2 Mixing in indoor air and inhalation Dissolved contamination Vapor Intrusion is… The migration of volatile chemicals from the subsurface into overlying buildings.Stack effectsMixing in indoor air and inhalationEnclosed spaceWind effectsAdvection/ConvectionQsoilCracksAir streamlinesBuilding zone of influenceConvectionVadose zoneDiffusionTop of capillaryzoneLTDiffusionWater TablePhase partitioningDissolved contaminationCgwto Csoil gas
3 VI isn’t….Ambient (background)On-site processesIndoor air sources
4 History of VI GuidanceJohnson and Ettinger (1991): “Heuristic Model for Predicting the Intrusion Rate of Contaminant Vapors into Buildings” - not updated since 2004; 1-DOSWER Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (Still Draft!)2005 – 3D VI model by Abreu and JohnsonDERR TDC Methodology for Vapor Intrusion AssessmentITRC Guidance
5 History of VI GuidanceOhio EPA Guidance May a bit of OSWER 2002, ITRC, and CAL EPA, plus Ohio EPA specific experienceBackground Indoor Air Concentrations of Volatile Organic Compounds in North American Residences (1990 – 2005): A Compilation of Statistics for Assessing Vapor Intrusion.EPA's Vapor Intrusion Database: Evaluation and Characterization of Attenuation Factors for Chlorinated Volatile Organic Compounds and Residential Buildings.2012 – VISL calculator and user’s guide
6 More….Conceptual Model Scenarios for the Vapor Intrusion PathwayIndoor Air Vapor Intrusion Mitigation Approaches, FAQs, etc.April US EPA Office of Underground Storage Tanks – Draft Petroleum Vapor Intrusion GuidanceApril U.S. EPA VI guidance (super secret document available from Inside EPA for a limited time only!) expected update ….?????October, 2014 – ITRC Petroleum Vapor Intrusion Fundamentals of Screening, Investigation, and Management
7 US EPA VISL calculator: Uses the RSL construct for indoor air values Applies attenuation factors to calculate screening values for soil gas and ground water (based on the 2012 US EPA VI Database)Adjust for exposure scenario (C/I vs residential)
8 What is an attenuation factor? AF () – unitless ratio of the indoor air concentration (Cindoor) to the subsurface contaminant concentrationVISL and OSWER: GW = CIA/(CGW*H*1000L/m3) = .001 (vapor at source) soil gas = CIA/CSG= .1 crawl space= CIA/CSG= 1However…soil gas = .03 (SG = 33 X IA)According to US EPA draft commentAs an example a building with TCE concentrations of 2,000 μg/m in soil gas and 2 3μg/m in indoor air would have an attenuation factor of (2 / 2000), or Similarly, a building with TCE concentrations of 5 μg/L in groundwater and 32μg/m in indoor air and a Henry’s law constant of would have an attenuation factor of (2/[5*0.118*1000]), or As defined in the equations above, the value of the AF decreases as the level of attenuation between the subsurface and building increases.
14 Proposed Changes Include RCRA COC List Clarify use of OSHA PELs Current (2010) Ohio EPA guidance: US EPA 2002 tables plus a few…Proposed: VISL calculator list plus H2S; special consideration for cis-1,2 DCEMajor change:Must have reliable inhalation toxicity factors (no extrapolation)The source vapor concentration < toxicity
15 Proposed ChangesUse VISL as front line screening for further evaluationMore robust mitigation/remedy alternatives sectionSampling for remedy verificationFrequencySite specificUpdate sampling SOPs and forms
17 Challenges Direct user to stepwise empirical data collection How much data are necessary to make a decision for evaluation and remedy?Use VISL calculator only?Allow J&E?If so, defaults only?When are building parameters engineering controls?Some other AF calculation?