Screening Criteria for the Petroleum Vapor Intrusion Pathway AEHS 22 nd Annual International Conference on Soil, Sediment, Water & Energy Mission Valley Marriott, San Diego, California Petroleum Vapor Intrusion Platform Session 1 Wednesday March 21, 2012, 1:30 5:30 pm by Robin V. Davis, P.G. Project Manager Utah Department of Environmental Quality Leaking Underground Storage Tanks rvdavis@utah.gov 801-536-4177
OBJECTIVE Understand d why so many LUST sites exist nationwide id yet few report cases of petroleum vapor intrusion to indoor air Develop Screening/Exclusion criteria to screen out low-risk sites Avoid unnecessary, $costly$, intrusive PVI investigations SCOPE Petroleum Vapor Database: - Evaluate PVI pathway by compiling basic, highquality field data Soil type Depth to groundwater Depth & thickness of LNAPL Contaminant source concentrations in dissolved & vapor phases Extent & degree of contamination Show mechanisms, characteristics & trends of petroleum hydrocarbon vapor biodegradation
Petroleum Vapor Database Compilation of soil vapor data from subsurface multi-depth & sub-slab sample points, paired with concurrent source strength data ~170 Sites, ~1000 Measurements of Concurrent SV, GW & Soil Data Canada 2/13 United States 56/304 Australia 112/608 Perth Sydney MAP KEY 56 # Geographic Locations (sites) Evaluated 304 # Paired concurrent measurements of benzene subsurface soil vapor & source strength Tasmania (Davis, R.V., 2009, updated 2011) (Wright, J., 2011, Australian data)
Characterize Site Know Full Extent t & Degree of Gas Petroleum Vapor Sources Station (required by CFR Title 40 Part 280) Building Construct Conceptual Site Model UST system Contaminated Soil, shallow Strong Vapor Source from LNAPL & Contaminated Soil Clean aerobic soil Weak Vapor Source from Dissolved Plume Contaminated Soil & LNAPL RAOULT S LAW Dissolved contamination HENRY S LAW
Results of Field Data & Published Studies Subsurface soil is a natural bioreactor: - Biodegradation of Petroleum Hydrocarbons by hundreds/thousands microbial genera/species proven by 100 years of published research - Characteristics of petroleum biodegradation & vapor attenuation are wellunderstood & predictable - Aerobic biodegradation occurs in soil containing sufficient Oxygen needed to attenuate vapors, 1%-4% O2 - Clean aerobic soil provides a natural barrier to PVI where there is sufficient separation distance between source & receptors - Vapors attenuate with 5-8 feet thickness of clean (uncontaminated) oxygenated (aerobic) overlying soil - Vapors attenuate up to 1,000,000-fold, most 1000-10,000-fold No reported cases of petroleum vapor intrusion from low-strength sources Causes of petroleum vapor intrusion: i - LNAPL, contaminated soil or high dissolved concentrations near or in direct contact with buildings, sumps, elevator shafts
Developing Screening/Exclusion Criteria PVI Database: - Line-by-line analysis of the international field data - Plot data, evaluate trends Determine thickness of clean overlying soil required to attenuate vapors associated with: - Dissolved sources - LNAPL & Soil Sources Determine acceptable soil gas concentrations at depth that attenuate to 10-06 risk for indoor air exposure - Subsurface bio-attenuation factors
Method for Measuring Vapor Attenuation from Dissolved Sources Feet bgs 0 Multi-Depth Vapor Monitoring Well Beaufort, SC, Lahvis et al 1999 NJ-VW-2 3ft Benzene vapor concentrations at depth <1 ug/m 3 5 8 feet Clean overlying soil 4 ft 7 ft 2,300 ug/m 3 16,700 ug/m 3 DTW ~11 ft 10 11 ft 145,000 ug/m 3 Estimated Contaminated Soil Zone Benzene in GW 16,000 ug/l 15 FORMULA: 11 ft 3 ft = 8 ft clean overlying soil
Screening Criteria for Dissolved Benzene & TPH (Exterior + Sub-Slab) Benzene: Soil Vapor & Dissolved Paired Measurements TPH: Soil Vapor & Dissolved Paired Measurements Near-Slab Multi-Depth, Sub-Slab Benzene: 199 exterior/near-slab + 37 sub-slab = 236 total All Soil Types Near-Slab Multi-Depth, Sub-Slab TPH: 73 exterior/near-slab + 24 sub-slab = 97 total All Soil Types S oil R equired to e ne Vapors, fe et ickness Clean ttenuate Benze Th A t 10 9 8 7 6 5 4 3 2 1 0 1 10 100 1,000 10,000 100,000 Benzene, dissolved, ug/l e d to e t S oil R equire H Vapors, fee c kness Clean A ttenuate TPH Thic A 10 9 8 7 6 5 4 3 2 1 0 1 100 10,000 1,000,000 TPH, dissolved, ug/l 5 feet Clean Overlying Soil Attenuate Vapors Associated with Dissolved Benzene <1,000 ug/l, TPH <10,000 ug/l
Separation Distance v. Dissolved Source Strength (slide courtesy Matt Lahvis, Shell, 2011, RV Davis database) SOIL GAS CONCENTR RATION (ug g/m3) KEY POINTS 1000 100 10 1 0.1 0.01 BENZENE TAGE OF SITES PERCEN 50% 40% 30% 20% 10% 0% 67 SITES 161 LOCATIONS 298 SAMPLES GROUNDWATER CONCENTRATIONS 10% 10% 0 10 20 30 40 50 DISTANCE ABOVE WATER TABLE (ft) 32% 46% Measured Non Detect 95th Percentile 95 th Percentile soil gas concentrations ti = 31 ug/m3 ~50 % sites where 1< C GW <15 mg/l Soil gas data collected from dissolved phase retail sites implies limited PVI risk (<31 ug/m3) unless groundwater is in contact with building foundation 5 feet of soil overlying high-strength dissolved sources attenuate vapors to low levels 1%
Separation Distance v. Dissolved Source Strength: Benzene (slide courtesy of Jackie Wright, Environmental Risk Sciences, Sydney, Australia, 2011) Soil Gas Concentrations Associated with Dissolved Source Strengths (ug/m3) Dissolved phase, B(SG) < 50 µg/m 3 Dissolved phase, B(SG) > 50 and <1000 µg/m 3 LNAPL, B(SG) < 50 µg/m 3 LNAPL, B(SG) > 50 and < 1,000 µg/m 3 LNAPL, B(SG) > 1,000 and <100,000 000 µg/m 3 LNAPL, B(SG) > 100,000 µg/m 3 1.5 m (5 feet) clean soil required to attenuate vapours associated with Benzene in GW <1 mg/l Distance, Sour rce to Soil Gas measurement (m) Separation
2 Methods for Evaluating Vapor Attenuation from LNAPL & Soil Sources th feet bgs 0 5 10 VW-7 Hal s, Green River, VW7, 6/26/07 6/26/07 Utah (UDEQ) O2 & CO2 (% v/v) 0 5 10 15 20 Oxygen Carbon Dioxide Benzene Method 1: 20 ft DTW 11 clean cea SV (Davis, R. 2009) = 9 feet TOTAL soil thickness Method 2: 15 ft top contam 11 ft top clean soil = 4 feet CLEAN soil needed to attenuate vapors (Davis, R. 2010) Dep 15 contaminated soil zone 20 1.E+00 1.E+02 1.E+04 1.E+06 1.E+08 Benzene (ug/m3)
Thick kness of Ov verlying Soil l, feet Method 1 Results for LNAPL Sources (All soil types. 43 paired SV benzene & LNAPL Events) 30 25 20 15 10 5 Sample events beneath buildings Refineries 30 ft TOTAL (clean + contaminated smear zone) soil attenuates benzene vapors associated with LNAPL 0 Chillum Chatterton Hal s Mission Valley Coachella-2 Coachella-3 Refinery, Unknown US Location
Method 2 Results for LNAPL & Soil Sources Benzene 48 exterior/near-slab + 23 sub-slab = 71 total Benzene SV Sample Event over LNAPL & Soil Sources TPH 17 exterior/near-slab + 19 sub-slab slab = 36 total TPH SV Sample Event over LNAPL & Soil Sources Near-Slab Multi-Depth, Sub-Slab Near-Slab Multi-Depth, Sub-Slab erlying LNAPL L apors, feet Clean Soil Ove o Attenuate Va hickness of C Required to Th 10 9 8 7 6 5 4 3 2 1 0 Refineries erlying LNAPL L apors, feet lean Soil Ove o Attenuate Va hickness of C Required to ~8 ft CLEAN overlying soil attenuates vapors associated with LNAPL/Soil Sources Th 10 9 8 7 6 5 4 3 2 1 0
Separation Distance v. LNAPL Source Strength: Benzene (slide courtesy of Matt Lahvis, Shell, 2011, R. Davis & J. Wright databases) SOIL GAS CONCENTRA ATION (ug/ /m3) 10000000 1000000 100000 10000 1000 100 10 1 0.1 BENZENE 62 SITES 218 LOCATIONS 503 SAMPLES measured non detect 0 10 20 30 40 50 DISTANCE ABOVE SOURCE (ft) KEY POINTS 4-5 order of magnitude decrease in benzene vapor concentrations (<100 ug/m3) at a distance of 15 feet above the source 15 feet of TOTAL soil thickness attenuate vapors to <1000 ug/3
Separation Distance v. LNAPL Source Strength: Benzene (slide courtesy of J. Wright (2011) Benzene in Soil Gas (µg/m 3 ) 100000000 10000000 1000000 100000 10000 1000 100 10 1 0.1 No SG concentrations exceeding HSL and 5% of HSL where Benzene vs Separation Distance separation NAPL Source distance > 10m Really should only focus on those site where depth <10m LNAPL exclusion distance >10m HSL 5% of HSL 0.01 0 2 4 6 8 10 12 14 16 18 20 Separation Distance (m) Clay Sand Sandy Clay X US Data
Determine Acceptable At-Depth Soil Gas Concentrations Determine at-depth soil gas concentrations that attenuate to 10-0606 risk for indoor air exposure - Derive Subsurface Attenuation Factors PVI Database: - Line-by-line analysis - Plot data, evaluate trends
Method for Measuring Magnitude of Subsurface Vapor Attenuation Attenuation Factor AF = Ratio of Shallow Subsurface Vapor Concentration Divided by Deep AF = Shallow SV Benzene, ug/m 3 Deep SV Benzene, ug/m 3 Beaufort, SC NJ-VW2 (Lahvis, et al., 1999) Oxygen Carbon Dioxide Benzene O2 & CO2 (% V/V) 0 5 10 15 20 25 0 Field Example: ~1 ug/m AF 3 = = 7E-06 145,000 ug/m 3 10 5 Benzene in GW 16,000 ug/l ~1,000,000x 000x contaminant reduction Low AF 15 1.E+00 1.E+02 1.E+04 1.E+06 1.E+08 Benzene (ug/m3) = High Attenuation of Contaminant Concentrations = Significant Attenuation = <0.001, >1000-fold
Distribution of the Magnitude of Subsurface Petroleum Vapor Attenuation Factors Benzene TPH (RV Davis database, 2009-2011) Numbe er of Soil Vapor Sample Event ts 150 120 90 60 30 0 Number of Soil Vapor Samp ple Events 200 160 120 80 40 0 <1.E-04 1.E-03 1.E-02 1.E-01 >1.E-01 Benzene TPH Subsurface Vapor Attenuation Factors Screen these out Reason 1: No Reason 2: Low Reason 3: Clean Source Rapid Overlying Soil Strength Attenuation Near High- Strength Source Numb ber of Soil Vapor Sample Events 100 80 60 40 20 0 <1.E-04 3 Reasons for Insignificant AF Most events exhibit Benzene very low, TPH significant AFs <10,000x 1.E-03 Reasonable AF 100x to 1000x 1.E-02 Subsurface Vapor Attenuation Factors
Numerical Model (Fig. 3 Abreu et al 2009, modified) Effect of Oxygen-Driven Biodegradation and Magnitude of Subsurface Attenuation on Benzene Vapor Source Concentration at Depth Beneath Buildings - Weak vapor source strength 100,000 ug/m3 located 3 m (10 ft) beneath building - Benzene in GW 1,000-4,000 ug/l - Vapors attenuate to 10 ug/m3, 1.2 m (4 ft) beneath building, 1.8 m (6 ft) above source - Medium vapor source strength 1,000,000 ug/m3 - Benzene in GW >4,000 ug/l - Vapors attenuate to 10 ug/m3, 0.75 m (2.5 ft) beneath building, 2.25 m (7.4 ft) above source - Strong vapor source 10,000,000 ug/m3 - LNAPL - Vapors attenuate to 10 ug/m3, at building slab, 3 m (10 ft) above source Depth below grade (met ters) Benzene Vapors Hydrocarbon vapors diffuse upward Oxygen Atmospheric Oxygen diffuses downward Horizontal Distance from Building Center (meters)
Numerical Model (Fig. 10 Abreu et al 2009, modified) Effects of Benzene Vapor Source Concentration, Source Depth, and Attenuation additional attenuation = ~1.E 04 related to biodegradation KEY POINTS 10,000x (1E-04) bioattenuation of benzene vapors up to 10,000,000 ug/m3 within 2 m (5-6 ft) of building foundation ation Factor α Subsu urface Attenua 100,000 1,000,000 10,000,000 100,000,000 1,000,000,000 Benzene Vapor Source Concentration (ug/m3) Benzene vapors are attenuated to 10 ug/m3 No BiodegradationL = 2m(approximate) (NOTE: 10,000 ug/l = 10,000,000 ug/m3)
Field-Observed Benzene Soil Gas Attenuation Factors for Distances <5 feet Above Source AT TTENUATIO ON FACTO OR (DIMENS SIONLESS) KEY 10 POINTS -1 Benzene vapors attenuate >1000x (10E-03) within 5 feet of benzene soil gas 10,000-100,000 ug/m3 and often up to 1,000,000 ug/m3 Field-observed subsurface attenuation factors support the model results SOIL GAS ATTENUATION FACTORS (BENZENE) )FOR DISTANCES <= 5 FT (slide courtesy of Matt Lahvis 2010, 2011) 10 0 affected by non detects 10-2 10-3 n=15 10-4 10-5 10-6 10-7 7 sites 10 locations n = 7 3 sites 5 locations n = 7 6 sites 6 locations SOURCE CONCENTRATION IN SOIL GAS (C SG ) (ug/m 3 )
Compare Field-Observed Soil Gas Data to BioVapor Analytical Model Beaufort, NJ-VW-2 (Lahvis et al, 1999) AF=0.1, O2=1%, foc=0.5% McHugh, DeVaull & Newberry, Find it at: api.org BioVapor Estimates Bio-Attenuation of PHC Vapors Based on Field Data: Dissolved Sources Vapor Sources Associated with LNAPL and Contaminated Soil A Useful Tool for Screening Sites for the PVI Pathway
BioVapor Analytical Model Compared to Beaufort, South Carolina (Lahvis et al 1999) - Soil vapors associated with Dissolved Benzene 16,000 ug/l, TPH-g 67,100 ug/l Beaufort, SC (Lahvis et al, 1999) Soil Vapor Field Data Compared to BioVapor Model from Dissolved Source Beaufort, SC (Lahvis et al, 1999) Soil Vapor Field Data Compared to BioVapor Model from dissolved source - BioVapor Model under-predicts subsurface attenuation by 100x to 10,000x Benzene Field-Measured, ug/m3 Benzene BioVapor Prediction, ug/m3, AF=0.1, O2=1%, foc=0.5%, Bare Earth Benzene BioVapor Prediction, ug/m3, AF=0.1, O2=1%, foc=0.5%, Pavement TPH-gro Field-Measured, ug/m3 TPH-gro Bio Vapor Prediction, ug/m3, AF=0.1, O2=1%, foc=0.5%, Bare Earth TPH-gro Bio Vapor Prediction, ug/m3, AF=0.1, O2=1%, foc=0.5%, Pavement TPH-gro Bio Vapor Prediction, ug/m3, AF=0.1, O2=1%, foc=0.5%, Aerobic Depth Spe Benzene BioVapor Prediction, ug/m3, AF=0.1, O2=1%, foc=0.5%, Aerobic Depth=3.4 0 0 3 3 De epth, feet bls 6 D e pth, feet bls 6 9 Benzene in GW 16,000 ug/l 9 TPH in GW 67,100 ug/l 12 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 Benzene, ug/m3 12 1.0E-01 1.0E+01 1.0E+03 1.0E+05 1.0E+07 1.0E+09 TPH-gro, ug/m3
BioVapor Analytical Model Compared to Chatterton, t BC, Sub-Slab SG-BC Sl b & Multi-Depth th10-1-97 Beneath 1Building, 10-1-97 1 (Hers, 2006) et al 2000) Benzene - Soil vapors associated Soil Vapor with Field Benzene-Rich Data Compared to BioVapor LNAPL, Model Multi-Depth Sub-Slab & Exterior - BioVapor Model under-predicts subsurface attenuation by 10,000x to 1,000,000x Benzene Field-Measured, ug/m3 Benzene Bio Vapor Prediction, ug/m3, O2=1%, foc=0.5% Benzene Bio Vapor Prediction, ug/m3, O2=1%, foc=0.5%, Aerobic Depth 3.28 ft -5 Building Slab De epth, feet bls 0 5 10 LNAPL, benzene rich 1.0E+00 1.0E+02 1.0E+04 1.0E+06 1.0E+08 Benzene, ug/m3
Reference Screening Criteria Published & Cited Values (after Lahvis & DeVaull, 2011) Database & Site Type Benzene Soil Gas Screening Level (ug/m3) Screening/Exclusion Distance (feet) Screening/Exclusion Concentration Benzene (ug/l) Other Criteria Davis, R.V. (2009, 2010) International Petroleum Non-detect (0-<1000), Vapor Database 10, 100 5 <1000 5 feet for TPH <10,000 000 ug/l 8 LNAPL 30 ft poorly-characterized sites Lahvis (2011) R.V. Davis & J. Wright (retail sites only, no refineries) 100 0 <15,000 Dissolved phase only, BTEX <75,000 ug/l 15 LNAPL McHugh et al (2010) various publications, professional judgement 10 Dissolved phase only 30 LNAPL Peargin & Kolhatkar (2011) Chevron, all sites 5-10 <1000 Wright, J. (2011) Australia & U.S. sites, all sites + refineries 15 >1000 10, 50, 100, 1000 5 <1000 30 LNAPL California various references, R.V. Davis, McHugh et al 50, 100 5 <100 no SG Oxygen measured 5 <1000 with SG Oxygen measured >4% 10 <1000 no SG Oxygen measured 30 LNAPL Indiana various references, (RV Davis 2009-2010, McHugh et al 2010) 5 <1000 no SG Oxygen requirement AFs for GW & SG 30 LNAPL Distances apply vertically & horizontally New Jersey various uncited references NONE 5 <100 no SG Oxygen measured 5 <1000 with SG Oxygen measured >2% 10 <1000 no SG Oxygen measured 100 LNAPL Horizontal & vertical distance Wisconsin Davis, R.V., 2009, Luo et al 2009, McHugh et al, 2010 NONE 5 <1000 20 >1000 Exclusion distances apply vertically & horizontally 30 LNAPL
Conclusions PVI pathway not complete when following Criteria apply: Dissolved Sources - 5 feet CLEAN soil overlying Benzene <1,000 ug/l, TPH <10,000 000 ug/l - >5 feet CLEAN soil overlying Benzene >1,000 ug/l, TPH >10,000 ug/l LNAPL Sources - 8 to 15 feet CLEAN soil overlying top of LNAPL smear zone or soil sources - 30 feet TOTAL soil including smear zone for poorly characterized sites & refineries Soil Sources - 5 feet CLEAN soil = TPH <100 mg/kg, PID <100 ppm-v (gasoline), <10 ppm-v (diesel) Vapor Sources - Petroleum vapors are attenuated below the receptor - Oxygen in soil vapor ~1%-4% - If measuring soil vapor, analyze ALL COCs, O2, CO2, methane, others - Oxygen to Carbon Dioxide ratios demonstrate petroleum biodegradation - Apply Subsurface Attenuation Factors to vapor concentrations
Recommendations Fully characterize sites, determine full extent, degree of contamination Collect/Use ALL lines of evidence to assess PVI pathway Apply Screening/Exclusion Criteria in deciding if soil vapor sampling is necessary
THANK YOU Acknowledgments EPA OUST/ORD/States PVI Work Group API Petroleum Vapor Intrusion Work Group Bruce Bauman, Roger Claff, Harley Hopkins George DeVaull, Shell Global Solutions Blayne Hartman, Hartman Environmental Geoscience Tom McHugh, GSI Environmental John Menatti, Utah DEQ Tom Peargin, Chevron-Texaco Lynn Spence, P.E., Spence Engineering Todd Ririe, BP Matt Lahvis, Shell Global Solutions Jackie Wright, Environmental Risk Sciences
Comparison of Field-Measured & Henry s Law Constant-Predicted Soil Vapor Concentrations Located 0-3 feet Above Dissolved Source KEY POINTS - HLC analysis is laboratorybased, does not account for biodegradation - HLC overpredicts near- source concentrations by up to 10,000x at low- mediumstrength sources Soil Vap por, ug/m3 1.E+07 1.E+06 1.E+05 1.E+04 1.E+03 1.E+02 1.E+01 Benzene: Field-Measured Soil Vapor Benzene: Henry's Law-Predicted Soil Vapor Anomalies due to smear zone soil, surface sources, or higher actual dissolved concentrations 1.E+00 di 1 10 100 1000 1,000 10,000000 100,000000 Benzene in GW, ug/l <=3 feet separation from depth to source and depth to deep vapor sample point