EPA 910/9-92-019
INTERIM FINAL
GUIDELINES FOR DEVELOPING RISK,-BASED CLEANUP LEVELS AT
RCRA SITES IN REGION 10
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
REGION 10
WASTE MANAGEMENT BRANCH
SEATTLE, WASHINGTON 98101
Work Assignment No.
EPA Region
Date Prepared
Contract No.
Prepared by
PRC Project Manager
Telephone
EPA Work Assignment Manager
Telephone
041-R300801
10
March 31, 1992
068-W9-0009
PRC Environmental Management, Inc.
Susan Turnblom
206/624-2692
Marcia Bailey
206/553-0684
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LIST OF TABLES
Table Page
1 POTENTIAL EXPOSURE PATHWAYS FOR HUMAN RECEPTORS 7
2 PRIMARY EXPOSURE PATHWAYS FOR ECOLOGICAL RECEPTORS 25
LIST OF FIGURES
Figure Page
1 OVERVIEW OF RCRA CLEAN-UP LEVEL DEVELOPMENT 4
111
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ACRONYMS AND ABBREVIATIONS
AAC Alaska Administrative Code
CERCLA Comprehensive Environmental Response, Compensation and Liability Act
CFR Code of Federal Regulations
DEQ Oregon Department of Environmental Quality
DDE dichlorodiphenyltrichloroethene
DDT dichlorodiphenyltrichloroethane
EPA U.S. Environmental Protection Agency
FR Federal Register
FY fiscal year
g grams
HEAST Health Effects Assessment Summary Tables
IRIS Integrated Risk Information System
L liters
lethal concentration to SO percent of the organisms
lowest-observed-adverse-effect-level
cubic meters
maximum contaminant level
milligrams per kilogram per day
micrograms per liter
NOAEL no-observed-adverse-effect-level
OSWER Office of Solid Waste and Emergency Response
PCB polychlorinated biphenyl
ppm parts per million
RCRA Resource Conservation and Recovery Act
RDX hexahydro- 1 ,3,5-trinitro- 1 ,3,5-triazine
RFI RCRA facility investigation
USC United States Code
WAC Washington Administrative Code
LC50
LQAEL
m
MCL
mg/kg-day
IV
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GLOSSARY
Action levels: Health-based and environment-based contaminant levels for environmental media
(i.e., soil, groundwater, surface water, air) determined by EPA to be indicators for protection of
human health and the environment. If contamination exceeding these action levels is identified
during a RCRA facility investigation, EPA or an authorized state agency must decide if further
analysis is required. Action levels, if exceeded, typically trigger a corrective measures study.
Acute effects: Adverse human or ecological impacts caused by very short-term exposure to
contaminants.
Bioaccumulation: The process by which substances that are very slowly metabolized or excreted
increase in concentration in living organisms as they breathe contaminated air, drink
contaminated water, or eat contaminated food.
Bioconcentration: The ratio of a contaminant concentration in living tissue to its concentration
in a specific environmental medium.
Biomagnification: The process by which concentration of a substance increases as it is ingested
by smaller organisms that are eaten in turn by larger organisms, thereby moving up the food
chain.
Bio-uptake: A process in plants in which water and minerals from the soil are absorbed and
incorporated within the plant. Contaminants (especially ones that are highly soluble in water)
may also be absorbed and incorporated by plants through this process.
Chlorotic (vegetation): A condition of green plants seen as a yellowing disease of the green parts
of the plants.
Chronic effects: Adverse human or ecological impacts caused by long-term exposure to
contaminants.
Cleanup levels: The contaminant concentrations to which a contaminated environmental medium
(e.g., soil, groundwater, surface water, air) must be cleaned or remediated, in order to adequately
protect human health and the environment. Although similar to action levels, cleanup levels
differ in the following ways:
EPA or an authorized state establishes cleanup levels on a site-by-site basis during
the remedy selection process
The current and reasonably expected future uses of the site may be taken into
account when establishing the cleanup levels
Concentration response evaluation: The process of characterizing the relationship between the
concentration of a contaminant in an exposure medium (such as air or water) and the incidence
of response in the exposed population.
Dose-response evaluation: The process of quantitatively evaluating toxicity information and
characterizing the relationship between the dose of a contaminant received and the incidence of
adverse health effects in the exposed population.
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Ecological eodpoint: A physical, chemical, or biological parameter that is characteristic of an
organism, population, or ecosystem and is potentially affected by contaminants. Endpoints may
include effects on individual organisms, communities, and ecosystems (e.g., reduced larvae
production in a particular species, reduction of key populations, or disruption of community
structure in an ecosystem).
Ecosystem: The integrated and interdependent populations of species along with their remains
and the minerals, chemicals, water, and atmosphere on which they depend for sustenance and
shelter.
Exposure pathways: The various ways a contaminant in a given medium can come into contact
with a receptor. For example, possible exposure pathways for contaminated, soil include ingestion
of the soil, inhalation of the soil as dust, inhalation of volatile organics emanating from the soil,
and dermal contact with the soil.
Exposure route: The way an environmental contaminant can enter an organism. The three
primary routes are ingestion, inhalation, and dermal .contact.
Hazard index: An estimate of the risk associated with a specified exposure to a noncarcinogenic
contaminant, expressed as the ratio of a substance exposure level over a specified time period to a
reference dose for that substance derived from a similar exposure.
Indicator species: A species whose life history is well understood and whose condition or health
is selected to be representative of the health of a larger ecosystem.
Linearized multistage model: One of a number of mathematical models and procedures used to
extrapolate from carcinogenic responses observed at high doses to responses expected at low
doses.
Mutagen: Any substance that can cause a change in genetic material.
Receptor An organism (human, plant, or animal) that is potentially exposed to chemical
contamination from a site.
Reference dose: An estimate (with uncertainty spanning an order of magnitude or greater) of a
daily exposure level for the human population, including sensitive subpopulations, that is likely to
carry no appreciable risk of deleterious effects during a lifetime.
Slope factor: A plausible upper-bound estimate of the probability of an individual developing
cancer as a result of a lifetime of exposure to a particular level of a potential carcinogen.
Systemic toxicant: A chemical that produces adverse health effects distant from the point of
contact through absorption and distribution in the body.
Threshold: The exposure level of a chemical at which a physiological effect begins to be evident.
Toxicity value: A numerical expression of a dose-response relationship for a particular substance.
The most common toxicity values used in EPA risk assessments are reference doses (for
noncarcinogenic effects) and slope factors (for carcinogenic effects).
VI
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EXECUTIVE SUMMARY
This guidance document provides procedures for developing human and ecological health-
based cleanup levels for contaminated sites undergoing corrective action and clean closure under
the Resource Conservation and Recovery Act (RCRA). The procedures are presented in a step-
by-step approach intended for use by U.S. Environmental Protection Agency (EPA) permit
writers and regulatory compliance officials. The analysis presented here will enable RCRA site
managers to identify sites for which federal or state promulgated action levels may be used as
cleanup criteria, versus sites requiring exposure-based risk calculations to address site-specific
problems. This document also describes situations that are likely to require expert technical
assistance. Application of these procedures is intended for RCRA sites where hazardous waste or
hazardous constituents have been released and where contaminated environmental media (that is,
soil, surface water, sediment, groundwater, or air) and contaminant concentrations have been
identified by means of environmental sampling and analysis.
Using the step-by-step process presented in this document for developing cleanup levels,
regulatory personnel should be prepared to answer the following questions for a contaminated site
undergoing corrective action and clean closure under RCRA:
Are all receptors and pathways likely to be affected by site contamination
identified?
Are promulgated standards or criteria available for use as cleanup levels?
Can action levels published in 55 FR 30865-30867 (proposed Subpart S
Appendix A) be used as cleanup levels? (These can be used only if the potential
receptors are human.)
Must cleanup levels be calculated using published reference doses and slope
factors?
Must cleanup levels be adjusted to account for multiple contaminants or multiple
exposure pathways?
Is there a potential ecological problem at the site requiring special consideration
during the cleanup level determination and evaluation?
This document provides equations for calculating cleanup levels when there are no
promulgated standards for contaminants of concern. In addition, references are provided for
state standards and protocols that should be used or considered for use in developing cleanup
levels. These guidelines recommend consultation with human health risk assessment specialists
and ecologists for the more complex, technical aspects of the assessment process.
Vll
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1.0 INTRODUCTION
This guidance document provides procedures for developing human and ecological health-
based cleanup levels for contaminated sites undergoing corrective action and clean closure under
the Resource Conservation and Recovery Act (RCRA). The procedures are presented in a step-
by-step approach intended for use by U.S. Environmental Protection Agency (EPA) permit
writers and regulatory compliance officials. The analysis presented here will enable RCRA site
managers to identify sites for which promulgated action levels (described in detail in Sections 2.3
and 3.3) may be used as cleanup criteria, versus sites requiring exposure-based risk calculations
to address site-specific problems. This document also describes the situations that are likely to
require expert technical assistance. Application of these procedures is intended for RCRA sites
where hazardous waste or hazardous constituents have been released and where contaminated
environmental media (that is, soil, surface water, sediment, groundwater, or air) and contaminant
concentrations have been identified by means of environmental sampling and analysis.
This approach is intended to be consistent with the Comprehensive Environmental
Response, Compensation and Liability Act (CERCLA), known as Superfund. Where RCRA
guidelines and proposed rules do not specify procedures, Superfund guidance is used.
This guidance document is a companion document to Northwest RCRA Corrective Action
Strategy (EPA 1990b), and also complements RCRA Facility Investigation (RFI) Guidance (EPA
1989b).
This document is organized into two main parts: Section 2 focuses on developing cleanup
levels protective of human health, and Section 3 focuses on developing cleanup levels protective
of ecological species and systems.
1.1 HUMAN HEALTH AND ECOLOGICAL RISK ASSESSMENTS: AN OVERVIEW
Human health and ecological risk assessments as described in Chapter 8 of the RCRA
facility investigation guidance (EPA 1989b) are conducted in two steps: identification of
potential exposure pathways, and comparison of site contaminant concentrations with human
health and ecological criteria (action levels). Action levels for carcinogens are set as
concentrations associated with an excess upper bound lifetime cancer risk of IxlO"6 due to
continuous constant lifetime exposure.
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Under the RCRA corrective action process, an action level is the contaminant
concentration that triggers an investigation such as a corrective measures study. Examples of
action levels include but are not limited to the following:
Groundwater Maximum contaminant levels (MCLs)
* Soil Concentrations listed in 55 FR 3086S-30867, Appendix A
(proposed Subpart S), July 27, 1990
Surface water MCLs for drinking water; water quality criteria for multiple
water uses
Air Concentrations listed in 55 FR 30865-30867, Appendix A
(proposed Subpart S), July 27, 1990
s
Often the cleanup level is set at the action level, because action levels are calculated to be
health-protective. Cleanup levels may be less stringent than action levels, if it can be
demonstrated that the higher cleanup level concentrations are protective of human health and the
environment. Cleanup levels may be more stringent than action levels if there are multiple
contaminants at a site or multiple exposure pathways for an individual chemical. Also, state
regulations may be more restrictive than action levels.
In order to clean-close a facility or part of a facility, it must be demonstrated that the
cleanup levels are protective of human health and the environment or that they do not exceed
background contaminant levels.
If action levels are not available or are not sufficiently protective, risk-based cleanup
levels can be calculated for a contaminated site once contaminants of concern, contaminated
media, and important exposure pathways are identified. These calculations incorporate toxicity
values and exposure assumptions to derive an acceptable concentration for each contaminant in
each environmental medium.
An example of an action level that may not be sufficiently protective is the MCL for
benzene, which is 5 micrograms per liter (/ig/L). The excess lifetime cancer risk calculated for
residential ingestion of water contaminated with 5 fig/L benzene is 8x10~6, which is above the
target risk level of IxlO*6. The health-based concentration for benzene is 1 pg/L (calculated
using the equation presented in Appendix 1). It may be appropriate to set the cleanup level at
the lower risk-based level, depending on site-specific conditions. In some cases the acceptable
risk-based level may be lower than the analytical detection limit, and it may be necessary to
select a value other than the risk-based level for cleanup.
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1.2 SETTING RISK-BASED CLEANUP LEVELS : THE DUAL PROCESS
Both human and ecological health should be considered when calculating cleanup levels at
a site. Cleanup levels are always calculated to be protective of human health. Cleanup levels
based on ecological health need to be determined if specific exposure pathways and ecological
receptors are identified at a site. The procedures for calculating cleanup levels based on human
risk assessment are different from those used for calculating cleanup levels based on ecological
risk assessment. Both procedures should be applied at each site; the processes can be conducted
either simultaneously or sequentially.
A quantitative approach to deriving human Health-based cleanup levels is presented here,
while the approach to developing ecological risk-based cleanup levels is qualitative. For human
health risk assessment, numerical standards are used and calculations are performed to yield
specific contaminant concentrations in each environmental medium. In ecological risk
assessment, the many site-specific conditions and impacts resulting from the complex
interrelationships among chemicals taken up by the ecological receptors are weighed and assessed
in a series of judgements on the relative risks. In this way, one or more contaminant-medium-
receptor pathways are identified as the greatest threats to ecological health at a site. An
ecologically based cleanup level is determined for each contaminant in each medium by weighing
considerations of technical feasibility and the economic, social, and ecological value of species at
risk.
Figure 1 shows the dual process of developing cleanup levels for a RCRA site. The left-
hand side of the flowchart is specific to human health-based cleanup levels, and the right-hand
side shows the steps in developing cleanup levels based on ecological assessment.
Before either process is begun, contaminants of concern at a site must be identified. The
list of site contaminant concentrations should be produced from RCRA facility investigation
reports, corrective measures study reports, sampling reports, or monitoring reports.
Once site contaminants are identified, the first step in the human health risk assessment is
identification of exposure pathways. If state or federal criteria or standards have been
promulgated for an identified exposure pathway and contaminant of concern, these criteria can
be used as cleanup levels. If no promulgated criteria exist for a specific contaminant or
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Ecological
Risk Assessment
Human Health
Risk Assesment
Figure 1. Overview of RCRA Clean-Up Level Development
il OVCMVCWMW IO/MI
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pathway, Appendix A of Subpart S should be consulted. If the site contaminant concentration is
above concentrations listed in Appendix A, Subpart S, the values listed in Appendix A of
Subpart S should be used as cleanup levels. It should be noted that Subpart S action levels are
based on residential land use assumptions. If the contaminant is not given in the Subpart S,
Appendix A table, then land use should be determined for a site. If industrial land use
assumptions are appropriate for use in developing cleanup levels, then Subpart S assumptions are
not applicable. Once land use is determined, appropriate exposure assumptions should be made
and combined with toxicity criteria to calculate risk-based concentrations. If cleanup levels are
to be developed based on industrial land use, then exposure assumptions found in the "Standard
Default Exposure Factors" can be used (EPA 1991b). If no toxicity criteria exist, a risk assessor
should be consulted. If toxicity criteria exist and there are numerous contaminants of concern at
a site, then contaminants contributing the greatest risk can be determined and cleanup levels can
be calculated for these contaminants.
Once contaminants are identified, a field survey is conducted and potential receptors are
identified. Next it is determined whether exposure pathways exist for specific receptors. If not,
there is no need to calculate ecologically based cleanup levels for the site. If exposure pathways
are identified for specific receptors, then it should be determined whether promulgated criteria
or standards exist for the contaminant of concern in the appropriate medium. If criteria have
been established, then these criteria should be considered as cleanup levels. If not, it is likely
that consultation with an ecologist will be needed to assist with defining assessment and
measurement endpoints and determining whether adequate data are available, whether the system
can be modeled, and whether on-site sampling is needed. Once all the necessary data are
collected and evaluated, cleanup levels can be decided upon. Some sites will only require
calculation of human health risk-based cleanup levels. However, for sites requiring development
of both types of cleanup levels, the two levels should be compared and the more stringent of the
two adopted as the cleanup level.
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2.0 CLEANUP LEVELS BASED ON HUMAN HEALTH RISK ASSESSMENT
This section describes the steps to follow when developing cleanup levels based on human
health risk assessment. The main elements of the procedure are:
Identification of exposure pathways
Identification of available promulgated criteria or standards
Use of Subpart S Appendix A
Use of risk-based cleanup calculations
Once preliminary cleanup levels have been derived, they can be adjusted to account for multiple
contaminants and multiple pathways, as needed.
2.1 IDENTIFICATION OF EXPOSURE PATHWAYS
It is important to identify the complete exposure pathways and important receptors at a
site so that health-based cleanup levels that are protective of all potential receptors can be
developed.
Table 1 summarizes potential exposure pathways for human receptors at a typical site.
Exposure pathways are identified within each pertinent exposure scenario. There are several
exposure scenarios that may be applicable at a given facility. Those most commonly evaluated
are the industrial and residential exposure scenarios. The residential scenario is the more
conservative of the two (i.e., it results in more protective cleanup levels). Agricultural and
recreational scenarios may be important depending upon facility location and identification of the
most exposed individual. Most often the residential or industrial exposure scenario is used for
developing cleanup levels. However, if the individual subject to the greatest exposure to site-
related contaminants is the recreational user of a nearby stream or lake, then a recreational
scenario may be sufficiently protective.
The pathways listed in Table 1 should be evaluated to identify the contaminated media
for which cleanup levels should be developed. At some sites, a small fraction of the potential
exposure pathways may be relevant. At other sites, all pathways listed may be important.
Cleanup levels should be determined for a specific medium, such as soil, rather than for each
individual exposure pathway. For soils, it is important to consider the potential for contaminants
in soil to reach groundwater. Some contaminants are relatively immobile, such as inorganic
contaminants (e.g., lead, cadmium) and will not be likely to pose a significant threat to
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TABLE 1
POTENTIAL EXPOSURE PATHWAYS FOR HUMAN RECEPTORS*
Contaminated
Medium
Exposure
Scenario
Potential
Exposure
Pathway
Important for
Calculation of
Cleanup Levels?
Groundwater
Residential/agricultural
UM at potable water
Ingestion of water
Inhalation of volatile*
Dermal contact with
water
'Transfer to food crops
or livestock and
subsequent ingestion
Yes, if volatile* present
Yes, for organic
contaminants of
concern
Site-specific
determination
Industrial use a*
potable water
Ingestion of water
Inhalation of volatile*
Dermal contact with
water
Yes
Site-specific
determination
Site-specific
determination
Surface water and
sediment
Residential/agricultural
or industrial use as
potable water
Ingestion of water
Inhalation of volatile*
Dermal contact with
water
Transfer to food crops
or livestock and
subsequent ingestion
Yes
Yes, if volatile! present
Ye*, for organic
contaminant* of
concern
Site-*pecific
determination
Recreational u*e or
subiiitence fiihing
Consumption of fish
and seafood
Site-specific
determination
Recreational use or
trespasser
Ingection of water
Dermal contact with
water
Ingestion of sediment
Dermal contact with
sediment
Site-specific
determination
Site-specific
determination
Site-specific
determination
Site-specific
determination
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TABLE 1 (continued)
Contaminated
Medium
Exposure
Scenario
Potential
Expoiurc
Pathway
Important for
Calculation of
Cleanup Level*?
Soil
Residential or
agricultural
Incidental toil ingestion
Dermal contact with
oil
Yes
Inhalation of
, p articulates/volatilei
from coil
Consumption of
produce, meat, milk
Ye.
Site-specific
determination
Soil a* potential source
to groundwater
Site-specific
determination
Industrial
Soil ingestion
Dermal contact with
soil
Inhalation of
particulates/volatUes
from soil
Soil as potential source
to groundwater
Site-specific
Air
Residential or
agricultural
Industrial
Inhalation of
p articulates/volatile*
from stack or other
emissions
Inhalation of
p articulates/volatile!
from stack or other
emissions
Site-specific
determination
Site-specific
determination
a Modified from EPA (IBOld)
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groundwater quality. Other contaminants, such as the organics benzene and trichloroethylene, are
relatively soluble in water and much more mobile and likely to mdVe from the soil to the
groundwater. The cleanup level calculated for each medium should include consideration of all
pathways that contribute to exposure or risk. For example, the cleanup levels for soil should be
developed using all possible exposure routes for soil that are appropriate at a site (e.g., ingestion,
dermal contact, inhalation of soil as dust particles).
There are three primary routes by which toxic agents can enter the body:
Ingestion of contaminated water and food (e.g., fruits, vegetables, fish, shellfish),
and incidental ingestion of soil
Inhalation of vapors or dust '
Dermal contact with water or soil
For an exposure pathway to be considered important or complete at a site, there must be a
receptor that is exposed to contamination via this pathway. A receptor is any organism that may
be exposed to the contamination. In this section, receptor refers to any human (e.g., trespasser,
schoolchild, area resident) who might be exposed to site-related contaminants by one or more
pathways.
When developing cleanup levels for air, the most exposed individual outside the facility
boundary should be considered. For clean closure of a waste unit, it is assumed that the most
exposed individual is at the boundary of the unit. For cleanups under the corrective action
process, the most exposed individual is identified on a site-specific basis. Air concentration
should be measured at the location of the human receptor who is subject to the greatest exposure.
Equations are presented in Appendix 1 for use in calculating cleanup levels based on
residential exposures. If other exposure scenarios such as industrial, agricultural, or recreational
are used to calculate cleanup levels, Region 10 risk assessment guidance (EPA 1991d) and Risk
Assessment Guidance for Super fund (EPA 1989c) should be consulted for the appropriate
equations.
2.2 IDENTIFICATION OF PROMULGATED CRITERIA AND STANDARDS
When developing cleanup levels for a site, the site manager must take into consideration
promulgated federal and state standards or criteria for environmental media contaminated by site
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activities. Currently, federal standards exist for drinking water supplies and surface water bodies
(marine and freshwater).
MCLs have been established for a number of inorganic and organic chemicals in drinking
water supplies. These concentrations should not be exceeded in groundwater or in surface water
unless there are compelling scientific reasons to accept such exceedances.
At this time, the other promulgated federal criteria are the national ambient air quality
standards for key pollutants and the ambient water quality criteria. Concentrations are
established for surface waters. Standards exist for protection of human health from ingestion of
§
contaminants in water and fish, and for protection of human health from fish ingestion only.
These water quality criteria are provided for protection of aquatic life also.
An example of promulgated state criteria is found in the Washington Model Toxics
Control Act (WAC 173-340), which establishes cleanup levels for groundwater and soil. In
Oregon, the Department of Environmental Quality cleanup policy establishes background
concentrations as target cleanup levels for RCRA facilities when feasible.
Information on specific state standards and criteria is available through the following
agencies:
Alaska Department of 907-563-6529
Environmental Conservation
Juneau, Alaska
Idaho Department of Health 208-334-0550
and Welfare, Division of
the Environment
Boise, Idaho
Oregon Department of 503-229-5696
Environmental Quality
Portland, Oregon
Washington Department 206-459-6000
of Ecology
Olympia, Washington
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2.3 CLEANUP LEVELS FOR CONTAMINANTS LACKING CRITERIA AND
STANDARDS
If there are no promulgated criteria or standards (as outlined above) for the chemical of
concern, then the procedures described in this section should be followed. This section explains
when to use the Subpart S Appendix A action levels as cleanup levels, and when health-based
cleanup levels should be calculated. It may be necessary to adjust both types of cleanup levels to
account for multiple contaminants or multiple exposure pathways, as well as the potential for soil
contaminants to leach to groundwater, as explained at the end of this section.
2.3.1 Use of Subpart S Appendix A Action Levels as Cleanup Levels *
If a contaminant is listed in Subpart S Appendix A, a concentration-based screening can
be performed as follows:
1) Determine the site contaminant concentration in the specific medium.
2) Compare the site concentration to the value listed in Subpart S Appendix A. If
the concentration is below that listed in Subpart S Appendix A, then eliminate the
contaminant from consideration for cleanup. If the concentration is equal to or
greater than that listed, then use the Subpart S Appendix A value as the cleanup
level.
3) Read Sections 2.4 and 2.5 below to determine if adjustments to the cleanup levels
are needed for multiple contaminants or multiple pathways.
If the contaminant is not listed in Subpart S Appendix A, then cleanup levels should be calculated
as described in Section 2.3.2 below.
2.3.2 Calculation of Health-Based Cleanup Levels
If no promulgated criteria or standards are available, and if the contaminant is not listed
in Subpart S Appendix A, then health-based cleanup levels must be calculated. This section
explains land use classification, standard assumptions (federal, regional, and state), and critical
toxicity values that must be used in the calculations. In addition, guidance is provided for
identifying the contaminants posing the greatest health threats, in order to focus the cleanup
efforts.
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2.3.2.1 Classification of Land Use
The evaluation of a site to determine appropriate cleanup levels is based in part upon the
appropriate land use scenario. Depending on assumptions regarding future site uses, either a
residential scenario or an industrial scenario is typically chosen. A residential scenario results in
more conservative (i.e., more protective) cleanup levels, because it is assumed that adults and
children live or will live on the site and are or will be exposed to contaminants 24 hours a day.
In the industrial scenario, exposure is assumed only for adults and only during working hours.
The residential scenario is usually used for calculating cleanup levels. An example of a possible
exception is for sites in Washington that fulfill the industrial criteria listed in the Model Toxics
Control Act cleanup regulation. The residential scenario should be used if workers or owners and
their families live on-site at an industrial facility, of if future use of the property might include
residential use.
A site may be considered industrial for cleanup of soil in Washington if it meets all of the
following requirements of the Model Toxics Control Act cleanup regulation:
The site is zoned or otherwise officially designated for industrial use
The site is currently used for industrial purposes or has a history of use for
industrial purposes
Adjacent properties are currently used for industrial purposes or are designated
for industrial use
The site is expected to be used for industrial purposes for the foreseeable future
because of site zoning, statutory or regulatory restrictions, comprehensive plans,
adjacent land use, and other relevant factors
If the site meets the requirements for industrial classification, then the risk-based cleanup
level may be based on 10*5 excess lifetime cancer risk instead of 10*6 (for soil contamination by
carcinogenic contaminants only).
Determination of cleanup levels for groundwater, surface water, and air is the same for
all sites regardless of land use classification as industrial or residential for soil cleanup.
Groundwater and surface water are always cleaned up to target levels such as MCLs or drinking
water standards unless there are extenuating site-specific circumstances.
If the air pathway is a significant exposure pathway for a site, cleanup levels are
calculated for a specific location depending on the type of cleanup planned. For clean closure it
is assumed that the most exposed individual is at the unit boundary, and air contaminant
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concentrations must be equal to or below the health-based level at the unit boundary. Under the
corrective action process, the most exposed individual is identified on a site-specific basis and
may be someone living across the street from the facility, a worker living on the site, or a
resident a mile away, depending on site characteristics.
2.3.2.2 Use of Appropriate Exposure Assumptions
The exposure assumptions used in this document to calculate cleanup levels are found in
Appendices D and E of the proposed Subpart S rule (EPA 1990a). These exposure assumptions
were developed to address human health concerns, and are consistent with current federal and
Region 10 CERCLA guidance. These exposure assumptions are based on residential exposure
assumptions and should be used in calculations at most sites.
For sites that can be cleaned up based on industrial exposure assumptions, the industrial
exposure assumptions provided in EPA (1991b), Standard Default Exposure Factors, should be
used in cleanup level calculations.
2.3.2.3 Use of Critical Toxicity Values
Critical toxicity values are reference doses and slope factors that are used frequently in
risk assessments. Reference doses are used to evaluate the noncarcinogenic toxic effects of
chemicals; slope factors are used to evaluate the carcinogenic effects of chemicals.
2.3.2.3.1 Toxicity Values for Noncarcinogens
The reference dose for a specific chemical, expressed in units of milligrams per kilogram
per day (mg/kg-day), represents an estimated intake rate that is unlikely to produce measurable
adverse effects over a lifetime of exposure. The reference dose is usually based on the
relationship between the dose of a noncarcinogen and the occurrence of systemic toxic effects in
experimental animals or humans. It is a specific assumption of this method that there is a
threshold intake rate below which toxic effects do not occur. Generally, a no-observed-
adverse-effect-level (NOAEL) or dose is divided by uncertainty factors to derive a reference
dose that is intended to protect the most sensitive members of the population.
The uncertainty factors are usually multiples of 10, with each factor representing a
specific area of uncertainty inherent in extrapolation from the available data. Uncertainty factors
are used to account for the following:
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Variation in the general population (intended to protect sensitive subpopulations
such as children and the elderly)
Extrapolation from animal data to humans
Derivation of a NOAEL from a subchronic study rather than a chronic study
Use of a lowest-observed-adverse-effect-level (LOAEL) rather than a NOAEL
Once a reference dose for a chemical is verified by EPA, it is used to evaluate long-term
noncarcinogenic risks at a site. This reference dose is compared with the expected site dose
(calculated using the procedure described in Appendix 1) to determine whether chronic effects
might occur. Chronic effects are those adverse health effects that result from long-term exposure
to relatively low levels of a substance. A hazard indjex is calculated to determine if
noncarcinogenic toxic effects may be of concern based on an estimated exposure level or dose.
The hazard index expresses the likelihood that exposure will result in noncarcinogenic toxic
effects. It is the ratio of an exposure level to a reference dose. A hazard index of 1.0 or less
indicates that long-term exposure to the chemical is not likely to cause an adverse health effect.
Hazard indices are not probabilistic estimates of risk, however.
2.3.2.3.2 Toxicity Values for Carcinogens
For chemicals classified by EPA as potential human carcinogens, risk is evaluated
differently, because noncarcinogenic and carcinogenic effects are believed to have entirely
different mechanisms of action. Typically, animal carcinogenicity studies are conducted using
relatively high doses. To evaluate the probability of developing cancer at the lower doses more
frequently encountered in the environment, the linearized multistage model is used. This
mathematical model expresses excess cancer risk as a function of exposure. The model is based
on the assumption that even a single, low-dose exposure to a carcinogen may result in cancer. In
other words, it is assumed that there is no threshold dose for carcinogens.
Using the linearized multistage model, the 95th percentile confidence limit of the slope
from the dose-response curve is calculated. The dose-response curve is generated by graphically
plotting response against dose. The slope of the dose-response curve defines the steepness of the
curve. The linearized multistage model assumes that a line drawn through the dose-response data
points rises at a rate or steepness that is likely to overestimate rather than underestimate the true
rate or steepness of the dose-response curve. This slope factor, expressed in units of (mg/kg-
day)*1, provides a health-protective estimate of the probability of cancer developing from
exposure over a lifetime. By definition, there is only a 5 percent chance that the probability of
developing cancer is higher.
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To calculate the cancer risk associated with exposure to a contaminant at a site, the dose
from a given exposure route first must be estimated. Then the estimated dose is multiplied by
the chemical-specific slope factor to derive the estimated risk. Cancer risk is expressed as the
chance of an individual in a population developing cancer, e.g., one in a million or 1x10 .
EPA assigns weight-of-evidence classifications to potential carcinogens. Under this
system, a chemical is classified in one of six groups, defined as follows:
Group A - chemicals for which sufficient data exist to support a causal association
between exposure to the agent and cancer in humans
Group Bl - chemicals for which there is limited evidence of carcinogenicity from
human exposure studies but sufficient evidence of carcinogenicity from animal
studies
Group B2 - chemicals for which there is inadequate evidence of carcinogenicity
from human exposure studies but sufficient evidence of carcinogenicity from
animal studies
Group C - chemicals for which there is limited evidence of carcinogenicity from
animal studies
Group D - chemicals for which the carcinogenicity data base is inadequate
Group £ - chemicals exhibiting no evidence of a carcinogenic response in humans
or animals
The reference doses or slope factors used to calculate cleanup levels are available from the
EPA Integrated Risk Information System (IRIS), a computer data base (EPA 1991c). Reference
doses or slope factors not available from IRIS may be listed in the most recent EPA Health
Effects Assessment Summary Tables (HEAST) (EPA 199la), which are updated quarterly. If
there is no reference dose or slope factor listed for a chemical, the following EPA offices may be
consulted:
Health and Environmental Environmental Criteria
Assessment Section and Assessment Office
Region 10 EPA Mail Stop 114
ES-098 26 West Martin Luther King Dr.
1200 Sixth Avenue Cincinnati, Ohio 45268
Seattle, Washington 513-569-7300
206-553-6699 FTS 684-7300
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2.3.2.4 Identification of Contaminants Presenting the Greatest Health Risks
It should be determined whether only a few or many contaminants pose the primary
threat. Chemicals that contribute a small percentage of the overall threat as determined by a
risk-based screening process should be eliminated. The screening process is outlined below. This
process was developed by Region 10 EPA to address multiple contaminants at CERCLA sites.
1) List maximum concentration of each contaminant in each medium
2) Calculate risk-based concentrations for each contaminant, as described in
Appendix 1 of this document
3) Eliminate a contaminant from screening if the maximum concentration in water is:
, »
<10 cancer risk screening value, or
<0.1 hazard index screening value
4) Eliminate a contaminant from screening if the maximum concentration in soil is:
<10"7 cancer risk screening value, or
<0.1 hazard index screening value
5) Include remaining contaminants for further consideration in calculating cleanup
levels
As stated in Step 2 above, the screening level should be determined using the equations provided
in Appendix 1. As indicated in Step 3, the default screening level at which carcinogenic
contaminants can be eliminated is based on 10~6 risk in groundwater. Step 4 shows that for soil,
contaminants with concentrations exceeding 10"7 risk should be included for further
consideration in calculating cleanup levels for a site. This lower risk factor is used because
additional pathways such as dermal contact and inhalation are not taken into account in the
calculations and could result in significantly higher exposures for some chemicals. For
noncarcinogens, because multiple pathways and multiple contaminants may result in cumulative
effects, the screening concentration should be based on a hazard index of 0.1, rather than 1.0,
which is the usual level of concern.
It can be assumed that if no single sample maximum value exceeds a concentration
representing a human health risk concern, total exposure to the contaminant is not of concern.
Six inorganic constituents that are not associated with toxicity to humans under normal
circumstances are aluminum, calcium, iron, magnesium, potassium, and sodium. No quantitative
toxicity information is available for these elements from EPA sources, and they can generally be
eliminated from consideration during development of cleanup levels.
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Additional contaminant characteristics to be considered (in consultation with a risk
assessor) include the following:
Persistence
Mobility (including potential for soil contaminants to leach to groundwater)
Natural background concentration
Frequency of detection
Degradation products
Bioaccumulation characteristics
Treatability
If after screening it is found that more than one or two contaminants contribute to the
health threat, then cleanup levels must be adjusted to take multiple contaminants into
consideration (see Section 2.4 and Appendix 1).
2.3.2.5 Calculation of Cleanup Levels
Cleanup levels should be calculated using the equations provided in Appendix 1. As an
example, assume that RDX (hexahydro-l,3,5-trinitro-l,3,5-triazine), an ordnance or munitions
compound, is the contaminant of concern in groundwater and that ingestion of groundwater is
the only pathway to be considered. RDX is not listed in Subpart S Appendix A. Consulting the
IRIS data base (EPA 1991c) or HEAST (EPA 199la), it is found that RDX has toxicity values for
both toxic noncarcinogenic and carcinogenic effects. The slope factor is 0.11 (mg/kg-day)*1, and
the oral reference dose is 0.003 mg/kg-day.
Using the equations presented in Appendix 1, the following cleanup levels can be
calculated for carcinogenic and noncarcinogenic effects of RDX in groundwater.
2.3.2.5.1 Carcinogenic Effects
The equation for calculating health-based cleanup levels in water is:
CM - [R x 70 kg x 70 yr]/[CSF x 2L/day x 70 yr]
(See Appendix 1 for an explanation of the individual terms in the equation).
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Substituting the appropriate values for R and CSF, the equation becomes
CM « [1
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after the risk-based screening process, then the target risk level is adjusted to 0.1 rather than J.O
(i.e., divide the calculated contaminant concentration [Ca, CB, CJ By 10).
If more than 10 contaminants remain after risk-based screening, then a risk assessor
should be consulted for assistance in adjusting cleanup levels to take all the contaminants into
consideration.
2.5 ADJUSTMENT OF CLEANUP LEVELS FOR MULTIPLE PATHWAYS
If there are multiple exposure pathways, cleanup levels should be adjusted to be
protective against potential exposure by more than one pathway. The cleanup levels for
individual contaminants obtained from Subpart S Appendix A, or derived by methods given in
Appendix 1, should be divided by two if there are two exposure pathways. If there are three
exposure pathways for a given medium at a site, divide by three, and so on.
The potential for contaminants to leach from soil into groundwater and the subsequent
degradation of groundwater should be taken into consideration when developing cleanup levels.
Cleanup levels developed on the basis of soil ingestion only may not be low enough to protect the
groundwater from degradation. Currently there is no specific guidance for quantifying or
estimating risks to groundwater from contaminated soil. However, EPA headquarters is
investigating various modeling approaches to address this issue.
2.6 RESULT OF HUMAN HEALTH-BASED ANALYSIS
Once the human health risk assessment process and the step-by-step process for
developing cleanup levels are understood, regulatory officials should be prepared to answer the
following questions regarding a contaminated site undergoing corrective action or clean closure
under RCRA:
Have receptors and pathways that are likely to be affected by site contamination
been identified?
Are promulgated federal or state criteria or standards available?
Can action levels published in Subpart S Appendix A be used as cleanup levels?
Must cleanup levels be calculated using published reference doses and slope
factors?
Must cleanup levels be adjusted to account for multiple contaminants or multiple
exposure pathways?
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Risk-based cleanup levels are associated with varied levels of uncertainty, depending on
many factors (e.g., confidence that land use assumptions are correct). If residential land use
assumptions were used to develop cleanup levels, then the cleanup levels may be more protective
than they need to be if the site is an industrial facility. The toxicity values (slope factors and
reference doses) used in calculations are associated with a number of uncertainties. These include
the following:
Animal studies are used to develop human toxicity criteria
Chronic effects are often extrapolated from subchronic or acute studies
Sensitive subpopulations (such as children or the elderly) may not have been
considered ,
Other sources of uncertainty stem from how the cleanup levels are calculated. For
example, cleanup levels in soil are derived based on the ingestion route of exposure. This may
not be protective enough if the inhalation or dermal contact routes of exposure are important
pathways for the chemicals of concern.
Additional uncertainty for soil cleanup levels is associated with whether or not the soil
contaminants will leach to groundwater. Risk-based cleanup levels may not be low enough to
protect against this occurrence.
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3.0 CLEANUP LEVELS BASED ON ECOLOGICAL RISK ASSESSMENT
This section follows the steps outlined in the flowchart under cleanup levels based on
ecological assessment (Figure 1). The first steps are performance of a field survey and
identification of potential receptors. The next step is to identify exposure pathways for specific
receptors. If no pathways exist at a site, it is not necessary to develop cleanup goals based on
ecological assessment. If exposure pathways do exist for specific receptors at or near a site, then
the next step is determining whether federal or state standards or criteria exist for the exposure
pathway or medium. Laws and regulations containing promulgated standards in Region 10 are
listed in Section 3.3. If there are criteria or standards for a contaminant of concern, these criteria
may be used as cleanup levels, if appropriate. EPA has developed and promulgated specific
ambient water quality criteria for protection of aquatic life in surface waters (EPA 1986b).
General guidelines are provided for evaluating the ecological health-protectiveness and
practicality of the standards.
If there are no promulgated criteria or standards (such as water quality criteria) for the
contaminants of concern, consultation with an ecologist may be needed to define ecological
assessment and measurement endpoints for the site and to determine if data are available for the
identified endpoints. If sufficient data are not available, the ecologist can assist in determining
whether the potentially impacted system can be modeled using existing site information, or
whether additional sampling and ecological assays will be needed before the ecological effects of
site contamination can be assessed.
Because of the complexity of variables involved in identifying appropriate ecological
receptors and contaminant concentrations that may cause harm to them, a quantitative analysis of
ecological risk, similar to the approach to human health risk, is not available. Therefore, the
ecological factors are generally incorporated qualitatively rather than quantitatively into the
development of cleanup levels.
The following sections describe in detail the steps to follow and questions to be asked
when examining the potential ecological impact of site contamination.
3.1 PERFORMANCE OF FIELD SURVEY AND IDENTIFICATION OF POTENTIAL
RECEPTORS
The field survey can be performed at the same time as the field inspection. The purpose
of the survey is to confirm the presence of potentially affected biota and determine whether
symptoms of environmental damage are apparent. Visible signs of environmental contamination
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and degradation should be recorded. Potential receptors should be noted. Plant and animal
species, plant and animal communities, or entire ecosystems may be classified as ecological
receptors. These receptors can be identified with the aid of information from local, state, and
federal agencies and published species lists. The following questions should be answered during
this portion of the process:
Is there obvious evidence of environmental degradation that may be related to site
contamination?
Such evidence may include the following:
Stained, barren soils
Chlorotic (i.e., yellowed, discolored) or other signs of stressed vegetation
Unusually thick layer of leaves or other detritus (i.e., dead vegetation)
Dead or unhealthy organisms near sites of contamination in amounts above normal
(e.g., dead fish on the shores of lakes or streams)
Visible or other sensory evidence of chemical contamination (e.g., oily film or
foam on surface water, chemical odor from water or soils)
Reports by employees or neighbors of unusual environmental occurrences (e.g.,
dead birds, dying trees, absence of usual visitor or resident species, unusual
behavior exhibited by animals)
If any of these conditions is evident, then an ecologist should be consulted to assist with
incorporating these environmental factors into the development of cleanup levels.
Are there threatened or endangered species that are likely to be exposed to site contaminants?
To identify species that are threatened or endangered, 50 CFR 17.11 and 17.12 (U.S. Fish
and Wildlife Service List of Endangered and Threatened Wildlife and Plants) may be consulted.
To identify critical habitats (necessary for breeding, feeding, nesting, and sustaining life)
for endangered or threatened species, the U.S. Fish and Wildlife Service may be consulted.
Published information is available on location of critical habitats. Additionally, The Nature
Conservancy maintains a data base for identification of critical wildlife habitats in specific
regions.
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If there are endangered or threatened species that depend on the site as critical habitat,
the following laws and regulations apply:
Endangered Species Act of 1973 (16 USC 1531 et seq.)
50 CFR Part 200
50 CFR Part 402
Fish and Wildlife Coordination Act (16 USC 661 et seq.)
«
Can animals and plants be identified in contaminated areas of the ecosystem?
Once contaminated areas are identified at a site, the organisms (receptors) that nest, feed,
grow, reproduce, or otherwise come in contact with the contaminated areas can be identified.
Information on geographical distribution of fish and wildlife may be obtained from many
sources including the following:
U.S. Forest Service
U.S. Bureau of Land Management
U.S. Soil Conservation Service
U.S. Fish and Wildlife Service
* Biologists at local universities, park services, and state agencies
The completed field survey should provide information necessary for determining
whether there is currently ecological damage as a result of site contamination or whether there
are potential ecological receptors. If no ecological receptors are identified, cleanup levels derived
to protect human health should be used. If potential ecological receptors are identified, then the
steps outlined below should be followed to develop cleanup levels that are protective against
ecological impacts.
3.2 IDENTIFICATION OF EXPOSURE PATHWAYS FOR SPECIFIC RECEPTORS
The effect of any contaminant on an ecological receptor is highly dependent on both the
receptor and the chemical properties of the contaminant.
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When a contaminant enters an ecosystem it may reach a receptor by various exposure
pathways depending on the organism, the contaminant, and the ecosystem. For example, water-
soluble contaminants such as metals that are found in soils are frequently taken up by plants.
These contaminated plants can then pose risks to both ecological and human receptors. Common
ecological exposure pathways are shown in Table 2. Depending on the contaminant and the
contaminated medium, one or all of the pathways listed in the table might exist at a site.
Before the effects of a contaminant on a receptor organism can be evaluated, it is
necessary to know the quantity of the chemical reaching the receptor, which depends on
characteristics of the contaminant, the organism, and the environment. The following questions
should be answered during this portion of the process:
t
Which organisms are exposed to contaminants from the site, and what are the significant routes
of exposure?
Appendix 2 provides two examples of hypothetical sites that have several potential
ecological exposure pathways and ecological receptors. Potentially important exposure pathways
for specific receptors at a hypothetical landfill site include:
Vegetation growing in contaminated soil
Fish swimming in a nearby stream
Other aquatic organisms in contact with sediments and surface water in the stream
Terrestrial animals feeding on aquatic organisms
Terrestrial animals in contact with stream water
Biota in the wetland ecosystem
Birds feeding and nesting in the area
Once important pathways and receptors that may be in contact with contaminants are
identified, it is possible to identify the environmental media that require cleanup to protect the
environment from further degradation. For example, if fish in a nearby stream might be
affected by site contaminants in the water, it may be important to clean up contaminated surface
water. If vegetation is growing in contaminated soil, then the soil requires cleanup to levels that
are protective of vegetation or the organisms likely to depend on the vegetation for food.
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TABLE 2
PRIMARY EXPOSURE PATHWAYS FOR ECOLOGICAL RECEPTORS
Dermal/
Inhalation/ Ingestion Ambient
Receptor Respiration Food/Water Contact
Animals
Plants
Mammals x
Birds x
Amphibians x
Reptiles t x
Insects x x
Other invertebrates x x
Finfish x x x
Mollusks x x
Crustaceans x x
Terrestrial plants x*
Aquatic plants x*
*Bio-uptake
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At this point it may be evident that there are no likely ecological receptors or that there is
no pathway for exposure. In that case it will not be necessary to go further in the process.
Cleanup levels based on human health risk are expected to be sufficiently protective in these
instances.
If ecological exposure pathways are likely to exist for site contaminants, then the
following questions should be answered with respect to the specific contaminants of concern.
Are the contaminants of concern at the site mobile in the environment (i.e., are they soluble and
likely to migrate)?
Mobile contaminants that tend to migrate off-site have greater potential for reaching
more environmental receptors. To determine the mobility of specific contaminants, the following
resources may be consulted:
Vershueren, Karel, 1983. Handbook of Environmental Data on Organic Chemicals.
2nd edition. Van Nostrand Reinhold Co.
Kabata-Pendias, A. and H. Pendias, 1984. Trace Elements in Soils and Plants.
CRC Press.
Mobile receptors within an ecosystem can spread contamination from the site as well.
Herbivores (i.e., plant eaters) such as deer and mice may eat contaminated vegetation, then drop
contaminated feces off-site. Birds may carry contaminated vegetation off-site for nesting.
Predators eating contaminated prey may spread contamination through excretory channels.
Do the contaminants of concern bioaccumulate or biomagnify?
Bioaccumulation is the process by which a substance is concentrated in a certain organism
or tissue. The extent and nature of exposure is affected by the tendency of an organism to
bioaccumulate the chemical and by the kind of tissue in which the chemical is stored.
Bioconcentration is expressed as the ratio of the contaminant concentration in tissue to the
concentration in a specific medium, and is a way to measure bioaccumulation. Contaminants that
bioaccumulate may have increased potential to cause toxicity in a receptor organism or in a
receptor that feeds on that organism. The following references may be helpful in determining
the bioaccumulation potential of individual contaminants:
Vershueren, Karel, 1983. Handbook of Environmental Data on Organic Chemicals.
2nd edition. Van Nostrand Reinhold Co.
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Kabata-Pendias, A. and H. Pendias, 1984. Trace Elements in Soils and Plants.
CRC Press.
Biomagnification is the process in which a substance moves up the food chain, being
ingested by small organisms that are eaten in turn by larger organisms. The substance becomes
increasingly concentrated as it moves up the chain. Contaminants that biomagnify may not cause
impacts on the original receptor (such as algae that absorb contaminants in a pond) but may have
serious impacts on predator species at the top of the food chain (such as birds that eat fish that
eat algae). The following example illustrates biomagnification in the food chain. In a Dutch elm
disease control program, the pesticide DDT (dichlorodiphenyltrichloroethane) was applied as a 6
percent (i.e., 6 parts per hundred) suspension in water. Directly after treatment, leaves had a
DDT residue of 183-283 parts per million (ppm), underlying soil had 1-18 ppm, and leaves
falling in autumn had 20-30 ppm. Earthworms eating the fallen leaves had DDT residues of 120
ppm, and robins dying from eating earthworms contained residues in the brain in excess of 340
ppm.
If there are potentially affected ecological receptors, and the contaminants at a site are
expected to bioaccumulate or biomagnify in the receptors, adjustments in cleanup levels may be
needed. The types of contaminants that are likely to bioaccumulate or biomagnify are usually
highly lipophilic [such as DDT, polychlorinated biphenyls (PCBs), and dioxins] or highly stable
(like DDT, PCBs, and metals). A few parts per million of PCBs in sediments can move up the
food chain through zooplankton, fish, and marine birds, with resulting concentrations of several
parts per thousand in the marine birds.
Are the contaminants degraded or transformed into other toxic compounds in the ecosystem?
Biotic and abiotic reactions in the environment can greatly impact the toxicity of many
contaminants. For example, ethylene glycol (i.e., antifreeze) and cyanide can both be oxidized to
form innocuous breakdown products. Chromium VI, under specific environmental
circumstances, is reduced to the less toxic chromium III. Other products, however, can become
more persistent or toxic when released in the environment. Elemental mercury can be converted
to methyl mercury by microbial methylation in sediments. Methyl mercury is fat-soluble and
readily bioaccumulates, biomagnifying from plankton to fish, to fish-eating birds. Fish may
carry high body burdens of mercury with minimal observable effects. Higher predators, such as
birds and mammals, would be at greater risk. Overall, methylation of inorganic compounds, such
as mercury, may lower the acute toxicity (when compared to the inorganic salt), but the
ecological risk is increased because of the tendency of the methylated compound to
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bioaccumulate. The pesticide DDT is converted to DDE (dichlorodiphenyltrichloroethene); it is
DDE, not DDT, that is the primary cause of eggshell thinning and resultant mortality of certain
bird species. Depending on site contaminants and their potential breakdown products, additional
sampling may be required or cleanup levels might require adjustment to account for more toxic
breakdown products.
Are the contaminants distributed in specific zones of the ecosystem?
Contaminant disposal locations are important factors in identifying the impacted
environmental receptors at a site. Ecosystems are divided into vertical and horizontal zones that
vary in biotic and abiotic components. The distribution of a contaminant is an important factor
in identifying the affected organism and exposure pathways. For example, a contaminant
deposited on soil can affect soil microorganisms, soil invertebrates, vegetation, and decomposition
processes, while a contaminant deposited on the forest canopy (i.e., tree tops) affects vegetative
growth and tree dwellers.
In another example, a chemical of high molecular weight and low water solubility such as
PCBs deposited in an aquatic habitat where they would tend to sink to the bottom and partition
into the sediments poses less threat to organisms near the surface than to bottom dwellers.
Are the contaminants indirectly toxic to the receptors?
A contaminant may not be directly toxic to an organism through ingestion or exposure but
may alter the normal state of the ecosystem, causing conditions that may be toxic to receptors.
For example, contaminants that raise or lower pH levels can render nutrients unavailable to
plants. Contaminants in a water supply might have low toxicity for fish but might reduce free
oxygen thus killing fish by suffocation rather than poisoning.
The following references may be helpful in estimating the toxicity of chemicals to
ecological receptors:
Lyman, W.J., et al., 1982. Handbook of Chemical Property Estimation Methods.
McGraw-Hill Book Company.
EPA, 1986b. Super fund Public Health Evaluation Manual. EPA 540/1-86/060.
OSWER Directive 9285.4-1. U.S. Environmental Protection Agency. October
1986.
Kabata-Pendias, A. and H. Pendias, 1984. Trace Elements in Soils and Plants.
CRC Press.
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Vershueren, Karel, 1983. Handbook of Environmental Data on Organic Chemicals.
2nd edition. Van Nostrand Reinhold Co.
The enzymatic, metabolic, and reproductive systems of ecological receptors may react to
contaminants very differently than do the systems of human receptors. In addition, since some
organisms spend all their time in contaminated sediments, respiring and absorbing contaminants,
even low concentrations of certain contaminants can have severe ecological effects. Ecological
effects vary greatly depending on contaminants of concern and ecological receptors. Review of
relevant literature and available guidance is essential in accurately identifying potential effects.
3.3
IDENTIFICATION OF PROMULGATED CRITERIA AND STANDARDS
The next step in the process is determining whether promulgated criteria or standards
exist for the contaminants in the medium of concern.
Are any promulgated environmental standards applicable to contaminants found at the site?
Federal and state environmental agencies have established regulatory standards for
contaminants in air, water, and soil. Laws and regulations that provide cleanup levels are listed
below:
Federal Regulations (administered by EPA)
40 CFR 61
40 CFR 50
Clean Water Act Section 304
Provides regulations on national emission standards for
hazardous pollutants
Provides regulations on national primary and secondary
ambient air quality standards
Establishes water quality standards under Section 303 of the
Clean Water Act
EPA 440/5-86-001
Provides quality criteria for water, May 1, 1986, updated
September 7, 1990
CERCLA Section 121(d)(2)(B)(I)
Requires that determination of federal water quality criteria
be based on designated or potential use of the media
affected, the purposes of the criteria, and current
information
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State Regulations in Region 10
Alaska (administered by Alaska Department of Environmental Conservation)
18AACSO Alaska air quality control regulations
18AAC70 Alaska water quality standards
Idaho (administered by Idaho Department of Health and Welfare, Division of the Environment)
Title 1, Chapter 2 Idaho water quality standards and waste water treatment
requirements
Oregon (administered by Oregon Department of Environmental Quality)
Oregon air control pollution laws Oregon Administrative Rules, Chapter 340
Title 7 of the revised statutes: Division 31 ambient air quality standards
Oregon air pollution
control regulations
Oregon water pollution Oregon Administrative Rules, Chapter 340
control regulations Division 40 groundwater quality protection
Division 41 water quality standards
Oregon solid waste regulations Oregon Administrative Rules, Chapter 340
Division 120 hazardous substance remedial action rules
Washington (administered by Washington Department of Ecology)
WAC 173-470 Ambient air quality standard for particulate matter
WAC 173-474 Ambient air quality standard for sulfur oxides
WAC 173-475 Ambient air quality standards for carbon monoxide, ozone,
nitrogen dioxide
WAC 173-480 Ambient air quality standard for radionuclides
WAC 173-481 Ambient air quality standard for fluorides
WAC 173-201 Washington water quality standards
WAC 173-200 Washington groundwater quality standards
WAC 173-204 Sediment management standards
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WAC 173-340 Model Toxics Control Act
WAC 173-340-720 Groundwater cleanup standards
WAC 173-340-730 Surface water cleanup standards
WAC 173-340-740 Soil cleanup standards
WAC 173-340-750 Industrial soil cleanup standards
WAC 173-340-760 Cleanup standards to protect air quality
WAC 173-340-770 Sediment cleanup standards
WAC 173-303 Washington dangerous waste regulations
Once specific criteria or standards that could apply to contaminated media at a site are
identified, these criteria should be evaluated in terms of practical cleanup considerations. It may
not be technically possible to meet a particular cleanup criterion. For example, the chronic
ambient freshwater criterion for dieldrin is 0.0019 /ig/L, which is an order of magnitude lower
than the current analytical method detection limit. Other considerations include economic
concerns and social importance or relevance of the ecological receptor.
3.4 CLEANUP LEVELS FOR CONTAMINANTS LACKING CRITERIA AND STANDARDS
EPA has developed and promulgated specific ambient water quality criteria for protection
of aquatic life in surface waters (EPA 1986b) that represent protective concentrations of common
contaminants. In addition, EPA has several guidance documents available for developing water
quality criteria based on toxicity studies (EPA 1985).
Water quality criteria have been developed based on results of bioassays using
invertebrates such as Daphnia and fish such as fathead minnows. Criteria for certain compounds
have also been developed by organizations other than EPA. For example, Oak Ridge National
Laboratory has developed water quality criteria for ordnance compounds such as trinitrotoluene
and dinitrotoluene (ORNL 1987). These documents can be consulted to develop cleanup levels in
surface waters.
There has also been extensive work on potentially toxic effects from contaminated
sediments. The state of Washington recently developed marine sediment quality standards for
several contaminants of concern (WAC 173-204). These standards are based on results of
bioassays and calculated apparent-effects-thresholds (i.e., sediment contaminant concentrations
above which statistically significant biological effects are always expected). The U.S. Army
Corps of Engineers and EPA both require toxicity testing of dredged sediments prior to disposal.
Results of those studies may be useful for determining toxic effects on ecological receptors in
contaminated sediments.
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Thus, for marine and fresh surface waters and for marine sediments, a great volume of
data exists for assessing potential toxic effects and subsequently developing cleanup levels
protective of ecological receptors. Thorough literature searches may be necessary to identify and
interpret these data and their relevance to ecologically based cleanups.
Unfortunately, similar volumes of data are not available for contaminated soils and
freshwater sediments. Specific risk-based soil and freshwater sediment values for ecological
receptors have not been developed. Limited bioassay data are available, however, based on
earthworm testing, root elongation, and bioassay testing of soil extracts. At this time, there are
no readily available models for determining contaminant uptake from soils by ecological
receptors. Developing health-based soil cleanup levels for terrestrial receptors is, therefore, a
difficult and challenging task associated with a high degree of uncertainty, and one that will
likely require a good deal of professional judgement.
3.5 SELECTION OF ASSESSMENT AND MEASUREMENT ENDPOINTS
If no standards or criteria are promulgated for the contaminants of concern in the media
of concern, completion of the ecological risk assessment requires the identification of ecological
endpoints suitable for measurement. Ecological endpoints are physical or biological parameters
characteristic of the ecosystem that can be affected by contaminants.
Assessment endpoints are formal expressions of the environmental values to be protected.
They are the environmental characteristics which, if significantly affected, would indicate a need
for cleanup. An example would be primary productivity of an ecosystem. Assessment endpoints
are considered along with political, legal, economic, and ethical values to arrive at cleanup levels
and plans for cleanup.
A measurement end point is a quantitative expression of an observed or measured effect of
the hazard; it is a measurable environmental characteristic that is related to the characteristic
chosen as an assessment endpoint. For example, if the assessment endpoint is identified as being
decreased abundance of fish, an LC50 toxicity test (lethal concentration to SO percent of the
organisms) can be conducted with leachate or contaminated sediment to relate environmental
concentrations with potential ecological effects. Sometimes the assessment endpoint and the
measurement endpoint are the same. For example, if the assessment endpoint for a waste site is
decreased abundance of green sunfish in a stream adjoining the site, then abundance of the
sunfish can be measured and related to abundance in reference sites. However, because some
potential assessment endpoints are not observable or measurable, and because assessments are
32
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often limited to using available standard data, measurement endpoints are often surrogates for
assessment endpoints. For example, if the assessment endpoint is reduced production of green
sunfish in the stream due to toxic effects of leachate from a landfill, productivity cannot be
measured in the time allotted to a typical field survey, and toxic effects cannot be reliably
separated in the field from other effects on productivity. In that case, use of toxicity test
endpoints is appropriate. Toxicity test endpoints are typically standard EPA test endpoints such
as fathead minnow LC50 for the leachate contaminants. When the measurement endpoint is not
the same as the assessment endpoint, a model is used to express the relationship between the two.
A literature search may be necessary to determine if available site data and published
ecological data provide an adequate data base to assess ecological impacts and, consequently,
develop cleanup levels. If insufficient information exists, an ecologist can assist with determining
whether the site ecosystem can be modeled with available site information to develop cleanup
levels. If the system cannot be modeled, additional sampling may be needed in order to develop
cleanup levels.
Developing cleanup levels to protect ecological receptors is not as straightforward as
developing human health-based cleanup levels. However, guidelines exist for developing
ecologically based cleanup levels that use data from toxicity tests such as aquatic, soil, and
sediment bioassays (EPA 1988b).
3.6 RESULT OF ECOLOGICAL RISK-BASED ANALYSIS
If an ecological problem exists at a site, special consideration must be given to the cleanup
level determination and evaluation. The cleanup level must be evaluated for its protectiveness of
the appropriate ecological receptors. However, the process of developing ecologically based
cleanup levels is more complex than that of developing human health-based cleanup levels.
Once the process outlined in Section 3 of this document is understood, a site manager
should be prepared to determine whether the presence of ecological receptors at the site will
require lower detection limits and additional sampling. If additional sampling is needed, it is
critical to have a well-designed study that focuses on specific endpoints and quantitative cleanup
criteria.
At the completion of the process for developing cleanup levels based on ecological
assessment, regulatory officials in consultation with ecologists should be prepared to answer the
following questions for a contaminated site undergoing corrective action or closure under RCRA:
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Are there signs of environmental contamination or degradation at the site?
Are there potential ecological receptors, especially endangered or threatened
species, at or near the site?
Are there exposure pathways for site contaminants to reach ecological receptors?
Do site contaminants pose a toxic hazard to receptors (i.e., are contaminants
directly or indirectly toxic; will they bioconcentrate or biomagnify)?
Can promulgated standards or criteria be used as cleanup levels?
Must ecological endpoints be defined for the site?
Does an adequate data base exist to assess ecological impacts?
Can the ecosystem be modeled?
Is further site sampling needed?
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4.0 BIBLIOGRAPHY
EPA, 1985. Guidelines for Deriving Numerical National Water Quality Criteria for the
Protection of Aquatic Organisms and Their Uses. Office of Research and Development, U.S.
Environmental Protection Agency. Duluth, MN.
EPA, 1986a. Superfund Public Health Evaluation Manual. EPA 540/1-86/060. U.S.
Environmental Protection Agency. October 1986.
EPA, 1986b. Quality Criteria for Water 1986. EPA 440/5-86-001. Office of Water Regulations
and Standards. U.S. Environmental Protection Agency.
EPA, 1987. Role of Acute Toxicity Bioassays in the Remedial Action Process at Hazardous Waste
Sites. EPA/600/8-87/044. U.S. Environmental Protection Agency.
EPA, 1988a. CERCLA Compliance With Other Laws Manual. EPA/540/G-89-006. Office of
Solid Waste and Emergency Response, U.S. Environmental Protection Agency.
EPA, 1988b. Protocols for Short-Term Toxicity Screening of Hazardous Waste Sites. EPA
600/3-88/029. U.S. Environmental Protection Agency.
EPA, 1989a. The Nature and Extent of Ecological Risks at Superfund Sites and RCRA Facilities.
EPA/230-03-89-043. U.S. Environmental Protection Agency.
EPA, 1989b. RCRA Facility Investigation (RFI) Guidance. Interim Final. EPA 530/SW-
89-031. Office of Solid Waste and Emergency Response, U.S. Environmental Protection Agency.
EPA, 1989c. Risk Assessment Guidance for Superfund, Volume I - Human Health Evaluation
Manual (Part A). Interim Final. EPA 540/1-89/002. U.S. Environmental Protection Agency.
EPA, 1989d. Risk Assessment Guidance for Superfund, Volume II - Environmental Evaluation
Manual. Interim Final. EPA 540/1-89/001. U.S. Environmental Protection Agency.
EPA, 1989e. Summary of Ecological Risks, Assessment Methods, and Risk Management
Decisions in Superfund and RCRA. EPA/230-30-89-046. U.S. Environmental Protection
Agency.
EPA, 1989f. Technical Appendix: Exposure Analysis of Ecological Receptors. For inclusion in
Superfund Exposure Assessment Manual. Office of Emergency and Remedial Response, U.S.
Environmental Protection Agency.
EPA, 1990a. 40 CFR 264, 265, 270, and 271. Corrective Action for Solid Waste Management
Units at Hazardous Waste Management Facilities. Proposed Rule. U.S. Environmental Protection
Agency. 55 Federal Register 30798-30884 (July 27, 1990).
EPA, 1990b. Northwest RCRA Corrective Action Strategy. EPA 910/9-90-016. U.S.
Environmental Protection Agency.
EPA, 199la. Health Effects Assessment Summary Tables. Annual FY-1991. Updated Quarterly.
OERR 9200.6-303(91-1). Office of Emergency and Remedial Response, U.S. Environmental
Protection Agency.
EPA, 1991b. Human Health Evaluation Manual, Supplemental Guidance: Standard Default
Exposure Factors. Office of Solid Waste and Emergency Response, U.S. Environmental
Protection Agency.
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EPA, 1991c. Integrated Risk Information System. On-line data base. U.S. Environmental
Protection Agency.
EPA, 1991d. Supplemental Risk Assessment Guidance for Superfund. U.S. Environmental
Protection Agency, Region 10. Draft. August 16, 1991.
McEwen, F.L. and Stephenson, G.R., 1979. The Use and Significance of Pesticides in the
Environment. John Wiley and Sons, New York.
Kabata-Pendias, A. and H. Pendias, 1984. Trace Elements in Soils and Plants. CRC Press.
Lyman, W.J., et al., 1982. Handbook of Chemical Property Estimation Methods. McGraw-Hill
Book Company.
Mitre Corporation, 1990. General Guidance for Ecological Risk Assessment at Air Force
Installations. Prepared for U.S. Air Force.
\
ORNL 1987. Water Quality Criteria for 2,4-Dinitrotoluene and 2,6-Dinitrotoluene. Final
Report. ORNL-6312. Oak Ridge National Laboratory.
Oregon Administrative Rules (OAR) 340-122-010 to 340-122-110. Environmental Cleanup
Rules.
Oregon Department of Environmental Quality, 1990. Clean Closure Cleanup Standards for
RCRA Facilities. Interoffice memo from John Boik to DEQ Hazardous and Solid Waste File.
February 1, 1990; Revised October 19, 1990.
Technical Resources, Inc., 1988. Selection and Ranking of Endpoints for Ecological Risk
Assessment. Prepared for U.S. Environmental Protection Agency Exposure Assessment Group
under Contract No 68-02244199.
WAC 173-340. The Model Toxics Control Act Cleanup Regulation. Washington Administrative
Code. February 11, 1991.
Vershueren, Karel, 1983. Handbook of Environmental Data on Organic Chemicals. 2nd edition.
Van Nostrand Reinhold Co.
WAC 173-204. Sediment Management Standards. Washington Administrative Code. April 1991.
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APPENDIX 1
CALCULATING RISK-BASED CONCENTRATIONS
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CALCULATING RISK-BASED CONCENTRATIONS
Risk-based concentrations can be calculated for individual chemicals using the following
exposure assumptions and equations, which were adapted from Appendices D and E of 40 CFR
264, 265, 270, and 271, Corrective Action for Solid Waste Management Units at Hazardous Waste
Management Facilities, Proposed Rule (July 27, 1990). These assumptions and equations are used
to estimate risks from residential exposures. If industrial, recreational, or agricultural exposures
are expected to be a more reasonable basis for cleanup levels, then EPA's Risk Assessment
Guidance for Superfund, Volume I, Human Health Evaluation Manual, Part A (EPA 1989c) and
the Standard Default Exposure Factors (EPA 1991b) should be consulted.
EXPOSURE ASSUMPTIONS
1. In deriving cleanup levels for hazardous constituents in groundwater, assume a water
intake of 2 liters/day for a 70-kg adult for a 70-year lifetime exposure period.
2. In deriving cleanup levels for hazardous constituents in air, assume an air intake of 20
cubic meters/day for a 70-kg adult for a 70-year lifetime exposure period.
In deriving cleanup levels for hazardous constituents in soil that are known or suspected
carcinogens, assume a soil intake of 0.1 gram/day for a 70-kg adult for a 70-year lifetime
exposure period.
4. In deriving cleanup levels for hazardous constituents in soil, for constituents other than
known or suspected carcinogens, assume a soil intake of 0.2 gram/day for a 16-kg child
for a 5-year exposure period (age 1-6).
5. In deriving cleanup levels for hazardous constituents in surface water designated by the
state for use as a drinking water source, assume a water intake of 2 liters/day for a
70-kg adult for a 70-year lifetime exposure period, unless intake of aquatic organisms is
also of concern. If intake of aquatic organisms is of concern, ambient water quality
criteria should be used. If criteria do not exist for the contaminant of concern, then risk
assessment specialists should be consulted for more detailed calculations.
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EQUATIONS FOR CALCULATING RISK-BASED CONCENTRATIONS
Independent calculations are performed to derive risk-based contaminant concentrations
for noncarcinogens and carcinogens. For a contaminant that has both noncarcinogenic and
carcinogenic effects (that is, it has both a reference dose and a slope factor), cleanup levels
should be calculated for both types of effects, and the more health-protective cleanup level
should be used.
EQUATIONS FOR NONCARCINOGENIC CONTAMINANT EFFECTS
For systemic toxicants (i.e., noncarcinogens), the following general equation should be
used to calculate risk-based concentrations:
CB- [reference dose x W]/I (1)
Where
Cn - risk-based concentration in medium (units are medium-dependent)
reference dose = chemical-specific reference dose (mg/kg-day)
W - body weight (kg)
I = intake assumption (units are medium-dependent)
This general equation can be used to calculate cleanup levels in air, soil, and water. The
specific equations are listed in order
For noncarcinogens in air
Ca - [reference dose x 1,000 Hg/mg x 70 kg]/[20 m3/day] (2)
Where
Ca - risk-based concentration in air (Jig/m3)
reference dose - chemical-specific reference dose (mg/kg-day)
W - 70-kg adult
I - 20 m3/day
1-2
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For noncarcinogens in soil:
C, - [reference dose x 16 kg]/[0.2 g/day x 0.001 kg/g] (3)
Where
Cg = risk-based concentration in soil (mg/kg)
reference dose = chemical-specific reference dose (mg/kg-day)
W = 16 kg (5-year-old child)
I - 0.2 g/day
For noncarcinogens in water
C^ - [reference dose x 70 kg]/[2 L/dayJ ' (4)
Where
C = risk-based concentration in water (mg/L)
reference dose = chemical-specific reference dose
W = 70-kg adult
I = 2 L/day
In order to take into account multiple noncarcinogenic contaminants in an individual
pathway, divide the cleanup level obtained using the above equations by the number of
contaminants. For example, if there are five soil contaminants, then first calculate the cleanup
level for each contaminant using equation (3) above. Then divide each cleanup level by 5 to
derive a cleanup level that does not exceed a combined hazard index of 1.0 for soil ingestion.
EQUATIONS FOR CARCINOGENIC CONTAMINANT EFFECTS
For carcinogens, the following general equation should be used to calculate risk-based
concentrations:
C, - [R x W x LT]/[CSF x I x ED] (5)
Where
Cn = risk-based concentration in medium (units are medium-dependent)
R = assumed risk level (dimensionless)(10~6 target risk level)
W = body weight (kg)
LT = assumed lifetime (years)
CSF = chemical-specific cancer slope factor
I = intake assumption (units are medium-dependent)
ED = exposure duration (years)
1-3
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This general equation is modified to calculate risk-based cleanup levels in air, soil, and
water as follows:
For carcinogens in air
C, - [R x 1,000/ig/mg x 70 yr x 70 kg]/[CSF x 20 m3/day x 70 yr] (6)
Where
Ca = risk-based concentration in air (/ig/m3)
R - 10"6 or 10'5
W - 70-kg adult
LT - 70-year lifetime
CSF = chemical-specific cancer slope factor
I - 20 m3/day
ED = 70-year exposure duration
For carcinogens in soil:
C§ = [R x 70 kg x 70 yr]/[CSF x 0.1 g/day x 0.001 kg/g x 70 yr] (7)
Where
Cs = risk-based concentration in soil (mg/kg)
R- 10'6orlO'5
W » 70-kg adult
LT = 70-year lifetime
CSF = chemical-specific cancer slope factor
I « 0.1 g/day
ED « 70-year exposure duration
For carcinogens in water.
CM - [R x 70 kg x 70 yr]/[CSF x 2 L/day x 70 yr] (8)
Where
CM « risk-based concentration in water (mg/L)
R - 10'6
W « 70-kg adult
LT - 70-year lifetime
CSF ** chemical-specific cancer slope factor
I - 2 L/day
ED = 70-year exposure duration
1-4
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In order to take into account multiple carcinogenic contaminants in an individual
pathway, the above equations can be modified by substituting an adjusted target risk level (R).
If R = 10 instead of 10~6, the resulting cleanup levels will yield an overall target risk of 10~6 if
there are 10 or fewer chemicals. Cleanup levels are still calculated for individual contaminants,
but these individual contaminant levels are adjusted to account for the presence of multiple
contaminants. This adjustment can be made in the same way for all three of the above equations.
1-5
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APPENDIX 2
IDENTIFYING EXPOSURE PATHWAYS
TWO EXAMPLE SITES
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IDENTIFYING EXPOSURE PATHWAYS: TWO EXAMPLE SITES
To illustrate the identification of exposure pathways and receptors, two examples of
typical sites are described below.
EXAMPLE No. 1: MILL SITE
This hypothetical mill, located on the banks of a major river, historically allowed effluent
from dye processes to discharge directly to the river. The site has extensive soil contamination,
and contaminated groundwater beneath the site discharges into the river. Sediment sampling in
the river adjacent to the site has shown contamination. Baseball playing fields are located on the
northeast portion of the site property, several residences are located near the site, and a park is
proposed for development along the river near the site.
The potential exposure pathways and receptors likely to be of concern at the mill site are
identified by evaluating the information provided in Table 1 (on page 7) and reviewing the land
uses and other features of the site and vicinity:
Potential Human Exposure Pathways at the Site
Incidental ingestion of soil
Dermal contact with soil
Inhalation of contaminated dust particles in the air
Ingestion of groundwater
Recreational contact with the river
Ingestion of contaminated fish from the river
Potential Ecological Exposure Pathways at the Site
Contact with contaminated soils
Contact with contaminated surface water and sediments in the river
Ingestion of contaminated surface water and sediments in the river
Inhalation of contaminated dust particles in the air
Ingestion of contaminated soil
2-1
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Ingestion of contaminated vegetation
Ingestion of contaminated prey
Potential Human Receptors at the Site
Children playing in yards, playgrounds, or schools in the vicinity of the site
coming into contact with the site soil
Nearby residents or site workers who could inhale dust generated by disturbed
soils on the site
Nearby residents or site workers using groundwater or surface water as drinking
water
Recreational users of the river (for fishing, boating, or swimming) who contact
contaminated water or sediments or eat fish caught in the river
Potential Ecological Receptors at the Site
Fish, amphibians, insects, and invertebrates in the river ingesting and respiring in
contaminated sediments and water
Plants growing in contaminated soil or water
Birds and other animals eating fish and drinking from the river
Herbivores consuming contaminated vegetation
Benthic organisms contacting contaminated sediments and water in the river
Predators consuming contaminated prey
EXAMPLE No. 2: HYPOTHETICAL LANDFILL SITE
Potential exposure pathways at a hypothetical municipal landfill located near a residential
development, a public school, and a stream are illustrated in Figure 2-1. Typical sources of
contamination at landfills include emissions to air, leaching to groundwater, and subsurface gas
formation and migration.
The following potential exposure pathways and receptors of concern at the hypothetical
landfill site are:
2-2
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lng*s!lon,
D»imal Contact,
IIoeonc»ntitjHon
lah*i,
Sti*om*.
Wbltandt
Surface
Bunofl
Duti.
VbMMiaHon
landfll Gat
Ingetnon,
Inhalation.
D«imal
Conlocl
Olr*cl
Con lac I
IT
m///////4
Municipal
Landfill
landfill Gas.
lng*iHon,
WbMw Supply
UGINO
tout*
FIGURE 2-1
SCHEMATIC DIAGRAM OF HYPOTHETICAL LANDFILL SITE
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Potential Human Exposure Pathways at the Site
Inhalation of contaminated dust particles in the air
Inhalation of volatile contaminants in vapors and gases
Ingestion of groundwater
Recreational contact with the nearby stream
Ingestion of contaminated fish from the nearby stream
Potential Ecological Exposure Pathways at the Site
Inhalation of contaminated dust particles in the air
Inhalation of volatile contaminants in vapors and gases
Ingestion of contaminated surface water
Contact with contaminated sediments and surface water in the stream
Ingestion of contaminated vegetation
Ingestion of contaminated prey
Potential Human Receptors at the Site
Children at the school inhaling contaminants
Nearby residents inhaling contaminants in air and ingesting and inhaling
contaminants in drinking water
Recreational users of the nearby stream for wading, swimming, or fishing
Potential Ecological Receptors at the Site
Vegetation growing in contaminated soil
Fish swimming in the stream
Other aquatic organisms in contact with sediments and surface water in the stream
Terrestrial animals in contact with stream water
Terrestrial animals feeding on aquatic organisms
Biota in the wetland ecosystem
2-4
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The hypothetical landfill shown in Figure 2-1 illustrates multiple exposure pathways. At
this site, groundwater that is a source for domestic wells is contaminated with volatile organic
compounds. In a residential setting an individual using water from a contaminated well could be
exposed to these volatile contaminants by three pathways:
Ingestion of contaminated water
Inhalation of volatile contaminants during showering and other household
activities
Dermal contact with contaminated water during showering and other household
activities
h
A risk assessment specialist can assist in determining the significance of the potential exposure
pathways and the need for adjustment of the cleanup levels to account for multiple pathways.
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