Vapor Intrusion Investigation of Buildings Migration of VOCs

Vapor Intrusion: Investigation of Buildings Migration of VOCs through the building foundation and lessons learned from the detailed field investigation of the vapour intrusion process at Altus and Hill Air Force Bases Vingsted Center Monday, March 9, 2009 GSI ENVIRONMENTAL INC. Houston, Texas www. gsi-net. com (713) 522 -6300 temchugh@gsi-net. com SITE BUILDING Air Exchange source area

Vapor Intrusion: Investigation of Buildings l United States Regulatory Framework l Spatial and Temporal Variability l Impact of Indoor Sources on VI Investigations Air Flow and VOC Migration Around Buildings l Controlled Investigation of Vapor Intrusion in Buildings l Conclusions and Recommendations 2

Effect of Building Pressure on VOC Transport Gas flow from subsurface into Lower building pressure Gas flow from Higher building pressure building EXAMPLES Residence in winter (chimney effect); bathroom, kitchen vents Flow in building into subsurface EXAMPLES Flow out Building HVAC designed to maintain positive pressure Bi-directional flow between building and subsurface Variable building pressure Reversible flow Low Pressure High Pressure UPWARD VOC TRANSPORT High Pressure Low Pressure EXAMPLES Barometric pumping; variable wind effects DOWNWARD VOC TRANSPORT 4

Effect of Weather on Building Pressure COLD WEATHER WIND + + + wind - soil subslab fill Stack Effect: Warm air leaks through roof creating negative building pressure KEY POINT: + soil subslab fill Wind on Building creates pressure gradient that results in air flow. Temperature and wind create pressure gradients that influence air movement in and around buildings. 5

Effect of Mechanical Ventilation Examples in Houses: - HVAC system - Exhaust fans (kitchen, bath) - Furnace - Other combustion appliances (water heater, cloths dryer, etc) MECHANICAL VENTILATION KEY POINT: Mechanical ventilation can create localized or building-wide pressure differences that drive air flow. 6

Pressure Gradient Measurements: School Building, Houston, Texas Differential Pressure (Pascals) Pos. Pressure Transducer Neg. Pressure Time (July 14 -15, 2005) KEY POINT: Pressure gradient frequently switches between positive and negative within a single day. 7

Pressure Gradient Measurements: Tropical Storm Cindy Differential Pressure (Pascasl) Positive pressure: HVAC High south wind Pressure Transducer Pos. Pressure Neg. Pressure High north wind & low atmospheric pressure Test Site Storm Track: TS Cindy Time (July 5 -6, 2005) KEY POINT: Pressure gradients potentially influenced by wide variety of factors. Measurements document nonrepresentative sampling conditions. 8

Interpretation of VOC Measurements PRESSURE CONDITION INTERPRETATION OF VOC DATA Negative Pressure “ Worst Case” VI conditions. Positive Pressure No current VOC transport from subsurface. Indoor VOCs due to background sources. Pressure Reversal Bi-directional VOC transport. Carefully consider potential sources of measured indoor and sub-slab VOCs. KEY POINT: Pressure gradients drive VOC transport. Multiple indoor VOC sampling events may be needed to measure VI. 9

Typical Building VI Investigation: Outdoor, Indoor, and Sub-Slab Sampling Data at Apartment Complex Concurrent sampling of sub-slab, indoor air, KEY POINT: and outdoor air. 10

Vapor Sampling: No Vapor Intrusion VOC Concentration (ug/m 3) at Residence in Illinois INDOOR AIR AMBIENT AIR BELOW SLAB S 11

Common indoor sources of VOCs Used as air freshener and indoor pesticide for moths and carpet beetles. p-Dichlorobenzene BTEX Petroleum-based solvents, paints, glues, gasoline from attached garages. 1, 2 -DCA Emitted from molded plastic objects (e. g. , toys, Christmas decorations). KEY POINT: Even at sites with no subsurface source, these chemicals will commonly be detected in indoor air and sub-slab samples. 1, 2 -DCA = 1, 2 -dichloroethane 12

VOC Transport Model: Bidirectional Flow n Model simulates advective transport of chemicals between building air and subsurface soil through building slab. Positive Pressure Negative Pressure 13

Model Results: Transient Indoor VOC Source VOC Conc. vs. Time: Transient Source Indoor PRESSURE Sub-Slab BIDIRECTIONAL VOC TRANSPORT KEY POINT: VOCs from building can be trapped below slab. Vapors trapped below slab 14

Vapor Intrusion: Investigation of Buildings l United States Regulatory Framework l Spatial and Temporal Variability l Impact of Indoor Sources on VI Investigations l Air Flow and VOC Migration Around Buildings Controlled Investigation of Vapor Intrusion in Buildings l Conclusions and Recommendations 15

Study Design: Sampling Program MEASUREMENT Measure VOC concentrations in and around building under baseline and induced negative PROGRAM: pressure conditions. MEDIUM SF 6 s s s 1. 5 Radon Analyses Samples per Building Ambient Air VOCs, Radon 1 -3 Indoor Air VOCs, Radon, SF 6 3 -5 Subslab VOCs, Radon, SF 6 3 -5 16

Study Design: Building Pressure Sample Event 2: Induced Negative Pressure Building Pressure Sample Event 1: Baseline Conditions TIME 0. 5 soil -2. 5 subslab fill soil 17

Study Design: Test Site TEST SITE: Three single-family residences over a TCE plume near Hill AFB in Utah 18

Study Results: Impact of Depressurization on Air Flow Gradient (Pa) Baseline Depressure Change in Air Exchange Rate (AER) AER Ratio (Depressure/ Baseline) Cross-Foundation Pressure Gradient soil 7. 00 6. 00 5. 00 4. 00 3. 00 2. 00 1. 00 0. 00 Res. #1 Res. #2 Res. #3 subslab fill KEY Induction of negative building pressure resulted POINT: in 3 to 6 -fold increase in air exchange rate. 19

Study Results: Chemical Concentration Ratios SS Source Indoor Source Residence #1 Depressurization Samples Concentration Ratio (Sub-slab/Indoor air) Baseline Samples Residence #2 SS Source Indoor Source Residence #3 Sub-slab to indoor air concentration ratio provides KEY POINT: an indication of the likely source of the chemical. However, multiple sources may contribute to indoor air impact. 20

Study Results: Volatile Chemical Detection Frequency Sub-slab Gas Samples Detection Frequency Indoor Air Samples Baseline Samples Depressurization Samples All chemicals commonly detected in indoor air samples. KEY POINT: Chemicals w/ subsurface sources (Radon and TCE) more commonly detected in sub-slab samples. 21 Note: Detection frequency is for combined sample set from all three residences.

Study Results: Impact of Depressurization on VOC Concentration Indoor Source 10 10 Radon TCE 1 0. 1 Res. #2 Concentration Ratio (Depressurization/ Baseline) VOC Conc. in indoor air Concentration Ratio (Depressurization/ Baseline) Subsurface Source Res. #3 1, 2 -DCA PCE 1 0. 1 Res. #1 Baseline) 1 Res. #2 Location Res. #3 Concentration Ratio (Depressurization/ Baseline) 10 Radon TCE 0. 1 Res. #3 Location 10 (Depressurization/ VOC Conc. in subslab gas Concentration Ratio Location Res. #2 SF 6 Benzene 1 0. 1 Res. #2 Location Res. #3 22

Study Results: Impact on VOC Conc. BUILDING Air Exchange VOCs from subsurface source VOCs from indoor source (TCE, Radon) Benzene) (DCA, PCE, SF 6, VOC conc. in indoor air VOC conc. in sub-slab gas 23

Building Depressurization: Project Findings “Worst Case” Vapor Intrusion Impact of Building Pressure on Evaluation of Vapor Intrusion KEY POINT: n n Building depressurization does NOT appear to increase the magnitude of vapor intrusion. Building depressurization improves ability to detect vapor intrusion by increasing the contrast between VOCs from indoor vs. subsurface sources. Cia Low Pressure High Pressure Use building depressurization to increase contrast between indoor and subsurface sources of VOCs. 24

Vapor Intrusion: Investigation of Buildings l United States Regulatory Framework l Spatial and Temporal Variability l Impact of Indoor Sources on VI Investigations l Air Flow and VOC Migration Around Buildings l Controlled Investigation of Vapor Intrusion in Buildings Recommendations 25

Vapor Intrusion: Recommendations l General Strategy l Groundwater Sampling l Soil Gas Sampling l Indoor Air Sampling l Non-VOC Measurements l Typical Building Sampling Program 26

VOCs: Practical Tips from the Field It’s Background, Stupid For Petroleum, Run Full VOC Scan Cartridges are Funky, Summas are Re-Used n VOCs are pervasive. You will always find hits in indoor air. n Use radon as a tracer to control for background. n Run full Method T 0 -15 scan to be able to distinguish petroleum hydrocarbon composition of soil vapor vs. indoor air. n Sorbent cartridges affected by moisture, less repeatable. n Summa canister preferable, but have individually-certified clean. Summa Canister 27

Accounting for Variability Understand variability in VOC concentration: 1) Indoor Air: 2) Subsurface: Single sample can accurately characterize well-mixed space. Consider multiple measurement locations and sample events: - Separate sample events by months - Evaluate uncertainly based on observed variability KEY POINT: Skip samples to don’t increase knowledge: (e. g. , multiple indoor samples; daily resamples. )

Vapor Intrusion: Recommendations l General Strategy l Groundwater Sampling l Soil Gas Sampling l Indoor Air Sampling l Non-VOC Measurements l Typical Building Sampling Program 29

Groundwater Interface Key Physical Processes at GW Interface Evapotranspiration 30

Distribution of TCE in Shallow Groundwater Based on >150 water table samples KEY POINT: VOC distribution at water table is difficult to predict and may be very different from deeper GW plume. Graphic from presentation by Bill Wertz (NYSDEC) made at ESTCP-SERDP Conference, December 2008. 31

Groundwater Sampling: Key Considerations KEY POINT: - Understand physical processes at water table. - For vapor intrusion, collect water samples from top of water table. 32

Vapor Intrusion: Recommendations l General Strategy l Groundwater Sampling l Soil Gas Sampling l Indoor Air Sampling l Non-VOC Measurements l Typical Building Sampling Program 33

Soil Gas Sampling: Considerations Where Does Your Sample Come From? Goal: Minimize the flow of gas in subsurface due to sample collection Sample Volume: Lab often needs only 50 m. L of sample. Use ≤ 1 L sample vessel (not 6 L Summa), if available. Purge Volume: Use small diameter sample lines to minimize purge volume. Sample Rate: Use lower flow rate in fine grain soils to minimize induced vacuum. Flexibility required to allow use of KEY POINT: newly validated sample collection and analysis methods. 34

Soil Gas Sample Collection: Scheme for Summa Canister 35

Soil Gas Sampling: Sample Collection Pressure gauge Flow controller Shallower Sample Point Deeper Sample Point 36

Soil Gas Sampling: Leak Tracers Apply to towel and place in enclosure or wrap around fittings. Liquid Tracer Gas Tracer • Examples: DFA, isopropyl alcohol, pentane • High concentrations in samples may cause elevated detection limits for target analytes (Check w/ lab before using) Photo from Blayne Hartman Inject periodically or continuously into enclosure around fittings and sample point: • Examples: Helium, SF 6 • On-site analysis (helium) • Potentially more quantitative DFA = 1, 1 -difluoroethane, SF 6 = sulfur hexafluoride Photo from Todd Mc. Alary 37

Soil Gas Sampling: Gas Phase Leak Tracer Gas Sample Point Shroud Field Meter for Leak Tracer 38

Soil Gas Sampling: Summas vs. Sorbent Tubes Summa Canisters Sorbent Tubes n n Most accepted in U. S. Simple to use n n Less available outside U. S. Canisters are re-used, subject to carry-over contamination n n More available world wide Better for SVOCs* n Use is more complex - pump calibration - backpressure - breakthrough of COC - selection of sorbent * = Analysis for SVOCs not typically required, but sometimes requested by regulators. 39

Summa vs Sorbent: Side-by-Side Results Comparison: Summa / Sorbent (ug/m 3) SG-03 SG-02 SG-04 TCE PCE 20. 5 / 10. 5 292 / 149 3070 / 1357 22, 200 / 5917 KEY POINT: Even skilled practitioners see up to 4 x difference between Summa and sorbet tube results. <2. 7 / <1. 7 187 / 225 Reference: Odencrantz et al. , 2008, Canister v. Sorbent Tubes: Vapor Intrusion Test Method Comparison, Proceedings of the Sixth International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, California, May 2008. PHOTO PROVIDED BY: beacon-usa. com 1 -800 -878 -5510 40

Vapor Intrusion: Recommendations l General Strategy l Groundwater Sampling l Soil Gas Sampling l Indoor Air Sampling l Non-VOC Measurements l Typical Building Sampling Program 41

Indoor Sampling: Overview Sample Location Considerations n ■ Recommend sampling in lowest level and consider sampling next highest level ► Investigate COC patterns ■ Consider sampling near potential indoor sources or preferential pathways ► Attached garage, industrial source ► Basement sump, bathroom pipes ■ Collect at least one outdoor sample ► Compare indoor and outdoor ■ Consider collection subslab samples (concurrent with indoor air samples) ► Compare indoor and subslab or near-slab 42

Indoor Sampling: Sample Locations ■ ■ Placement of samplers Place at breathing-level height Avoid registers, drafts Remember to sample for appropriate length of time ► § § ► Typically 24 hours for residential Typically 8 -24 hours for occupational Collect indoor and subslab samples concurrently QA Samples: Collect greater of one duplicate per day or one per 20 samples. (Collect additional QA samples if required by regs. ) NOTE: Little value to collect multiple samples in a single building zone (e. g. same room), unless collecting QA duplicates. 43

Sample Collection Sub-Slab Sampling Measure VOC concentration below building foundation Outdoor Air Sampling Document ambient conditions 44

Vapor Intrusion: Recommendations l General Strategy l Groundwater Sampling l Soil Gas Sampling l Indoor Air Sampling l Non-VOC Measurements l Typical Building Sampling Program 45

VI Investigation Methods: Non-VOC Measurements Radon Naturally occurring tracer gas measures attenuation through building foundation. Building Pressure Magnitude and duration of building pressure fluctuations: negative vs. positive building pressure. Air Exchange Rate of ambient air entry into building. Supports mass flux evaluations. KEY POINT: Non-VOC measurements can be used to evaluate vapor intrusion while avoiding background VOC issues. 46

Radon: Measurement Options Cost/ Sample $10 -50 Indoor Air n Home Test Methods: Charcoal Canister, electret, alpha detector n Air Samples: $100 Radon concentration measured at off-site lab * Sub. Foundation n Air Sample: $100 Radon concentration measured at off-site lab * n Electret: Placed over hole $25 -50 in foundation (questionable accuracy) Key Point: n Radon analysis less expensive than VOC analysis ($200 -250/sample for VOCs by TO-15). * Off-site analysis provided by Dr. Doug Hammond, University of Southern California 47

Radon (Ra) as Tracer for Foundation Attenuation Test Results Indoor Ra = 0. 9 p. Ci/L Sub-slab Ra = 833 p. Ci/L Ambient Ra = 0. 3 p. Ci/L AF Calculation 0. 9 - 0. 3 AFss-ia = 833 = 0. 00048 n No common indoor sources of radon. BENEFITS: n Lower analytical costs compared to VOCs. n Less bias caused by non-detect results indoors. n Can be used for long-term testing (up to 6 months). 48

Air Exchange: What ‘n How BUILDING What Rate at which indoor air is replaced by ambient (fresh) air. Air Exchange ESTIMATION METHODS Ventilation Standards Tracer Gas Recommended ventilation rates for commercial building. Measure dilution of tracer gas to determine air exchange rate ASHRAE Std. 62. 1 -2004 SF 6 WHY: n Better understand observed VOC attenuation. n Use value model or mass flux calculation. J&E = Johnson and Ettinger model. 49

Recommended Building Ventilation Rates ANSI / ASHRAE Standard 62. 1 – 2004 Ventilation for Acceptable Indoor Air Quality Building Type USEPA Default (Residential) Air Exchanges (per day) 6 Office Space 12 Supermarket 17 Classroom 68 Restaurant 102 KEY POINT: High Building Ventilation Buildings designed for high density use will have high air exchange rates. 50

Air Exchange: Measured Values How: n Release tracer gas (SF 6 or helium) into building at constant rate. Test Building n Measure steady-state concentration of gas in building. n Calculate air exchange based on release rate, concentration, and building volume. KEY POINT: Site-specific measurement provides most accurate measure of air exchange under current operating conditions. 51

Vapor Intrusion: Recommendations l General Strategy l Groundwater Sampling l Soil Gas Sampling l Indoor Air Sampling l Non-VOC Measurements l Typical Building Sampling Program 52

Residential Building Investigation: Recommended Sampling Program GAS MEASUREMENTS: MEDIUM s 1. 5 Radon BUILDING PRESSURE: Ambient Air VOCs, Radon 1 Indoor Air VOCs, Radon 1 -2 (lowest level) Subslab Gas s s Analyses Samples per Building VOCs, Radon 3 -5 For more definitive results, conduct sampling program under induced negative pressure and positive pressure building conditions. 53

Guidelines for Vapor Intrusion Evaluation Identifying Sites Needing VI Mitigation 1 Indoor Air > Risk Limit? Indoor air conc’s. > applicable limits. 2 Subslab Vapors > Risk Limit Subslab vapors > applicable limits. 3 Building Pressure Supports VI Pressure gradient supports soil gas flow into building KEY POINT: > Std? S >Std? air SG Step-wise approach can help distinguish Swell ! VI sources from indoor sources. 54

Guidelines for Vapor Intrusion Evaluation Identifying Sites Needing VI Mitigation 1 2 3 Indoor Air > Risk Limit? Indoor air conc’s. > applicable limits. Subslab Vapors > Risk Limit Subslab vapors > applicable limits. Building Pressure Supports VI Pressure gradient supports soil gas flow into building KEY POINT: Cause = 4 Indoor/Ambient Source? Data set shows clear > Std? indoor/ambient source. S >Std? air SG Radon Data Suggest Actual VI? 5 Rn attenuation factor suggests VOCs may enter house, too. Rn S Rn Rn Pressurization shows Actual VI ? 6 Pressurization and P depressurization of bldg. show VI through slab. air Step-wise approach can help distinguish Swell ! VI sources from indoor sources. 55

Acknowledgements Support provided by by the Environmental Security Technology Certification Program (ESTCP) Projects ER-0423 and ER-0707 Project Reports: www. estcp. org (Search “ 0423” & “ 0707”) Special Thanks to: Tim Nickels and Danny Bailey (GSI) Sam Brock (AFCEE) Kyle Gorder (Hill AFB) Blayne Hartman David Folks (Envirogroup), Todd Mc. Alary (Geosyntec)