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 Center
Monday, March 9, 2009
SITE BUILDING
Air Exchange
GSI ENVIRONMENTAL INC.
Houston, Texas
www.gsi-net.com (713) 522-6300
[email protected]
source
area
Vapor Intrusion: Wazzat?
BUILDING
Effect on
indoor air
quality?
Soil source
area
GW source
area
KEY
POINT:
Vapors in
subsurface
Vapor intrusion is the movement of volatile
chemicals into buildings from below ground.
2
Introduction
Limitations of VOC Measurements
LIMITATION
DETAILS
High
Variability
High spatial and temporal variability:
- Conservative assumptions OR
- Large number of samples
Indoor
Sources
Difficulty separating vapor intrusion
from indoor sources of VOCs:
- Affects indoor and sub-slab samples
False
Positives
Low levels of VOCs often detected in
soil gas and indoor air samples:
- Summa carry over contamination
- Lab contamination
- Unexpected minor sources
ss
ss
ss
ss
Gas
Summa
Canister
KEY
VOC measurements alone often provide a
POINT: confusing picture of vapor intrusion.
3
Introduction
Physical
Barriers to
Vapor
Intrusion
KEY POINT:
Non-VOC
measuremen
ts can
provide
improved
understandin
g of vapor
intrusion.
A
Unsaturated
Soil
Source
Area
Building foundation:
(A) Low permeability
foundation without cracks
or unsealed penetrations;
(B) Positive building pressure
B
A
B
A
B
Vadose Zone
(A) High moisture content
fine-grained soil layer
(B) Aerobic Biodegradation
Groundwater Interface:
(A) Clean water lens;
(B) Saturated confining layer
Aquifer
4
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
l
Conclusions and Recommendations
5
Vapor Intrusion: Regulatory Framework
l
USEPA Framework
l
State Regulations
l
Petroleum vs. Chlorinated VOCs
l
Site-Specific Screening
l
Mass Flux Evaluations
6
Overview of USEPA VI Guidance
Conceptual Model for Vapor Intrusion:
BUILDING
3
Air
Exchange
Unsaturated
Soil
Affected Soil
2
Affected GW
Groundwater
-Bearing Unit
KEY
POINT:
1
Building
Attenuation
Due to
Exchange with
Ambient Air
Advection and
Diffusion
Through
Unsaturated
Soil and
Building
Foundation
Partitioning
Between Source
and Soil Vapor
Regulatory guidance assumes vapor migration
through soils and building foundation based on
conservative assumptions.
7
Typical Vapor Intrusion Screening Process
Screening Steps
CHEMICAL
CRITERIA
GW
SCREENING
Chemicals
GW
Yes
could cause
conc. > VI
VI impact
screening
based on
levels
volatility
and toxicity
No
NFA
No
NFA
Field Measurements
DISTANCE
CRITERIA
Current or
Yes future
Yes
buildings
within 10 30 m of edge
of impact.
No
NFA
SOIL GAS/
SUB-SLAB
SCREENING
INDOOR AIR
TESTNG
Soil gas/
Yes
sub-slab
conc. >
VI screening
levels
indoor air
concentrations
other
measurements
indicate vapor
intrusion
impact
No
NFA
No
NFA
Yes
Mitigation/
Remediation
KEY POINT
Step-wise VI investigation
process recommended by most
VI regulatory guidance.
8
USEPA VI Screening Values: Key COCs
Indoor Air
(ug/m3)
Sub-slab
(ug/m3)
Groundwater
(mg/L)
Benzene
0.31
3.1
0.005*
Ethylbenzene
2.2
22
0.70*
MTBE
3000
30000
120
PCE
0.81
8.1
0.005*
TCE
0.022
0.22
0.005*
Vinyl Chloride
0.28
2.8
0.002*
Lindane
0.0066
0.066
0.011
KEY
Under EPA guidance, GW impacts above MCLs usually
POINT: require VI investigation (i.e., ALL corrective action sites).
* = Value based on MCL, risk-based number would be lower.
9
Vapor Intrusion: Regulatory Framework
l
USEPA Framework
l
State Regulations
l
Petroleum vs. Chlorinated VOCs
l
Site-Specific Screening
l
Mass Flux Evaluations
10
Overview of VI Guidance
State Vapor Intrusion Guidance
Who
n Draft or final guidance from
NY, NJ, WI, CA, PA, MA, MI,
NH, and others.
Highlights
n NJ: Screening values account
for petroleum biodeg.
n MA: Screening values based
on indoor background.
Lowlights
n NY: Screening based on
sub-slab and indoor
data only.
n All: Screening values vary
by >100x between states.
KEY
POINT:
SITE BUILDING
Affected Soil
Affected GW
Approach to vapor intrusion varies widely
between states. State guidance evolving rapidly.
11
Indoor Air Limits: USEPA vs. States
USEPA VI Guide1 New Jersey
(ug/m3)
(ug/m3)
Texas1
(ug/m3)
Range
Benzene
0.31
2*
3.1
10x
Ethylbenzene
2.2
1,100
1000
500x
MTBE
3000
2*
94
1500x
PCE
0.81
3*
42
45x
TCE
0.022
3*
14
640x
Vinyl Chloride
0.28
1*
2.8
10x
Lindane
0.0066
N/A
0.5
76x
KEY POINT:
Indoor air, soil gas, and GW screening values
vary widely between states.
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.
12
Vapor Intrusion: Regulatory Framework
l
USEPA Framework
l
State Regulations
l
Petroleum vs. Chlorinated VOCs
l
Site-Specific Screening
l
Mass Flux Evaluations
13
Subslab to Indoor Air AF
Petroleum Hydrocarbons
1000
100
10
1
CORRELATION ? NO (p = 0.11)
0.1
10
100
1000
10000
GW Concentration (ug/L)
Observable
Relationship
Cia vs. Cgw ?
Cgw = COC conc. In groundwater;
Indoor Air Concentration ( ug/m3)
Indoor Air Concentration ( ug/m3)
Correlation Between Groundwater
Concentration and Indoor Air??
Chlorinated Solvents
1000
100
10
1
0.1
CORRELATION ?
YES (p <0.001)
0.01
0.001
0.1
1
10
100
1000
10000
GW Concentration (ug/L)
n Petroleum Hydrocarbons:
No
n Chlorinated Solvents:
Yes - Direct
Cia = COC conc. In indoor air;
14
(p = 0.11) = Probability = 11% that slope of best-fit line = 0 (I.e., no trend).
Petroleum Biodeg. AF
Petroleum Biodegradation Conceptual Model
Comax
CHmin
Aerobic
Biodegradation
Possible

Co>Comin
No Aerobic
Biodegradation
Co<Comin
Oxygen
L
Hydrocarbon
Comin
Vapor Source Zone
CHmax
Vapor
Concentration
KEY
Correlation between oxygen consumption
POINT: and hydrocarbon attenuation.
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.
15
Petroleum Vapor Intrusion:
Industry Experience
BUILDING
2
Shallow NAPL
directly impacts
building wall
or floor.
3
Unsaturated
Soil
Preferential
pathway
allows vapors
to enter
building.
NAPL
NAPL
1
Sump draws
NAPL or
dissolved
hydrocarbons
into building.
KEY
POINT:
Affected GW
GroundwaterBearing Unit
For petroleum sites, vapor intrusion is generally
associated with two factors acting together shallow sources and preferential pathways.
16
Vapor Intrusion: Regulatory Framework
l
USEPA Framework
l
State Regulations
l
Petroleum vs. Chlorinated VOCs
l
Site-Specific Screening
l
Mass Flux Evaluations
17
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.
18
Vapor Intrusion: Regulatory Framework
l
USEPA Framework
l
State Regulations
l
Petroleum vs. Chlorinated
l
Site-Specific Screening
l
Mass Flux Evaluations
19
Groundwater Screening
Mass Flux Evaluations
SITE BUILDING
MASS
BALANCE
APPROACH:
Mass flux into
building must be
< vertical mass
flux out of
groundwater.
Key
Point:
ER
Fia2
h
Fia1
Mass Balance
Fsv = Fgw1 - Fgw2
Fsv = Fia1 = Fia2
L
Unsaturated
Soil
Fsv
GW-Bearing
Unit
V
source
area
Fgw1
Fgw2
High variability in subsurface VOC concentrations
may limit use of mass flux analysis for vapor intrusion
evaluation.
20
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
l
Conclusions and Recommendations
21
Project Overview
Study
Approach:
7
5
4
ss
ss
High density of
data collected
around individual
buildings at two
study sites.
Distribution of VOCs
1 Vertical GW profile
2 Vertical soil gas profile
3 Sub-slab data
4 Indoor air data
5 Ambient air data
ss
ss
3
1
8
6
2
1
Other Site Data
6 Physical soil properties
7 Indoor air exchange
8 Radon analysis
9 Cross-foundation pressure gradient
Sample Point Locations
Altus AFB Study Site:
Overview
Cluster 3
Cluster 2
Cluster 1
Sample Point Locations
Altus AFB Study Site:
Overview
Cluster 3
Cluster 2
Cluster 1
KEY
POINT:
Collect at least three samples from each
medium to quantify spatial variability.
Field Investigation
Altus AFB Demonstration: Field Program
Sample
point
cluster
Sub-slab
point
Vertical
soil gas
points
Pressure
transducer
Variability in Vapor Intrusion
n
Overview of VI Research Project
n Building-Scale Spatial Variability
n
Short and Long-Term Temporal Variability
n
Impact of Variability on Attenuation Factors
n
Conclusions and Recommendations
Building-Scale
Spatial Variability in VOC Conc.
Number of
Data Sets
Average
Variability*
Ambient
Air
Indoor
Air
Ambient
Air
6
0.55
Indoor
Air
8
0.26
Sub-slab
Sub-slab
12
0.96
Deeper
soil gas
Deeper
soil gas
Well
Headspace
7
0.96
13
0.92
10
6
4
0.90
1.35
0.21
Well
Headspace
Groundwater
Groundwater:
Altus AFB
Hill AFB
* = Variability expressed as average of the coefficient of variation for each data set of three samples from the medium during each
sampling event
KEY
POINT:
Spatial variability in subsurface media much
higher than in indoor or ambient air.
Variability in Vapor Intrusion
n
Overview of VI Research Project
n
Building-Scale Spatial Variability
n Short and Long-Term Temporal
Variability
n
Impact of Variability on Attenuation Factors
n
Conclusions and Recommendations
Short-term (3 weeks) Temporal Variability in Soil Gas
TCE Concentration (from Blayne Hartmen):
<2x variation
Probe A3 (TCE - Normalize d)
2
1.8
1.6
1.2
Probe A3-3' (Port 9)
1
Probe A3-8' (Port 10)
Probe A3-17' (Port 5)
0.8
0.6
0.4
0.2
Time (3/16/07 to 4/10/07)
19:11:25
22:07:58
1:07:19
4:06:59
7:06:41
22:44:15
1:43:56
4:03:12
7:02:55
10:02:36
13:02:18
16:02:01
8:45:32
11:45:15
14:44:57
17:44:39
20:44:22
23:44:04
2:43:47
5:43:29
22:53:46
1:51:43
4:51:04
7:50:44
10:50:26
0
13:50:09
Normalized Concentration
1.4
Short-Term Temporal Variability:
Timescale of days - Altus AFB
# of Paired Relative Percent Difference*
Samples < 30%
30 - 100% >100%
Ambient
Air
Indoor
Air
Ambient
Air
0
N/A
N/A
N/A
Indoor
Air
1
0
1
0
Sub-slab
Sub-slab
6
6
0
0
Deeper
soil gas
Deeper
soil gas
Well
Headspace
11
7
4
0
6
1
3
2
Groundwater
7
6
1
0
Well
Headspace
Groundwater
* = Relative percent difference (RPD) = (Sample 1 - Sample 2)/(Average of Sample 1 and Sample 2).
KEY
POINT:
61% of paired subsurface gas samples had RPD <30%.
9% had RPD >100% (3x difference).
Long-Term (8 Years)Temporal Variability in Indoor VOC
Concentration (from EnviroGroup):
5x Variation
Indoor Air DCE, ug/m3
10
1
0.1
0.01
Mar-97
Jul-98
Dec-99
Apr-01
Sep-02
Jan-04
Sample Date
H1
H2
H3
H4
H5
May-05
Oct-06
Long-Term (1 Year)Temporal Variability in Deep Soil Gas
VOC Concentration (from NYDEQ):
5x Variation
Longer-Term Temporal Variability:
Timescale of months - Altus AFB
Number of
Data Sets
Average
Variability*
Ambient
Air
Indoor
Air
Ambient
Air
0
N/A
Indoor
Air
0
N/A
Sub-slab
Sub-slab
6
1.02
Deeper
soil gas
Deeper
soil gas
Well
Headspace
10
0.80
5
0.96
Groundwater
6
0.52
Well
Headspace
Groundwater
* = Variability expressed as average of the coefficient of variation for each data set of three samples from the medium during each
sampling event
KEY
POINT:
For subsurface gas samples, longer-term
temporal variability is similar to spatial variability
Variability in Vapor Intrusion
n
Overview of VI Research Project
n
Building-Scale Spatial Variability
n
Short and Long-Term Temporal Variability
n Impact of Variability on Attenuation
Factors
n
Conclusions and Recommendations
Building-Scale Spatial Variability:
How Many Samples?
Number of Samples to
Estimate True VOC Conc.*
+/- 50%
+/- 67%
Ambient
Air
Indoor
Air
Ambient
Air
3
2
Indoor
Air
1
1
Sub-slab
Sub-slab
10
6
Deeper
soil gas
Deeper
soil gas
Well
Headspace
10
6
9
5
Groundwater:
Altus AFB
Hill AFB
9
20
1
5
11
1
Well
Headspace
Groundwater
* = Number of samples = [(Z-statistic*CV)/Error]2; CV = coefficient of variation; for 90% confidence level, Z-statistic = 1.64
KEY
POINT:
Lots of sample locations required to understand
VOC concentration in subsurface.
Long-Term Temporal Variability:
How Many Samples?
Number of Samples to
Estimate True VOC Conc.*
+/- 50%
+/- 67%
Ambient
Air
Indoor
Air
Ambient
Air
NC
NC
Indoor
Air
NC
NC
Sub-slab
Sub-slab
11
6
Deeper
soil gas
Deeper
soil gas
Well
Headspace
7
4
10
6
3
2
Well
Headspace
Groundwater
Groundwater:
* = Number of samples = [(Z-statistic*CV)/Error]2; CV = coefficient of variation; for 90% confidence level, Z-statistic = 1.64
KEY
POINT:
Sampling effort should be balanced to
characterized both spatial and temporal
variability.
Impact of Building-Scale
Variability:
Subsurface Measurements
Error Between Single Measurement
and Average VOC Concentration
Csubsurface
50%
45%
Key
Point:
40%
Probability
35%
30%
25%
20%
15%
10%
5%
0%
>2x
>3x
>5x
>10x
Error for Single Measurement
Single
measurement
may not
accurately
represent
subsurface
vapor
conditions.
Summary of Findings
Variability in VOC Concentration:
1) Indoor Air:
Spatial: Low
Temporal: Moderate
2) Subsurface:
Spatial: High
Short-Term Temporal: Low
Long-Term Temporal: High
KEY
POINT:
Sampling effort should be balanced to
characterized both spatial and long-term temporal
variability in the subsurface.
Vapor Intrusion: Investigation of Buildings
l
United States Regulatory Framework
l
Spatial and Temporal Variability
Impact of Indoor Sources on VI
Investigations
l
Air Flow and VOC Migration Around
Buildings
l
Controlled Investigation of
Vapor Intrusion in Buildings
l
Conclusions and Recommendations
39
Significance of Background Effects
Source of Background Indoor Air Impacts
Key Sources of VOCs in Indoor Air
n
n
n
n
n
n
n
Ambient air
Vehicles, gasoline
Paints, adhesives
Cleaning agents
Insecticides
Tobacco smoke
Cosmetics, etc.
REFERENCES:
n USEPA, 1991, “Building Air Quality Guide”
n OSHA, 1999, “Tech Manual for Indoor Air Investigation”
40
Average Indoor Air Quality Over Time
TRICHLOROETHENE
100.0
10.0
1.0
USEPA INDOOR AIR LIMIT
0.1
1986
KEY
POINT:
1991
1996
2001
2006
Average Background
Concentration (ug/m3)
Average Background
Concentration (ug/m3)
BENZENE
10.00
1.00
0.10
USEPA INDOOR AIR LIMIT
0.01
1986
1991
1996
2001
2006
Indoor use of chemicals has decreased.
However, average background concentration
remains well above USEPA risk limits.
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.
41
Indoor Air
Consumer Products Containing PCE
Product
ARAMCO Art and Crafts Goop
PCE
Concentration
Not Specified
Aleenes Patio & Garden Adhesive
70%
Gumout Brake Cleaner
50 - 90%
Liquid Wrench Lubricant w/ Teflon
65 - 80%
Plumbers Goop Adhesive
67.5%
Hagerty Silversmith Spray Polish
30.5%
Champion Spot it Gone
20 - 25%
KEY
Wide variety of consumer products still contain high
POINT: concentrations of PCE.
Source: http://householdproducts.nlm.nih.gov/cgi-bin/household/brands?tbl=chem&id=177
42
Range of
Reported Background
Concentration (ug/m3)
2004 Background vs.
USEPA Risk-Based Limits
Bkgrnd
Air
BENZENE
100
10
Indoor
Indoor 1
1
90th %
1
Ambient 1
Median
90th
%
Median
Median
Median
1
90th %
Ambient 1
90th %
10
Clean GW
PCE
10th %
10th %
0.1
10th
%
10th %
INDOOR LIMIT2
INDOOR AIR LIMIT2
0.01
0.1
0
KEY
POINT:
0.2
0.4
0.6
0.8
1
1.2
0
0.2
0.4
0.6
0.8
1
1.2
In 2004, background indoor and outdoor air
concentrations still exceed risk-based limits
for indoor air.
1) Background concentrations from Sexton et al. 2004 ES&T 38(2); 423-430.
2) USEPA Master Screening Values Table, September 2008
43
New Indoor Source of 1,2-DCA
CONCENTRATION
100%
1.0
90%
0.9
1,2-DCA Concentration
(ug/m3)
1,2-DCA Detection
Frequency (%)
DETECTION FREQUENCY
80%
70%
60%
50%
40%
30%
20%
10%
0%
2004
KEY
POINT:
2005
2006
2007
2008
Median 1,2-DCA Conc.
90%ile 1,2-DCA Conc.
0.8
0.7
0.6
0.5
0.4
USEPA INDOOR AIR LIMIT
0.3
0.2
0.1
0.0
<0.08
2004
<0.08
2005
<0.08
2006
2007
2008
Indoor concentration of 1,2-DCA increasing
over time. New indoor source = molded plastic
(e.g., toys, Christmas decorations).
Note: 1) 1,2-DCA = 1,2-dichloroethane
2) Indoor 1,2-DCA data from residential area in Colorado.
Data provided by Jeff Kurtz, Envirogroup ([email protected]) 44
Significance of Background Effects
Subslab Vent
TCE Background at Redfields, CO., Site
Cia in Single Home (ug/m3)
Pre-Remedy
Post Remedy
USEPA 1,1-DCE Limit
100
Indoor Air
Data
10
1,1-DCE
TCE
1
TCE
0.1
USEPA TCE Limit
0.01
- 100
0
100
200
300 400
500
KEY
FINDINGS
n TCE does NOT
change after
vent system
startup.
n Indoor TCE
NOT due to
vapor intrusion.
Time After Vent System Installation (Days)
Adapted from USEPA Seminar on Indoor Air Vapor Intrusion, January 2003, Dallas, Texas
45
Significance of Background Effects
Key Findings Re: USEPA VI Guidance
Risk-Based
Air Limits
background VOC conc’s in indoor air.
n 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.
False
Positives
BOTTOM
LINE:
n USEPA indoor air limits are < < typical
Accurate identification of vapor intrusion
impacts requires careful accounting of
indoor sources.
VOC = Volatile organic compound
46