by Robin V. Davis, P.G. Project Manager Utah Department of Environmental Quality Leaking Underground Storage Tanks Methods for Developing and Applying Screening Criteria for the Petroleum Vapor Intrusion Pathway Workshop 7 Tuesday March 24, :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., McHugh et al, 2010 Peargin and Kolhatkar, 2011 Wright, J., 2011, 2012, Australian data Lahvis et al, 2013 EPA Jan 2013, 510-R 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 Australian sites evaluated separately 816

Conceptual Characteristics of Petroleum Vapor Transport and Biodegradation After Lahvis et al 2013 GWMR 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 01 01

 >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 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 Utility line

LNAPL 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 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 Results of Empirical Studies Thickness of clean soil required to attenuate vapors associated with LNAPL and dissolved sources Screening Criteria

4 feet Benzene in GW 3180/ ug/L 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

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 ft15 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 INDICATORMEASUREMENTS 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 > 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, > 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/m 3 Shallow SV Benzene, ug/m 3 =AF ~7,000,000x contaminant reduction ~1 ug/m 3 145,000 ug/m 3 AF = = 7E-06 Measuring Magnitude of Subsurface Vapor Attenuation Subsurface Attenuation Factor (AF) = Ratio of shallow to deep vapor concentration

3 Reasons for Insignificant AFs 10x-100x Distribution of Magnitude of Subsurface Petroleum Vapor Attenuation Factors Screen these out Reasonable Screening AF 100x-1000x Most events exhibit Significant AFs >10,000x

EPA Modeling Studies Vertical and Lateral Attenuation Distances

Lateral Distance, meters Vertical Distance Below Grade, meters 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

U.S. and Australia Screening Criteria

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, <1000 Includes large industrial sites 30LNAPL California 5<100SG Oxygen not required 5<1000SG Oxygen required >4% 10<1000SG Oxygen not required 30LNAPL Indiana 5<1000 SG Oxygen not required Distances apply vertically & horizontally AFs for GW & SG 30 LNAPL New Jersey 5<100SG Oxygen not required 5<1000SG Oxygen required >2% 10<1000SG Oxygen not required 100LNAPLDistances apply vertically & horizontally Wisconsin 5<1000Distances apply vertically & horizontally 20> LNAPL

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