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

Applying Screening Criteria for the Petroleum Vapor Intrusion Pathway

Workshop 7Tuesday March 22, 2016

6:30 pm – 9:30 pmAssociation for Environmental Health & Sciences (AEHS)

25th Annual International Conference on Soil, Sediment, Water & EnergySan Diego, California

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

Source strength: LNAPL in soil and GW, and dissolved-phase 1000s of sample points and measurements at 100s of sites Extensive peer review and quality control checks Distances of vapor attenuation relative to source strength 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:

SCOPE

124/>1000Perth

Sydney

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

January 2013

Petroleum Vapor Database Report

Compilation of field data, concurrent measurements:• LNAPL in soil & GW• Dissolved sources• Associated soil vapor data

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

EPA OUST

January 2013

CAPILLARY ZONE

a) LNAPL SOURCE

UNSATURATED ZONE

SATURATED ZONE

sharp reaction

front

O2

VOCs

b) DI SSOLVED- 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

•Oxygen demand is a function of source strength

0 1

0 1

Signature Characteristics of Aerobic Biodegradation of Subsurface Petroleum Vapors

• Vapors attenuate in short distances

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

Tank 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

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 siteDefine extent & degree of contaminationApply Screening Criteria

Building

LNAPL in soil

LNAPL in soil & GW

Soil Boring/MW

Soil Boring/MW

Utility line

Construct Conceptual Site Model (CSM)

Multiple Lines of Evidence from Basic Site 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

LNAPL Indicators

12

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-phasePHCs >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)

15 ft clean soil

Soil, mg/kg 17-18ftBenzene 0.379TPH-g 200TPH-d 10.2

MW-17

CommercialBuilding

GW, mg/LBenzene 1.2TPH-g 16.6TPH-d <2.0

Step 1: Emergency? NOStep 2: Characterize Site, Develop CSM

• No Precluding Factors (dissolved plume is stable, no preferential pathways, no lead scavengers, <10% ethanol)

Step 3: Buildings within Lateral Inclusion Zone? YESStep 4: Sufficient Vertical Separation? YES

• Dissolved source 15 ft below building slab, 6 ft required• Soil contamination sufficiently deep, no LNAPL

No Further PVI Investigation

Case Study 1: Santa Clara, UT

5 ft

GW, mg/LBenzene 0.560TPH-g 10.8

MW

CommercialBuilding

LNAPL

Step 1: Emergency? NOStep 2: Characterize Site, Develop CSM, Precluding Factors? YES

• LNAPL plume not stable, in close proximity to building slabStep 3: Buildings within Lateral Inclusion Zone? YESStep 4: Sufficient Vertical Separation? NO

• LNAPL source 5 ft below building slab, 15 ft requiredStep 5: Sub-slab vapor sampling indicate PVI? NONo Further PVI Investigation

Case Study 2: Basin Mkt, Murray, UT

Sub-Slab VMPSoil Vapor, ug/m3

Benzene 5.4TPH-g <100O2 21%CO2 <0.2%

Soil, mg/kg 6 ftBenzene 6.55TPH-g 3410

5 ft

Soil, mg/kg 6 ftBenzene 32.4TPH-g 5280

MW

CommercialBuilding

LNAPL

Step 1: Emergency? NOStep 2: Characterize Site, Develop CSM, Precluding Factors? YES

• LNAPL plume not stable, in close proximity to building slabStep 3: Buildings within Lateral Inclusion Zone? YESStep 4: Sufficient Vertical Separation? NO

• LNAPL source 5 ft below building slab, 15 ft requiredStep 5: Sub-slab vapor and IA/OA sampling indicate PVI? YESStep 6: Mitigation: Indoor air filters, building demolition and source removal

Case Study 3: Hoagies, Farr West, UT

Sub-Slab VMP

Soil Vapor, ug/m3

Benzene 850,000TPH-g 85,000,000O2 8.3%CO2 8.4%

IA, ug/m3

Benzene 55TPH-g 2200

OA, ug/m3

Benzene 0.42TPH-g <100

CONCLUSIONS• Petroleum vapors biodegrade aerobically within short,

predictable distances from vapor sources• Applying Screening Criteria

– Avoids unnecessary PVI investigations– Provides evidence of potential or actual PVI

• 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