1. by Robin V. Davis, P.G., Project Manager, retired Utah Department of Environmental Quality Leaking Underground Storage Tanks robinhummingbird@gmail.com 801-300-7431 Applying Screening Criteria for the Petroleum Vapor Intrusion Pathway Workshop 7 Tuesday March 22, 2016 6:30 pm – 9:30 pm Association for Environmental Health & Sciences (AEHS) 25th Annual International Conference on Soil, Sediment, Water & Energy San Diego, California

2. 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

3. 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

4. 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

5. 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

6. 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 Oxygen demand is a function of source strength 01 01

7. 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

8. June 2015 Final PVI Guide EPA OUST http://www.epa.gov/oust/cat/pvi/pvi-guide-final-6-10-15.pdf Technical Guide For Addressing Petroleum 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

9. STEP 2 Characterize Site Define extent/degree of contamination Construct Conceptual Site Model NO YES Are Precluding Factors Present? (preferential pathways, other) Are Any Existing or Planned Buildings Within Lateral Inclusion Zone? STEP 3 Delineate Lateral Inclusion Zone YES STEP 4 Determine 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 5 Evaluate Vapor Source & Attenuation: 1.Measure Vapors Near-Slab & Near-Source, or 2.Measure Indoor Air & Concurrent Sub-Slab Vapors 3.If Contamination is in Direct Contact with Building, use Option 2 above Do Near-Slab & Near-Source Sampling Indicate PVI? Option 2 Option 1 NO YES STEP 6 Notify 1 st Responders Mitigate PVI Figure 1: Flowchart for Addressing PVI At Leaking Underground Storage Tank Sites (modified from EPA OUST 2015) YES STEP 1 Emergency? Community Engagement Required by 40CFR May occur at any step in the PVI investigation & mitigation process YES NO

10. 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 Criteria Building LNAPL in soil LNAPL in soil & GW Soil Boring/MW Utility line Construct Conceptual Site Model (CSM)

11. 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

12. LNAPL Indicators 12 LNAPL INDICATORMEASUREMENTS 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/m 3 ) (after Peargin and Kolhatkar 2011, Lahvis et al 2013, ITRC 2014, EPA 2015)

13. 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)

14. 15 ft clean soil Soil, mg/kg 17-18ft Benzene 0.379 TPH-g 200 TPH-d 10.2 MW-17 Commercial Building GW, mg/L Benzene 1.2 TPH-g 16.6 TPH-d <2.0 Step 1: Emergency? NO Step 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? YES Step 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

15. 5 ft GW, mg/L Benzene 0.560 TPH-g 10.8 MW Commercial Building LNAPL Step 1: Emergency? NO Step 2: Characterize Site, Develop CSM, Precluding Factors? YES LNAPL plume not stable, in close proximity to building slab Step 3: Buildings within Lateral Inclusion Zone? YES Step 4: Sufficient Vertical Separation? NO LNAPL source 5 ft below building slab, 15 ft required Step 5: Sub-slab vapor sampling indicate PVI? NO No Further PVI Investigation Case Study 2: Basin Mkt, Murray, UT Sub-Slab VMP Soil Vapor, ug/m 3 Benzene 5.4 TPH-g <100 O2 21% CO2 <0.2% Soil, mg/kg 6 ft Benzene 6.55 TPH-g 3410

16. 5 ft Soil, mg/kg 6 ft Benzene 32.4 TPH-g 5280 MW Commercial Building LNAPL Step 1: Emergency? NO Step 2: Characterize Site, Develop CSM, Precluding Factors? YES LNAPL plume not stable, in close proximity to building slab Step 3: Buildings within Lateral Inclusion Zone? YES Step 4: Sufficient Vertical Separation? NO LNAPL source 5 ft below building slab, 15 ft required Step 5: Sub-slab vapor and IA/OA sampling indicate PVI? YES Step 6: Mitigation: Indoor air filters, building demolition and source removal Case Study 3: Hoagies, Farr West, UT Sub-Slab VMP Soil Vapor, ug/m 3 Benzene 850,000 TPH-g 85,000,000 O2 8.3% CO2 8.4% IA, ug/m 3 Benzene 55 TPH-g 2200 OA, ug/m 3 Benzene 0.42 TPH-g <100

17. 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

18. THANK YOU