Discerning Background Sources
from Vapor Intrusion
Jeffrey Kurtz, Ph.D. and David Folkes, PE
EnviroGroup Limited
Denver
Boston
Albuquerque
Seattle
Colorado Bar Association – October 26, 2005
Proliferation of Vapor Intrusion
Guidance
• At least 14 states, as well as the EPA,
have developed Vapor Intrusion Guidance
in the past few years.
• These documents vary widely in their
approach to, and discussion of,
background indoor air.
New Risk Levels for 1,1-DCE and
TCE
• Recently the EPA, and several states,
have implemented new risk levels for 1,1DCE and TCE.
• TCE is now the risk driver at many sites.
• TCE is a trace to major component of
many common consumer products.
Consumer Product Examples
•
•
•
•
•
•
•
•
correction fluids
paints & varnishes & removers
glues, adhesives and sealants
spot removers & laundry aids
rug cleaning fluids
metal cleaners
lubricants
pesticides
Approach for Separating Indoor
and Subsurface Sources
• Experience at several large sites led to
“lines of evidence” approach for separating
indoor & subsurface sources.
• Accepted by CDPHE and applied at
several Colorado sites.
Application
Lines of Evidence approach can be used to:
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Identify false positives
Limit unnecessary mitigation
Limit indoor air sampling
Identify indoor air COCs
Limit continued sampling & mitigation
VOC Ratio Method
• Principal line of evidence relies on basic
chemical properties of the chlorinated
volatile organic compounds (VOCs).
• This line of evidence requires at least 2
chlorinated VOCs in the subsurface.
VOC Chemical Properties
• Relative volatility (expressed as Henry’s
Law Constant). Factor of 50 range for
common chlorinated VOCs.
• Relative soil sorption (Koc) – similar for
most chlorinated VOCs.
• Relative degradability – similar for most
chlorinated VOCs.
Groundwater Sources
•
•
•
•
Calculate VOC ratios
Evaluate ratio trends over time
Evaluate spatial variation of ratios
Adjust for relative volatility of VOCs
(Henry’s Law Constants)
• Map predicted soil vapor ratios
• Predict indoor air ratios and TCE
concentrations
Soil Vapor Sources
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•
•
•
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Calculate VOC ratios
Evaluate ratio trends over time
Evaluate spatial variation of ratios
Map measured soil vapor ratios
Predict indoor air ratios and TCE concentrations
• High quality, reproducible soil vapor data
essential
COC Ratios (Soil Gas)
TCE (VI) = 0.5 x DCE
TCE 80 ug/m3
DCE 20 ug/m3
TCE 1000 ug/m3
DCE 2000 ug/m3
TCE (BG) = TCE (OBS) – TCE (VI)
TCE = 0.5 x DCE
Ideal Case
• Denominator is a VOC with no, or very
low, indoor air background (e.g. 1,1-DCE).
• Indoor air concentration of denominator
VOC is direct measure of vapor intrusion.
• Ratio directly predicts vapor intrusion
concentration of other COCs.
Typical Case
• Use a VOC with the lowest indoor air
background as the denominator in the
ratio (e.g. TCE).
• Indoor air concentration of the
denominator VOC is an upper limit
measure of vapor intrusion.
• Can estimate predicted upper limit vapor
intrusion concentration of other COCs
from the ratio.
Case Study
• A Colorado site with a large chlorinated
solvent groundwater plume.
• Groundwater COCs are TCE; 1,1-DCE;
PCE and 1,1,1-TCA.
• Hundreds of single family residences
overlying the plume.
• Documented vapor intrusion based on
indoor air 1,1-DCE.
Case Study
• Change in 1,1-DCE and TCE action levels
required re-evaluation of indoor air data.
• Decision needed on new extent of vapor
intrusion exceeding action levels.
• Indoor air background TCE caused
numerous “false” exceedances of action
level.
Case Study
• Background varies on a “house-by-house”
basis.
• Statistics from homes outside plume and
from post-mitigation indicate 15% of
homes in area would exceed action level
due to background.
• Household chemical surveys generally fail
to identify all indoor sources.
Case Study
• Groundwater COCs present in relatively
consistent proportions spatially.
• Little variation (or predictable trend) over
time in TCE/DCE in groundwater.
• Adjust groundwater ratios for relative
volatility (Henry’s Law Constants).
• Predict soil vapor TCE/DCE ratio.
Predicted TCE/DCE Ratio in Soil Vapor
Estimated DCE Plume Boundary (7 ug/L)
Interpolation Boundary
TCE/DCE > 0.5 (Henry’s Law Corrected)
TCE/DCE 0.4 – 0.5
TCE/DCE 0.3 – 0.4
TCE/DCE 0.2 – 0.3
TCE/DCE 0.1 – 0.2
TCE/DCE 0.01 – 0.1
Case Study
• Map predicted soil vapor TCE/DCE ratio.
• Compare to measured indoor air
TCE/DCE ratio.
• Generally excellent agreement, with some
prominent exceptions due to background.
• Edge of groundwater plume clearly
marked.
TCE / DCE Ratios in Pre Mitigation and Unmitigated Indoor Air
Estimated TCE 5 µg/L
Contour in Groundwater
0.01 – 0.3
0.31 – 1.0
TCE NOT DETECTED
/ DCE DETECTED
1.01 – 5.0
TCE DETECTED/ DCE
NOT DETECTED
> 5.0
TCE AND DCE
NOT DETECTED
Spatial Patterns
• General correlation with plume
• Absolute concentrations within plume can
be more variable and hard to correlate
• Indoor air COC ratios often indicate
anomalies
Spatial Patterns (IA Ratios)
TCE/DCE
0.30
TCE/DCE
0.29
TCE/DCE
0.35
TCE/DCE
0.41
TCE/DCE
6.2
TCE/DCE
0.27
TCE/DCE
0.38
TCE/DCE
0.17
TCE/DCE
0.58
TCE Source Attribution from Multi-media Ratio Comparison
Predominately Vapor
Intrusion Derived TCE
Predominately Indoor
Source (background) TCE
Estimated TCE 5 µg/L Contour
in Groundwater
Correlation with GW Plume
DCE > 7 ug/L
DCE > 0.49 ug/m3
Case Study Results
• TCE/DCE ratio pattern distinctly marks
edge of vapor intrusion – limits indoor air
sampling to define “extent”.
• TCE/DCE ratio for indoor air compared to
groundwater clearly shows locations with
“anomalously high” background TCE.
• TCE/DCE ratio allows direct determination
of maximum potential vapor intrusion
derived TCE.
Implications
• COC ratios for chlorinated VOCs can
provide an accurate method to separate
background from vapor intrusion.
• Can use ratios from groundwater, soil
vapor, or mitigation system emissions.
• Useful when at least two chlorinated VOCs
are present in the subsurface source.
Line of Evidence
Secondary Factors
• Building survey
• Indoor air background databases
Building Survey
• Identify potential background sources
– Household products
– Resident activities
• Options
– Delay testing
– Remove and test
• Residual impacts?
DCE
PCE
TCA
TCE
0.8 ug/L Line
1.6 ug/L Line
Date
DCE ND @ DL
10/20/2004
8/21/2004
6/22/2004
4/23/2004
2/23/2004
Begin process of
remodeling/cleaning
12/25/2003
10/26/2003
8/27/2003
6/28/2003
4/29/2003
2/28/2003
12/30/2002
10/31/2002
9/1/2002
7/3/2002
5/4/2002
3/5/2002
1/4/2002
11/5/2001
9/6/2001
7/8/2001
5/9/2001
1000
3/10/2001
1/9/2001
11/10/2000
Concentration (ug/m3) .
Residual Background Impacts
House 1300 Indoor Air Concentration Trend
New Owner 12/1/2003
100
10
1
0.1
0.01
1000
0.01
3/26/1998
5/25/1998
7/24/1998
9/22/1998
11/21/1998
1/20/1999
3/21/1999
5/20/1999
7/19/1999
9/17/1999
11/16/1999
1/15/2000
3/15/2000
5/14/2000
7/13/2000
9/11/2000
11/10/2000
1/9/2001
3/10/2001
5/9/2001
7/8/2001
9/6/2001
11/5/2001
1/4/2002
3/5/2002
5/4/2002
7/3/2002
9/1/2002
10/31/2002
12/30/2002
2/28/2003
4/29/2003
6/28/2003
8/27/2003
10/26/2003
12/25/2003
2/23/2004
4/23/2004
6/22/2004
8/21/2004
10/20/2004
12/19/2004
Concentration (ug/m3) .
Residual Background Impacts
House 1829 Indoor Air Concentration Trend
Start
Upgrade
Tenants 11/1/1999 Shellac used
100
10
1
0.1
Date
DCE
PCE
TCA
TCE
0.8 ug/L Line
1.6 ug/L Line
Background Databases
• Compare IA concentrations to “typical”
levels in published surveys
• Concentrations within typical ranges may
support other background LOE’s
Comparison of Various Measures of Mean Background Indoor Air
10.00
6.00
ug/m3
2.00
0.70
0.30
0.08
0.04
EPA (1998)
EPA (1991) Foster et al.(2002)
MADEP (1998)
Shaw&Singh Kurtz&Folkes(2002)
1,2-DCA
DCM
PCE
TCE
Databases Issues
• Data sparse for many compounds
• Comparability issues
– Building type and use differences
– Regional differences
– Time period differences
• Extremes often removed from databases
Site-specific background
• Control and/or mitigated buildings may not
be available
• Background study may be impractical,
especially for small sites
• Large number of samples required to
achieve required statistical confidence
Other Lines of Evidence
• Radon system emission levels/ratios
• Temporal patterns
Radon System Emission Ratios
TCE/DCE in Current Single Family Home System Emissions
Data from Jan 2001-June 2002 with DCE>1.0 ug/m3
2.0
1.2
0.8
0.4
0.0
M in-M ax
1125DA
1165DA
1205DA
1225DA
1235DA
1245DA
1285DA
1295DA
1305CL
1315CL
1319CL
4601LO
4800AZ
4800KA
4805AZ
4805KA
4815AZ
4820AZ
4825AZ
4835AZ
TCE/DCE
1.6
RESCODE
25%-75%
M edian value
Temporal Patterns
•
•
•
•
Requires indoor air tests over time
Post versus pre-mitigation concentrations
Change in resident
Correlation with activities
Pre vs Post Mitigation
.
3
Concentration (ug/m )
100
1,1 DCE
10
DCM
1,1 DCA
1,1,1 TCA
1
1,2 DCA
PCE
TCE
0.1
VC
0.01
-100
0
100
200
300
Days After System Installation
400
500
0.01
DCE
PCE
TCA
TCE
0.8 ug/L Line
1.6 ug/L Line
12/19/2004
10/20/2004
8/21/2004
6/22/2004
4/23/2004
2/23/2004
12/25/2003
10/26/2003
8/27/2003
6/28/2003
4/29/2003
2/28/2003
System
Start
12/30/2002
10/31/2002
9/1/2002
7/3/2002
5/4/2002
3/5/2002
1/4/2002
11/5/2001
9/6/2001
7/8/2001
5/9/2001
100
3/10/2001
1/9/2001
11/10/2000
9/11/2000
Concentration (ug/m3) .
Impact of Resident
House 1170 Indoor Air Concentration Trend
New Owner 11/21/2002
10
1
0.1
Date
DCE ND @ DL
33
Impact of Resident
House 5300 Indoor Air Concentration Trend
System
Start
New Owner 10/01/2002
100
10
1
0.1
38220
38160
38100
38040
37980
37920
37860
37800
37740
37680
37620
37560
37500
37440
37380
37320
37260
37200
37140
37080
37020
0.01
36960
Concentration (ug/m3) .
1000
Date
DCE
PCE
TCA
TCE
0.8 ug/L Line
1.6 ug/L Line
DCE ND @ DL
34
Summary
• Several lines of evidence may be needed
to separate background from vapor
intrusion sources of indoor air VOCs
• Comparison of COC ratios in various
media is often the most compelling LOE
• If available, temporal and spatial patterns
are also useful lines of evidence
Conclusions
• VOC ratios can provide more definitive
answers than assumed sub-slab to indoor
air attenuation factors or the JE Model.
• VOC ratios can discriminate background
on a “house-by-house” basis.
• VOC ratios can prevent the need for
“background sampling”.
Information Resources
• www.envirogroup.com
– Vapor Intrusion Newsletter signup
– Links by state and by topic
• jkurtz@envirogroup.com
– Questions