Transcript Slide 1

Evaluating the Petroleum
Vapor Intrusion Pathway
Studies of Natural Attenuation of
Subsurface Petroleum Hydrocarbons
& Recommended Screening Criteria
AEHS 27nd Annual International Conference on Soil, Sediment, Water
& Energy
Amherst, Massachusetts
Vapor Intrusion Workshop, Monday October 17, 2011, 8:00am-12:00pm
by
Robin V. Davis, P.G.
Project Manager
Utah Department of Environmental Quality
Leaking Underground Storage Tanks
[email protected] 801-536-4177
OBJECTIVE
•
Understand why so many LUST sites exist nationwide, but
few report cases of petroleum vapor intrusion to indoor air
•
Develop guidance for screening/exclusion criteria to
determine when PVI pathway is incomplete
•
Avoid unnecessary, $costly$ PVI investigations
SCOPE
•
Petroleum Vapor Database:
Compile basic, high-quality field data to evaluate vapor intrusion
pathway: soil type, source extent & degree, LNAPL, DTW,
contaminant concentrations in dissolved & vapor phases
•
Show mechanisms, characteristics & trends of petroleum
hydrocarbon vapor biodegradation
Recent Timeline & History
2002-2011
Work Groups & Studies of
Petroleum Hydrocarbon
Vapor Intrusion
•
2002: EPA OSWER Draft Guide for Vapor Intrusion Evaluations
- Comprehensive; cautious screening criteria
- Recommends for chlorinated hydrocarbons, NOT petroleum LUST sites because
biodegradation is not considered
- Recommends forming work group to study VI pathway for petroleum
•
2003-2005: EPA OUST/States Petroleum Vapor Intrusion Work Group
- Studied behavior of subsurface petroleum associated with PVI pathway
- Began compiling international database (U.S. & Canada)
- Work Group “put on hold,” disbanded…
•
2005-2009: Continued compiling, analyzing field data
- American Petroleum Institute (API) Work Group, peer-reviews petroleum
vapor database, compiles more data
- Screening criteria for low-risk sites published (Davis, R.V., 2009, LUSTLine #61)
•
2009-2011: EPA OUST/States PVI Work Group Revived
- Database much larger, EPA OUST peer-review in process
- Validating Bio Vapor Model: Analytical Model, accounts for biodegradation of
petroleum hydrocarbons in the subsurface (DeVaull and McHugh, 2010)
- EPA OUST preparing to publish PVI guidance by November 2012
Petroleum Vapor Database
Compilation of soil vapor data from subsurface multi-depth & sub-slab
sample points, paired with concurrent source strength data
Canada
~170 Sites, ~1000
Measurements of
Concurrent SV,
GW & Soil Data
2/13
United States
56/304
MAP KEY
56 # Geographic Locations
Australia
(sites) Evaluated
112/608
Perth
304 # Paired concurrent
Sydney
measurements of benzene
subsurface soil vapor &
source strength
(Davis, R.V., 2009, updated 2011)
Tasmania
(Wright, J., 2011, Australian data)
Characterize Site
• Know Full Extent & Degree of
Gas
Station
Building
UST
system
Petroleum Vapor Sources
• Construct Conceptual Site Model
Contaminated
Soil, shallow
Strong Vapor Source
from LNAPL &
Contaminated Soil
Contaminated Soil
& LNAPL
RAOULT’S LAW
Clean
aerobic soil
Weak Vapor Source
from
Dissolved Plume
HENRY’S LAW
Dissolved contamination
Results of Field Data
& Published Studies
• Subsurface soil is a natural bioreactor:
- Biodegradation of Petroleum Hydrocarbons by hundreds/thousands
microbial genera/species proven by 100 years of published research
- Characteristics of petroleum biodegradation & vapor attenuation are
well-understood & predictable
- Vapors attenuate with 5-8 feet thickness of clean (uncontaminated)
oxygenated (aerobic) overlying soil
- Clean soil contains sufficient Oxygen needed to attenuate vapors, ~4% O2
- Vapors attenuate up to 1,000,000-fold, most 1000-10,000-fold
• No reported cases of petroleum vapor
intrusion from low source strengths
• Causes of petroleum vapor intrusion:
- LNAPL, contaminated soil or high dissolved concentrations near
or in direct contact with buildings, sumps, elevator shafts
Recognize Signature Characteristics of
Aerobic Biodegradation & Attenuation of
Petroleum Hydrocarbon Vapors
Vapor Monitoring Well NJ-VW-2
Beaufort, SC, Lahvis et al, 1999
Beaufort, SC NJ-VW2
Sand, fine-grained,
silt
Oxygen
et al., 1999) vapors
8 ft clean(Lahvis,
soil attenuates
Carbon Dioxide
Subsurface Bio-AF=7E-07
Benzene
O2 & CO2 (% V/V)
0
5
10
15
20
25
Depth feet bgs
0
5
Benzene in GW
16,000 ug/L
10
15
1.E+00
1.E+02
1.E+04
Benzene (ug/m3)
1.E+06
1.E+08
Recognize Non-Attenuation of Vapors
due to Lack of Clean Overlying Soil
Conneaut, OH VMP-1
(Roggemans, 1998; Roggemans et al., 2001)
Subsurface
AF
7E-01 Bio-AF=7E-01
Oxygen
Carbon Dioxide
Benzene
O2 & CO2 (% V/V)
0
5
10
15
20
0
Contaminated Soil
(sand, silty sand)
5
10
15
1.E+00
1.E+02
1.E+04
1.E+06
Benzene (ug/m3)
1.E+08
Recognize Importance of Shallow
Vapor Completion Points
Example of apparent non-attenuation due to no shallow soil
completion point in 2006
VW-11
Hal’s, Green River, Utah
VW-11
Benzene SV, ug/m3
TPH SV, ug/m3
0
0
2
2
4
4
6
8
No attenuation
within
contaminated
zone
6
8
10
10
12
12
14
1.00E+00
Benzene SV, ug/m3
TPH SV, ug/m3
6/27/07
6/27/07
Depth, feet bgs
Depth, feet bgs
VW-11
8/26/06
8/26/06
Shallow points
confirm
attenuation
above
contaminated
zone
14
1.00E+03
1.00E+06
SV Concentration, ug/m3
1.00E+09
1.00E+00
1.00E+03
1.00E+06
SV Concentration, ug/m3
1.00E+09
Method for Expressing Magnitude of
Subsurface Vapor Attenuation
“Attenuation Factor” AF
= ratio of shallow subsurface vapor concentration divided by deep
Beaufort, SC NJ-VW2
(Lahvis, et al., 1999)
Oxygen
Carbon Dioxide
AF =
Shallow SV Benzene, ug/m3
0
Deep SV Benzene, ug/m3
AF
=
145,000 ug/m3
5
10
15
20
25
0
5
Field Example:
~1 ug/m3
Benzene
O2 & CO2 (% V/V)
= 7E-06
~1,000,000x contaminant reduction
Benzene in GW
16,000 ug/L
10
15
1.E+00
1.E+02
1.E+04
1.E+06
1.E+08
Benzene (ug/m3)
Low AF = Great attenuation of contaminants
Distribution of Magnitude of Subsurface
Petroleum Vapor Attenuation
Benzene
150
120
90
60
30
0
TPH
3 Reasons for
Insignificant
AF
200
160
120
80
40
0
<1.E-04
TPH
1.E-03
1.E-02
>1.E-01
Subsurface Vapor Attenuation Factors
Screen these out
Reason 1: No Reason 2: Low
Clean
Source
Overlying Soil
Strength
1.E-01
Reason 3:
Rapid
Attenuation
Near HighStrength
Source
Number of Soil Vapor Sample Events
Number of Soil Vapor Sample Events
Number of Soil Vapor Sample Events
Benzene
100
80
60
Most events exhibit
Benzene
TPH
very low AFs,
significant
attenuation
(<10,000x)
Reasonable
application
100x to
1000x
40
20
0
<1.E-04
1.E-03
1.E-02
Subsurface Vapor Attenuation Factors
Comparison of
Field Data to
Models
Beaufort, South Carolina (Lahvis et al 1999)
Very High-Strength Dissolved Source beneath Pavement
BioVapor Model under-predicts subsurface attenuation
by 100x to 10,000x
Beaufort, SC (Lahvis et al, 1999)
Soil Vapor Field Data Compared to BioVapor Model from dissolved source
Beaufort, SC (Lahvis et al, 1999)
Soil Vapor Field Data Compared to BioVapor Model from Dissolved Source
TPH-gro Field-Measured, ug/m3
Benzene Field-Measured, ug/m3
TPH-gro Bio Vapor Prediction, ug/m3, AF=0.1, O2=1%, foc=0.5%, Bare Earth
Benzene BioVapor Prediction, ug/m3, AF=0.1, O2=1%, foc=0.5%, Bare Earth
TPH-gro Bio Vapor Prediction, ug/m3, AF=0.1, O2=1%, foc=0.5%, Pavement
Benzene BioVapor Prediction, ug/m3, AF=0.1, O2=1%, foc=0.5%, Pavement
TPH-gro Bio Vapor Prediction, ug/m3, AF=0.1, O2=1%, foc=0.5%, Aerobic Depth Speci
0
0
3
3
Depth, feet bls
Depth, feet bls
Benzene BioVapor Prediction, ug/m3, AF=0.1, O2=1%, foc=0.5%, Aerobic Depth=3.4 ft bls
6
9
6
9
Benzene in GW
16,000 ug/L
12
1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07
TPH in GW
67,100 ug/L
12
1.0E-01
1.0E+01
1.0E+03
1.0E+05
Benzene, ug/m3
TPH-gro, ug/m3
1.0E+07
1.0E+09
Chatterton, SG-BC 10-1-97 (Hers et al 2000)
Soil VaporChatterton,
Source
over&Benzene-Rich
LNAPL,
Multi-Depth
Sub-Slab
BC, Sub-Slab
Multi-Depth Beneath Building,
10-1-97 (Hers,
2006)
Benzene
Soil Vapor Field Data Compared to BioVapor Model
BioVapor Model under-predicts subsurface attenuation
by 10,000x to 1,000,000x
Benzene Field-Measured, ug/m3
Benzene Bio Vapor Prediction, ug/m3, O2=1%, foc=0.5%
Benzene Bio Vapor Prediction, ug/m3, O2=1%, foc=0.5%, Aerobic Depth 3.28 ft
-5
Depth, feet bls
Building Slab
0
5
10
1.0E+00
LNAPL, benzene rich
1.0E+02
1.0E+04
1.0E+06
Benzene, ug/m3
1.0E+08
Numerical
Model
Effect of Vapor Source Concentration & Depth Beneath Buildings
Vapor source 100,000 ug/m3
(Abreu-Johnson
Model, Abreu et al
2009, API #4775)
Vapor source 1,000,000 ug/m3
Vapor source 10,000,000 ug/m3
Conclusions from Models
BioVapor Model
- Under-predicts subsurface attenuation & over-predicts PVI by
10xxxx for low-to-medium-high source strength
- Very high-strength sources likely need PVI investigation
Abreu-Johnson Numerical Model
- Vapors associated with low-to-medium source strengths
beneath average-size buildings are attenuated with a few feet of
clean overlying soil
- Oxygen occlusion beneath slab with high vapor
concentrations at shallow depths
Screening/Exclusion
Criteria
• PVI Database: line-by-line analysis of
field data, plot data
• Determine Thickness of Clean
Overlying Soil Required to Attenuate
Vapors Associated with:
- Dissolved Sources
- LNAPL & Soil Sources
Method for Evaluating Vapor
Attenuation from Dissolved Sources
Multi-Depth Vapor Monitoring Well
Beaufort, SC, Lahvis et al 1999
Feet
bgs
NJ-VW-2
0
5
8 feet Clean
overlying soil
3 ft
Benzene vapor
concentrations at depth
<1 ug/m3
4 ft
2,300 ug/m3
7 ft
16,700 ug/m3
Estimated
Contaminated
soil zone
10
DTW ~11 ft
11 ft
145,000 ug/m3
Benzene in GW 16,000 ug/L
15
FORMULA: 11 ft – 3 ft = 8 ft clean overlying soil
Screening Criteria for Dissolved
Benzene & TPH
(Exterior + Sub-Slab)
Benzene: Soil Vapor & Dissolved Paired Measurements
TPH: Soil Vapor & Dissolved Paired Measurements
Near-Slab
Multi-Depth,
Sub-Slab= 97 total
TPH: 73
exterior/near-slab
+ 24 sub-slab
Benzene: 199 Near-Slab
exterior/near-slab
+ 37 sub-slab
Multi-Depth,
Sub-Slab = 236 total
All Soil Types
All Soil Types
Thickness Clean Soil Required to
Attenuate TPH Vapors, feet
Thickness Clean Soil Required to
Attenuate Benzene Vapors, feet
10
9
8
7
6
5
4
3
2
1
0
1
10
100
1,000
10,000
100,000
10
9
8
7
6
5
4
3
2
1
0
1
100
10,000
1,000,000
Benzene, dissolved, ug/L
TPH, dissolved, ug/L
5 ft Clean Overlying Soil Attenuates Vapors Associated
with Dissolved Benzene <1,000 ug/L, TPH 10,000 ug/L
Separation Distance vs Source Strength:
Benzene
Soil Gas Concentrations Associated with
Source Strengths (ug/m3)
Dissolved phase, B(SG) < 50 µg/m 3
Dissolved phase, B(SG) > 50 and <1000 µg/m 3
LNAPL, B(SG) < 50 µg/m3
LNAPL, B(SG) > 50 and < 1,000 µg/m3
LNAPL, B(SG) > 1,000 and <100,000 µg/m3
LNAPL, B(SG) > 100,000 µg/m3
1.5 m (~5 ft) clean soil required to
attenuate vapours associated
with Benzene in GW <1 mg/L
Separation Distance, Source to Soil Gas
measurement (m)
(slide courtesy of Jackie Wright, Environmental Risk Sciences, Sydney, Australia)
Field-Based Screening/Exclusion
Distances from Soil Gas Data (Lahvis, M., 2011)
100%
BENZENE
1000000
100000
20 SITES
89 LOCATIONS
335 SAMPLES
90%
80%
PROBABILITY (%)
SOIL GAS CONCENTRATION (ug/m3)
10000000
10000
1000
100
10
BENZENE
60%
< 50 ug/m3
50%
< 100 ug/m3
40%
< 200 ug/m3
30%
20%
measured
non detect
1
70%
DETECTS
10%
0%
0.1
0
10
20
30
40
DISTANCE ABOVE SOURCE (ft)
50
0
5
10
15
20
25
DISTANCE ABOVE WATER TABLE (ft)
Example: Robin Davis (Utah DEQ) and Jackie Wright (Australia) soil-gas databases


1245 soil-gas measurements from 155 retail* sites and 664 sampling locations
For gasoline sources, dissolved and LNAPL
Exclusion distances based on conditional probability

P ( soil gas <100 ug/m3 | source distance > 5 ft) = 1 – (134/335) = 60%

P ( soil gas < 100 ug/m3 | source distance > 15 ft) = 1 – (17/335) = 95%
30
2 Methods for Evaluating Vapor
Attenuation from LNAPL & Soil Sources
Hals’, Green River,
Utah (UDEQ)
Oxygen
VW-7
6/26/07
Carbon Dioxide
Benzene
O2 & CO2 (% v/v)
0
5
10
15
20
Method 1 Formula:
20 ft DTW – 11 clean SV= 9
feet TOTAL soil thickness
0
Method 2 Formula:
15 ft top contam – 11 ft
top clean soil = 4 feet
CLEAN soil needed to
attenuate vapors
Depth feet bgs
5
10
contaminated
soil zone
15
20
1.E+00
1.E+02
1.E+04
1.E+06
Benzene (ug/m3)
1.E+08
Method 1 Results for
LNAPL Sources
(All soil types. 43 paired SV benzene & LNAPL Events)
Sample events beneath buildings
Thickness of Overlying Soil, feet
30
25
30 ft TOTAL
(clean +
contaminated
smear zone)
soil attenuates
benzene
vapors
associated
with LNAPL
Refineries
20
15
10
5
0
Chillum
Chatterton
Coachella-2
Hal’s
Coachella-3
Mission
Valley
Refinery, Unknown
US Location
Method 2 Results for
LNAPL & Soil Sources
Benzene
48 exterior/near-slab + 23 sub-slab = 71 total
Benzene SV Sample Event over LNAPL & Soil Sources
TPH
17 exterior/near-slab + 19 sub-slab = 36 total
TPH SV Sample Event over LNAPL & Soil Sources
Near-Slab Multi-Depth, Sub-Slab
10
9
8
7
6
5
4
3
2
1
0
Thickness of Clean Soil Overlying LNAPL
Required to Attenuate Vapors, feet
Thickness of Clean Soil Overlying LNAPL
Required to Attenuate Vapors, feet
Near-Slab Multi-Depth, Sub-Slab
10
9
8
7
6
5
4
3
2
1
0
~8 ft CLEAN overlying soil attenuates
vapors associated with LNAPL/Soil Sources
Screening Criteria–Published & Cited Values (after Lahvis & DeVaull, 2011)
Reference
Davis, R.V. (2009, 2010)
Lahvis (2011)
McHugh et al (2010)
Peargin & Kolhatkar
(2011)
Wright, J. (2011)
California
Indiana
New Jersey
Wisconsin
Database &
Site Type
International Petroleum
Vapor Database
R.V. Davis & J. Wright (retail
sites only, no refineries)
Benzene Soil Gas
Screening Level
(ug/m3)
Screening/Exclusion
Distance
(feet)
Screening/Exclusion
Concentration
Benzene (ug/L)
complete attenuation
5
<1000
8
LNAPL
0
<12,000
15
LNAPL
10
Dissolved phase only
30
LNAPL
0
<520
15
>520
5
<1000
30
LNAPL
5
<100
no SG Oxygen measured
5
<1000
with SG Oxygen measured >4% (?)
10
<1000
no SG Oxygen measured
30
LNAPL
5
<1000
10
<1000
30
LNAPL
5
<100
no SG Oxygen measured
5
<1000
with SG Oxygen measured >4% (?)
10
<1000
no SG Oxygen measured
30
15
5
<1000
20
>1000
30
LNAPL
100
various publications,
professional judgement
Chevron, all sites
Australia & U.S. sites, all
sites + refineries
various references, R.V.
Davis, McHugh et al
various references, R.V.
Davis, McHugh et al
various references, R.V.
Davis, McHugh et al
Davis, R.V., 2009 , Luo et al
2009, McHugh et al, 2010
300
10, 50, 100, 1000
Other
Criteria
5 feet for TPH <10,000 ug/L
Dissolved phase only
NONE
NONE
SG Oxygen requirement
Distances apply vertically &
horizontally
NONE
NONE
Horizontal distance required from
building structure to Benzene 15 ug/L
Distances apply vertically &
horizontally
Screening Criteria–Published & Cited Values (after Lahvis & DeVaull, 2011),
continued
Reference
Database &
Site Type
Benzene Soil
Gas
Screening Level
(ug/m3)
Screening/Exclusi
on Distance
(feet)
Screening/Exclusion
Concentration
Benzene (ug/L)
EPA OSWER (2002)
(1)
(1)
100
Dissolved phase only
100
LNAPL
30
Dissolved phase only
100
LNAPL
0
<1000
60
LNAPL
ASTM E 2600-08
(2008)
Atlantic PIRI (2006)
(2)
Modeling (Abreu &
Johnson, 2005)
(2)
NONE
(1) based on measured indoor data for one or more dissolved chlorinated
solvent groundwater plumes in Colorado.
(2) based on EPA OSWER (2002)
Other
Criteria
Spatial Data
Behavior of Vapors
Beneath & Exterior
to Buildings
Chatterton Research Site, British
Columbia, Canada
(Hers, et al 2000)
Building
SG-BC,
10/1/97
0
Fill, sandy silt
SG-BR
5/14/97
<1000
11%
10 %
<1000
10%
80,000
8%
Depth, feet bls
55,000
6%
5
Fill,
dredged
river sand
Bare soil
3%
50,000,000
25,000,000
1.0%
KEY
SG-BC
50,000,000
1.0%
Vapor sample
point identifier
Sub-Slab vapor
sample point
60,000,000
Sub-Surface vapor
sample point
50,000,000
1.0%
Benzene, ug/m3
Oxygen, %
LNAPL, benzene-rich
10
FIELD RESULTS: Oxygen is NOT
occluded by small building ~9 ft above
LNAPL source
0
20
Feet, horizontal
Perth, Australia
Very Large Building
0
410
<2
30-ft wide
concrete apron
Uncovered open ground
19,000,000
<0.5%
Depth, feet bls
(B. Patterson & G. Davis, ES&T 2009)
<50,000
10.7%
<50,000
19.9%
<50,000
18.8%
Lateral Extent of Oxygen & Biodegradation
5
35,000,000
<0.5%
Sand
35,000,000
<0.5%
10
<50,000
8.2%
<50,000
14.5%
<50,000
15.9%
1,200,000
8.2%
<50,000
4.5%
<50,000
4.6%
LNAPL, kerosene, low BTEX
FIELD RESULTS: Oxygen is
occluded by large building, but
reaches to ~30 ft laterally
beneath building. Exterior vapor
attenuation with ~5 ft clean soil &
~8 ft total soil above LNAPL.
KEY
Outdoor air sample
Indoor air sample
Sub-slab vapor sample
Sub-surface vapor sample
1,200,000 Total Petroleum Hydrocarbons, ug/m3
8.2% Oxygen, %
0
20
Feet, horizontal
Temporal Data
Behavior of Vapors
Beneath & Exterior to
Buildings Over Time
Chatterton Research Site,
British Columbia, Canada
SG-BC
Beneath Building
Chatterton SG-BC Beneath Building
Hers et al 2000
0
Building foundation slab
Benzene SV 9/2/97
(Hers et al, 2000)
SG-BR
~16 ft from Building Edge
Chatterton SG-BR ~16 ft from Building edge
Benzene SV 10/1/97
Hers et al 2000
Benzene SV 11/1/97
Benzene SV 3/18/98
0
Bare soil
Ben z en e S V 7/25/97
< Detection limits
Ben z en e S V 12/1/97
Depth, feet bgs
ft bgs
Depth, feet bgs
ft bgs
6
Ben z en e S V 3/18/98
8
4
Ben z en e S V 11/1/98
Ben z en e S V 2/19/99
6
8
10
1.E+00
Ben z en e S V 7/2/97
2
4
Ben z en e S V 5/14/97
Ben z en e S V 6/24/97
Benzene SV 6/1/98
2
Ben z en e S V 3/11/97
1.E+02
1.E+04
1.E+06
Benzene SV, ug/m3
1.E+08
1.E+10
10
1.E+00
1.E+02
FIELD RESULTS: Small building ~9 feet above
LNAPL. Vapors are attenuated below building slab
for all events near-slab, & sub-slab except the first.
1.E+04
1.E+06
Benzene SV, ug/m3
1.E+08
1.E+10
1
Characterize Site
(non-emergency conditions)
2
3
4
Decision
Matrix
Compare
Dissolved/LNAPL/Soil Field
Data to Screening Criteria
No Exceedance
Collect Soil Vapor
Data & Evaluate
Attenuation
No Exceedance
Compare IA/OA to
Screening or HealthBased Criteria
No Exceedance
6
5
Mitigate
No Exceedance
No Further PVI
Evaluation
Needed
Conclusions
• PVI pathway not complete when following Criteria apply:
Dissolved Sources
- 5 feet CLEAN soil overlying Benzene <1,000 ug/L, TPH <10,000 ug/L
LNAPL Sources
- 8 feet CLEAN soil overlying top of LNAPL smear zone or soil sources
- 30 feet TOTAL including smear zone; poorly-characterized sites
Soil Sources
- 5 feet CLEAN soil = TPH <100 mg/kg, PID <10 ppm-v, O2 ~4%
Vapor Sources
- Vapors are attenuated below the receptor
Recommendations
• Fully characterize sites
• Collect & use ALL lines of evidence to determine if PVI
pathway is complete
• Apply Screening/Exclusion Criteria in decision-making
THANK YOU
Acknowledgments
EPA OUST/ORD/States PVI Work Group
API Petroleum Vapor Intrusion Work Group
Bruce Bauman, Roger Claff, Harley Hopkins
George DeVaull, Shell Global Solutions
Blayne Hartman, Hartman Environmental Geoscience
Tom McHugh, GSI Environmental
John Menatti, Utah DEQ
Tom Peargin, Chevron-Texaco
Lynn Spence, P.E., Spence Engineering
Todd Ririe, BP
Matt Lahvis, Shell Global Solutions
Jackie Wright, Environmental Risk Sciences