Soil Vapor Intrusion Training In The New Economy*

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1 Soil Vapor Intrusion Training In The New Economy* Bill Wertz NYSDEC Robert Ettinger Geosyntec Consultants *John Fitzgerald was supposed to do this, but his plans were impacted by the New Economy NYSDEC

2 What is Soil Vapor Intrusion?

3 Components of Soil Vapor Intrusion : 4 P s People Pathway Pressure Pollutant

4 Pollutant Paradigm Shift What is a Source Area At some sites, 5-10 ppb VOCs could be a problem.

6 Pathway Soil Vapor Migration Pathway May Be Complex

7 Perched water table Regional water table graphic provided by Dominic DiGiulio, Ph.D. Office of Research and Development National Risk Management Research Laboratory, Ada, Oklahoma

12 Pressure Pressure Gradients Change Through Time

13 p Pressure Gradients are the dii driving force Induced by: convection (temp difference in winter) mechanical equipment (clothes dryers, exhaust) heating appliances a (combustion o air) air handlers and return air ductwork (furnaces) fireplace (combustion air) weather - barometric pressure changes, wind, rain

14 14

15 H-005 Building Pressure Differential vs Temperature l In H2O Pressure Differential P F Temperature Avg Pressure Differential

16 People

17 From Schuver USEPA

18 Vapor Intrusion Modeling Models are used for vapor intrusion evaluation, but there are a range of opinions about their use Models underestimate risk Models overestimate risk Models have limited it applicability - Can they evaluate range of conditions? Sub-slab samples Crawl space construction NAPL sources Biodegradation Models are only as good as the inputs used (GIGO) These uncertainties ti have led to frequent suggestions to simply monitor indoor air 18

19 Modeling vs Monitoring Indoor air sampling may be impractical due to background effects Models can aid in the determination of corrective action strategies and/or remediation objectives Risk evaluation for potential exposure scenarios can be addressed with modeling (key consideration for brownfields sites) Some combination of data collection and modeling is usually appropriate Need to confirm quality of model inputs and measured results before assessing whether the model is providing representative results 19

20 Vapor Intrusion Models There are more options than the Johnson and Ettinger Model Empirical Analytical Numerical USEPA Database Johnson and Ettinger (1991) VAPOURT (1989) Little et al. (1991) Sleep & Sykes (1989) San Diego SAM RUNSAT (1997) VOLASOIL (1996) Abreu beu&jo Johnson (2005) (005) Krylov and Ferguson (1998) VIM (2007) DLM - Johnson et al. (1999) Brown University (2007) BioVapor (2010) Model selection is dependent on what you know about the site and the level of desired assessment 20

21 USEPA Empirical Attenuation Factors 21

22 USEPA Empirical Attenuation Factors Empirical Attenuation Factors Source Median 95%ile Crawl Space NR Sub-Slab Soil Gas Soil ilgas Groundwater Many regulators are focusing on 95%ile values Be careful if simply using empirical factors 22

23 Baseline Vapor Intrusion Model (Johnson and Ettinger, 1991) Mixing in Breathing Zone Convective Transport into Building VOCs Diffusive Transport Source Partitioning Simplified screening model Assumes 1-D, steady-state state transport (i.e., source beneath building) Background and biodegradation effects neglected User inputs soil and building properties 23

24 Baseline Vapor Intrusion Model US EPA VAPOR INTRUSION ASSESSMENT MODEL (VIA_MODEL.xls) USEPA spreadsheets available for typical model application Input: generic soil and building properties Output: alpha and risk Frequently used as black box USEPA spreadsheets to be updated soon Stratum Site Name: Note: Cells with borders indicate parameters that may be changed by the user. Parameter Units Symbol Value Default Flag Comment Source Characteristics: Source medium Source Groundwater Groundwater concentration (ug/l) Cmedium 100 Depth below grade to water table (m) Ls 3.00 Average groundwater temperature ( o C) Ts Calc: Source vapor concentration (ug/m3) Cs Chemical: Chemical Name Chem Tetrachloroethylene CAS No. CAS Toxicity Factors Unit risk factor (ug/m 3 ) -1 URF 5.90E E-06 Reference concentration (ug/m 3 ) RfC 6.00E E+02 Building Characteristics: Building setting Bldg_Setting Residential Residential Foundation type Found_Type Basement w/ slab Basement w/ slab Depth below grade to base of foundation (m) Lb Foundation thickness (m) Lf Fraction of foundation area with cracks (-) eta 1.00E E-03 Enclosed space floor area (m2) Ab Enclosed space mixing height (m) Hb Indoor air exchange rate (1/hr) ach Qsoil/Qbuilding (-) Qsoil_Qb Calc: Building ventilation rate (m3/hr) Qb Calc: Average vapor flow rate into building (m3/hr) Qsoil Vadose zone characteristics: Stratum A (Top of soil profile): Stratum A SCS soil type SCS_A Sand Stratum A thickness (from surface) (m) hsa 3.00 Stratum A total porosity (-) nsa Stratum A water-filled porosity (-) nwsa Stratum A bulk density (g/cm 3 ) rhosa Stratum B (Soil layer below Stratum A): Stratum B SCS soil type SCS_B Not Present Stratum B thickness (m) hsb Stratum B total porosity (-) nsb Stratum B water-filled porosity (-) nwsb Stratum B bulk density (g/cm 3 ) rhosb Statum C (Soil layer below Stratum B): Stratum C SCS soil type SCS_C Not Present Stratum C thickness (m) hsc Stratum C total porosity (-) nsc Stratum C water-filled porosity (-) nwsc C bulk density (g/cm 3 ) rhosc Stratum directly above the water table Stratum A, B, or C src_soil Stratum A Height of capillary fringe (m) hcz Capillary zone total porosity (-) ncz Capillary zone water filled porosity (-) nwcz Exposure Parameters: Target risk for carcinogens (-) Target_CR 1.00E E-06 Target hazard quotient for non-carcinog (-) Target_HQ 1 1 Exposure Scenario Scenario Residential Residential Averaging time for carcinogens (yrs) ATc Averaging time for non-carcinogens (yrs) ATnc Exposure duration (yrs) ED Exposure frequency (days/yr) EF Exposure time (hrs/24 hrs) ET

25 Baseline Vapor Intrusion Model Typical site-specific specific considerations: Source concentration Soil porosity Soil moisture content Capillary fringe parameters Building ventilation rate Height abo ove water table (c cm) Calculated Water Distribution in Soils Default water content (cm 3 /cm 3 ) Sand Sandy Loam Loamy Sand Loam Silty Clay Water content (cm 3 /cm 3 ) Site-specific inputs may be different from defaults, but proper justification is needed 25

26 Baseline Vapor Intrusion Model Soil Gas Profile Modeling Utilize Soil lithology, Concentration measurements, and Modeling Demonstrate understanding of sub-surface surface transport Dept th (ft bgs) Vapor Migration Modeling Soil Profile 80 1.E-03 1.E-02 1.E-01 1.E+00 Scaled Concentration 26

27 Biodegradation Model (Johnson, et al., 1999) Mixing i in Breathing Zone Convective Transport into Building Biodegradation Zone (Dominant Layer) Source VOCs Diffusive i Transport Partitioning Similar to baseline model Applicable for petroleum hydrocarbon sites Limited availability 27

25 day-1 DLM = 1-10 ft bgs PCE Cgw = 0.79 ppb Benzene Cgw = 52500 ppb 60 1.E-08 1.

28 Biodegradation Model Example Application Cluster 2 0 Benzene Detects Benzene ND DLM PCE Detects PCE NDs JEM Lithology Depth (ft) t1/2 = 2.8 d lambda = 0.25 day-1 DLM = 1-10 ft bgs PCE Cgw = 0.79 ppb Benzene Cgw = ppb 60 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 Dimensionless Concentration (C/Csource) 28

29 BioVapor Model (API, 2010) API Disclaimer: The model is not expected to provide highly accurate predictions when a single set of input parameter values is used to represent a single site. Rather, the model is expected to help the user identify a reasonable range of potential outcomes that result from varying key input parameter values to account for the uncertainty and variability associated with site conditions. 29

30 Three-Dimensional Numerical Model (Abreu and Johnson, 2005) 0 th bgs (m) Dept x(m) The next generation for simulations Provides many additional capabilities 30

31 Effect of Biodegradation on Attenuation Factors Attenuation n Factor 1.E-02 1E-03 1.E03 1.E-04 1.E-05 1.E-06 1.E-07 1.E-08 1.E-09 Dissolved phase NAPL Biodegradation is likely to have a significant effect on a for non-napl sources This effect is more pronounced for deeper sources For NAPL sources, effect of biodegradation on a may be minimal due to oxygen depletion 1E10 1.E 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 L = 2 m bgs, λ = 0.79 (1/h) L = 5 m, λ = 0.79 (1/h) L = 1 m, No Biodegradation L: source-foundation distance Modeling Assumptions: Benzene source Sand soil Basement scenario = 0.79 h -1 31

32 Summary Modeling provides an additional line of evidence for evaluation of the vapor intrusion i pathway Exercise care in application of models Confirm model is appropriate for site conditions Verify model inputs Vapor intrusion modeling can assist in: Understanding the vapor intrusion pathway Planning investigation and corrective action strategies Simulate future conditions (i.e., redevelopment scenarios) 32

33 VI Assessment Strategies Action Risk Resources Conceptual Site Model Knowledge

34 VI Evaluation Is An Iterative Process Uncertainty Uncertainty Uncertainty Site Conceptual Model Site Conceptual Model Site Conceptual Model Data Collection Data Collection VI Decision VI Decision VI Decision Sampling Round 1 Sampling Round 2 Sampling Round 3 There Will Always Be Uncertainty As Perceived Risk Allowable Uncertainty

35 VI Evaluation GOAL Efficiently & Effectively Identify & Address Impacted Structures Determine the Nature and Extent of Contaminant Source Determine The Extent of Potentially Impacted Structures Take Necessary Actions to Address Exposures (Short-Term) Take Necessary Actions to Reduce Source of Contamination (Long-Term) Reduce e Unce ertaint ty

36 Typical VI Evaluation Process Safety / Acute Risk Screening Immediate Action? Yes Confirmation Sampling No Initial Screening? No Exceed RBSLs? Site-Specific Assessment No Sufficient Data? Yes Monitor? No Risk Exceedance? STOP Mitigation Yes

37 Typical VI Investigation Sites typically fall into 4 categories: No Brainer Not Sure No problem Mitigate Collect data Mitigate or Monitor An improved evaluation process should decrease the uncertainty in the selected corrective action 37

Stack Effect (IA/SS Pressure Differential) Influenced by Temperature Differences Furnace

Influenced by Pressure Differential Subslab Source Strength Nature & Distribution of Flow

Source Strength Grain Size and Effective Porosity (Height of Capillary Fringe) Adsorbtion

1, 2007) Attenua ation Biodegradation Non Chlorinated VOCs Diffusive Mass Flux Influenced

38 Stack Effect (IA/SS Pressure Differential) Influenced by Temperature Differences Furnace & Other Combustion Devices Air Leakage Wind Load Background Sources Advective Mass Flux Influenced by Pressure Differential Subslab Source Strength Nature & Distribution of Flow Pathways Source Concentration at Top of Capillary Fringe Influenced by Groundwater VOC Source Strength Grain Size and Effective Porosity (Height of Capillary Fringe) Adsorbtion Desorbtion Infiltration IA/SS Mixing IA/SS Mixing Capillary Zone From ITRC (Figure 2.1, 2007) Attenua ation Biodegradation Non Chlorinated VOCs Diffusive Mass Flux Influenced by VOC Source Strength Grain Size and Effective Porosity Moisture Content Adsorbtion Desorbtion

39 Identify the Nature and Extent of Contaminant Source Look at Historical Data Collect Groundwater Grab Samples and Install Groundwater Wells What Is The Necessary Data Density? Identify Structures With Potential VI Impacts Model - Sample Soil Gas? - Sample Structures [Less Certain More oeceta Certain]

40 Look at Historical Data Soil Source vs Groundwater Source (Both?) Chlorinated vs Non-chlorinated Compounds DNAPL or LNAPL Present Geologic Setting Population Setting Quality of The Information?

41 Some Broad Generalizations Soil Source Site (No Groundwater Impacts) Focus on Vadose Zone Transport: Diffusion i Advective Flow (Near Buildings) Preferential Pathways Modeling - Soil Gas - Structure Samples

42 Some Broad Generalizations Non-Chlorinated Groundwater Source (Including LNAPL & Smear Zone) EtblihNt Establish Nature and det Extent tof fgroundwater Contamination (at the Water Table) Is it necessary to Find the edge of the plume? Focus on Vadose Zone Transport: Biodegradation Vadose Zone Stratigraphic Profiling

44 Methane ppmv Benzene Benzene ug/m3 CO2 % O2 % Depth BGS Concentration No Substantial Biodegradation Monitoring MP 1 (2008) Points 1S - 1D BGS Methane Benzene Co2 O

45 Methane ppmv Benzene ug/m3 CO2 % O2 % Substantial Biodegradation Monitoring Points 10S - 10D MP-10 (2008) BGS Methane Benzene Co2 O

46 Methane ppmv Benzene ug/m3 CO2 % O2 % MP 2 BGS Methane Monitoring Benzene Points Co2 2S - 2DO2?

48 Structure Sampling O 2 Fosters Biodegradation

49 Results of Greenpoint Structure Sampling for Benzene Benzene Ambient First Floor Basement Subslab ug/m Sample ID

50 Results of Structure Sampling for m,p -Xylene Xl m,p-xylene Ambient First Floor Basement Subslab g/m3 u Sample ID

51 At Petroleum Sites Environmental Data (Groundwater and Soil Gas Profiles) May Often Be Sufficient For Making Good VI Decisions

52 Some Broad Generalizations e at Chlorinated Groundwater Source Establish Nature and Extent of Groundwater Contamination (at the Water Table) Is it necessary to Find the edge of the plume? Soil Gas vs. Subslab Data

53 Identify the Nature and Extent of Contaminant Source Groundwater Data Collected September 2007-December 2007 From 125 Water Table Grabs & 43 Wells Natural Neighbor Interpolation

54 Identify Structures With Potential VI Impacts Previously Sampled 113

55 Natural Neighbor Interpolation Identify Structures With Potential VI Impacts

56 Test Conceptual Model

58 Area of Subslab Impacts Mirrors Area of Groundwater Impacts But Not All Structures Above The Plume Are Impacted One Possible Approach Blanket Mitigate Structures Above Hot Spots Increase Sampling Density in Uncertain Areas

59 The Patchy Fog Conceptual Model When Designing A Structure Sampling Plan You Need To Recognize That There May Be A Considerable Range in Subslab Concentrations Between and Beneath Structures In A Given Area!

60 Legend OA = Outdoor Air BA= Basement SSA = Subslab A SSB = Subslab B SSC = Subslab C TCE Structure Sampling Results November April 2007 Structure Sampling Results

Indoor Air Sampling and Addressing Background Sources Indoor air sampling may seem to be a direct assessment approach, but is typically conducted during higher tier of investigation Several

61 Indoor Air Sampling and Addressing Background Sources Indoor air sampling may seem to be a direct assessment approach, but is typically conducted during higher tier of investigation Several challenges to indoor air sampling Occupant disruption Temporal and spatial variability Background effects Discovery of data May be more practical to collect indoor air samples in occupational setting 61

62 Definition Indoor Air Background Concentrations of chemicals found in indoor air that are not due to subsurface impacts from a release. Background Sources Ambient Air Building Materials Household Activities Consumer Products 62

63 Indoor Air Sources Paints Gasoline Powered Equipment Tobacco Smoke Glues/Adhesives Dry Cleaning Expect detections of VOCs in any indoor air sample Cleaners/ Solvents 63

64 Chemicals in Household Products NIH Household Products Database 64

65 Ratio of Indoor to Outdoor Concentrations From USEPA BASE study Minimum, maximum, 5, 25, 50, 75, 95th percentiles From: Girman, J. Air Toxics Exposure in Indoor Environments, EPA Workshop on Air Toxics Exposure Assessment,

66 Background and Target Indoor Air Concentrations USEPA,

67 Resolving Background Contributions Comparison to Literature Values Tracer compounds Mitigation System Evaluation 67

68 Example Background Indoor Air Concentrations Consider background range as well 68as typical values

69 Background Concentration of 1,2-DCA DETECTION FREQUENCY CONCENTRATION on ) CA Detecti quency (%) 1,2-DC Freq 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 1,2-DCA Concentrati ion (u g/m 3 ) Median 1,2-DCA Conc. 90%ile 1,2-DCA Conc. USEPA INDOOR AIR LIMIT 0% <0.08 <0.08 < ,2 DCA Background Source: Detailed study identified molded plastic ornaments manufactured in China as source for 1,2 DCA. Note: 1) 1,2-DCA = 1,2-dichloroethane From McHugh et al., Also see Doucette et al., GWMR, 2010

70 Attenuation Factors for Single Building Biased by Background Sources Note number of compounds with attenuation factor > 1 Variability in attenuation factors due to background effects or analytical limitations From USEPA, Assessment of Vapor Intrusion in Homes Near the Raymark Superfund Site Using Basement and Sub-Slab Slab Air Samples. 70

71 Attenuation Factors for Single Building Potentially biased by background sources Biased by Background Sources From USEPA, Assessment of Vapor Intrusion in Homes Near the Raymark Superfund Site Using Basement and Sub-Slab Slab Air Samples. 71

72 Evaluation of Engineering Controls: Colorado Redfield Study From: Folkes, D.: Vapor Intrusion Assessment and Mitigation - Practical Issues and Lessons Learned, EPA Office of Solid Waste RCRA Corrective Action EI Forum, August 15-17,

73 Summary Chemicals from occupant activities and/or building construction ti will result in detection ti during indoor air sampling Background sources make evaluation of vapor intrusion pathway more difficult Source determination Risk management Pathway modeling Assessment of engineering controls Background sources must be considered when collecting indoor air samples Communication of background issues with building occupants is key 73

74 Data Interpretation More to Come Tomorrow NYSDEC

75 Vapor Intrusion Mitigation Active Remediation Institutional Controls Engineering gco Controls o o Radon System (Sub-slab Depressurization) o Passive Vapor Barrier o HVAC System Modifications o Indoor Air Filtration i o Intrinsically Safe Building Design 75

76 Mitigation System Considerations Effectiveness Mitigation i i systems are not typically 100% effective O&M Requirements System O&M Performance monitoring Cost Installation costs may be much less than monitoring costs Impact on Occupants Aesthetics ti Costs 76

77 Sub-Slab Slab Depressurization 77

78 Sub-Slab Slab Depressurization Can be designed for large buildings 78

79 Active Systems for New Buildings 79

80 Sub-Slab Slab Depressurization Initial Performance Verification Sub-slab vacuum confirmation Confirm vacuum on vent pipe and/or cross-slab slab vacuum Indoor air sampling Long-Term Performance Monitoring Monitor vacuum on vent pipe and/or cross-slab slab vacuum 80

81 Sub-Slab Slab Depressurization n (ug/m3 ) DCE Conc centratio Action Level Days After System Installation Redfields Site - Source: Folkes, 2002 Common to achieve % reduction 81

82 Sub-Slab Slab Depressurization Advantages Effective for most building types >90% concentration reductions possible Performance monitoring can be non-chemical (vacuum measurements, electrical consumption records) Disadvantages Long-term O&M May not work in wet soil conditions (shallow water table) Suction pit and riser pipe need to be located inside building Aesthetics / Noise May require e sealing floors & walls May require air permit 82

83 Passive Vapor Barrier 83

84 Passive Vapor Barrier Concrete Floor Slab Sand Geomembrane Gravel PVC Pipe w. holes Sub-slab base 84

85 Roof Top Turbines

86 This system sucks, and that s exactly ywhat we wanted it to do 86

87 Passive Vapor Barrier Advantages Applicable to new or existing buildings Minimal O&M due to no moving parts Convertible to active if required to meet objectives Disadvantages Possible diffusion through barrier Stakeholder confidence 87

88 HVAC System Modification Increased fresh air intake & positive pressurization Confirmed P of 0.01 to 0.08 in-h 2 O 88

89 Evaluation of Engineering Controls: Building Pressurization Trichloroethene 1000 Calculated from Soil Gas Pre-Mitigation Indoor Air Outdoor Air Post-Mitigation Indoor Air maximum 75th median th minimum TCE Conc centration ( g/m 3 ) TCE 89

90 Evaluation of Engineering Controls: Building Pressurization Benzene 3 ) Benzen ne Concentra ation ( g/m Calculated from Soil Gas Pre-Mitigation Indoor Air Outdoor Air Post-Mitigation Indoor Air maximum 75th median 25th minimum Benzene 90

91 HVAC Modification Advantages Effective, especially for large commercial or industrial buildings Applies to new or existing buildings Rapid to implement Disadvantages Generally more costly than other approaches in hot or cold climates Control - Settings may be modified by occupant Not commonly an option for single family residences May already be happening 91

92 Indoor Air Filtration Typical Residential Unit Size of a shop vac 22 lbs. carbon Effective up to 1500 sq. ft. 3-speed 400 cfm fan, runs whisper quiet Electricity = 60 watt light bulb 92

93 Indoor Air Filtration Advantages Applicable to new or existing buildings Quick &easyto install in residences Improves air quality in general (including background) Disadvantages Not effective in high VOC background scenarios (e.g., smoker) Spent carbon waste stream Rely on building occupant to operate Aesthetics Costly O&M 93

94 Intrinsically Safe Building Design 94

95 Intrinsically Safe Building Design 95

96 Mitigation Technologies Technology Pros Cons Applications Passive Barrier Often simple addition Limitedit dt data on long-term New Construction ti to construction effectiveness activities Passive Venting Low O&M cost Limited effectiveness Lower Upgradeable to SSD concentration areas Sub-Slab Depressurization Proven technology Wide acceptance Higher capital cost Air permitting needs variable Similar to Rn systems. Proven effectiveness. HVAC Operation Modification Indoor Air Treatment Potentially low capital cost Quick Installation High O&M cost Occupant comfort Difficult to control Potentially higher capital cost Difficult to control Buildings with continuous HVAC operation Interim Measure 96

97 Summary Not all sites are the same Select preferred method considering geology, source location & type, & magnitude of required reduction Active and passive controls may be used to address VI concerns Cost of installation can be significantly less than O&M costs 97

98 Expect Surprises

Updated J&E Model VIAModel.xls

Updated J&E Model VIAModel.xls Helen Dawson, Ph.D. USEPA Region 8 AEHS Spring 2006 What s Different? Combines screening and advanced versions of the groundwater and soil gas spreadsheets. Provides default