based on MCL, risk-based number would be lower.
0.005*
0.70*
120
0.005*
0.002*
0.011
0.005*
KEY POINT:
Under EPA guidance, GW impacts above MCLs usually require VI investigation (i.e., ALL corrective action sites).
10
Vapor Intrusion: Regulatory FrameworkVapor Intrusion: Regulatory Framework
USEPA Framework
State Regulations
Petroleum vs. Chlorinated VOCs
Site-Specific Screening
Mass Flux Evaluations
USEPA Framework
State Regulations
Petroleum vs. Chlorinated VOCs
Site-Specific Screening
Mass Flux Evaluations
11
KEY POINT:
Draft or final guidance from NY, NJ, WI, CA, PA, MA, MI, NH, and others.
NJ: Screening values account for petroleum biodeg.
MA: Screening values based on indoor background.
NY: Screening based on sub-slab and indoor data only.
All: Screening values vary by >100x between states.
Approach to vapor intrusion varies widely between states. State guidance evolving rapidly.
Who
High-lights
Low-lights
State Vapor Intrusion GuidanceOverview of VI GuidanceOverview of VI Guidance
SITE BUILDINGSITE BUILDING
Affected GWAffected GWAffected GWAffected GW
Affected SoilAffected Soil
12
Benzene
Ethylbenzene
Indoor Air Limits: USEPA vs. States
USEPA VI Guide1
(ug/m3)New Jersey
(ug/m3)
0.31 2*
KEY POINT: Indoor air, soil gas, and GW screening values vary widely between states.
2.2 1,100
3000MTBE 2*
Range
Vinyl Chloride
Lindane
0.022TCE 3*
0.28 1*
0.0066 N/A
0.81PCE 3*
1) USEPA Limits based on 10-6 cancer risk, Texas limits based on 10-5 cancer risk * = Value based on TO-15 detection limit, risk-based value would be lower.
3.1
1000
94
14
2.8
0.5
42
Texas1
(ug/m3)
10x
500x
1500x
640x
10x
76x
45x
13
Vapor Intrusion: Regulatory FrameworkVapor Intrusion: Regulatory Framework
USEPA Framework
State Regulations
Petroleum vs. Chlorinated VOCs
Site-Specific Screening
Mass Flux Evaluations
USEPA Framework
State Regulations
Petroleum vs. Chlorinated VOCs
Site-Specific Screening
Mass Flux Evaluations
14
0.1
1
10
100
1000
10 100 1000 100000.001
0.01
0.1
1
10
100
1000
0.1 1 10 100 1000 10000
Observable RelationshipCia vs. Cgw ?
Chlorinated SolventsPetroleum Hydrocarbons
Ind
oo
r A
ir C
on
cen
trat
ion
( u
g/m
3)
Ind
oo
r A
ir C
on
cen
trat
ion
( u
g/m
3)
CORRELATION ? NO (p = 0.11)
CORRELATION ? YES (p <0.001)
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).
GW Concentration (ug/L) GW Concentration (ug/L)
Petroleum Hydrocarbons: No
Chlorinated Solvents: Yes - Direct
Correlation Between Groundwater Concentration and Indoor Air??
Subslab to Indoor Air AF
15
Oxygen
AerobicBiodegradationPossibleCo>Co
min
No AerobicBiodegradationCo<Co
min Comin CH
max
Hydrocarbon
Vapor Source Zone
Vapor Concentration
CHmin Co
max
L
Petroleum Biodeg. AF
Petroleum Biodegradation Conceptual Model
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.
KEY POINT:
Correlation between oxygen consumption and hydrocarbon attenuation.
16
KEY POINT:
For petroleum sites, vapor intrusion is generally associated with two factors acting together - shallow sources and preferential pathways.
Petroleum Vapor Intrusion: Industry Experience
Preferential pathway allows vapors to enter building.
1
NAPLNAPL
NAPLNAPL
Affected GW
Groundwater-Bearing Unit
Sump draws NAPL or dissolved hydrocarbons into building.
Shallow NAPL directly impacts building wall or floor.
BUILDING
32
Unsaturated
Soil
17
Vapor Intrusion: Regulatory FrameworkVapor Intrusion: Regulatory Framework
USEPA Framework
State Regulations
Petroleum vs. Chlorinated VOCs
Site-Specific Screening
Mass Flux Evaluations
USEPA Framework
State Regulations
Petroleum vs. Chlorinated VOCs
Site-Specific Screening
Mass Flux Evaluations
18
Site-Specific Screening: Vadose Zone
• Fine-grained soils (e.g., silt and clay) expected to inhibit vapor intrusion.
• However, available field data does not show clear relationship between soil type and vapor intrusion risk.
19
Vapor Intrusion: Regulatory FrameworkVapor Intrusion: Regulatory Framework
USEPA Framework
State Regulations
Petroleum vs. Chlorinated
Site-Specific Screening
Mass Flux Evaluations
USEPA Framework
State Regulations
Petroleum vs. Chlorinated
Site-Specific Screening
Mass Flux Evaluations
20
Mass Flux EvaluationsGroundwater ScreeningGroundwater Screening
Key Point:
High variability in subsurface VOC concentrations may limit use of mass flux analysis for vapor intrusion evaluation.
Mass flux into building must be < vertical mass flux out of groundwater.
MASS BALANCEAPPROACH:
source area
VGW-Bearing
Unit
Unsaturated
Soil
Fia1
L
Fsv
Fia2ERh
SITE BUILDING
Fgw1 Fgw2
Mass Balance
Fsv = Fgw1 - Fgw2
Fsv = Fia1 = Fia2
21
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
ss
ssssss
Distribution of VOCs
Vertical GW profile Vertical soil gas profile Sub-slab data Indoor air data Ambient air data
12345
Study Approach:
High density of data collected around individual buildings at two study sites.
Project Overview
1
23
45
6
788
1
Other Site Data
Physical soil properties Indoor air exchange Radon analysis Cross-foundation pressure gradient
67899
Altus AFB Study Site: Overview
Cluster 1
Cluster 2
Cluster 3
Sample Point Locations
Sample Point Locations
Altus AFB Study Site: Overview
Cluster 1
Cluster 2
Cluster 3
KEY POINT:
Collect at least three samples from each medium to quantify spatial variability.Collect at least three samples from each medium to quantify spatial variability.
Altus AFB Demonstration: Field Program
Field Investigation
Sample point cluster
Sub-slab point
Vertical soil gas points
Pressure transducer
Variability in Vapor Intrusion
Overview of VI Research Project
Building-Scale Spatial Variability Short and Long-Term Temporal Variability
Impact of Variability on Attenuation Factors
Conclusions and Recommendations
Building-Scale Spatial Variability in VOC Conc.
IndoorAir
Indoor Air
Sub-slab
Deeper soil gas
Ground-water
Number of Data Sets
Average Variability*
6
Spatial variability in subsurface media much higher than in indoor or ambient air.
KEY POINT:
* = Variability expressed as average of the coefficient of variation for each data set of three samples from the medium during each sampling event
Sub-slab
Deeper soil gas
Groundwater:Altus AFBHill AFB
Well Headspace
WellHeadspace
Ambient Air
AmbientAir
8
12
7
13
1064
0.55
0.26
0.96
0.96
0.92
0.901.350.21
Overview of VI Research Project
Building-Scale Spatial Variability
Short and Long-Term Temporal Variability
Impact of Variability on Attenuation Factors
Conclusions and Recommendations
Variability in Vapor Intrusion
Probe A3 (TCE - Normalized)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
13:50:0910:50:267:50:444:51:041:51:43
22:53:465:43:292:43:47
23:44:0420:44:2217:44:3914:44:5711:45:158:45:32
16:02:0113:02:1810:02:367:02:554:03:121:43:56
22:44:157:06:414:06:591:07:19
22:07:5819:11:25Time (3/16/07 to 4/10/07)
Normalized Concentration
Probe A3-3' (Port 9)
Probe A3-8' (Port 10)
Probe A3-17' (Port 5)
Short-term (3 weeks) Temporal Variability in Soil Gas TCE Concentration (from Blayne Hartmen):
<2x variation
Short-Term Temporal Variability:Timescale of days - Altus AFB
IndoorAir
Indoor Air
Sub-slab
Deeper soil gas
Ground-water
# of Paired Samples
Relative Percent Difference*
0
61% of paired subsurface gas samples had RPD <30%. 9% had RPD >100% (3x difference).
KEY POINT:
* = Relative percent difference (RPD) = (Sample 1 - Sample 2)/(Average of Sample 1 and Sample 2).
Sub-slab
Deeper soil gas
Groundwater
Well Headspace
WellHeadspace
Ambient Air
AmbientAir
1
6
11
6
7
N/A
1
0
4
3
1
< 30% 30 - 100% >100%
N/A
0
6
7
1
6
N/A
0
0
0
2
0
Long-Term (8 Years)Temporal Variability in Indoor VOC Concentration (from EnviroGroup):
5x Variation
0.01
0.1
1
10
Mar-97 Jul-98 Dec-99 Apr-01 Sep-02 Jan-04 May-05 Oct-06
Sample Date
Indoor Air DCE, ug/m3
H1 H2 H3 H4 H5
Long-Term (1 Year)Temporal Variability in Deep Soil Gas VOC Concentration (from NYDEQ): 5x Variation
IndoorAir
Indoor Air
Sub-slab
Deeper soil gas
Ground-water
Number of Data Sets
Average Variability*
0
For subsurface gas samples, longer-term temporal variability is similar to spatial variability
KEY POINT:
* = Variability expressed as average of the coefficient of variation for each data set of three samples from the medium during each sampling event
Sub-slab
Deeper soil gas
Groundwater
Well Headspace
WellHeadspace
Ambient Air
AmbientAir
0
6
10
5
6
N/A
N/A
1.02
0.80
0.96
0.52
Longer-Term Temporal Variability:Timescale of months - Altus AFB
Variability in Vapor Intrusion
Overview of VI Research Project
Building-Scale Spatial Variability
Short and Long-Term Temporal Variability
Impact of Variability on Attenuation Factors
Conclusions and Recommendations
Building-Scale Spatial Variability: How Many Samples?
IndoorAir
Indoor Air
Sub-slab
Deeper soil gas
Ground-water
+/- 50%
Number of Samples to Estimate True VOC Conc.*
3
Lots of sample locations required to understand VOC concentration in subsurface.
KEY POINT:
* = Number of samples = [(Z-statistic*CV)/Error]2; CV = coefficient of variation; for 90% confidence level, Z-statistic = 1.64
Sub-slab
Deeper soil gas
Groundwater:Altus AFBHill AFB
Well Headspace
WellHeadspace
Ambient Air
AmbientAir
1
10
10
9
9201
2
1
6
6
5
5111
+/- 67%
IndoorAir
Indoor Air
Sub-slab
Deeper soil gas
Ground-water
+/- 50%
Number of Samples to Estimate True VOC Conc.*
NC
Sampling effort should be balanced to characterized both spatial and temporal variability.
KEY POINT:
* = Number of samples = [(Z-statistic*CV)/Error]2; CV = coefficient of variation; for 90% confidence level, Z-statistic = 1.64
Sub-slab
Deeper soil gas
Groundwater:
Well Headspace
WellHeadspace
Ambient Air
AmbientAir
NC
11
7
10
3
NC
NC
6
4
6
2
+/- 67%
Long-Term Temporal Variability: How Many Samples?
Impact of Building-Scale Variability:
Pro
bab
ility
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
>2x >3x >5x >10x
Error for Single Measurement
Csubsurface
Error Between Single Measurement and Average VOC Concentration
Subsurface Measurements
Key Point:
Single measurement may not accurately represent subsurface vapor conditions.
Variability in VOC Concentration:
1) Indoor Air:
2) Subsurface:
Spatial: Low
Temporal: Moderate
Summary of Findings
Spatial: High
Short-Term Temporal: Low
Long-Term Temporal: High
Sampling effort should be balanced to characterized both spatial and long-term temporal variability in the subsurface.
KEY POINT:
39
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
40
Key Sources of VOCs in Indoor Air
Source of Background Indoor Air Impacts
REFERENCES:
USEPA, 1991, “Building Air Quality Guide”
OSHA, 1999, “Tech Manual for Indoor Air Investigation”
Ambient air Vehicles, gasoline Paints, adhesives Cleaning agents Insecticides Tobacco smoke Cosmetics, etc.
Significance of Background EffectsSignificance of Background Effects
41
0.1
1.0
10.0
100.0
1986 1991 1996 2001 2006
0.01
0.10
1.00
10.00
1986 1991 1996 2001 2006
Indoor use of chemicals has decreased. However, average background concentration remains well above USEPA risk limits.
Average Indoor Air Quality Over TimeAverage Indoor Air Quality Over Time
Note: 1) Average background indoor air concentrations reported in various studies by year of publication. 2) Indoor air limits (10-6) from USEPA Draft Vapor Intrusion Guidance, November 2002.
KEY POINT:
TRICHLOROETHENEBENZENE
Ave
rag
e B
ackg
rou
nd
C
on
cen
trat
ion
(u
g/m
3 )
Ave
rag
e B
ackg
rou
nd
C
on
cen
trat
ion
(u
g/m
3 )
USEPA INDOOR AIR LIMITUSEPA INDOOR AIR LIMIT
42
ARAMCO Art and Crafts Goop
Aleenes Patio & Garden Adhesive
Consumer Products Containing PCE
Product
Gumout Brake Cleaner
PCE Concentration
Hagerty Silversmith Spray Polish
Champion Spot it Gone
Plumbers Goop Adhesive
Liquid Wrench Lubricant w/ Teflon
Source: http://householdproducts.nlm.nih.gov/cgi-bin/household/brands?tbl=chem&id=177
Not Specified
70%
50 - 90%
67.5%
30.5%
20 - 25%
65 - 80%
KEY POINT:
Wide variety of consumer products still contain high concentrations of PCE.
Indoor AirIndoor Air
43
In 2004, background indoor and outdoor air concentrations still exceed risk-based limits for indoor air.
2004 Background vs. USEPA Risk-Based Limits2004 Background vs. USEPA Risk-Based Limits
1) Background concentrations from Sexton et al. 2004 ES&T 38(2); 423-430.2) USEPA Master Screening Values Table, September 2008
KEY POINT:
PCEBENZENE
Ran
ge
of
Rep
ort
ed B
ackg
rou
nd
C
on
cen
tra
tio
n
(ug
/m3)
0.1
1
10
100
0 0.2 0.4 0.6 0.8 1 1.2
INDOOR AIR LIMIT2
90th %
10th %
Median
90th %
10th %
Median
0.01
0.1
1
10
0 0.2 0.4 0.6 0.8 1 1.2
INDOOR LIMIT2
90th %
10th %
Median
90th %
Median
Clean GW
Bkgrnd Air
Bkgrnd Air
Ambient 1
Indoor 1
Ambient 1
Indoor 1
10th %
44
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
2004 2005 2006 2007 2008
Indoor concentration of 1,2-DCA increasing over time. New indoor source = molded plastic (e.g., toys, Christmas decorations).
New Indoor Source of 1,2-DCANew Indoor Source of 1,2-DCA
Note: 1) 1,2-DCA = 1,2-dichloroethane
KEY POINT:
CONCENTRATIONDETECTION FREQUENCY
1,2-
DC
A D
etec
tio
n
Fre
qu
ency
(%
)
1,2-
DC
A C
on
cen
trat
ion
(u
g/m
3 )
USEPA INDOOR AIR LIMIT
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
2004 2005 2006 2007 2008
<0.08 <0.08 <0.08
Median 1,2-DCA Conc.
90%ile 1,2-DCA Conc.
2) Indoor 1,2-DCA data from residential area in Colorado. Data provided by Jeff Kurtz, Envirogroup (jkurtz@envirogroup.com)
45
TCE Background at Redfields, CO., SiteTCE Background at Redfields, CO., SiteSignificance of Background EffectsSignificance of Background Effects
Adapted from USEPA Seminar on Indoor Air Vapor Intrusion, January 2003, Dallas, Texas
- 100 100 200 300 400 500
0.01
0.1
1
10
100
Post RemedyPre-Remedy
TCE
1,1-DCE
USEPA TCE Limit
USEPA 1,1-DCE Limit
Time After Vent System Installation (Days)
Cia in
Sin
gle
Ho
me
(u
g/m
3)
1,1-DCE
TCE
Indoor Air Data
Subslab VentSubslab Vent
0
KEY FINDINGS
TCE does NOT change after vent system startup.
Indoor TCE NOT due to vapor intrusion.
46
Key Findings Re: USEPA VI Guidance
USEPA indoor air limits are < < typical background VOC conc’s in indoor air.
USEPA indoor air limits are < < typical background VOC conc’s in indoor air.
Accurate identification of vapor intrusion impacts requires careful accounting of indoor sources.
VOC = Volatile organic compound
Significance of Background EffectsSignificance of Background Effects
USEPA VI Screening Values are not accurate for the prediction of indoor air impacts. Use of screening values will result in a high false positive rate.
USEPA VI Screening Values are not accurate for the prediction of indoor air impacts. Use of screening values will result in a high false positive rate.
Risk-Based Air Limits
False Positives
BOTTOM LINE:
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