engineers | scientists | architects | constructors THE VAPOR INTRUSION PATHWAY DANIEL G. GREENE, CPG
MISCONCEPTIONS
MISCONCEPTIONS
VAPOR INTRUSION • The migration of volatile chemical from the subsurface into overlying building (USEPA 2002) Commerc ercial/Indus ial/Industr trial ial Worker ker Reside dent nt Living over Plume Working over Plume Basement or Crawl Space Without Basement Migrati gration on of of plume vapor ors s to to i indoor oor air
VAPOR INTRUSION PHENOMENON AND BUILDING DEPRESSURIZATION Stack Effects Wind Exhaust Fans P to 50 Pa Strongest 3- 6‘ Furnace combustion Up to 20- 25’
CONCEPTUAL SITE MODEL • Refine the Conceptual Site Model as Additional Data is Generated
THANK YOU Daniel G. Greene, CPG Fishbeck, Thompson, Carr & Huber, Inc. (FTCH) 1515 Arboretum Drive Grand Rapids, MI 49546 Email – dggreene@ftch.com Phone – 616.464.3761
VAPOR INTRUSION PATHWAY • Vapor intrusion is not soil, groundwater, or a contaminant compound. • Vapor intrusion is an exposure pathway resulting from the migration of volatile chemicals from the subsurface into overlying buildings with human receptors. • The exposure pathway inculdes three main elements: • A source of VOCs. • A migration route. • A human receptor.
VOLATILE ORGANIC COMPOUNDS - VOCS • Vo Volat atile ile organ anic ic co compo pound unds (VO VOCs Cs) are organic chemicals that have a high vapor pressure at ordinary room temperature. • Petroleum Hydrocarbons – Including Benzene, Toluene, Ethylbenzene, and Xylene. • Chlorinated Volatile Organic Compounds – PCE, TCE, DCE, and Vinyl Chloride. • Landfill Gas – Methane • Other – Hydrogen Sulfide, Mercury • Relea leases: ses: • Leaking aking Unde derg rground round St Storage ge Tank nk Si Site tes • Dry Cl Clean aners • Indu dustria strial manufa ufact cturing uring usi sing ng de degreaser reasers s (Ch Chlorin orinated ated So Solvent vents) s) • Transpo nsporta rtati tion on sp spills lls • House sehold hold use se
WINTER windows closed… Less fresh air infiltration frost layer
SITE CONSIDERATIONS • Geologic/Hydrogeologic Condition • Soil Types, Thickness, Layers • Capillary fringe 0.2m to 1 m • Depth to groundwater <3m • Groundwater in contact with structure • Distance to a Vapor Source
BUILDING CONSIDERATIONS • Building Specific Input Values • Floor space length and width • Not all rooms interconnect • Building Mixing Height • Indoor Air Exchange Rates • Foundation and floor type, thickness • Utilities, Preferential Pathways • Distance to a Vapor Source
EVALUATING THE VAPOR INTRUSION PATHWAY • MDEQ Recommends a step-wise, risk-based approach (up to four steps) • Step 1 – Pathway Screening Assessment • Review existing information (Phase I ESAs, MDEQ Files, previous investigation data, site history) • Develop a Conceptual Site Model – Site Hypothesis • Source depth and distance to building (laterally and vertically) • Geology (including preferential pathways) • Chemical type and concentration (petroleum vs chlorinated solvent) • Building characteristics (construction, conditions, cracks, sumps, utilities) • Receptor characteristics • Before Site Investigation Begins Develop a Conceptual Site Model • Refine Conceptual Site Model as needed
EVALUATING THE VAPOR INTRUSION PATHWAY • Step 2 – Soil Gas Investigation • Conduct or complete a soil gas investigation to determine which receptors may be at risk • Use CSM (and MDEQ Guidance) to assist in selecting sampling locations • Use CSM (and Part 201 Tier 1, Tier 2, Tier 3A, or Tier 3B Criteria) to evaluate if response actions may be necessary • May need to proceed to Step 3 if proper soil gas data cannot be collected • May proceed directly to Step 4
EVALUATING THE VAPOR INTRUSION PATHWAY • Step 3 – Building Specific Vapor Investigation (including one or more of the following: • Interior Building Survey • Collect information about the building use • Building construction and condition • Occupancy and floor plan layout • Potential vapor entry locations • Other building features that can influence the potential for VI risk • Conducting sub-slab soil gas sampling (based on results of the IBS) • Conduct indoor air sampling (if water present or acute risks are being evaluated) • Evaluate the need for response actions throughout each phase
EVALUATING THE VAPOR INTRUSION PATHWAY • Step 4 – Response Actions • Source-Area Remediation • Building Control for Vapor Mitigation • Institutional Controls
VAPOR INTRUSION SCREENING LEVELS AND CRITERIA • VI Tier 1 Screening Levels • If Tier 1 SLs are exceeded, then a person must evaluate if additional response activity is required • Implement an appropriate response action. • Evaluate VIAP using Tier 2 generic unrestricted residential criteria • Evaluate VIAP using Tier 3A criteria • Evaluate VIAP using Tier 3B criteria
VAPOR INTRUSION SCREENING LEVELS AND CRITERIA • VI Tier 1 Screening Levels • VI Tier 1 Screening Levels are initial screening levels used to identify a release of a hazardous substance as a source of vapors or a vapor cloud and assume the following: • Concrete floors, concrete or block walls • Groundwater in contact with building • Attenuation factor of 0.03 • Soils are homogeneous, isotropic sand at 10 degrees C
VAPOR INTRUSION SCREENING LEVELS AND CRITERIA • VI Tier 2 Generic Unrestricted Criteria are based on: • Concrete floors, concrete or block walls • Groundwater in contact with building, unless if is >3 meters • Attenuation factor of 0.03 • Soils are homogeneous, isotropic sand at 10 degrees C
VAPOR INTRUSION SCREENING LEVELS AND CRITERIA • VI Tier 2 Generic Unrestricted Criteria are Tier 1 SLs that incorporate facility specific geologic and physical site conditions to establish generic criteria for unrestricted residential use. • Based on soil and soil temperature facility-specific input values • Depth to groundwater (if >3 meters), seasonal fluctuations, MDEQ-approved methodology • Soil criteria assume slab on grade • Groundwater criteria assume basement foundation • Soil types from Table 2. • Site specific soil data may be used.
VAPOR INTRUSION SCREENING LEVELS AND CRITERIA • VI Tier 3A Generic Criteria are based on input values specific to the site based on the following: • MDEQ approved soil and soil temperature values. • The shallowest depth to groundwater (considering seasonal variability) • MDEQ approved facility-specific values for land use and building information (Table 10)
VAPOR INTRUSION SCREENING LEVELS AND CRITERIA • VI Tier 3A Generic Unrestricted Criteria are Tier 2 SLs that incorporate facility specific land use or building information, or both, that require a land or resource use restriction. • Based on soil and soil temperature facility-specific input values • Depth to groundwater (if greater than 3 meters), seasonal fluctuations, MDEQ-approved methodology • Soil criteria assume slab on grade • Groundwater criteria assume basement foundation • Soil types from Table 2.
VAPOR INTRUSION SCREENING LEVELS AND CRITERIA • VI Tier 3B Generic Criteria are developed using an alternate method or model approved by the MDEQ. • Data must be demonstrated to be representative of site-specific conditions and undergo a sensitivity and validation analysis. • Building parameters may include: • Air exchange rate, enclosed-space floor thickness/length/width, enclosed-space height • Must include evaluation of smaller areas contained within structure • Must include evaluation of how footings, walls, air exchange patterns impact the data • Must include evaluate of whether the inputs used aer representative of actual site conditions.
VAPOR INTRUSION SCREENING LEVELS AND CRITERIA • VI Tier 3B Generic • Different Model or Methods may be used to assess: • Heterogeneous or multilayer soil present at a property • A vapor source that consists solely of dissolved phase petroleum • A NAPL vapor source • A finite source in unsaturated soil
MITIGATION ALTERNATIVES • Active subsurface depressurization systems employed to mitigate VI include the following: • Sub-Slab Depressurization System (SSDS) • Sub-Membrane Depressurization System • Block Wall Depressurization System • Drain Tile Depressurization System • Passive Subsurface Depressurization Systems • Sub-Slab Ventilation Systems (SSVS) • Alternative Mitigation Methods • active HVAC modifications (not appropriate for residential buildings); soil vapor extraction; aerated floor systems; spray on barriers (supplemental approach only); subsurface pressurization; heat recovery ventilator; IA treatment (designed as a temporary method); limit or prohibit access to affected areas of building; immediate removal of source.
DUE CARE OBLIGATIONS • What is “Due Care” • In Inte tended ded to to a allow ow safe fe use of of con onta taminated minated prop operties ties while e prot otecting ting public ic healt lth, h, safet fety, y, and d welfare. are. • Wh When do do I ha have Due Ca Care obl bliga igations tions? • Not withstanding any statutory exemptions, a person has due care obligations when that person has knowledge that their property (owner or operator) is contaminated.
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