Hazard Ranking System Issue Analysis:
Indoor Air Contamination
MITRE
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Hazard Ranking System Issue Analysis:
Indoor Air Contamination
Thomas F. Wolfinger
August 1987
MTR-86W132
SPONSOR:
U.S. Environmental Protection Agency
CONTRACT NO.:
EPA-68-01-7054
The MITRE Corporation
Metrek Division
7525 Colshire Drive
McLean, Virginia 22102-3481
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Department Approval:
MITRE Project Approval:
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ABSTRACT
This report presents an option for revising the air pathway of
the EPA Hazard Ranking System (HRS) to address situations of indoor
air contamination arising from uncontrolled hazardous waste sites.
The HRS is used by EPA to rank uncontrolled waste sites based on
their relative threat to human health and the environment. Highly
ranked sites are placed on the National Priorities List for further
investigation and possible remedial action. The revision option
is structurally similar to the current HRS air pathway. The
revision option can be used to assess sites based on the degree of
contamination detected in the indoor air, relative to human-health-
based benchmark concentrations, and on the size of the population
potentially affected by the contamination.
Suggested Keywords: Superfund, Hazard ranking, Hazardous waste,
Indoor air contamination.
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TABLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS vii
LIST OF TABLES vii
1.0 INTRODUCTION 1
1.1 Background 1
1.2 Issue Description 3
1.3 Organization of Report 5
2.0 BACKGROUND ON THE HAZARD RANKING SYSTEM 7
3.0 A METHOD FOR EVALUATING INDOOR AIR CONTAMINATION SITES 13
3.1 Discussion of Indoor Contamination from Uncontrolled 13
Waste Sites
3.2 Overview of the Indoor Air Pathway 18
3.2.1 Release Category 21
3.2.2 Waste Characteristics Category 23
3.2.3 Targets Category 25
3.2.4 Pathway Score 28
3.3 Step-By-Step Instructions for the Indoor Air Pathway 28
4.0 IMPLICATIONS 37
5.0 BIBLIOGRAPHY 39
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LIST OF ILLUSTRATIONS
Figure Number Page
1 Basic HRS Structure 11
2 Structure of the Indoor Air Pathway 19
LIST OF TABLES
Table Number Page
1 HRS Scoring Factors 9
2 Ranges of Estimated Levels of Organic Vapors 15
in Ambient Air of Household Basements
in Niagara Falls, NY
3 Concentration Multiplier 26
4 Illustrative Table of Population Factor Values 27
5 Illustrative Adaptation of Current HRS Ground 29
Water Pathway Target Population Factor Matrix
6 Worksheet 1: Contaminant Record 31
7 Worksheet 2: Concentration Multiplier 32
8 Worksheet 3: Toxicity-Concentration 33
9 Worksheet 4: Score Sheet 35
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1.0 INTRODUCTION
1.1 Background
The Comprehensive Environmental Response, Compensation, and
Liability Act of 1980 (CERCLA) (PL 96-510) requires the President to
identify national priorities for remedial action among releases or
threatened releases of hazardous substances. These releases are to
be identified based on criteria promulgated in the National
Contingency Plan (NCP). On July 16, 1982, EPA promulgated the
Hazard Ranking System (HRS) as Appendix A to the NCP (40 CFR 300;
47 FR 31180, 12 July 1982). The HRS comprises the criteria required
under CERCLA and is used by EPA to estimate the relative potential
hazard posed by releases or threatened releases of hazardous
substances.
The HRS is a means for applying uniform technical judgment
regarding the potential hazards presented by a release relative to
other releases. The HRS is used in identifying releases as national
priorities for further investigation and possible remedial action by
assigning numerical values (according to prescribed guidelines) to
factors that characterize the potential of any given release to
cause harm. The values are manipulated mathematically to yield a
single score that is designed to indicate the potential hazard posed
by each release relative to other releases. This score is one of
the criteria used by EPA in determining whether the release should
be placed on the National Priorities List (NPL).
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During the original NCP rulemaking process and the subsequent
application of the HRS to specific releases, a number of technical
issues have been raised regarding the HRS. These issues concern the
desire for modifications to the HRS to further improve its
capability to estimate the relative potential hazard of releases.
The issues include:
Review of other existing ranking systems suitable for ranking
hazardous waste sites for the NPL.
Feasibility of considering ground water flow direction and
distance, as well as defining "aquifer of concern," in
determining potentially affected targets.
Development of a human food chain exposure evaluation
methodology.
Development of a potential for air release factor category in
the HRS air pathway.
Review of the adequacy of the target distance specified in
the air pathway.
Feasibility of considering the accumulation of hazardous
substances in indoor environments.
Feasibility of developing factors to account for
environmental attenuation of hazardous substances in ground
and surface water.
Feasibility of developing a more discriminating toxicity
factor.
Refinement of the definition of "significance" as it relates
to observed releases.
Suitability of tne current rfRS default value for an unknown
waste quantity.
Feasibility of determining and using hazardous substance
concentration data.
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Feasibility of evaluating waste quantity on a hazardous
constituent basis.
Review of the adequacy of the target distance specified in
the surface water pathway.
Development of a sensitive environment evaluation
methodology.
Feasibility of revising the containment factors to increase
discrimination among facilities.
Review of the potential for future changes in laboratory
detection limits to affect the types of sites considered for
the NPL.
Each technical issue is the subject of one or more separate but
related reports. These reports, although providing background,
analysis, conclusions and recommendations regarding the technical
issue, will not directly affect the HRS. Rather, these reports will
be used by an EPA working group that will assess and integrate the
results and prepare recommendations to EPA management regarding
future changes to the HRS. Any changes will then be proposed in
Federal notice and comment rulemaking as formal changes to the NCP-
The following section describes the specific issue that is the
subject of this report.
1.2 Issue Description
Several issues relevant to the HRS air pathway have been raised
by Congress and by public comments on the NPL and NPL rulemaking
actions. An analysis of these issues and the options developed for
revising the air pathway as a result of the analysis are presented
in Wolfinger, 1987. One of these issues relates to the applicability
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of the HRS to assessing sites which may pose significant indoor air
contamination problems. These indoor air contamination sites arise
as a result of the migration of air contaminants from an
uncontrolled waste site through the ground or air, and the eventual
accumulation of the contaminants in the air within buildings. The
waste site from which the contaminants originated may or may not be
readily identifiable. The present HRS evaluation of the air pathway
is applicable only to the release of contaminants directly into the
open air, subsequent transport in the atmosphere, and eventual human
exposure and other environmental effects. Implicitly, the
evaluation assumes a relatively high population, generally low
concentration average exposure situation. The structure and rating
factor values used in the current HRS targets category reflect this
assumption. However, the phenomenon of contaminant migration into
the confined atmosphere of buildings is somewhat inconsistent with
these assumptions. Transport of contaminants from a source in such
cases may be through the ground, as well as through the atmosphere,
and may result in relatively low population, high concentration
exposure situations.
The purpose of this paper is to present a preliminary air
pathway evaluation mechanism applicable to indoor air contamination
sites, compatible with the current structure of the HRS. This
mechanism is designed to be incorporated into the HRS. Alternately,
it could be adapted for use to screen sites for further monitoring
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in support of possible NPL listing (e.g., as a result of a health
advisory).
The evaluation mechanism presented is preliminary. Thus, a
number of questions that arise in the approach remain to be answered.
Of greatest importance are those questions associated with monitoring
requirements, the sources of detected contaminants, and the distance
at which targets are included in the evaluation. Since similar
questions are under study in respect to the other HRS pathways,
these questions could not be resolved as part of this effort.
1.3 Organization of Report
Section 2 presents background information on the Hazard Ranking
System (HRS). Section 3 presents an overview of the phenomena of
indoor air pollution from uncontrolled waste sites. The mechanism
for evaluating indoor contamination sites within the context of the
HRS is also discussed in Section 3. Section 4 discusses the
implication for program costs and NPL listing that might arise if
the evaluation mechanism were adopted as part of the HRS.
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2.0 BACKGROUND ON THE HAZARD RANKING SYSTEM
The HRS is designed to screen uncontrolled waste sites based on
the information compiled in a site investigation. The HRS addresses
three hazard modes: migration, fire, and explosion, and direct
contact. The migration mode site score (HRS score) is used to
determine whether the site is to be placed on the NPL for further
investigation and possible remedial action. The latter two mode
scores are not used in computing the HRS score but are included in
the HRS as indicators of the need for emergency response.
The migration mode consists of three potential migration
pathways representing the major routes of environmental transport
common to uncontrolled hazardous waste sites: ground water, surface
water, and air. Each pathway is structured similarly using three
factor categories: release, waste characteristics, and targets.
The release category reflects the likelihood that the site has,
is, or will release contaminants to the environment. If available
monitoring data indicate that the site is releasing or has released
contaminants, then an "observed release" has been demonstrated. If
no such observed release can be demonstrated, then the release
category is evaluated using route characteristics and containment
factors. These factors are largely physical characteristics of the
sites and their surrounding environments. It is important to note
that the ground water and surface water routes contain factors for
route characteristics and containment while the air route does not.
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This permits sites to be evaluated for their potential to release
contaminants to these two pathways in cases where documentation of
an observed release is lacking. The current HRS requires that
ambient air monitoring data support a conclusion that the site is,
or has been, emitting contaminants before the site can receive a
nonzero air route score. Wolfinger (1987) discusses options for
adding factors to the HRS air pathway that reflect the potential of
a site to release air contaminants.
The waste characteristics category reflects the inherent hazard
of the contaminants that have been or might be released. The factors
included in the waste characteristics categories address qualitative
and quantitative characteristics of the wastes and waste contaminants
found on the sites. The targets category constitutes a measure of
the population and resources that might be adversely affected by the
release. The factor categories and the rating factors contained in
them are illustrated in Table 1.
For each pathway, the site is assigned a value for each
applicable factor. The factor values are then multiplied by
weighting factors and summed within factor categories. The resulting
factor category scores are then multiplied and normalized to form a
route score. Thus, for each site, three route scores are produced,
each on a scale of 0 to 100. These route scores are referred to as
follows:
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TABLE 1
HRS SCORING FACTORS
Pathway
Factor Category
Ground Water
Surface Water
Air
Release
Waste
Characteristics
Targets
Monitoring data
or
Depth to aquifer of
concern
Net precipitation
Permeability
Physical state
Physical state
Containment
Toxicity/persistence
Quantity
Ground water use
Distance/population
Monitoring data
Facility slope and
terrain
Rainfall
Distance to receiving
water
Physical state
Physical state
Containment
Toxicity/persistence
Quantity
Surface water use
Distance/population
Distance to sensitive
environment
Monitoring data
or
Reactivity/
incompatibility
Toxicity
Quantity
Land use
Distance/population
Distance to
sensitive
environment
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Ground water migration route score (S )
Surface water migration route score (S )
ST*
Mr migration route score (S )
The overall site migration score, or HRS score, (S ) then is
calculated as the root mean square (ELMS) of the pathway scores:
> 99 1/2
Sm = (l/1.73)[(Sgw)2 + (Ssw)2 + CSa)2]
The RMS procedure was chosen to emphasize the highest scoring route
while giving some consideration to secondary and tertiary routes.
This procedure is illustrated in Figure 1. (For a more detailed
discussion of the HRS see 40 CFR 300 or 47 FR 31180, 12 July 1982.)
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Observed Release
0 or 45 pts
or
Route
Characteristics &
Containment*
0-45 pts
GW
SW
A
Waste
Characteristics
0-26 pts
0-26 pts
0-20 pts
'Not Included in Air Pathway
GW = Ground Water Pathway
SW = Surface Water Pathway
A = Air Pathway
Targets
GW
SW
A
0-49 pts
0-55 pts
0-39 pts
Pathway Score
0-100 pts
Normalized
FIGURE 1
BASIC MRS STRUCTURE
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3.0 A METHOD FOR EVALUATING INDOOR AIR CONTAMINATION SITES
3.1 Discussion of Indoor Contamination from Uncontrolled Waste Sites
The release of contaminants from an uncontrolled waste site
directly into the atmosphere is a common, well known phenomenon. A
review of the processes that could result in the release of air
contaminants from uncontrolled waste sites leads to the conclusion
that nearly all waste sites either currently emit, have emitted, or
will emit air pollutants. The exceptions are those sites whose
containment is such that it forms (and will continue to form) an
impermeable barrier between the contaminants and the atmosphere.
Whether the pollutants are emitted in sufficient concentration to
cause concern, or even be detected, depends on numerous site-specific
factors. A review of the phenomena of contaminant releases from
uncontrolled waste sites into the atmosphere can be found in
Wolfinger, 1987.
A less common, but nonetheless well known, phenomena is the
transport of gaseous contaminants through the soil and their eventual
escape into the interior of buildings. Such inground gas transport
can occur directly as the result of pressure gradients or through
diffusion processes. Alternately, the gas might be dissolved in,
and move through and with, the ground water, eventually volatilizing
and escaping into the air. The relative importance of these two
basic inground transport pathways is unknown but can be expected
to be dependent on the nature of the contaminants and the
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characteristics of the soil surrounding the waste site. Once the
contaminants have escaped from the soil, they can enter the
atmosphere directly or, more importantly for this analysis, enter
into the basements of buildings near the waste site.
Once inside the buildings, these contaminants may become
trapped, resulting in the buildup of contaminant concentrations in
the indoor air. Contaminant concentrations in such instances may
reach high levels, as shown in Table 2. Pellizzari (1982) indicates
that the contaminant concentrations illustrated in this table
probably arose from the Love Canal disposal site. Several other
researchers have reported elevated concentrations of contaminants In
buildings that they believe resulted from uncontrolled waste site
releases, many significantly removed in distance from the source
(Kim et al., 1980; James, Kinman, and Nutini, 1985; Miner and
Beizer, 1985; and Pellizzari, 1982). The weight-of-evidence
indicates that these contaminants could probably be traced to
uncontrolled waste sites. However, no one has demonstrated
conclusively that the contaminant concentrations reported arose from
subsurface transport of air contaminants. The contaminants may have
arisen from in-house sources or from infiltration of ambient air
contaminants. Alternately, as Indicated in the analyses of Foster
and Chrostowski (1986 and 1987) and others, indoor air contamination
can arise from the use of contaminated water for purposes such as
showering, cooking, and other household activities. These
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TABLE 2
RANGES OF ESTIMATED LEVELS OF ORGANIC VAPORS
IN AMBIENT AIR OF HOUSEHOLD BASEMENTS
IN NIAGARA FALLS, NY
Chemical
Concentration Range (ug/m^)
Chlorobenzene
Dichloro benzene Isomers (3)a
Trichlorobenzene Isomers (3)
Tetrachlorobenzene Isomers (2)
Pentachlorobenzene
Chlorotoluene Isomers (2)
Dichlorotoluene Isomers (3)
Trichlorotoluene Isomers (4)
Tetrachlorotoluene Isomer
Bromotoluene Isomer
Chloronaphthalene Isomer
1, 2-Dichloropropane
Pentachlorobutadiene Isomer
1, 3-Hexachlorobutadiene
Benzene
ND
0.65
0.07
0.03
T
1.7
0.13
0.06
0.03
T
0.08
1
0.03
T
- 4.2
- 190
- 33
- 20
- 0.49
- 490
- 370
- 0.157
- 4.1
- 4.4
- 3.4
.4
T
- 0.41
- 520
aValues are the sum of the individual isomers detected.
ND: Not detected.
T: Trace.
Source: Pellizzari, Edo D., "Analysis of Organic Vapor Emissions
near Industrial and Chemical Waste Disposal Sites,"
Environmental Science and Technology, Vol. 16, No. 11,
1982, pp. 781-785.
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considerations emphasize the Importance of determining the source of
detected indoor air contaminants when evaluating sites for possible
Inclusion on the NPL.
As discussed in Wolfinger, 1987, releases of air contaminants
into the atmosphere typically result in low dosage, large population
exposure situations. A large number of individuals might each be
exposed to a generally low contaminant concentration. The degree of
exposure depends on numerous site-specific factors. In contrast,
releases of air contaminants into buildings typically result in
situations of low population, sometimes high dosage exposure. In
such situations, a much smaller number of individuals might be
exposed to fairly high contaminant concentrations.
The phenomenon of off-site transport of contaminants through
the soil and into buildings is, overall, very different from the
more common ambient air transport phenomena addressed in the HRS air
pathway. These differences have Implications for the structure and
assumptions underlying any site evaluation mechanism. First, due to
the gaps in current knowledge about inground air contaminant
transport phenomena (particularly in the areas of unsteady-state
release and transport and contaminant retardation) and difficulties
in developing potentially needed data at a site, it would be very
difficult to assess the potential of a site to release contaminants
into buildings nearby. Thus, no provision is made for a "potential
to release" option in the evaluation mechanism discussed below.
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Second, since each individual is exposed to a generally higher
concentration in an indoor contamination situation and there are
generally fewer exposed individuals, the population target factor
tables currently used in the HRS would be inappropriate for use in
assigning values to indoor contamination sites. Rather, the factor
tables should reflect a high concentration, low population exposure
situation. This implies that the population needed to achieve a
given value should be lower than in the current, "outdoor" HRS air
pathway.
The third difference is that the interiors of most buildings,
particularly residences, may have measurable concentrations of the
same contaminants present at waste sites, even when the buildings
are not affected by waste sites. Benzene, for example, is a fairly
common contaminant found in the basements of houses not affected by
waste sites. Benzene may arise from infiltration of outside air,
smoking, or from oil or gas heaters. As another example, a
household resident may keep an old container of pesticide, such as
DDT, for lawn and garden use. The pesticide may escape from the can
while it is stored, resulting in a detectable concentration in a
garage or basement completely unrelated to any waste site. Because
of this, it is generally difficult to determine whether contaminants
detected indoors arise from nearby uncontrolled waste sites or from
nonwaste related sources such as natural gas furnaces or solvents
and pesticides stored indoors. A more complete discussion of the
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phenomena of building contamination can be found in Pellizzari,
1982; Pellizzari et al., 1985; and Wallace et al., 1984 and 1985.
The following sections describe an HRS-compatible mechanism for
evaluating indoor air contamination from uncontrolled hazardous
waste sites. This mechanism might be used in place of the current
air pathway in those situations where the risk posed by indoor
contamination is greater than that posed by outdoor contamination
(as indicated by comparing the indoor and "outdoor" pathway scores).
In such cases, the score from this indoor air pathway would be used
in place of the current air pathway score.
3.2 Overview of the Indoor Air Pathway
The proposed indoor air pathway is structured so as to be
compatible with the current HRS air pathway (see Figure 2). The
indoor air pathway score is the normalized product of an "observed
release" score, a waste characteristics score, and a targets score.
"Observed release" has a somewhat different interpretation in the
indoor air pathway than in the other HRS pathways. In the current
HRS, an "observed release" is said to have occurred whenever
available monitoring data indicate that the site has released air
contaminants. As a rule of thumb, an order of magnitude elevation
above background levels is considered "significant" in evaluating
sites using the current HRS, although each set of data is evaluated
on its own merits. Alternate criteria for significance are
currently under EPA review (see Brown, 1986).
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Evidence
of
Release
X
Waste
Characteristics
- Toxicity
Concentration
Targets
- Population
within 1/2 Mile
Radius
Score (S,A)
= (Normalized to
Base 100)
FIGURE 2
STRUCTURE OF THE INDOOR AIR PATHWAY
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However, no such "significance" requirement is included in the
indoor air pathway for two reasons. First, it is nearly impossible
to define a "background" concentration for a building since there is
a wide variation in indoor air contaminant concentrations between
buildings (Wallace et al., 1984 and 1985). Also, in principle, no
data would be available on the "background" concentrations for the
particular buildings in question. Second, no such requirement is
needed since the concentration factor included in the waste
characteristics category of the indoor air pathway precludes the
situation in which a site with nonhazardous exposure concentrations
would receive an indoor air pathway score (see Section 3.2.2).
In contrast to the current HRS, a very strict quality control
requirement needs to be placed on data used to show an "observed
release" in the buildings in question. This restriction is
necessary to distinguish contaminant concentrations that arise from
uncontrolled waste sites from those that arise from other sources,
particularly indoor sources. Moreover, as discussed above, the
indoor air pathway does not provide for a potential to release
option. Thus, the use of the indoor pathway is intentionally
restricted to only those sites at which off-site contaminant
migration into buildings can be conclusively demonstrated.
Two other significant differences are evident between the
indoor air pathway and the current HRS air pathway. First, since
high quality contaminant concentration data are required before the
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pathway may be used, a combined contaminant toxicity-concentration
factor is used in the waste characteristics category. Second, the
targets category consists only of a population factor. The
definition of the population-at-risk and the evaluation approach
differ from those in the current HRS air pathway, requiring fewer
people at risk to achieve the same factor value.
The following discussion describes these factors in greater
detail.
3.2.1 Release Category
The release category in the indoor air pathway is very simple.
If the available data indicate that air contaminants have escaped
from an uncontrolled waste site into the interior of surrounding
buildings, then a release score of 45 is assigned to the site. If
the data do not support such a conclusion, then a score of 0 is
assigned. No provision is made for a "potential to release" option
within the release category. Regardless of the indoor air pathway
score, the site should still be evaluated using the outdoor air
pathway to determine if the site could receive a higher HRS score
using the current air pathway.
As stated above, it is crucial to determine that the
contaminants concentrations detected did not arise from indoor
sources or from some other source within or near the building.
Rather, the contaminants should be attributable to an uncontrolled
waste site. For the purposes of the indoor pathway, a CERCIA
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contaminant whose presence in the atmosphere of the building in
question cannot be attributed to a source other than a possible
uncontrolled waste site is considered a "critical" contaminant. The
need to ensure that the contaminants arose from a waste site places
restrictions on the nature and quality of data used to conclude that
an observed release has occurred. Detailed requirements for
determining that an observed release has occurred have not yet been
developed. These requirements would include restrictions on
sampling equipment and protocols and may also include a requirement
for an indoor source inventory.
However, the actual location of the waste sites contributing to
situations of indoor air contamination may not be known at the time
the contamination is investigated. This has occurred several times
in the past, in particular, at the Love Canal disposal site. Similar
situations have also occurred in the past in cases of ground water
contaminant plumes having no readily identifiable source. Several
approaches could be used to address the question of source
attribution in the indoor air pathway. One approach is to employ a
"negative" approach, i.e., if a contaminant cannot be traced to any
known source within the building or any known source other than a
possible uncontrolled waste site, then the contaminant can be
assumed to have escaped from a waste site. This option addresses
the question of unknown sources and allows buildings themselves to
be declared "sites". An alternate approach would be to require that
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an uncontrolled waste site that has received wastes containing the
critical contaminants be identified within a reasonable distance of
the contaminated building before the site is evaluated under this
pathway. A third variation would be to require that outside
monitoring, such as soil gas or ground water monitoring, indicate
the presence of the critical contaminant below the surface.
Alternately, the building in question may be located on the
site itself. The indoor air pathway is to be employed, however,
only if the building is currently in use, or is vacant and not
associated with the waste disposal activity. Thus, data from
on-site buildings used to support a waste disposal operation cannot
be used in this approach. This restriction is imposed as required
in Section 101:22(A) of CERCLA.
3.2.2 Waste Characteristics Category
Two factors are reflected in the waste characteristics category:
critical contaminant toxicity and concentration (as measured in the
buildings in question). These factors are evaluated for each
critical contaminant and the resulting factors values multiplied to
form a combined toxicity-concentration value. The maximum calculated
toxicity-concentration value is used in evaluating the site score.
Critical contaminant toxicity is evaluated using the same
approach as in the outdoor air pathway (see 47 FR 31219-31243,
16 July 1982). Critical contaminant concentration is evaluated
using a benchmark approach. In such an approach, the concentration
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is evaluated based on its relative magnitude in comparison with a
given benchmark concentration. Possible benchmark concentrations
include Threshold Limit Values (TLV), Short Term Exposure Levels
(STEL), and Acceptable Daily Intakes (ADI) via inhalation. Threshold
Limit Values and Short Term Exposure Levels are defined in American
Conference of Governmental Industrial Hygienists, 1985. Acceptable
Daily Intakes for some chemicals have been set by EPA (U.S.
Environmental Protection Agency, October 1986).
Critical contaminant concentration is evaluated as follows. If
the affected buildings are industrial or commercial, the benchmark
concentration of each critical contaminant is the 8-hour average
Threshold Limit Value (TLV) of the contaminant. TLVs define the
levels below which occupational exposures to each particular
contaminant is expected not to pose an undue risk to the worker.
The benchmark concentration should reflect the types of exposure
situations associated with indoor air contamination. Characteristics
of particular interest are the classes of exposed individuals (e.g.,
children as well as adults), the duration of exposures (e.g.,
longer-term for children, shorter-term for working adults), and the
temporal variations in inhalation rates (sleeping versus waking).
An adaptation of the proposed revisions to the HRS toxicity factor
discussed in DeSesso et al., 1986, recognizing the different
characteristics of indoor versus outdoor exposures, should be
investigated.
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The critical contaminant concentration value is defined based
on the ratio of the maximum detected concentration to the benchmark
concentration and using the scale shown in Table 3. If the site
contains several buildings of different types, the maximum calculated
score should be used. However, the benchmark concentration used in
these calculations must be consistent with the type of building
affected (i.e., residential versus industrial/commercial). The use
of data from a commercial building and a residential benchmark, for
example, is not permitted even if residential buildings are also
affected.
3.2.3 Targets Category
A single target factor is used to reflect the population at risk
from the escaped contaminants. For purposes of this calculation,
the target population consists of the population residing in the
area around the site plus any permanent, nonresident employees
working in the area. Distance would be measured from the
contaminated buildings, and from the uncontrolled waste site as
well, if its location is known, as is currently done in the ground
water pathway. Table 4 defines an illustrative population factor
evaluation method in terms of the population living or working
within a 1/2-mile target distance limit. The distance of 1/2 mile
was chosen for illustrative purposes only. A final distance could
not be developed since few data are available showing the geographic
extent of sub-surface air contaminant transport. This distance is
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TABLE 3
CONCENTRATION MULTIPLIER
Ratio of Contaminant Concentration
to Benchmark Concentration Multiplier
Less than 0.1 0
Greater than or equal to 0.1 but less than 1.0 1
Greater than or equal to 1.0 and less than 10 2
Greater than or equal to 10 3
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TABLE 4
ILLUSTRATIVE TABLE OF POPULATION FACTOR VALUES
Population On-site or Within 1/2
Mile of Site or Building Value
0 0
1 1
2-10 2
11-30 3
31 - 100 4
Greater than 100 5
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smaller than the 4-mile target distance limit used in the current HRS
air pathway, since no data are available indicating that uncontrolled
waste sites affect indoor air at substantial distances from the sites.
An alternate approach is to adapt the current HRS target distance
factor value tables used for the ground water pathway. One such
adaptation is presented in Table 5. Such an approach might be better
than a strict 1/2 mile limit since ground water is considered to be
an important transport media in cases of building contamination.
3.2.4 Pathway Score
The score for the indoor air pathway is the product of the
release category score, the waste characteristics score and the
targets score normalized to a scale of 0 to 100. The greater of this
score and the "outdoor" air pathway score could be used as the air
pathway score in computing the HRS migration score.
3.3 Step-By-Step Instructions for the Indoor Air Pathway
This section presents preliminary step-by-step instructions for
evaluating sites using the indoor air pathway. The instructions are
provided to illustrate how a site would be evaluated using the
approach described above.
The pathway would be employed only when the available air
monitoring data include contaminant concentration data taken indoors
and when the contamination cannot be attributed to any nearby source
other than a possible waste site.
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TABLE 5
ILLUSTRATIVE ADAPTATION OF CURRENT HRS GROUND
WATER PATHWAY TARGET POPULATION FACTOR MATRIX
Value for Distance to Nearest Building
From Hazardous Substance
Population*
1
101
1,001
3,001
10
0
- 100
- 1,000
- 3,000
- 10,000
,000+
0
0
0
0
0
0
0
1
0
4
8
12
16
20
2
0
6
12
18
24
30
3
0
8
16
24
32
35
4
0
10
20
30
35
40
*Population within 3 miles
Distance to Nearest Building Value
Greater than 3 miles 0
>2 to 3 miles 1
>1 to 2 miles 2
2,000 feet to 1 mile 3
Less than 2,000 feet 4
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Step It Determine the concentrations of CERCLA contaminants in
the building. Record the data on Worksheet 1: Contaminant Record
(Table 6). Determine the potential sources of any detected
contaminants within the building. Contaminants that cannot be
attributed to any nearby or indoor source other than a possible
uncontrolled waste site are considered critical contaminants.
Documentation of the rational for determining that a contaminant is
a critical contaminant must be provided by the analyst evaluating
the site. If the concentration of any critical contaminant indicates
that an indoor observed release from a waste site has occurred,
assign a release value of 45. Otherwise, assign a release value
of 0.
Step 2; For each critical contaminant, record the detected
concentration on Worksheet 2: Concentration Multiplier (Table 7)
and determine the benchmark concentrations as indicated in the
preceding discussion.* Record the benchmark values on Worksheet 2.
Step 3; Calculate the ratio of each critical contaminant
concentration to its benchmark value, and determine the concentration
multiplier as indicated in Table 3. Record the multiplier for each
critical contaminant on Worksheet 2 and Worksheet 3t Toxicity-
Concentration (Table 8).
*The recommended benchmark for commercial/industrial buildings is
the Threshold Limit Value, as determined by the American Conference
of Governmental Industrial Hygienists. Benchmarks for residential
buildings are under development.
30
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TABLE 6
WORKSHEET 1: CONTAMINANT RECORD
Contaminant Critical*
CAS Number Concentration Units Contaminant
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Observed Release Score
Rationale for considering contaminants to be critical
contaminants (use additional sheets as necessary):
*Contaminants that cannot be attributed to any nearby or indoor
source other than a possible uncontrolled waste site are considered
critical contaminants. This column is used to indicate that a
contaminant is considered by the analyst to be a critical
contaminant.
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TABLE 7
WORKSHEET 2: CONCENTRATION MULTIPLIER
Contaminant Contaminant
CAS Number Concentration Benchmark Ratio Multiplier
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
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TABLE 8
WORKSHEET 3: TOXICITY-CONCENTRATION
Contaminant Concentration
CAS Number Toxicity Score Multiplier* Product
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Maximum value calculated
*From Worksheet 2.
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Step 4; For each critical contaminant, determine the toxicity
value as indicated in the Tables 4, 6, and 7 and page 42 of the HRS
User's Manual (47 FR 31219-31243, 16 July 1982). Record the
contaminant toxicity values for each contaminant on Worksheet 3.
Step 5; Calculate the product of the toxicity factor value and
contaminant multiplier for each critical contaminant as indicated
on Worksheet 3. Identify the largest value and record it on
Worksheet 3.
Step 6; Record the observed release value from Worksheet 1 and
the toxicity-concentration value from Worksheet 3 on Worksheet 4:
Score Sheet (Table 9).
Step 7; Evaluate the population exposed using the population
factor table (e.g., Table 4) and record the population value on
Worksheet 4.
Step 8; Compute the indoor air pathway score as indicated on
Worksheet 4.
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TABLE 9
WORKSHEET 4: SCORE SHEET
1. OBSERVED RELEASE VALUE
2. TOXICITY-CONCENTRATION VALUEa
3. POPULATION VALUEb
4. Multiply lines 1x2x3
5. Divide line 4 by 2025 Sąa
aFrom Worksheet 3.
bFrom Population Scoring Table (e.g., Table 4).
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4.0 IMPLICATIONS
The incorporation of this indoor air pathway would have several
implications for the HRS. First, since the pathway requires that
fairly comprehensive, expensive monitoring data be developed in
order to evaluate the site, the potential costs of use of the indoor
air pathway may be significant. These costs would arise from the
monitoring requirements, as the cost of calculating the waste
characteristics and targets scores would be negligible in comparison.
Current estimates of the cost to determine the presence of waste
site contaminants in indoor air in residential buildings range from
$4,000 to $4,500 per house, exclusive of labor costs (personal
communication, Turpin, 1986). This cost reflects the minimum
necessary under the most favorable conditions. Cost at complex
sites (e.g., those with nearby point sources) will be higher.
Second, there are two important differences between the factors
used in this indoor air pathway and the other HRS pathways; the lack
of a potential to release option and the use of a concentration
factor. This first difference is particularly important since the
lack of a "potential to release" option in the current HRS air
pathway has been identified as a weakness in the current approach.
This weakness has been discussed by Congress in its deliberations on
CERCLA reauthorization. In response to these concerns, an effort is
underway to develop a "potential to release" option for the HRS air
pathway (Wolfinger, 1987). Thus, a potential to release option for
37
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an indoor air pathway may also be required. Further, the use of a
concentration factor in this pathway raises the question of the use
of similar factors in the other pathways.
Finally, several technical Issues remain to be resolved before
this indoor air pathway could be incorporated into the HRS. These
include the development of benchmark concentration values for
residences, the preparation of monitoring requirements and guidance,
and the finalization of the target distance limit.
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5.0 BIBLIOGRAPHY
American Conference of Governmental Industrial Hygienists, ILVs
Threshold Limit Values and Biological Exposure Indices for 1985-86,
American Conference of Governmental Industrial Hygienists,
Cincinnati, OH, 1985.
Brown, Richard D., Hazard Ranking System Issue Analysis; Use of
Significance in Determining Observed Release, (MTR-86W101), The
MITRE Corporation, McLean, VA, July 1986.
DeSesso, John et al., Hazard Ranking System Issue Analysis;
Toxicity as a Ranking Factor, (MTR-86W128), The MITRE Corporation,
McLean, VA, July 1986.
Foster, Sarah A. and Paul C. Chrostowski, "Integrated Household
Exposure Model for Use of Tap Water Contaminated with Volatile
Organic Chemicals," (86-12.3), Presented at the 79th Annual Meeting
of the Air Pollution Control Association, Held on June 22-27, 1986
in Minneapolis, MN, Air Pollution Control Association, Pittsburgh,
PA, 1986.
Foster, Sarah A. and Paul C. Chrostowski, "Inhalation Exposures to
Volatile Organic Contaminants in the Shower," (87-42.6), Presented
at the 80th Annual Meeting of the Air Pollution Control Association,
Held on June 21-26, 1987 in New York, NY, Air Pollution Control
Association, Pittsburgh, PA, 1987.
James, S. C., R. N. Kinman and D. L. Nutini, "Toxic and Flammable
Gases," Contaminated Land; Reclamation and Treatment, Michael A.
Smith, ed., Plenum Press, New York, NY, 1985.
Kim, C. Stephen et al., "Love Canal: Chemical Contamination and
Migration," Proceedings of the National Conference on Management of
Uncontrolled Hazardous Waste Sites, Held on October 15-17, 1980 in
Washington, DC, Hazardous Materials Control Research Institute,
Silver Spring, MD, 1980, pp. 212-219.
Miller, Joseph J. and Mark B. Beizer, "Air Quality in Residences
Adjacent to an Active Hazardous Waste Disposal Site," (85-73.7),
Presented at the 78th Annual Meeting of the Air Pollution Control
Association, Held on June 16-21, 1985 in Detroit, MI, Air Pollution
Control Association, Pittsburgh, PA, 1985.
Office of Technology Assessment, Habitability of the Love Canal
Area; An Analysis of the Technical Basis for the Decision on the
Habitability of the Emergency Declaration Area, Office of Technology
Assessment, Washington, DC, June 1983.
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Fellizzari, Edo D., "Analysis of Organic Vapor Emissions near
Industrial and Chemical Waste Disposal Sites," Environmental Science
and Technology, Vol. 16, No. 11, 1982, pp. 781-755T
Pellizzari, E. D. et al., Interim Report on the Total Exposure
Assessment Methodology (TEAM) Study; First Season, Northern New
Jersey, (Draft), U.S. Environmental Protection Agency, Washington,
DC, June 1985.
Rowe, William D., An Anatomy of Risk, John Wiley & Sons, New York,
NY, 1977.
Turpin, Rodney D., U.S. Environmental Protection Agency,
Environmental Response Team, personal communication, January 1986.
U.S. Environmental Protection Agency, Damages and Threats Caused by
Hazardous Material Sites, (EPA-430/9-80-004), U.S. Environmental
Protection Agency, Washington, DC, May, 1980.
U.S. Environmental Protection Agency, Superfund Public Health
Evaluation Manual. (EPA 540/1-86/060, OSWER Directive 9285.4-1),
U.S. Environmental Protection Agency, Washington, DC, October 1986.
Wallace, Lance A. et al., "Personal Exposures, Indoor-Outdoor
Relationships, and Breath Levels of Toxic Air Pollutants Measured
for 355 Persons in New Jersey," Atmospheric Environment, Vol. 19,
No. 10, 1985, pp. 1651-1661.
Wallace, Lance A. et al., "Personal Exposures, Outdoor
Concentrations, and Breath Levels of Toxic Air Pollutants Measured
for 425 Persons in Urban, Suburban and Rural Areas," Presented at
the 77th Annual Meeting of the Air Pollution Control Association,
Held on June 25, 1984 in San Francisco, CA, Air Pollution Control
Association, Pittsburgh, PA, 1984.
Wolfinger, Thomas F., Hazard Ranking System Issue Analysis; Options
for Revising the Air Pathway, (MTR-86W53), The MITRE Corporation,
McLean, VA, August 1987.
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