AEHS Westcoast Conference Work Shop, March 22, 2017 San Diego, CA Case Studies of Innovative Use of Tracers, Indicators and Field GC/MS for Assessing the Vapor Intrusion Pathway Stack effect & temperature Ian Hers, Paul Hurst, Parisa Jourabchi Golder Associates Radon Measurement
Presentation Outline Literature search on use of radon as indicator or tracer of chlorinated vapour intrusion (CVI) Case study of use of radon as indicator Case study of use of HAPSITE as field screening tool Introduction to evaluation of potential CVI through weather indicators Case study of weather indicators March 20, 2017 2
Framework Use of Radon in VI Studies Indicator (potential for CVI) Tracer (move with CVI chemicals, background studies) Surrogate (semi-quantitative predictor of CVI) Conceptual model considerations for CVI and Rn (credit to Henry Schuver for concept) Source location CVI and Rn are different Generation rate CVI variable, Rn less variable (but affected by soil moisture) Fate & Transport CVI sorbs, Rn does not Vapor Depletion CVI slow, Rn fast (1/2 life of 3.8 d) Background CVI yes, Rn no (granite counters?) Building factors & driving forces CVI & Rn same What are the processes and time scales for Rn vs CVI mass flux? 3/20/2017 3
Effect of Moisture on Rn Emanation Rate Figure from Hosodo et al. 2007 1 3/20/2017 1 4 Masahiro HOSODA, Michikuni SHIMO, Masato SUGINO, Masahide FURUKAWA & Masahiro FUKUSHI (2007) Effect of Soil Moisture Content on Radon & Thoron Exhalation, J. of Nuclear Science & Technology, 44:4, 664-6722
Use of Rn as Tracer - Comparison of Rn and CVOC Attenuation Factors (AFs) 1 Table from McHugh et al. 2008 1 - Rn subslab-to-indoor air AFs ~ 0.001-0.006 (houses) Compare to Little et al. Avg a = 0.0016 (national); Mosley et al. Avg. a = 0.004 (N=10); DiGuilio et al. 2006 Avg a = 0.004 (N=9); King et al. 2010 (a = 0.002, range = 0.0006 to 0.0034 (N = 19) (Alaska) Even in low Rn areas Rn in soil gas typically > 1000X higher than ambient (0.7 pci/l), therefore, Rn is an effective tracer March 20, 2017 5 1 McHugh et al. 2008. The use of Rn measurements for evaluation of VOC intrusion. Environmental Forensics, 9: 107-114.
VOC AF 2.5OM Use of Radon as Tracer Comparison of Rn and CVOC Attenuation Factors Figure from Lutes et al. 2010 Used Electret for Rn Preferential VOC pathway, indoor background VOCs? Smaller VOC source, greater VOC variability? 1.5OM Rn Attenuation factor (AF) 3/20/2017 Lutes et al. 2010. Radon Tracer as a Multipurpose Tool to Enhance Vapor Intrusion Assessment and Mitigation. https://oaspub.epa.gov/eims/eimscomm.getfile?p_download_id=498943 6
ASU Sun Devil Manor (SDM) Use of Rn as Possible Indicator of TCE Concentrations Fig from Holton et al 2012 1 Rn elevated, but TCE is not seasonal differences in TCE mass flux but constant Rn baseline? Many of the higher concentration peaks match But not all 1 Statistical analysis of 24-hr Rn and TCE data indicated correlation (R 2 =0.37) 2 2 Kurtz et al. 2017. New Analysis of the ASU SDM Data, AEHS EPA 2017 Workshop, San Diego, Mar 21. 3/20/2017 7
Increasing PCE Decreasing PCE Decreasing Rn USEPA Indianapolis House Use of Radon as Possible Indicator of CVI Intrusion Figure from USEPA 2015 1 and Lutes 2017 1 Time series analysis of increase in 24-hr Rn & PCE indicated correlation (R 2 =0.41), no analysis found of absolute values Could this be due to reservoir effect and different sources/time-scales for flux events Increasing Rn 1 http://cfpub.epa.gov/si/si_public_record_report.cfm?direntryid=309644 2 Lutes 2017. Indicators, Tracers and Surrogates, Why Use Them, Probability Analysis, Definitions and Examples, AEHS EPA 2017 Workshop, San Diego, Mar 21. March 20, 2017 8 1 Simple, Efficient, and Rapid Methods to Determine the Potential for Vapor Intrusion into the Home: Temporal Trends, Vapor Intrusion Forecasting, Sampling Strategies, and Contaminant Migration Routes. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-15/070, 2015.
USEPA Indianapolis House Use of Radon as Possible Indicator of CVI Intrusion Table from USEPA 2015 1 Rn is quite stable PCE is more variable 1 Is there pattern emerging? Is Rn generally less variable and more stable than VOC, but tracks VOC intrusion at short time scales for initial forcing event. Could there be a reservoir depletion limitation for VOC? http://cfpub.epa.gov/si/si_public_record_report.cfm?direntryid=309644 March 20, 2017 9 1 Simple, Efficient, and Rapid Methods to Determine the Potential for Vapor Intrusion into the Home: Temporal Trends, Vapor Intrusion Forecasting, Sampling Strategies, and Contaminant Migration Routes. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-15/070, 2015.
Case Study Use of Radon as VI Tracer Radon testing conducted at five buildings as added line of evidence as tracer to assess pathway completeness Buildings were old commercial/industrial buildings, from 1930 s-1940 s, with variable construction, and hence subslab and indoor air concentrations were also variable Radon testing was identified as possible means to better understand variability and better predictor attenuation factor as compared to modelling Use of RAD7 for direct Rn reading of sub slab 3/20/2017 10
Case Study Use of Radon as VI Tracer Sample Collection (Gasbag samples) Samples collected using a 60 cc polypropylene syringe Syringe was purged and then used to transfer approximately 240 cc of air into a Tedlar bag. Samples were shipped to the University of Southern California for analysis. Sample Collection (RAD7) Thoron (radon-220) protocol used 2 minute purge before each sample Sniff test mode, six, five minute samples at each location Results of first two tests discarded and remaining four Use of RAD7 for direct averaged for final result Rn reading of sub slab 3/20/2017 11
Case Study - VI Tracer Using Radon Measured attenuation factors using RAD7 and gasbag samples comparable Location RAD7 AF Gasbag AF Location 5 0.006 0.004 Location 4 0.006 0.008 Use of RAD7 for direct Rn reading of sub slab 3/20/2017 12
Case Study - VI Tracer Using Radon (Fill below slab) s 1 PCE 10-4 Slab-at-grade Basement Rn AFs were generally greater than CVOCs AFs (up to 10X) Could CVOCs AFs be lower because of smaller CVOC source or greater subslab variability? Use of RAD7 for direct Rn reading of sub slab 3/20/2017 13
Case Study - VI Tracer Using Radon 2 Rn AFs were 4-10X lower than CVOCs AFs One possibility is indoor source of CVOCs But typically indoor sources of cdce are limited Another possible explanation is characteristics of building and Use of RAD7 for direct preferential pathways Rn reading of sub slab 3/20/2017 14
Case Study - VI Tracer Using Radon Conclusions Radon AF s were variable compared to VOC AF s. Varying building and sub-slab configurations/conditions including a) some locations with shared HVAC, others with dedicated units, b) poor condition slabs and c) numerous reconfigurations of inside space all causes additional uncertainty Potential indoor sources cause uncertainty in comparisons. RAD 7 and Gasbag AF similar (0.006 vs 0.008 at Location 1 and 0.021 vs 0.023 at Location 5). Radon AF somewhat helpful to better understand VI processes and compare to measured VOC AF s in a multiple lines of evidence approach. Use of RAD7 for direct Rn reading of sub slab 3/20/2017 15 1 Building construction: 2 storey building with below grade basement
Case Study Additional VI Investigation Using HAPSITE Location 5 Former electronics manufacturer VOC plume in fractured shale/limestone bedrock Buildings were old and basements constructed on bedrock outcrops Basement had evidence of water infiltration and significant cracks 16
Case Study VI Investigation Using HAPSITE Location 5 Real-time assessment of PCE and TCE concentrations Portable Gas Chromatography Mass Spectrometer (GC/MS) - Inficon HAPSITE Pathway and exposure samples obtained Clearly indicated intrusion of CVOCs through pathways Speculated pathways and water infiltration could potentially have resulted in high AFs 17
Case Study VI Investigation Using HAPSITE Location 5 Sample Location PCE (ug/m 3 ) TCE (ug/m 3 ) Floor wall interface 12.00 3.06 Slab crack / gap 22.86 1.97 Floor wall interface 12.07 4.41 Floor wall interface 28.75 3.08 Near ASTs 28.75 3.08 Very large slab crack / gap 103.86 6.97 Very large slab crack / gap 96.50 6.95 Very large slab crack / gap 32.61 3.50 Open pipe in slab 5.63 0.45 Open pipe in slab 4.41 0.49 Slab crack / gap 0.00 0.00 Slab crack / gap 20.76 2.02 Slab crack / gap 28.76 2.69 Indoor air 18.97 1.58 Sample Location PCE (ug/m 3 ) TCE (ug/m 3 ) Indoor air 1.61 0.23 Slab crack / gap 1.28 0.19 Drain 24.66 9.36 Drain 17.68 5.23 Drain 2.96 0.75 Drain 3.18 0.67 Sink 3.90 0.82 Slab crack / gap 2.63 0.64 HAPSITE testing helped identify pathways, benefits are improved basis for mitigation 18
Case Study VI Investigation Using HAPSITE Location 5 Pros Analyze large number of samples, identify pathways, which was very useful Real-time results Potentially lower laboratory costs Investigate routes for vapour intrusion and spatial variability throughout tenant space Aid to make timely decisions regarding mitigation measures if warranted Cons Typically need to confirm results with standard laboratory methods Must carefully calibrate to use quantitatively Instrument error is up to approximately +/- 40% Not a time averaged measurement (1 min samples) Not an overly stable instrument (note there are other options with respect to field GC/MS) March 20, 2017 19
CVI Weather Indicators Weather indicators potentially include Outdoor temperature Indoor-outdoor temperature difference Solar stack effect? Wind speed Wind chill Wind direction Barometric pressure Snow and frost cover Snowmelt Rainfall Water level change Conceptual Site Model (regional considerations, building factors) Analysis (autocorrelation, time element, significance) Practical Indicators (e.g., DT) (how robust, geographically applicable?) March 20, 2017 20
Weather Indicators of Vapor Intrusion Potential The influence of weather indicators is variable Some potentially influence building pressures; building depressurization drives vapor intrusion (e.g., temperature, wind, barometric pressure) Some potentially influence soil vapor fate and transport (e.g., snow and frost, rainfall) The importance of weather indicators will depend on climate and building type; commercial building may be less affected than residential building The time scales for weather indicators are variable Weather indicators are potentially a leading metric (assist in planning) and lagging metric (assist in data interpretation) March 20, 2017 21
Weather Indicators Case Study Site in Calgary, Alberta Chlorinated solvent contamination in groundwater Sand and gravel deposits Depth to water table ~ 4 to 7 m Small to medium sized houses, most with half-basement or basement Data is for un-mitigated houses March 20, 2017 22
Weather Indicators Case Study Differential pressure between basement and outdoor air measured using Engineering Solutions Omniguard III Outdoor pressure lead protected from wind (placed in PVC cylinder) Weather data obtained from met station 17 km from Site Analysis to date has addressed relationship between temperature, wind, barometric pressure and building pressures Relationship between weather indicators and indoor TCE concentrations is in-progress (complicated!) March 20, 2017 23
Differential Pressure (indooroutdoor) (Pa) Differential Pressure (indooroutdoor) (Pa) Weather Indicator Case Study Daily Avg Pressure & Temperature 1 0.5 0-0.5-1 -1.5-2 -2.5-3 y = 0.1948x - 3.0075 R² = 0.63 0 10 20 Outdoor Temperature (oc) 1 0.5 0-0.5-1 -1.5-2 -2.5-3 N = 14 houses Daily Avg Pressure & Wind Speed y = -0.1626x + 1.369 R² = 0.53 0 10 20 30 Wind speed (km/hr) March 20, 2017 24
Differential Pressure (indooroutdoor) (Pa) Differential Pressure (indooroutdoor) (Pa) Weather Indicator Case Study Daily Avg Pressure & Temperature 1 0.5 0-0.5-1 -1.5-2 -2.5-3 y = 0.1948x - 3.0075 R² = 0.63 0 10 20 Outdoor Temperature (oc) 1 0.5 0-0.5-1 -1.5-2 -2.5-3 Daily Avg Pressure & Wind Speed y = -0.1626x + 1.369 R² = 0.53 0 10 20 30 Wind speed (km/hr) March 20, 2017 25
Differential Pressure (indoor - outdoor) (Pa) 0-2 -4-6 Weather Indicator Case Study Hourly Pressure and Wind Data -8-10 y = -0.1858x + 0.4715 R² = 0.65 0 10 20 30 40 50 Wind Speed (km/hr) March 20, 2017 26
Multiple Regression Analysis Temperature and Wind SUMMARY OUTPUT Regression Statistics Multiple R 0.871 R Square 0.758 Adjusted R Square 0.714 Standard Error 0.556 Observations 14.000 Improves regression from R 2 of 0.63 for temperature alone to 0.76 for temperature and wind (76% of variation explained by temperature and wind) ANOVA df SS MS F Significanc e F Regression 2 10.665 5.333 17.238 0.000407 Residual 11 3.403 0.309 Total 13 14.068 Coefficien ts Standard Error t Stat P-value Lower 95% Upper 95% Lower 95.0% Upper 95.0% Intercept -1.147 0.906-1.267 0.231-3.140 0.846-3.140 0.846 Temperature 0.138 0.043 3.177 0.009 0.042 0.234 0.042 0.234 Wind -0.094 0.039-2.386 0.036-0.181-0.007-0.181-0.007 Temperature a better predictor than wind, but both significant at alpha = 0.05 March 20, 2017 27
Conclusions Radon holds promise as tracer or indicator of chlorinated vapor intrusion (CVI) There are differences in the CSM between radon and chlorinated solvent VI that should be recognized, including potential mass flux differences Interesting finding for Indianapolis house was that increasing temperature difference was better indicator of CVI than absolute temperature Variability in source location and size, preferential pathways and other factors can confound analysis Several weather indicators of potential CVI can be considered Case study showed that building depressurization was correlated to temperature difference and less so to wind speed
Future of VI Monitoring!? If you have questions please contact Dr. Ian Hers, Golder Associates ihers@golder.com March 20, 2017 29
Conceptual Model for Pressures Stack Effect Wind Effect Canada Mortgage and Housing (2004). Air Pressure and the Building Envelope March 20, 2017 30