the vapor intrusion pathway daniel g. greene, cpg - dan...vapor intrusion pathway •vapor intrusion...

engineers | scientists | architects | constructors

THE VAPOR INTRUSION PATHWAY

DANIEL G. GREENE, CPG

MISCONCEPTIONS

VAPOR INTRUSION

• The migration of volatile chemical from the subsurface into overlying building (USEPA 2002)

Commercial/Industrial WorkerWorking over Plume

Resident Living over PlumeBasement or Crawl Space Without Basement

Migration of plume vapors to indoor air

VAPOR INTRUSION PHENOMENON AND BUILDING DEPRESSURIZATION

Furnace combustion

Stack Effects

Wind

Exhaust Fans

P to 50 Pa

Up to 20-25’

Strongest 3-6‘

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 – [email protected]

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

• Volatile organic compounds (VOCs) 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

• Releases:• Leaking Underground Storage Tank Sites• Dry Cleaners• Industrial manufacturing using degreasers (Chlorinated Solvents)• Transportation spills• Household use

WINTER

frost layer

windows closed…

Less fresh air infiltration

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


• 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


• 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


• 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


• 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


• 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


• 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.


• 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)


• 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.


• 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.


• 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”

• Intended to allow safe use of contaminated properties while protecting public health, safety, and welfare.

• When do I have Due Care obligations?

• Not withstanding any statutory exemptions, a person has due care obligations when that person has knowledge that their property (owner or operator) is contaminated.

DUE CARE DUTIES –EXEMPT IF MIGRATING ONTO PROPERTY

a) Prevent exacerbation of existing contamination

b) Mitigate unacceptable exposure to contaminants

c) Take reasonable precautions against reasonably forseeable acts or omissions of a third party and the consequences that foreseeably could result from those actions

DUE CARE DUTIESREQUIREMENT FOR SITE OWNERSa) 1b)1 c)1

d) Provide reasonable cooperation, assistance, and access to person authorized to conduct the response/corrective activities

e) Comply with land or resource use restrictions

f) Do not impede the effectiveness or integrity of land or resource use restrictions

DUE CARE NOTIFICATIONS

• For Part 201 Sites

• Notice MDEQ of Abandoned or Discarded Containers

• Notice MDEQ and Neighbors of Off-Site Migration

• Mitigate and fire/explosion hazard and notify the fire department

• Notice to easement holders if conditions would cause unacceptable exposure to person working in easement

CONCLUSIONS AND RECOMMENDATIONS

• Vapor Intrusion Concerns are Real

• Investigate and Mitigate, as needed

• Remember Due Care Obligations

• Use Professional Services

• Geology, Engineering, Legal Advice/Services

• New Property Acquisition or Construction

• Consider Property Selection, be cautions of Closed Part 201/Part 213 Sites

• Consider Regulatory/Criteria Changes

• Plan to be VI Compliant or VI Ready

• Future Developments in the VI Field

BEFORE WE START

• Introduction

• Audience• Building/Property Owners, Manufacturing, Industrial Processes, Hazardous Materials

Use, Employees• Located in a manufacturing areas, industrial parks, brownfield zones, NEIGHBORS• Do you breathe air? Do you work or live indoors?

• Goals• Help you become aware of VI concerns and support decisions for future facility planning

(site selection, property purchases, new construction)• Save you thousands of dollars on potential investigation/mitigation• Avoid third party law suits – Save millions?

• Misconceptions

the vapor intrusion pathway daniel g. greene, cpg - dan...vapor intrusion pathway •vapor intrusion...

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