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INFORMATION
BULLETIN
April 1989
OSWER Directive No. 9200.5-302
Issue #2
This is the second bulletin designed to inform those
persons involved in the Superfund pre-remedial
process of possible data collection changes brought
about by proposed revisions to the Hazard Ranking
System (HRS) as required by the Superfund Amend-
ments and Reauthorization Act of 1986 (SARA). The
revisions to the HRS were proposed on December
23, 1988. Following the public comment period, the
Agency expects the final rule to be published in Jan-
uary 1990. The purpose of this Bulletin is to discuss
data collection elements and procedures that might
be appropriate if the final rule were to be promul-
gated in substantially the same form that it has been
proposed. It is important for the reader to under-
stand that substantial changes are possible as a
result of public comment, ongoing research, and
other facets of the rule-making process. Changes to
the rule will, of course, result in changes to the sug-
gested data collection procedures. Final guidance
on how to conduct Preliminary Assessments (PAs),
Screening Site Inspections (SSIs), and Listing Site
Inspections (LSIs) will be issued shortly after the
revised HRS is published as a final rule. This docu-
ment is designed to assist Regional pre-remedial
staff, State offices functioning under cooperative
agreements, other Federal agencies, and contrac-
tors in conducting data collection activities during
the interim period between proposal and promulga-
tion of the revised HRS.
SARA Directives
SARA requires that the HRS be revised to account
for several factors not included in the original model
Specifically, Section 105 of SARA requires that the
new HRS take into account, to the extent possible,
the following:
• Damage to natural resources associated with
releases or threatened releases that may affect
the human food chain.
•	Contamination or potential contamination of the
ambient air that is associated with a release or
threatened release.
Section 105 also requires that human health risks
associated with contamination or potential contami-
nation of surface waters be appropriately assessed
where such surface water is, or can be, used for
recreation or potable water consumption. Addition-
ally, Section 118 of SARA states that high priority
(for National Priorities List [NPL] listing) shall be
given to facilities where the release of hazardous
substances or pollutants has resulted in the contam-
ination or closing of drinking water wells or a princi-
pal drinking water supply.
Section 125 of SARA requires that the HRS be
revised with respect to facilities which contain sub-
stantial volumes of wastes from fossil-fuel combus-
tion (e.g., fly ash, bottom ash, and slag waste) in a
manner which assures appropriate consideration of
each of the following site-specific characteristics:
•The quantity, toxicity, and concentrations of haz-
ardous constituents.
•The extent of, and the potential for, the release
of hazardous constituents into the environment.
•	The degree of risk to human health and the
environment.
Finally, SARA requires the Environmental Protection
Agency (EPA) to modify the HRS so that, "to the
maximum extent feasible, [it] accurately assesses
the relative degree of risk to human health and the
environment posed by sites and facilities subject to
review." Therefore, a number of changes to the
HRS have been proposed by the Agency. In the pro-
posed rule for the revised HRS, all of the factors
from the current HRS have been revised in some
way, with some "new" factors added and some
"old" factors deleted. (Please refer to the Federal
Register [Vol. 53, No. 247, pp. 51962-52081, Decem-
ber 23, 1988], which presents the complete text

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of the proposed revised HRS.) The proposed
changes that could have a significant impact on
pre-remedial data collection activities include the
following:
•Onsite Exposure Pathway—This is a new path-
way for the revised HRS; soil sampling of resi-
dential, school, or day-care center property may
be important.
•	Site Definition—With some exceptions, the site
is defined as an aggregation of sources (i.e.,
where the wastes were deposited, placed, or
stored) rather than by the extent of contamina-
tion, including migration; such definition may
require source and onsite sampling, or aerial
photography, to delineate the "site." Targets are
distance weighted (or for the surface water path-
way, dilution weighted), so target distance from
the "site" is important.
•Drinking Water Targets—Quantitative evidence
of actual (as opposed to potential) exposure to
contaminated drinking water is stressed; target
distances have been increased. Potential targets
are distance- or dilution-weighted.
•	Environmental Effects—Actual and potential
environmental impacts will receive greater
emphasis; target distances are increased, and
the types of "sensitive" environments to be con-
sidered have been expanded.
•	Air Route—An observed release will no longer
be required to score the air route; a mechanism
to evaluate the potential for an air release has
been included in response to SARA Section 105.
The method to assess potential air releases is
based on the physical characteristics of the site,
the physical and chemical characteristics of the
hazardous substances associated with the site,
and the ways in which the hazardous substances
are contained.
•	Observed Release—The boundaries of a site
will generally not be "extended" because of an
observed release; with some important excep-
tions, target distances will be measured from the
sources of contamination at the site (or from the
probable point where contaminants enter a sur-
face water body), rather than measuring the
extent of contamination. The meaning of "signifi-
cantly above background" has been quantified.
•	Hazardous Waste Quantity—The proposed
tiered approach would allow for the use of the
actual amount of hazardous constituents if ade-
quate sampling and analytical methods have
been utilized, or if comprehensive process data
or waste disposal records are available; if these
concentration data are not available, waste quan-
tity-as-deposited could be used. If waste quan-
tity-as-deposited data are not available, then
source volume or area could be used.
Pre-Remedial Process Changes
Procedural changes in pre-remedial activities, such
as the expanded preliminary assessment (PA) and
the division of the Site Inspection (SI) stage into two
sequential components, the screening site inspec-
tion (SSI) and the listing site inspection (LSI), are
already in place (see Figure 1).
The PA stage of the pre-remedial process primarily
focuses on obtaining "desktop" data for those
important HRS factors which enable the investigator
to derive a projected HRS score that is representa-
tive of the site. At the present time, approximately
50% of the sites receiving PAs are recommended
for SSIs. The SSI builds upon data collected during
the PA by verifying and augmenting the data, as well
as by collecting additional data, including environ-
mental samples (usually 10-20 samples per site), to
further characterize the site. The purpose of sam-
pling during the SSI is to identify the types of con-
taminants present, to assess whether a release of
hazardous substances has occurred, to look for evi-
dence of actual human and environmental exposure
to contaminants, and to determine the likelihood of
the site scoring high enough on the HRS to be rec-
ommended for an LSI. The LSI is conducted only on
sites that have a high probability of being listed on
the NPL as one of the nation's worst hazardous
waste sites. The LSI evaluates all appropriate path-
ways through expanded sampling and results in an
HRS scoring package.
This issue of the Bulletin will not focus on specific
elements of the PA, SSI, or LSI; rather, it will dis-
cuss the cumulative body of data needed to com-
plete the pre-remedial process for sites that have a
high probability of being placed on the NPL. At the
present time, it is estimated that between 5 and
10% of the sites on the Comprehensive Environ-
mental Response, Compensation, and Liability Infor-
mation System (CERCLIS) will result in an NPL list-
ing. Most sites will then only receive a subset of the
evaluation activities described in this document,
depending on the point in the process when it is
decided that they do not warrant further Superfund
pre-remedial action. Regardless of where the spe-
cific data collection activities occur in the pre-
remedial process, the major objective of the PA,
SSI, and LSI process is to determine the proper dis-
position of a site (i.e., NPL or non-NPL), based on
the factors found in the HRS. The HRS remains the
primary mechanism by which a site is evaluated for
placement on the NPL.
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Figure 1
PRE-REMEDIAL STAGE OF SUPERFUND PROCESS
PA RESULTS
DISCOVERY

CERCLIS

PRELIMINARY




ASSESSMENT
HIGH
PRIORITY
MEDIUM
PRIORITY
NO FURTHER
REMEDIAL
ACTION
PLANNED

SCREENING
Sis




LISTING
Sis
RESPONSE BY
OTHERS
RCRA
SUBTITLE C&D
SMCRA
NO FURTHER REMEDIAL
ACTION PLANNED
INFORMATION PROVIDED
TO STATES
ASSESSMENT FOR REMOVAL ACTION
The present issue of the Bulletin is based on infor-
mation that is provided in greater detail in the
Federal Register. It will briefly describe the proposed
HRS revisions that affect multiple pathways and
individual pathways and then discuss how the
changes might affect data collection procedures.
The suggested approach involves separating data
collection into the following elements: background
data collection, site/environs reconnaissance, and
sampling. It is important to keep in mind that some
of the information listed under background data col-
lection and site/environs reconnaissance will be
gathered during a PA; however, these data will then
be refined and augmented during the SSI, with lim-
ited environmental samples collected as well. During
the LSI, all appropriate pathways will be evaluated,
and the suggested approach will provide the data
needed for a complete HRS package.
Each of the three data collection elements is dis-
cussed below.
• Background Data Collection Activities—This will
encompass obtaining and reviewing available
reports, maps, and photographs for "desktop"
information that is needed for the HRS. Exam-
ples include U.S. Geological Survey (USGS)
maps and reports to obtain hydrogeologic and
stream flow data, Soil Conservation Service
(SCS) soil-type maps, information from file
searches, data on fishery resources, data on
nearby drinking water sources and usage, aerial
photography to assist in "site" definition as well
as determining land uses and recreation areas
surrounding the site, and census reports to
obtain population figures.
• Site/Environs Reconnaissance—The data collec-
tion activities for site/environs reconnaissance
will include determining source dimensions,
source containment, site accessibility, and the
locations of nearby receptors or targets; confirm-
ing nearby land uses and recreational water use;
and characterizing drainage areas and surface
water bodies (flow type, stream bed morphology,
etc.) if gauging station information is not
available.
•Sampling Strategy—The SSI sampling strategy
should be appropriate to support the recommen-
dation that a site move forward to an LSI or be
designated as "no further remedial action
planned." As stated previously, the purpose of
sampling during the SSI is to identify the types of
contaminants present, to assess whether a
release of hazardous substances has occurred,
and to look for evidence of actual human and
environmental exposure to contaminants. The
LSI sampling strategy should be sufficient to
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document an observed release, when appropri-
ate; characterize sources and waste types;
determine the areal extent of "onsite" contami-
nation; and, if warranted, determine the actual
contamination to drinking water, recreational, and
environmental resources.
Although specific guidance as to the full extent and
character of each phase of the pre-remedial process
is not yet available, it is fair to say that PA, SSI, and
LSI activities will each comprise a subset of the data
collection activities described in the following sec-
tions. A discussion on integrating all aspects of
the pre-remedial process is given at the end of the
Bulletin. The reader should be aware that the items
discussed in this Bulletin are proposed changes.
Several of the proposed factors could be deleted or
modified, based on comments on the proposed HRS
and subsequent revisions for the final HRS.
HRS Revisions Affecting
Multiple Pathways
The following is a summary discussion of the HRS
revisions to factor categories that affect multiple
migration pathways. These categories include haz-
ardous waste quantity, toxicity, observed release,
distance/dilution weighting, risk to the maximally
exposed individual, the use of health-based
benchmarks in evaluating target populations, and
sensitive environments.
Hazardous Waste Quantity: In the current HRS,
hazardous waste quantity is calculated as the
amount of waste deposited containing hazardous
substances. For the revised HRS, the Agency is
proposing a tiered approach that will allow the use
of the best available data. The Agency will consider
three levels of information, in order of preference:
1.	Amount of hazardous constituents (or the actual
amount [mass] of hazardous substances
deposited at the site).
2.	Amount of waste quantity as deposited (total
waste stream).
3.	Disposal capacity of sources (volume or area).
The Agency believes that the tiered approach will
encourage the use of concentration data, when it is
available, and will also provide a site-specific mea-
sure when site waste-stream quantity is not known,
rather than using a generic default value. This
approach applies to the ground water, surface
water, and air pathways. The hazardous waste
quantity factor for these pathways reflects the mag-
nitude and duration of potential releases. For the
onsite exposure pathway, the question is not
whether hazardous substances have been released
and have migrated, but rather whether there is
potential direct contact with the contaminated area.
The waste quantity factor for this pathway would
therefore be evaluated, based on the areal extent of
surficial contamination. If information on the areal
extent of contamination is not available, default
measures applicable to each source type can be
used to assign a value by using the following data
(in order of preference): amount of hazardous sub-
stances deposited at the site, amount of waste as
deposited, and source volumes.
Toxicity: This is one of the factors in the waste
characteristics category that is evaluated for all
pathways. Under the current HRS, toxicity is evalu-
ated based primarily on acute toxicity of hazardous
substances. To account for chronic exposure in
addition to acute exposure, the Agency is proposing
to evaluate hazardous substances for three kinds of
toxicity: acute toxicity, carcinogenicity, and chronic
noncarcinogenicity. In cases where a score can be
derived for all three kinds of toxicity, the highest of
the three scores will become the value assigned for
the toxicity factor. The Agency is also proposing to
include aquatic toxicity ratings to assess potential
risks to ecosystems. Table values for toxicity and
other waste characteristics will be developed so that
the appropriate HRS score for the hazardous sub-
stance^) present can be easily identified.
Observed Release: The scoring approach for this
category will remain the same; however, the Agency
is proposing criteria which more precisely define
when an analytically measured release is to be con-
sidered significantly above background. The pro-
posed criteria are as follows:
•	If no background concentration is detected, a
significant release is three or more times the
detection limit.
•	If the background concentration is greater than
or equal to the detection limit but less than two
times that limit, a significant release is greater
than or equal to three times the applicable back-
ground concentration or greater than or equal to
four times the detection limit, whichever is less.
•	If the background concentration is greater than
or equal to twice the detection limit, a significant
release is greater than or equal to twice the
applicable background concentration.
Distance/Dilution Weighting of Targets: The current
HRS directly weights the population factor by
distance/dilution only for the air pathway. The
Agency is proposing that the revised HRS use
distance- and dilution-weighting factors for all path-
ways to calculate the scores for population and sen-
sitive environments that are potentially exposed to
contamination. The weighting factors would reflect
the expected decreased concentration (i.e., dose)
from exposure as substances disperse or are
diluted.
Risk to the Maximally Exposed Individual (MEI): To
improve the overall assessment of potential risks to
human health, EPA is proposing to consider the
maximally exposed individual, or those individuals
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who are potentially exposed to the highest concen-
trations (and thus receive the highest dose) of the
hazardous substance in question. In most cases,
the MEI risk for the ground water pathway will be
assessed based on the distance from the site to the
nearest drinking water well. (Exceptions are karst
aquifers and wells showing attributable contamina-
tion above health-based benchmarks.) Within the
surface water pathway, the MEI is represented by
the dilution-weighting factor that is assigned to the
nearest drinking water intake. (Exceptions are any
intake showing attributable contamination above
health-based benchmarks.) For the air pathway, the
MEI would be based on the distance from the emis-
sion sources on the site to the nearest individual,
which is represented by the distance to the closest
residence or regularly occupied building or area.
Use of Health-Based Benchmarks: The current
HRS does not consider whether the specific concen-
trations of hazardous constituents in affected media
are above health-based benchmarks, but only
whether these contaminants are significantly above
background levels. In response to SARA directives,
the Agency is proposing revisions to the ground
water and surface water pathways that would take
into account situations where contaminants detected
are not only above background levels, but also
above health-based standards. The target popula-
tion factors in both of these pathways have been
divided into four groups: (1) population exposed to
contaminant concentrations above health-based
benchmarks; (2) population exposed to concentra-
tions that are above background levels, and are
greater than 0.1% of the health-based benchmarks;
(3) population exposed to concentrations that are
above background levels, but do not exceed 0.1%
of the health-based benchmarks; and (4) population
with no documented exposure, referred to as the
potentially exposed population. Those exposed indi-
viduals in the first and second groups are empha-
sized more than those in the third group. The indi-
viduals in the fourth group (individuals with potential
exposure) will be distance/dilution weighted.
Sensitive Environments: In the current HRS, if more
than one sensitive ecosystem exists within the tar-
get distance, only the one with the highest score is
included. The proposed HRS will base the sensitive
environment factor in the surface water and air
pathways on the sum of the values for all appropri-
ate sensitive environments within the target dis-
tance, with each ecosystem weighted for distance or
dilution. For the onsite exposure pathway, only ter-
restrial sensitive environments with observed con-
tamination will be considered. The types of sensitive
environments considered for each pathway have
been significantly expanded as well.
HRS Revisions Affecting
Individual Pathways
GROUND WATER MIGRATION PATHWAY
The proposed revisions to the ground water migra-
tion pathway respond to SARA's stipulation to accu-
rately assess the relative degree of risk to human
health and the environment and to "give a high pri-
ority to facilities where the release of hazardous
substances ... has resulted in the closing of drink-
ing water wells or has contaminated a principal
drinking water supply." The revised ground water
pathway would retain the same structure as in the
current HRS. In both versions, the likelihood of
release to ground water is multiplied by the score
from the waste characteristics category and from
the targets category to obtain an overall pathway
score. However, the individual parameters specific
to each category will change. The proposed
changes include these general considerations:
•	Evaluation of targets and scoring of aquifers—
In the revised HRS, if more than one aquifer
underlies a site, each of the aquifers is scored,
and the aquifer with the highest score is used to
evaluate the site. The targets to be evaluated are
those that draw water from the aquifer being
evaluated and from all overlying aquifers (except
for injection wells and similar situations).
•	Distance weighting of targets—Because, under
most circumstances, the concentration of haz-
ardous substances declines as the substances
migrate from a site, the revised HRS would apply
distance/dilution weighting to targets located at
varying distances from a site to better reflect the
differential exposures and risks. For the ground
water pathway, distance/dilution weighting of
targets would be used for the potentially
exposed populations.
•	Distances considered in evaluating aquifers and
targets—EPA is proposing to extend the target
distance limit within which population is evalu-
ated from 3 to 4 miles from the sources. Target
populations drawing water from wells beyond the
4-mile limit could be counted if they exhibit docu-
mented contamination attributable to the site.
The Agency is proposing to evaluate aquifer
interconnections within a 2-mile radius and aqui-
fer discontinuities within a 4-mile radius.
•	Aquifer interconnections and discontinuities—
Interconnected aquifers can be combined for
scoring purposes. Two or more aquifers are con-
sidered interconnected if they act as a single
hydrologic unit. Evidence of hydrologic intercon-
nection includes pump tests, contamination
shown in a deeper layer, absent or discontinuous
confining layers, or indications that an upper
aquifer provides significant if not total recharge
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to the lower aquifer. Aquifer discontinuities result
when a geologic, topographic, or other structural
feature completely transects an aquifer, and thus
prevents water from flowing out of or Into the
aquifer. If a discontinuity exists within the target
area, any part of the aquifer beyond the disconti-
nuity is not counted unless the discontinuity does
not entirely transect the target area.
•	Consideration of karst aquifers—In the current
HRS, sites with karst terrain are not given any
special consideration. The proposed revisions
would reflect the high potential for contaminants
to migrate through karst aquifers with little
reduction in concentration of hazardous
substances.
Among the other proposed changes to the HRS for
the ground water pathway are the following:
Potential to Release: This category contains one
new factor: sorptive capacity. The physical state fac-
tor has been deleted for the revised HRS. Four
other factors—depth to aquifer, hydraulic conductiv-
ity, net precipitation, and containment—have been
revised.
•	Sorptive Capacity—This is a new factor, which
reflects the potential for geologic materials to
chemically absorb substances and thereby retard
hazardous substance migration. The sorptive
capacity factor is based on the composition and
thickness of geologic materials beneath the site.
•	Depth to Aquifer/Hydraulic Conductivity—In the
current HRS, the depth to aquifer factor assigns
a value of zero to an aquifer deeper than 150
feet. In the revised HRS, aquifers with depths up
to and exceeding 800 feet would be assigned
values using a matrix that combines depth with
hydraulic conductivity. The scoring for hydraulic
conductivity is now based on the thickness and
properties of all intervening strata, not just the
one with the lowest permeability. In combination,
these two factors give an indication of the rela-
tive travel time required for substances to reach
an underlying aquifer.
•	Net Precipitation—Under the revised HRS, net
precipitation is determined by using a methodol-
ogy based on the summation of 12 monthly net
precipitation values {with negative values set to
zero), rather than seasonal or annual net precipi-
tation. As a result, the net precipitation value will
better reflect the potential of hazardous sub-
stances to migrate to aquifers.
•Containment—The revised HRS expands the
range of values that could be assigned for this
factor and provides more detailed descriptions of
each type of containment.
Waste Characteristics: Under the current HRS, a
score was assigned for waste characteristics by
evaluating the toxicity and persistence of hazardous
substances. In the revised HRS, the Agency is pro-
posing to combine toxicity with mobility rather than
persistence for the air and ground water pathways.
The toxicity/mobility of the substances identified
does not have to be researched, but generally will
be available in look-up tables. Waste quantity is also
a factor under this category. Refer to the previous
discussion on waste characteristics in the section
HPS Revisions Affecting Multiple Pathways.
Ground Water Targets: Currently, the ground water
targets category is evaluated by considering two
factors: ground water use and a matrix factor that
combines distance to the nearest well with the pop-
ulation served by ground water. Four factors are
proposed to be evaluated under this category for
the revised HRS: ground water use, Wellhead pro-
tection areas, the MEI, and population served seg-
mented into four types of exposure (see HRS Revi
sions Affecting Multiple Pathways).
To support the proposed revisions to the ground
water pathway, some more detailed, site-specific
information may need to be collected. Recommen-
dations for background data collection, site/environs
reconnaissance, and sampling strategy with respect
to the ground water pathway are discussed below.
Background data collection:
•Collect information on the type and quantity of
waste disposed at the site and source
containment.
•Seek archival aerial photography to assist in
"site" definition.
•Collect USGS reports, well logs, and other avail-
able geologic data to delineate stratigraphy near
the site.
•	Collect data on the population drinking ground
water drawn from within the target distance limit,
allocated to seven distance rings. If more than
one aquifer is used, determine the population
drinking from each aquifer.
•	Look for documented quantitative evidence of
nearby drinking water wells contaminated with
substances attributable to the site. Qualitative
evidence can be used to establish sampling
locations.
Site/environs reconnaissance:
•Consider using current aerial photography if
defining the "site" is difficult to do during the site
reconnaissance.
•Take photographs, detailed notes, and dimension
measurements needed to determine "as depos-
ited" waste locations, containment, and waste
quantity.
•	Confirm the MEI location/distance, as well as
other major drinking water targets.
Sampling strategy:
•	Sample waste areas to determine the types of
hazardous substances present and to estimate
source dimensions, if appropriate.
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•	Sample to establish an observed release if such
is likely; the closest downgradient well is the
best candidate; in general, "extending" the site
is no longer a consideration.
•	Consider the need to drill boreholes or perform
geophysical studies to determine stratigraphy
underlying the site if existing data are not
adequate.
•	Sample selected nearby drinking water wells, if
they are likely to be contaminated with sub-
stances attributable to the site.
SURFACE WATER MIGRATION PATHWAY
Some of the major changes to the surface water
pathway under consideration are in response to
SARA's requirements regarding the need to take
into account, to the extent possible, the damage to
natural resources that may affect the human food
chain. Another major requirement of SARA is that
the revised HRS appropriately assess the risk from
use of contaminated (or potentially contaminated)
surface waters for recreation or potable drinking
water. To meet the general and specific provisions
of SARA, the surface water pathway will consider
threats to human health through drinking water, the
human food chain, and recreational water use, as
well as threats to sensitive environments. The
Agency is proposing to place more emphasis on
environmental damage and to expand the types of
environments considered. Each of these threats will
be evaluated separately for waste characteristics
(except hazardous waste quantity) and targets. The
likelihood of release category evaluation will be
common to all threats, as will the proposed target
distance increase to 15 miles downstream for both
flowing and static water. Populations and environ-
ments that are potentially exposed to contamination
will be dilution weighted. The weighting factor is
related to flow characteristics of the surface water
body, and reflects the diminishing risks as sub-
stances are diluted.
As in the current HRS, the likelihood of release cat-
egory is evaluated as an observed release or as a
potential to release. The observed release category
is discussed in the section HRS Revisions Affecting
Multiple Pathways. The potential to release category
assesses the likelihood for hazardous substances to
migrate from a site to surface water. It is proposed
that this category replace the route characteristics
and containment factors from the current HRS with
two new factors; potential to release by overland
flow and potential to release by flooding. These two
factors are discussed below:
Potential to Release by Overland Flow: A score for
overland release potential can be derived by calcu-
lating the sum of two factors: runoff value and dis-
tance to surface water. The runoff value includes
three parameters—runoff curve number, rainfall, and
upgradient drainage area. The runoff curve number
is based on land use and hydrologic soil type
between the source and surface water. It is a mea-
sure of the ability of soils and the type of land sur-
face to minimize runoff. The rainfall parameter has
been proposed to change from a 1-year, 24-hour
rainfall to a 2-year, 24-hour rainfall. The drainage
area provides a measure of the amount of land sur-
face area that can carry runoff across the site. The
factor for distance to the nearest surface water
body is a measure of the potential for hazardous
substances transported via overland flow from the
site to reach a surface water body. For the pro-
posed HRS, only surface water bodies within 2
miles of the site are to be evaluated.
Potential to Release by Flooding: This proposed
new category considers the potential for hazardous
substances to be released to a surface water body
when a site is flooded. The potential for release due
to flooding is determined by multiplying a flood con-
tainment factor (i.e., methods that are being used, if
any, to prevent the release of hazardous substances
if a site is inundated by a flood) by a flood fre-
quency factor. The value assigned will depend on
the expected frequency of flooding, for which con-
tainment is judged to be inadequate.
The waste characteristics of hazardous substances
are evaluated for each of the four threats by adding
a value from a matrix of toxicity and persistence to
a value based on hazardous waste quantity. Haz-
ardous waste quantity and toxicity are discussed
in the section HRS Revisions Affecting Multiple
Pathways. Persistence of hazardous substances is
evaluated based on the expected reduction of the
hazardous substance concentration as a result of
five decay processes over the target distance limit.
A value for persistence will be assigned, based on
the half-life of the hazardous substance in surface
water and the type of surface water body (e.g., river,
stream, or lake). The calculation of a value for waste
characteristics differs slightly for each threat cate-
gory or subpathway, as discussed below.
Waste Characteristics for Drinking Water Threat:
For each substance actually or potentially released
from the site, persistence will be combined with tox-
icity in a matrix. The substance with the highest
toxicity/persistence value will be used in calculating
the drinking water waste characteristics category
value.
Waste Characteristics for Human Food Chain
Threat: Toxicity and persistence will be evaluated
for those substances with the highest bioaccumula-
tion potential value. Otherwise, hazardous waste
quantity and toxicity/persistence are calculated in
the same way as the drinking water waste charac-
teristics factor. However, the hydrologic category
used to assign the persistence value will be based
on the predominant type of water body between the
probable point of entry and the nearest fishery.
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Waste Characteristics for Human Recreation
Threat: Toxicity and persistence will be evaluated
for those substances with the highest dose adjust-
ing factor value. The dose adjusting factor repre-
sents the ratio of the dose to an individual that
would be obtained via recreation to the dose that
would be obtained via consumption of the same
water.
Waste Characteristics for Environmental Threat:
Ecosystem toxicity will be combined in a matrix with
persistence and will be evaluated for all hazardous
substances at the site which are available to migrate
to the surface water body. Because exposure of
sensitive environments is more likely to be chronic
than acute, ecosystem toxicity scores will be
assigned by using the following hierarchy of data:
EPA chronic water quality criteria for the substance;
EPA acute water quality criteria for the substance;
or the lowest LC50 value reported in peer-reviewed
literature for the substance.
The targets category reflects the human population
and sensitive environments possibly at risk from an
actual or potential release of hazardous substances.
As mentioned previously, each of the four threats is
evaluated separately as a subpathway for waste
characteristics and targets. Targets are discussed
below.
Drinking Water Targets: A value for the drinking
water targets score is assigned based on evaluating
surface water use, population, and the MEt. The
MEI is discussed in the section HRS Revisions
Affecting Multiple Pathways. The surface water use
factor is divided into two subfactors: drinking water
use and other water uses. The drinking water use
factor takes into account whether the drinking water
is a public or private water supply and whether
alternative drinking water supplies exist. Other sur-
face water uses include commercial crop irrigation,
livestock watering, and food preparation. The popu-
lation factor is an indicator of the number of people
actually or potentially at risk from exposure to haz-
ardous substances in drinking water.
This factor will consider population groups seg-
mented by actual or potential exposure, as previ-
ously discussed in the section on the Use of Health-
Based Benchmarks.
Human Food Chain Targets: The human food chain
target value is derived by summing two factors:
population and fishery use. The population factor
value is the sum of two subfactors: potential human
food chain contamination and actual human food
chain contamination. Actual human food chain con-
tamination is demonstrated when there is attribut-
able contamination above Food and Drug Adminis-
tration (FDA) action level standards, or when a
fishery has been closed and the hazardous sub-
stance that caused the closing has been docu-
mented in an observed release from the site. If the
conditions for actual human food chain contamina-
tion are not met, scoring of the fishery is based on
potential contamination. The fishery use factor
reflects the nature and utility of fisheries located
along the target distance limit. A value is assigned
for commercial fishing, subsistence fishing, and rec-
reational or sport fishing.
Human Recreational Targets: This category has
been added to consider threats from dermal contact,
inhalation, and ingestion during water recreation
activities (i.e., swimming or fishing). The recreational
use value is derived from an accessibility/attractive-
ness factor (e.g., designated swimming beaches,
boat ramps, boat rental facilities, marinas, camp-
grounds, etc.) for the recreation area, and from the
number of people residing within the specified target
distance categories for the recreation area.
Environmental Targets: This category will be used
to evaluate the threat associated with actual or
potential release of hazardous substances to
surface-water-related sensitive environments. The
revised HRS places more emphasis on actual envi-
ronmental exposure and expands the types of envi-
ronments to be considered. Sensitive environments
are divided into three exposure groups: those with
contamination above ecological-based benchmarks;
those with contamination not exceeding ecological-
based benchmarks, but above background levels;
and those that could potentially be contaminated.
Recommendations for the surface water data collec-
tion methodology are discussed below.
Background data collection:
•	Collect USGS reports and other available data on
hydrology near the site; also obtain topographic
maps, floodplain maps, and SCS soil-type maps.
•Collect information on type and quantity of waste
deposited and on source containment.
•	Seek archival aerial photography to assist in
"site" definition and determination of overland
flow paths.
•	Determine the size of the target population,
based on the location of water supply intakes
within the target distance limit.
•	Collect data on fishery production, recreational
water use, and sensitive environments within the
target distance.
•	Obtain the required average flow rates at target
locations from USGS or other sources.
•	Look for documented quantitative evidence of
"attributable" contamination near drinking water
intakes, sensitive environments, fisheries, and
recreation areas. Qualitative evidence can be
used to establish sampling locations.
Site/environs reconnaissance:
•	Consider using current aerial photography to
help define the "site" and overland flow paths.
•	Take photographs, detailed notes, and dimension
and distance measurements needed to determine
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"as deposited" waste locations, containment,
waste quantity, and characteristics of the over-
land flow path and drainage area for each
source.
•	Estimate stream width and depth, as well as the
type of flow (quiet flowing or turbulent), or
develop estimates of watershed area if data on
flow rates are not available.
•	Recommend visual reconnaissance to document
the accessibility/attractiveness of recreation
areas adjacent to surface water bodies and to
characterize "quiet flowing" streams.
Sampling strategy:
•	Sample waste areas to determine the types of
hazardous substances present and to estimate
source dimensions, if appropriate.
•	Sample primarily to document an observed
release near the probable point of entry into a
surface water body.
•	Recommend sampling at nearby drinking water
intakes, fisheries, recreation areas, and sensitive
environments which meet both of the following
conditions: contamination is likely at the sampling
location, and contamination is likely attributable
to the site.
•Consider sampling sediments to "extend" the
point from which to measure the 15-mile target
distance limit if contamination attributable to the
site is likely to be found and if there is a signifi-
cant target which could be included.
AIR MIGRATION PATHWAY
The principal revision to the air pathway responds
to Section 105(a) of SARA and concerns the addi-
tion of a mechanism to evaluate potential air con-
tamination in the absence of data to document an
observed release. Observed release has not
changed substantially for the air pathway (but do
refer to the section HRS Revisions Affecting Multiple
Pathways). The general changes to the hazardous
waste quantity, toxicity, and target factors are also
discussed in HRS Revisions Affecting Multiple
Pathways.
Three factors are used to evaluate a site's potential
to release hazardous substances: source type,
source mobility, and source containment. Source
type considers the size and type of waste disposal
locations (e.g., drums, lagoon, landfill, etc.). Each
emission source on the site that meets a minimum
size requirement is assigned a source-type factor
value. Source mobility reflects the propensity of a
hazardous substance to migrate from a source as a
gas or a particulate. For gaseous substances, the
mobility factor will be based on three physical/
chemical characteristics: vapor pressure, Henry's
constant, and dry relative soil volatility. (Look-up
tables will be provided to give these values for a
number of substances.) For particulates, the mobility
factor will be evaluated, based on the Thornthwaite
Precipitation-Effectiveness (PE) index, a surrogate
measure of the relative moisture content of the soil.
The third factor, containment, evaluates the ability of
natural or man-made barriers to inhibit the release
of hazardous substances.
Recommendations for the data collection methodol-
ogy to evaluate the air pathway are discussed
below.
Background data collection:
•	Collect information on the type, quantity, and dis-
posal mode of waste deposited, as well as any
historical information on air releases from the
site.
•	Seek archival aerial photography to assist in
"site" definition.
•	Collect data on population distribution and loca-
tion of sensitive environments within the target
distance, allocated to eight distance categories;
the target distance will remain 4 miles.
•	Collect information to identify the closest of each
of the six types of land uses within 4 miles
(commercial/industrial/institutional, single-family
residential, multi-family residential, parks, prime
agricultural, and non-prime agricultural).
Site/environs reconnaissance:
•Take photographs, detailed notes, and dimension
measurements needed to determine emission
sources, containment, "as deposited" waste
locations, and waste quantity.
•	Consider using current aerial photography if
defining the "site" during the site reconnais-
sance is difficult.
•	Recommend visual reconnaissance to determine/
confirm the distance to the MEI and the closest
of each of the six types of land uses and their
distance from the site.
Sampling strategy:
•	Suggest discretion/prioritization in obtaining
samples intended for Contract Laboratory Pro-
gram (CLP) analysis; based on site conditions,
climatology, and equipment requirements, sam-
pling to prove an observed release may not be
appropriate at all sites.
•	As a general rule, formal sampling for air release
data may not be necessary; consider collecting
data for the potential to release category; also
field screening data may be used to determine
whether a return air-sampling site visit is
warranted.
ONSITE EXPOSURE PATHWAY
One of the most significant changes to the HRS
under evaluation is the addition of a fourth pathway,
the onsite exposure pathway. Although the current
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HRS includes a direct contact pathway that evalu-
ated the potential for direct exposure to hazardous
substances at a site, the score for this pathway was
not included in the total HRS migration score. How-
ever, to respond to SARA's directives and based on
an assessment of approximately 100 Records of
Decision, a new exposure pathway was developed,
and it is proposed that its score be included in a
site's overall HRS score. To score any of the factors
under this pathway, there must be documented, ana-
lytical evidence of contamination above background
levels in soils, seeps, surficial or shallow buried
wastes, or in surface impoundments. If there is no
such evidence, this pathway will receive a score of
zero. Specific factors of the onsite exposure path-
way are described below.
Likelihood of Exposure (Resident or Onsite
Population): The resident population likelihood of
exposure would be evaluated based on the pres-
ence of contamination and not on release potential.
If there is no analytical evidence of soil contamina-
tion or of hazardous substances present in sources
containing shallow wastes (e.g., lagoons), then this
factor and the onsite exposure pathway will receive
a value of zero.
Targets (Resident or Onsite Population): The
resident-population targets category is based on
three factors: high-risk population, total resident
population, and terrestrial sensitive environments.
For any of these three population groups to be con-
sidered, there must be observed contamination
attributable to the site within the property boundary
of a residence, school, or day-care center, or within
the boundaries of a terrestrial sensitive environment.
The three resident-population target factors are dis-
cussed below.
• High-risk population—This population group
includes children under 7 years of age and is
evaluated because research has shown that chil-
dren have a higher soil ingestion rate than
adults. The children counted should include
those who live on or attend school or day care
on the contaminated property.
Total resident population—The total resident
population includes everyone who lives on or
goes to school or day care on the contaminated
property.
Sensitive environments—For this pathway, only
terrestrial sensitive environments are considered.
Aquatic ecosystems are addressed in the surface
water pathway.
Likelihood of Exposure (Nearby Population): This
category will be scored by considering the quantity
of waste on the site and the accessibility and fre-
quency of use of the site. The waste quantity will be
evaluated primarily based on the area of contamina-
tion. For those sources where the areal extent of
contamination is not readily determined, default
mechanisms applicable to each source type can be
used to assign a value. Accessibility reflects the
measures taken to limit access (natural or man-
made barriers). As with Likelihood of Exposure (Resi-
dent Population), if there is no evidence of soil con-
tamination, or of hazardous substances present in
sources containing shallow wastes, then this factor
and the pathway will receive a value of zero.
Targets (Nearby Population): Individuals will be
counted in the nearby population if they live or
attend school or day care within 1-mile travel
distance of the contaminated site.
Recommendations for background data collection,
site/environs reconnaissance, and sampling strategy
for the onsite exposure pathway are discussed
below.
Background data collection:
•	Look for existing file information, analytical data,
and aerial photography to examine the types of
waste disposed and the patterns of disposal.
•Obtain population data within 1-mile travel dis-
tance of the "site" (possibly subset of air data).
The 1-mile travel distance is the overland dis-
tance an individual would have to travel to reach
the site.
•	Refine population data, if necessary, to identify
"high risk" populations for the resident
population.
•Determine whether the site is near any terrestrial
sensitive environments (subset of air data).
Site/environs reconnaissance:
•	Measure areas of apparent contamination (e.g.,
stained soils) or of shallow waste disposal areas
(e.g., lagoons).
•Take photographs and field notes to document
the accessibility factor.
•Conduct a visual reconnaissance to determine/
confirm the location of residences, day-care cen-
ters, schools, and terrestrial sensitive environ-
ments, and to determine the 1-mile travel
distance.
Sampling strategy:
•	The onsite pathway requires analytical demon-
stration of onsite surficial contamination; other-
wise, the pathway receives a score of zero.
•	For the onsite pathway, the "site" is defined by
the extent of attributable surficial contamination.
It is not necessary to define the full extent of
onsite contamination or all locations of surficial
contamination. Carefully evaluate "prime" loca-
tions to find contamination and try to define
areas with as few samples as possible. Make
maximum use of screening techniques using
portable instruments to narrow down/focus on
areas to sample for complete laboratory analysis.
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• Sample primarily to document surficial contami-
nation at residential terrestrial properties,
schools, day-care centers, and terrestrial sensi-
tive environments where there is a strong
probability that contamination exists at these
locations.
After reading all of this, you may feel a bit over-
whelmed. It is important to keep in mind that this is
a building process. Much of the data collected dur-
ing the PA and SSI will be used for the LSI or will
be augmented by data collected at the LSI stage. It
is also important to remember that the revised HRS
allows for new parameters to be considered, but it
does not mean that data for all of them have to be
collected. For instance, the Agency is proposing to
use the amount of hazardous constituents as a
means of calculating the hazardous waste quantity
factor so that it is a more accurate reflection of rela-
tive risk. However, the Agency realizes that deter-
mining the amount of hazardous constituents within
the hazardous wastes at a site is, in many cases,
technically difficult. Therefore, a tiered approach has
been proposed so that if these concentration data
are not available, waste quantity as deposited could
be used, as could source volume or source area. It
is also worth remembering that if a factor under a
specific category (e.g., total resident population
under the targets category for the onsite exposure
pathway) is assigned the maximum value, it may not
be necessary to collect data for the remaining fac-
tors (i.e., high-risk population and terrestrial sensi-
tive environments). However, do keep in mind that
values for some factors may be changed during the
review and comment period.
What, you might ask, does all of the preceding
mean for those planning PAs and Sis (both SSIs
and LSIs) under the revised HRS? First, in terms of
background data collection, one should research
and review available information sources to define
the hydrogeology underlying the site; identify, locate,
and inventory drinking water supplies within the new
target distances; gather USGS stream flow data and
fishery production data for surface water bodies
near the site; obtain U.S. Census Bureau data to
determine population within the designated ring dis-
tances; collect and review pertinent existing water,
soils, and air monitoring data; and search files (e.g.,
State, EPA Region, etc.) for appropriate HRS data.
With regard to site/environs reconnaissance data
collection, one should attempt to delineate the "as
deposited" site; identify nearby land uses and recre-
ational water use; verify important distances (e.g.,
nearest well, school, residence) and dimensions
(e.g., waste quantity areas, volume); and record suf-
ficient observational information to satisfy the
requirements for the containment factor. Last, in
terms of revised site inspection sampling strategies
(primarily applicable to LSIs), it is important to incor-
porate the following new data considerations: the
onsite exposure pathway requires analytical demon-
stration of onsite contamination; emphasis should
be placed on sampling to document actual exposure
to drinking water contamination if there is reason to
believe that such exposure exists; source and onsite
samples may be needed to identify substances
present and to delineate the "as deposited" site.
Sampling primarily to "extend" the site is generally
no longer appropriate—emphasis should be on
proving the observed release. Sampling during SSIs
(limited to 10-20 samples per site) should focus on
identifying the types of contaminants present,
assessing whether a release of hazardous sub-
stances has occurred, and looking for evidence of
actual human and environmental exposure to
contaminants.
Guidance for conducting PAs, SSIs, and LSIs using
the revised HRS will be available from EPA Head-
quarters and Regional personnel once the HRS is
published as a final rule. Whereas the Bulletin pro-
vides information on the collection of all of the data
needed to complete the pre-remedial process, the
guidance documents will focus on what specific data
collection activities should be completed at each
individual stage. Finally, please do refer to the
Federal Register (Vol. 53, No. 247, pp. 51962-52081,
December 23, 1988) for full information regarding
the proposed revised HRS.
The SI/HRS Information Bulletin is published by the
United States Environmental Protection Agency. For
more information, contact Kevin Donovan at EPA
Headquarters at (202) 475-9749 or Helene Kasser at
NUS Corporation, (703) 522-8802.
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