Presentation at Ontario MOE Soil Vapour Intrusion Information Session – January 27, 2011 Draft Technical Guidance: Soil Vapour Intrusion Assessment, November 2010 Camilo Martinez, P.Geo Ian Hers, P.Eng., Ph.D. and Michael Z’graggen, M.Sc Community Based Risk Assessment Coordinator Soil Vapour Intrusion Practice Leaders Ministry of the Environment Golder Associates Ltd. Standards Development Branch . Agenda 10:00-10:15 Introduction 10:15-11:30 Overview of Soil Vapour Guidance 11:30-12:00 Questions and Answers 2 2 Why is this Guidance Needed? Chlorinated � Many contaminated sites impacted solvent plume by volatile chemicals � Vapour intrusion may result in potential health risks to communities and workers � Need for guidance on approach and methods within Ontario regulatory framework Source Redfield Site, Courtesy Envirogroup 3 3
Guidance Development Process � Golder Associates contracted by MOE to write draft guidance � Peer review conducted by Geosyntec Consultants � Initial consultation and review by a stakeholders Advisory Group (February 2009) � Additional consultation and review by BILD Reference Group in December 2010, followed by current broader consultation – comments requested by the end of January. � Stakeholder consultation January 201. � Guidance will be posted on the EBR for further comments. 4 4 Document Outline Chapter 2 - Overview vapour intrusion assessment process Chapter 3 - Conceptual Site Model (CSM) Chapter 4 - Tiered Screening Process Chapter 5 - Soil Vapour Characterization Chapter 6 - Indoor Air Quality (IAQ) Monitoring Guidance Chapter 7 - Background Assessment Chapter 8 - Reporting and 5 5 Document Outline Appendix I - Detailed CSM Appendix II - Identification of Contaminants of Potential Concern Appendix III - Selected Analytical Methods Appendix IV - Recommended Health-Based Indoor Air Target Levels for Brownfield sites 6 6
Soil Vapour Guidance Main Objectives � Promote the understanding of the behaviour and migration of soil vapours, � Assist identifying sites where VI may be an issue, � Assist qualified professionals conducting vapour intrusion assessments and risk assessments, and � Assist MOE staff in conducting reviews. 7 7 Experience Base ATLANTIC HEALTH CANADA USEPA 2002 ITRC 2007 PIRI 2006 2008 ► See also Science Advisory Board for Contaminated Sites of BC (SABCS 2006, update January 2011), Cal DTSC 2010, EPRI 2005, API 2005. 8 8 Overview of Soil Vapour Intrusion Assessment Process (Chapter 2) � Site characterization and continuous development of the conceptual site model (CSM) � Tiered or phased assessment process (although not necessarily sequential) • Preliminary screening & comparison to MOE SCS • Screening level vapour intrusion assessment – soil vapour characterization, limited model adjustment • Detailed vapour intrusion assessment, further modelling flexibility and use of site-specific data. 9 9
Overview of Soil Vapour Intrusion Assessment Process � Multiple lines-of-evidence approach where appropriate ( e.g ., different media, models, other data) � Vapour intrusion mitigation � Community outreach Process Flowchart from Chapter 2 10 10 Conceptual Site Model (Chapter 3) � Fate and transport processes are described: • Diffusion • Advection • Biodegradation • Sorption � Followed by CSM scenarios of interest USEPA 2002 11 11 Conceptual Site Model � Scenarios of Interest Fresh Precipitation water lens • Fresh-water lens • Interface plume infiltration Fresh-water lens (non- • Preferential pathways contaminated groundwater) Capillary Transition Zone • Lateral diffusion NAPL Source • Barometric pumping • Stack effect Falling • Seasonal factors (cold weather) water table Why are CSMs important? Falling water table – Inform sampling design NAPL Source apillary Transition Zone 12 12
Conceptual Site Model – Aerobic Biodegradation Aerobic biodegradation of BTEX and alkane (hexane, octane) vapours is relatively rapid process – supports bioattenuation factors 13 13 Site Screening Process (Chapter 4) � Preliminary screening � Screening level vapour intrusion assessment � Detailed vapour intrusion assessment 14 14 Preliminary Screening � Are there chemicals of potential concern for vapour intrusion? � Does site represent safety or acute health risk concern (e.g., potential explosive conditions, odours)?– If yes take appropriate actions � Are buildings (current or future) located sufficiently close to contamination? • 30 m for non-degrading chemicals • 15 m for aerobically biodegradable chemicals* * Defined in MGRA spreadsheet as BTEX, hexane, naphthalene, and hydrocarbon fractions 15 15
Generic Screening Measured soil and/or groundwater concentrations are compared to MOE standards. � Check precluding conditions to determine whether generic MOE soil and groundwater standards for the soil vapour intrusion pathway can be applied. � Compare soil and/or groundwater concentrations to MOE standards (S-IA or GW2 component values) for soil and groundwater � If a precluding condition is present or concentrations exceed MOE S-IA or GW2, further assessment should be considered. 16 16 Precluding or Modifying Conditions � Shallow depth to water table – When < 3 m use MOE Tables 6 & 7 (use attenuation factor equal to 0.02) � Very high gas permeability media – Use Tables 6 and 7 � Earthen basements - Unless source > 5 m from building � Gas under pressure � Subsurface utility conduits connecting contamination source and building 17 17 Screening Level Vapour Intrusion (VI) Assessment Compare measured groundwater and soil vapour concentrations to screening levels. � Conduct additional site characterization � Calculate groundwater and soil vapour screening levels (GWSLs and SVSLs) � Selected Brownfield target indoor air concentrations are provided in Appendix IV � Use Modified Generic Risk Assessment (MGRA) Model or peer-reviewed model ( e.g. , USEPA Superfund J&E model) following guidelines for input parameter selection 18 18
Screening Level VI Assessment – Site Characterization � Multiple lines of evidence approach introduced (also essential under detailed risk assessment) � Pro’s and con’s for different media � Guidelines for data collection and interpretation are provided � An overview is provided in Chapter 4 with additional details in Chapter 5 19 19 Screening Level VI Assessment – Multiple Lines-of-Evidence (MLE) What is MLE? • Testing of different media (soil, Outdoor groundwater, soil vapour, air) Air • Sampling at multiple locations Indoor Air • Consideration of non-chemical factors (e.g., geology, building Soil Gas factors, biodegradation) Subslab Soil Gas • Modeling • Data interpretation integrated with CSM Groundwater 20 20 Screening Level VI Assessment – Multiple Lines-of-Evidence (cont) Why MLE? • Reduce uncertainty Outdoor • Improve assessments Air • Help determine if VI Indoor Air pathway is complete ( i.e. , background issue) Soil Gas Subslab Soil Gas Caveat : Sampling should be strategic (not all LOE’s may be needed) Groundwater 21 21
Pro’s and Con’s Different Media Media Pro’s Con’s Soil Data typically available, low Partitioning highly uncertain, high cost, low temporal variability spatial variability, may be bias Ground Data typically available, low Partitioning uncertain, not water cost, moderate temporal representative if unsaturated zone variability contamination source External Avoids partitioning, more Often high spatial variability, soil direct indication exposure, shallow data may not be vapour may integrate sources representative Subslab Closer to receptor, avoids Intrusive, cost, small scale spatial vapour lateral variability variability can be high Air Most direct indication (only Intrusive, cost, temporal variability for existing building) moderate to high, background issues 22 Screening Level VI Assessment – Soil Data Challenges Dr. John Cherry, Federal Contaminated Sites National Workshop, May 2010 PCE release experiment Borden site - Vadose zone excavation 23 23 Spatial Data to Illustrate Issues for Soil Vapour Characterization TCE Subslab Soil TCE measured at 3 different H-009 Sub-Slab Trends TCE Gas Concentrations 300 locations below house Wertz, NYSDEC, 2009 250 200 ug/m3 150 100 50 0 O N D J F M A M J J A S O N Casper, WY Soil gas TPH 2’ depth Subslab A Subslab B Subslab C 11 DCE Soil Gas Concentrations Dawson, 2005 USEPA Hydrocarbon Concentrations Below Slab 24 Luo, 2006 ASU 24 GOLDER ASSOCIATES
Temporal Data to Illustrate Issues for Soil Vapour Characterization Deep Soil Gas TCE Concentrations Log Scale in Groundwater, Shallow Soil Gas Shallow and Deep Soil Gas Wertz, 2007 Groundwater Monthly Sampling Log Scale TCE Concentrations in Soil Gas (1.5 m depth) Showing Seasonal Variations McAlary, 2009 25 25 Temporal Data to Illustrate Issues for Soil Vapour Characterization (Paul Johnson, ASU – Casper, WY) Pressure difference across slab Pressure Difference Buildings can “breath” both ways! (implications for subslab vapour sampling) 26 26 Modelling Study (Illustrates spatial variability and effect of biodegradation) What if you sample out here? Building Oxygen 3-D Numerical Vapors Model (this is a slice through the house) V. High gasoline concentrations Abreu & Johnson, ES&T, 2005 Slightly lower gasoline concentrations 27 27
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