Lutes, C., L. Lund, J. Lowe and K. Hallberg “Petroleum Vapor Intrusion Strategies at UST and non-UST Sites Under 2015 EPA and 2014 ITRC Guides” Oral presentation at the 26th Annual International Conference on Soil, Water, Energy and Air, March 2016, San Diego.

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AEHS 26th Annual West Coast Conference March 2016, San Diego
Petroleum Vapor Intrusion
Strategies at UST and non-UST
Sites Under 2015 EPA and 2014
ITRC Guides
Chris Lutes, Loren Lund, John Lowe, Keri
Hallberg

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Topics
• Differences between available guidance documents.
• “Precluding Factors” that Can Prevent Screen Outs – A
Realistic View
• Lessons Learned
• Changes on the horizon

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Achieving Closure at PVI Sites
Regulatory
Driver
“In contrast to chlorinated solvents, petroleum hydrocarbons generally
biodegrade rapidly under aerobic conditions ... and justifies a different
approach for addressing PVI than for VI from chlorinated solvents”
(EPA 2015 Final PVI Guide)
Provides path to screen out low-risk
PVI sites → first of it’s kind
Key
Point

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3 Guidance Documents – All Discuss
Biodegradation - But Key Procedural Differences
Photos from USTA.edu,
fedcenter.gov and EPA.gov

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Comparing the 2 EPA Guides
OUST PVI Guide OSWER VI Guide
Straightforward screening approaches
with numerical distance criteria
Multiple lines of evidence analysis;
significant requirement for
interpretation and regulatory judgment
Often can screen out with existing
data (such as boring logs, soil and
groundwater concentrations)
“At a minimum a soil gas survey…. at
multiple locations and depth intervals”
Lateral separation may be on the
same scale as the vertical separation
distance (e.g. 6-15’) but a greater
lateral distance downgradient.
Lateral inclusion distance generally
100 ft from plume.
Attenuation factor graphs take into
account biodegradation as a function
of separation distance and source
strength
“The recommended groundwater and
“near-source” soil gas attenuation
factors do not, however, include the
effects of biodegradation”

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Can PVI Guide Be Applied to Non UST Sites?
ITRC PVI guide can be used at non-UST PHC sites (ITRC,
Oct 2014)
EPA PVI guide applies to underground storage tank (UST)
sites, but...
– “It may also be helpful at comparable non-UST sites ...
such as refineries, terminals, pipelines, and large scale
storage sites” (EPA 2015 PVI Guide)
– “(Technical Guide For Addressing Petroleum Vapor
Intrusion At Leaking Underground Storage Tank Sites
(EPA 2015b))….may also be useful ……at non-UST sites
that are similar in size to a typical Subtitle I UST release.”
(EPA 2015 OSWER Guide)

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Applying PVI Guide to NonUST Sites
So What is “similar in size to a typical subtitle I UST release”????
– “Before the implementation of the 1998 upgrade requirements…
indicated that 35% of UST systems nationwide exhibited leak rates
above 1.2 gallons/day.” (Young 2002)
– Mechanical line leakage detectors historically designed for >3
gallons/hour; Manual inventory reconciliation (>1 gallon per hour)
(Farahnak and Drewy 1998);
– current requirements are for detection of leaks >0.2 gallons/hour
(http://www.anr.state.vt.us/dec/wastediv/ust/pubs/ustleakdetection.p
df, https://www.epa.gov/sites/production/files/2014-
03/documents/stot05_4-6-09.pdf)
– Example literature case study “Small Scale Recovery” UST 967
gallons gasoline rapidly released (Smith and Scoles)

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Recognizing and Managing Precluding Factors
Simple screening applied as long as no precluding factors, such as:
– Presence of non-PHCs that biodegrade too slowly (high ethanol E-20, lead
scavenger additives)
– Preferential transport pathways (fractured rock)
– Oxygen transport inhibition by low permeability soil or very large buildings
– High organic matter content soil (peat)
– Insufficient thickness of clean, biologically active soil (i.e. <2% moisture)
Expertise is needed to evaluate precluding factors
– Educate stakeholders not see “precluding factors” everywhere –
microbiological systems are adaptable
– Focused site assessment can if necessary address potential precluding
factors
Technical
Challenges
Available
Solutions

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Are Large Buildings an Important Precluding Factor?
3-D Modeling Of Aerobic Biodegradation Of Petroleum Vapors: Effect
Of Building Area Size On Oxygen Concentration Below The Slab (EPA
510-R-13-002) Ran 160 simulations. Found the probability of an oxygen
shadow developing increases with:
• Increasing building area (including surrounding pavement area)
• Increasing source vapor concentration
• Decreasing depth of vapor source beneath the building
• Increasing transport time (assuming the source PHC vapor concentrations
are stable)
Example Concentration results for source vapor concentration of 10,000,000
μg/m3 at depth of 15 ft (4.6 m), 1 year transport

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When Are Large Buildings an Important Precluding
Factor?
Source Vapor
Concentration
(μg/m3)
Building
Dimensions (ft)
Vadose Zone
Depth (ft)
Transport Time
(years)
Oxygen
Shadow?
100,000 up to 2073x2073 as shallow as 5 as long as 50 NO
1,000,000 98x98 5 9 NO
1,000,000 131x131 5 9 YES
1,000,000 2073x2073 15 20 NO
10,000,000 33x33 5 1 YES
10,000,000 98x98 15 1 YES
10,000,000 66x66 15 20 NO
Only very strong sources, very
shallow, cause oxygen shadows
under impermeable slabs.
Key
Point

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Soil Organic Matter A Potential Interference
Dissolved Source Beneath Bldg
TPH < 30,000 µg/L; or
Benzene <5,000 µg/L
TPH < 250 mg/kg; or
Benzene <10 mg/kg
TPH < 30,000 µg/L; or
Benzene <5,000 µg/L
TPH < 250 mg/kg; or
Benzene <10 mg/kg
LNAPL Present Beneath Bldg
Clean
biologically
active soil
Universal nature of the FID detector can lead to
erroneous results for TPH when biogenic
material, or other anthropogenic chemicals are
comingled with petroleum compounds. (See
Kelly-Hooper, 2012)

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Soil Organic Matter A Potential Interference:
Clean, Biologically Active Soil Definition
• Based on EPA (2013a), clean, biologically active soil does not contain
LNAPL, EPA recommends LNAPL thresholds of 100 mg/kg TPH (fresh
gasoline) and 250 mg/kg TPH (weathered gasoline and diesel).
• Natural peat soils and process soils reported as having 2000-4000
mg/kg “TPH” (Kelly Hooper 2013) Canada-Wide Standard (CWS) for
Petroleum Hydrocarbons in Soil – Tier 1 Method (CCME 2001a) GC-
FID
• Not all peat soils are anaerobic – aerobic processes do occur (Iiyama,
2012; Magnusson, 1993)

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Lessons Learned from Multiple Sites
• Operation of biosparging, air sparging or bioventing systems near
buildings need careful monitoring for VI concerns. Complex
interactions between rain events, preferential pathways and
remediation systems are possible.
• Moving sites with long historic data sets based on groundwater
protection, to a focus on vapor intrusion, requires significant changes
in the mind set of the project team. For example accepted soil
screening criteria may have been based on migration to groundwater,
but are interpreted as a generic “acceptable level”.
• Older USTs have limited data sets/little delineation.
• Be clear with project teams re the use of individual data points vs.
interpolated contours in PVI evaluations.
• In prioritizing VI investigations across large groups of buildings with
multiple sources; current approaches do not easily allow quantitative
comparison of chlorinated solvent VI and PVI concerns.

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What’s Coming Next?
Photo from http://oceanexplorer.noaa.gov/
• States are slowly updating PVI
regulatory guidance
• EPA refinery rule fence line
monitoring and Aliso
Canyon/Porter Ranch leak are
increasing public awareness of
petroleum facility air emissions

16. Thank you!
© 2016 CH2M
Delivering Sustainable Solutions to Complex Local Challenges, Worldwide
Chris Lutes
Christopher.Lutes@ch2m.com