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Brownfields Technology Primer:
I Vapor Intrusion Considerations
for Redevelopment
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Solid Waste and EPA 542-R-08-001
Emergency Response March 2008
(5203P) www.epa.gov/brownfields
www.brownfieldstsc.org
Brownfields Technology Primer:
Vapor Intrusion Considerations
for Redevelopment
U.S. Environmental Protection Agency
Office of Solid Waste and Emergency Response
Brownfields and Land Revitalization Technology Support Center
Washington, DC 20460
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BROWNFIELDS TECHNOLOGY PRIMER
VAPOR INTRUSION CONSIDERATIONS FOR REDEVELOPMENT
Notice and Disclaimer
Preparation of this document was funded by the U.S. Environmental Protection Agency (EPA)
under Contract No. 68-W-02-034. It was prepared for EPA's Brownfields and Land
Revitalization Technology Support Center (BTSC), which responds to requests from EPA
regional offices, states, localities, and tribes to provide support for brownfield sites related to
the use of technology for site investigations and cleanups.
The document is intended as a primer only, not guidance. EPA recommends that users refer to
existing guidance documents (some references are provided herein) regarding vapor intrusion
characterization and mitigation techniques. The primer was subjected to the Agency's
administrative and expert review and was approved for publication as an EPA document.
Mention of trade names or commercial products does not constitute an endorsement or
recommendation for use.
An electronic version of the primer can be downloaded from BTSC's website at
http://www.brownfieldstsc.orq. A limited number of hard copies are available free of charge by
mail from EPA's National Service Center for Environmental Publications at the following
address (please allow 4 to 6 weeks for delivery):
EPA/National Service Center for Environmental Publications
P.O. Box 42419
Cincinnati, OH 45242
Phone: 1-800-490-9198
Fax: 301-604-3408
Email: nscep@bps-lmit.com
For further information about this document, please contact Mike Adam of EPA's Office of
Superfund Remediation and Technology Innovation at 703-603-9915 or by e-mail at
adam. m ichael(S)epa. qov.
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BROWNFIELDS TECHNOLOGY PRIMER
VAPOR INTRUSION CONSIDERATIONS FOR REDEVELOPMENT
Table of Contents
1.0 BACKGROUND 1
1.1 What Is Vapor Intrusion? 1
1.2 Why Is Vapor Intrusion a Concern? 3
1.3 Where Is Vapor Intrusion a Concern? 5
1.4 How Does Vapor Intrusion Impact Brownfields Redevelopment? 5
1.5 How Is Vapor Intrusion Regulated and What Guidance Is Available? 6
Guidance Documents: 6
States: 8
2.0 ASSESSING THE POTENTIAL FOR VAPOR INTRUSION 10
2.1 Developing the Conceptual Site Model 10
2.2 Sampling and Analysis: 11
Groundwater and Bulk Soil Sampling: 12
Soil Gas Sampling 12
Passive Soil Gas Survey: 14
Sub-Slab Sampling: 15
Indoor Air Sam pling: 16
2.3 Using Predictive Models: 17
3.0 MITIGATION OF VAPOR INTRUSION 19
3.0 MITIGATION OF VAPOR INTRUSION 19
3.1 Passive Mitigation Methods: 20
Sealing Cracks: 20
Passive Barriers: 20
Passive Venting: 21
3.2 Active Mitigation Methods 21
Depressurization: 21
Sub-slab Soil Pressurization: 22
Building Pressurization: 23
3.3 Strategies for New Construction 23
3.4 Operation and Maintenance of Residential Systems 24
4.0 CONCLUSIONS 25
APPENDIX A: Know Your State! Available State Guidance Regarding Vapor Intrusion 27
APPENDIX B: Additional Sampling and Analysis Information 31
APPENDIX C: Acronyms and Glossary 36
APPENDIX D: References 40
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VAPOR INTRUSION CONSIDERATIONS FOR REDEVELOPMENT
List of Figures
Figure 1. Migration of Soil Vapors to Indoor Air 4
Figure 2. Installation of Soil Gas Probe Near House 14
Figure 3. Examples of Passive Soil Gas Samplers 15
Figure 4. Examples of Air/ Soil Vapor Sample Collection Devices: Canister, Sampling Bags,
and Sorbent Tubes 17
Figure 5. Schematic of Active Soil Depressurization System 22
List of Tables
Table 1. EPA Regional Brownfields Coordinators 9
Table 2. Sampling Options for the Assessment of Vapor Intrusion 13
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BROWNFIELDS TECHNOLOGY PRIMER
VAPOR INTRUSION CONSIDERATIONS FOR REDEVELOPMENT
1.0 BACKGROUND
Redevelopment of brownfield sites plays an important role in stimulating the economic
revitalization of communities by bringing vacant or underutilized properties into productive use
and offsetting the need to develop open land, or "green space." Along with the normal financial
and business risks associated with developing property, brownfields redevelopers must
manage environmental risk, including that due to vapor intrusion—-the migration of chemical
vapors from contaminated soil and groundwater into buildings. The core message of this
primer is that early consideration of vapor intrusion beginning during the Phase I environmental
site assessment will help ensure that redevelopment protects the health of current and future
building occupants. In addition, incorporating relatively inexpensive mitigation (prevention)
techniques into the construction of new buildings, rather than retrofitting them later, will result
in significant cost savings and help avoid the occurrence of vapor intrusion in the future.
Because there are many available, cost-effective approaches to mitigation, vapor intrusion
need not stand in the way of brownfields redevelopment.
This primer is designed for land revitalization stakeholders1 concerned about vapor intrusion,
including property owners, municipalities, and real estate developers. It provides an overview
of the vapor intrusion issue and how it can affect redevelopment. It also summarizes
techniques for quickly and cost effectively assessing the potential for vapor intrusion, as well
as techniques for mitigating it.
The topics covered will familiarize stakeholders with options for addressing vapor intrusion to
help them communicate with their project contractors and consultants. The "Quick Look" box at
the beginning of each section summarizes the important points that follow. For reference, a list
of acronyms and a glossary are provided in Appendix C. Text boxes throughout the primer and
Appendices B, C, D, and E provide additional detail and resources for those readers who
would like to know more.
1.1 What Is Vapor Intrusion? Vapor intrusion is an exposure pathway—a way that people
may come in contact with environmental contaminants. Vapor intrusion exposes building
occupants to potentially toxic levels of vapors when volatile chemicals (those that readily
evaporate) present in contaminated soil or groundwater emit vapors that migrate into overlying
buildings. It is similar to the more familiar problem of radon, a gas that is emitted naturally from
soil and bedrock and enters buildings through cracks and openings in the foundation and
through porous building materials. (Text box 1.)
Both volatile chemicals and semivolatile chemicals (those that evaporate more slowly) can
pose a vapor intrusion problem. Examples of volatile and semi-volatile chemicals include
degreasers, dry-cleaning solvents, gasoline and petroleum (including benzene), naphthalene,
polychlorinated biphenyls (PCBs), and certain pesticides. Volatile chemicals are primarily
1 This primer is not intended for audiences requiring in-depth technical explanations or guidance related to vapor
intrusion.
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VAPOR INTRUSION CONSIDERATIONS FOR REDEVELOPMENT
A Quick Look at Vapor Intrusion
vy Determining the potential for vapor intrusion should begin early during the Phase I environmental site
assessment.
car Vapor intrusion exists when volatile or semivolatile chemicals in soil or groundwater migrate toward
buildings and enter through cracks and openings in the foundation and walls.
fy Inhalation of vapors may cause chronic and acute health effects.
fy The potential for vapor intrusion exists even though industrial activities may have never occurred on a
property.
US" States may have specific vapor intrusion guidance that needs to be considered.
fff" The Interstate Technology and Regulatory Council's guidance documents describe a "multiple lines of
evidence" approach to assessing vapor intrusion.
tcr Contact environmental agencies to ensure that the most up-to-date and appropriate guidance is followed.
organic but also comprise metallic mercury, which is inorganic. For ease of discussion, this
primer refers to chemicals that may result in vapor intrusion as volatile organic compounds, or
"VOCs." (Other references may refer to "volatile chemicals of concern" or "vapor-forming
chemicals.") However, it distinguishes between volatile and semivolatile, as well as organic
and inorganic chemicals, where
necessary.
As illustrated in Figure 1, VOCs in
contaminated soil and groundwater em it
vapors that rise through the pore space
of the unsaturated zone above the
water table. (Where bedrock underlies a
property, the vapors move through
fractures and openings in the rock.)
These vapors, also known as "soil gas,"
can move laterally as well as vertically
from the source of contamination.
Lateral movement can increase as
groundwater plumes migrate away from
the source of contamination or if the
ground surface is paved or frozen,
preventing escape of vapors upwards.
The movement of soil gas is controlled
by the processes of diffusion and
advection. Diffusion causes vapors to
TEXT Box 1: VAPOR INTRUSION AND RADON
Vapor intrusion is similar to the behavior of radon. As a
result, the mitigation approaches developed for vapor
intrusion are often similar to those for radon. Radon, a
colorless, odorless gas, is formed from the decay of
radium, a radioactive element that occurs naturally in the
bedrock and soil in some areas of the country. Radon
poses a threat to the health of building occupants once the
gas migrates at high enough levels from soil and rock into
homes and the work place. According to EPA estimates,
inhalation of toxic radon decay products is the leading
cause of lung cancer among non-smokers. For more
information and EPA recommended action levels, see:
http://www.epa.gov/radon/healthrisks.html.
Today, testing for radon in buildings is common, as is the
installation of mitigation systems to prevent entry of radon.
Buildings also may be retrofitted to mitigate the problem.
As testimony to the effectiveness of these mitigation
methods, nearly two million radon retrofits have been
installed and more than a half million homes have been
constructed using radon reduction techniques. For more
information on radon mitigation, read EPA's guide, Building
RadonOut (EPA, 2001).
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BROWNFIELDS TECHNOLOGY PRIMER
VAPOR INTRUSION CONSIDERATIONS FOR REDEVELOPMENT
spread from the higher concentrations closest to the source of contamination toward low
concentrations in uncontaminated areas. Advection is the movement of soil gas from areas of
higher to lower pressure.
As diffusion causes vapors to rise through soil or bedrock, they tend to accumulate under
building foundations and other barriers such as pavement. These barriers create a "capping
effect," which inhibits upward movement of vapors. Because of cracks and other openings in
building foundations, these barriers are not impenetrable. Vapor intrusion generally occurs
when advection (movement due to pressure differences) draws vapors indoors via these
openings. The pressure beneath a building is typically higher than the pressure indoors due to
a phenomenon called "building depressurization." Depressurization causes buildings to draw
soil gas indoors. Soil gas that does not pass within the zone of influence of the building will
continue to migrate within the subsurface or escape to the atmosphere. Vapors that pass
within the zone of influence will be drawn in through cracks in the foundation or through
openings associated with utility lines, sump pumps, etc.
Depressurization is caused by "leaky" heating and ventilation systems, exhaust fans, and stack
and wind effects (Figure 1) that reduce the pressure indoors. Stack effects cause building
depressurization as a result of differences in indoor and outdoor temperatures. As warmer
indoor air rises and exits the top of the building, the resulting pressure differences induce
vapor flow into the bottom of the building. Stack effects can transport vapors to upper floors of
a building via stairwells, elevator shafts, ductwork, etc. Wind currents passing over a building
can also cause pressure differences that affect the flow of vapors into the building. For more
information on stack and wind effects, consult EPA's Indoor Air Guide at
http://www.epa.gov/iaq/schools/tfs/guide2.html.
1.2 Why Is Vapor Intrusion a Concern? Vapor intrusion poses a potential risk to the
health of residents, workers, and other occupants who breathe the vapors inside buildings. In
the past, cleanup of brownfields and other contaminated sites focused on protecting human
health by preventing exposure to contaminants through direct contact (e.g., children playing in
contaminated soil) or ingestion (e.g., residents drinking contaminated groundwater from wells).
As we have learned more about vapor intrusion, however, it has become clear that the
potential for risk of inhaling chemical vapors due to vapor intrusion may still need to be
addressed.
If vapor intrusion is a concern at a property to be developed, we recommend that a risk
assessment by qualified personnel be conducted to evaluate the degree of risk to future
building occupants. The question of risk posed to building occupants by vapor intrusion will
depend on the toxicity of the chemical, the concentration of the chemical vapor in the indoor
air, the age and health of the occupants, the amount of time the occupants spend in the
building, and other variables. In rare instances, and in extreme cases, significant buildup of
vapors from a nearby highly contaminated source (e.g., gasoline from leaking underground
storage tanks or methane from landfills) may pose an immediate risk of fire or explosion. In
other cases, at concentration levels often associated with a detectable odor, short-term
exposures may cause acute health effects such as headache, nausea, and eye and respiratory
irritation. But more commonly, the potential risk to building occupants comes from inhaling,
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BROWNFIELDS TECHNOLOGY PRIMER
VAPOR INTRUSION CONSIDERATIONS FOR REDEVELOPMENT
over time, lesser amounts of chemical vapors that have accumulated indoors. The
contamination may not have a detectable odor; however, long-term exposure to even low-
levels of certain vapors may increase the risk of chronic health effects, such as cancer and
other diseases.
Figure 1. Migration of Soil Vapors to Indoor Air. Three conditions must exist for environmental-
contaminant vapors to reach the interior of buildings: vapors from contaminated soil or groundwater must
migrate to the subsurface near the building foundation, entry routes into the building must be present, and
there must be driving forces (e.g., stack and wind effects) present that can move the vapors through these
entry routes (ASTM, 2005).
stack
effects
vapor intrusion
through
floor-wall cracks
,
;
\
vapor intrusion
through cracks in
foundation slab
water table
soil vapor migration
groundwater
plume of VOCs
soil contaminated with VOCs
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BROWNFIELDS TECHNOLOGY PRIMER
VAPOR INTRUSION CONSIDERATIONS FOR REDEVELOPMENT
1.3 Where Is Vapor Intrusion a Concern? Vapor intrusion is a potential concern at any
building—existing or planned—located near soil or groundwater contaminated with VOCs.
EPA's draft guidance for evaluating the vapor intrusion pathway defines "near" as
contamination within 100 feet (laterally or vertically) of buildings, unless there is a conduit that
intersects the soil gas migration route that would allow soil gas to migrate further than 100 feet
(EPA, 2002). A conduit is any passageway, such as a sand or gravel layer, buried utility line, or
animal burrow, that facilitates the flow of soil gas. The guidance further notes that vapor
intrusion is associated with contamination found in the unsaturated zone (the soil above the
water table) or in the uppermost portion of the saturated zone (just below the water table) as
opposed to deep within the saturated zone. Fluctuations in the water table level due to
seasonal precipitation changes or pumping may increase soil gas concentrations where
contamination exists.
Properties with potential VOC contamination are common in industrial and commercial areas.
They include current and former manufacturing and chemical processing plants, warehouses,
landfills, coal gasification plants, train yards, dry cleaners, and gas stations. Improper use,
storage, or transport of chemicals at these facilities may have resulted in a release of
contaminants to the environment creating the potential for future vapor intrusion issues. In
addition to industrial and commercial activities, roadside dumping, pesticide spraying, or even
improper disposal of household chemicals via a septic field may also release contaminants to
the environment. Therefore, the potential for vapor intrusion should be considered at all types
of properties considered for redevelopment.
Even "greenspace" properties that have not previously been occupied or developed may
contain VOC contamination. Because groundwater plumes and soil gas can migrate laterally,
the contamination source need not be on the property to be redeveloped to pose a vapor
intrusion problem. The actual source(s) of vapor intrusion (e.g., landfill wastes, contaminated
soil, or buried drums) may be present on a neighboring property or on a property some
distance away. Depending on the degree of contamination and geology, contaminants
dissolved in groundwater plumes can flow beneath a property from sources located a mile or
two upgradient (in the direction opposite groundwater flow and plume migration). Because of
the large size of migrating groundwater plumes, they may be the greatest contributor to the
vapor intrusion problem.
1.4 How Does Vapor Intrusion Impact Brownfields Redevelopment? Awareness of
vapor intrusion as a potential for exposure to soil and groundwater contamination has raised
concerns about public health risks and liability during property transactions. However, if vapor
intrusion is considered along with other potential exposure pathways commonly evaluated
(e.g., ingestion of or direct contact with soil and groundwater), land revitalization stakeholders
can eliminate potential health risks and facilitate transactions. Early proactive evaluation of
vapor intrusion can make available more options for the mitigation and redevelopment. In
addition, preconstruction mitigation measures are less expensive than post-construction
remediation and structure retrofits.
The potential for vapor intrusion should be considered during the Phase I or the follow-on
Phase II environmental site assessment for any brownfield property transaction. This would
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VAPOR INTRUSION CONSIDERATIONS FOR REDEVELOPMENT
include looking at the past history of the property, neighboring properties, site geology and
hydrogeology, and the condition of existing buildings for conditions conducive to vapor
intrusion. If the potential is found to exist, then an appropriate sampling and analysis plan for
site characterization can be developed in Phase II so that vapor intrusion can be evaluated
and mitigated. (These topics are discussed further in Sections 2.0 and 3.0, respectively.)
Subsequent changes in the use of a property, such as converting an industrial building to loft
apartments, may require reevaluation of the vapor intrusion pathway (EPA, 2002).
The American Society for Testing and Materials (ASTM) is developing a standard to address
vapor intrusion as it can impact real estate transactions (Buonicore, 2006). The standard will
supplement the Phase I environmental site assessment process and can be designed to help
decide whether or not there is a reasonable probability that vapor intrusion could present an
environmental risk or liability.
1.5 How Is Vapor Intrusion Regulated and What Guidance Is Available? Vapor
intrusion is an exposure pathway, and as an exposure pathway, it should be considered by
environmental practitioners when evaluating potential health risks from soil or groundwater
contaminated with VOCs. Both EPA and state agencies recognize the importance of this
pathway and have issued guidance documents to guide practitioners in their assessment of
the vapor intrusion pathway. In addition, several state documents also provide guidance for
evaluating and mitigating the potential health risks. At the time of this writing, however, neither
EPA nor the states regulate how assessments and mitigation must be performed.
Guidance Documents: EPA issued the OSWER2 Draft Guidance for Evaluating the Vapor
Intrusion to Indoor Air Pathway from Groundwater and Soils in 2002. The premise of the
OSWER draft guidance is to use sampling data collected from outside the building, such as
soil gas, sub-slab, and/or groundwater samples discussed in Section 2.2, to estimate indoor air
concentrations of vapors. These estimates are compared to risk-based concentrations for
indoor air in residential settings. The guidance also allows evaluation of non-residential
settings through use of the Johnson and Ettinger or "J&E" model (See Section 2.3). Use of the
OSWER draft guidance is not recommended typically for sites with petroleum-related
contamination, such as former gas stations (Text box 2).
The draft guidance (EPA, 2002) suggests beginning assessment with the development of a
conceptual site model (CSM; a depiction of site conditions, see section 2.1) and leads the user
through a series of questions arranged in a three-tiered approach. If at any time in the three-
tiered approach insufficient data are available to answer the questions posed, the EPA (2002)
draft guidance recommends the collection of additional samples and site information. An
indication of a complete pathway requires an assessment of the risk resulting from breathing
the indoor air. If at any time during the approach the vapor intrusion pathway can be ruled
"incomplete," there is no need to proceed further. However, if site conditions or uses change in
the future, the site would be re-evaluated to determine if a complete pathway has developed
and mitigation is now necessary. For more information on this guidance, see:
http://www.epa.qov/correctiveaction/eis/vapor.htm.
2 OSWER is EPA's Office of Solid Waste and Emergency Response.
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VAPOR INTRUSION CONSIDERATIONS FOR REDEVELOPMENT
The Interstate Technology & Regulatory Council (ITRC)— a coalition of states, the District of
Columbia, tribal and industrial representatives, and several federal partners—recently
published Vapor Intrusion Pathway: A Practical Guideline (2007a), which is a framework
intended for use with existing state and federal guidance or policy. This framework
incorporates multiple lines of evidence and follows a 13-step approach to evaluating the
potential for vapor intrusion. Lines of evidence include the locations of sources, distribution of
groundwater contaminants and soil gas at the site, sub-slab concentrations (soil gas beneath
building foundations), indoor and outdoor air concentrations, background concentrations,
presence of conduits, and building construction plans or details. This approach helps
determine whether a site warrants no further action, additional investigation, or mitigation.
ITRC emphasizes the importance of developing an accurate CSM that is representative of site
conditions, so that it can be used to assist with planning and make sure the site data is used
properly. This guidance also provides detailed information on site investigation and mitigation
approaches.
ITRC's companion document, Vapor Intrusion Pathway: Investigative Approaches for Typical
Scenarios (2007b), walks users through using the guidance for varying scenarios, such as
different contaminated properties (e.g., service station, dry cleaner, and industrial facility) and
different receptors (e.g., residential neighborhood, commercial building, and a vacant lot with
proposed brownfields development).
EPA has also published Guidance for Evaluating Landfill Gas Emissions from Closed or
Abandoned Facilities (EPA, 2005a). This guidance provides procedures and a set of tools for
evaluating landfill gas emissions to ambient air, soil gas migration due to landfill-gas pressure
gradients (differences in pressure), as well as vapor intrusion into buildings. The risks of
inhaling vapors can be evaluated, in addition to the hazards of both on-site and off-site
methane explosions and landfill fires.
TEXT Box 2:
THE DRAFT EPA GUIDANCE AND PETROLEUM-CONTAMINATED SITES
Available scientific literature suggests that petroleum contamination biodegrades more readily
than most other types of VOCs; in other words, microbes found naturally in the soil can break
down petroleum into less harmful compounds relatively quickly. Although the OSWER draft
guidance allows observations of the effects of biodegradation to be considered in its approach,
it does not predict the effects of biodegradation. As a result, application of the draft guidance to
petroleum compounds may overestimate the impact of vapor intrusion, if observations are not
considered. As a result, as mentioned in Section 1.5, the guidance recommends using the
approach documented in Use of Risk-Based Decision Making in UST Corrective Action
Programs (EPA, 1995a) to assess vapor intrusion at petroleum-contaminated sites.
Additional technical information is available from ITRC (2007a, b) and API (2005), while some
state guidance documents, California's and New Jersey's, for example (Appendix B), provide
more specific direction about how to evaluate biodegradation as a factor in reducing vapor
intrusion at petroleum sites.
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VAPOR INTRUSION CONSIDERATIONS FOR REDEVELOPMENT
States: As of this writing, at least 21 states have issued guidance documents dealing with
vapor intrusion. State guidance, where it exists, supersedes the existing EPA guidance
documents. The specific state documents and the URLs for finding them on the Internet are
listed in Appendix A. As is evident by the titles, state guidance documents range in scope and
address varying issues related to vapor intrusion. Several state documents, like Ohio's
Methodology for Vapor Intrusion Assessment, base their approach to assessing vapor intrusion
on the OSWER draft guidance, but have modifications. Therefore, it is recommended that
relevant state agencies be contacted concerning vapor intrusion issues to ensure appropriate
guidance is followed.
Because awareness and concern for vapor intrusion continues to grow and the science and
technology behind it continues to improve, new documents are likely to be published soon and
existing ones replaced. Therefore, stakeholders should contact appropriate state agencies to
ensure that the most up-to-date and appropriate guidance is followed. A list of contacts can be
found at: http://www.itrcweb.Org/vaporintrusionresources/4 2 07VI contact list.xls.
Stakeholders also may contact their EPA Regional Brownfields Coordinator, listed in Table 1,
for information on brownfields and assistance with their vapor intrusion questions.
TEXT Box 3: ITRC's SURVEY OF
STATES ON VAPOR INTRUSION
In 2004, the ITRC conducted a survey regarding
vapor intrusion regulations. A total of 41 state
agencies and Canada responded. The survey
results, which include responses to questions on
the contaminated media, evaluation of risk,
sampling procedures, and mitigation approaches,
are available to view or download at
http://www.itrcweb.org/vaporintrusion/ITRC VI Sur
vey 8-17-05/ITRC 1 VI Survey lndex.htm.
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VAPOR INTRUSION CONSIDERATIONS FOR REDEVELOPMENT
Table 1. EPA Regional Brownfields Coordinators
EPA
Region
1
2
3
4
5
6
7
8
9
10
States/Te rri to ri es
in Region
Connecticut,
Massachusetts,
Maine, New
Hampshire, Rhode
Island, Vermont
New Jersey, New
York, Puerto Rico,
Virgin Islands
District of Columbia,
Delaware, Maryland,
Pennsylvania,
Virginia, West
Virginia
Alabama, Florida,
Georgia, Kentucky,
Mississippi, North
Carolina, South
Carolina, Tennessee
Illinois, Indiana,
Michigan,
Minnesota, Ohio,
Wisconsin
Arkansas,
Louisiana, New
Mexico, Oklahoma,
Texas
Iowa, Kansas,
Missouri, Nebraska
Colorado, Montana,
North Dakota, South
Dakota, Utah,
Wyoming
American Samoa,
Arizona, California,
Guam, Hawaii,
Majuro, Nevada,
Trust Territories
Alaska, Idaho,
Oregon, Washington
Brownfields
Coordinator
Diane Kelley
Ramon Torres
Tom Stolle
Mike Norman
Deborah Orr
Monica Chapa
Smith
Susan Klein
Dan Heffernan
Debbie Schechter
(Acting)
Susan Morales
Phone
(617)918-1424
(212)637-4309
(215)814-3129
(404) 562- 8792
(312) 886-7576
(214)665-6780
(913)551-7786
(303) 312-7074
(415)972-3093
(206) 553-7299
E-mail
kelley. diane@epa.gov
torres.ramon@epa.gov
stolle. tom@epa.gov
norman.michael@epa.gov
orr.deborah@epa.gov
smith.monica@epa.gov
klein.susan@epa.gov
heffernan.daniel@epa.gov
schechter.debbie@epa.gov
morales.susan@epa.gov
Also found at: http://www.epa.gov/swerosps/bf/corcntct.htm
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VAPOR INTRUSION CONSIDERATIONS FOR REDEVELOPMENT
2.0 ASSESSING THE POTENTIAL FOR VAPOR INTRUSION
There are many tools available to environmental practitioners for assessing the potential for
vapor intrusion. This section summarizes several of these tools—conceptual site models,
sampling and analysis equipment, and predictive models—to familiarize land revitalization
stakeholders with common terminology and to understand the state of the science and
technology behind vapor intrusion assessments.
A Quick Look at Assessment
Gathering sufficient information for an accurate conceptual site model is important for assessing vapor
intrusion and determining the appropriate mitigation approaches.
The upfront cost of an early thorough site characterization can be offset by the ultimate cost savings of
installing proper mitigation early and the resulting protection of the health of building occupants.
Information gained from environmental sampling (e.g., groundwater, bulk soil, soil gas, sub-slab soil gas,
and indoor air) and predictive modeling can be used together to build and evolve a conceptual site model.
There are many sampling tools available for assessing vapor intrusion.
Evaluation of vapor intrusion can be complicated by background sources of vapors commonly found in
homes, businesses, and industry.
Predictive model results involve a certain amount of uncertainty, which can be minimized by using as
many site-specific measurements as possible.
2.1 Developing the Conceptual Site Model: Developing a conceptual site model (CSM) is
an important first step for assessing contaminated sites and the potential for vapor intrusion.
Briefly, a CSM is a picture and narrative of the site contamination: how it got there, whether or
not it is migrating or degrading, its distribution across the site, who might be exposed to it, and
what risk-reduction strategies are most feasible. CSM development actually begins during the
Phase I environmental site assessment with collection and evaluation of site history and
reconnaissance information. During subsequent site characterization activities, the CSM can
be augmented and refined, as necessary, with site-specific information on source areas,
contaminant properties, stratigraphy, hydrogeology, exposure pathways, and potential
receptors.
Building and refining a thorough CSM may involve a combination of techniques and tools to
understand the subsurface, but specifically, investigations for vapor intrusion often include
collecting samples of soil, groundwater, soil vapor, and/or indoor air. Investigators may use
sampling in combination with predictive models. These topics are discussed further in Sections
2.2 and 2.3. Gathering sufficient information for a CSM is important for assessing vapor
intrusion and determining cleanup and mitigation approaches. Developing a CSM by
aggregating this information helps focus attention on areas where uncertainties in site
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TEXT Box 4: WHAT is TRIAD?
Triad is a collaborative approach that helps land
revitalization stakeholders work toward faster, better,
and cheaper site characterization and cleanup,
setting the stage for appropriate redevelopment.
information exist, and direct further
information gathering and sampling efforts to
where they may be needed most. Reducing
these uncertainties and developing a robust
CSM can provide more reliable results when
implementing the appropriate approaches to
assessing vapor intrusion, or the predictive
models in Section 2.3.
Sample collection and analysis as well as
other site assessment activities used to
develop the CSM can be expensive; however,
the expense of thorough, upfront
characterization can be offset by the ability to
plan for proper mitigation. Decisions
regarding the number and types of samples to
collect, where to collect them, and how to
analyze them while minimizing costs can be
improved using EPA's Triad approach. (See
Text box 4.) Consistent with the Triad, ITRC
(2007a) describes CSM development as an
iterative sampling process where additional
data is collected only when it is necessary to
meet the needs of "making informed
decisions." EPA encourages Triad in
developing a CSM and managing uncertainty.
More information on development of CSMs
can be found in the draft OSWER (EPA,
2002) and ITRC (2007a) (includes a checklist)
guidances.
2.2 Sampling and Analysis: Collecting
samples for chemical analysis is the primary
way in which a CSM is augmented and
refined with site-specific data. Sampling not
only helps evaluate the amount of
contamination present beneath or inside a
building, it can help environmental
practitioners identify the source and extent of
contamination, possible receptors, and risk levels. The sampling tools and analytical
techniques selected for an investigation will depend, in a large part, on the current CSM.
Table 2 summarizes the advantages and disadvantages of the various options for sampling:
groundwater, bulk soil, soil gas, sub-slab soil gas, and indoor air. The following subsections
briefly describe some of the tools available for collecting these samples. Additional information
Triad uses these guiding principles:
• A systematic planning process, which includes
participation of all stakeholders to determine
the types of data required and to develop a
dynamic work strategy that guides the project
but maintains the flexibility to make decisions
and adapt as data are analyzed.
• Transparent discussion of uncertainty
management, data representativeness, and
end goals.
• An evolving CSM that can be updated and
used at all stages of the project and is updated
through a dynamic work strategy.
• Innovative sampling and data management
technologies to help manage uncertainty
involved in taking and analyzing samples
• Project teams that have effective
communication, trust, and diverse expertise in
appropriate fields.
This framework allows all stakeholders to have the
opportunity to review the same information as they
participate in the decision-making process. Early
Involvement by regulators is important for success.
EPA's Triad Resource Center (www.triadcentral.org')
has resources to guide stakeholders through the
Triad approach.
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on these tools as well as common laboratory and field-based analytical methods for soil gas
and air samples, is contained in Appendix B. Readers seeking more information on sampling
tools and sampling strategies can find it in Appendix B of ITRC's guideline (ITRC, 2007a).
Although not discussed here, supplemental data for the multiple-lines-of-evidence approach,
including differential pressure measurements, meteorological data, and chemical fingerprinting
(ITRC 2007a), may provide valuable information to refine the CSM.
Groundwater and Bulk Soil Sampling: Groundwater sampling helps indicate whether a
source in the unsaturated zone is contaminating groundwater, which may result in vapor
intrusion occurrences downgradient (in the direction of groundwater flow) of the source. The
OSWER draft guidance (EPA, 2002) allows the use of groundwater sampling results to
estimate the vapor concentrations expected inside a building due to vapor intrusion.
The guidance does not recommend that bulk soil samples be used, because it is not possible
to rule out a potential vapor intrusion problem based on soil sample data. However, it may be
possible to show a problem does exist, particularly when the contamination is limited to
semivolatile organic compounds (SVOCs). In any case, both soil and groundwater sampling
are critical in the development of a CSM by helping to locate and delineate potential sources
and plumes, identify potential receptors of contamination, and choose a cleanup approach.
Guidelines for choosing groundwater sampling locations are included in Appendix B.
Soil Gas Sampling: Like groundwater samples, soil gas samples are used in the OSWER
draft guidance to estimate expected indoor air concentrations. Soil gas sampling and analysis
results tend to be most reliable where the contaminant concentrations are high and soils are
more permeable (in other words, they allow for freer movement of soil gas). Soil gas sampling
is limited to the unsaturated zone above the water table and cannot be performed at sites
directly underlain by bedrock or having less than five feet of soil depth.
Soil gas samples collected near a known source of contamination best represent source vapor
concentrations. Collecting soil gas samples that most closely represent the vapor intrusion to a
building often requires collecting soil gas samples close to the building. However, sampling too
close to the building could potentially damage the building or lead to inaccurate results.
Vertical profiling—taking samples at several depths in one location—is recommended to get a
sense of vertical distribution of vapors near the building, although sampling at shallow depths
(less than five feet) is to be avoided due to possible influence of atmospheric or "ambient" air
on the sample (EPA, 2002). For buildings constructed slab on grade, deep soil gas samples
should be collected to offset any bias due to ambient air that could occur by sampling too close
to the ground surface.
Because of the complex distribution of contaminants and soil layers beneath a site, soil gas
concentrations may vary widely across a property. Because soil gas samples are collected
outside the footprint of the building, they may not accurately represent the contaminant
concentrations present under the building as a result of the capping effect. Properties to be
developed with no existing buildings present an additional problem because soil gas samples
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Table 2. Sampling Options for the Assessment of Vapor Intrusion
Option
Pros
Cons
Groundwater
sampling
Indicates whether or not a
contaminant source in the
unsaturated zone is
contaminating groundwater.
Helps assess potential
downgradient impacts of vapor
intrusion.
Can be performed at properties
having no existing buildings.
Does not represent vapor
concentrations at the source.
Requires utility clearance to drill
boring for monitoring well.
Requires legal access agreement
and permit.
Bulk soil sampling
• Search and delineate extent of
contamination in the unsaturated
zone.
• Can be performed at properties
having no existing buildings.
VOC loss on sampling may be
significant.
Vapor concentrations may be
underestimated.
Requires utility clearance to drill
boring.
Requires legal access agreement
and permit.
Soil gas sampling
Near the source, it provides an
estimate of source vapor
concentration.
Near buildings, it can be
performed without entering the
structure.
Can be performed at properties
having no existing buildings.
Significant lateral and vertical spatial
variability.
Results may not be representative of
vapor concentrations under
buildings.
Requires utility clearance to advance
probe.
Requires legal access agreement.
Passive soil gas
survey
Can cost-effectively identify hot
spots or areas of needing
additional investigation.
Easy to perform.
Works better than other soil gas
sampling methods in low-
permeability soil.
Can be performed at properties
having no existing buildings.
Yields semi-quantitative results.
Data reported in mass, not
concentration.
There is a two- to three-week delay
in results.
Sub-slab sampling of
vapors beneath
buildings
Establishes vapor concentration
directly below indoor air space.
Closest subsurface sample to
receptors.
Method is intrusive.
Requires legal access agreement
and entry into buildings.
Cannot be performed at properties
having no existing buildings.
Indoor air sampling
• Indoor air concentrations directly
measured.
Indoor contaminants and lifestyle
sources may bias the data.
Method is intrusive.
Requires legal access agreement
and entry into buildings.
Cannot perform at properties having
no existing buildings.
Table adapted from EPA, 2007.
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Figure 2. Installation of Soil Gas Probe Near a House. Soil gas probes are a
primary method of collecting samples to measure soil-gas chemical concentrations.
Photo Courtesy of H&P Mobile Geochemistry in Carlsbad, CA.
collected from an open field will under-predict concentrations that collect under buildings due
to the capping effect.
Soil gas probes are the primary tools for collecting soil gas samples (Figure 2). Where sub-
slab sampling is impractical, probes can be installed adjacent to a structure at an angle to
sample underneath a building. Care should be taken to avoid significant disturbance of the soil
when installing probes. The installation and use of soil gas probes are explained in Appendix
B.
Passive Soil Gas Survey: A passive soil gas survey is another line of information that can be
used to evaluate soil gas for vapor intrusion. These surveys are often used to direct other
sampling. Passive soil gas samplers consist of an adsorbent material in a container that is
placed in a small-diameter boring in the unsaturated zone, typically at a depth of less than
three feet (Figure 3). The device is left underground for a set period of time—usually one to two
weeks—before the adsorbent material is retrieved and analyzed for masses of contaminants.
Passive soil samplers estimate the total mass of each contaminant (essentially the total
amount measured in grams) accumulated over the time they are left underground—typically
one to two weeks. This approach does not yield concentrations of soil gas contaminants (the
amount per a given volume); thus, the results are not directly comparable to those from soil
gas probes.
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Because the adsorbent material irreversibly
accumulates contaminants and over a
longer period of time than active sampling,
short-term variations in soil gas movement
will have less of an impact on detecting
contaminants, and smaller amounts of
contaminants can be detected.
Use of passive soil gas samplers can help
confirm the presence of contaminants in
soil gas. However, the absence of a
detection of contaminants in a sampler
does not necessarily mean a complete
absence of contaminants in the soil gas, as
soil gas distribution in the subsurface
typically is not uniform and the sampler
may not be located in an optimal area to
intercept the gases.
However, many of these samplers are
usually deployed at once, often in a grid
pattern over the area of concern; and by
comparing contaminant masses measured
across a property, passive soil gas
sampling can augment a CSM by helping
to identify the location of sources, "hot
spots" (areas of high concentrations), and
preferential pathways. Unlike soil gas
probes, passive soil gas samplers can also
be used to detect some SVOCs.
Sub-Slab Sampling: Sub-slab samples
are samples of soil gas collected just
beneath the building foundation, whether a
basement floor or slab-on-grade. Soil gas probes designed specifically for sub-slab sampling
are used to collect samples (Appendix B).
Sub-slab samples should be located beneath areas of the slab where there are no cracks or
openings nearby. Avoiding cracks and openings is important for calculating the attenuation
factor3 that is used in predictive models and vapor intrusion guidance. This may not be easy
because cracks and openings may not be obvious, and furniture, appliances, utilities, etc. may
Figure 3. Examples of Passive Soil Gas
Samplers. Passive samplers measure total mass of
contaminant that accumulates over the time they are
left in the ground. These samplers can add a line of
evidence to the CSM that can help identify hot spots
and preferential pathways.
Top two photos courtesy of Beacon Environmental Services, Inc. Bel
Air, MD. Bottom three photos courtesy of W.L. Gore & Associates,
Inc. Elkton, MD.
The attenuation factor is a measure of how soil and building properties limit the intrusion of organic vapors into
overlying buildings. It is defined as the concentration of the contaminant in the indoor air divided by the
concentration of the contaminant in soil gas orgroundwater.
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limit access to certain desired sampling points. In addition, care must be taken to avoid
structural damage and drilling holes through rebar, utilities, etc.
Sub-slab samples are thought to better represent potential vapor intrusion concentrations and
potential risk than soil gas samples collected outside the building footprint. Additionally,
investigators may use sub-slab samples to distinguish the contribution of vapor intrusion to
indoor concentrations, because sub-slab sampling is generally not biased by indoor sources of
contaminants the way indoor air sampling can be. However, the primary obstacle to obtaining
sub-slab samples, is that they require access to the building and drilling %-inch-diameter holes
in the foundation, which may not be allowed by the building owner.
ITRC's guideline (ITRC, 2007a) includes a rule of thumb that if sub-slab concentrations are
1,000 to 10,000 times greater than the target indoor levels, then the probability of
unacceptable vapor intrusion is sufficient to warrant proactive mitigation without further
characterization. This scenario may not be valid for all sites, but it points out that the property
owner will have to decide when costs of further site characterization are more than mitigation.
Indoor Air Sampling: Where possible, samples of the indoor air should be collected to aid in
the assessment of vapor intrusion. Deciding where and when to collect samples is important
as indoor air and ambient air (the surrounding outdoor air) samples tend to exhibit
considerable degree of variability over time. Concentrations of vapors can vary from home to
home on the same block by a couple of orders of magnitude, and concentrations may rise and
fall seasonally, with higher concentrations during cold months when windows and doors stay
shut and heating systems stay on. During warmer months when windows and doors are open,
vapors are ventilated to the outdoors.
Concentrations within a building are typically higher in the lower level near the sub-slab.
Therefore, indoor air samples should be collected
in the basement, if present, or on the first floor.
Elevated concentrations may also be present in
upper stories, however, as a result of circulation
by heating, venting, and air-conditioning (HVAC)
systems or if a conduit such as a bathroom pipe
connects the lower and upper levels.
TEXT Box 5:
IMPACT OF BACKGROUND SOURCES
ON EVALUATING VAPOR INTRUSION
The evaluation of vapor intrusion is often
complicated by contaminant vapors from other
sources present in most households or
businesses. These sources include cleaning
products, hobby supplies, paints and solvents,
carpet, cigarette smoke, and a host of other
common items. Evaluation can also be
complicated by outdoor sources such as
emissions from gas stations, dry cleaners, and
smokestacks, which can enter the building
through open windows and doors. As a result,
indoor air samples should be considered in
conjunction with sub-slab samples from below
the foundation and ambient air samples to
help distinguish vapor intrusion from these
background sources.
Evaluation of indoor air concentrations can be
complicated by the presence of contaminant
vapors from "background" sources present in
most households and office buildings, such as
cleaning products, hobby supplies, paints and
solvents, carpet, cigarette smoke, dry-cleaned
clothing and a host of other common items. Thus,
an inventory should be conducted prior to indoor
air sampling to identify potential indoor sources of
VOCs and SVOCs that may affect the evaluation.
To minimize the impact of background sources, it
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Figure 4. Air/Soil Vapor Sample Collection Devices: Canister, Sampling
Bags, and Sorbent Tubes. These devices are used to collect air samples so they can be
transported to a laboratory (either on site or off site) for chemical analysis. Some devices may be
left on site for several days or weeks, and some sampling techniques may require property
access. Engaging stakeholders early on is important so they understand the procedure, space,
and time requirements of the sampling/monitoring events that may be required even after
redevelopment and occupancy.
Photos Courtesy of EPA's Raymark OU2 Photo Gallery
(httD://www.eDa.aov/Reaion1/suDerfund/sites/ravmark/ou2Dhotos.htm1 and Environmental Suoolv Comoanv. Inc.
is recommended that a building survey be conducted and obvious sources of indoor air vapors
be removed from the building prior to sampling. All indoor sources may not be immediately
apparent; less-obvious indoor sources such as non-functioning vapor traps on waste lines to
sewer may contribute to indoor air contamination (ITRC 2007a).
In addition to indoor source identification and removal, indoor measurements should be
considered in conjunction with sub-slab measurements to help distinguish vapor intrusion from
background sources within the building. Differences in the ratios of contaminant concentrations
in the sub-slab and the indoor air may suggest which is the primary source of vapors.
Sampling of the outdoor air should also be considered in conjunction with indoor air sampling
to assess the contribution of possible outdoor sources of air pollution, such as a nearby gas
station, highway, or industries.
Figure 4 illustrates some of the sampling devices used to collect indoor air samples. The same
devices are also used to collect soil gas samples from soil vapor probes and sub-slab probes.
These devices are explained further in Appendix B. Appendix B also summarizes the analytical
methods and real-time measurement devices used in the assessment of vapor intrusion.
2.3 Using Predictive Models: Predictive computer models are useful tools for assessing
the potential for vapor intrusion to occur at a property, particularly when limited field
measurements can be collected. However, the results should be used with caution as their
uncertainty increases with the uncertainty of the data input. In the absence of adequate field
measurements, models require that data input be based on assumptions made about the CSM
(e.g., concentrations of contaminants, complexity of the site geology/hydrogeology, and
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characteristics of the building). Models can yield a wide range of results depending on these
assumptions.
Data uncertainty is an issue when interpreting the results of any model—particularly when
making risk-based decisions. Uncertainty in model results can arise from uncertainties in both
data input (i.e., How well do they represent field conditions?) and the model itself (e.g., Does
the conceptual basis for the model adequately represent the site? And, is there sufficient
knowledge to make this determination?) (EPA, 2005b). As described by ITRC (2007a), other
lines of evidence can also be considered. Uncertainty in model results can be minimized by
using as many site-specific measurements as possible for data input to the model. Although
site-specific data are highly recommended, sufficient field measurements are not always
practical or possible at a site due to site access issues. As a result, most models allow for
using estimated values of input parameters or default values based on typical averages cited
in the literature.
A commonly used, screening-level model for assessing vapor intrusion is the Johnson and
Ettinger or"J&E" model (J&E, 1991; Johnson et al., 1998, 1999). (Use of the J&E model may
be suggested in the second and third tiers of the vapor intrusion assessment approach
described in the OSWER draft guidance.) This model simulates one-dimensional diffusion of
soil gas through unsaturated soil and both diffusion and advection through the building
foundation. The J&E model is based on a number of simplifying assumptions regarding
contaminant distribution and occurrence, subsurface characteristics, vapor transport, and
building construction. The J&E model should be used only when site conditions match the
model assumptions using reasonable, site-specific, or regulator-approved input (EPA, 2004a).
The J&E model can be used to calculate the expected contaminant concentration in indoor air
given a measured or estimated concentration in soil gas or groundwater. Or, it can be used to
calculate the allowable building concentration given for a specified increased cancer risk or
hazard quotient (used to define non-cancer risks) for a residential scenario. For ease of use,
EPA incorporated the J&E model into Excel spreadsheets (available for download at:
http://www.epa.qov/oswer/riskassessment/airmodel/iohnson ettinqer.htm. Click on "3-Phase
System Models and Soil Gas Models.")
TEXT Box 6:
TYPES OF PREDICTIVE MODELS
EPA's paper, Review of Recent Research on Vapor
Intrusion (EPA, 2005c), summarizes and provide
sources for further information on several of the
predictive models and equations used to evaluate the
vapor intrusion pathway. More recently developed
numerical models allow for three-dimensional
movement of soil gas (Abreu and Johnson, 2005).
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3.0 MITIGATION OF VAPOR INTRUSION
Whether existing structures will be renovated or new buildings constructed, vapor intrusion can
be mitigated at brownfield sites. Eliminating the source of contamination can be more
protective of human health and the environment than mitigation alone, but it may not be
technically feasible, cost effective, or well suited to site redevelopment (EPA, 2004b).
Depending on the nature of contamination present, source elimination may involve a
combination of activities, such as excavating contaminated soil for treatment and disposal,
pumping and treating groundwater plumes, or soil vapor extraction to remove vapors. There
also are a number of remediation technologies available to treat soil and groundwater in place,
which avoids the hazard and added expense of handling and disposing large volumes of waste
(http://www.cluin.org/techfocus/).
Eliminating the source of contamination is unlikely to immediately protect building occupants
from vapor intrusion, however. Because remediation can take years, institutional controls (Text
box 7) may be required to prevent or limit development of certain parcels until cleanup has
sufficiently reduced risks. In addition, mitigation may be necessary. For example, existing
buildings may need to be retrofitted with vapor mitigation systems, and new construction may
require design elements that incorporate the mitigation of vapor intrusion. This section focuses
on both passive and active mitigation methods for vapor intrusion. Treatment of the indoor air
itself is not considered here because this approach is not common, and treatment systems are
expensive to install and operate as well as difficult to maintain.
A Quick Look at Mitigation
Mitigation approaches should be considered during the development of the CSM (See
Section 2).
Eliminating the source of contamination can be the best way to prevent vapor intrusion,
but source elimination may not be technically feasible, abate immediate risks, or
affordable.
or Early awareness and consideration of the potential for vapor intrusion facilitates use of
mitigation strategies before building occupants can be exposed to harmful vapors.
Proactively incorporating mitigation strategies into new construction provides more
options for mitigation.
Mitigation strategies used in construction of new buildings are more cost effective and
tend to function better than retrofits.
Institutional controls may be required to inform owners and occupants of the vapor
intrusion mitigation measures and to ensure ongoing operation of those systems.
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Note that mitigation methods for vapor intrusion T R
are similar to those for radon gas (EPA, 1994), ' EXT box ':
WHAT ARE INSTITUTIONAL
CONTROLS?
Institutional controls are legal or administrative
actions that help minimize the potential for
human exposure to contamination by ensuring
appropriate land or resource use. Examples
include restrictive covenants, zoning
restrictions, and special building permit
requirements.
but due to the much lower target vapor
concentrations the design and performance
assessment of such systems requires a more
robust approach.
3.1 Passive Mitigation Methods: Passive
mitigation methods to vapor intrusion generally
prevent vapor intrusion by blocking entry
through the building foundation. It is usually
simpler and more cost-effective to prevent the
entry of soil vapor than remove soil vapors using
active approaches, although active mitigation methods are generally more effective at meeting
regulatory standards for the vapor intrusion pathway. Selection of approach will depend on site
circumstances, including the amount of contaminant reduction in the vapor required. The
primary passive approaches are to seal cracks, install a passive barrier, and install a passive
venting system.
Sealing Cracks: Cracks and openings in the building foundation are the primary routes of
vapor entry. Thus, sealing cracks in the floors and walls as well as gaps around utility conduits
is an important first step in preventing vapor intrusion. Similarly, gaps around utilities, sumps,
and elevator shafts also should be properly sealed. Sealing cracks and gaps may also be
necessary when used with other mitigation strategies, such as sub-slab depressurization to
ensure efficiency.
In existing buildings, cracks may be difficult to find, and as buildings age, more cracks tend to
appear and seals tend to fail. Buildings that are in seismically active areas may be particularly
prone to additional cracking and compromising of existing seals. And despite sealing cracks,
walls made of porous cinder blocks may still allow vapor entry.
In studies of radon gas, a thorough job of sealing cracks and openings typically only results in
a 50-70 percent reduction in radon entry (EPA, 1988). As a result, EPA does not recommend
radon mitigation solely by sealing cracks because this approach has not been shown to lower
levels significantly or consistently (EPA, 2003). Thus, additional mitigation also may be needed
to prevent vapor intrusion.
Passive Barriers: Passive barriers are materials or structures installed below a building to
block the entry of vapors (ITRC, 2007a). Barriers are usually installed during construction, but
they can be installed in existing buildings with a crawl space, if needed. Typically, a passive
barrier comprises a sheet of polyethylene plastic or equivalent geomembrane installed beneath
a slab-on-grade foundation and sealed to the foundation walls or footings. The seams created
by the overlapping sheets must be completely sealed as well. Passive barriers are only
effective if they are not compromised by holes, tears, or a poor seal around the foundation, so
their integrity must be tested after installation. Passive barriers without an underlying venting
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layer are not likely to be effective unless the subsurface conditions are conducive to natural
venting (ITRC, 2007a).
Passive Venting: Where vapor intrusion may be anticipated in new construction, passive
venting systems may be used to safeguard against vapor intrusion. These systems are often
combined with passive barriers. Typically, perforated collection pipes are installed in a layer of
permeable sand or gravel to direct vapors to the edges of the foundation. Often, such
collection pipes are connected to a main header point that runs up through or along the
building's inner or outer wall and exhausts above the roofline. If the permeable layer is vented
directly to the atmosphere, no exhaust pipes are needed.
Because passive systems rely on wind currents to induce vapor flow through the pipes, they
are ineffective at removing vapors on days that aren't windy. If the wind blows toward the
exhaust pipe at the roof line, it may blow vapors back down to the sub-slab region. Thus,
active systems (Section 3.2), which use electric fans to induce vapor flow, are more
consistently effective at mitigating vapor intrusion. Passive venting systems can be converted
to an active depressurization system when needed.
3.2 Active Mitigation Methods: Active approaches to mitigating vapor intrusion remove
the driving force behind vapor migration, which is the higher pressure that exists in the sub-
slab area relative to indoors. By lowering the pressure beneath the sub-slab or passive barrier
or inducing a higher pressure in the building, vapor flow is neutralized or reversed.
Depressurization: There are several types of depressurization systems, including sub-slab
depressurization (also called sub-slab suction), sub-membrane depressurization, block-wall
suction, and drain-tile suction. In most instances, mitigation of residential structures requires a
sub-slab depressurization system (Mosley, 2005), which can be installed in houses with
basements or slab-on-grade construction. They are similar to passive venting systems, except
that they include a fan to induce a level of sub-slab depressurization that compensates for the
depressurization of the building. In practice, these systems often operate by sweeping
contaminated soil vapor from the sub-slab region (Figure 5). Installed properly, these fans
should operate quietly without disruption to building occupants. Depressurization systems offer
the added benefit of reducing radon concentrations, moisture, and mold (Mosley, 2005).
In existing buildings, holes are drilled into the
sub-slab for installation of 4-inch diameter
vertical PVC pipes. The optimum location for the
pipes is near the center of the sub-slab; however,
this location is often inconvenient to building
occupants. Therefore, pipes are more likely to be
installed at the perimeter of a room, but should
not be too close to the building footing to avoid
short circuiting of ambient air down the exterior
wall. The pipes are connected by manifold and
equipped with a fan (typically made of PVC to
prevent corrosion) to draw vapors up the pipe, or
TEXT Box 8:
FOR MORE INFORMATION ON
MITIGATION...
A more detailed discussion of mitigation
methods, including pros and cons of each
method and a comparison of typical
applications and costs, can be found in Section
4 of ITRC's recent guideline (ITRC, 2007a) and
in Table 1 of EPA, 2007. Appendix X2 of ASTM
E 2435-05 also details design, installation, and
maintenance for engineering controls (i.e.,
mitigation technologies).
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Exhaust
Piping
Figure 5. Schematic of Active Soil Depressurization System. This system
provides a pathway for the vapors to vent to the outside air, instead of migrating into the
building. Consideration of possible mitigation processes should be considered before the
characterization process so that key design parameters can be evaluated during the field
investigations. For more information see ASTM E2435-05, 2005.
Figure Source: New Jersey Department of Environmental Protection fact sheet on Subsurface Depression Systems
(www.nj.gov/dep/srp/community/factsheets/subsurface01.pdf.)
stack. The stack is vented to the outdoors at the top of the building in accordance with ASTM
2121. Although the location of the stack vent is usually at the discretion of the owner, care
should be taken to position it so that it is not near a window, deck, or other location where air
can be inhaled or drawn back into the building or neighboring buildings. If the soil beneath the
building is not very permeable or if the gravel subbase is discontinuous, additional suction
points may be needed. After installation, a demonstration of a negative pressure under the
entire slab can be used to confirm the performance of the system.
Submembrane depressurization systems are similar to sub-slab depressurization systems
except that they are installed below the passive barrier during construction, or can be
retrofitted in buildings with crawl spaces. The vertical pipes that penetrate the passive barrier
should be well sealed. Block-wall suction systems involve the removal of vapors that
accumulate in basement walls constructed of hollow blocks. Drain-tile suction systems apply
suction to existing water drainage systems that circle a building, in order to remove vapors.
Sub-slab Soil Pressurization: A sub-slab soil pressurization system is similar to a
depressurization system except that the fan is reversed to pressurize the sub-slab and divert
flow away from the foundation. This approach is only used for high permeability soil and when
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other options fail. It is generally not recommended because it can exacerbate vapor intrusion in
some situations.
Building Pressurization: Building pressurization involves adjusting the building's heating,
ventilation, and air-conditioning (HVAC) system or installing a new system to maintain a
positive pressure indoors relative to the sub-slab area. This approach is more common for
large commercial buildings and can be the most cost effective if the existing HVAC system
already maintains a positive pressure (ITRC, 2007a). Having to increase the pressure will
result in larger energy costs, particularly if significant heating and cooling is required.
Replacing an HVAC system will be significantly more expensive.
Modifications to an HVAC system should be designed to avoid condensation of water resulting
from excessive humidity. Excess moisture can foster the growth of mold, which has significant
negative impacts on indoor air quality and potentially the health of building occupants.
Conversely, in some climates HVAC modifications might lead to uncomfortably low levels of
humidity (EPA, 2007b).
3.3 Strategies for New Construction: New construction affords the opportunity to plan a
redevelopment according to the CSM. For example, new building construction could be
targeted to the portions of the site that are least prone to vapor intrusion, such as those areas
furthest from the contaminant source or upgradient of a groundwater plume. In addition,
construction could incorporate strategies that minimize vapor intrusion induced by stack and
wind effects and ventilate vapors. Such strategies include using a raised building design or
including an open-air parking garage on the lower level of the building. Plans for new buildings
could also proactively consider the potential for vapor intrusion by incorporating mitigation
strategies into construction.
Buildings should be designed and constructed to minimize potential entry pathways for vapors
and minimize the pressure differences that draw them in. Examples of design elements that
can be evaluated include elevator shafts (and drains), utility corridors and penetrations, and
basement sumps. HVAC systems in new construction can be designed to limit entry pathways
and conduits, and/or create positive pressure inside the building. Incorporating vapor intrusion
mitigation strategies into new construction provides more options for mitigation and can save
costs in the long run. For example, aggregate placed beneath the foundation slab and the
installation of passive ventilation systems can facilitate incorporation of further post-
construction mitigation systems. Another possibility is configuring radon mitigation systems,
required in high-radon areas, to mitigate vapor intrusion as well.
It is estimated that incorporating mitigation strategies in residential-building (typical single-
family home) design costs from $120 to $1000-or only 15-40 percent of the $800-$2500 cost
of retrofitting the building later (Mosley, 2006). Not only are they more cost effective, but
systems incorporated into new construction tend to function better than retrofits. Thus, it can
be beneficial both in terms of costs and functionality to install a passive barrier and passive
venting system in the anticipation that vapor intrusion may occur, even if it is not currently a
problem.
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3.4 Operation and Maintenance of Residential Systems: Land revitalization stakeholders
should be involved in helping their consultants develop an operation and maintenance (O&M)
plan that identifies who will be responsible for the O&M of residential systems and for how
long. Over time, breakdowns in the system can occur. Fans may need to be serviced, leaks
may develop, or exhaust stacks may break. When a system is installed, it should be
understood by all stakeholders who will be responsible for O&M: e.g., the building owner or
lessee, developer, or overseeing regulatory agency. Also, they should decide how long the
system may need to operate to meet treatment objectives: e.g., until the groundwater plume is
treated, until contaminant concentrations are no longer detected in indoor air, or as long as the
building is occupied. Additional considerations include: Will samples be collected to ensure the
system is functioning and that venting to the atmosphere does not result in additional risk to
people nearby? And, who will collect and analyze the samples?
If the building owner/lessee is responsible for O&M, this should be understood at the time of
purchase through, for example, a maintenance agreement along with information about whom
to call with questions or problems. Typically, if the property falls under the domain of a
regulatory program such as CERCLA, the regulatory agency overseeing cleanup will be
responsible for conducting or overseeing monitoring system performance and/or monitoring
indoor air to ensure risk levels are not exceeded. This communication about vapor intrusion
and the O&M of a mitigation system can be critically important. For example, building owners
may be concerned about the electrical costs for operating a system, and decide to turn off the
system. However, a typical residential sub-slab depressurization system requires negligible
power compared to home appliances and lighting. Therefore, turning off the system may save
little in relative costs, and the system will now likely be less consistent and effective in reducing
the vapor concentrations inside the building.
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4.0 CONCLUSIONS
Vapor intrusion is an exposure pathway that potentially affects thousands of brownfield sites
considered for redevelopment, and even sites that have no known history of contamination or
industrial activities. It is important for land revitalization stakeholders involved in brownfields
redevelopment to recognize the potential for vapor intrusion to avoid liability, construction
delays, and expense. The key to cost-effective and comprehensive solutions to vapor intrusion
is considering the issue early in the redevelopment process— before final building design and
construction. Early consideration makes available more options for cleanup, prevention, and
abatement. It also saves money and time in the long run, thus ensuring that the vapor intrusion
pathway is not a deal breaker when it comes to redevelopment.
Interest in investigating this pathway continues to grow and development of new and reliable
means for sampling and analysis is occurring at the federal and state levels. Many states have
already issued guidance, and others are in the process of developing new guidance regarding
sampling, modeling, and risk assessment for vapor intrusion.
A thorough CSM incorporating adequate site characterization is an important tool that can
assist decision-makers with ensuring that redevelopment can protect human health. A
collaborative, systematic approach that includes all appropriate stakeholders will ensure
progress. There are several sampling techniques already available to aid in vapor intrusion
investigations, including some real-time measurement technologies that are a key component
of Triad. Proven and relatively inexpensive prevention and abatement technologies are
available to eliminate vapor intrusion risk.
For more information on addressing vapor intrusion sites, please contact the Brownfields and
Land Revitalization Technology Support Center (BTSC). Information on the BTSC and support
contacts for both brownfields and Superfund sites are listed on http://www.brownfieldstsc.orq/.
Updates will be posted as they become available.
Other sources of information include:
• The EPA Ground Water and Ecosystems Research Division's summaries of its vapor
intrusion related research at http://www. epa. qov/ada/topics/vapor. htm I.
• EPA documents related to vapor intrusion, many of which are archived online at the
Technology Innovation and Field Service Division's (TIFSD) CLeanUp Information
(CLU-IN) website at www.cluin.org.
• The Triad Resource Center (www.triadcentral.org), a website maintained by TIFSD,
which is devoted to providing information that hazardous waste site managers and
cleanup practitioners need to implement the Triad approach effectively.
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The Indoor Air Vapor Intrusion Database (http://iavi.rti.org), which allows regulators and
other stakeholders to submit site-specific vapor-intrusion data to support development
of screening-level predictions of vapor attenuation. The website also lists upcoming
vapor intrusion workshops and conferences and provides links to guidance documents
and other references.
The references listed in Appendix D of this document.
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APPENDIX A: Know Your State! Available State Guidance Regarding Vapor Intrusion
State
Available Guidance4
Alaska
Evaluation of Vapor Intrusion Pathway at Contaminated Sites (Draft), 16 pp, 2006.
http://www.dec.state.ak.us/spar/csp/guidance/draft vap intr tm 6 28.doc
Inhalation of Diesel Vapor in Indoor Air, Technical Memorandum 02-001, 7 pp, 2002.
http://www.dec.state.ak.us/spar/csp/guidance/indoor air 12 02.pdf
California
Guidance for Assessing Exposures and Health Risks at Existing and Proposed School Sites, Excel spreadsheet for
calculating risk, updated July 12, 2006.
http://www.oehha.ca.gov/public info/public/kids/schools2604.html
Screening for Environmental Concerns at Sites with Contaminated Soil and Groundwater, Interim Final, 2005.
http://www.swrcb.ca.gov/rwqcb2/esl.htm
Use of California Human Health Screening Levels (CHHSLs) in Evaluation of Contaminated Properties, 67 pp, 2005.
http://www.calepa.ca.gov/Brownfields/documents/2005/CHHSLsGuide.pdf
Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air, 105 pp, 2004. (Revised
February 7, 2005)
http://www.dtsc.ca.gov/AssessingRisk/upload/HERD POL Eval Subsurface Vapor Intrusion interim final.pdf
Advisory - Active Soil Gas Investigations, 25 pp, 2003.
http://www.dtsc.ca.gov/loader.cfm?url=/commonspot/security/getfile.cfm&pageid=94677
CalTOX: A Total Exposure Model for Hazardous Waste Sites
http://www.dtsc.ca.gov/AssessingRisk/ctox dwn.cfm
Colorado
Policy on an Interim Risk Evaluation and Management Approach forPCE, 3 pp, 2006.
http://www.cdphe.state.co.us/hm/pcepolicy.pdf
Policy on an Interim Risk Evaluation and Management Approach for TCE, 2 pp, 2006.
http://www.cdphe.state.co.us/hm/tcepolicv.pdf
Draft Indoor Air Guidance, 58 pp, 2004.
http://www.cdphe.state.co.us/hm/indoorair.pdf
Guidance for Analysis of Indoor Air Samples, 9 pp, 2000.
http://www.cdphe.state.co.us/hm/airsmpl.pdf
Petroleum Storage Tank Owner/Operator Guidance Document, 45 pp, 1999.
http://oil.cdle.state.co.us/OIL/Technical/Guidance%20Documents/guidancedoc.asp
List is current as of April 2007.
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Connecticut
Significant Environmental Hazard Condition Notification Threshold Concentrations, Reference Table A: Volatile Organic
Substances, 2005.
http://ct.gov/dep/cwp/view.asp?a=2715&q=324964&depNav GID=1626
Connecticut's Remediation Standard Regulations Volatilization Criteria: Proposed Revisions, 50 pp, 2003.
http://ct.gov/dep/cwp/view.asp?a=2715&q=325012
http://ct.gov/dep/lib/dep/site clean up/remediation regulations/RvVolCh.pdf
Delaware
Policy Concerning the Investigation, Risk Determination and Remediation for the Vapor Intrusion Pathway, 32 pp,
March 2007.
http://www.dnrec.state.de.us/dnrec2000/Divisions/AWM/sirb/policy%20concern07008.pdf
Idaho
Risk Evaluation Manual, Appendix C: Evaluation of the Indoor Air Inhalation Pathway, 2004.
http://www.deq.idaho.gov/Applications/Brownfields/download/appx all.pdf
Indiana
Indiana's pilot program guidance is intended to provide interim guidance, not requirements, for site investigation.
Indiana Department of Environmental Management Draft Vapor Intrusion Pilot Program Guidance, 90 pp, April 26,
2006.
http://www.in.gov/idem/catalog/factsheets/la-712-fs.pdf
Louisiana
Risk Evaluation/Corrective Action Program (RECAP), 119 pp, October 20, 2003
http://www.deg.louisiana.gov/portal/tabid/131/Default.aspx
Maine
Edited/Adapted Field Guideline for Protecting Residents from Inhalation Exposure to Petroleum Vapors, 34 pp, 2000.
http://www.maine.gov/dep/rwm/petroleum/pdf/inhaexpfg.pdf
Guideline for Protecting Residents from Inhalation Exposure to Petroleum Vapors, 271 pp, 1998.
http://www.maine.gov/dep/rwm/petroleum/pdf/inhalexp.pdf
Massachusetts
Indoor Air Sampling and Evaluation Guide, WSC Policy #02-430, 157 pp, 2002.
http://www.mass.gov/dep/cleanup/laws/02-430.pdf
Guidelines for the Design, Installation, and Operation of Sub-Slab Depressurization Systems, 15 pp, December 1995.
http://www.mass.gov/dep/cleanup/laws/ssd1e.pdf
Massachusetts Contingency Plan Numerical Standards: GW-2
http://www.mass.gov/dep/cleanup/laws/gw2.htm
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Michigan
RRD Operational Memorandum No. 1: Part 201 Generic Cleanup Criteria/Part 213 Risk Based Cleanup Levels, 2004.
http://www.michigan.goV/deq/0.1607.7-135-3311 4109 9846 30022-101581-.00.html
Sampling and Analysis, Attachment 3: Indoor Air Designated Methods and Target Detection Limits, RRD Operational
Memorandum No. 2, 7 pp, 2004.
http://www.deq.state.mi.us/documents/deq-rrd-OpMemo 2 Attachment3.pdf
Technical Memorandum: Residential Soil Volatilization to Indoor Air, Inhalation Criteria for Trichloroethylene (CAS# 79-
01-6), 33 pp, 2004. http://www.michigan.gov/documents/mshda mf tee volatilization 114937 7.pdf
Evaluation of the Michigan Department of Environmental Quality's Generic Groundwaterand Soil Volitization [sic] to
Indoor Air Inhalation Criteria, 67 pp, 2001.
http://www.michigan.gov/documents/iirept 3693 7.pdf
Part 201: Generic Groundwaterand Soil Volatilization to Indoor Air Inhalation Criteria: Technical Support Document, 39
pp, 1998.
http://www.deq.state.mi.us/documents/deq-erd-tsd5.pdf
Part 213, Risk-Based Screening Levels (RBSLs) for Groundwaterand Soil Volatilization to Indoor Air, Operational
Memorandum No. 4, Attachment 8, 38 pp, 1998.
http://www.deq.state.mi.us/documents/deq-std-op4att8.pdf
Minnesota
Indoor Air Sampling at VOC Contaminated Sites: Introduction, Methods, and Interpretation of Results, 17 pp, 2004.
http://www.health.state.mn.us/divs/eh/hazardous/topics/iasampling.pdf
Vapor Intrusion Assessments Performed During Site Investigations, Guidance Document 4-01 a, 13 pp, 2005.
http://www.pca.state.mn.us/publications/c-prp4-01a.pdf
Missouri
Missouri Risk-Based Corrective Action (MRBCA) Technical Guidance, Appendix H: Measurement of Soil Vapor Levels,
16 pp, 2006.
http://www.dnr.mo.qov/env/hwp/mrbca/mrbca.htm
Missouri Risk-Based Corrective Action (MRBCA) Process for Petroleum Storage Tank Sites, Appendix C: Evaluation of
Indoor Inhalation Pathway, 9 pp, 2004.
http://www.dnr.mo.qov/env/hwp/tanks/mrbca-pet/docs/mrbca-pet-appendix-c.pdf
Nebraska
Nebraska has no individual guidance. However, the topic of vapor intrusion is discussed in Risk-Based Corrective
Action (RBCA) at Petroleum Release Sites: Tier 1/Tier 2 Assessments & Reports, 2004.
http://www.deq.state.ne.us/Publica.nsf/a9f87abbcc29fa1f8625687700625436/66fdec793aefc4b286256a93005b8db87O
penDocument
New
Hampshire
Vapor Intrusion Guidance, 44 pp, July 2006.
http://www.des.state.nh.us/orcb/doclist/pdf/vapor intrusion.pdf
GW-2 Methodology, 2 pp, 2006.
http://www.des.state.nh.us/orcb/doclist/pdf/Revised GW-2 Methodoloqy.pdf
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New Jersey
New York
Ohio
Oregon
Pennsylvania
Wisconsin
New Jersey Johnson & Ettinger Spreadsheets, 2006.
http://www.ni.aov/dep/srp/auidance/vaporintrusion/niie.htm
Several reports at http://www.ni. qov/dep/srp/quidance/vaporintrusion/ includinq:
Vapor Intrusion Guidance, 282 pp, 2005
http://www.ni.aov/dep/srp/auidance/vaporintrusion/via.htm
Indoor Air VOC Sampling and Analysis Requirements, 2 pp, 2003
http://www.ni.aov/dep/srp/auidance/vaporintrusion/ia samplina rea.pdf
Several reports at http://www.health.state.ny.us/environmental/indoors/vapor intrusion/ includina:
Guidance for Evaluating Soil Vapor Intrusion in the State of New York, 2006
http://www.health.state.nv.us/environmental/investiaations/soil aas/svi auidance/
Strategy For Evaluating Soil Vapor Intrusion at Remedial Sites in New York (DER-13), 16 pp, 2006.
http://www.dec.state.nv.us/website/der/taams/der13.pdf or http://www.dec.state.nv.us/website/der/auidance/vapor/
Indoor Air Sampling and Analysis Guidance, 4 pp, 2005.
http://www.health.state.nv.us/environmental/indoors/air/auidance.htm
Methodology for Vapor Intrusion Assessment, 4 pp, 2005.
http://www.epa.state.oh.us/derr/rules/vapor.pdf
Screening Model for Volatilization from Soil to Indoor Air at Heating Oil Tank Sites (Excel spreadsheet to be used with
Risk-Based Decision Making for the Remediation of Petroleum-Contaminated Sites at
http://www.dea.state.or.us/la/rbdm.htm).
http://www.dea.state.or.us/la/tanks/hot/screeninamodel.htm
Section IV.A.4, "Vapor Intrusion into Buildings from Groundwater and Soil under the Act 2 Statewide Health Standard,"
(26 pp, 2002) in the Recycling Program Technical Guidance Manual.
http://www.dep.state.pa.us/dep/subiect/advcoun/cleanup/2002/BoldedVaporGuidance 100702.pdf
Chemical Vapor Intrusion and Residential Indoor Air: Guidance for Environmental Consultants and Contractors, 16 pp,
2003. [Provides background on vapor intrusion but basically refers readers to EPA guidance and the Johnson and
Ettinger model.]
http://www.dhfs.wisconsin.aov/eh/Air/fs/VI prof.htm
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APPENDIX B: Additional Sampling and Analysis Information
Groundwater and Bulk Soil Sampling: When collecting groundwater samples for the
assessment of groundwater plumes that are suspected to be a cause of vapor intrusion, it is
recommended that samples be collected near the source at locations selected to determine
representative concentrations under the building. Sufficient sampling should be conducted to
understand the extent of the plume. Both traditional drill rig and direct push technologies can
be used to install permanent monitoring wells or point-in-time (temporary) groundwater
sampling points (EPA, 1991; EPA, 2005d). Similarly both technologies can be used to advance
borings to sample soil. Both soil and groundwater samples should be collected so as to
minimize the loss of VOCs in the sample due to volatilization. In addition, when collecting
groundwater samples for the purpose of assessing the vapor intrusion pathway, samples
should be collected from the upper portion of the groundwater column at or near the water
table because the soil gas from a groundwater source diffuses from the portion of the
contaminant plume nearest the water table.
Confidence in groundwater data can be increased through the use of a short screened interval
across the surface of the water table, the use of low-flow sampling procedures, and a variety of
other depth-discrete sampling protocols (EPA, 2002). Possible fluctuations in water table
elevation would need to be considered when positioning screens in permanent monitoring
wells. The possibility of seasonal variations in the water table or plume diving (where a plume
is forced progressively deeper with increasing distance from the contaminant source as
precipitation recharges the water table) should be considered as well.
Appendix E of the EPA draft guidance provides a list of standards for groundwater sampling,
published by ASTM.
Soil Gas Sampling: Soil gas probes are the primary method of collecting samples to measure
concentrations of contaminants in soil gas. The American Petroleum Institute (API) also
suggests two alternatives to soil gas probes—passive soil gas samplers and flux chambers—for
use in instances where probes are not practicable, such as where site access is limited for
probe installation or where soil is fine-grained or has high moisture content. These devices
measure contaminant mass and mass flux, respectively, rather than contaminant
concentration. By using several of these devices to collect samples across an unpaved area, it
may be possible to measure the potential or relative potential of vapor intrusion at sites at
which development is planned in the future. If the area is paved a small portion of the paving
can be removed to allow for installation.
Soil gas probes are narrow-diameter, hollow, copper or stainless steel rods installed vertically
into the soil to withdraw soil gas at depth for analysis. The rods can be installed in small
augered borings, or by direct push technology or drilling, which is typically quicker and less
expensive. In some situations, probes can be installed at an angle to sample underneath a
building, rather than adjacent to it. Care should be taken to avoid significant disturbance of the
soil when installing probes.
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Soil gas probes are most effective at collecting samples in permeable soil having little
moisture. Soil gas enters the rods through the bottom opening or a short (6- to 12-inch) screen,
which is positioned at a depth of interest. The length of rods is attached to a sampling tube and
a sampling device (as described later in this section) near the sampling location. The probe is
first purged of standing air to ensure a more representative sample.
The gap between the soil gas probe and sampling tube must be well sealed to prevent dilution
of the sample with ambient air (the outdoor air surrounding the property of interest). Tracer
gases have been suggested for use as a quality assurance/ quality control (QA/QC) device to
verify integrity of the soil gas probe seal and determine if the sample is being diluted by
surface air during collection (New York Department of Health, 2005). A container, such as
cardboard box or a plastic bag, is placed over the probe and filled with one of many possible
tracer gases. A soil vapor sample is collected from the probe and analyzed for the tracer gas.
A concentration of more than 20 percent of the tracer is considered evidence of surface air
infiltration of the sample.
The American Petroleum Institute (API, 2005) describes and compares the probe installation
options, how to collect and analyze soil vapor samples, and how to interpret the results. The
discussion is geared toward petroleum-contaminated sites, but much of the information can be
applied to other VOC sites as well.
Sub-Slab Sampling: To identify optimum sub-slab sampling locations, a reconnaissance of
the building should be performed prior to sampling to locate any cracks or openings in the
foundation and to find out if the building owner has any concerns with proposed sampling
locations. Due to possible impact of wind on sub-slab concentrations, atmospheric conditions
should be monitored at the time of sampling, and sampling should be avoided on unusually
windy days. It is also recommended that two or three samples be collected at each building, if
possible (EPA, 2006a).
Sub-slab probes are constructed of a brass or stainless steel, narrow-diameter tube inserted
into a hole drilled through the foundation and into the underlying soil. The hole can be drilled
with a hand-held, rotary hammer drill. The upper few inches of the annulus between the tube
and the drilled hole is sealed flush to the floor with grout to prevent extraction of indoor air and
dilution of the sample. Between samples, the top of the tube is covered with a threaded cap,
which can be installed flush with floor level so it does not protrude into the living space. Soil
gas samples are withdrawn and analyzed from the sub-slab probes in the same manner as soil
gas probes. These probes can be used to design and assess the performance of mitigation
systems, if such systems are needed.
In the absence of a standard sub-slab probe installation and sampling method, EPA's Office of
Research and Development (ORD) and Region 1 recently developed an installation method
that was tested in a vapor intrusion investigation at the Raymark Superfund Site (EPA, 2006b).
ORD's probe installation method involves counter sinking a small hole within a larger hole in
the foundation. The probe fits flush in the 1-inch-diameter outer hole, which is drilled into the
top 1 inch of the slab. A %-inch diameter inner hole penetrated the slab and about 2 inches of
the sub-slab material to provide an opening and prevent clogging of the probe. Use of a screen
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was unnecessary. The annular space between the holes was grouted to ensure a tight seal.
EPA's Environmental Response Team subsequently redesigned the probe using
chromatographic-grade stainless steel and gas-tight fittings.
Additionally, ORD developed a method to assess vapor intrusion using basement (indoor air)
and sub-slab samples that could be used for building-by-building vapor intrusion determin-
ations. Contaminant concentrations in the indoor air were determined to be a result of vapor
intrusion if:
(1) a VOC was detected in groundwater or soil-gas samples collected in the vicinity of the
building; and
(2) statistical testing of the sampling data supported vapor intrusion, which required the use of
an "indicator" vapor known to be associated only with subsurface contamination (EPA, 2006c).
Basement/sub-slab concentration ratios of indicator contaminants (known to be associated
only with subsurface contamination) were compared with those of other VOCs detected. The
results revealed that detections of three indicator VOCs in indoor air consistently were caused
by vapor intrusion, but the presence of a fourth occasionally generated false positives and
negatives.
Air/Soil Vapor Sample Collection Devices: Air sample collection devices encase air samples
so they can be transported to a laboratory (either on site or off site) for chemical analysis.
Devices are available to take a "grab" sample at a point in time or a time-integrated sample,
which provides a time-weighted average. Selecting an approach will depend on the CSM (e.g.,
Are vapor intrusion rates expected to be steady or vary throughout the day?) and when access
to the building is permitted. The document, Superfund Program Representative Sampling
Guidance Volume 2: Air (EPA, 1995b), explains a number of devices. Air sample collection
devices commonly used at vapor intrusion sites—canisters, sampling bags, and sorbent
tubes/cartridges—are discussed here (Figure 4; see Section 2.2):
• Canisters collect bulk air samples and measure time-weighted average concentrations.
They can be placed in a building for a selected period of time (typically 24 hours) and
will provide an average concentration for that period. For typical risk-based
measurements, the canisters are placed at sitting height. Canisters can also be
attached to soil gas probes to collect soil gas samples over a selected period.
Canisters vary in size depending on the length of the sampling period. They come
equipped with evacuated systems or pressure systems to draw in air samples. The flow
meter must be well-calibrated before sampling begins. Evacuated systems, which use
the pressure difference between the evacuated canister and ambient air to pull the
sample into the canister, are the easiest to use. A critical orifice attached to the canister
to draw the sample in at a constant rate over the sampling period until the canister is
near atmospheric pressure. Pressure systems use a pump to push air into the canister,
but involve a lot of effort to certify that the pumps are clean enough to satisfy data
quality objectives.
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• Sampling bags collect grab samples of bulk air at a point in time. The bags are made of
an impermeable material, such as Tedlar™, with a stainless steel or polypropylene
fitting to which the sample tube is attached. Samples are generally collected in the bags
using a "lung" system, which uses a pump to create a vacuum around the bag in a
drum. This, in turn, draws air from the source into the bag without the potential for
cross-contamination from the pump. Sampling bags need to be analyzed within a few
hours of collection, so field-based analytical methods are recommended.
• Sorbent tubes and cartridges differ from canisters and sampling bags in that they do not
collect bulk air samples for analysis. Instead, a sorbent-filled tube (or cartridge) is
opened and connected to a sample pump to draw air in through the tube. Contaminants
are trapped onto the surface of the sorbent. The tube is then sealed with caps until the
sorbent is analyzed. Depending upon the sorbent material, it can be analyzed using
either solvents (solvent extraction) or heat (thermal desorption). Tubes and cartridges
are available with a variety of sorbent materials and are generally preferred over
canisters and sampling bags when sampling for SVOCs.
Air/Soil Vapor Sample Analyses: Both fixed-laboratory and field-based techniques are
available for analysis of soil gas, sub-slab, and indoor air samples. Fixed-laboratory analyses
refer to those analyses conducted off site at a certified commercial laboratory. Samples are
collected at the site and delivered to the laboratory, which analyzes them within a specified
turnaround time. The data undergoes a rigorous QA/QC process to ensure they are useable
for their stated purpose. Therefore, it can take weeks to receive the analytical data. An
expedited turnaround time can be requested to reduce the wait, but the per-sample cost for
expedited analyses can double or triple.
Field-based analytical methods (a key component of the Triad approach) are conducted using
portable instruments that can be brought on site for real-time measurements of ambient air,
indoor air, soil gas, and sub-slab sample concentrations. Some field-based analyses can
provide the same level of QA/QC as fixed-laboratory analyses. However, the faster and often
more economical field-based methods allow for higher density sampling of a site. Higher
density sampling can help refine the CSM for improved decision making. Typically, a
combination of the two types of samples is recommended in a site investigation. Field-based
methods include the following analytical devices. Additional information on air sampling tools
can be found in the Superfund Program Representative Sampling Guidance (EPA, 1995b).
• A field-portable GC/MS operated by a trained operator, can be used for on-site analysis
of air samples. To run a field-portable GC/MS, the operator must know the range of
expected concentrations. The operator runs the GC/MS in different modes to identify
the chemicals present in the sample, measure their concentrations, and attain a lower
detection limit, if necessary, for chemicals known to be in the subsurface.
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MORE ON TAGA HARDWARE
TAGA is equipped with a low-pressure
chemical ionization (LPCI) source
operating in conjunction with a triple-
quadrupole MS/MS to identify and
quantify organic compounds. The vehicle
also is equipped with several GCs to aid
in identification and confirmation
analysis. Use of TAGA have been shown
to resolve vapor intrusion issues, such as
identifying subsurface sources, "lifestyle"
sources, atmospheric sources, and
ambient sources of contaminants in
indoor air (Mickunas, 2005).
EPA's National Environmental Response
Team operates the Trace Atmospheric Gas
Analyzer (TAGA), a vehicle-mounted
laboratory instrument capable of real-time
direct air sampling and analysis of organics in
indoor and ambient air on site. The 36-foot bus
is equipped with analytical equipment to
identify and quantify organic compounds.
Use of equipment like TAGA at vapor intrusion
sites can cut the time and costs spent for
traditional fixed-laboratory analyses, and can
provide the same level of QA/QC. Results of
the one-minute TAGA on-site analyses and
laboratory analyses of 24-hour Summa canisters for indoor air samples have been
shown to be comparable. Furthermore, analyses of Tedlar™ bag grab samples using
TAGA were also comparable to Summa canisters (Mickunas, 2005).
The MicroGas Analyzer is a portable instrument that measures and graphs the levels of
carbon monoxide, carbon dioxide, methane, hydrocarbons, nitrogen oxides, and oxygen
in an air or soil gas sample (nitrogen oxides are measured separately). Such
measurements can be useful in monitoring soil gas from landfills and assessing the
potential for bioremediation of petroleum contaminants.
For real-time detection of VOCs for evaluation of possible entry pathways (e.g., cracks
or openings in the floor or wall, sumps, elevator shafts, etc.) monitoring with hand-held
instruments such as photoionization detectors (PIDs), flame ionization detectors (FIDs),
or combustible gas indicators (CGIs) may be appropriate. Most instruments are limited
to the parts per million by volume range, however, and would not resolve lower
concentrations of contaminants. PIDs and CGIs can be used for field screening to
identify immediate dangers due to hazardous levels of VOCs. (ITRC, 2007a).
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APPENDIX C: Acronyms and Glossary
API American Petroleum Institute
ASTM American Society for Testing and Materials
BTSC Brownfields and Land Revitalization Technical Support Center
CERCLA Comprehensive Environmental Response, Compensation, and Liability Act
CGI combustible gas indicator
CSM conceptual site model
EPA U.S. Environmental Protection Agency
FID flame ionization detector
GC gas chromatograph(y)
HVAC heating, ventilation, and air conditioning
ITRC Interstate Technology and Regulatory Council
J&E Johnson and Ettinger
LPCI low-pressure chemical ionization
MS mass spectrometer (spectrometry)
NAPL non-aqueous phase liquid
O&M operation and maintenance
ORD Office of Research and Development
OSWER Office of Solid Waste and Emergency Response
PCB polychlorinated biphenyl
PID photoionization detector
PVC polyvinyl chloride
QA/QC quality assurance and quality control
SVOC semivolatile organic compound
TAGA trace atmospheric gas analyzer
TCE trichloroethene
UST underground storage tank
VOC volatile organic compound
Acute health effect - Health problems, such as headache, nausea, and eye and respiratory
irritation, caused by short-term exposure (within hours or days) to contaminants. In the case of
vapor intrusion, acute health effects are often associated with a detectable odor of chemical
vapors.
Advection - the movement of soil gas from areas of higher to lower pressure. Advection due
to building depressurization is often the driving force for the movement of vapors from the soil
gas in the sub-slab to indoor air.
Ambient air - Air unaffected that surrounds a building and is unaffected by vapor intrusion.
Ambient air samples are collected outdoors and away from openings in the building (windows,
stacks, etc.) that vent indoor air.
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Background sources - Objects within a building (e.g., cleaning products, hobby supplies,
paints and solvents, carpet, cigarette smoke, dry-cleaned clothing) that emit chemical vapors
not due to vapor intrusion. An inventory of chemicals should be conducted prior to indoor air
sampling to identify potential background sources of VOCs and SVOCs that may affect indoor
air sampling results.
Biodegradation - The breakdown of harmful chemicals into less harmful ones by microbes
found naturally in soil. If the biodegradation of VOCs that readily biodegrade (e.g., petroleum-
related compounds) is not considered in the evaluation of vapor intrusion, it may lead to the
overestimation of vapor intrusion impacts.
Brownfield - Real property, the expansion, redevelopment, or reuse of which may be
complicated by the presence or potential presence of a hazardous substance, pollutant, or
contaminant.
Capping effect - Inhibition of the upward movement of soil gas due to the presence of
building foundations and other barriers such as pavement.
Chronic health effect - Health problems, such as cancer, liver or kidney disease, and
reproductive difficulties, caused by long-term exposure to even low-levels of contaminants.
Conceptual site model - A picture and narrative of the site contamination: how it got there,
whether or not it is migrating or degrading, its distribution across the site, who might be
exposed to it, and what risk-reduction strategies are most feasible. Development of a
conceptual site model begins during the Phase I environmental site assessment and is
continually modified throughout the characterization and cleanup process.
Conduit - A passageway in the subsurface (e.g., a sand or gravel layer, buried utility line, or
animal burrow) or in the building foundation (e.g., a sump, elevator shaft, or utility line) that
facilitates the flow of soil gas.
Depressurization - Phenomenon that causes buildings to draw soil gas indoors— via cracks
in the foundation or through openings associated with utility lines, sump pumps, etc.—when the
pressure beneath a building is higher than the pressure indoors. Depressurization is caused by
"leaky" heating and ventilation systems, exhaust fans, and stack and wind effects that reduce
the pressure indoors.
Diffusion - Movement of vapors from areas of high concentrations closest to the source of
contamination toward lower concentrations in uncontaminated areas.
Exposure pathway - A way that people may be exposed to (come in contact with)
environmental contaminants.
Green space - Vegetated land separating or surrounding areas of intensive residential or
industrial use and devoted to parks, playgrounds, trails, gardens, habitat restoration, and other
recreational uses.
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Hazard quotient - A number used in environmental risk assessment to define the probability
that adverse non-cancer health risks will occur.
Hot spot - Area of high contaminant concentrations.
Institutional controls - Legal or administrative actions that help minimize the potential for
human exposure to contamination by ensuring appropriate land or resource use. Examples
include restrictive covenants, zoning restrictions, and special building permit requirements.
Lines of evidence - The various ways of proving or disproving the potential for vapor intrusion
before drawing conclusions about the risks posed. Lines of evidence include the locations of
sources, distribution of groundwater contaminants and soil gas at the site, sub-slab
concentrations (if buildings are present), indoor and outdoor air concentrations, background
concentrations, presence of conduits, and building construction plans or details. More
information on lines-of-evidence can be found in ITRC, 2007a.
Mitigation - Engineering approaches to preventing vapor intrusion to a building.
Phase I environmental site assessment - The process of determining whether or not
contamination is present on a parcel of real property for the purpose of identifying potential or
existing environmental contamination liabilities. A Phase I assessment does not include
collection or analysis of samples.
Phase II environmental site assessment - An investigation following and based on the
Phase I environmental site assessment that involves the collection of samples of
environmental media (e.g., soil and groundwater) for chemical analysis.
Predictive model - Computer model used to assess the potential for vapor intrusion to occur
at a property. Models are used as a line of evidence particularly when limited field
measurements can be collected.
Radon - A colorless, odorless gas formed from the decay of radium, a radioactive element
that occurs naturally in the bedrock and soil in some areas of the country. Mitigation methods
for vapor intrusion are similar to those for radon gas, but due to the much lower target vapor
concentrations the design and performance assessment of such systems requires a more
robust approach.
Receptors - In the case of vapor intrusion, persons who may be exposed to indoor air
contaminants resulting from vapor intrusion.
Risk assessment - Qualitative and quantitative evaluation of the risk posed to human health
and/or the environment by the actual or potential presence or use of pollutants.
Screening-level model - Computer software tool often used to determine if a potential indoor
inhalation exposure pathway exists and, if such a pathway is present, whether long-term
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BROWNFIELDS TECHNOLOGY PRIMER
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exposure increases the occupants' risk for cancer or other toxic effects to an unacceptable
level.
Soil gas -Vapors emitted from volatile and semivolatile organic compounds (and mercury) at
contaminated sites and found in the pore space of soil.
Soil gas probe - The primary tool for collecting soil gas samples
Stack effects - Pressure differences inside and outside a building caused by differences in
indoor and outdoor temperatures. As warmer indoor air rises and exits the top of the building,
the resulting pressure differences induce vapor flow into the bottom of the building.
Sub-slab - Beneath the foundation of a building.
Triad - An innovative approach to decision-making for hazardous waste site characterization
and remediation. It offers a technically defensible methodology for managing decision
uncertainty that leverages innovative characterization tools and strategies. The primary
components of Triad are systematic planning, dynamic work strategies, and real-time
measurement systems.
Upgradient - The direction opposite groundwater flow and plume migration, both of which
move downgradient.
Vapor attenuation factor - A measure of how soil and building properties limit the intrusion of
organic vapors into overlying buildings. It is defined as the concentration of the contaminant in
the indoor air divided by the concentration of the contaminant in soil gas or groundwater.
Vapor intrusion - The migration of chemical vapors from contaminated soil and groundwater
into overlying buildings.
Volatile organic compounds - Chemicals that readily evaporate.
Water table - The level below which the ground is saturated with groundwater.
Wind effects - Pressure differences inside and outside a building caused by wind currents
passing over and around the building. Wind effects can induce the flow of vapors into a
building.
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APPENDIX D: References
Abreu, Lillian D. V., and Paul C. Johnson, 2005. Effect of Vapor Source-Building Separation
and Building Construction on Soil Vapor Intrusion as Studied with a Three-Dimensional
Numerical Model. Environmental Science and Technology. Volume 39, pp. 4550-4561.
American Petroleum Institute (API), 2005. Collecting and Interpreting Soil Gas Samples from
the Vadose Zone: A Practical Strategy for Assessing the Subsurface Vapor-to-indoor Air
Migration Pathway at Petroleum Hydrocarbon Sites. Regulatory Analysis and Scientific Affairs.
Publication Number 4741. November.
http://groundwater.api.org/soilgas/files/4741final111805.pdf
American Society for Testing and Materials [ASTM], 2005. Standard Guide for
Application of Engineering Controls to Facilitate Use or Redevelopment of Chemical-Affected
Properties. E-2435-05.
Buonicore, 2006. ASTM Vapor Intrusion Assessment Standard for Real Estate Transactions:
Status Report. Presentation for RTM Webinar. November 29 2006.
EPA 1988. Application of Radon Reduction Methods, EPA/625/5-88/024, August 31.
EPA, 1991. Handbook of Suggested Practices for the Design and Installation of Ground-Water
Monitoring Wells (Revised) EPA No. 600489034. 231 pp.
EPA, 1994. Model Standards and Techniques for Control of Radon in New Residential
Buildings. EPA 402-R-94-009. March.
http://www.epa.gov/radon/pubs/newconst.htmlffMethods
EPA, 1995a. Use of Risk-Based Decision Making in UST Corrective Action Programs. EPA
Office of Underground Storage Tanks. OSWER Directive 9610.17. March 1.
http://www.epa.gov/OUST/directiv/od961017.pdf
EPA, 1995b. Superfund Program Representative Sampling Guidance. Volume 2: Air (Short-
Term Monitoring) Interim Final. EPA Environmental Response Team. OSWER Directive
9360.4-09. EPA540/R-95/1. December.
http://www.clu-in.org/download/char/SF Rep Samp Guid air.pdf
EPA, 1999a. Monitored Natural Attenuation of Petroleum Hydrocarbons. U.S. EPA Remedial
Technology Fact Sheet. EPA/600/F-98/021. May.
http://www.cluin.org/download/remed/pet-hyd.pdf
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EPA, 1999b. Compendium of Methods for Determination of Toxic Compounds in Ambient Air,
2nd Edition, Compendium Method TO-15: Determination of Volatile Organic Compounds
(VOCs) in Air Collected in Specially-Prepared Canisters and Analyzed by Gas
Chromatography/
Mass Spectrometry (GC/MS). EPA/625-R-96/010b. January.
http://www.epa.gov/ttnamti1/files/ambient/airtox/to-15r.pdf
EPA, 1999c. Compendium of Methods for Determination of Toxic Compounds in Ambient Air,
2nd Edition, Compendium Method TO-17: Determination of Volatile Organic Compounds in
Ambient Air Using Active Sampling onto Sorbent Tubes. EPA/625-R-96/010b. January.
http://www.epa.gov/ttnamti1/files/ambient/airtox/to-17r.pdf
EPA, 2001. Building Radon Out: A Step-by-Step Guide on how to Build Radon-Resistant
Homes. EPA Office of Air and Radiation. EPA/402-K-01-002. April.
http://www.epa.gov/iaq/radon/images/buildradonout.pdf
EPA, 2002. OSWER Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway
from Groundwater and Soils. EPA 530-D-02-004. November.
http://www.epa.gov/correctiveaction/eis/vapor/complete.pdf
EPA, 2003. Consumer's Guide to Radon Reduction, EPA 402-K-03-002, Revised February
2003.
http://www.epa.gov/radon/pubs/consguid.pdf
EPA, 2004a. User's Guide for Evaluating Subsurface Vapor Intrusion into Buildings. Office of
Emergency and Remedial Response. Prepared by Environmental Quality Management.
Revised February 22.
http://www.epa.gov/oswer/riskassessment/airmodel/pdf/2004 0222 3phase users guid
e.pdf
EPA, 2004b. Design Solutions for Vapor Intrusion and Indoor Air Quality. EPA 500-F-04-004.
March.
http://www.epa.gov/brownfields/facts/vapor intrusion.pdf
EPA, 2005a. Guidance for Evaluating Landfill Gas Emissions from Closed or Abandoned
Facilities. Prepared by Thomas Robertson and Josh Dunbar, Environmental Quality
Management, Inc. EPA-600/R-05/123a. September.
http://clu-in.org/download/char/epa-600-r-05-123.pdf
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EPA, 2005b. Uncertainty and the Johnson-Ettinger Model for Vapor Intrusion Calculations.
Prepared by James W. Weaver, Ecosystems Research Division, National Exposure Research
Laboratory ,and Fred D. Tillman, National Research Council, National Exposure Research
Laboratory. EPA/600/R-05/110. September.
http://www.epa.gov/athens/publications/reports/Weaver600R05110UncertaintvJohnson
Ettinger.pdf
EPA, 2005c. Review of Recent Research on Vapor Intrusion. Office of Research and
Development. Prepared by Fred D. Tillman, National Research Council, National Exposure
Research Laboratory and James W. Weaver, Ecosystems Research Division, National
Exposure Research Laboratory. EPA/600/R-05/106. September.
http://www.epa.gov/athens/publications/reports/Weaver600R05106ReviewRecentResea
rch.pdf
EPA, 2005d. Groundwater Sampling and Monitoring with Direct Push Technologies. OSWER
No. 9200.1-51. EPA 540/R-04/005. August.
http://www.clu-in.org/download/char/540r04005.pdf
EPA, 2006a. Vapor Intrusion—Assessment Update. Training manual from the 16th Annual
Training Conference NARPM 2006. New Orleans, LA. June 19-23.
EPA, 2006b. Assessment of Vapor Intrusion in Homes Near the Raymark Superfund Site
Using Basement and Sub-Slab Air Samples. Office of Research and Development (ORD),
National Risk Management Research Laboratory. Prepared by Dominic C. DiGiulio and Cindy
Paul, ORD, Ground Water and Ecosystems Restoration Division; Raphael Cody and Richard
Willey, Region 1; Scott Clifford and Peter Kahn, New England Regional Laboratory; Ronald
Mosley, ORD National Risk Management Research Laboratory; and Annette Lee and Kaneen
Christensen, Xpert Design and Diagnostics, LLC. EPA/600/R-05/147
http://www.epa.gov/ada/download/reports/600R05147/600R05147.pdf
EPA, 2006c. Comparison of Geoprobe® PRT and AMS GVP Soil-Gas Sampling Systems with
Dedicated Vapor Probes in Sandy Soils at the Raymark Superfund Site. EPA/600/R-06/111.
November.
http://www.epa.gov/ada/download/reports/600R06111/600R06111 .pdf
EPA, 2007. Subsurface Characterization for Vapor Intrusion: Vadose Zone Sources.
Presentation by Gary Newhart, EPA, at the NARPM Annual Training Conference. Baltimore,
MD. May 22, 2007.
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Interstate Technology & Regulatory Council (ITRC), 2007a. Vapor Intrusion Pathway: A
Practical Guideline. 172 pages. January 2007.
http://www.itrcweb.org/DocumentsA/l-1.pdf
Interstate Technology & Regulatory Council (ITRC), 2007b. Vapor Intrusion Pathway:
Investigative Approaches for Different Scenarios. 52 pages. January 2007.
http://www.itrcweb.org/DocumentsA/l-1A.pdf
Johnson, P.C. and R. A. Ettinger (J&E), 1991. Heuristic Model for Predicting the Intrusion Rate
of Contaminant Vapors into Buildings. Environmental Science and Technology. Vol. 25. pages
1145-1152.
Johnson, P.C., M.W. Kemblowski, and R.L. Johnson, 1998. Assessing the Significance of
Subsurface contaminant Vapor Migration to Enclosed Spaces: Site-Specific Alternative to
Generic Estimates. American Petroleum Institute Technical Bulletin Number 4674.
Johnson, P.C., M.W. Kemblowski, and R.L. Johnson, 1999. Assessing the Significance of
Subsurface Contaminant Vapor Migration to Enclosed Spaces: Site-Specific Alternative to
Generic Estimates. Journal of Soil Contamination. Volume 8. pages 389-421.
Mickunas, Dave, 2005. Use of Field Analytics to Solve Vapor Intrusion Issues. Presentation
made at the Fall 2005 Meeting of EPA's Technical Support Project. San Antonio, TX. October
26.
http://www.epa.gov/tio/tsp/download/2005 fall/wednesdav/2 mickunas.pdf
Mosley, 2006. Radon and Radon Mitigation Theory and Practice. Presentation materials from
the National Association of Remedial Project Managers (NARPM) Conference in New Orleans.
http://www.epanarpm.org/narpm2006/afteraction coursematerials.htmff
Mosley, 2005. Engineering Design Considerations for Mitigation of Vapor Intrusion. Presented
at the Conference of National Association of Remedial Project Managers, Phoenix, AZ. May
24.
New York State Department of Health, 2005. Guidance for Evaluating Soil Vapor Intrusion in
the State of New York. Public Comment Draft. February.
http://www.health.state.ny.us/nvsdoh/gas/svi guidance/
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