Design Solutions for Vapor
Intrusion and Indoor Air Quality
EPA's Brownfields Program is designed to empower states, communities, and other stakeholders in economic redevelopment to
work together in a timely manner to prevent, assess, safely clean up, and sustainably reuse brownfields. A brownfield is a property,
the expansion, redevelopment, or reuse of which may be complicated by the presence or potential presence of a hazardous
substance, pollutant, or contaminant. EPA's Brownfields Program provides financial and technical assistance for brownfields
revitalization, including grants for environmental assessment, cleanup, and job training.
PURPOSE
This fact sheet provides an overview of technical and health
issues regarding chemical vapor intrusion into indoor air, and
how to address these issues to foster land redevelopment.
This document will discuss how to:
• anticipate the potential for vapor intrusion;
• evaluate the extent of the problem; and
• prevent or correct the problem.
BACKGROUND
EPA's mission is to protect human health and to safeguard the
natural environment. Part of achieving this mission includes
evaluating sites for contamination and the risk it potentially
poses to people and the environment.
As redevelopment of cleaned-up sites becomes more
prevalent, assessment and elimination of contamination risks
is crucial. Quantifying and eliminating these risks includes
assessment of the exposure pathways. Exposure pathways
are the ways that people can be exposed to contamination
such as breathing contaminated air, drinking contaminated
water, or touching contaminated soil. Vapor intrusion is one
exposure pathway that can cause potentially serious risks if
left unaddressed.
WHAT is VAPOR INTRUSION?
Vapor intrusion is the entry of a specific type of contaminant,
volatile organic compounds (VOCs), to indoor air from
underlying contamination in soil and groundwater. VOCs
readily disperse into air — even into the small air spaces
within soil and underneath a structure.
Indoor air pollution detected at a site may not necessarily be a
result of vapor intrusion. Background or preexisting levels of
contaminants may be present from chemical use in the building
or from ambient air. It is often difficult to distinguish between
contamination attributable to vapor intrusion and contamination
due to background levels. Regardless, the risk caused by
vapor intrusion should be investigated and quantified if it is
suspected.
The Vapor Intrusion Pathway
1 I I I I I I
VAPOR INTRUSION NEED NOT HINDER
REDEVELOPMENT
Although vapor intrusion is a serious concern, it need not be an
impediment to redevelopment. Vapor intrusion problems can
be properly addressed through investigating the history of site
activity, and the nature and extent of contamination.
Depending on the phase of redevelopment and whether
existing structures will be renovated or new buildings will be
erected, vapor intrusion can be prevented or corrected. It is
often more protective of human health and the environment
and more cost effective in the long run to eliminate the
contamination if possible.
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ANTICIPATING THE POTENTIAL FOR VAPOR
INTRUSION
Certain hazardous waste sites are more likely to cause vapor
intrusion problems than others. Vapor intrusion is typically
associated with petroleum products and chlorinated solvents or
other VOCs in soil and groundwater. Accordingly, the vapor
intrusion pathway should be investigated at sites with or near
this type of contamination. VOCs are often associated with
former gas stations, bus stations, dry cleaning and laundering
facilities, automotive repair shops, and other sites where
petroleum products or solvents were stored, handled, or
transferred and had the potential to be spilled.
Certain environmental conditions such as a high water table
(short depth to groundwater), some types of soils, and
fractured bedrock can increase the likelihood of intrusion.
Coarsely grained soils allow contamination to migrate longer
distances more quickly and escape more readily to the
atmosphere. The close spacing of finely grained soils allows
for greater upward movement of liquid, a process called
capillary action, which may bring contaminated groundwater
closer to the building. Contaminants are generally unable to
move through very fine soils such as clay, except in cases
where vertical fractures are present in these soils.
VOCs can seep through foundation cracks, holes in concrete
floors, and small gaps around pipes and utility lines. The age
of a structure's foundation, its floor construction, and the
existence of drain and tile sumps can also contribute to vapor
intrusion. Vapor intrusion can occur in buildings with or
without basements.
Some vapors, such as VOCs, may enter structures at low
contamination levels, and building ventilation systems may
prevent harmful vapor buildup. In other cases, chemicals may
accumulate in buildings at concentrations high enough to
create fire and explosion hazards. In addition, VOCs may or
may not have a noticeable odor and may be present at levels
posing acute or chronic health risks. EPA suggests evaluating
vapor intrusion when a site has, or is near, contaminated soil or
groundwater.
EVALUATING VAPOR INTRUSION
EPA has developed a Draft Guidance for Evaluating the Vapor
Intrusion to Indoor Air Pathway from Groundwater and Soils
(www.epa.gov/correctiveaction/eis/vapor.htm). Research on
vapor intrusion is rapidly developing, and this guidance
represents EPA's latest recommendations on this evolving
subject. EPA received many comments on the guidance and
anticipates continued updates to its content. The current
guidance details a three-tiered approach to evaluating the
vapor intrusion pathway: Primary Screening, Secondary
Screening, and Site-Specific Pathway Assessment. Each tier
contains a set of questions to guide the user towards a
determination of whether the vapor intrusion exposure
pathway is complete and if so, presents unacceptable risks.
The guidance also provides contaminant concentration levels
to help screen for soil and groundwater conditions in residential
settings. Screening level concentrations appropriate for
commercial settings may be developed according to the
procedures outlined in Appendix D of the guidance.
Modeling tools may assist in the evaluation of the vapor
intrusion threat, but any model used should take into account
site-specific conditions. Typically, these models allow the user
to examine a range of possible site conditions and a
subsequent range of resulting impacts. One of the most
commonly used is the Johnson and Ettinger (1991) Model for
Subsurface Vapor Intrusion Into Buildings, available on EPA's
web site (www.epa.gov/superfund/programs/risk/airmodel/
johnson_ettinger.htm). EPA's version of this model is designed
to produce data appropriate for residential settings. To apply
this model to commercial settings, data parameters should be
checked and revised as appropriate. Modeling is a helpful tool
when combined with site investigation and risk assessment, but
does not serve as a sufficient evaluation of the vapor intrusion
pathway alone.
PREVENTING VAPOR INTRUSION
Steps can be taken before site redevelopment to prevent vapor
intrusion. Some examples of prevention include: ensuring that
VOC contamination is removed from the site (and sent to a
proper treatment and disposal facility); preventing upward
contaminant migration with an impermeable barrier such as a
clay cap; and venting soil gas to outdoor air before it can reach
indoor spaces.
The local community should be notified of and involved in the
redevelopment process to allow citizens to express their
concerns and expectations regarding how to address the
cleanup of the source of the vapor intrusion. More information
on community involvement in site cleanup and redevelopment,
and how communities can get expert help in making decisions
about cleanup in their neighborhoods, can be found at:
www.epa.gov/superfund/tools and www.toscprogram.org.
Brownfields Fact Sheet
Vapor Intrusion
Solid Waste
and Emergency
Response (5105)
EPA 500-F-04-004
March 2004
www. epa. gov/brownfields/
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CORRECTING VAPOR INTRUSION
Source removal is the most thorough way to prevent a vapor
intrusion problem. However, source removal may not address
immediate risks, be cost effective, be well suited to site
redevelopment, or be possible. At sites where the source of
contamination cannot be completely eliminated, other solutions
to vapor intrusion problems can be implemented. Building
techniques that serve to provide a vapor barrier between
interior spaces and soil (or groundwater) can be combined
with structures that provide an escape route for soil vapor to
vent to the atmosphere rather than into indoor air. It may be
possible to add ventilation systems to existing buildings and to
seal entrances for vapors such as foundation cracks, holes in
concrete floors, small gaps around pipes and utility lines, and
sumps. Some ventilation systems operate effectively without
the use of energy, while others may require connection to a
power supply.
Correcting indoor air quality problems may only require
passive systems — those that increase ventilation by providing
an escape route for vapors to vent to the outdoors. When air
quality levels present an unacceptable threat to human health,
active systems that create and maintain flow from indoor air
spaces to the outside through use of fans or blowers may be
more appropriate. Such systems must be designed so that
vented air is not drawn back into other air intake systems or
windows. Furthermore, designs that are effective for solving
vapor intrusion problems in commercial buildings may not be
appropriate for residential dwellings.
After taking steps to block the vapor intrusion pathway, a plan
should be developed to ensure that these steps are working
correctly. This plan should include monitoring air quality and
the operation of any ventilation systems. Many systems
designed for correcting radon gas problems are effective for
vapor intrusion. More information on these systems can be
found at www.epa.gov/radon and additional sources of
information regarding remediating contaminated soil and
groundwater at hazardous waste sites can be found through a
search of the main site — www.epa.gov.
Elimination of the threat of fire or explosion associated with
vapor intrusion should involve measures to stop gas migration
as far from structures as possible. The buildup of volatile
compounds underneath or adjacent to buildings may not
present the risk of acute or chronic health effects, but may
threaten to ignite.
For sites where vapor intrusion problems originate with
contaminated groundwater, steps should be taken to prevent
entry of water to subsurface building levels. As with soil
vapor entry problems, preventing seepage of water into
basements and subsurface structures includes sealing cracks
and holes in foundations and ensuring that sump systems are
functioning properly. Groundwater remediation techniques are
numerous, including pump and treat systems, permeable
reactive barriers, air sparging, vertical containment barriers,
and in-situ bioremediation. Different remediation methods
may be more suited to certain site-specific circumstances. For
more information on these and other groundwater remediation
techniques, consult the references in the "For More
Information" section and visit EPA's web site at
www.epa.gov/tio/remed.htm.
FOR MORE INFORMATION
Draft Guidance for Evaluating the Vapor Intrusion to Indoor
Air Pathway from Groundwater and Soils (November 2002)
www. epa. gov/correctiveaction/eis/vapor. htm
Evaluating the Vapor Intrusion into Indoor Air (November
2002)
www.epa.gov/correctiveaction/eis/vapor/f02052.pdf
Groundwater Cleanup: Overview of Operating Experience at
28 Sites (September 1999)
www.epa.gov/swertiol/download/remed/ovopex.pdf
Johnson and Ettinger (1991) Model for Subsurface Vapor
Intrusion into Buildings
www .epa.gov/superfund/programs/risk/airmodel/
johnson_ettinger. htm
EPA Regional Brownfields Contacts
www.epa.gov/brownfields/contacts. htm
Superfund Community Involvement Toolkit
www.epa.gov/superfund/tools/index.htm
Innovative Remediation Technologies
www.epa.gov/tio/remed. htm
EPA Office of Air & Radiation Radon Site
www.epa.gov/radon
Hazardous Substance Outreach Programs for Communities
www. toscprogram. org
Brownfields Fact Sheet
Vapor Intrusion
Solid Waste
and Emergency
Response (5105)
EPA 500-F-04-004
March 2004
www. epa. gov/brownfields/
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