Indicators, Tracers, and Surrogates of Chlorinated Vapor Intrusion Pressure and Wind as Indicators

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1 Innovation that provides sustainable solutions to complex challenges worldwide Indicators, Tracers, and Surrogates of Chlorinated Vapor Intrusion Pressure and Wind as Indicators State-of-the-Science for Indicators, Tracers, and Surrogates of Chlorinated Vapor Intrusion: Supplemental Measurements for Minimizing the Number of Chemical Indoor Air Samples Needed USEPA VI Workshop, March 20 th, 2018 Chase Holton, Ph.D. CH2M is now Jacobs worldwide

2 Agenda Vapor Intrusion (VI) Conceptual Site Model (CSM) Pressure and Wind Pressure: Barometric vs. Differential Pressure VI Guidance and Pressure Data Building Pressure Cycling (BPC) Data Collection Methods Available Evidence, Case Studies Wind: Wind Speed and Wind direction VI Guidance and Wind Available Evidence, Case Studies Summary Looking Forward

3 How do pressure and wind influence the VI CSM? Advection transport mechanism by which soil gas moves due to pressure differences Pressure differences, caused by environmental factors (including wind) and building operations, can indicate Building under-pressurization (VI on ) Building over-pressurization (VI off ) Image source: CA DTSC, 2011

4 24-h Averaged Outdoor-Indoor Differential Pressure [Pa] Aug-10 Sep-10 Oct-10 Nov-10 Dec-10 Jan-11 Feb-11 Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11 Nov-11 Dec-11 Jan-12 Feb-12 Mar-12 Apr-12 May-12 Jun-12 Jul-12 Aug-12 Sep-12 Oct-12 Barometric Pressure vs. Differential Pressure Barometric pressure (atmospheric): Measurement of weight exerted by air at a given point Differential pressure: Difference in pressure between two points h Ave. dp(out-in) Data from Holton et al., 2013

5 Current VI Guidance and Pressure For defining a complete VI pathway The building(s) is(are) susceptible to soil gas entry, which means openings exist for the vapors to enter the building and driving forces (e.g., air pressure differences between the building and the subsurface environment) exist to draw the vapors from the subsurface through the openings into the building(s) USEPA Final VI Guidance (June, 2015) On data representativeness and interpretation measure the pressure difference between the indoors and the subsurface, which provides a complementary line of evidence to support data evaluation and interpretation and is a more direct means of assessing building underpressurization than is monitoring weather/climate factors (e.g., air temperature, wind speed). USEPA Final VI Guidance (June, 2015)

6 Current VI Guidance and Pressure On data representativeness and interpretation The collection of ambient temperature and barometric pressure readings during the collection of IA samples including ambient air samples (or subslab pressure differential during SSSG sampling) are appropriate to verify data representativeness NJ DEP VI Technical Guidance (August, 2016) Measurement of the pressure gradient between the subslab and overlying structure can assist in interpreting the direction of vapor transport, whether into or out of the structure. OH EPA VI Guidance (May, 2010)

7 Building Pressure Cycling (BPC) Methods BPC methods involve temporary pressurization and/or depressurization to buildings and compartments Often coupled with real-time screening devices BPC methods have been applied to temporarily induce or inhibit VI to Determine near-worst case mass discharge/flux into a structure Distinguish between indoor, ambient, and subslab sources Identify atypical preferential pathways and other vapor entry points Image(s): Holton et al., 2015 (top), CH2M (now Jacobs) project photo (bottom)

8 5/6/16 19:12 5/6/16 21:36 5/7/16 0:00 5/7/16 2:24 5/7/16 4:48 5/7/16 7:12 5/7/16 9:36 5/7/16 12:00 5/7/16 14:24 5/7/16 16:48 Average Differential Pressure (Pa) Outdoor to Indoor Air dp and Subslab to Indoor Air dp During BPC Baseline Outdoor to Indoor Air dp (Pa) Subslab to Indoor air dp (Pa) Depressurization (5 pa) Depressurization (10 pa) Data from Holton et al., 2017 Date + Time

9 How do we measure pressure? Pressure sensor coupled with data acquisition module Image source: P300 Pressure Sensor ( (left), Sun Devil Manor pressure sensors (Holton et al., 2013) (middle), Differential pressure at 4-SS under natural conditions at Sun Devil Manor (Holton, 2015)

10 How do we measure pressure? Pressure sensor coupled with data acquisition module Omniguard 4 Rental: ~$150/week Image source: Omniguard 4 differential pressure monitor, Sun Devil Manor (left), Differential pressure at 4-SS under natural conditions at Sun Devil Manor (Holton, 2015)

11 Aug-10 Sep-10 Oct-10 Nov-10 Dec-10 Jan-11 Feb-11 Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11 Nov-11 Dec-11 Jan-12 Feb-12 Mar-12 Apr-12 May-12 Jun-12 Jul-12 Aug-12 Sep-12 Oct h Averaged Outdoor-Indoor Differential Pressure [Pa] Pressure as an Indicator: When do we sample? Data from Holton et al., h Ave. dp(out-in)

12 Aug-10 Sep-10 Oct-10 Nov-10 Dec-10 Jan-11 Feb-11 Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11 Nov-11 Dec-11 Jan-12 Feb-12 Mar-12 Apr-12 May-12 Jun-12 Jul-12 Aug-12 Sep-12 Oct h Averaged Outdoor-Indoor Differential Pressure [Pa] Pressure as an Indicator: When do we sample? Data from Holton et al., h Ave. dp(out-in)

13 Aug-10 Sep-10 Oct-10 Nov-10 Dec-10 Jan-11 Feb-11 Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11 Nov-11 Dec-11 Jan-12 Feb-12 Mar-12 Apr-12 May-12 Jun-12 Jul-12 Aug-12 Sep-12 Oct h Averaged Outdoor-Indoor Differential Pressure [Pa] Pressure as an Indicator: When do we sample? VI on VI off -3 Data from Holton et al., h Ave. dp(out-in)

14 Aug-10 Sep-10 Oct-10 Nov-10 Dec-10 Jan-11 Feb-11 Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11 Nov-11 Dec-11 Jan-12 Feb-12 Mar-12 Apr-12 May-12 Jun-12 Jul-12 Aug-12 Sep-12 Oct h Averaged Outdoor-Indoor Differential Pressure [Pa] 24-h Averaged Indoor Air TCE [ppb v ] Pressure as an Indicator: When do we sample? Data from Holton et al., h Ave. dp(out-in) 24-h Ave. TCE

15 Pressure as an Indicator: Hosangadi et al. (2017) Reported short-term increases in indoor air TCE concentrations and subslab-to-indoor differential pressure following decreases in barometric pressure. Strong relationship between indoor air TCE concentrations and subslab-to-indoor differential pressure when differential pressure was greater than zero (r 2 = ) Data from Hosangadi et al. (2017), Exhibit 3

16 Wind as an Indicator: Wind loading on building walls can cause building under-pressurization and/or over-pressurization Wind data is readily available from local weather stations Wind data is generally considered lower strength line of evidence without differential pressure comparison Image source: Sun Devil Manor Met Station (left), Wind rose (right) from Sun Devil Manor data (December 2010 and February 2011)

17 Wind speed (mph) 30 IA IA 25 Wind Speed Time (d) Data from Holton et al., 2012

18 Wind speed (mph) Pressure at 5-SS (Pa) IA IA Wind Speed P at 5-SS Time (d) Data from Holton et al., 2012

19 Case Study: Vandenberg AFB Building

20 Cross Slab Differential Pressure (30 days) Not much difference from one day to the next, except for occasional anomalies Generally very small differences between indoor and subslab

21 Wind (km/hr) Pressure (Pa) Pressure (Pa) Cross-Slab Pressure and Wind Speed on one day (May 22, 2017) :00 4:00 8:00 12:00 16:00 20:00 0:00 Time (HH:MM) Wind speed varies considerably over the day, with no significant effect on subslab pressure differential 21

22 Current VI Guidance and Wind On natural depressurization Wind creates a low-pressure region as air moves over the roof. This low pressure pulls air from the subsurface through the stack. NJ DEP VI Technical Guidance (August, 2016) On sampling locations Subslab sampling should not be conducted near the edges of the foundation due to the effects of wind on the representativeness of contaminant concentrations CA DTSC VI Guidance (October, 2011)

23 Summary Looking Forward Pressure measurements are useful, inexpensive indicators of when vapor intrusion is occurring May not be useful in large, open buildings Wind data is useful for explaining VI CSMs when differential pressure data also supports conclusions USEPA and State guidance documents generally support use of pressure data to explain VI CSMs and sample representativeness More case studies are needed to improve current understanding of benefits and limitations of pressure as an indicator

24 References Holton, C., Luo, H., Guo, Y., Gorder, K., Dettenmaier, E., Johnson, P. C. Long-Term and Short- Term Variation of Indoor Air Concentration at a Vapor Intrusion Study Site. The 22nd Annual International Conference on Soil, Water, Energy, and Air, San Diego, CA, March 19-22, Holton, C., Luo, H., Guo, Y. Dahlen, P., Gorder, K., Dettenmaier, E., Johnson, P. C. Evaluation of Selected Environmental Factors at a Vapor Intrusion Study Site. The 23rd Annual International Conference on Soil, Water, Energy, and Air, San Diego, CA, March 21, Holton, C., Guo, Y., Luo, H., Dahlen, P., Gorder, K., Dettenmaier, E., Johnson, P.C. Long-Term Evaluation of the Controlled Pressure Method for Assessment of the Vapor Intrusion Pathway. Environmental Science & Technology, 2015, 49, Holton, C. Evaluation of Vapor Intrusion Pathway Assessment Through Long-Term Monitoring Studies, Doctoral Dissertation, Arizona State University, May U.S. Environmental Protection Agency (USEPA) OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air, Office of Solid Waste and Emergency Response. June. Hosangadi, V., Shaver, B., Hartman, B., Pound, M., Kram, M. L., Frescura, C. High-Frequency Continuous Monitoring to Track Vapor Intrusion Resulting from Naturally Occurring Pressure Dynamics. Remediation, 2017, 27(2), 9-25.

25 Questions? Chase Holton, Ph.D. Copyright Jacobs March 23, worldwide

26 Questions for the audience Any experience with pressure or wind monitoring under natural conditions? Was it a useful indicator? How was the data collected (methods, frequency, duration)?