1. Tribal Lands & Environment Forum (TLEF)
Applying Screening Criteria for the Petroleum Vapor Intrusion Pathway
presented to
Tribal Lands & Environment Forum (TLEF)
Petroleum Vapor Intrusion Session
Thursday August 18, 2016, 10:30 pm – 12:00 pm
Mohegan Sun Resort Uncasville, Connecticut by
Robin V. Davis, P.G., Retired Environmental Scientist/Project Manager,
Utah Department of Environmental Quality
Leaking Underground Storage Tanks

2. OBJECTIVES Understand Show Apply Screening Criteria
Why petroleum vapor intrusion (PVI) is very rare despite so many petroleum LUST sites
Causes of PVI
Show
Mechanisms, characteristics, degree of vapor bioattenuation
Distances of vapor attenuation relative to source strength
Apply Screening Criteria
Screen out low-risk sites
Avoid unnecessary, costly investigation
PVI investigations are very intrusive physically and socially
The objective of studying and evaluating the behavior of subsurface petroleum vapors is to understand why, with so many LUST sites worldwide, the PVI pathway is rarely complete. Using basic, routine field data enables us to develop and apply screening criteria to determine when PVI investigations are necessary.

3. Field and Published Data from 3 Countries
SCOPE
Field and Published Data from 3 Countries
EPA Database Report of Empirical Studies, Jan. 2013
Paired, concurrent measurements of source strength and associated soil gas measurements from 1000s of sample points at 100s of sites
Extensive peer review and quality control checks
Quantified distances of vapor attenuation relative to source strength
Guidance Documents Issued:
Some US States
Australia 2012
ITRC October 2014
EPA final PVI June 2015
The scope of evaluating the PVI pathway involved collecting and compiling basic site data (soil, GW, vapor data) to the EPA Petroleum Vapor Database. A LUST site must be fully characterized by collecting basic, good-quality data wherein the nature, extent and degree of contamination and contaminant sources are fully defined (required by 40 CFR Part 280), and provide knowledge of contaminant distribution in soil and groundwater, including temporal effects such as fluctuating DTW. Once these subsurface characteristics are understood, LUST PMs can better understand if the PVI pathway may be complete and if VI investigations are really necessary. VI investigations are costly and highly invasive to properties and their occupants, and unnecessary work should be avoided.
Time Line of Studies and EPA Publications
2002: EPA OSWER Draft Guide for Vapor Intrusion Evaluations
: EPA OUST/States Petroleum Vapor Intrusion Work Group
: Work Group hiatus, continued independent data compilation, analysis
: EPA OUST/States PVI Work Group Revived
2011: EPA OUST Petroleum Hydrocarbons and Chlorinated Hydrocarbons Differ in Their Potential for Vapor Intrusion
2012: EPA OUST Approach for Developing Lateral and Vertical Distances
2013: EPA OUST Evaluating Empirical Data for Screening Petroleum Sites (“Petroleum Vapor Database Report”)
2014: EPA OUST Approach Using Hydrocarbon Concentrations in Soil Gas to Evaluating Potential for PVI
2015: EPA OUST publishes final PVI Guidance

4. Petroleum Vapor Database of Field Studies
EPA OUST Jan. 2013
4/13
70/816
Canada
United States
124/>1000
Perth
Sydney
Tasmania
Australia
EPA OUST Petroleum Database Report
Original database provided by Davis, R.V, 2011.
Data analyzed for 74 Sites, 829 paired measurements of concurrent contaminant source strength and associated vapor data, additional 64 benzene vapor measurements without specific source strength data. More than 70 sub-slab measurements.
Source strengths are divided into dissolved-phase, LNAPL in groundwater, and residual LNAPL in vadose zone soil.
Australian data analyzed separately because of limited access to raw data.
Australian sites evaluated separately
MAP KEY
REFERENCES 70
# geographic locations evaluated
Davis, R.V.,
McHugh et al, 2010
Peargin and Kolhatkar, 2011
Wright, J., 2011, 2012, Australian data
Lahvis et al, 2013
EPA Jan 2013, 510-R
816
# paired concurrent measurements
of subsurface benzene soil vapor
& source strength

5. Results of Subsurface Petroleum Vapor Bioattenuation Studies
>100 years of research proves:
Rapid aerobic biodegradation of vapors by 1000s of indigenous microbes
Vapors attenuate within a few feet of sources
No cases of PVI from low-strength sources
Causes of PVI are well-known

6. Causes of Petroleum Vapor Intrusion
High-strength source in direct contact with building (LNAPL, high dissolved, adsorbed)
Preferential pathway: bad connections of utility lines; natural fractured and karstic rocks 1
BUILDING 4
Unsaturated Soil
LNAPL
LNAPL
High-strength source in close proximity to building, within GW fluctuation zone 3
Preferential pathway: sumps, elevator shafts
Affected GW 2
LNAPL
Groundwater-Bearing Unit
Practical field experience and published literature of field studies show that petroleum vapor intrusion impacts are generally associated with:
Direct contact of LNAPL or very high dissolved concentrations to a building foundation
Close proximity of LNAPL or very high dissolved concentrations to a building foundation that fluctuation GW levels bring contamination in direct contact with building
Direct contact of LNAPL or very high dissolved concentrations to building sumps, elevator shafts
Direct contact of LNAPL or very high dissolved concentrations with preferential pathway (e.g., improperly-sealed utility lines)
Key Points:
Field data confirm that petroleum vapor intrusion impacts are associated with high contaminant concentrations, and that vapor intrusion does not occur with low concentrations of petroleum hydrocarbons dissolved in groundwater or adsorbed in soil.
Drawing after Todd Ririe, 2009
High-Strength Sources
Direct contact or close proximity to buildings
Preferential pathways: engineered & natural 6

7. Preferential Pathway: Engineered
Petroleum Source
(ITRC PVI Tech Reg, 2014)

8. Preferential Pathway: Natural
(ITRC PVI Tech Reg, 2014)

9. Petroleum Vapor Database Report
EPA OUST
Petroleum Vapor Database Report
January 2013
The Database Report is a compilation and analysis of field data from Davis , and more data compiled by EPA OUST from various US states and Australia. The database consists of thousands of measurements of soil gas and concurrent associated source strengths from hundreds of sites.
January 2013
Compilation & analysis of concurrent field data measurements:
LNAPL in soil & GW
Dissolved sources
Associated soil vapor data
Quantifies distances of vapor attenuation

10. O2/Hydrocarbon Vapor Profile O2/Hydrocarbon Vapor Profile
Conceptual Characteristics of Petroleum Vapor Transport and Aerobic Biodegradation
KEY POINTS
Subsurface soil is a natural bioreactor
Aerobic biodegradation of vapors is rapid, occurs over short distances as a sharp reaction front
Oxygen demand is a function of source strength
Strong LNAPL sources (panel a) use much more oxygen, and vapors attenuate in longer distances than weak sources (panel b) 1
O2/Hydrocarbon Vapor Profile
Figure 1 Lahvis et al 2013 1
O2/Hydrocarbon Vapor Profile
After Lahvis et al 2013 GWMR

11. Field Characteristics of Petroleum Vapor Transport and Aerobic Biodegradation
Profile of Subsurface Multi-Depth Vapor Sample Points and
Concentrations of Benzene, Oxygen, and Carbon Dioxide
Sharp Reaction Front
7 feet separation distance
Vapor profiles of multi-depth vapor probes showing the signature characteristics of aerobic biodegradation of petroleum hydrocarbon (PHC): Aerobic soil microbes use oxygen in the process of capturing the carbon as food from the petroleum hydrocarbon. The resulting waste product is carbon dioxide. Therefore, near the contaminant source, O2 is depleted and CO2 is enriched. As the PHC is biodegraded, PHC vapor concentrations decrease, and O2 and CO2 rebound to near-atmospheric concentrations.
Typical O2, CO2, PHC vapor profiles: petroleum vapors naturally biodegrade & attenuate with sufficient thickness of “clean” or non-source vadose zone soil
1000’s of such measurements yield consistent, predictable results
Extent and magnitude of vapor attenuation can be quantified, and Screening Criteria developed and applied
Vapors are aerobically biodegraded quickly by oxygen-consuming microbes, waste product carbon dioxide
Vapors attenuate in short distances, even from a strong source

12. EPA OUST Final PVI Guide Technical Guide For Addressing
Petroleum Vapor Intrusion
At Leaking Underground Storage
Tank Sites
June 11, 2015
This guide presents Screening Criteria that are based on the findings of the EPA OUST Petroleum Database Report.
June 2015
DESCRIBES
Thickness of Clean, Non-Source Soil Required to Attenuate Vapors Associated with LNAPL in Soil and GW, and Dissolved Sources
Using Multiple Lines of Evidence for Site Characterization and Screening

13. PVI Pathway Not Likely Complete
Figure 1: Flowchart for Addressing PVI At Leaking Underground Storage Tank Sites (modified from EPA OUST 2015)
STEP 2
Characterize Site
Define extent/degree of contamination
Construct Conceptual Site Model NO
STEP 3
Delineate Lateral Inclusion Zone
STEP 1
Emergency?
Are Precluding
Factors Present?
(preferential pathways, other) NO
Are Any Existing or Planned Buildings Within Lateral Inclusion
Zone? NO
YES
STEP 5
Evaluate Vapor Source & Attenuation:
Measure Vapors Near-Slab & Near-Source , or
Measure Indoor Air & Concurrent Sub-Slab Vapors
If Contamination is in Direct Contact with Building, use Option 2 above
Models may be used only to explain observed vapor behavior
YES
YES
STEP 4
Determine Vertical Separation Distance for Each Building
STEP 6
Notify 1st Responders
Mitigate PVI
Community Engagement
Required by 40CFR
May occur at any step in the PVI investigation & mitigation process NO
Is Thickness of Clean Soil >Minimum Vertical Separation Distance?
YES
Simple, logical decision-making process comprised of 6 basic steps.
Notes
Precluding factors include the following:
Preferential transport pathways (natural or engineered) that connect a vapor source to a building
Expanding or mobile plume
Soil moisture below 2%, the wilting point
Extensive impermeable surface cover
High peat content of soil
Presence of non-petroleum fuel constituents
Presence of lead scavengers
>10% Ethanol
STEP 5: Models may be used to explain observed PHC vapor behavior (EPA PVIScreen):
EPA PVI Guide June 2015, p. 103, Fig. 9 (Attenuation Factors estimated from numerical model)
EPA PVI Guide June 2015, p. 109:
Computer model simulations must not be used as a sole line of evidence when evaluating and screening potential PVI sites.
The role of models in PVI screening is to explain observed behavior of PHC vapors, which means subsurface PHC vapor samples must be collected and the model adjusted for field-measured parameters.
Option 2
Option 1
YES
YES
Do Sub-Slab & Indoor Air Sampling Indicate PVI?
Do Near-Slab & Near-Source Sampling Indicate PVI? NO
PVI Pathway Not Likely Complete NO

14. Construct Conceptual Site Model (CSM) Dissolved contamination
Collect basic site data, characterize site
Define extent & degree of contamination
Apply Screening Criteria
Building
Soil Boring/MW
Soil Boring/MW
Utility line
LNAPL in soil
Clean Soil
UST system
Site characterization is routine and necessary in order to know if receptors are impacted. Title 40 of the Code of Federal Regulations, Part 280 for leaking USTs requires that sites be fully characterized by conducting subsurface investigations wherein the full extent and degree of contamination are defined. The presence and thickness of “clean” or non-source soil above contaminant sources are generally known in the early phases of site characterization by advancing and logging soil borings, and completing as GW monitoring wells.
Non-source soil, also called “Clean Soil.” is free of LNAPL and contains the necessary oxygen for biodegrading PHCs. Clean, non-source soil is easily characterized by logging borings/MWs, field PID measurements , visual and olfactory observations of soil cores, and collecting soil samples and analyzing for constituents of concern.
Build a Conceptual Site Model based on site-specific data.
Volatile compounds associated with LNAPL, contaminated soil, and very high dissolved contaminant concentrations can generate very high vapor concentrations that, when in close proximity to buildings or utilities, can cause PVI. Those conditions are the only known cases of petroleum vapor intrusion: There are no known or reported cases of petroleum vapor intrusion associated with low dissolved-phase concentrations at or near buildings or utilities.
Contaminants partition to vapor phase from soil and LNAPL source according to Raoult’s Law. Contaminants dissolved in GW partition to vapor phase according to Henry’s Law Constant.
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 14

15. Multiple Lines of Evidence Using Basic Site Characterization Data
Soil Data
Analyze for petroleum constituents
Continuous soil coring and logging, PID measurements, visual and olfactory description
Groundwater Data
Analyze for petroleum constituents
Visual and olfactory description
Flow direction and gradient
Soil Vapor Data, if needed
Analyze for petroleum constituents PLUS Oxygen, Carbon Dioxide, Methane, Nitrogen
Computer model simulations (eg PVIScreen) can be used to:
Explain field-observed behavior of vapors
Models cannot be used as a sole line of evidence when evaluating and screening PVI sites

16. LNAPL Indicators LNAPL INDICATOR MEASUREMENTS
Current or historic presence of LNAPL in groundwater or soil
Visual evidence:
Sheen on groundwater or soil, soil staining, measurable
product thickness
Groundwater, dissolved-phase
PHCs >0.2 times effective solubilities (Bruce et al. 1991)
Benzene >1-5 mg/L
TPH-gro >20-30 mg/L
TPH-dro >5 mg/L
Soil, adsorbed-phase
PHCs >effective soil saturation (Csat)
Benzene >10 mg/kg
TPH-gro > mg/kg
EPA >100 mg/kg unweathered gasoline
>250 mg/kg weathered gasoline, diesel
Soil field measurements
Organic vapor analyzer/PID/OVA of soil cores
Gasoline-contaminated soil: >100 ppm-v to >500 ppm-v
Diesel-contaminated soil: >10 ppm-v
Soil Gas measurements
O2 depleted, CO2 enriched with increasing distance
from source
Elevated aliphatic soil gas concentrations (eg Hexane >100,000ug/m3)
Indicators of LNAPL based on field and numerical studies, and example of multiple lines of evidence that are used to characterize and evaluate sites.
(after Peargin and Kolhatkar 2011, Lahvis et al 2013, ITRC 2014, EPA 2015)

17. Table 3: Recommended Vertical Separation Distance Between
Top of Contamination and Building Foundation (EPA OUST 2015) **
EPA OUST 2013 is the database report “Evaluation Of Empirical Data To Support Soil Vapor Intrusion Screening Criteria for Petroleum Hydrocarbons,” Jan EPA-510-R ITRC adopted the 15-feet and 18-feet for small and industrial sites, respectively. **
* Vertical separation distance = Thickness of clean, biologically active soil between top of contamination and building foundation
** 18 feet for petroleum industrial sites (refineries, terminals, pipelines) (EPA OUST 2013; ITRC 2014)

18. Results of Empirical Studies and Screening Criteria
Various methods of data analysis yield similar results
Dissolved Sources require 5-6 feet separation:
Benzene <5 mg/L
TPH <30mg/L
LNAPL Sources require feet separation:
Benzene >5 mg/L, >10 mg/kg
TPH >30mg/L, > mg/kg
18 feet separation required for large industrial sites
“Clean Soil” within separation distance:
Non-source soil, LNAPL-free, biologically active, sufficient oxygen and moisture to bioattenuate vapors
EPA 2015: <100 mg/kg TPH “clean” soil

19. Case Study 1: Basin Mkt, Murray, UT
On-Site
Convenience Store MW
Sub-Slab VMP
Soil Vapor, ug/m3
Benzene 5.4
TPH-g <100
O %
CO <0.2%
6 ft
LNAPL
GW, mg/L
Benzene 0.560
TPH-g
Soil, mg/kg 6-7 ft
Benzene 6.55
TPH-g
Step 1: Emergency? NO
Step 2: Characterize Site, Define Extent & Degree of Contamination, Develop CSM
No Precluding Factors: dissolved plume stable, no pref. pathways or lead scavengers, <10% ethanol
Step 3: Buildings within Lateral Inclusion Zone? YES
Step 4: Sufficient Vertical Separation? NO
LNAPL soil contamination, TPHg >100 mg/kg, 15 ft required for LNAPL source
Step 5: Sub-slab vapor sampling indicate PVI? NO
No Further PVI Investigation

20. Case Study 2: Hoagies, Farr West, UT
IA, ug/m3
Benzene 55
TPH-g
On-Site
Convenience
Store
OA, ug/m3
Benzene 0.42
TPH-g <100 MW
Sub-Slab VMP
Soil Vapor, ug/m3
Benzene 850,000
TPH-g 85,000,000
O %
CO %
5 ft
Soil, mg/kg 6 ft
Benzene 32.4
TPH-g
LNAPL
Of interest, the slab attenuation factor is 650,000x
Step 1: Emergency? NO
Step 2: Characterize Site, Define Extent & Degree of Contamination, Develop CSM
No Precluding Factors: no pref. pathways or lead scavengers, <10% ethanol
Step 3: Buildings within Lateral Inclusion Zone? YES
Step 4: Sufficient Vertical Separation? NO
LNAPL soil & GW sources, 15 ft required
Step 5: Sub-slab vapor sampling indicate PVI? YES
Step 6: PVI Mitigation: Indoor air filtration, source removal (building demolition & excavation most effective)

21. CONCLUSIONS
Petroleum vapors biodegrade aerobically within short, predictable distances from vapor sources
Applying Screening Criteria
Provides evidence of potential or actual PVI
Avoids unnecessary PVI investigations
Adequate Site Characterization, Multiple Lines of Evidence are important for accurately applying Screening Criteria
Short-Cuts = Data Gaps
Unnecessary PVI Investigations
Undetected presence of PVI
Overly conservative TPH criteria can result in unnecessary PVI investigations

22. THANK YOU