byRobin V. Davis, P.G., Retired Environmental Scientist/Project Manager, Utah Department of Environmental QualityLeaking Underground Storage Tanksrobinhummingbird@gmail.com 801-300-7431

Applying Screening Criteria for the Petroleum Vapor Intrusion Pathway

Tribal Lands & Environment Forum (TLEF)

Petroleum Vapor Intrusion SessionThursday August 18, 2016, 10:30 pm – 12:00 pm

Mohegan Sun ResortUncasville, Connecticut

presented to

OBJECTIVES• Understand

Why petroleum vapor intrusion (PVI) is very rare despite so many petroleum LUST sites

Causes of PVI

• Show Mechanisms, characteristics, degree of vapor bioattenuation

Distances of vapor attenuation relative to source strength

• Apply Screening Criteria Screen out low-risk sites

Avoid unnecessary, costly investigation

PVI investigations are very intrusive physically and socially

Field and Published Data from 3 Countries

Paired, concurrent measurements of source strength and associated soil gas measurements from 1000s of sample points at 100s of sites

Extensive peer review and quality control checks

Quantified distances of vapor attenuation relative to source strength

• EPA Database Report of Empirical Studies, Jan. 2013

Some US States

Australia 2012

ITRC October 2014

EPA final PVI June 2015

• Guidance Documents Issued:

SCOPE

124/>1000

PerthSydney

Tasmania

Australia

Davis, R.V., 2009-2011McHugh et al, 2010Peargin and Kolhatkar, 2011Wright, J., 2011, 2012, Australian dataLahvis et al, 2013EPA 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

>100 years of research proves:

• Rapid aerobic biodegradation of vapors by 1000s of indigenous microbes

• Vapors attenuate within a few feet of sources

No cases of PVI from low-strength sources

Causes of PVI are well-known

Results of Subsurface Petroleum Vapor Bioattenuation Studies

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

41

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

January 2013Compilation & analysis of concurrent field data measurements:

• LNAPL in soil & GW

• Dissolved sources

• Associated soil vapor data

• Quantifies distances of vapor attenuation

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

EPA OUST

January 2013

Petroleum Vapor Database Report

• Subsurface soil is a natural

bioreactor

• Aerobic biodegradation of

vapors is rapid, occurs over

short distances as a sharp

reaction front

• Oxygen demand is a

function of source strength

– Strong LNAPL sources (panel a) use much more oxygen, and vapors attenuate in longer distances than weak sources (panel b)

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 Aerobic Biodegradation

O2/Hydrocarbon

Vapor Profile

O2/Hydrocarbon

Vapor Profile

0 1

0 1

KEY POINTS

After 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 25

Benzene (ug/m3)

Dep

th,

feet

belo

w g

rad

e

O2 & CO2 (% V/V)

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

Oxygen

Carbon Dioxide

Benzene

Benzene in GW

16 mg/L

• Vapors attenuate in short distances, even from a strong source

• Vapors are aerobically biodegraded quickly by oxygen-consuming microbes, waste

product carbon dioxide

Sharp

Reaction

Front

Field Characteristics of Petroleum Vapor Transport and Aerobic Biodegradation

7 feet

separation

distance

Profile of Subsurface Multi-Depth Vapor Sample Points and Concentrations of Benzene, Oxygen, and Carbon Dioxide

June 2015

Final PVI GuideEPA OUST

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

Technical Guide For AddressingPetroleum Vapor Intrusion

At Leaking Underground StorageTank Sites

June 11, 2015

• Thickness of Clean, Non-Source Soil Required to Attenuate Vapors Associated with LNAPL in Soil and GW, and Dissolved Sources

• Using Multiple Lines of Evidence for Site Characterization and Screening

DESCRIBES

STEP 2Characterize Site

• Define extent/degree of contamination

• Construct Conceptual Site Model

NO

YES

Are PrecludingFactors Present?

(preferential pathways, other)

Are Any Existing or Planned Buildings

Within Lateral Inclusion

Zone?

STEP 3Delineate Lateral

Inclusion Zone

YES

STEP 4Determine Vertical Separation Distance

for Each Building

NO

Do Sub-Slab & Indoor Air Sampling

Indicate PVI?

PVI Pathway Not Likely Complete

Is Thickness of Clean Soil

>Minimum Vertical Separation Distance?

STEP 5Evaluate Vapor Source & Attenuation:1. Measure Vapors Near-Slab

& Near-Source , or2. Measure Indoor Air &

Concurrent Sub-Slab Vapors3. If Contamination is in Direct

Contact with Building, use Option 2 above

4. Models may be used only to explain observed vapor behavior

Do Near-Slab & Near-Source

Sampling Indicate PVI?

Option 2

Option 1

NONO

NO YES

YES

STEP 6• Notify 1st

Responders• Mitigate PVI

Figure 1: Flowchart for Addressing PVI At Leaking Underground Storage Tank Sites (modified from EPA OUST 2015)

YES

STEP 1Emergency?

Community Engagement

• Required by 40CFR

• May occur at any step in the PVI investigation & mitigation process

YES

NO

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

Collect basic site data, characterize site

Define extent & degree of contamination

Apply Screening CriteriaBuilding

LNAPL in soil

LNAPL in soil & GW

Soil Boring/MW

Soil Boring/MW

Utility line

Construct Conceptual Site Model (CSM)

Multiple Lines of Evidence Using BasicSite Characterization Data• Soil Data

Analyze for petroleum constituents Continuous soil coring and logging, PID measurements, visual

and olfactory description

• Groundwater Data Analyze for petroleum constituents Visual and olfactory description Flow direction and gradient

• Soil Vapor Data, if needed Analyze for petroleum constituents PLUS Oxygen,

Carbon Dioxide, Methane, Nitrogen

• Computer model simulations (eg PVIScreen) can be used to: Explain field-observed behavior of vapors Models cannot be used as a sole line of evidence when

evaluating and screening PVI sites

LNAPL Indicators

16

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 >1-5 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 Peargin and Kolhatkar 2011, Lahvis et al 2013, ITRC 2014, EPA 2015)

Table 3: Recommended Vertical Separation Distance Between

Top of Contamination and Building Foundation (EPA OUST 2015)

* Vertical separation distance = Thickness of clean, biologically active soil between top of

contamination and building foundation

**

**

** 18 feet for petroleum industrial sites (refineries, terminals, pipelines) (EPA OUST 2013; ITRC 2014)

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:

6 ft

GW, mg/L

Benzene 0.560

TPH-g 10.8

MW

On-Site Convenience Store

LNAPL

Step 1: Emergency? NO

Step 2: Characterize Site, Define Extent & Degree of Contamination, Develop CSM

• No Precluding Factors: dissolved plume stable, no pref. pathways or lead scavengers, <10% ethanol

Step 3: Buildings within Lateral Inclusion Zone? YES

Step 4: Sufficient Vertical Separation? NO

• LNAPL soil contamination, TPHg >100 mg/kg, 15 ft required for LNAPL source

Step 5: Sub-slab vapor sampling indicate PVI? NO

No Further PVI Investigation

Case Study 1: Basin Mkt, Murray, UT

Sub-Slab VMP

Soil Vapor, ug/m3

Benzene 5.4

TPH-g <100

O2 21%

CO2 <0.2%

Soil, mg/kg 6-7 ft

Benzene 6.55

TPH-g 3410

5 ft

Soil, mg/kg 6 ft

Benzene 32.4

TPH-g 5280

MW

On-Site Convenience

Store

LNAPL

Case Study 2: Hoagies, Farr West, UT

Sub-Slab VMP

Soil Vapor, ug/m3

Benzene 850,000

TPH-g 85,000,000

O2 8.3%

CO2 8.4%

IA, ug/m3

Benzene 55

TPH-g 2200

OA, ug/m3

Benzene 0.42

TPH-g <100

Step 1: Emergency? NO

Step 2: Characterize Site, Define Extent & Degree of Contamination, Develop CSM

• No Precluding Factors: no pref. pathways or lead scavengers, <10% ethanol

Step 3: Buildings within Lateral Inclusion Zone? YES

Step 4: Sufficient Vertical Separation? NO

• LNAPL soil & GW sources, 15 ft required

Step 5: Sub-slab vapor sampling indicate PVI? YES

Step 6: PVI Mitigation: Indoor air filtration, source removal (building demolition & excavation most effective)

CONCLUSIONS• Petroleum vapors biodegrade aerobically within short,

predictable distances from vapor sources

• Applying Screening Criteria

– Provides evidence of potential or actual PVI

– Avoids unnecessary PVI investigations

• Adequate Site Characterization, Multiple Lines of Evidence are important for accurately applying Screening Criteria

• Short-Cuts = Data Gaps

– Unnecessary PVI Investigations

– Undetected presence of PVI

• Overly conservative TPH criteria can result in unnecessary PVI investigations

THANK YOU