Vapor Intrusion: Investigation of Buildings

Vapor Intrusion: Investigation of Buildings SITE BUILDING Air Exchange source area 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

Vapor Intrusion: Investigation of Buildings lUnited States Regulatory Framework lSpatial and Temporal Variability lImpact of Indoor Sources on VI Investigations Air Flow and VOC Migration Around Buildings lControlled Investigation of Vapor Intrusion in Buildings lConclusions and Recommendations

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

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

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

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

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

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

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

S Vapor Sampling: No Vapor Intrusion VOC Concentration (ug/m3) at Residence in Illinois INDOOR AIR AMBIENT AIR BELOW SLAB

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

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

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

Vapor Intrusion: Investigation of Buildings lUnited States Regulatory Framework lSpatial and Temporal Variability lImpact of Indoor Sources on VI Investigations lAir Flow and VOC Migration Around Buildings Controlled Investigation of Vapor Intrusion in Buildings lConclusions and Recommendations

s s Study Design: Sampling Program Measure VOC concentrations in and around building under baseline and induced negative pressure conditions. MEASUREMENT PROGRAM: Samples per Building Analyses MEDIUM SF6 VOCs, Radon Ambient Air 1 - 3 1.5 s VOCs, Radon, SF6 Indoor Air 3 - 5 Radon VOCs, Radon, SF6 Sub-slab 3 - 5

0.5 -2.5 Building Pressure Building Pressure TIME TIME Study Design: Building Pressure Sample Event 2: Induced Negative Pressure Sample Event 1: Baseline Conditions subslab fill soil soil

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

7.00 (Depressure/Baseline) 6.00 AER Ratio 5.00 4.00 3.00 2.00 1.00 0.00 Res. #1 Res. #2 Res. #3 Study Results: Impact of Depressurization on Air Flow Cross-Foundation Pressure Gradient Change in Air Exchange Rate (AER) Baseline Depressure Gradient (Pa) subslab fill soil KEYPOINT: Induction of negative building pressure resulted in 3 to 6-fold increase in air exchange rate.

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

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

Concentration Ratio Baseline) (Depressurization/ 10 Concentration Ratio 1 Baseline) (Depressurization/ 0.1 Res. #1 Res. #2 Res. #3 Location Study Results: Impact of Depressurization on VOC Concentration Indoor Source Subsurface Source 10 10 Radon TCE 1,2-DCA PCE VOCConc. in indoor air Concentration Ratio 1 1 Baseline) (Depressurization/ 0.1 0.1 Res. #1 Res. #2 Res. #3 Res. #1 Res. #2 Res. #3 Location Location 10 Radon TCE SF6 Benzene VOCConc.in sub-slab gas Concentration Ratio 1 (Depressurization/ Baseline) 0.1 Res. #1 Res. #2 Res. #3 Location

BUILDING Air Exchange Study Results: Impact on VOC Conc. VOCs from subsurface source VOCs from indoor source (DCA, PCE, SF6, Benzene) (TCE, Radon) VOCconc. in indoor air VOCconc. in sub-slab gas

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

Vapor Intrusion: Investigation of Buildings lUnited States Regulatory Framework lSpatial and Temporal Variability lImpact of Indoor Sources on VI Investigations lAir Flow and VOC Migration Around Buildings lControlled Investigation of Vapor Intrusion in Buildings Recommendations

Vapor Intrusion: Recommendations lGeneral Strategy lGroundwater Sampling lSoil Gas Sampling lIndoor Air Sampling lNon-VOC Measurements lTypical Building Sampling Program

Summa Canister VOCs: Practical Tips from the Field n VOCs are pervasive. You will always find hits in indoor air. n Use radon as a tracer to control for background. It’s Background, Stupid For Petroleum, Run Full VOC Scan n Run full Method T0-15 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. Cartridges are Funky, Summas are Re-Used

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

Groundwater Interface Key Physical Processes at GW Interface Evapotranspiration

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

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

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 mL of sample. Use ≤1L sample vessel (not 6L 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 newly validated sample collection and analysis methods. KEY POINT:

Soil Gas Sample Collection:Scheme for Summa Canister

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

Photo from Blayne Hartman Photo from Todd McAlary Soil Gas Sampling: Leak Tracers Apply to towel and place in enclosure or wrap around fittings. • Examples: DFA, isopropyl alcohol, pentane • High concentrations in samples may cause elevated detection limits for target analytes (Check w/ lab before using) Liquid Tracer Inject periodically or continuously into enclosure around fittings and sample point: Gas Tracer • • Examples: Helium, SF6 • • On-site analysis (helium) • Potentially more quantitative DFA = 1,1-difluoroethane, SF6 = sulfur hexafluoride

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

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

PHOTO PROVIDED BY: beacon-usa.com 1-800-878-5510 Summa vs Sorbent: Side-by-Side Results Comparison: Summa / Sorbent (ug/m3) SG-04 SG-03 SG-02 TCE 20.5 / 10.5 292 / 149 <2.7 / <1.7 PCE 3070 / 1357 22,200 / 5917 187 / 225 Even skilled practitioners see up to 4x difference between Summa and sorbettube results. KEYPOINT: 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.

Indoor Sampling:Overview • Sample Location Considerations • 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

Little value to collect multiple samples in a single building zone (e.g. same room), unless collecting QA duplicates. NOTE: 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.)

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

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

Radon: Measurement Options Cost/Sample $10-50 $100 $100 $25-50 nHome Test Methods:Charcoal Canister, electret, alpha detector nAir Samples:Radon concentration measured at off-site lab * Indoor Air nAir Sample:Radon concentration measured at off-site lab * nElectret:Placed over hole in foundation (questionable accuracy) Sub-Foundation 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

Test Results AF Calculation Indoor Ra =0.9 pCi/L Ambient Ra =0.3 pCi/L AFss-ia = = 0.00048 Sub-slab Ra =833 pCi/L 0.9 - 0.3 833 Radon (Ra) as Tracer for Foundation Attenuation • No common indoor sources of radon. • Lower analytical costs compared to VOCs. • Less bias caused by non-detect results indoors. • Can be used for long-term testing (up to 6 months). BENEFITS:

BUILDING Air Exchange ASHRAE Std. 62.1-2004 SF 6 Air Exchange: What ‘n How Rate at which indoor air is replaced by ambient (fresh) air. What ESTIMATION METHODS Recommended ventilation rates for commercial building. Ventilation Standards Measure dilution of tracer gas to determine air exchange rate Tracer Gas nBetter understand observed VOC attenuation. nUse value model or mass flux calculation. WHY: J&E = Johnson and Ettinger model.

Building Type Air Exchanges(per day) Recommended Building Ventilation Rates ANSI / ASHRAE Standard 62.1 – 2004 Ventilation for Acceptable Indoor Air Quality USEPA Default (Residential) 6 Office Space 12 Supermarket 17 Classroom 68 High Building Ventilation Restaurant 102 Buildings designed for high density use will have high air exchange rates. KEYPOINT:

Air Exchange: Measured Values How: Test Building nRelease tracer gas (SF6or helium) into building at constant rate. nMeasure steady-state concentration of gas in building. nCalculate air exchange based on release rate, concentration, and building volume. Site-specific measurement provides most accurate measure of air exchange under current operating conditions. KEY POINT:

Vapor Intrusion: Investigation of Buildings