DRAFT GUIDANCE
FOR
EVALUATING THE VAPOR INTRUSION TO INDOOR AIR PATHWAY
FROM GROUNDWATER AND SOILS
(Subsurface Vapor Intrusion Guidance)
I. INTRODUCTION
A. General
One of the primary objectives of the Office of Solid Waste and Emergency Response
(OSWER) under EPA's Strategic Plan is stated as:
"By 2005, EPA and its state, tribal and local partners will reduce or control the
risk to human health and the environment at, more than 374,000 contaminated
Superfund, RCRA, underground storage tank (UST), brownfields and oil sites,
and have the planning and preparedness capabilities to respond successfully to all
known emergencies to reduce the risk to human health and the environment."
In order to effectively "reduce or control the risk to human health and the environment,"
it is necessary to determine if specific exposure pathways exist. If an exposure pathway
exists, we need to evaluate the site to determine whether contamination is present at
levels that may pose a significant risk to human health or the environment.
B.
What Is The Intent Of This Guidance?
This draft guidance specifically addresses the evaluation of a single exposure pathway -
the "vapor intrusion pathway." The intent of this draft guidance is to provide a tool to
help the user conduct a screening evaluation as to whether or not the vapor intrusion
exposure pathway is complete and, if so, whether it poses an unacceptable risk to human
health. A complete pathway means that humans are exposed to vapors originating from
site contamination. The approach suggested in this draft guidance begins with simple and
generally reasonable conservative screening approaches and gradually progresses toward
a more complex assessment involving increasingly greater use of site-specific data. For
those sites determined to have an incomplete vapor intrusion pathway, EPA generally
recommends that further consideration of the current site situation is not needed. For
those sites determined to have a complete pathway, recommendations are provided on
how to evaluate whether the pathway does or does not pose a potential significant risk to
human health.
This guidance is not intended to provide recommendations on how to delineate the extent
of risk or how to eliminate the risk, only to determine if there is a potential for an
unacceptable risk. We generally recommend that a reevaluation of a screened-out site be
carried out if site conditions or building/facility uses change in a way that might change
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the screening-out decision or other new information suggests greater conservatism is
warranted in assessing this exposure pathway.
Please recognize that this is a guidance document, not a regulation. This document
presents current technical and policy recommendations of the Office of Solid Waste and
Emergency Response, based on our current understanding of the phenomenon of
subsurface vapor intrusion. EPA personnel (and of course, states) are free to use and
accept other technically sound approaches, either on their own initiative, or at the
suggestion of responsible parties or other interested parties. In addition, personnel who
use this guidance document are free to modify the approach recommended in this
guidance. This guidance document does not impose any requirements or obligations on
EPA, states, or the regulated community. Rather, the sources of authority and
requirements for addressing subsurface vapor intrusion are the relevant statutes and
regulations (e.g., RCRA, CERCLA and the NCP).
C. At What Sites Are We Currently Suggesting You Use This Guidance?
The draft guidance is suggested for use at RCRA Corrective Action, CERCLA (National
Priorities List and Superfund Alternative Sites ), and Brownfields sites, but is not
recommended for use at Subtitle I Underground Storage Tank (UST) sites at this time.
The draft guidance recommends certain conservative assumptions that may not be
appropriate at a majority of the current 145,000 petroleum releases from USTs. As such,
the draft guidance is unlikely to provide an appropriate mechanism for screening the
vapor pathway at UST sites.
We recommend that State and Regional UST corrective action programs continue to use
a risk based decision making approach as described in OSWER Directive 9610.17: Use of
Risk-Based Decision Making in UST Corrective Action Program to address this pathway.
A majority of State programs are successfully implementing this directive at their UST
cleanups and use the recommended approaches where appropriate, to prioritize and
remediate their sites, including risk associated with vapor migration to indoor air in a
manner that is protective of human health and the environment.
EPA also acknowledges that there are many unique issues specific to petroleum releases
from underground storage tanks. EPA is forming an EPA-State working group to further
study the behavior of petroleum and petroleum products in the subsurface associated with
the vapor intrusion pathway.
D. What Is The Scope Of The Guidance?
This draft guidance is intended to address the incremental increases in exposures and
risks from subsurface contaminants that may be intruding into indoor air. The
approaches suggested in this draft guidance are primarily designed to ensure protection of
the public in residential settings but may be adjusted for other land uses (e.g.,
commercial/industrial, recreational), so that human exposures in non-residential settings
may also be considered under this guidance, as described below.
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1) Occupational settings where persons are in a working situation.
There may be occupational settings where persons present are employees and hazardous
constituents may be intruding into the air space from the vapor intrusion pathway. Such
settings could include workplaces where workers are handling hazardous chemicals (e.g.,
manufacturing facilities) similar to or different from those in the subsurface
contamination, as well as other workplaces, such as administrative and other office
buildings where chemicals are not routinely handled in daily activities. OSHA and EPA
have agreed that OSHA generally will take the lead role in addressing occupational
exposures. Workers will generally understand the workplace (e.g., Occupational Safety
and Health Administration, OSHA) regulations (and monitoring, as needed) that already
apply and provide for their protection. For example, workplaces are subject to a written
Hazard Communication and Monitoring Plan.
In general, therefore, EPA does not expect this guidance be used for settings that are
primarily occupational.! However, employees and their employers may not be aware of
subsurface contaminants that may be contributing to the indoor air environment of their
workplaces, particularly since vapor intrusion may include constituents that are no longer
or were never used in a particular workplace, may originate from elsewhere, or be
modified by bio-degradation or other subsurface transformation processes. Therefore, we
recommend that regional or State authorities notify the facility of the potential for this
exposure pathway to cause a hazard or be recognized as a hazard and suggest that they
consider any potential risk that may result. Any change in the future use of the
building/facility might suggest a need to reevaluate the indoor air pathway.
2) Non-residential settings where persons are in a non-working situation.
Non-residential buildings may need to be evaluated where people (typically non-workers
- see above) may be exposed to hazardous constituents entering into the air space from
the subsurface. This would include for example buildings where the general public may
be present, e.g., schools, libraries, hospitals, hotels, and stores. EPA recommends the
appropriate environmental (public health protection) screening levels be applied to these
situations.
The recommendations in this guidance may be appropriate for such situations, although
we recommend adjustments appropriate for non-residential exposure durations, the
building specific air volumes and air exchange rates, as well as other relevant factors be
considered. The model used in this guidance accommodates the inclusion of these kinds
of variables and for comparison of computed values with the recommended numerical
criteria in Tables 2 and 3.
'it should be noted that at CERCLA sites, the cleanup levels are generally determined either by
ARARs or risk range considerations; the OSHA standards are not ARARs under the CERCLA
statute and regulations. Therefore, there may be instances (under CERCLA and other cleanup
programs) where standards other than the OSHA standards are used to determine whether the
exposure pathway presents a risk to human health.
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E. Will This Guidance Supersede Existing Guidance?
This draft guidance supersedes the draft RCRA El Supplemental Guidance for Evaluating
the Vapor Intrusion to Indoor Air Pathway (December 2001). It does not supersede State
guidance. However, we believe that States will find this guidance useful and States will
consider this guidance in making Current Human Exposures Under Control El
determinations. Additionally, the lead regulatory authority for a site may determine that
criteria other than those recommended herein are more appropriate for the specific site or
area. For example, site-specific indoor air criteria may differ from the generic indoor air
criteria generally recommended in this guidance and, consequently, the corresponding
soil gas or groundwater screening levels may differ. Also, the site-specific relationship
between indoor air concentrations and subsurface soil gas or groundwater concentrations
may differ from that assumed in developing this guidance. Therefore, we suggest that the
first step generally be to consult with the lead regulatory authority to identify the most
appropriate approach for evaluation of any potential vapor intrusion to indoor air
pathway.
F. Will We Continue To Evaluate Data And Revise This Document
Accordingly?
Vapor intrusion is a rapidly developing field of science and policy and this draft guidance
is intended to aid in evaluating the potential for human exposure via this pathway given
the state-of-the-science at this time. EPA will continue to explore this area and improve
our understanding of this complex exposure pathway. As our understanding improves,
this guidance will be revised as appropriate. EPA and State site managers are encouraged
to provide OSWER with relevant site information that can be added to the OSWER
database to facilitate EPA's efforts (for more information see Site-Specific
Investigations).
II.
EXPLANATION OF VAPOR INTRUSION
Vapor Intrusion is the migration of volatile chemicals from the subsurface into overlying
buildings. Volatile chemicals in buried wastes and/or contaminated groundwater can
emit vapors that may migrate through subsurface soils and into indoor air spaces of
overlying buildings in ways similar to that of radon gas seeping into homes, as shown in
Figure 1. (However, this guidance is not intended for evaluation of intrusion of radon
gas.) As the figure illustrates, this vapor intrusion pathway may be important for
buildings both with and without a basement.
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l«sr ;
mobile HAPt)
Figure 1: Generalized schematic of the pathway for subsurface vapor intrusion
into indoor air.
A. Why Should You Be Concerned With This Pathway?
In extreme cases, the vapors may accumulate in dwellings or occupied buildings to levels
that may pose near-term safety hazards (e.g., explosion), acute health effects, or aesthetic
problems (e.g., odors). Typically however, the chemical concentration levels are low or,
depending on site-specific conditions, vapors may not be present at detectable
concentrations. In residences with low concentrations, the main concern is whether the
chemicals may pose an unacceptable risk of chronic health effects due to long-term
exposure to these low levels. A complicating factor in evaluating the potential chronic
risk from vapor intrusion is the potential presence of some of the same chemicals at or
above background concentrations (from the ambient (outdoor) air and/or emission
sources in the building e.g., household solvents, gasoline, cleaners) that may pose,
separately or in combination with vapor intrusion, a significant human health risk.
B. How Is This Exposure Pathway Different From Other Pathways?
The inhalation exposure pathway from vapor intrusion differs from other pathways in
several respects. First, there is much less experience for risk assessors to draw upon
when assessing the subsurface vapor to indoor air pathway than there is for the
assessment of other pathways (e.g., groundwater ingestion and direct exposure to
contaminated soils). Consequently, the key issues and technical challenges are not as
fully understood. Second, response options will typically be different. For example,
where groundwater used as drinking water is found to be highly contaminated, the
groundwater plume may be cleaned up or its volume/concentration reduced, or people
may drink bottled water, or they can be connected to other potable sources. In the case of
significant vapor intrusion, ventilation is likely the most appropriate approach. Third,
assessing the vapor intrusion pathway can be more complex than assessing other
pathways because it typically involves the use of indirect measurements and modeling
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(e.g., using soil gas or groundwater data) to assess the potential for indoor inhalation
risks. Fourth, it is our judgment that indoor air sampling results can be misleading
because it is difficult and sometimes impossible to eliminate or adequately account for
contributions from "background" sources.
III. SUMMARY OF DRAFT GUIDANCE
This draft guidance employs a tiered approach to assist the user in determining whether
the exposure pathway is complete (i.e., subsurface vapors intrude into indoor air spaces);
and, if so, whether the vapors are present at levels that may pose an unacceptable
exposure risk. Although vapors may be present in soils beneath a building, the vapors
may or may not pose a risk to human health. It may also be predicted that a plume would
reach a development or that future construction may occur over a plume that would result
in a potential for exposure via this pathway. Estimating human health risk from indoor
air exposure depends upon human exposure to the vapors. If contaminant vapors do not
enter the building, the exposure pathway from the source of contamination to a person
(receptor) is not "complete," and in such circumstances the person cannot be considered
to be at risk from indoor air exposure due to vapor intrusion. In other situations, vapors
may enter the building, but be present at such low levels that the risk is considered
negligible. However, in some cases, vapors may seep into a building and accumulate at
levels that may pose an unacceptable risk to human health.
A. How Should You Use This Draft Guidance?
The overall approach presented here is similar to that used in the February 5,1999,
RCRA Corrective Action Current Human Exposures Under Control El Guidance.
Record sheets containing a series of questions guide users through a recommended series
of analytical steps to help determine if the subsurface vapor intrusion into indoor air
pathway is complete and may present unacceptable risks. The record sheets encourage
documentation of the facts and considerations that typically drive responses.
Documentation is important to ensure clarity and transparency of the decisions. We
recommend those who use this guidance consider the technical objectives, apply
professional judgment, and attempt to assess the completeness of the vapor intrusion
pathway in a technically defensible fashion. Users may find the discussions included in
the attached Appendices to be useful in applying professional judgment to the evaluation
of the vapor intrusion pathway.
B.
How Do I Start And What Are The Different Tiers?
OSWER's fundamental approach to evaluating contaminated sites uses Guidance for the
Data Quality Objectives (DQO) Process, EPA QA/G-4 (EPA/600/R-96/055;August
2000); (URL = hUp://www.epa.gov/quaiity/qs^docs/g4-final.pdf) which calls for
proceeding in a careful stepwise fashion. We recommend that site investigators use the
specific sequential approach outlined in the DQO process to adequately determine the
nature and extent of contamination, and identify' potential exposure pathways and
receptors that may be at risk (see Appendix A for more information). The first step in the
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DQO process is to develop a Conceptual Site Model (CSM). A CSM is a three-
dimensional "picture" of site conditions illustrating the contaminant sources, their
movement of contaminants in the environment, their exposure pathways and the potential
receptors (see Appendix B for more information).
The flowchart presented in Figure 2 summarizes the evaluation approach presented in this
draft guidance. There are three tiers of assessment that involve increasing levels of
complexity and specificity.
Tier 1 - Primary Screening is designed to be used with general knowledge of a
site and the chemicals known or reasonably suspected to be present in the
subsurface; it does not call for specific media concentration measurements for
each constituent of concern;
Tier 2 - Secondary Screening is designed to be used with some limited site-
specific information about the contamination source and subsurface conditions
(e.g., measured or reasonably estimated concentrations of target chemicals in
groundwater or soil gas, and depth of contamination and soil type); and
Tier 3 - Site-Specific Pathway Assessment involves collecting more detailed site-
specific information and conducting confirmatory subslab and/or indoor air
sampling.
The evaluation process shown in Figure 2 presents a logical and linear progression
designed to screen out sites ordinarily not needing further consideration and focuses
attention on those sites that generally need further consideration of the vapor intrusion
pathway or action. We suggest that a user of this guidance start at tier 1. However, the
user does not need to begin with tier 1 and may proceed directly to tier 2 or 3 if they so
choose. In addition, as noted earlier, the user may use other technically sound
approaches in evaluating the vapor intrusion pathway.
C. What Are The Steps Associated With Each Tier And How Do I Use Them?
Tier 1 - Primary Screening: This step is designed to help quickly identify whether or
not a potential exists at a specific site for subsurface vapor intrusion, and, if so, whether
immediate action may be warranted. Criteria recommended for making these
determinations under the guidance are presented in Questions 1 through 3, which focus
on identifying:
a) if chemicals of sufficient volatility and toxicity are present or reasonably
suspected to be present (Question 1);
b) if inhabited buildings are located (or will be constructed under future
development scenarios - except for Environmental Indicator
determinations, see section IV.C below) above or in close proximity to
subsurface contamination (Question 2); and
c) if current conditions warrant immediate action (Question 3).
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If the Primary Screening does not support a conclusion that the pathway is incomplete, or
that immediate action is warranted to mitigate risks, we recommend the user proceed to
Secondary Screening.
Tier 2 - Secondary Screening: This analysis involves comparing measured or
reasonably estimated concentrations of target chemicals in various media (groundwater,
soil gas, and/or indoor air) to recommended numerical criteria identified in Questions 4
and 5. These "generic criteria" reflect generally reasonable worst-case conditions.
Question 4 provides a conservative first-pass screening of groundwater and soil gas data
Question 5 (based on a mathematical model) considers the relationship (if any) between
groundwater and soil gas target criteria to such site-specific conditions as depth of
contamination and soil type. Under the guidance, the site risk manager may choose to
select media-specific target concentrations for screening at three cancer risk levels: 10"4,
10"5, and 10"6, or a hazard quotient of 1 for non-cancer risk, whichever is appropriate.
When results from secondary screening do not support a determination that the pathway
is incomplete, we recommend the user proceed to the Site-Specific Pathway Assessment.
Tier 3 - Site-Specific Pathway Assessment: This tier specifically examines vapor
migration and potential exposures in more detail (Question 6). At this level of
assessment, the guidance generally recommends direct measurement of foundation air
and/or indoor air concentrations from a subset of the potentially affected buildings and
complementary site-specific mathematical modeling as appropriate. Modeling is
considered to be useful for determining which combination of complex factors (e.g., soil
type, depth to groundwater, building characteristics, etc.) lead to the greatest impact and,
consequently, aid in the selection of buildings to be sampled. It is recommended that
sampling of subslab or crawlspace vapor concentrations and/or sampling of indoor air
concentrations be conducted before a regulator makes a final decision that there is not a
potential problem with respect to vapor intrusion. When indoor air sampling is
conducted to determine if a significant risk exists, we recommend that it be conducted
more than once and the sampling program be designed to identify ambient (outdoor) and
indoor air emission sources of contaminants.
IV. USE OF THIS GUIDANCE
A. Under What Conditions Do We Recommend You Consider This
Pathway/Guidance?
We recommend that you consider the possibility of exposure by this pathway if you have
or suspect the presence, in soil or groundwater, of volatile chemicals (Henry's Law
Constant > 10"5 atm m3/mol) at your site as follows:
located 100 ft or less in depth or
located in close proximity to existing buildings or future buildings (see Primary
Screening Question #2 for definition of close proximity) or
To the expected footprint of potential future buildings (for non-El
determinations).
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B. Does This Guidance Address Setting Risk Management Goals?
No. The tiered approach to evaluating the vapor intrusion pathway described in this
guidance uses computed target media-specific concentrations generally based on
consensus toxicity values, where available, to aid in determining whether an unacceptable
inhalation exposure risk is posed by the site contamination. The tables in this guidance
provide target media-specific concentrations that may be used (where appropriate) for
those contaminants for which a determination has been made that a pathway is complete.
An adequate site evaluation demands careful consideration of all relevant chemical and
site-specific factors as well as appropriate application of professional judgment. Risk
management action decisions may need to consider other factors depending on the
regulatory program that applies and/or site-specific circumstances. We recommend that
the lead regulatory authority select the most appropriate value to consider for site
evaluation purposes.
C. How Is The Guidance To Be Used In Making Current Human Exposures
Under Control Environmental Indicator (El) Determinations?
We recommend that the approaches suggested in this guidance be used, where
appropriate, to support Current Human Exposures Under Control El determinations.
However, we do not believe that confirmatory sampling will generally be necessary in
that context. Current Human Exposures Under Control El determinations are intended to
reflect a reasonable conclusion by EPA or the State that current human exposures are
under control with regard to the vapor intrusion pathway and current land use conditions.
We believe that not recommending confirmatory sampling is appropriate because of the
conservative nature of the assumptions made. Additionally, the recommended
approaches are designed to help site decision makers to differentiate those sites for which
there is more likely to be unacceptable vapor intrusion from those where unacceptable
vapor intrusion exposures are less likely.
Finally, this guidance provides targeted indoor air concentrations set at 10"4,10"5, and 10"6
(incremental individual lifetime cancer risk) levels and a Hazard Quotient (HQ) of 1 for
non-cancer risk. For the purposes of making Current Human Exposures Under Control
El determinations with respect to vapor intrusion under RCRA and CERCLA, EPA
generally recommends the use of 10"5 values. This level, in EPA's view, serves as a
generally reasonable screening mechanism for the vapor intrusion pathway.
Additionally, it takes into account practical issues associated with the analytical
difficulties in taking air measurements and the possible presence of many constituents of
concern due to contributions from "background" sources, including ambient (outdoor) air
and/or emitted from indoor sources.
D. How Will This Guidance Be Used In The RCRA And CERCLA (Superfund)
Programs?
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We recommend that this draft guidance be used in making Current Human Exposures
Under Control El determinations at RCRA and NPL sites, as well as in CERCLA
remedial investigations and RCRA facility investigations. It is not designed to help the
site decision makers conduct a more detailed (e.g., site-specific) assessment of current
and future risks at NPL sites and it does not address cumulative risk that includes other
exposure pathways.2 Likewise, this draft guidance is not designated to be used during the
process for determining whether, and to what extent, cleanup action is warranted at these
sites.
E. What Has Changed From Previous Guidance Related To Vapor Intrusion
That I Should Be Aware Of?
This draft guidance provides improved methodologies designed to be used at any site
evaluation involving a potential vapor intrusion pathway. Much work has been done to
improve methodologies and coordinate various cleanup programmatic interests,
especially the major OSWER regulatory programs, in developing this vapor intrusion
guidance. EPA believes that this guidance should prove useful and beneficial to these
programs as well as to others by providing the most up-to-date recommended approach
for use in evaluating potential exposures via the vapor intrusion pathway. Specifically, it
should be noted that:
The Johnson and Ettinger Model (1991) is used in Questions 5 and 6 of this draft
guidance. EPA/OSWER re-evaluated the strengths and limitations of the model
which led to revisions of the previous spreadsheets developed by the Superfund
Program in 1997. The revisions include new default parameters that EPA
generally recommends be used in vapor intrusion pathway evaluations. The new
spreadsheets are available on the following website at:
http://www.epa.gov/superfund/programs/risk/airmodel';johnson _ettinger.htm
EPA is also issuing Supplemental Guidance for Developing Soil Screening Levels
for Superfund Sites (SG) (OSWER 9355.4-24) which updates the 1996 Soil
Screening Guidance and includes non-residential exposure scenarios. The site-
specific methodologies and tools presented in the SG are consistent with this
vapor intrusion guidance.
As further improvements in practice are developed, for example sampling
techniques described in Appendix E, they will be further evaluated and considered
for updating of this vapor intrusion guidance and notification on the OSWER
website.
2 The draft guidance does not specifically address the issue of "additive risk" At sites where there
are a limited number of constituents in the subsurface environment, this likely is not an issue.
However, at those sites where a number of contaminants are identified in the subsurface emoronment,
the Regions and states may want to consider the additively of these contaminants. For further
guidance on additively, you could review Section 2.1.1 of the Soil Screening Guidance: Technical
Background Document, EPA/540/R-95/128, May 1996.
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F. If I Have Indoor Air Measurements Do I Need To Follow All The Steps
Described In This Guidance?
We do not recommend that indoor air quality monitoring be conducted prior to going
through the steps recommended in this guidance. In those cases where indoor air quality
data are available at the beginning of the evaluation, however, we generally recommend
that these data be considered. We recommend that a site-specific evaluation be
performed simultaneously with the subsurface assessment if indoor air concentrations
exceed target levels. In some cases, the responsible party or others may decide to
proactively eliminate exposures through avoidance or mechanical systems as a cost-
effective approach. This option may be appropriate at any time in the assessment.
In addition, there may be circumstances in which a lead authority or a responsible party
elects to initiate indoor air quality monitoring to determine whether there are any
potential risks rather than pursue assessment of the pathway via the steps recommended
in this guidance. If a responsible parry decides to initiate indoor air monitoring,
coordination and approval of air monitoring plans with the lead regulatory authority is
recommended.3
G. What Else Might I Consider If I Have Indoor Air Concentrations Data?
Using other information in conducting a screening evaluation of the vapor intrusion
pathway beyond the guidance presented in this document may be appropriate and would
be consistent with the need to consider all relevant data/information in screening and/or
assessing vapor intrusion to a building. For example, in some cases, a building may be
positively pressurized as an inherent design of the heating, ventilation, and air
conditioning system. It may be possible to show that the pathway, in this case, is
incomplete, at the current time, by demonstrating a significant pressure differential from
the building to the subsurface.
H. How Should "Background" Be Considered In Evaluating The Contribution
Of Subsurface Contamination To Indoor Air Contamination?
We believe that it is critical to consider the presence of background concentrations in
assessing the vapor intrusion pathway. Background concentrations may be impacted by
volatile chemicals commonly found in the home or found in local atmospheric emissions.
For example, in urban areas air quality is often affected by multiple atmospheric emission
sources. In addition, human activities (e.g., smoking, craft hobbies) or consumer
products (e.g., cleaners, paints, and glues) typically found in the home provide additional
indoor vapor emission sources that can contribute to increased indoor air concentrations
of some chemicals. In fact, there may be dozens of detectable chemicals in indoor air
even absent subsurface contribution. These two types of sources can contribute to
background indoor air levels of VOCs, and we recommend they be considered in
3 While proactive indoor air monitoring may be initiated at any time, EPA recommends that it is
generally not necessary if the pathway can be confirmed to be incomplete considering other site-
specific data and factors.
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evaluating the contribution of subsurface contamination to indoor air contamination in
dwellings at a cleanup site. Additionally, we recommend that: 1) an inspection be
conducted of the residence, 2) an occupant survey be completed to adequately identify
the presence of (or occupant activities that could generate) any possible indoor air
emissions of target VOCs in the dwelling (see appendices E, H and I), 3) all possible
indoor air emission sources be removed, and 4) ambient (outdoor) air samples be
collected in conjunction with any indoor air samples. We recommend the evaluation of
existing indoor air data focus on constituents (and any potential degradation products)
present in subsurface sources of contamination. We recommend the relative
contributions of background sources be carefully considered (see Appendix I) in order to
properly assess the potential inhalation exposure risks that can be attributed to the vapor
intrusion pathway.
It may be a challenge to distinguish "background" (ambient outdoor and indoor air)
sources of vapors from site-related contamination. However, we recommend vapors
attributable to background sources be accounted for during the "Site Specific
Assessment" to properly assess the potential risk posed by exposures via the vapor
intrusion pathway. To the extent practicable, we recommend that background sources of
contamination be removed or excluded from the site dwellings or occupied buildings
selected for sampling before any indoor air sampling is conducted. If this is not possible,
then we recommend the contribution from these sources be carefully considered when
evaluating any indoor air sampling results. (See Site-Specific Question # 6)
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Compile Site Information
Develop Data Quality Objectives
Develop Conceptual Site Model
Tier 1 - Primary Screening
Determine if volatile and toxic chemicals are present (see Table 1).
Determine if inhabited buildings are, or in the future could potentially be, located near subsurface contaminants.
If toxic volatile chemicals are present and current, or future, human exposure is suspected, proceed with
screening.
Determine if potential risks warrant immediate action.
If immediate action does not appear to be necessary, proceed to secondary screening.
Tier 2 - Secondary Screening
Question 4
If indoor air data are available, compare to appropriate target concentration (Table 2a, b, or c).
If indoor air data exceed the target concentration proceed to Question 6.
Determine if there is any potential for contamination of soils in the unsaturated zone.
If contamination of the unsaturated zone is suspected, assess soil gas data.
If contamination of the unsaturated zone is not suspected, assess groundwater data.
Compare soil gas or groundwater data to appropriate target concentration (Table 2a, b, or c).
If groundwater data exceed the target concentration, assess soil gas data.
If soil gas data exceed the target concentration proceed to Question 5.
Determine if data are adequate to characterize the site and support an assessment
If adequate data are not available, develop a sampling and analysis plan that satisfies the established data
quality objectives.
Determine if site conditions, or data limitations, would preclude the use of generic attenuation factors
used in Tables 2a, b, and c.
If appropriate data do not exceed target media concentration, pathway is considered to be incomplete.
Question 5
Determine if there is any potential for contamination of soils in the unsaturated zone.
If contamination of the unsaturated zone is suspected, assess soil gas data.
If contamination of the unsaturated zone is not suspected, assess groundwater data.
Compare soil gas or groundwater data to appropriate target concentration (Table 3a, b, or c).
If groundwater data exceed the target concentration, assess soil gas data.
If soil gas data exceed the target concentration proceed to Question 6.
If adequate data are not available, develop a sampling and analysis plan that satisfies the established data quality
objectives.
Determine if site conditions, or data limitations, would preclude the use of scenario-specific attenuation factors used in
Tables 3a, b, and c.
* If appropriate data do not exceed target media concentration, pathway is considered to be incomplete.
Tier 3 - Site Specific Pathway Assessment
Question 6
Determine if the nature and extent of contamination has been adequately characterized to identify the buildings that
are most likely to be impacted.
If no, develop a sampling and analysis plan that satisfies the data quality objectives.
Compare sub-slab soil gas or indoor air data to appropriate target concentration.
If sub-slab data exceed target concentration, assess indoor air data.
Determine whether or not site data meet data quality objectives and background/ambient sources have been adequately
accounted for.
Determine if exposure pathway is complete.
Figure 2. Schematic flow diagram: evaluation process recommended in guidance.
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IV. TIER 1 - Primary Screening
Primary Screening is designed to help quickly screen out sites at which the vapor
intrusion pathway does not ordinarily need further consideration, and point out the sites
that do typically need further consideration. This evaluation involves determining
whether any potential exists at a specific site for vapor intrusion to result in unacceptable
indoor inhalation risks and, if so, whether immediate action may be warranted.
Recommended criteria for making these determinations are presented in Questions 1
through 3, which focus on identifying:
a) if chemicals of sufficient volatility and toxicity are present or reasonably
suspected to be present (Question 1):
b) if inhabited buildings are located (or will be constructed under future
development scenarios - except for Environmental Indicator
determinations, see section IV. C below) above or in close proximity to
subsurface contamination (Question 2); and
c) if current conditions warrant immediate action (Question 3).
This primary screening process is illustrated in a flow diagram included in Appendix C.
A.
Ql:
Primary Screening - Question #1
Are chemicals of sufficient volatility and toxicity known or reasonably
suspected to be present in the subsurface (e.g., in unsaturated soils, soil gas,
or the uppermost portions of the ground water and/or capillary fringe - see
Table 1)? (We recommend this consideration involve DQOs (see Appendix A)
used in acquiring the site data as well as an appropriately scaled Conceptual Site
Model (CSM) for vapor intrusion (see Appendix B).)
If YES - check here, check off the relevant chemicals on Table 1, and continue
with Question 2. The chemicals identified here (and any degradation products)
are evaluated as constituents of potential concern in subsequent questions.
If NO - check here, provide the rationale and references below, and then go to the
Summary Page to document that the subsurface vapor to indoor air pathway is
incomplete (i.e., no further consideration of this pathway is needed); or
If sufficient data are not available, go to the Summary Page and document the
need for more information. After collecting the necessary data, Question 1 can
then be revisited with the newly collected data to re-evaluate the completeness of
the vapor intrusion pathway.
/. What is the goal of this question?
This question is designed to help quickly screen out sites at which the vapor intrusion
pathway generally does not need further consideration. This evaluation involves
determining whether or not any potential exists at a specific site for the vapor intrusion
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pathway to result in unacceptable indoor air inhalation risks. Table 1 lists chemicals that
may be found at hazardous waste sites and indicates whether, in our judgment, they are
sufficiently volatile (Henry's Law Constant > 10"5 atm m3/mol) to result in potentially
significant vapor intrusion and sufficiently toxic (either an incremental lifetime cancer
risk greater than 10"6 or a non-cancer hazard index greater than 1, or in some cases both)
to result in potentially unacceptable indoor air inhalation risks. The approach used to
develop Table 1 is documented in Appendix D and can be used, where appropriate, to
evaluate volatile chemicals not included in the Table. We recommend that if any of the
chemicals listed in Table 1 that are sufficiently volatile and toxic are present at a site,
those chemicals become constituents of potential concern for the vapor intrusion pathway
and are evaluated in subsequent questions in this guidance. If the chemicals listed in
Table 1 are not present at a site, and no other volatile chemicals are present, we suggest
that the vapor intrusion pathway be considered incomplete and no further consideration
of this pathway is needed.
2. What should you keep in mind?
In evaluating the available site data, we recommend the DQOs used in collecting the data
be reviewed to ensure those objectives are consistent with the DQOs for the vapor
intrusion pathway (see Appendix A). We recommend the detection limits associated with
the available groundwater data be reviewed to ensure they are not too high to detect
volatile contaminants of potential concern. Also, we suggest that the adequacy of the
definition of the nature and extent of contamination in groundwater and/or the vadose
zone be assessed to ensure that all contaminants of concern and areas of contamination
have been identified. Additionally, we recommend groundwater concentrations be
measured or reasonably estimated using samples collected from wells screened at, or
across the top of the water table. We recommend users read Appendices B (Conceptual
Site Model for the Vapor Intrusion Pathway) and E (Relevant Methods and Techniques)
to obtain a greater understanding of the important considerations in evaluating data for
use in screening assessments of the vapor intrusion pathway.
3. Rationale and References:
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B.
Q2:
Primary Screening - Question #2
Are currently (or potentially) inhabited buildings or areas of concern under
future development scenarios located near (see discussion below) subsurface
contaminants found in Table 1?
If YES - check here, identify buildings and/or areas of concern below, and
document on the Summary Page whether the potential for impacts from the vapor
intrusion pathway applies to currently inhabited buildings or areas of concern
under reasonably anticipated future development scenarios, or both. (Note that for
El considerations, we recommend only current risks be evaluated.) Then proceed
with Question 3.
If NO - check here, describe the rationale below, and then go to the Summary
Page to document that there is no potential for the vapor intrusion pathway to
impact either currently inhabited buildings or areas of concern under future
development scenarios (i.e., no further evaluation of this pathway is needed).
(Note that for El considerations, only current risks are evaluated.); or
If sufficient data are not available - check here and document the need for more
information on the Summary Page. After collecting the necessary data, Question
2 can then be revisited with the newly collected data to re-evaluate the
completeness of the vapor intrusion pathway.
1. What is the goal of this question?
The goal of this question is to help determine whether inhabited buildings currently are
located (or may be reasonably expected to be located under future development
scenarios) above or in close proximity to subsurface contamination that potentially could
result in unacceptable indoor air inhalation risks. If inhabited buildings and/or future
development are not located "near"' the area of concern, we suggest that the vapor
intrusion pathway be considered incomplete and no further consideration of the pathway
should be needed.
For the purposes of this question, "inhabited buildings" are structures with enclosed air
space that are designed for human occupancy. Table 1, discussed above in Question 1,
lists the "subsurface contaminants demonstrating sufficient volatility and toxicity" to
potentially pose an inhalation risk. We recommend that an inhabited building generally
be considered "near" subsurface contaminants if it is located within approximately 100 ft
laterally or vertically of known or interpolated soil gas or groundwater contaminants
listed in Table 1 (or others not included in table 1 - see Question 1) and the
contamination occurs in the unsaturated zone and/or the uppermost saturated zone. If the
source of contamination is groundwater, we recommend migration of the contaminant
plume be considered when evaluating the potential for future risks. The distance
suggested above (100 feet) may not be appropriate for all sites (or contaminants) and,
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consequently, we recommend that professional judgment be used when evaluating the
potential for vertical and horizontal vapor migration.
2. How did we develop the suggested distance?
The recommended distance is designed to allow for the assessment to focus on buildings
(or areas with the potential to be developed for human habitation) most likely to have a
complete vapor intrusion pathway. Vapor concentrations generally decrease with
increasing distance from a subsurface vapor source, and eventually at some distance the
concentrations become negligible. The distance at which concentrations are negligible is
a function of the mobility, toxicity and persistence of the chemical, as well as the
geometry of the source, subsurface materials, and characteristics of the buildings of
concern. Available information suggests that 100 feet laterally and vertically is a
reasonable criterion when considering vapor migration fundamentals, typical sampling
density, and uncertainty in defining the actual contaminant spatial distribution. The
recommended lateral distance is supported by empirical data from Colorado sites where
the vapor intrusion pathway has been evaluated. At these sites, no significant indoor air
concentrations have been found in residences at a distance greater than one house lot
(approximately 100 feet) from the interpolated edge of ground water plumes.
Considering the nature of diffusive vapor transport and the typical anisotropy in soil
permeability, in our judgment a similar criterion of 100 feet for vertical transport is
generally conservative. These recommended distances will be re-evaluated and, if
necessary, adjusted by EPA as additional empirical data are compiled.
3. What should you keep in mind when evaluating this criterion ?
It is important to consider whether significant preferential pathways could allow vapors
to migrate more than 100 feet laterally. For the purposes of this guidance, a "significant"
preferential pathway is a naturally occurring or anthropogenic subsurface pathway that is
expected to have a high gas permeability and be of sufficient volume and proximity to a
building so that it may be reasonably anticipated to influence vapor intrusion into the
building. Examples include fractures, macropores, utility conduits, and subsurface drains
that intersect vapor sources or vapor migration pathways. Note that naturally occurring
fractures and macropores may serve as preferential pathways for either vertical or
horizontal vapor migration, whereas anthropogenic features such as utility conduits are
relatively shallow features and would likely serve only as a preferential pathway for
horizontal migration. In either case, we recommend that buildings with significant
preferential pathways be evaluated even if they are further than 100 ft from the
contamination.
We also recommend that the potential for mobile "vapor clouds" (gas plumes) emanating
from near-surface sources of contamination into the subsurface be considered when
evaluating site data. Examples of such mobile "vapor clouds" include: 1) those
originating in landfills where methane may serve as a carrier gas; and 2) those originating
in commercial/industrial settings (such as dry cleaning facilities) where vapor can be
released within an enclosed space and the density of the chemicals' vapor may result in
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significant advective transport of the vapors downward through cracks/openings in floors
and into the vadose zone. In these cases, diffusive transport of vapors is usually
overridden by advective transport, and the vapors may be transported in the vadose zone
several hundred feet from the source of contamination.
Finally, this guidance is intended to be applied to existing groundvvater plumes as they
are currently defined (e.g., MCLs, State Standards, or Risk-Based Concentrations).
However, it is very important to recognize that some non-potable aquifers may have
plumes that have been defined by threshold concentrations significantly higher than
drinking-water concentrations. In these cases, contamination that is not technically
considered part of the plume may still pose significant risks via the vapor intrusion
pathway and, consequently, the plume definition may need to be expanded. Similarly,
we recommend evaluating the technologies used to obtain soil gas and indoor air
concentrations to determine if appropriate methods were used to ensure adequate data
quality at the time analyses were conducted.
4. Identify Inhabited Buildings (or Areas With Potential for Future Residential
Development) Within Distances of Possible Concern:
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C. Primary Screening Stage Question #3
Q3: Does evidence suggest immediate action may be warranted to mitigate
current risks?
If YES - check here and proceed with appropriate actions to verify or eliminate
imminent risks. Some examples of actions may include but are not limited to
indoor air quality monitoring, engineered containment or ventilation systems, or
relocation of people. The action(s) should be appropriate for the site-specific
situation.
If NO - check here and continue with Question 4.
1. What is the goal of this question ?
This question is intended to help determine whether immediate action may be warranted
for those buildings identified in Question 2 as located within the areas of concern. For
the purposes of this guidance, "immediate action" means such action is necessary to
verify or abate imminent and substantial threats to human health.
2. What are the qualitative criteria generally considered sufficient to indicate a
need for immediate actions?
Odors reported by occupants, particularly if described as "chemical," or "solvent," or
"gasoline." The presence of odors does not necessarily correspond to adverse health
and/or safety impacts and the odors could be the result of indoor vapor sources; however,
we believe it is generally prudent to investigate any reports of odors as the odor threshold
for some chemicals exceeds their respective acceptable target breathing zone
concentrations.
Physiological effects reported by occupants (dizziness, nausea, vomiting, confusion, etc.)
may, or may not be due to subsurface vapor intrusion or even other indoor vapor sources,
but, should generally be evaluated.
Wet basements, in areas where chemicals of sufficient volatility and toxicity (see
Table 1) are known to be present in groundwater and the water table is shallow
enough that the basements are prone to groundwater intrusion or flooding. This has
been proven to be especially important where there is evidence of light, non-aqueous
phase liquids (LNAPLs) floating on the water table directly below the building, and/or
any direct evidence of contamination (liquid chemical or dissolved in water) inside the
building.
Short-term safety concerns are known, or are reasonably suspected to exist, including:
a) measured or likely explosive or acutely toxic concentrations of vapors in the building
or connected utility conduits, sumps, or other subsurface drains directly connected to the
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building and b) measured or likely vapor concentrations that may be
flammable/combustible, corrosive, or chemically reactive.
3. Rationale and Reference(s):
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V. TIER 2 - SECONDARY SCREENING
The vapor intrusion pathway is complex and, consequently, we recommend that a
comprehensive assessment of this pathway using all available lines of evidence be
conducted before drawing conclusions about the risks posed by this pathway. Users are
encouraged to consider the evidence for vapor intrusion in sequential steps, starting with
the source of vapors (contaminated ground water or unsaturated soils), proceeding to soil
gas in the unsaturated zone above the source, and upward to the exposure point (e.g.,
subslab or crawlspace vapor). Then, if indicated by the results of previous steps, collect
and evaluate indoor air data. In our judgment, this sequential evaluation of independent
lines of evidence provides a logical and cost-effective approach for identifying whether
or not subsurface vapor intrusion is likely to contribute significantly to unacceptable
indoor air quality. However, in those cases where indoor air quality data are available at
the beginning of an evaluation, this guidance recognizes these data will generally be
considered early in the process.
Collection of indoor air quality data without evidence to support the potential for vapor
intrusion from subsurface sources can lead to confounding results. Indoor air quality can
be influenced by 'background' levels of volatile chemicals. For example, consumer
products typically found in the home (e.g., cleaners, paints, and glues) or occupant
activities (e.g., craft hobbies, smoking) may serve as contributory sources of indoor air
contaminants. Additionally, ambient (outdoor) air in urban areas often contains
detectable concentrations of many volatile chemicals. In either case, the resulting indoor
air concentrations can be similar to or higher than levels that are calculated to pose an
unacceptable chronic inhalation risk in screening calculations. In fact, there may be
dozens of detectable chemicals in indoor air even absent subsurface contributions. Thus,
we recommend focusing the evaluation of existing indoor air data on constituents (and
any potential degradation products) present in subsurface sources of contamination. We
recommend considering the relative contributions of background sources (see
Appendices E and I) in order to properly assess the potential inhalation exposure risks
that can be attributed to the subsurface vapor intrusion pathway.
Using a sequential approach, the secondary screening suggested in this guidance involves
comparing available measured or reasonably estimated concentrations of constituents of
potential concern (identified in Question 1) in groundwater and/or soil gas to target
concentrations identified in Questions 4 and 5. More detailed studies, including
foundation and/or indoor air sampling and vapor intrusion modeling, are generally
conducted in the site-specific assessment in Question 6. The sequential evaluation
approach is illustrated in flow diagrams included in Appendix C. Question 4 uses
conservative "generic" attenuation factors that reflect generally reasonable worst-case
conditions for a first-pass screening of groundwater and soil gas data. Question 5 uses
attenuation factors (based on a generally conservative use of the Johnson-Ettinger
mathematical model) that relate groundwater and soil gas target concentrations to such
site-specific conditions as depth of contamination and soil type. In performing the
secondary screening assessment, the user will need to identify whether the contamination
(source of vapors) occurs in groundwater or in the unsaturated zone. In our judgment, if
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there is a contaminant source in the unsaturated zone, soil gas data are needed to evaluate
the vapor intrusion pathway in the vicinity of the unsaturated zone source. However, we
recommend that groundwater data still be evaluated, particularly if the plume extends
beyond an unsaturated zone source of vapors, but only in conjunction with soil gas data.
If the secondary screening indicates the vapor intrusion pathway is complete, the
guidance recommends the user perform a site-specific assessment following the
guidelines in Question 6. If the secondary screening indicates this pathway is incomplete
and/or does not pose an unacceptable risk to human health, then no further assessment of
the pathway is recommended, unless conditions change.
The media-specific target concentrations used in Questions 4 and 5 were developed
considering a generic conceptual model for vapor intrusion consisting of a groundwater
and/or vadose zone source of volatile vapors that diffuse upwards through unsaturated
soils towards the surface. Under the model, the soil in the vadose zone is considered to
be relatively homogeneous and isotropic, though horizontal layers of soil types can be
accommodated. The receptors at the surface used in the model are residents in homes
with poured concrete foundations (e.g., basement or slab on grade foundations or
crawlspace homes with a liner or other vapor barrier). The underlying assumption for
this generic model is that site-specific subsurface characteristics will tend to reduce or
attenuate vapor concentrations as vapors migrate upward from the source and into
structures. Thus, application of the secondary screening target concentrations
necessitates at least rudimentary knowledge of the contamination source, subsurface
conditions (e.g., measured or reasonably estimated concentrations of target chemicals in
soil or groundwater, and depth of contamination and soil type), and building construction
at the site (e.g., foundation type). Specific factors that may result in unattenuated or
enhanced transport of vapors towards a receptor, and consequently are likely to render the
use of the secondary screening target concentrations inappropriate, are discussed in each
question below. Factors such as biodegradation that can result in accelerated attenuation
of vapors are not considered in the conceptual model. In general, it is recommended that
the user consider whether the assumptions underlying the generic conceptual model are
applicable at each site, and use professional judgment to make whatever adjustments
(including not considering the model at all) are appropriate.
A. Secondary Screening - Question #4: Generic Screening
Q4(a): Are indoor air quality data available? (Collection of indoor air quality data
without evidence to indicate the potential for vapor intrusion from subsurface
sources is not recommended at this level of screening, but if such data are
available, we recommend they be evaluated along with the available subsurface
data)
If YES - check here and proceed to Question 4(b).
If NO - check here and proceed to Subsurface Source Identification - Question
4(c).
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Q4(b): Do measured indoor air concentrations of constituents of potential concern
identified in Question 1 (and any degradation products) exceed the target
concentrations given in Tables 2(a), 2(b), or 2(c)?
If YES - check here, document representative indoor air concentrations on Table
2, and initiate a site-specific assessment following the guidelines in Question 6.
(We recommend the user also proceed with the subsurface evaluation to evaluate
whether there is sufficient evidence to indicate the elevated indoor concentrations
are due to vapor intrusion from subsurface sources, and not from background or
other sources)
If NO - check here and proceed to Subsurface Source Identification - Question
4(c). (Here, the recommendation to proceed with the subsurface evaluation is
based on the assumption that only limited indoor air data are available and,
therefore, the available subsurface data need to be evaluated to ensure that all
possible areas potentially affected by the vapor intrusion pathway are evaluated.
However, in our judgment, if the site has been adequately characterized and
sufficient indoor air data are available (see Question 6 for a discussion of data
needs), the pathway is incomplete and/or does not pose an unacceptable risk to
human health, and no further assessment of the pathway is recommended.
Document the finding as described in Question 6.)
Subsurface Source Identification:
Q4(c): Is there any potential contamination (source of vapors) in the unsaturated
zone soil at any depth above the water table? (In our judgment, if there is a
contaminant source in the unsaturated zone, soil gas data are needed to evaluate
the vapor intrusion pathway in the vicinity of the source and, consequently, use of
the groundwater target concentrations may be inappropriate. However, we
recommend that groundwater data still be evaluated, particularly if a contaminant
plume extends beyond the unsaturated zone source, but that the evaluation be
performed only in conjunction with an evaluation of soil gas data. Other vapor
sources that typically make the use of groundwater target concentrations
inappropriate include: 1) those originating in landfills where methane may serve
as a carrier gas; 2) those originating in commercial/industrial settings (such as dry
cleaning facilities) where vapor can be released within an enclosed space and the
density of the chemicals' vapor may result in significant advective transport of the
vapors downward through cracks/openings in floors and into the vadose zone; and
3) leaking vapors from underground storage tanks. In these cases, diffusive
transport of vapors is often overridden by advective transport and the vapors may
be transported in the vadose zone several hundred feet from the source of
contamination.)
If YES-check here and skip to Soil Gas Assessment - Question 4 (g) below.
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If NO- check here and continue with Groundwater Assessment - Question 4(d)
below.
Groundwater Assessment:
Q4(d): Do measured or reasonably estimated groundwater concentrations exceed
the generic target media-specific concentrations given in Tables 2(a), 2(b), or
2(c)? (For more information on the use of data for this part, please see the sections
below entitled "How should data be used in this question?" and "How do you
know you have unusable data?".)
If YES (or if the detection limit for any constituents of potential concern is above
the target concentration) - check here and document representative groundwater
concentrations on Table 2. If soil gas data are available, proceed to Soil Gas
Assessment - Question 4(g) below, otherwise proceed to Question 5.
If NO - check here and proceed to Question 4(e).
Q4(e): Is the nature and extent of groundwater contamination adequately
characterized (see Appendices B & E) in areas with inhabited buildings (or areas
with the potential for future development of inhabited buildings)?
If YES - check here and continue with Question 4(f) below.
If NO - check here, go to Summary Page and document that more information is
needed. We recommend the next step be expeditious collection of the needed
data in accordance with proper DQOs. Question 4 can then be revisited with the
newly collected data to re-evaluate the completeness of the vapor intrusion
pathway.
Q4(f): Are there site conditions and/or data limitations that make the use of the
recommended generic groundwater attenuation factors inappropriate? We
recommend this consideration involve comparison of the generic conceptual
model to an appropriately scaled and updated Conceptual Site Model (CSM) for
vapor intrusion (see Appendix B), as well as the proper DQOs (see Appendix A).
We also recommend evaluation of the generic attenuation factors used to develop
the media-specific attenuation factors (see the section below titled "What is in
Tables 2(a), 2(b), and 2(c) and how did we develop them?" and Appendix F.)
Factors that, in our judgment, typically make the use of generic groundwater
attenuation factors inappropriate include:
LJ Very shallow groundwater sources (e.g., depths to water less than 5 ft
below foundation level); or
U Relatively shallow groundwater sources (e.g., depths to water less than 15
ft below foundation), and one or more of the following:
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o buildings with significant openings to the subsurface (e.g., sumps,
unlined crawlspaces, earthen floors), or
o significant preferential pathways, either naturally-occurring and/or
anthropogenic (see discussion below under "What Should I Keep
in Mind When Evaluating Data"), or
o buildings with very low air exchange rates (e.g., < 0.25/hr) or very
high sustained indoor/outdoor pressure differentials (e.g., > 10
Pascals).
If YES - check here, briefly document the issues below, and proceed to Site-
Specific Assessment - Question 6.
If NO - check here, briefly document the rationale below and document on the
Summary Page that the groundwater data indicate the pathway is incomplete
and/or does not pose an unacceptable risk to human health. In order to increase
confidence in the assessment that the pathway is incomplete, we recommend that
soil gas data also be evaluated (Question 4(g)).
If sufficient data (of acceptable quality) are not available - check here, go to
Summary Page and document that more information is needed. We recommend
the next step be expeditious collection of the needed data in accord with proper
DQOs. Question 4 can then be revisited with the newly collected data to re-
evaluate the completeness of the vapor intrusion pathway.
Soil Gas Assessment:
Q4(g): Do measured or reasonably estimated soil gas concentrations exceed the
generic target media-specific concentrations given in Tables 2(a), 2(b), or 2(c)
(see Appendix D)? For more information on the use of data for this part, please
see the section below entitled "How should data be used in this question?"
If YES (or if the detection limit for any constituents of potential concern is above
the target concentration) - check here. Document representative soil gas
concentrations on Table 2 and proceed to Question 5.
If NO - check here and proceed to Question 4(h).
Q4(h): Is the nature and extent of soil contamination adequately characterized and
has an adequate demonstration been made to show that the soil gas sampling
techniques used could reasonably detect an elevated concentration of vapors
if they were present in the site setting?
If YES - check here and continue with Question 4(i) below.
If NO - check here. Skip to Summary Page and document that more information
is needed. We recommend the next step be expeditious collection of the needed
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data in accord with proper DQOs. Question 4 can then be revisited with the
newly collected data to re-evaluate the completeness of the vapor intrusion
pathway.
Q4(i): Are there site conditions and/or data limitations that may make the use of
generic soil gas attenuation factors inappropriate? (We recommend that this
consideration involve an appropriately scaled and updated Conceptual Site Model
(CSM) for vapor intrusion (see Appendix B), as well as the proper DQOs (see
Appendix A). We also recommend evaluation of the generic attenuation factors
used to develop the media-specific attenuation factors (see the section below titled
"What is in Tables 2(a), 2(b), and 2(c) and how did we develop them?" and
Appendix F.))
Factors that, in our judgment, typically make the use of generic soil gas
attenuation factors inappropriate include:
LJ Shallow soil contamination vapor sources (e.g., less than 15 ft below
foundation level), and one or more of the following:
o buildings with significant openings to the subsurface (e.g., sumps,
unlined crawlspaces, earthen floors), or
o significant preferential pathways, either naturally-occurring and/or
anthropogenic (see discussion below under "What Should I Keep
in Mind When Evaluating Data"), or
o buildings with very low air exchange rates (e.g., < 0.25/hr) or very
high sustained indoor/outdoor pressure differentials (e.g., > 10
Pascals).
If YES - check here, briefly document the issues below, and proceed to Site-
Specific Assessment - Question 6.
If NO - check here, briefly document the rationale below and document on the
Summary Page that the soil gas data indicate the pathway is incomplete and/or
does not pose an unacceptable risk to human health. In this case, no further
assessment of the vapor intrusion pathway is recommended.
If sufficient data (of acceptable quality) are not available - check here, go to
Summary Page and document that more information is needed. We recommend
the next step be expeditious collection of the needed data in accord with proper
DQOs or proceed to Question 5. When additional data are collected, Question 4
can then be revisited with the newly collected data to re-evaluate the
completeness of the vapor intrusion pathway.
1. What is the goal of this question ?
Question 4 is intended to allow a rapid screening of available site data using measured or
reasonably estimated groundwater and/or soil gas concentrations. The term "measured or
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reasonably estimated" is used above (and throughout this document) in recognition of the
fact that measurements adjacent to or in all buildings of concern may not be practical or
necessary. For example, groundwater concentrations beneath buildings are commonly
estimated from concentrations collected in wells distributed about a larger area of
interest.
2, How should data be used in this question ?
Question 4 calls for comparison of site data with generic target media-specific
concentrations given in Tables 2(a), 2(b), and 2(c). These target media-specific
concentrations correspond to indoor air concentrations associated with a specific
incremental lifetime cancer risk of (a) 10"4, (b) 10"5, (c) 10"6 or a hazard quotient greater
than 1 (whichever is more restrictive). Under this question, the user selects the
appropriate screening risk level for the site and compares the soil gas and/or groundwater
concentrations observed at the site to the corresponding target media concentrations in
the table. If the detection limit for any constituent of potential concern is above its target
screening level, we recommend the user continue the evaluation as though the target level
is exceeded.
In order to select the appropriate target media concentrations for comparison, it is
important to identify whether a source of vapors in an area occurs in the unsaturated zone
(contaminated soil). This allows the site data to be segregated into two categories: a) data
representing areas where contaminated groundwater is the only source of contaminant
vapors, and b) data representing areas where the underlying unsaturated zone soil
contains a source of vapors. In case (a) either the groundwater or soil gas target
concentrations in Tables 2(a), 2(b), or 2(c) are generally appropriate to use. In case (b),
we recommend that only soil gas target concentrations and soil gas samples collected
above the vapor source zone be used. This is because the groundwater target
concentrations have been derived assuming no other vapor sources exist between the
water table and the building foundation. However, we recommend that groundwater data
still be evaluated, particularly if a contaminant plume extends beyond the unsaturated
zone source, but the evaluation be performed only in conjunction with an evaluation of
soil gas data In either case, because of the complexity of the vapor intrusion pathway,
we recommend that professional judgment be used when applying the target
concentrations.
This screening approach is based on a conceptual model that assumes diffusive transport
of vapors in the unsaturated zone. Consequently, we recommend the target
concentrations used in this secondary screening not be applied to data from sites in which
advection significantly influences vapor transport. Thus, the exclusionary criteria listed
above in Questions 4(f) and 4(i) are designed to identify those situations in which
advective vapor transport may result in unattenuated or enhanced vapor intrusion (e.g.,
shallow vapor sources at depths less than 15 ft below foundation level and buildings with
significant openings to the subsurface, or very high sustained pressure differentials, or
significant vertical preferential pathways).
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3. What is in Tables 2(a), 2(b), and 2(c) and how did we develop them?
Tables 2(a), 2(b), or 2(c) contain generally recommended target concentrations for indoor
air, soil gas, and groundwater for each chemical listed. A separate table is provided for
each of the three cancer risk levels considered (a) 10"4, (b) 10"5, and (c) 10 including
non-cancer risk values where applicable for Hazard Quotient = 1. Details regarding the
derivation of Tables 2(a), 2(b), and 2(c) are provided in Appendix D. The tabulated
indoor air concentrations are risk-based screening levels calculated following an
approach consistent with EPA's Supplemental Guidance for Developing Soil Screening
Levels for Superfund Sites (EPA, 2002). These recommended target indoor air
concentrations were calculated using toxicity information current as of the date indicated
on the tables. The user is encouraged to visit the EPA web-page to determine whether
updated tables are available.
The soil gas and groundwater target concentrations were calculated to correspond to the
target indoor air concentrations using media-specific attenuation factors. Shallow soil
gas (e.g., subslab gas and soil gas measured at 5 feet or less from the base of the
foundation) is conservatively assumed to intrude into indoor spaces with an attenuation
factor of 0.1. Note that in general samples taken less than 5 feet below the building
foundation are not recommended unless the sample was taken from directly under the
foundation slab or repeated sampling is performed to ensure a representative soil gas
value. For deep soil gas (e.g., soil gas samples taken at depths greater than
approximately 5 feet below the foundation level), an attenuation factor of 0.01 (generally
considered reasonably conservative) is used to calculate target concentrations. For
groundwater, an attenuation factor of 0.001 (generally considered reasonably
conservative) is used in combination with the conservative assumption that the
partitioning of chemicals between groundwater and soil vapor is assumed to obey
Henry's Law. (Note that if the risk-based concentration calculated for groundwater falls
below the chemical's MCL, the MCL is recommended as the target concentrations.)
EPA generally considers the attenuation factors used in this guidance to be reasonable
upper bound values based on data from sites where paired indoor air, soil gas and
groundwater samples were available (see Appendix F), and also theoretical
considerations.
4. How do you know if you have usable data?
In comparing available site data to the target media-specific target concentrations in
Table 2, we recommend that DQOs used in collecting the data be consistent with DQOs
for the vapor intrusion pathway and that the sampling issues specific to evaluating this
pathway be considered (see Appendices A and E). Some examples of sampling issues
that we recommend be considered are: 1) groundwater samples be taken from wells
screened (preferably over short intervals) across the top of the water table (only volatile
contaminants in the uppermost portions of an aquifer, including the capillary fringe, are
likely to volatilize into the vadose zone and potentially migrate into indoor air spaces); 2)
fluctuations in water table elevation can lead to elevated source vapor concentrations and
thus, we recommend soil gas samples be considered in these areas; 3) we recommend soil
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gas samples be taken as close to the areas of interest as possible and preferably from
directly underneath the building structure; and 4) as vapors are likely to migrate upward
through the coarsest and/or driest material, we recommend that soil gas samples be
collected from these materials. More detail regarding considerations for using
groundwater and soil gas data to evaluate the vapor intrusion pathway are provided in
Appendix E.
5. What should I keep in mind when evaluating data?
It is important to consider whether significant preferential pathways could allow vapors
to migrate farther and at greater concentrations than expected. For purposes of this
guidance, a preferential pathway is a naturally-occurring and/or anthropogenic subsurface
'pathway' that is expected to have a high intrinsic gas permeability (vadose zone) or high
conductivity (saturated zone) and thus influence the flow or migration of contaminated
vapors or groundwater. A preferential pathway is likely to have a significant influence
on vapor intrusion if it is of sufficient volume and proximity to a currently occupied
building so that it may be reasonably anticipated to influence the migration of
contaminants to, or into, the building. Significant vertical preferential pathways may
result in higher than anticipated concentrations in the overlying near surface soils,
whereas significant horizontal preferential pathways may result in elevated
concentrations in areas on the periphery of subsurface contamination. Naturally
occurring preferential pathways may include fractured vadose zone geology or very
permeable soils located between a relatively shallow source of contamination and a
building. Anthropogenic preferential pathways may include utility conduits or
subsurface drains that are directly connected to a building and a source of vapors. In
highly developed residential areas, extensive networks of subsurface utility conduits
could significantly influence the migration of contaminants. EPA recommends that
buildings with significant preferential pathways be evaluated closely even if they are
further than 100 feet from the contamination.
6. What if I have bulk soil data ?
Soil (as opposed to soil gas) sampling and analysis is not currently recommended for
assessing whether or not the vapor intrusion pathway is complete. This is because of the
large uncertainties associated with measuring concentrations of volatile contaminants
introduced during soil sampling, preservation, and chemical analysis, as well as the
uncertainties associated with soil partitioning calculations. Thus, bulk soil target
concentrations were not derived and the use of bulk soil target concentration is not
generally recommended. Note however, if a NAPL source is suspected, a soil sample
may be necessary to determine whether a NAPL source is present. Also, bulk soil
concentration data could be used in a qualitative sense for delineation of sources, where
appropriate. For example, high soil concentrations would indicate impacted soils;
unfortunately, the converse is not always true and it is our judgment that non-detect
analytical results can not be interpreted to indicate the absence of a vapor source.
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7. Rationale and Reference(s):
Document Risk Level Used (Circle One): KK4, (b) 10 5, or (c) 106
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B. Secondary Screening - Question #5: Semi-Site Specific Screening
Q5(a): Do groundwater and/or soil gas concentrations for any constituents of
potential concern exceed target media-specific concentrations by a factor
greater than 50? (Evaluation of limited site data in Question 5 allows the user to
potentially screen sites using target concentrations that are higher by a factor of
up to 50 times greater than the generic target concentrations used in Question 4.
If observed concentrations are greater than 50 times the generic target
concentrations, we recommend expeditious site-specific evaluation.)
If YES - check here and briefly document the issues below and go to Site-
Specific Assessment - Question 6.
If NO - check here and continue with Question 5(b).
Q5(b): Are there site conditions and/or data limitations under which we would not
recommend the use of semi-site specific attenuation factors (based on the
Johnson-Ettinger Model)? (To determine whether use of the Johnson-Ettinger
model is appropriate, we recommend the user consider an appropriately scaled
and updated Conceptual Site Model (CSM) for vapor intrusion (see Appendix B)
and DQOs (see Appendix A). We also recommend users refer to Appendix G,
which lists the limitations of the Johnson-Ettinger Model.)
Factors that, in our judgment, typically make the use of semi-site specific
attenuation factors inappropriate include:
U Very shallow vapor sources (e.g., depths less than 5 ft below foundation
level); or
U Relatively shallow vapor sources (e.g., depths less than 15 ft below
foundation level), and one or more of the following:
o buildings with significant openings to the subsurface (e.g., sumps,
unlined crawlspaces, earthen floors), or
o significant preferential pathways, either naturally-occurring and/or
anthropogenic (see discussion in Question 4), or
o buildings with very low air exchange rates (e.g., < 0.25/hr) or very
high sustained indoor/outdoor pressure differentials (e.g., > 10
Pascals), or
o soil types outside the range shown in Table 4, or
LJ Any other situation for which the Johnson-Ettinger Model is deemed
inappropriate.
If YES - check here and briefly document the issues below and go to Site-
Specific Assessment - Question 6.
If NO - check here and continue with Question S(c).
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If sufficient data (of acceptable quality) are not available - check here and skip to
Summary Page and document that more information is needed. We recommend
that the next step be expeditious collection of the needed data in accord with
proper DQOs. Question 5 can then be revisited with the newly collected data to
re-evaluate the completeness of the vapor intrusion pathway.
Q5(c): Are the depth to vapor source and the overlying unsaturated zone soil type
adequately characterized in areas with inhabited buildings (or areas with the
potential for future development of inhabited buildings)?
If YES - check here and continue with Question 5(d) below.
If NO - check here, go to Summary Page and document that more information is
needed. We recommend the next step be expeditious collection of the needed
data in accord with proper DQOs. Question 5 can then be revisited with the
newly collected data to re-evaluate the completeness of the vapor intrusion
pathway.
Subsurface Source Identification
Q5(d):Is there any potential contamination (source of vapors) in the unsaturated
zone soil at any depth above the water table? (In our judgment, if there is a
contaminant source in the unsaturated zone, soil gas data are needed to evaluate
the vapor intrusion pathway in the vicinity of the source and, consequently, use of
the groundwater target concentrations may be inappropriate. However, we
recommend that groundwater data still be evaluated, particularly if a contaminant
plume extends beyond the unsaturated zone source, but that the evaluation be
performed only in conjunction with an evaluation of soil gas data. Other vapor
sources that we believe typically make the use of groundwater target
concentrations inappropriate include: 1) those originating in landfills where
methane may serve as a carrier gas; 2) those originating in commercial/industrial
settings (such as dry cleaning facilities) where vapor can be released within an
enclosed space and the density of the chemicals' vapor may result in significant
advective transport of the vapors downward through cracks/openings in floors and
into the vadose zone; and 3) leaking vapors from underground storage tanks. In
these cases, diffusive transport of vapors is often overridden by advective
transport and the vapors may be transported in the vadose zone several hundred
feet from the source of contamination.)
If YES - check here and skip to Soil Gas Assessment - Question 5(f) below.
If NO - check here and continue with Groundwater Assessment - Question 5(e)
below.
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Groundwater Assessment:
Q5(e):Do measured or reasonably estimated groundwater concentrations exceed the
target media-specific concentrations given in Tables 3(a), 3(b), or 3(c) for the
appropriate attenuation factor (given that the conditions listed above in 5(b) are
not present and that sampling issues described Appendix E have been
considered)?
If YES - check here, document the soil type, depth to groundwater and
attenuation factor used in the assessment on the summary page, and document the
representative groundwater concentrations on Table 3. If soil gas data are
available, proceed to Soil Gas Assessment - Question 5(1) below, otherwise
proceed to Site Specific Assessment - Question 6,
If NO - check here and document that the groundwater data indicate that the
pathway is incomplete and/or does not pose an unacceptable risk to human
health on the Summary Page. In order to increase confidence in the assessment
that the pathway is incomplete, EPA recommends that soil gas data also be
evaluated following the soil gas assessment guidelines below (Question 5(1)).
Soil Gas Assessment:
Q5(f): Do measured or reasonably estimated soil gas concentrations exceed the
target media-specific concentrations given in Tables 3(a), 3(b), or 3(c) for the
appropriate attenuation factor (given that the conditions listed above in 5(b) are
not present, or that other site specific factors make consideration of this analysis
inappropriate, and that sampling issues described in Appendix E have been
considered)?
If YES - check here, document the soil type, depth to source and attenuation
factor used in the assessment on the summary page, document representative soil
gas concentrations on Table 3 and proceed to Site Specific Assessment -
Question 6
If NO - check here and document that the subsurface vapor to indoor air pathway
is incomplete and/or does not pose an unacceptable risk to human health on the
Summary Page. In this case, we recommend no further assessment of the vapor
intrusion pathway.
/. What is the goal of this question ?
The goal of this question is to provide a means of evaluating the vapor intrusion pathway
using tables of generally recommended target media-specific concentrations that
incorporate limited site-specific information. Specifically, Question 5 factors in
consideration of soil type and depth to source in screening the available groundwater and
soil gas data Soil gas- and groundwater-to-indoor air attenuation factors generally
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depend (as described in Appendix G) on building characteristics, chemical type, soil type,
and depth of the source (which is defined as either a measured soil gas concentration at
the specified sample collection depth below the building, or the ground water
concentration at the depth of the water table). By using the Johnson and Ettinger Model
(1991) and keeping all factors besides source depth and soil type constant (and
reasonably conservative), a set of attenuation factors can be derived that allows for the
selection of semi-site specific target media concentrations that are more representative of
the user's site. The semi-site-specific target values provided in Question 5 are less
conservative (higher by a factor of 2 to 50 times, depending on soil type and depth to
source) than the generic screening values used in Question 4. The increase in target
concentrations corresponds to a decrease in the calculated attenuation factors as depth to
source increases and soil type becomes finer grained (see Figures 3(a) and (b) and
Section 3 below). In our judgment, if observed concentrations are greater than 50 times
the generic target concentrations provided in Question 4, there is no benefit in using the
criteria in Question 5 and we recommend expeditious site-specific evaluation.
2. How do you use the Graphs and the Tables?
The user selects a representative attenuation factor for soil gas from Figure 3(a) and for
groundwater from Figure 3(b) based on measured site-specific information about soil
type and depth to source. The selected attenuation factors are then rounded up to the
nearest attenuation factor shown in Figure 3. Then, the columns in Tables 3(a), 3(b), and
3(c) corresponding to the attenuation factors selected from Figure 3(a) or 3(b) can be
used to determine the appropriate target media concentrations for this level of screening.
The values in Tables 3(a), 3(b), and 3(c) were derived as discussed in Appendix D.
3. How did we develop the media-specific target concentrations?
The Johnson and Ettinger (1991) Model was used as described in Appendix G to
calculate the attenuation factors shown in Figures 3(a) and 3(b). Generally reasonable
building characteristics were selected and held constant in these calculations and the
chemicals were assumed not to degrade. To capture the effect of changes in soil
properties, the U.S. Soil Conservation Service (SCS) soil texture classifications were
considered, and a subset of these was selected. This subset was chosen so that their
relevant properties (porosity and moisture content) would collectively span the range of
conditions most commonly encountered in the field. Then, plots of attenuation factor
versus depth were calculated, and these results are presented in Figures 3(a) and 3(b).
The two graphs are different because the soil gas attenuation factors (Figure 3(a)) do not
have to account for transport across the capillary fringe whereas the groundwater
attenuation factors (Figure 3(b)) do. Details of the input parameters and calculations used
to derive the graphs are included in Appendix G.
4. , What should you keep in mind when using the graphs?
The generally recommended depth to source used to select a scenario-specific attenuation
factor is: 1) the vertical separation between the soil gas sampling point and the building
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foundation for use of Figure 3 (a), or 2) the vertical separation between the water table
and the building foundation for use of Figure 3(b). Note that we recommend that
groundwater or soil gas samples collected at depths less than 5 feet (1.5m) below the
building foundation not be evaluated with these graphs. If contaminated groundwater is
within 5 feet of the foundation level, or if the only soil gas samples available for
screening were obtained from depths less than 5 feet below foundation level and the soil
gas concentrations are greater than target levels, we recommend the user perform a site
specific assessment. If the depth to source across the site varies, we recommend that the
minimum depth be used in this assessment.
We recommend that the soil type used to select a scenario-specific attenuation factor
represent the material most permeable to vapors between the building foundation and the
contaminant source (e.g., the coarsest and/or driest soils). The graphs below use the U.S.
Soil Conservation Service system of soil classification, in which the soil texture classes
are based on the proportionate distribution of sand, silt and clay sized particles in soil.
The generally preferred method for determining the SCS soil class is to use lithological
information combined with the results of grain size distribution tests on selected soil
samples. Table 4 below has been developed to assist users in selecting an appropriate
SCS soil type in cases where lithological and grain size information is limited. Note that
in Table 4 there is no soil texture class represented as consisting primarily of clay.
Exclusion of clay was deliberate since homogenous unfractured clay deposits are rare.
Table 4. Guidance for selection of soil type curves in Figures 3(a) and 3(b).
If your boring log indicates that the following materials
are the predominant soil types
Sand or Gravel or Sand and Gravel, with less than about 12 % fines,
where "fines" are smaller than 0.075 mm in size.
Sand or Silty Sand, with about 12 % to 25 % fines
Silty Sand, with about 25 % to 50 % fines
Silt and Sand or Silty Sand or Clayey, Silty Sand or Sandy Silt or
Clayey, Sandy Silt, with about 50 to 85 % fines
Then we recommend the
following texture
classification when obtaining
the attenuation factor.
Sand
Loamy Sand
Sandy Loam
Loam
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5. Rationale for Selecting Semi-Site Specific Attenuation Factor and References):
Document Risk Level Used (Circle One): 10 4, (b) 10 5, or (c) 10''
36
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s
£
LL
§
o
Q.
Figure 3a- DRAFT
Vapor Attenuation Factors - Soil Vapor to Indoor Air Pathway
Basement Foundations
1.0E-02
2.0E-03
1.0E-05
5 10 15 20
Depth to Contamination from Foundation (m)
30
-Sand
- Sandy Loam
- Loamy Sand
-Loam
Figure 3b- DRAFT
Vapor Attenuation Factors - Ground Water to Indoor Air Pathway
Basement Foundations
1 DE-02-n
1.0E-05
-Sand
5 10 15 20
Depth to Contamination from Foundation (m)
25
30
- Sandy Loam
- Loamy Sand
-Loam
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VI. Tier 3 - Site-Specific Assessment
If primary and secondary screening results do not assist in excluding the existence of a
vapor intrusion pathway, we recommend a site-specific assessment. In this case, this
guidance recommends: (1) direct measurement of foundation air concentrations before
any indoor air measurements; (2) direct measurement of indoor air concentrations
coupled with a home survey (see Appendix H) and sampling to identify background
sources of vapor in ambient (outdoor) and/or indoor air; 3) removal of all indoor air
sources before sampling indoors; and (4) complementary site-specific mathematical
modeling as appropriate. The sampling of foundation air (e.g., subslab and /or
crawlspace air) and ambient (outdoor) air in conjunction with indoor air is intended to
distinguish the exposures that originate from subsurface contaminant vapor intrusion
from those due to background sources.
The recommended site-specific modeling is intended to be complementary to the more
direct building-related measurements collected from a selected subset of the potentially
impacted buildings. Considering the complexities involved in evaluating the vapor
intrusion pathway (due to the sensitivity of attenuation factors to soil type, depth to
source, and building characteristics), mathematical modeling may be useful in
determining which combination of factors leads to the greatest impact and, consequently,
aid in identifying appropriate buildings to be sampled. However, if an appropriate model
is not available or cannot be modified to represent the conceptual site model, the only
available option may be a site-specific assessment that relies entirely on direct measures
of potential exposures.
We recommend that since site-specific assessments are based on direct evidence
(confirmatory sampling of subslab or crawlspace vapor concentrations and/or indoor air
concentrations), decisions made that "no further action with respect to vapor intrusion is
needed", are likely to be "final decisions." Additionally, we recommend that the
approaches suggested in the site-specific assessment be used, where appropriate, to
support Current Human Exposures Under Control El determinations. However, we do
not believe that confirmatory sampling will generally be necessary in that context.
Current Human Exposures Under Control El determinations are intended to reflect a
reasonable conclusion by EPA or the State that current human exposures are under
control with regard to the vapor intrusion pathway and current land use conditions. We
believe that not recommending confirmatory sampling to support Current Human
Exposures Under Control El determinations is appropriate because of the conservative
nature of the assumptions made.
If buildings are not available or not appropriate for sampling, for example in cases where
future potential impacts need to be evaluated, we recommend mathematical modeling be
used to evaluate the potential for unacceptable inhalation risks due to the vapor intrusion
pathway. Where modeling indicates there is the potential that vapor intrusion may result
in unacceptable exposures, other more direct measures of potential impacts, such as
emission flux chambers or soil gas surveys, may need to be conducted in areas underlain
by subsurface contamination. Alternately, it may be appropriate to reduce potential
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exposures with a mechanical ventilation system in the event buildings are constructed
over subsurface vapor sources. EPA recommends that these sites be reevaluated when
they are being developed, as appropriate, and that management decisions be made based
on evaluation results at that time.
The data collected during site-specific evaluations of the vapor intrusion pathway can
also serve to increase the level of understanding about key issues and important factors in
the assessment of this pathway. Because the Agency is interested in improving the
understanding of the modeling approach to evaluate the vapor intrusion pathway, EPA
requests that the relevant data collected in site specific assessments be submitted
electronically to an EPA repository that will be established by OSWER EPA plans to
develop a database structure specific to vapor intrusion evaluations to facilitate electronic
entry of the relevant data and electronic submission to the repository. Once developed,
EPA plans to make the database structure accessible through OERR's and OSW's web
sites.
EPA plans to review and analyze these submitted data on an ongoing basis and consider
appropriately refining this draft guidance for assessing the vapor intrusion pathway. EPA
plans to post any revisions/addenda on the OSWER's website.
A. Site Specific Assessment - Question 6
Q6(a): Have the nature and extent of contaminated soil vapor, unsaturated soil,
and/or groundwater as well as potential preferential pathways and overlying
building characteristics been adequately characterized to identify the most-
likely-to-be-impacted buildings? (Consider an appropriately-scaled Conceptual
Site Model (CSM) for vapor intrusion (see Appendix B) and DQOs (see
Appendix A)).
_ If YES - check here, briefly document the basis below and proceed to Question
6(b). If a model was used, we recommend it be an appropriate and applicable
model that represents the conceptual site model. If other means were used,
document how you determined the potentially most impacted areas to sample.
If NO, or if insufficient data (of acceptable quality) are available - check here,
briefly document the needed data below, and skip to the Summary Page and
document that more information is needed. After collecting the additional data,
you can return to this question. However, if indoor air data are available go to
Question 6(e).
Q6(b): Are you conducting an El determination and are you using an appropriate
and applicable model?
If YES - check here and continue with Question 6(c) below.
If NO - check here and continue with Question 6(d).
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Q6(c): Does the model predict an unacceptable risk? (EPA recommends that
predictive modeling can be used to support Current Human Exposures Under
Control El determinations without confirmatory sampling to support this
determination. Current Human Exposures Under Control El determinations are
intended to reflect a reasonable conclusion by EPA or the State that current
human exposures are under control with regard to the vapor intrusion pathway
and current land use conditions.)
If YES - check here and continue with Question 6(d) below.
If NO - check here and document that the Pathway is Incomplete and/or does not
pose an unacceptable risk to human health for El determinations. However, this
determination does not necessarily reflect a final decision that the site is clean
without confirmatory sampling.
Q6(d): Are subslab soil gas data available?
If YES - check here and continue with Question 6(e) below.
If NO - check here and continue with Question 6(g).
Q6(e): Do measured subslab soil gas concentrations exceed the target shallow soil
gas concentrations given in Tables 2(a), 2(b), or 2(c)?
If YES - check here, document representative subslab soil gas concentrations on
Table 2, collect indoor air data and go to Question 6(g).
If NO - check here and continue to Question 6(1).
Q6(f): Is the subslab sampling data adequate? (We recommend doing subslab
sampling before indoor air sampling) Some factors we recommend for
consideration in this question include:
Do analytical results meet the required detection thresholds?
Do the data account for seasonal and/or temporal transience?
Do the data account for spatial variability?
Is there any reason to suspect random (sampling) or systematic (analytical) error?
How do the data account for the site conceptual model?
Was "background" ambient (outdoor) air or other vapor sources considered?
If YES - check here and document that the Pathway is Incomplete and/or does
not pose an unacceptable risk to human health.
If NO or unsure - check here, briefly document the needed data below, and skip to
the Surnmary Page and document that more information is needed. After
collecting the additional data, return to Question 6(e).
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Q6(g): Do measured indoor air concentrations exceed the target concentrations
given in Tables 2(a), 2(b), or 2(c)? (We recommend that before any indoor air
sampling occurs: 1) an inspection of the residence be conducted, 2) an occupant
survey be completed to adequately identify the presence of (or occupant activities
that could generate) any possible indoor air emissions of target VOCs in the
dwelling (see appendix E, H and I), 3) all possible indoor air emission sources be
removed, and 4) that the analysis be done only for the constitutes of potential
concern found on the site.)
If YES - check here, document representative indoor air concentrations on Table
2, and go to Question 6(i).
If NO - check here and continue to Question 6(h).
Q6(h): Do the indoor air concentrations adequately account for seasonal variability
and represent the most impacted buildings or area (see Appendix E)? Some
factors we recommend for consideration in this question include:
Do analytical results meet the required detection thresholds?
Do the data account for seasonal and/or temporal transience?
Do the data account for spatial variability?
Is there any reason to suspect random (sampling) or systematic (analytical) error?
How do the data account for the site conceptual model?
If YES - check here, document that Pathway is Incomplete and/or does not pose
an unacceptable risk to human health. If a model was used to predict the indoor
air concentrations also document the relationship between the predicted
concentrations and the measured concentrations.
If NO - check here, go to the summary page and document that more information
is needed. If the data do not account for seasonal variability, we recommend
designing a sampling plan to account for seasonal variability, resample and return
to Question 6(g). If the data do not represent most impacted building or area, skip
to the Summary Page and document that more information is needed. After
collecting the additional data, you can return to Question 6(g).
Q6(i): Have background sources of vapor in indoor air and ambient (outdoor) air
been adequately accounted for?
If YES - check here, document results and document that Pathway is Complete.
If a model was used to predict the indoor air concentrations, also document the
relationship between the predicted concentrations and the measured
concentrations.
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If NO - check here, briefly document the needed data below, and skip to the
Summary Page and document that more information is needed. After collecting
the additional data, you can return to Question 6(g).
/. What is the goal of this question ?
The Site-Specific Pathway Assessment is designed to be used where site-specific
conditions warrant further consideration prior to concluding either that the pathway is
incomplete, or that some form of exposure control may be needed. In general, this final
step recommends direct measures of potential impacts (e.g., building-specific foundation
vapor concentrations - subslab sampling and/or indoor air concentrations) coupled with
site-specific mathematical modeling where an appropriate model is available. However,
EPA recommends that predictive modeling can be used to support Current Human
Exposures Under Control El determinations without confirmatory sampling these
determination. Current Human Exposures Under Control El determinations are intended
to reflect a reasonable conclusion by EPA or the State that current human exposures are
under control with regard to the vapor intrusion pathway and current land use conditions.
The purpose of this site-specific approach is to help assess whether or not the vapor
intrusion pathway is a likely problem. It is not meant to provide detailed guidance on
how to delineate the extent of impacted buildings.
Z How should you complete this evaluation?
We recommend that the first step in conducting the site-specific evaluation be to update
the site-specific conceptual site model and determine what additional information (e.g.,
direct sampling) you may need to determine the most-likely-to-be-impacted buildings
(e.g., professional judgment or a model such as the J&E model). Confirmatory
subslab/crawlspace and/or indoor air sampling is recommended at a percentage of the
buildings at each potentially affected site that you have determined to be the most-likely-
to-be-impacted. If sampling confirms that unacceptable inhalation risks due to vapor
intrusion do not occur at the site, we recommend that the vapor intrusion pathway be
considered incomplete and/or does not pose an unacceptable risk to human health. If
sampling confirms that any building is impacted on the site, we recommend that the
pathway be considered complete. In such case, we recommend that further analysis be
conducted to delineate the extent of the impacted building(s) and that mitigation or
avoidance measures be considered for the impacted buildings. These tasks are critically
important, but are outside the scope of this guidance.
3. Why do we recommend updating your conceptual site model?
A conceptual model of the site and potential subsurface vapor transport and vapor
intrusion mechanisms will be needed to adequately support the Site-Specific Pathway
Assessment recommended in this guidance. We recommend that the site-specific
conceptual model be developed in the typical source-pathway-receptor framework, and
that it identify how the site-specific conceptual model is similar to, and different from,
the generic conceptual model used in this guidance (see Introduction and Secondary
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Screening). Under the guidance approach, key components of the conceptual model need
to be justified with site-specific data, including, but not limited to, the source (chemical
constituents, concentrations, mass, phase distribution, depth, and aerial extent), pathway
(soil texture, moisture, and layering) and building (building design, construction, and
ventilation). Some of the necessary data might already be available from previous site
characterization efforts, but if not, we recommend collecting or developing appropriate
site-specific data for evaluating the vapor intrusion pathway.
4. What should you keep in mind when you conduct indoor air or subslab
sampling?
Collection of indoor air quality data without evidence to indicate the potential for vapor
intrusion from subsurface sources can lead to confounding results. Indoor air quality can
be influenced by 'background' levels of volatile chemicals (e.g., due to indoor and/or
outdoor ambient sources). For example, consumer products typically found in the home
(e.g., cleaners, fuels, paints, and glues) may serve as ancillary sources of indoor air
contaminants. Additionally, ambient outdoor air in urban areas often contains detectable
concentrations of many volatile chemicals. In either case, the resulting indoor air
concentrations can be similar to or higher than levels that are calculated to pose an
unacceptable chronic inhalation risk. Thus, we recommend the evaluation of existing
indoor air data focus on constituents (and any potential degradation products) present in
subsurface sources of contamination and the relative contributions of background sources
be considered (see Appendix I). Additionally, see Appendix E for other items to keep in
mind when doing subslab sampling.
5. What direct measurements should be considered and what do they mean ?
Direct measures of indoor air and building foundation air (e.g., subslab and/or crawlspace
concentrations) are recommended to verify whether or not the vapor intrusion pathway is
complete. We recommend that the building specific sampling program be designed to
identify and account for background sources. Prior to indoor air sampling, it is
recommended that an inspection of the residence be conducted and an occupant survey be
completed to adequately identify the presence of (or occupant activities that could
generate) any possible indoor air emission sources of target VOCs in the dwelling (see
discussion above and Appendices E, H & I) and then, if possible remove these sources.
The Massachusetts Department of Environmental Protection (MA DEP) has prepared a
useful Indoor Air Sampling and Evaluation Guide (April 2002) which is available at the
following URL: http://wvvw.state.Tna.us/dep/ors/files/indair.pdf.
In collecting indoor air samples, it is important to recognize that indoor air quality can be
influenced by 'background' levels of volatile chemicals (e.g., due to indoor and/or
outdoor ambient sources), as discussed in the above section. Thus, we recommend the
evaluation of existing indoor air data focus on constituents (and any potential degradation
products) present in subsurface sources of contamination and determine the relative
contributions of background sources (see Appendix I) in order to properly assess the
potential inhalation exposure risks that can be attributed to the subsurface vapor intrusion
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pathway. Where air concentrations in upper level living spaces are greater than basement
levels, intrusion is not likely to have occurred. Indoor air quality data also are subject to
homeostatic fluctuations and temporal trends. Thus, to properly evaluate the indoor air
data, we recommend that sufficient information be obtained to identify seasonal and
spatial variations in indoor air concentrations. Additionally, we recommend careful
consideration of subsurface data from the site in order to determine whether the most
likely to be impacted structures were sampled.
Sampling of foundation air (e.g., subslab and/or crawlspace air) provides a direct measure
of the potential for exposures from vapor intrusion. When collected in conjunction with
indoor air sampling, foundation samples can be used to identify the exposures that
originate from vapor intrusion and distinguish those due to background sources. Subslab
vapor is defined as the soil gas in contact with the building envelope immediately beneath
or within the sub-floor construction materials. Subslab samples are recommended to be,
but do not need to be, collected via holes through the flooring as close to the center of the
floor space as possible. Soil gas sampling using angled or horizontal borings from
outside under the foundation also may be effective. Appendix E provides more detailed
recommendations on subslab and soil gas sampling methodologies. The recommended
attenuation factor for sub-slab soil gas samples in this step is 0.1 (see Appendix F). The
recommended attenuation factor to apply for crawl-space air samples is 1.0 (i.e., the same
as target indoor air concentrations).
6. Why should you consider using site-specific modeling at this time?
Site-specific modeling is intended to complement the evaluation of samples collected
from a subset of the potentially impacted buildings. We recommend that only models
appropriate for the site setting be used and that the direct evidence from the sampled
buildings be used to verify the accuracy of the model's site-specific predictive capability.
Where predictions and direct evidence from the indoor air sampling are consistent, the
model can be used to direct the selection of buildings to be sampled. Considering the
complex influence of soil type, depth to groundwater, and building characteristics on
vapor attenuation factors, the model may help to determine which combination of factors
leads to the greatest impact. Additionally, the model may be used to justify the decreased
need for more direct evidence from the remaining contaminated area We recommend
that site-specific modeling be performed with inputs derived from direct measurements at
the site. This may necessitate the collection of more detailed information regarding
subsurface properties, nature and extent of contamination, and building construction
characteristics.
EPA has developed a spreadsheet version of the Johnson and Ettinger (JE) Model (1991),
which is one of the available screening level models for evaluating the vapor intrusion
pathway. As described in Question 5, the JE Model was used to develop conservative
attenuation factors linked to soil type and depth to source at a site. This model and
documentation for the model are available at the following web site:
URL = http://'www. epa-gov/superfand/proerams/risk/airtnodel/iohnsoT^etiinger. httn
44
-------
If the JE model is used in a site-specific assessment of the vapor intrusion pathway, we
recommend that model inputs and assumptions that are different from the generic
assumptions used in Question 5 and described in Appendix G be supported with site-
specific information. If a model other than the JE Model is used, EPA recommends
model inputs and outputs be identified and appropriately justified.
7. How do you appropriately involve the community when evaluating the vapor
intrusion pathway?
Prior to conducting any direct sampling efforts, we recommend appropriately involving
the community. It has been our experience that proper community involvement efforts
are critical to the effective implementation of this level of screening. We recommend
that users refer to the Community Involvement Guidance in Appendix H. Under the
approach recommended in this guidance, we recommend the user consider the following:
1) getting to know the neighborhood, key stakeholders and the concerns of the
community; 2) informing stakeholders of the situation; 3) developing a community
involvement plan that highlights key community concerns; 4) obtaining written
permission, and involving the property owner in identifying or removing potential indoor
air sources, including inspection of residence and completing an occupant survey: 5) fully
communicating sampling results (with visuals, maps etc.); and 6) a commitment to
ongoing communications activities throughout site cleanup efforts. Appendix H contains
and cites examples of guidance that could be considered for site-specific adaptation for
interaction/involvement with building/dwelling occupants prior to indoor air sampling.
8. What do you do if the pathway is found to be complete?
If the pathway is judged to be complete during the Site-Specific Screening, the next
recommended step is to identify the impacted buildings or areas of concern. This may
result in some buildings or areas being included and some being excluded from the areas
of concern. For these areas, we recommend that the pathway be considered to remain
complete unless some action is taken to reduce occupants' exposure to the site
contamination. Possible actions include:
o engineered containment systems (subslab de-pressurization, soil vacuum
extraction, vapor barriers),
o ventilation systems (building pressurization, indoor air purifiers),
o avoidance (temporary or permanent resident relocation), or
o removal actions to reduce the mass and concentrations of subsurface
chemicals to acceptable levels (i.e., remediation efforts).
This draft guidance is not intended to provide direction on how to fully delineate the
extent of impacted buildings or what action should be taken after the pathway is
confirmed. It is intended to be a quick screening process to help guide the user in
determining if vapor intrusion is or is not a problem on the site.
45
-------
9. Rationale and Reference(s):
Document Risk Level Used (Circle One): 10 4, (b) 10 5, or (c) 10'
46
-------
VII. VAPOR INTRUSION PATHWAY SUMMARY PAGE
Facility Name:
Facility Address:
Primary Screening Summary
U Ql: Constituents of concern Identified?
__ _ Yes
_ _ No (If NO, skip to the conclusion section below and check NO to indicate the pathway is incomplete,)
LI Q2: Currently inhabited buildings near subsurface contamination?
__ __ Yes
No
Areas of future concern near subsurface contamination?
No (If NO, skip to the conclusion section below and check NO to indicate the pathway is incomplete.)
U Q3: Immediate Actions Warranted?
____ Yes
No
Secondary Screenine Summary
LJ Vapor source identified:
_ Groundwater
___ Soil
_ Insufficient data
LJ Indoor air data available?
_ _ Yes
___ No
LJ Indoor air concentrations exceed target levels?
_ Yes
No
47
-------
U Subsurface data evaluation: (Circle appropriate answers below)
Medium
Groundwater
Soil Gas
Q4 Levels
Exceeded?
YES/NO/NA/INS
YES / NO / NA / INS
Q5 Levels
Exceeded?
YES/NO/NA/INS
YES/NO/NA/INS
Data Indicates
Pathway is Complete?
YES / NO / INS
YES /NO /INS
NA = not applicable
INS insufficient data available to make a determination
Site-Specific Summary
U
U
Have the nature and extent of subsurface contamination, potential preferential
pathways and overlying building characteristics been adequately characterized to
identify the most-likely-to-be-impacted buildings?
Yes
No
N/A
EPA recommends that if a model was used, it be an appropriate and applicable model
that represents the conceptual site model. If other means were used, document how
you determined the potentially most impacted areas to sample. EPA recommends
that predictive modeling can be used to support Current Human Exposures Under
Control El determinations without confirmatory sampling to support this
determination. Current Human Exposures Under Control El determinations are
intended to reflect a reasonable conclusion by EPA or the State that current human
exposures are under control with regard to the vapor intrusion pathway and current
land use conditions. Therefore, if conducting evaluation for an El determination,
document that the Pathway is Incomplete and/or does not pose an unacceptable risk
to human health for El determinations.
Are you making an El determination based on modeling and does the model
prediction indicate that determination is expected to be adequately protective to
support Current Human Exposures Under Control El determinations?
Yes
No
N/A
U Do subslab vapor concentrations exceed target levels?
Yes
No
N/A
48
-------
U Do indoor air concentrations exceed target levels?
Yes
No
Conclusion
Is there a Complete Pathway for subsurface vapor intrusion to indoor air?
Below, check the appropriate conclusion for the Subsurface Vapor to Indoor Air Pathway
evaluation and attach supporting documentation as well as a map of the facility.
NO - the "Subsurface Vapor Intrusion to Indoor Air Pathway" has been verified
to be incomplete for the
facility, EPA ID # , located at
This determination is based on a review of site information, as suggested in this
guidance, check as appropriate:
for current and reasonably expected conditions, or
based on performance monitoring evaluations for engineered exposure
controls. This determination may be re-evaluated, where appropriate,
when the Agency/State becomes aware of any significant changes at the
facility.
YES -The "Subsurface Vapor to Indoor Air Pathway" is Complete. Engineered
controls, avoidance actions, or removal actions taken include:
UNKNOWN - More information is needed to make a determination.
Locations where References may be found:
Contact telephone and e-mail numbers:
(name)
(phone #)
(e-mail) _
49
-------
Reminder: As discussed above, this is a guidance document, not a regulation.
Therefore, conclusions reached based on the approaches suggested in this guidance
are not binding on EPA or the regulated community. If information suggests that
the conclusions reached using the approaches recommend are inappropriate, EPA
may (on it's own initiative or at the suggestion of interested parties) choose to act at
variance with these conclusions.
50
-------
References
Burning of Hazardous Waste in Boilers and Industrial Furnaces: Final Rule (58 FR
7135, February 21, 1991)
Draft Exposure Assessment Guidance forRCRA Hazardous Waste Combustions
Facilities (April/May 1994)
Guidance for the Data Quality Objectives (POP} Process. EPA OA/G 4. (EPA/600/R-
96/055; August 2000);(URL = http://www.epa.gov/quality/qs_docs/g4_final.pdQ
Johnson andEttineer (JE) Model (19911
(URL = hltp://ww\v.epa.gov/superfund/pfograrm/fisk/''airmodel/johnson_ettin^er.htm)
Massachusetts Department of Environmental Protection (MA PEP) Indoor Air
Sampttne and Evaluation Guide - WSC PolicvW2-430 (April 2002) (URL =
http://%vw\v.state.Tna.us/dep/bwsc/finalpol.him)
EPA Strategic Plan - Goal 5: Better Waste Management. Restoration of Contaminated
Waste Sites, and Emergency Response (0.40-41) CEP A 190-R-00-002): ( URL =
http://www.epa.gov/ocfo/plan/2000strategicplan.pd0
RCRA Corrective Action Environmental Indicator (El} Guidance f Feb 5. 1999)
fURL = littp:/,'\vvvw.epa.gov/epaoswer/hazwaste/ca/eis/ei guida.pdf )
RCRA draft Supplemental Guidance for Evaluating the Vapor Intrusion to Indoor Air
Pathway (EPA/600/SR-93/140 - Dec 2001)
(URL=hUp://vvww.epa.gov'/epao.swer//ha/.waste/ca/eis/vapor.hmi)
Supplemental Guidance for Developins Soil Screening Levels for Super fund Sites
( Peer Review Draft: March 2001) Office of Emergency and Remedial Response/EPA
( URL = hup://www.epa.gov/superfund/resoufces/soil/ssgmarch01.pelf )
[final version will issue concurrently with the Subsurface Vapor Intrusion Guidance.}
Use of Risk-Based Decision Makine in UST Corrective Action Programs. OSWER
Directive 9610.17 (EPA; Mar 1,1995);(URL=
http://wmv.epa.gov/swerastl/directiv/od961017.htni)
51
-------
Table 1
Table 2
Table 3
Appendix A. Data Quality Assurance Considerations
Appendix B. Development Of Conceptual Site Model (CMS) For Assessment Of The
Vapor Intrusion Pathway
Appendix C. Detailed Flow Diagrams Of The Evaluation Approach Used In This
Guidance
Appendix D. Development Of Tables 1, 2, And 3
Appendix E. Relevant Methods and Techniques
Appendix F. Empirical Attenuation Factors And Reliability Assessment
Appendix G. Considerations For The Use Of Johnson and Ettinger Vapor Intrusion
Model
Appendix H. Community Involvement Guidance
Appendix I. Consideration of Background Indoor Air VOC Levels In Evaluating The
Subsurface Vapor Intrusion Pathway
52
-------
Table 1: Question 1 Summary Sheet
CAS No.
83329
75070
67641
75058
98862
107028
107131
309002
319846
62533
120127
56553
100527
71432
50328
205992
207089
65850
100516
100447
91587
319857
92524
111444
108601
117817
542881
75274
75252
106990
71363
85687
86748
75150
56235
57749
126998
108907
109693
124481
75456
75003
67663
95578
75296
218019
1S6592
1 23739
98828
72548
72559
50293
53703
132649
96128
106934
541731
95501
106467
91941
75718
Chemical
Acenaphthene
Acetaldehyde
Acetone
Acetonitrile
Acetophenone
Acroleln
Acrylonitrile
Aldrm
alpha-HCH (alpha-BHC)
Aniline
Anthracene
Benz(a)anthracene
Benzaldehyde
Benzene
Benzo(a)pyrene
Benzo(b)fluoranthene
Benzo(k)fluoranthene
Benzole Acid
Benzyl alcohol
Benzylchloride
beta-Chloronaphthalene
beta-HCH (beta-BHC)
Biphenyl
Bis(2-chloroethyl)ether
Bis(2-chloroisopropyl)ether
Bis(2-ethylhexyl)phthalate
Bls(chloromethyl)ether
Sromodichloromethane
Bramoform
1,3-Sutadiene
Butanol
Butyl benzyl phthalate
Carbazole
Carbon disullide
Carbon tetrachloride
Chlordane
2-Chloro-1,3-butadiene(chloroprene)
Chloro benzene
1-Chlorobutane
Chlorodibromomethane
Chlarodifluoromethane
Chloroethane (ethyl chloridel
Chloroform
2-Chlorophenol
2-Chloropropane
Chrysene
cis-1,2-Dichloroethylene
Crotonaldehyde (2-butenal)
Cumene
DDD
DDE
DDT
Dibenz(a, h)anthracene
Dibenzofuran
1 ,2-Di bromo-3-ohloropropa ne
1.2-Dibromoethane (ethylene dibramide)
1 ,3-Dichlorobe nze ne
1 ,2-Dichlorobenzene
1 ,4-Oichlorobenzene
3,3-Dichlorobenzidine
Oichlorodifluoromethane
Is Chemical
Sufficiently
Toxic? '
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
NO
YES
YES
YES
YES
YES
NO
NO
YES
YES
YES
YES
YES
YES
YES
NO
YES
YES
YES
YES
YES
NO
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
Is Chemical Sufficiently
Volatile?2
YES
YES
YES
YES
YES
YES
YES
YES
YES
NO
YES
NO
YES
YES
NO
YES
NO
NO
NO
YES
YES
NO
YES
YES
YES
NO
YES
YES
YES
YES
NO
NO
NO
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
NO
YES
NO
NO
YES
YES
YES
YES
YES
YES
NO
YES
Check Here If
Known or
Reasonably
Suspected To
Be Present9
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
DRAFT
Table 1
November 20, 2002
-------
Tablet: Question 1 Summary Sheet.
CAS No.
75343
107062
75354
120832
78875
542756
60571
84662
105679
131113
84742
534521
51285
121142
605202
117840
115297
72208
106898
60297
141786
100414
75218
97632
206440
86737
110009
58899
76448
1024573
87683
118741
77474
67721
110543
74908
193395
78831
78591
7439976
126987
72435
79209
96333
74839
74873
108872
74953
75092
78933
108101
80626
91576
108394
95487
106455
99081
1634044
108383
91203
104518
Chemical
1 , 1 -Oichloroethane
1,2-Dichloroethane
1,1-Dichloroethvlene
2,4-Diehlorophenol
1 ,2-Diehloropropane
1,3-Oichloropropene
Dieldrin
Diethylphthalate
2,4-Dimethylphenol
Dimethvlphthalate
Di-n-butyLehthalate
4,6-Dinitro-2-methylphenol (4,6-dinitro-o-cresol)
2,4-Dinitrophenol
2,4-Dinjtrotoluene
2.6-Dinitrotoluene
Di-rvoctyl phthalate
Endosulfan
Endrin
Epichlorohydrin
Ethyl ether
Ethylacetate
Ethylbenzene
Ethylene oxide
Ethylmethacrylate
Fluoranthene
Fluorene
Furan
gamma-HCHJLindane)
Heptaohlor
Heptachlor epoxide
Hexachlora-1 ,3-butadiene
Hexachlorobenzene
Hexachlorocyclopentadiene
Hexachloroethane
Hexane
Hydrogen cyanide
I ndenof 1 .2.3-cd)pyrene
Isobutanol
tsophorone
Mercury (elemental)
Methacrylonitrile
Methoxychlor
Methyl acetate
Methyl acrvlate
Methyl bromide
Methyl chloride (chloromethane)
M ethylcycl ohexa ne
Methylene bromide
Methylene chloride
Methylethylketone (2-butanone)
Methylisobutylkelone
Methylmethaciylate
2-Meftylnaphthalene
3-Methylphenol (m-cresol)
2-Methylphenol (o-cresol)
4-Methylphenol (p-cresol)
m-Nitrotoluene
MTBE
m-Xyiene
Naphthalene
n-Butylbenzene
Is Chemical
Sufficiently
Toxic? '
YES
YES
YES
YES
YES
YES
YES
YES
YES
NA
NO
YES
YES
YES
YES
NO
YES
YES
YES
YES
YES
YES
YES
YES
NO
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
NO
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
Is Chemical Sufficiently
Volatile? '
YES
YES
YES
NO
YES
YES
YES
NO
NO
NO
NO
NO
NO
NO
NO
YES
YES
NO
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
NO
YES
YES
YES
YES
YES
YES
NO
YES
NO
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
NO
NO
NO
NO
YES
YES
YES
YES
Check Here If
Known or
Reasonably
Suspected To
Be Present3
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
DRAFT
Table 1
November 20, 2002
-------
Table 1: Question 1 Summary Sheet.
CAS No.
98953
100027
79469
924163
621647
86306
103651
88722
95476
106478
87865
108952
99990
106423
129000
110861
135988
100425
98066
630206
79345
127184
108883
8001352
156605
76131
120821
79005
71556
79016
75694
95954
88062
96184
95636
108678
108054
75014
Chemical
Nitrobenzene
4-Nitrophenol
2-Nilropropane
N-Nflroso-di-n-butylamine
N-Nitrosodi-n-propvlamine
N-Nitrosodiphenylamtne
n-Propylbenzene
o-Nitrotoluene
o-Xylene
p-Chloroaniline
Pentachlorophenol
Phenol
p-Nitrotoluene
p-Xylene
Pyrene
Pyridine
sec-Butylbenzene
Styrene
tert-Butylbenzene
1,1,1 ,2-Tetrachloroethane
1 , 1 ,2,2-Tetrachloroethane
Tetrachloroethylene
Toluene
Toxaphene
trans-1 ,2-Diohloroethylene
l.l^-Trichloro-l^-tnfluoroethane
1 ,2,4-Triohtorobenzene
1 , 1 , 2-Trichloroetha ne
1,1,1-Trichlofoethane
Trichloroelhytene
Trichlorofluoromethane
2, 4, 5-Trichlorophenol
2,4,6-Trichlorophenol
1 ,2,3-Triohloropropane
1 ,2,4-Trimethylbenzene
1,3,5-Trimethylbenzene
Vinyl acetate
Vinyl chloride (chloroethene)
Is Chemical
Sufficiently
Toxic? 1
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
Is Chemical Sufficiently
Volatile? *
YES
NO
YES
YES
NO
NO
YES
YES
YES
NO
NO
NO
NO
YES
YES
NO
YES
YES
YES
YES
YES
YES
YES
NO
YES
YES
YES
YES
YES
YES
YES
NO
NO
YES
YES
YES
YES
YES
Check Here If
Known or
Reasonably
Suspected To
Be Present3
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
1 A chemical is considered sufficiently toxic if the vapor concentration of the pure component (see Appendix D) poses an incremental lifetime
cancer risk g mater than 1CT* or a non-can cer hazard index greater than 1.
' A chemical is considered sufficiently volatile if its Henry's Law Constant s 1 K 1Q'5 atm-m^mol or greater (US EPA, 1991)
s Users should check off compounds that meet the criteria for toxicity and volatility and are known or reasonably suspected to be present.
DRAFT
Table 1
November 20, 2002
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APPENDIX A
DATA QUALITY ASSURANCE CONSIDERATIONS
The assessment of information to determine if there is a problem associated with the migration of
volatile compounds from the groundwater will require the collection and assessment of
environmental data and possibly the use of modeling as part of the assessment As the guidance
indicates, decisions to screen out sites after the first tier of screening from further analysis should
be based either upon definitive measurement data or upon multiple lines of converging
information. The ability to measure contamination levels in different media and to characterize
the variability associated with sampling are key considerations.
OSWER expects that site-specific projects assess the impact of groundwater contaminants on
indoor VOCs will be addressed by an approved Quality Assurance Project Plan (QAPP). This
appendix is intended to provide a few recommendations on developing a QAPP, which need to
follow EPA Requirements for Quality Assurance Project Plans (QA/R-5).
Recommendation 1: Using the Conceptual Site Model, develop the project plan and
quality assurance project plan through a process that involves all key players and share
these materials with interested parties in draft form so that potential study weaknesses
can be addressed early.
The collection and assessment of data, or the use of a mode! for the assessment of the data,
warrants the development of a Quality Assurance Project Plan as part of a systematic planning
process (EPA, 2000a,b, 2001). The EPA Region 1 guidance on the Quality Assurance Project
Plan may be a useful reference that can aid site managers (EPA, 1999).
Data Quality Objectives (DQOs) play a central role in the systematic planning process as they
help to ensure that the data collected will be of sufficient quality to support their intended use.
Data Quality Objectives will generally be addressed within the Quality Assurance Project Plan
and are typically a critical element in the planning for much of the work that EPA undertakes.
The Agency guidance for DQOs, Guidance for the Data Quality Objectives Process (G-4),
provides useful information to implement DQOs (EPA, 2000c).
Table A-l summarizes the steps in the DQO process, the purpose of each step, and provides
some examples of how plans could be structured.
Table A-2 summarizes the sensitivity/detection limits of a variety of currently available methods
for the analysis of VOCs along with estimated cost information. Table A-2 has been prepared to
summarize some information that can serve as a general guide but should be updated as
individual projects are undertaken.
A-l
-------
The determination of the analytic and sampling methods to use, the number of samples, location
of samples, and timing is a challenging task that will be related to a number of factors, including
the values for screening and risk that will use the monitored results. These sampling issues can
be addressed, at least in part, by employing software that has been designed to optimize
sampling so that confidence in results will be maximized. Visual Sample Plan
(VSP)[http://dqo.pnl.gov/vsp/] has been developed to provide statistical solutions to sampling
design, mathematical and statistical algorithms, and a user-friendly visual interface, while
answering the following two important questions in sample planning:
How many samples are needed?
The algorithms involved in determining the number of samples needed can be quite
involved and intimidating to the non-expert. VSP aids in the calculation of the number of
samples often needed for various scenarios at different costs.
Where should the samples be taken?
Sample placement based on professional judgment is prone to bias. VSP provides the
alternative of random or gridded sampling locations overlaid on the site map.
References
EPA, 1999. EPA New England Compendium of Quality Assurance Project Plan
Requirements and Guidance. EPA, Region 1, Boston, MA
(http:/7wvvrvv.epa.gov/NE/measure/qappcompendium.pdf).
EPA, 2000a. EPA Order 5360, LA2, Policy and Program Requirements for the Mandatory
Agency-wide Quality System. EPA, Washington, D.C.
fhttp://'w\vw.epa.gov/quality/qs-docs/'5360-l.pdf).
EPA, 2000b. EPA Quality Manual for Environmental Programs. EPA, Washington, D.C.
(http://www.epa.gov/quality/qs-docs/5360.pdf).
EPA, 2000c. Guidance for the Data Quality Objectives Process (G-4). EPA, Washington, D.C
fiutp://www.epa.gov/qualtty/qs-docs/g4-final.pdfl
EPA, 2001. EPA Requirements for QA Project Plans (QA/R-5) EPA, Washington, D.C
(hnp:/Vwww.epa.gov/quaUty/'qSKiocs/r5-fmal.pdfland
(http://www.epa.gov/OU ALITY/qapps.html^
Visual Sample Plan (VSP)[http://dqo.pnl.gov/vsp/]
A-2
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For example, "If any measured VOC
concentration in groundwater is above the
action level for groundwater screening in
Question 5c, then further assessment
(including soil gas concentrations, and
possibly indoor air concentrations,
depending on the magnitude of the
concentrations) should be performed as
appropriate.
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Decision errors could result from failing to
appreciate uncertainty in sampling, analysis
or performing analyses. Decision
performance goals may be useful in
managing uncertainty. The use of a
computer program, such as Visual Sample
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managing uncertainties associated with
sampling and analysis.1
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Table A-2. VOC Analytical Methods, their Detection Limits and Estimated Costs
( compiled July 2002)
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A-6
-------
VOC Methods Analyte Lists
List 1 Office of Solid Waste SW 846 Method 8260 C
Acetone
Acetonitrile
Acrolein (Propenal)
Acrylonitrile
Allyl alcohol
Allyl chloride
Benzene
Benzyl chloride
Bis(2-chloroethyl)sulfide
Bromoacetone
Bromochloromethane
Bromodichlorometha ne
Bromoform
Bromomethane
n-Butanol
2-Butanone (MEK)
t-Butyl alcohol
Carbon disulfide
Carbon tetrachloride
Chloral hydrate
Chlorobenzene
Chlorodibromomethane
Chloroethane
2-Chloroethanol
2-Chloroethyl vinyl ether
Chloroform
Chloromethane
Chloroprene
3-Chloropropionitrile
Crotonaldehyde
1,2-Dibromo-3-chloropropane
1,2-Dibromoethane
Dibromomethane
1,2-Dichlorobenzene
1,3-Dichlorobenzene
1,4-Dichlorobenzene
cis-1,4-Dichloro-2-butene
trans-1,4-Dichloro-2-butene
Dichlorodifluoromethane
1,1-Dichloroethane
1,2-Dichloroethane
1,1 -Dichloroethene
trans-1,2-Dichloroethene
1,2-Dichloropropane
1,3-Dichloro-2-propanol
cis-1,3-Dichloropropene
trans-1,3-Dichloropropene
1,2,3,4-Diepoxybutane
Diethyl ether
1,4-Dioxane
Epichlorohydrin
Ethanol
Ethyl acetate
Ethylbenzene
Ethylene oxide
Ethyl meth aery late
Hexachlorobutadiene
Hexachloroethane
2-Hexanone
2-Hydroxypropionitrile
lodomethane
Isobutyl alcohol
Isopropylbenzene
Malononttrile
Methacrylonitrile
Methanol
Methylene chloride
Methyl methacrylate
4-Methyl-2-pentanone (MIBK)
Naphthalene
Bromobenzene
1,3-Dichloropropane
n-Butylbenzene
2,2-Dichloropropane
sec-Butylbenzene
1,1-Dichloropropene
tert-Buty I benzene
p-lsopropyltoluene
Chloroacetonitrile
Methyl acrylate
1-Chlorobutane
Methyl-t-butyl ether
1-Chlorohexane
Pentafluorobenzene
2-Chlorotoluene
n-Propylbenzene
4-Chlorotoluene
1,2,3-Trichlorobenzene
Dibromofluoromethane
1,2,4-Trimethylbenzene
cis-1,2-Dichloroethene
1,3,5-trimethylbenzene
A-7
-------
VOC Methods Analyte Lists (cont.)
List 2 EPA Office of Water Method 524.2
Chloroform
Bromodichloromethane
Bromoform
Chlorodibromomethane
Bromobenzene
Bromochloromethane
Bromomethane
n-Butylbenzene
tert-Butylbenzene
Chloroethane
Chloromethane
o-Chlorotoluene
p-Chlorotoluene
Dibromomethane
m-Dichlorobenzene
Dichlorodifluoromethane
1,1-Dichloroethane
1,3-Dichloropropane
2,2-Dichloropropane
1,1-Dichloropropene
1,3-Dlchloropropene
Fluorotrichloromethane
Hexachlorobutadiene
Isopropylbenzene
p-isopropyltoluene
Naphthalene
n-Propylbenzene
1,1,2,2-Tetrachloroethane
1,1,1,2-Tetrachloroetha ne
1,2,3-Trtchlorobenzene
1,2,3-Trichloropropane
1,2,4-Trimethylbenzene
1,3,5 -Trimethylbenzene
List 3 OERR (Superfund) CLP Statement
Of Work OLM04.2
1,1-Dichloroethane
1,1-Dichloroethene
1,1,1-Trichloroethane
1,1,2-Trichioro-
1,1,2-Trichloroethane
1,1,2,2-Tetrachloroethane
1,2-Dibromo-3-chloropropane
1,2-Dibromoethane
1,2-Dichlorobenzene
1,2-Dichloroethane
1,2-Dichloropropane
1,2,2-trifluoroethane
1,2,4-Trichlorobenzene
1,3-Dichlorobenzene
1,4-Dichlorobenzene
2-Butanone [ 78-93-3 ]
2-Hexanone
4-Methyl-2-pentanone
Acetone
Benzene
Bromodichloromethane
Bromoform
Bromomethane
Carbon Disulfide
Carbon Tetrachloride [56-23-5]
Chlorobenzene
Chloroethane
Chloroform [67-66-3]
Chloromethane
cis-1,2-Dichloroethene
cis-1,3-Dichloropropen e
Cyclohexane [110-82-7]
Dibromochloromethane
Dichlorodifluoromethane
Ethylbenzene
Isopropylbenzene
Methyl tert-Butyl Ether
Methyl Acetate
Methylcyclohexane
Methylene Chloride
Styrene
Tetrachloroethene
Toluene
trans-1,2-Dichloroethene
trans-1,3-Dichloropropene
Trichloroethene
Trichlorofluoromethane
Vinyl Chloride
Xylenes (total)
A-8
-------
VOC Methods Analyte Lists (cont)
List 4 OERR (Superfund) CLP Statement
of Work OLC03.2
List 5 Office of Solid Waste SW 846
Method 5041
1,1-Dichloroethane
1,1-Dichloroethene
1,1,1-Trichloroethane
1,1,2-Trichloro-1,2,2-trifluoroethane
1,1,2-Trichloroethane
1,1,2,2-Tetrachloroethane
1,2-Dibromo-3-chloropropane
1,2-Dibromoethane
1,2-Dichlorobenzene
1,2-Dichloroethane
1,2-Dichloropropane
1,2,3-Trichlorobenzene
1,2,4-Trichlorobenzene
1,3-Dichlorobenzene
1,4-Dichlorobenzene
2-Butanone
2-Hexanone
4-Methyl-2-pentanone
Acetone
Benzene
Bromochtoromethane
Bro mo di chlo ro metha ne
Bromoform
Bro mo methane
Carbon Disulfide
Carbon Tetrachloride
Chlorobenzene
Chloroethane
Chloroform
Chloromethane
cis-1,2-Dichloroethene
cis-1,3-Dichloropropene
Cyclohexane
Dibromochloromethane
Dichlorodifluoromethane
Ethylbenzene
Isopropyl benzene
Methyl Acetate
Methyl tert-Butyl Ether
Methylcyclohexane
Methylene Chloride
Styrene
Tetrachloroethene
Toluene
trans-1,2-Dichloroethene
trans-1,3-Dichloropropene
Trichloroethene
Trichlorofluoro methane
Vinyl Chloride
Xylenes (total)
Acetone
Acrylonitrile
Benzene
Bromodichloromethane
Bromoform
Bromomethane
Carbon disulfide
Carbon tetrachloride
Chlorobenzene
Chlorodibromomethane
Chloroethane
Chloroform
Chloromethane
Dibromomethane
1,1-Dichloroethane
1,2-Dichloroethane
1,1-Dichloroethene
trans-1,2-Dichloroethene
1,2-Dichloropropane
cis-1,3-Dichloropropene
trans-1,3-Dichloropropene
Ethylbenzene
lodomethane
Methylene chloride
Styrene
1,1,2,2-Tetrachloroethane
Tetrachloroethene
Toluene
1,1,1 -Trich loroethane
1,1,2-Trichloroethane
Trichloroethene
Trich lorofluoromethane
1,2,3-Trichloropropane
Vinyl chloride
Xylenes
A-9
-------
VOC Methods Analyte Lists (cont.)
List 6 NIOSH Method 1003
List? NIOSH Method 1501
Benzyl chloride
Bromoform
Carbon tetrachlorideab
Chlorobenzene
Chlorobromomethane
Chloroform
o-Dichlorobenzene
p-Dichlorobenzene
1,1-Dichloroethane
1,2-Dichloroethylene
Ethylene dichloride
Hexachloroethane
1,1,1-trichloroethane
Tetrachloroethylene
1,1,2-Trichloroethane
1,2,3-Trichloropropane
1 -tert-buty l-4-methylbenzene
a-methylstyrene
benzene
cumene
dimethyl benzene (p-xylene) (meta)
ethylbenzene
isopropenylbenzene
isopropylbenzene
methylbenzene
methylstyrene
methylvinylbenzene (ortho)
naphthalene
p-tert-butyltoluene
styrene
toluene
vinyl benzene
xylene
A-10
-------
VOC Methods Analyte Lists (cont.)
List 8 EPA Office of Air and Radiation TO-15 & TO-17
1,1 -Dimethylhydrazine;
1,1,2-Trichloroethane;
1,1,2,2-Tetrachloroethane;
1,2-Dibromo-3-chloropropane;
1,2-Epoxybutane (1,2-butylene oxide);
1,2-Propyleneimine (2-methylazindine);
1,2,4-Trichlorobenzene;
1,3-Butadiene;
1,3-Dichloropropene;
1,3-Propane sultone;
1,4-Dichlorobenzene (p-);
1,4-Dioxane (1,4 Diethylene oxide);
2-Nitropropane;
2,2,4-Trimethyl pentane;
Acetaldehyde (ethanai);
Acetonitrile (cyanomethane);
Acetophenone;
Acrolein (2-propenal);
Acrylamide;
Acrylic acid;
Acrylonitrile (2-propenenitrile);
AJIyl chloride (3-chloropropene);
Aniline (aminobenzene);
Benzene;
Benzyl chloride (a-chlorotoluene);
Beta-Propiolactone;
Bis(2-Chloroethyl)ether;
Bis(chloromethyl) ether;
Bromoform (tribromomethane);
Carbon tetrachloride;
Carbon disulfide;
Carbonyl sulfide;
Catechol (o-hydroxyphenol);
Chloroacetic acid;
Chtorobenzene;
Chloroform;
Chloromethyl methyl ether;
Chloroprene (2-chloro-1,3-butadiene);
Cresylic acid (ere so I isomer mixture);
Cumene (isopropylbenzene);
Diazome thane;
Diethyl sulfate;
Dimethyl sulfate;
Dimethylcarbamyl chloride;
Epichlorohydrin (l-chloro-2,3-epoxy propane);
Ethyl acrylate,
Ethyl carbamate (urethane);
Ethyl chloride (chloroethane);
Ethylbenzene;
Ethylene dibromide (1,2-dibromoethane);
Ethylene dichloride (1,2-dichloroethane);
Ethylene oxide;
Ethyleneimine (aziridine);
Ethylidene dichloride (1,1-dichloroethane);
Formaldehyde;
Hexachlorobutadiene;
Hexachloroethane;
Hexane;
Isophorone;
m-Xylene;
Methanol;
Methyl methacrylate;
Methyl isobutyl ketone (hexone);
Methyl chloride (chloromelhane);
Methyl bromide (bromomethane);
Methyl ethyl ketone (2-butanone);
Methyl isocyanate;
Methyl iodide (iodomethane);
Methyl chloroform (1,1,1 trichloroethane);
Methyl tert-butyl ether;
Methylene chloride;
Methylhydrazine;
N-N itrosodimethylamine;
N-Nitrosomorpholine;
N-Nitrso-N-methylurea;
Nitrobenzene;
N,N-Dimethylaniline;
N, N-Dimethylformamide;
o-Cresol;
o-Xylene;
p-Xylene;
Phenol;
Phosgene;
Propionaldehyde;
Propylene dichloride (1,2-dichloropropane);
Propylene oxide;
Styrene oxide;
Styrene;
Tetrachloroethylene;
Toluene;
Trichloethylene;
Triethylamine;
Vinyl acetate;
Vinyl bromide (bromoethene);
Vinyl chloride (chloroethene);
Vinylidene chloride (1,1-dichloroethylene);
Xylenes {isomer & mixtures);
A-ll
-------
APPENDIX B
DEVELOPMENT OF A CONCEPTUAL SITE MODEL (CSM)
FOR ASSESSMENT OF THE VAPOR INTRUSION PATHWAY
1. Introduction
A conceptual site model (CSM) is a simplified version (picture and/or description) of a complex
real-world system. A CSM is not an analytical or mathematical computer model (although a
detailed CSM may serve as a foundation for such models). The goal for developing a CSM in
the assessment of the vapor intrusion pathway is to assemble a comprehensive (as possible)
three-dimensional "picture" based on available reliable data describing the sources of the
contamination, the release/transport mechanisms, the possible subsurface pathways, and the
potential receptors, as well as historical uses of the site, cleanup concerns expressed by the
community, and future land use plans. All the important features relevant to characterization of
a site should be included in a CSM and any irrelevant ones excluded. The CSM should present
both a narrative and a visual representation of the actual or predicted relationships between
receptors (humans and/or ecological entities) and the contaminants at the site, as well as reflect
any relevant background levels.
Development of a CSM is an important first step in planning and scoping any site assessment
designed to determine the potential impacts of contamination on public health and the
environment. In documenting current site conditions, a CSM should be supported by maps,
cross sections and site diagrams, and the narrative description should clearly distinguish what
aspects are known or determined and what assumptions have been made in its development. The
CSM should provide all interested parties a conceptual understanding of the potential for
exposure to any hazardous contaminants at a site. As such, it serves as an essential tool to aid
management decisions associated with the site and also serves as a valuable communication tool
both internally with the "site team" and externally with the community.
A well-defined, detailed CSM will facilitate the identification of additional data needs and
development of appropriate Data Quality Objectives (DQOs) in planning any sample
collection/analyses to support the site risk assessment. It can also provide useful information for
prompt development of a strategy for early response actions if the vapor intrusion pathway is
considered to be complete and may pose an imminent potential risk to public health.
Because the CSM is likely to evolve over the course of the site assessment process, it should be
considered dynamic in nature. Integration of newly developed information is an iterative process
that can occur throughout the early stages of the site assessment process. This should include
stakeholder input from persons who are knowledgeable about the community and activities
which may have generated the contaminants or affected their movement. As additional data
become available during implementation of the site assessment DQO process, the CSM should
be updated. Such updates could also suggest iterative refinement of the DQO process
(optimization step), since changes in the CSM may lead to identification of additional data or
B-l
-------
information not previously recognized as needed. As a fundamental site assessment tool, the
CSM warrants prompt updating and distribution to interested parties during the site assessment
process.
2. Collecting Existing Site Data
The following general types of information are important for preparing a CSM:
site maps, sample location maps, aerial photos
historical site activity, chronology of land use, populations information
State soil surveys
published data on local and regional climate, soils, and hydrogeology
any previous site studies and actions (e.g. Preliminary Assessment/Site
Investigation)
an overview of the nature and extent of the contamination
The CSM developed should identify, in as comprehensive a manner as possible, all potential or
suspected sources of contamination (soil, groundwater, soil gas, etc.); the types and
concentrations of contamination detected at the site; all potential subsurface pathways, including
preferential pathways; and the media and buildings associated with each pathway cleanup.
Additional considerations that may be important to include in developing an optimal CSM for
use in management decisions are presented below.
3. Additional Considerations for CSM Development for the Vapor Intrusion Pathway
sensitive populations, including but not limited to:
- the elderly
- pregnant or nursing women
- infants
- children
- people suffering from chronic illnesses
people exposed to particularly high levels of contaminants
circumstances where a disadvantaged population is exposed
( Environmental Justice situation)
significant contamination sources
- NAPLs
- very shallow contaminated groundwater or soil
vapor transport pathways (see Figure B-l)
- diffusion upwards
- lateral vapor transport
- preferential vapor pathways such as fractured sediments or utility features
B-2
-------
potential non-site related sources of contaminants
- ambient (outdoor) air sources
- indoor air emission sources
building construction quality
- foundation type (basement, slab on grade, crawlspace)
- foundation integrity
building use
- open windows (etc.)
4. Organizing Existing Site Data for Inclusion in a CSM
The Conceptual Site Model Summary presented in Attachment A of the Soil Screening
Guidance: User's Guide contains four detailed forms for compiling site data useful in
developing a CSM for soil screening purposes. These CSM Summary forms systematically
organize the site data according to general site information, soil contaminant source
characteristics, exposure pathways and receptors. Planning Table 1 presented in the Risk
Assessment Guidance for Superfund: Volume I - Human Health Evaluation Manual* Part D ~
Standardized Planning. Reporting, and Review of "Superfund Risk Assessments may be used in
a similar manner to prepare/supplement the CSM. Planning Table 1 is intended to accompany
the CSM and present the possible receptors, exposure routes, and exposure pathways, as well as
the rationale for selection or exclusion of each potential exposure pathway. The exposure
pathways that were examined and excluded from analysis and the exposure pathways that will be
evaluated qualitatively or quantitatively in the site risk assessment are clearly reflected when
Planning Table 1 is used. Either of these systematic site information organizing formats that are
useful for CSM development can also be used to communicate risk information about the site to
interested parties outside EPA. The systematic and comprehensive approach encouraged by
compilation of data and information in these standard formats, like other steps in the site risk
assessment process, may suggest further refinement of the CSM.
Constructing Conceptual Site Model Diagrams
An example of a complete CSM including diagrams prepared for soil screening purposes can be
found in Attachment A of the Soil Screening Guidance: User's Guide. A software application
that can generate CSM diagrams and reflect relevant site data has been developed (DOE). The
Site Conceptual Exposure Model Builder can be found on the internet.
( URL = http://tis-nt.eh.doe.gov/oepa/programs/scem.cfm)
* Additional Resources for CSM Development Guidance
B-3
-------
(1) The following provide more specific guidance for developing a CSM for cleanup programs:
Soil Screening Guidance: User's Guide. Part 2.1 and Attachment A; EPA-540-R-96-
018. Office of Emergency and Remedial Response/EPA. July 1996.
Supplemental Guidance for Developing Soil Screening Levels for Super fund Sites
Office of Emergency and Remedial Response/EPA
Risk Assessment Guidance for Superfund (RAGS): Volume I - Human Health
Evaluation Manual. Part D - (Standardized Planning, Reporting, and Review of
Superfund Risk Assessments), Final December 2001. Pub. # - 9285.7-47; Chapter 2 -
Risk Considerations in Project Scoping; EPA - Office of Emergency and Remedial
Response.
Site Conceptual Exposure Model Builder - User Manual - for PC (Windows version)
application to assist in preparing a site model; U.S. Dept of Energy, RCRA/CERCLA
Division; July 1997.
Guidance for Conducting Remedial Investigations and Feasibility Studies under
CERCLA. EPA 540-G-89-004. Office of Emergency and Remedial Response/EPA .
1989.
Expedited Site Assessment Tools for Underground Storage Tank Sites: A Guide for
Regulators. Chapter 2. EPA 510-B-97-001; Office of Underground Storage Tanks/EPA;
March 1997.
(2) Selected risk assessment guidance and related documents that contain discussions
concerning necessary problem formulation, and planning and scoping prior to conducting a risk
assessment can provide some additional perspective to consider in preparation of a Conceptual
Site Model.
Quality Assurance Guidance for Conducting Brownfields Site Assessments. EPA 540-
R-98-038; OSWER 9230.0-83P; PB98-963307; September 1998,
Guidelines for Ecological Risk Assessment. EPA 630-R-95-002F, Federal Register Vol
63, pp.26846-26924, May 14, 1998.
Framework for Cumulative Risk Assessment - External Review Draft. EPA 630-P-02-
001 A; Risk Assessment Forum; April 23, 2002.
Risk Characterization Handbook. EPA 100-B-00-002, December 2000.
Guidance For The Data Quality Objectives Process - EPA OA/G-4: EPA-600-R-96-
055; September 1994.
B-4
-------
«t^^
Figure B-l. Example of Conceptual Site Model cross section diagram illustrating potential subsurface vapor
intrusion pathways
B-5
-------
APPENDIX C
DETAILED FLOW DIAGRAMS OF THE EVALUATION APPROACH
USED IN THE GUIDANCE
-------
PRIMARY SCREENING
1. Are chemicals of sufficient
volatility and toxicity present?
NO
YES
i
2. Are currently (or potentially)
inhabited buildings or areas of
concern under future
development scenarios located
near subsurface
contaminants of potential
concern identified in Q1?
.NO
YES
I
3. Does evidence suggest
immediate action may be
warranted?
YES-
Proceed with
Appropriate
Action
NO
Proceed to
Secondary
Screening
-------
SECONDARY SCREENING
Question 4 - Generic Screening
(TL = appropriate media specific target level)
4(a) Indoor air
data available?
YES
NO
Proceed to Q6
Site Specific
Assessment
YES
4(c) Does contamination
(source of vapors) occur in
unsaturated zone soil at any
depth above the water table?
YES
4(e) Groundwater
characterization
adequate?
If soil gas data are
available proceed
to 4(g), otherwise
proceed to Q5.
YES
4(f) Precluding
factors present?
YES
INO
Proceed to Q6
Site Specific
Assessment
Groundwater Assessment
Indicates Pathway Incomplete
Recommended | >
4(g) SG > TL?
NO
4(h) Soil gas data
adequate?
YES
YES
4(i) Precluding
factors present?
YES
Proceed to Q6
Site Specific
Assessment
;NO
Soil Gas Assessement
Indicates Pathway Incomplete
-------
SECONDARY SCREENING
Question 5 - Semi-Site Specific Screening
(TL = appropriate media specific target level)
areGWorSG
concentrations
>50xTL?
YES
Proceed to Q6
Site Specific
Assessment
'NO
5(b) Precluding
factors
present?
YES
F
Proceed to Q6
Site Specific
Assessment
!NO
5(c) Depth to water
and soil type data
adequate?
YES
NO
Acquire needed
data and re-evaluate.
YES
5(d) Does contamination
(source of vapors)
occur in the unsaturated
zone at any depth
above the water table?
; NO
NO
If soil gas data are
available proceed
to 5(f), otherwise
proceed to 06
Groundwater Assessment
Indicates Pathway Incomplete
- .| RecommendedJ--
[RecommendedJ
fr- 5(0 SG > TL?
NO
YES
Proceed to Q6
Site Specific Assessment
Soil Gas Assessement
Indicates Pathway Incomplete
-------
SITE SPECIFIC SCREENING
Question 6
(TL = appropriate media specific target level)
6(a) Have the nature and extent of
contamination, potential preferential
and overlying building characteristics
adequately characterized to identify the
likely-to-be-impacted buildings?
NO
YES
6(b) Conducting El determination
an appropriate and applicable
YES
6(c) Does the model predict
an unacceptable risk?
NO
YES
Pathway Is
Incomplete
for El
Determinations
6(d) Sublab vapor
data available?
NO
YES
6(f) Subslab vapor
data adequate?
YES
6(h) IA data adequate to
account for seasonal
variability and represent
most impacted areas?
< NO
NO
6(i) IA data adequate
to account
ambient and
background
sources?
-------
APPENDIX D
DEVELOPMENT OF TABLES 1,2, AND 3
1. Introduction
This appendix describes the data and calculations used to develop Tables 1, 2, and 3 in the guidance.
Table 1 lists chemicals that may be present at hazardous waste sites and indicates whether, in our
judgment, they are of sufficient toxicity and volatility to result in a potentially unacceptable indoor
inhalation risk. Tables 2 and 3 provide generally recommended target concentrations for
contaminants in indoor air, groundwater, and soil gas. For non-carcinogens, these values are based
on the appropriate reference concentration, and for carcinogens, they are calculated using a method
consistent with the approach in EPA's Supplemental Guidance for Developing Soil Screening
Levels (EPA, to be published). Only chemicals that are, in our judgment, sufficiently volatile and
toxic to pose an inhalation risk are included in Tables 2 and 3. The approach described here also
can be used, as appropriate, to evaluate chemicals not listed in the tables.
2. Description of Tables 1, 2 and 3
Table 1 lists the chemicals that may be found at hazardous waste sites and indicates whether, in our
judgment, they are sufficiently toxic and volatile to result in a potentially unacceptable indoor
inhalation risk. It also provides a column for checking off the chemicals found or reasonably
suspected to be present in the subsurface at a site. Under this approach, a chemical is considered
sufficiently toxic if the vapor concentration of the pure component (see Section 4 below) poses an
incremental lifetime cancer risk greater than 10"6 or results in a non-cancer hazard index greater than
one (see Section 5 below). A chemical is considered sufficiently volatile if its Henry's Law
Constant is 1 x 10"5 atm-m3/mol or greater (US EPA, 1991). In our judgement, if a chemical does
not meet both of these criteria, it need not be further considered as part of the evaluation.
Table 2 provides generic soil gas and groundwater screening concentrations corresponding to risk-
based concentrations for indoor air in residential settings calculated using the methodology
described in Section 5 below. Blank columns are included to allow the user to enter measured or
reasonably estimated concentrations specific to a site. The target soil gas and groundwater
concentrations are calculated using generic vapor intrusion attenuation factors (see Appendix F) as
described in Sections 6 and 7 below.
Table 3 provides soil gas and groundwater screening concentrations for a select set of attenuation
factors. Guidance for selecting the appropriate attenuation factor to use is given in Question 5. As
with Table 2, the target soil gas and groundwater concentrations are calculated using the approach
described in Sections 6 and 7 below and correspond to risk-based concentrations for indoor air in
residential settings calculated using the methodology described in Section 5 below.
The target concentrations in Tables 2 and 3 are screening levels. They are not intended to be used
as clean-up levels nor are they intended to supercede existing criteria of the lead regulatory
authority. The lead regulatory authority for a site may determine that criteria other than those
provided herein are appropriate for the specific site or area. Thus, we recommend that the user's
initial first step should involve consultation with their lead regulatory authority to identify the most
appropriate criteria to use.
D-l
-------
3.
Data Sources
Chemical Property Data - The source of chemical data used to calculate the values in Tables 1,
2. and 3 is primarily EPA's Superfund Chemical Data Matrix (SCDM) database. EPA's
WATER9 database was used for chemicals not included in the SCDM database.
Toxicity Values - EPA's Integrated Risk Information System (IRIS) is the generally preferred
source of carcinogenic unit risks and non-carcinogenic reference concentrations (RfCs) for
inhalation exposure.1 The following two sources were consulted, in order of preference, when
IRIS values were not available: provisional toxicity values recommended by EPA's National
Center for Environmental Assessment (NCEA) and EPA's Health Effects Assessment Summary
Tables (HEAST). If no inhalation toxicity data could be obtained from IRIS, NCEA, or HEAST,
we derived extrapolated unit risks and/or RfCs using toxicity data for oral exposure (cancer
slope factors and/or reference doses, respectively) from these same sources utilizing the same
preference order.2 Target concentrations that were calculated using these extrapolated toxicity
values are clearly indicated in Tables 2 and 3. Note that for most compounds, extrapolation
from oral data introduces considerable uncertainty into the resulting inhalation value. Values
obtained from inhalation studies or from pharmacokinetic modeling applied to oral doses will be
less uncertain than those calculated using the equations below.
EPA's Integrated Risk Information System (IRIS) currently does not include carcinogenicity data
for TCE, a volatile contaminant frequently encountered at hazardous waste sites. The original
carcinogenicity assessment for TCE, which was based on a health risk assessment conducted in
the late 1980's, was withdrawn from IRIS in 1994. The Superfund Technical Support Center has
continued to recommend use of the cancer slope factor from the withdrawn assessment, until a
reassessment of the carcinogenicity of TCE is completed. In 2001, the Agency published a draft
of the TCE toxicity assessment for public comment.3 In this guidance, we have calculated TCE
target concentrations using a cancer slope factor identified in that document, which is available
on the National Center for Environmental Assessment (NCEA) web site. We selected this slope
factor because it is based on state-of-the-art methodology. However, because this document is
still undergoing review, the slope factor and the target concentrations calculated for TCE are
subject to change and should be considered "provisional" values.
!U.S. EPA. 2002. Integrated Risk Information System (1RJS). http:/Avww.epa.gov/iriswebp/irisifiiiJcx.litrBl.
November.
"The oral-to-inhalation extrapolations assume an adult inhalation rate (IR) of 20 m'/day and an adult body
weight (BW) of 70 kg. Unit risks (URs) were extrapolated from cancer slope factors (CSFs) using the following
equation:
UR (Mg/m3)-1 = CSF (mg/kg/d)'1 * IR (m'/d) * (1/BW) (kg1) * (10'3 mg/ng)
Reference concentrations (RfCs) were extrapolated from reference doses (RfDs) using the following equation:
RfC (mg/m3) = RfD (mg/kg/d) * (1/IR) (m3/d)-' * BW (kg)
3US EPA, Trichloroethylene Health Risk Assessment: Synthesis and Characterization - External Review
Draft, Office of Research and Development, EPA/600/P-01/002A, August, 200).
D-2
-------
Table D-l summarizes the toxicity values used in this guidance document, along with their
sources. The table also indicates which unit risks and RfCs have been extrapolated from oral
toxicity values and whether the indoor air target concentration is based on an oral extrapolated
toxicity value. Please note that toxicity databases such as IRIS are routinely updated as new
information becomes available; this table is current as of November 2002. Users of this
guidance are strongly encouraged to research the latest toxicity values for contaminants of
interest from the sources noted above. In the next year, IRIS reassessments are expected for
several contaminants commonly found in subsurface contamination whose inhalation toxicity
values today are based upon extrapolation.
4. Maximum Pure Component Vapor Concentration
The maximum possible vapor concentration is that corresponding to the pure chemical at the
temperature of interest. In this case, all calculations were performed at the reference temperature of
25C using the equation:
= S * H * 103 ug/mg * 103 L/m3
where
Cmax. = maximum pure component vapor concentration at 25C [ug/m3],
S = pure component solubility at 25C [mg/L], and
H = dimensionless Henry's Law Constant at25C [(mg/L- vapor)/(mg/L - H2O)].
To determine if a chemical is sufficiently toxic to potentially pose an unacceptable inhalation risk,
the calculated pure component vapor concentrations were compared to target indoor air
concentrations corresponding to an incremental lifetime cancer risk greater than 10"* or a non-cancer
hazard index greater than one.
5. Target Indoor Air Concentration to Satisfy Both the Prescribed Cancer Risk Level
and the Target Hazard Index.
The target breathing zone indoor air concentrations in Tables 1,2, and 3 are risk-based screening
levels for ambient air. The indoor air concentrations for non-carcinogens are set at the appropriate
reference concentration, and the concentrations for carcinogens are calculated following an
approach consistent with EPA's Supplemental Guidance for Developing Soil Screening Levels
(EPA, to be published). The toxicily values on which the calculations are based are listed in Table
D-l, which also shows the source of the toxicity data. Separate carcinogenic and non-carcinogenic
target concentrations were calculated for each compound when both unit risks and reference
concentrations were available. When inhalation toxicity values were not available, unit risks and/or
reference concentrations were extrapolated from oral slope factors and/or reference doses,
respectively. For carcinogens, target indoor air concentrations were based on an adult residential
exposure scenario and assume exposure of an individual for 350 days per year over a period of 30
years. For non-carcinogens, target indoor air concentrations are set at the corresponding reference
concentration. An inhalation rate of 20 mVday and a body weight of 70 kg are assumed and have
been factored into the inhalation unit risk and reference concentration toxicity values.
D-3
-------
For carcinogens,
Ccancer (Jig/m3) = [
-------
R = gas constant (0.082 1 L-atm/mole-K),
T = absolute temperature (298 K), and
MW = molecular weight (g/mole).
The calculated target indoor air concentrations are listed in Tables 2 and 3 along with a column
indicating whether cancer or non-cancer risks drive the target concentration. A separate column
indicates whether risks are calculated using provisional, oral-extrapolated toxicity values (i.e.,
inhalation values extrapolated from oral CSFs or RfDs) (see Table D-l).
6. Target Soil Gas Concentration Corresponding to Target Indoor Air Concentration
The target soil gas concentration corresponding to a chemical's target indoor air concentration was
calculated by dividing the indoor air concentration by an appropriate attenuation factor (see
Questions 4 and 5 in the guidance and Appendix F). The attenuation factor represents the factor by
which subsurface vapor concentrations migrating into indoor air spaces are reduced due to diffusive,
advective, and/or other attenuating mechanisms. The attenuation factor can be empirically
determined or calculated using an appropriate vapor intrusion model. Once the appropriate
attenuation factor was determined, the target soil concentration was calculated as:
C«^ [ug/m3] = C^, [ug/m3] / a
or
[ppbv] = C,^. [ppbv] / a
where
Csai-gas = target soil gas concentration [jig/m3] and
a = attenuation factor (ratio of indoor air concentration to source vapor concentration)
If C^.^ exceeds the maximum possible pure chemical vapor concentration, the designation "*" is
entered in the table. If C^^ exceeds the maximum possible pure chemical vapor concentration at
25C, but Cfrfi does not, then "**" is entered in the table.
7. Target Groundwater Concentration Corresponding to Target Indoor Air
Concentration
The target groundwater concentration corresponding to a chemical's target indoor air concentration
is calculated by dividing the target indoor air concentration by an appropriate attenuation factor (see
Questions 4 and 5 in the guidance and Appendix F) and then converting the vapor concentration to
an equivalent groundwater concentration assuming equilibrium between the aqueous and vapor
phases at the water table. Diffusion resistances across the capillary fringe are assumed to be
accounted for in the value of a. The equilibrium partitioning is assumed to obey Henry's Law so
that:
C, [|ig/L] = Cy. [(ig/m3] * ID'3 m3/L * 1/H *l/a
D-5
-------
where
Cg^, = target groundwater concentration,
a = attenuation factor (ratio of indoor air concentration to source vapor concentration).
H = dimensionless Henry's Law Constant at 25C [(rag/L - vapor)/(rag/L - H2O)].
If C^g^jj, exceeds the maximum possible pure chemical vapor concentration, the designation "*" is
entered in the table. If C^ exceeds the aqueous solubility of the pure chemical, but C^g^ does not,
then "**" is entered in the table
If the calculated groundwater target concentration is less than the Maximum Contaminant Level
(MCL) for the compound, the target concentration is set at the MCL. Target concentrations set
at the MCL are indicated in Tables 2 and 3 by this symbol ("f")-
D-6
-------
8. References
US EPA, 1991, Risk Assessment Guidance for Superfund: Volume 1 - Human Health Evaluation
Manual, Part B.
IRIS - Integrated Risk Information System - US EPA Office of Research and Development -
National Center for Environmental Assessment. [ht1p://www.epa.gov/iriswebp/iris/mdex.httnl]
November 2002,
US EPA, Supplemental Guidance for Developing Soil Screening Levels, Office of Emergency
and Remedial Response, OSWER 9355.4-24 (EPA, to be published).
US EPA, Trichloroethylene Health Risk Assessment: Synthesis and Characterization - External
Review Draft, Office of Research and Development, EPA/600/P-01/002A, August 2001.
D-7
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APPENDIX E - RELEVANT METHODS AND TECHNIQUES
I. Introduction
This appendix provides information on sampling and analysis methodologies that can be used to
help evaluate vapor intrusion into indoor air. It should be noted that not all of these methods
were developed specifically for this purpose. The Office of Research and Development (ORD)
is evaluating the available methods to determine their applicability, and when methods have low
reliability (e.g., sub-slab sampling), developing new protocols.
The technical references provided in this appendix originate from a variety of sources including
non-EPA documents which may provide regional and state site managers, as well as the
regulated community, useful technical information. However, such non-EPA documents do not
replace current EPA or OSWER guidance or policies.
II. Site Characterization
Characterization of a site involves the collection of data and the development of a conceptual site
model (See Appendix B) to assist in making decisions on the risks posed by contaminants to
critical receptors. A variety of data may be employed in the process, and the data should be
assessed for their quality and usefulness in making critical decisions on the risks posed by a site.
Different media may be sampled with a variety of methods and may be analyzed in a variety of
ways. We recommend that experts from appropriate disciplines be assembled at an early stage to
develop objectives for the site investigation and to develop a sampling and analytical plan
meeting data quality objectives (DQOs).
The Office of Research and Development's National Exposure Research Laboratory (NERL) has
prepared a Compact Disk (CD) entitled "Site Characterization Library, Volume 1, Release 2.5,"
which contains more than 20,000 pages and 84 documents of guidance for the characterization of
sites that can be searched, read, and printed (EPA/600/C-02/002). The documents are readable
using Adobe Acrobat software. Twenty-five software programs are also included. The CD may
be obtained from the National Center for Environmental Publications (NCEP). The CD
identifies the following ASTM standards for site characterization:
D 5314 Guide for Soil Gas Monitoring in the Vadose Zone
D 4696 Guide for Pore-Liquid Sampling from the Vadose Zone
D 3404 Guide to Measuring Matric Potential in the Vadose Zone Using Tensiometers
D 4944 Test Method for Field Determination of Water (Moisture) Content of Soil by the
Calcium Carbide Gas Pressure Tester Methods
E-l
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D 3017 Test Method for Water Content of Soil and Rock In-Place by the Nuclear Method
(Shallow Depth)
D 5220 Test Method for Water Content of Soil and Rock In-Place by Neutron Depth
Probe Method
D 6031 Test Method for Logging In Situ Moisture Content and Density of Soil and Rock
by the Nuclear Method in Horizontal, Slanted and Vertical Access Tubes
Other relevant ASTM methods include:
D6235
D5730
Standard Practice for Expedited Site Characterization of Vadose Zone and
Around Water Contamination at Hazardous Waste Contaminated Sites
Guide for Site Characterization for Environmental Purposes with Emphasis on
Soil. Rock, the Vadose Zone, and Groundwater
III. Groundwater Sampling and Analysis for VOCs
Prior to using groundwater data for evaluating the vapor intrusion pathway, we recommend that
you establish that LNAPL is not floating on the groundwater, as the VOCs can partition directly
from the pure product to the vapor phase rather than from the dissolved phase. This can be
indicated by analytical results from water samples taken at the water table having values higher
than the theoretical solubility for the specific LNAPL compounds present.
If possible, we recommend that groundwater samples be collected from wells screened at or
across the top of the water table. This point of collection is necessary to be consistent with the
derivation of the target groundwater criteria in Table 2, which assumes equilibrium partitioning
between the aqueous and vapor phases and uses Henry's Law Constant to calculate source vapor
concentrations corresponding to groundwater concentrations. It should be recognized that
samples from groundwater monitoring wells maybe a blend of groundwater from different levels
across the screened interval. This may result in either under- or over-estimation of the
groundwater contaminant concentration at the top of the aquifer. For example, at site locations
where concentrations are highest near the water table, the in-well blending will provide data with
a negative bias (concentrations lower than representative). This may occur at locations where
LNAPL is found near the water table, where recharge rates are low, or sites where there is an
interface-zone plume (a fluctuating water table facilitates interactions between a vapor plume
and the shallow groundwater). At other sites, shallow groundwater may have relatively low
concentrations, and in-well blending will provide data with a positive bias (concentrations higher
than representative). Examples include sites with a high rate of recharge from above, which can
create a layer of shallow groundwater with little or no contamination that acts as a barrier to
volatilization of vapors from deeper groundwater. [For more information, see Fitzpatrick, N. A..
Fitzgerald, J. J. 1996. "An Evaluation of Vapor Intrusion Into Buildings Through a Study of
Field Data," Proceedings of the 11th Annual Conference on Contaminated Soils, University of
Massachusetts at Amherst.]
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Confidence in the groundwater data can be increased through the use of a narrowly screened
interval across the water table, the use of low flow sampling procedures to minimize mixing, or a
variety of other depth-discrete sampling protocols. Methods of sampling such as direct push
using a Geoprobe or cone penetrometers should concentrate on the upper few feet of the ground
water.
There are numerous ASTM standards for groundwater sampling. Assuming wells already exist
for sampling VOCs, the following standards are recommended:
D 5980 Standard Guide for Selection and Documentation of Existing Wells for Use in
Environmental Site Characterization and Monitoring
D 6634 Standard Guide for the Selection of Purging and Sampling Devices for Ground-
Water Monitoring Wells
D 5903 Guide for Planning and Preparing a Ground-Water Sampling Event
D 6452 Guide for Purging Methods for Wells Used for Ground-Water Quality
Investigations
D 4448 Standard Guide for Sampling Ground-Water Monitoring Wells
D 6771 Standard Practice for Low-Flow Purging and Sampling for Wells and Devices
Used for Ground-Water Quality Investigations
D 6564 Standard Guide for Field Filtration of Ground Water Samples
D 6517 Standard Guide for Field Preservation of Ground Water Samples
D 3694 Practices for Preparation of Sample Containers and for Preservation of Organic
Constituents
D 6089 Guide for Documenting a Ground-Water Sampling Event
The following ASTM standards are useful if a monitoring system is not already in place:
D 5612 Standard Guide for Quality Planning and Field Implementation of a Water
Quality Measurement Program
D 5730 Standard Guide for Site Characterization for Environmental Purposes with
Emphasis on Soil, Rock, the Vadose Zone and Ground Water
D 6286 Standard Guide for Selection of Drilling Methods for Environmental Site
Characterization
E-3
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D 6001 Standard Guide for Direct-Push Water Sampling for Geoenvironmental
Investigations
D 5092 Standard Practice for Design and Installation of Ground-Water Monitoring Wells
in Aquifers
D 5521 Standard Guide for Development of Ground-Water Monitoring Wells in Granular
Aquifers
Other Related ASTM Standards:
D 6312 Standard Guide for Developing Appropriate Statistical Approaches for Ground-
Water Detection Monitoring Programs
D 5241 Standard Practice for Micro-Extraction of Water for Analysis of Volatile and
Semi-Volatile Organic Compounds in Water
D 5314 Standard Guide for Soil Gas Monitoring in the Vadose Zone
D 4696 Standard Guide for Pore-Liquid Sampling from the Vadose Zone
IV. Indoor Air Sampling and Analysis
Indoor air sampling and analysis provide the most direct estimate of inhalation exposures.
However, source attribution for the many compounds typically present in indoor air can be
challenging. Constituents of indoor air can originate from indoor emission sources, from
ambient (outdoor) air contributions, as well as from possible vapor intrusion of contaminated
groundwater. Each of these sources can introduce concentrations of volatile chemicals to the
indoor environment sufficient to pose an unacceptable health risk. In addition, concentrations of
compounds found in indoor air are often subject to temporal and spatial variations, which may
complicate estimates of exposure. If source attribution is pursued, then we recommend that the
various potential sources contributing to the total concentration of a compound be identified.
This is typically very challenging and may involve a series of measurements, or actions, whose
purpose is to isolate the individual source contributions. Before conducting an indoor air
sampling plan, we recommend consideration be made to other management options, such as
proactive exposure controls, which may be cost competitive. Appendix A provides guidance in
executing the DQO process for planning an indoor air-monitoring program.
Prior to indoor air sampling, we recommend conducting an inspection of the residence and an
occupant survey to adequately identify the presence of any possible indoor air emission sources
of (or occupant activities that could generate) target VOCs in the dwelling (see Appendices H &
I). An indoor air quality survey has several components, and we recommend that it be consistent
with data quality protocols appropriate for risk assessment (see Risks Assessment Guidance for
Superfund Part B http:/7vv\vw.epa.gov/superfund''program''risk,''ragsb/index.htrn or EPA/540/R-
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92/003). The Massachusetts Department of Environmental Protection (MA DEP) has prepared
an Indoor Air Sampling and Evaluation Guide (April 2002) which is available at the following
URL: http://www.sta1 e. ma.us/dep/ors/files/'indair.pdf.
Many aspects of the protocols used for ambient air can also be applied to indoor air sampling
(e.g., EPA TO-15 and TO-17 methods). Specially treated stainless steel evacuated canisters or
adsorbent tubes are appropriate for sampling and we recommend that they be combined with an
analytical method capable of obtaining the detection limits identified in the DQO process. To
facilitate a reliable comparison of analytical results, a standard condition for sampling is
recommended. Some guidance in establishing a standard monitoring condition is given in the
following paragraphs.
We recommend that sampling units be placed within the normal breathing zone, 2 to 5 feet above
the floor, in the lowest inhabited area. It is generally advisable to collect at least one 24-hour
sample in both the probable place of highest concentration (e.g., basement) and in the main
living area. Two or more sampling events at each location are desirable. Typically, we
recommend that the house be closed (windows and doors shut) 12 to 24 hours before the
measurements begin and the use of appliances that induce large pressure differences (e.g.
exhaust fans, clothes dryers, operating fireplaces) be avoided during this time. Additionally, we
recommend avoiding sampling locations adjacent to windows and air supplies.
We recommend gas sampling that will be used for direct assessment of vapor intrusion meet or
exceed requirements for demonstrating method acceptability as specified in EPA Methods TO-
15 (canister-based sample collection) and TO-17 (sorbent tube-based sample collection) or
appropriately modified to achieve a lower method detection limit (MDL) corresponding to a
given life-time risk level. Note: To achieve detection at or below the published 10~s to 10"* risk
levels for many target compounds, the MDLs for TO-15 or TO-17, in our judgment, must be
considerably below 0.5 ppbv.
To achieve TO-15 and TO-17 method acceptability, we recommend that a sampling and analysis
protocol meet the recommended performance criteria for an enhanced method detection limit,
replicate precision, and audit accuracy at compound concentrations corresponding to the 10"5 or
10"6 risk levels, and special attention be paid to quality control measures. Sufficiently low
sample container blanks, analytical system blanks, analytical interferences, etc., are all implied in
the ability to meet the technical acceptance criteria.
To ensure reliable measurements are obtained, we recommend that multiple simultaneous
samples (more than one canister or sorbent tube) be taken for every sampling event and from the
same inlet so that variability in nominally identical samples can be documented. Also, we
recommend that knowledge of the performance of the analytical system be demonstrated,
including blank response, the MDLs, calibration of the target compounds at or near the sample
concentration range, and the likelihood of interferences. These are common sense considerations
that are covered in TO-15 and TO-17, but call for special attention at the low concentration
levels being considered.
E-5
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Note: At this point in the development of the best approach to sorbent tube sampling (TO-17),
reduction of co-collected water on the sorbent tubes is sometimes important to achieve a linear
analytical response such as with ion trap mass spectrometers. Therefore, we recommend that
preliminary experiments be performed to document the effect of different water vapor levels on
analytical performance. Also, the interaction of target compounds with reactive compounds, e.g.
ozone, depends on the extent to which the reactive compounds exist in the indoor air and the
reaction rates. Until this specific problem with sampling is addressed, we recommend that the
ozone concentration be determined at every sampling event. Also, an interaction of ozone with
adsorbed compounds can destroy the compound. Certain target compounds have been tested for
this (see McClenny, W.A., Oliver, K.D., Jacumin, H.H., Jr., and Daughtrey, E.H., Jr., 2002,
Ambient volatile organic compound (VOC) monitoring using solid adsorbants - recent U.S. EPA
developments, JEM 4(5) 695 - 705).
Recommended publications:
Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air,
Second Edition, EPA/625/R-96/010b
- 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). pp. 15-1 through 15-62
- Method TO-17, Determination of Volatile Organic Compounds in Ambient Air using
Active Sampling on Sorbent Tubes, pp. 17-1 through 17-49
- Compendium of Methods for the Determination of Air Pollutants in Indoor Air,
EPA/600/4-90-010
V. Soil Gas Sampling
Soil gas sampling and analysis results tend to be more reliable at locations and depths where high
contaminant concentrations are present and where the soils are relatively permeable. Reliability
of the results tends to be lower in lower permeability settings and when sampling shallow soil
gas. In both cases, leakage of atmospheric air into the samples is a valid concern. Consequently,
it is recommended that samples collected at depths less than 5 feet below ground surface (bgs)
not be used for this analysis, unless they are collected immediately below the building
foundation several feet in from the edge (e.g., subslab samples). Reliability of soil gas sampling
can be assessed by: a) measuring a vertical profile and inspecting to see if measured
concentrations decrease with increasing distance from the vapor source, and b) checking to see if
vapor concentrations correlate qualitatively and quantitatively with available groundwater
concentration data For example, with groundwater sources the highest soil gas concentrations
should correlate with the highest groundwater concentrations, and vapor concentrations collected
immediately above groundwater should not exceed the value calculated using Henry's Law.
Parallel analysis of oxygen, carbon dioxide, and nitrogen in soil gas samples can often be used to
help assess the reliability of a given sample result. Reliability is typically improved by using
E-6
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fixed probes and by ensuring that leakage of atmospheric air into the samples is avoided during
purging or sampling. To avoid dilution of the sampling region, we recommend using the
minimum purge volume deemed adequate to flush the sampling system With respect to the
spatial distribution of sampling points, close proximity to the building(s) of concern is generally
preferred; however, it may be possible to reasonably estimate concentrations based on data from
soil gas samples collected about a larger area. Additionally, as vapors are likely to migrate
upward preferentially through the coarsest and driest material, we recommend soil gas samples
be collected from the most permeable zones in the vadose zone underlying the inhabited
buildings. Concentrations should be lower in the high permeability zones than the low
permeability zones.
The velocity at which soil gas should be sampled is influenced by the soil permeability, and the
volume of sample taken will determine the zone of soil that is sampled. The effects of low-
versus high-velocity and micro- versus macro-volume soil gas sampling techniques are currently
being evaluated.
Measurement of VOCs in the Subslab Soil Gas
Subslab sampling may entail drilling a series (e.g., 3 to 5) of small diameter (e.g., 9/16") holes in
the foundation of a residential building. It may be advantageous to install flush mounted
stainless steel or brass vapor probes in contaminant free cement. We recommend sampling be
performed using EPA Method TO-15 or TO-17.
The preferred measurement location is in the central portion of the slab, well away from the
edges where dilution is more likely to occur. We recommend the hole be plugged with a
material such as tape or pliable caulk (VOC free) immediately after drilling the hole to minimize
the disturbance of the sub slab concentrations. When drilling the hole, care should be taken not
to puncture the surface of soil underneath. In cases where there is aggregate soil underneath the
foundation, this care may not be important, but if the soil has a slightly compacted layer on top
with a slight subsidence under the slab this compacted layer may actually provide some
resistance to the entry of soil gas from underneath. In this case, a subslab sample can be
collected by slowly pulling a volume of gas from the void of the subsidence. This initial
measurement may be representative of the soil gas typically entering the house. After the
subslab with undisturbed soil has been sampled, it may be instructive to penetrate the surface of
the soil and resample. We recommend the subslab samples be collected at several locations to
obtain representative values. It is important to not disturb the subslab region by applying
excessive pressures that might induce dilution of vapors in this region. Significant pressures
might result from excessive slamming of doors, or from appliances such as: exhaust fans, clothes
dryers, downdraft grills, ceiling or roof mounted attic fans, or certain combinations of open
windows on a windy day. If the subslab region is disturbed, it may require many hours to return
to a steady state condition.
Additional points to consider before drilling into the foundation are whether or not the home has
an existing vapor barrier, or is a tension slab. In either case, alternative sampling methods may
be preferable.
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Measurement of VOC's in soil gas using slam bar methods
Slam bar methods have been widely used to measure contaminants in soil gas. The results of
these measurements have been highly variable. Because this technique is frequently used for
relatively shallow sampling, it is, in our judgment, prone to errors from dilution by surface air.
This is especially true when the hole is punched or drilled with one instrument that is then
replaced by a measurement probe (sometime of smaller diameter). We recommend great care be
taken to ensure that leakage air does not enter the sample. Only the volume of air sufficient to
flush the probe and sampling line should be extracted before collecting the sample. The larger
the purge/sample volume, the larger the subsurface area of influence; if the contamination is
contained within non-preferential flow paths or small discrete locations, a large purge/sample
volume will dilute the concentration of contaminants.
Measurement of VOC's in soil gas using push probe methods
This approach seems to be emerging as a powerful tool for conducting soil gas measurements.
OSWER is working'with ORD and will update this section on the EPA/OSWER website as
further refinements of these methods are developed.
Recommend publications:
Soil Vapor Extraction Technology: Reference Handbook - Soil Vapor Extraction Technology:
Reference Handbook March 1990. Environmental Protection Agency, Risk Reduction
Engineering Lab. EPA/540/2-91/003
VI. Soil Sampling and Analysis
Soil sampling and analysis is not recommended for assessing whether or not the vapor intrusion
pathway is complete. This is because the uncertainties associated with soil partitioning
calculations, as well as the uncertainties associated with soil sampling and soil chemical analyses
for volatile organic chemicals, are so great that, that in our judgment, use of soil concentrations
for assessment of this pathway is not technically defensible. Thus, soil concentration criteria
were not derived and the use of soil criteria is not encouraged in this guidance. Soil
concentration data might, however, be used in a qualitative sense for delineation of sources
provided the soil samples are preserved immediately upon collection with methanol. For
example, high soil concentrations (e.g. >1000 mg/kg TPH) would definitely indicate impacted
soils; unfortunately, the converse is not always true and we recommend that non-detect analytical
results not be interpreted to conclude the absence of a vapor source.
VII. Other Issues
We recommend that detection limits be considered when choosing which media to sample and
how to interpret the results. The properties of some chemicals and the biases in the analytical
methods may be such that the sensitivity of detection is higher in one medium than another. For
E-8
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example, a high Henry's constant (H>1) chemical might be detectable in soil gas when the
concentration in groundwater falls below the detection limit (e.g., vinyl chloride).
We recommend that transformation products also be considered when selecting the chemicals of
concern. For example, 1,1.1 -trichloroethane (111 TCA) may be abiotically converted to 1,1-
dichloroethene (11DCE) in groundwater, so that we recommend looking for both chemicals at
111TC A spill sites.
E-9
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APPENDIX F
EMPIRICAL ATTENUATION FACTORS
AND RELIABILITY ASSESSMENT
1. Introduction
The empirical attenuation factors used in this guidance were derived through review of
data from sites with paired indoor air and soil gas and/or groundwater concentrations.
These data have been compiled into a database with the structure and elements illustrated
in Figure F-l.
The database contains information from 15 sites (CO - 5 Sites; CA - 1 Site; CT - 1 Site;
MA - 7 Sites; and MI - 1 Site). Fifteen VOCs are represented: BTEX, Chloroform, 1,1-
Dichloroethane, 1,2-Dichloroethane, 1,1-Dichloroethylene, cis-l,2-DichIoroethylene,
trans- 1,2-Dichloroethylene, Tetrachloroethylene, 1,1,1-Trichloroethane, 1,1,2-
Trichloroethane, Trichloroethylene and Vinyl chloride. The result is a database with 274
total residence and chemical combinations, 35 of which represent BTEX compounds and
the remaining 239 represent chlorinated hydrocarbons. Groundwater data are available
for the entire set of residence and chemical combinations. Soil gas data are available only
for 40 of the residence and chemical combinations.
The information in the database was used to calculate groundwater-to-indoor air and soil
gas-to-indoor air attenuation factors for each of the chemicals measured at each of the
residences monitored. The distributions of these calculated attenuation factors were used
to define a conservative empirical attenuation factor for each medium, as described in
Sections 2, 3, and 4 below.
An assessment was performed using the same database to determine the reliability of the
selected attenuation factors for screening in residences with indoor air concentrations
exceeding the target levels corresponding to a cancer risk of 10"6 and 10"5. The
reliability assessment was performed by determining the number of false negative and
false positives corresponding to the selected attenuation factor using the guidelines
described in Section 6 below.
2. Calculation of Attenuation Factors
The attenuation factor represents the ratio of the indoor air concentration measured in a
residence to the vapor concentration measured in the subsurface materials underlying or
adjacent to the residence. For soil gas, the attenuation factor (a) is calculated simply as:
a =
' indoor
c
soil gas
where
F-l
-------
= measured indoor air concentration [ug/m3]
= measured soil gas concentration [ug/m3]
For groundwater, the attenuation factor is calculated as:
indoor
f-> I]
groundwater c
where
Cgroundwater = measured groundwater concentration [ug/L] x 1000 L/m3
Hc = dimensionless Henry's Law Constant [--]
Henry's Law Constant is used to convert the measured groundwater concentration to a
corresponding equilibrium soil gas concentration. Field data suggest that this conversion
may result in over prediction of the soil gas concentration (by as much as a factor often)
directly above the contaminated groundwater. However, this is not always the case and
consequently Henry's Constant is used here without a correction factor.
In the database, attenuation factors are calculated using only those residences and
chemicals for which both the indoor air and subsurface measurements were above the
chemical's method detection limit (MDL). Because the subsurface concentrations are
generally greater than the measured indoor air concentrations, the calculated attenuation
factors are values less than one.
3. Groundwater-to-Indoor Air Attenuation Factor
The distribution of groundwater-to-indoor air attenuation factors is shown in Figures F-2
and F-3. Figure F-2 shows the distribution of attenuation factors for all residences in the
database with associated measured indoor air and groundwater concentrations above the
chemicals' MDLs. The calculated attenuation factors range from 10"' to IO"7. This range
includes attenuation factors calculated for homes with high indoor air concentrations as
well as for homes with indoor air concentrations at levels typical of background
concentrations (Table F-l). Figure F-3 compares the distribution shown in Figure F-2 to
the distribution of the subset of attenuation factors corresponding to residences with
indoor air concentrations greater than the typical background levels (e.g., geometric mean
of the mean background values shown in Table F-l). As can be seen in Figure F-3, fewer
than 5% of the residences with indoor air concentrations above typical background levels
have attenuation factors greater than 0.001 (1/1000). This means that for 95% of the
residences in the database, the groundwater-to-indoor air attenuation factor is less than
0.001 (1/1000) and, consequently, this value (0.001) is considered to be a generally
reasonable upper-bound value.
F-2
-------
4. Soil Gas-to-Indoor Air Attenuation Factor
The shallow soil gas to indoor air attenuation factor represents the ratio of the indoor air
concentration to the soil gas concentration at some shallow depth. For the purposes of
this guidance, shallow soil gas samples are defined as those obtained either from directly
below the foundation or from depths less than 5 feet below foundation level. Figure F-4
shows the distribution of subslab-to-indoor air attenuation factors for the subset of
residences with indoor concentrations greater than the subslab concentration measured
below the residence's foundation. As can be seen in the plot, approximately 15% of the
residences have attenuation factors greater than 0.1 (1/10), or conversely, about 85% of
the residences have attenuation factors smaller than 0.1 (1/10). Consequently, an
attenuation factor of 0.1 was used to represent a generally reasonable upper-bound value
for the case where the soil gas concentration immediately beneath a foundation is used
(e.g., the indoor air concentration would not be expected to exceed 1/10 of the
concentration immediately below the foundation). This value is also supported by an
analysis of the dilution that occurs due to ventilation of a house. An attenuation factor of
0.1 suggests that 10% or less of the air exchanged in a house originates from the
subsurface. This value is conservatively assumed to apply to shallow soil gas samples (<
5 feet below foundation level) as well as subslab samples.
Deep soil gas samples are defined for the purposes of this guidance as those obtained just
above the water table or from depths greater than 5 feet below foundation level. A
smaller attenuation factor than that used for shallow soil gas is warranted as the deep soil
gas samples represent a more direct measurement of the source vapor concentration and
are subject to less variability than is observed for shallow soil gas samples. On the other
hand, a more conservative value than that used for groundwater is warranted, as there is
not the added safety factor incorporated in the groundwater attenuation factor, which
assumes equilibrium partitioning of chemicals between groundwater and soil vapor
(Henry's Law). Consequently, a value of 0.01 was selected for deep soil gas.
5. BTEX versus Chlorinated Hydrocarbon Attenuation Factors
To be conservative, the recommended criteria developed for this guidance have been
established assuming that the chemicals do not degrade as they migrate through the
vadose zone. It should be recognized that many chemicals of interest do biodegrade. For
example, petroleum hydrocarbon vapors will biodegrade in the presence of oxygen, and
field studies have shown this biodegradation to be very significant in some settings. In
contrast, analysis of data from sites impacted with chlorinated solvents suggest that
degradation is insignificant for these compounds. The impact of biodegradation can be
seen in the distribution of attenuation factors for BTEX compounds versus chlorinated
hydrocarbons (Figure F-5). Figure F-5 suggests a three-fold to ten-fold decrease in
attenuation factor for BTEX compounds.
Unfortunately, the significance of the biodegradation has also been highly variable, and
the factors that determine its significance are not yet fully understood. In a very general
sense, it is expected that aerobic biodegradation will have limited effect in settings where
F-3
-------
oxygen re-supply is limited, and also will have little effect on the attenuation factors used
for soil gas samples collected near a building. At this time, we recommend that the
significance of biodegradation be determined through collection of vertical soil gas
profiles beneath the buildings of concern. The occurrence of aerobic biodegradation will
be reflected qualitatively in the oxygen and contaminant soil vapor profiles, and the
quantitative effects can be estimated by the methods described in Johnson et al. (1999), or
other defensible analysis methods. It is unlikely that the extensive site-specific
information required to determine the influence of biodegradation will be available in the
initial stages of site characterization. Therefore, we believe that it is generally prudent to
assume that biodegradation is not a factor when screening sites for vapor intrusion issues.
6. Reliability Assessment
The reliability of the evaluation approach used in Questions 4, 5, and 6 of this guidance
was assessed using the database described above in Section 1 of this appendix. For the
assessment at the generic screening level (Question 4). the target levels in Tables 2(a) and
2(b) were used. For the assessment of Question 5, the target levels in Tables 3(a) and
3(b) were used. For Question 6, the Johnson and Ettinger Model was applied as
described in Appendix G using the updated default model parameters. The following
sections briefly describe the analysis and results. This analysis shows that the evaluation
approach used in this guidance yields reliable results at both the 10~5 and IO"6 cancer risk
levels when assessing the vapor intrusion pathway at all sites reviewed.
6.1 Analysis Approach
Cancer risk levels at both the 10"5 and 10"6 levels were evaluated. Table 2 was used to
select target levels for evaluation of Question 4. For Question 5, the appropriate
attenuation factor to use when selecting screening levels from Table 3 was determined
from the figures 3a and 3b in Question 5 of the guidance as a function of site-specific
SCS soil types and depth to groundwater. For the Question 6 assessment, information on
foundation type (either slab-on-grade or basement) and building mixing height was
incorporated into the analysis (basement defaults were used for buildings with crawl
spaces) and a site-specific attenuation factor was calculated.
The assessment was performed by determining the number of false negative and false
positives obtained using the most recently available toxicity data. As shown in Table F-
2, a false negative occurs when a chemical's measured indoor air concentration exceeds
the target level, but the measured groundwater (or soil gas) concentration does not. False
negatives may appear if indoor or ambient (outdoor) sources of VOCs are present and
they exceed the indoor air target level at the selected risk level. A false positive occurs
when a chemical's measured indoor air concentration is below the target level, but the
measured groundwater (or soil gas) concentration is above the target level. Correct
positives and correct negatives are defined in a similar fashion, as shown in Table F-2.
F-4
-------
6.2 Results
In order to effectively understand the results, it is important to differentiate between
samples, buildings, and sites. There are seven sites evaluated in this analysis (Alliant,
Eau Claire, Hamilton-Sunstrand, LAFB, MADEP, Mountain View, and Uncasville).
Each site has one or more buildings. For example, the Alliant site has only one building.
LAFB has 13 buildings and Mountain View has seven buildings. Each building has its
own unique address. Several samples were taken at each building. Each sample consists
of paired indoor air and groundwater concentrations for a unique chemical at a certain
building. The number of samples and the number of chemicals identified in these
samples varies by building.
The results are grouped into two types of tables. Tables F-3 (risk level 10"5) and F-5
(risk level 10"6) organize the results by building at each site. It shows whether or not a
building has a correct negative, correct positive, false negative, or false positive result.
An important note regarding Tables F-3 and F-5 is the difference between buildings that
are not applicable for vapor intrusion analysis ("NA" is added to the results of these
buildings) and buildings with wet basements. Buildings that are not applicable are those
where the depth from the bottom of the foundation (whether it be a basement or slab-on-
grade) to groundwater contamination is less than 1.5 meters (5 feet). This is one of the
precluding factors listed in the guidance. We still included results for these buildings, but
marked their results with an "NA" to indicate that they would be excluded from this
analysis according to protocols set forth in the guidance. The false negative, false
positive, correct negative, and correct positive results for non-NA buildings are summed
at the bottom of each table.
The second set of results presents outcomes by chemical at each site. Tables F-4 (risk
level IO"5) and F-6 (risk level 10"6) show the number of false positive and false negative
outcomes for each chemical at each site. They do not indicate whether the false results
occur in just one or two buildings at the site, or evenly across all buildings. It is
important to note that the numbers in these tables are counts of samples, not of buildings.
Therefore, it is possible to have a false negative result for a chemical at a particular site,
but each building at that site can have correct positive results based on the outcomes for
other chemicals. It is also important to note that results for those samples that are
considered not applicable (NA) according to the criteria discussed in the guidance are
not included in this table.
Tables F-3 and F-5 show that the evaluation approach used in this guidance yields no
false negatives with respect to sites or buildings at either the IO'5 or IO"6 cancer risk level.
Tables F-4 and F-6 show that for most chemicals either no or few false negatives are
obtained, with the exception of tetrachloroethene and 1,2-dichloroethane. These two
chemicals show a number of false negatives, especially at the IO"6 cancer risk level. It is
important to note, however, that both of these chemicals are typically found as
background contaminants, which may account for some of the false negatives. Several of
the chemical-specific false negative results shown in Tables F-4 and F-6 also appear to
F-5
-------
result from limiting the ground water target concentration to the MCL if the calculated
target concentration would be less than the MCL.
Table F-l. Background indoor air concentrations for selected volatile organic
compounds. All concentrations expressed in ug/m3.
1 . 1 .2-Tn-;hio-09thaw
iAietane :
iDDE
Shsh and
Singix. 1938}
?7V4_
""foil
1S.J
41
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: 28
30
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10:0
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0 13
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3
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Foster «<«!
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J4
JS
14"
.M
Ri;!:o.esaj
8.3?
4 S3 :
21
Shah and Singh (1988): ES&T, VI. 22. No.12, pp. 1381-1388, 1988
Samfietd (1992): EPA-600-R-92-025, 1992.
Brown era/. (1994): Indoor Air, 4:123-134, 1994.
NOPES (1990): EPA/600/3-90/003, January 1990.
Sheldon (1992): California Air Resources Board, Final Report, January 1992.
MADEP (September 1998): From: Background Documentation for the Development ofMCP
Numerical Stds" April 1994, Table 4.2, except 1,1-dichloroethene (EPA TEAM study) and
methylene chloride (Stolwijk, JAJ, 1990)
EPA IAQ Reference Manual (July 1991): Results from Wallace (1987), except toluene: Seifert &
Abraham (1982).
Foster et a/., (2002): Foster, S.J, J.P. Kurtz, and A.K. Woodland, Background indoor air risks at
selected residences in Denver, Colorado, 2002
F-6
-------
Table F-2. Evaluation criteria for the reliability assessment.
Measurement
C(GW)
C(IA)
C(GW)
C(IA)
C(GW)
C(IA)
C(GW)
C(IA)
Relationship
>
^^
^
<
<
>
>
^
Vapor Intrusion
Screening Level
GWSL |
IASL !
GWSL i
IASL |
GWSL |
IASL |
GWSL 1
IASL |
Condition
CORRECT
POSITIVE
CORRECT
NEGATIVE
FALSE
NEGATIVE
FALSE
POSITIVE
F-7
-------
1
Table F-3
False Negative and False Positive Indoor Air Predictions Based on Comparison of Groundwater Concentrations
to Target Levels, by Building at Each Site
Site Name
Alliant
Eau Claire
H amilton-Sunstrand
LAFB
WADEP
Mountain View
Uncasvllle
Address
Residence F
Residence K
Residence S
6800 Fern Dr.
6800OsageSt
6800 Ruth Way
6801 Avrum Dr.
6801 Fern Dr.
6810 Jordan Dr.
6811 Ruth Way
6820 Fern Dr.
6821 Mariposa St.
6621 Pecos
6831 Navajo St.
6831 Zuni St.
6840 Mariposa
UA02
UA03
UA04
UA05
UA18
UA19
UA21
UA22
UA23
UA24
UA25
UA26
UA28
0907 A Hull
0907 B Hull
1019Lynnf
11707Quincy
12092 B Marble
1525 A Marble
1525 B Marble
2797ATewks
2797 B Tewks
Residence 1
Residence 2
Residence 3
Residence 4
Residence 6
Residence 7
Residence 8
Residence A
Residences
Residence D
Residence E
Vapor Intrusion
Q41
NA(CP)
NA(CP)
NA(CP)
NA(CP)
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
fp ?
NA(CP)
NA(CP)
NA(FP)
NA(CP)
CP
NA(CP)
NA(CP)
NA(FP)
NA(FP)
CP
CP
CP
CP
CP
CP
CP
NA(CP)
NA(CP)
NA(CN)
NA(CP)
Vapor Intrusion
Q52
NA(CP)
WB
WB
WB
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
, , fr
WB
WB
NA(FP)
NA(CP)
CP
NA(CP)
NA(CP)
NA(FP)
NA(FP)
CP
CP
CP
CP
CP
CP
CP
NA(CP)
NA(CP)
NA(CN)
NA(CP)
Compound(s) Responsible for
False Result3
Trichloroethylene
Benzene, Ethylbenzene, Toluene
Benzene
Benzene, Ethylbenzene, Toluene
Benzene, Ethylbenzene, Toluene
Kev:
CP=Correct Positive; CN = Correct Negative
:P=False Positive; FN=False Negative
JA=Not applicable due to precluding factor-depth from foundation to groundwater contamination is less than 1.5 m
i/VB=Wet Basement. This condition precludes the use of Figure 3 (for Q5).
4otes:
Site data was compared to indoor air and groundwater screening values in Table 2.
Site data was compared to indoor air and groundwater screening values in Table 3. The appropriate attenuation factor in this
!When false positive or false negative outcomes resulted with both Q4 and Q5, the same compounds were responsible for the false
autcome in each scenario.
F-8
-------
Table F-3 (continued)
Summary Table
False Negative and False Positive Indoor Air Predictions Based on Comparison of Ground water Concentrations to Target
Levels, by Building at Each Site
Q4
Number
33
1
0
16
34
Percent
97.1%
2.9%
0.0%
47.1%
05
Number
33
1
0
11
34
Percent
97.1%
2.9%
0.0%
32.4%
Total CP and CN
Total FP
Total FN
Total NA and WB
Total Number of Buildings
Key:
CP=Correct Positive; CN = Correct Negative
FP=False Positive; FN=False Negative
NA=Not applicable due to precluding factor-depth from foundation to groundwater contamination is less than 1.5 m.
WB=Wet Basement. This condition precludes the use of Figure 3 (for Q5).
Notes:
1 Site data was compared to indoor air and groundvvater screening values in Table 2.
Site data was compared to indoor air and groundwater screening values in Table 3. The appropriate attenuation factor in this
analysis was obtained from Figure 3.
"When false positive or false negative outcomes resulted with both Q4 and Q5, the same compounds were responsible for the false
outcome in each scenario.
F-9
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1
Table F-5
False Negative and False Positive Indoor Air Predictions Based on Comparison of Groundwater Concentrations to Target Levels,
by Building at Each Site
Site Name
Address
Vapor Intrusion
Q41
Vapor Intrusion
Q52
J&E Site Compound(s) Responsible for
Specific* False Result4
Alliant NA(CP) NA(CP) NA(CP)
Eau Claire R essence F NA(CP) WB WB
Residence K NA(CP) WB WB
Residences NA(CP) WB WB
Hamilton-Sunstrand 6800 Fern Dr. CP CP CP
6800 Osage St. CP CP CP
6800 Ruth Way CP CP CP
6801 Avrum Or. CP CP CP
6801 Fern Dr. CP CP CP
6810 Jordan Dr. CP CP CP
6811 Ruth Way CP CP CP
6820 Fern Dr. CP CP CP
6821 Mariposa St. CP CP CP
6821 Pecos CP CP CP
6831 NavajoSt. CP CP CP
6831 Zuni St. CP CP CP
6840 Mariposa CP CP CP
LAFB UA02 CP CP CP
UA03 CP CP CP
UA04 CP CP CP
UA05 CP CP CP
UA18 CP CP CP
UA19 CP CP CP
UA21 CP CP CP
UA22 CP CP CP
UA23 CP CP CP
UA24 CP CP CP
UA25 CP CP CP
UA26 CP CP CP
UA28 CP CP CP
MADEP 0907 A Hull NA(CP) WB WB
0907 B Hull NA(CP) WB WB
1019Lynnf NA(CP) NA(CP) NA(CP)
11707 Quincy NA(CP) NA(CP) NA(CP)
12092 B Marble CP CP CP
1525 A Marble NA(CP) NA(CP) NA(FN) Trichloroelhylene
1525 B Marble NA(CP) NA(CP) NA(FN) Trichloroethylene
2797ATewks NA(CP) NA(CP) NA(CP)
2797BTewks NA(CP) NA(CP) NA(CP)
Mountain View Residence 1 CP CP CP
Residence 2 CP CP CP
Residences CP CP CP
Residence 4 CP CP CP
Residence 6 CP CP CP
Residence 7 CP CP CP
Residences CP CP CP
Uncasville Residence A NA(CP) NA(CP) NA(CP)
Residences NA(CP) NA(CP) NA(CP)
Residence D NA(FN) NA(FN) NA(FN)
Residence E NA(CP) NA(CP) NA(CP)
Key:
CP=Correct Positive; CN «= Correct Negative
FP=False Positive; FN=False Negative
MA-Not applicable due to precluding factor-depth from foundation to groundwater contamination is less than 1.5 m.
WB=Wet Basement. This condition precludes the use of Figure 3 (for Q5) and the use of the Johnson and Ettinger Model.
Motes:
|Site data was compared to indoor air and groundwater screening values in Table 2.
'Site data was compared to indoor air and groundwater screening values in Table 3. The appropriate attentuation factor in this analysis was
obtained from Figure 3.
'Site specific soil type, depth to groundwater, and building foundation type were used in the Johnson and Ettinger (J&E) model.
4 When false positive or false negative outcomes resulted with both Q4 and Q5, the same compounds were responsible for the false
outcome in each scenario.
Tetrachloroethylene
F-12
-------
Table F-5 (continued)
Summary Table
False Negative and False Positive Indoor Air Predictions Based on Comparison of Groundwater Concentrations to Target Levels, by
Building at Each Site
R=1xKr*
Q4
QS
Number
34
0
0
16
Percent
100.0%
0,0%
0.0%
Number
34
0
0
16
Percent
100.0%
0.0%
0.0%
J&E Site Specific
Number Percent
34
0
0
16
100.0%
0.0%
0.0%
Total CP and CN
Total FP
Total FN
Total NA and WB
Total Number of Buildings 34 34 34
Key:
CP=Correct Positive; CN = Correct Negative
FP=False Positive: FN-False Negative
NA=Not applicable due to precluding factor-depth from foundation to groundwater contamination is less than 1.5 m.
WB=Wet Basement. This condition precludes the use of Figure 3 (for QS) and the use of the Johnson and Ettinger Model.
Notes:
Site data was compared to indoor air and groundwater screening values in Table 2.
Site data was compared to indoor air and groundwater screening values in Table 3. The appropriate attentuation factor in this analysis was
obtained from Figure 3.
3 Site specific soil type, depth to groundwater, and building foundation type were used in the Johnson and Ettinger (J&E) model.
* When false positive or false negative outcomes resulted with both Q4 and Q5, the same compounds were responsible for the false outcome in
each scenario.
F-13
-------
of Ground Water Concentrations to Target Levels, by Chemical1
Table F-6
ased on Comparison
{isk = 1x1(T
idoor Air Predictions E
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in the empirical database with indoor air and groundwater measurements above their
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Measured Attenuation Factors
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with concentrations above MDLs and above typical background levels.
F-17
-------
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Figure F-4. Distribution of subslab-to-indoor air attenuation factors for residences for the
subset of residences with indoor concentrations greater than the subslab concentrations
measured below the residence's foundation. Subslab data were available for only one site
the Lowry Air Force Base in Colorado.
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chlorinated hydrocarbons (CHC).
F-18
-------
APPENDIX G
CONSIDERATIONS FOR THE USE OF THE
JOHNSON AND ETTINGER VAPOR INTRUSION MODEL
1. Introduction
At sites where soils or groundwater contain volatile or semi-volatile chemicals of concern, there
is the potential for chemical vapors to migrate from the subsurface into indoor air spaces.
Assessment of this potential indoor inhalation exposure pathway requires an understanding of the
processes influencing vapor transport in the vadose zone and into buildings.
Johnson and Ettinger (1991) introduced a screening-level model for estimating the transport of
contaminant vapors from a subsurface source into indoor air spaces. The model is a one-
dimensional analytical solution to diffusive and convective transport of vapors formulated as an
attenuation factor that relates the vapor concentration in the indoor space to the vapor
concentration at the source. To facilitate use of the Johnson-Ettinger Model (JEM), EPA in 1997
developed spreadsheet versions of the model that calculate indoor air concentrations and
associated health risks. A total of six spreadsheets were developed: a first tier and a more
advanced version for each potential vapor sourcegroundwater, bulk soil, and soil gas. The
spreadsheets were later updated in 2000 and 2002. The current spreadsheets may be downloaded
from the web site:
http://www. epa. go v/superfund/programs/risk/airmodel/iohnson_ettinger. htm
This appendix addresses the assumptions and limitations that we recommend be considered when
the Johnson and Ettinger model as implemented by EPA is employed in the evaluation of the
vapor intrusion pathway. This appendix also provides guidance for the model's use both as a
first-tier screening level tool to identify sites needing further assessment and as a site-specific
tool to estimate indoor air impacts resulting from vapor intrusion.
2. Assumptions and Limitations of the Johnson and Ettinger Model
The Johnson-Ettinger Model (JEM) was developed for use as a screening level model and,"
consequently, is based on a number of simplifying assumptions regarding contaminant
distribution and occurrence, subsurface characteristics, transport mechanisms, and building
construction. The assumptions of the JEM as implemented in EPA's spreadsheet version are
listed in Table G-l along with the implications of and limitations posed by the assumptions.
Also provided in the table is an assessment of the likelihood that the assumptions can be verified
through field evaluation. The JEM assumptions are typical of most simplified models of
subsurface contaminant transport with the addition of a few assumptions regarding vapor flux
into buildings.
G-l
-------
The JEM as implemented by EPA assumes the subsurface is characterized by homogeneous soil
layers with isotropic properties. The first tier spreadsheet versions accommodate only one layer;
the advanced spreadsheet versions accommodate up to three layers. Sources of contaminants
that can be modeled include dissolved, sorbed, or vapor sources where the concentrations are
below the aqueous solubility limit, the soil saturation concentration, and/or the pure component
vapor concentration. The contaminants are assumed to be homogeneously distributed at the
source. All but one of the spreadsheets assumes an infinite source. The exception is the
advanced model for a bulk soil source, which allows for a finite source. For the groundwater and
bulk soil models, the vapor concentration at the source is calculated assuming equilibrium
partitioning. Vapor from the source is assumed to diffuse directly upward (one-dimensional
transport) through uncontaminated soil (including an uncontaminated capillary fringe if
groundwater is the vapor source) to the base of a building foundation, where convection carries
the vapor through cracks and openings in the foundation into the building. Both diffusive and
convective transport processes are assumed to be at steady state. Neither sorption nor
biodegradation is accounted for in the transport of vapor from source to the base of the building.
The assumptions described above and in Table G-l suggest a number of conditions that under
most scenarios would preclude the application of the JE model as implemented by EPA. These
include:
The presence or suspected presence of residual or free-product nonaqueous phase liquids
(LNAPL, DNAPL, fuels, solvents, etc) in the subsurface.
The presence of heterogeneous geologic materials (other than the three layers in the
advanced spreadsheets) between the vapor source and building. The JE model does not
apply to geologic materials that are fractured, contain macropores or other preferential
pathways, or are composed of karst.
Sites where significant lateral flow of vapors occurs. These can include geologic layers
that deflect contaminants from a strictly upward motion and buried pipelines or conduits
that form preferential paths. Permeability contrasts between layers greater than 1000
times also are likely to cause lateral flow of vapors. The model assumes the source of
contaminants is directly below the potential receptors.
Very shallow groundwater where the building foundation is wetted by the groundwater.
Very small building air exchange rates (e.g., <0.25/hr)
Buildings with crawlspace structures or other significant openings to the subsurface (e.g.,
earthen floors, stone buildings, etc.). The EPA spreadsheet only accommodates either
slab on grade or basement construction.
* Contaminated groundwater sites with large fluctuations in the water table elevation. In
these cases, the capillary fringe is likely to be contaminated, whereas in the groundwater
source spreadsheets, the capillary fringe is assumed to be uncontaminated.
Sites with transient (time-varying) flow rates and/or concentrations and for which a
steady state assumption is not conservative.
G-2
-------
In theory, the above limitations are readily conceptualized, but in practice the presence of these
limiting conditions may be difficult to verify even when extensive site characterization data are
available. Conditions that are particularly difficult to verify in the field include the presence of
residual NAPLs in the unsaturated zone and the presence and influence of macropores, fractures
and other preferential pathways in the subsurface. Additionally, in the initial stages of
evaluation, especially at the screening level, information about building construction and water
table fluctuations may not be available. Even the conceptually simple assumptions (e.g., one-
dimensional flow, lack of preferential pathways) may be difficult to assess when there are
limited site data available.
3. Guidance for Application of the JEM as a First-Tier Screening Level Tool
Use of the JEM as a first-tier screening tool to identify sites needing further assessment
necessitates careful evaluation of the assumptions listed in the previous section to determine
whether any conditions exist that would render the JEM inappropriate for the site. If the model
is deemed applicable at the site, we recommend that care be taken to ensure reasonably
conservative and self-consistent model parameters are used as input to the model. Considering
the limited site data typically available in preliminary site assessments, the JEM can be expected
to predict only whether or not a risk-based exposure level will be exceeded at the site. Precise
prediction of concentration levels is not possible with this approach.
The suggested minimum site characterization information for a first-tier evaluation of the vapor
intrusion pathway includes: site conceptual model, nature and extent of contamination
distribution, soil lithologic descriptions, groundwater concentrations and/or possibly near source
soil vapor concentrations. The number of samples and measurements needed to establish this
information varies by site, and it is not possible to provide a hard and fast rule. We do not
recommend use of bulk soil concentrations unless appropriately preserved during sampling.
Based on the conceptual site model, the user can select the appropriate spreadsheet
corresponding to the vapor source at the site and determine whether to use the screening level
spreadsheet (which accommodates only one soil type above the capillary fringe) or the more
advanced version (which allows up to three layers above the capillary fringe). As most of the
inputs to the JEM are not collected during a typical site characterization, conservative inputs are
typically estimated or inferred from available data and other non-site-specific sources of
information.
The uncertainty in determining key model parameters and sensitivity of the JEM to those key
model parameters is qualitatively described in Table G-2. As shown in the table, building-
related parameters with moderate to high uncertainty and model sensitivity include: Qsoil,
building crack ratio, building air-exchange rate, and building mixing height. Building related
parameters with low uncertainty and sensitivity include: foundation area, depth to base of
foundation, and foundation slab thickness. Of the soil-dependent properties, the soil moisture
parameters clearly are of critical importance for the attenuation value calculations.
A list of generally reasonable conservative model input parameters for building-related
parameters is provided in Table G-3, which also provides the practical range, typical or mean
G-3
-------
value (if applicable), and most conservative value for these parameters. For building parameters
with low uncertainty and sensitivity, only a single "fixed" value corresponding to the mean or
typical value is provided in Table G-3. Soil-dependent properties are provided in Table G-4 for
soils classified according to the US SCS system. If site soils are not classified according to the
US SCS, Table G-5 can be used to assist in selecting an appropriate SCS soil type corresponding
to the available site lithologic information. Note that the selection of the soil texture class should
be biased towards the coarsest soil type of significance, as determined by the site
characterization program
The recommended values provided in Tables G-3 and G-4 were used in the advanced versions of
the JEM spreadsheet to develop the graphs of attenuation factors provided in Question 5 of this
draft guidance. These input parameters were developed considering soil-physics science,
available studies of building characteristics, and expert opinion. Consequently, the input
parameters listed in Tables G-3 and G-4 are considered default parameters for a first-tier
assessment, which should in most cases provide a reasonably (but not overly) conservative
estimate of the vapor intrusion attenuation factor for a site. Justification for the building-related
and soil-dependent parameter values selected as default values for the JEM is described below.
3. J. Justification of Default Soil-Dependent Properties
The default soil-dependent parameters recommended for a first tier assessment (Table G-4)
represent mean or typical values, rather than the most conservative value, in order to avoid
overly conservative estimates of attenuation factors. Note, however, that the range of values for
some soil properties can be very large, particularly in the case of moisture content and hydraulic
conductivity. Consequently, selecting a soil type and corresponding typical soil property value
may not accurately or conservatively represent a given site. Also, Table G-4 does not provide
estimates of soil properties for very coarse soil types, such as gravel, gravelly sand, and sandy
gravel, etc, which also may be present in the vadose zone. Consequently, in cases where the
vadose zone is characterized by very coarse materials, the JEM may not provide a conservative
estimate of attenuation factor.
As discussed above, the JEM is sensitive to the value of soil moisture content. Unfortunately,
there is little information available on measured moisture contents below buildings; therefore,
the typical approach is to use a water retention model (e.g., van Genuchten model) to
approximate moisture contents. For the unsaturated zone, the selected default value for soil
moisture is a value equal to half-way between the residual saturation value and field capacity,
using the van Genuchten model-predicted values for U.S. SCS soil types. For the capillary
transition zone, a moisture content corresponding to the air entry pressure head is calculated
using the van Genuchten model. When compared to other available water retention models, the
van Genuchten model yields somewhat lower water contents, which results in more conservative
estimates of attenuation factor. However, the soil moisture contents listed in Table G-4 are
based on agricultural samples, which are likely to have higher water contents than soils below
building foundations and, consequently, result in less conservative estimates of attenuation
factor.
G-4
-------
3,2. Justification of Default Building-Related Properties
Building Air Exchange Rate (Default Value = 0.25 hf1)
Results from 22 studies for which building air exchange data are available are summarized in
Hers et al. (2001). There is a wide variation in ventilation rates ranging from about 0.1 air
exchanges per hour (AEH) for energy efficient "air-tight" houses (built in cold climates) (Fellin
and Otson, 1996) to over 2 AEH (AHRAE (1985), upper range). In general, ventilation rates
will be higher in summer months when natural ventilation rates are highest. One of the most
comprehensive studies of U.S. residential air exchange rates (sample size of 2844 houses) was
conducted by Murray and Burmaster (1995). The data set was analyzed on a seasonal basis, and
according to climatic region. When all the data was analyzed, the 10th, 50th and 90th percentile
values were 0.21, 0.51 and 1.48 AEH. Air exchange rates varied depending on season and
climatic region. For example, for the winter season and coldest climatic area (Region 1, Great
Lakes area and extreme northeast US), the 10th, 50th and 90th percentile values were 0.11, 0.27
and 0.71 AEH. In contrast, for the winter season and warmest climatic area (Region 4, southern
CA, TX, Florida, Georgia), the 10th, 50* and 90th percentile values were 0.24, 0.48 and 1.13
AEH. While building air exchange rates would be higher during the summer months, vapor
intrusion during winter months (when house depressurization is expected to be most significant)
would be of greatest concern. For this draft guidance, a default value of 0.25 for air exchange
rate was selected to represent the lower end of these distributions.
Crack Width and Crack Ratio (Default Value = 0.0002 for basement house; = 0.0038 for slab-
on-grade house)
The crack width and crack ratio are related. Assuming a square house and that the only crack is
a continuous edge crack between the foundation slab and wall ("perimeter crack"), the crack
ratio and crack width are related as follows:
Crack Ratio =
4 (Crack Width)\As\ibsurface Foundation Area
Subsurface Foundation Area
Crack Ratio = Crack Width x 4 x (Subsurface Foundation Area)A0.5/Subsurface Foundation
Area
There is little information available on crack width or crack ratio. One approach used by radon
researchers is to back calculate crack ratios using a model for soil gas flow through cracks and
the results of measured soil gas flow rates into a building. For example, the back-calculated
values for a slab/wall edge crack based on soil gas-entry rates reported in Nazaroff (1992),
Revzan et al. (1991) and Nazaroff et al. (1985) range from about 0.0001 to 0.001. Another
possible approach is to measure crack openings although this, in practice, is difficult to do.
Figley and Snodgrass (1992) present data from ten houses where edge crack measurements were
made. At the eight houses where cracks were observed, the cracks widths ranged from hairline
G-5
-------
cracks up to 5 mm wide, while the total crack length per house ranged from 2.5 m to 17.3 m.
Most crack widths were less than 1 mm The suggested defaults for crack ratio in regulatory
guidance, literature and models also vary. In ASTM E1739-95, a default crack ratio of 0.01 is
used. The crack ratios suggested in the VOLASOIL model (developed by the Dutch Ministry of
Environment) range from 0.0001 to 0.000001. The VOLASOIL model values correspond to
values for a "good" and "bad" foundation, respectively. The crack ratio used by Johnson and
Ettinger (1991) for illustrative purposes ranged from 0.001 to 0.01. The selected default values
fall within the ranges observed.
Building Area and Subsurface Foundation Area (Default Value = 10m by 10 m)
The default building area is based on the following information:
default values used in the Superfund User's Guide (9.61 m by 9.61 m or 92.4 m2),
and
default values used by the State of Michigan, as documented in Part 201, Generic
Groundwater and Soil Volatilization to Indoor Air Inhalation Criteria: Technical
Support Document (10.5 m by 10.5 m of 111.5 m2)
The Michigan guidance document indicates that the 111.5 m2 area approximately corresponds to
the 10* percentile floor space area for residential single family dwellings, based on statistics
compiled by the U.S. DOC and U.S. HUD. The typical, upper and lower ranges presented in
Table G-3 are subjectively chosen values. The subsurface foundation area is a function of the
building area, and depth to the base of the foundation, which is fixed.
Building Mixing Height (Default Value = 2.44 mfor slab-on-grade scenario; = 3.66 mfor
basement scenario)
The JEM assumes that subsurface volatiles migrating into the building are completely mixed
within the building volume, which is determined by the building area and mixing height. The
building mixing height will depend on a number of factors including the building height, the
heating, ventilation and air conditioning (HV AC) system operation, environmental factors such
as indoor-outdoor pressure differentials and wind loading, and seasonal factors. For a single-
story house, the variation in mixing height can be approximated by the room height. For a multi-
story house or apartment building, the mixing height will be greatest for houses with HVAC
systems that result in significant air circulation (e.g., forced-air heating systems). Mixing heights
would likely be less for houses with electrical baseboard heaters. It is likely that mixing height
is, to some degree, correlated to the building air exchange rate.
There are little data available that provide for direct inference of mixing height. There are few
sites, with a small number of houses where indoor air concentrations were above background,
and where both measurements at ground level and the second floor were made (CDOT,
Redfields, Eau Claire). Persons familiar with the data sets for these sites indicate that in most
cases a fairly significant reduction in concentrations (factor of two or greater) was observed,
G-6
-------
although at one site (Eau Claire, "S" residence), the indoor TCE concentrations were similar in
both the basement and second floor of the house. For the CDOT site apartments, there was an
approximate five-fold reduction between the concentrations measured for the first floor and
second floor units (Mr. Jeff Kurtz, EMSI, personal communication, June 2002). Less mixing
would be expected for an apartment since there are less cross-floor connections than for a house.
The value chosen for a basement house scenario (3.66 m) would be representative of a two-fold
reduction or attenuation in vapor concentrations between floors.
Qsoii (Default Value = 5 L/min)
The method often used with the JEM for estimating the soil gas advection rate (Qsoii) through the
building envelope is an analytical solution for two-dimensional soil gas flow to a small
horizontal drain (NazaroiT 1992) ("Perimeter Crack Model"). Use of this model can be
problematic in that QSOJI values are sensitive to soil-air permeability and consequently a wide
range in flows can be predicted.
An alternate empirical approach is to select a QSOii value on the basis of tracer tests (i.e., mass
balance approach). When soil gas advection is the primary mechanism for tracer intrusion into a
building, we recommend the Qsoii be estimated by measuring the concentrations of a chemical
tracer in indoor air, outdoor air and in soil vapor below a building, and measuring the building
ventilation rate (Hers et al. 2000a; Fischer et al. 1996; Garbesi et al. 1993; Rezvan et al. 1991;
Garbesi and Sextro, 1989). The Qsoa values measured using this technique are compared to
predicted rates using the Perimeter Crack model, for sites with coarse-grained soils. The
Perimeter Crack model predictions are both higher and lower than the measured values, but
overall are within one order of magnitude of the measured values. Although the Qsoii predicted
by models and measured using field tracer tests are uncertain, the results suggest that a "typical"
range for houses on coarse-grained soils is on the order of 1 to 10 L/min. A disadvantage with
the tracer test approach is that there are only limited data, and there do not appear to be any
tracer studies for field sites with fine-grained soils.
It is also important to recognize that the advective zone of influence for soil gas flow is limited to
soil immediately adjacent to the building foundation. There is some data on pressure coupling
that provides insight on the extent of the advective flow zone. For example, Garbesi et al. (1993)
report a pressure coupling between soil and experimental basement (i.e., relative to that between
the basement and atmosphere) equal to 96 % directly below the slab, between 29 % and 44 % at
1 m below the basement floor slab, and between 0.7 % and 27 % at a horizontal distance of 2 m
from the basement wall. At the Chatterton site in Canada, the pressure coupling immediately
below the building floor slab ranged from 90 % to 95 % and at a depth of 0.5 m was on the order
of 50 %. These results indicate that the advective zone of influence will likely be limited to a
zone within 1 mto 2 m of the building foundation.
Since the advective flow zone is relatively limited in extent, the soil type adjacent to the building
foundation is of importance. In many cases, coarse-grained imported fill is placed below
foundations, and either coarse-grained fill, or disturbed, loose fill is placed adjacent to the
G-7
-------
foundation walls. Therefore, a conservative approach for the purposes of this draft guidance is to
assume that soil gas flow will be controlled by coarse-grained soil, and not to rely on the possible
reduction in flow that would be caused by fine-grained soils near the house foundation. For
these reasons, a soil gas flow rate of 5 L/min (midpoint between 1 and 10 L/min) was chosen as
the input value.
4. Guidance for Application of JEM as a Site-Specific Tool
We generally recommend use of the JE model as a site-specific tool only where the site
conceptual model matches the restrictive assumptions. When these assumptions cannot be met,
we recommend that other models or direct measurement be substituted, because there is no a
priori scientific reason to believe that the model is adequate to represent complex site conditions.
If the JE model is deemed applicable to the site, critical model parameters from site data are
needed. We recommend that site-specific information include soil moisture, soil permeability,
building ventilation rate, and subslab as well as deep vapor concentrations.
In order to ensure the model can reproduce observed field observations, we recommend the
model output be compared with measured concentrations, fluxes and/or other model outputs.
Calibration has been developed as a process for minimizing the differences between model
results and field observations. Through model calibration a parameter set is selected that causes
the model to best fit the observed data When done properly, this process establishes that the
conceptualization and input parameters are appropriate for the site. Because of the number of
parameters to be identified, calibration is known to produce non-unique results. This is
particularly the case in heterogeneous environments where every parameter of the model can
vary from point to point. Confidence in the model, however, is increased by using the calibrated
model to predict the response to some additional concentration or flux data (i.e., that were not
previously used in calibration). At each step in this process, additional site investigation data
improve knowledge of the behavior of the system.
From a regulatory standpoint, the JE model when used as a site-specific tool typically should be
calibrated to predict within an order of magnitude the indoor air concentrations resulting from
intrusion of vapors from the subsurface. Consequently, prior to its use, we recommend an
evaluation of the critical input parameters be performed. If the uncertainty in the critical
parameters cannot be reduced to yield an order of magnitude estimate of indoor air
concentrations, it may not be practical to perform the modeling.
G-8
-------
5. References
American Society for Testing and Materials (ASTM). 1995. Standard Guide for Risk-Based
Corrective Action Applied at Petroleum Release Sites. E-1739-95.
American Society of Heating, Refrigerating, and Air-Conditioning Engineers, ASHRAE
Handbook-1985 Fundamentals, chap. 22, Atlanta, GA.
Fellin, P. and R. Otson. 1996. The Effectiveness of Selected Materials in Moderation of Indoor
VOC Levels, In Volatile Organic Compounds in the Environment, ASTM STP 1261,
W.Wang, J. Schnoor, and J. Doi, Eds., American Society for Testing and Materials, 1996, pp.
135-146.
Figley, D.A., Snodgrass, L.J. June 21-26, 1992. "Comparative Foundation Air Leakage
Performance of Ten Residential Concrete Basements", Proceedings of the 85th Annual
Meeting of Air and Waste Management Association.
Fischer, M.L., Bentley, A.J., Dunkin, K.A., Hodgson, A.T., Nazaroff, W.W., Sextro, R.G.,
Daisey, J.M. 1996. Factors Affecting Indoor Air Concentrations of Volatile Organic
Compounds at a Site of Subsurface Gasoline Contamination. Environ. Sci. Technol. 30 (10),
2948-2957.
Garbesi, K., Sextro, R.G., Fisk, W.J., Modera, M.P., Revzan, K.L. 1993. Soil-Gas Entry into an
Experimental Basement: Model Measurement Comparisons and Seasonal Effects. Environ.
Sci. Technol. 27(3), 466-473.
Garbesi, K. and Sextro, R.G. 1989. Modeling and Field Evidence of Pressure-Driven Entry of
Soil Gas into a House through Permeable Below-Grade Walls. Environ. Sci. Technol. 23(12),
1481-1487.
Hers, I., Evans, D, Zapf-Gilje, R. and Li, L. 2002. Comparison, Validation and Use of Models
for Predicting Indoor Air Quality from Soil and Groundwater Contamination. J. Soil and
Sediment Contamination, 11 (4), 491-527.
Hers, I., R. Zapf-Gilje, L. Li, L. and J. Atwater. 2001. The use of indoor air measurements to
evaluate exposure and risk from subsurface VOCs. J. Air & Waste Manage. Assoc. 51: 174-
185.
Johnson, P.C. and R. Ettinger 1991. "Heuristic Model for Predicting the Intrusion Rate of
Contaminant Vapours into Buildings" Environmental Science and Technology, 25 #8, 1445-
1452.
G-9
-------
Murray, D.M.; Burmaster, D.E. Residential air exchange rates in the United States: empirical and
estimated parametric distributions by season and climatic region. Risk Anal. 1995, 15, 459-
465.
Nazaroff, W.W. May 1992. "Radon Transport from Soil to Air", Review of Geophysics, 30 #2,
137-160.
Nazaroff, W.W., Feustel, H., Nero, A.V., Revzan, K.L., Grimsrud, D.T., Essling, M.A., Toohey,
R.E. 1985. "Radon Transport into a Detached One-Story House with a Basement"
Atmospheric Environment, 19(1) 31-46.
Revzan, K.L., Fisk, W.J., Gadgil, A.J. 1991. "Modelling Radon Entry into Houses with
Basements: Model Description and Verification" Indoor Air, 2,173-189.
G-10
-------
Table G-l. Assumptions and Limitations of the Johnson and Ettinger Vapor Intrusion
Model
Assumption
Contaminant
No contaminant free-liquid/precipitate
phase present
Contaminant is homogeneously
distributed within the zone of
contamination
No contaminant sources or sinks in the
building.
Equilibrium partitioning at contaminant
source.
Chemical or biological transformations
are not significant (model will predict
more intrusion)
Subsurface Characteristics
Soil is homogeneous within any
horizontal plane
All soil properties in any horizontal
plane are homogeneous
The top of the capillary fringe must be
below the bottom of the building floor in
contact with the soil.
EPA version of JE Model assumes the
capillary fringe is uncontaminated.
Transport Mechanisms
One-dimensional transport
Two separate flow zones, one diffusive
one convective.
Vapor-phase diffusion is the dominant
mechanism for transporting contaminant
vapors from contaminant sources located
away from the foundation to the soil
region near the foundation
Implication
JEM not representative of NAPL
partitioning from source
Indoor sources of contaminants
and/or sorption of vapors on
materials may confound
interpretation of results.
Groundwater flow rates are low
enough so that there are no mass
transfer limitations at the source.
Tendency to overpredict vapor
intrusion for degradable
compounds
Stratigraphy can be described by
horizontal layers (not tilted
layers)
Source is directly below
building, stratigraphy does not
influence How direction, no
effect of two- or three-
dimensional flow patterns.
No diffusion (disperson) in the
convective flow zone. Plug flow
in convective zone
Neglects atmospheric pressure
variation effects, others?
Field Evaluation
NAPL presence-easier to evaluate
for floating product or soil
contamination sites. Most DNAPL
sites with DNAPL below the water
table defy easy characterization.
Survey building for sources,
assessment of sinks unlikely
Not likely
From literature
Observe pattern of layers and
unconformities. Note: In simplified
JEM layering is not considered
Observe location of source, observe
stratigraphy, pipeline conduits, not
likely to assess two- and three-
dimensional pattern.
Not likely
Not likely
G-n
-------
Straight-line gradient in diffusive flow
zone.
Diffusion through soil moisture will be
insignificant (except far compounds with
very low Henry's Law Constant
Convective transport is likely to be most
significant in the region very close to a
basement, or a foundation, and vapor
velocities decrease rapidly with
increasing distance from a structure
Vapor flow described by Darcy's law
Steady State convection
Uniform convective flow near the
foundation
Uniform convective velocity through
crack or porous medium
Significant convective transport only
occurs in the vapor phase
All contaminant vapors originating from
directly below the basement will enter
the basement, unless the floor and walls
are perfect vapor barriers. (Makes model
over est. vapors as none can flow around
the building)
Contaminant vapors enter structures
primarily through cracks and openings in
the walls and foundation
Inaccuracy in flux estimate at
match point between diffusive
and convective sections of the
model.
Transport through air phase only.
Good for volatiles. Only low
volatility compounds would fail
this and they are probably not the
compounds of concern for vapor
intrusion
Porous media flow assumption.
Flow not affected by barometric
pressure, infiltration, etc.
Flow rate does not vary by
location
No variation within cracks and
openings and constant pressure
field between interior spaces and
the soil surface
Movement of soil water not
included in vapor impact
Model does not allow vapors to
flow around the structure and not
enter the building
Flow through the wall and
foundation material itself
neglected
Not likely
From literature value of Henry's
Law Constant.
Not likely
Observations of fractured rock,
fractured clay, karst, macropores,
preferential flow channels.
Not likely
Not likely
Not likely
Not likely
Not likely
Observe numbers of cracks and
openings. Assessment of
contribution from construction
materials themselves not likely
G-12
-------
Table G-2. Uncertainty and Sensitivity of Key Parameters for the Johnson & Ettinger
Model.
nput Parameter
Total Porosity
Unsaturated Zone Water-filled Porosity
Capillary Transition Zone Water-filed Porosity
Capillary Transition Zone Height
Soil Bulk Density
Qsoil
Soil air permeability
Building Depressurzation
Henry's Law Constant (for single chemical)
Free-Air DHusion Coefficient (single chemical)
Building Air Exchange Rate
Building Mixing Height
Subsurface Foundation Area
Depth to Base of Foundation
Building Crack Ratio
Crack Moisture Content
Building Foundation Slab Thickness
Parameter
Uncertainty
or Variability
Variability
Low
Moderate to High
Moderate to High
Moderate to High
Low
High
High
Moderate
Low to Moderate
Low
Moderate
Moderate
Low to Moderate
Low
High
High
Low
Shallower Contami-
nation Building
Undwpressurized
Low
Low to Moderate
Moderate to High
Moderate to High
Low
Moderate to High
Moderate to High
Moderate
Low to Moderate
Low
Moderate
Moderate
Low to Moderate
Low
Low
Low
Low
Parameter Sensitivity
Deeper Contaml- Shallower Contami-
natlon Building nation Building
Under-pressurized Not Underpressurlzed
Low
Moderate to High
Moderate to High
Moderate to High
Low
Low to Moderate
Low to Mode rate
Low to Moderate
Low to Moderate
Low
Moderate
Moderate
Low to Moderate
Low
Low
Low
Low
Low
Moderate to High
Moderate to High
Moderate to High
Low
N/A
N/A
N/A
Lowto Moderate
Low
Moderate
Moderate
Lowto Moderate
Low
Moderate to High
Moderate to High
Low
Deeper Contami-
nation Building
Not Underprcssurized
Low
Moderate to High
Moderate to High
Moderate to High
Low
N/A
N/A
N/A
Lowto Moderate
Low
Moderate
Moderate
Lowto Moderate
Low
Lowto Moderate
Lowto Moderate
Low
Table G-3. Building-Related Parameters for the Johnson & Ettinger Model - First Tier
Assessment
Input Parameter
Total Porosity
Unsaturated Zone Water-filled Porosity
Capillary Transition Zone Water-filled Porosity
Capillary Transition Zone Height
Qsoil1
Soil air permeability
Building Oepressurization
Henry's Law Constant (for single chemical)
Free- Air Diffusion Coefficient (single chemical)
Building Air Exchange Rate
Building Mixing Height - Basement scenario
Building Mixing Height - Slab-on-grade scenario
Building Footprint Area - Basement Scenario
Building Footprint Area - Slab-on-Grade Scenario
Subsurface Foundation Area Basement Scenario
Subsurface Foundation Area - Slab-on-Grade Scenario
Depth to Base of Foundation - Basement Scenario
Depth to Base of Foundation - Slab-on-Grade Scenario
Perimeter Crack Width
Building Crack Ratio - Slab-on-Grade Scenario
Building Crack Ratio - Basement Scenario
Crack Dust Water-Filled Porosity
Building Foundation Slab Thickness
Units
crn'/cm3
crn^/cm*
cm /cm
cm'/cm3
L/min
mj
Pa
-
-
hr"'
m
m
m2
m!
m2
m2
m
m
mm
dimensionless
dimensionless
cm'/cm3
m
Typical or Conservative
Mean Value Range Value
*************** Specific to soil texture, see Table G-4 ****
*************** Specific to soil texture, see Table G-4 ****
********* Specific to soil texture, see Table G-4 **"
*.,****.**«**« specific to soil texture, see Table G-4 ****
5 1-10 10
............... specific to soil texture, see Table G-4 ""
4 0-15 15
...««.....«.».... specific to chemical *"*««««**
....................... specific to chemical ****************
05 0.1-1.5 0.1
366 244-488 2.44
2.44 2.13-3.05 2.13
120 80-200+ 80
120 80-200+ 80
208 152-313+ 152
127 85-208+ 85
2 N/A N/A
0.15 N/A N/A
1 0.5-5 5
000038 000019-00019 0.0019
00002 0.0001-0001 0001
Dry N/A N/A
0.1 N/A N/A
Modeled
,.........,.....,
5
N/A
«««***«««««*»**
*»*«*««***«
025
366
244
100
100
180
106
2
0.15
1
000038
000020
Dry
0.1
The values given for Qsoil are representative of sand, but are recommended for other soil types as well because
coarse-grained soil or disturbed fine-grained soil often is found below and adjacent to foundations.
G-13
-------
Table G-4. Soil-Dependent Properties for the Johnson & Ettinger Model - First Tier
Assessment.
US. Soil
Conaarvation
Sarviei (SCS)
Soil Taxtur*
Q.y
day Lam
Loam
Loamy Sand
Silt
911 Loon
SHtyday
Slty day Loan
Said
Sandy Clay
Sandy Clay Loam
Sandy Loam
Loamy Sand
Saturated
Watar
Content
Total Poroalty
. (cnflcnf]
0.469
0.442
0399
0.39
0.499
0.439
0.431
0482
0376
0385
0.384
0387
0.39
Reaidual
Wltar
Content
«, tcm'tan')
0098
0.079
0061
OD48
O.OS
0.065
0.111
009
0053
0.117
0.063
0.039
0.049
Un«a titrated Zon»
Watar-FilM Poroarty
Maan or Typical
(fCyj^^ia
*.«iui[t»n''cm3)
0215
0168
0.143
0.076
0.167
0.130
0.216
0193
0.054
0.197
0.146
0.103
0.076
Ranga
lan'lcnf]
0098-033
0079-0%
0061-024
0.048-0.1
0.054.28
0.065-0.3
0.11-0.32
0.094.31
0.05M.065
0 117-0 28
00634.23
0039-0.17
0.049-0.1
ConaervaHva
»..,.., (on1 Ion')
0098
0079
0.061
0049
0.050
0.065
0.111
0090
0.053
0.117
0.063
0.039
0049
Modalad
«.., fcm'/cm')
0.215
0168
0148
0.076
0.167
0.180
0.216
0.198
0054
0.197
0146
0.103
0.076
Capillary TranaRion Zona
Saturated
Watar
Content
Total Poroaity
1, (cm'/cm'}
0.459
0442
0.398
039
0.489
0439
0.481
0482
0.375
0385
0384
0.387
0.39
*,..,
Cap
-------
APPENDIX H
COMMUNITY INVOLVEMENT GUIDANCE
RECOMMENDATION FOR WHAT TO DO IF YOU HAVE A NEIGHBORHOOD
NEEDING INDOOR AIR SAMPLING DUE TO SUBSURFACE VAPOR INTRUSION
As in any effort that strives for good community involvement, these five key principles are
important considerations:
Be proactive in engaging the community,
Listen carefully to what community members are saying.
Take the time needed to deal with community concerns.
Change plans where community suggestions have merit.
Explain to the community what is being done, by whom and why.
The following provides an outline of recommended public participation activities that are
consistent with EPA's 1996 RCRA Public Participation Manual (EPA 530-R-96-007S) OSW
September 1996
(URL = http:/7\\/vv\v.epa.gov/epaoswer/liazwaste/penmt/pubpart/manual.htm) and the Superfund
Community Involvement Handbook ( EPA 540-K-01-003) OERR April 2002 ( URL =
ht(p://ww\v.epa.gov/superfund''tools/cagy'ci_handbook.pdf1 considered appropriate for
addressing vapor intrusion concerns. These activities may occur concurrently or sequentially.
/. Get to know the neighborhood, key stakeholders and the concerns of the community
Demographics
Elected officials (Congressional, local, and state)
Homeowners association (HOA) board
Local school district officials, principals, etc.
Local church leaders
Residents
Languages - English-speaking or not; will translation capability be needed?
Media ( although typically the media will seek you out; at least some sense of
their interest can be useful. Press statements are usually reserved for announcing
major milestones or for particularly hot button issues.)
Local health department(s)
Local or neighboring businesses
Conduct briefings with most key stakeholders (face-to-face meetings preferred,
but not always possible)
Conduct community interviews (determine some number to conduct)
Consider other possibilities to listen to community members' concerns e.g.
hotline, public availability sessions
H-l
-------
2. Establish a mailing list of all interested parties
In establishing a mailing list, it is important to clarify that anybody can sign up and that
no cost is involved.
3. Inform stakeholders of the situation
Part of informing and educating the community is the distribution of information. Easy
to understand and technically accurate flyers describing the history of the spill or
contamination, the chemicals of concern, the potential risks that may be posed, and who
to contact for more information are usually well received by the community. Anticipate
that people will want information and be ready to give it to them. Consider use of web
pages and establishing a knowledgeable person as a contact to call for accurate
information.
Send a letter/newsletter explaining the situation and the need for indoor air
sampling and invite them to an open house/informational meeting
Hold an open house/informational meeting to explain:
- environmental conditions at the site;
- health impacts;
- indoor air sampling;
- what level of remediation is needed; and
- the type(s)of remediation (have pictures of ventilation systems)
(Note: we recommend having (oxicoiogists, health professionals, or other knowledgeable
individuals available for this meeting)
Devote one booth to explaining indoor air sampling, include a SUMMA cannister
Devote one booth at the open house/informational meeting to obtaining
permission to conduct the indoor air sampling
Conduct an exit poll of people as they leave the open house to determine the
effectiveness of the meeting and whether it met their needs
Note: include many visuals/maps in this meeting
4. Develop a community involvement/public participation plan - We recommend the plan
highlight key community concerns, establish goals and objectives, and identify a
commitment to ongoing communications activities. At RCRA sites, a community
involvement plan that is a component of a RCRA 3008(h) order specifying
implementation of a remedy is enforceable.
H-2
-------
5. Implement the Public Participation Plan
Establish an information repository; consider using web pages
Establish knowledgeable persons who can provide accurate information as key
points of contact
Establish a hotline that includes a recorded message of key activities for the week
or determined period of time and allows caller to leave message/ask questions,
and be sure to call them back
Establish a mailing list of all interested parties
Prepare periodic status updates/newsletters
* Other items as needed
For areas targeted for indoor air sampling:
Contact individuals via phone and mail and seek written permission to sample
If no response, then send a certified letter
If still no response, document that resident was contacted but did not give
permission to sample
If at all possible, try to visit homes not responding and talk directly with
occupants
6. Conduct indoor air sampling
Schedule appointments to 1) conduct an inspection of the residence, complete an
occupant survey to adequately identify the presence of (or occupant activities that
could generate) any possible indoor air emissions of target VOCs in the dwelling,
2) remove possible sources, and 3) conduct residential sampling
Be prompt on the day scheduled for sampling
Send someone extremely knowledgeable and articulate about the indoor air
sampling to accompany technical folks who do the sampling; if necessary, include
a translator
7. Communicate indoor air sampling results
Send letters to residents with their individual indoor air sampling results
Follow-up with a phone call to explain results
Hold an open house/informational meeting to share sampling results and answer
any questions
Note: include map of area sampled and indicate the levels found
8. Continually evaluate what communication activities are needed to optimize public
participation and community involvement
H-3
-------
Additional Tools- to increase effectiveness of involvement with community
residents
The following are examples of pre-sampling interview forms that may be adapted by others for
site specific use to facilitate interaction/involvement with building/dwelling occupants prior to
indoor air sampling:
Occupied Dwelling Questionnaire developed by the OERR Emergency Response Team
(below).
Massachusetts Department of Environmental Protection - Indoor Air Sampling Guide
(April 2002) Appendix 2 of this document provides an Indoor Air Quality Building
Survey form and a set of Instructions for Residents of Homes to Be Sampled. These can
be found at:
http://w\vw, state, ma. us/dep/bwsc/final pol .htm
H-4
-------
OCCUPIED DWELLING QUESTIONNAIRE
Indoor Air Assessment Survey
Date:
1. Name:
Address:
2.
3.
4.
Home Phone:
Work Phone:
What is the best time to call to speak with you?_
At: Work Q or HomeQ?
Are you the Owner Q, Renter tJ, Other G (please specify)_
of this Home/Structure?
Total number of occupants/persons at this location?_
Number of children? Ages?
5. How long have you lived at this location?
General Home Description
6. Type of Home/Structure (check only one): Single Family Home Q, Duplex Q,
7.
9.
Condominium^!, Townhouse Q, Other Q
Home/Structure Description: number of floors
Basement? YesQ No Q
Crawl Space? Yes Q No Q
If Yes, under how much of the house's area? %
Age of Home/Structure: years, Not sure/Unknown Q
General Above-Ground Home/Structure construction (check all that apply):
Wood Q, Brick Q, Concrete Q, Cement block Q, Other Q
10. Foundation Construction (check all that apply):
Concrete slab Q
Fieldstone Q
Concrete block Q
H-5
-------
Elevated above ground/grade
Other
11. What is the source of your drinking water (check all that apply)?
Public water supply Q
Private well Q
Bottled water Q
Other, please specify
12. Do you have a private well for purposes other than drinking?
Yes Q No Q
If yes, please describe what you use the well
for:
13. Do you have a septic system? YesQ No Q Not used Q Unknown Q
14. Do you have standing water outside your home (pond, ditch, swale)? YesQ
Basement Description, please check appropriate boxes.
If you do not have a basement go to question 23.
15. Is the basement finished Q or unfinished Q?
16. If finished, how many rooms are in the basement? _
How many are used for more than 2 hours/day?
17. Is the basement floor (check all that apply) concrete Q, tile Q, carpeted Q, dirt Q,
otherQ(describe) _ ?
18. Are the basement walls poured concrete Q, cement block Q, stone Q, wood Q, brick LJ,
otheiQ _ ?
1 9. Does the basement have a moisture problem (check one only)?
Yes, frequently (3 or more times/yr) CJ
Yes, occasionally ( 1-2 times/yr) Q
Yes, rarely (less than 1 time/yr) Q
NO a
20. Does the basement ever flood (check one only)?
Yes, frequently (3 or more times/yr) Q
Yes, occasionally (1-2 times/yr) 3
Yes, rarely (less than 1 time/yr) G
NO a
21. Does the basement have any of the following? (check all that apply) Floor cracks Q,
Wall cracks Q, Sump Q, Floor drain Q, Other hole/opening in floor Q
(describe) _
H-6
-------
22. Are any of the following used or stored in the basement (check all that apply)
Paint Q Paint stripper/remover Q Paint thinner Q
Metal degreaser/cleaner Q Gasoline Q Diesel fuel Ul Solvents G Glue Q
Laundry spot removers Q Drain cleaners Q Pesticides Q
23. Have you recently (within the last six months) done any painting or remodeling in your
home? YesQ NoQ
If yes, please specify what was done, where in the home, and what month:
24.
25.
26.
27.
28.
29.
30.
Have you installed new carpeting in your home within the last year? Yes Q No
If yes, when and where?
Do you regularly use or work in a dry cleaning service (check only one box)?
Yes, use dry-cleaning regularly (at least weekly)Q
Yes, use dry-cleaning infrequently (monthly or Iess)Q
Yes, work at a dry cleaning service Q
NO a
Does anyone in your home use solvents at work?
Yes Q If yes, how many persons
No Q If no, go to question 28
If yes for question 26 above, are the work clothes washed at home? Yes Q No
Where is the washer/dryer located?
Basement Q
Upstairs utility room Q
Kitchen Q
Garage Q
Use a Laundromat Q
Other, please specify Q
If you have a dryer, is it vented to the outdoors? Yes Q No Q
What type(s) of home heating do you have (check all that apply)
Fuel type: GasQ, Oil Q, Electric Q, Wood Q, Coal Q, Other_
Heat conveyance system: Forced hot air Q
Forced hot water Q
Steam Q
Radiant floor heat Q
Wood stove Q
Coal furnace Q
Fireplace Q
Other
H-7
-------
31.
32.
33.
36.
37.
38.
39.
40.
Do you have air conditioning? Yes Q No Q. If yes, please check the appropriate type(s)
Central air conditioning Q
Window air conditioning unit(s)Ul
Other Q, please specify
Do you use any of the following? Room fans G, Ceiling fans Q, Attic fan G
Do you ventilate using tfie fan-only mode of your central air conditioning or forced air
heating system? YesG NoG
Has your home had termite or other pesticide treatment: Yes Q No Q Unknown G
If yes, please specify type of pest controlled,
and approximate date of service
34. Water Heater Type: Gas Q, Electric G, By furnace G, Other
G
Water heater location: Basement Q, Upstairs utility room G, Garage Q, Other G (please
describe)
35. What type of cooking appliance do you have? Electric G, Gas G, Other
Is there a stove exhaust hood present? Yes G No Q
Does it vent to the outdoors? Yes G No G
Smoking in Home:
NoneQ, Rare (only guests)G, Moderate (residents light smokers)G,
Heavy (at least one heavy smoker in household)G
If yes to above, what do they smoke?
Cigarettes G Cigars G
PipeQ Other G
Do you regularly use air fresheners? Yes G No G
Does anyone in the home have indoor home hobbies of crafts involving: None G
Heating G, soldering G, welding G, model glues G, paint G, spray paint,
wood finishing G, Other Q Please specify whattype of hobby:
41. General family/home use of consumer products (please circle appropriate): Assume that
Never = never used, Hardly ever = less than once/month, Occasionally = about
once/month, Regularly = about once/week, and Often = more than once/week.
Product
Frequency of Use
Spray-on deodorant
Never Hardly ever Occasionally Regularly Often
H-8
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Aerosol deodorizers
Insecticides
Disinfectants
(Question 41, continued)
Product
Never Hardly ever Occasionally Regularly Often
Never Hardly ever Occasionally Regularly Often
Never Hardly ever OccasionaDy Regularly Often
Frequency of Use
Window cleaners Never Hardly ever Occasionally Regularly Often
Spray-on oven cleaners Never Hardly ever Occasionally Regularly Often
Nail polish remover Never Hardly ever Occasionally Regularly Often
Hair sprays Never Hardly ever Occasionally Regularly Often
42. Please check weekly household cleaning practices:
Dusting Q
Dry sweeping LJ
Vacuuming Q
Polishing (furniture, etc) Q
Washing/waxing floors Q
Other Q
43. Other comments:
H-9
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APPENDIX I
CONSIDERATION OF BACKGROUND INDOOR AIR VOC LEVELS IN
EVALUATING THE SUBSURFACE VAPOR INTRUSION PATHWAY
1. General
We recommend that the presence of background indoor air concentrations of VOCs at a site be
carefully considered in evaluating the vapor intrusion to indoor air pathway at the site. The
concentrations of VOCs detected in indoor air may originate from the subsurface contamination
and/or they may represent typical concentrations of VOCs in that building from other sources.
Consequently, indoor air sampling results may be difficult to interpret when background
concentrations of the same VOCs emitted from other sources are present, if efforts are not made
to identify and quantify the background concentrations.
Prior to indoor air sampling, it is generally important to conduct an inspection of the residence
and an occupant survey to adequately identify the presence of (or occupant activities that could
generate) any possible indoor air emission sources of target volatile organic chemicals (VOCs)
in the dwelling (see Appendix H). For example, sources of indoor contaminants typically found
in the home include consumer products (e.g., cleaners, paints, and glues), occupant activities
(e.g., craft hobbies, smoking), and some construction materials. VOCs in ambient (outdoor) air
may also contribute to indoor air background levels, though typically the main sources of
background concentrations of VOCs in indoor air background arise from indoor activities or
products used indoors. Any of these sources may result in relatively high background indoor air
concentrations.
It is also important to recognize that typically there is high variability' in background indoor air
VOC concentrations both within and between buildings, so that small numbers of background
samples typically available should be carefully interpreted. If there is more than one potential
constituent of concern, we recommend that the ratios of potential constituents be used to
distinguish subsurface-derived VOCs from those contributed by other non-subsurface-related
sources (i.e, indoor air and/or ambient (outdoor) air emission sources). Collecting paired
samples (spatially and temporally) of both indoor air and soil vapor data may also assist with
establishing the constituents of concern.
Comparative review of VOCs air sampling results taken in various parts of a building may reveal
contaminant concentration gradients or hot spots among the various floors or rooms in the
building. Such gradients or hot spots shown in upper floors may indicate the indoor air VOC
levels originated from other indoor emission sources rather than subsurface contamination,
whereas, gradients or hot spots in basements or lower levels could suggest a scenario that is
consistent with subsurface vapor intrusion or a preferential pathway. A contemporaneous
ambient (outdoor) air sample may be useful to include for comparison to indoor concentrations
and aid in characterizing possible background contribution from ambient (outdoor) air. More
detail about indoor air sampling protocols is provided in Appendix E.
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We recommend that all information on background indoor air concentrations be considered
along with all of the information collected about the site and the nature of the contamination
when conducting any site-specific risk assessments, determining appropriate risk management
actions, and in advising citizens via risk communications. We recommend that the assessment of
background contribution focus on the constituents and degradation products observed in the
subsurface. However, while it is important to identify background indoor air concentrations, we
recommend that they not be discounted when making a determination or communicating with the
public about site-related impact and/or risk.
2. CERCLA Guidance on the Role of Background
EPA recently published the "Role of Background in the CERCLA Cleanup Program"
(OSWER 9285.6-07P; APR 2002; URL = hup://www.epa.gov/superfund/proferams/risk/role.pdn
outlining a preferred approach for the consideration of background constituent concentrations of
hazardous substances, pollutants, and contaminants in certain steps of the remedy selection
process at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA
or "Superfund") sites. This policy recommends that when conducting site risk assessments
contaminant concentrations attributable to background sources should not be eliminated from
further consideration, since it could result in the loss of important risk information for those
potentially exposed, even though cleanup may or may not eliminate a source of risks caused by
background levels. This policy encourages a baseline risk assessment approach that retains
constituents that exceed risk-based screening concentrations and encourages addressing site-
specific background issues at the end of the risk assessment phase. Although VOCs and indoor
air concerns are not explicit in the CERCLA "Role of Background..." it seems to suggest that
VOCs with both subsurface site release-related and background-related sources should be
included in any site risk assessment. Consistent with the CERCLA "Role of Background..."it is
recommended that any significant background concentrations of VOCs be discussed in the risk
characterization in a comprehensive manner along with any available data distinguishing the
background contribution from site release-related VOC concentrations.
3. State Guidance Examples
Some states have developed specific approaches to considering indoor air background
concentrations of VOCs when evaluating a cleanup site. Measurements of background VOC
concentrations taken before any site-related contamination of the indoor air may have occurred
are considered ideal. However, this type of data is rarely available. Given the variability in
background concentrations in buildings, studies of representative indoor air background VOCs
are preferred. In some cases, data may be available from background studies that have been
conducted in representative "on-site" buildings out of the contamination zone or in nearby "off-
site" buildings. The Colorado Department of Public Health and Environment (personal
communication, August 2002) has stated that post-remediation studies of background indoor air
VOCs provide reliable data.
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