by Robin V. Davis, P.G. Project Manager Utah Department of Environmental Quality Leaking Underground Storage Tanks rvdavis@utah.gov 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

Avoid unnecessary additional investigation, soil gas/air sampling

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

• Vapors aerobically biodegraded by oxygen-consuming microbes, waste product carbon dioxide

• Vapors attenuate in short distances

Vapor Bioattenuation Limited by Contaminated Soil

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)

De

pth

, fe

et

be

low

gra

de

O2 & CO2 (% V/V)

Conneaut, OH VMP-1

(Roggemans, 1998; Roggemans et al., 2001)

Oxygen

Carbon Dioxide

Benzene

LNAPL in Soil (sand, silty sand)

8/26/06 6/27/07

Importance of Shallow Vapor Completion Points

Shallower point confirms attenuation above contaminated soil zone

Shallow completion too deep

Example of apparent non-attenuation until shallow vapor point installed in non-contaminated soil

VW-11 Hal’s, Green River, Utah

No attenuation within 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

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)

O2 & CO2 (% V/V)

Santa Clara, UT VW-4 1/19/2009

4 feet Benzene in GW

3180/ ug/L

1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06

0

2

4

6

8

10

0 5 10 15 20 25

Benzene (ug/m3)

De

pth

, fe

et

bg

s

O2 & CO2 (% v/v)

Jackson’s, UT VMW-4 9/29/08

Oxygen, %

Carbon Dioxide, %

Benzene, ug/m3

Benzene in GW

12,000 ug/L

4.94 feet

Dissolved Sources

= Distance between top of source and deepest clean vapor point

Thickness of clean soil needed to attenuate vapors

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

9.5 feet

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)

De

pth

, fe

et

be

low

gra

de

O2 & CO2 (% V/V)

Beaufort, SC NJ-VW2 Lahvis, et al., 1999

Oxygen

Carbon Dioxide

Benzene

Benzene in GW

16,000 ug/L

8 feet

LNAPL Sources

= Distance between top of LNAPL and deepest clean vapor point

Thickness of clean soil needed to attenuate vapors

Screening Distances

95%-100% Confidence

Dissolved Sources Benzene Vapors vs. Distance of Attenuation

LNAPL Sources (small sites) Benzene Vapors vs. Distance of Attenuation

5 ft 15 ft

13 feet, 95% Confidence

Lahvis et al 2013 Results of Vapor Attenuation from LNAPL Sources

• Different analysis, similar results

• 13 ft vertical

separation attenuates LNAPL source vapors

LNAPL Indicators

17

LNAPL INDICATOR MEASUREMENTS

Current or historic presence of LNAPL

in groundwater or soil

Visual evidence:

Sheen on groundwater or soil, soil staining, measurable thickness

Groundwater, dissolved-phase

PHCs >0.2 times effective solubilities

(Bruce et al. 1991)

Benzene >3-5 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 >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

(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

Field Example:

Deep SV Benzene, ug/m3

Shallow SV Benzene, ug/m3

= AF

~7,000,000x contaminant reduction

~1 ug/m3

145,000 ug/m3 AF = = 7E-06

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)

0

5

10

15

0 5 10 15 20 25

O2 & CO2 (% V/V)

1.E+00 1.E+02 1.E+04 1.E+06 1.E+08

Benzene (ug/m3)

Oxygen

Carbon Dioxide

Benzene

Benzene in GW

16,000 ug/L

0

20

40

60

80

100

1.E-021.E-03<1.E-04

Subsurface Vapor Attenuation Factors

Nu

mb

er

of

So

il V

ap

or

Sa

mp

le E

ve

nts

Benzene TPH

0

30

60

90

120

150

Reason 1: No

Clean

Overlying Soil

Reason 2: Low

Source

Strength

Reason 3:

Rapid

Attenuation

Near High-

Strength

Source

Nu

mb

er

of

So

il V

ap

or

Sa

mp

le E

ve

nts Benzene TPH

3 Reasons for

Insignificant

AFs 10x-100x

0

40

80

120

160

200

>1.E-011.E-011.E-021.E-03<1.E-04

Subsurface Vapor Attenuation Factors

Nu

mb

er

of

So

il V

ap

or

Sa

mp

le E

ve

nts

Benzene TPH

Distribution of Magnitude of Subsurface

Petroleum Vapor Attenuation Factors

Screen these out Reasonable Screening

AF 100x-1000x

Most events

exhibit Significant

AFs >10,000x

http://www.epa.gov/oswer/vaporintrusion/documents/vi-cms-v11final-2-24-2012.pdf

EPA Modeling Studies Vertical and Lateral Attenuation Distances

Lateral Distance, meters

Ve

rtic

al

Dis

tan

ce B

elo

w G

rad

e,

mete

rs

10 20 30 40 80 90 50 60 70

0

2

4

6

8

0

2

4

6

8

LNAPL Vapor Source

200,000,000 ug/m3

8 m deep (26 ft)

Lateral

Attenuation

5m (16 ft)

Building with

Basement

Vertical

Attenuation

6m (20 ft)

Oxygen

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

Reference

Screening

Distance

(feet)

Screening

Concentration

Benzene, TPH (ug/L)

Other

Criteria

EPA OUST Petroleum

Database Report

5

15

<5000, <30,000

LNAPL

LNAPL UST sites. 18 ft for large sites.

Clean soil <250 mg/kg TPH

Wright, J., Australia,

2011 5 <1000 Includes large industrial sites

30 LNAPL

California 5 <100 SG Oxygen not required

5 <1000 SG Oxygen required >4%

10 <1000 SG Oxygen not required

30 LNAPL

Indiana

5 <1000 SG Oxygen not required

Distances apply vertically & horizontally

AFs for GW & SG 30 LNAPL

New Jersey 5 <100 SG Oxygen not required

5 <1000 SG Oxygen required >2%

10 <1000 SG Oxygen not required

100 LNAPL Distances apply vertically & horizontally

Wisconsin 5 <1000 Distances apply vertically & horizontally

20 >1000

30 LNAPL

THANK YOU