by Robin V. Davis, P.G. Project Manager Utah Department of Environmental Quality Leaking Underground Storage Tanks [email protected]801-536-4177 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
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Robin Davis-PVI Workshop-25th AEHS San Diego March 2015
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by Robin V. Davis, P.G. Project Manager Utah Department of Environmental Quality Leaking Underground Storage Tanks [email protected] 801-536-4177
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
OBJECTIVES Understand why petroleum vapor intrusion (PVI) is
very rare despite so many petroleum LUST sites
Show mechanisms, characteristics, degree of vapor bioattenuation
Show distances of vapor attenuation, apply as Screening Criteria, screen out low-risk sites
Understand causes of PVI
SCOPE Field studies published by work groups, individuals
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
Data compiled to an empirical database:
Some US States
Australia 2012
EPA draft PVI April 2013
ITRC October 2014
EPA ORD Issue Paper 2014
Guidance Documents Issued:
EPA Petroleum Vapor Database Jan. 2013
124/>1000
Perth Sydney
Tasmania
Australia
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
REFERENCES
4/13
70/816
Canada
United States
MAP KEY
# geographic locations evaluated
# paired concurrent measurements
of subsurface benzene soil vapor
& source strength
70
Petroleum Vapor Database of Empirical Studies EPA OUST Jan. 2013
Australian sites evaluated separately
816
CAPILLARY ZONE
a) LNAPL SOURCE
UNSATURATED ZONE
SATURATED ZONE
sharp reaction
front
O2
VOCs
b) DISSOLVED-PHASE SOURCE
CAPILLARY ZONE
UNSATURATED ZONE
SATURATED ZONE
high massflux
limited mass flux
sharp reaction
front
constituent distributions
O2
VOCs
constituent distributions
Conceptual Characteristics of Petroleum Vapor Transport and Biodegradation
After Lahvis et al 2013 GWMR
O2/Hydrocarbon
Vapor Profile
O2/Hydrocarbon
Vapor Profile
KEY POINTS
• 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
0
1
0
1
>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
Bioattenuation Study Results Subsurface Petroleum Vapor
Causes of Petroleum Vapor Intrusion
Preferential pathway: sumps, elevator shafts
High-strength source in direct contact with building (LNAPL, high dissolved, adsorbed)
Groundwater-Bearing Unit
BUILDING
Unsaturated Soil
Affected GW
LNAPL
LNAPL
4 1
3
LNAPL
High-strength source in close proximity to building, within GW fluctuation zone
2
Drawing after Todd Ririe, 2009
High-Strength Sources Direct contact or close proximity to buildings
Preferential pathways: engineered & natural
Preferential pathway: bad connections of utility lines; natural fractured and karstic rocks
UST system
Dissolved contamination
Clean Soil
High vapor concentrations, high mass flux
from LNAPL & soil sources
Low vapor concentrations, low
mass flux from dissolved sources
Define extent & degree of contamination
Apply Screening Criteria Building
Collect Basic Data, Characterize Site, Construct Conceptual Site Model
LNAPL in soil
LNAPL in soil & GW
Soil Boring/MW Soil Boring/MW
Utility line
1.E+00 1.E+02 1.E+04 1.E+06 1.E+08
0
5
10
15
0 5 10 15 20
Benzene (ug/m3)
O2 & CO2 (% V/V)
Coachella, CA COA-2 (Ririe, et al 2002)
1.E+001.E+021.E+041.E+061.E+08
-5
0
5
10
15
20
0 5 10 15 20 25
Benzene (ug/m3)
Salina Cash Saver VMW-1 (UDEQ 7/27/07)
OA
IA
LNAPL
LNAPL
1.E+00 1.E+02 1.E+04 1.E+06 1.E+08
0
5
10
15
0 5 10 15 20 25
Benzene (ug/m3)
Dep
th,
fee
t b
elo
w g
rad
e
O2 & CO2 (% V/V)
Beaufort, SC NJ-VW2 (Lahvis, et al., 1999)
Oxygen
Carbon Dioxide
Benzene
Benzene in GW
16,000 ug/L
Signature Characteristics of Aerobic Biodegradation of Subsurface Petroleum Vapors