Methods for Developing and
Applying Screening Criteria for the
Petroleum Vapor Intrusion Pathway
Workshop 7
Tuesday March 24, 2015
6:30 pm – 9:30 pm
Association for Environmental Health & Sciences (AEHS)
25th Annual International Conference on Soil, Sediment, Water & Energy
San Diego, California
by
Robin V. Davis, P.G.
Project Manager
Utah Department of Environmental Quality
Leaking Underground Storage Tanks
rvdavis@utah.gov 801-536-4177
OBJECTIVES
 Understand why petroleum vapor intrusion (PVI) is
very rare despite so many petroleum LUST sites
 Understand causes of PVI
 Show mechanisms, characteristics, degree of vapor
bioattenuation
 Show distances of vapor attenuation, apply as
Screening Criteria, screen out low-risk sites
 Avoid unnecessary additional investigation,
soil gas/air sampling
SCOPE
 Field studies published by work groups, individuals
 Data compiled to an empirical database:
EPA Petroleum Vapor Database Jan. 2013



Source strength: LNAPL in soil and GW, dissolved-phase
Associated soil gas measurements from 1000s of sample points
at 100s of sites
Extensive peer review and quality control checks
 Guidance Documents Issued:

Some US States

Australia 2012

EPA draft PVI April 2013

ITRC October 2014

EPA ORD Issue Paper 2014
Petroleum Vapor Database of
Empirical Studies EPA OUST Jan. 2013
Canada
4/13
Australia
United States
70/816
124/>1000
Perth
Sydney
Tasmania
Australian sites evaluated separately
MAP KEY
70 # geographic locations evaluated
816 # paired concurrent measurements
of subsurface benzene soil vapor
& source strength
REFERENCES
Davis, R.V., 2009-2011
McHugh et al, 2010
Peargin and Kolhatkar, 2011
Wright, J., 2011, 2012, Australian data
Lahvis et al, 2013
EPA Jan 2013, 510-R-13-001
Conceptual Characteristics of Petroleum
Vapor Transport and Biodegradation
a) LNAPL SOURCE
O2
UNSATURATED ZONE
high mass
flux
sharp
reaction
front
VOCs
CAPILLARY ZONE
0
1
O2/Hydrocarbon
constituent
Vapor Profile
SATURATED ZONE
distributions
b) DISSOLVED-PHASE SOURCE
UNSATURATED ZONE
limited mass
flux
CAPILLARY ZONE
SATURATED ZONE
• Aerobic biodegradation of
vapors is rapid, occurs over
short distances
• LNAPL sources have high
mass flux, vapors attenuate
in longer distances than
dissolved sources
• Sufficient oxygen supply
relative to its demand,
function of source strength
O2
VOCs
KEY POINTS
sharp
reaction
front
0
1
O2/Hydrocarbon
constituent
Vapor Profile
distributions
After Lahvis et al 2013 GWMR
Subsurface Petroleum Vapor
Bioattenuation Study Results
 >100 years of research proves rapid vapor
biodegradation by 1000s of indigenous microbes
 Studies show vapors biodegrade and attenuate
within a few feet of sources
 No cases of PVI from low-strength sources
 Causes of PVI are well-known
Causes of Petroleum Vapor Intrusion
1
BUILDING
High-strength source in
direct contact with
building (LNAPL, high
dissolved, adsorbed)
4
Unsaturated
Soil
Preferential pathway:
bad connections of
utility lines; natural
fractured and karstic
rocks
LNAPL
LNAPL
3
Affected GW
Preferential
pathway: sumps,
elevator shafts
2
LNAPL
Groundwater-Bearing Unit
Drawing after Todd Ririe, 2009
High-Strength Sources
 Direct contact or close proximity to buildings
 Preferential pathways: engineered & natural
High-strength
source in close
proximity to
building, within GW
fluctuation zone
Collect Basic Data, Characterize Site,
Construct Conceptual Site Model
 Define extent & degree of contamination
 Apply Screening Criteria
Building
Soil Boring/MW
Soil Boring/MW
Utility line
LNAPL
in soil
Clean Soil
UST
system
High vapor
concentrations,
high mass flux
from LNAPL & soil
sources
Low vapor
concentrations, low
mass flux from
dissolved sources
LNAPL in
soil & GW
Dissolved contamination
Signature Characteristics of Aerobic Biodegradation
of Subsurface Petroleum Vapors
Oxygen
Carbon Dioxide
Benzene
Beaufort, SC NJ-VW2
(Lahvis, et al., 1999)
0
5
O2 & CO2 (% V/V)
10
15
Salina Cash Saver VMW-1
(UDEQ 7/27/07)
Coachella, CA COA-2
(Ririe, et al 2002)
0
-5
O2 & CO2 (% V/V)
20
25
0
0
5
10
15
20
5
10
15
20
25
OA
IA
0
Depth, feet below grade
0
5
5
5
10
10
LNAPL
10
LNAPL
15
Benzene in GW
16,000 ug/L
15
1.E+00
1.E+02
1.E+04
1.E+06
1.E+08
15
1.E+00
1.E+02
Benzene (ug/m3)
1.E+04 1.E+06
Benzene (ug/m3)
1.E+08
20
1.E+001.E+021.E+041.E+061.E+08
Benzene (ug/m3)
• Vapors aerobically biodegraded by oxygen-consuming microbes,
waste product carbon dioxide
• Vapors attenuate in short distances
Vapor Bioattenuation Limited by
Contaminated Soil
Oxygen
Carbon Dioxide
Benzene
Conneaut, OH VMP-1
(Roggemans, 1998; Roggemans et al., 2001)
O2 & CO2 (% V/V)
0
5
10
15
20
Depth, feet below grade
0
5
LNAPL in Soil
(sand, silty sand)
10
15
1.E+00
1.E+02
1.E+04
1.E+06
Benzene (ug/m3)
1.E+08
Importance of Shallow Vapor Completion Points
Example of apparent non-attenuation until shallow
vapor point installed in non-contaminated soil
VW-11 Hal’s, Green River, Utah
8/26/06
Shallow
completion
too deep
No attenuation
within
contaminated
soil zone
6/27/07
Shallower point
confirms
attenuation above
contaminated soil
zone
EPA OUST Jan. 2013
Results of Empirical Studies
http://www.epa.gov/oust/cat/pvi/PVI_Database_Report.pdf
•
Thickness of clean soil required to attenuate vapors
associated with LNAPL and dissolved sources
•
Screening Criteria
Dissolved Sources
Jackson’s, UT
Santa Clara, UT
Oxygen, %
Carbon Dioxide, %
Benzene, ug/m3
VMW-4 9/29/08
VW-4 1/19/2009
O2 & CO2 (% v/v)
0
5
10
15
20
25
0
0
5
O2 & CO2 (% V/V)
10
15
20
25
0
Depth, feet bgs
2
5
4
4.94 feet
Benzene in GW
12,000 ug/L
6
10
8
Benzene in GW
3180/ ug/L
10
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
Benzene (ug/m3)
1.E+05
1.E+06
15
1.E+00
1.E+02
1.E+04
1.E+06
4 feet
1.E+08
Benzene (ug/m3)
Thickness of clean soil needed to attenuate vapors
= Distance between top of source and deepest clean vapor point
LNAPL Sources
Oxygen
Beaufort, SC
Carbon Dioxide
NJ-VW2 Lahvis, et al., 1999
COA-2 Ririe, et al 2002
O2 & CO2 (% V/V)
Benzene
O2 & CO2 (% V/V)
0
5
10
15
20
25
0
Coachella, CA
0
5
10
15
20
0
Depth, feet below grade
9.5 feet
5
5
8 feet
10
10
Benzene in GW
16,000 ug/L
15
1.E+00
1.E+02
1.E+04
1.E+06
Benzene (ug/m3)
1.E+08
15
1.E+00
1.E+02
1.E+04
1.E+06
1.E+08
Benzene (ug/m3)
Thickness of clean soil needed to attenuate vapors
= Distance between top of LNAPL and deepest clean vapor point
Screening Distances
Dissolved Sources
LNAPL Sources (small sites)
Benzene Vapors vs. Distance of Attenuation
Benzene Vapors vs. Distance of Attenuation
5 ft
15 ft
95%-100% Confidence
Lahvis et al 2013
Results of Vapor Attenuation from LNAPL Sources
13 feet, 95% Confidence
•
Different
analysis, similar
results
•
13 ft vertical
separation
attenuates
LNAPL source
vapors
LNAPL Indicators
LNAPL INDICATOR
MEASUREMENTS
Current or historic presence of LNAPL Visual evidence:
in groundwater or soil
Sheen on groundwater or soil, soil staining, measurable thickness
Groundwater, dissolved-phase
PHCs >0.2 times effective solubilities
Benzene >3-5 mg/L
TPH-gro >20-30 mg/L
TPH-dro >5 mg/L
(Bruce et al. 1991)
Soil, adsorbed-phase
PHCs >effective soil saturation (Csat)
Benzene >10 mg/kg
TPH-gro >250-500 mg/kg
Soil field measurements
Organic vapor analyzer/PID/OVA of
soil cores
Gasoline-contaminated soil: >500 ppm-v
Diesel-contaminated soil: >10 ppm-v
Soil Gas measurements
-
O2 shows no increase and CO2 shows no decrease with
increasing distance from source
Elevated aliphatic soil gas concentrations, eg Hexane >100,000 ug/m3
17
(after EPA 2013; Lahvis et al 2013)
Results of Empirical Studies for
Developing Screening Criteria
 Various methods of data analysis yield similar results
 Dissolved Sources require 5 feet separation distance:
• Benzene <5 mg/L
• TPH
<30mg/L
 LNAPL Sources require 15 feet separation distance:
• Benzene >5 mg/L, >10 mg/kg
• TPH
>30mg/L, >250-500 mg/kg
• 18 feet separation required for large industrial sites
 Soil within separation distance:
• LNAPL-free soil contains sufficient oxygen to bioattenuate vapors
• “Clean” (non-source), biologically active, sufficient oxygen and moisture
• EPA: <100 mg/kg TPH “clean” soil
Measuring Magnitude of Subsurface
Vapor Attenuation
Subsurface Attenuation Factor (AF)
= Ratio of shallow to deep vapor concentration
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
25
20
15
0
5
Field Example:
~1 ug/m3
Benzene
O2 & CO2 (% V/V)
= 7E-06
~7,000,000x contaminant reduction
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
Distribution of Magnitude of Subsurface
Petroleum Vapor Attenuation Factors
Benzene
TPH
3 Reasons for
Insignificant
AFs 10x-100x
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
150
120
90
60
30
0
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
Most events
exhibit Significant
Benzene
TPH
AFs >10,000x
100
Reasonable Screening
AF 100x-1000x
80
60
40
20
0
<1.E-04
1.E-03
1.E-02
Subsurface Vapor Attenuation Factors
EPA Modeling Studies
Vertical and Lateral Attenuation Distances
http://www.epa.gov/oswer/vaporintrusion/documents/vi-cms-v11final-2-24-2012.pdf
Building with
Basement
Vertical Distance Below Grade, meters
0
LNAPL Vapor Source
200,000,000 ug/m3
8 m deep (26 ft)
2
Vertical
Attenuation
6m (20 ft)
4
6
8
10
0
Lateral
Attenuation
5m (16 ft)
20
30
40
50
60
70
Oxygen
80
90
Model:
20 ft vertical
16 ft lateral
Field Data:
15 ft vertical
8 ft lateral
Conclusions:
- Models under-predict
attenuation
- Vapors attenuate in
shorter distances
laterally than vertically
2
4
6
8
Lateral Distance, meters
Screening Criteria
U.S. and Australia
Reference
Screening
Distance
(feet)
Screening
Concentration
Benzene, TPH (ug/L)
EPA OUST Petroleum
Database Report
5
15
<5000, <30,000
LNAPL
Wright, J., Australia,
2011
5
<1000
30
LNAPL
5
<100
SG Oxygen not required
5
<1000
SG Oxygen required >4%
10
<1000
SG Oxygen not required
30
LNAPL
5
<1000
California
Indiana
New Jersey
Wisconsin
30
LNAPL
Other
Criteria
LNAPL UST sites. 18 ft for large sites.
Clean soil <250 mg/kg TPH
Includes large industrial sites
SG Oxygen not required
Distances apply vertically & horizontally
AFs for GW & SG
5
<100
SG Oxygen not required
5
<1000
SG Oxygen required >2%
10
<1000
SG Oxygen not required
100
LNAPL
Distances apply vertically & horizontally
5
<1000
Distances apply vertically & horizontally
20
>1000
30
LNAPL
THANK YOU