EPA/540/R-92/OC4
Publication 9285.7-01 C
December 1991
Risk Assessment Guidance
for Superfuncl:
Volume I
Human Health Evaluation
Manual
(Part C, Risk Evaluation of
Remedial Alternatives)
Interim
Office of Emergency and Remedial Response
U.S. Environmental Protection Agency
Washington, DC 20460
Printed on Recycled Paper
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NOTICE
The policies set out in this document are intended solely as guidance; they are not final U.S.
Environmental Protection Agency (EPA) actions. These policies are not intended, nor can they be relied
upon, to create any rights enforceable by any party in litigation with the United States. EPA officials may
decide to follow the guidance provided in this document, or to act at variance with the guidance, based on an
analysis of specific site circumstances. The Agency also reserves the right to change this guidance at any time
without public notice.
This guidance is based on policies in the Final Rule of the National Oil and Hazardous Substances
Pollution Contingency Plan (NCP), which was published on March 8, 1990 (55 Federal Re&ster 8666). The
NCP should be considered the authoritative source.
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CONTENTS
Page
NOTICE . . . . ii
EXHIBITS -v
DEFINITIONS . . . . , - vi
ACRONYMS/ABBREVIATIONS viii
ACKNOWLEDGEMENTS xi
PREFACE xii
1.0 INTRODUCTION .. . 1
1.1 SCOPE AND OVERVIEW OF PART C 1
1.1.1 Scope 1
1.1.2 Overview 3
1.2 RELEVANT STATUTES, REGULATIONS, AND GUIDANCE . . . 6
1.2.1 CERCLA/SARA '.' 6
1.2.2 NCP . . ,6
1.2.3 Other Relevant Guidance 7
1.3 LEVEL OF EFFORT .' 7
1.4 IMPORTANCE OF RISK COMMUNICATION . . 7
1.5 MANAGEMENT AND DOCUMENTATION 8
1.6 ORGANIZATION OF THE DOCUMENT 8
2.0 RISK EVALUATION DURING THE FEASIBILITY STUDY 11
2.1 RISK EVALUATION DURING DEVELOPMENT AND SCREENING
OF ALTERNATIVES . . 11
2.1.1 Consideration of Long-term Human Health Risks 11
2.1.2 Consideration of Short-term Human Health Risks 11
2.2 RISK EVALUATION DURING DETAILED ANALYSIS OF ALTERNATIVES 12
2.2.1 Evaluation of Long-term Human Health Risks for Detailed Analysis 14
2.2.2 Evaluation of Short-term Human Health Risks for Detailed Analysis 15
2.3 CASE STUDIES - 20
3.0 RISK EVALUATION AFTER THE FEASIBILITY STUDY ; - 25
3.1 RISK EVALUATION FOR THE PROPOSED PLAN . 25
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CONTENTS (Continued)
Page
3.2 DOCUMENTATION OF RISKS IN THE ROD 25
3.3 RISK EVALUATION DURING REMEDIAL DESIGN/REMEDIAL ACTION 25
3.3.1 Risk Evaluation During Remedial Design 26
3.3.2 Monitoring Short-term Health Risks During Implementation 26
3.33 Assessing Attainment of Selected Remediation Levels
During implementation , 26
3.3.4 Evaluation of Residual Risk -. 26
3.4 RISK EVALUATION DURING FIVE-YEAR REVIEWS . 27
3.4.1 Purpose of Five-year Reviews ., 27
3.4.2 Sites That Receive Five-year Reviews '.'.'.'.'. 27
3.4.3 Risk-related Activities During Five-year Reviews 28
REFERENCES 29
APPENDIX A SELECTED REMEDIATION TECHNOLOGIES AND ASSOCIATED
POTENTIAL RELEASES 31
APPENDIX B QUANTIFYING POTENTIAL RELEASES FROM SELECTED
REMEDIATION TECHNOLOGIES 43
B.I SOILS HANDLING TECHNOLOGIES 43
B.2 THERMAL DESTRUCTION TECHNOLOGIES 43
B.3 SOLIDIFICATION/STABILIZATION TREATMENT TECHNOLOGIES 44
B.4 REFERENCES FOR DETERMINING RELEASES RESULTING FROM REMEDIAL
ACTIVITIES ; 45
B.4.1 Various Remedial Activities 45
B.4.2 Soils Handling '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 45
B.4.3 Thermal Destruction 45
B.4.4 Stabilization/Solidification 47
APPENDIX C SHORT-TERM TOXICITY VALUES 49
Cl BACKGROUND ON EXPOSURE DURATION 49
C.2 EXISTING SHORT-TERM TOXICITY VALUES '. 50
>»
C2.1 Toxicity Values for Assessing Risk of Noncarcinogenic Effects for Short-term
Exposure 50
C.2.2 Specific Carcinogenic Risk Values for Short-term Exposures 54
APPENDIX D
RADIATION REMEDIATION TECHNOLOGIES 57
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EXHIBITS
Exhibit Page
1-1 RELATIONSHIP OF HUMAN HEALTH EVALUATION TO THE
CERCLA PROCESS , 2
1-2 SUMMARY OF RISK EVALUATIONS OF REMEDIAL
ALTERNATIVES . . 4
1-3 RISK EVALUATION OF REMEDIAL ALTERNATIVES IN
THE CERCLA PROCESS . 5
" 2-1 ILLUSTRATION OF AN EXPOSURE PATHWAY FOR A REMEDIAL ACTION 17
2-2 ILLUSTRATION OF CUMULATIVE EXPOSURES FROM MULTIPLE RELEASES. 18
A-l REMEDIATION TECHNOLOGY DESCRIPTIONS r .32
A-2 REMEDIATION TECHNOLOGIES AND SOME POTENTIALLY
SIGNIFICANT RELEASES 37
D-l POTENTIAL RELEASES OF RADIOACTIVITY ASSOCIATED WITH
RADIATION REMEDIATION TECHNOLOGIES 58
D-2 DEGREE OF POTENTIAL SHORT- AND LONG-TERM RISKS ASSOCIATED
WITH RADIATION REMEDIATION TECHNOLOGIES 62
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DEFINITIONS
Term
Definition
Applicable or Relevant and
Appropriate Requirements
(ARARs)
Exposure Pathway
Exposure Point
Exposure Route
Final Remediation Levels
Long-term Risks
Preliminary Remediation Goals
(PRGs)
"Applicable" requirements are those clean-up standards, standards
of control, and other substantive environmental protection
requirements, criteria, or limitations promulgated under federal or
state law that specifically address a hazardous substance, pollutant,
contaminant, remedial action, location, or other circumstance at a
Comprehensive Environmental Response, Compensation, and
Liability Act (CERCLA) site. "Relevant and appropriate"
requirements are those clean-up standards which, while not
"applicable" at a CERCLA site, address problems or situations
sufficiently similar to those encountered at the CERCLA site that
their use is well-suited to the particular site. ARARs can be action-
specific, location-specific, or chemical-specific.
The course a chemical or physical agent takes from a source to an
exposed organism. An exposure pathway describes a unique
mechanism by which an individual or population is exposed to
chemicals or physical agents at or originating from a site. Each
exposure pathway includes a source or release from a source, an
exposure point, and an exposure route. If the exposure point differs
from the source, a transport/exposure medium (e.g., air) or media
(in cases of intermedia transfer) also would be indicated.
A location of potential contact between an organism and a chemical
or physical agent.
The way a chemical or physical agent comes in contact with an
organism (i.e., by ingestion, inhalation, dermal contact).
Chemical-specific clean-up levels that are documented in the
Record of Decision (ROD). They may differ from preliminary
remediation goals (PRGs). because of modifications resulting from
consideration of various uncertainties, technical and exposure
factors, and all nine selection-of-remedy criteria outlined in the
National Oil and Hazardous Substances Pollution Contingency Plan
(NCP).
Risks that remain after remedy implementation is complete (i.e.,
residual risks).
Initial clean-up goals that (1) are protective of human health and
the environment and (2) comply with ARARs. They are developed
early in the process based on readily available information and are
modified to reflect results of the baseline risk assessment. They
also are used during analysis of remedial alternatives in the
remedial investigation/feasibility study (RI/FS).
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DEFINITIONS (Continued)
Term
Definition
Remedial Alternative
Remedial Action
Risk-based Concentrations
Short-term Risks
An action considered in the feasibility study intended to reduce or
eliminate significant risks to human health and/or the environment
at a site. A range of remedial alternatives are considered in detail
by the FS while the selection of a specific remedial alternative over
others is documented in the ROD.
The selected alternative that is documented in the ROD.
Concentration levels for individual chemicals that correspond to a
specific cancer risk level (e.g., 10"6, 10"4) or hazard quotient (HQ)
or hazard index (HI) (e.g., less than or equal to 1). They are
generally selected as preliminary or final remediation goals when
ARARs are not available.
Risks that occur during implementation of a remedial alternative.
Some "short-term" risks can occur over a period of many years (e.g.,
risk associated with air stripper emissions).
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ACROlSfYMS/ABBREVIATIONS
Acronym/
Abbreviation
Definition
ACGIH
AIC
APCD
ARARs
ATSDR
CEGL
CERCLA
CFR
ECAO
EEGL
EPA
HEAST
HHEM
HI
HQ
IDLH
IRIS
LOAEL
MCL
MRL
NCP
NIOSH
NOAEL
NRC
American Conference of Governmental Industrial Hygienists
Acute Inhalation Criteria
Air Pollution Control Device.
j
Applicable or Relevant and Appropriate Requirements
Agency for Toxic Substances and Disease Registry
Continuous Exposure Guidance Level
Comprehensive Environmental Response, Compensation, and Liability Act
Code of Federal Regulations
Environmental Criteria and Assessment Office
Emergency Exposure Guidance Level
U.S. Environmental Protection Agency
Health Effects Assessment Summary Tables
Human Health Evaluation Manual
Hazard Index
Hazard Quotient
Immediately Dangerous to Life and Health
Integrated Risk Information System
Lowest-observed-adverse-effect-level
Maximum Contaminant Level
Minimal Risk Level
National Oil and Hazardous Substances Pollution Contingency Plan
National Institute for Occupational Safety and Health
No-observed-adverse-effect-level
National Research Council
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ACRONYMS/ABBREVIATIONS (Continued)
Acronym/
Abbreviation
Definition
ORD
OSHA
PEL
POTW
PPE
PRO
QA/QC
RAGS
RCRA
REL
RfC
RfD
RI/FS
RME
ROD
RPM
RQ
RREL
SARA
SPEGL
TLV-C
TLV-STEL
TLV-TWA
TSC
Office of Research and Development
Occupational Safety and Health Administration
Permissible Exposure Level
Publicly Owned Treatment Works
Personal Protective Equipment
Preliminary Remediation Goal
Quality Assurance/Quality Control
Risk Assessment Guidance for Superfund
Resource Conservation and Recovery Act
Recommended Exposure Level
Reference Concentration
Reference Dose
Remedial Investigation/Feasibility Study
Reasonable Maximum Exposure
Record of Decision
Remedial Project Manager
Reportable Quantity
Risk Reduction Engineering Laboratory
Superfund Amendments and Reauthorization Act
Short-term Public Emergency Guidance Level
Threshold Limit Values - Ceiling
Threshold Limit Values - Short-term Exposure Limit
Threshold Limit Values - Time-weighted Average
Superfund Health Risk Technical Support Center
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ACRONYMS/ABBREVIATIONS (Continued)
Acronym/
Abbreviation
Definition
TSCA
VOCs
Toxic Substances Control Act
Volatile Organic Compounds
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ACKNOWLEDGEMENTS
This manual was developed by the Toxics Integration Branch (TIB) of EPA's Office of Emergency and
Remedial Response, Hazardous Site Evaluation Division. A large number of EPA regional and headquarters
managers and technical staff (see below) provided valuable input regarding the organization, content, and
policy implications of the manual throughout its development.
ICF Incorporated provided technical assistance to EPA in the development of this manual, under
Contract Nos. 68-01-7389,68-W8-0098, and 68-03-3452. S. Cohen and Associates (SC&A) provided assistance
in the development of Appendix D, under EPA Contract No. 68-D9-0170.
WORKGROUP
EPA HEADQUARTERS
Office of Emergency and Remedial Response:
Office of Radiation Programs:
Office of General Counsel:
Office of Policy, Planning, and Evaluation:
Office of Waste Programs Enforcement:
Office of Health and Environmental Assessment:
Rhea Cohen, David Cooper,
Steve Golian, Jennifer Sutler, Ed Hanlon,
James Konz, Tracy Ldy, Bruce Means
Bob Dyer
Larry Starfield
Pepi Lecayo
Steve Ells
Kevin Garrahan
EPA REGIONAL OFFICES
Region 1:
Region 5:
Region 6:
Region 10:
Ann-Marie Burke, Jeri Weiss
Alison Hiltner, Jae Lee,
Andrew Podowski
Jon Rauscher
Judi Schwarz, Carol Sweeney
OTHER EPA OFFICES
Risk Reduction Engineering Laboratory:
Office of Air Quality Planning and Standards:
Office of Health and Environmental Assessment:
STATE AGENCIES
Michigan Department of Natural Resources:
New Jersey Department of Environmental Protection:
Pat Lafornara
Fred Hauchman
Pei-Fung Hurst
Chris Flaga
Linda Cullen
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PREFACE
Risk Assessment Guidance for Superjund: Volume I Human Health Evaluation Manual
(RAGS/HHEM) Part C is one of a three-part series. Part A addresses the baseline risk assessment; Part B
addresses the development of risk-based preliminary remediation goals. Part C provides guidance on the
human health risk evaluations of remedial alternatives that are conducted during the feasibility study, during
selection and documentation of a remedy, and during and after remedy implementation. Part C provides
general guidance to assist in site-specific risk evaluations and to maintain flexibility in the analysis and
decision-making process. This guidance does not discuss the evaluation of ecological effects that takes place
during remedy selection and implementation, nor does it discuss the risk management decisions that are
necessary at a CERCLA site (e.g., selection of final remediation goals). The potential users of Part C are
persons involved in the remedy selection and implementation process, including risk assessors, risk assessment
reviewers, remedial project managers, and other decision-makers.
This manual is being distributed as an interim document to allow for a period of field testing and
review. RAGS/HHEM will be revised in the future, and Parts A, B, and C will be incorporated into a single
final guidance document. Additional information for specific subject areas is being developed for inclusion
in a later revision. These areas include:
development of short-term inhalation toxicity values;
short-term worker health and safety issues; and
determination of attainment of final remediation goals.
Comments addressing usefulness, changes, and additional areas where guidance is needed should be
sent to:
U.S. Environmental Protection Agency
Toxics Integration Branch (OS-230).
Office of Emergency and Remedial Response
401 M Street, SW
Washington, DC 20460
Telephone:
FAX:
202-260-9486
202-260-6852
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CHAPTER 1
INTRODUCTION
This guidance has been developed by the U.S.
Environmental Protection Agency (EPA) to assist
remedial project managers (RPMs), risk assessors,
site engineers, and others in using risk information
at Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA) sites
to both evaluate remedial alternatives during the
feasibility study (FS) and to evaluate the human
health risk associated with the selected remedial
alternative during and after its implementation.
Part C provides general guidance to assist in site-
specific risk evaluations and to maintain flexibility
in the decision-making process.
Risk assessment is one of many tools that
RPMs use in selecting the best remedy for a site.
Other important tools (not addressed in this
guidance) involve the assessments of technical
feasibility, applicable or relevant and appropriate
requirements (ARARs), cost, and
implementability.
This guidance is the third part (Part C) in the
series Risk Assessment Guidance for Superfund:
Volume I Human Health Evaluation Manual
(RAGS/HHEM). Part A of this guidance (EPA
1989g) describes how to conduct a site-specific
baseline risk assessment; the information in Part A
is necessary background for Part C. Part B (EPA
1991c) provides guidance for calculating risk-based
concentrations that may be used, along with
ARARs and other information, to develop
preliminary remediation goals (PRGs) during
project scoping. PRGs (and final remediation
levels set in the Record of Decision [ROD]) can
be used throughout the analyses in Part C to assist
in evaluating the human health risks of remedial
alternatives. Exhibit 1-1 illustrates the major
correspondence of RAGS/HHEM activities with
the steps in the CERCLA remedial process.
, The steps for conducting a risk evaluation of
remedial alternatives are discussed in general terms
in Chapters 2 and 3; more detailed guidance for
conducting short-term evaluations is provided in
Appendices A through D. (See the box in the next
column for a description of how the terms short-
SHORT-TERM RISK VS. LONG-TERM RISK
For the purposes of this guidance, short-term
risks are those that occur during implementation of
a remedial alternative. Some "short-term" risks can
occur over a period of many years (e.g., risk
associated with air stripper emissions). In contrast,
long-term risks are those that remain after remedy
implementation is complete (i.e., residual risks).
term risk and long-term risk differ in this
guidance.) The remainder of this chapter:
presents the scop&and an overview of Part C;
discusses the statutes, regulations, and
guidance relevant to the evaluation of
remedial alternatives;
describes appropriate levels of effort for risk
evaluations of remedial alternatives;
discusses the importance of risk
communication;
addresses the role of the RPM and the need
for documentation; and
presents the organization of the remainder of
this document.
1.1 SCOPE AND OVERVIEW OF
PARTC
1.1.1 SCOPE
As discussed in Section 1.2 below, some of the
nine criteria that are described in the National Oil
and Hazardous Substances Pollution Contingency
Plan (NCP) and that are used to evaluate remedial
alternatives during the remedial investigation/
feasibility study (RI/FS), involve a direct use of
risk-related information. Several aspects of these
criteria (e.g., short-term risks to workers and
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EXHIBIT 1-1
RELATIONSHIP OF THE HUMAN HEALTH EVALUATION
TO THE CERCLA PROCESS
CERCLA REMEDIAL PROCESS
Scoping
Remedial
Investigation
Fusibility
Study
-
Remedy Selection
and Record of
Decision
Remedial Design/
Remedial Action
Deletion/
Five-year Review
HUMAN HEALTH EVALUATION MANUAL
PART A
Baseline Risk Assessment
PARTB
Development of Risk-based
Preliminary Remediation Goals
PARTC
Risk Evaluation of Remedial Alternatives
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surrounding community, long-term effectiveness)
are discussed in detail in this guidance. Other
criteria that do not directly involve health risk
(e.g., implementability, cost) with the exception
of community acceptance are mentioned briefly
but are not discussed in detail.
Remedial alternatives, in addition to being
evaluated for the degree to which they protect
human health, are evaluated for their potential to
protect ecological receptors. RAGS/HHEM
Part C does not address ecological risk assessment
(see the next box). However, ecological guidance
specific to evaluating remedial alternatives in the
CERCLA program will be developed following
finalization of Agency guidance on ecological risk
assessment.
EVALUATING ECOLOGICAL EFFECTS OF
REMEDIAL ALTERNATIVES
Remedial actions, by their nature, can alter
or destroy aquatic and terrestrial habitat. This
potential for destruction or alteration of habitat
and subsequent consequences must be evaluated
so that it can be considered during the selection of
a remedial alternative and during its
implementation.
This document does not address the
evaluation of ecological risks. Future guidance for
ecological evaluations is planned, however. At
present, ecological evaluations should be based on
the best professional judgment of experienced
ecologists and/or aquatic or environmental
toxicologists.
The guidance in this document applies to sites
contaminated with non-radioactive hazardous
substances and those contaminated with
radionuclides. Appendix D provides additional
guidance specific to radionuclide sites.
Note that this guidance is limited to the use of
risk assessment in evaluating remedial alternatives.
Part C does not provide guidance on the risk
management decisions that must be made when
evaluating alternatives and selecting a remedy (e.g.,
balancing of the nine NCP criteria, selection of
final remediation goals and levels) or engineering
judgments that affect the evaluation of alternatives
(e.g., determining whether an alternative is likely
to achieve remediation goals). ' These issues are
addressed in other guidance or in guidance that'
currently is being developed.
1.1.2 OVERVIEW
The process of evaluating remedial alternatives
begins in the development and screening stage of
the FS and extends into the detailed analysis stage.
The major goal for the risk evaluation during these
steps is to provide decision-makers with specific
information that they may need in choosing among
alternatives. Additional risk evaluations may need
to be conducted during the proposed plan, during
the design and implementation of the remedy, and
after the remedy is complete (e.g., during "five-year
reviews"). These activities are discussed below and
throughout this guidance.
Exhibit 1-2 summarizes the levels of effort, and
purposes of the risk evaluations of remedial
alternatives, while Exhibit 1-3 illustrates when
these activities take place within the context of the
CERCLA remedial process.
Identification and Screening of Technologies
and Alternatives. During this stage, a range of
remedial alternatives is identified, if necessary, and
each alternative is evaluated with respect to
effectiveness, implementability, and cost. This
process may consist of two steps: (1) identification
and screening of technologies and (2) development
and screening of alternatives. These steps are
often combined into a single step (as reflected in.
this guidance). Those alternatives that are clearly
unfavorable relative to other alternatives in terms
of effectiveness (e.g., very high perceived risk) or
implementability, or that are grossly excessive in
cost are dropped from consideration after this
screening. Part of the evaluation of effectiveness
involves human health risk (e.g., risks to the
community and remediation workers), and Chapter
2 of this document provides guidance on evaluating
these factors. RAGS/HHEM Part C does not
discuss evaluating factors such as implementability
and cost.
Detailed Analysis of Alternatives. During the
detailed analysis stage, alternatives are evaluated
according to each of the nine NCP evaluation
criteria, and then are compared to each other.
Both long-term effectiveness (i.e., residual risk)
and short-term effectiveness (i.e., risk to the
community and remediation workers during
remedy implementation) are evaluated during the
detailed analysis. Chapter 2 and Appendices A
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EXHIBIT 1-2
SUMMARY OF RISK EVALUATIONS OF REMEDIAL ALTERNATIVES
STAGE
Screening of
Alternatives
(Section 2.1)
Detailed Analysis
of Alternatives
(Section 2.2)
Proposed Plan
(Section 3.1)
Record of Decision
(Section 3.2)
. Remedial Design
(Section 3.3)
Remedial Action
(Section 3.3)
Five-year Review
(Section 3.4)
LEVEL OF EFFORT
Short-term
Risk*
Qualitative
Qualitative or
Quantitative"1
Qualitative or
Quantitative11
Qualitative or
Quantitative"1
Qualitative or
Quantitative"1
Quantitative
Generally not
applicable
Long-term
Risk
Qualitative
Qualitative or
Quantitatived
Qualitative or
Quantitative"1
Qualitative or
Quantitative11
Qualitative or
Quantitative"1
Quantitative
Quantitative
PRIMARY PURPOSE OF RISK EVALUATION1
Short-term Risk'
Identify (and eliminate from consideration)
alternatives with clearly unacceptable short-term
risks.
Evaluate short-term risks of each alternative to
community and on-site remediation workers
during implementation so that these risks can be
compared among alternatives.
Refine previous analyses, as needed, based on
newly developed information.
Document short-term risks that may occur
during remedy implementation.
Refine previous analyses, as needed, and
identify need for engineering controls or other
measures to mitigate risks.
Ensure protection of workers and community by
monitoring emissions or exposure
concentrations, as needed.
Generally not applicable.
Long-term Risk
Identify (and eliminate from consideration)
alternatives with clearly unacceptable long-term risks.
Evaluate long-term (residual) risk of each alternative
and its ability to provide continued protection over
time so that these risks can be compared among
alternatives.
Refine previous analyses, as needed, based on newly
developed information.
Document risks that may remain after completion of
remedy and determine need for five-year reviews.
Refine previous analyses, as needed, and identify
need for engineering' controls or other measures to
mitigate risks.
Evaluate whether remediation levels specified in
ROD have been attained and evaluate residual risk
after completion of remedy to ensure protectiveness.
Confirm that remedy (including any engineering or
institutional controls) remains operational and "
functional and evaluate whether clean-up standards
are still protective.
a Level of effort (i.e., qualitative or quantitative) refers only to the level of risk evaluation that is generally expected. Levels other than those presented here, or
combinations of levels, are possible. See the main text of this document for additional discussion on level of effort.
b Purpose presented in this exhibit for each stage is only the primary purpose; other purposes may exist. See the main text of this document for additional information:
0 Short-term risk refers to risks that occur during remedy implementation.
d Text box in Section 2.2 lists considerations for deciding whether a qualitative or quantitative risk evaluation is needed for these stages.
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EXHIBIT 1-3
RISK EVALUATION OF REMEDIAL ALTERNATIVES IN THE
CERCLA PROCESS
STAGES IN REMEDIATION
Remedial
investigation
Feasibility
Study
Selection of
Remedy
Remedial Design/
Remedial Action
Deletion/
Five-year Review
Evaluate Risks
During Screening
and Detailed
Analysis of
Alternatives
Develop Proposed
Plan and
Document Risks
of Alternatives
in Record of
Decision
Evaluate Risks
During Remedial
Design/Remedial
Action
Revisit
Protectiveness
Evaluate Attainment of
Final Goals and
Residual Risk
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through D of this document provide guidance on
the evaluation of the risk-related aspects of long-
term effectiveness (residual risk and permanence),
and short-term effectiveness. (As with the
screening of alternatives, Chapter 2 generally does
not discuss evaluation of the other criteria, which
do not directly involve human health risk
considerations.) The resulting risk information is
incorporated into the overall detailed analysis
process described in the Guidance for Conducting
Remedial Investigations and Feasibility Studies
Under CERCLA (RI/FS Guidance; EPA 1988c).
Proposed Plan and ROD. Risk evaluations are
generally conducted during the development of the
proposed plan and ROD only when new
information concerning risks of the remedial
alternatives is generated. Chapter 3 provides
guidance on the evaluation of risks for the
proposed plan and ROD stage.
Remedial Design/Remedial Action (RD/RA).
Risk-related evaluations may also be conducted for
some sites during implementation of the selected
remedy. These activities, discussed briefly in
Chapter 3, include: (1) refining risk evaluations as
necessary when designing the remedy;
(2) monitoring potential short-terra health impacts
on the community and workers; (3) assessing
attainment of final remediation levels selected in
the ROD; and (4) evaluating residual risk.
Five-year Review. Under the NCP, five-year
reviews are required for sites as long as hazardous
substances remain onsite above levels that allow
unlimited use and unrestricted exposure, and are
also conducted as a matter of policy for long-term
remedial action sites even if no hazardous
substances are expected to remain after completion
of the action. Chapter 3 briefly addresses the
consideration of risk during five-year reviews.
1.2 RELEVANT STATUTES,
REGULATIONS, AND
GUIDANCE
As discussed in RAGS/HHEM Part A, there is
a hierarchy of requirements and guidance in
CERCLA, beginning'with the laws enacted by
Congress, followed by the regulations, and then the
guidance developed by EPA. This section
addresses this hierarchy within the context of the
risk evaluation of remedial alternatives.
1.2.1 CERCLA/SARA
CERCLA, commonly called Superfund, was
enacted by Congress in 1980 in response to the
dangers posed by sudden or otherwise uncontrolled
releases of hazardous substances, pollutants, or
contaminants into the environment. The
Superfund Amendments and Reauthorization Act
(SARA) was enacted in 1986. (All references to
CERCLA in this guidance should be interpreted as
"CERCLA as amended by SARA.")
Section 121 of CERCLA requires that
remedies be protective of human health and the
environment, satisfy ARARs, be cost-effective, and
utilize permanent solutions and alternative
treatment technologies to the maximum extent
practicable. Section 121(c) of CERCLA requires
a periodic review of remedial actions, at least every
five years after initiation, for as long as hazardous
substances that may pose a threat to human health
or the environment remain at the site. The
information in this manual provides guidance for
evaluating the protectiveness of remedial
alternatives at a site in terms of the human health-
related aspects of these CERCLA requirements.
Some considerations include protectiveness,
effectiveness in terms of risk reduction, and degree
of hazard for substances remaining at the site.
1.2.2 NCP
The NCP is the main set of regulations
developed by EPA to implement CERCLA. The
most recent NCP was published on March 8, 1990
(55 Federal Register 8666-8865) and is codified at
40 Code of Federal Regulations (CFR) Part 300.
Section 300.430(e)(l) of the NCP describes a two-
stage evaluation of remedial alternatives: a
screening evaluation of a range of alternatives, if
necessary, followed by a detailed analysis of the
most promising alternatives. The NCP also
describes activities that follow selection and
implementation of the selected remedial
alternative.
Screening. NCP section 300.430(e)(7)
indicates that, if necessary and to the extent
sufficient information is available, alternatives
should be screened out if determined to be
ineffective, not implementable, or grossly excessive
in cost. Some aspects of effectiveness involve
considerations of human health risk and are
discussed in this guidance.
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Detailed Analysis. The NCP establishes nine
criteria in section 300.430(e)(9)(iii) to use in
evaluating alternatives in detail and in selecting a
remedy. Parts of three of these criteria overall
protection of human health and the environment,
long-term effectiveness and permanence, and short-
term effectiveness directly relate to risks and
therefore are the focus of this guidance. The
actual selection of a remedy for any given site
ultimately is based on consideration of the nine
criteria. This guidance also discusses the
importance of risk communication to the
community as it relates to the criterion of
community acceptance.
Five-year Reviews. NCP section
300.430(f)(4)(ii) provides that if a remedial
alternative is selected that results in hazardous
substances (or pollutants or contaminants)
remaining at the site above levels that allow for
unrestricted exposure and unlimited use, such
remedy should be reviewed at least every five years
after initiation of the selected remedial alternative.
1.2.3 OTHER RELEVANT GUIDANCE
Three CERCLA program documents are
important background for the guidance presented
in this document RAGS/HHEM Parts A and B
(EPA 1989g; EPA 1991c), and the RI/FS Guidance
(EPA 1988c). Parts A and B provide guidance on
conducting a baseline risk assessment and on
developing risk-based concentrations, respectively,
that should be used in evaluating remedial
alternatives. The activities conducted during a risk
evaluation of remedial alternatives are somewhat
similar to the activities conducted during a baseline
risk assessment. (Chapter 2 discusses in more
detail the similarities and differences.) The RI/FS
Guidance describes the major activities and
analyses that are conducted during the RI/FS. See
the references at the end of this document for
other relevant background guidance.
1.3 LEVEL OF EFFORT
The level of effort for risk evaluations of
remedial alternatives depends primarily on the site-
specific questions that must be answered in order
to select and implement a remedy. In addition,
site-specific factors such as the complexity of the
site, the number of alternatives considered for the
site, the available resources, and the amount of
available data may affect the level of effort. In
most cases, a qualitative rather than a detailed
quantitative evaluation of both long-term and
short-term risks is all that is needed to select the
most appropriate alternative. A quantitative risk
evaluation of remedial alternatives will not need to
be conducted for all sites. In all cases, the baseline
risk assessment provides much of the risk-related
information needed for the detailed analysis of
alternatives, especially for those alternatives that
involve limited or no action.
For many sites, the risk evaluations of
remedial alternatives during the FS are conducted
in a qualitative manner. That is, the risk
evaluations during both the screening and detailed
analysis stages for these sites will not be at all
quantitative. At other sites, a more quantitative
analysis of the long-term and/or short-term risks
associated with the remedial alternatives may be
needed during the detailed analysis. In these
situations, the risk evaluation generally needs to
incorporate more site-specific information.
A guiding principle is that the risk evaluation
should be tailored to provide the RPM with
specific information that he or she needs for
supporting the selection or design of a remedy
(e.g., the relative risks associated with alternatives,
the alternatives that best meet the remediation
goals). Because of the differences in information
needs and available data for sites, in the complexity
of sites, and in available methods, models, and
resources for evaluation, all of the components of
this guidance will not be applicable to all sites.
Chapter 2 provides some additional factors to
consider when deciding on the level of effort to
use for the risk evaluation of remedial alternatives.
1.4 IMPORTANCE OF RISK
COMMUNICATION
As noted earlier, while overall protection of
human health and the environment is one of the
threshold criteria established by the NCP for use in
evaluating alternatives and selecting a remedy,
community acceptance of the remedy is a
modifying criterion (NCP section 300.430(e) (9)
(iii)). The CERCLA program encourages and
promotes public participation during all phases of
the decision-making process at CERCLA sites.
Just as risk information is used by RPMs and other
EPA staff to assist in evaluation of remedial
alternatives during the FS and to evaluate the
selected remedial alternative during and after its
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implementation, risk information also will be
employed by the public in their acceptance of a
selected remedy. Good communication of the risks
of the remedy to the public is crucial to the
community's acceptance of the remedy.
There is no single procedure for good risk
communication. The actual mechanism used and
the messages delivered will vary from site to site
and will depend upon the public, their level of
concern, the complexity of the site, the
contaminants of concern, and the proposed
remedial alternative. RPMs are encouraged to
work with the risk assessor and community
relations coordinator for the site to develop the
appropriate means to communicate risks from the
remedial alternative or any residual risks. RPMs
should consider using fact sheets, public meetings,
and the release of draft documents or "risk
communication" summaries as vehicles for risk
communication. Community Relations in
Superfund: A Handbook (EPA 1988a) offers
guidance on planning and conducting CERCLA
community relations activities.
Regardless of the vehicles chosen for risk
communication, the following rules, from Seven
Cardinal Rules of Risk Communication (EPA
1988Q, should be kept in mind.
Accept and involve the public as a legitimate
partner.
Plan carefully and evaluate your efforts.
Listen to the public's specific concerns.
Be honest, frank, and open.
Coordinate and collaborate with other credible
sources.
Meet the needs of the media.
Speak clearly and with compassion.
As provided under the NCP, risk
communication, public participation, and
community relations at CERCLA sites begin well
before the remedy selection phase. This is
important, as communities near CERCLA sites
may begin with a degree of outrage that must be
addressed before effective communication can
begin. Community relations, public involvement,
and good risk communication continue throughout
the RI/FS process. A well-informed public will be
better able to comment on and provide input to
technical decisions. Establishing credibility
through community relations, public participation,
and effective risk communication practices early in
the CERCLA process leads to greater community
acceptance of the selected remedy.
1.5 MANAGEMENT AND
DOCUMENTATION
One role of an RPM in the risk evaluation of
remedial alternatives is to make risk management
decisions. The RPM must have a comprehensive
understanding of the risk evaluation in order to
make these decisions. The first box on the next
page provides questions that RPMs and other
decision-makers should ask about the risks of
remedial alternatives at their sites. The second
box provides guidance on where to document the
evaluations addressed in RAGS/HHEM Part C.
1.6 ORGANIZATION OF THE
DOCUMENT
The remainder of this guidance is organized
into two additional chapters and four appendices,
as follows:
Chapter 2: Risk Evaluation During the
Feasibility Study;
Chapter 3: Risk Evaluation After ,the
Feasibility Study;
Appendix A: Selected Remediation
Technologies and Associated Potential
Releases;
Appendix B: Guidance for Quantifying
Potential Releases from Selected Remediation
Technologies;
Appendix C: Short-term Toxicity Values; and
Appendix D: Radiation Remediation
Technologies.
In addition, several boxes,.such as those below,
provide useful information. A second kind of box,
a "shadow" box, provides case studies. These boxes
are presented at the end of Chapter 2.
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QUESTIONS RPMs SHOULD ASK ABOUT HUMAN HEALTH RISKS OF REMEDIAL ALTERNATIVES
Which technologies can readily achieve all preliminary remediation goals (PRGs) in a given medium? What
uncertainties are involved in this determination?
Which alternatives will clearly not address the significant human exposure pathways identified in the baseline risk
assessment?
Are the expected residual risks or short-term risks from one alternative significantly different from another?
What other risk-based benefits (e.g., shorter time to achieving goals) are realized by selecting one alternative over
another?
Will implementation of specific technologies create new chemicals of concern or new significant exposures or risks
for the surrounding community?
Is there a need for engineering controls or other measures to mitigate risks during implementation? Are such
controls available? How reliable are these controls?
Does the remedial alternative result in hazardous substances remaining at the site such that a five-year review or
reviews would be required?
DOCUMENTATION OF RISK EVALUATIONS
The risk evaluation conducted during the development and screening of alternatives (Section 2.1) and during the
detailed analysis of alternatives (Section 2.2) should be documented in the FS.
The proposed plan (Section 3.1) should contain a summary of the risk evaluations for the alternatives, including
any new risk information identified during development of the proposed plan.
The ROD (Section 3.2) should contain the results of the risk evaluations of the alternatives and the preferred
alternative, including any results developed since the proposed plan.
Any significant changes identified during RD/RA (Section 3.3) in the risk evaluations should be documented (e.g.,
in a memorandum).
Each five-year review (Section 3.4) should contain a statement on protectiveness and, if necessary, a recalculation
of risk and/or a new risk assessment.
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CHAPTER 2
RISK EVALUATION DURING
THE FEASIBILITY STUDY
The FS generally is a two-step process of
evaluating remedial alternatives: (1) screening, if
necessary, and (2) a more detailed analysis for
those alternatives that pass the screening. The
RI/FS Guidance provides information on
conducting the FS and describes all of the
evaluations that are performed. Some of these
evaluations pertain to human health risk, and the
guidance in this chapter assists in these
evaluations. (Ecological effects of remedial
alternatives not discussed in RAGS/HHEM
Part C also must be considered during the FS.)
2.1 RISK EVALUATION DURING
DEVELOPMENT AND
SCREENING OF
ALTERNATIVES
The overall objective of the development and
screening of alternatives is to identify an
appropriate range of waste management options,
some of which will be analyzed more fully in the
detailed analysis phase. This process usually takes
place relatively early in the RI/FS process, during
project scoping (before the baseline risk
assessment is completed).
The NCP specifies that the long-term and
short-term aspects of three criteria effectiveness,
implementability, and cost should be used to
guide the development and screening of remedial
alternatives. At screening, those alternatives that
are clearly unacceptable in terms of effectiveness
or implementability or are grossly excessive in cost
may be eliminated from further consideration.
Consideration of effectiveness involves
evaluating the long-term and short-term human
health risks among other factors associated
with a remedial alternative. The criteria of
implementability and cost are not related to risk
and, therefore, are not discussed in this document.
2.1.1 CONSIDERATION OF LONG-TERM
HUMAN HEALTH RISKS
The long-term human health risks associated
with a remedial alternative are those risks that will
remain after the remedy is complete (i.e., residual
risks). Evaluating long-term risks might ideally
include an assessment of the risks associated with
treatment residuals and untreated wastes (for a
treatment-based remedy), or an evaluation of the
remedy's ability to provide protectiveness over time
(for a containment-based remedy). This approach
might simply involve comparing estimates of the
final concentrations that a remedy is expected to
achieve in a medium with the PRGs for those
chemicals in that medium. At the screening stage,
however, this evaluation typically is based on
professional judgment and the experience of the
CERCLA program staff. Quantifying residual risks
during screening generally is not necessary. For
example, a technology may be evaluated during
screening for its potential to treat the classes or
treatability groups of chemicals present at the
site (e.g., volatile organics, halogenated organics,
non-volatile metals) rather than its ability to meet
chemical-specific PRGs. See Section 2.2.1 for
additional information on long-term risks
associated with remedial alternatives.
2.1.2 CONSIDERATION OF SHORT-TERM
HUMAN HEALTH RISKS
The short-term human health risks.associated
with a remedial alternative are those risks that
occur during implementation of the remedial
alternative (e.g., risks associated with emissions
from an onsite air stripper). Because some
remedies may take many years to complete, some
"short-term" risks may actually occur over a period
of many years. Populations that may be exposed to
chemicals during remedy implementation include:
(1) people who live and work in the vicinity of the
site and (2) workers who are involved in site
remediation. As with the consideration of long-
term risks, this evaluation is based primarily on
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many simplifying assumptions and on professional
judgment at the screening stage and is intended to
identify alternatives with clearly unacceptable
short-term risks. See Section 2.2.2 and Appendices
A and D for additional information on evaluating
alternatives for short-term risks during screening
and development of alternatives.
2.2 RISK EVALUATION DURING
DETAILED ANALYSIS OF
ALTERNATIVES
The overall objective of the detailed analysis of
alternatives is to obtain and present the
information that is needed for decision-makers to
select a remedial alternative for a site. This
detailed analysis usually takes place during the
later stages of the Rl/FS process (i.e.", near the end
of or after the baseline risk assessment, when
PRGs may have been modified). As discussed
previously, two of the balancing criteria assessed
during the detailed evaluation long-term
effectiveness and short-term effectiveness involve
an evaluation of risk. In addition, these criteria
are considered in evaluating the criterion of overall
protection of human health and the environment.
The risk evaluations of remedial alternatives
involve the same general steps as the baseline risk
assessment: exposure assessment, toxicity
assessment, and risk characterization. The box on
this page discusses the connection between the
baseline risk assessment and the risk evaluations of
remedial alternatives.
The guidance provided in this section assists in
assembling and using available site-specific
information for the purpose of completing the
detailed analysis of remedial alternatives,
specifically the evaluation of criteria that pertain to
human health risks. The box on the next page lists
several sources of information that can be used in
the risk evaluations that are conducted during the
RI/FS. The box on page 14 addresses the question
of whether a quantitative evaluation is needed.
The case studies at the end of this chapter-provide
examples of a qualitative and a quantitative
evaluation of long-term and short-term risks during
the detailed analysis.
CONNECTION BETWEEN THE BASELINE
RISK ASSESSMENT AND THE RISK EVAL-
UATION OF REMEDIAL ALTERNATIVES
A risk evaluation of remedial alternatives
follows the same general steps as a baseline risk
assessment. Detailed guidance on each step is
provided in RAGS/HHEM Part A, which must be
reviewed and understood lav the risk assessor
before a risk evaluation of remedial alternatives is
conducted. Note, however, that the baseline risk
assessment typically is more quantitative and
requires a higher level of effort than the risk
evaluation of remedial alternatives. Other
differences (and similarities) are listed below.
Evaluate Exposure (Fart A Chapter 6)
The source of releases for the baseline risk
assessment is untreated site contamination,
while the source of releases for the evaluation
of remedial alternatives is the remedial action
itself (plus any remaining waste).
Exposure pathways associated with
implementation of remediation technologies
may include some pathways and populations
that were not present (or of concern) under
baseline conditions.
'The evaluation of short-term exposures
associated with remedial alternatives may
consider a number of different releases that
occur over varying durations.
Evaluate Toxicity (Part A Chapter 7)
The risk evaluation of remedial alternatives
often involves less-than-lifetime exposures that
require appropriate short-term toxicity values
to characterize risk or hazard.
The risk evaluation of remedial alternatives
may include an analysis of chemicals that were
not present under baseline conditions (i.e.,
created as a result of the remedial alternative).
Characterize Risks (Part A Chapter 8)
A risk evaluation of remedial alternatives
generally considers risks to onsite workers, as
well as risks to the surrounding community.
There are additional uncertainties involved in
evaluating risks of remedial alternatives that
are not considered in the baseline risk
assessment (e.g., confidence in performance of
remedies and patterns of predicted releases,
confidence in attainment of clean-up levels).
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SOURCES OF INFORMATION FOR RISK EVALUATIONS DURING THE FS
Baseline Risk Assessment. Much of the data collected during the baseline risk assessment can also be used
to calculate the long-term residual risk associated with a remedial alternative. Some of the data may be applicable
to calculation of risks during the remedial action. Some of the information from the baseline risk assessment that may
be useful for analyzing the risks associated with the remedial alternative includes:
exposure setting, including exposed populations and future land use (RAGS/HHEM Part A, Section 6.2);
e exposure pathways, including sources of contamination, chemicals of concern, fate and transport of chemicals
after release, and exposure points (RAGS/HHEM Part A, Section 6.3);
general exposure considerations, including contact rate, exposure frequency, and duration (RAGS/HHEM
Part A, Section 6.4); ,
exposure concentrations, including monitoring data, modeling results, and media-specific results
(RAGS/HHEM Part A, Section 6.5);
estimates of chemical intake (RAGS/HHEM Part A, Section 6.6);
toxicity information (e.g., changes/additions to Integrated Risk Information System [IRIS] and Health Effects
Assessment Summary Tables [HEAST]) (RAGS/HHEM Part A, Chapter 7);
quantitation of risks (RAGS/HHEM Part A, Section 8.6); and
uncertainties associated with toxicity assessment, exposure assessment, and baseline risk characterization
(RAGS/HHEM Part A, Sections 6.8, 7.6, and 8.5).
Treatability Studies. Treatability investigations are site-specific laboratory or field studies, performed either with
laboratory screening, bench-scale, or pilot-scale study (see Section 5.3 of the RI/FS Guidance). Generic studies for
technologies (e.g., those performed by a vendor) can also contain useful information. Treatability studies may provide
risk-related data such as (1) information on short-term emissions and (2) information on removal efficiencies of a
technology. This information may be especially useful when considering innovative technologies. Guide to Conducting
Treatability Studies under CERCLA (under development by EPA's Risk Reduction Engineering Laboratory) provides
a three-tiered approach to conducting treatability studies during screening, selection, and design of remedial
alternatives. Chapter 5 of the RI/FS Guidance, especially Section 5.6, provides information on evaluating the
applicability of the treatability study results (e.g., determination of usefulness, documentation, usefulness of residual
information,, application of laboratory/ bench/pilot studies to full-scale system).
Feasibility Studies or Other Analyses for Comparable Sites. If a risk evaluation of one of the alternatives being
considered was conducted during the FS (or later stages) for a site with similar wastes and similar conditions, some
of the information that was developed may be helpful in characterizing the short-term or long-term risks associated
with that alternative. This type of information should be examined carefully to determine .whether the analyses are
appropriate for the site currently being evaluated. Differences in the types of hazardous substances present,
characteristics of environmental media, meteorological conditions, locations of receptors, or other factors could result
in large differences in the risk evaluation.
The Engineering and Technical Support Center of EPA's Risk Reduction Engineering Laboratory (513-569-7406
or FTS 684-7406) can provide information concerning treatability studies and evaluations of remedial technologies.
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FACTORS TO CONSIDER WHEN DECIDING
WHETHER A QUANTITATIVE RISK
EVALUATION IS NEEDED
The decision of whether to conduct a
quantitative or qualitative risk evaluation depends
on: (1) whether the relative short-term or long-
term effectiveness of alternatives is an important
consideration in selecting an alternative and (2) the
"perceived risk" associated with the alternative.
The perceived risk includes both the professional
judgment of the site engineers and risk assessors
and the concerns of neighboring communities.
Some factors that generally lead to a higher
perceived risk are as follows:
close proximity of populations;
presence of highly or acutely toxic chemicals;
technologies with high release potential, either
planned or "accidental";
high uncertainties in the nature of releases
(e.g,, amount or identity of contaminants
released) such as might exist with use of
certain innovative technologies;
multiple contaminants and/or exposure
pathways affecting the same individuals;
multiple releases occurring simultaneously
(e.g., from technologies operating in close
proximity);
* multiple releases occurring from remedial
actions at several operable units in close
proximity; and
releases occurring over long periods of time.
If consideration of these (or other) factors
leads to a high perceived risk for an alternative, a
more quantitative evaluation, including emission
modeling and/or detailed treatability studies, may
be helpful in the decision-making process. For
example, if one alternative considered for a site
involves extensive excavation in an area that is very
close to residential populations, then a more
quantitative evaluation of short-term risks may be
needed to evaluate this alternative. In addition,
other factors, such as available data and resources,
may affect the level of detail for these risk
evaluations.
2.2.1 EVALUATION OF LONG-TERM
HUMAN HEALTH RISKS FOR
DETAILED ANALYSIS
Evaluation of the long-term human health
risks associated with a remedial alternative
involves: (1) evaluating residual risk and
(2) evaluating the alternative's ability to provide
protection over time.
Evaluate Residual Risk. Because PRGs
generally are based on chronic human health risk.
considerations (e.g., ARARs such as maximum
contaminant levels (MCLs), or risk-based
concentrations), they usually provide the standard
to use to evaluate long-term health risks. When
site engineers are developing alternatives and
determining whether a technology is capable of
achieving PRGs, they are in effect evaluating
residual risk. (Therefore, the results from using
RAGS/HHEM Part B and other guidance on
remediation goals are very important for this part
of the analysis.)
Most of the time it will be sufficient for the
detailed analysis to indicate whether or not an
alternative has the potential to achieve the PRGs,
rather than to quantify the risk that will remain
after implementation of the alternative. If more
detailed information concerning long-term risk is
needed to select an alternative (e.g., to determine
the more favorable of two otherwise similar
alternatives), then it may be useful to determine
whether one alternative is more certain to achieve
the PRGs than the other, whether (or to what
extent) one may be able to surpass (i.e., achieve
lower concentrations than) the PRGs, or whether
one may be able to achieve the goals in a shorter .
time.
Certain remedial technologies (e.g.,
incineration) may produce new contaminants that
were not present at the site under baseline
conditions. The risks associated with these
additional substances generally should be
evaluated. Another consideration in evaluating
the residual risk associated with some alternatives
is the level of confidence in the ability of the
remedy as a whole to achieve the site engineers'
predictions. For some technologies (e.g., ground-
water extraction and treatment technologies), past
experience has indicated that, in some situations,
it may be difficult or impossible to achieve the
predicted goals. This information on the
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uncertainty associated with an alternative may be
an important factor in selecting a remedy.
After the individual technologies comprising a
remedial alternative have been examined
separately, then the alternative as a whole should
be examined to determine the extent to which it
meets the PRGs for all of the contaminated media
and all of the contaminants of concern. Even if
PRGs will be met, potential cumulative effects on
human health due to multiple contaminants,
media, or exposures may need to be considered. If
an alternative will not meet the PRGs for all
media or contaminants of concern or if cumulative
effects are a concern, this information should be
highlighted in the presentation of the results of the
detailed analysis.
Evaluate Protectiveness Over Time.
Evaluating -whether an alternative is likely to
maintain the specified level of protectiveness over
time (often referred to as "permanence") involves
using expert engineering judgment. In particular,
if an alternative relies on engineering or
institutional controls to reduce or eliminate
exposure to contaminated media, then the ability
of these controls to maintain protectiveness should
be considered. These types of remedies provide
protection by reducing or eliminating exposure to
hazardous substances rather than eliminating the
hazardous substances or reducing their
concentrations, volumes, or toxicity. Failure of
such remedies could lead to an increase in
exposure and therefore an increase in risk. For
example, if a remedy includes the capping of
contaminated soils, then the potential future
exposures due to cap failure include direct contact
with soils and the leaching of contaminants to
ground water. The worst-case situation of
complete containment system failure is unlikely to
occur, however, because five-year reviews (see
Section 3.4) are conducted at all sites where wastes
are managed onsite above concentration levels that
allow for unrestricted use and unlimited exposure.
2.2.2 EVALUATION OF SHORT-TERM
HUMAN HEALTH RISKS FOR
DETAILED ANALYSIS
Short-term health risks generally include any
current baseline risks plus any new risks that
would occur while implementing the remedy. As
discussed previously, the evaluation of potential
short-term risks involves the same general steps as
in the baseline risk assessment. These steps,
however, generally will not be conducted in the
same level of detail for the FS.
Other important points concerning level of
effort should be emphasized here. For example,
the Resource Conservation and Recovery Act
(RCRA) has performance standards for many
commonly used CERCLA remedial technologies
(e.g., incineratiqn). The risks associated with many
of these technologies were analyzed in developing
these standards, and the standards were set such
that the risks associated with operation of the
technology would be acceptable. Therefore, a
detailed evaluation of the risks associated with
RCRA-regulated technologies generally would not
be necessary. On the other hand, depending on
site-specific factors such as the toxicity of site
contaminants and the proximity of populations, a
more detailed evaluation of short-term risks may
indeed be appropriate.
Detailed analyses may also be appropriate for
less-characterized technologies (e.g., innovative
technologies). In addition, alternatives with
multiple short-term releases or substantial baseline
risks may need a more detailed evaluation to
determine whether cumulative risks are expected to
be within acceptable levels.
Of special note is that the short-term risk
evaluation for remedial alternatives during the
detailed analysis includes an evaluation of the
potential for short-term risks to two groups of
individuals: (1) neighboring populations (which
include onsite workers not associated with
remediation) and (2) onsite workers associated
with remediation.
Appendices A through D provide information
that can be used when a more quantitative
evaluation of short-term risks is needed to support
the selection of a remedy. Chapter 8 of
RAGS/HHEM Part A also provides guidance on
characterizing short-term risk.
Evaluate Short-term Exposure. A qualitative
exposure assessment for remedial alternatives
during the detailed analysis generally involves
just as in the baseline risk assessment, but in a less
quantitative manner using the concept of
reasonable maximum exposure (RME) to evaluate
release sources, receiving media, fate and transport,
exposure points, exposure routes, and receptors
associated with a particular alternative.
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An important difference between the baseline
risk assessment and the risk evaluation of remedial
alternatives involves exposure sources. For the
baseline risk assessment, the source of exposure is
untreated site contamination. For remedial
alternatives, however, the potential sources of
exposure are the releases that result from the
implementation of remedial technologies. In
additipn, some remedial alternatives (e.g.,
incineration, biodegradation) may result in new
chemicals that were not previously assessed for the
site.
The first step of the exposure assessment
involves identifying the types of releases associated
with a particular waste management approach.
During the detailed analysis, methods for
mitigating potentially significant short-term
releases should be examined, and releases that are
expected to be most difficult to control should be
highlighted.
Appendices A and D of this guidance each
contain two matrices that should assist in
characterizing the releases that may occur during
remedy implementation. Exhibit A-l provides a
brief description of common remedial technology
processes, and Exhibit A-2 summarizes potential
releases to different media during the normal
operation of various technologies. Exhibit D-l
provides a summary of releases associated with
radiation remedial technologies, and Exhibit D-2
includes a qualitative estimate of the potential
Short-term risks posed by a radiation remedial
technology.
After the releases and their receiving media
have been identified, the next step of the exposure
assessment is to determine whether major exposure
pathways exist Characterizing site-specific
exposure pathways involves identifying:
the general fate and transport of the
contaminants that are released from the
technology (e.g., downwind transport);
the potential exposure points and receptors
(e.g., nearby downwind residents); and
potential exposure routes (e.g., inhalation).
Exhibit 2-1 illustrates an example of an exposure
pathway for a remedial alternative. More detailed
information concerning exposure pathways is
available in Chapter 6 of RAGS/HHEM Part A.
The flow charts contained in Exhibit 6-6 of Part A
are particularly useful in determining the
populations potentially exposed by releases into a
particular medium. Transfers of contaminants
from one medium to other media also are
addressed.
At this point, a quantitative exposure
assessment if needed would involve (in
addition to identifying release sources, exposure
routes, and exposure points):
quantifying releases;
evaluating environmental fate and transport;
determining exposure point concentrations;
and
calculating intakes.
All of these steps are discussed in Chapter 6 of
RAGS/HHEM Part A.
Throughout the short-term exposure
assessment, the assessor must continually ask
whether the potential exposure warrants the level
of quantitation being used. At times, the answer
may not be known until the end of the exposure
assessment. For example, if short-term exposure
was estimated to be very similar to long-term
exposure, it would not be necessary to expend
resources to obtain the short-term toxicity
information needed to quantitatively characterize
risk.
A major difference between the exposure
assessment conducted during the baseline risk
assessment and the one conducted during the risk
evaluation of remedial alternatives is the
evaluation of the timing and duration of releases.
Because a number of different activities will lake
place during implementation, it is likely that the
quantities of hazardous substances released to the
environment will vary over time. For example, as
seen in Exhibit 2-2, one remedy can have several
distinct phases, each with .different exposure
potentials. It may be important to determine the
sequence of events and likely activities at each
phase of the remediation, so that the exposure
point can be evaluated for each phase. This will
also ensure that appropriate short-term exposure
durations are identified and that the potential for
releases to occur simultaneously and thus result in
cumulative risk is considered. As seen in
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EXHIBIT 2-1
ILLUSTRATION OF AN EXPOSURE
PATHWAY FOR A REMEDIAL ACTION
Exposure Medium
(Air)
Exposure
Point
Transport Medium (Air)
Prevailing Wind Direction
Inhalation
Exposure Route
Volatile Organic
Compounds
round Water
Pump and Treat
Apparatus
Contaminated
Ground Water
Exhibit 2-2, this issue is complicated by the
possible presence of baseline exposures.
Appendix B provides references organized
based on several important categories of remedial
technologies that can be consulted to quantify
the release of and therefore exposure to
contaminants. The information in Appendix B
includes a brief discussion of considerations in
release modeling and monitoring, a list of key
technology-related parameters generally needed as
inputs for models (e.g., meteorological conditions,
operation characteristics, soil/media
characteristics), an annotated list of primary
references, and a list of additional references.
Evaluate Short-term Toxicity. The'releases
that may occur during implementation of a
remedial alternative, and hence the exposure-point
concentrations, generally last for varying durations
and correspond to less-than-lifetime exposures.
Consequently, any toxicity values used to evaluate
the risks from these, shorter exposures must
correspond to the duration of the release (or
exposure). Three exposure durations, in addition
to longer-term exposures, may be of concern at
CERCLA sites undergoing remediation: single
exposure events (minutes, hours, or single day),
very short-term exposures (up to two weeks), and
short-term exposures (two weeks to seven years).
Note that the chronic toxicity values for
noncarcinogenic effects used most frequently in the
baseline risk assessment may not be appropriate
without modification for exposures of less than
seven years (otherwise they may be unnecessarily
conservative).
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EXHIBIT 2-2
ILLUSTRATION OF CUMULATIVE EXPOSURE FROM MULTIPLE RELEASES
00
Exposure
Cumulative
Cumulative
Residual
Technology 1
Technology 2
Baseline (Uncontrolled)
Baseline (Uncontrolled)
Residual
Time
Note: The graph illustrates how nearby populations at some sites could be exposed to both residual risks
and risks from remediation technologies. The cumulative exposure illustrated is the sum of residual
exposure and exposures associated with releases from Technologies 1 and 2. This exhibit is for illustration
purposes only and is not meant to imply that this level of quantitation is neccesary or even desired.
-------
Appendix C contains information concerning
the use of short-term toxicity values.
RAGS/HHEM Part A provides additional
information on assessment of contaminant toxicity.
As discussed in Appendix C, the Supeirfund Health
Risk Technical Support Center CTSQ should be
consulted in all cases where short-term toxicity
values are needed.
Characterize Short-term Risks to the
Community. During risk characterization,
exposure and toxicity information is brought
together to provide a measure or indication of the
magnitude and timing of short-term health risks (if
any) from the remedial alternatives. As discussed
previously, risk assessors may choose to
characterize the short-term risks to the community
(i.e., persons who live or work in the vicinity of the
site) quantitatively for some sites and qualitatively
for others. When short-term risks are not
expected to be a problem for a site, a more
qualitative evaluation generally is appropriate. In
these cases, a qualitative evaluation of the
magnitude, duration, and/or likelihood of the
exposures and risks should be conducted, and
assessors could describe short-term risks in a
qualitative manner relative to the results of the
baseline risk assessment.
A quantitative evaluation of short-term risks is
most likely to be useful when the types, levels,
and/or availability of hazardous substances are
expected to change significantly as a result of
remediation. If quantitative exposure estimates
and toxicity data are available, then a more
quantitative risk characterization may be
conducted. The quantitative method that is used
to characterize these risks depends in part on the
toxicity values that have been identified. Some of
these toxicity values (e.g., subchronic reference
doses) must be combined with the results of the
exposure assessment (i.e., intakes). The results of
risk characterizations using this type of toxicity
value will be of the same type as those generated
in the baseline risk assessment: hazard quotients
(or indices) or excess individual lifetime cancer
risks. If the toxicity values incorporate exposure
assumptions (e.g., as in one- and ten-day health
advisories), then these values are compared with
exposure concentrations to determine whether the
risks are above acceptable levels. Appendix C
provides additional information on short-term
toxicity values.
Cumulative effects from multiple releases or
multiple chemicals should also be considered, if
possible. If the risk characterization is qualitative,
then a discussion of the potential for cumulative
risks from multiple chemicals and/or exposure
pathways (e.g., due to simultaneous
implementation of several remedial technologies)
should be provided. If the results of the risk
characterization are more quantitative (e.g., cancer
risks and hazard quotients), then the information
concerning duration and timing of releases can be
used to calculate the cumulative risks or hazard
indices for those releases that will occur at the
same time and affect the same populations. If the
results of the quantitative risk characterization are
comparisons with short-term toxicity criteria, then
the total exposure concentrations can be calculated
for releases that occur at the same time and affect
the .same populations. These total exposure
concentrations then can be compared to the short-
term toxicity criteria. See Chapter 8 of
RAGS/HHEM Part A for additional guidance on
characterizing short-term human health risks.
Characterize Short-term Risks to Workers.
Worker health and safety issues should also be
considered during the development of the FS. The
Worker Protection Standards for Hazardous Waste
at 40 CFR 311 and 29 CFR 1910.120 establish
requirements for worker protection at CERCLA
sites, including requirements for planning (i.e.,
health and safety plans, and emergency response
plans), training, and medical surveillance.
Although the standards encompass areas that are
not directly related to worker risk
(e.g., illumination and sanitation), they also specify
requirements in areas that are directly relevant to
worker health risks. Specifically, once a remedy is
selected, the Worker Protection Standards require
that implementation of that remedy proceed with
the following risk-related considerations:
site characterization and analyses prior to
commencing remedial activities, specifically
risk identification (see 29 CFR 1910.120(c));
proper use of engineering controls, work
practices and personal"protective equipment
(PPE) for employee protection (see 29 CFR
1910.120(g)); and
preparation of emergency response plans that
specify how the site employees will be
protected while responding to onsite
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emergencies that may occur (see 29 CFR
1910.120(1)).
It is important to note, however, that factors not
associated directly with hazards particular to a
given site (e.g., risk of accidents during offsite
motor vehicle transport) are not usually considered
during the FS, but instead should be addressed
prior to remediation in the site health and safety
plan.
The exact nature of the assessment of worker
safety issues for a remedial alternative will vary
with each site. For many types of sites and
remedial alternatives, the risks to workers will be
well-characterized and will not require much
additional site-specific analysis. These issues will
be addressed in more detail in the site-specific
health and safety plan. Thus, a qualitative
assessment of worker risk is appropriate for most
sites during the FS and can be based on three
types of risk.
Potential for exposure to hazardous substances
during onsite remedial activities. The most
significant factor determining the potential for
exposure to hazardous substances is the nature
of the onsite contamination. Because onsite
remediation workers are equipped with the
appropriate PPE and are required to use
appropriate engineering controls, their risk
generally should be minimal. Factors that
affect the potential for exposure, however,
include the likelihood of PPE failure. In
general, more restrictive PPE is more likely to
fail due to considerations such as worker
mobility and visibility constraints, and
potential for worker heat stress.
Potential for injury due to physical hazards.
Onsite remediation workers may be exposed to
hazards other than exposure to hazardous
substances. Hazards such as explosion, heat
stress, and precarious work environments may
also pose threats to workers.
Potential for exposure during emergency
response activities (assuming the need arises
for onsite emergency response). Part of the
design of a remedial alternative should
consider the. potential for worker exposure
during emergency responses that may be
required in the event of remedy failure. For
some remedial alternatives, it is possible that
emergency assistance would be handled in part
by onsite workers, with offsite assistance (e.g.,
county HAZMAT teams) as required.
Alternatively, it is possible that an emergency
response plan would require the evacuation of
onsite remediation workers and use of offsite
emergency responders.
2.3 CASE STUDIES
The following two case studies provide
examples of the evaluations of long-term and
short-term risks that are conducted during the
detailed analysis. Both case studies present an
evaluation of only one technology for one of
several alternatives that are considered for the
hypothetical site. An actual detailed analysis
would include a similar evaluation for other
technologies and alternatives as well. The two
sites considered in the case studies are identical in
all respects, except one: the XYZ Co. site
considered in Case Study #1 is distant from
residential or worker populations, while the ABC
Co. site considered in Case Study #1 is adjacent to
a residential neighborhood. A more quantitative
analysis was conducted in Case Study #2 because
of concern for potential short-term exposures to
the neighboring community.
The sites presented in these case studies are
abandoned industrial facilities that are
contaminated with various volatile organic
compounds (VOCs) and heavy metals. VOCs
contaminate both the soil and ground water at the
sites, while metals are found in the soil only. A
number of leaking drums were stored above
ground at the sites and were removed prior to the
RI. There are also two lagoons filled with
hazardous sludges. City ground-water wells are
located approximately 1/4 mile from the' sites.
VOCs have been detected in the wells at levels
high enough to force the city to use an alternate
water source.
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CASE STUDY #1:
QUALITATIVE EVALUATION DURING DETAILED ANALYSIS
[Note: This case study presents an evaluation of only one technology for only one of several remedial
alternatives; an actual detailed analysis would address other technologies and alternatives as well. All data in
this case study are for illustration purposes only.]
Remedial Alternatives
Based on the, results of the development and screening of alternatives, the site engineers have identified five
alternatives (A through E) to be evaluated for use as remedies at the XYZ Co. site. One of the technologies
included in Alternative C is ground-water pumping and air stripping for the VOCs in ground water.
Evaluation of Long-term Risks
Meeting PRGs for all contaminants in ground water is uncertain at this point due to the complex nature of
the contaminated aquifer. If after remedy implementation it is determined that Alternative C does not meet PRGs
for all contaminants in ground water, then the residual risk remaining after implementation will be examined to
determine whether other measures need to be taken to assure protectiveness. There are no residual risks for media
other than ground water for the pump-and-treat/air stripping component of Alternative C.
Evaluation of Short-term Risks
The time-frame for air stripping of VOCs from ground water at the XYZ Co. site and therefore the time
frame considered for evaluating short-term risks is at least 20 years, and possibly as many as 50, depending on
factors such as the specific.aquifer characteristics. .
Releases and Receiving Media. The most likely release of concern from an air stripper is the release of air
contaminated with VOCs. The type of air stripper being considered for the XYZ Co. site generally achieves 99
percent or better removal of VOCs from water. The vapor phase VOCs contained in the air stripper off-gases then
can be removed if necessary using air pollution control devices such as granular activated carbon columns or an
afterburner, which generally achieve 90 to 99 percent destruction or removal of contaminants from the vapor phase.
However, there will still be some small release of contaminants that may need to be examined further during the
design stage of this remedy (if selected). Also, air pollution control devices will produce residues that in turn may
need to be treated. Other releases associated with air stripping include treated water containing residual organic
contaminants that will be released to surface water, and, possibly, fugitive air emissions due to leaky valves and
fittings.
Fate and Transport. Exposure Points, and Exposure Routes. The release of VOCs into the air during air
stripping at the XYZ Co. site could result in inhalation of volatiles transported through the air. However, the
nearest target population is over one mile from the site. Long-term average concentrations may be a concern, as
well as shorter-term or peak concentrations that may occur under certain conditions (e.g., temperature inversions).
Short-term Risks. The time period of exposure to air stripper off-gases (20 to 50 years) is a significant portion
of a human lifetime. However, because the concentrations of VOCs in ground water are not unusually high, the
releases associated with the air stripper are well-characterized, and there is no nearby target population, quantitation
of these risks is not needed to select a preferred alternative.
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CASE STUDY #2:
QUANTITATIVE EVALUATION DURING DETAILED ANALYSIS
(Note: This case study presents an evaluation of only one technology for only one of several remedial
alternatives; an actual detailed analysis would address other technologies and alternatives as well. All data in
this case study are for illustration purposes onlv.1
Remedial Alternatives
Based on the results of the development and screening of alternatives, the site engineers have identified five
alternatives (A through E) to be evaluated for use as remedies at the ABC Co. site. One of the technologies
included in Alternative C is ground-water pumping and air stripping for the VOCs in ground water. [For this case
study, only benzene from the pump-and-treat component of the remedial alternative will be analyzed in detail. In
an actual analysis, each contaminant of concern and each component of the remedy may need to be analyzed in a
similar fashion.]
Evaluation of Long-term Risks
The RI has shown that the organic contaminants in the ground water are adsorbed to the aquifer material and
are also dissolved in the ground water. The remediation goal for benzene will be readily met in the treated water,
which will subsequently be discharged into the nearby surface water. Remediation of the water remaining in the
aquifer, however, is much less certain. The residual concentration of benzene in this remaining water will depend
on several factors, including'the adsorptive characteristics of benzene with the aquifer material, the specific pumping
regimen, and the length of time that this technology is implemented. If, at a later stage (e.g., during the five-year
review), it is determined that the contaminants are not being extracted at the desired levels, the pumping regimen
may need to be modified (or some other approach may be needed). At a minimum, the pumping of ground water
is expected to be an effective barrier against further contaminant migration. Due to the uncertainty regarding the
residual concentration of contaminants that may remain in ground water, the permanence of the pump-and-treat
technology, in terms of future risks, is unknown at this time.
Evaluation of Short-term Risks
Short-term impacts due to air emissions from air stripping are expected to be the most significant risks from
the pump-and-treat component of the remedy at ABC Co. site. [This case study does not consider fugitive emissions
from sources "upstream" of the air stripper (e.g., separators, holding tanks, treatment tanks), although these sources
may have been evaluated in an actual risk assessment.] In order to assess these risks during the detailed analysis
stage, exposure concentrations from the ABC Co. site will be estimated by combining emissions modeling with
dispersion modeling. Before proceeding with this analysis, the following steps were taken.
*.
An appropriate atmospheric fate and transport model, derived from the SCREEN model developed by EPA's
Office of Air Quality and Planning Standards was chosen. (A more complete listing and comparison of
atmospheric fate models is given in Table 3-2 of the Superfund Exposure Assessment Manual [EPA 1988e].)
Required inputs for the atmospheric fate and transport model were obtained. These inputs included the
emission rate of contaminants from the air stripper into the atmosphere (based on contaminant concentrations
in ground water, system flow rate efficiency of the air stripping process, and efficiency of the air pollution
control device); atmospheric dispersion factors for contaminants; and meteorological data (wind speed, prevalent
direction, stability, mixing height, and temperature). More detailed parameters, such as surface roughness
height and specific topographic features, were not required for the model that was chosen.
(Continued)
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CASE STUDY #2:
QUANTITATIVE EVALUATION.DURING DETAILED ANALYSIS
. (Continued)
The population that will be affected by short-term releases was identified. This information was obtained from
the baseline risk assessment, and was based on the population distribution and density of the surrounding
community, and meteorological data such as the prevailing wind direction.
The toxicity characteristics of the contaminants were obtained from the baseline risk assessment.
Exposure Assessment. Releases are expected to occur during both the construction and the implementation
stages of the pump-and-treat technology. The time frame for each of these stages varies and, therefore, the release
and exposure potential also will vary. The most probable release of concern from implementation of the air stripper
[the focus of this case study] has been identified as the release of air contaminated with volatile organic chemicals
(VOCs) from the stripping tower to the atmosphere. Benzene is one of the volatile contaminants in the ground
water being treated, and is expected to be present as a residual in the stripper off-gases. The following equation
(EPA, Emission Factors for Superfand Remediation Technologies, Draft, Office of Air Quality Planning and
Standards, 1990) was used to calculate the benzene emission rate into the air stripper off-gases:
ER(g/s) = C x Qin x (SE/100) x K
where ER = emission rate of benzene (g/s)
C = concentration of benzene in water = 2.5 mg/L
Qin = influent water flow rate = 1700 L/min
SE = stripping efficiency of tower for benzene = 99.99%
K = constant to convert units = 1.67 x 10"5 (g-min/mg-s)
An SE of 99.99 percent is used in these calculations to determine the reasonable maximum emission rate of benzene
into the air. Actual SEs would be between 90 and 99.99 percent, depending on several operating parameters.
Solving this equation, ER = 0.071 g/s.
Because this system will use an air pollution control device (APCD) such as granular activated carbon (GAG)
columns to remove contaminants from gases released to the atmosphere, ER is the rate of release of benzene from
the ground water into the stripper off-gases rather than the rate of release of benzene directly to the atmosphere.
The release rate of benzene to the atmosphere, therefore, can be calculated using the following equation:
q = ER x (1 - DRE/100)
where q = mass release rate to atmosphere (g/s)
ER = emission rate from air stripper to APCD = 0.071 g/s
DRE = destruction/removal efficiency of APCD = 95%
A DRE of 95 percent is used to obtain a reasonable maximum release rate to the atmosphere. Applications of
similar APCDs achieve 95 to 98 percent destruction and removal efficiency for benzene in air. Solving for the
atmospheric release rate of benzene, q = 0.0035 g/s.
Using fate and transport modeling [analysis not shown], the atmospheric release rate of benzene is converted
to an exposure point concentration at a residence 250 m downwind of the site. The short-term air concentration
(24-hour average) of benzene is estimated to be 6 x 10'4 mg/m3. The average annual longer-term concentration of
benzene in air at the site boundary, as determined by the same model, is estimated to be 3.4 x 10"4 mg/m3.
(Continued)
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CASE STUDY #2:
QUANTITATIVE EVALUATION DURING DETAILED ANALYSIS
(Continued)
The only potential exposure pathway identified for releases from the air stripper is the air (inhalation) pathway.
Because the toxicity criterion used to characterize short-term risk is a threshold concentration (see Toxicity
Assessment below), a short-term intake does not need to be calculated. The longer-term intake is needed to
evaluate the cancer risk associated with inhalation of benzene. This intake is calculated by first obtaining the long-
term site-specific exposure duration of 30 years from the baseline risk assessment. (An exposure duration of 30
years is used because, while the time for implementation of the pump and air stripping technology may be up to 50
years, an individual is not expected to stay in the community for more than 30 years. If the maximum time for
implementation were less than the exposure duration identified in the baseline risk assessment, then exposure would
be computed using the maximum implementation time as the exposure duration.) Using other exposure values
obtained from the baseline risk assessment (e.g., inhalation rate of 20 m3/day), the longer-term (lifetime average)
intake of benzene due to the air stripper is approximately 7.3 x 10'5 mg/kg-day.
These concentrations and intakes are based on conservative steady-state assumptions regarding atmospheric
conditions. Therefore, there is uncertainty surrounding the atmospheric data (which are inputs to the model) that
could lead to higher (but probably lower) concentrations. For example, variations in wind speed and direction will
result in different contaminant concentrations for both maximum short-term and long-term exposure point
concentrations. Some amount of published research data is available (mainly from water treatment plant studies)
on the reliability of the APCDs used in air stripping. This information, combined with data from previous program
experience, indicates that the uncertainty associated with the effectiveness of the APCDs is low.
Toxicity Assessment. To assess risk from exposure to the short-term benzene concentration (24-hour average),
a toxicity criterion corresponding to a similar exposure duration is used. One such criterion, identified through
consultation with the TSC, is EPA's acute inhalation criteria (AIC). The AIC provides a threshold level above which
acute inhalation exposure to benzene could result in toxicity to the most sensitive target organ (bone marrow and
the immune system). The AIC for benzene is 190 ug/rn3:. [In this case study, the AIC for benzene was assumed
to be readily available. In an actual risk evaluation, this may not always be the case. When toxicity information is
not readily available especially when, as in this case study, the longer-term exposure point concentration is not
significantly different from the shorter-term point concentration (and the longer-term has toxicity information)then
either delaying the assessment or expending resources to obtain the shorter-term toxicity information is not
recommended.]
To assess risk from exposure to the longer-term benzene concentration (annual average) for the 30-year
exposure duration, the inhalation cancer slope factor for benzene of 0.029 (mg/kg-day)'1 is identified from the
baseline risk assessment.
Risk Characterization. Short-term risk to the community from benzene is determined by comparing the
short-term concentration of 6 x 10^ mg/m3 (i.e., 0.6 ug/m3), with the AIC of 190 ug/m3, to result in a ratio of 0.003.
Because this ratio is less than 1, short-term risk to the community solely from benzene is considered to be unlikely.
Using the longer-term intake of 7.3 x 10'5 mg/kg/day, and the slope factor of 0.029 (nig/kg/day)'1, the upper-
bound excess individual lifetime cancer risk to the community from long-term exposure to benzene in the
atmospheric releases from the air stripper is approximately 2 x 10'*, within EPA's acceptable risk range.
[Uncertainties associated with the site-specific exposure information and the toxicity information, discussed in
more detail in the baseline risk assessment, also are important to consider at this stage of the analysis.]
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CHAPTERS
RISK EVALUATION AFTER
THE FEASIBILITY STUDY
After the FS is completed, a remedy is
proposed, and, if selected, is documented in the
ROD. Following this, the remedy is designed and
implemented, and then deletion/five-year reviews of
the site take place. This chapter discusses the role
of risk information during these activities. Note.
however, that not all of these risk evaluations nor
a significant level of quantitation may be needed
for every site. The guiding principle is that risk
evaluations after the FS should be conducted as
necessary to ensure that the remedy is protective.
3.1 RISK EVALUATION FOR
THE PROPOSED PLAN
The purpose of a risk evaluation during the
proposed plan stage is to refine previous analyses
conducted during the FS, as needed. If new
information becomes available during the public
comment period for the proposed plan, additional
analysis of the alternatives may need to be
conducted at this time. If additional analysis is
conducted, it should be conducted for all the
alternatives, as appropriate, and not just for the
preferred alternative.
3.2 DOCUMENTATION OF
RISKS IN THE ROD
Several risk-related analyses should be
documented in the ROD. The comparative
analysis section should include a discussion of risk
as it pertains to the three risk-related criteria:
long-term effectiveness, short-term effectiveness,
and overall protection of human health and the
environment. The discussion of overall protection
of human health and the environment should
include a discussion of how the remedy will
eliminate, reduce, or control the risks identified in
the baseline risk assessment and whether exposure
will be reduced to acceptable levels. The
discussion of long-term effectiveness (and
permanence) should address, where appropriate,
the residual risk from untreated waste remaining at
the site. The part of the decision summary that
focuses on the selected remedy should present:
the chemical-specific remediation levels to be
attained at the conclusion of the response
action;
the corresponding chemical-specific risk levels;
the points (or areas) of compliance for the
media being addressed; and
the lead agency's basis for the remediation
levels (e.g., risk calculation, ARARs).
In addition, the ROD should indicate whether the
site will require five-year reviews (see Section 3.4).
In some cases, additional risk information (e.g.,
anticipated post-remedy cumulative risk for an
environmental medium or for a site) may need to
be included in the ROD.
Interim Final Guidance on Preparing Superfund
Decision Documents (EPA 1989f), Role of the
Baseline Risk Assessment in Superfund Remedy
Selection Decisions (EPA 1991d), and
RAGS/HHEM Part B provide additional
information on documenting risks in the ROD.
3.3 RISK EVALUATION DURING
REMEDIAL DESIGN/
REMEDIAL ACTION
The activities during remedy design and
implementation that may involve consideration of
risk include refining risk evaluations during
remedial design, monitoring short-term risks,
evaluating attainment of remedial levels in the
ROD, and evaluating residual risk.
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3.3.1 RISK EVALUATION DURING
REMEDIAL DESIGN
The process of evaluating long-term and short-
term risks, which began during the FS and may
have continued during development of the
proposed plan, also may continue during design of
the selected remedy for some sites. The purpose
for risk evaluations during the remedial design is
to ensure that the selected remedy will be
protective. These evaluations can be conducted by:
(1) refining previous analyses, as needed, and/or
(2) identifying the need for engineering controls or
other measures to mitigate risks. Methods for
evaluating long-term and short-term risks are
discussed in more detail in Chapter 2.
3.3.2 MONITORING SHORT-TERM
HEALTH RISKS DURING
IMPLEMENTATION
If the potential for short-term health effects
due to releases during remedy implementation
needs to be assessed (e.g., due to high uncertainty
concerning predicted risks to communities or
remediation workers), a sampling and analysis
strategy to accurately determine exposure
concentrations should be developed. This strategy
may need to consider the following elements:
location of sampling;
sample collection and handling procedures;
chemicals to be monitored and methods used;
and
statistical considerations regarding the analysis
of results.
The monitored exposure concentrations should be
compared to short-term health-based benchmarks
(see Appendix C) to help in determining whether
the release presents a threat to human health.
33,3 ASSESSING ATTAINMENT OF
SELECTED REMEDIATION LEVELS
DURING IMPLEMENTATION
The RPM, risk assessor, and others should be
involved in developing a sampling and analysis
plan to measure whether the selected remedy has
attained the remediation levels in the ROD. As in
the baseline risk assessment, this sampling and
analysis should provide data that can be used to
develop RME estimates. This plan is site-specific
and may need to consider the same elements
presented in Section 3.3.2, plus the relevant
remediation levels for the chemicals of concern.
The plan for measuring attainment should
ensure that sufficient data to evaluate
protectiveness of human health will be available.
For example, at a minimum, those chemicals that
contribute to major portions of the site risk should
be selected for measuring attainment. The two-
volume set Statistical Methods for Evaluating the
Attainment of Cleanup Standards (EPA 1988d)
outlines a number of statistical methods that can
be used to measure attainment. EPA is developing
additional guidance on this topic.
3.3.4 EVALUATION OF RESIDUAL RISK
This step which may be conducted at
completion of the remedy and perhaps during a
five-year review (see next section) may be
needed to ensure that the remedy is protective.
This step may be different from the assessment of
attainment of remediation levels selected in the
ROD because it may more closely consider the
expected land use and cumulative effects (e.g., due
to multiple chemicals or exposure pathways).
Residual risk estimates can be conducted at any
time after the remedy has commenced until the
end of the remedy. Typically, a final evaluation of
the cumulative site risk may be done following
completion of the final operable unit to ensure
that residual risks from multiple contaminants,
pathways, and operable units that affect the same
individuals are at protective levels.
In general, the same equations, exposure
parameters, and toxicity values that were used to
determine the baseline risk for a site can be used
to assess the final clean-up (risk) level that a
remedy has achieved. The concentrations that are
used to calculate these risks, however, are the final
measured concentrations of the contaminants that
remain at the site, not the remediation levels in
the ROD. The following are other potential
differences between the baseline risk assessment
and evaluation of residual risks.
Significant levels of "new" chemicals (e.g., that
were not identified during the baseline risk
assessment but that may have resulted from
the remedy or were not discovered until after
remedy implementation) should be considered
in evaluating residual risk.
-26-
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Changes in land use since the time of the
baseline risk assessment may require changes
in exposure parameters (e.g., contact rates,
exposure frequency and duration).
Toxicity values may have been updated since
the baseline risk assessment. The most recent
toxicity values in IRIS and HEAST should be
used in calculating residual risk.
For some sites where engineering or
institutional controls rather than treatment-based
remedies are employed, the concentrations of
chemicals in a contaminated medium may remain
the same as the baseline concentrations. The risk
will have been reduced or eliminated, however, by
mitigation or elimination of the exposure pathway
(e.g., by mitigating direct contact with soil by using
a cap or institutional controls, or eliminating
ingestion of contaminated drinking water by
providing an alternate water supply). These risk
reductions and associated exposure assumptions
should be clearly presented.
3.4 RISK EVALUATION DURING
FIVE-YEAR REVIEWS
Section 121(c) of CERCLA provides for
reviews of remedies that result in hazardous
substances remaining at the site no less often than
every five years after the initiation of the remedies.
The purpose of the reviews is to assure that human
health and the environment are being protected by
the remedial alternative that was implemented.
The remainder of this section briefly describes
the purpose of five-year reviews, the sites for which
five-year reviews are conducted, and the risk-
related activities that may be conducted during
five-year reviews. More detailed guidance
regarding five-year reviews is available in Structure
and Components of Five-year Reviews (EPA 1991e).
3.4.1 PURPOSE OF FIVE-YEAR REVIEWS
A five-year review is intended to ensure that a
remedy remains protective of human health and
the environment. The more specific goals of a
five-year f eview are:
to confirm that the remedy (including any
engineering or institutional controls) remains
operational and functional; and
to evaluate whether clean-up standards (based
on risk or ARARs) are still protective.
The first goal may be accomplished primarily
through a review of the operation and maintenance
records for a site and through a site visit and
limited analysis. The second goal includes an
analysis of requirements that have been
promulgated by the federal or state governments
since ROD signature to determine whether they
are ARARs and whether they call into question
the protectiveness of a remedy.
In addition to considering ARARs for
substances designated as contaminants of concern
in the ROD, the reviews may include changes in
ARARs for substances not addressed under
contaminants of concern. Where remediation
levels in the ROD were based on risk calculations
(rather than ARARs), then new information
such as revised toxicity values or exposure
parameters that could influence the
.protectiveness of the remedy should be considered.
Based on this analysis, the reviewer can determine
whether the original remediation levels set out in
the ROD are still protective.
3.4.2 SITES THAT RECEIVE FIVE-YEAR
REVIEWS
Two types of five-year reviews are conducted:
statutory and policy. . Statutory reviews are
conducted for remedies selected after the
enactment of SARA where, after the remedy is
complete, hazardous substances are present above
levels that allow for unlimited use and unrestricted
exposure. These sites generally include: (1) sites
with remedies requiring access or land-use
restrictions or controls (i.e., remedies that achieve
protectiveness through the use of engineering or
institutional controls); and (2) sites with remedies
that achieve protectiveness for the current use, but
include restrictions on activities due to limits on
exposure (i.e., sites cleaned up to levels that would
be protective for a nonresidential land use, but
would not be protective for residential or other
land use). Policy reviews are conducted for: (1)
sites with long-term remedial actions (LTRAs) or
other remedies that require five years or longer to
achieve levels that would allow for unlimited use
and unrestricted exposure and (2) remedies
selected before the enactment of SARA where
hazardous substances are present above levels that
allow for unlimited use and unrestricted exposure.
-27-
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Statutory reviews may be discontinued only if
levels of hazardous substances fall permanently to
a point that would allow unlimited use and
unrestricted exposure. Policy reviews for LTRAs
should be discontinued when the remediation goals
specified in the ROD are achieved, assuming these
levels allow for unlimited use and unrestricted
exposure. Achievement of these levels must be
verified by an appropriate period of monitoring.
3.4.3 RISK-RELATED ACTIVITIES DURING
FIVE-YEAR REVIEWS
Three levels of effort have been defined for
five-year reviews. The following are risk-related
activities conducted for the three levels.
At Level I, the reviewer will consider the risk
assessment information contained in the ROD
and ROD summary.
At Level II, the reviewer will conduct a
recalculation of the original baseline risk
assessment using information obtained during
the review (e.g., new toxicity data). If
appropriate, additional data may be collected.
Ongoing monitoring may provide such data.
At Level III, the reviewer will reevaluate the
risk assessment, and, if appropriate, conduct a
new risk assessment. Such an assessment may
be appropriate in order to address a new site
condition, such as a new exposure pathway.
New data may be collected as necessary for the
risk assessment. If possible, however, existing
data should be used.
The appropriate level of review depends on
site-specific conditions and the confidence level for
the selected remedy. The proposed level of the
first review is to be included in the ROD. A Level
I review should be appropriate in all but a few
cases where site-specific circumstances suggest
another level either at the outset of the review or
because findings of the review suggest the need for
further analysis. A Level III review would not be
proposed in the ROD, but would be initiated in
response to specific concerns regarding the
performance of the remedy or the risks at the site.
The level of effort, particularly for subsequent
reviews, also depends on the initial findings of the
review. Structure and Components of Five-year
Reviews (EPA 1991e) provides additional
information concerning the appropriate level for
reviews and the activities that are conducted at
each level.
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REFERENCES
U.S. Environmental Protection Agency (EPA). 1988a. Community Relations in Superfund: A Handbook.
Interim Version. Office of Emergency and Remedial Response. EPA/540/6-88/002 (OSWER Directive
9230.0-3B).
EPA. 1988b. Guidance on Remedial Actions for Contaminated Ground Water at Superfund Sites. Interim
Final. Office of Emergency and Remedial Response. EPA/540/G-88/003 (OSWER Directive 9283.1-2).
EPA 1988c. Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA,
Interim Final. Office of Emergency and Remedial Response. EPA/540/G-89/004 (OSWER Directive
9355.3-01).
EPA 1988d. Statistical Methods for Evaluating the Attainment of Superfund Cleanup Standards Volume I:
Soils and Soil Media. Office of Policy, Planning, and Evaluation. EPA 230/02-89-042.
~*
EPA 1988e. Superfund Exposure Assessment Manual. Office of Emergency and Remedial Response.
EPA/540/1-88/001 (OSWER Directive 9285.5-1).
EPA. 1988f. Seven Cardinal Rules of Risk Communication. Office of Public Liason. OPA-87-020.
EPA 1989a. Considerations in Ground Water Remediation at Superfund Sites. Office of Emergency and
Remedial Response. OSWER Directive 9355.4-03.
EPA 1989b., Ecological Assessment of Hazardous Waste Sites: A Field and Laboratory Reference.
Environmental Research Laboratory. EPA/600/3-89/013.
EPA 1989c. Estimation of Air Emissions from Clean-up Activities at Superfund Sites. Office of Air Quality
Planning and Standards. EPA-450/1-89-003.
EPA 1989d. Exposure Factors Handbook. Office of Health and Environmental Assessment. EPA/600/8-
89/043.
EPA. 1989e. Interim Guidance for Soil Ihgestion Rates. Office of Solid Waste and Emergency Response.
OSWER Directive 9850.4.
EPA 1989f. Interim Final Guidance on Preparing Superfund Decision Documents. Office of Emergency
and Remedial Response. OSWER Directive 9335.3-02.
EPA. 1989g. Risk Assessment Guidance for Superfund: Volume I Human Health Evaluation Manual
(Part A, Baseline Risk Assessment). Interim Final. Office of Emergency and Remedial Response.
EPA/540/1-89/002.
EPA 1989h. Risk Assessment Guidance for Superfund: Volume II Environmental Evaluation Manual.
Interim Final. Office of Emergency and Remedial Response. EPA/540/1-89/001A (OSWER Directive
9285.7-01).
EPA 1990a. Guidance for Data Useability in Risk Assessment. Office of Solid Waste and Emergency
Response. EPA/540/G-90/008 (OSWER Directive 9285.7-05).
EPA. 1990b. Guidance on Remedial Actions for Superfund Sites with PCB Contamination. Office of
Emergency and Remedial Response. EPA/540/G-90/007 (OSWER Directive 9355.4-01).
-29-
-------
EPA. 1991a. Conducting Remedial Investigations/Feasibility Studies for CERCLA Municipal Landfill Sites.
Office of Emergency and Remedial Response. EPA/540/P-91/001 (OSWER Directive 9355.3-11).
EPA. 1991b. Risk Assessment Guidance for Superfimd, Volume 1, Human Health Evaluation Manual,
Supplemental Guidance: "Standard Default Exposure Factors". Office of Emergency and Remedial
Response. OSWER Directive 9285.6-03.
EPA. 1991C. Risk Assessment Guidance for Superfund: Volume I Human Health Evaluation Manual
(Part B, Development of Risk-based Preliminary Remediation Goals). Interim. Office of Emergency and
Remedial Response. OSWER Directive 9285.7-01B.
EPA. 1991d. Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions. Office of
Solid Waste and Emergency Response. OSWER Directive 9355.0-30.
EPA. 1991e. Structure and Components of Five-year Reviews. Office of Emergency and Remedial
Response. OSWER Directive 9355.7-02.
EPA 1991f. Guidance on Oversight of Potentially Responsible Party Remedial Investigations and Feasibility
Studies. Office of Solid Waste and Emergency Response. EPA/540/G-91/010a (OSWER Directive
9835.1(c)).
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APPENDIX A
SELECTED REMEDIATION TECHNOLOGffiS
AND ASSOCIATED POTENTIAL RELEASES
This appendix contains two exhibits designed
to assist during the FS in identifying some of the
potential releases that are associated with
commonly used remediation technologies. Exhibit
A-l briefly describes each of the process options of
each technology in Exhibit A-2. Exhibit A-2
summarizes several potential releases to air or
water of common remedial technologies. Process
variations for which potential releases are similar
are combined under the technology category.
Potential releases to surface water or ground water
are included in the "water" column. "Other"
releases include treatment residuals that need
further treatment or proper disposal. In most
cases, this column refers to sludge or solid residues
that may also be hazardous.
Risk Reduction Engineering Laboratory
(RREL; Cincinnati, Ohio) plans and conducts
engineering, research, and development related to
treatment of solid and hazardous wastes. RREL
personnel,provide site-specific technical services
involving specific treatment technologies and
CERCLA response processes including:
analysis of treatment alternatives,
treatability studies,
remedial design review,
construction QA/QC methods, and
contaminant source control and geotechnical
test methods.
Regional EPA CERCLA staff should direct
questions regarding evaluations of remediation
technologies, previous experience with remediation
technologies, and releases associated with
remediation technologies to the Engineering and
Treatment Technical Support Center, RREL at
FTS 684-7406 or 513-569-7406.
-31-
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EXHIBIT A-l
REMEDIATION TECHNOLOGY DESCRIPTIONS
to
Technologies
Description of Process
SOIL AND SLUDGE
Soil Handling
Soil Excavation, Transport,
Dumping, and Grading
These processes use mechanized equipment to move contaminated soil. For some
treatment techniques, soil must be removed from a contaminated site and be transported
for treatment. Soil is then returned and replaced at either the original excavation or
another disposal site. Grading is a technique which can reduce infiltration into
contaminated soils and can also control runoff.
Thermal Destruction These are destruction processes which control temperature and oxygen availability, and
convert hazardous materials to carbon dioxide, water, and other products of combustion.
Circulating Bed Incineration
Rotary Kiln Incineration
Fluidized Bed Incineration
Infrared Incineration
Pyrolysis
Wastes and auxiliary fuel are introduced into the combustion chamber. Air is forced up
through the chamber from the bottom to promote mixing and complete combustion.
Particulate and gaseous products of combustion exit from the top of the combustion
chamber for treatment and disposal.
The combustion chamber is a rotating, inclined cylinder which mixes combusting materials
as it rotates. Wastes are fed into the chamber at the high end, along with air and auxiliary
fuel. Exhaust gases are treated and released, and ash residue is collected on the low end of
the kiln.
A bed of inert particles (e.g., sand) lies at the bottom of the cylindrical combustion
chamber. Air is forced up through the bed and the particles are fluidized (i.e., the particles
"float" in the airstream). Wastes and fuel are injected at the top of the chamber, into the
fluidized mass, where the mixture combusts. The turbulent atmosphere in the chamber
provides good mixing of wastes to ensure complete combustion and efficient heat transfer.
Waste.materials are fed into the furnace on a conveyor belt, and pass through on a wire
mesh belt. Heating elements provide infrared energy, oxidizing the materials. Waste gases
are passed through a secondary combustion chamber; ash exits on the conveyor.
Organics are slowly volatilized at lower temperatures than incineration processes. Waste is
fed into the primary combustion chamber and thermally treated without sufficient oxygen to
completely combust. Volatilized organics pass to a secondary chamber and are incinerated.
Solid residues from the primary chamber receive other treatment.
(Continued)
-------
EXHIBIT A-l (Continued)
REMEDIATION TECHNOLOGY DESCRIPTIONS
OJ
Technologies
Wet Air Oxidation
Aqueous Thermal Decomposition
Description of Process
The high temperature and high pressure properties of water are utilized in destroying
wastes. Contaminated solutions are treated at high temperatures (>600° C) and pressures
(3400 psi to 3700 psi). Contaminants are oxidized to simple organic compounds as large
amounts of oxygen are dissolved in solution.
Aqueous thermal decomposition works on the same principles as wet air oxidation, without
the addition of excess oxygen.
Dechlorination
Glycolate Dechlorination
Using a specific solvent, chlorine atom(s) are removed from chlorinated hazardous
materials, and toxic compounds are converted to less toxic, more water-soluble compounds.
Reaction products are more easily removed from soil and more easily treated.
Biological Treatment
Composting
In-situ Biodegradation
Slurry-phase Biodegradation
Solid-phase Biodegradation
Contaminated material is mixed with bulking agents (e.g., sawdust, wood chips) and placed
in reactor vessels or piles. Aeration, temperature, and nutrient levels are controlled to
encourage microbial growth. Microorganisms then metabolize contaminants, breaking them
down into less-harmful materials.
Microorganisms are encouraged to decompose contaminants in soil without excavating the
soil and placing it in a controlled reactor. Nutrients, oxygen, and other necessary materials
can be injected into the contaminated area.
The wastes are mixed with water to achieve an aqueous mixture. The mixture is then
treated in a bioreactor, where it is mixed continuously to contact microorganisms and
contaminants. The bioreactor serves as a controlled environment for contaminant
degradation.
Soils are excavated and treated above ground so that treatment conditions can be closely
monitored iand adjusted to conditions that are ideal for biodegradation. Materials are
treated in a prepared area which can include volatile emissions collection and leachate
collection.
(Continued)
-------
I
EXHIBIT A-l (Continued)
REMEDIATION TECHNOLOGY DESCRIPTIONS
Technologic
Description of Process
Vacuum/Vapor Extraction, Thermal Pesorption
Low Temperature Thermal
Stripping
Air, pressure, heat, and/or mechanical agitation provides a driving force for volatilizing and
removing contaminants from soil into an airstream for further treatment. Separating
contaminants from soil simplifies the final treatment of contaminants
In-situ Vacuum/Steam Extraction
VOCs are removed from soil by applying a vacuum to wells that are placed in the
contaminated soil. VOC vapors are collected and treated above ground. Some systems also
inject hot air or steam into contaminated zones, raising temperatures and volatilizing organic
chemicals.
Chemical Extraction & Soil Washing
In-situ Chemical Treatment
Treatment chemicals are applied directly to contaminated soil. A variety of compounds can
be applied, including neutralizing agents, oxidants, solidification/stabilization agents, and
nutrients for biological treatment.
Chemical Extraction & Soil
Washing
Contaminants are washed from the excavated soil into a chemical solvent. The liquid is
treated to remove and destroy contaminants, and the solvent is reused.
In-situ Soil Flushing
Inorganic or organic contaminants are extracted from soil by washing the soil with solvents.
Solvents are recovered, contaminants are extracted, and the solvents are recirculated
through the soils. ^
Immobilization
Capping
Contaminated soil is covered with low-permeability layers of synthetic textiles or clay. The
cap is designed to limit infiltration of precipitation and thus prevent migration of
contaminants away from the site and into ground water.
Solidification/Stabilization
Wastes are converted to chemically stable forms or are bound in a stable matrix. Chemical
reactions are utilized to transform hazardous materials into new, non-hazardous materials.
The goal is to prevent migration of contaminants.
In-situ Vitrification
Electrodes are placed vertically into the contaminated soil region, and an electrical current is
applied. The soil is melted by the resulting high temperatures. When the melt cools and
solidifies, the resulting material is stable and glass-like, with contaminants bound in the solid.
(Continued)
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EXHIBIT A-l (Continued)
REMEDIATION TECHNOLOGY DESCRIPTIONS
w
en
; Technologies
Description of Process
GROUND AND SURFACE WATER
Natural Attenuation
Aeration/Air Stripping
Filtration
Sedimentation
Granular Activated Carbon (GAC)
Adsorption
Ion Exchange
Chemical Treatment
Biological Treatment
Contaminants in an aquifer disperse and dilute through natural ground-water transport.
Some natural degradation may occur.
Contaminants, usually volatile organic compounds, are transferred from liquid phase to
gaseous phase. By contacting contaminated water with clean air, dissolved VOCs are
transferred to the airstream to create equilibrium between the phases. The process takes
place in a cylindrical tower packed with inert material which allows sufficient 'air/water
contact to remove volatiles from water. Contaminants are then removed from the
airstream.
Filtration removes suspended solids from liquids by passing the mixture through a porous
medium.
Solids that are more dense than liquid settle by gravity and can be removed from the liquid.
Chemicals to aid settling maybe added. Settled solids result in a sludge which may be
treated further.
GAC is packed in vertical columns, and contaminated water flows through it by gravity.
GAC has a high surface area to volume ratio, and many compounds readily bond to the
carbon surfaces. Contaminants from water are thus adsorbed to the carbon, and effluent
water has a lower contaminant concentration. Water may be passed through several of
these columns to complete contaminant removal. Spent carbon (i.e., carbon trial has
reached its maximum adsorption capacity) is regenerated by incineration.
As contaminated water flows through the reactor vessel, ions of contaminants are adsorbed
to a synthetic resin in the vessel. The resin attracts and adsorbs contaminant ions, while
releasing non-harmful ions into the treated water.
Chemicals can be added to contaminated waters to chemically change or to remove
constituents. Precipitation can be accomplished through pH control; solutions can be
neutralized; contaminants can be oxidized; and solids can be settled out of solution.
Microorganisms in controlled-environment reactors are utilized to decompose contaminants
in water. Nutrients, pH, temperature, and oxygen availability are controlled. The organisms
degrade contaminants into simpler, safer compounds.
(Continued)
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EXHIBIT A-l (Continued)
REMEDIATION TECHNOLOGY DESCRIPTIONS
Technologies
Description of Process
Membrane Separation
Reverse Osmosis
Elecirodialysis
A semi-permeable membrane is used lo separate dissolved contaminants from liquids. High
pressure is applied to the contaminated solution, which drives only the liquid through the
membrane. The result is a highly concentrated contaminated solution on the high pressure
side of the membrane, and a purified liquid on the opposite side of the membrane.
This process concentrates ionic species that arc in aqueous solution. The solution is passed
through alternate cation-permeable and anion-pcrmeablc membranes that have an applied
electric polcntial. This potential provides a driving force for ion migration.
-------
EXHIBIT A-2
REMEDIATION TECHNOLOGIES AND SOME POTENTIALLY SIGNIFICANT RELEASES
Technologies
Air
Water"
Otherb
SOIL AND SLUDGE TECHNOLOGIES
Soil Handling
Soil Excavation, Transport,
Dumping, Screening and
Grading
Fugitive emissions of
particulates and volatiles
Runoff or leaching of
contaminants to surface or
ground water
' Seepage or runoff to nearby
soil
Thermal Destruction
Incineration: Rotary Kiln,
Fluidized Bed, Circulating
Bed, and Infrared
Pyrolysis ,
Wet Air Oxidation
Aqueous Thermal
Decomposition
Fugitive and stack emissions
of metal fumes; particulates,
including metals and salts;
and products of incomplete
combustion, including organic
compounds, acid gases, CO,
NOX, and SOX
Fugitive and stack emissions
of metal fumes; particulates,
including metals and salts;
and products of incomplete
combustion, including organic
compounds, acid gases, CO,
NO,,, and SOX
Fugitive emissions of volatile
organic compounds
Fugitive emissions of volatile
organic compounds
Discharge of scrubber liquor
and blowdown
Discharge of scrubber liquor
and blowdown
Discharge of metals and
unoxidized organics
« Discharge of metals and
unoxidized organics
Disposal of ash and other
solid residues
Disposal of ash and other
solid residues
Disposal of sludge residues
Disposal of sludge residues
(Continued)
-------
r
OJ
EXHIBIT A-2 (Continued)
REMEDIATION TECHNOLOGIES AND SOME POTENTIALLY SIGNIFICANT RELEASES
Technologies
Air
Water1
Other1
Dechlorination
Glycolate Dechlorination
Fugitive emissions of volatile
organic compounds
Discharge of spent solvents
and degraded contaminants
to surface water, or leaching
to ground water
Biological Treatment
Composting
In-situ Biodegradation
Slurry-phase or Solid-phase
Biodegradation
Fugitive emissions of
particulates and volatile
organics
Fugitive emissions of volatile
organics
Fugitive emissions of volatile
organics
Leaching of metals and/or
organics
Leaching of metals and/or
organics
« Discharge of treated water
Discharge of non-degraded
byproducts in slurry liquor
and treated effluent
Runoff to surface water or to
ground water (with solid-
phase process)
Disposal of residual biomass
which may contain
hazardous metals and
refractory organics
Vacuum/Vapor Extraction, Thermal Desorption
Low Temperature Thermal
Stripping
In-situ Vacuum/Steam
Extraction
Stack emissions of volatile
organics
Fugitive emissions of volatile
organics
Fugitive emissions of volatile
organics
Discharge of scrubber
blowdown
Discharge of contaminant
condensate
Discharge of contaminant or
water condensate
Disposal or regeneration of
spent activated carbon
(Continued)
-------
U)
VO
EXHIBIT A-2 (Continued)
REMEDIATION TECHNOLOGIES AND SOME POTENTIALLY SIGNIFICANT RELEASES
Technologies
Air
Water"
Other*
Chemical Extraction & Soil Washing
In-situ Chemical Treatment
Chemical or Solvent
Extraction
Soil Washing
In-situ Soil Flushing
Fugitive emissions of volatile
organic compounds
Fugitive emissions of volatile
organic compounds
Fugitive emissions of volatile
organic compounds
-\ '
Fugitive emissions of volatile
organic compounds
Runoff of uncontained
treatment chemicals
Post-extraction discharge of
wastewater with extracted
contaminants
Post-washing discharge of
wastewater with extracted
contaminants
Leaching of contaminated
flush water, acids, bases,
chelating agents, or
surfactants
Possible solvent residuals in
treated soil
Possible solvent residuals in
treated soil
Discharge of foam with
metals and organics
Deposition of sedimentation
sludge residuals
Deposition of untreated,
contaminated fines
Immobilization
Capping
Solidification/Stabilization
Fugitive emissions of
particulates and volatiles
during cap construction
Fugitive emissions of
particulates and volatiles
Leaching of contaminants to
ground water
None likely
Lateral movement of volatile
organic compounds after
capping
Potential leaching to soils
and ground water of
contaminants from deposited
material over time
(Continued)
-------
i.
c
EXHIBIT A-2 (Continued)
REMEDIATION TECHNOLOGIES AND SOME POTENTIALLY SIGNIFICANT RELEASES
Technologies
In-silu Vitrification
Air
Surface fugitive emissions of
volatile organics and volatile
metals during the process
Water*
Discharge of scrubber
solution
Possible contamination of
ground water under the
treatment area
Other*
Potential lateral migration of
vaporized or leached
contaminants into the soil
that surrounds the vitrified
monolith
GROUNDWATER AND SURFACE WATER TECHNOLOGIES
Non-Treatment Actions
Natural Attenuation
Pump without Treatment
Air Stripping
Filtration/Settling
Granular Activated Carbon
Adsorption
Emissions of volatile organic
compounds
Emissions of volatile organic
compounds
Stack and fugitive emissions
of volatile organics
Fugitive emissions of volatile
organic compounds from
settling basin
None likely
Aquifer discharge to surface
water "
Continued aquifer transport
of contaminants
Discharge of untreated water
to surface water or Publicly
Owned Treatment Works
(POTW)
Seepage of untreated water
Discharge to surface water of
effluent treated water with
residual metals, particulates, ,
or nonvolatile organics
Discharge of effluent water
containing dissolved solids or
unremoved particles
Discharge of effluent with
non-adsorbable, low
molecular weight compounds
Disposal of sludge residuals
from POTW
Disposal of backwash or
cleaning residues
Disposal of filter cake or
sludge containing organics,
metals, or other inorganics
Disposal and/or regeneration
of spent carbon
(Continued)
-------
EXHIBIT A-2 (Continued)
REMEDIATION TECHNOLOGIES AND SOME POTENTIALLY SIGNIFICANT RELEASES
Technologies
Ion Exchange
Chemical Treatment
Biological Treatment
Air
None likely
Fugitive emissions of volatile
organic compounds from
treatment tanks
* Emissions of volatile organics
in aerobic treatment or due
to aeration
Water"
Discharge of backwash water
Discharge of effluent with
treatment residues
» Discharge of effluent with
unremoved solids
Other11
Disposal and/or regeneration
of spent resins
Disposal of treatment
sludges
Disposal of treatment
sludges
Membrane Separation
Reverse Osmosis
Electrodialysis
None likely
None likely
Discharge of effluent
containing unfiltered organics
(depends on filter membrane
used)
Discharge of treated effluent
Discharge of concentrate
stream with contaminants
removed from treated water
/
Discharge of concentrate
stream with contaminants
removed from treated water
Notes:
a In genera], seepage and leaching are more likely to affect ground water, but could also contaminate surface water. Runoff and discharge are releases that will most
likely contaminate surface water, but could also contaminate ground water.
b Other releases include treatment residuals that need further treatment or proper disposal. In most cases, this column refers to sludge or solid residues that may also
be hazardous.
-------
REFERENCES FOR APPENDIX A
Peavy, Howard S., Donald R. Rowe, and George Tchobanoglous. 1985. Environmental Engineering. McGraw-
Hill, New York.
U.S. Environmental Protection Agency (EPA). 1987. A Compendium of Technologies Used in the Treatment
of Hazardous Wastes. Center for Environmental Research Information. EPA/625/8-87/014 (NTIS PB90-
274093/XAB).
EPA. 1988. Technology Screening Guide for Treatment ofCERCLA Soils and Sludges. Office of Research and
Development. EPA/540/2-88/004 (OSWER Directive 9380.0-25, NTIS PB89-132674).
EPA. 1989. Summary of Treatment Technology Effectiveness for Contaminated Soil. Office of Emergency and
Remedial Response. EPA 540/2-89/-53.
EPA. 1990. National Technical Guidance Series, Air/Superfimd Manual, Volume 3. Office of Air Quality
Planning and Standards. EPA-450/1-89-003 (NTIS PB89 180061/AS).
EPA. 1990. The Superfund Innovative Technology Evaluation Program, Progress and Accomplishments Fiscal
Year 1989. Office of Solid Waste and Emergency Response. EPA/540/5-90/001 (NTIS PB90-216516/XAB).
EPA. 1991. Comments from Laurel Staley, Ed Bates, Ron Lewis, Teri Shearer, John Herrmann, Paul
dePercin, Ed Earth. Coordinated by Mary Gaughan, Superfund Technology Demonstration Group, Cincinnati,
Ohio.
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APPENDIX B
QUANTIFYING POTENTIAL RELEASES FROM
SELECTED REMEDIATION TECHNOLOGIES
Remediation activities at hazardous waste sites
have the potential to cause emissions and impacts
in addition to those being addressed. Potential
emission sources during remediation include point
sources of treatment residuals such as incinerator
stacks; fugitive emissions from treatment
equipment leakage; and areal sources of volatile
organics and fugitive dusts from the disturbed
surface of a contaminated land area. Uncontrolled
releases can result in exposures to contaminants in
soils, surface water, ground water, and ambient air
surrounding the treatment equipment. . The
following sections provide descriptions of several
common remediation activities to serve as
examples of the considerations involved in
quantifying technology-specific releases. This
appendix also contains a list of references that can
be useful in quantifying potential air releases for a
variety of remediation technologies.
B.1 SOILS HANDLING
TECHNOLOGIES
Soils handling is a major component of nearly
all ex-situ technologies for treating contaminated
soils. Soil handling activities include: excavation;
transportation (e.g., to storage or treatment areas);
dumping (e.g., onto trucks or piles); storage; and
grading the treated or replaced soil. Any or all of
these activities may result in fugitive dust
emissions, the main type of release from soils
handling. These emissions can carry organic
and/or inorganic contaminants, which may be
bound to soil particles, for great distances away
from the site. Soil handling activities also can
increase volatile organic emissions by exposing
contaminated soil to the atmosphere, and through
agitation of the soil.
Some of the important parameters that may
affect the fugitive dust emissions potential at a
contaminated site are listed in the box below.
These parameters depend on site and remedial
activity characteristics. Details can be obtained
from onsite observation or from.vendors and/or
operators. Some or all of these parameters may
already have been considered in the RI/FS.
Fugitive dust emission factors (mass, per unit
operation) or rates (mass per unit time, derived
from emission factors) for volatile. organic,
paniculate and/or metal contaminants during each
soil handling remedial activity can be estimated
using equations and procedures outlined in the
documents listed in Section B.4. These emission
factors or rates can be used as inputs to fate and
transport models, which are used to generate
exposure point concentrations. Additional
information on exposure assessment can be
obtained from Chapter 2 of this guidance and
Chapter 6 of RAGS/HHEM Part A,
KEY PARAMETERS AFFECTING
RELEASES FROM SOILS HANDLING
Area of working surface
Agitation factor
Drop height (when transferring soil)
Storage pile geometry
Soil moisture content
Soil silt content
Meteorological conditions
Chemical characteristics
B.2 THERMAL DESTRUCTION
TECHNOLOGIES
Thermal destruction uses high temperature
and controlled conditions to oxidize and/or degrade
a substance into simple combustion products such
as CO2, H2O vapor, SO2, NOX, HC1 gases, and ash.
Thermal destruction methods can be used to
destroy organic contaminants in liquid, gaseous,
and solid waste streams. Incinerators are by far
the best known and most studied thermal
destruction devices. In many cases, thermal
destruction techniques that do not have sufficient
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emission data can be assumed to have emission
characteristics similar to incinerators.
Emission sources from incinerators include
process emissions and fugitive emissions.
Incinerator process emissions include stack gas,
bottom ash, and air pollution control device
residuals. Fugitive emissions include uncontrolled
or undetected equipment leakage. Process
emission estimation methods for organic
compounds, metals, particulates, and acid gases
(HC1, SO2, and HF) can be obtained from EPA
(1985a) (see Section B.4.1). Fugitive emission
sources and equations for estimating emissions are
detailed in EPA (1989) (see Section B.4.1) and
Holton and Travis (1984) (see Section B.4.3).
Fugitive emissions from soils handling prior to
incineration can be estimated using the guidance
given in Section B.I on soils handling.
Emissions from thermal destruction
technologies generally can be estimated using any
one of the approaches listed below. (These
methods do not directly account for removal of
contaminants by air pollution control devices that
may be used to treat emissions from thermal
destruction devices.)
Default approach: Thermal destruction devices
at most contaminated sites may be required to
meet the requirements under federal
regulations such as RCRA or the Toxic
Substances Control Act (TSCA), since these
requirements are generally considered ARARs.
RCRA requires at least 99.99% destruction
and removal of regulated organic constituents
from wastes. TSCA requires 99.9999%
destruction and removal for wastes containing
PCBs and dioxins. Thus, organic emissions
from thermal destruction of hazardous waste
can be estimated by assuming that the above
requirements of RCRA and TSCA will be
exactly met, for pollutants covered by those
regulations. Similar requirements can be used
to estimate HC1 emissions, but this approach
may not provide estimates for paniculate or
air emissions.
Trial run approach: Federal regulations such
as RCRA and TSCA require trial burns to
demonstrate removal efficiencies. Whenever
trial burn data for the waste in question exist
they can be used to estimate the emissions
that might occur during actual remedy
implementation. Data obtained from trial
burns at different sites or different operable
units. from the same site can be used for
estimating emissions.
Theoretical or empirical approach:
Theoretical or applicable empirical equations
often called models can be used to
estimate emissions. These models correlate
incinerator operating parameters and pollutant
emission rates.
Some of the important parameters that may
affect the emissions associated with thermal
destruction technologies are listed in the box
below. Many of these parameters are device
dependent and can be obtained from onsite
observation or from vendors and/or operators.
KEY PARAMETERS AFFECTING
RELEASES FROM THERMAL
DESTRUCTION
Waste feed rate
Burn temperature
Residence time
Excess air rate
Facility size/type
Atomization
Control device efficiency
Chemical characteristics
B.3 SOLIDIFICATION/
STABILIZATION
TREATMENT
TECHNOLOGIES
Solidification/stabilization technologies are
used to immobilize the toxic and hazardous
constituents in the waste by changing those
constituents into immobile forms, binding them in
an immobile, insoluble matrix, and/or binding them
in a matrix that minimizes the material surface
exposed to solvents. Except for emerging
technologies that involve in-situ treatment, the
implementation of stabilization or solidification
generally involves several of the soils handling
activities discussed in Section B.I. The box below
lists some of the key parameters affecting releases
associated with solidification/ stabilization. These
parameters depend on the specific
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solidification/stabilization process. These can be
obtained from onsite observation or from vendors
and/or operators.
KEY PARAMETERS AFFECTING
RELEASES FROM
SOLIDIFICATION/STABILIZATION
TREATMENT TECHNOLOGIES
Binder type
Batch size
Waste/binding agent ratio
Mixing time/efficiency
Curing time
Meteorological conditions
Chemical characteristics
B.4 REFERENCES FOR
DETERMINING RELEASES
RESULTING FROM
REMEDIAL ACTIVITIES
Provided below are references containing
discussions of remedial activities and
methodologies for determining releases associated
with these activities. The references presented
under the heading of various remedial activities
contain information regarding the majority of
remedial activities that may occur at a site
(including soils handling, thermal destruction, and
stabilization/solidification). The remaining
references contain information specific to the
activity listed in the heading. See the references
provided for the main text of RAGS/HHEM Part
C, especially the RI/FS Guidance (EPA 1988c), for
additional references.
B.4.1 VARIOUS REMEDIAL ACTIVITIES
Primary References
Environmental Protection Agency (EPA). 1985a.
Handbook: Remedial Action at Waste Disposal.
Sites (Revised). Hazardous Waste Engineering
Research Laboratory. EPA/625/6-85/006
(NTIS PB87-201034/XAB).
Provides information on remedial
technologies, selection of appropriate
remediation technologies for a given waste
site, and planning remedial activities. Includes
discussions of onsite and offsite disposal of
wastes and soil, removal and containment of
contaminated sediments, and in-situ
treatments.
EPA. 1989. Estimation of Air Emissions from
Cleanup Activities at Superfund Sites.
Air/Superfund National Technical Guidance
Study Series, Volume 3. Office of Air Quality
Planning and Standards. EPA/450/1-89/003
(NTIS PB89-180061/XAB),
This , document provides a step-by-step
protocol for estimating air quality impacts
resulting from site remediation. Presents
emissions estimation techniques for thermal
destruction devices, air stripping of ground
water, in-situ venting, soils handling, and
solidification/stabilization.
Additional References
EPA. 1990. Emission Factors for Superfimd
Remediation Technologies. Draft. Office of
Air Quality Planning and Standards.
EPA. 1988. Superfund Removal Procedures
Revision Number Three. Office of Emergency
and Remedial Response. OSWER Directive
9360.03B.
EPA 1986. Superfund Remedial Design and
Remedial Action Guidance. Office of
Emergency and Remedial Response. OSWER
Directive 9355.0-4A.
B.4.2 SOILS HANDLING
Primary References
EPA. 1985b. AP-42: Compilation of Air Pollution
Emission Factors, Fourth Edition. Office of
Air and Radiation. NTIS PB86-124906.
This document contains emissions data
obtained from source tests, material balance
studies, engineering estimates, and other
sources. Emission factors and equations are
derived from sand and gravel processing
(Section 8.19.1), crushed stone operations
(Section 8.19.2), surface coal mining (Section
8.2.4), and fugitive dust sources (Section 11.2).
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EPA. 1985c. Rapid Assessment of Exposure to
Particulate Emissions from Surface
Contamination Sites. EPA/600/A-85/002.
This document provides a methodology for
rapid assessment of inhalation exposures to
respirable particulate emissions from surface
contaminated sites. The methodology consists
of a site survey procedure and particulate
emission factor equations for wind and
mechanical entrainment processes.
EPA. 1990. Development of Example Procedures
for Evaluating the Air Impacts of Soil
Excavation Associated with Superfund Remedial
Actions. Office of Air Quality Planning and
Standards. EPA/450/4-90/014 (NTIS PB90-
255662/XAB).
This document identifies and defines
computational requirements for estimating air
impacts from remediation of CERCLA sites.
The estimation of air impacts from two
example sites employing soil excavation are
discussed. Modified Research Triangle
Institute (RTI) land treatment equations are
used for calculating emissions from
excavations.
Additional References
Baxter, R.A. and D.M. Wilbur. 1983. Fugitive
Particulate Matter and Hydrocarbon Emission
Factors from Mining, Handling, and Storing
Diatomite. AeroVironment, Inc. Pasadena,
California.
EPA. 1977. Technical Guidance for Control of
Industrial Process Fugitive Particulate
Emissions. Office of Air Quality and Planning
Standards. EPA/450/3-77/010 (NTIS PB-272
288/2).
EPA. 1985d. Modeling Remedial Actions at
Uncontrolled Hazardous Waste Sites. Office of
Emergency and Remedial Response, Office of
Solid Waste and Emergency Response.
EPA/540/2-85/001 (OSWER Directive
9355.0-8).
Orlemann, J.A. and G.A. Jutze. 1983. Fugitive
Particulate Dust Control Technology. Noyes
Publications. Park Ridge, New Jersey.
B.4.3 THERMAL DESTRUCTION
Primary References
Holton, G.A. and C.C. Travis. 1984. Methodology
for Predicting Fugitive Emissions for
Incinerator Facilities. Environmental Progress
3:2. Oak Ridge National Lab., Health &
Safety Research Division. Oak Ridge, TN.
Error analysis and Monte Carlo modeling
techniques are used to predict fugitive
emissions caused by leaky pump fittings,
sampling connections, flanges, storage tanks,
and other non-stack equipment. Ten
equations and three parameter value tables are
provided for emission calculations.
Travis, C.C., E.L. Etnier, G.A. Holton, F.R.
O'Donnel, and D.M. Hetrick. 1984.
Inhalation Pathway Risk Assessment of
Hazardous Waste Incineration Facilities. Oak
Ridge National Lab. Oak Ridge, Tennessee.
ORNL/TM-9096.
This report evaluates the relative importance
of plant design and waste physicochemical
variables on human inhalation exposure and
health risk using two hypothetical incineration
facility designs of three sizes each, burning
three different generic wastes. Fugitive
emissions are calculated using equations
relating incinerator facility operation and
configuration to fugitive emissions.
Trenholm, A. and D. Oberacker. 1985. "Summary
of Testing Program at Hazardous Waste
Incinerators." Proceedings Annual Solid
Waste Research Symposium. Environmental
Protection Agency. Cincinnati, Ohio. Report
No. CONF-8504112.
This article summarizes the results of tests
conducted at eight full-scale hazardous
incineration facilities.
Additional References
Cheremisinoff, P.N. 1986. "Special Report:
Hazardous Materials and Sludge Incineration."
Journal of the Air Pollution Engineering
18:12(32-38).
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EPA. 1984. Performance Evaluation of Full-scale
Hazardous Waste Incinerators. (Five
volumes.) Industrial Environmental Research
Laboratory. Cincinnati, OH. EPA-600/2-84-
181 a-e (NTIS PB85-129500).
'Lee, C.C., G.L. Huffman, and D.A. Oberacker.
1986. "Hazardous/Toxic Waste Incineration."
Journal of the Air Pollution Control Association
36:8.
Oppelt, E.T. 1987. "Incineration of Hazardous
Waste, A Critical Review." Journal of the Air
Pollution Control Association. 37:5.
Staley, L.J., G.A. Holton, F.R. O'Dormel, and C.A.
Little. 1983. "An Assessment of Emissions
from a Hazardous Waste Incineration Facility,
Incineration and Treatment of Hazardous
Waste." Proceedings of the Eighth Annual
Research Symposium. EPA-600/9-83/003.
Wallace, D.D., A.R. Trenholm, and D.D. Lane.
1985. "Assessment of Metal Emissions from
Hazardous Waste Incinerators." Proceedings
78th APCA Annual Meeting. Paper 85-77. Air
Pollution Control Association. Pittsburgh,
Pennsylvania.
B.4.4 STABILIZATION/SOLIDIFICATION
Primary References
Cullinane, M.J., L.W. Jones, and P.O. Malone.
1986. Handbook for Stabilization/Solidification
of Hazardous Waste. Hazardous Waste
Engineering Research Laboratory. EPA/540/2-
86/001.
Hill, R.D. 1986. Stabilization/Solidification of
Hazardous Waste. Hazardous Waste
Engineering Research Lab. EPA/600/D-
86/028.
This document discusses techniques such as
sorption, lime-fly ash Pozzolan process,
Pozzolan-Portland process, thermoplastic
microencapsulation, and other techniques.
Additional References
Cullinane, MJ. and L.W. Jones. 1985. Handbook
for Stabilization/Solidification of Hazardous
Waste. Prepared for: Environmental
Protection Agency, Hazardous Waste
Engineering Research Laboratory. Office of
Research and Development. EPA/540/2-86-
001.
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APPENDIX C
SHORT-TERM TOXICITY VALUES
The short-term ^ effectiveness criterion 'for
evaluating remedial' alternatives includes an
evaluation of the risks due to the short-term
exposure of populations to contaminants during
remedy implementation. Such short-term risks
generally include both baseline risks from existing
site contamination and new risks that would occur
during the implementation of a remedy. In some
cases, potential exposures and risks due to short-
term exposures should be quantitatively assessed;
however, there is no simple or widely accepted
method for estimating such risks. Therefore, in all
cases where short-term toxicitv values are needed.
TSC should be consulted. EPA's Environmental
Criteria and Assessment Office (ECAO; where
TSC is located) will maintain the data files for the
most appropriate short-term toxicity values for
evaluating risks from remedial alternatives. To
obtain the most up-to-date information, regional
EPA CERCLA staff must contact:
Superfund Health Risk Technical
Support Center
Environmental Criteria and Assessment Office
U.S. Environmental Protection Agency
Mail Stop 114
26 West Martin Luther King Drive
Cincinnati, OH 45268
Phone: 513-569-7300 (FTS-684-7300)
FAX: 513-569-7159 (FTS-684-7159)
Requests from others must be submitted to the
TSC in writing and must contain the following
information for consideration:
CERCLA site name, site location, and 12-digit
site number;
name and phone number of the RPM; and
detailed description of the risk assessment
related question.
The remainder of this appendix provides some
general background on exposure duration issues
and an .overview of some of the existing methods
for deriving short-term human health toxicity
values.
C.1 BACKGROUND ON
EXPOSURE DURATION
In assessing short-term risks of remedial
alternatives, the time frame (e.g., hours, days,
weeks up to seven years) is generally of a much
shorter duration than that identified in the
baseline risk assessment. Nevertheless, there are
a number of types of toxicity values that have been
developed to characterize risk due to these short-
term exposures. Some of these types depend on
concentration- or dose-based threshold limits that
are used as guidance levels for protection of
specific populations from specific exposures (e.g.,
guidance levels intended to protect healthy workers
from daily occupational exposure to chemicals in
the workplace). In this section, the types of
exposure durations commonly suggested or implied
by the toxicity value types (discussed later) are
presented.
Releases that may occur during remedy
implementation could last for varying durations
but are expected, in most if not all cases, to give
rise to less-than-lifetime exposures. Furthermore,
releases that occur during remediation may result
in exposure levels much higher than those
preceding remediation. Different risk levels may-
be associated with these different exposure
durations (assuming the same dose rate) and with
various exposure concentrations. Therefore, it is
important that the dose- or concentration-based
toxicity values that are chosen to characterize the
short-term risks be based on appropriate exposure
durations. Exposure durations associated with
existing methods for characterizing short-term risks
include hours, days, weeks, months, and years
(generally up to seven years).
Currently, RAGS/HHEM Part A defines three
exposure durations, apart from long-term exposure,
that may be of concern at CERCLA sites: single
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exposure event, very short-term exposure, and
short-term (subchronic) exposure.
Single Exposure Event. The majority of
chemicals are capable of producing an adverse
health effect after a single exposure event,
depending on the intensity of exposure. For
developmental toxicants, irritants, and
neurological poisons, a single, low level
exposure event can result in effects after
minutes, hours, or a day.
Very Short-term Exposure. For some acute
toxicants, multiple exposures over several days
could result in an adverse effect. For these
chemicals, the exposure is assessed over days
or weeks (up to two weeks).
Short-term (Subchronic) Exposure. Exposure
lasting anywhere from two weeks to seven
years to low concentrations of a chemical can
also produce adverse effects; this exposure is
assessed by averaging it over the specific
duration.
During evaluations of remedial alternatives, it
may be important to assess exposure (and risk or
hazard) for all relevant exposure durations. Both
the shortest time period of exposure, from peak or
accidental releases, to the cumulative exposure
over the entire time period of the remedy
implementation, may need to be considered.
Quantitative assessment is contingent, however,
upon the availability of adequate exposure
characterization. Exposure models used to predict
concentrations have not for the most part been
validated over the short durations considered for
single exposure events (e.g., minutes to hours). At
best, meteorological data are collected on an
hourly basis at a site removed from the location of
interest; using these data to derive a model to
predict exposure concentrations for durations
shorter than those for the meteorological data may
produce results that could not be supported
scientifically. In addition, the need to evaluate
peak .exposures as well as longer-term average
exposures during remedy implementation depends
on a number of considerations, including the
degree of risk or hazard associated with the longer-
term exposure and the difference between the
predicted peak and average exposure
concentrations.
A review of the types of (duration-specific)
toxicity values that are available (discussed later in
this appendix) indicates that a number of the types
correspond to various durations that are relevant
to releases during remedy implementation.
Because a toxicity value generally is specific to a
certain duration, however, risk may need to be
characterized separately for the three short-term
exposure durations.
C.2 EXISTING SHORT-TERM
TOXICITY VALUES
In this section, commonly encountered short-
term toxicity values are summarized. These values
are: (1) concentration and dose threshold values
primarily for noncarcinogenic effects; and (2)
specific short-term carcinogenic risk values. A
section is provided on each of these toxicity value
categories.
C.2.1 TOXICITY VALUES FOR ASSESSING
RISK OF NONCARCINOGENIC
EFFECTS FOR SHORT-TERM
EXPOSURE
Toxicity values designed to characterize the
risk of noncarcinogenic effects are summarized in
the following subsections. Further information on
the suitability of these values for various CERCLA
exposure scenarios can be obtained from the TSC.
C.2.1.1 Developmental Toxicant Reference Dose
(RfDdt) and Reference Concentration
(RfCdl)
RfDdts and RfCdts are developed for chemicals
that have been shown to cause adverse effects in a
developing organism. EPA's Human Health
Assessment Group of the Office of Health and
Environmental Assessment is in the process of
developing RfDdt and RfCdt values and the
methodology for their derivation. As proposed by
EPA (EPA 1989b), these values.will likely be
derived from the no-observed-adverse-effect-level
(NOAEL) or lowest-observed-'adverse-effect-level
(LOAEL) in a manner consistent with the
derivation of reference doses (RfDs) and reference
concentrations (RfCs), and without adjustment for
short exposure duration. RfDdts are expressed in
terms of dose and RfCdts are expressed as an air
concentration. Additional information on these
criteria is available in EPA's Proposed
Amendments to the Guidelines for the Health
Assessment of Suspected Developmental Toxicants
(EPA 1989b), or by contacting the Reproductive
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and Developmental Toxicology Branch of the
Office of Health and Environmental Assessment at
202-260-7331 (FTS-260-7331).
Currently (i.e., at the date of publication of
this guidance), developmental toxicity is considered
in the derivation of EPA criteria for
noncarcinogenic effects (including RfDs and RfCs
for subchronic and chronic exposure and drinking
water Health Advisories [HAs]). That is, these
criteria are set at levels considered protective for
developmental effects as well as for other
noncarcinogenic effects.
C.2.1.2 Subchronic Reference Dose (RfDs) and
Reference Concentration (RfCs)
RfDss and RfCss are developed by ECAO and
are used to characterize potential noncarcinogenic
effects associated with short-term exposures (two
weeks to seven years as defined in RAGS/HHEM
Part A). To date, approximately 305 RfDss and 60
RfCss have been published. These RifDs and RfCs
are developed based on NOAELs or LOAELs
identified from subchronic (i.e., usually j>90 days
but less-than-chronic) toxicity studies. RfDss are
expressed in terms of dose and RfCss are expressed
as air concentrations. Subchronic RfDs and RfCs
are available in HEAST. The derivation of RfDss
is described in more detail in RAGS/HHEM
Part A.
C.2.1.3 One-day, Ten-day, and Longer-term
Drinking Water Health Advisories (HAs)
Drinking water HAs developed by EPA
provide guidance to assist state and local officials
responsible for public health protection during
emergency situations involving drinking water
contamination. HAs are derived in a manner
reasonably consistent with oral RfD methodology.
Accordingly, these HA values constitute suitable
criteria for evaluating short-term oral exposure.
The HA concentrations include a margin of safety
to protect sensitive members of the population
(e.g., children, the elderly, pregnant women).
"One-day HA" is the term used to describe the
concentration of a chemical in drinking water that
is not expected to cause any adverse
noncarcinogenic effects for one day of exposure,
with a margin of safety. The "Ten-day HA"
describes the concentration of a chemical in
drinking water that is not expected to cause any
adverse noncarcinogenic health effects for two to
ten consecutive days of exposure, with a margin of
safety. The "Longer-term HA" is the concentration
of a chemical in drinking water that is not
expected to cause any adverse noncarcinogenic
effects up to approximately seven years of
exposure. ("Lifetime HAs" that are protective for
exposure over a lifetime are also developed based
on chronic RfDs.)
In general, the HAs described here are
protective of only noncarcinogenic effects. These
values are expressed as concentrations in drinking
water but can be converted to mg/kg/day doses by
using the assumptions that were applied in their
calculation: consumption of 1 L/day by a 10 kg
child (one-, ten-, and longer-term HAs) and 2
L/day by a 70-kg adult (lifetime HA).
Approximately 140 HAs have been developed by
EPA for each exposure duration. (HAs are briefly
described in RAGS/HHEM Part A.)
C.2.1.4 Acute Inhalation Criteria (AIC)
A report describing the derivation of AICs for
benzene and beryllium is available through the
TSC. AICs are derived as criteria for single, short-
duration (up to an hour or a few hours) inhalation
exposures, as may occur from releases during
remediation. The AICs are based on noncancer
endpoints and are expressed as air concentrations.
AICs have been derived for a limited number of
chemicals using EPA RfC methodology, modified
as required for this acute exposure scenario. The
modification consists of using the NOAEL (or
LOAEL) as reported in the study without
adjustment for exposure duration (hours/24 hours).
Because these criteria are conceptually consistent
with inhalation RfCs, they are a good basis for
assessing short-term risks from single, very short
exposures. The TSC should be contacted for
additional AIC values.
C.2.1.5 Minimal Risk Levels (MRLs)
MRLs are derived by the Agency for Toxic
Substances and Disease-Registry (ATSDR) from
human or animal studies for threshold effects on
chemicals found at CERCLA hazardous waste
sites. MRLs are developed for both inhalation and
oral exposures; oral MRLs are expressed as doses
and inhalation MRLs are expressed as
concentrations in air. Estimates of exposure
posing minimal risk to humans are made for the
most sensitive noncarcinogenic endpoint (including
developmental and reproductive endpoints) for
three different exposure durations (i.e., acute,
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intermediate, and chronic). These exposure
durations for which MRLs are derived are as
follows: acute MRL 1 to 14 days; intermediate
MRL 15 to 364 days; chronic MRL .>365
days. MRLs are developed using an approach that
is consistent with EPA RfD methodology (i.e.,
identification of a NOAEL or LOAEL and
application of uncertainty factors to reflect human
variability and, where appropriate, the uncertainty
of extrapolating from laboratory animal data to
humans).
Acute inhalation MRLs differ from AIC in
regard to adjustment for exposure duration. The
guidance for derivation of acute inhalation MRLs
specifies that "exposure periods of less than 24
hours in the toxicity study from which the MRL is
derived, can be adjusted to one day" (ATSDR
1991); this adjustment is commonly carried out.
No such adjustment is carried out in the derivation
of AICs, which are intended to serve as guidance
for acute, very short, and single, exposures (e.g.,
ranging from less than an hour to a few hours,
perhaps as inadvertent releases during
remediation).
MRLs can be found in the ATSDR
Toxicological Profile documents in the Health
Effects Summary section, on the Levels of
Significant Exposure figure (graph). The bottom
of the dotted line on the graph represents the
MRL. Except in the earliest ATSDR Toxicological
Profiles, MRL values and the endpoints on which
they are based are also identified in the text
accompanying the figure. To date, approximately
62 acute MRLs (38 oral, 24 inhalation) have been
derived by ATSDR. As with other short-term
toxicity values, guidance regarding use of the MRL
must be sought from the TSC.
C.2.1.6 Emergency Exposure Guidance Level
(EEGL), Short-term Public Emergency
Guidance Level (SPEGL), and
Continuous Exposure Guidance Level
(CEGL)
EEGLs and CEGLs are exposure guidance
levels developed by the National Research Council
(NRC 1986) specifically for military personnel
operating under emergency conditions. Therefore,
setting of these levels involves consideration of
various factors (such as age distribution, length of
exposure, and susceptibility) that are different from
those related to the general population. These
guidance levels are published in the NRC (1984-
1988) Emergency and Continuous Exposure
Guidance Levels for Selected Airborne
Contaminants. To date, 43 chemicals have been
evaluated by NRC.
The EEGL is defined as the air concentration
of a substance that is acceptable for the
performance of specific tasks during rare
emergencies usually lasting from 1 to 24 hours
(i.e., it is a ceiling guidance level for a single
emergency exposure) (NRC 1986). EEGLs are
intended to prevent irreversible harm or serious
impairment of judgment or performance.
Exposure at an EEGL might produce reversible
effects, and therefore should not be considered
hygienic or safe. Acute toxicity is the primary
basis for establishing an EEGL. However, even
brief exposure to some substances might have the
potential to increase the risk of cancer or other
delayed effects. ' Derivation of an EEGL may
involve application of an uncertainty factor of ten
to extrapolate from animal data to humans, but no
other species adjustments are applied. Some
EEGLs are based on extrapolation of oral data.
EEGLs are based on the most sensitive or most
important noncarcinogenic health effects known.
Because EEGLs are derived for healthy military
personnel during rare emergencies, and are not
intended to protect against reversible effects, they
should not be applied directly to the general
population (NRC 1986).
The SPEGL is defined as a suitable
concentration for unpredicted, single, short-term
emergency exposure of 1 to 24 hours of the general
public. SPEGLs take into account the wide range
of susceptibility of the general public. The SPEGL
is generally estimated by applying an uncertainty
factor of two to ten to the EEGL, to account for
sensitive groups such as children, the elderly,
and persons with serious debilitating diseases.
NRC (1986) suggests that a safety factor of two
(i.e., EEGL x 0.5) is appropriate to protect more
sensitive groups, such as children or the elderly,
and that a safety factor of ten (i.e., EEGL x 0.1) is
appropriate for fetuses or newborns. Because the
SPEGL is derived from the EEGL, the
considerations discussed above with regard to the
EEGL also apply to SPEGLs.
The CEGL is defined as a ceiling
concentration of a chemical in air to which military
personnel can be exposed for up to 90 days
without immediate or delayed adverse effects or
degradation of performance (NRC 1986). CEGLs
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are not derived for carcinogens. When data from
chronic studies are available, they can be used to
derive CEGLs. A CEGL is generally estimated,
however, by applying an uncertainty factor of 10 to
100 to the EEGL (i.e., EEGL x 0.01 to 0.1),
depending on the evidence for detoxification or
accumulation of the substance in the body. Where
there is evidence of substantial detoxification, a
safety factor of ten is recommended by NRC
(1986). If there is no evidence of detoxification or
detoxification is slow, a safety factor of 100 might
be more appropriate. If the substance accumulates
in tissues, such as halogenated biphenyls and
metals, even higher factors are recommended by
NRC (1986). Other considerations discussed with
regard to the EEGL also apply to CEGLs derived
from EEGLs.
C.2.1.7 Threshold Limit Values Short-term
Exposure Limits (TLV-STELs),
Threshold Limit Values Time-
weighted Averages (TLV-TWA), and
Threshold Limit Values Ceiling
(TLV-C)
TLVs are concentrations developed by the
American Conference of Governmental Industrial
Hygienists (ACGIH) to protect workers from
adverse effects of occupational exposure to
airborne chemicals. However, because
occupational exposure limits are not intended to
protect sensitive workers or other populations, are
not intended for the assessment of community air
pollution or continuous exposure, may not
incorporate the most recent lexicological data, may
be based on unpublished documentation that is not
available for review, and may differ from EPA
derivations with respect to weight-of-evidence
considerations and use of uncertainty factors, EPA
does not endorse the general use of occupational
exposure limits in deriving EPA criteria. In
addition, it should be noted that the TLVs for a
fair number of chemicals are derived by analogy to
other chemicals because health effects data are
inadequate or lacking.
The TLV-STELs are 15-minute time-weighted
average (TWA) exposures that should not be
exceeded at any time during the eight-hour work
day/40-hour workweek and should not occur more
than four times a day, with at least 60 minutes
between successive exposures in the STEL range
(ACGIH 1990). The TLV-STEL is established to
prevent workers from suffering irritation, chronic
or irreversible tissue damage, or narcosis of
sufficient degree to increase the likelihood of
accidental injury. Use of the TLV-STEL should be
limited to very short, single exposure events.
STELs are recommended for substances with acute
effects recognized from high short-term exposures
in either humans or animals (ACGIH 1990).
Approximately 115 TLV-STELs have been
published by ACGIH.
The TLV-TWA is the time-weighted average
concentration for a normal eight-hour workday/40-
hour workweek to which nearly all workers may be
exposed, day after day, without adverse effects.
The TLV-C is a concentration that should not be
exceeded during any part of the working exposure.
The ACGIH uses the TLV-C for substances that
are particularly fast acting and hence are best
controlled by a ceiling limit. In excess of 500
TLV-TWAs and fewer than 50 TLV-Cs have been
published by ACGIH. .
C.2.1.8 Permissible Exposure Levels (PELs) and
Recommended Exposure Limits (RELs)
PELs are enforceable occupational exposure
standards developed by the Occupational Safety
and Health Administration (OSHA). They are
meant to protect workers against catastrophic
effects (such as cancer; cardiovascular, liver, and
kidney damage; and lung diseases) as well as more
subtle effects resulting in central nervous system
damage, narcosis, respiratory effects, and sensory
irritation. The PELs are generally adopted from
(existing) secondary guidance levels (e.g., ACGIH's
TLV-TWAs and TLV-STELs and the
recommended exposure limits [RELs] developed by
the National Institute for Occupational Safety and
Health [NIOSH]), and nearly 400 are available
from OSHA. EPA's reservations concerning the
use of TLVs as the basis for criteria to protect the
general population (see Section C.2.1.7) apply also
to PELs and RELs.
C.2.1.9 Other Miscellaneous Methods
The following are some other methods that
risk assessors or RPMs may encounter.
Immediately Dangerous to Life and Health
(IDLH) Guidelines. IDLH guidelines are
developed by NIOSH. These air concentration
limits are for 30-minute exposures under what
are essentially emergency conditions, and
generally far exceed corresponding TLV-TWA,
TLV-STELs or PELs. IDLH guidelines were
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determined only for the purpose of respirator
selection. These guidelines are intended to be
the maximum air concentration from which, in
the event of respirator failure, a worker could
escape within 30 minutes without experiencing
any escape-impairing or irreversible health
effects (NIOSH 1985). Many of the IDLH
exposure levels are so high that they define
levels at which severe toxic effects
(unconsciousness, incapacitation, intolerable
irritation or death) would be likely (Alexeef et
al. 1989). Therefore, the IDLH guidelines are
not suitable as benchmark guidelines for acute
exposure and may be higher than would be
useful even as a guideline for immediate
evacuation.
CERCLA Section 102 (a) Reportable
Quantities (RQs). RQs are developed by EPA
based on, among other factors, acute toxicity,
chronic noncarcinogenic toxicity, and
carcinogenicity. RQs define the quantity in
pounds above which a release is considered
potentially hazardous (or, at least, warrants
reporting) under CERCLA section 102(a).
The documentation for RQs may contain
health effects information that would be useful
in determining criteria for short-term exposure
but are not by themselves useful in
characterizing risks from releases that might
occur at a CERCLA site.
C.2.2 SPECIFIC CARCINOGENIC RISK
VALUES FOR SHORT-TERM
EXPOSURES
r
There is relatively little guidance available on
characterizing risks from short-term exposure to
carcinogens. For cancer endpoints, most of the
currently available values are specific to lifetime
exposure. Many experimental investigations of
carcinogenicity involve high-dose, long-duration
exposure to compensate for the small number of
animals that are used. Carcinogenicity data on
short-term or single exposures are virtually
nonexistent for most chemicals. For most
chemicals, the current scientific view is that any
exposure, no matter how short in duration, can
result in a carcinogenic risk. Characterizing this
risk is complicated, however, because of factors
such as age at first exposure and mechanism of the
carcinogen's action. Consistent with
RAGS/HHEM Part A and the Guidelines for
Carcinogen Risk Assessment (EPA 1986a), the
preferred approach would be to consider
cumulative dose, averaged over a lifetime. This
method is discussed in Section C.2.2.1.
Several investigators have reported additional
methods to characterize the effects from short-term
exposure to carcinogens. Some of these methods
are currently being investigated by EPA but are
not recommended for short-term carcinogenic
assessments at this time. However, brief
summaries of these methods are provided below
with documentation for the interested reader to
pursue.
C.2.2.1 RAGS/HHEM Part A Method
RAGS/HHEM Part A currently recommends
that lifetime average exposures always be used to
estimate carcinogenic risks. 'That is, because the
cancer toxicity values (i.e., SFs) are based on
lifetime average exposures, Part A recommends
that less-than-lifetime exposures be converted to
equivalent lifetime values for the assessment of
risk. (This is also the. recommended approach in
EPA's Guidelines for Carcinogenic Risk
Assessment [EPA 1986].) In this manner, risks
from short-term exposures would be averaged over
a 70-year lifetime, with modifications for specific
chemicals if appropriate, and, therefore, may
appear to be relatively minor in comparison to
risks from longer-term exposures. While adjusting
less-than-lifetime exposure to an equivalent
lifetime exposure may be valid for relatively long
exposure durations, this adjustment for short-term
exposures may underestimate the risk for
"early-stage" carcinogens (i.e., DNA-damaging
agents).
C.2.2.2 Office of Research and Development
(ORD) Interim Method for
Vinyl Chloride
EPA's ORD (EPA 1989a) used a study by
Drew et al. (1983) to determine that the lifetime
carcinogenic risk from vinyl chloride inhalation
increases when exposure occurs early in life. Drew
et al. showed that the effects from exposure to
vinyl chloride depend on both age at initial
exposure and duration of exposure. His data
showed that children face higher risks than adults
for exposures of a given duration. Cogliano stated
that if risk for partial lifetime exposures is
estimated by ignoring the age at initial exposure
and considering only the duration, the risk will be
underestimated for children and overestimated for
adults over 30. He proposed that risk for partial
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lifetime exposure to vinyl chloride be: (1)
estimated as being proportional to the remaining
lifetime of the exposed individual, and (2) adjusted
depending on the length of exposure. The author
also stated that, at this time, this analytical
technique is applicable only to vinyl chloride arid
should not be applied to any other substances.
The TSC should be contacted for further guidance
on assessing risks from vinvl chloride.
C.2.2.3 EEGLs for Carcinogens
The NRC (1986) has developed a method for
deriving EEGLs (1 to 24-hour exposure guidelines)
for inhaled carcinogens when the computed cancer
risk associated with the toxicity-based EEGL (see
Section C.2.1.6) is more than one in 10,000. In
these cases, the EEGL is lowered so that the risk
is not more than one in 10,000 (LslO"4). The NRC
method draws on the analysis of Crump and Howe
(1984). and appears to employ a higher level of
acceptable lifetime risk (i.e., IxlO'4) than the
RAGS/HHEM Part A method. This method is
discussed in further detail in Criteria and Methods
for Preparing Emergency Guidance Level (EEGL),
Short-term Public Emergency Guidance Level
(SPEGL), and Continuous Exposure Guidance Level
(CEGL) Documents (NRC 1986). The 24-hour
EEGL for a carcinogen is estimated as follows:
EEGL =
d x 25.600 x
2.8
R
level of risk at d
where:
d . = lifetime exposure level (air
concentration), as computed by a
regulatory agency or by the NRC
Committee on Toxicology in
accordance with procedures used by
regulatoryagencies (multistage model)
associated with "acceptable" level of
cancer risk, e.g., IxlO"6 level of risk,
25,600 = number of days in a lifetime (25,600
days = 70 years); application of this
duration factor assumes that
carcinogenic effects are a linear
function of the total (cumulative)
dose,
2.8 = a factor to account for uncertainties
regarding which stage of
carcinogenesis is affected by the
substance and for the likely youth of
military personnel; the NRC (1986)
states that "the maximal additional
risk that these considerations
contribute is a factor of 2.8," based on
the "data of Crump and Howe
(1984)," and
R = target acceptable risk level (e.g.,
IxlO"4) for one day of exposure.
The reservations with this method concern the
choice of a higher target risk level (IxlO'4) in
combination with other assumptions of this
method, and the origin of the above uncertainty
factor of 2.8. The origin of this uncertainty factor
is not explained adequately by NRC (1986), nor is
it apparent in the cited paper (Howe and Crump
1986).
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REFERENCES FOR APPENDIX C
Drew, R.T., Boorman G.A., Haseman J.K., McConnell, E.E., Busey, W.M., Moore J.A. 1983. The Effect of
Age and Exposure Duration on Cancer Induction by a Known Carcinogen in Rats, Mice, and Hamsters. Toxic.
Appl. PharmacoL 68:120-130.
Crump, K.S., Howe, R.B. 1984. The Multistage Model with a Time-dependent Dose Pattern: Applications
to Carcinogenic Risk Assessment. Risk Analysis 4 (3): 163-176.
National Institute of Occupational Safety and Health (NIOSH). 1985. NIOSH Pocket Guide to Chemical
Hazards. U.S. Department of Health and Human Services. Washington, DC.
Environmental Protection Agency (EPA). 1986. Guidelines for Carcinogenic Risk Assessment. 52 Federal
Register 33992.
National Research Council (NRC). 1986. Criteria and Methods for Preparing Emergency Exposure Guidance
Level (EEGL), Short-term Public Emergency Guidance Level (SPEGL), and Continuous Exposure Guideline Level
(CEGL) Documents. Prepared by the Committee on Toxicology. National Academy Press. Washington, DC.
Alexeef, G.V., Lipsett, M.J., and Kizer, K.W. 1989. Problems associated with the use of Immediately
Dangerous to Life and Health (IDLH) values for estimating the hazard of accidental chemical releases. Amer.
Ind. Hyg. Assoc. J. 50(11):598-605.
EPA. 1989a. Internal memorandum from J. Cogliano to S. Bayard. Status of Vinyl Chloride Assessment.
Office of Health and Environmental Assessment.
EPA. 1989b. Proposed Amendments to the Guidelines for the Health Assessment of Suspected
Developmental Toxicants. 45 Federal Register 9386-9403.
American Conference of Governmental and Industrial Hygienists (ACGIH). 1990. Documentation of the
Tftreshold Limit Values and Biological Exposure Indices. Cincinnati, OH.
Agency for Toxic Substances and Disease Registry (ATSDR). 1991. Guidance for the Preparation of a
Toxicological Profile.
Howe, R.B. 1991. Personal communication,-telephone conversation with W. Stiteler, Syracuse Research
Corporation, January 30, 1991.
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APPENDIX D
RADIATION REMEDIATION TECHNOLOGIES
This appendix presents two exhibits designed
to assist the RPM with the process of using risk
information to evaluate and select remediation
technologies for sites contaminated with
radioactive substances. The first exhibit, Exhibit
D-l, summarizes the potential routes by which
radioactivity may be released to the air, ground
water, surface water, or other media when remedial
technologies are implemented. Similar to Exhibit
A-2 in Appendix A, Exhibit D-l groups process
variations with similar potential release
mechanisms under the technology categories.
Exhibit D-l includes ground and surface water
releases under the "water" column, and includes
other unique release mechanisms under the "other"
column. The reader is referred to.EPA's report,
Assessment of Technologies for the Remediation of
Radioactivefy Contaminated Superfimd Sites
(EPA/540/2-90/001), for descriptions of each
technology listed in Exhibits D-l and D-2.
The second exhibit, Exhibit D-2, presents a
qualitative estimate of the potential short-term
risks posed by each technology during its
implementation phase, and its potential long-term
risks anticipated after cleanup. Potential short-
term risks and potential long-term risks are
classified as being low, moderate, or high, or some
combination of these levels. This classification
scheme is based on the potential for releases of
radioactivity arising from the use of these
technologies to lead to potential short- and long-
term risks. Under this scheme, "low" means a low
potential for releases of radioactivity assuming a
reasonable worst-case scenario and therefore, a low
potential for human health or environmental risk.
"Moderate" means a moderate potential for release
and risk, and "high" refers to a high potential for
release and risk.
Although the determinations of low, moderate,
and high potential risks presented in Exhibit D-2
are based on the professional judgment of
experienced risk assessors, they are provided only
to the RPMs for making preliminary technology
screening decisions. The actual risks associated
with a remedial alternative at a specific site must
be evaluated on a case-by-case basis. That is,
technologies rated as high potential risk should not
necessarily be eliminated from consideration, nor
should technologies rated as low potential risk be
considered safe, without evaluation of site-specific
factors.
The Agency recognizes that other
determinations of degree of potential risks are
possible and may be acceptable. (In fact, if
remediation technologies are properly designed
and excuted, few, if any, of the potential releases
and risks may be expected.) Therefore, the RPM
is encouraged to consider all qualified sources of
technical information when selecting a radiation
remedial technology based on site-specific
conditions.
Potential releases of mixed radioactive and
nonradioactive hazardous substances are not
covered in this appendix due to the limited number
of technologies currently available, and the
complexities involved in identifying release
pathways and mechanisms. Because releases of
mixed waste contaminants will warrant additional
risk evaluation and considerations, RPMs should
consult with a radiation protection specialist prior
to selecting a remedial design for these types of
sites.
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EXHIBIT D-l
POTENTIAL RELEASES OF RADIOACTIVITY ASSOCIATED WITH
RADIATION REMEDIATION TECHNOLOGIES
Technologies*
Air
Water*
Other*
SOIL AND SLUDGE TECHNOLOGIES
Natural Attenuation
(Non-treatment Action)
Potential emissions of
radioactive particulates and
volatiles
Continued migration of radionuclides
to ground water and possible transport
to surface water
External radiation exposure due to
gamma-emitting radionuclides in
soil
Soil Handling
Soil Excavation,
Transport, and Offsite
Disposal
Resuspension of radioactive
particulates
Enhanced emissions of volatile
radionuclides
Enhanced runoff or leaching of
radionuclides to surface water or
ground water
Seepage/runoff to soil
Enhanced external radiation
exposure of workers during
excavation, handling, shipping, and
disposal
Offsite migration of radioactivity
due to transport by contaminated
vehicles or equipment
Soil Washing, Extraction, & Bioremediation
Soil Washing with Water
Resuspension of radioactive soil
particles and enhanced
emissions of volatile
radionuclides during handling
and treatment
Spills, leaching, and/or runoff of
residual radionuclides in washed soil
or in process water
Accumulation of dissolved or
suspended radionuclides in recycled
water/solvents
Enhanced external radiation
exposure from gamma-emitting
radionuclides in soil .
(Continued)
-------
EXHIBIT D-l (Continued)
POTENTIAL RELEASES OF RADIOACTIVITY ASSOCIATED WITH
RADIATION REMEDIATION TECHNOLOGIES
Technologies'
Air
Water*
Other*
Soil Washing, Extraction, & Bioremediation (Continued)
Chemical Extraction
Bioremediation
Potential emissions of volatile
chemicals and radioactive
participates and volatiles during
handling and treatment
1
Areal or fugitive emissions of
radioactive particulates and
volatiles
Exhaust stack emissions of
incinerated biosorbants
containing residual radioactivity
Spills, leaching, and/or runoff of
residual radionuclides in process
water
Accumulation of dissolved or
suspended radionuclides in recycled
water/solvents
Discharge of process water
containing residual radioactivity
Inadvertent spills or leaching of
radionuclides
Immobilization
Capping
Continued emissions of some
volatile radionuclides after
capping
Leaching and horizontal migration of
radionuclides to ground water with
rain water infiltration ,
Spills or leakage of extract with
high concentrations of radioactive
contaminants and solvents from
storage tanks
External radiation exposure from
biomass containing residual
gamma-emitting radionuclides
Partial reduction of external
radiation exposure
(Continued)
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EXHIBIT D-l (Continued)
POTENTIAL RELEASES OF RADIOACTIVITY ASSOCIATJ
RADIATION REMEDIATION TECHNOLOGIES
WITH
Technologies*
Air
Water*
Other*
In-situ Vitrification
Volatilization of certain
radionuclides during treatment
Cracks or fissures in vitrified
mass may act as conduits for the
release of volatile radionuclides
Possible leaching and migration of
radionuclides to ground water due to
soil matrix destabilization
.External radiation exposure in
radium contaminated soils due to
the buildup of radon decay
products
GROUND WATER AND SURFACE WATER TECHNOLOGIES
Natural Attenuation
(Non-treatment Action)
Potential buildup of volatile
radionuclides (eg, radon) in
ground-water and municipal
water distribution systems
Continued transport of radionuclides
to the aquifer and possible discharge
to surface water
Potential deposition of radioactive
sediments in surface water over
large areas (eg, river basins)
Filtration
Fugitive emissions of volatile
radionuclides
Discharge of effluent water containing
dissolved radioactive solids
Potential leaching of radionuclides
from filter cakes or sludge
External radiation exposure from
radioactive cakes or sludge
Granular Activated
Carbon Adsorption
Potential stack emissions of
volatile radionuclides upon
saturation or breakthrough
Discharge of treated water containing
residual radioactive contamination
Possible release of radionuclides due
to backflushing and/or regeneration
Potential external radiation
exposure due to the sorption and
buildup of gamma-emitting
radionuclides
Ion Exchange
Potential for off-gassing of
volatile radioactive decay
products from parent nuclides
on resin columns
Discharge of treated water containing
residual radioactive contamination
Possible release of radionuclides due
to backflushing or regeneration
Potential external radiation
exposure due to the buildup of
gamma-emitting radionuclides
(Continued)
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EXHIBIT D-l (Continued)
POTENTIAL RELEASES OF RADIOACTIVITY ASSOCIATED WITH
RADIATION REMEDIATION TECHNOLOGIES
NOTES
* Source for radiation remediation technologies: US Environmental Protection Agency (EPA). 1990. Assessment of Technologies for the Remediation of
Radioactively Contaminated Superfund Sites. EPA/540/2-90/001.
a In general, seepage and leaching are more likely to affect ground water, but could also lead to surface water contamination. Runoff and discharge are
releases that will most likely contaminate surface water, but may also lead to ground-water contamination.
b Other releases include treatment residuals requiring further remediation and/or special handling and disposal considerations. External radiation exposure
due to the presence of gamma-emitting radionuclides in treatment residues should also be considered as a potential human health exposure pathway, even
though this pathway does not involve the physical release of radionuclides into the environment. The risk assessor should also consider other common
technologies used to remediate ground water and surface water contaminated with radioactive substances, such as aeration, evaporation, distillation and
solvent extration, not included in Exhibits D-l or D-2. *
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EXHIBIT D-2
DEGREE OF POTENTIAL SHORT- AND LONG-TERM RISKS ASSOCIATED WITH
RADIATION REMEDIATION TECHNOLOGIES
Technologies*
Potential for
Short-term Risks
Potential for
Long-term Risks
Comments
SOIL AND SLUDGE TECHNOLOGIES
Natural Attenuation
(Non-treatment
Action)
High
High
The No Action alternative will not meet the two NCP threshold criteria: (1)
protection of human health and environment, and (2) compliance with ARARs
Migration and release of radioactive contaminants would be expected to continue
unless abated or mitigated
Soil Handling
Soil Excavation,
Transport, and Offsite
Disposal
Moderate/High
None/Low
During excavation, the potential for short-term radiation risks to remedial workers
onsite and to the general public.ofisite may be moderate to high
Once the source or sources of radioactivity has or have been removed, the
potential for long-term risks should be minimal or non-existent, depending on the
level of residual radioactivity remaining onsite
Soil Washing, Extraction, & Bioremediation
Soil Washing with
Water
Chemical Extraction
Moderate
Moderate/High
Low
Low/Moderate
During excavation and soil washing, the potential for short-term radiation risks to
remedial workers onsite and to the general public offsite may be moderate
Depending on the level of residual radioactivity remaining, the potential for long-
term risks may be low to moderate
During excavation and chemical extraction, the potential for short-term radiation
risks to workers onsite and to the general public offsite may be moderate to high
The potential for long-term risks depend upon the chemical and radiological
characteristics of the treated soil recycled back into native soil
(Continued)
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EXHIBIT D-2 (Continued)
DEGREE OF POTENTIAL SHORT- AND LONG-TERM RISKS ASSOCIATED WITH
RADIATION REMEDIATION TECHNOLOGIES
Technologies*
Potential for
Short-term
Risks
Potential for
Long-term
Risks
Comments
Soil Washing, Extraction, & Bioremediation (Continued)
Bioremediation
Moderate
Moderate
Accidental spillage of radioactivity from biotreatment solutions, off-gassing of volatile
radionuclides, and elevated external radiation exposures may contribute to the potential for
moderate short-term radiation risks
Long-term risks depend upon the chemical and radiological characteristics of the treated
soil recycled back into native soil In general, these risks should be low to moderate
Immobilization
Capping
Low/Moderate
Moderate/High
Short-term radiation risks to workers and offsite populations should be low to moderate,
provided that the source or sources of radioactivity are not excavated before capping
Since the sources of radioactivity will be left in place, long-term risks to human health and
the environment may be moderate to high depending on the extent to which the cap is
capable of preventing the migration of radionuclides in the future
In-situ
Vitrification
Moderate/High
Moderate
Initially, both radiation and physical hazards contribute to the moderate to high potential
for short-term radiation risks posed by the use of this technology, primarily to onsite
workers '
Since the stability and long-term integrity of vitrified soils containing radioactive materials
remain unverified in the field at the present time, and since the buildup of radon decay
products in vitrified soils may increase external exposure rates with time, potential long-
term radiation risks to the general public may be moderate to high
(Continued)
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I
EXHIBIT D-2 (Continued)
DEGREE OF POTENTIAL SHORT- AND LONG-TERM RISKS ASSOCIATED WITH
RADIATION REMEDIATION TECHNOLOGIES
Technologies*
Potential for
Short-term
Risks
Potential for
- Long-term
Risks
Comments
GROUND WATER AND SURFACE WATER TECHNOLOGIES
Natural
Attenuation
(Non-treatment
Action)
High
High
The No Action alternative will not meet the two NCP threshold criteria: (1) protection of
human health and environment, and (2) compliance with ARARs
Releases of radioactive contaminants to ground water and surface water would be
expected to continue unless abated or mitigated
Filtration
Low/Moderate
Low
The potential for short-term radiation risks to workers and the public will depend on a
number of factors, including: (1) the concentrations of radionuclides in the ground or
surface waters; (2) the efficiencies of filtration systems; (3) the breakthrough time, and;
(4) the change-out or regeneration cycle time In general, these potential risks are
expected to be low to moderate
The potential for long-term risks will also depend on the factors listed above, but will
depend primarily on the concentration of radionuclides in ground water or surface water
remaining to be treated (ie, concentrations (and risks) may be expected to fall off with
treatment) Potential risks to the general public may be expected to be low The handling
and disposal of filter materials and sludges containing radionuclides may pose risks to
workers if radioactivity concentrations exceed federal or state standards
(Continued)
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EXHIBIT D-2 (Continued)
o
I
DEGREE OF POTENTIAL SHORT- AND LONG-TERM RISKS ASSOCIATED WITH
RADIATION REMEDIATION TECHNOLOGIES
i
'fe
Technologies*
Potential for
Short-term
Risks
Potential for
Long-term
Risks
Comments
GROUND WATER AND SURFACE WATER TECHNOLOGIES
Granular
Activated Carbon
Adsorption
Ion Exchange
Low/Moderate
Low/Moderate
Low
Low
1 The buildup of radon and radon progeny on activated charcoal may increase both
potential short- and long-term risks of external radiation exposures to workers
Regeneration of GAG may release radionuclides that are not well sorbed Disposal of
spent GAG containing elevated concentrations of lead-210 (and chemical contaminants)
may pose handling problems Buildup of radon and other radionuclides on GAG also
depends on: (1) the concentrations of radionuclides in the ground or surface waters; (2)
collection efficiencies; (3) GAG breakthrough time, and; (4) the change-out or
regeneration cycle time
Similar to the potential risks posed by the treatment of radionuclides in ground water and
surface water using filtration or carbon absorption techniques, the potential for short- and
long-term risks posed by the collection of radionuclides on ion exchange resins depends
primarily on the radionuclide-specific collection efficiency and water concentrations In
general, these potential risks may be low to moderate
* Source for radiation remediation technologies: U.S. Environmental Protection Agency (EPA). 1990. Assessment of Technologies for the Remediation of
Radioactively Contaminated Superfund Sites. Office of Solid Waste and Emergency Response. EPA/540/2-90/001. '
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