Lessons from Petroleum Hydrocarbon and Chlorinated Solvent Sites Extensively Monitored for Vapor Intrusion By Todd McAlary Geosyntec Consultants, Inc. EPA Workshop on Vapor Intrusion San Diego, CA March 14, 2008
Outline Petroleum Hydrocarbon Sites: 1) Refinery, WY Shallow source (0.5 to 5 ft) 2) Enid, OK Intermediate source (14-20 ft), Low K 3) Hooven,, OH Deep Source (50 to 60 ft) Chlorinated Solvent Sites: 4) Shallow (5 ft) soil gas probes seasonality 5) Deep soil gas probes (15, 45, 63 ft) VOCs & SVOCs 6) Real-time monitoring of indoor air quality - background
Spatial and Temporal Variability in Hydrocarbon and Oxygen Concentrations Beneath a Building Above a Shallow NAPL Source Emma Hong Luo 1, Paul Dahlen 1, Paul Johnson 1, Todd Creamer 2, Tom Peargin, Paul Lundegard 4, Blayne Hartman 5, Lilian Abreu 6, and Todd McAlary 6 1 -ASU, 2 -Trihydro, 4 -Lundegard and Associates, 5 -H&P Labs, 6 -Geosyntec Consultants. Lundegard & Associates Arizona State University, Trihydro Corporation, H&P Labs, Lundegard & Assoc. and Geosyntec Consultants
Former Refinery Site Light petroleum distillate (gasoline-range components) Soil is a mixture of sand, gravel, fill. Water table at about 12 to 15 feet (shallower historically) Arizona State University, Trihydro Corporation, H&P Labs, Lundegard & Assoc. and Geosyntec Consultants
Arizona State University, Trihydro Corporation, H&P Labs, Lundegard & Assoc. and Geosyntec Consultants
Arizona State University, Trihydro Corporation, H&P Labs, Lundegard & Assoc. and Geosyntec Consultants
Source Characteristics Depth to top-of-source varies from 0.5 to 5.0 ft, as shown on contours. Utilities There are utility conduits beneath the slab (Note location 16). The slab was poured, then cut into 6 segments with saw-cut expansion slots Saw-Cut Expansion Slots Arizona State University, Trihydro Corporation, H&P Labs, Lundegard & Assoc. and Geosyntec Consultants
Sub-Slab Soil Gas Snapshot Oxygen Concentration (%) TPH Concentration (mg/l) 1. Rapid TPH attenuation laterally and vertically over short distances [ft] in areas where O 2 is present, consistent with model results 2. Spatial variability >10,000X, strongly linked to source depth Arizona State University, Trihydro Corporation, H&P Labs, Lundegard & Assoc. and Geosyntec Consultants
GC Real-Time Sampling Away from Foundation: Source Zone (4 ft BGS) and Shallow Vapor-Only Area (2 ft BGS) Under-Foundation and Near-Crack: Sub-Slab (0.5 ft BGS) and Source Area (4 ft BGS) Arizona State University, Trihydro Corporation, H&P Labs, Lundegard & Assoc. and Geosyntec Consultants
200 Location #A-4ft-BGS 25 Real-Time GC Sampling 150 100 50 0 200 150 100 50 0 TPH [mg/l] CO2 [% v/v] O2 [% v/v] 0 10 20 30 40 50 60 70 80 25 TPH [mg/l] Location #9-Sub-Slab- Time [d] 0.5 ft BGS CO2 [% v/v] O2 [% v/v] Source zone depth concentrations appear to be relatively stable with time Sub-slab/near-crack variability with time 0 10 20 30 40 50 60 70 80 Time [d] Arizona State University, Trihydro Corporation, H&P Labs, Lundegard & Assoc. and Geosyntec Consultants 20 15 10 5 0 20 15 10 5 0 [v/v%] [v/v%]
Sub-slab pressure minus indoor air pressure (Pa) 30 25 20 15 10 5 0-5 Wind Speed vs ΔP Controlled by Other Factors Controlled by Wind Location #9 December 2005 4 m/s = 9 mph 0 2 4 6 8 10 12 2hr average wind speed [m/s] Arizona State University, Trihydro Corporation, H&P Labs, Lundegard & Assoc. and Geosyntec Consultants
Sub-slab O 2 vs ΔP Near a Crack Sub-Slab O 2 Concentration (%) 16 14 12 10 8 6 4 2 0 Flow Into Soil Autosampler-#9-SS: Oxygen concentration vs. P subslab-indoor (day 0 to day Flow Into Building -4-2 0 2 4 6 8 10 12 Pressure difference Psubslab-Pindoor [Pa] Arizona State University, Trihydro Corporation, H&P Labs, Lundegard & Assoc. and Geosyntec Consultants
Results
Lessons from Case #1 Very Shallow Source leads to consistently elevated TPH and low O 2 in most probes Degradation occurs rapidly where O 2 is present 10 4 spatial variability in sub-slab slab = f(source depth) Buildings breathe both ways Affected by weather (wind and barometric pressure) Samples are insensitive to purge rate or volume 14
A CASE STUDY ON THE INFLUENCE OF AEROBIC BIODEGRADATION ON VAPOR INTRUSION AT A FORMER REFINERY PROPERTY Todd McAlary, Paul Nicholson, David Bertrand, Lilian Abreu, and Robert Ettinger Geosyntec Consultants, Inc. AWMA Specialty Conference On Vapor Intrusion Providence, RI - Sept 27, 2007 15
Schematic Cross Section Nested Soil Gas Sample Sub-slab Soil Gas Sample Multi-Level Soil Gas Sample SSP-1 to 11 N10 N11 N12 N13 N20 6 ft Unsaturated zone 9 ft N18 N19 12 ft Saturated zone LNAPL Silty Clay Sandy Aquifer 20 ft 16
LIF Log Residual NAPL from about 20 to about 38 ft bgs (within confined aquifer) 17
Sampling Locations 18
Depth to Water Table 10 11 12 Depth to Water (ft btoc) 13 14 15 16 Event 1: October 2006 (severe drought) 17 18 19 Event 2: June 2007 (very moist) 20 10/10/2006 11/29/2006 1/18/2007 3/9/2007 4/28/2007 6/17/2007 19
Soil Texture Grv Sand crs medium fine Silt Clay 100 90 80 A slightly finer-grained layer at about 7 feet bgs 1 to 2 feet 4 to 5 feet 7 to 8 feet 10 to 11 feet 13 to 14 feet 17 to 18 feet 18 to 19 feet 19 to 20 feet 70 60 50 40 30 20 10 Cumulative Weight Retained (%) Otherwise, fairly uniform at 75 to 90% silt and fine sand 0 10 1 0.1 0.01 0.001 0.0001 Particle Size (mm) 20
Compression -fit ball valve Probe Design ¼-inch Nyla-Flow tubing (volume approximately 10 ml/ft) bentonite/water slurry 3.25-inch diameter corehole 6 inches dry granular bentonite 18-inches filter sand (pore volume approximately 1L) GeoProbe Stainless Steel Screen
Soil Gas Sampling Shut-in test to verify no obvious leaks Purging and field screening using Tedlar bag and lungbox for O 2, CO 2, CH 4, Helium & PID Sampling in 1 L Summa canisters for analysis by TO-15 & Helium 22
Pneumatic Testing Equivalent to a step-test of a groundwater well
Specific Capacity (October, 2006) 10 1 Q/s (L/min/in-H2O) 0.1 Shallow Intermediate Deep 0.01 0.001 0 20 40 60 80 100 120 140 160 Probe Number 34 probes Q/s = flow rate (L/min) divided by vacuum (in-h20)
Rate of Vacuum Dissipation Probe Vacuum (in-h2o) 100 90 80 70 60 50 40 30 20 10 0 0 20 40 60 80 100 120 140 160 Hours After Pneumatic Test (selected low-flow probes only)
Specific Capacity 2006 vs 2007 Many probes showed little change Increased flow mostly in 9 and 12 ft probes Decreased flow mostly in shallow (6 ft) probes
Reproducibility 2 blind duplicates to each of 4 Labs About 15% RPD within a lab Up to factor of 2 variation between labs Average of 8 samples: benzene = 17 ppmv Sampled 3 weeks later: benzene = 15 ppmv
Comparison of Inter-Lab Duplicates Strong positive correlation over 6 order of magnitude: indicates good data quality 1:1 line Some possible matrix interference issues - coelution Concentrations in ppbv
Helium Tracer Data 100% 90% 80% 70% First Round Second Round Percent Leakage 60% 50% 40% 30% 20% 10% 0% 0 20 40 60 80 100 120 140 Probe Number 21 of 270 samples had leaks >5% (100% passed shut-in test) All but two were corrected using Helium and Mass Balance
Sub-Slab Slab Oxygen (%) (June, 2007) 30
Sub-Slab Slab TVOC (µg/l)( TVOC is lowest where oxygen is highest 31
Long-Term Temporal Variability N-11 N-12 Depth Oct-06 Jun-07 Oct-06 Jun-07 6 ft bgs 9 ft bgs 12 ft bgs Benzene µg/m 3 <3.2 2,200 7.9 500 TPH µg/m 3 2,000 8,000,000 1,000 1,000,000 Oxygen % 18 0.0 20.3 0.2 Benzene µg/m 3 40,000 41,000 12,000 16,000 TPH µg/m 3 46,000,000 40,000,000 700,000 2,000,000 Oxygen % 1 0.6 4.6 2.03 Benzene µg/m 3 42,000 42,000 33,000 44,000 TPH µg/m 3 40,000,000 40,000,000 10,000,000 10,000,000 Oxygen % 4.1 6.9 5.0 6.5 SS-1 SS-2 SS-3 Oct-06 Jun-07 Oct-06 Jun-07 Oct-06 Jun-07 Benzene µg/m 3 <48 <41 <12 <43 <8.8 11 TPH µg/m 3 10,000 200,000 10,000 300,000 10,000 1,000 Oxygen % 6.6 0.0 6.6 0.4 12.8 3.4 9 and 12 ft deep samples are relatively stable 32
Short-Term Temporal Variability Day SS-1 SS-2 SS-3 1 2 3 4 5 TPH µg/m 3 10,000 400,000 300,000 200,000 200,000 Benzene µg/m 3 11 <190 <87 <68 <41 O 2 % 1.21 1.1 0.5 1.27 0.1 TPH µg/m 3 600,000 700,000 200,000 300,000 400,000 Benzene µg/m 3 <42 <130 <44 <61 <43 O 2 % 1.39 0.8 0.5 1.1 0.1 TPH µg/m 3 1,000 900 600 1,000 400 Benzene µg/m 3 <2.2 <2.8 <2.5 11 <2.3 O 2 % 2.11 1.3 5.2 5.85 3.5 Range is generally a factor of 2 or so about the mean 33
Lessons from Case #2 Deep samples show much less spatial and or temporal variability compared to shallow samples Seasonal changes in rainfall affect shallow gas permeability, O 2 and hydrocarbons Short-term term variability is minimal by comparison Soil gas sampling in low K soil requires special care He tracer provided unique insight re. leaks Laboratory variability is minimal 34
Case Study #3 Deep Hydrocarbon Source 35
Vertical Profiles of O 2, CO 2, VOCs 36
Vertical Profiles Outside of Plume 37
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Effect of Vapor Source Concentration and Depth Modeling Assumptions: Benzene source Sand soil Basement scenario λ = 0.79 h -1 Biodegradation is likely to have a significant effect on α for non-napl sources This effect is more pronounced for deeper sources For NAPL sources, effect of biodegradation on α may be minimal due to oxygen depletion L: source-foundation distance (Abreu et al., 2007) Attenuation Factor 1.E-02 1.E-03 1.E-04 1.E-05 1.E-06 1.E-07 1.E-08 1.E-09 1.E-10 Dissolved phase 0.1 1 10 100 1000 Vapor Source Concentration (mg/l) L = 1 m, λ = 0.79 (1/h) L = 3 m, λ = 0.79 (1/h) L = 10 m, λ = 0.79 (1/h) L = 10 m, No Biodegradation 39 L = 1 m L = 2 m All 3 sites match reasonably well to model predictions L = 2 m bgs, λ = 0.79 (1/h) L = 5 m, λ = 0.79 (1/h) L = 1 m, No Biodegradation NAPL L = 3 m L = 5 m L = 10 m
Lessons from Case #3 Deeper hydrocarbons undergo more degradation Vertical profiles of O 2 and CO 2 help identify biological activity Measured profiles match 1-D 1 D and 3-D 3 D Models Generic attenuation factors for hydrocarbon sites should be a function of source depth 40
Case Study #4: Long Term Seasonality in Soil Gas Data Sandy soil, water table at about 8 to 16 ft TCE in soil gas monitored spring & fall for > decade Soil gas samples from 5 ft bgs PID screening prior to sample collection
Conceptual Model
SGP12 SGP11 SGP10 SGP1 SGP5 SGP2 Former UST
Water Levels vs Time ~ 1 to 2 ft seasonal range in water level Generally < 2ft water table fluctuations
10000 1000 100 10 1 Spring TCE in Soil Gas Spring TCE vs Time? Mar-95 Sep-95 Mar-96 Sep-96 Mar-97 Sep-97 Mar-98 Sep-98 Mar-99 Sep-99 Mar-00 Sep-00 Mar-01 Sep-01 Mar-02 Sep-02 Mar-03 Sep-03 Mar-04 Sep-04 Mar-05 Sep-05 Mar-06 Sep-06 Mar-07 Time SGP1 SGP2 SGP5 SGP11 SGP10 SGP12 Mar-94 Sep-94
10000 1000 100 10 1 Late Summer TCE vs Time 7/17/96 1/17/97 7/17/97 1/17/98 7/17/98 1/17/99 7/17/99 1/17/00 7/17/00 1/17/01 7/17/01 1/17/02 7/17/02 1/17/03 7/17/03 1/17/04 7/17/04 1/17/05 7/17/05 1/17/06 7/17/06 1/17/07 7/17/07 Fall TCE in Soil Gas Time SGP1 SGP2 SGP5 SGP11 SGP10 SGP12
Spring&Fall TCE in Soil Gas All TCE Concentrations vs Time 10000 1000 SGP1 SGP2 SGP5 100 SGP11 SGP10 SGP12 10 1 3/1/94 9/1/94 3/1/95 9/1/95 3/1/96 9/1/96 3/1/97 9/1/97 3/1/98 9/1/98 3/1/99 9/1/99 3/1/00 9/1/00 3/1/01 9/1/01 3/1/02 9/1/02 3/1/03 9/1/03 3/1/04 9/1/04 3/1/05 9/1/05 3/1/06 9/1/06 3/1/07 9/1/07 Time
Lessons from Case #4 Seasonal variability can influence data ~10X at this site (shallow sandy soil) Is heating season always conservative? Annually, trends are consistent, so soil gas data are reproducible Decreasing trend over time due to remediation
Case Study #5: Deeper Soil Gas Samples for VOCs & SVOCs Layered Sandstone/Mudstone, water table at about 200 ft TCE, PCE and SVOCs in soil gas monitored for ~ decade Soil gas samples from 15, 45 and 63 ft bgs PID screening prior to sample collection
Conceptual Model Soil Gas Samples
Dec-07 Jun-07 1000000 100000 10000 1000 100 10 1 0.1 Depth = 15 ft bgs Jun-02 Dec-02 Jun-03 Dec-03 Jun-04 Dec-04 Jun-05 Dec-05 Jun-06 Dec-06 Sampling Date SVOC 1 SVOC 2 SVOC 3 SVOC 4 PCE TCE Dec-01 Jun-01 Dec-00 Jun-00 Jun-99 Dec-99 Concentration (ppb v)
Dec-07 Jun-07 1000000 100000 10000 1000 100 10 1 0.1 Depth = 45 ft bgs Jun-02 Dec-02 Jun-03 Dec-03 Jun-04 Dec-04 Jun-05 Dec-05 Jun-06 Dec-06 Sampling Date SVOC 1 SVOC 2 SVOC 3 SVOC 4 PCE TCE Dec-01 Jun-01 Dec-00 Jun-00 Jun-99 Dec-99 Concentration (ppb v)
1000000 100000 10000 1000 100 10 1 0.1 Depth = 63 ft bgs VOCs & SVOCs low? Only SVOCs low? Dec-01 Jun-02 Dec-02 Jun-03 Dec-03 Jun-04 Dec-04 Jun-05 Dec-05 Jun-06 Dec-06 Jun-07 Dec-07 Sampling Date SVOC 1 SVOC 2 SVOC 3 SVOC 4 PCE TCE Jun-01 Dec-00 Jun-00 Jun-99 Dec-99 Concentration (ppb v)
Lessons from Case #5 Deeper soil gas samples show less seasonal variability than shallow soil gas samples SVOCs are as reproducible as VOCs Even with considerable care, occasional samples may have a bias
Case Study #6: Background Source Former DoD site (now reused - commercial) TCE and PCE > Screening levels in: 8 groundwater wells (1 to 3 events: 1994-2006) 4 sub-slab slab samples (4 events: 2003-2008) 2008) 6 indoor air samples (5 events: 2003-2008) 2008) However: Ratio of TCE:PCE not consistent in SS and IA Higher TCE than expected in indoor air Businesses include electronics
Commercial Building Layout 105 180 30 50 70 80 130 60 120
HVAC Review and Monitoring Vent rate is sufficient to maintain slight positive pressure inside building
EPA TAGA Unit
Unit 180 Unit 80 TCE barely detectable (~0.1 ppbv) TCE ~1 ppbv PCE all <DL (<0.1 ppbv) Crack in Floor TCE ~1ppbv in Unit 80, but no increase at crack
Unit 60 Unit 50 Bathroom 1 Floor Drain Hole in Floor TCE ~3 ppbv TCE ~3pbv, but no increase above cracks or holes
Unit 70 Toolboxes warehouse office TCE ~3ppbv in warehouse, increase near toolboxes
Unit 105 Up to ~150 ppbv in warehouse Up to ~50 ppbv in office Up to 150 ppbv TCE in Unit 105 Warehouse Sub-slab TCE ~ 10 ppbv (vapor extrusion?)
Lessons from Case #6 Three different types of data (GW, SS, IA) may not be sufficient for a clear understanding Multiple Lines of Evidence includes: Comparison to expected attenuation factors Compound ratios (between media, over time) Building inventory Building HVAC operations Real-Time monitoring can resolve VI questions
Summary Each site has unique conditions, but vapor behavior is consistent with theory Otherwise: check conceptual model, data quality Customize assessment and data interpretation to site-specific specific conditions Lessons should be helpful for sites with less data