Screening Criteria to Evaluate Vapor Intrusion Risk from Lead Scavengers Ravi Kolhatkar, Emma Luo, Tom Peargin, Natasha Sihota, Gary Jacobson Chevron Matthew Lahvis Shell Global Solutions (US), Inc. Qiong (June) Lu, Janice C. Paslawski, SNC-Lavalin, Inc.
Outline Background lead scavengers use, occurrence, fate and transport, PVI vs. CVI Empirical evaluation of screening criteria Estimation of aerobic biodegradation rate constants from existing soil vapor profiles (calibration of analytical vapor transport models) Conclusions Future steps 2
Lead scavengers - Use and Properties Lead scavengers added in leaded gasoline to prevent lead oxide deposits that could foul engines 1925 - Ethylene dibromide (EDB) 1 st use in leaded gasoline 1940s - Ethylene dichloride (EDC) use started Leaded gasoline phase-out - mid 1980 s to mid 1990 s EDC/EDB in groundwater from gasoline releases >20 years old EDC & EDB still used as lead scavenger in aviation gas & racing fuels Water Solubility (mg/l) Log K ow (-) VP at 25 o C (mm Hg) Henry s Law Constant at 25 o C (-) Benzene 1790 2.13 94.8 0.227 EDB 3910 1.74 11.2 0.027 EDC 8600 1.47 78.9 0.048 3
Lead scavengers - Biodegradation Aerobic biodegradation EDB t 1/2 (days to weeks), aerobic co-metabolism with methane and other alkanes shown to enhance rate EDC t 1/2 (days to several months) Anaerobic biodegradation usually via reductive dehalogenation EDB t 1/2 (months) EDC t 1/2 (months to years) Biodegradation less understood compared to BTEX 4
PVI vs. CVI EPA 2012 5
Empirical Development of VI Screening Criteria for Lead Scavengers 2015 EPA OUST PVI guidance document Established vertical screening distance criteria for benzene (see Figure) However, it identified lack of rigorous quantification of EDC and EDB biodegradation as a data gap Presence of lead scavengers considered a precluding factor to apply vertical distance screening approach Motivation Determine if concentration and distance based screening criteria can be established for VI evaluation of lead scavengers The screening criteria can help fill the data gap and enable appropriate screening of sites with lead scavengers Vertical Screening Distance Criteria for Benzene 6
Soil Vapor Screening Levels vs. Current Analytical Method (EPA TO-15) Soil vapor screening levels are o EDC - Achievable with current analytical methods o EDB - Likely not achievable with current analytical methods Compound Soil Vapor Screening Level* (µg/m 3 ) 10-6 excess cancer risk (residential) 10-5 excess cancer risk (residential) Soil Vapor Analytical Method Detection Limits (EPA TO-15) Conventional Low Level SIM EDC 3.7 37 2.0 0.40 0.12 EDB 0.16 1.6 3.8 0.77 0.23 * Soil vapor screening level - based on Table 8, Technical Guide For Addressing Petroleum Vapor Intrusion at Leaking Underground Storage Tank Sites (EPA 510-R-15-001), Assumes attenuation factor of 0.03 for soil vapor to indoor air, http://www.epa.gov/vaporintrusion/vapor-intrusion-screening-levels 7
Soil Vapor Concentration and Groundwater Concentration Data Analysis Reviewed data from over 140 PVI investigation sites Able to analyze 116 pairs of EDC and 72 pairs of EDB soil vapor & groundwater concentration data from 26 sites that met the following criteria Site with history likely to suggest leaded gasoline releases 1. Absence of petroleum-impacted vadose zone soil 2. Monitoring wells within 30 ft of the soil vapor probe and sampled within same quarter 3. Data Quality: Properly constructed permanent soil vapor probes Summa canister sampling Leak detection with helium, 1,1-difluoroethane or isopropanol as a tracer EPA method TO-15 or 8260B for soil vapor analysis 8
Three selection criteria for GW and soil vapor data MW within 30 ft. of soil vapor probe, sampled within same quarter <30 ft apart Vadose Zone Source SUMMA canister, leak detection, TO-15 or 8260B He 2 3 1 Fixed probes, nylon or Teflon tubing 9
1,000 µg/l benzene in groundwater as a conservative estimate to distinguish LNAPL from dissolved sources 100,000 10,000 Median 6,068 µg/l 1,000 100 1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106 113 120 127 134 141 148 155 162 169 176 183 190 197 204 211 218 225 232 239 246 253 260 267 Benzene (ug/l) 5 th percentile 836 µg/l Monitoring Wells Peargin & Kolhatkar, 2011 10
EDC vapors sourced from dissolved plumes (defined as GW benzene < 1000 µg/l) 50 40 70 data points (6 detects) <3.7 ug/m3 3.7-37 ug/m3 > 37 ug/m3 soil vapor screening level for 10-6 excess cancer risk Vertical Separation Distance (ft) 30 20 10 15 ft RL = 1000 ug/m 3 7 ug/m 3 0.8 1.4 50 ug/m 3 12 9.6 ug/m 3 0 0.1 1.0 10.0 100.0 1,000. GW EDC concentration (µg/l) 11
EDC vapors sourced from LNAPL (defined as GW benzene > 1000 µg/l) 12
EDC transport analysis Only 6 soil vapor detections out of 116 data points. No EDC vapor concentrations over 37 µg/m 3 (soil vapor screening level for 10-5 excess cancer risk level) were observed at vertical separation distances over 10 ft. The large number of ND vapor concentrations at RL < 37 µg/m 3 EDC suggest significant vadose zone attenuation for EDC from both dissolved and LNAPL sources: however, There is limited soil vapor data at GW EDC concentrations over 100 µg/l (~ GW VISL at 10-5 excess cancer risk) Interference from other petroleum hydrocarbon vapors raised the RL above 37 µg/m 3 EDC for vapor samples collected above higher strength LNAPL sources (benzene >1000 µg/l, EDC >100 µg/l) 13
EDB data EDB soil vapor screening level for 10-5 excess cancer risk (1.6 µg/m 3 ) is close to the vapor analytical reporting limit Interference from other petroleum hydrocarbon vapors raised the EDB RL above 1.6 µg/m 3 Available data is therefore not sufficient to empirically determine vertical screening distance criteria for EDB 14
Conclusions Empirical Evaluation EDC EDB For dissolved sources and LNAPL sources with EDC GW < 100 µg/l, vertical screening distance of 15 ft. appears to be adequate for EDC Current data set is not sufficient to determine criteria for LNAPL sources with EDC GW > 100 µg/l Due to the very low screening level concentration for EDB relative to analytical reporting limits, this data set is not sufficient to determine vertical screening distance criteria for EDB 15
Modeling: Motivation BENZENE CONCENTRATION IN SOIL GAS (µg/m 3 ) 10000000 1000000 100000 10000 1000 100 10 1 0.1 LNAPL BENZENE Detect (272 samples) Non Detect (195 samples) screening distance 0 10 20 30 40 50 DISTANCE ABOVE SOURCE - TOP OF RESIDUAL-PHASE LNAPL (ft) 0.99 0.95 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.05 0.01 vertical screening distance evaluation for EDC is difficult because of a large number of non-detect soil-gas data CUMULATIVE FRACTION OF SOIL-GAS CONCENTRATION DATA (dimensionless) Separation Distance (ft) 50 40 30 20 10 46 data points (all < RL) Vertical screening distance for benzene (15 ft) RL = 140 ug/m 3 LNAPL <3.7 ug/m3 3.7-37 ug/m3 > 37 ug/m3 RL = 4400 ug/m 3 RL = 1000 ug/m 3 0 0.1 1.0 10.0 100.0 1,000.0 10,000. GW EDC concentration (µg/l) too many NDs! 16
Modeling (BioVapor*): EDC * http://www.api.org/environment-health-and-safety/clean-water/ground- Water/VaporIntrusion/Biovapor-Form Monitoring Well Vapor Probe DISSOLVED PHASE SOURCE LNAPL SOURCE 1 st -order rate constant (aerobic) calibrated to measured soil-gas -- as defined in ITRC PVI Vapor Intrusion guidance App. I no bio no bio http://www.itrcweb.org/petroleumvi -Guidance/ L z VADOSE ZONE C SG = measured increasing bio increasing bio vadose zone assumed homogenous/isotropic C source based on AF = 0.1 (default value in BioVapor) key COPCs: aerobic aerobic EDC benzene C source = C GW * H * AF * 1000 C GW = measured anaerobic aliphatics/aromatics: concentrations defined from benzene concentrations in groundwater (BioVapor Manual) SATURATED ZONE DISSOLVED PHASE LNAPL no analysis of soil gas data w/ RLs > Fick s law known/measured estimated 17
MODEL RESULTS - EDC EDC BENZENE CONDITION Detects - median (95% CI) DeVaull (2015) (95% CI) 1 st -ORDER AEROBIC DEGRADATION RATE CONSTANT EDC (WATER) (1/hr) 0.010 (0.0022 0.043) 0.087 (0.001 0.78) SCREENING DISTANCE EDC in GW (95% concs *) (ft) 6 (3 13) 2 (0.7 6) SCREENING DISTANCE EDC in GW (max concs **) (ft) 9 (5 20) 6 (1.1 10) API (2008) 0.0011-0.0023 < 13 < 19 LNAPL (median) > 0.0070 < 8 < 11 Dissolved (median) > 0.00093 < 19 < 29 Non Detects (median) > 0.00083 < 20 < 31 C IA = 0.11 µg/m 3 VERTICAL SCREENING DISTANCE VAPOR SOURCE * 95% concentrations of EDC (440 µg/l) and benzene (704 µg/l) in GW ** max concentrations of EDC (1,330 µg/l) and benzene (16,890 µg/l) in GW aerobic biodegradation rates computed from empirical data are ~ 2 orders of magnitude < benzene; consistent w/ literature values vertical screening distance for EDC = (9 ft) < benzene (15 ft) 18
MODEL RESULTS - EDC k w = 0.01/hr OKAY EDC OKAY sand: porosity = 0.375 cm 3 /cm 3 moisture = 0.054 cm 3 /cm 3 f oc = 0% target IA concentration (EDC) = 0.11 µg/m 3 OKAY for AF < 1.68E-5 (3,300 µg/l EDC in GW); total hydrocarbon vapor source concentration < 10.6 mg/l; or vertical separation distance > 9 ft 19
Conclusions Empirical Evaluation EDC EDB For dissolved sources and LNAPL sources with EDC GW < 100 µg/l, vertical screening distance of 15 ft. appears to be adequate for EDC Current data set is not sufficient to determine criteria for LNAPL sources with EDC GW > 100 µg/l Due to the very low screening level concentration for EDB relative to analytical reporting limits, this data set is not sufficient to determine vertical screening distance criteria for EDB. Modeling EDC Vertical screening distances derived from modelling of empirical soil gas/groundwater data for EDC are < 15 ft. (i.e., screening distance derived for benzene of 15 ft. is conservative) 20
Future Steps Identify other existing soil vapor and groundwater datasets to continue empirical evaluation (API project) 21
References Watwood ME, White CS, Dahm CN. 1991. Methodological modifications for accurate and efficient determination of contaminant biodegradation in unsaturated calcareous soils. Appl Environ Microbiol 57:717-720. API. 2008. The Environmental behavior of Ethylene Dibromide and 1,2-Dicholoethane in Surface Water, Soil and Groundwater Publication 4774. API. 2010. "BIOVAPOR A 1-D Vapor Intrusion Model with Oxygen-Limited Biodegradation (Version 2.0)." Washington, DC: American Petroleum Institute. http://www.api.org/environment-health-and-safety/clean-water/ground- Water/Vapor-Intrusion/Biovapor-Form.aspx. Peargin, T. and R. Kolhatkar. 2011. "Empirical data supporting groundwater benzene concentration exclusion criteria for petroleum vapor intrusion investigations." International Symposium on Bioremediation and Sustainable Environmental Technologies, Reno, Nevada, June 27-30. https://projects.battelle.org/bioremediationsymposium/2011bio_proceedings/papers/d-53_ppr.pdf EPA. 2012. Petroleum Hydrocarbons And Chlorinated Solvents Differ In Their Potential For Vapor Intrusion. http://www.epa.gov/oust/cat/pvi/pvicvi.pdf Lahvis, M. A., Hers, I., Davis, R. V., Wright, J., DeVaull, G. E. 2013a. "Vapor Intrusion Screening at Petroleum UST Sites." Groundwater Monitoring & Remediation 33 (2):53-67. Interstate Technology & Regulatory Council (ITRC). 2014. Petroleum Vapor Intrusion:. Fundamentals of Screening, Investigation, and Management. Interstate Technology and Regulatory Council, Vapor Intrusion Team, Washington, D.C. October. http://itrcweb.org/petroleumvi-guidance EPA. 2015. Technical Guide For Addressing Petroleum Vapor Intrusion At Leaking Underground Storage Tank Sites, EPA 510-R-15-001, http://www.epa.gov/sites/production/files/2015-06/documents/pvi-guide-final-6-10-15.pdf DeVaull, G. 2015. Biovapor Model: Use, Application, Comparisons. National Tanks Conference & Expo., Las Vegas, Nevada, September 13. http://www.neiwpcc.org/tanksconference/tanks2015presentations/1- Sunday/Petroleum%20Vapor/4%20- %20PVI%20%20BioVapor_Intro_and_Applications%20(DeVaull)%20Sept%202015.pdf 22