United States Office of
Environmental Protection
Agency Emergency Response
Directive 9285.7-20FS
Solid Waste andPB94-963314
EPA/540/F-94/031
September 1995
wEPA Establishing an Observed Release
Office of Emergency and Remedial Response
Quick Reference Fact Sheet
Abstract
EPA uses the Hazard Ranking System (HRS) (40 CFR Part 300, App. A) to evaluate Superfund sites to be proposed on the
National Priorities List (NPL). Based on the HRS criteria, an observed release is established when contaminants have
migrated away from a site through environmental media. This fact sheet describes an observed release, the data required, and
the process used to document it. Efficient sampling also is emphasized to optimize the use of limited resources, which is
especially important in light of conducting integrated assessments under the Superfund Accelerated Cleanup Model (SACM).
Introduction
When planning a Site Inspection, an integrated assessment
should be considered as appropriate under the Superfund
Accelerated Cleanup Model (SACM). This planning would
incorporate a sampling strategy that should maximize
remedial and removal resources.
Three categories of sampling generally are performed
during a Site Inspection (SI):
• Source sampling to establish the presence of
hazardous substances at a site;
• Sampling in the media of concern to establish an
observed release, with background sampling
corresponding to the source to establish attribution;
• Quality Assurance/Quality Control (QA/QC);
sampling (e.g, field blanks) to ensure data integrity.
Although all three of these categories are important, this
fact sheet pertains to the second category of sampling, and
discusses resource conservation by using available data
and an integrated sampling approach.
Determining an Observed Release
An observed release is based on evidence that
contaminants have migrated from a site through a pathway
or medium. The Hazard Ranking System (HRS)
establishes two general criteria to document an observed
release: there must be evidence of a hazardous substance
in the medium of concern at a concentration significantly
above the background level, and the release of the
hazardous substance must be at least partially attributable
to the site under investigation {Hazard Ranking System,
Final Rule, 40 CFR Part 300, App. A). An observed
release can be determined either by chemical analysis of
samples, or by directly observing the release of the
hazardous substance (to be documented) into the medium
of concern (see Figure 1). Observed releases can occur
through the ground-water, surface water, and air migration
pathways. In contrast, the soil exposure pathway is
evaluated for observed contamination where targets
(human populations, resources, and sensitive environments)
may come into direct contact with contaminants. (For more
information on the soil exposure pathway, refer to the fact
sheet Establishing Areas of Observed Contamination,
September 1995, OSWER Directive 9285.7-18FS.)
The documentation of an observed release by chemical
analysis should be accompanied with information on
background level and attribution. Attribution requires
evidence that the hazardous substance detected in a
medium resulted from some portion of the release from the
site. Background levels are established by sampling or by
using other acceptable information, such as published or
existing sample data. Existing data or data from
background samples should be generated by sampling and
analytical methods similar to those used for the release
data {Hazard Ranking System Guidance
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Figure 1: Flowchart for Establishing an Observed Release Under the MRS
Not applicable to ground-vtatar plum* »ite» with unknown
QSWER Dlmctlva 9345.1-07 (p. 50;
Manual, November 1992, OSWER Directive 9345.1-07). (For
more information on establishing background levels, refer to the
fact sheet Establishing Background Levels, September 1995,
OSWER Directive 9285.7-19FS.)
Documenting an observed release is a prerequisite for evaluating
actual contamination at targets. Actual contamination at targets
indicates a high likelihood of exposure to hazardous substances.
Note that the detection of contamination at targets is not in itself
sufficient to establish an observed release or actual
contamination (OSWER Directive 9345.1 -07). The level of actual
contamination is determined by comparing the release
concentration to health-based or ecological benchmark values,
where available. Level I contamination is at or above
substance-specific benchmarks; Level II is detection below
benchmark values.
Resource Considerations
Generally, the SI is a limited-scope biased sampling event.
However, under SACM, traditional remedial Sis should be
integrated with traditional removal site assessments. The Data
Quality Objective (DQO) process provides a logical framework
for planning multiple field investigations, thereby fulfilling the
integrated site assessment goal of cross-program response
planning and allowing optimal cross-program data usability. (See
Data Quality Objectives Process for Superfund, September 1993,
OSWER Directive 9355.9-01 for further details on the DQO
process.)
When possible, available data should be used to meet SI
objectives so that resources are conserved (see Exhibit 1).
Samples can be strategically collected to establish an observed
release and to include one or more targets (i.e.,
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Exhibit 1: Considerations when Assessing the Need for Sampling
• Is there an imminent or current threat to human health or the environment? Is a removal action warranted? Sample
at targets if human or environmental exposure to contaminants is suspected. Always sample for public health
concerns.
• Can sampling meet both removal and remedial site assessment objectives? If yes, and site conditions warrant, an
integrated sampling approach may be used. (For more information, refer to Integrating Removal and Remedial Site
Assessment Investigations, September 1993, OSWER Directive 9345.1-16FS.)
• What are the objectives of the SI? Table 4-7 in Guidance for Performing Site Inspections Under CERCLA, 1992,
OSWER Directive 9345.1-05, provides guidelines on the number of samples recommended for a focused, expanded,
or single SI as part of an observed release sampling strategy.
• Could the pathway critically affect the site Hazard Ranking System (HRS) score (> 28.50)? If yes, must an observed
release be documented for that pathway to achieve that site score? If no, evaluating the pathway for potential
contamination may be sufficient (particularly for less critical pathways).
• What are the pathway criteria? Are targets nearby? Each HRS pathway has certain criteria for determining and
limiting target distance with respect to contaminants. For example, for the soil exposure pathway, contamination
must be documented within a zero to two feet depth from the surface, and contamination must be on the property
and within 200 feet of targets. For the surface water pathway, the surface water body must be within two overland
miles of the site or source. Sample collection should be avoided if sampling cannot meet the pathway criteria.
dual purpose sampling). Analytical data with appropriate and
adequate quality assurance/quality control (QA/QC) are
needed, since benchmarks are expressed in concentration
units.
The Agency for Toxic Substances and Disease Registry
(ATSDR) should be consulted when there is the potential for
human exposure to toxic substances. The sampling approach
for these sites should include data collection for the human
exposure information that ATSDR uses to determine if a
health advisory is needed. ATSDR also uses this data in the
preparation of a public health assessment, which is required
within 12 months of proposal to the National Priorities List.
Observed Release by Direct Observation
To establish an observed release by direct observation, a
hazardous substance must be observed or known to have
been released into the medium of concern. Existing analytical
data or other references, such as manifests, should be used
to document that the hazardous substance is present or
known to have been released (OSWER Directive 9345.1-07.
See Exhibit 2 for examples of an observed release by direct
observation.
For the ground-water pathway, an observed release by direct
observation may be documented with information that
hazardous materials have come to be located or deposited in
the aquifer of concern (OSWER Directive 9345.1-07).
For the surface water pathway, direct observation to
establish an observed release can be documented by:
• Seeing hazardous substances entering the water
body through migration or knowing they have
entered through direct deposition;
• Natural flooding of a source area so that hazardous
substances come in direct contact with the water:
in this case, the presence of a hazardous substance
sigaificantly above background prior to flooding
must be demonstrated (OSWER Directive 9345.1-
07). Historical data may be sufficient to document
flood levels, the presence of a hazardous substance,
and its direct contact with flooded waters;
• Adverse effects (e.g., fish kill) associated with the
release of a hazardous substance to surface water.
Note that inference requires extensive
documentation and verified attribution (OSWER
Directive 9345.1-07).
For the air pathway, direct observation may be established
by demonstrating adverse effects from a release (OSWER
Directive 9345.1-07).
Observed Release by Chemical Analysis
An observed release can be documented when samples
from the media of concern exhibit contamination
significantly above background levels, and the
contaminants are attributable to the source. Since
concentrations of contaminants usually decrease with
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Exhibit 2: Examples of an Observed
Release by Direct Observation
For Different Media
• Ground-water pathway-Hazardous
substances placed into an old quarry
where the water table has risen above
the level of the deposited materials.
• Surface water pathway--An
impoundment leachate seep seen
entering a stream. (Collect a sample
from the leachate to document hazardous
substances.) Also, effluent known to
contain hazardous substances (through
manifests) seen entering a surface water
body.
• Air pathway—A field logbook entry and
photodocumentation of a dust cloud
originating from a tailings pile. A sample
of the fine particulate matter from the
pile showing the presence of hazardous
substances will verify the release
(OSWER Directives 9345.1-05 and
9345.1-07).
distance from a source, sampling near sources will
better establish an observed release and attribution
(Guidance for Performing Site Inspections Under
CERCLA, September 1992, OSWER Directive
9345.1-05). At a minimum, one validated sample and
a background level are required to document a release,
even if earlier or later sampling fails to show a release.
Varying results could be due in part to intermittent
releases (OSWER Directive 9345.1-07).
To document an observed release by chemical
analysis, the following criteria must be met (except for
radionuclides, which are discussed later in this fact
sheet):
• The release of a hazardous substance must be
at least partially attributable to a source at the
site. (Note: This does not apply to
ground-water plume sites with unknown
sources.)
• The sample concentration must be greater than
or equal to the appropriate detection limit (40
CFR Part 300, App. A).
• If the background level is below its detection
limit, the sample concentration must be greater
than or equal to the background detection limit.
• If the background level is greater than or equal
to its detection limit, the sample concentration
must be at least three times the background
concentration (OSWER Directive 9345.1-07).
• The detection limits must be calculated or determined
properly. The detection limit used for comparison often
depends on the source of the analytical data. Detection
limits may be different for release and background
samples. Detection limits such as those provided by the
Contract Laboratory Program (CLP) may be used
(OSWER Directive 9345.1-07).
Observed release sampling variables differ according to the
medium, or pathway. These variables include temporal and
spatial variation, hazardous substances present, and
documentation of location and collection conditions.
Ground-water Pathway
For the ground-water pathway, certain types of wells,
including monitoring, irrigation, or drinking water wells, may be
used to establish an observed release. To establish an
observed release, the well(s) closest to the contamination
source should be sampled. It is preferable to select
background well(s) outside the influence of a source and in
the same zone of the same aquifer being evaluated.
Cross-gradient or upgradient background sample locations are
used when flow gradient information is available.
(Ground-water flow gradient information is not required for
HRS scoring purposes.) Establishing an observed release in
the ground-water pathway could be further complicated by
uncertainties about ground-water flow direction, and any
resultant uncertainty about background and attribution.
Caution should be exercised regarding the use of wells that
are close to the site to determine background levels. For
example, landfills and impoundments could interfere with
natural ground-water flow. Pumping also may affect
ground-water direction and plume movement. If available,
pumping rates of nearby wells (including those sampled) may
serve as a useful source of information for addressing both
sample comparability and contaminant effect. Note: The
same well may not necessarily be used to document actual
contamination of targets. For a target population, actual
contamination should be documented using a drinking water
well.
The characteristics of suspected contaminants in ground
water should be considered when selecting sample locations
and depths. Contaminants in ground water may not be evenly
dispersed. For example, oils and organic substances lighter
than water (light non-aqueous phase liquids [LNAPLs]) tend
to float on top of the water table. Contaminants heavier than
water (dense non-aqueous phase liquids [DNAPLs]) sink to
the bottom of the water column (OSWER Directive
9345.147).
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Surface Water Pathway
Aqueous effluent, sediment, and tissue samples from
sessile, benthic organisms are used to document an
observed release to the surface water pathway.
Generally, at least two samples (aqueous or sediment)
are required for documenting an observed release in
the surface water pathway. They are: a background
sample slightly upstream of the Probable Point of
Entry (PPE) for contaminants from the site or source;
and a sample act or slightly downstream of the PPE.
Exceptions to this two sample minimum requirement
are when: 1) the surface water body originates at the
site (no upstream background exists), 2) multiple PPEs
exist, or 3) tidal flow exists. In the first case, one
sample may be sufficient to document a release. In the
second case, it may be advisable to sample upstream
of each PPE. In this case, sampling is necessary at the
PPE or downstream of each PPE to establish an
observed release. In the third case, background data
may need to be collected inside and outside the tidal
area.
Aqueous samples may be used to document current
releases to a surface water body. A preferred way is
to collect the downstream sample first, and to collect
aqueous samples before sediments to avoid the
introduction of any contaminants not associated with
the site or medium. Aeration of a sample should be
minimized to prevent reducing the concentration of
contaminants such as volatile organic chemicals.
Seasonal and other potential variations such as
irrigation and flooding should be considered when
sampling in this pathway. Deep, slow-moving surface
water bodies often exhibit some chemical or thermal
stratification. Stratification can occur where two
streams converge. Additionally, the absorption or
dilution of substances is affected by stream movement,
and depositional conditions vary within the riffles or
close to stream edges (OSWER Directive 9345.1-07).
Sediment samples may be used to document historical
releases to a surface water body. Ideally, the
characteristics of the suspected contaminant(s) should
be known in order to select the best sample medium,
location, and sampling method. Often, sediments are
scoured and deposited in bends of streams and other
flowing surface water bodies. Sample from like areas
(e.g., inside bend deposition areas) for comparability.
Grain size, organic content, and structure can affect
adsorbance of substances to sediments, possibly
introducing bias to the samples. For example, trichloroethylene
(TCE) could adsorb to certain particles (OSWER Directive
9345. l-07).When possible, differentiate sediments from soils,
especially when sampling along the edge of a water body. Note
that in arid or semiarid locations (less than 20 inches mean
annual precipitation), "sediments" include areas with
intermittently flowing waters as well as contiguous
intermittently flowing ditches. Contamination in these areas
should be evaluated in the surface water pathway (40 CFR
Part 300, App. A).
Tissue sampling can pose challenges for comparability because
of differences between members of the same species,
differences between species, variations within a study
population, species mobility, and tissue differentiation. The
target sample species should be examined for type of organism,
approximate age, gender, size of population, migratory nature,
and seasonal, feeding, spawning, or other periodic activities that
influence concentration of substances within the organism
(OSWER Directive 9345.1-07). Due to the potential difficulty
of collecting comparable samples, tissue samples are more
readily used to document actual contamination instead of an
observed release. It is prudent to collect tissue samples in
concert with other sampling activities when documenting an
observed release.
For tissue sampling, both the rationale for the tissue selection
and the accuracy of measurement should be established. Edible
tissues from sessile, benthic organisms are preferred for HRS
evaluation. (Generally, non-sessile benthic organisms, finfish,
amphibians, and reptiles should not be used.)
Note that the surface water pathway requires sampling at or
beyond the target to establish actual contamination; in contrast,
the ground-water pathway requires sampling at the target.
Air Pathway
It is important to consider temporal variability in air sampling
because large variations in substance concentration can occur
over a very short time. Emissions characteristics depend upon
topography and changeable atmospheric conditions, including
temperature, pressure, wind speed and direction, precipitation,
and atmospheric stability.
Monitoring wind direction is important in documenting migration
of hazardous substances from the source. Wind roses, which
detail the percentage of predominant wind direction, should be
developed for the sampling period to document shifts in wind
direction (OSWER Directive 9345.1-07).
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For the air pathway, an air sample may be used to
document both an observed release and actual
contamination of targets within a certain radius from the
source. An observed release by chemical analysis can be
difficult to establish for the air pathway because of the
challenge of obtaining comparable and verifiable samples.
Under the HRS, EPA evaluates outdoor ambient air
conditions only, indoor air samples are not evaluated for
this pathway (OSWER Directive 9345.1-07).
Partial Attribution and Multiple Source Sites
Sources of contamination other than those from the site are
often present. For example, substances may originate from
non-point sources such as pesticide application, and from
products containing lead.
Establishing background levels is especially important when
attributing hazardous substances to varied sources.
Background and site sample data should be from the same
medium using similar sampling and analytical methods.
Background samples should be collected from outside the
influence of contamination from the site under
investigation, but do not have to be free of contamination
for purposes of attribution. The data need only support that
the sample concentration is beyond an established
background level. The location of other potential sources
should be thoroughly reviewed and documented so that the
appropriate background sampling locations can be selected.
Background levels for ubiquitous substances should
account for local variability; several samples may be
required to establish the background levels (OSWER
Directive 9345.1-07).
Where attribution is questionable, sampling should be done
to gather analytical data demonstrating that the
contamination is at least partially attributable to the site.
Contamination from sites sometimes can be isolated by
identifying hazardous substance unique to the site under
investigation. Special analytical services and close
evaluation of data may be required to identify these
hazardous substances. Information about the disposal
practices and waste products of nearby facilities may help
identify target compounds associated with the site
(OSWER Directive 9345.1-05).
Attribution may be established through the use of
manifests, labels, records, oral or written statements, or
other information regarding hazardous substances present
at the site or at alternative sources. If these references
confirm the presence of a hazardous substance at the site,
attribution generally can be established even if specific
sources where the substance was deposited cannot be
documented (OSWER Directive 9345.1-07).
Sufficient samples from the site under investigation and
from other known potential sources (or other adjacent
areas) should be obtained to demonstrate that an increase
in contaminant levels is attributable to the site. Additional
information beyond analytical samples may be required if
the other sites release intermittently. To attribute
contamination sufficiently, collect the following data:
• Concentration gradients (e.g., samples from multiple
wells or a series of samples between the site and
alternative sources)
• Flow gradients and other information about the
media of concern
• Data that associate the site with a unique substance
or unique ratios of different substances (OSWER
Directive 9345.1-07).
Complex factors affecting attribution (e.g., soil
contamination in an industrial area) may require conducting
an Expanded Site Inspection (ESI). In many cases,
attribution concerns may be addressed by characterizing
other sources at a site and those of neighboring sites
(OSWER Directive 9345.1-05).
To establish attribution for the ground-water pathway, it is
preferable to sample wells located between site sources
and other sources. Three wells generally are needed to
define flow direction and to verify the source versus
another source. For surface water, a sample may be
collected downstream of or at the confluence. It may be
necessary to sample background and attribution along each
tributary if multiple sources are located upstream (OSWER
Directive 9345.1-07).
Transformation Products
It is possible to establish an observed release based on
documenting the existence of a transformation product, if
the transformation product is itself a hazardous substance.
In these cases, the observed release must be documented
by chemical analysis (OSWER Directive 9345.1-07).
Transformation products are substances found when a
hazardous substance is changed in the environment by
physical, chemical, or biological processes. Most
transformation products at hazardous waste sites are the
result of degradation (OSWER Directive 9345.1-07).
In order to attribute the parent substances and the
transformation product to the site, the presence of a
transformation product in a sample at a level significantly
above the background level(s) should be documented.
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The following references may be useful for documenting
parent substances and transformation products:
• Site-specific studies on the transformation process
by qualified research organizations (e.g., U.S.
Government agencies, universities)
• Technical reports on transformation from EPA's
Office of Research and Development
• Databases containing EPA-reviewed information
Articles from peer-reviewed journals
• Textbooks on soil, environmental microbiology,
biotechnology, and biotreatment processes and their
effectiveness (OSWER Directive 9345.1-07).
For determining an observed release, conditions at the site
must be conducive to, or must not impede, transformation,
and at least one source must be able to release the
substance to a pathway (OSWER Directive 9345.1-07).
Radionuclide Sites
The criteria for documenting an observed release by direct
observation apply to radionuclides. Table 7-1 in the
Hazard Ranking System, Final Rule provides the HRS
factor categories that are evaluated differently when
radionuclides are present (40 CFR Part 300, App. A).
Radionuclide sites are divided into three groups for
documenting an observed release by chemical analysis:
• Radionuclides that exist naturally and ubiquitous
radionuclides
• Man-made radionuclides which are not ubiquitous
• External gamma radiation (for the soil exposure
pathway only). For gamma radiation, measure the
exposure rate at one meter above ground. (For
more information, refer to the fact sheet
Establishing Background Levels, September 1995,
OSWER Directive 9285.7-19FS.)
Observed releases from a combination of radionuclides and
hazardous wastes (mixed waste) should be documented
separately. Establishing an observed release requires:
• Identification of the radionuclide of concern and the
physical and chemical properties of the radionuclide;
• On-site and background levels for that radionuclide;
and
• Detection limit for the radionuclide.
Specific requirements for establishing an observed release
for each of the three groups of radionuclides can be found
in Section 7.1.1 of the Hazard Ranking System, Final
Rule (40 CFR Part 300, App. A).
Summary
Documenting an observed release requires evidence that
the concentration of the hazardous substance of concern
significantly exceeds the background level. The hazardous
substance must be attributable at least in part to the site
under investigation (except for sites with ground-water
contamination from unknown sources). Establishing an
observed release requires thorough documentation. The
sampling design of the SI should attempt to meet multiple
HRS data needs with a limited number of samples.
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