Robin-PVI Workshop 25th Tanks Conf Phx, 9-13-15

by Robin V. Davis, P.G. Project Manager Utah Department of Environmental Quality Leaking Underground Storage Tanks [email protected] 801-536-4177

Developing and Applying Screening Criteria for the

Petroleum Vapor Intrusion Pathway

Petroleum Vapor Intrusion Workshop Sunday September 13, 2015

1:00 pm – 5:00 pm

25th National Tanks Conference Phoenix, Arizona

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 relative to source strength

Understand causes of PVI

Apply as Screening Criteria, screen out low-risk sites, avoid unnecessary investigation, soil gas/air sampling

Field Data from 3 Countries, Published Field Studies

Paired, concurrent measurements of source strength and associated soil gas measurements

Source strength: LNAPL in soil and GW, dissolved-phase

1000s of sample points and measurements at 100s of sites

Extensive peer review and quality control checks

Distances of vapor attenuation quantified

EPA Database Report of Empirical Studies, Jan. 2013

Some US States

Australia 2012

ITRC October 2014

EPA final PVI June 2015

Guidance Documents Issued:

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

EPA OUST Jan. 2013

Australian sites evaluated separately

816

Petroleum Vapor Database of Field Studies

January 2013

Petroleum Database Report

• Compilation of field data: LNAPL in soil & GW, & dissolved

sources, and concurrent associated vapor data

http://www.epa.gov/oust/cat/pvi/PVI_Database_Report.pdf

http://www.epa.gov/oust/cat/pvi/pvi-guide-final-6-10-15.pdf

June 2015

Final PVI Guide

• Thickness of clean, non-source soil required to attenuate

vapors associated with LNAPL in soil & GW, & dissolved

sources

EPA OUST PVI Guide, Figure 1 Decision Flow Chart for Evaluating PVI

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

• LNAPL sources have high

mass flux, vapors attenuate

in longer distances than

dissolved sources

• Aerobic biodegradation of

vapors is rapid, occurs over

short distances

• Oxygen demand is a

function of source strength

0

1

0

1

UST system

Dissolved contamination

Clean, Non-Source 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

>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

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

(ITRC PVI Tech Reg, 2014)

Preferential Pathway: Engineered

Petroleum Source

(ITRC PVI Tech Reg, 2014)

Preferential Pathway: Natural

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

• Good vapor point completion ensures atmospheric influences are none/minimal

VW-11 Hal’s, Green River, Utah

No attenuation within contaminated soil zone

Probe A3 (TCE - Normalized)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

13

:50

:09

10

:50

:26

7:5

0:4

4

4:5

1:0

4

1:5

1:4

3

22

:53

:46

5:4

3:2

9

2:4

3:4

7

23

:44

:04

20

:44

:22

17

:44

:39

14

:44

:57

11

:45

:15

8:4

5:3

2

16

:02

:01

13

:02

:18

10

:02

:36

7:0

2:5

5

4:0

3:1

2

1:4

3:5

6

22

:44

:15

7:0

6:4

1

4:0

6:5

9

1:0

7:1

9

22

:07

:58

19

:11

:25

Time (3/16/07 to 4/10/07)

No

rma

lize

d C

on

ce

ntr

ati

on

Probe A3-3' (Port 9)



Soil Gas Temporal Study, EPA-ORD

3’ bgs

8’ bgs

15’ bgs

• >500 points per probe collected once per hour over 4 week period

• Soil gas concentrations varied by <10% even for probes only 3 feet

below the surface.

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

Method for Determining Thickness of Clean Soil Required to

Attenuate Vapors Associated with Dissolved Sources

Thickness of clean soil needed to attenuate vapors

= Distance between top of dissolved source and deepest clean vapor point

0

1

2

3

4

5

6

7

8

9

10

1 100 10,000 1,000,000

Th

ick

ne

ss

Cle

an

So

il R

eq

uir

ed

to

Att

en

ua

te T

PH

Va

po

rs

, fe

et

TPH, dissolved, ug/L

Near-Slab Multi-Depth, Sub-Slab

TPH: Soil Vapor & Dissolved Paired Measurements

All Soil Types

0

1

2

3

4

5

6

7

8

9

10

1 10 100 1,000 10,000 100,000

Th

ickn

es

s

Cle

an

S

oil R

eq

uir

ed

to

Att

en

uate

Ben

zen

e V

ap

ors

, fe

et

Benzene, dissolved, ug/L

Near-Slab Multi-Depth, Sub-Slab

Benzene: Soil Vapor & Dissolved Paired Measurements

All Soil Types

TPH: 73 exterior/near-slab + 24 sub-slab = 97 total Benzene: 199 exterior/near-slab + 37 sub-slab = 236 total

2009-2011 Analysis of Petroleum Vapor

Database for Dissolved Sources

5 feet of clean soil attenuates vapors associated with

dissolved sources: Benzene 1,000 ug/L, TPH 10,000 ug/L

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

Method for Determining Thickness of Clean Soil Required to

Attenuate Vapors Associated with LNAPL Sources

Thickness of clean soil needed to attenuate vapors

= Distance between top of LNAPL source and deepest clean vapor point

0

1

2

3

4

5

6

7

8

9

10

Th

ick

ne

ss o

f C

lea

n S

oil O

ve

rly

ing

LN

AP

LR

eq

uir

ed

to

Att

en

ua

te V

ap

ors

, fe

et

TPH SV Sample Event over LNAPL & Soil Sources

0

1

2

3

4

5

6

7

8

9

10

Th

ick

ne

ss o

f C

lea

n S

oil O

ve

rly

ing

LN

AP

LR

eq

uir

ed

to

Att

en

ua

te V

ap

ors

, fe

et

Benzene SV Sample Event over LNAPL & Soil Sources

Benzene TPH

48 exterior/near-slab + 23 sub-slab = 71 total 17 exterior/near-slab + 19 sub-slab = 36 total

1 Refinery Site

Sites Sites

2009-2011 Results of Vapor Attenuation

from LNAPL and Soil Sources

8 feet of clean soil attenuates vapors associated with

LNAPL and Soil Sources

Screening Distances

95%-100% Confidence for LUST Sites 93% Confidence for Refineries, Terminals

Dissolved Sources Benzene Vapors vs. Distance of Attenuation

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

6 ft 15 ft

Lahvis et al 2013 Results of Vapor Attenuation from LNAPL Sources

• Slightly different analysis, similar results

• 95% Confidence

that 13 ft vertical separation attenuates LNAPL source vapors

13 ft

LNAPL Indicators

24

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 >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

EPA 2015 >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)

(after EPA 2015; Lahvis et al 2013)

Various methods of data analysis yield similar results

• Benzene <5 mg/L • TPH <30mg/L

LNAPL Sources require 13-15 feet separation: • Benzene >5 mg/L, >10 mg/kg • TPH >30mg/L, >250-500 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

Dissolved Sources require 5-6 feet separation:

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

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

Oxygen

Benzene in GW

16,000 ug/L

TPH in GW

67,100 ug/L

RESULTS BioVapor Model under-predicts subsurface attenuation by

100x to 10,000x

Compared to BioVapor Model

Beaufort, South Carolina (Lahvis et al 1999)

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 Soil Gas Oxygen not required

5 <1000 Soil Gas Oxygen required >4%

10 <1000 Soil Gas Oxygen not required

30 LNAPL

Indiana


Distances apply vertically & horizontally

AFs for GW & SG 30 LNAPL

New Jersey 5 <100 Soil Gas Oxygen not required

5 <1000 Soil Gas Oxygen required >2%


100 LNAPL Distances apply vertically & horizontally

Wisconsin 5 <1000 Distances apply vertically & horizontally

20 >1000

30 LNAPL

THANK YOU