byRobin V. Davis, P.G.Project ManagerUtah Department of Environmental QualityLeaking Underground Storage Tanksrvdavis@utah.gov 801-536-4177

24th Annual

September 16-18, 2013

Methods for Developing and Applying Screening Criteria for the Petroleum Vapor Intrusion Pathway

National Tanks ConferenceDenver, Colorado

OBJECTIVES

• Understand causes of PVI

• Understand why there are so many petroleum LUST sites, yet petroleum vapor intrusion (PVI) is very rare

• Petroleum Vapor Database compiled from basic field data routinely collected at LUST sites plus soil vapor data

• Show characteristics, mechanisms, magnitude of petroleum hydrocarbon vapor biodegradation and attenuation vertically and laterally

SCOPE

• Work Groups, literature research, publishing, field data compilation to an empirical petroleum vapor database, EPA OUST peer-review and publishing as national guidance

• Apply Screening Criteria using basic site data to screen out (exclude) low-risk sites from PVI pathway, and avoid unnecessary, costly soil vapor/air sampling

Causes of Petroleum Vapor Intrusion Based on Field Evidence

Preferential pathway: sewer line as conduit for vapors to enter building. Natural conduits include fractured or karstic rocks.

Preferential pathway: sump or elevator shaft draws LNAPL/high dissolved into building

High-strength source (LNAPL, high dissolved & adsorbed) in direct contact with building

KEY POINTS:

Vapor intrusion caused by:

Groundwater-Bearing Unit

BUILDING

Unsaturated Soil

Affected GW

LNAPLLNAPL

LNAPLLNAPL

41

3

LNAPLLNAPL

High-strength source (LNAPL, high dissolved & adsorbed) in close proximity to building

2

Drawing after Todd Ririe, 2009

� High-strength sources in direct contact or close proximity to buildings

� Anthropogenic & natural preferential pathways

5-6 feet

• Aerobic biodegradation of petroleum hydrocarbon vapors is a robust, rapid process, and occurs over short distances.

Slide courtesy of Lahvis et al 2013 GWMR; Matt Lahvis & Ian Hers et al, Battelle, June 2013.

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

• Key Need: Sufficient oxygen supply relative to oxygen demand, which is a function of PHC source strength and contaminant mass flux.

8-15 feet

KEY POINTS:

• Vapors associated with dissolved sources attenuate in shorter distances than for LNAPL due to source strength & contaminant mass flux.

Conceptual Characteristics of Subsurface Aerobic Biodegradation and Relative Distances of Attenuation

UST system

Dissolved contamination

Clean soil

Contaminated soil & LNAPL

High vapor concentrations from LNAPL & soil sources

Low vapor concentrations from

dissolved source

• Define extent & degree of soil & GW contamination (Title 40 CFR Part 280)

• Construct Conceptual Site Model

• Apply Screening Criteria

Gas Station

Building

Characterize Site

Contaminated soil

Petroleum Vapor Database

# Geographic Locations (sites) Evaluated

# Paired concurrent measurements of benzene subsurface soil vapor & source strength

56

MAP KEY

112/608Perth

304

2/13

56/304

Sydney

Tasmania

Compilation of Paired, Concurrent Measurements of Contaminant Source Strength & Soil Vapor Data

Canada

United States

Australia

(EPA Jan 2013, 510-R-13-001)

(Wright, J., 2011, Australian data)

(Davis, R.V., 2009, updated 2011)

(Lahvis et al 2013, GWMR)

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

, ft

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)

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 GW16,000 ug/L

• Typical O2, CO2, PHC vapor profiles: petroleum vapors naturally biodegrade & attenuate with sufficient thickness of clean vadose zone soil

• 1000’s of such measurements yield consistent, predictable results

Signature Field Characteristics of Subsurface Aerobic Biodegradation and Actual Distances of Attenuation

KEY POINTS:

• Extent & magnitude of vapor attenuation can be quantified, & Screening Criteria developed & applied

• Determine thickness of clean overlying soil required to attenuate vapors associated with:

Developing Screening Criteria

• Petroleum Vapor Empirical Database

- Dissolved sources- LNAPL & soil sources

- High-quality field data peer-reviewed & QA/QC’d by EPA (EPA 2013)

- Measurements of concurrent source strength & vapor concentrations

- Plot data, evaluate trends

Method for Determining Thickness of Clean Soil Required to Attenuate Vapors Associated with

Dissolved Sources

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, fe

et

bls

O2 & CO2 (% V/V)

Santa Clara, UT(UDEQ #6-046, IVB)VW-4 1/19/2009

4 feetBenzene in GW 3180/ ug/L

Formula: Distance between top of dissolved groundwater source and deepest clean vapor point = thickness of clean soil (feet) needed to attenuate vapors

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)

Dep

th,

feet

bg

s

O2 & CO2 (% v/v)

Jackson’s, UTUDEQ #3-098, LVOVMW-4 9/29/08

Oxygen, %

Carbon Dioxide, %

Benzene, ug/m3

Benzene in GW 12,000 ug/L

4.94 feet

Near-Slab Multi-Depth, Sub-Slab

0

1

2

3

4

5

6

7

8

9

10

1 100 10,000 1,000,000

TPH, dissolved, ug/L

Th

ick

ne

ss

Cle

an

So

il R

eq

uir

ed

to

A

tte

nu

ate

TP

H V

ap

ors

, fe

et

TPH: Soil Vapor & Dissolved Paired Measurements

All Soil Types

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

(Exterior + Sub-Slab)

Analysis of Petroleum Vapor Database for Dissolved Sources

5-6 feet CLEAN overlying soil attenuates vapors associated with

dissolved benzene 1,000-5,000 ug/L, TPH 10,000-30,000 ug/L

LNAPL PHC INDICATORS (EPA 2013; Lahvis et al 2013)

11

LNAPL INDICATOR MEASURES AND SCREENING VALUES

Current or historic presence of

LNAPL in groundwater

Visual evidence in field and/or laboratory: sheen on groundwater

and in soil, measurable thickness in groundwater wells, filter,

shake & dye tests, fluorescence

Groundwater : concentration of PHCs

>0.2 times effective solubilities

(Bruce et al. 1991)

Soil: concentration of PHCs

>effective soil saturation (Csat)

Groundwater (dissolved-phase concentrations)

Benzene >3-5 mg/L

TPHg >20-30 mg/L

TPH-d >5 mg/L

Soil (adsorbed-phase concentrations)

Benzene: >10 mg/kg

TPHg: >250-500 mg/kg

Organic vapor analyzer (PID, OVM)

field measurements of soil cores

Gasoline-contaminated soil: >500 ppm-v

Diesel-contaminated soil: >10 ppm-v

Soil Gas: PHC vapor, O2 and CO2

profiles

PHC vapor and CO2 soil gas concentrations show no decrease

and O2 shows no increase with increasing distance from source

Soil Gas: elevated aliphatic soil gas

concentrationse.g., Hexane >100,000 ug/m3

VW-7

6/26/07

0

5

10

15

20

0 5 10 15 20

O2 & CO2 (% v/v)

De

pth

fe

et

bg

s

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

Benzene (ug/m3)

Oxygen

Carbon Dioxide

Benzene

Hal’s, Green River, VW7, 6/26/07

Utah (UDEQ)

LNAPL & contaminated

soil/smear zone

FORMULA

Distance between deepest clean vapor point (top of contaminated soil) and shallowest hot point

= 15 ft top contaminated soil –11 ft deepest clean vapor point

= 4 feet CLEAN soil needed to attenuate vapors

4 feet

Method for Determining Thickness of Clean Soil Required to Attenuate Vapors Associated with

LNAPL & Soil Sources

Near-Slab Multi-Depth, Sub-Slab

0

1

2

3

4

5

6

7

8

9

10

Th

ick

ne

ss

of

Cle

an

So

il O

ve

rly

ing

LN

AP

L

Re

qu

ire

d t

o A

tte

nu

ate

Va

po

rs,

fee

t

TPH SV Sample Event over LNAPL & Soil Sources

Near-Slab Multi-Depth, Sub-Slab

0

1

2

3

4

5

6

7

8

9

10

Th

ick

ne

ss

of

Cle

an

So

il O

ve

rly

ing

LN

AP

L

Re

qu

ire

d t

o A

tte

nu

ate

Va

po

rs,

fee

t

Benzene SV Sample Event over LNAPL & Soil Sources

Benzene TPH

8-15 feet CLEAN overlying soil attenuates vapors

associated with LNAPL and Soil Sources

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

1 Refinery Site

Sites Sites

(Exterior + Sub-Slab, all soil types, UST and non-UST sites)

Analysis of Petroleum Vapor Database for LNAPL & Soil Sources

NEW !

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

Jan. 2013

NEW !April 8, 2013

PVI draft

SCREENING CRITERIA FOR THE PVI PATHWAY

* Vertical separation distance is the thickness of clean soil

(TPH <100 mg/kg) required to attenuate vapors associated

with the various media source strengths.

Notes

- Vertical distance from source to receptor expected to apply

in lateral direction from source edge.

- Source edge defined by concentrations shown above, or

other state-specific regulatory requirements.

(EPA OUST PVI draft PVI guide, April 2013)

NO FURTHER PVI PATHWAY

EVALUATION NECESSARY

SITE SCREENING PROCESS FOR THE PVI PATHWAY

Precluding Factors

present? (e.g., preferential pathways)

Buildings within lateral

inclusion distance from source edge?

Buildings within vertical

inclusion distance from

source?

Further PVI investigation or vapor control required (e.g., further site investigation, soil

vapor sampling, modeling)

No acute exposure emergency, or

explosive conditions

NO

YES

YES

NO

NO

YES

Utah DEQ LUST

program will use

this decision-

making process

when the EPA

OUST guide is

finalized

�5-6 feet clean soil overlying:

Benzene <1-<5 mg/L

TPH <10-<30 mg/L

�8-15 feet clean soil overlying top of LNAPL smear zone & soil sources

Dissolved Sources

• No further PVI investigation necessary

when the following conditions apply:

LNAPL & Soil Sources

“Clean” Soil

�TPH <100-<250 mg/kg contains sufficient oxygen needed to support aerobic

biodegradation of PHC vapors

Soil Vapor Sampling

�Petroleum vapors are attenuated below the receptor

� If measuring soil vapor, analyze all petroleum COCs, O2, CO2, methane, N2,

others (TPH fractions)

�Oxygen to Carbon Dioxide ratios demonstrate petroleum biodegradation

Conclusions• One empirical database was analyzed using different methods, and

results of criteria for screening sites for the PVI pathway are similar

THANK YOU