Vapor Intrusion: Investigation of Buildings Overview of the US vapour intrusion framework, empirical attenuation factors, and the conceptual understanding of soil gas and building dynamics Vingsted Center Monday, March 9, 2009 GSI ENVIRONMENTAL INC. Houston, Texas (713) source area Air Exchange SITE BUILDING

2 Vapor Intrusion: Wazzat? KEY POINT: Vapor intrusion is the movement of volatile chemicals into buildings from below ground. BUILDING GW source area Soil source area Vapors in subsurface Effect on indoor air quality?

3 Indoor Sources False Positives Difficulty separating vapor intrusion from indoor sources of VOCs: - Affects indoor and sub-slab samples Low levels of VOCs often detected in soil gas and indoor air samples: - Summa carry over contamination - Lab contamination - Unexpected minor sources High Variability LIMITATION DETAILS VOC measurements alone often provide a confusing picture of vapor intrusion. KEY POINT: Limitations of VOC Measurements Gas High spatial and temporal variability: - Conservative assumptions OR - Large number of samples Summa Canister Introduction

4 Physical Barriers to Vapor Intrusion KEY POINT: Non-VOC measuremen ts can provide improved understandin g of vapor intrusion. Introduction A B A B A B

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

6 Vapor Intrusion: Regulatory Framework USEPA Framework State Regulations Petroleum vs. Chlorinated VOCs Site-Specific Screening Mass Flux Evaluations USEPA Framework State Regulations Petroleum vs. Chlorinated VOCs Site-Specific Screening Mass Flux Evaluations

7 Conceptual Model for Vapor Intrusion: KEY POINT: Regulatory guidance assumes vapor migration through soils and building foundation based on conservative assumptions. Building Attenuation Due to Exchange with Ambient Air Advection and Diffusion Through Unsaturated Soil and Building Foundation Partitioning Between Source and Soil Vapor Groundwater -Bearing Unit Air Exchange BUILDING Unsaturated Soil Affected Soil Affected GW Overview of USEPA VI Guidance

8 NFA Mitigation/ Remediation Typical Vapor Intrusion Screening Process Step-wise VI investigation process recommended by most VI regulatory guidance. KEY POINT Chemicals could cause VI impact based on volatility and toxicity CHEMICAL CRITERIA GW conc. > VI screening levels GW SCREENING Soil gas/ sub-slab conc. > VI screening levels SOIL GAS/ SUB-SLAB SCREENING indoor air concentrations other measurements indicate vapor intrusion impact INDOOR AIR TESTNG No Yes No Screening Steps Field Measurements Current or future buildings within m of edge of impact. DISTANCE CRITERIA

9 Benzene Ethylbenzene USEPA VI Screening Values : Key COCs Indoor Air (ug/m 3 ) Sub-slab (ug/m 3 ) MTBE Groundwater (mg/L) Vinyl Chloride Lindane TCE PCE 8.1 * = Value based on MCL, risk-based number would be lower * 0.70* * 0.002* * KEY POINT: Under EPA guidance, GW impacts above MCLs usually require VI investigation (i.e., ALL corrective action sites).

10 Vapor Intrusion: Regulatory Framework USEPA Framework State Regulations Petroleum vs. Chlorinated VOCs Site-Specific Screening Mass Flux Evaluations USEPA Framework State Regulations Petroleum vs. Chlorinated VOCs Site-Specific Screening Mass Flux Evaluations

11 KEY POINT: Draft or final guidance from NY, NJ, WI, CA, PA, MA, MI, NH, and others. NJ: Screening values account for petroleum biodeg. MA: Screening values based on indoor background. NY: Screening based on sub-slab and indoor data only. All: Screening values vary by >100x between states. Approach to vapor intrusion varies widely between states. State guidance evolving rapidly. Who High- lights Low- lights State Vapor Intrusion Guidance Overview of VI Guidance SITE BUILDING Affected GW Affected Soil

12 Benzene Ethylbenzene Indoor Air Limits : USEPA vs. States USEPA VI Guide 1 (ug/m 3 ) New Jersey (ug/m 3 ) 0.312* KEY POINT: Indoor air, soil gas, and GW screening values vary widely between states , MTBE 2* Range Vinyl Chloride Lindane TCE 3* * N/A 0.81 PCE 3* 1) USEPA Limits based on cancer risk, Texas limits based on cancer risk * = Value based on TO-15 detection limit, risk-based value would be lower Texas 1 (ug/m 3 ) 10x 500x 1500x 640x 10x 76x 45x

13 Vapor Intrusion: Regulatory Framework USEPA Framework State Regulations Petroleum vs. Chlorinated VOCs Site-Specific Screening Mass Flux Evaluations USEPA Framework State Regulations Petroleum vs. Chlorinated VOCs Site-Specific Screening Mass Flux Evaluations

14 Observable Relationship C ia vs. C gw ? Chlorinated Solvents Petroleum Hydrocarbons Indoor Air Concentration ( ug/m 3 ) CORRELATION ? NO (p = 0.11) CORRELATION ? YES (p <0.001) C gw = COC conc. In groundwater; C ia = COC conc. In indoor air; (p = 0.11) = Probability = 11% that slope of best-fit line = 0 (I.e., no trend). GW Concentration (ug/L) Petroleum Hydrocarbons: No Chlorinated Solvents: Yes - Direct Correlation Between Groundwater Concentration and Indoor Air?? Subslab to Indoor Air AF

15 Oxygen Aerobic Biodegradation Possible C o >C o min No Aerobic Biodegradation C o <C o min C o min C H max Hydrocarbon Vapor Source Zone Vapor Concentration C H min C o max L  Petroleum Biodeg. AF Petroleum Biodegradation Conceptual Model From Roggemans et al., 2001, Vadose Zone Natural Attenuation of Hydrocarbon Vapors: An Empirical Assessment of Soil Gas Vertical Profile Data, API’s Soil and Groundwater Technical Task Force Bulletin No. 15. KEY POINT: Correlation between oxygen consumption and hydrocarbon attenuation.

16 KEY POINT: For petroleum sites, vapor intrusion is generally associated with two factors acting together - shallow sources and preferential pathways. Petroleum Vapor Intrusion: Industry Experience Preferential pathway allows vapors to enter building. 1 NAPL NAPL Affected GW Groundwater- Bearing Unit Sump draws NAPL or dissolved hydrocarbons into building. Shallow NAPL directly impacts building wall or floor. BUILDING 3 2 Unsaturated Soil

17 Vapor Intrusion: Regulatory Framework USEPA Framework State Regulations Petroleum vs. Chlorinated VOCs Site-Specific Screening Mass Flux Evaluations USEPA Framework State Regulations Petroleum vs. Chlorinated VOCs Site-Specific Screening Mass Flux Evaluations

18 Site-Specific Screening: Vadose Zone Fine-grained soils (e.g., silt and clay) expected to inhibit vapor intrusion. However, available field data does not show clear relationship between soil type and vapor intrusion risk.

19 Vapor Intrusion: Regulatory Framework USEPA Framework State Regulations Petroleum vs. Chlorinated Site-Specific Screening Mass Flux Evaluations USEPA Framework State Regulations Petroleum vs. Chlorinated Site-Specific Screening Mass Flux Evaluations

20 Mass Flux Evaluations Groundwater Screening Key Point: High variability in subsurface VOC concentrations may limit use of mass flux analysis for vapor intrusion evaluation. Mass flux into building must be < vertical mass flux out of groundwater. MASS BALANCE APPROACH: source area V GW-Bearing Unit Unsaturated Soil F ia1 L Fsv F ia2 ER h SITE BUILDING F gw1 F gw2 Mass Balance F sv = F gw1 - F gw2 F sv = F ia1 = F ia2

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

Distribution of VOCs Vertical GW profile Vertical soil gas profile Sub-slab data Indoor air data Ambient air data Study Approach: High density of data collected around individual buildings at two study sites. Project Overview Other Site Data Physical soil properties Indoor air exchange Radon analysis Cross-foundation pressure gradient

Altus AFB Study Site: Overview Cluster 1 Cluster 2 Cluster 3 Sample Point Locations

Altus AFB Study Site: Overview Cluster 1 Cluster 2 Cluster 3 KEY POINT: Collect at least three samples from each medium to quantify spatial variability.

Altus AFB Demonstration: Field Program Field Investigation Sample point cluster Sub-slab point Vertical soil gas points Pressure transducer

Variability in Vapor Intrusion Overview of VI Research Project Building-Scale Spatial Variability Short and Long-Term Temporal Variability Impact of Variability on Attenuation Factors Conclusions and Recommendations

Building-Scale Spatial Variability in VOC Conc. Indoor Air Indoor Air Sub-slab Deeper soil gas Ground- water Number of Data Sets Average Variability* 6 Spatial variability in subsurface media much higher than in indoor or ambient air. KEY POINT: * = Variability expressed as average of the coefficient of variation for each data set of three samples from the medium during each sampling event Sub-slab Deeper soil gas Groundwater: Altus AFB Hill AFB Well Headspace Well Headspace Ambient Air Ambient Air

Overview of VI Research Project Building-Scale Spatial Variability Short and Long-Term Temporal Variability Impact of Variability on Attenuation Factors Conclusions and Recommendations Variability in Vapor Intrusion

Short-term (3 weeks) Temporal Variability in Soil Gas TCE Concentration (from Blayne Hartmen): <2x variation

Short-Term Temporal Variability: Timescale of days - Altus AFB Indoor Air Indoor Air Sub-slab Deeper soil gas Ground- water # of Paired Samples Relative Percent Difference* 0 61% of paired subsurface gas samples had RPD <30%. 9% had RPD >100% (3x difference). KEY POINT: * = Relative percent difference (RPD) = (Sample 1 - Sample 2)/(Average of Sample 1 and Sample 2). Sub-slab Deeper soil gas Groundwater Well Headspace Well Headspace Ambient Air Ambient Air N/A < 30% %>100% N/A

Long-Term (8 Years)Temporal Variability in Indoor VOC Concentration (from EnviroGroup): 5x Variation

Long-Term (1 Year)Temporal Variability in Deep Soil Gas VOC Concentration (from NYDEQ): 5x Variation

Indoor Air Indoor Air Sub-slab Deeper soil gas Ground- water Number of Data Sets Average Variability* 0 For subsurface gas samples, longer-term temporal variability is similar to spatial variability KEY POINT: * = Variability expressed as average of the coefficient of variation for each data set of three samples from the medium during each sampling event Sub-slab Deeper soil gas Groundwater Well Headspace Well Headspace Ambient Air Ambient Air N/A Longer-Term Temporal Variability: Timescale of months - Altus AFB

Variability in Vapor Intrusion Overview of VI Research Project Building-Scale Spatial Variability Short and Long-Term Temporal Variability Impact of Variability on Attenuation Factors Conclusions and Recommendations

Building-Scale Spatial Variability: How Many Samples? Indoor Air Indoor Air Sub-slab Deeper soil gas Ground- water +/- 50% Number of Samples to Estimate True VOC Conc.* 3 Lots of sample locations required to understand VOC concentration in subsurface. KEY POINT: * = Number of samples = [(Z-statistic*CV)/Error] 2 ; CV = coefficient of variation; for 90% confidence level, Z-statistic = 1.64 Sub-slab Deeper soil gas Groundwater: Altus AFB Hill AFB Well Headspace Well Headspace Ambient Air Ambient Air /- 67%

Indoor Air Indoor Air Sub-slab Deeper soil gas Ground- water +/- 50% Number of Samples to Estimate True VOC Conc.* NC Sampling effort should be balanced to characterized both spatial and temporal variability. KEY POINT: * = Number of samples = [(Z-statistic*CV)/Error] 2 ; CV = coefficient of variation; for 90% confidence level, Z-statistic = 1.64 Sub-slab Deeper soil gas Groundwater: Well Headspace Well Headspace Ambient Air Ambient Air NC NC /- 67% Long-Term Temporal Variability: How Many Samples?

Impact of Building-Scale Variability: Probability Error for Single Measurement C subsurface Error Between Single Measurement and Average VOC Concentration Subsurface Measurements Key Point: Single measurement may not accurately represent subsurface vapor conditions.

Variability in VOC Concentration: 1) Indoor Air: 2) Subsurface: Spatial: Low Temporal: Moderate Summary of Findings Spatial: High Short-Term Temporal: Low Long-Term Temporal: High Sampling effort should be balanced to characterized both spatial and long-term temporal variability in the subsurface. KEY POINT:

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

40 Key Sources of VOCs in Indoor Air Source of Background Indoor Air Impacts REFERENCES: USEPA, 1991, “Building Air Quality Guide” OSHA, 1999, “Tech Manual for Indoor Air Investigation” Ambient air Vehicles, gasoline Paints, adhesives Cleaning agents Insecticides Tobacco smoke Cosmetics, etc. Significance of Background Effects

41 Indoor use of chemicals has decreased. However, average background concentration remains well above USEPA risk limits. Average Indoor Air Quality Over Time Note:1) Average background indoor air concentrations reported in various studies by year of publication. 2) Indoor air limits (10 -6 ) from USEPA Draft Vapor Intrusion Guidance, November KEY POINT: TRICHLOROETHENE BENZENE Average Background Concentration (ug/m 3 ) USEPA INDOOR AIR LIMIT

42 ARAMCO Art and Crafts Goop Aleenes Patio & Garden Adhesive Consumer Products Containing PCE Product Gumout Brake Cleaner PCE Concentration Hagerty Silversmith Spray Polish Champion Spot it Gone Plumbers Goop Adhesive Liquid Wrench Lubricant w/ Teflon Source: Not Specified 70% % 67.5% 30.5% % % KEY POINT: Wide variety of consumer products still contain high concentrations of PCE. Indoor Air

43 In 2004, background indoor and outdoor air concentrations still exceed risk-based limits for indoor air Background vs. USEPA Risk-Based Limits 1) Background concentrations from Sexton et al ES&T 38(2); ) USEPA Master Screening Values Table, September 2008 KEY POINT: PCE BENZENE Range of Reported Background Concentration (ug/m 3 ) INDOOR AIR LIMIT 2 90 th % 10 th % Median 90 th % 10 th % Median INDOOR LIMIT 2 90 th % 10 th % Median 90 th % Median Clean GW Bkgrnd Air Ambient 1 Indoor 1 Ambient 1 Indoor 1 10 th %

44 Indoor concentration of 1,2-DCA increasing over time. New indoor source = molded plastic (e.g., toys, Christmas decorations). New Indoor Source of 1,2-DCA Note:1) 1,2-DCA = 1,2-dichloroethane KEY POINT: CONCENTRATION DETECTION FREQUENCY 1,2-DCA Detection Frequency (%) 1,2-DCA Concentration (ug/m 3 ) USEPA INDOOR AIR LIMIT <0.08 Median 1,2-DCA Conc. 90%ile 1,2-DCA Conc. 2) Indoor 1,2-DCA data from residential area in Colorado. Data provided by Jeff Kurtz, Envirogroup

45 TCE Background at Redfields, CO., Site Significance of Background Effects Adapted from USEPA Seminar on Indoor Air Vapor Intrusion, January 2003, Dallas, Texas Post Remedy Pre-Remedy TCE 1,1-DCE USEPA TCE Limit USEPA 1,1-DCE Limit Time After Vent System Installation (Days) C ia in Single Home (ug/m 3 ) 1,1-DCE TCE Indoor Air Data Subslab Vent 0 KEY FINDINGS TCE does NOT change after vent system startup. Indoor TCE NOT due to vapor intrusion.

46 Key Findings Re: USEPA VI Guidance USEPA indoor air limits are < < typical background VOC conc’s in indoor air. Accurate identification of vapor intrusion impacts requires careful accounting of indoor sources. VOC = Volatile organic compound Significance of Background Effects USEPA VI Screening Values are not accurate for the prediction of indoor air impacts. Use of screening values will result in a high false positive rate. Risk-Based Air Limits False Positives BOTTOM LINE: