Better Data, Better Models, Better Decisions – Improving the Journey from Investigation to Mitigation at Potential Vapor Intrusion Sites Todd N. Creamer, P.G. Portsmouth, New Hampshire Cary, North Carolina January 23, 2014 Association of Environmental & Engineering Geologists – Carolinas Outline 1. Building our VI CSM 2. Indoor air is complex – here are new tools for:  Temporal integration – Quantitative Passive Samplers  Parsing background sources – Building Pressure Cycling 3. The right tools + solid, flexible CSM = Better mitigation  Less invasive  Lower cost  Improved effectiveness  Less energy consumption 2 1. VI CSM How might this picture apply? 3 3 1. Vapor Intrusion Pathway Conceptual Model 4 Technically complex and challenging. 2. Indoor Air is Complex Temporal Variability (Paul Johnson et al., 2012) Long Term Average 5 How can we better represent long term exposure? How can we evaluate background or indoor contributions? 2. Indoor Air is Complex Benefits of Quantitative Passive Sampling     Simple Cheap Easy to ship Discrete to deploy  Time-weighted average concentration (up to week or month)  Longer deployment = lower RLs  Long history in Industrial Hygiene 6 6 Five Passive Samplers Waterloo Membrane Sampler™ Automated Thermal Desorption (ATD) Tubes 3M OVM 3500™ SKC Ultra II™ Radiello™ 7 Fundamentals  Known exposure duration  Laboratory analysis of adsorbed mass  Calculate concentration as shown     88 C0 M k-1 t = concentration of analyte in air (µg/m3) = mass of analyte collected by the sorbent = uptake rate (mL/min) = sampling time (min) 9 2. Approaches for Indoor Air Background Assessment  Comparison to literature values  Compound ratio analysis  Statistical evaluation  Compound-specific stable isotope analysis  Building pressure cycling 10 10 Building Pressure Cycling Concept Use blower doors and/or HVAC system adjustment to: • induce vapor intrusion • induce vapor extrusion • find leaks in the slab • quantify leakiness of building enclosure 11 Building Pressure Cycling to sort background from VI – Small Bldg 12 Over-Pressurized 10 10 Induced Vapor Intrusion 5 8 Baseline Pressure 6 0 -5 4 Under-Pressurized 2 -10 0 -15 0 1 2 Differential Pressure (Pascals) VOC Concentration (ug/m3) 12 3 4 5 Time 6 7 8 9 VOC Concentrations (µg/m3) Differential Pressured (Pascals) 15 Vapor Intrusion CSM  Active manufacturing  Hundreds of employees  Data sets include:  Indoor air  Sub-slab soil gas  Groundwater  Soil  Outdoor air  Concrete slab 13 Sorbed to rafters Concrete 250,000 ft2 Shallow soil Groundwater  250,000 ft2 preemptive mitigation would be very expensive  Can we discriminate indoor & subsurface sources to reduce scope? Analysis to build a VI CSM Hypothesis: VI is more significant than indoor sources of VOCs. Location A Location B Location C Location A Location D Location C Location E Location E 14 A Plan to Test Hypothesis 𝑆𝑆 −𝑄𝑄 ∗ 𝑡𝑡 𝑆𝑆IA Pressurize facility & sample 𝐶𝐶(𝑡𝑡) = �𝐶𝐶𝑜𝑜 − � 𝑒𝑒𝑒𝑒𝑒𝑒 � �+ 𝑄𝑄 HAPSITE field GC/MS 15 𝑉𝑉 𝑄𝑄 Overcoming Challenges in the Field 𝑆𝑆 −𝑄𝑄 ∗ 𝑡𝑡 𝑆𝑆 𝐶𝐶(𝑡𝑡) = �𝐶𝐶𝑜𝑜 − � 𝑒𝑒𝑒𝑒𝑒𝑒 � �+ 𝑄𝑄 𝑉𝑉 𝑄𝑄 HAPSITE field GC/MS 16 What does it take to pressurize 4,000,000 ft3 & what do you get? TCE Upper Level - South Interior source only Upper Level - North Vapor intrusion only 17 Lower Level 3. Flexible VI CSM  Entrainment into roof-mounted air handlers via  Vertical shafts 18 Shallow soil 3. Flexible CSM Improves Conceptual Mitigation Plan Targeted SS Venting  Pressurize basement  Targeted SS venting Plus:  Seal shafts  Protect air intakes 19 Shallow soil Pressurize 3. Many mitigation tools to choose from          20 20 Sub-slab venting (SSV) Sub-slab depressurization (SSD) Vertical venting & pressurization barriers Building pressurization Sub-slab pressurization Membranes and seals Aerated flooring Indoor air treatment (activated carbon) Passive, active or semi-passive options 3. Use the CSM to match mitigation tool to site 21 21 Example CSM Design objective Mitigation match 1. House over dilute PCE in groundwater Maintain 6 Pa across slab Radon-style SSD 2. Manufacturing facility over localized impacts to soil Dilute VOCs in specific Targeted SSV area of sub-slab soil gas by ≥1000x 3. New institutional construction on Brownfield Exchange ≥0.25 subslab pore volumes per hour (6/day) Aerated flooring Green, low-cost mitigation tool: aerated flooring 22 22 Refresher on installation: sub-slab depressurization (SSD) 1. Install suction pt. 2. Measure ΔP 3. If no good, then a) get bigger fan, or b) add 2nd suction pt., or Fan c) seal cracks 4. Repeat Advective flow -∆P 23 Multiple Suction Point SSD  Yellow: ΔP < design criterion  Blue: ΔP > design criterion  ~energy expenditure plot: too much in some areas and not enough in others From McAlary et al., 2011 24 24 Traditional Radon SSD Radius of Influence -2” -0.2” -0.02” Minimum -∆P Conductive medium  Negative pressure decrease exponentially with distance  Multiple suction points needed to meet min -∆P 25 25 Aerated flooring Radius of Influence -2” -0.2” -0.02” Minimum -∆P Open void  Negative pressure relatively constant with distance  Lower vacuum can be applied at suction point 26 26 Aerated flooring construction A plastic form used to create a continuous void below concrete slabs 27 27 Concrete is poured over the forms 28 28 Thank you & Acknowledgements Passive Samplers:  Todd McAlary and Hester Groenevelt, Geosyntec Consultants, Inc.,  T. Gorecki and Suresh Seethapathy, University of Waterloo,  D. Crump, Cranfield University,  P. Sacco, Fondazione Salvatore Maugeri,  Heidi Hayes, Air Toxics Limited,  Michael Tuday, Columbia Analytical Services,  Brian Schumacher, USEPA,  Paul Johnson, Arizona State University Building Pressure Cycling:  Paul Nicholson and Bill Wertz, Geosyntec Consultants, Inc.  Turner Building Science  Confidential large facility owner Aerated Flooring:  Dave Folkes, Geosyntec Consultants, Inc. 29