United States Solid Waste And 9285.701A
Environmental Protection Emergency Response July 1989
(OS-230) Pre-Publication Copy
vxEPA Risk Assessment
Guidance For
Superfund
Human Health
Evaluation Manual
Part A
Interim Final
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OSWER Directive 9285.7-Ola
INTERIM FINAL
RISK ASSESSMENT GUIDANCE
FOR SUPERFUND
Volume I: Human Health Evaluation Manual
Office of Emergency and Remedial Response
U.S. Environmental Protection Agency
Washington, D.C. 20460
September 29, 1989
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ABOUT THE REVISION . . .
WHAT FT EPA's Human Health Evaluation Manual is a revision of the Superfund Public
IS Health Evaluation Manual (SPHEM; October 1986); it is Volume I of the two-volume set
called Risk Assessment Guidance for Superfund. This manual has three main parts: the
baseline risk assessment (Part A); refinement of preliminary remediation goals (Part B); and
evaluation of remedial alternatives (Part C). (Only Part A is included in the first
distribution; see below.)
WHO IT'S Risk assessors, risk assessment reviewers, remedial project managers (RPMs), and risk
FOR managers involved in Superfund site cleanup activities will benefit from this revision.
WHAT'S This revision builds upon the process established in SPHEM and provides more detailed
NEW guidance on many of the procedures used to assess health risk. New information and
techniques are presented that reflect the extensive Superfund program experience conducting
health risk assessments at Superfund sites. Policies established and refined over the years
-- especially those resulting from the proposed National Oil and Hazardous Substances
Pollution Contingency Plan (NCP) -- have been updated and clarified. Additionally, the
links between the human health evaluation, the environmental evaluation, and the remedial
investigation/feasibility study (RI/FS) have been strengthened.
In Part A you will find:
For the risk assessor -- Updated procedures and policies, specific equations and
variable values for estimating exposure, and a hierarchy of toxicity data sources.
For the risk assessment reviewer -- A baseline risk assessment outline for consistent
presentation of risk information and format, and a reviewer's checklist to ensure
appropriate quality and content of the risk assessment.
For the RPM -- A comprehensive overview of the risk assessment process in the
RI/FS, a checklist for RPM involvement throughout the process, and a complete
index for quick reference.
For the risk manager -- An expanded chapter on risk characterization (Chapter 8)
to help summarize and present risk information for the decision-maker, and more
detailed descriptions of uncertainties in the assessment.
DISTRIBU- This manual is being distributed as an interim final document while the proposed NCP is
TION PLAN being finalized. After the final NCP is published, the manual will be updated and finalized.
Parts B and C - which were not distributed as interim final because they are highly
dependent on possible revisions to the NCP - will be added. Periodically, updates of
portions of the manual will be distributed.
WHERE Toxics Integration Branch
TO SEND Office of Emergency and Remedial Response
COMMENTS 401 M Street, SW (OS-230)
Washington, DC 20460
Phone: 202-475-9486
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NOTICE
The policies and procedures set forth here are intended solely as guidance to EPA and other
government employees and contractors. This guidance does not constitute rulemaking by the Agency, and
cannot be relied on to create a substantive or procedural right enforceable by any party in litigation with
the United States. EPA may take action that is at variance with the policies and procedures in this manual
and may change them at any time without public notice.
This interim final guidance is based on policies in the proposed revisions to the National Oil and
Hazardous Substances Pollution Contingency Plan (NCP), which were published on December 21, 1988 (53
Federal Register 51394). The final NCP may adopt policies different than those in this manual and should,
when promulgated, be considered the authoritative source. A final version of this manual will be published
after the revised NCP is promulgated.
Following the date of its publication, this manual is intended to be used as guidance for all human
health risk assessments conducted as part of Superfund remedial investigations and feasibility studies.
Issuance of this manual does not invalidate human health risk assessments completed before (or in progress
at) the publication date and based on previously released Agency guidance.
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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. Linda Cullen provided overall project
management, contract supervision, and technical coordination for the project under the direction of Bruce
Means, Chief of TIB's Health Effects Program.
The EPA Workgroup (comprised of members listed on the following page) provided valuable input
regarding the organization, content, and policy implications of the manual throughout its development. The
project manager especially wishes to acknowledge the assistance of the Workgroup Subcommittee
Chairpersons: Rebecca Madison, Bruce Means, Sue Norton, Georgia Valaoras, Craig Zamuda, and Larry
Zaragoza.
Other significant contributors to the manual included Joan Fisk, Michael Hurd, and Angelo Carasea
of the Analytical Operations Branch (Office of Emergency and Remedial Response); Paul White, Anne
Sergeant, and Jacqueline Moya of the Exposure Assessment Group (Office of Research and Development);
and Barnes Johnson of the Statistical Policy Branch (Office of Policy, Planning, and Evaluation). In
addition, many thanks are offered to the more than 60 technical and policy reviewers who provided
constructive comments on the document in its final stages of development.
ICF Incorporated provided technical assistance to EPA in support of the development of this
manual, under Contract No. 68-01-7389.
Robert Dyer, Chief of the Environmental Studies and Statistics Branch, Office of Radiation
Programs, served as project manager for Chapter 10 (Radiation Risk Assessment Guidance), with assistance
from staff in the Bioeffects Analysis Branch and the regional Radiation Program Managers. Chapter 10
was prepared by S. Cohen and Associates, Incorporated (SC&A), under Contract No. 68-02-4375.
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WORKGROUP
EPA HEADQUARTERS
Office of Emergency and Remedial Response:
Office of Solid Waste:
Office of Waste Programs Enforcement:
Office of Solid Waste and Emergency Response:
Office of Policy, Planning, and Evaluation:
Office of General Counsel:
Office of Research and Development:
Office of Water:
EPA REGIONAL OFFICES
Region I:
Region V:
Region VI:
Region X:
OTHER EPA OFFICES
Great Lakes National Program Office, IL:
Office of Health and Environmental
Assessment, OH:
Office of Air Quality Planning and
Standards, NC:
Marlene Berg
David Cooper
Linda Cullen
Carla Dempsey
Steve Golian
Bruce Means
Pat Mundy
Sandra Panetta
Stephanie Irene
Georgia Valaoras
Larry Zaragoza
Charlotte White
Craig Zamuda
Joe Freedman
Rebecca Madison
Sue Norton
Frank Gostomski
Robert Zeller
Sarah Levinson
Dan Bicknell
Pamela Blakley
Fred Reitman
Dana Davoli
David Tetta
Cynthia Fuller
Chris DeRosa
Fred Hauchman
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TABLE OF CONTENTS
Page
INTRODUCTION
CHAPTER 1 INTRODUCTION ........................................... 1-1
1.1 OVERVIEW OF THE HUMAN HEALTH EVALUATION PROCESS
IN THE RI/FS ............................................... 1-3
1.1.1 Project Scoping ........................................... 1-4
1.1.2 Site Characterization (RI) ................................... 1-4
1.1.3 Feasibility Study .......................................... 1-8
1.2 OVERALL ORGANIZATION OF THE MANUAL ..................... 1-10
CHAPTER 2 STATUTES, REGULATIONS, GUIDANCE, AND STUDIES RELEVANT
TO THE HUMAN HEALTH EVALUATION .......................... 2-1
2.1 STATUTES, REGULATIONS, AND GUIDANCE GOVERNING HUMAN
HEALTH EVALUATION ....................................... 2-1
2.1.1 CERCLA and SARA ...................................... 2-1
2.1.2 National Contingency Plan (NCP) .............................. 2-4
2.1.3 Remedial Investigation/Feasibility Study Guidiance .................. 2-5
2.1.4 ARARs Guidance ......................................... 2-7
2.1.5 Superfund Exposure Assessment Manual ......................... 2-8
2.2 RELATED SUPERFUND STUDIES ................................ 2-8
2.2.1 Endangerment Assessments .................................. 2-8
2.2.2 ATSDR Health Assessments .................................. 2-9
2.2.3 ATSDR Health Studies ..................................... 2-10
CHAPTER 3 GETTING STARTED: PLANNING FOR THE HUMAN HEALTH
EVALUATION IN THE RI/FS .................................. 3-1
3.1 Goal of the RI/FS ............................................. 3-1
3.2 Goal of the RI/FS Human Health Evaluation .......................... 3-1
3.3 Operable Units ............................................... 3-2
3.4 RI/FS Scoping ................................................ 3-2
3.5 Level of Effort/Level of Detail of the Human Health Evaluation ............. 3-3
PART A -- BASELINE RISK ASSESSMENT
CHAPTER 4 DATA COLLECTION ......................................... 4-1
4.1 BACKGROUND INFORMATION USEFUL FOR DATA COLLECTION ...... 4-1
4.1.1 Types of Data ........................................... 4-1
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4.1.2 Data Needs and the RI/FS 4-2
4.1.3 Early Identification of Data Needs 4-3
4.1.4 Use of the Data Quality Objectives (DQO) Guidance 4-4
4.1.5 Other Data Concerns 4-4
4.2 REVIEW OF AVAILABLE SITE INFORMATION 4-4
4.3 ADDRESSING MODELING PARAMETER NEEDS 4-5
4.4 DEFINING BACKGROUND SAMPLING NEEDS 4-5
4.4.1 Types of Background 4-5
4.4.2 Background Sampling Locations 4-8
4.4.3 Background Sample Size 4-8
4.4.4 Comparing Background Samples to Site-Related Contamination 4-9
4.5 PRELIMINARY IDENTIFICATION OF POTENTIAL HUMAN EXPOSURE 4-10
4.5.1 General Information 4-10
4.5.2 Soil 4-11
4.5.3 Ground Water 4-12
4.5.4 Surface Water and Sediment 4-13
4.5.5 Air 4-14
4.5.6 Biota 4-15
4.6 DEVELOPING AN OVERALL STRATEGY FOR SAMPLE COLLECTION 4-16
4.6.1 Determine Sample Size 4-17
4.6.2 Establish Sampling Locations 4-18
4.6.3 Determine Types of Samples 4-19
4.6.4 Consider Temporal and Meteorological Factors 4-19
4.6.5 Use Field Screening Analyses 4-20
4.6.6 Consider Time and Cost of Sampling 4-21
4.7 QA/QC MEASURES 4-21
4.7.1 Sampling Protocol 4-21
4.7.2 Sampling Devices 4-21
4.7.3 QC Samples 4-22
4.7.4 Collection Procedures 4-22
4.7.5 Sample Preservation 4-22
4.8 SPECIAL ANALYTICAL SERVICES 4-22
4.9 TAKING AN ACTIVE ROLE DURING WORKPLAN DEVELOPMENT AND
DATA COLLECTION 4-22
4.9.1 Present Risk Assessment Sampling Needs at Scoping Meeting 4-22
4.9.2 Contribute to Workplan and Review Sampling and Analysis Plan 4-23
4.9.3 Conduct Interim Reviews of Field Investigation Outputs 4-24
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CHAPTER 5 DATA EVALUATION 5-1
5.1 COMBINING DATA AVAILABLE FROM SITE INVESTIGATIONS 5-2
5.2 EVALUATION OF ANALYTICAL METHODS 5-5
5.3 EVALUATION OF QUANTITATION LIMITS 5-7
5.3.1 Sample Quantitation Limits (SQLs) That Are Greater Than
Reference Concentrations 5-7
5.3.2 Unusually High SQLs 5-10
5.3.3 When Only Some Samples in a Medium Test Positive for a Chemical 5-10
5.3.4 When SQLs Are Not Available 5-11
5.3.5 When Chemicals Are Not Detected in Any Samples in a Medium 5-11
5.4 EVALUATION OF QUALIFIED AND CODED DATA 5-11
5.4.1 Types of Qualifiers 5-11
5.4.2 Using the Appropriate Qualifiers 5-16
5.5 COMPARISON OF CONCENTRATIONS DETECTED IN BLANKS WITH
CONCENTRATIONS DETECTED IN SAMPLES 5-16
5.6 EVALUATION OF TENTATIVELY IDENTIFIED COMPOUNDS 5-17
5.6.1 When Few TICs Are Present 5-18
5.6.2 When Many TICs Are Present 5-18
5.7 COMPARISON OF SAMPLES WITH BACKGROUND 5-18
5.7.1 Use Appropriate Background Data 5-19
5.7.2 Identify Statistical Methods 5-19
5.7.3 Compare Chemical Concentrations with Naturally Occurring Levels 5-19
5.7.4 Compare Chemical Concentrations with Anthropogenic Levels 5-19
5.8 DEVELOPMENT OF A SET OF CHEMICAL DATA AND INFORMATION
FOR USE IN THE RISK ASSESSMENT 5-20
5.9 FURTHER REDUCTION IN THE NUMBER OF CHEMICALS (OPTIONAL) . . . 5-20
5.9.1 Conduct Initial Activities 5-20
5.9.2 Group Chemicals by Class 5-22
5.9.3 Evaluate Frequency of Detection 5-22
5.9.4 Evaluate Essential Nutrients 5-23
5.9.5 Use a Concentration-Toxicity Screen 5-23
5.10 SUMMARY AND PRESENTATION OF DATA 5-24
5.10.1 Summarize Data Collection and Evaluation Results in Text 5-27
5.10.2 Summarize Data Collection and Evaluation Results in Tables and Graphics . . 5-27
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CHAPTER 6 EXPOSURE ASSESSMENT 6-1
6.1 BACKGROUND 6-1
6.1.1 Components of an Exposure Assessment 6-1
6.1.2 Reasonable Maximum Exposure 6-4
6.2 STEP 1: CHARACTERIZATION OF EXPOSURE SETTING 6-5
6.2.1 Characterize Physical Setting 6-5
6.2.2 Characterize Potentially Exposed Populations 6-6
6.3 STEP 2: IDENTIFICATION OF EXPOSURE PATHWAYS 6-8
6.3.1 Identify Sources and Receiving Media 6-8
6.3.2 Evaluate Fate and Transport in Release Media 6-11
6.3.3 Identify Exposure Points and Exposure Routes 6-11
6.3.4 Integrate Information on Sources, Releases, Fate and Transport, Exposure
Points, and Exposure Routes Into Exposure Pathways 6-17
6.3.5 Summarize Information on All Complete Exposure Pathways 6-17
6.4 STEP 3: QUANTIFICATION OF EXPOSURE: GENERAL
CONSIDERATIONS 6-19
6.4.1 Quantifying the Reasonable Maximum Exposure 6-19
6.4.2 Timing Considerations 6-23
6.5 QUANTIFICATION OF EXPOSURE: DETERMINATION OF EXPOSURE
CONCENTRATIONS 6-24
6.5.1 General Considerations for Estimating Exposure Concentrations 6-24
6.5.2 Estimate Exposure Concentrations in Ground Water 6-26
6.5.3 Estimate Exposure Concentrations in Soil 6-27
6.5.4 Estimate Exposure Concentrations in Air 6-28
6.5.5 Estimate Exposure Concentrations in Surface Water 6-29
6.5.6 Estimate Exposure Concentrations in Sediments 6-30
6.5.7 Estimate Chemical Concentrations in Food 6-31
6.5.8 Summarize Exposure Concentrations for Each Pathway 6-32
6.6 QUANTIFICATION OF EXPOSURE: ESTIMATION OF CHEMICAL
INTAKE 6-32
6.6.1 Calculate Ground-water and Surface Water Intakes 6-34
6.6.2 Calculate Soil, Sediment, or Dust Intakes 6-39
6.6.3 Calculate Air Intakes 6-43
6.6.4 Calculate Food Intakes 6-43
6.7 COMBINING CHEMICAL INTAKES ACROSS PATHWAYS 6-47
6.8 EVALUATING UNCERTAINTY 6-47
6.9 SUMMARIZING AND PRESENTING THE EXPOSURE ASSESSMENT
RESULTS 6-50
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CHAPTER 7 TOXICITY ASSESSMENT 7-1
7.1 TYPES OF TOXICOLOGICAL INFORMATION CONSIDERED IN
TOXICITY ASSESSMENT 7-3
7.1.1 Human Data 7-3
7.1.2 Animal Data 7-5
7.1.3 Supporting Data 7-5
7.2 TOXICITY ASSESSMENT FOR NONCARCINOGENIC EFFECTS 7-5
7.2.1 Concept of Threshold 7-6
7.2.2 Derivation of an Oral RfD (RfD0) 7-6
7.2.3 Derivation of an Inhalation RfD (RfD,-) 7-8
7.2.4 Derivation of a Subchronic RfD (RfD^) 7-8
7.2.5 Derivation of a Developmental Toxicant RfD (RfDA) 7-9
7.2.6 One-day and Ten-day Health Advisories 7-9
7.2.7 Verification of RfDs 7-10
7.3 TOXICITY ASSESSMENT FOR CARCINOGENIC EFFECTS 7-10
7.3.1 Concept of Nonthreshold Effects 7-10
7.3.2 Assigning a Weight of Evidence 7-11
7.3.3 Generating a Slope Factor 7-11
7.3.4 Verification of Slope Factors 7-13
7.4 IDENTIFYING APPROPRIATE TOXICITY VALUES FOR
SITE RISK ASSESSMENT 7-13
7.4.1 Gather Toxicity Information for Chemicals Being Evaluated 7-13
7.4.2 Determine Toxicity Values for Noncarcinogenic Effects (RfDs) 7-15
7.4.3 Determine Toxicity Values for Carcinogenic Effects (Slope Factors) 7-16
7.5 EVALUATING CHEMICALS FOR WHICH NO TOXICITY VALUES ARE
AVAILABLE 7-16
7.5.1 Route-to-Route Extrapolation 7-16
7.5.2 Dermal Exposure 7-16
7.5.3 Generation of Toxicity Values 7-16
7.6 UNCERTAINTIES RELATED TO TOXICITY INFORMATION 7-19
7.7 SUMMARIZATION AND PRESENTATION OF THE TOXICITY INFORMATION 7-20
7.7.1 Toxicity Information for the Main Body of the Text 7-20
7.7.2 Toxicity Information for Inclusion in an Appendix 7-20
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CHAPTER 8 RISK CHARACTERIZATION 8-1
8.1 REVIEW OF OUTPUTS FROM THE TOXICITY AND EXPOSURE
ASSESSMENTS 8-1
8.1.1 Gather and Organize Information 8-4
8.1.2 Make Final Consistency and Validity Check 8-4
8.2 QUANTIFYING RISKS 8-6
8.2.1 Calculate Risks for Individual Substances 8-6
8.2.2 Aggregate Risks for Multiple Substances 8-11
8.3 COMBINING RISKS ACROSS EXPOSURE PATHWAYS 8-15
8.3.1 Identify Reasonable Exposure Pathway Combinations 8-15
8.3.2 Sum Cancer Risks 8-16
8.3.3 Sum Noncancer Hazard Indices 8-16
8.4 ASSESSMENT AND PRESENTATION OF UNCERTAINTY 8-17
8.4.1 Identify and Evaluate Important Site-Specific Uncertainty Factors 8-17
8.4.2 Identify/Evaluate Toxicity Assessment Uncertainty Factors 8-22
8.5 CONSIDERATION OF SITE-SPECIFIC HUMAN STUDIES 8-22
8.5.1 Compare with ATSDR Health Assessment 8-24
8.5.2 Compare with Other Available Site-Specific Epidemiological or Health Studies 8-24
8.6 SUMMARIZATION AND PRESENTATION OF THE BASELINE RISK
CHARACTERIZATION RESULTS 8-25
8.6.1 Summarize Risk Information in Text 8-25
8.6.2 Summarize Risk Information in Tables 8-26
CHAPTER 9 DOCUMENTATION, REVIEW, AND MANAGEMENT TOOLS FOR THE RISK
ASSESSOR, REVIEWER, AND MANAGER 9-1
9.1 DOCUMENTATION TOOLS 9-1
9.1.1 Basic Principles 9-1
9.1.2 Baseline Risk Assessment Report 9-2
9.1.3 Other Key Reports 9-3
9.2 REVIEW TOOLS 9-3
9.3 MANAGEMENT TOOLS 9-14
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CHAPTER 10 RADIATION RISK ASSESSMENT GUIDANCE 10-1
10.1 RADIATION PROTECTION PRINCIPLES AND CONCEPTS 10-3
10.2 REGULATION OF RADIOACTIVELY CONTAMINATED SITES 10-8
10.3 DATA COLLECTION 10-10
10.3.1 Radiation Detection Methods 10-10
10.3.2 Reviewing Available Site Information 10-14
10.3.3 Addressing Modeling Parameter Needs 10-14
10.3.4 Defining Background Radiation Sampling Needs 10-14
10.3.5 Preliminary Identification of Potential Exposure 10-15
10.3.6 Developing a Strategy for Sample Collection 10-15
10.3.7 Quality Assurance and Quality Control (QA/QC) Measures 10-16
10.4 DATA EVALUATION 10-16
10.4.1 Combining Data from Available Site Investigations 10-17
10.4.2 Evaluating Analytical Methods 10-17
10.4.3 Evaluating Quantitation Limits 10-17
10.4.4 Evaluating Qualified and Coded Data 10-20
10.4.5 Comparing Concentrations Detected in Blanks with Concentrations
Detected in Samples 10-20
10.4.6 Evaluating Tentatively Identified Radionuclides 10-21
10.4.7 Comparing Samples with Background 10-21
10.4.8 Developing a Set of Radionuclide Data and Information for
Use in a Risk Assessment 10-21
10.4.9 Grouping Radionuclides by Class 10-21
10.4.10 Further Reduction in the Number of Radionuclides 10-21
10.4.11 Summarizing and Presenting Data 10-22
10.5 EXPOSURE AND DOSE ASSESSMENT 10-22
10.5.1 Characterizing the Exposure Setting 10-23
10.5.2 Identifying Exposure Pathways 10-23
10.5.3 Quantifying Exposure: General Considerations 10-24
10.5.4 Quantifying Exposure: Determining Exposure Point Concentrations 10-25
10.5.5 Quantifying Exposure: Estimating Intake and Dose Equivalent 10-26
10.5.6 Combining Intakes and Doses Across Pathways 10-27
10.5.7 Evaluating Uncertainty 10-27
10.5.8 Summarizing and Presenting Exposure Assessment Results 10-27
10.6 TOXICITY ASSESSMENT 10-27
10.6.1 Hazard Identification 10-28
10.6.2 Dose-Response Relationships 10-30
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10.7 RISK CHARACTERIZATION 10-32
10.7.1 Reviewing Outputs from the Toxicity and Exposure Assessments 10-32
10.7.2 Quantifying Risks 10-32
10.7.3 Combining Radionuclide and Chemical Cancer Risks 10-33
10.7.4 Assessing and Presenting Uncertainties 10-33
10.7.5 Summarizing and Presenting the Baseline Risk Characterization Results . . . 10-34
10.8 DOCUMENTATION, REVIEW, AND MANAGEMENT TOOLS FOR THE RISK
ASSESSOR, REVIWER, AND MANAGER 10-34
PART B -- REFINEMENT OF PRELIMINARY REMEDIATION GOALS
[Reserved]
PART C -- RISK EVALUATION OF REMEDIAL ALTERNATIVES
[Reserved]
APPENDICES
APPENDIX A ADJUSTMENTS FOR ABSORPTION EFFICIENCY A-l
A.1 ADJUSTMENTS OF TOXICITY VALUE FROM ADMINISTERED TO
ABSORBED DOSE A-l
A.2 ADJUSTMENT OF EXPOSURE ESTIMATE TO AN ABSORBED DOSE A-3
A.3 ADJUSTMENT FOR MEDIUM OF EXPOSURE A-3
APPENDIX B INDEX B-l
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LIST OF EXHIBITS
Exhibit Page
1-1 Risk Information Activities in the RI/FS Process 1-5
1-2 Part A: Baseline Risk Assessment 1-7
2-1 Relationship of Documents Governing Human Health Evaluation 2-2
2-2 Role of the Human Health Evaluation in the Superfund Remedial Process 2-6
4-1 Elements of a Conceptual Evaluation Model 4-6
4-2 Examples of Modeling Parameters for Which Information May Need To Be
Obtained During a Site Sampling Investigation 4-7
5-1 Data Evaluation 5-3
5-2 Example of Output Format for Validated Data 5-4
5-3 Examples of the Types of Data Potentially Unsuitable for a Quantitative
Risk Assessment 5-6
5-4 CLP Laboratory Data Qualifiers and Their Potential Use in Quantitative
Risk Assessment 5-12
5-5 Validation Data Qualifers and Their Potential Use in Quantitative
Risk Assessment 5-14
5-6 Example of Table Format for Presenting Chemicals Sampled in
Specific Media 5-25
5-7 Example of Table Format for Summarizing Chemicals of Potential
Concern in All Media Sampled 5-26
6-1 The Exposure Assessment Process 6-3
6-2 Illustration of Exposure Pathways 6-9
6-3 Common Chemical Release Sources at Sites in the Absence of
Remedial Action 6-10
6-4 Important Physical/Chemical and Environmental Fate Parameters 6-12
6-5 Important Considerations for Determining the Environmental Fate and
Transport of the Chemicals of Potential Concern at a Superfund Site 6-13
6-6 Flow Chart for Fate and Transport Assessments 6-14
6-7 Matrix of Potential Exposure Routes 6-18
6-8 Example of Table Format for Summarizing Complete Exposure Pathways at a Site . . 6-20
6-9 Generic Equation for Calculating Chemical Intakes 6-21
6-10 Example of Table Format for Summarizing Exposure Concentrations 6-33
6-11 Residential Exposure: Ingestion of Chemicals in Drinking Water
(and Beverages Made Using Drinking Water) 6-35
6-12 Residential Exposure: Ingestion of Chemicals in Surface Water While Swimming . . . 6-36
6-13 Residential Exposure: Dermal Contact with Chemicals in Water 6-37
6-14 Residential Exposure: Ingestion of Chemicals in Soil 6-40
6-15 Residential Exposure: Dermal Contact with Chemicals in Soil 6-41
6-16 Residential Exposure: Inhalation of Airborne (Vapor Phase) Chemicals 6-44
6-17 Residential Exposure: Food Pathway ~ Ingestion of Contaminated Fish
and Shellfish 6-45
6-18 Residential Exposure: Food Pathway - Ingestion of Contaminated
Fruits and Vegetables 6-46
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6-19 Residential Exposure: Food Pathway -- Ingestion of Contaminated
Meats, Eggs, and Dairy Products 6-48
6-20 Example of Table Format for Summarizing Values Used to Estimate
Exposure 6-49
6-21 Example of Uncertainty Table for Exposure Assessment 6-51
6-22 Example of Table Format for Summarizing the Results of the
Exposure Assessment - Current Land Use 6-52
7-1 Steps in Toxicity Assessment 7-4
7-2 Example of Table Format for Toxicity Values: Potential Noncarcinogenic Effects . . . 7-17
7-3 Example of Table Format for Toxicity Values: Potential Carcinogenic Effects 7-18
8-1 Steps in Risk Characterization 8-3
8-2 Example of Table Format for Cancer Risk Estimates 8-7
8-3 Example of Table Format for Chronic Hazard Index Estimates 8-8
8-4 Example of Table Format for Subchronic Hazard Index Estimates 8-9
8-5 Example of Presentation of Impact of Exposure Assumptions on
Cancer Risk Estimate 8-21
8-6 Example of Presentation of Impact of Exposure Assumptions on
Hazard Index Estimate 8-23
8-7 Example of Presentation of Relative Contribution of Individual
Chemicals to Exposure Pathway and Total Cancer Risk Estimates 8-27
8-8 Example of Presentation of Relative Contribution of Individual
Chemicals to Exposure Pathway and Total Hazard Index Estimates 8-28
9-1 Suggested Outline for a Baseline Risk Assessment Report 9-4
9-2 Reviewer Checklist 9-9
9-3 Checklist for Manager Involvement 9-15
10-1 Radiological Characteristics of Selected Radionuclides Found at Superfund Sites . . . 10-5
10-2 Types of Field Radiation Detection Instruments 10-11
10-3 Types of Laboratory Radiation Detection Instruments 10-13
10-4 Examples of Lower Limits of Detection (LLD) For Selected Radionuclides
Using Standard Analytical Methods 10-18
10-5 Summary of EPA's Radiation Risk Factors 10-31
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PREFACE
The Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA)
requires that actions selected to remedy hazardous
waste sites be protective of human health and the
environment. CERCLA also mandates that when
a remedial action results in residual contamination
at a site, future reviews must be planned and
conducted to assure that human health and the
environment continue to be protected. As part of
its effort to meet these and other CERCLA
requirements, EPA has developed a set of
manuals, together entitled Risk Assessment
Guidance for Superfiind. The Human Health
Evaluation Manual (Volume I) provides guidance
for developing health risk information at
Superfund sites, while the Environmental
Evaluation Manual (Volume II) provides guidance
for environmental assessment at Superfund sites.
Guidance in both human health evaluation and
environmental assessment is needed so that EPA
can fulfill CERCLA's requirement to protect
human health and the environment.
The Risk Assessment Guidance for Superfund
manuals were developed to be used in the
remedial investigation/feasibility study (RI/FS)
process at Superfund sites, although the analytical
framework and specific methods described in the
manuals may also be applicable to other
assessments of hazardous wastes and hazardous
materials. These manuals are companion
documents to EPA's Guidance for Conducting
Remedial Investigations and Feasibility Studies
Under CERCLA (October 1988), and users should
be familiar with that guidance. The two
Superfund risk assessment manuals were developed
with extensive input from EPA workgroups
comprised of both regional and headquarters staff.
These manuals are interim final guidance; final
guidance will be issued when the revisions
proposed in December 1988 to the National Oil
and Hazardous Substances Pollution Contingency
Plan (NCP) become final.
Although human health risk assessment and
environmental assessment are different processes,
they share certain common information needs and
generally can use some of the same chemical
sampling and environmental setting data for a site.
Planning for both assessments should begin during
the scoping stage of the RI/FS, and site sampling
and other data collection activities to support the
two assessments should be coordinated. An
example of this type of coordination is the
sampling and analysis of fish or other aquatic
organisms; if done properly, data from such
sampling can be used in the assessment of human
health risks from ingestion and in the assessment
of damages to and potential effects on the aquatic
ecosystem.
The two manuals in this set target somewhat
different audiences. The Environmental Evaluation
Manual is addressed primarily to remedial project
managers (RPMs) and on-scene coordinators
(OSCs), who are responsible for ensuring a
thorough evaluation of potential environmental
effects at sites. The Environmental Evaluation
Manual is not a detailed "how-to" type of
guidance, and it does not provide "cookbook"
approaches for evaluation. Instead, it identifies
the kinds of help that RPMs/OSCs are likely to
need and where they may find that help. The
manual also provides an overall framework to be
used in considering environmental effects. An
environmental evaluation methods compendium
published by EPA's Office of Research and
Development, Ecological Assessments of Hazardous
Waste Sites: A Field and Laboratory Reference
Document (EPA/600/3-89/013), is an important
reference to be used with the manual.
The Human Health Evaluation Manual is
addressed primarily to the individuals actually
conducting health risk assessments for sites, who
frequently are contractors to EPA, other federal
agencies, states, or potentially responsible parties.
It also is targeted to EPA staff, including those
responsible for review and oversight of risk
assessments (e.g., technical staff in the regions)
and those responsible for ensuring adequate
evaluation of human health risks (i.e., RPMs).
The Human Health Evaluation Manual replaces a
previous EPA guidance document, The Superfund
Public Health Evaluation Manual (October 1986),
which should no longer be used. The new manual
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incorporates lessons learned from application of
the earlier manual and addresses a number of
issues raised since the earlier manual's publication.
Issuance of the new manual does not invalidate
human health risk assessments completed before
(or in progress at) the publication date.
The Human Health Evaluation Manual
provides a basic framework for health risk
assessment at Superfund sites, as the
Environmental Evaluation Manual does for
environmental assessment. The Human Health
Evaluation Manual differs, however, by providing
more detailed guidance on many of the procedures
used to assess health risk. This additional level
of detail is possible because of the relatively large
body of information, techniques, and guidance
available on human health risk assessment and the
extensive Superfund program experience
conducting such assessments for sites. Even
though the Human Health Evaluation Manual is
considerably more specific than the Environmental
Evaluation Manual, it also is not a "cookbook,"
and proper application of the guidance requires
substantial expertise and professional judgment.
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INTRODUCTION
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CHAPTER 1
INTRODUCTION
The Comprehensive Environmental Response,
Compensation, and Liability Act of 1980, as
amended (CERCLA, or "Superfund"), establishes
a national program for responding to releases of
hazardous substances into the environment/ The
National Oil and Hazardous Substances Pollution
Contingency Plan (NCP) is the regulation that
implements CERCLA.2 Among other things, the
NCP establishes the overall approach for
determining appropriate remedial actions at
Superfund sites. The overarching mandate of the
Superfund program is to protect human health
and the environment from current and potential
threats posed by uncontrolled hazardous substance
releases, and the NCP echoes this mandate.
To help meet this Superfund mandate, EPA's
Office of Emergency and Remedial Response has
developed a human health evaluation process as
part of its remedial response program. The
process of gathering and assessing human health
risk information described in this manual is
adapted from well-established chemical risk
assessment principles and procedures (NAS 1983;
CRS 1983; OSTP 1985). It is designed to be
consistent with EPA's published risk assessment
guidelines (EPA 1984; EPA 1986a-e; EPA 1988a;
EPA 1989a) and other Agency-wide risk
assessment policy. The Human Health Evaluation
Manual revises and replaces the Superfund Public
Health Evaluation Manual (EPA 1986f).5 It
incorporates new information and builds on
several years of Superfund program experience
conducting risk assessments at hazardous waste
sites. In addition, the Human Health Evaluation
Manual together with the companion
Environmental Evaluation Manual (EPA 1989b)
replaces EPA's 1985 Endangerment Assessment
Handbook, which should no longer be used (see
Section 2.2.1).
The goal of the Superfund human health
evaluation process is to provide a framework for
developing the risk information necessary to assist
decision-making at remedial sites. Specific
objectives of the process are to:
• provide an analysis of baseline risks4
and help determine the need for action
at sites;
• provide a basis for determining levels
of chemicals that can remain onsite and
still be adequately protective of public
health;
• provide a basis for comparing potential
health impacts of various remedial
alternatives; and
• provide a consistent process for
evaluating and documenting public health
threats at sites.
The human health evaluation process
described in this manual is an integral part of the
remedial response process defined by CERCLA
and the NCP. The risk information generated by
the human health evaluation process is designed
to be used in the remedial investigation/feasibility
study (RI/FS) at Superfund sites. Although risk
information is fundamental to the RI/FS and to
the remedial response program in general,
Superfund site experience has led EPA to balance
the need for information with the need to take
action at sites quickly and to streamline the
remedial process. Revisions proposed to the NCP
in 1988 reflect EPA program management
principles intended to promote the efficiency and
effectiveness of the remedial response process.
Chief among these principles is a bias for action.
EPA's Guidance for Conducting Remedial
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Investigations and Feasibility Studies Under
CERCLA (EPA 1988b) also was revised in 1988
to incorporate management initiatives designed to
streamline the RI/FS process and to make
information collection activities during the RI
more efficient. The Risk Assessment Guidance for
Super/and, of which this Human Health Evaluation
Manual is Volume I,5 has been developed to
reflect the emphasis on streamlining the remedial
process. The Human Health Evaluation Manual
is a companion document to the RI/FS guidance.
It provides a basic framework for developing
health risk information at Superfund sites and also
gives specific guidance on appropriate methods
and data to use. Users of the Human Health
Evaluation Manual should be familiar with the
RI/FS guidance, as well as with other guidances
referenced throughout later chapters of this
manual.
The Human Health Evaluation Manual is
addressed primarily to the individuals actually
conducting human health evaluations for sites
(frequently contractors to EPA, other federal
agencies, states, or potentially responsible parties).
It also is targeted to EPA staff responsible for
review and oversight of risk assessments (e.g.,
technical staff in the regions) and those
responsible for ensuring an adequate evaluation of
human health risks (i.e., remedial project
managers, or RPMs). Although the terms risk
assessor and risk assessment reviewer are used in
this manual, it is emphasized that they generally
refer to teams of individuals in appropriate
disciplines (e.g., toxicologists, chemists,
hydrologists, engineers). It is recommended that
an appropriate team of scientists and engineers be
assembled for the human health evaluation at
each specific site. It is the responsibility of
RPMs, along with the leaders of human health
evaluation teams, to match the scientific support
they deem appropriate with the resources at their
disposal.
Individuals having different levels of scientific
training and experience are likely to use the
manual in designing, conducting, and reviewing
human health evaluations. Because assumptions
and judgments are required in many parts of the
analysis, the individuals conducting the evaluation
are key elements in the process. The manual is
not intended to instruct non-technical personnel
how to perform technical evaluations, nor to allow
professionals trained in one discipline to perform
the work of another.
KEY PLAYERS IN SUPERFUND
SITE RISK ASSESSMENT/
RISK MANAGEMENT
Risk Assessor. The individual or team of individuals
who actually organizes and analyzes site data, develops
exposure and risk calculations, and prepares human
health evaluation (i.e., risk assessment) reports. Risk
assessors for Superfund sites frequently are contractors
to EPA, other federal agencies, states, or potentially
responsible parties.
Risk Assessment Reviewer. The individual or team of
individuals within an EPA region who provides technical
oversight and quality assurance review of human health
evaluation activities.
Remedial Project Manager (RPMX The individual who
manages and oversees all RI/FS activities, including the
human health evaluation, for a site. The RPM is
responsible for ensuring adequate evaluation of human
health risks and for determining the level of resources
to be committed to the human health evaluation.
Risk Manager. The individual or group of individuals
who serves as primary decision-maker for a site,
generally regional Superfund management in
consultation with the RPM and members of the
technical staff. The identity of the risk manager may
differ from region to region and for sites of varying
complexity.
The Human Health Evaluation Manual
admittedly cannot address all site circumstances.
Users of the manual must exercise technical and
management judgment, and should consult with
EPA regional risk assessment contacts and
appropriate headquarters staff when encountering
unusual or particularly complex technical issues.
The first three chapters of this manual
provide background information to help place the
human health evaluation process in the context of
the Superfund remedial process. This chapter
(Chapter 1) summarizes the human health
evaluation process during the RI/FS. The three
main parts of this process -- baseline risk
assessment, refinement of preliminary remediation
goals, and remedial alternatives risk evaluation
-- are described in detail in subsequent chapters.
Chapter 2 discusses in a more general way the
role of risk information in the overall Superfund
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Page 1-3
remedial program by focusing on the statutes,
regulations, and guidance relevant to the human
health evaluation. Chapter 2 also identifies and
contrasts Superfund studies related to the human
health evaluation. Chapter 3 discusses issues
related to planning for the human health
evaluation.
1.1 OVERVIEW OF THE HUMAN
HEALTH EVALUATION
PROCESS IN THE RI/FS
Section 300.430 of the proposed revised NCP
reiterates that the purpose of the remedial process
is to implement remedies that reduce, control, or
eliminate risks to human health and the
environment. The remedial investigation and
feasibility study (RI/FS) is the methodology that
the Superfund program has established for
characterizing the nature and extent of risks posed
by uncontrolled hazardous waste sites and for
developing and evaluating remedial options. The
1986 amendments to CERCLA reemphasized the
original statutory mandate that remedies meet a
threshold requirement to protect human health
and the environment and that they be cost-
effective, while adding new emphasis to the
permanence of remedies. Because the RI/FS is an
analytical process designed to support risk
management decision-making for Superfund sites,
the assessment of health and environmental risk
plays an essential role in the RI/FS.
This manual provides guidance on the human
health evaluation activities that are conducted
during the RI/FS. The three basic parts of the
RI/FS human health evaluation are:
(1) baseline risk assessment (described in
Part A of this manual);
(2) refinement of preliminary remediation
goals (Part B); and
(3) remedial alternatives risk evaluation
(Part C).
Because these risk information activities are
intertwined with the RI/FS, this section describes
those activities in the context of the RI/FS
process. It relates the three parts of the human
health evaluation to the stages of the RI/FS,
which are:
• project scoping (before the RI);
• site characterization (RI);
• establishment of remedial action
objectives (FS);
• development and screening of
alternatives (FS); and
• detailed analysis of alternatives (FS).
Although the RI/FS process and related risk
information activities are presented in a fashion
that makes the steps appear sequential and
distinct, in practice the process is highly
interactive. In fact, the RI and FS are conducted
concurrently. Data collected in the RI influences
the development of remedial alternatives in the
FS, which in turn affects the data needs and scope
of treatability studies and additional field
investigations. The RI/FS should be viewed as a
flexible process that can and should be tailored to
specific circumstances and information needs of
individual sites, not as a rigid approach that must
be conducted identically at every site. Likewise,
the human health evaluation process described
here should be viewed the same way.
Two concepts are essential to the phased
RI/FS approach. First, initial data collection
efforts develop a general understanding of the site.
Subsequent data collection effort focuses on filling
previously unidentified gaps in the understanding
of site characteristics and gathering information
necessary to evaluate remedial alternatives.
Second, key data needs should be identified as
early in the process as possible to ensure that
data collection is always directed toward providing
information relevant to selection of a remedial
action. In this way, the overall site
characterization effort can be continually scoped
to minimize the collection of unnecessary data and
maximize data quality.
The RI/FS provides decision-makers with a
technical evaluation of the threats posed at a site,
a characterization of the potential routes of
exposure, an assessment of remedial alternatives
(including their relative advantages and
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Page 1-4
disadvantages), and an analysis of the trade-offs in
selecting one alternative over another. EPA's
interim final Guidance for Conducting Remedial
Investigations and Feasibility Studies under
CERCLA (EPA 1988b) provides a detailed
structure for the RI/FS. The RI/FS guidance
provides further background that is helpful in
understanding the place of the human health
evaluation in the RI/FS process. The role that
risk information plays in these stages of the RI/FS
is described below; additional background can be
found in the RI/FS guidance and in a summary of
the guidance found in Chapter 2. Exhibit 1-1
illustrates the RI/FS process, showing where in the
process risk information is gathered and analyzed.
1.1.1 PROJECT SCOPING
The purpose of project scoping is to define
more specifically the appropriate type and extent
of investigation and analysis that should be
undertaken for a given site. During scoping, to
assist in evaluating the possible impacts of releases
from the site on human health and the
environment, a conceptual model of the site
should be established, considering in a qualitative
manner the sources of contamination, potential
pathways of exposure, and potential receptors.
(Scoping is also the starting point for the risk
assessment, during which exposure pathways are
identified in the conceptual model for further
investigation and quantification.)
PROJECT SCOPING
Program experience has shown that scoping is a very
important step for the human health evaluation process,
and both the health and environmental evaluation teams
need to get involved in the RI/FS during the scoping
stage. Planning for site data collection activities is
necessary to focus the human health evaluation (and
environmental evaluation) on the minimum amount of
sampling information in order to meet time and budget
constraints, while at the same time ensuring that enough
information is gathered to assess risks adequately. (See
Chapters for information on planning the human health
evaluation.)
The preliminary characterization during
project scoping is initially developed with readily
available information and is refined as additional
data are collected. The main objectives of scoping
are to identify the types of decisions that need to
be made, to determine the types (including
quantity and quality) of data needed, and to
design efficient studies to collect these data.
Potential site-specific modeling activities should
be discussed at initial scoping meetings to ensure
that modeling results will supplement the sampling
data and effectively support risk assessment
activities.
1.1.2 SITE CHARACTERIZATION (RI)
During site characterization, the sampling and
analysis plan developed during project scoping is
implemented and field data are collected and
analyzed to determine the nature and extent of
threats to human health and the environment
posed by a site. The major components of site
characterization are:
• collection and analysis of field data to
characterize the site;
• development of a baseline risk
assessment for both potential human
health effects and potential
environmental effects; and
• treatability studies, as appropriate.
Part of the human health evaluation, the
baseline risk assessment (Part A of this manual)
is an analysis of the potential adverse health
effects (current or future) caused by hazardous
substance releases from a site in the absence of
any actions to control or mitigate these releases
(i.e., under an assumption of no action). The
baseline risk assessment contributes to the site
characterization and subsequent development,
evaluation, and selection of appropriate response
alternatives. The results of the baseline risk
assessment are used to:
• help determine whether additional
response action is necessary at the site;
modify preliminary remediation goals;
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Page 1-5
EXHIBIT 1-1
RISK INFORMATION ACTIVITIES IN THE RI/FS PROCESS
RI/FS
STAGES
RISK
INFORMATION
ACTIVITIES
Project
Scoping
i
Review data
collected
in site
inspection
Review
sampling/
data
collection
plans
Formulate
preliminary
remediation
goals (PRGs)
Determine
level of
effort for
baseline risk
assessment
RI/FS:
Site Establishment of Development & Detailed
Characterization Remedial Action Screening of Analysis of
(RI) Objectives (FS) Alternatives (FS) Alternatives (FS)
*
Conduct Refine Conduct risk
risk on risk remedial
assessment assessment and alternatives
ARARs
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Page 1-6
• help support selection of the "no-action"
remedial alternative, where appropriate;
and
• document the magnitude of risk at a
site, and the primary causes of that risk.
Baseline risk assessments are site-specific and
therefore may vary in both detail and the extent
to which qualitative and quantitative analyses are
used, depending on the complexity and particular
circumstances of the site, as well as the availability
of applicable or relevant and appropriate
requirements (ARARs) and other criteria,
advisories, and guidance. After an initial planning
stage (described more fully in Chapter 3), there
are four steps in the baseline risk assessment
process: data collection and analysis; exposure
assessment; toxicity assessment; and risk
characterization. Each step is described briefly
below and presented in Exhibit 1-2.
Data collection and evaluation involves
gathering and analyzing the site data relevant to
the human health evaluation and identifying the
substances present at the site that are the focus
of the risk assessment process, (Chapters 4 and
5 address data collection and evaluation.)
An exposure assessment is conducted to
estimate the magnitude of actual and/or potential
human exposures, the frequency and duration of
these exposures, and the pathways by which
humans are potentially exposed. In the exposure
assessment, reasonable maximum estimates of
exposure are developed for both current and
future land-use assumptions. Current exposure
estimates are used to determine whether a threat
exists based on existing exposure conditions at the
site. Future exposure estimates are used to
provide decision-makers with an understanding of
potential future exposures and threats and include
a qualitative estimate of the likelihood of such
exposures occurring. Conducting an exposure
assessment involves analyzing contaminant
releases; identifying exposed populations;
identifying all potential pathways of exposure;
estimating exposure point concentrations for
specific pathways, based both on environmental
monitoring data and predictive chemical modeling
results; and estimating contaminant intakes for
specific pathways. The results of this assessment
are pathway-specific intakes for current and future
exposures to individual substances. (Chapter 6
addresses exposure assessment.)
The toxicity assessment component of the
Superfund baseline risk assessment considers: (1)
the types of adverse health effects associated with
chemical exposures; (2) the relationship between
magnitude of exposure and adverse effects; and (3)
related uncertainties such as the weight of
evidence of a particular chemical's carcinogenicity
in humans. Typically, the Superfund site risk
assessments rely heavily on existing toxicity
information developed on specific chemicals.
Toxicity assessment for contaminants found at
Superfund sites is generally accomplished in two
steps: hazard identification and dose-response
assessment. The first step, hazard identification,
is the process of determining whether exposure to
an agent can cause an increase in the incidence of
an adverse health effect (e.g., cancer, birth defect).
Hazard identification also involves characterizing
the nature and strength of the evidence of
causation. The second step, dose-response
evaluation, is the process of quantitatively
evaluating the toxicity information and
characterizing the relationship between the dose
of the contaminant administered or received and
the incidence of adverse health effects in the
exposed population. From this quantitative dose-
response relationship, toxicity values are derived
that can be used to estimate the incidence of
adverse effects occurring in humans at different
exposure levels. (Chapter 7 addresses toxicity
assessment.)
The risk characterization summarizes and
combines outputs of the exposure and toxicity
assessments to characterize baseline risk, both in
quantitative expressions and qualitative statements.
During risk characterization, chemical-specific
toxicity information is compared against both
measured contaminant exposure levels and those
levels predicted through fate and transport
modeling to determine whether current or future
levels at or near the site are of potential concern.
(Chapter 8 addresses risk characterization.)
The level of effort required to conduct a
baseline risk assessment depends largely on the
complexity of the site. In situations where the
results of the baseline risk assessment indicate
that the site poses little or no threat to human
health or the environment and that no further (or
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Page 1-7
EXHIBIT 1-2
PART A: BASELINE RISK ASSESSMENT
Data Collection and
Evaluation
• Gather and analyze relevant
site data
• Identify potential chemicals of
concern
Exposure Assessment
Analyze contaminant releases
Identify exposed populations
Identify potential exposure
pathways
Estimate exposure
concentrations for pathways
Estimate contaminant intakes for
pathways
Toxicity Assessment
• Collect qualitative and
quantitative loxicity information
• Determine appropriate toxiciry
values
Risk Characterization
Characterize potential for adverse
health effects to occur
— Estimate cancer risks
— Estimate noncancer hazard
quotients
Evaluate uncertainty
Summarize risk information
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Page 1-8
limited) action will be necessary, the FS should be
scaled-down as appropriate.
The documents developed during site
characterization include a brief preliminary site
characterization summary and the draft RI report,
which includes either the complete baseline risk
assessment report or a summary of it. The
preliminary site characterization summary may be
used to assist in identification of ARARs and may
provide the Agency for Toxic Substances and
Disease Registry (ATSDR) with the data necessary
to prepare its health assessment (different from
baseline risk assessment or other EPA human
health evaluation activities; see Chapter 2). The
draft RI report is prepared after the completion
of the baseline risk assessment, often along with
the draft FS report.
1.1.3
FEASIBILITY STUDY
The purpose of the feasibility study is to
provide the decision-maker with an assessment of
remedial alternatives, including their relative
strengths and weaknesses, and the trade-offs in
selecting one alternative over another. The FS
process involves developing a reasonable range of
alternatives and analyzing these alternatives in
detail using nine evaluation criteria. Because the
RI and FS are conducted concurrently, this
development and analysis of alternatives is an
interactive process in which potential alternatives
and remediation goals are continually refined as
additional information from the RI becomes
available.
Establishing protective remedial action
objectives. The first step in the FS process
involves developing remedial action objectives that
address contaminants and media of concern,
potential exposure pathways, and preliminary
remediation goals. Under the proposed revised
NCP and the interim RI/FS guidance, preliminary
remediation goals typically are formulated first
during project scoping or concurrent with initial
RI activities (i.e., prior to completion of the
baseline risk assessment). The preliminary
remediation goals are therefore based initially on
readily available chemical-specific ARARs (e.g.,
maximum contaminant levels (MCLs) for drinking
water). Preliminary remediation goals for
individual substances are refined or confirmed at
the conclusion of the baseline risk assessment
(Part B of this manual addresses the refinement
of preliminary remediation goals). These refined
preliminary remediation goals are based both on
risk assessment and on chemical-specific ARARs.
Thus, they are intended to be protective and to
comply with ARARs. The analytical approach
used to develop these refined goals involves:
• identifying chemical-specific ARARs;
• identifying levels based on risk
assessment where chemical-specific
ARARs are not available or situations
where multiple contaminants or multiple
exposure pathways make ARARs not
protective;
• identifying non-substance-specific goals
for exposure pathways (if necessary); and
• determining a refined preliminary
remediation goal that is protective of
human health for all substance/exposure
pathway combinations being addressed.
Development and screening of alternatives.
Once remedial action objectives have been
developed, general response actions, such as
treatment, containment, excavation, pumping, or
other actions that may be taken to satisfy those
objectives should be developed. In the process of
developing alternatives for remedial action at a
site, two important activities take place. First,
volumes or areas of waste or environmental media
that need to be addressed by the remedial action
are determined by information on the nature and
extent of contamination, ARARs, chemical-specific
environmental fate and toxicity information, and
engineering analyses. Second, the remedial action
"alternatives and associated technologies are
screened to identify those that would be effective
for the contaminants and media of interest at the
site. The information developed in these two
activities is used in assembling technologies into
alternatives for the site as a whole or for a
specific operable unit.
The Superfund program has long permitted
remedial actions to be staged through multiple
operable units. Operable units are discrete
actions that comprise incremental steps toward the
final remedy. Operable units may be actions that
completely address a geographical portion of a site
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Page 1-9
or a specific site problem (e.g., drums and tanks,
contaminated ground water) or the entire site.
Operable units include interim actions (e.g.,
pumping and treating of ground water to retard
plume migration) that must be followed by
subsequent actions to fully address the scope of
the problem (e.g., final ground-water operable
unit that defines the remediation goals and
restoration timeframe). Such operable units may
be taken in response to a pressing problem that
will worsen if unaddressed, or because there is an
opportunity to undertake a limited action that will
achieve significant risk reduction quickly. The
appropriateness of dividing remedial actions into
operable units is determined by considering the
interrelationship of site problems and the need or
desire to initiate actions quickly. To the degree
that site problems are interrelated, it may be most
appropriate to address the problems together.
However, where problems are reasonably
separable, phased responses implemented through
a sequence of operable units may promote more
rapid risk reduction.
In situations where numerous potential
remedial alternatives are initially developed, it may
be necessary to screen the alternatives to narrow
the list to be evaluated in detail. Such screening
aids in streamlining the feasibility study while
ensuring that the most promising alternatives are
being considered.
Detailed analysis of alternatives. During the
detailed analysis, each alternative is assessed
against specific evaluation criteria and the results
of this assessment arrayed such that comparisons
between alternatives can be made and key trade-
offs identified. Nine evaluation criteria, some of
which are related to human health evaluation and
risk, have been developed to address statutory
requirements as well as additional technical and
policy considerations that have proven to be
important for selecting among remedial
alternatives. These evaluation criteria, which are
identified and discussed in the interim final RI/FS
guidance, serve as the basis for conducting the
detailed analyses during the FS and for
subsequently selecting an appropriate remedial
action. The nine evaluation criteria are as
follows:
(1) overall protection of human health and
the environment;
(2) compliance with ARARs (unless waiver
applicable);
(3) long-term effectiveness and permanence;
(4) reduction of toxicity, mobility, or volume
through the use of treatment;
(5) short-term effectiveness;
(6) implementability;
(7) cost;
(8) state acceptance; and
(9) community acceptance.
Risk information is required at the detailed
analysis stage of the RI/FS so that each alternative
can be evaluated in relation to the relevant NCP
remedy selection criteria.
The detailed analysis must, according to the
proposed NCP, include an evaluation of each
alternative against the nine criteria. The first two
criteria (i.e., overall protectiveness and compliance
with ARARs) are threshold determinations and
must be met before a remedy can be selected.
Evaluation of the overall protectiveness of an
alternative during the RI/FS should focus on how
a specific alternative achieves protection over time
and how site risks are reduced.
The next five criteria (numbers 3 through 7)
are primary balancing criteria. The last two
(numbers 8 and 9) are considered modifying
criteria, and risk information does not play a
direct role in the analysis of them. Of the five
primary balancing criteria, risk information is of
particular importance in the analysis of
effectiveness and permanence. Analysis of long-
term effectiveness and permanence involves an
evaluation of the results of a remedial action in
terms of residual risk at the site after response
objectives have been met. A primary focus of this
evaluation is the effectiveness of the controls that
will be applied to manage risk posed by treatment
residuals and/or any untreated wastes that may be
left on the site, as well as the volume and nature
of that material. It should also consider the
potential impacts on human health and the
environment should the remedy fail. An
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evaluation of short-term effectiveness addresses
the impacts of the alternative during the
construction and implementation phase until
remedial response objectives will be met. Under
this criterion, alternatives should be evaluated with
respect to the potential effects on human health
and the environment during implementation of the
remedial action and the length of time until
protection is achieved.
1.2 OVERALL ORGANIZATION OF
THE MANUAL
The next two chapters present additional
background material for the human health
evaluation process. Chapter 2 discusses statutes,
regulations, guidance, and studies relevant to the
Superfund human health evaluation. Chapter 3
discusses issues related to planning for the human
health evaluation. The remainder of the manual
is organized by the three parts of the human
health evaluation process:
• the baseline risk assessment is covered
in Part A of the manual (Chapters 4
through 10);
• refinement of preliminary remediation
goals is covered in Part B of the manual
(not included as part of this interim final
version); and
• the risk evaluation of remedial
alternatives is covered in Part C of the
manual (not included as part of this
interim final version).
Chapters 4 through 8 provide detailed
technical guidance for conducting the steps of a
baseline risk assessment, and Chapter 9 provides
documentation and review guidelines. Chapter 10
contains additional guidance specific to baseline
risk assessment for sites contaminated with
radionuclides. Sample calculations, sample table
formats, and references to other guidance are
provided throughout the manual. All material is
presented both in technical terms and in simpler
text. It should be stressed that the manual is
intended to be comprehensive and to provide
guidance for more situations than usually are
relevant to any single site. Risk assessors need
not use those parts of the manual that do not
apply to their site.
Each chapter in Part A includes a glossary of
acronyms and definitions of commonly used terms.
The manual also includes two appendices:
Appendix A provides technical guidance for
making absorption adjustments and Appendix B
is an index.
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Page 1-11
ENDNOTES FOR CHAPTER 1
1. References made to CERCLA throughout this document should be interpreted as meaning "CERCLA, as amended by the Superfund
Amendments and Reauthorization Act of 1986 (SARA)."
2. 40 CFR Part 300. Proposed revisions to the NCP were published on December 21, 1988 (53 Federal Register 51394).
3. The term "public health evaluation" was introduced in the previous risk assessment guidance (EPA 1986f) to describe the assessment
of chemical releases from a site and the analysis of public health threats resulting from those releases, and Superfund site risk assessment
studies often are referred to as public health evaluations, or PHEs. The term "PHE" should be replaced by whichever of the three parts
of the revised human health evaluation process is appropriate: "baseline risk assessment," "documentation of preliminary remediation
goals," or "risk evaluation of remedial alternatives."
4. Baseline risks are risks that might exist if no remediation or institutional controls were applied at a site.
5. Volume II of the Risk Assessment Guidance for Superfund is the Environmental Evaluation Manual (EPA 1989b), which provides
guidance for the analysis of potential environmental (i.e., not human health) effects at sites.
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Page 1-12
REFERENCES FOR CHAPTER 1
Congressional Research Service (CRS), Library of Congress. 1983. A Review of Risk Assessment Methodologies. Washington, D.C.
Environmental Protection Agency (EPA). 1984. Risk Assessment and Management: Framework for Decisionmaking. EPA/600/9-
85/002.
Environmental Protection Agency (EPA). 1986a. Guidelines for Carcinogen Risk Assessment. 51 Federal Register 33992 (September
24, 1986).
Environmental Protection Agency (EPA). 1986b. Guidelines for Exposure Assessment. 51 Federal Register 34042 (September 24,
1986).
Environmental Protection Agency (EPA). 1986c. Guidelines for Mutagenicitv Risk Assessment. 51 Federal Register 34006 (September
24, 1986).
Environmental Protection Agency (EPA). 1986d. Guidelines tor the Health Assessment of Suspect Developmental Toxicants. 51
Federal Register 34028 (September 24, 1986).
Environmental Protection Agency (EPA). 1986e. Guidelines for the Health Risk Assessment of Chemical Mixtures. 51 Federal
Register 34014 (September 24, 1986).
Environmental Protection Agency (EPA). 1986f. Superfund Public Health Evaluation Manual. Office of Emergency and Remedial
Response. EPA/540/1-86/060. (OSWER Directive 9285.4-1).
Environmental Protection Agency (EPA). 1988a. Proposed Guidelines for Exposure-related Measurements. 53 Federal Register 48830
(December 2, 1988).
Environmental Protection Agency (EPA). 1988b. Guidance for Conducting Remedial Investigations and Feasibility Studies Under
CERCLA. Interim Final. Office of Emergency and Remedial Response. (OSWER Directive 9355.3-01).
Environmental Protection Agency (EPA). 1989a. Proposed Amendments to the Guidelines for the Health Assessment of Suspect
Developmental Toxicants. 54 Federal Register 9386 (March 6, 1989).
Environmental Protection Agency (EPA). 1989b. Risk Assessment Guidance for Superfund: Environmental Evaluation Manual.
Interim Final. Office of Emergency and Remedial Response. EPA/540/1 -89/001 A. (OSWER Directive 9285.7-01).
National Academy of Sciences (NAS). 1983. Risk Assessment in the Federal Government: Managing the Process. National Academy
Press. Washington, D.C.
Office of Science and Technology Policy (OSTP). 1985. Chemical Carcinogens: A Review of the Science and Its Associated Principles.
50 Federal Register 10372 (March 14, 1985).
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CHAPTER 2
STATUTES, REGULATIONS,
GUIDANCE, AND
STUDIES RELEVANT TO
THE HUMAN HEALTH
EVALUATION
This chapter briefly describes the statutes,
regulations, guidance, and studies related to the
human health evaluation process. The
descriptions focus on aspects of these documents
most relevant to human health evaluations and
show how recent revisions to the documents bear
upon the human health evaluation process.
Section 2.1 describes the following documents that
govern the human health evaluation:
• the Comprehensive Environmental
Response, Compensation, and Liability
Act of 1980 (CERCLA, or Superfund)
and the Superfund Amendments and
Reauthorization Act of 1986 (SARA);
• the National Oil and Hazardous
Substances Pollution Contingency Plan
(National Contingency Plan, or NCP);
• Guidance for Conducting Remedial
Investigations and Feasibility Studies Under
CERCLA (RI/FS guidance);
• CERCLA Compliance with Other Laws
Manual (ARARs guidance); and
• Superfund Exposure Assessment Manual
(SEAM).
Exhibit 2-1 shows the relationship of these
statutes, regulations, and guidances governing
human health evaluation. In addition, Section
2.2 identifies and briefly describes other Superfund
studies related to, and sometimes confused with,
the RI/FS human health evaluation. The types of
studies discussed are:
• endangerment assessments;
• ATSDR health assessments; and
• ATSDR health studies.
2.1 STATUTES, REGULATIONS,
AND GUIDANCE GOVERNING
HUMAN HEALTH
EVALUATION
This section describes the major Superfund
laws and program documents relevant to the
human health evaluation process.
2.1.1 CERCLA AND SARA
In 1980, Congress enacted the Comprehensive
Environmental Response, Compensation, and
Liability Act (CERCLA) (42 U.S.C. 9601 et seq.),
commonly called Superfund, in response to the
dangers posed by sudden or otherwise
uncontrolled releases of hazardous substances,
pollutants, or contaminants into the environment.
CERCLA authorized $1.6 billion over five years
for a comprehensive program to clean up the
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Page 2-2
EXHIBIT 2-1
RELATIONSHIP OF DOCUMENTS GOVERNING
HUMAN HEALTH EVALUATION
Statutes
Comprehensive Environmental Response,
Compensation, and Liability Act of 1980
(CERCLA or Superfund)
Superfund Amendments and
Rcauthorization Act of 1986 (SARA)
Regulation ("Blueprint" for
Implementing the Statutes)
National Oil and Hazardous Substances
Pollution Contingency Plan (NCP)
Guidance
RI/FS Guidance
Risk Assessment Guidance for Superfund (RAGS)
• Human Health Evaluation Manual (HHEM)
• Environmental Evaluation Manual (EEM)
ARARs Guidance
Superfund Exposure Assessment Manual (SEAM)
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worst abandoned or inactive waste sites in the
nation. CERCLA funds used to establish and
administer the cleanup program are derived
primarily from taxes on crude oil and 42 different
commercial chemicals.
The reauthorization of CERCLA is known
as the Superfund Amendments and
Reauthorization Act (SARA), and was signed by
the President on October 17, 1986. (All further
references to CERCLA in this appendix should be
interpreted as "CERCLA as amended by SARA.")
These amendments provided $8.5 billion for the
cleanup program and an additional $500 million
for cleanup of leaks from underground storage
tanks. Under SARA, Congress strengthened
EPA's mandate to focus on permanent cleanups
at Superfund sites, involve the public in decision
processes at sites, and encourage states and
federally recognized Indian tribes to actively
participate as partners with EPA to address these
sites. SARA expanded EPA's research,
development (especially in the area of alternative
technologies), and training responsibilities. SARA
also strengthened EPA's enforcement authority.
The changes to CERCLA sections 104 (Response
Authorities) and 121 (Cleanup Standards) have
the greatest impact on the RI/FS process.
Cleanup standards. Section 121 (Cleanup
Standards) states a strong preference for remedies
that are highly reliable and provide long-term
protection. In addition to the requirement for
remedies to be both protective of human health
and the environment and cost-effective, other
remedy selection considerations in section 121(b)
include:
• a preference for remedial actions that
employ (as a principal element of the
action) treatment that permanently and
significantly reduces the volume, toxicity,
or mobility of hazardous substances,
pollutants, and contaminants;
• offsite transport and disposal without
treatment as the least favored alternative
where practicable treatment technologies
are available; and
• the need to assess the use of alternative
treatment technologies or resource
recovery technologies and use them 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, pollutants, or contaminants that may
pose a threat to human health or the environment
remain at the site. If during a five-year review it
is determined that the action no longer protects
human health and the environment, further
remedial actions will need to be considered.
Section 121(d)(2)(A) of CERCLA
incorporates into law the CERCLA Compliance
Policy, which specifies that Superfund remedial
actions meet any federal standards, requirements,
criteria, or limitations that are determined to be
legally applicable or relevant and appropriate
requirements (i.e., ARARs). Also included is the
new provision that state ARARs must be met if
they are more stringent than federal requirements.
(Section 2.1.4 provides more detail on ARARs.)
Health-related authorities. Under CERCLA
section 104(i)(6), the Agency for Toxic Substances
and Disease Registry (ATSDR) is required to
conduct a health assessment for every site included
or proposed for inclusion on the National
Priorities List. The ATSDR health assessment,
which is fairly qualitative in nature, should be
distinguished from the EPA human health
evaluation, which is more quantitative. CERCLA
section 104(i)(5)(F) states that:
the term "health assessments" shall include
preliminary assessments of the potential risk
to human health posed by individual sites and
facilities, based on such factors as the nature
and extent of contamination, the existence of
potential pathways of human exposure
(including ground or surface water
contamination, air emissions, and food chain
contamination), the size and potential
susceptibility of the community within the
likely pathways of exposure, the comparison
of expected human exposure levels to the
short-term and long-term health effects
associated with identified hazardous
substances and any available recommended
exposure or tolerance limits for such
hazardous substances, and the comparison of
existing morbidity and mortality data on
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Page 2-4
diseases that may be associated with the
observed levels of exposure. The
Administrator of ATSDR shall use
appropriate data, risk assessments, risk
evaluations and studies available from the
Administrator of EPA.
There are purposeful differences between an
ATSDR health assessment and traditional risk
assessment. The health assessment is usually
qualitative, site-specific, and focuses on medical
and public health perspectives. Exposures to site
contaminants are discussed in terms of especially
sensitive populations, mechanisms of toxic
chemical action, and possible disease outcomes.
Risk assessment, the framework of the EPA
human health evaluation, is a characterization of
the probability of adverse effects from human
exposures to environmental hazards. In this
context, risk assessments differ from health
assessments in that they are quantitative, chemical-
oriented characterizations that use statistical and
biological models to calculate numerical estimates
of risk to health. However, both health
assessments and risk assessments use data from
human epidemiological investigations, when
available, and when human lexicological data are
unavailable, rely on the results of animal
toxicology studies.
2.1.2 NATIONAL CONTINGENCY PLAN
(NCP)
The National Contingency Plan provides the
organizational structure and procedures for
preparing for and responding to discharges of oil
and releases of hazardous substances, pollutants,
and contaminants. The NCP is required by
section 105 of CERCLA and by section 311 of the
Clean Water Act. The current NCP (EPA 1985)
was published on November 20, 1985, and a
significantly revised version (EPA 1988a) was
proposed December 21, 1988 in response to
SARA. The proposed NCP is organized into the
following subparts:
• Subpart A - Introduction
• Subpart B - Responsibility and
Organization for Response
• Subpart C - Planning and Preparedness
• Subpart D - Operational Response
Phases for Oil Removal
• Subpart E -- Hazardous Substance
Response
• Subpart F - State Involvement in
Hazardous Substance Response
• Subpart G ~ Trustees for Natural
Resources
• Subpart H ~ Participation by Other
Persons
• Subpart I - Administrative Record for
Selection of Response Action
• Subpart J -- Use of Dispersants and
Other Chemicals
Subpart E, Hazardous Substance Response,
contains a detailed plan covering the entire range
of authorized activities involved in abating and
remedying releases or threats of releases of
hazardous substances, pollutants, and
contaminants. It contains provisions for both
removal and remedial response. The remedial
response process set forth by the proposed NCP
is a seven-step process, as described below. Risk
information plays a role in each step.
Site discovery or notification. Releases of
hazardous substances, pollutants, or contaminants
identified by federal, state, or local government
agencies or private parties are reported to the
National Response Center or EPA. Upon
discovery, such potential sites are screened to
identify release situations warranting further
remedial response consideration. These sites are
entered into the CERCLA Information System
(CERCLIS). This computerized system serves as
a data base of site information and tracks the
change in status of a site through the response
process. Risk information is used to determine
which substances are hazardous and, in some
cases, the quantities that constitute a release that
must be reported (i.e., a reportable quantity, or
RQ, under CERCLA section 103(a)).
Preliminary assessment and site inspection
(PA/SI). The preliminary assessment involves
collection and review of all available information
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Page 2-5
and may include offsite reconnaissance to evaluate
the source and nature of hazardous substances
present and to identify the responsible party(ies).
At the conclusion of the preliminary assessment,
a site may be referred for further action, or a
determination may be made that no further action
is needed. Site inspections, which follow the
preliminary assessment for sites needing further
action, routinely include the collection of samples
and are conducted to help determine the extent
of the problem and to obtain information needed
to determine whether a removal action is
warranted. If, based on the site inspection, it
appears likely that the site should be considered
for inclusion on the National Priorities List
(NPL), a listing site inspection (LSI) is conducted.
The LSI is a more extensive investigation than the
SI, and a main objective of the LSI is to collect
sufficient data about a site to support Hazard
Ranking System (HRS) scoring. One of the main
objectives of the PA/SI is to collect risk-related
information for sites so that the site can be scored
using the HRS and priorities may be set for more
detailed studies, such as the RI/FS.
Establishing priorities for remedial action.
Sites are scored using the HRS, based on data
from the PA/SI/LSI. The HRS scoring process is
the primary mechanism for determining the sites
to be included on the NPL and, therefore, the
sites eligible for Superfund-financed remedial
action. The HRS is a numerical scoring model
that is based on many of the factors affecting risk
at a site. A revised version of the HRS (EPA
1988b) was proposed December 23, 1988.
Remedial investigation/feasibility study
(RI/FS). As described in Section 1.1, the RI/FS
is the framework for determining appropriate
remedial actions at Superfund sites. Although
RI/FS activities technically are removal actions
and therefore not restricted to sites on the NPL
(see sections 101(23) and 104(b) of CERCLA),
they most frequently are undertaken at NPL sites.
Remedial investigations are conducted to
characterize the contamination at the site and to
obtain information needed to identify, evaluate,
and select cleanup alternatives. The feasibility
study includes an analysis of alternatives based
on the nine NCP evaluation criteria. The human
health evaluation described in this manual, and
the environmental evaluation described elsewhere,
are the guidance for developing risk information
in the RI/FS.
Selection of remedy. The primary
consideration in selecting a remedy is that it be
protective of human health and the environment,
by eliminating, reducing, or controlling risks posed
through each pathway. Thus, the risk information
developed in the RI/FS is a key input to remedy
selection. The results of the RI/FS are reviewed
to identify a preferred alternative, which is
announced to the public in a Proposed Plan.
Next, the lead agency reviews any resulting public
comments on the Proposed Plan, consults with the
support agencies to evaluate whether the preferred
alternative is still the most appropriate, and then
makes a final decision. A record of decision
(ROD) is written to document the rationale for
the selected remedy.
Remedial design/remedial action. The
detailed design of the selected remedial action is
developed and then implemented. The risk
information developed previously in the RI/FS
helps refine the remediation goals that the remedy
will attain.
Five-year review. Section 121 (c) of CERCLA
requires a periodic review of remedial actions, at
least every five years after initiation of such
action, for as long as hazardous substances,
pollutants, or contaminants that may pose a threat
to human health or the environment remain at
the site. If it is determined during a five-year
review that the action no longer protects human
health and the environment, further remedial
actions will need to be considered.
Exhibit 2-2 diagrams the general steps of the
Superfund remedial process, indicating where in
the process the various parts of the human health
evaluation are conducted.
2.1.3 REMEDIAL INVESTIGATION/
FEASIBILITY STUDY GUIDANCE
EPA's interim final Guidance for Conducting
Remedial Investigations and Feasibility Studies
Under CERCLA (EPA 1988c) provides a detailed
structure for conducting field studies to support
remedial decisions and for identifying, evaluating,
and selecting remedial action alternatives under
CERCLA. This 1988 guidance document is a
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Page 2-6
EXHIBIT 2-2
ROLE OF THE HUMAN HEALTH EVALUATION IN
THE SUPERFUND REMEDIAL PROCESS
Preliminary Assessment/
Site Inspection/Listing
Site Inspection
(PA/SI/LSI)
HRS Scoring/
NPL Listing
Remedial
Investigation/
Feasibility
Study
(RI/FS)
PART A
Baseline Risk
Assessment
(RD
PARTC
Risk Evaluation
of Remedial
Alternatives (FS)
PART B
Development/
Refinement
of Preliminary
Remediation
Goals (FS)
* The RI/FS can be undertaken prior to NPL listing.
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Page 2-7
revision of two separate guidances for remedial
investigations and for feasibility studies published
in 1985. These guidances have been consolidated
into a single document and revised to:
• reflect new emphasis and provisions of
SARA;
• incorporate aspects of new or revised
guidance related to RI/FSs;
• incorporate management initiatives
designed to streamline the RI/FS
process; and
• reflect experience gained from previous
RI/FS projects.
The RI/FS consists of the following general
steps:
• project scoping (during the RI);
• site characterization (RI);
• establishment of remedial action
objectives (FS);
• development and screening of
alternatives (FS); and
• detailed analysis of alternatives (FS).
Because Section 1.1 describes each of these steps,
focusing on the role that risk information plays in
the RI/FS, a discussion of the steps is not
repeated here. The RI/FS guidance provides the
context into which the human health evaluation
fits and should be used in conjunction with this
manual.
2.1.4 ARARS GUIDANCE
The interim final CERCLA Compliance with
Other Laws Manual (EPA I988d; EPA 1989a), or
ARARs guidance, was developed to assist in the
selection of onsite remedial actions that meet the
applicable or relevant and appropriate
requirements (ARARs) of the Resource
Conservation and Recovery Act (RCRA), Clean
Water Act (CWA), Safe Drinking Water Act
(SDWA), Clean Air Act (CAA), and other federal
and state environmental laws, as required by
CERCLA section 121. Part I of the manual
discusses the overall procedures for identifying
ARARs and provides guidance on the
interpretation and analysis of RCRA requirements.
Specifically:
• Chapter 1 defines "applicable" and
"relevant and appropriate," provides
matrices listing potential chemical-
specific, location-specific, and action-
specific requirements from RCRA, CWA,
and SDWA, and provides general
procedures for identifying and analyzing
requirements;
• Chapter 2 discusses special issues of
interpretation and analysis involving
RCRA requirements, and provides
guidance on when RCRA requirements
will be ARARs for CERCLA remedial
actions;
• Chapter 3 provides guidance for
compliance with CW^. substantive (for
onsite and offsite actions) and
administrative (for offsite actions)
requirements for direct discharges,
indirect discharges, and dredge and fill
activities;
• Chapter 4 provides guidance for
compliance with requirements of the
SDWA that may be applicable or
relevant and appropriate to CERCLA
sites; and
• Chapter 5 provides guidance on
consistency with policies for ground-
water protection.
The manual also contains a hypothetical scenario
illustrating how ARARs are identified and used,
and an appendix summarizing the provisions of
RCRA, CWA, and SDWA.
Part II of the ARARs guidance covers the
Clean Air Act, other federal statutes, and state
requirements. Specifically:
• Chapter 1 provides an introduction to
Part II of the guidance, and also includes
extensive summary tables;
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Page 2-8
• Chapter 2 describes Clean Air Act
requirements and related RCRA and
state requirements;
• Chapters 3 and 4 provide guidance for
compliance with several other federal
statutes;
• Chapter 5 discusses potential ARARs for
sites contaminated with radioactive
substances;
• Chapter 6 addresses requirements specific
to mining, milling, or smelting sites; and
• Chapter 7 provides guidance on
identifying and complying with state
ARARs.
2.1.5 SUPERFUND EXPOSURE
ASSESSMENT MANUAL
The Superfund Exposure Assessment Manual
(EPA 1988e), which was developed by the
Superfund program specifically as a companion
document to the original Superfund Public Health
Evaluation Manual (EPA 1986), provides RPMs
and regional risk assessors with the guidance
necessary to conduct exposure assessments that
meet the needs of the Superfund human health
risk evaluation process. Specifically, the manual:
• provides an overall description of the
integrated exposure assessment as it is
applied to uncontrolled hazardous waste
sites; and
• serves as a source of reference
concerning the use of estimation
procedures and computer modeling
techniques for the analysis of
uncontrolled sites.
The analytical process outlined in the
Superfund Exposure Assessment Manual provides
a framework for the assessment of exposure to
contaminants at or migrating from uncontrolled
hazardous waste sites. The application of both
monitoring and modeling procedures to the
exposure assessment process is outlined in the
manual. This process considers all contaminant
releases and exposure routes and assures that an
adequate level of analytical detail is applied to
support the human health risk assessment process.
The exposure assessment process described in
the Superfund Exposure Assessment Manual is
structured in five segments:
(1) analysis of contaminant releases from a
subject site into environmental media;
(2) evaluation of the transport and
environmental fate of the contaminants
released;
(3) identification, enumeration, and
characterization of potentially exposed
populations;
(4) integrated exposure analysis; and
(5) uncertainty analysis.
Two recent publications from EPA's Office
of Research and Development, the Exposure
Factors Handbook (EPA 1989b) and the Exposure
Assessment Methods Handbook (EPA 1989c),
provide useful information to supplement the
Superfund Exposure Assessment Manual. All three
of these key exposure assessment references should
be used in conjunction with Chapter 6 of this
manual.
2.2 RELATED SUPERFUND
STUDIES
This section identifies and briefly describes
other Superfund studies related to, and sometimes
confused with, the RI/FS human health evaluation.
It contrasts the objectives and methods and
clarifies the relationships of these other studies
with RI/FS health risk assessments. The types of
studies discussed are endangerment assessments,
ATSDR health assessments, and ATSDR health
studies.
2.2.1 ENDANGERMENT ASSESSMENTS
Before taking enforcement action against
parties responsible for a hazardous waste site,
EPA must determine that an imminent and
substantial endangerment to public health or the
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Page 2-9
environment exists as a result of the site. Such a
legal determination is called an endangerment
assessment. For remedial sites, the process for
analyzing whether there may be an endangerment
is described in this Human Health Evaluation
Manual and its companion Environmental
Evaluation Manual. In the past, an endangerment
assessment often was prepared as a study separate
from the baseline risk assessment. With the
passage of SARA and changes in Agency practice,
the need to perform a detailed endangerment
assessment as a separate effort from the baseline
risk assessment has been eliminated.
For administrative orders requiring a remedial
design or remedial action, endangerment
assessment determinations are now based on
information developed in the site baseline risk
assessment. Elements included in the baseline
risk assessment conducted at a Superfund site
during the RI/FS process fully satisfy the
informational requirements of the endangerment
assessment. These elements include the following:
• identification of the hazardous wastes
or hazardous substances present in
environmental media;
• assessment of exposure, including a
characterization of the environmental
fate and transport mechanisms for the
hazardous wastes and substances present,
and of exposure pathways;
• assessment of the toxicity of the
hazardous wastes or substances present;
• characterization of human health risks;
and
• characterization of the impacts and/or
risks to the environment.
The human health and environmental
evaluations that are part of the RI/FS are
conducted for purposes of determining the
baseline risks posed by the site, and for ensuring
that the selected remedy will be protective of
human health and the environment. The
endangerment assessment is used to support
litigation by determining that an imminent and
substantial endangerment exists. Information
presented in the human health and environmental
evaluations is basic to the legal determination of
endangerment.
In 1985, EPA produced a draft manual
specifically written for endangerment assessment,
the Endangerment Assessment Handbook. EPA
has determined that a guidance separate from the
Risk Assessment Guidance for Superfund (Human
Health Evaluation Manual and Environmental
Evaluation Manual) is not required for
endangerment assessment; therefore, the
Endangerment Assessment Handbook will not be
made final and should no longer be used.
2.2.2 ATSDR HEALTH ASSESSMENTS
CERCLAsection 104(i), as amended, requires
the Agency for Toxic Substances and Disease
Registry (ATSDR) to conduct health assessments
for all sites listed or proposed to be listed on the
NPL. A health assessment includes a preliminary
assessment of the potential threats that individual
sites and facilities pose to human health. The
health assessment is required to be completed "to
the maximum extent practicable" before
completion of the RI/FS. ATSDR personnel,
state personnel (through cooperative agreements),
or contractors follow six basic steps, which are
based on the same general risk assessment
framework as the EPA human health evaluation:
(1) evaluate information on the site's
physical, geographical, historical, and
operational setting, assess the
demographics of nearby populations, and
identify health concerns of the affected
community (ies);
(2) determine contaminants of concern
associated with the site;
(3) identify and evaluate environmental
pathways;
(4) identify and evaluate human exposure
pathways;
(5) identify and evaluate public health
implications based on available medical
and toxicological information; and
(6) develop conclusions concerning the
health threat posed by the site and make
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Page 2-10
recommendations regarding
public health activities.
further
The purpose of the ATSDR health
assessment is to assist in the evaluation of data
and information on the release of toxic substances
into the environment in order to assess any
current or future impact on public health, develop
health advisories or other health-related
recommendations, and identify studies or actions
needed to evaluate and prevent human health
effects. Health assessments are intended to help
public health and regulatory officials determine if
actions should be taken to reduce human exposure
to hazardous substances and to recommend
whether additional information on human
exposure and associated risks is needed. Health
assessments also are written for the benefit of the
informed community associated with a site, which
could include citizen groups, local leaders, and
health professionals.
Several important differences exist between
EPA human health evaluations and ATSDR
health assessments. EPA human health
evaluations include quantitative, substance-specific
estimates of the risk that a site poses to human
health. These estimates depend on statistical and
biological models that use data from human
epidemiologic investigations and animal toxicity
studies. The information generated from a human
health evaluation is used in risk management
decisions to establish cleanup levels and select a
remedial alternative.
ATSDR health assessments, although they
may employ quantitative data, are more qualitative
in nature. They focus not only on the possible
health threats posed by chemical contaminants
attributable to a site, but consider all health
threats, both chemical and physical, to which
residents near a site may be subjected. Health
assessments focus on the medical and public
health concerns associated with exposures at a site
and discuss especially sensitive populations, toxic
mechanisms, and possible disease outcomes. EPA
considers the information in a health assessment
along with the results of the baseline risk
assessment to give a complete picture of health
threats. Local health professionals and residents
use the information to understand the potential
health threats posed by specific waste sites.
Health assessments may lead to pilot health effects
studies, epidemiologic studies, or establishment of
exposure or disease registries.
EPA's Guidance for Coordinating ATSDR
Health Assessment Activities with the Superfitnd
Remedial Process (EPA 1987) provides information
to EPA and ATSDR managers for use in
coordinating human health evaluation activities.
(Section 2.1, in its discussion of CERCLA,
provides further information on the statutory basis
of ATSDR health assessments.)
2.2.3 ATSDR HEALTH STUDIES
After conducting a health assessment,
ATSDR may determine that additional health
effects information is needed at a site and, as a
result, may undertake a pilot study, a full-scale
epidemiological study, or a disease registry. Three
types of pilot studies are predominant:
(1) a symptom/disease prevalence study
consisting of a measurement of self-
reported disease occurrence, which may
be validated through medical records if
they are available;
(2) a human exposure study consisting of
biological sampling of persons who have
a potentially high likelihood of exposure
to determine if actual exposure can be
verified; and
(3) a cluster investigation study consisting
of an investigation of putative disease
clusters to determine if the cases of a
disease are excessively high in the
concerned community.
A full-scale epidemiological study is an
analytic investigation that evaluates the possible
causal relationships between exposure to
hazardous substances and disease outcome by
testing a scientific hypothesis. Such an
epidemiological study is usually not undertaken
unless a pilot study reveals widespread exposure
or increased prevalence of disease.
ATSDR, in cooperation with the states, also
may choose to follow up the results of a health
assessment by establishing and maintaining
national registries of persons exposed to hazardous
substances and persons with serious diseases or
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illness. A registry is a system for collecting and
maintaining, in a structured record, information on
specific persons from a defined population. The
purpose of a registry of persons exposed to
hazardous substances is to facilitate development
of new scientific knowledge through identification
and subsequent follow-up of persons exposed to
a defined substance at selected sites.
Besides identifying and tracking of exposed
persons, a registry also is used to coordinate the
clinical and research activities that involve the
registrants. Registries serve an important role in
assuring the uniformity and quality of the
collected data and ensuring that data collection is
not duplicative, thereby reducing the overall
burden to exposed or potentially exposed persons.
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Page 2-12
REFERENCES FOR CHAPTER 2
Environmental Protection Agency (EPA). 1985. National Oil and Hazardous Substances Pollution Contingency Plan. Final Rule. 50
Federal Register 47912 (November 20, 1985).
Environmental Protection Agency (EPA). 1986. Superfund Public Health Evaluation Manual. Office of Emergency and Remedial
Response. EPA/540A-86/060. (OSWER Directive 9285.4-1).
Environmental Protection Agency (EPA). 1987. Guidance for Coordinating ATSDR Health Assessment Activities with the Superfund
Remedial Process. Office of Emergency and Remedial Response. (OSWER Directive 9285.4-02).
Environmental Protection Agency (EPA). 1988a. National Oil and Hazardous Substances Pollution Contingency Plan. Proposed Rule.
53 Federal Register 51394 (December 21, 1988).
Environmental Protection Agency (EPA). 1988b. Hazard Ranking System (HRS) for Uncontrolled Hazardous Substance Releases.
Proposed Rule. 53 Federal Register 51962 (December 23, 1988).
Environmental Protection Agency (EPA). 1988c. Guidance for Conducting Remedial Investigations and Feasibility Studies Under
CERCLA Interim Final. Office of Emergency and Remedial Response. (OSWER Directive 9355.3-01).
Environmental Protection Agency (EPA). 1988d. CERCLA Compliance with Other Laws Manual. Part I. Interim Final. Office of
Emergency and Remedial Response. (OSWER Directive 9234.1-01).
Environmental Protection Agency (EPA). 1988e. Superfund Exposure Assessment Manual. Office of Emergency and Remedial
Response. EPA/540/1-88/001. (OSWER Directive 9285.5-1).
Environmental Protection Agency (EPA). 1989a. CERCLA Compliance with Other Laws Manual. Part II. Interim Final. Office of
Emergency and Remedial Response. (OSWER Directive 9234.1-02).
Environmental Protection Agency (EPA). 1989b. Exposure Factors Handbook. Office of Health and Environmental Assessment.
EPA/600/8-89/043.
Environmental Protection Agency (EPA). 1989c. Exposure Assessment Methods Handbook. Draft. Office of Health and
Environmental Assessment.
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CHAPTER 3
GETTING STARTED: PLANNING
FOR THE HUMAN HEALTH
EVALUATION IN THE RI/FS
This chapter discusses issues related to
planning the human health evaluation conducted
during the RI/FS. It presents the goals of the
RI/FS process as a whole and the human health
evaluation in particular (Sections 3.1 and 3.2). It
next discusses the way in which a site that is
divided into operable units should be treated in
the human health evaluation (Section 3.3). RI/FS
scoping is discussed in Section 3.4, and Section 3.5
addresses the level of effort and detail necessary
for a human health evaluation.
3.1 GOAL OF THE RI/FS
The goal of the RI/FS is to gather
information sufficient to support an informed risk
management decision regarding which remedy
appears to be most appropriate for a given site.
The RI/FS provides the context for all site
characterization activity, including the human
health evaluation. To attain this goal efficiently,
EPA must identify and characterize hazards in a
way that will contribute directly to the selection
of an appropriate remedy. Program experience
has shown that Superfund sites are complex, and
are characterized by heterogeneous wastes, extreme
variability in contamination levels, and a variety
of environmental settings and potential exposure
pathways. Consequently, complete characterization
of a site during the RI/FS, in the sense of
eliminating uncertainty, is not feasible, cost-
effective, or necessary for selection of appropriate
remedies. This view has motivated the
"streamlined approach" EPA is taking to help
accomplish the goal of completing an RI/FS in 18
months at a cost of $750,000 per operable unit
and $1.1 million per site. The streamlined
approach recognizes that the elimination of all
uncertainties is not possible or necessary and
instead strives only for sufficient data to generally
characterize a site and support remedy selection.
The resulting remedies are flexible and incorporate
specific contingencies to respond to new
information discovered during remedial action and
follow-up.
3.2 GOAL OF THE RI/FS HUMAN
HEALTH EVALUATION
As part of the effort to streamline the
process and reduce the cost and time required to
conduct the RI/FS, the Superfund human health
evaluation needs to focus on providing
information necessary to justify action at a site
and to select the best remedy for the site. This
should include characterizing the contaminants,
the potential exposures, and the potentially
exposed population sufficiently to determine what
risks need to be reduced or eliminated and what
exposures need to be prevented. It is important
to recognize that information should be developed
only to help EPA determine what actions are
necessary to reduce risks, and not to fully
characterize site risks or eliminate all uncertainty
from the analysis.
In a logical extension of this view, EPA has
made a policy decision to use, wherever
appropriate, standardized assumptions, equations,
and values in the human health evaluation to
achieve the goal of streamlined assessment. This
approach has the added benefit of making human
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Page 3-2
health evaluation easier to review, easier to
understand, and more consistent from site to site.
Developing unique exposure assumptions or non-
standard methods of risk assessment should not be
necessary for most sites. Where justified by site-
specific data or by changes in knowledge over
time, however, non-standard methods and
assumptions may be used.
3.3 OPERABLE UNITS
Current practice in designing remedies for
Superfund sites often divides sites into operable
units that address discrete aspects of the site (e.g.,
source control, ground-water remediation) or
different geographic portions of the site. The
NCP defines operable unit as "a discrete action
that comprises an incremental step toward
comprehensively addressing site problems." RI/FSs
may be conducted for the entire site and operable
units broken out during or after the feasibility
study, or operable units may be treated
individually from the start, with focused RI/FSs
conducted for each operable unit. The best way
to address the risks of the operable unit will
depend on the needs of the site.
The human health evaluation should focus on
the subject of the RI/FS, whether that is an
operable unit or the site as a whole. The baseline
risk assessment and other risk information
gathered will provide the justification for taking
the action for the operable unit. At the same
time, personnel involved in conducting the human
health evaluation for a focused RI/FS must be
mindful of other potential exposure pathways, and
other actions that are being contemplated for the
site to address other potential exposures. Risk
analysts should foresee that exposure pathways
outside the scope of the focused RI/FS may
ultimately be combined with exposure pathways
that are directly addressed by the focused RI/FS.
Considering risks from all related operable units
should prevent the unexpected discovery of high
multiple pathway risks during the human health
evaluation for the last operable unit. Consider,
for example, a site that will be addressed in two
operable units: a surface soil cleanup at the
contamination source and a separate ground-water
cleanup. Risks associated with residuals from the
soil cleanup and the ground-water cleanup may
need to be considered as a cumulative total if
there is the potential for exposure to both media
at the same time.
3.4 RI/FS SCOPING
Planning the human health evaluation prior
to beginning the detailed analysis is an essential
step in the process. The RPM must make up-
front decisions about, for example, the scope of
the baseline risk assessment, the appropriate level
of detail and documentation, trade-offs between
depth and breadth in the analysis, and the staff
and monetary resources to commit.
Scoping is the initial planning phase of the
RI/FS process, and many of the planning steps
begun here are continued and refined in later
phases. Scoping activities typically begin with the
collection of existing site data, including data from
previous investigations such as the preliminary
assessment and site inspection. On the basis of
this information, site management planning is
undertaken to identify probable boundaries of the
study area, to identify likely remedial action
objectives and whether interim actions may be
necessary or appropriate, and to establish whether
the site may best be remedied as one site or as
several separate operable units. Once an overall
management strategy is agreed upon, the RI/FS
for a specific project or the site as a whole is
planned.
The development of remedial alternatives
usually begins during or soon after scoping, when
likely response scenarios may first be identified.
The development of alternatives requires:
• identifying remedial action objectives;
• identifying potential treatment, resource
recovery, and containment technologies
that will satisfy these objectives; and
• screening the technologies based on their
effectiveness, implementability, and cost.
Remedial alternatives may be developed to address
a contaminated medium, a specific area of the
site, or the entire site. Alternative remedial
actions for specific media and site areas either can
be carried through the FS process separately or
combined into comprehensive alternatives for the
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Page 3-3
entire site. The approach is flexible to allow
alternatives to be considered in combination at
various points in the process. The RI/FS guidance
discusses planning in greater detail.
3.5 LEVEL OF EFFORT/LEVEL OF
DETAIL OF THE HUMAN
HEALTH EVALUATION
An important part of scoping is determining
the appropriate level of effort/level of detail
necessary for the human health evaluation.
Human health evaluation can be thought of as
spanning a continuum of complexity, detail, and
level of effort, just as sites vary in conditions and
complexity. Some of the site-specific factors
affecting level of effort that the RPM must
consider include the following:
• number and identity of chemicals
present;
• availability of ARARs and/or applicable
toxicity data;
• number and complexity of exposure
pathways (including complexity of release
sources and transport media), and the
need for environmental fate and
transport modeling to supplement
monitoring data;
• necessity for precision of the results,
which in turn depends on site conditions
such as the extent of contaminant
migration, characteristics of potentially
exposed populations, and enforcement
considerations (additional quantification
may be warranted for some enforcement
sites); and
• quality and quantity of available
monitoring data.7
This manual is written to address the most
complex sites, and as a result not all of the steps
and procedures of the Superfund human health
evaluation process described in this manual apply
to all remedial sites. For example, Section 6.6
provides procedures and equations for estimating
chemical intakes through numerous exposure
routes, although for many sites, much of this
information will not apply (e.g., the exposure
route does not exist or is determined to be
relatively unimportant). This manual establishes
a generic framework that is broadly applicable
across sites, and it provides specific procedures
that cover a range of sites or situations that may
or may not be appropriate for any individual site.
As a consequence of attempting to cover the wide
variety of Superfund site conditions, some of the
process components, steps, and techniques
described in the manual do not apply to some
sites. In addition, most of the components can
vary greatly in level of detail. Obviously,
determining which elements of the process are
necessary, which are desirable, and which are
extraneous is a key decision for each site. All
components should not be forced into the assess-
ment of a site, and the evaluation should be
limited to the complexity and level of detail
necessary to adequately assess risks for the
purposes described in Sections 3.1 and 3.2.
Planning related to the collection and analysis
of chemical data is perhaps the most important
planning step. Early coordination among the risk
assessors, the remainder of the RI/FS team,
representatives of other agencies involved in the
risk assessment or related studies (e.g., ATSDR,
natural resource trustees such as the Department
of the Interior, state agencies), and the RPM is
essential and preferably should occur during the
scoping stage of the RI/FS. Detailed guidance on
planning related to collection and analysis of
chemical data is given in Chapter 4 of this
manual.
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Page 3-4
ENDNOTE FOR CHAPTER 3
1. All site monitoring data must be subjected to appropriate quality assurance/quality control programs. Lack of acceptable data may
limit by necessity the amount of data available for the human health evaluation, and therefore may limit the scope of the evaluation.
Acceptability is determined by whether data meet the appropriate data quality objectives (see Section 4.1.2).
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PART A
BASELINE RISK ASSESSMENT
-------
CHAPTER 4
DATA COLLECTION
Toxicity
Assessment
FROM:
• Site discovery
• Preliminary
assessment
•Site inspection
listing
Risk
Characterization
• Selection of
remedy
• Remedial
design
• Remedial
action
DATA COLLECTION
• Collect existing data
• Address modeling parameter
needs
• Collect background data
• Conduct preliminary exposure
assessment
• Devise overall strategy for
sample collection
• Examine QA/QC measures
• Identify special analytical needs
• Take active role during workplan
development and data collection
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CHAPTER 4
DATA COLLECTION
This chapter discusses procedures for
acquiring reliable chemical release and exposure
data for quantitative human health risk assessment
at hazardous waste sites/ The chapter is intended
to be a limited discussion of important sampling
considerations with respect to risk assessment; it
is not intended to be a complete guide on how to
collect data or design sampling plans.
Following a general background section
(Section 4.1), this chapter addresses the following
eight important areas:
(1) review of available site information
(Section 4.2);
(2) consideration of modeling parameter
needs (Section 4.3);
(3) definition of background sampling needs
(Section 4.4);
(4) preliminary identification of potential
human exposure (Section 4.5);
(5) development of an overall strategy for
sample collection (Section 4.6);
(6) definition of required QA/QC measures
(Section 4.7);
(7) evaluation of the need for Special
Analytical Services (Section 4.8); and
(8) activities during workplan development
and data collection (Section 4.9).
4.1 BACKGROUND INFORMATION
USEFUL FOR DATA
COLLECTION
This section provides background information
on the types of data needed for risk assessment,
overall data needs of the RI/FS, reasons and steps
for identifying risk assessment data needs early,
use of the Data Quality Objectives for Remedial
Response Activities (EPA 1987a,b, hereafter
referred to as the DQO guidance), and other data
concerns.
4.1.1 TYPES OF DATA
In general, the types of site data needed for
a baseline risk assessment include the following:
• contaminant identities;
ACRONYMS FOR CHAPTER 4
CLP = Contract Laboratory Program
DQO = Data Quality Objectives
FIT = Field Investigation Team
FSP = Field Sampling Plan
HRS = Hazard Ranking System
IDL = Instrument Detection Limit
MDL = Method Detection Limit
PA/SI = Preliminary Assessment/Site Inspection
QA/QC = Quality Assurance/Quality Control
QAPjP = Quality Assurance Project Plan
RAS = Routine Analytical Services
RI/FS = Remedial Investigation/Feasibility Study
SAP = Sampling and Analysis Plan
SAS = Special Analytical Services
SMO = Sample Management Office
SOW = Statement of Work
TAL = Target Analyte List
TCL = Target Compound List
TIC = Tentatively Identified Compound
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Page 4-2
DEFINITIONS FOR CHAPTER 4
Analytes. The chemicals for which a sample is analyzed.
Anthropogenic Background Levels. Concentrations of chemicals that are present in the environment due to human-made, non~
site sources (e.g., industry, automobiles).
Contract Laboratory Program (CLP). Analytical program developed for Superfund waste site samples to fill the need for legally
defensible analytical results supported by a high level of quality assurance and documentation.
Data Quality Objectives (DOOst. Qualitative and quantitative statements to ensure that data of known and documented quality
are obtained during an RI/FS to support an Agency decision.
Field Sampling Plan (FSP). Provides guidance for all field work by defining in detail the sampling and data gathering methods
to be used on a project.
Naturally Occurring Background Levels. Ambient concentrations of chemicals that are present in the environment and have
not been influenced by humans (e.g., aluminum, manganese).
Quality Assurance Project Plan (QAPjPV Describes the policy, organization, functional activities, and quality assurance and
quality control protocols necessary to achieve DQOs dictated by the intended use of the data (RI/FS Guidance).
Routine Analytical Services (RAS). The set of CLP analytical protocols that are used to analyze most Superfund site samples.
These protocols are provided in the EPA Statements of Work for the CLP (SOW for Inorganics, SOW for Organics) and
must be followed by every CLP laboratory.
Sampling and Analysis Plan (SAP). Consists of a Quality Assurance Project Plan (QAPjP) and a Field Sampling Plan (FSP).
Sample Management Office (SMO). EPA contractor providing management, operational, and administrative support to the
CLP to facilitate optimal use of the program.
Special Analytical Services (SAS). Non-standardized analyses conducted under the CLP to meet user requirements that cannot
be met using RAS, such as shorter analytical turnaround time, lower detection limits, and analysis of non-standard matrices
or non-TCL compounds.
Statement of Work (SOW) for the CLP. A document that specifies the instrumentation, sample handling procedures, analytical
parameters and procedures, required quantitation limits, quality control requirements, and report format to be used by CLP
laboratories. The SOW also contains the TAL and TCL.
Target Analyte List (TAL"). Developed by EPA for Superfund site sample analyses. The TAL is a list of 23 metals plus total
cyanide routinely analyzed using RAS.
Target Compound List (TCL'). Developed by EPA for Superfund site sample analyses. The TCL is a list of analytes (34
volatile organic chemicals, 65 semivolatile organic chemicals, 19 pesticides, 7 polychlorinated biphenyls, 23 metals, and
total cyanide) routinely analyzed using RAS.
contaminant concentrations in the key Most of these data are obtained during the
sources and media of interest;2 course of a remedial investigation/feasibility study
(RI/FS). Other sources of information, such as
characteristics of sources, especially preliminary assessment/site inspection (PA/SI)
information related to release potential; reports, also may be available.
and
4.1.2 DATA NEEDS AND THE RI/FS
characteristics of the environmental
setting that may affect the fate, transport, The RI/FS has four primary data collection
and persistence of the contaminants. components:
(1) characterization of site conditions;
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Page 4-3
(2) determination of the nature of the
wastes;
(3) risk assessment; and
(4) treatability testing.
The site and waste characterization components of
the RI/FS are intended to determine
characteristics of the site (e.g., ground-water
movement, surface water and soil characteristics)
and the nature and extent of contamination
through sampling and analysis of sources and
potentially contaminated media. Quantitative risk
assessment, like site characterization, requires data
on concentrations of contaminants in each of the
source areas and media of concern. Risk
assessment also requires information on other
variables necessary for evaluating the fate,
transport, and persistence of contaminants and
estimating current and potential human exposure
to these contaminants. Additional data might be
required for environmental risk assessments (see
EPA 1989a).
Data also are collected during the RI/FS to
support the design of remedial alternatives. As
discussed in the DQO guidance (EPA 1987a,b),
such data include results of analyses of
contaminated media "before and after" bench-scale
treatability tests. This information usually is not
appropriate for use in a baseline risk assessment
because these media typically are assessed only for
a few individual parameters potentially affected by
the treatment being tested. Also, initial
treatability testing may involve only a screening
analysis that generally is not sensitive enough and
does not have sufficient quality assurance/quality
control (QA/QC) procedures for use in
quantitative risk assessment.
4.1.3 EARLY IDENTIFICATION OF DATA
NEEDS
Because the RI/FS and other site studies
serve a number of different purposes (e.g., site
and waste characterization, design of remedial
alternatives), only a subset of this information
generally is useful for risk assessment. To ensure
that all risk assessment data needs will be met, it
is important to identify those needs early in the
RI/FS planning for a site. The earlier the
requirements are identified, the better the chances
are of developing an RI/FS that meets the risk
assessment data collection needs.
One of the earliest stages of the RI/FS at
which risk assessment data needs can be addressed
is the site scoping meeting. As discussed in the
Guidance for Conducting Remedial Investigations
and Feasibility Studies Under CERCLA (EPA
1988a, hereafter referred to as RI/FS guidance),
the scoping meeting is part of the initial planning
phase of site remediation. It is at this meeting
that the data needs of each of the RI/FS
components (e.g., site and waste characterization)
are addressed together. Scoping meeting attendees
include the RPM, contractors conducting the
RI/FS (including the baseline risk assessment),
onsite personnel (e.g., for construction), and
natural resource trustees (e.g., Department of
Interior). The scoping meeting allows
development of a comprehensive sampling and
analysis plan (SAP) that will satisfy the needs of
each RI/FS component while helping to ensure
that time and budget constraints are met. Thus,
in addition to aiding the effort to meet the risk
assessment data needs, this meeting can help
integrate these needs with other objectives of the
RI/FS and thereby help make maximum use of
available resources and avoid duplication of effort.
During scoping activities, the risk assessor
should identify, at least in preliminary fashion, the
type and duration of possible exposures (e.g.,
chronic, intermittent), potential exposure routes
(e.g., ingestion of fish, ingestion of drinking water,
inhalation of dust), and key exposure points (e.g.,
municipal wells, recreation areas) for each
medium. The relative importance of the potential
exposure routes and exposure points in
determining risks should be discussed, as should
the consequences of not studying them adequately.
Section 4.5 and Chapter 6 provide guidance for
identifying exposure pathways that may exist at
hazardous waste sites. If potential exposure
pathways are identified early in the RI/FS process,
it will be easier to reach a decision on the
number, type, and location of samples needed to
assess exposure.
During the planning stages of the RI/FS, the
risk assessor also should determine if non-routine
(i.e., lower) quantitation limits are needed to
adequately characterize risks at a site. Special
Analytical Services (SAS) of the EPA Contract
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Page 4-4
Laboratory Program (CLP) may be needed to
achieve such lower quantitation limits. (See
Section 4.8 for additional information concerning
quantitation limits.)
4.1.4 USE OF THE DATA QUALITY
OBJECTIVES (DQO) GUIDANCE
The DQO guidance (EPA 1987a,b) provides
information on the review of site data and the
determination of data quality needs for sampling
(see the box below).
OVERVIEW OF DQO GUIDANCE
According to the DQO guidance (EPA 1987a and
b), DQO are qualitative and quantitative statements
established prior to data collection, which specify the
quality of the data required to support Agency decisions
during remedial response activities. The DQO for a
particular site vary according to the end use of the data
(i.e., whether the data are collected to support
preliminary assessments/site inspections, remedial
investigations/feasibility studies, remedial designs, or
remedial actions).
The DQO process consists of three stages. In Stage
1 (Identify Decision Types), all available site information
is compiled and analyzed in order to develop a
conceptual model of the site that describes suspected
sources, contaminant pathways, and potential receptors.
The outcome of Stage 1 is a definition of the objectives
of the site investigation and an identification of data
gaps. Stage 2 (Identify Data Uses/Needs) involves
specifying the data necessary to meet the objectives set
in Stage 1, selecting the sampling approaches and the
analytical options for the site, and evaluating multiple-
option approaches to allow more timely or cost-effective
data collection and evaluation. In Stage 3 (Design Data
Collection Program), the methods to be used to obtain
data of acceptable quality are specified in such products
as the SAP or the workplan.
Use of this guidance will help ensure that all
environmental data collected in support of RI/FS
activities are of known and documented quality.
4.1.5 OTHER DATA CONCERNS
The simple existence of a data collection plan
does not guarantee usable data. The risk assessor
should plan an active role in oversight of data
collection to ensure that relevant data have been
obtained. (See Section 4.9 for more information
on the active role that the risk assessor must
play.)
After data have been collected, they should
be carefully reviewed to identify reliable, accurate,
and verifiable numbers that can be used to
quantify risks. All analytical data must be
evaluated to identify the chemicals of potential
concern (i.e., those to be carried through the risk
assessment). Chapter 5 discusses the criteria to
be considered in selecting the subset of chemical
data appropriate for baseline risk assessment.
Data that do not meet the criteria are not
included in the quantitative risk assessment; they
can be discussed qualitatively in the risk
assessment report, however, or may be the basis
for further investigation.
4.2 REVIEW OF AVAILABLE SITE
INFORMATION
Available site information must be reviewed
to (1) determine basic site characteristics, (2)
initially identify potential exposure pathways and
exposure points, and (3) help determine data
needs (including modeling needs). All available
site information (i.e., information existing at the
start of the RI/FS) should be reviewed in
accordance with Stage 1 of the DQO process.
Sources of available site information include:
• RI/FS scoping information;
• PA/SI data and Hazard Ranking System
(HRS) documentation;
• listing site inspection (LSI) data
(formally referred to as expanded site
inspection, or ESI);
• photographs (e.g., EPA's Environmental
Photographic Interpretation Center
[EPIC]);
• records on removal actions taken at the
site; and
• information on amounts of hazardous
substances disposed (e.g., from site
records).
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Page 4-5
If available, LSI (or ESI) data are especially useful
because they represent fairly extensive site studies.
Based on a review of the existing data, the
risk assessor should formulate a conceptual model
of the site that identifies all potential or suspected
sources of contamination, types and concentrations
of contaminants detected at the site, potentially
contaminated media, and potential exposure
pathways, including receptors (see Exhibit 4-1).
As discussed previously, identification of potential
exposure pathways, especially the exposure points,
is a key element in the determination of data
needs for the risk assessment. Details concerning
development of a conceptual model for a site are
provided in the DQO guidance (EPA 1987a,b) and
the RI/FS guidance (EPA 1988a).
In most cases, site information available at
the start of the RI/FS is insufficient to fully
characterize the site and the potential exposure
pathways. The conceptual model developed at this
stage should be adequate to determine the
remaining data needs. The remainder of this
chapter addresses risk assessment data needs in
detail.
4.3 ADDRESSING MODELING
PARAMETER NEEDS
As discussed in detail in Chapter 6,
contaminant release, transport, and fate models
are often needed to supplement monitoring data
when estimating exposure concentrations.
Therefore, a preliminary site modeling strategy
should be developed during RI/FS scoping to
allow model input data requirements to be
incorporated into the data collection requirements.
This preliminary identification of models and
other related data requirements will ensure that
data for model calibration and validation are
collected along with other physical and chemical
data at the site. Exhibit 4-2 lists (by medium)
several site-specific parameters often needed to
incorporate fate and transport models in risk
assessments.
Although default values for some modeling
parameters are available, it is preferable to obtain
site-specific values for as many input parameters
as is feasible. If the model is not sensitive to a
particular parameter for which a default value is
available, then a default value may be used.
Similarly, default values may be used if obtaining
the site-specific model parameter would be too
time consuming or expensive. For example,
certain airborne dust emission models use a
default value for the average wind speed at the
site; this is done because representative
measurements of wind speed at the site would
involve significant amounts of time (i.e., samples
would have to be collected over a large part of
the year).
Some model parameters are needed only if
the sampling conducted at a site is sufficient to
support complex models. Such model parameters
may not be necessary if only simple fate and
transport models are used in the risk assessment.
4.4 DEFINING BACKGROUND
SAMPLING NEEDS
Background sampling is conducted to
distinguish site-related contamination from
naturally occurring or other non-site-related levels
of chemicals. The following subsections define the
types of background contamination and provide
guidance on the appropriate location and number
of background samples.
4.4.1 TYPES OF BACKGROUND
There are two different types of background
levels of chemicals:
(1) naturally occurring levels, which are
ambient concentrations of chemicals
present in the environment that have not
been influenced by humans (e.g.,
aluminum, manganese); and
(2) anthropogenic levels. which are
concentrations of chemicals that are
present in the environment due to
human-made, non-site sources (e.g.,
industry, automobiles).
Background can range from localized to
ubiquitous. For example, pesticides ~ most of
which are not naturally occurring (anthropogenic)
- may be ubiquitous in certain areas (e.g.,
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EXHIBIT 4-1
ELEMENTS OF A CONCEPTUAL EVALUATION MODEL
VARIABLES
HYPOTHESES TO
BE TESTED
SOURCES
• CONTAMINANTS
• CONCENTRATIONS
•TIME
• LOCATIONS
• SOURCE EXISTS
• SOURCE CAN BE CONTAINED
• SOURCE CAN BE REMOVED
AND DISPOSED
• SOURCE CAN BE TREATED
• MEDIA
• RATES OF MIGRATION
• TIME
• LOSS AND GAIN FUNCTIONS
• PATHWAY EXISTS
• PATHWAY CAN BE
INTERRUPTED
• PATHWAY CAN BE
ELIMINATED
• TYPES
• SENSITIVITIES
• TIME
• CONCENTRATIONS
• NUMBERS
• RECEPTOR IS NOT
IMPACTED BY MIGRATION
OF CONTAMINANTS
• RECEPTOR CAN BE
RELOCATED
• INSTITUTIONAL CONTROLS
CAN BE APPLIED
• RECEPTOR CAN BE
PROTECTED
SOURCE: EPA 1987a
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EXHIBIT 4-2
EXAMPLES OF MODELING PARAMETERS FOR WHICH
INFORMATION MAY NEED TO BE OBTAINED DURING
A SITE SAMPLING INVESTIGATION
Type of Modeling
Modeling Parameters0
Source Characteristics
Soil
Ground-water
Air
Surface Water
Sediment
Biota
Geometry, physical/chemical conditions, emission rate, emission
strength, geography
Particle size, dry weight, pH, redox potential, mineral class, organic
carbon and clay content, bulk density, soil porosity
Head measurements, hydraulic conductivity (pump and slug test
results), saturated thickness of aquifer, hydraulic gradient, pH,
redox potential, soil-water partitioning
Prevailing wind direction, wind speeds, stability class, topography,
depth of waste, contaminant concentration in soil and soil gas,
fraction organic content of soils, silt content of soils, percent
vegetation, bulk density of soil, soil porosity
Hardness, pH, redox potential, dissolved oxygen, salinity,
temperature, conductivity, total suspended solids, flow rates
and depths for rivers/streams, estuary and embayment
parameters such as tidal cycle, saltwater incursion extent,
depth and area, lake parameters such as area, volume, depth,
depth to thermocline
Particle size distribution, organic content, pH, benthic oxygen
conditions, water content
Dry weight, whole body, specific organ, and/or edible portion
chemical concentrations, percent moisture, lipid content,
size/age, life history stage
a These parameters are not necessarily limited to the type of modeling with which they are
associated in this exhibit. For example, many of the parameters listed for surface water are also
appropriate for sediments.
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agricultural areas); salt runoff from roads during
periods of snow may contribute high ubiquitous
levels of sodium. Polycyclic aromatic
hydrocarbons (PAHs) and lead are other examples
of anthropogenic, ubiquitous chemicals, although
these chemicals also may be present at naturally
occurring levels in the environment due to natural
sources (e.g., forest fires may be a source of
PAHs, and lead is a natural component of soils in
some areas).
4.4.2 BACKGROUND SAMPLING
LOCATIONS
Background samples are collected at or near
the hazardous waste site in areas not influenced
by site contamination. They are collected from
each medium of concern in these offsite areas.
That is, the locations of background samples must
be areas that could not have received
contamination from the site, but that do have the
same basic characteristics as the medium of
concern at the site.
Identifying background location requires
knowing which direction is upgradient/upwind/
upstream. In general, the direction of water flow
tends to be relatively constant, whereas the
direction of air flow is constantly changing.
Therefore, the determination of background
locations for air monitoring requires constant and
concurrent monitoring of factors such as wind
direction.
4.4.3 BACKGROUND SAMPLE SIZE
In appropriate circumstances, statistics may
be used to evaluate background sample data.
Because the number of background samples
collected is important for statistical hypothesis
testing, at some sites a statistician should be
consulted when determining background sample
size. At all sites, the RPM should decide the
level of statistical analysis applicable to a
particular situation.
Often, rigorous statistical analyses are
unnecessary because site- and non-site-related
contamination clearly differ. For most sites, the
issue will not be whether a difference in chemical
concentrations can be demonstrated between
contaminated and background areas, but rather
that of establishing a reliable representation of the
extent (in three dimensions) of a contaminated
area. However, statistical analyses are required
at some sites, making a basic understanding of
statistics necessary. The following discussion
outlines some basic statistical concepts in the
context of background data evaluation for risk
assessment. (A general statistics textbook should
be reviewed for additional detail. Also, the box
below lists EPA guidance that might be useful.)
STATISTICAL METHODS GUIDANCE
Statistical Methods for Evaluating Ground-
water Monitoring Data from Hazardous Waste
Facilities (EPA 1988b)
Surface Impoundment Clean Closure
Guidance Manual (EPA 1988c)
Love Canal Emergency Declaration Area
Habitability Study (EPA 1988d)
Soils SamplingQualityAssurance Guide (EPA
1989b)
A statistical test of a hypothesis is a rule
used for deciding whether or not a statement (i.e.,
the null hypothesis) should be rejected in favor of
a specified alternative statement (i.e., the
alternative hypothesis). In the context of
background contamination at hazardous waste
sites, the null hypothesis can be expressed as
"there is no difference between contaminant
concentrations in background areas and onsite,"
and the alternative hypothesis can be expressed as
"concentrations are higher onsite." This expression
of the alternative hypothesis implies a one-tailed
test of significance.
The number of background samples collected
at a site should be sufficient to accept or reject
the null hypothesis with a specified likelihood of
error. In statistical hypothesis testing there are
two types of error. The null hypothesis may be
rejected when it is true (i.e., a Type I error), or
not rejected when it is false (i.e., a Type II error).
An example of a Type I error at a hazardous
waste site would be to conclude that contaminant
concentrations in onsite soil are higher than
background soil concentrations when in fact they
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are not. The corresponding Type II error would
be to conclude that onsite contaminant
concentrations are not higher than background
concentrations when in fact they are. A Type I
error could result in unnecessary remediation,
while a Type II error could result in a failure to
clean up a site when such an action is necessary.
In customary notations, a (alpha) denotes the
probability that a Type I error will occur, and ft
(beta) denotes the probability that a Type II error
will occur. Most statistical comparisons refer to
a, also known as the level of significance of the
test. If a = 0.05, there is a 5 percent (i.e., 1 in
20) chance that we will conclude that
concentrations of contaminants are higher than
background when they actually are not.
Equally critical considerations in determining
the number of background samples are ft and a
concept called "power." The power of a statistical
test has the value 1 - ft and is defined as the
likelihood that the test procedure detects a false
null hypothesis. Power functions for commonly
used statistical tests can be found in most general
statistical textbooks. Power curves are a function
of a (which normally is fixed at 0.05), sample size
(i.e., the number of background and/or onsite
samples), and the amount of variability in the
data. Thus, if a 15 percent likelihood of failing
to detect a false null hypothesis is desired (i.e., ft
= 0.15), enough background samples must be
collected to ensure that the power of the test is
at least 0.85.
A small number of background samples
increases the likelihood of a Type II error. If an
insufficient number of background samples is
collected, fairly large differences between site and
background concentrations may not be statistically
significant, even though concentrations in the
many site samples are higher than the few
background samples. To guard against this
situation, the statistical power associated with the
comparison of background samples with site
samples should be evaluated.
In general, when trying to detect small
differences as statistically significant, the number
of background samples should be similar to the
number of onsite samples that will be used for the
comparison(s) (e.g., the number of samples taken
from one well). (Note that this does not mean
that the background sample size must equal the
total number of onsite samples.) Due to the
inherent variability of air concentrations (see
Section 4.6), background sample size for air needs
to be relatively large.
4.4.4 COMPARING BACKGROUND
SAMPLES TO SITE-RELATED
CONTAMINATION
The medium sampled influences the kind of
statistical comparisons that can be made with
background data. For example, air monitoring
stations and ground-water wells are normally
positioned based on onsite factors and gradient
considerations. Because of this purposive
placement (see Section 4.6.1), several wells or
monitors cannot be assumed to be a random
sample from a single population and hence cannot
be evaluated collectively (i.e., the sampling results
cannot be combined). Therefore, the information
from each well or air monitor should be compared
individually with background.
Because there typically are many site-related,
media-specific sampling location data to compare
with background, there usually is a "multiple
comparison problem" that must be addressed. In
general, the probability of experiencing a Type I
error in the entire set of statistical tests increases
with the number of comparisons being made. If
a = 0.05, there is a 1 in 20 chance of a Type I
error in any single test. If 20 comparisons are
being made, it therefore is likely that at least one
Type I error will occur among all 20 tests.
Statistical Analysis of Ground-water Monitoring
Data at RCRA Facilities (EPA 1989c) is useful
for designing sampling plans for comparing
information from many fixed locations with
background.
It may be useful at times to look at
comparisons other than onsite versus background.
For example, upgradient wells can be compared
with downgradient wells. Also, there may be
several areas within the site that should be
compared for differences in site-related
contaminant concentration. These areas of
concern should be established before sampling
takes place. If a more complicated comparison
scheme is planned, a statistician should be
consulted frequently to help distribute the
sampling effort and design the analysis.
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A statistically significant difference between
background samples and site-related contamination
should not, by itself, trigger a cleanup action. The
remainder of this manual still must be applied so
that the lexicological -- rather than simply the
statistical - significance of the contamination can
be ascertained.
4.5 PRELIMINARY IDENTIFI-
CATION OF POTENTIAL
HUMAN EXPOSURE
A preliminary identification of potential
human exposure provides much needed
information for the SAP. This activity involves
the identification of (1) media of concern, (2)
areas of concern (i.e., general locations of the
media to be sampled), (3) types of chemicals
expected at the site, and (4) potential routes of
contaminant transport through the environment
(e.g., inter-media transfer, food chain). This
section provides general information on the
preliminary identification of potential human
exposure pathways, as well as specific information
on the various media. (Also, see Chapter 6 for
a detailed discussion of exposure assessment.)
4.5.1
GENERAL INFORMATION
Prior to discussing various specific exposure
media, general information on the following is
provided: media, types of chemicals, areas of
concern, and routes of contaminant transport is
addressed.
Media of concern (including biota). For risk
assessment purposes, media of concern at a site
are:
• any currently contaminated media to
which individuals may be exposed or
through which chemicals may be
transported to potential receptors; and
• any currently uncontaminated media that
may become contaminated in the future
due to contaminant transport.
Several medium-specific factors in sampling may
influence the risk assessment. For example,
limitations in sampling the medium may limit the
detailed evaluation of exposure pathways described
in Chapter 6. To illustrate this, if soil samples
are not collected at the surface of a site, then it
may not be possible to accurately evaluate
potential exposures involving direct contact with
soils or exposures involving the release of
contaminants from soils via wind erosion (with
subsequent inhalation of airborne contaminants by
exposed individuals). Therefore, based on the
conceptual model of the site discussed previously,
the risk assessor should make sure that
appropriate samples are collected from each
medium of concern.
Areas of concern. Areas of concern refer to
the general sampling locations at or near the site.
For large sites, areas of concern may be treated
in the RI/FS as "operable units," and may include
several media. Areas of concern also can be
thought of as the locations of potentially exposed
populations (e.g., nearest residents) or biota (e.g.,
wildlife feeding areas).
Areas of concern should be identified based
on site-specific characteristics. These areas are
chosen purposively by the investigators during the
initial scoping meeting. Areas of concern should
include areas of the site that:
(1) have different chemical types;
(2) have different anticipated concentrations
or hot spots;
(3) are a release source of concern;
(4) differ from each other in terms of the
anticipated spatial or temporal variability
of contamination;
(5) must be sampled using different
equipment; and/or
(6) are more or less costly to sample.
In some instances, the risk assessor may want
to estimate concentrations that are representative
of the site as a whole, in addition to each area of
concern. In these cases, two conditions generally
should be met in defining areas of concern: (1)
the boundaries of the areas of concern should not
overlap and (2) all of the areas of concern
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Page 4-11
together should account for the entire area of the
site.
Depending on the exposure pathways that
are being evaluated in the risk assessment, it may
not be necessary to determine site-wide
representative values. In this case, areas of
concern do not have to account for the entire
area of the site.
Types of chemicals. The types of chemicals
expected at a hazardous waste site may dictate the
site areas and media sampled. For example,
certain chemicals (e.g., dioxins) that
bioconcentrate in aquatic life also are likely to be
present in the sediments. If such chemicals are
expected at a particular site and humans are
expected to ingest aquatic life, sampling of
sediments and aquatic life for the chemicals may
be particularly important.
Due to differences in the relative toxicities of
different species of the same chemical (e.g., Cr+5
versus Cr+<5), the species should be noted when
possible.
Routes of contaminant transport. In addition
to medium-specific concerns, there may be several
potential current and future routes of contaminant
transport within a medium and between media at
a site. For instance, discharge of ground water or
surface runoff to surface water could occur.
Therefore, when possible, samples should be
collected based on routes of potential transport.
For cases in which contamination has not yet
reached points of human exposure but may be
transported to those areas in the future, sampling
between the contaminant source and the exposure
locations should be conducted to help evaluate
potential future concentrations to which
individuals may be exposed (e.g., through
modeling). (See Chapter 6 for additional
discussion on contaminant transport.)
4.5.2
SOIL
Soil represents a medium of direct contact
exposure and often is the main source of
contaminants released into other media. As such,
the number, location, and type of samples
collected from soils will have a significant effect
on the risk assessment. See the box on this page
for guidance that provides additional detailed
information concerning soil sampling, including
information on sampling locations, general soil
and vegetation conditions, and sampling
equipment, strategies, and techniques. In addition
to the general sampling considerations discussed
previously, the following specific issues related to
soil sampling are discussed below: the
heterogeneous nature of soils, designation of hot
spots, depth of samples, and fate and transport
properties.
SOIL SAMPLING GUIDANCE
Test Methods for Evaluating Solid Waste (SW-
846): Physical/Chemical Methods (EPA
1986a)
Field Manual for Grid Sampling of PCS Spill
Sites to Verify Cleanups (EPA 1986b)
A Compendium ofSuperfiind Field Operations
Methods (EPA 1987c)
Soil Sampling Quality Assurance Guide (EPA
Review Draft 1989b)
Heterogeneous nature of soils. One of the
largest problems in sampling soil (or other solid
materials) is that its generally heterogeneous
nature makes collection of representative samples
difficult (and compositing of samples virtually
impossible -- see Section 4.6.3). Therefore, a
large number of soil samples may be required to
obtain sufficient data to calculate an exposure
concentration. Composite samples sometimes are
collected to obtain a more homogeneous sample
of a particular area; however, as discussed in a
later section, compositing samples also serves to
mask contaminant hot spots (as well as areas of
low contaminant concentration).
Designation of hot spots. Hot spots (i.e.,
areas of very high contaminant concentrations)
may have a significant impact on direct contact
exposures. The sampling plan should consider
characterization of hot spots through extensive
sampling, field screening, visual observations, or
a combination of the above.
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Depth of samples. Sample depth should be
applicable for the exposure pathways and
contaminant transport routes of concern and
should be chosen purposively within that depth
interval. If a depth interval is chosen purposively,
a random procedure to select a sampling point
may be established. Assessment of surface
exposures will be more certain if samples are
collected from the shallowest depth that can be
practically obtained, rather than, for example, zero
to two feet. Subsurface soil samples are
important, however, if soil disturbance is likely or
if leaching of chemicals to ground water is of
concern, or if the site has current or potential
agricultural uses.
Fate and transport properties. The sampling
plan should consider physical and chemical
characteristics of soil that are important for
evaluating fate and transport. For example, soil
samples being collected to identify potential
sources of ground-water contamination must be
able to support models that estimate both
quantities of chemicals leaching to ground water
and the time needed for chemicals .to leach to and
within the ground water.
4.5.3
GROUND WATER
Considerable expense and effort normally are
required for the installation and development of
monitoring wells and the collection of ground-
water samples. Wells must not introduce foreign
materials and must provide a representative
hydraulic connection to the geologic formations of
interest. In addition, ground-water samples need
to be collected using an approach that adequately
defines the contaminant plume with respect to
potential exposure points. Existing potential
exposure points (e.g., existing drinking water wells)
should be sampled.
More detailed information concerning ground-
water sampling considerations (e.g., sampling
equipment, types, and techniques) can be found in
the references in the box on this page. In
addition to the general sampling considerations
discussed previously in Section 4.5.1, those specific
for ground water - hydrogeologic properties, well
location and depth, and filtered vs. unfiltered
samples - are discussed below.
GROUND-WATER SAMPLING
GUIDANCE
Practical Guide to Ground-water Sampling
(EPA 1985a)
A Compendium of SuperfundField Operations
Methods (EPA 1987c)
Handbook: Ground Water (EPA 1987d)
Statistical Methods for Evaluating Ground
Water from Hazardous Waste Facilities (EPA
1988b)
Guidance on Remedial Actions for
Contaminated Ground Water at Superfund
Sites (EPA 1988e)
Ground-water Sampling for Metals Analyses
(EPA 1989d)
Hydrogeologic properties. The extent to
which the hydrogeologic properties (e.g., hydraulic
conductivity, porosity, bulk density, fraction
organic carbon, productivity) of the aquifer(s) are
characterized may have a significant effect on the
risk assessment. The ability to estimate future
exposure concentrations depends on the extent to
which hydrogeologic properties needed to evaluate
contaminant migration are quantified. Repetitive
sampling of wells is necessary to obtain samples
that are unaffected by drilling and well
development and that accurately reflect
hydrogeologic properties of the aquifer(s).
Well location and depth. The location of
wells should be such that both the horizontal and
vertical extent of contamination can be
characterized. Separate water-bearing zones may
have different aquifer classifications and uses and
therefore may need to be evaluated separately in
the risk assessment. In addition, sinking or
floating layers of contamination may be present
at different depths of the wells.
Filtered vs. unfiltered samples. Data from
filtered and unfiltered ground-water samples are
useful for evaluating chemical migration in ground
water, because comparison of chemical
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Page 4-13
concentrations in unfiltered versus filtered samples
can provide important information on the form in
which a chemical exists in ground water. For
instance, if the concentration of a chemical is
much greater in unfiltered samples compared to
filtered samples, it is likely that the majority of
the chemical is sorbed onto paniculate matter and
not dissolved in the ground water. This
information on the form of chemical (i.e.,
dissolved or suspended on paniculate matter) is
important to understanding chemical mobility
within the aquifer.
If chemical analysis reveals significantly
different concentrations in the filtered and
unfiltered samples, try to determine whether there
is a high concentration of suspended particles or
if apparently high concentrations are due to
sampling or well construction artifacts.
Supplementary samples can be collected in a
manner that will minimize the influence of these
artifacts. In addition, consider the effects of the
following.
• Filter size. A 0.45 um filter may screen
out some potentially mobile particulates
to which contaminants are absorbed and
thus under-represent contaminant
concentrations. (Recent research
suggests that a 1.0 um may be a more
appropriate filter size.)
• Pumping velocity. Pumping at too high
a rate will entrain particulates (to which
contaminants are absorbed) that would
not normally be mobile; this could
overestimate contaminant concentrations.
• Sample oxidation. After contact with air,
many metals oxidize and form insoluble
compounds that may be filtered out; this
may underestimate inorganic chemical
concentrations.
• Well construction materials. Corrosion
may elevate some metal concentrations
even in stainless steel wells.
If unfiltered water is of potable quality, data
from unfiltered water samples should be used to
estimate exposure (see Chapter 6). The RPM
should ultimately decide the type of samples that
are collected. If only one type of sample is
collected (e.g., unfiltered), justification for not
collecting the other type of sample (e.g., filtered)
should be, provided in the sampling plan.
4.5.4
SURFACE WATER AND SEDIMENT
Samples need to be collected from any nearby
surface water body potentially receiving discharge
from the site. Samples are needed at a sufficient
number of sampling points to characterize
exposure pathways, and at potential discharge
points to the water body to determine if the site
(or some other source) is contributing to surface
water/sediment contamination. Some important
considerations for surface water/sediment sampling
that may affect the risk assessment for various
types and portions of water bodies (i.e., lotic
waters, lentic waters, estuaries, sediments) are
discussed below. More detailed information
concerning surface water and sediment sampling,
such as selecting sampling locations and sampling
equipment, types, and techniques, is provided in
the references given in the box below.
SURFACE WATER AND SEDIMENT
SAMPLING GUIDANCE
Procedures for Handling and Chemical
Analysis of Sediment and Water Samples
(EPA and COE 1981)
Sediment Sampling Quality Assurance User's
Guide (EPA 1984)
Methods Manual for Bottom Sediment Sample
Collection (EPA 1985b)
A Compendium ofSuperfund Field Operations
Methods (EPA 1987c)
An Overview of Sediment Quality in the
United States (EPA 1987e)
Proposed Guide for Sediment Collection,
Storage, Characterization and Manipulation
(The American Society for Testing and
Materials, undated)
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Page 4-14
Lotic waters. Lotic waters are fast-moving
waters such as rivers and streams. Variations in
mixing across the stream channel and downstream
in rivers and streams can make it difficult to
obtain representative samples. Although the
selection of sampling points will be highly
dependent on the exposure pathways of concern
for a particular site, samples generally should be
taken both toward the middle of the channel
where the majority of the flow occurs and along
the banks where flow is generally lower. Sampling
locations should be downgradient of any possible
contaminant sources such as tributaries or effluent
outfalls. Any facilities (e.g., dams, wastewater
treatment plants) upstream that affect flow volume
or water quality should be considered during the
timing of sampling. "Background" releases
upstream could confound the interpretation of
sampling results by diluting contaminants or by
increasing contaminant loads. In general,
sampling should begin downstream and proceed
upstream.
Lentic waters. Lentic waters are slow-moving
waters such as lakes, ponds, and impoundments.
In general, lentic waters require more samples
than lotic waters because of the relatively low
degree of mixing of lentic waters. Thermal
stratification is a major factor to be considered
when sampling lakes. If the water body is
stratified, samples from each layer should be
obtained. Vertical composites of these layers then
may be made, if appropriate. For small shallow
ponds, only one or two sample locations (e.g., the
intake and the deepest points) may be adequate
depending on the exposure pathways of concern
for the site. Periodic release of water should be
considered when sampling impoundments, as this
may affect chemical concentrations and
stratification.
Estuaries. Contaminant concentrations in
estuaries will depend on tidal flow and salinity-
stratification, among other factors. To obtain a
representative sample, sampling should be
conducted through a tidal cycle by taking three
sets of samples on a given day: (1) at low tide;
(2) at high tide; and (3) at "half tide." Each layer
of salinity should be sampled.
Sediments. Sediment samples should be
collected in a manner that minimizes disturbance
of the sediments and potential contamination of
subsequent samples. Sampling in flowing waters
should begin downstream and end upstream.
Wading should be avoided. Sediments of different
composition (i.e., mud, sand, rock) should not be
composited. Again, it is important to obtain data
that will support the evaluation of the potential
exposure pathways of concern. For example, for
pathways such as incidental ingestion, sampling of
near-shore sediments may be important; however,
for dermal absorption of sediment contaminants
during recreational use such as swimming, samples
from different points throughout the water body
may be important. If ingestion of benthic
(bottom-dwelling) species or surface water will be
assessed during the risk assessment, sediment
should be sampled so that characteristics needed
for modeling (e.g., fraction of organic carbon,
particle size distribution) can be determined (see
Section 4.3).
4.5.5
AIR
Guidance for developing an air sampling plan
for Superfund sites is provided in Procedures for
Dispersion Modeling and Air Monitoring for
Superfund Air Pathway Analysis (EPA 1989e).
That document is Volume IV of a series of four
technical guidance manuals called Procedures for
Conducting Air Pathway Analyses for Superfund
Applications (EPA 1989e-h). The other three
volumes of the series include discussions of
potential air pathways, air emission sources, and
procedures for estimating potential source
emission rates associated with both the baseline
site evaluation and remedial activities at the site.
Air monitoring information, along with
recommendations for proper selection and
application of air dispersion models, is included
in Volume IV. The section on air monitoring
contained in this volume presents step-by-step
procedures to develop, conduct, and evaluate the
results of air concentration monitoring to
characterize downwind exposure conditions from
Superfund air emission sources. The first step
addressed is the process of collecting and
reviewing existing air monitoring information
relevant to the specific site, including source,
receptor, and environmental data. The second
step involves determining the level of
sophistication for the air monitoring program; the
levels range from simple screening procedures to
refined techniques. Selection of a given level will
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Page 4-15
depend on technical considerations (e.g., detection
limits) and available resources. The third step on
air monitoring is development of the air
monitoring plan and includes determination of the
type of air monitors, the number and location of
monitors, the frequency and duration of
monitoring, sampling and analysis proce'dures, and
QA/QC procedures. Step four details the day-to-
day activities related to conducting the air
maintenance and calibration, and documentation
of laboratory results and QA/QC procedures. The
fifth and final step involves the procedures
necessary to (1) summarize and evaluate the air
monitoring results for validity, (2) summarize the
statistics used, (3) determine site-related air
concentrations (by comparison of upwind and
downwind concentrations), and (4) estimate
uncertainties in the results related to the
monitoring equipment and program and the
analytical techniques used in the laboratory.
Given the difficulties of collecting sufficient
air samples to characterize both temporal and
spatial variability of air concentrations, modeling
-- along or in conjunction with monitoring ~ is
often used in the risk assessment. For the most
efficient sampling program, the section in' Volume
IV on modeling should be used in conjunction
with the section on monitoring.
Volume IV also contains a comprehensive
bibliography of other sources of air monitoring
and modeling guidance. Note, however, that while
this volume contains an extensive discussion on
planning and conducting air sampling, it does not
provide details concerning particular monitoring
equipment and techniques. The box on this page
lists some sources of detailed information on air
sampling. The following paragraphs address
several specific aspects of air sampling: temporal
and spatial considerations, emission sources,
meteorological conditions.
Temporal and spatial considerations. The
goal of air sampling at a site is to adequately
characterize air-related contaminant exposures. At
a minimum, sampling results should be adequate
for predictive short-term and long-term modeling.
When evaluating long-term inhalation exposures,
sample results should be representative of the
long-term average air concentrations at the long-
term exposure points. This requires an air
sampling plan of sufficient temporal scale to
AIR SAMPLING GUIDANCE
Technical Assistance Document for Sampling
and Analysis of Toxic Organic Compounds in
Ambient Air (EPA 1983)
A Compendium of Superfund Field Operations
Methods (EPA 1987c)
Procedures for Dispersion Modeling and Air
Monitoring for Superfund Air Pathway
Analysis (EPA 19881)
encompass the range of meteorological and
climatic conditions potentially affecting emissions,
and of sufficient spatial scale to characterize
associated air concentrations at potential exposure
points. If acute or subchronic exposures resulting
from episodes of unusually large emissions are of
interest, sampling over a much smaller time scale
would be needed.
Emission sources. Selection of the
appropriate type of air monitor will depend on
the emission source(s) being investigated as well
as the exposure routes to be evaluated. For
example, if inhalation of dust is an exposure
pathway of concern, then the monitoring
equipment must be able to collect respirable dust
samples.
Meteorological conditions. Site-specific
meteorological conditions should be obtained (e.g.,
from the National Weather Service) or recorded
during the air sampling program with sufficient
detail and quality assurance to substantiate and
explain the air sampling results. The review of
these meteorological data can help indicate the
sampling locations and frequencies.
Meteorological characteristics also will be
necessary if air modeling is to be conducted.
4.5.6
BIOTA
Organisms sampled for human health risk
assessment purposes should be those that are
likely to be consumed by humans. This may
include animals such as commercial and game fish
(e.g., salmon, trout, catfish), shellfish (e.g., oysters,
clams, crayfish), fowl (e.g., pheasant, duck), and
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terrestrial mammals (e.g., rabbit, deer), as well as
plants such as grains (e.g., wheat, corn), vegetables
(e.g., spinach, carrots), and fruit (e.g., melons,
strawberries). An effort should be made to
sample species that are consumed most frequently
by humans. Guidance for collecting biota samples
is provided in the references given in the box
below. The following paragraphs address the
following special aspects of biota sampling:
portion vs. whole sampling, temporal concerns,
food preference, fish sampling, involvement by
other agencies.
BIOTA SAMPLING GUIDANCE
Food and Drug Administration's Pesticide
Analytical Manual (FDA 1977)
Cooperative Agreement on the Monitoring of
Contaminants in Great Lakes Sport Fish for
Human Health Purposes (EPA 1985c)
FDA's Pesticides and Industrial Chemicals in
Domestic Foods (FDA 1986)
A Compendium ofSuperfund Field Operations
Methods (EPA 1987c)
Guidance Manual for Assessing Human
Health Risks from Chemically Contaminated
Fish and Shellfish (EPA 1989i)
Portion vs. whole sampling. If only human
exposure is of concern, chemical concentrations
should be measured only in edible portion(s) of
the biota. For many fish species, estimates of
concentrations in fillets (skin on or skin off) are
the most appropriate measures of exposure
concentrations. Whole body measurements may
be needed, however, for certain species of fish
and/or for environmental risk assessments. For
example, for some species, especially small ones
(e.g., smelt), whole body concentrations are most
appropriate. (See Risk Assessment Guidance for
Superfund: Environmental Evaluation Manual
(EPA 1989a) for more information concerning
biota sampling for environmental assessment.)
The edible portion of an organism can vary with
species and with the potentially exposed
subpopulation.
Temporal concerns. Any conditions that may
result in non-representative sampling, such as
sampling during a species' migration or when
plants are not in season, should be avoided.
Food preferences. At some sites, human
subpopulations in the area may have different
food consumption patterns that need to be
evaluated. For example, some people commonly
eat the hepatopancreas of shellfish. In these
cases, organ concentrations would be most
appropriate for estimating exposure. Another
example of a less common food preference is
consumption of relatively large quantities of
seaweed and other less commonly eaten seafoods
in some Asian communities.
Fish sampling. It is recommended that fish
of "catchable" size be sampled instead of young,
small fish because extremely young fish are not
likely to be consumed. Older, larger fish also
generally are more likely to have been exposed to
site-specific contaminants for a long time,
although for some species (e.g., salmon) the
reverse is true. Both bottom-dwelling (benthic)
and open-water species should be sampled if both
are used as a food source.
Other agencies. Biota sampling may involve
other federal agencies such as the Fish and
Wildlife Service or the Department of Agriculture.
The equivalent state agencies also may be
involved. In such cases, these agencies should be
involved early in the scoping process.
4.6 DEVELOPING AN OVERALL
STRATEGY FOR SAMPLE
COLLECTION
For each medium at a site, there are several
strategies for collecting samples. The sampling
strategies for a site must be appropriate for use
in a quantitative risk assessment; if inappropriate,
even the strictest QA/QC procedures associated
with the strategy will not ensure the usability of
sample results. Generally, persons actually
conducting the field investigation will determine
the strategy. As discussed in Section 4.1, risk
assessors also should be involved in discussions
concerning the strategy. The following areas of
major concern (from a risk assessment
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perspective) are discussed in this section: sample
size, sampling location, types of samples, temporal
and meteorological factors, field analyses, and cost
of sampling. Many of these areas also are
discussed for specific media in Section 4.5. See
the box in the opposite column and Section 4.5
for more detailed guidance on sampling strategy.
4.6.1
DETERMINE SAMPLE SIZE
Typically, sample size and sample location
(see Section 4.6.2) are determined at the same
time. Therefore, much of the discussion in this
subsection is also pertinent to determining
sampling location. The discussion on statistics in
Section 4.4 is useful for both sample size and
location determinations.
A number of considerations are associated
with determining an appropriate number of
samples for a risk assessment. These
considerations include the following four factors:
(1) number of areas of concern that will be
sampled;
(2) statistical methods that are planned;
(3) statistical performance (i.e., variability
power, and certainty) of the data that
will be collected; and
(4) practical considerations of logistics and
cost.
In short, many decisions must be made by the
risk assessor related to the appropriate sample
size for an investigation. A statistician cannot
estimate an appropriate sample size without the
supporting information provided by a risk assessor.
The following paragraphs discuss these four factors
as they relate to sample size determinations.
Areas of concern. A major factor that
influences how many samples are appropriate is
the number of areas of concern that are
established prior to sampling. As discussed in the
next subsection, if more areas of concern are
identified, then more samples generally will be
needed to characterize the site. If the total
variability in chemical concentrations is reduced
substantially by subdividing the site into areas of
concern, then the statistical performance should
SAMPLING STRATEGY GUIDANCE
Test Methods for Evaluating Solid Waste (SW-
846): Physical/Chemical Methods (EPA
1986a)
Data Quality Objectives for Remedial
Response Activities: Development Process
(EPA 1987a)
Data Quality Objectives for Remedial
Response Activities: Example Scenario:
RIfFS Activities at a Site with Contaminated
Soils and Ground Water (EPA 1987b)
Expanded Site Inspection (ESI) Transitional
Guidance for FY 1988 (EPA 1987f)
Quality Assurance Field Operations Manual
(EPA 1987g)
Statistical Methods for Evaluating the
Attainment of Super/and Cleanup Standards:
Volume 1, Soils and Solid Media (EPA
Proposed Guidelines for Exposure-related
Measurements (EPA 1988g)
Interim Report on Sampling Design
Methodology (EPA 1988h)
Standard Handbook of Hazardous Waste
Treatment and Disposal (Freeman 1989)
Soil Sampling Quality Assurance Guide (EPA
1989b)
improve and result in a more accurate assessment
of the site.
Statistical methods. A variety of statistical
manipulations may need to be performed on the
data used in the risk assessment. For example,
there may be comparisons with background
concentrations, estimates of upper confidence
limits on means, and determinations of the
probability of identifying hot spots. Each of these
analyses requires different calculations for
determining a sample size that will yield a
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Page 4-18
specified statistical performance. Some of the
available guidance, such as the Ground-water
Monitoring guidance (EPA 1986c), the RCRA
Delisting guidance (EPA 1985d), and the Soils
Cleanup Attainment guidance (EPA 1988f),
address these strategies in detail.
Statistical performance (i.e., variability,
power, and certainty). If samples will be taken
from an area that is anticipated to have a high
degree of variability in chemical concentrations,
then many samples may be required to achieve a
specified level of certainty and power. If
contaminant concentrations in an area are highly
variable and only a few samples can be obtained,
then the risk assessor should anticipate (1) a great
deal of uncertainty in estimating mean
concentrations at the site, (2) difficulty in defining
the distribution of the data (e.g., normal), and (3)
upper confidence limits much higher than the
mean. Identification of multiple areas of concern
- each with its own set of samples and descriptive
statistics ~ will help reduce the total variability if
the areas of concern are defined so that they are
very different in their contaminant concentration
profiles. Risk assessors should discuss in the
scoping meeting both the anticipated variability in
the data and the desired power and certainty of
the statistics that will be estimated from the data.
As discussed in Section 4.4.3, power is the
likelihood of detecting a false null hypothesis.
Power is particularly important when comparing
site characteristics with background. For example,
if a 10 percent difference in mean concentrations
needs to be determined with 99 percent likelihood
(i.e., power of 0.99), a very large number of
samples will likely be needed (unless the site and
background variabilities are extremely low). On
the other hand, if the investigator is only
interested in whether the onsite average conditions
are 100 times larger than background or can
accept a lower chance of detecting the difference
if it exists (i.e., a lower power), then a smaller
sample size could be accommodated.
The other statistical performance quantity
besides power that may need to be specified is
the certainty of the calculations. One minus the
certainty is the significance level (i.e., a), or false
positive rate (see also Section 4.4.3). The higher
the desired certainty level (i.e., the lower the
significance level), the greater the true difference
must be to observe a statistical difference. In the
case of upper confidence limits on estimates of
mean concentrations, the higher the desired
certainty level, the higher will be the upper
confidence limit. This follows from the fact that
in general, as certainty increases (i.e., a becomes
smaller), the size of the confidence interval also
increases.
Practical considerations. Finally, questions
of practicality, logistics, sampling equipment,
laboratory constraints, quality assurance, and cost
influence the sample size that will be available for
data analysis. After the ideal sample size has
been determined using other factors, practical
considerations can be introduced to modify the
sample size if necessary.
4.6.2
ESTABLISH SAMPLING LOCATIONS
There are three general strategies for
establishing sample locations: (1) purposive, (2)
completely random, and (3) systematic. Various
combinations of these general strategies are
possible and acceptable.
Much of the discussion on statistics in the
preceding subsection and in Section 4.4 is
appropriate here. Typically, a statistician should
be consulted when determining sampling location.
Purposive sampling. Although areas of
concern are established purposively (e.g., with the
intention of identifying contamination), the
sampling locations within the areas of concern
generally should not be sampled purposively if the
data are to be used to provide defensible
information for a risk assessment. Purposively
identified sampling locations are not discouraged
if the objective is site characterization, conducting
a chemical inventory, or the evaluation of visually
obvious contamination. The sampling results,
however, may overestimate or underestimate the
true conditions at the site depending on the
strategies of the sampling team. Due to the bias
associated with the samples, data from purposively
identified sampling locations generally should not
be averaged, and distributions of these data
generally should not be modeled and used to
estimate other relevant statistics. After areas of
concern have been established purposively,
ground-water monitoring well locations,
continuous air monitor locations, and soil sample
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locations should be determined randomly or
systematically within the areas of concern.
Random sampling. Random sampling
involves selecting sampling locations in an
unbiased manner. Although the investigator may
have chosen the area of concern purposively, the
location of random sampling points within the
area should be independent of the investigator
(i.e., unbiased). In addition, the sampling points
should be independent of each other; that is, it
should not be possible to predict the location of
one sampling point based on the location of
others. Random sampling points can be
established by choosing a series of pairs of
random numbers that can be mapped onto a
coordinate system that has been established for
each area of concern.
Several positive features are associated with
data collected in a random sampling program.
First, the data can be averaged and used to
estimate average concentrations for the area of
concern (rather than simply an average of the
samples that were acquired). Second, estimates of
the uncertainty of the average and the
distributional form of the concentration
measurements are informative and simple to
estimate when they are determined from data that
were obtained randomly. Finally, if there is a
trend or systematic behavior to the chemical
concentrations (e.g., sampling is occurring along
a chemical gradient), then random sampling is
preferred because it reduces the likelihood that all
of the high concentration locations are sampled to
the exclusion of the low concentration locations.
Systematic sampling. Systematic sample
locations are established across an area of concern
by laying out a grid of sampling locations that
follow a regular pattern. Systematic sampling
ensures that the sampling effort across the area of
concern is uniform and that samples are collected
in each area. The sampling location grid should
be determined by randomly identifying a single
initial location from which the grid is constructed.
If such a random component is not introduced,
the sample is essentially purposive. The grid can
be formed in several patterns including square,
rectangular, triangular, or hexagonal, depending on
the shape of the area. A square pattern is often
the simplest to establish. Systematic sampling is
preferable to other types of sampling if the
objective is to search for small areas with elevated
concentrations. Also, geostatistical
characterizations -- as described in the DQO
guidance (EPA 1987a,b) ~ are best done with data
collected from a systematic sample.
Disadvantages of systematic sampling include
the need for special variance calculations in order
to estimate confidence limits on the average
concentration. The Soils Cleanup Attainment
guidance (EPA 1988f) discusses these calculations
in further detail.
4.6.3 DETERMINE TYPES OF SAMPLES
Another item of concern is the determination
of the types of samples to be collected. Basically,
two types of samples may be collected at a site:
grab and composite.
Grab samples. Grab samples represent a
single unique part of a medium collected at a
specific location and time.
Composite samples. Composite samples —
sometimes referred to as continuous samples for
air - combine subsamples from different locations
and/or times. As such, composite samples may
dilute or otherwise misrepresent concentrations
at specific points and, therefore, should be avoided
as the only inputs to a risk assessment. For
media such as soil, sediment, and ground water,
composite samples generally may be used to assess
the presence or absence of contamination;
however, they may be used in risk assessment only
to represent average concentrations (and thus
exposures) at a site. For example, "hot spots"
cannot be determined using composite samples.
For surface water and air, composite samples may
be useful if concentrations and exposures are
expected to vary over time or space, as will often
be the case in a large stream or river.
Composites then can be used to estimate daily or
monthly average concentrations, or to account for
stratification due to depth or varying flow rates
across a stream.
4.6.4 CONSIDER TEMPORAL AND
METEOROLOGICAL FACTORS
Temporal (time) and meteorological
(weather) factors also must be considered when
determining sampling strategies. The sampling
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Page 4-20
design should account for fluctuations in chemical
concentrations due to these factors because in
general, the variability in sampling results
increases with increasing complexity of these
factors. When these factors are complex,
specialized and detailed sampling designs are
needed to maintain a constant and certain level of
accuracy in the results. Countering this need,
however, is the cost of the sampling. The
following paragraphs address the interactions of
the single sampling event, annual/seasonal
sampling cycle, variability estimation, and the cost
of sampling.
Single sampling event. Variability measures
from a single sampling event will underestimate
the overall variability of concentrations across an
area of concern, which in turn will result in the
underestimation of the confidence limits on the
mean. The reason for this underestimation is that
temporal variability is not included in an
evaluation of the total environmental variability
at the site.
Annual/seasonal sampling cycle. The ideal
sampling strategy incorporates a full annual
sampling cycle. If this strategy cannot be
accommodated in the investigation, at least two
sampling events should be considered. These
sampling events should take place during opposite
seasonal extremes. For example, sampling periods
that may be considered extremes in temporal
sampling include (1) high water/low water, (2)
high recharge/low recharge, (3) windy/calm, and
(4) high suspended solids/clear water. This type
of sampling requires some prior knowledge of
regional seasonal dynamics. In addition, a
sampling team that can mobilize rapidly might be
needed if the particular year of sampling is not
typical and the extreme conditions occur at an
unusual time. See the box on this page for
examples of seasonal variability.
Variability estimation. The simple variance
estimators that are often used in risk assessment
require that the data are independent or
uncorrelated. Certain types of repeated samples,
however, (e.g., those from ground-water wells or
air monitors) actually are time series data that
might be correlated. In other words, the
concentration of a contaminant in an aquifer
measured at a well on a given day will depend, in
part, on what the concentration in the aquifer was
SEASONAL VARIABILITY
Regardless of the medium sampled, sample
composition may vary depending on the time of year
and weather conditions when the sample is collected.
For example, rain storms may greatly alter soil
composition and thus affect the types and concentrations
of chemicals present on solid material; heavy
precipitation and runoff from snowmelt may directly
dilute chemical concentrations or change the types of
chemicals present in surface water; heavy rain also may
result in sediment loading to water bodies, which could
increase contamination Or affect the concentrations Of
other contaminants through adsorption and settling in
the water column; if ground-water samples are collected
from an area heavily dependent on ground water for
irrigation, the composition of a sample collected during
the summer growing season may greatly differ from the
composition of a sample collected in the winter.
on the previous day. To reduce this dependence
(e.g., due to seasonal variability), sampling of
ground-water wells and air monitors should be
either separated in time or the data should be
evaluated using statistical models with variance
estimators that can accommodate a correlation
structure. Otherwise, if time series data that are
correlated are treated as a random sample and
used to calculate upper confidence limits on the
mean, the confidence limits will be
underestimated.
Ideally, samples of various media should be
collected in a manner that accounts for time and
weather factors. If seasonal fluctuations cannot be
characterized in the investigations, details
concerning meteorological, seasonal, and climatic
conditions during sampling must be documented.
4.6.5 USE FIELD SCREENING ANALYSES
An important component of the overall
sampling strategy is the use of field screening
analyses. These types of analyses utilize
instruments that range from relatively simple (e.g.,
hand-held organic vapor detectors) to more
sophisticated (e.g., field gas chromatographs).
(See Field Screening Methods Catalog [EPA 1987h]
for more information.) Typically, field screening
is used to provide threshold indications of
contamination. For example, on the basis of soil
gas screening, the field investigation team may
determine that contamination of a particular area
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is indicated and therefore detailed sampling is
warranted. Although field screening results
usually are not directly used in the risk
assessment, they are useful for streamlining
sampling and the overall RI/FS process.
4.6.6 CONSIDER TIME AND COST OF
SAMPLING
Two primary constraints in sampling are time
and cost. Time consuming or expensive sampling
strategies for some media may prohibit multiple
sampling points. For example, multiple ground-
water wells and air monitors on a grid sampling
pattern are seldom located within a single area of
concern. However, multiple surface water and soil
samples within each area of concern are easier to
obtain. In the case of ground water and air,
several areas of concern may have to be collapsed
into a single area so that multiple samples will be
available for estimating environmental variability
or so that the dynamics of these media can be
evaluated using accepted models of fate and
transport.
In general, it is important to remember when
developing the sampling strategy that detailed
sampling must be balanced against the time and
cost involved. The goal of RI/FS sampling is not
exhaustive site characterization, but rather to
provide sufficient information to form the basis
for site remediation.
4.7 QA/QC MEASURES
This section presents an overview of the
following quality assurance/quality control
(QA/QC) considerations that are of particular
importance for risk assessment sampling:
sampling protocol, sampling devices, QC samples,
collection procedures, and sample preservation.
Note, however, that the purpose of this discussion
is to provide background information; the risk
assessor will not be responsible for most QA/QC
evaluations.
The Quality Assurance Field Operations
Manual (EPA 1987g) should be reviewed. In
addition, the EPA Environmental Monitoring
Support Laboratory in Las Vegas, Nevada,
(EMSL-LV) currently is writing a guidance
document concerning the development of quality
assurance sample designs for Superfund site
investigations. Regional QA/QC contacts (e.g.,
the regional Environmental Services Division) or
EMSL-LV should be consulted if more
information concerning QA/QC procedures for
sampling is desired.
4.7.1 SAMPLING PROTOCOL
The sampling protocol for a risk assessment
should include the following:
• objectives of the study;
• procedures for sample collection,
preservation, handling, and transport;
and
• analytical strategies that will be used.
Presenting the objectives of the RI sampling is
particularly important because these objectives
also will determine the focus of the risk
assessment. There should be instructions on
documenting conditions present during sampling
(e.g., weather conditions, media conditions).
Persons collecting samples must be adequately
trained and experienced in sample collection. Test
evaluations of the precision attained by persons
involved in sample collection should be
documented (i.e., the individual collecting a
sample should do so in a manner that ensures
that a homogeneous, valid sample is reproducibly
obtained). The discussion of analytical strategies
should specify quantitation limits to be achieved
during analyses of each medium.
4.7.2 SAMPLING DEVICES
The devices used to collect, store, preserve,
and transport samples must not alter the sample
in any way (i.e., the sampling materials cannot be
reactive, sorptive, able to leach analytes, or cause
interferences with the laboratory analysis). For
example, if the wrong materials are used to
construct wells for the collection of ground-water
samples, organic chemicals may be adsorbed to the
well materials and not be present in the collected
sample.
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4.7.3 QC SAMPLES
Field QC samples (e.g., field blanks, trip
blanks, duplicates, split samples) must be
collected, stored, transported, and analyzed in a
manner identical to those for site samples. The
meaning and purpose of blank samples are
discussed in detail in Chapter 5. Field duplicate
samples are usually two samples collected
simultaneously from the same sampling location
and are used as measures of either the
homogeneity of the medium sampled in a
particular location or the precision in sampling.
Split samples are usually one sample that is
divided into equal fractions and sent to separate
independent laboratories for analysis. These split
samples are used to check precision and accuracy
of laboratory analyses. Samples may also be split
in the same laboratory, which can provide
information on precision. The laboratory
analyzing the samples should not be aware of the
identity of the field QC samples (e.g., labels on
QC samples should be identical to those on the
site samples).
4.7.4 COLLECTION PROCEDURES
Collection procedures should not alter the
medium sampled. The general environment
surrounding the location of the sample should
remain the same so that the collected samples
are representative of the situation due to the site
conditions, not due to conditions posed by the
sampling equipment.
4.7.5
SAMPLE PRESERVATION
Until analysis by the laboratory, any
chemicals in the samples must be maintained as
close to the same concentrations and identities
as in the environment from which they came.
Therefore, special procedures may be needed to
preserve the samples during the period between
collection and analysis.
Analytical Services (RAS) may not be appropriate
(e.g., lower detection limits may be needed),4 and
(2) chemicals other than those on the target
compound list (TCL; i.e., chemicals usually
analyzed under the Superfund program) may be
suspected at the site and therefore may need to be
analyzed. A discussion on the RAS detection
limits is provided in Chapter 5. Additional
information on SAS can be found in the User's
Guide to the Contract Laboratory Program (EPA
1988J).
In reviewing the historical data at a site, the
risk assessor should determine if non-TCL
chemicals are expected. As indicated above, non-
TCL chemicals may require special sample
collection and analytical procedures using SAS.
Any such needs should be discussed at the scoping
meeting. SAS is addressed in greater detail in
Chapter 5.
4.9 TAKING AN ACTIVE ROLE
DURING WORKPLAN
DEVELOPMENT AND DATA
COLLECTION
The risk assessor should be sure to take an
active role during workplan development and data
collection. This role involves three main steps:
(1) present risk assessment sampling needs
at the scoping meeting;
(2) contribute to the workplan and review
the Sampling and Analysis Plan; and
(3) conduct interim reviews of outputs of
the field investigation.
See Chapter 9 for information on the role of the
RPM during workplan development and data
collection.
4.8 SPECIAL ANALYTICAL
SERVICES
EPA's SAS, operated by the CLP, may be
necessary for two main reasons: (1) the standard
laboratory methods used by EPA's Routine
4.9.1 PRESENT RISK ASSESSMENT
SAMPLING NEEDS AT SCOPING
MEETING
At the scoping meeting, the uses of samples
and data to be collected are identified, strategies
for sampling and analysis are developed, DQOs
are established, and priorities for sample collection
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are assigned based on the importance of the data
in meeting RI/FS objectives. One of the RI/FS
objectives, of course, is the baseline risk
assessment. Therefore, the risk assessment data
needs and their fit with those of other RI/FS
components are discussed. If certain risk
assessment sampling needs are judged infeasible
by the scoping meeting attendees, all persons
involved with site investigation should be made
aware of the potential effects of exclusion on the
risk assessment.
4.9.2 CONTRIBUTE TO WORKPLAN AND
REVIEW SAMPLING AND ANALYSIS
PLAN
The outcome of the scoping meeting is the
development of a workplan and a SAP. The
workplan documents the decisions and evaluations
made during the scoping process and presents
anticipated future tasks, while the SAP specifies
the sampling strategies, the numbers, types, and
locations of samples, and the level of quality
control. The SAP consists of a quality assurance
project plan (QAPjP) and a field sampling plan
(FSP). Elements of the workplan and the SAP
are discussed in detail in Appendix B of the RI/FS
guidance (EPA 1988a). Both the workplan and
the SAP generally are written by the personnel
who will be involved in the collection of the
samples; however, these documents should be
reviewed by all personnel who will be using the
resulting sample data.
Review the workplan. The workplan should
describe the tasks involved in conducting the risk
assessment. It also should describe the
development of a preliminary assessment of public
health and environmental impacts at the site. The
risk assessor should review the completed
workplan to ensure that all feasible risk
assessment sampling needs have been addressed as
discussed in the scoping meeting. In particular,
this review should focus on the descriptions of
tasks related to:
• field investigation (e.g., source testing,
media sampling), especially with respect
to
- background concentrations by
medium,
-- quantification of present and future
exposures, e.g.,
- exposure pathways
- present and potential future land
use
- media that are or may be
contaminated
- locations of actual and potential
exposure
- present concentrations at
appropriate exposure points,
-- data needs for statistical analysis of
the above, and
- data needs for fate and transport
models;
• sample analysis/validation, especially with
respect to
-- chemicals of concern, and
-- analytical quantification levels;
• data evaluation; and
• assessment of risks.
In reviewing the above, the precise information
necessary to satisfy the remainder of this guidance
should be anticipated.
Review the SAP. The risk assessor should
carefully review and evaluate all sections of the
SAP to determine if data gaps identified in the
workplan will be addressed adequately by the
sampling program. Of particular importance is
the presentation of the objectives. In the QAPjP
component of the SAP, the risk assessor should
pay particular attention to the QA/QC procedures
associated with sampling (e.g., number of field
blanks, number of duplicate samples -- see Section
4.8). The SAP should document the detailed, site-
specific procedures that will be followed to ensure
the quality of the resulting samples. Special
considerations in reviewing the SAP are discussed
in Section 4.1.3.
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In reviewing the FSP, pay particular attention
to the information on sample location and
frequency, sampling equipment and procedures,
and sample handling and analysis. As discussed
in Section 4.5, the sampling procedures should
address:
• each medium of concern;
• background concentrations;
• all potential exposure points within each
medium;
• migration to potential exposure points,
including data for models;
• potential exposures based on possible
future land uses;
• sufficient data to satisfy concerns about
distributions of sampling data and
statistics; and
• number and location of samples.
The analytical plans in the FSP should be
reviewed to ensure that DQOs set during the
scoping meeting will be met.
The SAP may be revised or amended several
times during the site investigation. Therefore, a
review of all proposed changes to the sampling
and analysis plan that potentially may affect the
data needs for risk assessment is necessary. Prior
to any changes in the SAP during actual sampling,
compliance of the changes with the objectives of
the SAP must be checked. (If risk assessment
objectives are not specified in the original SAP,
they will not be considered when changes to an
SAP are proposed.)
4.9.3 CONDUCT INTERIM REVIEWS OF
FIELD INVESTIGATION OUTPUTS
All sampling results should be reviewed as
soon as they are available to determine if the risk
assessment data needs outlined in the workplan
have been met by the sampling. Compare the
actual number, types, and locations of samples
collected with those planned in the SAP.
Sampling locations frequently are changed in the
field when access to a planned sampling location
is obstructed. The number of samples collected
may be altered if, for instance, there is an
insufficient amount of a certain medium to collect
the planned number of samples (e.g., if several
wells are found to be dry).
If certain sampling needs have not been met,
then the field investigators should be contacted to
determine why these samples were not collected.
If possible, the risk assessor should obtain samples
to fill these data gaps. If time is critical, Special
Analytical Services (see Section 4.7) may be used
to shorten the analytical time. If this is not
possible, then the risk assessor should evaluate all
sampling results as discussed in Chapter 5,
documenting the potential effect that these data
gaps will have on the quantitative risk assessment.
In general, the risk assessment should not be
postponed due to these data gaps.
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Page 4-25
ENDNOTES FOR CHAPTER 4
1. Some information that is appropriate for the assessment of human health risks also may be suitable and necessary for an
environmental evaluation of the site. Procedures for conducting an environmental evaluation of the hazardous waste site are outlined
in the companion volume of this guidance, the Environmental Evaluation Manual (EPA 1989a), and are not discussed in this chapter.
2. The term "media" refers to both environmental media (e.g., soil) and biota (e.g., fish).
3. "Areas of Concern" within the context of this guidance should be differentiated from the same terminology used by the Great Lakes
environmental community. This latter use is defined by the International Joint Commission as an area found to be exceeding the Great
Lakes Water Quality Agreement objectives.
4. New routine services that provide lower detection limits are currently under development. Contact the headquarters Analytical
Operations Branch for further information.
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Page 4-26
REFERENCES FOR CHAPTER 4
American Society of Testing and Materials (ASTM). Undated. A Proposed Guide for Sediment Collection, Storage, Characterization.
and Manipulation. Draft. Available from G. Allen Burton, Dept of Biological Sciences, Wright State University, Dayton, Ohio
45435.
• Provides information concerning how to collect contaminated sediments, sediment spiking, dilution procedures,
and QA/QC. Will probably be in the annual ASTM manual.
Environmental Protection Agency (EPA). 1981. Procedures for Handling and Chemical Analysis of Sediment and Water Samples.
Great Lakes Laboratory.
Environmental Protection Agency (EPA). 1983. Technical Assistance Document for Sampling and Analysis of Toxic Organic
Compounds in Ambient Air. Office of Research and Development.
• Provides guidance to persons involved in designing and implementing ambient air monitoring programs for toxic
organic compounds. Includes guidance on selecting sampling/analytical methods, sampling strategy, QA
procedures, and data format. Outlines policy issues.
Environmental Protection Agency (EPA). 1984. Sediment Sampling Quality Assurance User's Guide. Environmental Monitoring
Support Laboratory. Las Vegas, NV. NTIS: PB-85-233-542.
• Overview of selected sediment models presented as a foundation for stratification of study of regions and
selection of locations for sampling sites, methods of sampling, sampling preparation and analysis. Discussion
of rivers, lakes, and estuaries.
Environmental Protection Agency (EPA). 1985a. Practical Guide to Ground-water Sampling. Environmental Research Laboratory.
Ada, OK. EPA 600/2-85/104.
• Contains information on laboratory and field testing of sampling materials and procedures. Emphasizes
minimizing errors in sampling and analysis.
Environmental Protection Agency (EPA). 1985b. Methods Manual for Bottom Sediment Sample Collection. Great Lakes National
Program Office. EPA 905/4-85/004.
• Provides guidance on survey planning, sample collection, document preparation, and quality assurance for
sediment sampling surveys. Sample site selection, equipment/containers, collection field observation, preservation,
handling custody procedures.
Environmental Protection Agency (EPA). 1985c. Cooperative Agreement on the Monitoring of Contaminants in Great Lakes Sport
Fish for Human Health Purposes. Region V, Chicago, IL.
• Discusses sampling protocols and sample composition used for sport fish (chinook salmon, coho salmon, lake
trout, and rainbow trout), maximum composite samples (5 fish) and length ranges which would be applicable
to hazardous waste sites contaminating lakes or streams used for recreational fishing.
Environmental Protection Agency (EPA). 1985d. Petitions to Delist Hazardous Wastes Guidance Manual. Office of Solid Waste.
EPA/530/SW-85/003.
Environmental Protection Agency (EPA). 1986a. Test Methods for Evaluating Solid Waste (SW-846): Physical/Chemical Methods.
Office of Solid Waste.
• Provides analytical procedures to test solid waste to determine if it is a hazardous waste as defined under RCRA. Contains
information for collecting solid waste samples and for determining reactivity, corrosivity, ignitability, composition of waste,
and mobility of waste compounds.
Environmental Protection Agency (EPA). 1986b. Field Manual for Grid Sampling of PCB Spill Sites to Verify Cleanups. Office of
Toxic Substances. EPA/560/5-86/017.
• Provides detailed, step-by-step guidance for using hexagonal grid sampling; includes sampling design, collection,
QA/QC and reporting.
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Page 4-27
Environmental Protection Agency (EPA). 1986c. Resource Conservation and Recovery Act CRCRA1 Ground-water Monitoring
Technical Enforcement Guidance Document. Office of Waste Programs Enforcement.
• Contains a detailed presentation of the elements and procedures essential to the design and operation of ground-
water monitoring systems that meet the goals of RCRA and its regulations. Includes appendices on statistical
analysis and some geophysical techniques.
Environmental Protection Agency (EPA). 1987a. Data Quality Objectives for Remedial Response Activities: Development Process.
Office of Emergency and Remedial Response and Office of Waste Programs Enforcement. EPA/540/G-87/003. (OSWER
Directive 9335.0-7B).
• Identifies (1) the framework and process by which data quality objectives (DQOs; qualitative and quantitative
statements that specify the quality of the data required to support Agency decisions during remedial response
activities) are developed and (2) the individuals responsible for development of DQOs. Provides procedures
for determining a quantifiable degree of certainty that can be used in making site-specific decisions. Provides
a formal approach to integration of DQO development with sampling and analysis plan development. Attempts
to improve the overall quality and cost effectiveness of data collection and analysis activities.
Environmental Protection Agency (EPA). 1987b. Data Quality Objectives for Remedial Response Activities: Example Scenario: RI/FS
Activities at a Site with Contaminated Soils and Ground Water. Office of Emergency and Remedial Response and Office of
Waste Programs Enforcement. EPA/540/G-87/004.
• Companion to EPA 1987a. Provides detailed examples of the process for development of data quality objectives
(DQOs) for RI/FS activities under CERCLA.
Environmental Protection Agency (EPA). 1987c. A Compendium of Superfund Field Operations Methods. Office of Emergency and
Remedial Response. EPA/540/P-87/001. (OSWER Directive 9355.0-14).
Environmental Protection Agency (EPA). 1987d. Handbook: Ground Water. Office of Research and Development. EPA/625/6-
87/016.
• Resource document that brings together the available technical information in a form convenient for personnel
involved in ground-water management. Also addresses minimization of uncertainties in order to make reliable
predictions about contamination response to corrective or preventative measures.
Environmental Protection Agency (EPA). 1987e. An Overview of Sediment Quality in the United States. Office of Water Regulations
and Standards.
• Good primer. Contains many references.
Environmental Protection Agency (EPA). 1987f. Expanded Site Inspection (ESI) Transitional Guidance for FY 1988. Office of
Emergency and Remedial Response. (OSWER Directive 9345.1-.02).
• Provides reader with a consolidated ready reference of general methodologies and activities for conducting
inspection work on sites being investigated for the NPL.
Environmental Protection Agency (EPA). 1987g. Quality Assurance Field Operations Manual. Office of Solid Waste and Emergency
Response.
• Provides guidance for the selection and definition of field methods, sampling procedures, and custody
responsibilities.
Environmental Protection Agency (EPA). 1987h. Field Screening Methods Catalog. Office of Emergency and Remedial Response.
• Provides a listing of methods to be used during field screening, and includes method descriptions, their
application to particular sites, their limitations and uses, instrumentation requirements, detection limits, and
precision and accuracy information.
Environmental Protection Agency (EPA). 1988a. Guidance for Conducting Remedial Investigations and Feasibility Studies Under
CERCLA. Interim Final. Office of Emergency and Remedial Response. (OSWER Directive 9355.3-01).
• Provides the user (e.g., EPA personnel, state agencies, potentially responsible parties (PRPs), federal facility
coordinators, and contractors assisting in RVFS -related activities) with an overall understanding of the RI/FS
process. Includes general information concerning scoping meetings, the development of conceptual models at
the beginning of a site investigation, sampling, and analysis.
-------
Page 4-28
Environmental Protection Agency (EPA). 19885. Statistical Methods for Evaluating Ground Water from Hazardous Waste Facilities.
Office of Solid Waste.
• Specifies five different statistical methods that are appropriate for ground-water monitoring. Outlines sampling
procedures and performance standards that are designed to help minimize the occurrence of Type I and Type
II errors.
Environmental Protection Agency (EPA). 1988c. Surface Impoundment Clean Closure Guidance Manual. Office of Solid Waste.
Environmental Protection Agency (EPA). 1988d. Love Canal Emergency Declaration Area Habitabilitv Study Report. Prepared by
CH2M Hill and Life Systems for EPA Region II.
• Provides a formal comparison of samples with background as well as detailed discussions concerning problems
associated with sampling to evaluate data.
Environmental Protection Agency (EPA). 1988e. Guidance on Remedial Actions for Contaminated Ground Water at Superfund Sites.
Interim Final. Office of Emergency and Remedial Response. (OSWER Directive 9283.1-2).
• Provides guidance to develop, evaluate, and select ground-water remedial actions at Superfund sites, focusing
on policy issues and establishing cleanup levels. Also includes discussion of data collection activities for
characterization of contamination.
Environmental Protection Agency (EPA). 1988f. Statistical Methods for Evaluating the Attainment of Superfund Cleanup Standards.
Volume I: Soils and Solid Media. Draft. Office of Policy, Planning, and Evaluation.
• Provides statistical procedures that can be used in conjunction with attainment objectives defined by EPA to
determine, with the desired confidence, whether a site does indeed attain a cleanup standard. It also provides
guidance on sampling of soils to obtain baseline information onsite, monitor cleanup operations, and verify
attainment of cleanup objectives.
Environmental Protection Agency (EPA). 1988g. Proposed Guidelines for Exposure-related Measurements. 53 Federal Register 48830
(December 2, 1988).
• Focuses on general principles of chemical measurements in various physical and biological media. Assists
those who must recommend, conduct, or evaluate an exposure assessment.
Environmental Protection Agency (EPA). 1988h. Interim Report on Sampling Design Methodology. Environmental Monitoring
Support Laboratory. Las Vegas, NV. EPA/600/X-88/408.
• Provide guidance concerning the statistical determination of the number of samples to be collected.
Environmental Protection Agency (EPA). 1988i. User's Guide to the Contract Laboratory Program. Office of Emergency and
Remedial Response.
Environmental Protection Agency (EPA). 1989a. Risk Assessment Guidance for Superfund: Environmental Evaluation Manual.
Interim Final. Office of Emergency and Remedial Response. EPA/540/1-89/001A. (OSWER Directive 9285.7-01).
Environmental Protection Agency (EPA). 1989b. Soil Sampling Quality Assurance Guide. Review Draft. Environmental Monitoring
Support Laboratory. Las Vegas, NV.
• Replaces earlier edition: NTIS Pb-84-198-621. Includes DQO's, QAPP, information concerning the purpose
of background sampling, selection of numbers of samples and sampling sites, error control, sample design,
sample documentation.
Environmental Protection Agency (EPA). 1989c. Statistical Analysis of Ground-water Monitoring Data at RCRA Facilities. Office
of Solid Waste.
Environmental Protection Agency (EPA). 1989d. Ground-water Sampling for Metals Analyses. Office of Solid Waste and Emergency
Response. EPA/540/4-89-001.
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Page 4-29
Environmental Protection Agency (EPA). 1989e. Air Superfund National Technical Guidance Series. Volume IV: Procedures for
Dispersion Modeling and Air Monitoring for Superfund Air Pathway Analysis. Interim Final. Office of Air Quality Planning and
Standards. Research Triangle Park, NC. EPA/450/1 -89/004.
• This volume discusses procedures for dispersion modeling and air monitoring for superfund air pathway analyses.
Contains recommendations for proper selection and application of air dispersion models and procedures to
develop, conduct, and evaluate the results of air concentration monitoring to characterize downwind exposure
conditions from Superfund air emission sources.
Environmental Protection Agency (EPA). 1989f. Air Superfund National Technical Guidance Series. Volume I: Application of Air
Pathway Analyses for Superfund Activities. Interim Final. Office of Air Quality Planning and Standards. Research Triangle Park,
NC. EPA/450/1-89/001.
• Provides recommended procedures for the conduct of air pathway analyses (APAs) that meet the needs of the
Superfund program. The procedures are intended for use by EPA remedial project managers, enforcement
project managers, and air experts as well as by EPA Superfund contractors. The emphasis of this volume is
to provide a recommended APA procedure relative to the remedial phase of the Superfund process.
Environmental Protection Agency (EPA). 1989g. Air Superfund National Technical Guidance Series. Volume II: Estimation of
Baseline Air Emissions at Superfund Sites. Interim Final. Office of Air Quality Planning and Standards. Research Triangle Park,
NC. EPA/450/1-89/002.
• This volume provides information concerning procedures for developing baseline emissions from landfills and
lagoons. Describes baseline emissions from both undisturbed sites and sites where media-disturbing activities
are taking place. The procedures described for landfills may be applied to solid hazardous waste, and those
for lagoons may be applied to liquid hazardous waste.
Environmental Protection Agency (EPA). 1989h. Air Superfund National Technical Guidance Series. Volume III: Estimation of Air
Emissions from Cleanup Activities at Superfund Sites. Interim Final. Office of Air Quality Planning and Standards. Research
Triangle Park, NC. EPA/450/1-89/003.
• This volume provides technical guidance for estimating air emissions from remedial activities at NPL sites that
may impact local air quality for both onsite workers at a site and the surrounding community while the remedial
activities are occurring. Discusses methods to characterize air quality impacts during soil removal, incineration,
and air stripping.
Environmental Protection Agency (EPA). 19891. Guidance Manual for Assessing Human Health Risks from Chemically Contaminated
Fish and Shellfish. Office of Marine and Estuarine Protection. EPA/503/8-89/002.
• Study designed to measure concentrations of toxic substances in edible tissues of fish and shellfish.
Environmental Protection Agency (EPA) and Army Corps of Engineers (COE). 1981. Procedures for Handling and Chemical Analysis
of Sediment and Water Samples. Technical Committee on Dredged and Fill Material. Technical Report EPA/DE-81-1.
Food and Drug Administration (FDA). 1977. Pesticide Analytical Manual. Volume I.
• Provides a skin-on fillet (whole fish sampling) protocol used in USEPA monitoring of sportfish in the Great
Lakes. Also includes information on compositing.
Food and Drug Administration (FDA). 1986. Pesticides and Industrial Chemicals in Domestic Foods.
• Provides guidance for sampling designs for fishery products from the market.
Freeman, H.M. 1989. Standard Handbook of Hazardous Waste Treatment and Disposal. McGraw-Hill. New York.
• Provides detailed information concerning sampling and monitoring of hazardous wastes at remedial action sites
(Chapters 12 and 13).
Gilbert, R.O. 1987. Statistical Methods for Environmental Pollution Monitoring. Van Nostrand Reinhold. New York.
• Provides statistical analysis information by providing sampling plans, statistical tests, parameter estimation
procedure techniques, and references to pertinent publications. The statistical techniques discussed are relatively
simple, and examples, exercise, and case studies are provided to illustrate procedures.
-------
CHAPTER 5
DATA EVALUATION
/FROM: N
•Site discovery
• Preliminary
assessment
• Site inspection
\»NPL listing ^
Toxicity
Assessment
Data Data
Collection Evaluation
Risk
Characterization
Exposure
Assessment
TO:
•Selection of
remedy
• Remedial
design
• Remedial
.. action
DATA EVALUATION
• Combine data available from
site investigations
• Evaluate analytical methods
• Evaluate quantitation limits
• Evaluate qualified and coded data
• Evaluate blanks
• Evaluate tentatively identified
compounds
• Compare site data with
background
• Identify chemicals of potential
concern
-------
CHAPTERS
DATA EVALUATION
After a site sampling investigation has been
completed (see Chapter 4), a large quantity of
analytical data is usually available. Each sample
may have been analyzed for the presence of over
one hundred chemicals, and many of those
chemicals may have been detected. The following
nine steps should be followed to organize the data
into a form appropriate for a baseline risk
assessment:
(1) gather all data available from the site
investigation and sort by medium
(Section 5.1);
(2) evaluate the analytical methods used
(Section 5.2);
(3) evaluate the quality of data with respect
to sample quantitation limits (Section
5.3);
(4) evaluate the quality of data with respect
to qualifiers and codes (Section 5.4);
(5) evaluate the quality of data with respect
to blanks (Section 5.5);
(6) evaluate tentatively identified compounds
(Section 5.6);
(7) compare potential site-related
contamination with background (Section
5.7);
(8) develop a set of data for use in the risk
assessment (Section 5.8); and
(9) if appropriate, further limit the number
of chemicals to be carried through the
risk assessment (Section 5.9).
Prior to conducting any of these steps, the
EPA remedial project manager (RPM) should be
consulted to determine if certain steps should be
modified, added, or deleted as a result of site-
specific conditions. Also, some of the steps may
be conducted outside the context of the risk
assessment (e.g., for the feasibility study). The
rationale for not evaluating certain data based on
any of these steps must be fully discussed in the
text of the risk assessment report.
The following sections address each of the
data evaluation steps in detail, and Exhibit 5-1
presents a flowchart of the process. The outcome
of this evaluation is (1) the identification of a set
ACRONYMS FOR CHAPTER 5
CLP = Contract Laboratory Program
CRDL ~ Contract-Required Detection Limit
CRQL = Contract-Required Quantitation
Limit
DL = Detection Limit
FIT - Field Investigation Team
IDL = Instrument Detection Limit
MDL = Method Detection Limit
ND = Non-detect
PE = Performance Evaluation
PQL = Practical Quantitation Limit
QA/QC = Quality Assurance/Quality Control
QL = Quantitation Limit
RAS = Routine Analytical Services
SAS = Special Analytical Services
SMO — Sample Management Office
SOW - Statement of Work
SQL = Sample Quantitation Limit
SVOC = Semivolatile Organic Chemical
TCL = Target Compound List
TIC => Tentatively Identified Compound
TOC = Total Organic Carbon
TOX « Total Organic Halogens
VOC = Volatile Organic Chemical
-------
Page 5-2
DEFINITIONS FOR CHAPTER 5
Chemicals of Potential Concern. Chemicals that are potentially site-related and whose data are of sufficient quality for use
in the quantitative risk assessment.
Common Laboratory Contaminants. Certain organic chemicals (considered by EPA to be acetone, 2-butanone, methylene
chloride, toluene, and the phthalate esters) that are commonly used in the laboratory and thus may be introduced into
a sample from laboratory cross-contamination, not from the site.
Contract-required Quantitation Limit (CRQL). Chemical-specific levels that a CLP laboratory must be able to routinely and
reliably detect and quantitate in specified sample matrices. May or may not be equal to the reported quantitation limit
of a given chemical in a given sample.
Detection Limit (PL). The lowest amount that can be distinguished from the normal "noise" of an analytical instrument or
method.
Non-dctects (NDs). Chemicals that are not detected in a particular sample above a certain limit, usually the quantitation limit
for the chemical in that sample. Non-detects may be indicated by a "U" data qualifier.
Positive Data. Analytical results for which measurable concentrations (i.e., above a quantitation limit) are reported. May have
data qualifiers attached (except a U, which indicates a non-detect).
Quantitation Limit (QL). The lowest level at which a chemical can be accurately and reproducibly quantitated. Usually equal
to the instrument detection limit multiplied by a factor of three to five, but varies for different chemicals and different
samples.
of chemicals that are likely to be site-related and
(2) reported concentrations that are of acceptable
quality for use in the quantitative risk assessment.
If the nine data evaluation steps are followed, the
number of chemicals to be considered in the
remainder of the risk assessment usually will be
less than the number of chemicals initially
identified. Chemicals remaining in the
quantitative risk assessment based upon this
evaluation are referred to in this guidance as
"chemicals of potential concern."
5.1 COMBINING DATA
AVAILABLE FROM SITE
INVESTIGATIONS
Gather data, which may be from several
different sampling periods and based on several
different analytical methods, from all available
sources, including field investigation team (FIT)
reports, remedial investigations, preliminary site
assessments, and ongoing site characterization and
alternatives screening activities. Sort data by
medium. A useful table format for presenting
data is shown in Exhibit 5-2.
Evaluate data from different time periods to
determine if concentrations are similar or if
changes have occurred between sampling periods.
If the methods used to analyze samples from
different time periods are similar in terms of the
types of analyses conducted and the QA/QC
procedures followed, and if the concentrations
between sampling periods are similar, then the
data may be combined for the purposes of
quantitative risk assessment in order to obtain
more information to characterize the site. If
concentrations of chemicals change significantly
between sampling periods, it may be useful to
keep the data separate and evaluate risks
separately. Alternatively, one could use only the
most recent data in the quantitative risk
assessment and evaluate older data in a qualitative
analysis of changes in concentrations over time.
The RPM should be consulted on the elimination
of any data sets from the risk assessment, and
justification for such elimination must be fully
described in the risk assessment report.
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Page 5-3
EXHIBIT 5-1
DATA EVALUATION
f Sampling data from
I each medium of concern
V (Sec. 5.1).
Analytical
method appropriate
for quantitative
risk assessment
Sec. 5.2)7
Eliminate data associated with
inappropriate methods. Possibly use
qualitatively in other risk
assessment sections.
Is a
chemical not detected
in a sample
(Sec. 5.3)?
quanititation limit (QL)
health-based reference
concentration?
Reanalyze or address
qualitatively,as appropriate.
If QL cannot be reduced
useOL or 1/2 QL as
proxy concentration, or
eliminate chemical in
sample, as appropriate
Do other
samples in same
medium test positive1'
Use QL or 1/2 QL as
proxy concentration.
Gene rally eliminate
chemical.
Qualifiers
and codes attached
to data (Sec. 5.4)'
Evaluate qualified data, and
eliminate, modify, or leave data
as they are, as appropriate.
Sample
concent rational Ox
ank concentration7
Blank
contamination
(Sec. 5.5)'
Common lab
contaminants?
Sample
concentration^ 5x
a* concentration'
Many
tentatively identified
compounds (TICs;
Sec. 5.6)?
Expected to be
present and are primary
contaminants at site'
Eliminate TICs (as appropriate).
Use SAS, if possible, to confirm identity and concentration
otherwise use TICs as they are (as appropriate).
Site
chemicals
equal to background
(Sec 5.7)?
/"chemicals of potential
I concern for quantitative
V risk assessment.
Calculate risk of background chemicals
separately from site-related chemicals.
NOTE: See text for details
concerning specific
steps in this flowchart.
-------
Page 5-4
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-------
Page 5-5
5.2 EVALUATION OF ANALYTICAL
METHODS
Group data according to the types of analyses
conducted (e.g., field screening analysis,
semivolatiles analyzed by EPA methods for water
and wastewater, semivolatiles analyzed by EPA's
Superfund Contract Laboratory Program [CLP]
procedures) to determine which analytical method
results are appropriate for use in quantitative risk
assessment. Often, this determination has been
made already by regional and contractor staff.
An overview of EPA analytical methods is
provided in the box below. Exhibit 5-3 presents
examples of the types of data that are not usually
appropriate for use in quantitative risk assessment,
even though they may be available from a site
investigation.
OVERVIEW OF THE CLP AND OTHER EPA ANALYTICAL METHODS
The EPA Contract Laboratory Program (CLP) is intended to provide analytical services for Superfund waste site samples.
As discussed in the User's Guide to the Contract Laboratory Program (EPA 1988a, hereafter referred to as the CLP User's
Guide), the program was developed to fill the need for legally defensible results supported by a high level of quality assurance
(i.e., data of known quality) and documentation.
Prior to becoming CLP laboratories, analytical laboratories must meet stringent requirements for laboratory space and
practices, instrumentation, personnel training, and quality control (QC), and also must successfully analyze performance
evaluation (PE) samples. Before the first samples are shipped to the laboratory, audits of CLP labs are conducted to verify all
representations made by laboratory management. Continuing performance is monitored by periodic PE sample analyses, routine
and remedial audits, contract compliance screening of data packages, and oversight by EPA.
Superfund samples are most commonly analyzed using the Routine Analytical Services (RAS) conducted by CLP laboratories.
Under RAS, all data are generated using the same analytical protocols specifying instrumentation, sample handling, analysis
parameters, required quantitation limits, QC requirements, and report format. Protocols are provided in the CLP Statement
of Work (SOW) for Inorganics (EPA 1988b) and the CLP Statement of Work for Organics (1988c). The SOWs also contain
EPA's target analyte or compound lists (TAL for inorganics, TCL for orgamcs), which are the lists of analytes and required
quantitation limits (QLs) for which every Superfund site sample is routinely analyzed under RAS. As of June 1989, analytes
on the TCL/TAL consist of 34 volatile organic chemicals (VOCs), 65 semivolatile organic chemicals (SVOCs), 19 pesticides,
7 polychlorinated biphenyls, 23 metals, and total cyanide. Finally, the SOW specifies data qualifiers that may be placed on
certain data by the laboratory to communicate information and/or QC problems.
CLP labs are required to submit RAS data packages to EPA's Sample Management Office (SMO) and to the EPA region
from which the samples originated within 35 days of receipt of samples. SMO provides management, operational, and
administrative support to the CLP to facilitate optimal use of the program. SMO personnel identify incomplete or missing
elements and verify compliance with QA/QC requirements in the appropriate SOW. In addition to the SMO review, all CLP
data are inspected by EPA-appointed regional data validators. Using Laboratory Data Validation Functional Guidelines issued
by EPA headquarters (hereafter referred to as Functional Guidelines for Inorganics {EPA 1988d] and Functional Guidelines
for Organics [EPA 1988e]), regional guidelines, and professional judgment, the person validating data identifies deviations from
the SOW, poor QC results, matrix interferences, and other analytical problems that may compromise the potential uses of the
data. In the validation process, data may be flagged with qualifiers to alert data users of deviations from QC requirements.
These qualifiers differ from those qualifiers attached to the data by the laboratory.
In addition to RAS, non-standard analyses may be conducted using Special Analytical Services (SAS) to meet user
requirements such as short turnaround time, lower QLs, non-standard matrices, and the testing of analytes other than those on
the Target Compound List. Under SAS, the user requests specific analyses, QC procedures, report formats, and timeframe
needed.
Examples of other EPA analytical methods include those described in Test Methods for Evaluating Solid Waste (EPA 1986;
hereafter referred to as SW-846 Methods) and Methods for Organic Chemical Analysis of Municipal and Industrial Wastewater
(EPA 1984; hereafter referred to as EPA 600 Methods). The SW-846 Methods provide analytical procedures to test solid waste
to determine if it is a hazardous waste as defined under the Resource Conservation and Recovery Act (RCRA). These methods
include procedures for collecting solid waste samples and for determining reactivity, corrosivity, ignitability, composition of waste,
and mobility of waste components. The EPA 600 Methods are used in regulatory programs under the Clean Water Act to
determine chemicals present in municipal and industrial wastewaters.
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Page 5-6
EXHIBIT 5-3
EXAMPLES OF THE TYPES OF DATA POTENTIALLY UNSUITABLE
FOR A QUANTITATIVE RISK ASSESSMENT
Analytical Instrument
or Method Purpose of Analysis Analytical Result
HNu Organic Vapor Detector Health and Safety, Total Organic Vapor
Field Screen
Organic Vapor Analyzer Health and Safety, Total Organic Vapor
Field Screen
Combustible Gas Indicator Health and Safety Combustible Vapors,
Oxygen-deficient
Atmosphere
Field Gas Chromatography0 Field Screen/Analytical Specific Volatile and
Method Semi-volatile Organic
Chemicals
" Depending on the detector used, this instrument can be sufficiently sensitive to yield adequate data for
use in a quantitative risk assessment; however, a confirming analysis by GC/MS should be performed on
a subset of the samples in a laboratory prior to use.
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Page 5-7
Analytical results that are not specific for a
particular compound (e.g., total organic carbon
[TOC], total organic halogens [TOX]) or results
of insensitive analytical methods (e.g., analyses
using portable field instruments such as organic
vapor analyzers and other field screening methods)
may be useful when considering sources of
contamination or potential fate and transport of
contaminants. These types of analytical results,
however, generally are not appropriate for
quantitative risk assessment; therefore, the risk
assessor may not want to include them in the
summary of chemicals of potential concern for the
quantitative risk assessment. In addition, the
results of analytical methods associated with
unknown, few, or no QA/QC procedures should
be eliminated from further quantitative use.
These types of results, however, may be useful for
qualitative discussions of risk in other sections of
the risk assessment report.
The outcome of this step is a set of site data
that has been developed according to a standard
set of sensitive, chemical-specific methods (e.g.,
SW-846 Methods [EPA 1986], EPA 600 Methods
[EPA 1984], CLP Statements of Work [EPA
1988b,c]), with QA/QC procedures that are well-
documented and traceable. The data resulting
from analyses conducted under the CLP, which
generally comprise the majority of results available
from a Superfund site investigation, fall into this
category.
Although the CLP was developed to ensure
that consistent QA/QC methods are used when
analyzing Superfund site samples, it does not
ensure that all analytical results are consistently
of sufficient quality and reliability for use in
quantitative risk assessment. Neither the CLP nor
QA/QC procedures associated with other methods
make judgments concerning the ultimate "usability"
of the data. Do not accept at face value all
remaining analytical results, whether from the CLP
or from some other set of analytical
methodologies. Instead, determine - according to
the steps discussed below - the limitations and
uncertainties associated with the data so that only
data that are appropriate and reliable for use in
a quantitative risk assessment are carried through
the process.
5.3 EVALUATION OF
QUANTITATION LIMITS
This step.involves evaluation of quantitation
limits and detection limits (QLs and DLs) for all
of the chemicals assessed at the site. This
evaluation may lead to the re-analysis of some
samples, the use of "proxy" (or estimated)
concentrations, and/or the elimination of certain
chemicals from further consideration (because they
are believed to be absent from the site). Types
and definitions of QLs and DLs are presented in
the box on the next page.
Before eliminating chemicals because they are
not detected (or conducting any other
manipulation of the data), the following points
should be considered:
(1) the sample quantitation limit (SQL) of
a chemical may be greater than
corresponding standards, criteria, or
concentrations derived from toxicity
reference values (and, therefore, the
chemical may be present at levels greater
than these corresponding reference
concentrations, which may result in
undetected risk); and
(2) a particular SQL may be significantly
higher than positively detected values in
other samples in a data set.
These two points are discussed in detail in the
following two subsections. A third subsection
provides guidance for situations where only some
of the samples for a given medium test positive
for a particular chemical. A fourth subsection
addresses the special situation where SQLs are not
available. The final subsection addresses the
specific steps involved with elimination of
chemicals from the quantitative risk assessment
based on their QLs.
5.3.1 SAMPLE QUANTITATION LIMITS
(SQLs) THAT ARE GREATER THAN
REFERENCE CONCENTRATIONS
As discussed in Chapter 4, QLs needed for
the site investigation should be specified in the
sampling plan. For some chemicals, however,
SQLs obtained under RAS or SAS may exceed
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Page 5-8
certain reference concentrations (e.g., maximum
contaminant levels [MCLs], concentrations
corresponding to a 10~6 cancer risk). The box on
the next page illustrates this problem. For certain
chemicals (e.g., antimony), the CLP contract-
required quantitation limits (CRQLs) exceed the
corresponding reference concentrations for
noncarcinogenic effects, based on the EPA-verified
reference dose and a 2-liter per day ingestion of
water by a 70-kilogram person.7 Estimation of
cancer risks for several other chemicals (e.g.,
arsenic, styrene) at their CRQLs yields cancer
risks exceeding W'4, based on the same water
ingestion factors. Most potential carcinogens with
EPA-derived slope factors have CRQLs that yield
cancer risk levels exceeding 10~6 in water, and
none of the carcinogens with EPA-derived slope
factors have CRQL values yielding less than 10"7
cancer risk levels (as of the publication date of
this manual; data not shown).
Three points should be noted when
considering this example.
(1) Review of site information and a
preliminary determination of chemicals
of potential concern at a site prior to
sample collection may allow the
specification of lower QLs (i.e., using
SAS) before an investigation begins (see
Chapter 4). This is the most efficient
way to minimize the problem of QLs
exceeding levels of potential concern.
(2) EPA's Analytical Operations Branch
currently is working to reduce the CRQL
values for several chemicals on the TCL
and TAL, and to develop an analytical
service for chemicals with special
standards (e.g., MCLs).
TYPES AND DEFINITIONS OF DETECTION LIMITS AND QUANTITATION LIMITS
Strictly interpreted, the detection limit (DL) is the lowest amount of a chemical that can be "seen" above the normal, random
noise of an analytical instrument or method. A chemical present below that level cannot reliably be distinguished from noise.
DLs are chemical-specific and instrument-specific and are determined by statistical treatment of multiple analyses in which the
ratio of the lowest amount observed to the electronic noise level (i.e., the signal-to-noise ratio) is determined. On any given
day in any given sample, the calculated limit may not be attainable; however, a properly calculated limit can be used as an overall
general measure of laboratory performance.
Two types of DLs may be described — instrument DLs (IDLs) and method DLs (MDLs). The 1DL is generally the lowest
amount of a substance that can be detected by an instrument; it is a measure only of the DL for the instrument, and does not
consider any effects that sample matrix, handling, and preparation may have. The MDL, on the other hand, takes into account
the reagents, sample matrix, and preparation steps applied to a sample in specific analytical methods.
Due to the irregular nature of instrument or method noise, reproducible quantitation of a chemical is not possible at the DL.
Generally, a factor of three to five is applied to the DL to obtain a quantitation limit (QL), which is considered to be the lowest
level at which a chemical may be accurately and reproducibly quantitated. DLs indicate the level at which a small amount would
be "seen," whereas QLs indicate the levels at which measurements can be "trusted."
Two types of QLs may be described - contract-required QLs (CRQLs) and sample QLs (SQLs). (Contract-required detection
limits [CRDL] is the term used for inorganic chemicals. For the purposes of this manual, however, CRQL will refer to both
organic and inorganic chemicals.) In order to participate in the CLP, a laboratory must be able to meet EPA CRQLs. CRQLs
are chemical-specific and vary depending on the medium analyzed and the amount of chemical expected to be present in the
sample. As the name implies, CRQLs are not necessarily the lowest detectable levels achievable, but rather are levels that a
CLP laboratory should routinely and reliably detect and quantitate in a variety of sample matrices. A specific sample may
require adjustments to the preparation or analytical method (e.g., dilution, use of a smaller sample aliquot) in order to be
analyzed. In these cases, the reported QL must in turn be adjusted. Therefore, SQLs, not CRQLs, will be the QLs of interest
for most samples. In fact, for the same chemical, a specific SQL may be higher than, lower than, or equal to SQL values for
other samples. In addition, preparation or analytical adjustments such as dilution of a sample for quantitation of an extremely
high level of only one compound could result in non-detects for all other compounds included as analytes for a particular
method, even though these compounds may have been present at trace quantities in the undiluted sample. Because SQLs take
into account sample characteristics, sample preparation, and analytical adjustments, these values are the most relevant QLs for
evaluating non-detected chemicals.
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Page 5-9
EXAMPLE OF HEALTH RISKS FROM INGESTION OF WATER CONTAMINATED
WITH SELECTED CHEMICALS AT THEIR QUANTITATION LIMITS"
Chemical
CRQL or
CAS # CRDL (ug/L)b CRDL/RfCc
Cancer Risk
at CRQL or CRDLd
Antimony
Arsenic
Benz(a)pyrene
Bis(2-CMoroethyl)ether
2,4-Dinitrotoluene
Hexachlorobenzene
N-NitrOso-di-n-dipropylamine
PCB-1254
PCB-1260
Sfyrene
Vinyl chloride
7440-36-0
7440-38-2
50-32-8
1H -44-4
121-14-2
118-744
621-64-7
11096-69-1
11096-82-5
100-42-5
75-01-4
60
10
10
10
10
10
10
1
1
5
10
4.3
SxlQ'4
3x10-3
3xlO-4
2xlO-4
5xlO'4
2X10'3
2xlO-4e
2xlO-4
4xlO'4
7xlO'4
a All values in this example are for illustration purposes only.
k CRQL = Contract-required quantitation limit (organics) of the Contract Laboratory Program (revised April 1989).
CRDL = Contract-required detection limit (inorganics) of the Contract Laboratory Program (revised July 1988).
The CRQL and CRDL values presented here are for the regular multi-media multi-concentration CLP methods.
c RfC = Reference concentration (based on the August 1989 reference dose for oral exposure, assuming a 70-kilogram
adult drinks 2 liters of contaminated water per day),
d Cancer Risk at CRQL or CRDL = Excess upper-bound lifetime cancer risk (based on the August 1989 slope factor for
oral exposure, assuming a 70-kilogram adult drinks 2 liters of contaminated water per day).
e PCB-1260 slope factor was used.
(3) In several situations, an analytical
laboratory may be able to attain QLs in
particular samples that are below or
above the CRQL values.
If SAS was not specified before sampling
began and/or if a chemical is not detected in any
sample from a particular medium at the QL, then
available modeling data, as well as professional
judgment, should be used to evaluate whether the
chemical may be present above reference
concentrations. If the available information
indicates the chemical is not present, see Section
5.3.5 for guidance on eliminating chemicals. If
there is some indication that the chemical is
present, then either re-analyze selected samples
using SAS, if time allows, or address the chemical
qualitatively. In determining which option is most
appropriate for a site, a screening-level risk
assessment should be performed by assuming that
the chemical is present in the sample at the SQL
(see Section 5.3.4 for situations where SQLs are
not available). Carry the chemical through the
screening risk assessment, essentially conducting
the assessment on the SQL for the particular
chemical. In this way, the risks that would be
posed if the chemical is present at the SQL can
be compared with risks posed by other chemicals
at the site.
Re-analyze the sample. This (preferred)
option discourages elimination of questionable
chemicals (i.e., chemicals that may be present
below their QL but above a level of potential
concern) from the risk assessment. If time allows
and a sufficient quantity of the sample is available,
submit a SAS request to re-analyze the sample
at QLs that are below reference concentrations.
The possible outcome of this option is inclusion
of chemicals positively detected at levels above
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Page 5-10
reference concentrations but below the QLs that
would normally have been attained under routine
analysis of Superfund samples in the CLP
program.
Address the chemical qualitatively. A second
and less desirable option for a chemical that may
be present below its QL (and possibly above its
health-based reference concentration) is to
eliminate the chemical from the quantitative risk
assessment, noting that if the chemical was
detected at a lower QL, then its presence and
concentration could contribute significantly to the
estimated risks.
5.3.2 UNUSUALLY HIGH SQLs
Due to one or more sample-specific problems
(e.g., matrix interferences), SQLs for a particular
chemical in some samples may be unusually high,
sometimes greatly exceeding the positive results
reported for the same chemical in other samples
from the data set. Even if these SQLs do not
EXAMPLE OF UNUSUALLY HIGH
QUANTITATION LIMITS
In this example, concentrations of semivolatile organic
chemicals in soils have been determined using the CLP's
RAS.
Concentration (ug/kg>
Chemical Sample 1 Sample 2 Sample 3 Sample 4
Phenol 330 Ua 390 19,000 U 490
a U = Compound was analyzed for, but not detected.
Value presented (e.g., 330 U) is the SQL.
The QLs presented in this example (i.e., 330 to 19,000
ug/kg) vary widely from sample to sample. SAS would
not aid in reducing the unusually high QL of 19,000
ug/kg noted in Sample 3, assuming it was due to
unavoidable matrix interferences. In this case, the result
for phenol in Sample 3 would be eliminated from the
quantitative risk assessment because it would cause the
calculated exposure concentrations (from Chapter 6) to
exceed the maximum detected concentration (in this
case 490 ug/kg). Thus, the data set would be reduced
to three samples: the non-detect in Sample 1 and the
two detected values in Samples 2 and 4.
exceed health-based standards or criteria, they may
still present problems. If the SQLs cannot be
reduced by re-analyzing the sample (e.g., through
the use of SAS or sample cleaning procedures to
remove matrix interferences), exclude the samples
from the quantitative risk assessment if they cause
the calculated exposure concentration (i.e., the
concentration calculated according to guidance in
Chapter 6) to exceed the maximum detected con-
centration for a particular sample set. The box
on this page presents an example of how to
address a situation with unusually high QLs.
5.3.3 WHEN ONLY SOME SAMPLES IN A
MEDIUM TEST POSITIVE FOR A
CHEMICAL
Most analytes at a site are not positively
detected in each sample collected and analyzed.
Instead, for a particular chemical the data set
generally will contain some samples with positive
results and others with non-detected results. The
non-detected results usually are reported as SQLs.
These limits indicate that the chemical was not
measured above certain levels, which may vary
from sample to sample. The chemical may be
present at a concentration just below the reported
quantitation limit, or it may not be present in the
sample at all (i.e., the concentration in the sample
is zero).
In determining the concentrations most
representative of potential exposures at the site
(see Chapter 6), consider the positively detected
results together with the non-detected results (i.e.,
the SQLs). If there is reason to believe that the
chemical is present in a sample at a concentration
below the SQL, use one-half of the SQL as a
proxy concentration. The SQL value itself can be
used if there is reason to believe the
concentration is closer to it than to one-half the
SQL. (See the next subsection for situations
where SQLs are not available.) Unless site-
specific information indicates that a chemical is
not likely to be present in a sample, do not
substitute the value zero in place of the SQL (i.e.,
do not assume that a chemical that is not detected
at the SQL would not be detected in the sample
if the analysis was extremely sensitive). Also, do
not simply omit the non-detected results from the
risk assessment.
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Page 5-11
5.3.4 WHEN SQLs ARE NOT AVAILABLE
A fourth situation concerning QLs may
sometimes be encountered when evaluating site
data. For some sites, data summaries may not
provide the SQLs. Instead, MDLs, CRQLs, or
even IDLs may have been substituted wherever a
chemical was not detected. Sometimes, no
detection or quantitation limits may be provided
with the data. As a first step in these situations,
always attempt to obtain the SQLs. because these
are the most appropriate limits to consider when
evaluating non-detected chemicals (i.e., they
account for sample characteristics, sample
preparation, or analytical adjustments that may
differ from sample to sample).
If SQLs cannot be obtained, then, for CLP
sample analyses, the CRQL should be used as the
QL of interest for each non-detected chemical,
with the understanding that these limits may
overestimate or underestimate the actual SQL.
For samples analyzed by methods different from
CLP methods, the MDL may be used as the QL,
with the understanding that in most cases this will
underestimate the SQL (because the MDL is a
measure of detection limits only and does not
account for sample characteristics or matrix
interferences). Note that the IDL should rarely
be used for non-detected chemicals since it is a
measure only of the detection limit for a
particular instrument and does not consider the
effect of sample handling and preparation or
sample characteristics.
5.3.5 WHEN CHEMICALS ARE NOT
DETECTED IN ANY SAMPLES IN A
MEDIUM
After considering the discussion provided in
the above subsections, generally eliminate those
chemicals that have not been detected in any
samples of a particular medium. On CLP data
reports, these chemicals will be designated in each
sample with a U qualifier preceded by the SQL or
CRQL (e.g., 10 U). If information exists to
indicate that the chemicals are present, they
should not be eliminated. For example, if
chemicals with similar transport and fate
characteristics are detected frequently in soil at a
site, and some of these chemicals also are detected
frequently in ground water while the others are
not detected, then the undetected chemicals are
probably present in the ground water and
therefore may need to be included in the risk
assessment as ground-water contaminants.
The outcome of this step is a data set that
only contains chemicals for which positive data
(i.e., analytical results for which measurable
concentrations are reported) are available in at
least one sample from each medium. Unless
otherwise indicated, assume at this point in the
evaluation of data that positive data to which no
uncertainties are attached concerning either the
assigned identity of the chemical or the reported
concentration (i.e., data that are not "tentative,"
"uncertain," or "qualitative") are appropriate for
use in the quantitative risk assessment.
5.4 EVALUATION OF QUALIFIED
AND CODED DATA
For CLP analytical results, various qualifiers
and codes (hereafter referred to as qualifiers) are
attached to certain data by either the laboratories
conducting the analyses or by persons performing
data validation. These qualifiers often pertain to
QA/QC problems and generally indicate questions
concerning chemical identity, chemical
concentration, or both. All qualifiers must be
addressed before the chemical can be used in
quantitative risk assessment. Qualifiers used by
the laboratory may differ from those used by data
validation personnel in either identity or meaning.
5.4.1 TYPES OF QUALIFIERS
A list of the qualifiers that laboratories are
permitted to use under the CLP - and their
potential use in risk assessment - is presented in
Exhibit 5-4. A similar list addressing data
validation qualifiers is provided in Exhibit 5-5.
In general, because the data validation process is
intended to assess the effect of QC issues on data
usability, validation data qualifiers are attached to
the data after the laboratory qualifiers and
supersede the laboratory qualifiers. If data have
both laboratory and validation qualifiers and they
appear contradictory, ignore the laboratory
qualifier and consider only the validation qualifier.
If qualifiers have been attached to certain data by
the laboratory and have not been removed,
revised, or superseded during data validation, then
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Page 5-12
EXHIBIT 5-4
CLP LABORATORY DATA QUALIFIERS AND THEIR POTENTIAL USE
IN QUANTITATIVE RISK ASSESSMENT
Qualifier Definition
Indicates:
Uncertain
Identity?
Uncertain
Concentration?
Include Data in Quantitative
Risk Assessment?
Inorganic Chemical Data:"
B Reported value is No
IDL.
U Compound was analyzed for, Yes
but not detected.
No
Yes
Yes
Value is estimated due to
matrix interferences.
No
Yes
Yes
M Duplicate injection precision
criteria not met.
No
Yes
Yes
N Spiked sample recovery not
within control limits.
No
Yes
Yes
S Reported value was determined No
by the Method of Standard
Additions (MSA).
W Post-digestion spike for furnace No
AA analysis is out of control
limits, while sample absorbance
is <50% of spike absorbance.
* Duplicate analysis was not No
within control limits.
No
Yes
Yes
Yes
Yes
Yes
Correlation coefficient for
MSA was <0.995.
No
Yes
Yes
Organic Chemical Data:*
U Compound was analyzed for,
but not detected.
Yes
Yes
(continued)
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Page 5-13
EXHIBIT 5-4 (continued)
CLP LABORATORY DATA QUALIFIERS AND THEIR POTENTIAL USE
IN QUANTITATIVE RISK ASSESSMENT
Indicates:
Uncertain Uncertain Include Data in Quantitative
Qualifier Definition Identity? Concentration? Risk Assessment?
J Value is estimated, No, for Yes ?
either for a tentatively TCL chem-
identified compound (TIC) icals;
or when a compound is present
(spectral identification Yes, for
criteria are met, but the TICs
value is
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Page 5-14
EXHIBIT 5-5
VALIDATION DATA QUALIFIERS AND THEIR
POTENTIAL USE IN QUANTITATIVE RISK ASSESSMENT
Qualifier Definition
Indicates:
Uncertain Uncertain Include Data in Quantitative
Identity? Concentration? Risk Assessment?
Inorganic and Organic Chemical Data:0
U The material was analyzed Yes
for, but not detected. The
associated numerical value
is the SQL.
J The associated numerical No
value is an estimated quantity.
R Quality control indicates that Yes
the data are unusable (compound
may or may not be present).
Re-sampling and/or re-analysis is
necessary for verification.
Z No analytical result (inorganic
data only).
Q No analytical result (organic
data only).
N Presumptive evidence of Yes
presence of material (tentative
identification).*
Yes
Yes
Yes
Yes
No
Yes
— = Not applicable
a Source: EPA 1988d,e.
b Organic chemical data only.
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Page 5-15
evaluate the laboratory qualifier itself. If it is
unclear whether the data have been validated,
contact the appropriate data validation and/or
laboratory personnel.
The type of qualifier and other site-specific
factors determine how qualified data are to be
used in a risk assessment. As seen in Exhibits
5-4 and 5-5, the type of qualifier attached to
certain data often indicates how that data should
be used in a risk assessment. For example, most
of the laboratory qualifiers for both inorganic
chemical data and organic chemical data (e.g., J,
E, N) indicate uncertainty in the reported
concentration of the chemical, but not in its
assigned identity. Therefore, these data can be
used just as positive data with no qualifiers or
codes. In general, include data with qualifiers that
indicate uncertainties in concentrations but not in
identification.
Examples showing the use of certain qualified
data are presented in the next two boxes. The
first box addresses the J qualifier, the most
commonly encountered data qualifier in Superfund
data packages. Basically, the guidance here is to
use J-qualified concentrations the same way as
EXAMPLE OF J QUALIFIERS
In this example, concentrations of volatile organic
chemicals in ground water have been determined using
the CLP's RAS.
Concentration (ug/L'j
Chemical Sample 1 Sample 2 Sample 3 Sample 4
Tetrachioro-
ethene 14,000 Ja 40 30 Ub
20J
8 J = The numerical value is an estimated quantity.
b U = Compound was analyzed for, but not detected.
Value presented (e.g., 30 U) is the SQL,
Tetrachlorethene was detected in three of four
samples at concentrations of 14,000 pg/L, 40 jig/1, and
20 ug/1; therefore, these concentrations — as well as the
non-detect - should be used in determining representa-
tive concentrations.
positive data that do not have this qualifier. If
possible, note potential uncertainties associated
with the qualifier, so that if data qualified with a
J contribute significantly to the risk, then
appropriate caveats can be attached.
EXAMPLE OF VALIDATED DATA
CONTAINING R QUALIFIERS
In this example, concentrations of inorganic chemicals
in ground water have been determined using the CLP's
RAS.
Concentration (us/L}
Chemical Sample 1 Sample 2 Sample 3 Sample 4
Manganese 310 500 Ra 30 URb 500
a R = Quality control indicates that the data are
unusable (compound may or may not be present).
b U = Compound was analyzed for, but not detected.
Value presented (e.g., 30 U) is the SQL.
These data have been validated, and therefore the R
qualifiers indicate that the person conducting the data
validation rejected the data for manganese in Samples
2 and 3. The "UR" qualifier means that manganese was
not detected in Sample 3; however, the data validator
rejected the non-detected result Eliminate these two
samples so that the data set now consists of only two
samples (Samples 1 and 4).
An illustration of the use of R-qualified data
is presented in the box in this column. The
definition, and therefore the use of the R
qualifier, differs depending on whether the data
have been validated or not. (Note that the CLP
formerly used R as a laboratory qualifier to
indicate low spike recovery for inorganics. This
has been changed, but older data may still have
been qualified by the laboratory with an R.) If it
is known that the R data qualifier indicates that
the sample result was rejected by the data
validation personnel, then this result should be
eliminated from the risk assessment; if the R data
qualifier was placed on the data to indicate
estimated data due to low spike recovery (i.e., the
R was placed on the data by the laboratory and
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Page 5-16
not by the validator), then use the R-qualified
data in a manner similar to the use of J-qualified
data (i.e., use the R-qualified concentrations the
same way as positive data that do not have this
qualifier). If possible, note whether the R-
qualified data are overestimates or underestimates
of actual expected chemical concentrations so that
appropriate caveats may be attached if data
qualified with an R contribute significantly to the
risk.
5.4.2 USING THE APPROPRIATE
QUALIFIERS
The information presented in Exhibits 5-4
and 5-5 is based on the most recent EPA
guidance documents concerning qualifiers: the
SOW for Inorganics and the SOW for Organics
(EPA 1988b,c) for laboratory qualifiers, and the
Functional Guidelines for Inorganics and the
Functional Guidelines for Organics (EPA 1988d,e)
for validation qualifiers. The types and definitions
of qualifiers, however, may be periodically updated
within the CLP program. In addition, certain
EPA regions may have their own data qualifiers
and associated definitions. These regional
qualifiers are generally consistent with the
Functional Guidelines, but are designed to convey
additional information to data users.
In general, the risk assessor should check
whether the information presented in this section
is current by contacting the appropriate regional
CLP or headquarters Analytical Operations
Branch staff. Also, if definitions are not reported
with the data, regional contacts should be
consulted prior to evaluating qualified data.
These variations may affect how data with certain
qualifiers should be used in a risk assessment.
Make sure that definitions of data qualifiers used
in the data set for the site have been reported
with the data and are current. Never guess about
the definition of qualifiers.
5.5 COMPARISON OF
CONCENTRATIONS
DETECTED IN BLANKS WITH
CONCENTRATIONS
DETECTED IN SAMPLES
Blank samples provide a measure of
contamination that has been introduced into a
sample set either (1) in the field while the
samples were being collected or transported to the
laboratory or (2) in the laboratory during sample
preparation or analysis. To prevent the inclusion
of non-site-related contaminants in the risk
assessment, the concentrations of chemicals
detected in blanks must be compared with
concentrations of the same chemicals detected in
site samples. Detailed definitions of different
types of blanks are provided in the box on the
next page.
Blank data should be compared with results
from samples with which the blanks are associated.
It is often impossible, however, to determine the
association between certain blanks and data. In
this case, compare the blank data with results
from the entire sample data set. Use the
guidelines in the following paragraphs when
comparing sample concentrations with blank
concentrations.
Blanks containing common laboratory
contaminants. As discussed in the CLP SOW for
Organics (EPA 1988c) and the Functional
Guidelines for Organics (EPA 1988e), acetone, 2-
butanone (or methyl ethyl ketone), methylene
chloride, toluene, and the phthalate esters are
considered by EPA to be common laboratory
contaminants. In accordance with the Functional
Guidelines for Organics (EPA 1988e) and the
Functional Guidelines for Inorganics (EPA 1988d),
if the blank contains detectable levels of common
laboratory contaminants, then the sample results
should be considered as positive results only if the
concentrations in the sample exceed ten times the
maximum amount detected in any blank. If the
concentration of a common laboratory
contaminant is less than ten times the blank
concentration, then conclude that the chemical
was not detected in the particular sample and, in
accordance with EPA guidance, consider the
blank-related concentrations of the chemical to be
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Page 5-17
TYPES OF BLANKS
Blanks are analytical quality control samples analyzed in the same manner as site samples. They are used in the measurement
of contamination that has been introduced into a sample either (1) in lie field while the samples were being collected or
transported to the laboratory or (2) in the laboratory during sample preparation or analysis, Four types of blanks -- trip, field,
laboratory calibration, and laboratory reagent (or method) - are described below. A discussion on the water used for the blank
also is provided.
Trip Blank. This type of blank is used to indicate potential contamination due to migration of volatile organic chemicals
(VOCs) from the air on the site or in sample shipping containers, through the septum or around the; lid of sampling vials, and
into the sample. A trip blank consists of laboratory distilled, deionized water in a 40-ml glass vial sealed with a teflon septum.
The blank accompanies the empty sample bottles to the field as well as the samples returning to the laboratory for analysis; it
is not opened until it is analyzed in the lab with the actual site samples. The containers and labels for trip blanks should be
the same as the containers and labels for actual samples, thus making the laboratory "blind" to the identity of the blanks.
Field Blank. A field blank is used to determine if certain field sampling or cleaning procedures (e.g., insufficient cleaning
of sampling equipment) result in cross-contamination of site samples. Like the trip blank, the field blank is a sample of distilled,
deionized water taken to the field with empty sample bottles and is analyzed in the laboratory along with the actual samples.
Unlike the trip blank, however, the field blank sample is opened in the field and used as a sample would be (e.g., it is poured
through cleaned sampling equipment or it is poured from container to container in the vicinity of a gas-powered pump). As
with trip blanks, the field blanks' containers and labels should be the same as for actual samples.
Laboratory Calibration Blank. This type of blank is distilled, deionized water injected directly into an instrument without
having been treated with reagents appropriate to the analytical method used to analyze actual site samples. This type of blank
is used to indicate contamination in the instrument itself, or possibly in the distilled, deionized water,
Laboratory Reagent or Method Blank. This blank results from the treatment of distilled, deionized water with all of the
reagents and manipulations (e.g., digestions or extractions) to which site samples will be subjected. Positive results in the
reagent blank may indicate either contamination of the chemical reagents or the glassware and implements used to store or
prepare the sample and resulting solutions. Although a laboratory following good laboratory practices will have its analytical
processes under control, in some instances method blank contamination cannot be entirely eliminated.
Water Used for Blanks. For all the blanks described above, results are reliable only if the water comprising the blank -was
clean. For example, if the laboratory water comprising the trip blank was contaminated with VOCs prior to being taken to the
field, then the source of VOC contamination in the trip blank cannot be isolated (see laboratory calibration blank).
the quantitation limit for the chemical in that
sample. Note that if all samples contain levels of
a common laboratory contaminant that are less
than ten times the level of contamination noted
in the blank, then completely eliminate that
chemical from the set of sample results.
Blanks containing chemicals that are not
common laboratory contaminants. As discussed
in the previously referenced guidance, if the blank
contains detectable levels of one or more organic
or inorganic chemicals that are not considered by
EPA to be common laboratory contaminants (e.g.,
all other chemicals on the TCL), then consider
site sample results as positive only if the
concentration of the chemical in the site sample
exceeds five times the maximum amount detected
in any blank. Treat samples containing less than
five times the amount in any blank as non-detects
and, in accordance with EPA guidance, consider
the blank-related chemical concentration to be the
quantitation limit for the chemical in that sample.
Again, note that if all samples contain levels of a
TCL chemical that are less than five times the
level of contamination noted in the blank, then
completely eliminate that chemical from the set of
sample results.
5.6 EVALUATION OF
TENTATIVELY IDENTIFIED
COMPOUNDS
Both the identity and reported concentration
of a tentatively identified compound (TIC) is
questionable (see the box on the next page for
background on TICs). Two options for addressing
TICs exist, depending on the relative number of
TICs compared to non-TICs.
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Page 5-18
5.6.1 WHEN FEW TICs ARE PRESENT
When only a few TICs are present compared
to the TAL and TCL chemicals, and no historical
or other site information indicates that either a
particular TIC may indeed be present at the site
(e.g., because it may be a by-product of a chemical
operation conducted when the site was active) or
that the estimated concentration may be very high
(i.e., the risk would be dominated by the TIC),
then generally do not include the TICs in the risk
assessment. Otherwise, follow the guidance
provided in the next subsection. Consult with the
RPM about omitting TICs from the quantitative
TENTATIVELY IDENTIFIED
COMPOUNDS
EPA's TCL may be a limited subset of the organic
compounds that could actually be encountered at a
particular site. Thus, although the CLP RAS requires
the laboratory to analyze samples only for compounds
on the TCL, the analysis of VOCs and SVQCs may
indicate the presence of additional organic compounds
not on the TCL. These additional compounds are
shown by "peaks" on the chromatograms. (A
chromatogram is a paper representation of the response
of the instrument to the presence of a compound.) The
CLP laboratory must attempt to identify the 30 highest
peaks (10 VOCs and 20 SVOCs) using computerized
searches of a library containing mass spectra (essentially
"fingerprints" for particular compounds). When the
mass spectra match to a certain degree, the compound
(or general class of compound) is named; however, the
assigned identity is in most cases highly uncertain.
These compounds are called tentatively identified
compounds (TICs).
The CLP SOW provides procedures to obtain a rough
estimate of concentration of TICs. These estimates,
however, are highly uncertain and could be orders of
magnitude higher or lower than the actual concentration.
For TICs, therefore, assigned identities may be
inaccurate, and quantitation is certainly inaccurate. Due
to these uncertainties, TIC information often is not
provided with data summaries from site investigations.
Additional sampling and analysis under SAS may reduce
the uncertainty associated with TICs and, therefore, TIC
information should be sought when it is absent from
data summaries.
risk assessment, and document reasons for
excluding TICs in the risk assessment report.
5.6.2 WHEN MANY TICs ARE PRESENT
If many TICs are present relative to the TAL
and TCL compounds identified, or if TIC
concentrations appear high or site information
indicates that TICs are indeed present, then
further evaluation of TICs is necessary. If
sufficient time is available, use SAS to confirm
the identity and to positively and reliably measure
the concentrations of TICs prior to their use in
the risk assessment. If SAS methods to identify
and measure TICs are unavailable, or if there is
insufficient time to use SAS, then the TICs should
be included as chemicals of potential concern in
the risk assessment and the uncertainty in both
identity and concentration should be noted (unless
information exists to indicate that the TICs are
not present).
5.7 COMPARISON OF SAMPLES
WITH BACKGROUND
In some cases, a comparison of sample
concentrations with background concentrations
(e.g., using the geometric mean concentrations of
the two data sets) is useful for identifying the
non-site-related chemicals that are found at or
near the site. If background risk might be a
concern, it should be calculated separately from
site-related risk. Often, however, the comparison
of samples with background is unnecessary because
of the low risk usually posed by the background
chemicals compared to site-related chemicals.
As discussed in Chapter 4, information
collected during the RI can provide information
on two types of background chemicals: (1)
naturally occurring chemicals that have not been
influenced by humans and (2) chemicals that are
present due to anthropogenic sources. Either type
of background chemical can be either localized or
ubiquitous.
Information on background chemicals may
have been obtained by the collection of site-
specific background samples and/or from other
sources (e.g., County Soil Conservation Service
surveys, United States Geological Survey [USGS]
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reports). As discussed in Chapter 4, background
concentrations should be from the site or the
vicinity of the site.
5.7.1 USE APPROPRIATE BACKGROUND
DATA
Background samples collected during the site
investigation should not be used if they were
obtained from areas influenced or potentially
influenced by the site. Instead, the literature
sources mentioned in the previous paragraph may
be consulted to determine background levels of
chemicals in the vicinity of the site. Care must be
taken in using literature sources, because the data
contained therein might represent nationwide
variation in a particular parameter rather than
variation typical of the geographic region or
geological setting in which the site is located. For
example, a literature source providing
concentrations of chemicals in ground water on a
national scale may show a wide range of
concentrations that is not representative of the
variation in concentrations that would be expected
at a particular site.
5.7.2 IDENTIFY STATISTICAL METHODS
In cases where background comparisons will
be made, any statistical methods that will be used
should be identified prior to the collection of
samples (see Chapter 4). Guidance documents
and reports that are available to aid in
background comparison are listed in Section 4.4.3.
Prior to conducting the steps discussed in the next
two subsections, the RPM should be consulted to
determine the type of comparison to be made, if
any. Both a justification for eliminating chemicals
based on a background comparison and a brief
overview of the type of comparison conducted
should be included in the risk assessment report.
5.7.3 COMPARE CHEMICAL
CONCENTRATIONS WITH
NATURALLY OCCURRING LEVELS
As defined previously, naturally occurring
levels are levels of chemicals that are present
under ambient conditions and that have not been
increased by anthropogenic sources. If inorganic
chemicals are present at the site at naturally
occurring levels, they may be eliminated from the
quantitative risk assessment. In some cases,
however, background concentrations may present
a significant risk, and, while cleanup may or may
not eliminate this risk, the background risk may
be an important site characteristic to those
exposed. The RPM will always have the option
to consider the risk posed by naturally occurring
background chemicals separately.
In general, comparison with naturally
occurring levels is applicable only to inorganic
chemicals, because the majority of organic
chemicals found at Superfund sites are not
naturally occurring (even though they may be
ubiquitous). The presence of organic chemicals
in background samples collected during a site
investigation actually may indicate that the sample
was collected in an area influenced by site
contamination and therefore does not qualify as
a true background sample. Such samples should
instead be included with other site samples in the
risk assessment. Unless a very strong case can be
made for the natural occurrence of an organic
chemical, do not eliminate it from the quantitative
risk assessment for this reason.
5.7.4 COMPARE CHEMICAL
CONCENTRATIONS WITH
ANTHROPOGENIC LEVELS
Anthropogenic levels are ambient
concentrations resulting from human (non-site)
sources. Localized anthropogenic background is
often caused by a point source such as a nearby
factory. Ubiquitous anthropogenic background is
often from nonpoint sources such as automobiles.
In general, do not eliminate anthropogenic
chemicals because, at many sites, it is extremely
difficult to conclusively show at this stage of the
site investigation that such chemicals are present
at the site due to operations not related to the
site or the surrounding area.
Often, anthropogenic background chemicals
can be identified and considered separately during
or at the end of the risk assessment. These
chemicals also can be omitted entirely from the
risk assessment, but, as discussed for natural
background, they may present a significant risk.
Omitting anthropogenic background chemicals
from the risk assessment could result in the loss
of important information for those potentially
exposed.
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Page 5-20
5.8 DEVELOPMENT OF A SET OF
CHEMICAL DATA AND
INFORMATION FOR USE IN
THE RISK ASSESSMENT
After the evaluation of data is complete as
specified in previous sections, a list of the samples
(by medium) is made that will be used to estimate
exposure concentrations, as discussed in Chapter
6 of this guidance. In addition, as shown in the
flowchart in Exhibit 5-1, a list of chemicals of
potential concern (also by medium) will be needed
for the quantitative risk assessment. This list
should include chemicals that were:
(1) positively detected in at least one CLP
sample (RAS or SAS) in a given
medium, including (a) chemicals with no
qualifiers attached (excluding samples
with unusually high detection limits), and
(b) chemicals with qualifiers attached
that indicate known identities but
unknown concentrations (e.g., J-qualified
data);
(2) detected at levels significantly elevated
above levels of the same chemicals
detected in associated blank samples;
(3) detected at levels significantly elevated
above naturally occurring levels of the
same chemicals;
(4) only tentatively identified but either may
be associated with the site based on
historical information or have been
confirmed by SAS; and/or
(5) transformation products of chemicals
demonstrated to be present.
Chemicals that were not detected in samples
from a given medium (i.e., non-detects) but that
may be present at the site also may be included
in the risk assessment if an evaluation of the risks
potentially present at the detection limit is
desired.
5.9 FURTHER REDUCTION IN
THE NUMBER OF
CHEMICALS (OPTIONAL)
For certain sites, the list of potentially site-
related chemicals remaining after quantitation
limits, qualifiers, blank contamination, and
background have been evaluated may be lengthy.
Carrying a large number of chemicals through a
quantitative risk assessment may be complex, and
it may consume significant amounts of time and
resources. The resulting risk assessment report,
with its large, unwieldy tables and text, may be
difficult to read and understand, and it may
distract from the dominant risks presented by the
site. In these cases, the procedures discussed in
this section - using chemical classes, frequency of
detection, essential nutrient information, and a
concentration-toxicity screen ~ may be used to
further reduce the number of chemicals of
potential concern in each medium.
If conducting a risk assessment on a large
number of chemicals is feasible (e.g., because of
adequate computer capability), then the
procedures presented in this section should not be
used. Rather, the most important chemicals (e.g.,
those presenting 99 percent of the risk) —
identified after the risk assessment — could be
presented in the main text of the report, and the
remaining chemicals could be presented in the
appendices.
5.9.1 CONDUCT INITIAL ACTIVITIES
Several activities must be conducted before
implementing any of the procedures described in
this section: (1) consult with the RPM; (2)
consider how the rationale for the procedure
should be documented; (3) examine historical
information on the site; (4) consider concentration
and toxicity of the chemicals; (5) examine the
mobility, persistence, and bioaccumulation
potential of the chemicals; (6) consider special
exposure routes; (7) consider the treatability of
the chemicals; (8) examine applicable or relevant
and appropriate requirements (ARARs); and (9)
examine the need for the procedures. These
activities are described below.
Consultation with the RPM. If a large
number of chemicals are of potential concern at
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Page 5-21
a particular site, the RPM should be consulted.
Approval by the RPM must be obtained prior to
the elimination of chemicals based on any of these
procedures. The concentration-toxicity screen in
particular may be needed only in rare instances.
Documentation of rationale. The rationale
for eliminating chemicals from the quantitative
risk assessment based on the procedures discussed
below must be clearly stated in the risk assessment
report. This documentation, and its possible
defense at a later date, could be fairly resource-
intensive. If a continuing need to justify this step
is expected, then any plans to eliminate chemicals
should be reconsidered.
Historical information. Chemicals reliably
associated with site activities based on historical
information generally should not be eliminated
from the quantitative risk assessment, even if the
results of the procedures given in this section
indicate that such an elimination is possible.
Concentration and toxicity. Certain aspects
of concentration and toxicity of the chemicals also
must be considered prior to eliminating chemicals
based on the results of these procedures. For
example, before eliminating potentially
carcinogenic chemicals, the weight-of-evidence
classification should be considered in conjunction
with the concentrations detected at the site. It
may be practical and conservative to retain a
chemical that was detected at low concentrations
if that chemical is a Group A carcinogen. (As
discussed in detail in Chapter 7, the weight-of-
evidence classification is an indication of the
quality and quantity of data underlying a
chemical's designation as a potential human
carcinogen.)
Mobility, persistence, and bioaccumulation.
Three factors that must be considered when
implementing these procedures are the mobility,
persistence, and bioaccumulation of the chemicals.
For example, a highly volatile (i.e., mobile)
chemical such as benzene, a long-lived (i.e.,
persistent) chemical such as dioxin, or a readily
taken-up and concentrated (i.e., bioaccumulated)
chemical such as DDT, probably should remain in
the risk assessment. These procedures do not
explicitly include a mobility, persistence, or
bioaccumulation component, and therefore the
risk assessor must pay special attention to these
factors.
Special exposure routes. For some chemicals,
certain exposure routes need to be considered
carefully before using these procedures. For
example, some chemicals are highly volatile and
may pose a significant inhalation risk due to the
home use of contaminated water, particularly for
showering. The procedures described in this
section may not account for exposure routes such
as this.
Treatability. Some chemicals are more
difficult to treat than others and as a result should
remain as chemicals of potential concern because
of their importance during the selection of
remedial alternatives.
ARARs. Chemicals with ARARs (including
those relevant to land ban compliance) usually are
not appropriate for exclusion from the quantitative
risk assessment based on the procedures in this
section. This may, however, depend in part on
how the chemicals' site concentrations in specific
media compare with their ARAR concentrations
for these media.
Need for procedures. Quantitative evaluation
of all chemicals of potential concern is the most
thorough approach in a risk assessment. In
addition, the time required to implement and
defend the selection procedures discussed in this
section may exceed the time needed to simply
carry all the chemicals of potential concern
through the risk assessment. Usually, carrying all
chemicals of potential concern through the risk
assessment will not be a difficult task, particularly
given the widespread use of computer spreadsheets
to calculate exposure concentrations of chemicals
and their associated risks. Although the tables
that result may indeed be large, computer
spreadsheets significantly increase the ability to
evaluate a number of chemicals in a relatively
short period of time. For these reasons, the
procedures discussed here may be needed only in
rare instances. As previously stated, the approval
of these procedures by the RPM must be obtained
prior to implementing any of these optional
screening procedures at a particular site.
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5.9.2 GROUP CHEMICALS BY CLASS
At times, toxicity values to be used in
characterizing risks are available only for certain
chemicals within a chemical class. For example,
of the polycyclic aromatic hydrocarbons (PAHs)
considered to be potential carcinogens, a slope
factor currently is available (i.e., as this manual
went to press) for benz(a)pyrene only. In these
cases, rather than eliminating the other chemicals
within the class from quantitative evaluation
because of a lack of toxicity values, it may be
useful to group data for such a class of chemicals
(e.g., according to structure-activity relationships
or other similarities) for consideration in later
sections of the risk assessment. For example, the
concentrations of only one group of chemicals
(e.g., carcinogenic PAHs) would be considered
rather than concentrations of each of the seven
carcinogenic PAHs currently on the TCL.
To group chemicals by class, concentrations
of chemicals within each class are summed
according to procedures discussed in Chapter 6 of
this guidance. Later in the risk assessment, this
chemical class concentration would be used to
characterize risk using toxicity values (i.e., RfDs
or slope factors) associated with one of the
chemicals in the particular class.
Three notes of caution when grouping
chemicals should be considered: (1) do not group
solely by toxicity characteristics; (2) do not group
all carcinogenic chemicals or all noncarcinogenic
chemicals without regard to structure-activity or
other chemical similarities; and (3) discuss in the
risk assessment report that grouping can produce
either over- or under-estimates of the true risk.
5.9.3 EVALUATE FREQUENCY OF
DETECTION
Chemicals that are infrequently detected may
be artifacts in the data due to sampling, analytical,
or other problems, and therefore may not be
related to site operations or disposal practices.
Consider the chemical as a candidate for
elimination from the quantitative risk assessment
if: (1) it is detected infrequently in one or
perhaps two environmental media, (2) it is not
detected in any other sampled media or at high
concentrations, and (3) there is no reason to
believe that the chemical may be present.
Available modeling results may indicate whether
monitoring data that show infrequently detected
chemicals are representative of only their sampling
locations or of broader areas. Because chemical
concentrations at a site are spatially variable, the
risk assessor can use modeling results to project
infrequently detected chemical concentrations over
broader areas when determining whether the
subject chemicals are relevant to the overall risk
assessment. Judicious use of modeling to
supplement available monitoring data often can
minimize the need for the RPM to resort to
arbitrarily setting limits on inclusion of
infrequently detected chemicals in the risk
assessment. Any detection frequency limit to be
used (e.g., five percent) should be approved by the
RPM prior to using this screen. If, for example,
a frequency of detection limit of five percent is
used, then at least 20 samples of a medium would
be needed (i.e., one detect in 20 samples equals
a five percent frequency of detection).
In addition to available monitoring data and
modeling results, the risk assessor will need to
consider other relevant factors (e.g., presence of
sensitive subpopulations) in recommending
appropriate site-specific limits on inclusion of
infrequently detected chemicals in the quantitative
risk assessment. For example, the risk assessor
should consider whether the chemical is expected
to be present based on historical data or any
other relevant information (e.g., known
degradation products of chemicals present at the
site, modeling results). Chemicals expected to be
present should not be eliminated. (See the
example of chemicals with similar transport and
fate characteristics in Section 5.3.5.)
The reported or modeled concentrations and
locations of chemicals should be examined to
check for hotspots, which may be especially
important for short-term exposures and which
therefore should not be eliminated from the risk
assessment. Always consider detection of
particular chemicals in all sampled media because
some media may be sources of contamination for
other media. For example, a chemical that is
infrequently detected in soil (a potential ground-
water contamination source) probably should not
be eliminated as a site contaminant if the same
chemical is frequently detected in ground water.
In addition, infrequently detected chemicals with
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Page 5-23
concentrations that greatly exceed reference
concentrations should not be eliminated.
5.9.4 EVALUATE ESSENTIAL NUTRIENTS
Chemicals that are (1) essential human
nutrients, (2) present at low concentrations (i.e.,
only slightly elevated above naturally occurring
levels), and (3) toxic only at very high doses (i.e.,
much higher than those that could be associated
with contact at the site) need not be considered
further in the quantitative risk assessment.
Examples of such chemicals are iron, magnesium,
calcium, potassium, and sodium.
Prior to eliminating such chemicals from the
risk assessment, they must be shown to be present
at levels that are not associated with adverse
health effects. The determination of acceptable
dietary levels for essential nutrients, however,
often is very difficult. Literature values
concerning acceptable dietary levels may conflict
and may change fairly often as new studies are
conducted. For example, arsenic - a potential
carcinogen ~ is considered by some scientists to
be an essential nutrient based on animal
experiments; however, acceptable dietary levels are
not well known (EPA 1988f). Therefore, arsenic
should be retained in the risk assessment, even
though it may be an essential nutrient at
undefined dietary levels. Another example of a
nutrient that is difficult to characterize is sodium.
Although an essential element in the diet, certain
levels of sodium may be associated with blood
pressure effects in some sensitive individuals
(although data indicating an association between
sodium in drinking water and hypertension are
inadequate [EPA 1987]).
Another problem with determining acceptable
dietary levels for essential nutrients is that
nutrient levels often are presented in the literature
as concentrations within the human body (e.g.,
blood levels). To identify an essential nutrient
concentration to be used for comparison with
concentrations in a particular medium at a site,
blood (or other tissue) levels of the chemical from
the literature must be converted to concentrations
in the media of concern for the site (e.g., soil,
drinking water).
For these reasons, it may not be possible to
compare essential nutrient concentrations with site
concentrations in order to eliminate essential
nutrient chemicals. In general, only essential
nutrients present at low concentrations (i.e., only
slightly elevated above background) should be
eliminated to help ensure that chemicals present
at potentially toxic concentrations are evaluated in
the quantitative risk assessment.
5.9.5 USE A CONCENTRATION-TOXICITY
SCREEN
The objective of this screening procedure is
to identify the chemicals in a particular medium
that -- based on concentration and toxicity - are
most likely to contribute significantly to risks
calculated for exposure scenarios involving that
medium, so that the risk assessment is focused on
the "most significant" chemicals.
Calculate individual chemical scores. Two
of the most important factors when determining
the potential effect of including a chemical in the
risk assessment are its measured concentrations at
the site and its toxicity. Therefore, in this
screening procedure, each chemical in a medium
is first scored according to its concentration and
toxicity to obtain a risk factor (see the box below).
Separate scores are calculated for each medium
being evaluated.
INDIVIDUAL CHEMICAL SCORES
Rij = (CV)(T»
where:
RIJ = risk factor for chemical i in
medium j;
Ctj =• concentration of chemical i in
medium j; and
T# = toxicity value for chemical i in
medium j (i.e., either the slope
factor or 1/RfD),
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Page 5-24
The units for the risk factor R,y depend on
the medium being screened. In general, the
absolute units do not matter, as long as units
among chemicals in a medium are the same. To
be conservative, the concentration used in the
above equation should be the maximum detected
concentration determined according to procedures
discussed in Chapter 6, and toxicity values should
be obtained in accordance with the procedures
discussed in Chapter 7.
Chemicals without toxicity values cannot be
screened using this procedure. Such chemicals
should always be discussed in the risk assessment
as chemicals of potential concern; they should not
be eliminated from the risk assessment. Guidance
concerning chemicals without toxicity values is
provided in Chapter 7.
For some chemicals, both oral and inhalation
toxicity values are available. In these cases, the
more conservative toxicity values (i.e., ones
yielding the larger risk factor when used in the
above equation) usually should be used. If only
one exposure route is likely for the medium being
evaluated, then the toxicity values corresponding
to that exposure route should be used.
Calculate total chemical scores (per medium).
Chemical-specific risk factors are summed to
obtain the total risk factor for all chemicals of
potential concern in a medium (see the box on
this page). A separate R; will be calculated for
carcinogenic and noncarcinogenic effects. The
ratio of the risk factor for each chemical to the
total risk factor (i.e., Rfy/R/) approximates the
relative risk for each chemical in medium j.
Eliminate chemicals. After carefully
considering the factors discussed previously in this
subsection, eliminate from the risk assessment
chemicals with R,y/Ry ratios that are very low
compared with the ratios of other chemicals in the
medium. The RPM may wish to specify a limit
for this ratio (e.g., 0.01; a lower fraction would be
needed if site risks are expected to be high). A
chemical that contributes less than the specified
fraction of the total risk factor for each medium
would not be considered further in the risk
assessment for that medium. Chemicals exceeding
the limit would be considered likely to contribute
TOTAL CHEMICAL SCORES
R
y * ;/ ...
where
Rj -total risk fector for medium j; and
R^ -f . . . -f Rfj =risk factors for
chemicals 1 through i in medium j.
significantly to risks, as calculated in subsequent
stages of the risk assessment. This screening
procedure could greatly reduce the number of
chemicals carried through a risk assessment,
because in many cases only a few chemicals
contribute significantly to the total risk for a
particular medium.
The risk factors developed in this screening
procedure are to be used only for potential
reduction of the number of chemicals carried
through the risk assessment and have no meaning
outside of the context of the screening procedure.
They should not be considered as a quantitative
measure of a chemical's toxicity or risk or as a
substitute for the risk assessment procedures
discussed in Chapters 6, 7, and 8 of this guidance.
5.10 SUMMARY AND
PRESENTATION OF DATA
The section of the risk assessment report
summarizing the results of the data collection and
evaluation should be titled "Identification of
Chemicals of Potential Concern" (see Chapter 9).
Information in this section should be presented in
ways that readily support the calculation of
exposure concentrations in the exposure
assessment portion of the risk assessment.
Exhibits 5-6 and 5-7 present examples of tables to
be included in this section of the risk assessment
report.
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EXHIBIT 5-6
EXAMPLE OF TABLE FORMAT FOR PRESENTING
CHEMICALS SAMPLED IN SPECIFIC MEDIA
Table X
Chemicals Sampled in Medium Y
(and in Operable Unit Z, if appropriate)
Name of Site, Location of Site
Chemical
Chemical A
* Chemical B
Frequency of
Detection0
3/25
25/25
Range
of Sample
Quantitation
Limits (units)
5 - 50
1 - 32
Range
of Detected
Concentrations
(units)
320 - 4600
16 - 72
Background
Levels
100 - 140
—
-- = Not available.
* Identified as a chemical of potential concern based on evaluation of data according to procedures
described in text of report.
a Number of samples in which the chemical was positively detected over the number of samples
available.
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Page 5-26
EXHIBIT 5-7
EXAMPLE OF TABLE FORMAT FOR SUMMARIZING
CHEMICALS OF POTENTIAL CONCERN IN
ALL MEDIA SAMPLED
Table W
Summary of Chemicals of
Potential Concern at Site X, Location Y
(and in Operable Unit Z, if appropriate)
Concentration
Chemical
Chemical A
Chemical B
Chemical C
Chemical D
Soils
(rag/kg)
5 - 1,100
0.5 - 64
2 - 12
Ground Water
(ug/L)
5 - 92
15 - 890
Surface Water
(ug/L)
2 - 30
50 - 11,000
Sediments Air
(ug/kg) (ug/m5)
100 - 45,000
0.1 - 940
— = Not available.
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Page 5-27
5.10.1 SUMMARIZE DATA COLLECTION
AND EVALUATION RESULTS IN TEXT
In the introduction for this section of the risk
assessment report, clearly discuss in bullet form
the steps involved in data evaluation. If the
optional screening procedure described in Section
5.9 was used in determining chemicals of potential
concern, these steps should be included in the
introduction. If both historical data and current
data were used in the data evaluation, state this
in the introduction. Any special site-specific
considerations in collecting and evaluating the
data should be mentioned. General uncertainties
concerning the quality associated with either the
collection or the analysis of samples should be
discussed so that the potential effects of these
uncertainties on later sections of the risk
assessment can be determined.
In the next part of the report, discuss the
samples from each medium selected for use in
quantitative risk assessment. Provide information
concerning the sample collection methods used
(e.g., grab, composite) as well as the number and
location of samples. If this information is
provided in the RI report, simply refer to the
appropriate sections. If any samples (e.g., field
screening/analytical samples) were excluded
specifically from the quantitative risk assessment
prior to evaluating the data, document this along
with reasons for the exclusion. Again, remember
that such samples, while not used in the
quantitative risk assessment, may be useful for
qualitative discussions and therefore should not be
entirely excluded from the risk assessment.
Discuss the data evaluation either by medium,
by medium within each operable unit (if the site
is sufficiently large to be divided into specific
operable units), or by discrete areas within each
medium in an operable unit. For each medium,
if several source areas with different types and
concentrations of chemicals exist, then the
medium-specific discussion for each source area
may be separate. Begin the discussion with those
media (e.g., wastes, soils) that are potential
sources of contamination for other media (e.g.,
ground water, surface water/sediments). If no
samples or data were available for a particular
medium, discuss this in the text. For soils data,
discuss surface soil results separately from those
of subsurface soils. Present ground-water results
by aquifer if more than one aquifer was sampled.
Discuss surface water/sediment results by the
specific surface water body sampled.
For each medium, identify in the report the
chemicals for which samples were analyzed, and
list the analytes that were detected in at least one
sample. If any detected chemicals were eliminated
from the quantitative risk assessment based on
evaluation of data (i.e., based on evaluation of
data quality, background comparisons, and the
optional screening procedures, if used), provide
reasons for the elimination in the text (e.g.,
chemical was detected in blanks at similar
concentrations to those detected in samples or
chemical was infrequently detected).
The final subsection of the text is a
discussion of general trends in the data results.
For example, the text may mention (1) whether
concentrations of chemicals of potential concern
in most media were close to the detection limits
or (2) trends concerning chemicals detected in
more than one medium or in more than one
operable unit at the site. In addition, the location
of hot spots should be discussed, as well as any
noticeable trends apparent from sampling results
at different times.
5.10.2 SUMMARIZE DATA COLLECTION
AND EVALUATION RESULTS IN
TABLES AND GRAPHICS
As shown in Exhibit 5-6, a separate table that
includes all chemicals detected in a medium can
be provided for each medium sampled at a
hazardous waste site or for each medium within
an operable unit at a site. Chemicals that have
been determined to be of potential concern based
on the data evaluation should be designated in the
table with an asterisk to the left of the chemical
name.
For each chemical, present the frequency of
detection in a certain medium (i.e., the number of
times a chemical was detected over the total
number of samples considered) and the range of
detected or quantified values in the samples. Do
not present the QL or similar indicator of a
minimum level (e.g., < 10 mg/L, ND) as the lower
end of the range; instead, the lower and upper
bound of the range should be the minimum and
maximum detected values, respectively. The range
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Page 5-28
of reported QLs obtained for each chemical in
various samples should be provided in a separate
column. Note that these QLs should be sample-
specific; CRQLs, MDLs, or other types of non-
sample-specific values should be provided only
when SQLs are not available. Note that the range
of QLs would not include any limit values (e.g.,
unusually high QLs) eliminated based on the
guidance in Section 5.3. Finally, naturally
occurring concentrations of chemicals used in
comparing sample concentrations may be provided
in a separate column. The source of these
naturally occurring levels should be provided in a
footnote. List the identity of the samples used in
determining concentrations presented in the table
in an appropriate footnote.
The final table in this section is a list of the
chemicals of potential concern presented by
medium at the site or by medium within each
operable unit at the site. A sample table format
is presented in Exhibit 5-7.
Another useful type of presentation of
chemical concentration data is the isopleth (not
shown). This graphic characterizes the monitored
or modeled concentrations of chemicals at a site
and illustrates the spatial pattern of
contamination.
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Page 5-29
ENDNOTE FOR CHAPTER 5
1. Note that the values in this example are for illustration purposes only. Many CRQLs and CRDLs are in the process of being
lowered, and the RfDs and slope factors may have changed.
-------
Page 5-30
REFERENCES FOR CHAPTER 5
Environmental Protection Agency (EPA). 1984. Methods for Organic Chemical Analysis of Municipal and Industrial Wastewater (EPA
600 Methods) as presented in 40 CFR Part 136, Guidelines Establishing Test Procedures for the Analysis of Pollutants Under
the Clean Water Act.
• Used to determine chemicals present in municipal and industrial wastewater as provided under the Clean Water Act.
Analytical methods for priority pollutants, including sample preparation, reagents, calibration procedures, QA/QC analytical
procedures, and calculations.
Environmental Protection Agency (EPA). 1986. Test Methods for Evaluating Solid Waste (SW-8461: Physical/Chemical Methods.
Office of Solid Waste.
• Provides analytical procedures to test solid waste to determine if it is a hazardous waste as defined under RCRA. Contains
information for collecting solid waste samples and for determining reactivity, corrosivity, ignitability, composition of waste,
and mobility of waste components.
Environmental Protection Agency (EPA). 1987. Drinking Water; Proposed Substitution of Contaminants and Proposed List of
Additional Substances Which May Require Regulation Under the Safe Drinking Water Act. 52 Federal Register 25720 (July 8,
1987).
Environmental Protection Agency (EPA). 1988a. User's Guide to the Contract Laboratory Program. Office of Emergency and
Remedial Response.
• Provides requirements and analytical procedures of the CLP protocols developed from technical caucus recommendations
for both organic and inorganic analysis. Contains information on CLP objectives and orientation, CLP structure, description
of analytical services, utilization of analytical services, auxiliary support services, and program quality assurance.
Environmental Protection Agency (EPA). 1988b. Contract Laboratory Program Statement of Work for Inorganics Analysis: Multi-
media, Multi-concentration. Office of Emergency and Remedial Response. SOW No. 788.
• Provides procedures required by EPA for analyzing hazardous waste disposal site samples (aqueous and solid) for inorganic
chemicals (25 elements plus cyanide). Contains analytical, document control, and quality assurance/quality control
procedures.
Environmental Protection Agency (EPA). 1988c. Contract Laboratory Program Statement of Work for Organics Analysis: Multi-
media, Multi-concentration. Office of Emergency and Remedial Response. SOW No. 288.
• Provides procedures required by EPA for analyzing aqueous and solid hazardous waste samples for 126 volatile, semi-
volatile, pesticide, and PCB chemicals. Contains analytical, document control, and quality assurance/quality control
procedures.
Environmental Protection Agency (EPA). 1988d. Laboratory Data Validation Functional Guidelines for Evaluating Inorganics Analysis.
Office of Emergency and Remedial Response.
• Provides guidance in laboratory data evaluation and validation for hazardous waste site samples analyzed under the EPA
CLP program. Aids in determining data problems and shortcomings and potential actions to be taken.
Environmental Protection Agency (EPA). 1988e. Laboratory Data Validation Functional Guidelines for Evaluating Organics Analysis
(Functional Guidelines for Organics). Office of Emergency and Remedial Response.
• Provides guidance in laboratory data evaluation and validation for hazardous waste site samples analyzed under the EPA
CLP program. Aids in determining data problems and shortcomings and potential actions to be taken.
Environmental Protection Agency (EPA). 1988f. Special Report on Ingested Inorganic Arsenic; Skin Cancer: Nutritional Essentiality.
Risk Assessment Forum. EPA 625/3-87/013.
• Technical report concerning the health effects of exposure to ingested arsenic. Includes epidemiologic studies suitable for
dose-response evaluation from Taiwan, Mexico, and Germany. Also includes discussions on pathological characteristics and
significance of arsenic-induced skin lesions, genotoxicity of arsenic, metabolism and distribution, dose-response estimates
for arsenic ingestion and arsenic as an essential nutrient.
-------
CHAPTER 6
EXPOSURE ASSESSMENT
FROM: ^
• Site discovery
• Preliminary
assessment
• Site inspection
\«NPUisting>
Toxicity
Assessment
Data i Data
Collection I Evaluation
Risk
Characterization
Exposure
TO:
•Selection of
remedy
• Remedial
design
• Remedial
. action
EXPOSURE ASSESSMENT
• Characterize physical setting
• Identify potentially exposed
populations
• Identify potential exposure
pathways
• Estimate exposure
concentrations
• Estimate chemical intakes
-------
CHAPTER 6
EXPOSURE ASSESSMENT
This chapter describes the procedures for
conducting an exposure assessment as part of the
baseline risk assessment process at Superfund
sites. The objective of the exposure assessment is
to estimate the type and magnitude of exposures
to the chemicals of potential concern that are
present at or migrating from a site. The results
of the exposure assessment are combined with
chemical-specific toxicity information to
characterize potential risks.
The procedures and information presented
in this chapter represent some new approaches to
exposure assessment as well as a synthesis of
currently available exposure assessment guidance
and information published by EPA. Throughout
this chapter, relevant exposure assessment
documents are referenced as sources of more
detailed information supporting the exposure
assessment process.
6.1 BACKGROUND
Exposure is defined as the contact of an
organism (humans in the case of health risk
assessment) with a chemical or physical agent
(EPA 1988a). The magnitude of exposure is
determined by measuring or estimating the
amount of an agent available at the exchange
boundaries (i.e., the lungs, gut, skin) during a
specified time period. Exposure assessment is the
determination or estimation (qualitative or
quantitative) of the magnitude, frequency,
duration, and route of exposure. Exposure
assessments may consider past, present, and future
exposures, using varying assessment techniques for
each phase. Estimates of current exposures can
be based on measurements or models of existing
conditions, those of future exposures can be based
on models of future conditions, and those of past
exposures can be based on measured or modeled
past concentrations or measured chemical
concentrations in tissues. Generally, Superfund
exposure assessments are concerned with current
and future exposures. If human monitoring is
planned to assess current or past exposures, the
Agency for Toxic Substances and Disease Registry
(ATSDR) should be consulted to take the lead in
conducting these studies and in assessing the
current health status of the people near the site
based on the monitoring results.
6.1.1 COMPONENTS OF AN
EXPOSURE ASSESSMENT
The general procedure for conducting an
exposure assessment is illustrated in Exhibit 6-1.
This procedure is based on EPA's published
Guidelines for Exposure Assessment (EPA 1986a)
and on other related guidance (EPA 1988a,
1988b). It is an adaptation of the generalized
exposure assessment process to the particular
needs of Superfund site risk assessments.
Although some exposure assessment activities may
have been started earlier (e.g., during RI/FS
scoping or even before the RI/FS process began),
the detailed exposure assessment process begins
after the chemical data have been collected and
ACRONYMS FOR CHAPTER 6
ATSDR = Agency for Toxic Substances and Disease
Regisuy
BCF = Bioconcentration Factor
GDI = Chronic Daily Intake
CEAM = Center for Exposure Assessment Modeling
NOAA = National Oceanographic and Atmospheric
Administration
NTGS = National Technical Guidance Studies
OAQPS = Office of Air Quality Planning and
Standards
RME = Reasonable Maximum Exposure
SDI ss Subchronic Daily Intake
SEAM « Superfund Exposure Assessment Manual
USGS = U.S. Geological Survey
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Page 6-2
DEFINITIONS FOR CHAPTER 6
Absorbed Dose. The amount of a substance penetrating the exchange boundaries of an organism after contact. Absorbed
dose is calculated from the intake and the absorption efficiency. It usually is expressed as mass of a substance absorbed
into the body per unit body weight per unit time (e.g., mg/kg-day).
Administered Dose. The mass of a substance given to an organism and in contact with an exchange boundary (e.g.,
gastrointestinal tract) per unit body weight per unit time (e.g., mg/kg-day).
Applied Dose. The amount Of a substance given to an organism, especially through dermal contact.
Chronic Daily Intake (CD II. Exposure expressed as mass of a substance contacted per unit body weight per unit time,
averaged over a long period of time (as a Superfund program guideline, seven years to a lifetime).
Contact Rate. Amount of medium (e.g., ground water, soil) contacted per unit time or event (e.g. liters of water ingested
per day).
Exposure. Contact of an organism with a chemical or physical agent. Exposure is quantified as the amount of the agent
available at the exchange boundaries of the organism (e.g., skin, lungs, gut) and available for absorption.
Exposure Assessment. The determination or estimation (qualitative or quantitative) of the magnitude, frequency, duration,
and route of exposure.
Exposure Event. An incident of contact with a chemical or physical agent. An exposure event can be defined by time (e.g.,
day, hour) or by the incident (e.g., eating a single meal of contaminated fish).
Exposure Pathway, 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 is included.
Exposure Point. A location of potential contact between an organism and a chemical or physical agent.
Exposure Route. The way a chemical or physical agent comes in contact with an organism (e.g., by ingestion, inhalation,
dermal contact).
Intake. A measure of exposure expressed as the mass of a substance in contact with the exchange boundary per unit body
weight per unit time (e.g., mg chemical/kg body weight-day). Also termed the normalized exposure rate; equivalent to
administered dose.
Lifetime Average Daily Intake. Exposure expressed as mass of a substance contacted per unit body weight per unit time,
averaged over a lifetime.
Subchronic Daily Intake fSDII. Exposure expressed as mass of a substance contacted per unit body weight per unit time,
averaged over a portion of a lifetime (as a Superfund program guideline, two weeks to seven years).
validated and the chemicals of potential concern
have been selected (see Chapter 5, Section 5.3.3).
The exposure assessment proceeds with the
following steps.
Step 1 -- Characterization of exposure setting
(Section 6.2). In this step, the assessor
characterizes the exposure setting with respect
to the general physical characteristics of the
site and the characteristics of the populations
on and near the site. Basic site
characteristics such as climate, vegetation,
ground-water hydrology, and the presence and
location of surface water are identified in this
step. Populations also are identified and are
described with respect to those characteristics
that influence exposure, such as location
relative to the site, activity patterns, and the
presence of sensitive subpopulations. This
step considers the characteristics of the
current population, as well as those of any
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Page 6-3
EXHIBIT 6-1
THE EXPOSURE ASSESSMENT PROCESS
STEP1
Characterize Exposure
Setting
• Physical Environment
• Potentially Exposed
Populations
STEP 3
Quantify Exposure
Exposure
Concentration
STEP 2
Identify Exposure
Pathways
• Chemical Source/
Release
• Exposure Point
• Exposure Route
Intake
Variables
Pathway-
Specific
Exposure
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Page 6-4
potential future populations that may differ
under an alternate land use.
Step 2 -- Identification of exposure pathways
(Section 6.3). In this step, the exposure
assessor identifies those pathways by which
the previously identified populations may be
exposed. Each exposure pathway describes
a unique mechanism by which a population
may be exposed to the chemicals at or
originating from the site. Exposure pathways
are identified based on consideration of the
sources, releases, types, and locations of
chemicals at the site; the likely environmental
fate (including persistence, partitioning,
transport, and intermedia transfer) of these
chemicals; and the location and activities of
the potentially exposed populations.
Exposure points (points of potential contact
with the chemical) and routes of exposure
(e.g., ingestion, inhalation) are identified for
each exposure pathway.
Step 3 -- Quantification of exposure (Section
6.4). In this step, the assessor quantifies the
magnitude, frequency and duration of
exposure for each pathway identified in Step
2. This step is most often conducted in two
stages: estimation of exposure concentrations
and calculation of intakes.
Estimation of exposure concentrations
(Section 6.5). In this part of step 3, the
exposure assessor determines the
concentration of chemicals that will be
contacted over the exposure period.
Exposure concentrations are estimated using
monitoring data and/or chemical transport
and environmental fate models. Modeling
may be used to estimate future chemical
concentrations in media that are currently
contaminated or that may become
contaminated, and current concentrations in
media and/or at locations for which there are
no monitoring data.
Calculation of intakes (Section 6.6). In this
part of step 3, the exposure assessor
calculates chemical-specific exposures for each
exposure pathway identified in Step 2.
Exposure estimates are expressed in terms
of the mass of substance in contact with the
body per unit body weight per unit time (e.g.,
mg chemical per kg body weight per day, also
expressed as mg/kg-day). These exposure
estimates are termed "intakes" (for the
purposes of this manual) and represent the
normalized exposure rate. Several terms
common in other EPA documents and the
literature are equivalent or related to intake
(see box on this page and definitions box on
page 6-2). Chemical intakes are calculated
using equations that include variables for
exposure concentration, contact rate, exposure
frequency, exposure duration, body weight,
and exposure averaging time. The values of
some of these variables depend on site
conditions and the characteristics of the
potentially exposed population.
TERMS EQUIVALENT OR
RELATED TO INTAKE
Normalized Exposure Rate. Equivalent to intake
Administered Dose. Equivalent to intake
Applied Dose. Equivalent to intake
Absorbed Dose. Equivalent to intake multiplied by
an absorption factor
After intakes have been estimated, they are
organized by population, as appropriate (Section
6.7). Then, the sources of uncertainty (e.g.,
variability in analytical data, modeling results,
parameter assumptions) and their effect on the
exposure estimates are evaluated and summarized
(Section 6.8). This information on uncertainty is
important to site decision-makers who must
evaluate the results of the exposure and risk
assessment and make decisions regarding the
degree of remediation required at a site. The
exposure assessment concludes with a summary of
the estimated intakes for each pathway evaluated
(Section 6.9).
6.1.2 REASONABLE MAXIMUM EXPOSURE
Actions at Superfund sites should be based
on an estimate of the reasonable maximum
exposure (RME) expected to occur under both
current and future land-use conditions. The
reasonable maximum exposure is defined here as
-------
Page 6-5
the highest exposure that is reasonably expected
to occur at a site. RMEs are estimated for
individual pathways. If a population is exposed
via more than one pathway, the combination of
exposures across pathways a.lso must represent an
RME.
Estimates of the reasonable maximum
exposure necessarily involve the use of
professional judgment. This chapter provides
guidance for determining the RME at a site and
identifies some exposure variable values
appropriate for use in this determination. The
specific values identified should be regarded as
general recommendations, and could change based
on site-specific information and the particular
needs of the EPA remedial project manager
(RPM). Therefore, these recommendations should
be used in conjunction with input from the RPM
responsible for the site.
In the past, exposures generally were
estimated for an average and an upper-bound
exposure case, instead of a single exposure case
(for both current and future land use) as
recommended here. The advantage of the two
case approach is that the resulting range of
exposures provides some measure of the
uncertainty surrounding these estimates. The
disadvantage of this approach is that the upper-
bound estimate of exposure may be above the
range of possible exposures, whereas the average
estimate is lower than exposures potentially
experienced by much of the population. The
intent of the RME is to estimate a conservative
exposure case (i.e., well above the average case)
that is still within the range of possible exposures.
Uncertainty is still evaluated under this approach.
However, instead of combining many sources of
uncertainty into average and upper-bound
exposure estimates, the variation in individual
exposure variables is used to evaluate uncertainty
(See Section 6.8). In this way, the variables
contributing most to uncertainty in the exposure
estimate are more easily identified.
6.2 STEP 1: CHARACTERI-
ZATION OF EXPOSURE
SETTING
The first step in evaluating exposure at
Superfund sites is to characterize the site with
respect to its physical characteristics as well as
those of the human populations on and near the
site. The output of this step is a qualitative
evaluation of the site and surrounding populations
with respect to those characteristics that influence
exposure. All information gathered during this
step will support the identification of exposure
pathways in Step 2. In addition, the information
on the potentially exposed populations will be
used in Step 3 to determine the values of some
intake variables.
6.2.1 CHARACTERIZE PHYSICAL
SETTING
Characterize the exposure setting with respect
to the general physical characteristics of the site.
Important site characteristics include the
following:
• climate (e.g., temperature,
precipitation);
• meteorology (e.g., wind speed and
direction);
• geologic setting (e.g., location and
characterization of underlying strata);
• vegetation (e.g., unvegetated, forested,
grassy);
• soil type (e.g., sandy, organic, acid,
basic);
• ground-water hydrology (e.g., depth,
direction and type of flow); and
• location and description of surface water
(e.g., type, flow rates, salinity).
Sources of this information include site
descriptions and data from the preliminary
assessment (PA), site inspection (SI), and remedial
investigation (RI) reports. Other sources include
county soil surveys, wetlands maps, aerial
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Page 6-6
photographs, and reports by the National
Oceanographic and Atmospheric Association
(NOAA) and the U.S. Geological Survey (USGS).
The assessor also should consult with appropriate
technical experts (e.g., hydrogeologists, air
modelers) as needed to characterize the site.
6.2.2 CHARACTERIZE POTENTIALLY
EXPOSED POPULATIONS
Characterize the populations on or near the
site with respect to location relative to the site,
activity patterns, and the presence of sensitive
subgroups.
Determine location of current populations
relative to the site. Determine the distance and
direction of potentially exposed populations from
the site. Identify those populations that are
closest to or actually living on the site and that,
therefore, may have the greatest potential for
exposure. Be sure to include potentially exposed
distant populations, such as public water supply
consumers and distant consumers of fish or
shellfish or agricultural products from the site
area. Also include populations that could be
exposed in the future to chemicals that have
migrated from the site. Potential sources of this
information include:
• site visit;
• other information gathered as part of
the SI or during the initial stages of the
Rl;
• population surveys conducted near the
site;
• topographic, land use, housing or other
maps; and
• recreational and commercial fisheries
data.
Determine current land use. Characterize
the activities and activity patterns of the
potentially exposed population. The following
land use categories will be applicable most often
at Superfund sites:
• residential;
• commercial/industrial; and
• recreational.
Determine the current land use or uses of
the site and surrounding area. The best source
of this information is a site visit. Look for
homes, playgrounds, parks, businesses, industries,
or other land uses on or in the vicinity of the site.
Other sources on local land use include:
• zoning maps;
• state or local zoning or other land use-
related laws and regulations;
• data from the U.S. Bureau of the
Census;
• topographic, land use, housing or other
maps; and
• aerial photographs.
Some land uses at a site may not fit neatly
into one of the three land use categories and
other land use classifications may be more
appropriate (e.g., agricultural land use). At some
sites it may be most appropriate to have more
than one land use category.
After defining the land use(s) for a site,
identify human activities and activity patterns
associated with each land use. This is basically
a "common sense" evaluation and is not based on
any specific data sources, but rather on a general
understanding of what activities occur in
residential, business, or recreational areas.
Characterize activity patterns by doing the
following.
• Determine the percent of time that the
potentially exposed population(s) spend
in the potentially contaminated area.
For example, if the potentially exposed
population is commercial or industrial,
a reasonable maximum daily exposure
period is likely to be 8 hours (a typical
work day). Conversely, if the population
is residential, a maximum daily exposure
period of 24 hours is possible.
• Determine if activities occur primarily
indoors, outdoors, or both. For example,
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Page 6-7
office workers may spend all their time
indoors, whereas construction workers
may spend all their time outdoors.
• Determine how activities change with
the seasons. For exampje, some
outdoor, summertime recreational
activities (e.g., swimming, fishing) will
occur less frequently or not at all during
the winter months. Similarly, children
are likely to play outdoors less frequently
and with more clothing during the winter
months.
• Determine if the site itself may be used
by local populations, particularly if access
to the site is not restricted or otherwise
limited (e.g., by distance). For example,
children living in the area could play
onsite, and local residents could hunt or
hike onsite.
• Identify any site-specific population
characteristics that might influence
exposure. For example, if the site is
located near major commercial or
recreational fisheries or shellfisheries,
the potentially exposed population is
likely to eat more locally-caught fish and
shellfish than populations located inland.
Determine future land use. Determine if any
activities associated with a current land use are
likely to be different under an alternate future
land use. For example, if ground water is not
currently used in the area of the site as a source
of drinking water but is of potable quality, future
use of ground water as drinking water would be
possible. Also determine if land use of the site
itself could change in the future. For example, if
a site is currently classified as industrial,
determine if it could possibly be used for
residential or recreational purposes in the future.
Because residential land use is most often
associated with the greatest exposures, it is
generally the most conservative choice to make
when deciding what type of alternate land use
may occur in the future. However, an assumption
of future residential land use may not be
justifiable if the probability that the site will
support residential use in the future is exceedingly
small.
Therefore, determine possible alternate future
land uses based on available information and
professional judgment. Evaluate pertinent
information sources, including (as available):
• master plans (city or county projections
of future land use);
• Bureau of the Census projections; and
• established land use trends in the general
area and the area immediately
surrounding the site (use Census Bureau
or state or local reports, or use general
historical accounts of the area).
Note that while these sources provide potentially
useful information, they should not be interpreted
as providing proof that a certain land use will or
will not occur.
Assume future residential land use if it seems
possible based on the evaluation of the available
information. For example, if the site is currently
industrial but is located near residential areas in
an urban area, future residential land use may be
a reasonable possibility. If the site is industrial
and is located in a very rural area with a low
population density and projected low growth,
future residential use would probably be unlikely.
In this case, a more likely alternate future land
use may be recreational. At some sites, it may be
most reasonable to assume that the land use will
not change in the future.
There are no hard-and-fast rules by which to
determine alternate future land use. The use of
professional judgment in this step is critical. Be
sure to consult with the RPM about any decision
regarding alternate future land use. Support the
selection of any alternate land use with a logical,
reasonable argument in the exposure assessment
chapter of the risk assessment report. Also
include a qualitative statement of the likelihood
of the future land use occurring.
Identify subpopulations of potential concern.
Review information on the site area to determine
if any subpopulations may be at increased risk
from chemical exposures due to increased
sensitivity, behavior patterns that may result in
high exposure, and/or current or past exposures
from other sources. Subpopulations that may be
-------
Page 6-8
more sensitive to chemical exposures include
infants and children, elderly people, pregnant and
nursing women, and people with chronic illnesses.
Those potentially at higher risk due to behavior
patterns include children, who are more likely to
contact soil, and persons who may eat large
amounts of locally caught fish or locally grown
produce (e.g., home-grown vegetables).
Subpopulations at higher risk due to exposures
from other sources include individuals exposed to
chemicals during occupational activities and
individuals living in industrial areas.
To identify subpopulations of potential
concern in the site area, determine locations of
schools, day care centers, hospitals, nursing homes,
retirement communities, residential areas with
children, important commercial or recreational
fisheries near the site, and major industries
potentially involving chemical exposures. Use
local census data and information from local
public health officials for this determination.
6.3 STEP 2: IDENTIFICATION
OF EXPOSURE PATHWAYS
This section describes an approach for
identifying potential human exposure pathways at
a Superfund site. An exposure pathway describes
the course a chemical or physical agent takes from
the source to the exposed individual. An exposure
pathway analysis links the sources, locations, and
types of environmental releases with population
locations and activity patterns to determine the
significant pathways of human exposure.
An exposure pathway generally consists of
four elements: (1) a source and mechanism of
chemical release, (2) a retention or transport
medium (or media in cases involving media
transfer of chemicals), (3) a point of potential
human contact with the contaminated medium
(referred to as the exposure point), and (4) an
exposure route (e.g., ingestion) at the contact
point. A medium contaminated as a result of a
past release can be a contaminant source for other
media (e.g., soil contaminated from a previous
spill could be a contaminant source for ground
water or surface water). In some cases, the source
itself (i.e., a tank, contaminated soil) is the
exposure point, without a release to any other
medium. In these latter cases, an exposure
pathway consists of (1) a source, (2) an exposure
point, and (3) an exposure route. Exhibit 6-2
illustrates the basic elements of each type of
exposure pathway.
The following sections describe the basic
analytical process for identifying exposure
pathways at Superfund sites and for selecting
pathways for quantitative analysis. The pathway
analysis described below is meant to be a
qualitative evaluation of pertinent site and
chemical information, and not a rigorous
quantitative evaluation of factors such as source
strength, release rates, and chemical fate and
transport. Such factors are considered later in
the exposure assessment during the quantitative
determination of exposure concentrations (Section
6.5).
6.3.1 IDENTIFY SOURCES AND
RECEIVING MEDIA
To determine possible release sources for a
site in the absence of remedial action, use all
available site descriptions and data from the PA,
SI, and RI reports. Identify potential release
mechanisms and receiving media for past, current,
and future releases. Exhibit 6-3 lists some typical
release sources, release mechanisms, and receiving
media at Superfund sites. Use monitoring data in
conjunction with information on source locations
to support the analysis of past, continuing, or
threatened releases. For example, soil
contamination near an old tank would suggest the
tank (source) ruptured or leaked (release
mechanism) to the ground (receiving media). Be
sure to note any source that could be an exposure
point in addition to a release source (e.g., open
barrels or tanks, surface waste piles or lagoons,
contaminated soil).
Map the suspected source areas and the
extent of contamination using the available
information and monitoring data. As an aid in
evaluating air sources and releases, Volumes I and
II of the National Technical Guidance Studies
(NTGS; EPA 1989a,b) should be consulted.
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Page 6-9
EXHIBIT 6-2
ILLUSTRATION OF EXPOSURE
PATHWAYS
Prevailing Wind Direction
Exposure
Point
Transport
Medium (Air)
Release Mechanism
(Volatilization)
Inhalation
Exposure
Route
'V
Release
Mechanism
(Spill)
Exposure
Medium
(Soil)
Release Mechanism
(Site Leaching)
Transport Medium
(Ground Water)
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Page 6-10
EXHIBIT 6-3
COMMON CHEMICAL RELEASE SOURCES AT
SITES IN THE ABSENCE OF REMEDIAL ACTION
Receiving
Medium
Release
Mechanism
Release Source
Air
Volatilization
Fugitive dust
generation
Surface wastes — lagoons,
ponds, pits, spills
Contaminated surface water
Contaminated surface soil
Contaminated wetlands
Leaking drums
Contaminated surface soil
Waste piles
Surface water
Surface runoff
Episodic overland
flow
Ground-water
seepage
Contaminated surface soil
Lagoon overflow
Spills, leaking containers
Contaminated ground water
Ground water
Leaching
Surface or buried wastes
Contaminated soil
Soil
Leaching
Surface runoff
Episodic overland
flow
Fugitive dust
generation/
deposition
Tracking
Surface or buried wastes
Contaminated surface soil
Lagoon overflow
Spills, leaking containers
Contaminated surface soil
Waste piles
Contaminated surface soil
Sediment
Biota
Surface runoff,
Episodic overland
flow
Ground-water
seepage
Leaching
Uptake
(direct contact,
ingestion, inhalation)
Surface wastes — lagoons,
ponds, pits, spills
Contaminated surface soil
Contaminated ground water
Surface or buried wastes
Contaminated soil
Contaminated soil, surface
water, sediment, ground
water or air
Other biota
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Page 6-11
6.3.2 EVALUATE FATE AND TRANSPORT
IN RELEASE MEDIA
Evaluate the fate and transport of the
chemicals to predict future exposures and to help
link sources with currently contaminated media.
The fate and transport analysis conducted at this
stage of the exposure assessment is not meant to
result in a quantitative evaluation of media-
specific chemical concentrations. Rather, the
intent is to identify media that are receiving or
may receive site-related chemicals. At this stage,
the assessor should answer the questions: What
chemicals occur in the sources at the site and in
the environment? In what media (onsite and
offsite) do they occur now? In what media and
at what location may they occur in the future?
Screening-level analyses using available data and
simplified calculations or analytical models may
assist in this qualitative evaluation.
After a chemical is released to the
environment it may be:
• transported (e.g., convected downstream
in water or on suspended sediment or
through the atmosphere);
• physically transformed (e.g., volatilization,
precipitation);
• chemically transformed (e.g., photolysis,
hydrolysis, oxidation, reduction, etc.);
• biologically transformed (e.g,
biodegradation); and/or
• accumulated in one or more media
(including the receiving medium).
To determine the fate of the chemicals of
potential concern at a particular site, obtain
information on their physical/chemical and
environmental fate properties. Use computer data
bases (e.g., SRC's Environmental Fate,
CHEMFATE, and BIODEG data bases; BIOSIS;
AQUIRE) and the open literature as necessary
as sources for up-to-date information on the
physical/chemical and fate properties of the
chemicals of potential concern. Exhibit 6-4 lists
some important chemical-specific fate parameters
and briefly describes how these can be used to
evaluate a chemical's environmental fate.
Also consider site-specific characteristics
(identified in Section 6.2.1) that may influence
fate and transport. For example, soil
characteristics such as moisture content, organic
carbon content, and cation exchange capacity can
greatly influence the movement of many chemicals.
A high water table may increase the probability of
leaching of chemicals in soil to ground water.
Use all applicable chemical and site-specific
information to evaluate transport within and
between media and retention or accumulation
within a single medium. Use monitoring data to
identify media that are contaminated now and the
fate pathway analysis to identify media that may
be contaminated now (for media not sampled) or
in the future. Exhibit 6-5 presents some
important questions to consider when developing
these pathways. Exhibit 6-6 presents a series of
flow charts useful when evaluating the fate and
transport of chemicals at a site.
6.3.3 IDENTIFY EXPOSURE POINTS AND
EXPOSURE ROUTES
After contaminated or potentially
contaminated media have been identified, identify
exposure points by determining if and where any
of the potentially exposed populations (identified
in Step 1) can contact these media. Consider
population locations and activity patterns in the
area, including those of subgroups that may be of
particular concern. Any point of potential contact
with a contaminated medium is an exposure point.
Try to identify those exposure points where the
concentration that will be contacted is the
greatest. Therefore, consider including any
contaminated media or sources onsite as a
potential exposure point if the site is currently
used, if access to the site under current conditions
is not restricted or otherwise limited (e.g., by
distance), or if contact is possible under an
alternate future land use. For potential offsite
exposures, the highest exposure concentrations
often will be at the points closest to and
downgradient or downwind of the site. In some
cases, highest concentrations may be encountered
at points distant from the site. For example, site-
related chemicals may be transported and
deposited in a distant water body where they may
be subsequently bioconcentrated by aquatic
organisms.
-------
Page 6-12
EXHIBIT 6-4
IMPORTANT PHYSICAL/CHEMICAL AND
ENVIRONMENTAL FATE PARAMETERS
Koc provides a measure of the extent of chemical partitioning between organic carbon and water at
equilibrium. The higher the Koc, the more likely a chemical is to bind to soil or sediment than to
remain in water.
Kd provides a soil or sediment-specific measure of the extent of chemical partitioning between soil
or sediment and water, unadjusted for dependence upon organic carbon. To adjust for the
fraction of organic carbon present in soil or sediment (f^), use Kd = K^xfoc. The higher the Kd,
the more likely a chemical is to bind to soil or sediment than to remain in water.
K^ provides a measure of the extent of chemical partitioning between water and octanol at
equilibrium. The greater the K ow the more likely a chemical is to partition to octanol than to
remain in water. Octanol is used as a surrogate for lipids (fat), and Kow can be used to predict
bioconcentration in aquatic organisms.
Solubility is an upper limit on a chemical's dissolved concentration in water at a specified temperature.
Aqueous concentrations in excess of solubility may indicate sorption onto sediments, the
presence of solubilizing chemicals such as solvents, or the presence of a non-aqueous phase
liquid.
Henry's Law Constant provides a measure of the extent of chemical partitioning between air and water at
equilibrium. The higher the Henry's Law constant, the more likely a chemical is to volatilize
than to remain in the water.
Vapor Pressure is the pressure exerted by a chemical vapor in equilibrium with its solid or liquid form at
any given temperature. It is used to calculate the rate of volatilization of a pure substance from a
surface or in estimating a Henry's Law constant for chemicals with low water solubility. The
higher the vapor pressure, the more likely a chemical is to exist in a gaseous state.
Diffusivity describes the movement of a molecule in a liquid or gas medium as a result of differences in
concentration. It is used to calculate the dispersive component of chemical transport. The
higher the diffusivity, the more likely a chemical is to move in response to concentration
gradients.
Bioconcentration Factor (BCF) provides a measure of the extent of chemical partitioning at equilibrium
between a biological medium such as fish tissue or plant tissue and an external medium such as
water. The higher the DCF. the greater the accumulation in living tissue is likely to be.
Media-specific Half-life provides a relative measure of the persistence of a chemical in a given medium,
although actual values can vary greatly depending on site-specific conditions. The greater the
half-life, the more persistent a chemical is likely to be.
-------
Page 6-13
EXHIBIT 6-5
IMPORTANT CONSIDERATIONS FOR DETERMINING
THE ENVIRONMENTAL FATE AND TRANSPORT
OF THE CHEMICALS OF POTENTIAL CONCERN
AT A SUPERFUND SITE
• What are the principal mechanisms for change or removal in each of the environmental
media?
• How does the chemical behave in air, water, soil, and biological media? Does it
bioaccumulate or biodegrade? Is it absorbed or taken up by plants?
• Does the agent react with other compounds in the environment?
• Is there intermedia transfer? What are the mechanisms for intermedia transfer? What
are the rates of the intermedia transfer or reaction mechanism?
How long might the chemical remain in each environmental medium? How does its
concentration change with time in each medium?
• What are the products into which the agent might degrade or change in the environment?
Are these products potentially of concern?
• Is a steady-state concentration distribution in the environment or in specific segments of
the environment achieved?
-------
Page 6-14
EXHIBIT 6-6
FLOW CHART FOR
FATE AND TRANSPORT ASSESSMENTS
Environmental fate and transport assessment: atmosphere
Contaminant Release
Potential
Volatilization of
Contaminants
from Site
Consider Direction
and Rate of
Contaminant
Migration within
Air; Major
Mechanisms: Wind
Currents,
Dispersion
Potential Release of
Fugitive Dust/
Contaminated
Particles from Site
Consider Direction and
Distance of Particulate
Movement with Wind
Currents; Major
Mechanisms: Wind Speed,
Particle Size, Gravitational
Settling, Precipitation
Could
Contaminants
Potentially Reach
Agricultural,
Hunting or
Fishing Areas?
No
Yes
Consider Transfer
of Contaminants to
Plants or Animals
Consumed by Hu-
mans; Assess Fate
in these Media
Determine
Probable
Boundaries of
Elevated
Concentrations
Identify
Populations
Directly Exposed
to Atmospheric
Contaminants
Could
Contaminants
Potentially
Reach Surface
Water?
Consider Transfer
of Contaminants
to Surface Water;
Assess Fate in
this Medium
Source: Adapted from EPA 1988b.
(continued)
-------
Page 6-15
EXHIBIT 6-6 (continued)
FLOW CHART FOR
FATE AND TRANSPORT ASSESSMENTS
Environmental fate and transport assessment: surface water and sediment
Contaminant Release
I
Release to Surface Water 1
! 1
Consider Direction and Rate of Conta
Migration Within Waterbody
Assess Distance Downstream, or Areas of Lake
Major Mechanisms: Currents in Affected Rive
Dispersion in Impoundments: Tidal Currents s
Estuaries; Partitioning to Sedime
minant
s and Estuaries
nd Flushing in
lit
_t
Estimate Surface Water Contaminant Concentrations
Major Factors: Source Release Strength, Dilution Volume
r~
Could Exchange
of Water
Between Surface
Water and
Ground Water
be Significant?
f
No 1
<
r
Yes
i
Consider
Transfer of
Contaminants
to Ground
Water; Assess
Fate in this
Medium
*
Could Water be
Used for Irriga-
tion or Watering
Livestock, or
Does Waterbody
Support
Commercial or
Sport Fish
Population?
t
No 1
'
r
Yes
i
\
Consider
Transfer of
Contaminants to
Plants or
Animals
Consumed by
Humans; Assess
Fate in these
Media
*
Is Contaminant
Volatile?
• <">
ir
Consider
Sediment as a
, Source of
Surface Water
Contaminants
t t
No Yes
i 1
Identify Human
Populations
Directly
Exposed to
Surface
Water
Consider
Transfer of
Contaminants
to Air;
Assess Fate
in this Medium
Estimate
ncentrations
i Sediment
1
Identify Human
Populations
Directly
Exposed to
Sediment
Source: Adapted from EPA I988b.
(continued)
-------
Page 6-16
EXHIBIT 6-6 (continued)
FLOW CHART FOR
FATE AND TRANSPORT ASSESSMENTS
Environmental fate and transport assessment: soils and ground water
Contaminant Release
1
Release to Soils at or
Surrounding the Site
Consider Rate of Contaminant Percolation Through Unsaturated
Soils Rased on Soil Permeabilities, Water or Liquid Recharge Rates
Release to Ground
Water Beneath Site
Could
Contaminants
Potentially
Reach Ground
Water?
Does
Contaminated
Soil Support
Edible Species?
Are Contaminants Vola-
tile? Are Contaminants
in Fine Particle Form or
Sorbed to Particulates?
I I
Consider Direction and Rate of
Ground Water Flow Using
Available Hydrogeologic Data,
or by Assuming These Will Ap-
proximate Surface Topography
Ves
No
Yes
No
Yes
Consider
Transfer of
Contaminants
to Surface
Water; Assess
Fate in this
Medium
Yes
Is Well Water Used for
Irrigation or for Watering
Livestock, or Could it be?
Identify
Human
Populations
Directly
Exposed to
Well Water
JL
No
Consider Transfer of Contami-
nants to Plants or Animals
Consumed by Humans;
Assess Fate in these Media
No
Yes
Could Contaminants
Reach A Surface
Waterbody?
* t
Could Contaminants
Reach Any Wells
Located
Downgradient?
t +
Is Plume Sufficiently Near
Ground Surface to Allow
Direct Uptake of Contami-
nated Ground Water by
Plants or Animals?
No
Yes
Consider Transfer of
Contaminants to
Atmosphere: Assess
Fate in this Medium
Identify Human
Populations
Directly Exposed
to Soils
Source: Adapted from EPA 1988b.
-------
Page 6-17
After determining exposure points, identify
probable exposure routes (i.e., ingestion,
inhalation, dermal contact) based on the media
contaminated and the anticipated activities at the
exposure points. In some instances, an exposure
point may exist but an exposure route may not
(e.g., a person touches contaminated soil but is
wearing gloves). Exhibit 6-7 presents a
population/exposure route matrix that can be used
in determining potential exposure routes at a site.
6.3.4 INTEGRATE INFORMATION ON
SOURCES, RELEASES, FATE AND
TRANSPORT, EXPOSURE POINTS,
AND EXPOSURE ROUTES INTO
EXPOSURE PATHWAYS
Assemble the information developed in the
previous three steps and determine the complete
exposure pathways that exist for the site. A
pathway is complete if there is (1) a source or
chemical release from a source, (2) an exposure
point where contact can occur, and (3) an
exposure route by which contact can occur.
Otherwise, the pathway is incomplete, such as the
situation where there is a source releasing to air
but there are no nearby people. If available from
ATSDR, human monitoring data indicating
chemical accumulation or chemical-related effects
in the site area can be used as evidence to
support conclusions about which exposure
pathways are complete; however, negative data
from such studies should not be used to conclude
that a pathway is incomplete.
From all complete exposure pathways at a
site, select those pathways that will be evaluated
further in the exposure assessment. If exposure
to a sensitive subpopulation is possible, select that
pathway for quantitative evaluation. All pathways
should be selected for further evaluation unless
there is sound justification (e.g., based on the
results of a screening analysis) to eliminate a
pathway from detailed analysis. Such a
justification could be based on one of the
following:
• the exposure resulting from the pathway
is much less than that from another
pathway involving the same medium at
the same exposure point;
• the potential magnitude of exposure
from a pathway is low; or
• the probability of the exposure occurring
is very low and the risks associated with
the occurrence are not high (if a
pathway has catastrophic consequences,
it should be selected for evaluation even
if its probability of occurrence is very
low).
Use professional judgment and experience to
make these decisions. Before deciding to exclude
a pathway from quantitative analysis, consult with
the RPM. If a pathway is excluded from further
analysis, clearly document the reasons for the
decision in the exposure assessment section of the
risk assessment report.
For some complete pathways it may not be
possible to quantify exposures in the subsequent
steps of the analysis because of a lack of data on
which to base estimates of chemical release,
environmental concentration, or human intake.
Available modeling results should complement and
supplement the available monitoring data to
minimize such problems. However, uncertainties
associated with the modeling results may be too
large to justify quantitative exposure assessment
in the absence of monitoring data to validate the
modeling results. These pathways should
nevertheless be carried through the exposure
assessment so that risks can be qualitatively
evaluated or so that this information can be
considered during the uncertainty analysis of the
results of the exposure assessment (see Section
6.8) and the risk assessment (see Chapter 8).
6.3.5 SUMMARIZE INFORMATION ON
ALL COMPLETE EXPOSURE
PATHWAYS
Summarize pertinent information on all
complete exposure pathways at the site by
identifying potentially exposed populations,
exposure media, exposure points, and exposure
routes. Also note if the pathway has been
selected for quantitative evaluation; summarize the
justification if a pathway has been excluded.
Summarize pathways for current land use and any
alternate future land use separately. This
summary information is useful for defining the
scope of the next step (quantification of exposure)
-------
Page 6-18
EXHIBIT 6-7
MATRIX OF POTENTIAL EXPOSURE ROUTES
Exposure Medium/ Residential Commercial/Industrial Recreational
Exposure Route Population Population Population
Ground Water
Ingestion
Dermal Contact
Surface Water
Ingestion
Dermal Contact
Sediment
Incidental Ingestion
Dermal Contact
Air
Inhalation of Vapor
Phase Chemicals
Indoors
Outdoors
Inhalation of
Particulates
Indoors
Outdoors
Soil/Dust
Incidental Ingestion
Dermal Contact
Food
Ingestion
Fish and Shellfish
Meat and Game
Dairy
Eggs
Vegetables
L
L
L
L
C
C
L
L
L
L
L,C
L, C
L
L
L, C
L
L
A
A
A
A
A
A
A
A
A
A
A
A
—
—
—
—
"
—
—
L, C
L, C
C
L, C
—
L
—
L
L, C
L, C
L
L
L
L
L
L = lifetime exposure
C — exposure in children may be significantly greater than in adults
A = exposure to adults (highest exposure is likely to occur during occupational activities)
— = Exposure of this population via this route is not likely to occur.
-------
Page 6-19
and also is useful as documentation of the
exposure pathway analysis. Exhibit 6-8 provides
a sample format for presenting this information.
6.4 STEP 3: QUANTIFICATION
OF EXPOSURE: GENERAL
CONSIDERATIONS
The next step in the exposure assessment
process is to quantify the magnitude, frequency
and duration of exposure for the populations and
exposure pathways selected for quantitative
evaluation. This step is most often conducted in
two stages: first, exposure concentrations are
estimated, then, pathway-specific intakes are
quantified. The specific methodology for
calculating exposure concentrations and pathway-
specific exposures are presented in Sections 6.5
and 6.6, respectively. This section describes some
of the basic concepts behind these processes.
6.4.1 QUANTIFYING THE REASONABLE
MAXIMUM EXPOSURE
Exposure is defined as the contact of an
organism with a chemical or physical agent. If
exposure occurs over time, the total exposure can
be divided by a time period of interest to obtain
an average exposure rate per unit time. This
average exposure rate also can be expressed as a
function of body weight. For the purposes of this
manual, exposure normalized for time and body
weight is termed "intake", and is expressed in units
of mg chemical/kg body weight-day.
Exhibit 6-9 presents a generic equation for
calculating chemical intakes and defines the intake
variables. There are three categories of variables
that are used to estimate intake:
(1) chemical-related variable - exposure
concentration;
(2) variables that describe the exposed
population ~ contact rate, exposure
frequency and duration, and body weight;
and
(3) assessment-determined
averaging time.
variable
Each intake variable in the equation has a
range of values. For Superfund exposure
assessments, intake variable values for a given
pathway should be selected so that the
combination of all intake variables results in an
estimate of the reasonable maximum exposure for
that pathway. As defined previously, the
reasonable maximum exposure (RME) is the
maximum exposure that is reasonably expected to
occur at a site. Under this approach, some intake
variables may not be at their individual maximum
values but when in combination with other
variables will result in estimates of the RME.
Some recommendations for determining the values
of the individual intake variables are discussed
below. These recommendations are based on
EPA's determination of what would result in an
estimate of the RME. As discussed previously, a
determination of "reasonable" cannot be based
solely on quantitative information, but also
requires the use of professional judgment.
Accordingly, the recommendations below are based
on a combination of quantitative information and
professional judgment. These are general
recommendations, however, and could change
based on site-specific information or the particular
needs of the risk manager. Consult with the RPM
before varying from these recommendations.
Exposure concentration. The concentration
term in the intake equation is the arithmetic
average of the concentration that is contacted over
the exposure period. Although this concentration
does not reflect the maximum concentration that
could be contacted at any one time, it is regarded
as a reasonable estimate of the concentration
likely to be contacted over time. This is because
in most situations, assuming long-term contact
with the maximum concentration is not
reasonable. (For exceptions to this generalization,
see discussion of hot spots in Section 6.5.3.)
Because of the uncertainty associated with
any estimate of exposure concentration, the upper
confidence limit ("i.e.. the 95 percent upper
confidence limit) on the arithmetic average will be
used for this variable. There are standard
statistical methods which can be used to calculate
the upper confidence limit on the arithmetic
mean. Gilbert (1987, particularly sections 11.6
and 13.2) discusses methods that can be applied
to data that are distributed normally or log
normally. Kriging is another method that
-------
Page 6-20
EXHIBIT 6-8
EXAMPLE OF TABLE FORMAT FOR SUMMARIZING
COMPLETE EXPOSURE PATHWAYS AT A SITE
Potentially Exposed
Population
Exposure Route, Medium
and Exposure Point
Pathway Selected
for Evaluation?
Reason for Selection
or Exclusion
Current I,and Use
Residents
Residents
Industrial
Workers
Future Land Use
Residents
Residents
Ingestion of ground water
from local wells down-
gradient of the site
Inhalation of chemicals
volatilized from ground
water during home use
Direct contact with
chemicals of potential
concern in soil on the
site
Direct contact with chemi-
cals of potential concern
in soil on the site
Ingestion of chemicals
that have accumulated in
fish located in onsite
ponds
Yes
Yes
Yes
Yes
No
Residents use ground
water from local wells
as drinking water.
Some of the chemicals
of potential concern in
ground water are volatile,
and ground water is used
by local residents.
Contaminated soil is in
an area potentially used
by outside maintenance
workers.
Area could be developed
in the future as a
residential area.
The potential for signifi-
cant exposure via this
pathway is low because
none of the chemicals of
potential concern accumulate
extensively in fish.
-------
Page 6-21
EXHIBIT 6-9
GENERIC EQUATION FOR CALCULATING
CHEMICAL INTAKES
I = C x CR x EFD „ 1
BW AT
Where:
I = intake; the amount of chemical at the exchange boundary
(mg/kg body weight-day)
Chemical-related variable
C = chemical concentration; the average concentration contacted
over the exposure period (e.g., ing/liter water)
Variables that describe the exposed population
CR = contact rate; the amount of contaminated medium contacted
per unit time or event (e.g., liters/day)
EFD = exposure frequency and duration; describes how long and how
often exposure occurs. Often calculated using two terms
(EF and ED):
EF = exposure frequency (days/year)
ED = exposure duration (years)
BW = body weight; the average body weight over the exposure period
(kg)
Assessment-determined variable
AT = averaging time; period over which exposure is averaged (days)
-------
Page 6-22
potentially can be used (Clark 1979 is one of
several reference books on kriging). A statistician
should be consulted for more details or for
assistance with specific methods.
If there is great variability in measured or
modeled concentration values (such as when too
few samples are taken or when model inputs are
uncertain), the upper confidence limit on the
average concentration will be high, and
conceivably could be above the maximum detected
or modeled value. In these cases, the maximum
detected or modeled value should be used to
estimate exposure concentrations. This could be
regarded by some as too conservative an estimate,
but given the uncertainty in the data in these
situations, this approach is regarded as reasonable.
For some sites, where a screening level
analysis is regarded as sufficient to characterize
potential exposures, calculation of the upper
confidence limit on the arithmetic average is not
required. In these cases, the maximum detected
or modeled concentration should be used as the
exposure concentration.
Contact rate. Contact rate reflects the
amount of contaminated medium contacted per
unit time or event. If statistical data are available
for a contact rate, use the 95th percentile value
for this variable. (In this case and throughout this
chapter, the 90th percentile value can be used if
the 95th percentile value is not available.) If
statistical data are not available, professional
judgment should be used to estimate a value
which approximates the 95th percentile value. (It
is recognized that such estimates will not be
precise. They should, however, reflect a
reasonable estimate of an upper-bound value.)
Sometimes several separate terms are used to
derive an estimate of contact rate. For example,
for dermal contact with chemicals in water,
contact rate is estimated by combining information
on exposed skin surface area, dermal permeability
of a chemical, and exposure time. In such
instances, the combination of variables used to
estimate intake should result in an estimate
approximating the 95th percentile value.
Professional judgment will be needed to determine
the appropriate combinations of variables. (More
specific guidance for determining contact rate for
various pathways is given in Section 6.6.)
Exposure frequency and duration. Exposure
frequency and duration are used to estimate the
total time of exposure. These terms are
determined on a site-specific basis. If statistical
data are available, use the 95th percentile value
for exposure time. In the absence of statistical
data (which is usually the case), use reasonable
conservative estimates of exposure time. National
statistics are available on the upper-bound (90th
percentile) and average (50th percentile) number
of years spent by individuals at one residence
(EPA 1989d). Because of the data on which they
are based, these values may underestimate the
actual time that someone might live in one
residence. Nevertheless, the upper-bound value of
30 years can be used for exposure duration when
calculating reasonable maximum residential
exposures. In some cases, however, lifetime
exposure (70 years by convention) may be a more
appropriate assumption. Consult with the RPM
regarding the appropriate exposure duration for
residential exposures. The exposure frequency and
duration selected must be appropriate for the
contact rate selected. If a long-term average
contact rate (e.g., daily fish ingestion rate averaged
over a year) is used, then a daily exposure
frequency (i.e., 365 days/year) should be assumed.
Body weight. The value for body weight is
the average body weight over the exposure period.
If exposure occurs only during childhood years,
the average child body weight during the exposure
period should be used to estimate intake. For
some pathways, such as soil ingestion, exposure
can occur throughout the lifetime but the majority
of exposure occurs during childhood (because of
higher contact rates). In these cases, exposures
should be calculated separately for age groups
with similar contact rate to body weight ratios; the
body weight used in the intake calculation for
each age group is the average body weight for that
age group. Lifetime exposure is then calculated
by taking the time-weighted average of exposure
estimates over all age groups. For pathways
where contact rate to body weight ratios are fairly
constant over a lifetime (e.g., drinking water
ingestion), a body weight of 70 kg is used.
A constant body weight over the period of
exposure is used primarily by convention, but also
because body weight is not always independent of
the other variables in the exposure equation (most
notably, intake). By keeping body weight
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constant, error from this dependence is minimized.
The average body weight is used because, when
combined with the other variable values in the
intake equation, it is believed to result in the best
estimate of the RME. For example, combining a
95th percentile contact rate with a 5th percentile
body weight is not considered reasonable because
it is unlikely that smallest person would have the
highest intake. Alternatively, combining a 95th
percentile intake with a 95th percentile body
weight is not considered a maximum because a
smaller person could have a higher contact rate to
body weight ratio.
Averaging time. The averaging time selected
depends on the type of toxic effect being assessed.
When evaluating exposures to developmental
toxicants, intakes are calculated by averaging over
the exposure event (e.g., a day or a single
exposure incident). For acute toxicants, intakes
are calculated by averaging over the shortest
exposure period that could produce an effect,
usually an exposure event or a day. When
evaluating longer-term exposure to
noncarcinogenic toxicants, intakes are calculated
by averaging intakes over the period of exposure
(i.e., subchronic or chronic daily intakes). For
carcinogens, intakes are calculated by prorating
the total cumulative dose over a lifetime (i.e.,
chronic daily intakes, also called lifetime average
daily intake). This distinction relates to the
currently held scientific opinion that the
mechanism of action for each category is different
(see Chapter 7 for a discussion). The approach
for carcinogens is based on the assumption that
a high dose received over a short period of time
is equivalent to a corresponding low dose spread
over a lifetime (EPA 1986b). This approach
becomes problematic as the exposures in question
become more intense but less frequent, especially
when there is evidence that the agent has shown
dose-rate related carcinogenic effects. In some
cases, therefore, it may be necessary to consult a
toxicologist to assess the level of uncertainty
associated with the exposure assessment for
carcinogens. The discussion of uncertainty should
be included in both the exposure assessment and
risk characterization chapters of the risk
assessment report.
6.4.2 TIMING CONSIDERATIONS
At many Superfund sites, long-term exposure
to relatively low chemical concentrations (i.e.,
chronic daily intakes) are of greatest concern. In
some situations, however, shorter-term exposures
(e.g., subchronic daily intakes) also may be
important. When deciding whether to evaluate
short-term exposure, the following factors should
be considered:
• the toxicological characteristics of the
chemicals of potential concern;
• the occurrence of high chemical
concentrations or the potential for a
large release;
• persistence of the chemical in the
environment; and
• the characteristics of the population that
influence the duration of exposure.
Toxicity considerations. Some chemicals can
produce an effect after a single or very short-term
exposure to relatively low concentrations. These
chemicals include acute toxicants such as skin
irritants and neurological poisons, and
developmental toxicants. At sites where these
types of chemicals are present, it is important to
assess exposure for the shortest time period that
could result in an effect. For acute toxicants this
is usually a single exposure event or a day,
although multiple exposures over several days also
could result in an effect. For developmental
toxicants, the time period of concern is the
exposure event. This is based on the assumption
that a single exposure at the critical time in
development is sufficient to produce an adverse
effect. It should be noted that the critical time
referred to can occur in almost any segment of
the human population (i.e., fertile men and
women, the conceptus, and the child up to the age
of sexual maturation [EPA 1989e]).
Concentration considerations. Many
chemicals can produce an effect after a single or
very short-term exposure, but only if exposure is
to a relatively high concentration. Therefore, it
is important that the assessor identify possible
situations where a short-term exposure to a high
concentration could occur. Examples of such a
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Page 6-24
situation include sites where contact with a small,
but highly contaminated area is possible (e.g., a
source or a hot spot), or sites where there is a
potential for a large chemical release (e.g.,
explosions, ruptured drums, breached lagoon
dikes). Exposure should be determined for the
shortest period of time that could produce an
effect.
Persistence considerations. Some chemicals
may degrade rapidly in the environment. In these
cases, exposures should be assessed only for that
period of time in which the chemical will be
present at the site. Exposure assessments in these
situations may need to include evaluations of
exposure to the breakdown products, if they are
persistent or toxic at the levels predicted to occur
at the site.
Population considerations. At some sites,
population activities are such that exposure would
occur only for a short time period (a few weeks
or months), infrequently, or intermittently.
Examples of this would be seasonal exposures
such as during vacations or other recreational
activities. The period of time over which
exposures are averaged in these instances depends
on the type of toxic effect being assessed (see
previous discussion on averaging time, Section
6.4.1).
6.5 QUANTIFICATION OF
EXPOSURE: DETERMINA-
TION OF EXPOSURE
CONCENTRATIONS
This section describes the basic approaches
and methodology for determining exposure
concentrations of the chemicals of potential
concern in different environmental media using
available monitoring data and appropriate models.
As discussed in Section 6.4.1, the concentration
term in the exposure equation is the average
concentration contacted at the exposure point or
points over the exposure period. When estimating
exposure concentrations, the objective is to
provide a conservative estimate of this average
concentration (e.g., the 95 percent upper
confidence limit on the arithmetic mean chemical
concentration).
This section provides an overview of the basic
concepts and approaches for estimating exposure
concentrations. It identifies what type of
information is needed to estimate concentrations,
where to find it, and how to interpret and use it.
This section is not designed to provide all the
information necessary to derive exposure
concentrations and, therefore, does not detail the
specifics of potentially applicable models nor
provide the data necessary to run the models or
support concentration estimates. However,
sources of such information, including the
Superfund Exposure Assessment Manual (SEAM;
EPA 1988b) are referenced throughout the
discussion.
6.5.1 GENERAL CONSIDERATIONS FOR
ESTIMATING EXPOSURE
CONCENTRATIONS
In general, a great deal of professional
judgment is required to estimate exposure
concentrations. Exposure concentrations may be
estimated by (1) using monitoring data alone, or
(2) using a combination of monitoring data and
environmental fate and transport models. In most
exposure assessments, some combination of
monitoring data and environmental modeling will
be required to estimate exposure concentrations.
Direct use of monitoring data. Use of
monitoring data to estimate exposure
concentrations is normally applicable where
exposure involves direct contact with the
monitored medium (e.g., direct contact with
chemicals in soil or sediment), or in cases where
monitoring has occurred directly at an exposure
point (e.g., a residential drinking water well or
public water supply). For these exposure
pathways, monitoring data generally provide the
best estimate of current exposure concentrations.
As the first step in estimating exposure
concentrations, summarize available monitoring
data. The manner in which the data are
summarized depends upon the site characteristics
and the pathways being evaluated. It may be
necessary to divide chemical data from a particular
medium into subgroups based on the location of
sample points and the potential exposure
pathways. In other instances, as when the
sampling point is an exposure point (e.g., when
the sample is from an existing drinking water well)
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Page 6-25
it may not be appropriate to group samples at all,
but may be most appropriate to treat the sample
data separately when estimating intakes. Still, in
other instances', the assessor may wish to use the
maximum concentration from a medium as the
exposure concentration for a given pathway as a
screening approach to place an upper bound on
exposure. In these cases it is important to
remember that if a screening level approach
suggests a potential health concern, the estimates
of exposure should be modified to reflect more
probable exposure conditions.
In those instances where it is appropriate to
group sampling data from a particular medium,
calculate for each exposure medium and each
chemical the 95 percent upper confidence limit on
the arithmetic average chemical concentration.
See Chapter 5 for guidance on how to treat
sample concentrations below the quantitation
limit.
Modeling approaches. In some instances, it
may not be appropriate to use monitoring data
alone, and fate and transport models may be
required to estimate exposure concentrations.
Specific instances where monitoring data alone
may not be adequate are as follows.
• Where exposure points are spatially
separate from monitoring points.
Models may be required when exposure
points are remote from sources of
contamination if mechanisms for release
and transport to exposure points exist
(e.g., ground-water transport, air
dispersion).
• Where temporal distribution of data is
lacking. Typically, data from Superfund
investigations are collected over a
relatively short period of time. This
generally will give a clear indication of
current site conditions, but both long-
term and short-term exposure estimates
usually are required in Superfund
exposure assessments. Although there
may be situations where it is reasonable
to assume that concentrations will
remain constant over a long period of
time, in many cases the time span of the
monitoring data is not adequate to
predict future exposure concentrations.
Environmental models may be required
to make these predictions.
• Where monitoring data are restricted by
the limit of quantitation. Environmental
models may be needed to predict
concentrations of contaminants that may
be present at concentrations that are
below the quantitation limit but that may
still cause toxic effects (even at such low
concentrations). For example, in the
case of a ground-water plume discharging
into a river, the dilution afforded by the
river may be sufficient to reduce the
concentration of the chemical to a level
that could not be detected by direct
monitoring. However, as discussed in
Section 5.3.1, the chemical may be
sufficiently toxic or bioaccumulative that
it could present a health risk at
concentrations below the limit of
quantitation. Models may be required
to make exposure estimates in these
types of situations.
A wide variety of models are available for
use in exposure assessments. SEAM (EPA 1988b)
and the Exposure Assessment Methods Handbook
(EPA 1989f) describe some of the models
available and provide guidance in selecting
appropriate modeling techniques. Also, the
Center for Exposure Assessment Modeling
(CEAM - Environmental Research Laboratory
(ERL) Athens), the Source Receptor Analysis
Branch (Office of Air Quality Planning and
Standards, or OAQPS), and modelers in EPA
regional offices can provide assistance in selecting
appropriate models. Finally, Volume IV of the
NTGS (EPA 1989c) provides guidance for air and
atmospheric dispersion modeling for Superfund
sites. Be sure to discuss the fate and transport
models to be used in the exposure assessment with
the RPM.
The level of effort to be expended in
estimating exposure concentrations will depend on
the type and quantity of data available, the level
of detail required in the assessment, and the
resources available for the assessment. In general,
estimating exposure concentrations will involve
analysis of site monitoring data and application of
simple, screening-level analytical models. The
most important factor in determining the level of
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Page 6-26
effort will be the quantity and quality of the
available data. In general, larger data sets will
support the use of more sophisticated models.
Other considerations. When evaluating
chemical contamination at a site, it is important
to review the spatial distribution of the data and
evaluate it in ways that have the most relevance
to the pathway being assessed. In short, consider
where the contamination is with respect to known
or anticipated population activity patterns. Maps
of both concentration distribution and activity
patterns will be useful for the exposure
assessment. It is the intersection of activity
patterns and contamination that defines an
exposure area. Data from random sampling or
from systematic grid pattern sampling may be
more representative of a given exposure pathway
than data collected only from hot spots.
Generally, verified GC/MS laboratory data
with adequate quality control will be required to
support quantitative exposure assessment. Field
screening data generally cannot be incorporated
when estimating exposure concentrations because
they are derived using less sensitive analytical
methods and are subject to less stringent quality
control.
Other areas to be considered in estimating
exposure concentrations are as follows.
• Steady-state vs. non-steady-state
conditions. Frequently, it may be
necessary to assume steady-state
conditions because the information
required to estimate non-steady-state
conditions (such as source depletion
rate) is not readily available. This is
likely to overestimate long-term exposure
concentrations for certain pathways.
• Number and type of exposure parameters
that must be assumed. In developing
exposure models, values for site-specific
parameters such as hydraulic
conductivity, organic carbon content of
soil, wind speed and direction, and soil
type may be required. These values may
be generated as part of the RI. In cases
where these values are not available,
literature values may be substituted. In
the absence of applicable literature
values, the assessor must consider if a
reliable exposure concentration estimate
can be made.
• Number and type of fate processes to
be considered. In some cases, exposure
modeling may be limited to
considerations of mass balance, dilution,
dispersion, and equilibrium partitioning.
In other cases, models of more complex
fate processes, such as chemical reaction,
biodegradation, and photolysis may be
needed. However, prediction of such
fate processes requires significantly larger
quantities of model calibration and
validation data than required for less
complex fate processes. For those sites
where these more complex fate processes
need to be modeled, be sure to consult
with the RPM regarding the added data
requirements.
6.5.2 ESTIMATE EXPOSURE
CONCENTRATIONS IN GROUND
WATER
Exposure concentrations in ground water can
be based on monitoring data alone or on a
combination of monitoring and modeling. In
some cases, the exposure assessor may favor the
use of monitoring data over the use of complex
models to develop exposure concentrations. It is
most appropriate to use ground-water sampling
data as estimates of exposure concentrations when
the sampling points correspond to exposure
points, such as samples taken from a drinking
water tap. However, samples taken directly from
a domestic well or drinking water tap should be
interpreted cautiously. For example, where the
water is acidic, inorganic chemicals such as lead
or copper may leach from the distribution system.
Organic chemicals such as phthalates may migrate
into water from plastic piping. Therefore,
interpretations of these data should consider the
type and operation of the pumping, storage, and
distribution system involved.
Most of the time, data from monitoring wells
will be used to estimate chemical concentrations
at the exposure point. Several issues should be
considered when using monitoring well data to
estimate these concentrations. First, determine if
the aquifer has sufficient production capacity and
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Page 6-27
is of sufficient quality to support drinking water
or other uses. If so, it generally should be
assumed that water could be drawn from anywhere
in the aquifer, regardless of the location of
existing wells relative to the contaminant plume.
In a few situations, however, it may not be
reasonable to assume that water will be drawn
from directly beneath a specific source (e.g., a
waste management unit such as a landfill) in the
future. In these cases, it should be assumed that
water could be drawn from directly adjacent to the
source. Selection of the location(s) used to
evaluate future ground-water exposures should be
made in consultation with the RPM. Second,
compare the construction of wells (e.g., drinking
water wells) in the area with the construction of
the monitoring wells. For example, drinking water
wells may draw water from more than one aquifer,
whereas individual monitoring wells are usually
screened in a specific aquifer. In some cases it
may be appropriate to separate data from two
aquifers that have very limited hydraulic
connection if drinking water wells in the area
draw water from only one of them. Consult a
hydrogeologist for assistance in the above
considerations.
Another issue to consider is filtration of
water samples. While filtration of ground-water
samples provides useful information for
understanding chemical transport within an aquifer
(see Section 4.5.3 for more details), the use of
filtered samples for estimating exposure is very
controversial because these data may
underestimate chemical concentrations in water
from an unfiltered tap. Therefore, data from
unfiltered samples should be used to estimate
exposure concentrations. Consult with the RPM
before using data from filtered samples.
Ground-water monitoring data are often of
limited use for evaluating long-term exposure
concentrations because they are generally
representative of current site conditions and not
long-term trends. Therefore, ground-water models
may be needed to estimate exposure
concentrations. Monitoring data should be used
when possible to calibrate the models.
Estimating exposure concentrations in ground
water using models can be a complex task because
of the many physical and chemical processes that
may affect transport and transformation in ground
water. Among the important mechanisms that
should be considered when estimating exposure
concentrations in ground water are leaching from
the surface, advection (including infiltration, flow
through the unsaturated zone, and flow with
ground water), dispersion, sorption (including
adsorption, desorption, and ion exchange), and
transformation (including biological degradation,
hydrolysis, oxidation, reduction, complexation,
dissolution, and precipitation). Another
consideration is that not all chemicals may be
dissolved in water, but may be present instead in
nonaqueous phases that float on top of ground
water or sink to the bottom of the aquifer.
The proper selection and application of soil
and ground-water models requires a thorough
understanding of the physical, chemical, and
hydrogeologic characteristics of the site. SEAM
(EPA 1988b) provides a discussion of the factors
controlling soil and ground-water contaminant
migration as well as descriptions of various soil
and ground-water models. For more in-depth
guidance on the selection and application of
appropriate ground-water models, consult
Selection Criteria for Mathematical Models Used in
Exposure Assessments: Ground-water Models (EPA
1988c). As with all modeling, the assessor should
carefully evaluate the applicability of the model to
the site being evaluated, and should consult with
a hydrogeologist as necessary.
If ground-water modeling is not used, current
concentrations can be used to represent future
concentrations in ground water assuming steady-
state conditions. This assumption should be noted
in the exposure assessment chapter and in the
uncertainties and conclusions of the risk
assessment.
6.5.3 ESTIMATE EXPOSURE
CONCENTRATIONS IN SOIL
Estimates of current exposure concentrations
in soil can be based directly on summarized
monitoring data if it is assumed that
concentrations remain constant over time. Such
an assumption may not be appropriate for some
chemicals and some sites where leaching,
volatilization, photolysis, biodegradation, wind
erosion, and surface runoff will reduce chemical
concentrations over time. Soil monitoring data
and site conditions should be carefully screened to
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identify situations where source depletion is likely
to be important. SEAM (EPA 1988b) gives
steady-state equations for estimating many of these
processes. However, incorporating these processes
into the calculation of exposure concentrations for
soil involves considerable effort. If a modeling
approach is not adopted in these situations,
assume a constant concentration over time and
base exposure concentrations on monitoring data.
This assumption should be clearly documented.
In evaluating monitoring data for the
assessment of soil contact exposures, the spatial
distribution of the data is a critical factor. The
spatial distribution of soil contamination can be
used as a basis for estimating the average
concentrations contacted over time if it is assumed
that contact with soil is spatially random (i.e., if
contact with soil in all areas of the site is equally
probable). Data from random sampling programs
or samples from evenly spaced grid networks
generally can be considered as representative of
concentrations across the site. At many sites
however, sampling programs are designed to
characterize only obviously contaminated soils or
hot spot areas. Care must be taken in evaluating
such data sets for estimating exposure
concentrations. Samples from areas where direct
contact is not realistic (such as where a steep
slope or thick vegetation prevents current access)
should not be considered when estimating current
exposure concentrations for direct contact
pathways. Similarly, the depth of the sample
should be considered; surface soil samples should
be evaluated separately from subsurface samples
if direct contact with surface soil or inhalation of
wind blown dust are potential exposure pathways
at the site.
In some cases, contamination may be
unevenly distributed across a site, resulting in hot
spots (areas of high contamination relative to
other areas of the site). If a hot spot is located
near an area which, because of site or population
characteristics, is visited or used more frequently,
exposure to the hot spot should be assessed
separately. The area over which the activity is
expected to occur should be considered when
averaging the monitoring data for a hot spot. For
example, averaging soil data over an area the size
of a residential backyard (e.g., an eighth of an
acre) may be most appropriate for evaluating
residential soil pathways.
6.5.4 ESTIMATE EXPOSURE
CONCENTRATIONS IN AIR
There are three general approaches to
estimating exposure concentrations in air: (1)
ambient air monitoring, (2) emission
measurements coupled with dispersion modeling,
and (3) emission modeling coupled with dispersion
modeling. Whichever approach is used, the
resulting exposure concentrations should be as
representative as possible of the specific exposure
pathways being evaluated. If long-term exposures
are being evaluated, the exposure concentrations
should be representative of long-term averages.
If short-term exposures are of interest, measured
or modeled peak concentrations may be most
representative.
If monitoring data have been collected at a
site, their adequacy for use in a risk assessment
should be evaluated by considering how
appropriate they are for the exposures being
addressed. Volume II of the NTGS (EPA 1989b)
provides guidance for measuring emissions and
should be consulted when evaluating the
appropriateness of emission data. See Chapter 4
(Section 4.5.5) for factors to consider when
evaluating the appropriateness of ambient air
monitoring data. As long as there are no
significant analytical problems affecting air
sampling data, background levels are not
significantly higher than potential site-related
levels, and site-related levels are not below the
instrument detection limit, air monitoring data can
be used to derive exposure concentrations. There
still will be uncertainties inherent in using these
data because they usually are not representative
of actual long-term average air concentrations.
This may be because there were only a few sample
collection periods, samples were collected during
only one type of meteorological or climatic
condition, or because the source of the chemicals
will change over time. These uncertainties should
be mentioned in the risk assessment.
In the absence of monitoring data, exposure
concentrations often can be estimated using
models. Two kinds of models are used to
estimate air concentrations: emission models that
predict the rate at which chemicals may be
released into the air from a source, and dispersion
models that predict associated concentrations in
air at potential receptor points.
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Outdoor air modeling. Emissions may occur
as a result of the volatilization of chemicals from
contaminated media or as a result of the
suspension of onsite soils. Models that predict
emission rates for volatile chemicals or dust
require numerous input parameters, many of
which are site-specific. For volatile chemicals,
emission models for surface water and soil are
available in SEAM (EPA 1988b). Volume IV of
the NTGS (EPA 1989c) also provides guidance for
evaluating volatile emissions at Superfund sites.
Emissions due to suspension of soils may result
from wind erosion of exposed soil particles and
from vehicular disturbances of the soil. To
predict soil or dust emissions, EPA's fugitive dust
models provided in AP42 (EPA 1985b) or models
described in SEAM (1988b) may be used.
Volume IV of the NTGS (EPA 1989c) also will
be useful in evaluating fugitive dust emissions at
Superfund sites. Be sure to critically review all
models before use to determine their applicability
to the situation and site being evaluated. If
necessary, consult with air modelers in EPA
regional offices, the Exposure Assessment Group
in EPA headquarters or the Source Receptor
Analysis Branch in OAQPS.
After emissions have been estimated or
measured, air dispersion models can be applied to
estimate air concentrations at receptor points. In
choosing a dispersion model, factors that must be
considered include the type of source and the
location of the receptor relative to the source.
For area or point sources, EPA's Industrial Source
Complex model (EPA 1987a) or the simple
Gaussian dispersion models discussed in SEAM
(EPA 1988b) can provide air concentrations
around the source. Other models can be found
in Volume IV of the NTGS (EPA 1989c). The
Source Receptor Analysis Branch of OAQPS also
can be contacted for assistance. Again, critically
review all models for their applicability.
Indoor air modeling. Indoor emissions may
occur as a result of transport of outdoor-generated
dust or vapors indoors, or as a result of
volatilization of chemicals indoors during use of
contaminated water (e.g., during showering,
cooking, washing). Few models are available for
estimating indoor air concentrations from outside
sources. For dust transport indoors, it can
generally be assumed that indoor concentrations
are less than those outdoors. For vapor transport
indoors, concentrations indoors and outdoors can
be assumed to be equivalent in most cases.
However, at sites where subsurface soil gas or
ground-water seepage are entering indoors, vapor
concentrations inside could exceed those outdoors.
Vapor concentrations resulting from indoor use of
water may be greater than those outdoors,
depending on the emission source characteristics,
dispersion indoors, and indoor-outdoor air
exchange rates. Use models discussed in the
Exposure Assessment Methods Handbook (EPA
1989f) to evaluate volatilization of chemicals from
indoor use of water.
6.5.5 ESTIMATE EXPOSURE
CONCENTRATIONS IN SURFACE
WATER
Data from surface water sampling and
analysis may be used alone or in conjunction with
fate and transport models to estimate exposure
concentrations. Where the sampling points
correspond to exposure points, such as at
locations where fishing or recreational activities
take place, or at the intake to a drinking water
supply, the monitoring data can be used alone to
estimate exposure concentrations. However, the
data must be carefully screened. The complexity
of surface water processes may lead to certain
limitations in monitoring data. Among these are
the following.
• Temporal representativeness. Surface
water bodies are subject to seasonal
changes in flow, temperature, and depth
that may significantly affect the fate and
transport of contaminants. Releases to
surface water bodies often depend on
storm conditions to produce surface
runoff and soil erosion. Lakes are
subject to seasonal stratification and
changes in biological activity. Unless the
surface water monitoring program has
been designed to account for these
phenomena, the data may not represent
long-term average concentrations or
short-term concentrations that may occur
after storm events.
• Spatial representativeness. Considerable
variation in concentration can occur with
respect to depth and lateral location in
surface water bodies. Sample locations
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should be examined relative to surface
water mixing zones. Concentrations
within the mixing zone may be
significantly higher than at downstream
points where complete mixing has taken
place.
• Quantitation limit limitations. Where
large surface water bodies are involved,
contaminants that enter as a result of
ground-water discharge or runoff from
relatively small areas may be significantly
diluted. Although standard analytical
methods may not be able to detect
chemicals at these levels, the toxic effects
of the chemicals and/or their potential
to bioaccumulate may nevertheless
require that such concentrations be
assessed.
• Contributions from other sources.
Surface water bodies are normally subject
to contamination from many sources
(e.g., pesticide runoff, stormwater,
wastewater discharges, acid mine
drainage). Many of the chemicals
associated with these sources may be
difficult to distinguish from site-related
chemicals. In many cases background
samples will be useful in assessing site-
related contaminants from other
contaminants (see Section 4.4).
However, there may be other cases
where a release and transport model may
be required to make the distinction.
Many analytical and numerical models are
available to estimate the release of contaminants
to surface water and to predict the fate of
contaminants once released. The models range
from simple mass balance relationships to
numerical codes that contain terms for chemical
and biological reactions and interactions with
sediments. In general, the level of information
collected during the RI will tend to limit the use
of the more complex models.
There are several documents that can be
consulted when selecting models to estimate
surface water exposure concentrations, including
SEAM (EPA 1988b), the Exposure Assessment
Methods Handbook (EPA 1989f), and Selection
Criteria for Mathematical Models Used in Exposure
Assessments: Surface Water Models (EPA 1987b).
SEAM lists equations for surface water runoff and
soil erosion and presents the basic mass balance
relationships for estimating the effects of dilution.
A list of available numerical codes for more
complex modeling also is provided. The selection
criteria document (EPA 1987b) provides a more
in-depth discussion of numerical codes and other
models. In addition, it provides guidelines and
procedures for evaluating the appropriate level of
complexity required for various applications. The
document lists criteria to consider when selecting
a surface water model, including: (1) type of water
body, (2) presence of steady-state or transient
conditions, (3) point versus non-point sources of
contamination, (4) whether 1, 2, or 3 spatial
dimensions should be considered, (5) the degree
of mixing, (6) sediment interactions, and (7)
chemical processes. Each of the referenced
documents should be consulted prior to any
surface water modeling.
6.5.6 ESTIMATE EXPOSURE
CONCENTRATIONS IN SEDIMENTS
In general, use sediment monitoring data to
estimate exposure concentrations. Sediment
monitoring data can be expected to provide better
temporal representativeness than surface water
concentrations. This will especially be true in the
case of contaminants such as PCBs, PAHs, and
some inorganic chemicals, which are likely to
remain bound to the sediments. When using
monitoring data to represent exposure
concentrations for direct contact exposures, data
from surficial, near-shore sediments should be
used.
If modeling is needed to estimate sediment
exposure concentrations, consult SEAM (EPA
1988b). SEAM treats surface water and sediment
together for the purpose of listing available
models for the release and transport of
contaminants. Models for soil erosion releases
are equally applicable for estimating exposure
concentrations for surface water and sediment.
Many of the numerical models listed in SEAM
and the surface water selection criteria document
(EPA 1987b) contain sections devoted to sediment
fate and transport.
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Page 6-31
6.5.7 ESTIMATE CHEMICAL
CONCENTRATIONS IN FOOD
Fish and shellfish. Chemical concentrations
in fish and shellfish may be measured or
estimated. Site-specific measured values are
preferable to estimated values, but before using
such values, evaluate the sampling plan to
determine if it was adequate to characterize the
population and species of concern (see Section
4.5.6 for some sampling considerations). Also
examine analytical procedures to determine if the
quantitation limits were low enough to detect the
lowest concentration potentially harmful to
humans. Inadequate sampling or high levels of
quantitation may lead to erroneous conclusions.
In the absence of adequate tissue
measurements, first consider whether the chemical
bioconcentrates (i.e., is taken up from water) or
bioaccumulates (i.e., is taken up from food,
sediment, and water). For example, low molecular
weight volatile organic chemicals do not
bioaccumulate in aquatic organisms to a great
extent. Other chemicals accumulate in some
species but not in others. For example, PAHs
tend to accumulate in mollusk species but not in
fish, which rapidly metabolize the chemicals. For
those chemicals that bioconcentrate in aquatic
species of concern, use the organism/water
partition coefficient (i.e., bioconcentration factor,
or BCF) approach to estimate steady-state
concentrations. BCFs that estimate concentrations
in edible tissue (muscle) are generally more
appropriate for assessing human exposures from
fish or shellfish ingestion than those that estimate
concentrations in the whole body, although this is
not true for all aquatic species or applicable to all
human populations consuming fish or shellfish.
When data from multiple experiments are
available, select the BCF from a test that used a
species most similar to the species of concern at
the site, and multiply the BCF directly by the
dissolved chemical concentration in water to
obtain estimates of tissue concentrations. Be
aware that the study from which the BCF is
obtained should reflect a steady state or
equilibrium condition, generally achieved over
long-term exposures (although some chemicals
may reach steady state rapidly in certain species).
For some chemicals, BCFs may overestimate tissue
levels in fish that may be exposed only for a short
period of time.
When no BCF is available, estimate the BCF
with a regression equation based on octanol/water
partition coefficients (K^). Several equations are
available in the literature. Those developed for
chemicals with structural similarities to the
chemical of concern should be used in preference
to general equations because of better statistical
correlations.
The regression equation approach to
estimating BCFs can overestimate or
underestimate concentrations in fish tissue
depending upon the chemical of concern and the
studies used to develop the regression equations.
For example, high molecular weight PAHs (such
as benz(a)pyrene) with high K^ values lead to
the prediction of high fish tissue residues.
However, PAHs are rapidly metabolized in the
liver, and do not appear to accumulate
significantly in fish. Regression equations using
KOH, cannot take into account such
pharmacokinetics, and thus may overestimate
bioconcentration. On the other hand, studies used
to develop regression equations which were not
representative of steady-state conditions will tend
to underestimate BCFs.
Typical methods for estimating fish tissue
concentrations are based on dissolved chemical
concentrations in water. While chemicals present
in sediment and biota may also bioaccumulate in
fish, there are only limited data available to
estimate contributions to fish from these sources.
However, chemicals that readily adsorb to
sediments, such as PCBs, can be present in surface
water at concentrations below detection limits and
still significantly bioaccumulate. Some models are
available to assess the contribution of chemical
concentrations in sediment to chemical
concentrations in aquatic biota. CEAM (ERL
Athens) may be of assistance in choosing and
applying an appropriate model.
Plants. Site-related chemicals may be present
in plants as a result of direct deposition onto
plant surfaces, uptake from the soil, and uptake
from the air. When possible, samples of plants or
plant products should be used to estimate
exposure concentrations. In the absence of
monitoring data, several modeling approaches are
available for estimating exposure concentrations in
plants. Use of these models, however, can
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Page 6-32
introduce substantial uncertainty into an exposure
assessment.
If deposition onto plants is the source of the
chemical, air deposition modeling can be used in
conjunction with plant interception fractions to
estimate uptake. The plant interception fraction
can be estimated by methods published in the
literature or can be developed for a specific crop
by considering crop yield and the area of the plant
available for deposition.
If soil contamination is the source of the
chemical, calculate the concentration in plants by
multiplying soil to plant partition coefficients by
soil concentrations. Use the open literature or
computerized data bases to obtain these
coefficients from field, microcosm, or laboratory
experiments that are applicable to the type of
vegetation or crop of concern (see EPA 1985c
sludge documents for some). In the absence of
more specific information, use general BCFs
published in the literature that are not crop-
specific (see Baes et al. 1984 for some). When
using these parameters, it is important to consider
that many site-specific factors affect the extent of
uptake. These factors include pH, the amount of
organic material present in soil, and the presence
of other chemicals.
When literature values are not available,
consider equations published in the literature for
estimating uptake into the whole plant, into the
root, and translocation from the root into above
ground parts (see Calamari et al. 1987). Such
methods require physical/chemical parameters such
as KOH, or molecular weight and were developed
using a limited data base. Scientific judgment
must always be applied in the development and
application of any partition coefficient, and
caution must be applied in using these values in
risk assessment.
Terrestrial animals. Use tissue monitoring
data when available and appropriate for estimating
human exposure to chemicals in the terrestrial
food chain. In the absence of tissue monitoring
data, use transfer coefficients together with the
total chemical mass ingested by an animal per day
to estimate contaminant concentrations in meat,
eggs, or milk. Data to support modeling of
uptake by terrestrial animals generally are not
available for birds, but are available for some
mammalian species. Terrestrial mammals such as
cattle are simultaneously exposed to chemicals
from several sources such as water, soil, corn
silage, pasture grass, and hay. Cattle ingest
varying amounts of these sources per day, each of
which will contain a different contaminant
concentration. Because all sources can be
important with regard to total body burden, an
approach based upon the daily mass of chemical
ingested per day is recommended because it can
be applied to input from many sources.
Obtain transfer coefficients from the
literature (see Ng et al. 1977, 1979, 1982; Baes et
al. 1984 for some), or calculate them directly from
feeding studies (see Jensen et al. 1981; Jensen and
Hummel 1982; Fries et al. 1973; Van Bruwaene
et al. 1984). In the absence of this information,
use regression equations in the literature for the
estimation of transfer coefficients (see Travis and
Arms 1988). It is important to be aware that
regression equations that use feeding study results
from short-term exposures may underestimate
meat or milk concentrations. In addition,
regression equations which rely on K^ values may
overestimate exposures for chemicals such as
benz(a)pyrene that are rapidly metabolized.
Information on the amount of feed, soil and water
ingested by dairy and beef cows is available in the
literature and should be combined with chemical
concentrations in these media to estimate a daily
dose to the animal.
6.5.8 SUMMARIZE EXPOSURE
CONCENTRATIONS FOR EACH
PATHWAY
Summarize the exposure concentrations
derived for each pathway. Exhibit 6-10 presents
a sample format.
6.6 QUANTIFICATION OF
EXPOSURE: ESTIMATION
OF CHEMICAL INTAKE
This section describes the methodology for
calculating chemical-specific intakes for the
populations and exposure pathways selected for
quantitative evaluation. The general equation for
estimating intake was shown in Exhibit 6-9.
Remember that the intakes calculated in this step
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Page 6-33
EXHIBIT 6-10
EXAMPLE OF TABLE FORMAT FOR SUMMARIZING
EXPOSURE CONCENTRATIONS
Populations/Pathways
Exposure
Concentration
Comments
Current Residents
Ingestion of ground water:
Benzene
Chlordane
Cyanide
9ug/L
5.3 ug/L
llug/L
Concentrations are the 95 percent
upper confidence limit on the
arithmetic average of measured
concentrations in downgradient
monitoring wells.
Direct contact with soil:
Manganese
Selenium
Mercury
1200 mg/kg
48 mg/kg
2 mg/kg
Concentrations are the 95 percent
upper confidence limit on the
arithmetic average of measured
concentrations in onsite surface
soils.
Inhalation of dust:
Manganese
Selenium
Mercury
1 mg/m3
0.04 mg/m3
0.002 mg/m3
Concentrations are based on esti-
mates of fugitive dust generation
and dispersion to nearby homes.
Concentration inputs for air model
are 95 percent upper confidence
limit on the arithmetic average of
measured concentrations in onsite
soil.
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Page 6-34
are expressed as the amount of chemical at the
exchange boundary (e.g., skin, lungs, gut) and
available for absorption. Intake, therefore, is not
equivalent to absorbed dose, which is the amount
of a chemical absorbed into the blood stream.
The sections that follow give standard
equations for estimating human intakes for all
possible exposure routes at a site. Values for
equation variables are presented for use in
evaluating residential exposures. Considerations
for deriving pathway-specific variable values for
populations other than residential (i.e.,
commercial/industrial or recreational) also are
given. In general, both upper-bound (e.g., 95th
percentile or maximum values) and average (mean
or median) values are presented. These values
can be used to calculate the RME or to evaluate
uncertainty. A general discussion of which
variable values should be used to calculate the
RME was provided in Section 6.4.1; more specific
guidance follows. A discussion of the uncertainty
analysis is presented in Section 6.8.
The information presented below is organized
by exposure medium and exposure route.
6.6.1 CALCULATE GROUND-WATER AND
SURFACE WATER INTAKES
Individuals may be exposed to chemicals of
potential concern in ground water and surface
water by the following routes:
(1) ingestion of ground water or surface
water used as drinking water;
(2) incidental ingestion of surface water
while swimming; and
(3) dermal contact with ground water or
surface water.
Inhalation exposures to chemicals that have
volatilized from surface or ground water are
covered in Section 6.6.3.
Intake from drinking water. Calculate
residential intakes from ingestion of ground water
or surface water used as drinking water, using the
equation and variable values presented in Exhibit
6-11. As discussed in section 6.5.3, chemical
concentration in water (CW) should be based on
data from unfiltered samples. Develop pathway-
specific variable values as necessary. Ingestion
rates (IR) could be lower for residents who spend
a portion of their day outside the home (e.g., at
work). Also, exposure frequency (EF) may vary
with land use. Recreational users and workers
generally would be exposed less frequently than
residents.
Intake from ingestion of surface water while
swimming. Calculate intakes from incidental
ingestion of surface water while swimming. Use
the equation and variable values presented in
Exhibit 6-12. Chemical concentration in water
(CW) should represent unfiltered concentrations.
Incidental ingestion rates (IR) while swimming
have not been found in the available literature.
SEAM (EPA 1988b) recommends using an
incidental ingestion rate of 50 ml/hour of
swimming. Exposure duration (ED) will generally
be less for recreational users of a surface water
compared to residents living near the surface
water. Workers are not expected to be exposed
via this pathway.
Intake from dermal contact. Calculate
intakes from dermal contact with water while
swimming, wading, etc., or during household use
(e.g., bathing).
Use the equation and variable values
presented in Exhibit 6-13. In this case, the
calculated exposure is actually the absorbed dose.
not the amount of chemical that comes in contact
with the skin (i.e., intake). This is because
permeability constants (PC) reflect the movement
of the chemical across the skin to the stratum
corneum and into the bloodstream. Be sure to
record this information in the summary of
exposure assessment results so that the calculated
intake is compared to an appropriate toxicity
reference value in the risk characterization
chapter. Note that PC are based on an
equilibrium partitioning and likely result in an
over-estimation of absorbed dose over short
exposure periods (e.g., < 1 hr). The open
literature should be consulted for chemical-specific
PC values. The values in SEAM (EPA 1988b) are
currently being reviewed and should not be used
at this time. If chemical-specific PC values are
not available, the permeability of water can be
used to derive a default value. (See Blank et al.
[1984] for some values [e.g., 8.4xlO~4cm/hr].) Note
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Page 6-3S
EXHIBIT 6-11
RESIDENTIAL EXPOSURE: INGESTION OF
CHEMICALS IN DRINKING WATER a
(AND BEVERAGES MADE USING DRINKING WATER)
Equation:
Intake (mg/kg-day) = CW \ IR x EF x ED
BWxAT
Where:
CW =
IR =
EF =
ED =
BW =
AT =
Chemical Concentration in Water (ing/liter)
Ingestion Rate (liters/day)
Exposure Frequency (days/year)
Exposure Duration (years)
Body Weight (kg)
Averaging Time (period over which exposure is averaged — days)
Variable Values:
CW:
IR:
EF:
ED:
BW:
AT:
Site-specific measured or modeled value
2 liters/day (adult, 90th percentile; EPA 1989d)
1.4 liters/day (adult, average; EPA 1989d)
Age-specific values (EPA 1989d)
Pathway-specific value (for residents, usually daily — 365 days/year)
70 years (lifetime; by convention)
30 years (national upper-bound time (90th percentile)
at one residence; EPA 1989d)
9 years (national median time (50th percentile) at one residence;
EPA 1989d)
70 kg (adult, average; EPA 1989d)
Age-specific values (EPA 1985a, 1989d)
Pathway-specific period of exposure for noncarcinogenic effects
(i.e., ED x 365 days/year), and 70 year lifetime for carcinogenic
effects (i.e., 70 years x 365 days/year).
a
See Section 6.4.1 and 6.6.1 for a discussion of which variable values should be used to calculate the
reasonable maximum exposure. In general, combine 95th or 90th percentile values for contact rate
and exposure frequency and duration variables.
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Page 6-36
EXHIBIT 6-12
RESIDENTIAL EXPOSURE:
INGESTION OF CHEMICALS IN SURFACE WATER
WHILE SWIMMING0
Equation:
Intake (mg/kg-day) = CW x CR x ET x EF x ED
BW x AT
Where:
CW =
CR =
ET =
EF =
ED =
BW =
AT =
Chemical Concentration in Water (mg/liter)
Contact Rate (liters/hour)
Exposure Time (hours/event)
Exposure Frequency (events/year)
Exposure Duration (years)
Body Weight (kg)
Averaging Time (period over which exposure is averaged — days)
Variable Values:
CW:
CR:
ET:
EF:
ED:
BW:
AT:
Site-specific measured or modeled value
50 ml/hour (EPA 1989d)
Pathway-specific value
Pathway-specific value (should consider local climatic conditions
[e. g., number of days above a given temperature] and age of
potentially exposed population)
7 days/year (national average for swimming; USDOI in
EPA i988b, EPA 1989d)
70 years (lifetime; by convention)
30 years (national upper-bound time (90th percentile) at one
residence; EPA 1989d)
9 years (national median time (50th percentile) at one residence;
EPA 1989d)
70 kg (adult, average; EPA 1989d)
Age-specific values (EPA 1985a, 1989d)
Pathway-specific period of exposure for noncarcinogenic effects
(i.e., ED x 365 days/year), and 70 year lifetime for carcinogenic
effects (i.e., 70 years x 365 days/year).
° See Section 6.4.1 and 6.6.1 for a discussion of which variable values should be used to calculate the
reasonable maximum exposure. In general, combine 95th or 90th percentile values for contact rate
and exposure frequency and duration variables.
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Page 6-37
EXHIBIT 6-13
RESIDENTIAL EXPOSURE:
DERMAL CONTACT WITH CHEMICALS IN WATER"
Equation
Where:
CW =
SA =
PC =
ET =
EF =
ED =
CF =
BW =
AT =
Absorbed Dose tmg/kg-dav) = CW x SA x PC x ET x EF x ED x CF
BWxAT
Chemical Concentration in Water (rag/liter)
Skin Surface Area Available for Contact (cm2)
Chemical-specific Dermal Permeability Constant (cm/hr)
Exposure Time (hours/day)
Exposure Frequency (days/year)
Exposure Duration (years)
Volumetric Conversion Factor for Water (1 liter/1000 cm3)
Body Weight (kg)
Averaging Time (period over which exposure is averaged — days)
1
Variable Values:
CW: Site-specific measured or modeled value
SA:
50th Percentile Total Bodv Surface Area (m2) (EPA 1989d. 1985a)
AGE (YRS) MALE FEMALE
3 < 6 0.728 0.711
6 < 9 0.931 0.919
9 < 12 1.16 1.16
12 < 15 1.49 1.48
15 < 18 1.75 1.60
Adult 1.94 1.69
50th Percentile Bodv Part-specific Surface Areas for Males (m2) (EPA 1989d. 1985a)
AGE (YRS) ARMS HANDS LEGS
3 < 4 0.096 0.040 0.18
6 < 7 0.11 0.041 0.24
9 < 10 0.13 0.057 0.31
Adult 0.23 0.082 0.55
See Section 6.4.1 and 6.6.1 for a discussion of which variable values should be used to calculate the
reasonable maximum exposure. In general, combine 95th or 90th percentile values for contact rate and
exposure frequency and duration variables. Use 50th percentile values for SA; see text for rationale.
(continued)
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Page 6-38
EXHIBIT 6-13 (continued)
RESIDENTIAL EXPOSURE:
DERMAL CONTACT WITH CHEMICALS IN WATER"
NOTE: Values for children were calculated using age-specific body surface areas and the average
percentage of total body surface area represented by particular body parts in children,
presented in EPA 198Sa. Values for adults presented in EPA I989d or calculated from
information presented in EPA 1985a. Information on surface area of other body parts (e.g.,
head, feet) and for female children and adults also is presented in EPA 198Sa, 1989d.
Differences in body part surface areas between sexes is negligible.
PC: Consult open literature for values [Note that use of PC values results in
an estimate of absorbed dose.]
ET: Pathway-specific value (consider local activity patterns if information
is available)
2.6 hrs/day (national average for swimming; USDOI in
EPA 1988b, EPA 1989d)
EF: Pathway-specific value (should consider local climatic conditions
[e. g., number of days above a given temperature] and age of potentially
exposed population)
7 days/year (national average for swimming; USDOI in EPA 1988b,
EPA 1989d)
ED: 70 years (lifetime; by convention)
30 years (national upper-bound time (90th percentile) at one residence;
EPA 1989d)
9 years (national median time (50th percentile) at one residence;
EPA 1989d)
CF: 1 liter/1000 cm3
BW: 70 kg (adult, average; EPA 1989d)
Age-specific values (EPA 1985a, 1989d)
AT: Pathway-specific period of exposure for noncarcinogenic effects
(i.e., ED x 365 days/year), and 70 year lifetime for carcinogenic effects
(i.e., 70 years x 365 days/year).
"See Section 6.4.1 and 6.6.1 for a discussion of which variable values should be used to calculate
the reasonable maximum exposure. In general, combine 95th or 90th percentile values for
contact rale and exposure frequency and duration variables.
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Page 6-39
that this approach may underestimate dermal
permeability for some organic chemicals.
To calculate the reasonable maximum
exposure for this pathway, 50th percentile values,
instead of 95th percentile values, are used for the
area of exposed skin (SA). This is because
surface area and body weight are strongly
correlated and 50th percentile values are most
representative of the surface area of individuals of
average weight (e.g., 70 kg) which is assumed for
this and all other exposure pathways. Estimates
of exposure for this pathway are still regarded as
conservative because generally conservative
assumptions are used to estimate dermal
absorption (PC) and exposure frequency and
duration.
Consider pathway-specific variations for the
intake variables. SA will vary with activity and
the extent of clothing worn. For example, a
greater skin surface area would be in contact with
water during bathing or swimming than when
wading. Worker exposure via this pathway will
depend on the type of work performed at the site,
protective clothing worn, and the extent of water
use and contact.
6.6.2 CALCULATE SOIL, SEDIMENT, OR
DUST INTAKES
Individuals may be exposed to chemicals of
potential concern in soil, sediment, or dust by the
following routes:
(1) incidental ingestion; and
(2) dermal contact.
Inhalation exposures to airborne soil or dust are
discussed in Section 6.6.3.
Incidental ingestion. Calculate intakes from
incidental ingestion of chemicals in soil by
residents using the equation and variable values
presented in Exhibit 6-14. Consider population
characteristics that might influence variable values.
Exposure duration (ED) may be less for workers
and recreational users.
The value suggested for ingestion rate (IR)
for children 6 years old and younger are based
primarily on fecal tracer studies and account for
ingestion of indoor dust as well as outdoor soil.
These values should be viewed as representative
of long-term average daily ingestion rates for
children and should be used in conjunction with
an exposure frequency of 365 days/year. A term
can be used to account for the fraction of soil or
dust contacted that is presumed to be
contaminated (FI). In some cases, concentrations
in indoor dust can be equal to those in outdoor
soil. Conceivably, in these cases, FI could be
equal to 1.0.
For ingestion of chemicals in sediment, use
the same equation as that used for ingestion of
soil. Unless more pathway-specific values can be
found in the open literature, use as default
variable values the same values as those used for
ingestion of soil. In most instances, contact and
ingestion of sediments is not a relevant pathway
for industrial/commercial land use (a notable
exception to this could be workers repairing
docks).
Dermal contact. Calculate exposure from
dermal contact with chemicals in soil by residents
using the equation and variable values presented
in Exhibit 6-15. As was the case with exposure to
chemicals in water, calculation of exposure for this
pathway results in an estimate of the absorbed
dose, not the amount of chemical in contact with
the skin (i.e., intake). Absorption factors (ABS)
are used to reflect the desorption of the chemical
from soil and the absorption of the chemical
across the skin and into the blood stream.
Consult the open literature for information on
chemical-specific absorption factors. In the
absence of chemical-specific information, use
conservative assumptions to estimate ABS.
Again, as with dermal exposure to water, 50th
percentile body surface area (SA) values are used
to estimate contact rates. These values are used
along with average body weight because of the
strong correlation between surface area and body
weight. Contact rates may vary with time of year
and may be greater for individuals contacting soils
in the warmer months of the year when less
clothing is worn (and hence, more skin is available
for contact). Adherence factors (AF) are available
for few soil types and body parts. The literature
should be reviewed to derive AF values for other
soil types and other body parts. Exposure
frequency (EF) is generally determined using site-
specific information and professional judgment.
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Page 6-40
EXHIBIT 6-14
RESIDENTIAL EXPOSURE:
INGESTION OF CHEMICALS IN SOIL°
Equation:
Intake (mg/kg-day) = CS x IR x CF x FI x EF x ED
BWxAT
Where:
CS = Chemical Concentration in Soil (mg/kg)
IR = Ingestion Rate (mg soil/day)
CF = Conversion Factor (10-6 kg/mg)
FI = Fraction Ingested from Contaminated Source (unitless)
EF = Exposure Frequency (days/years)
ED = Exposure Duration (years)
BW = Body Weight (kg)
AT = Averaging Time (period over which exposure is averaged — days)
Variable Values:
CS: Site-specific measured value
IR: 200 mg/day (children, 1 through 6 years old; EPA 1989g)
100 mg/day (age groups greater than 6 years old; EPA 1989g)
NOTE: IR values are default values and could change based
on site-specific or other information. Research is currently ongoing
to better define ingestion rates. IR values do not apply to individuals
with abnormally high soil ingestion rates (i.e., pica).
CF: 10 "6 kg/mg
FI: Pathway-specific value (should consider contaminant location and
population activity patterns)
EF: 365 days/year
ED: 70 years (lifetime; by convention)
30 years (national upper-bound time (90th percentile) at one
residence; EPA 1989d)
9 years (national median time (50th percentile) at one residence;
EPA 1989d)
BW: 70 kg (adult, average; EPA 1989d)
16 kg (children 1 through 6 years old, 50th percentile; EPA 1985a)
AT: Pathway-specific period of exposure for noncarcinogenic effects
(i.e., ED x 365 days/year), and 70 year lifetime for carcinogenic effects
(i.e., 70 years x 365 days/year).
" See Section 6.4.1 and 6.6.2 for a discussion of which variable values should be used to calculate
the reasonable maximum exposure. In general, use 95th or 90th percentile values for contact rate
and exposure frequency and duration variables.
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Page 6-41
EXHIBIT 6-15
RESIDENTIAL EXPOSURE:
DERMAL CONTACT WITH CHEMICALS IN SOIL'
Equation:
Absorbed Dose (mg/kg-day) = CS x CF x SA x AF x ABS x EF x ED
BW x AT
Where:
CS =
CF =
SA =
AF =
ABS =
EF =
ED =
BW =
AT =
Chemical Concentration in Soil (mg/kg)
Conversion Factor (10 ~6 kg/ing)
Skin Surface Area Available for Contact (cm2/event)
Soil to Skin Adherence Factor (ing/cm2)
Absorption Factor (unitless)
Exposure Frequency (events/year)
Exposure Duration (years)
Body Weight (kg)
Averaging Time (period over which exposure is averaged — days)
Variable Values:
CS:
CF:
SA:
Based on site-specific measured value
10"* kg/mg
50th Percentile Total Body Surface Area (ma) (EPA 1989d. 1985a)
AGE (YRS)
3 < 6
6 < 9
9 < 12
12 < 15
15 < 18
Adult
0.728
0.931
1.16
1.49
1.75
1.94
FEMALE
0.711
0.919
1.16
1.48
1.60
1.69
50th Percentile Body Part-specific Surface Areas for Males (m2) (EPA 1989d. 1985a)
AGE (YRS)
3 < 4
6 < 7
9 < 10
Adult
ARMS
0.096
0.11
0.13
0.23
HANDS
0.040
0.041
0.057
0.082
LEGS
0.18
0.24
0.31
0.55
NOTE:
Values for children were calculated using age-specific body surface areas and the average percentage
of total body surface area represented by particular body parts in children, presented in EPA 198Sa.
Values for adults presented in EPA 1989d or calculated from information presented in EPA 1985a.
a See Section 6.4.1 and 6.6.2 for a discussion of which variable values should be used to calculate the reason-
able maximum exposure. In general, combine 95th or 90th percentile values for contact rate and exposure
frequency variables. Use 50th percentile values for SA; see text for rationale.
(continued)
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Page 6-42
EXHIBIT 6-15 (continued)
RESIDENTIAL EXPOSURE:
DERMAL CONTACT WITH CHEMICALS IN SOIL"
NOTE (continued): Information on surface area of other body parts (e.g., head, feet) and for female
children andadults also is presented in EPA 1985a, 1989d. Differences in body part surface
areas between sexes is negligible.
AF: 1.45 mg/cm2 — commercial potting soil (for hands; EPA 1989d, EPA
1988b)
2.77 mg/cm2 — kaolin clay (for hands; EPA 1989d, EPA 1988b)
ABS: Chemical-specific value (this value accounts for desorption of
chemical from the soil matrix and absorption of chemical across
the skin; generally, information to support a determination of ABS is
limited — see text)
EF: Pathway-specific value (should consider local weather conditions
[e.g.,number of rain, snow and frost-free days] and age of potentially
exposed population)
ED: 70 years (lifetime; by convention)
30 years (national upper-bound time (90th percentile) at one residence;
EPA 1989d)
9 years (national median time (50th percentile) at one residence;
EPA 1989d)
BW: 70 kg (adult, average; EPA 1989d)
Age-specific values (EPA 1985a, 1989d)
AT: Pathway-specific period of exposure for noncarcinogenic effects
(i.e., ED x 365 days/year), and 70 year lifetime for carcinogenic effects
(i.e., 70 years x 365 days/year).
" See Section 6.4.1 and 6.6.2 for a discussion of which variable values should be used to calculate the
reasonable maximum exposure. In general, combine 95th or 90th percentile values for contact rale
and exposure frequency and duration variables.
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Page 6-43
"Best guess" values for children potentially useful
in risk assessments are 3 times/week for fall and
spring days (>32°F) and 5 times/week for summer
days when children are not attending school. As
discussed previously, in some cases, concentrations
in indoor dust could be equal to that in outdoor
environments. Therefore, at some sites, EF could
be 365 days/year. Worker and recreational user
contact rates are dependent on the type of activity
at the site. Exposure duration (ED) and exposure
frequency (EF) may be lower for workers and
recreational users.
For dermal contact with sediment or dust,
use the same equation as that for dermal contact
with soil. As default values, also use the variable
values given for dermal contact with soil unless
more pathway-specific values can be found in the
open literature. Adherence factors for some
sediments (particularly sandy sediments) are likely
to be much less than for soils because contact
with water may wash the sediment off the skin.
Exposure frequency for sediments also is probably
lower than that for soils at many sites.
6.6.3
CALCULATE AIR INTAKES
Individuals may be exposed to chemicals of
potential concern in air by inhalation of chemicals
in the vapor phase or adsorbed to particulates.
Dermal absorption of vapor phase chemicals is
considered to be lower than inhalation intakes in
many instances and generally is not considered in
Superfund exposure assessments.
As with other pathways, the inhalation
intakes are expressed in units of mg/kg-day. The
combination of inhalation intakes with inhalation
RfDs (expressed in concentration units of mg/nv3)
will be discussed in Chapters 7 and 8.
Inhalation of vapor-phase chemicals.
Calculate intakes from inhalation of vapor phase
chemicals using the equation and variable values
presented in Exhibit 6-16. Consider variations
with land use. Exposure time (ET) will generally
be less for workers and recreational users. For
exposure times less than 24 hours per day, an
hourly inhalation rate (IR) based on activity, age,
and sex should be used instead of the daily IR
values. Exposure duration (ED) may also be less
for workers and recreational users.
Inhalation of particulate phase chemicals.
Calculate intakes from inhalation of particulate
phase chemicals by modifying the equations and
variable values presented in Exhibit 6-16 for
vapor-phase exposures. Derive inhalation
estimates using the particulate concentration in
air, the fraction of the particulate that is
respirable (i.e., particles 10 um or less in size)
and the concentration of the chemical in the
respirable fraction. Note that it may be necessary
to adjust intakes of particulate phase chemicals if
they are to be combined with toxicity values that
are based on exposure to the chemical in the
vapor phase. This adjustment is done in the risk
characterization step.
6.6.4
CALCULATE FOOD INTAKES
Individuals may be exposed by ingestion of
chemicals of potential concern that have
accumulated in food. The primary food items of
concern are:
(1) fish and shellfish;
(2) vegetables and other produce; and
(3) meat, eggs, and dairy products (domestic
and game species).
Ingestion of fish and shellfish. Calculate
intakes from ingestion of fish and shellfish using
the equation and variable values given in Exhibit
6-17. Exposure will depend in part on the
availability of suitable fishing areas. The chemical
concentration in fish or shellfish (CF) should be
the concentration in the edible tissues (when
available). The edible tissues will vary with
aquatic species and with population eating habits.
Residents near major commercial or recreational
fisheries or shell fisheries are likely to ingest
larger quantities of locally caught fish and shellfish
than inland residents. In most instances, workers
are not likely to be exposed via this pathway,
although at some sites this may be possible.
Ingestion of vegetables or other produce.
Calculate intakes from ingestion of contaminated
vegetables or other produce using the equation
and variable values given in Exhibit 6-18. This
pathway will be most significant for farmers and
for rural and urban residents consuming
homegrown fruits and vegetables. For
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Page 6-44
EXHIBIT 6-16
RESIDENTIAL EXPOSURE:
INHALATION OF AIRBORNE (VAPOR PHASE) CHEMICALS
ab
Equation:
Intake (mg/kg-day) = CA x IR x ET x EF x ED
BWxAT
Where:
CA =
IR =
ET =
EF =
ED =
BW =
AT =
Contaminant Concentration in Air (mg/m3)
Inhalation Kate (m3/hour)
Exposure Time (hours/day)
Exposure Frequency (days/year)
Exposure Duration (years)
Body Weight (kg)
Averaging Time (period over which exposure is averaged — days)
Variable Values:
CA:
IR:
ET:
EF:
ED:
BW:
AT:
Site-specific measured or modeled value
30 nvVday (adult, suggested upper bound value; EPA 1989d)
20 m3/day (adult, average; EPA 1989d)
Hourly rates (EPA 1989d)
Age-specific values (EPA 1985a)
Age, sex, and activity based values (EPA 1985a)
0.6 m3/hr — showering (all age groups; EPA 1989d)
Pathway-specific values (dependent on duration of exposure-related
activities)
12 minutes — showering (90th percentile; EPA 1989d)
7 minutes — showering (50th percentile; EPA 1989d)
Pathway-specific value (dependent on frequency of showering or other
exposure-related activities)
70 years (lifetime; by convention)
30 years (national upper-bound time (90th percentile) at one residence;
EPA 1989d)
9 years (national median time (50th percentile) at one residence;
EPA 1989d)
70 kg (adult, average; EPA 1989d)
Age-specific values (EPA 1985a, 1989d)
Pathway-specific period of exposure for noncarcinogenic effects
(i.e., ED x 365 days/year), and 70 year lifetime for carcinogenic effects
(i.e., 70 years x 365 days/year).
" See Section 6.4.1 and 6.6.3 for a discussion of which variable values should be used to calculate the
reasonable maximum exposure. In general, use 95th or 90th percentile values for contact rate and
exposure frequency and duration variables.
The equation and variable values for vapor phase exposure can be used with modification to calculate
particulate exposure. See text.
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Page 6-45
EXHIBIT 6-17
RESIDENTIAL EXPOSURE: FOOD PATHWAY —
INGESTION OF CONTAMINATED FISH AND SHELLFISH*
Equation:
Intake (mg/kg-day) = CF x IR x FI x EF x ED
BWxAT
Where:
CF
IR
FI
EF
ED
BW
AT
Contaminant Concentration in Fish (rag/kg)
Ingestion Rate (kg/meal)
Fraction Ingested from Contaminated Source (unitless)
Exposure Frequency (meals/year)
Exposure Duration (years)
Body Weight (kg)
Averaging Time (period over which exposure is averaged — days)
Variable Values:
CF:
IR:
FI:
EF:
ED:
BW:
AT:
Site-specific measured or modeled value
0.284 kg/meal (95th percentile for fin fish; Pao et al. 1982)
0.113 kg/meal (50th percentile for fin fish; Pao et al. 1982)
132 g/day (95th percentile daily intakes averaged over three days
for consumers of fin fish; Pao et al. 1982)
38 g/day (50th percentile daily intake, averaged over three days
for consumers of fin fish; Pao et al. 1982)
6.5 g/day (daily intake averaged over a year; EPA 1989d.
NOTE: Daily intake values should be used in conjunction with
an exposure frequency of 365 days/year.)
Specific values for age, sex, race, region and fish species are
available (EPA 1989d, 1989h)
Pathway-specific value (should consider local usage patterns)
Pathway-specific value (should consider local population patterns
if information is available)
48 days/year (average per capita for fish and shellfish; EPA Tolerance
Assessment System in EPA 1989h)
70 years (lifetime; by convention)
30 years (national upper-bound time (90th percentile) at one residence;
EPA 1989d)
9 years (national median time (50th percentile) at one residence;
EPA 1989d)
70 kg (adult, average; EPA 1989d)
Age-specific values (EPA 1985a, 1989d)
Pathway-specific period of exposure for noncarcinogenic effects
(i.e., ED x 365 days/year), and 70 year lifetime for carcinogenic effects
(i.e., 70 years x 365 days/year).
"See Section 6.4.1 and 6.6.4 for a discussion of which variable values should be used to calculate the
reasonable maximum exposure. In general, use 95th or 90th percentile values for intake rate and
exposure frequency and duration variables.
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Page 6-46
EXHIBIT 6-18
RESIDENTIAL EXPOSURE: FOOD PATHWAY —
INGESTION OF CONTAMINATED FRUITS AND VEGETABLES
Equation:
Intake (mg/kg-day) = CF x IR x FI x EF x ED
BVVxAT
Where:
CF
IR
FI
EF
ED
BW
AT
Contaminant Concentration in Food (mg/kg)
Ingestion Rate (kg/meal)
Fraction Ingested from Contaminated Source (unitless)
Exposure Frequency (meals/year)
Exposure Duration (years)
Body Weight (kg)
Averaging Time (period over which exposure is averaged — days)
Variable Values:
CF:
IR:
FI:
BW:
AT:
Site-specific measured value or modeled value based on soil
concentration and plant:soil accumulation factor or deposition factors
Specific values for a wide variety of fruits and vegetables are available
(Pao et al. 1982)
Pathway-specific value (should consider location and size of
contaminated area relative to that of residential areas, as well as
anticipated usage patterns)
Pathway-specific value (should consider anticipated usage patterns)
70 years (lifetime; by convention)
30 years (national upper-bound time (90th percentile) at one residence;
EPA 1989d)
9 years (national median time (50th percentile) at one residence;
EPA 1989d)
70 kg (adult, average; EPA 1989d)
Age-specific values (EPA 1985a, 1989d)
Pathway-specific period of exposure for noncarcinogenic effects
(i.e., ED x 365 days/year), and 70 year lifetime for carcinogenic effects
(i.e., 70 years x 365 days/year).
"See Section 6.4.1 and 6.6.4 for a discussion of which variable values should be used to calculate the
reasonable maximum exposure. In general, use 95th or 90th percentile values for contact rate and
exposure frequency and duration variables.
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Page 6-47
contaminated backyard gardens, the fraction of
food ingested that is contaminated (FI) can be
estimated using information on the fraction of
fruits or vegetables consumed daily that is home
grown (HF). EPA (1989d) provides HF values for
fruit (0.20, average; 0.30 worst-case) and
vegetables (0.25, average; 0.40, worst-case).
(Worst-case values can be used as estimates of the
95th percentile value.) Pao et al. (1982) provides
specific values for a variety of fruits and
vegetables.
Workers are not likely to be exposed via this
pathway. Recreational users could be exposed
from consuming wild fruits or vegetables from the
site, although such exposures are likely to be
negligible.
Ingestion of meat, eggs, and dairy products.
Calculate intakes from ingestion of contaminated
meat and dairy products using the equation and
variable values given in Exhibit 6-19. Derive
pathway-specific values as necessary. Rural
residents may consume poultry as well as livestock
and wild game that have been exposed to
contaminants at the site. The fraction of food
ingested daily that is contaminated (FI) can be
estimated for beef and dairy products using
information provided in EPA (1989d) on the
fraction of these foods that is homegrown (HF).
HF for beef is estimated to be 0.44 (average) and
0.75 (worst-case). HF for dairy products is
estimated to be 0.40 (average) and 0.75 (worst-
case). (Worst-case values can be used as estimates
of the 95th percentile value.) Consider land-use
variations. Workers are not likely to be exposed
via this pathway. Exposure duration (ED) and
exposure frequency (EF) will likely be less for
recreational users (e.g., hunters).
6.7 COMBINING CHEMICAL
INTAKES ACROSS
PATHWAYS
As discussed previously, the RME at a site
reflects the RME for a pathway as well as the
RME across pathways. A given population may
be exposed to a chemical from several exposure
routes. For example, residents may be exposed to
chemicals in ground water via ingestion of
drinking water and via inhalation of chemicals that
have volatilized from ground water during its use.
They also could be exposed to chemicals in vapors
or dust that have migrated from the site. To
calculate an exposure that is a reasonable
maximum across pathways, it may be necessary to
combine the RME for one pathway with an
estimate of more typical exposure for another
pathway (see Section 8.3.1). The average variable
values identified in the previous sections can be
used to calculate intakes for these more typical
exposures. At this point in the assessment,
estimated intakes are not summed across
pathways; this is addressed in the risk
characterization chapter. However, the assessor
should organize the results of the previous
exposure analyses (including any estimates of
typical exposure) by grouping all applicable
exposure pathway for each exposed population.
This organization will allow risks from appropriate
exposures to be combined in the risk
characterization chapter (see Exhibit 6-22 for a
sample summary format).
6.8 EVALUATING
UNCERTAINTY
The discussion of uncertainty is a very
important component of the exposure assessment.
Based on the sources and degree of uncertainty
associated with estimates of exposure, the
decision-maker will evaluate whether the exposure
estimates are the maximum exposures that can be
reasonably expected to occur. Section 8.4 provides
a discussion of how the exposure uncertainty
analysis is incorporated into the uncertainty
analysis for the entire risk assessment.
The discussion of uncertainty in the exposure
assessment chapter should be separated into two
parts. The first part is a tabular summary of the
values used to estimate exposure and the range of
these values. The table should include the
variables that appear in the exposure equation as
well as those used to estimate exposure
concentrations (e.g., model variables). A simple
example of this table is shown in Exhibit 6-20.
For each variable, the table should include the
range of possible values, the midpoint of the
range (useful values for this part are given in
Exhibits 6-11 through 6-19), and the value used to
estimate exposure. In addition, a brief description
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Page 6-48
EXHIBIT 6-19
RESIDENTIAL EXPOSURE: FOOD PATHWAY —
INGESTION OF CONTAMINATED MEAT, EGGS,
AND DAIRY PRODUCTS"
Equation:
Intake (mg/kg-day) = CF x IR x FI x EF x KD
BWxAT
Where:
CF = Contaminant Concentration in Food (mg/kg)
IR = Ingestion Rate (kg/meal)
FI = Fraction Ingested from Contaminated Source (unitless)
EF = Exposure Frequency (meals/year)
ED = Exposure Duration (years)
BVV = Body Weight (kg)
AT = Averaging Time (period over which exposure is averaged — days)
Variable Values:
CF: Site-specific measured or modeled value. Based on soil
concentrations, plant (feed) accumulation factors, and feed-to-meat
or feed-to-dairy product transfer coefficients
IR: 0.28 kg/meal — beef (95th percentile; Pao et al. 1982)
0.112 kg/meal — beef (50th percentile; Pao et al. 1982)
Specific values for other meats are available (Pao et al. 1982)
0.150 kg/meal — eggs (95th percentile; Pao et al. 1982)
0.064 kg/meal — eggs (50th percentile; Pao et al. 1982)
Specific values for milk, cheese and other dairy products are available
(Pao et al. 1982)
FI: Pathway-specific value (should consider location and size of contaminated
area relative to that of residential areas, as well as anticipated usage
patterns)
EF: Pathway-specific value (should consider anticipated usage patterns)
ED: 70 years (lifetime; by convention)
30 years (national upper-bound time (90th percentile) at one residence;
EPA 1989d)
9 years (national median time (50th percentile) at one residence;
EPA1989d)
BW: 70 kg (adult, average; EPA 1989d)
Age-specific values (EPA 1985a, 1989d)
AT: Pathway-specific period of exposure for noncarcinogenic effects
(i.e., ED x 365 days/year), and 70 year lifetime for carcinogenic effects
(i.e., 70 years x 365 days/year).
a See Section 6.4.1 and 6.6.4 for a discussion of which variable values should be used to calculate
the reasonable maximum exposure. In general, use 95th or 90th percentile values for contact rate
and exposure frequency and duration.
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Page 6-49
EXHIBIT 6-20
EXAMPLE OF TABLE FORMAT FOR SUMMARIZING
VALUES USED TO ESTIMATE EXPOSURE
Variable
Range
Midpoint
Value Used
Brief Rationale
PCB concentration ND - 3,500 250
in soil (nig/kg) (arithmetic mean)
Chronic exposure
(rag/kg)
1,400 95th percentile upperbound
estimate of mean concentration
Acute exposure
(rag/kg)
3,500
Maximum detected concentration
Adult soil ingestion 0 - 170 17
rate (mg/d) (arithmetic mean)
100 Range based on assumptions
regarding soil adherence and
percent ingestion. Value used
is from EPA 1989g.
Exposure frequency
(days/wk)
1-7
Best professional judgment.
Exposure duration
(years)
1-20
10
20
Best professional judgment.
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Page 6-50
of the selection rationale should be included. The
discussion that accompanies the table in the
exposure assessment chapter should identify which
variables have the greatest range and provide
additional justification for the use of values that
may be less certain.
The second part of the uncertainty discussion
is to summarize the major assumptions of the
exposure assessment, to discuss the uncertainty
associated with each, and to describe how this
uncertainty is expected to affect the estimate of
exposure. Sources of uncertainty that should be
addressed include 1) the monitoring data, which
may or may not be representative of actual
conditions at the site; 2) the exposure models,
assumptions and input variables used to estimate
exposure concentrations; and 3) the values of the
intake variables used to calculate intakes. Each
of these sources should be discussed in the
summary section of the exposure assessment. A
table may be useful in summarizing this
information. Exhibit 6-21 presents a sample
format.
A supplemental approach to uncertainty
analysis is to use analytical methods (e.g., first-
order uncertainty analysis) or numerical methods
(e.g., Monte Carlo analysis). These methods and
their limitations are described in greater detail in
Section 8.4 It is recommended that these analyses
be used only after approval of the EPA project
manager, and then, only as a part of the
uncertainty analysis (and not as a basis for the
reasonable maximum exposure).
6.9 SUMMARIZING AND
PRESENTING THE EXPOSURE
ASSESSMENT RESULTS
At this point, the exposure assessor should
summarize the results of the exposure assessment.
The summary information should be presented in
table format and should list the estimated
chemical-specific intakes for each pathway. The
pathways should be grouped by population so that
risks can be combined across pathways as
appropriate. The summary information should be
further grouped by current and future use
categories. Within these categories, subchronic
and chronic daily intakes should be summarized
separately. Exhibit 6-22 presents a sample format
for this summary information. In addition to the
summary table, provide sample calculations for
each pathway, to aid in the review of the
calculations.
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Page 6-51
EXHIBIT 6-21
EXAMPLE OF AN UNCERTAINTY TABLE FOR
EXPOSURE ASSESSMENT
EFFECT ON EXPOSURE "
ASSUMPTION
Potential
Magnitude
for Over-
Estimation
of Exposure
Potential
Magnitude
for Under-
Estimation
of Exposure
Potential
Magnitude
for Over-
or Under
Estimation
of Exposure
Environmental Sampling and Analysis
Sufficient samples may not have
been taken to characterize the media
being evaluated, especially with
respect to currently available soil data.
Systematic or random errors in the
chemical analyses may yield erroneous
data.
Moderate
Low
Fate and Transport Modeling
Chemicals in fish will be at Low
equilibrium with chemical
concentrations in water.
Use of a Gaussian dispersion model
to estimate air concentrations offsite.
Use of a box model to estimate Low
air concentrations onsite.
Use of Cowherd's model to estimate
vehicle emission factors.
Moderate
Low
Exposure Parameter Estimation
The standard assumptions regarding
body weight, period exposed, life
expectancy, population characteristics,
and lifestyle may not be representative
of any actual exposure situation.
The amount of media intake is assumed Moderate
to be constant and representative
of the exposed population.
Assumption of daily lifetime Moderate to
exposure for residents. High
Use of "hot spot" soil data for Moderate to
upper-bound lifetime exposure High
Moderate
As a general guideline, assumptions marked as "low", may affect estimates of exposure by less than one
order of magnitude; assumptions marked "moderate" may affect estimates of exposure by between one and
two orders of magnitude; and assumptions marked "high" may affect estimates of exposure by more than
two orders of magnitude.
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Page 6-52
EXHIBIT 6-22
EXAMPLE OF TABLE FORMAT FOR SUMMARIZING
THE RESULTS OF THE EXPOSURE ASSESSMENT-
CURRENT LAND USE*
Population
Residents
Exposure Pathway
Ingestion of ground water
that has migrated from
the site to downgradient
local wells
Inhalation of chemicals
that have volatilized from
ground water during use
Ingestion of fish
that have accumulated
chemicals in nearby
lake
Chemical
Benzene
Chlordane
Phenol
Cyanide
Nitrobenzene
Benzene
Chlordane
MEK
Phenol
Chronic Daily Intake
Carcinogenic
Effects
0.00025
0.00015
c
c
c
0.000013
0.00008
c
c
(CDI) (mc/kg-day)
Noncarcinogenic
Effects
b
0.00035
0.1
0.0003
0.0001
b
0.00019
0.005
0.08
" Similar tables should be prepared for all subchronic daily intake (SDI) estimates as well as for all CDI
and SDI estimates under future land use conditions.
CDI for noncarcinogenic effects not calculated for benzene because it does not have an EPA-verified
chronic reference dose (as of the publication dale of this manual).
c CDI for carcinogenic effects not calculated for chemicals not considered by EPA to be potential human
carcinogens (as of the publication date of this manual).
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REFERENCES FOR CHAPTER 6
Baes, C.F., III, Sharp, R.D., Sjoreen, A.L., and Shore, R. W. 1984. A Review and Analysis of Parameters for Assessing Transport of
Environmentally Released Radionuclides through Agriculture. Oak Ridge National Laboratory. Prepared for U.S. Department
of Energy. ORNL-5786.
Blank, I.H., Moloney, J., Alfred, B.S., Simon, I., and Apt, C. 1984. The Diffusion of Water Across the Stratum Corneum as a Function
of its Water Content. J. Invest. Derm. 82:188-194.
Calamari, D., Vighi, M., and Bacci, E. 1987. The Use of Terrestrial Plant Biomass as a Parameter in the Fugacity Model.
Chemosphere. 16:2539-2364.
Clark, I. 1979. Practical Geostatistics. Applied Science Publishers, Ltd. London.
Environmental Protection Agency (EPA). 1985a. Development of Statistical Distributions or Ranges of Standard Factors Used in
Exposure Assessments. Office of Health and Environmental Assessment.
Environmental Protection Agency (EPA). 1985b. Compilation of Air Pollutant Emission Factors. Volume 1. Stationary Point and
Area Sources. Fourth Edition. Office of Research and Development. Research Triangle Park, NC.
Environmental Protection Agency (EPA). 1985c. Environmental Profiles and Hazard Indices for Constituents of Municipal Sludge.
Office of Water. (Individual documents are available for a number of substances).
Environmental Protection Agency (EPA). 1986a. Guidelines for Exposure Assessment. 51 Federal Register 34042 (September 24,
1986).
Environmental Protection Agency (EPA). 1986b. Guidelines for Carcinogen Risk Assessment. 51 Federal Register 33992 (September
24, 1986).
Environmental Protection Agency (EPA). 1987a. Industrial Source Complex (ISC') Dispersion Model User's Guide. Volume I. Office
of Air Quality Planning and Standards. Research Triangle Park, NC. EPA/450/4-88/002a.
Environmental Protection Agency (EPA). 1987b. Selection Criteria for Mathematical Models Used in Exposure Assessments: Surface
Water Models. Office of Health and Environmental Assessment. EPA/600/8-87/042.
Environmental Protection Agency (EPA). 1988a. Proposed Guidelines for Exposure-related Measurements. 53 Federal Register 48830
(December 2, 1988).
Environmental Protection Agency (EPA). 1988b. Superfund Exposure Assessment Manual. Office of Emergency and Remedial
Response. EPA/540/1-88/001. (OSWER Directive 9285.5-1).
Environmental Protection Agency (EPA). 1988c. Selection Criteria for Mathematical Models Used in Exposure Assessments: Ground-
water Models. Office of Health and Environmental Assessment. EPA/600/8-88/075.
Environmental Protection Agency (EPA). 1989a. Air Superfund National Technical Guidance Series. Volume I: Application of Air
Pathway Analyses for Superfund Activities. Interim Final. Office of Air Quality Planning and Standards. Research Triangle Park,
NC. EPA/450/1-89/001.
Environmental Protection Agency (EPA). 1989b. Air Superfund National Technical Guidance Series. Volume II: Estimation of
Baseline Air Emissions at Superfund Sites. Interim Final. Office of Air Quality Planning and Standards. Research Triangle Park,
NC. EPA/450/1-89/002.
Environmental Protection Agency (EPA). 1989c. Air Superfund National Technical Guidance Series. Volume IV: Procedures for
Dispersion Modeling and Air Monitoring for Superfund Air Pathway Analysis. Interim Final. Office of Air Quality Planning and
Standards. Research Triangle Park, NC. EPA/450/1-89/004.
Environmental Protection Agency (EPA). 1989d. Exposure Factors Handbook. Office of Health and Environmental Assessment.
EPA/600/8-89/043.
Environmental Protection Agency (EPA). 1989e. Proposed Amendments to the Guidelines for the Health Assessment of Suspect
Developmental Toxicants. 54 Federal Register 9386 (March 6, 1989).
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Environmental Protection Agency (EPA). 1989f. Exposure Assessment Methods Handbook. Draft. Office of Health and
Environmental Assessment.
Environmental Protection Agency (EPA). 1989g. Interim Final Guidance for Soil Ingestion Rates. Office of Solid Waste and
Emergency Response. (OSWER Directive 9850.4).
Environmental Protection Agency (EPA). 1989h. Guidance Manual for Assessing Human Health Risks From Chemically Contaminated
Fish and Shellfish. Office of Marine and Estuarine Protection. EPA/503/8-89/002.
Fries, G.F., Marrow, G.S., and Gordon, C.H. 1973. Long-term Studies of Residue Retention and Excretion by Cows Fed a
Polychlorinated Biphenyl (Aroclor 1254). J. Agric. Food Chem. 21:117-121.
Gilbert, R.O. 1987. Statistical Methods for Environmental Pollution Monitoring. Van Nostrand Reinhold. New York.
Jensen, D.J., Hummel, R.A., Mahle, N.H., Kocher, C.W., and Higgins, H.S. 1981. A Residue Study on Beef Cattle Consuming 2,3,7,8-
Tetrachlorodibenzo-p-dioxin. J. Agric. Food Chem. 29:265-268.
Jensen, D.J. and Hummel, R.A. 1982. Secretion of TCDD in Milk and Cream Following the Feeding of TCDD to Lactating Dairy
Cows. Bull. Env. Contam. Toxicol. 29:440-446.
Ng, Y.C., Colsher, C.S., Quinn, D.J. and Thompson, S.E. 1977. Transfer Coefficients for the Prediction of the Dose to Man Via the
Forage-Cow-Milk Pathway from Radionuclides Released to the Biosphere. Lawrence Livermore National Laboratory, Univ.
California. Prepared for U.S. Dept. of Energy. UCRL-5139.
Ng, Y.C., Colsher, C.S., and Thompson, S.E. 1979. Transfer Factors for Assessing the Dose from Radionuclides in Agricultural
Products. Biological Implications of Radionuclides Released From Nuclear Industries. In: Proceedings of an International
Symposium on Biological Implications of Radionuclides Released from Nuclear Industries. Vienna. March 26-30,1979. IAEA-
SM-237/54. Vol. II.
Ng, Y.C., Colsher, C.S., and Thompson, S.E. 1982. Transfer Coefficients for Assessing the Dose from Radionuclides in Meat and Eggs.
Lawrence Livermore National Laboratory. NUREG/CR-2976.
Pao, E.M., Fleming, K.H., Gueuther, P.M., and Mickle, SJ. 1982. Food Commonly Eaten by Individuals: Amount Per Day and Per
Eating Occasion. U.S. Department of Agriculture.
Schaum, J.L. 1984. Risk Analysis of TCDD Contaminated Soil. Office of Health and Environmental Assessment, U.S. Environmental
Protection Agency. EPA/600/8-84/031.
Travis, C.C. and Arms, A.D. 1988. Bioconcentration of Organics in Beef, Milk, and Vegetation. Environ. Sci. Technol. 22:271-274.
Van Bruwaene, R., Gerber, G.B., Kerchmann, R., Colard, J. and Van Kerkom, J. 1984. Metabolism of 51Cr, 54Mn, 59Fe and 60Co
in Lactating Dairy Cows. Health Physics 46:1069-1082.
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CHAPTER 7
TOXICITY ASSESSMENT
/FROM: "
•Site discovery
• Preliminary
assessment
•Site inspection
\»NPL listing ^
Data
Collection
ToxicHy
Assessment
i Data
! Evaluation
Risk
Characterization
Exposure
Assessment
•Selection of
remedy
• Remedial
design
• Remedial
, action >
TOXICITY ASSESSMENT
• Gather qualitative and quantitative
toxicity information for substances
being evaluated
• Identify exposure periods for which
toxicity values are necessary
• Determine toxicity values for
noncarcinogenic effects
• Determine toxicity values for
carcinogenic effects
-------
CHAPTER?
TOXICITY ASSESSMENT
The purpose of the toxicily assessment is to
weigh available evidence regarding the potential
for particular contaminants to cause adverse
effects in exposed individuals and to provide,
where possible, an estimate of the relationship
between the extent of exposure to a contaminant
and the increased likelihood and/or severity of
adverse effects.
Toxicity assessment for contaminants found
at Superfund sites is generally accomplished in
two steps: hazard identification and dose-response
assessment. These two steps were first discussed
in the National Academy of Sciences' publication
entitled Risk Assessment in the Federal Government
- Managing the Process and more recently in
EPA's Guidelines for Carcinogen Risk Assessment
(NAS 1983, EPA 1986). The first step, hazard
identification, is the process of determining
whether exposure to an agent can cause an
increase in the incidence of a particular adverse
health effect (e.g., cancer, birth defect) and
whether the adverse health effect is likely to occur
in humans. Hazard identification involves
characterizing the nature and strength of the
evidence of causation. The second step, dose-
response evaluation. is the process of
quantitatively evaluating the toxicity information
and characterizing the relationship between the
dose of the contaminant administered or received
and the incidence of adverse health effects in the
exposed population. From this quantitative dose-
response relationship, toxicity values (e.g.,
reference doses and slope factors) are derived that
can be used to estimate the incidence or potential
for adverse effects as a function of human
exposure to the agent. These toxicity values are
used in the risk characterization step to estimate
the likelihood of adverse effects occurring in
humans at different exposure levels.
Toxicity assessment is an integral part of the
overall Superfund site risk assessment. Although
toxicity information is critical to the risk
assessment, the amount of new lexicological
evaluation of primary data required to complete
this step is limited in most cases. EPA has
performed the toxicity assessment step for
numerous chemicals and has made available the
resulting toxicity information and toxicity values,
which have undergone extensive peer review. At
some sites, however, there will be significant data
analysis and interpretation issues that should be
addressed by an experienced lexicologist. This
chapter provides step-by-slep guidance for localing
EPA loxicily assessments and accompanying
values, and advises how lo deiermine which values
are mosl appropriale when multiple values exist
Prior lo Ihis procedural discussion, background
ACRONYMS FOR CHAPTER 7
ADI *=
AIC =
A1S =
CRAVE =
ECAO =
HAD =
HEA =
HEAST =
HEED =
HEEP =
IRIS =
LOAEL =
NOAEL =
NOEL =
RfD =
Acceptable Daily Intake
Acceptable Intake for Chronic Exposure
Acceptable Intake for Subchronic
Exposure
Carcinogen Risk Assessment
Verification Endeavor
Environmental Criteria and Assessment
Office
Health Assessment Document
Health Effects Assessment
Health Effects Assessment Summary
Tables
Health and Environmental Effects
Document
Health and Environmental Effects
Profile
Integrated Risk Information System
Lowest-Observed-Adverse-Effect-Level
No-Observed-Adverse-Effect-Level
No-Observed-Effect-Level
Reference Dose (when used without
other modifiers, RfD generally refers to
chronic reference dose)
Developmental Reference Dose
Subchronic Reference Dose
-------
Page 7-2
DEFINITIONS FOR CHAPTER 7
Acceptable Daily Intake (ADIV An estimate similar in concept to the RfD, but derived using a less strictly defined methodology.
RfDs have replaced ADIs as the Agency's preferred values for use in evaluating potential noncarcinogenic health effects
resulting from exposure to a chemical.
Acceptable Intake for Chronic Exposure fAIC). An estimate similar in concept to the RfD, but derived using a !ess strictly
defined methodology. Chronic RfDs have replaced AICs as the Agency's preferred values for use in evaluating potential
noncarcinogenic health effects resulting from chronic exposure to a chemical,
Acceptable Intake for Subchronic Exposure CAISt. An estimate similar in concept to the subchronic RfD, but derived using a
less strictly defined methodology. Subehrome RfDs have replaced AISs as the Agency's preferred values for Use in
evaluating potential noncarcinogenic health effects resulting from subchronic exposure to a chemical.
Chronic Reference Dose fRtDV An estimate (with uncertainty spanning perhaps an order of magnitude or greater) of a daily
exposure level for the human population, including sensitive subpopulations, that is likely to be without an appreciable risk
of deleterious effects during a lifetime. Chronic RfDs are specifically developed to be protective for long-term exposure
to a compound (as a Superfund program guideline, seven years to lifetime).
Developmental Reference Dose (RfDj;). An estimate (with uncertainty spanning perhaps an order of magnitude or greater)
of an exposure level for the human population, including sensitive subpopulations, that is likely to be without an appreciable
risk of developmental effects. Developmental RfDs are used to evaluate the effects of a single exposure event.
Dose-response Evaluation. The process of quantitatively evaluating toxicity information and characterizing the relationship
between the dose of a contaminant administered or received and the incidence of adverse health effects in the exposed
population. From the quantitative dose-response relationship, toxicity values are derived that are used in the risk
characterization step to estimate the likelihood of adverse effects occurring in humans at different exposure levels,
Hazard Identification. The process of determining whether exposure to an agent can cause an increase in the incidence of a
particular adverse health effect (e.g., cancer, birth defect) and whether the adverse health effect is likely to occur in humans.
Integrated Risk Information System (IRISV An EPA data base containing verified RfDs and slope factors and up-to-date health
risk and EPA regulatory information for numerous chemicals. IRIS is EPA's preferred source for toxicity information for
Superfund.
Lowest-Observed-Adverse-Effect-Level (LOAELV In dose-response experiments, the lowest exposure level at which there are
statistically or biologically significant increases in frequency or severity of adverse effects between the exposed population
and its appropriate control group.
No-Observed-Adverse-Effect-Level (NOABU). In dose-response experiments, an exposure level at which there are no statistically
or biologically significant increases in the frequency or severity of adverse effects between the exposed population and its
appropriate control; some effects may be produced at this level, but they are not considered to be adverse, nor precursors
to specific adverse effects. In an experiment with more than one NOAEL. the regulatory focus is primarily on the highest
one, leading to the common usage of the term NOAEL to mean the highest exposure level without adverse effect.
No-Observed-Effect-Level CNOBL). In dose-response experiments, an exposure level at which there are no statistically or
biologically significant increases in the frequency or severity of any_ effect between the exposed population and its appropriate
control.
Reference Dose (RfD>. The Agency's preferred toxicity value for evaluating noncarcinogenic effects resulting from exposures
at Superfund sites. See specific entries for chronic RfD, subchronic RfD, and developmental RfD. The acronym RfD,
when used without other modifiers, either refers generically to all types of RfDs or specifically to chronic RfDs; it never
refers specifically to subchronic or developmental RfDs.
(continued)
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Page 7-3
DEFINITIONS FOR CHAPTER 7
(continued)
Slope Factor. A plausible upper-bound estimate of the probability of a response per unit intake of a chemical over a lifetime.
The slope factor is used to estimate an upper-bound probability of an individual developing cancer as a result of a lifetime
of exposure to a particular level of a potential carcinogen.
Subchronic Reference Dose (RfD,). An estimate (with uncertainty spanning perhaps an order of magnitude or greater) of a
daily exposure level for the human population, including sensitive subpopulations, that is likely to be without an appreciable
risk of deleterious effects during a portion of a lifetime (as a Superfund program guideline, two weeks to seven years).
Toxicitv Value. A numerical expression of a substance's dose-response relationship that is used in risk assessments. The most
common toxicity values used in Superfund program risk assessments are reference doses (for noncarcinogenic effects) and
slope factors (for carcinogenic effects).
Weight of Evidence Classification. An EPA classification system for characterizing the extent to which the available data indicate
that an agent is a human carcinogen. Recently, EPA has developed weight-of-evidence classification systems for some other
kinds of toxic effects, such as developmental effects.
information regarding EPA's methods for toxicity
assessment is provided to assist the risk assessor
in understanding the basis of the toxicity values
and the limitations of their use. The steps of the
toxicity assessment are illustrated in Exhibit 7-1.
Derivation and interpretation of toxicity
values requires lexicological expertise and should
not be undertaken by those without training and
experience. Detailed guidance for deriving toxicity
values is beyond the scope of this document. For
those persons interested in obtaining additional
information about EPA's methods for toxicity
assessment, references to appropriate guidance
documents are given throughout this chapter.
7.1 TYPES OF TOXICOLOGICAL
INFORMATION CONSIDERED
IN TOXICITY ASSESSMENT
This section summarizes information from
several EPA documents (especially EPA 1989a, f)
on the basic types of data used in toxicity
assessment. As part of the hazard identification
step of the toxicity assessment, EPA gathers
evidence from a variety of sources regarding the
potential for a contaminant to cause adverse
health effects (carcinogenic and noncarcinogenic)
in humans. These sources may include controlled
epidemiologic investigations, clinical studies, and
experimental animal studies. Supporting
information may be obtained from sources such as
in vitro test results and comparisons of structure-
activity relationships.
7.1.1 HUMAN DATA
Well-conducted epidemiologic studies that
show a positive association between an agent and
a disease are accepted as the most convincing
evidence about human risk. At present, however,
human data adequate to serve as the sole basis of
a dose-response assessment are available for only
a few chemicals. Humans are generally exposed
in the workplace or by accident, and because these
types of exposures are not intentional, the
circumstances of the exposures (concentration and
time) may not be well known. Often the
incidence of effects is low, the number of exposed
individuals is small, the latent period between
exposure and disease is long, and exposures are to
mixed and multiple substances. Exposed
populations may be heterogeneous, varying in age,
sex, genetic constitution, diet, occupational and
home environment, activity patterns, and other
cultural factors affecting susceptibility. For these
reasons, epidemiologic data require careful
interpretation. If adequate human studies
(confirmed for validity and applicability) exist,
these studies are given first priority in the dose-
response assessment, and animal toxicity studies
are used as supportive evidence.
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Page 7-4
EXHIBIT 7-1
STEPS IN TOXICITY ASSESSMENT
Step 1: Gather Toxicity Information-
Qualitative and Quantitative-
for Substances Being Evaluated
Step 2: Identify Exposure Periods for
Which Toxicity Values Are Necessary
Step 3: Determine Toxicity Values for
Noncarcinogenic Effects
Step 4: Determine Toxicity Values for
Carcinogenic Effects
Step 5: Summarize Toxicity Information
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Page 7-5
Human studies having inadequate exposure-
response information for a quantitative assessment
are often used as supporting data. Such studies
may establish a qualitative relationship between
environmental exposures and the presence of an
adverse effect in exposed human populations. For
example, case reports of exposures resulting in
effects similar to the types of effects observed in
animals provide support for the conclusions drawn
from the animal data.
7.1.2 ANIMAL DATA
The toxicity data base for most chemicals
lacks sufficient information on toxic effects in
humans. In such cases, EPA may infer the
potential for the substance to cause an adverse
effect in humans from toxicity information drawn
from experiments conducted on non-human
mammals, such as the rat, mouse, rabbit, guinea
pig, hamster, dog, or monkey. The inference that
humans and animals (mammals) are similar, on
average, in intrinsic susceptibility to toxic
chemicals and that data from animals can in many
cases be used as a surrogate for data from humans
is the basic premise of modern toxicology. This
concept is particularly important in the regulation
of toxic chemicals. There are occasions, however,
in which observations in animals may be of
uncertain relevance to humans. EPA considers
the likelihood that the agent will have adverse
effects in humans to increase as similar results are
observed across sexes, strains, species, and routes
of exposure in animal studies.
7.1.3 SUPPORTING DATA
Several other types of studies used to support
conclusions about the likelihood of occurrence of
adverse health effects in humans are described
below. At the present time, EPA considers all of
these types of data to be supportive, not
definitive, in assessing the potential for adverse
health effects in humans.
Metabolic and other pharmacokinetic studies
may be used to provide insights into the
mechanism of action of a particular compound.
By comparing the metabolism of a compound
exhibiting a toxic effect in an animal with the
corresponding metabolism in humans, evidence for
the potential of the compound to have toxic
effects in humans may be obtained.
Studies using cell cultures or microorganisms
may be used to provide insights into a compound's
potential for biological activity. For example, tests
for point mutations, numerical and structural
chromosome aberrations, DNA damage/repair, and
cell transformation may provide supportive
evidence of carcinogenicity and may give
information on potential mechanisms of
carcinogenicity. It should be noted, however, that
lack of positive results in short-term tests for
genotoxicity is not considered a basis for
discounting positive results in long-term
carcinogenicity studies in animals.
Structure-activity studies (i.e., predictions of
toxicologic activity based on analysis of chemical
structure) are another potential source of
supporting data. Under certain circumstances, the
known activity of one compound may be used to
estimate the activity of another structurally related
compound for which specific data are lacking.
7.2 TOXICITY ASSESSMENT FOR
NONCARCINOGENIC EFFECTS
This section summarizes how the types of
toxicity information presented in Section 7.1 are
considered in the toxicity assessment for
noncarcinogenic effects. A reference dose, or
RfD, is the toxicity value used most often in
evaluating noncarcinogenic effects resulting from
exposures at Superfund sites. Additionally, One-
day or Ten-day Health Advisories (HAs) may be
used to evaluate short-term oral exposures. The
methods EPA uses for developing RfDs and HAs
are described below. Various types of RfDs are
available depending on the exposure route (oral
or inhalation), the critical effect (developmental
or other), and the length of exposure being
evaluated (chronic, subchronic, or single event).
This section is intended to be a summary
description only; for additional details, refer to the
appropriate guidelines and other sources listed as
references for this chapter (especially EPA 1986b,
EPA 1989b-f).
A chronic RfD is defined as an estimate
(with uncertainty spanning perhaps an order of
magnitude or greater) of a daily exposure level for
the human population, including sensitive
subpopulations, that is likely to be without an
-------
Page 7-6
appreciable risk of deleterious effects during a
lifetime. Chronic RfDs are specifically developed
to be protective for long-term exposure to a
compound. As a guideline for Superfund program
risk assessments, chronic RfDs generally should be
used to evaluate the potential noncarcinogenic
effects associated with exposure periods between
7 years (approximately 10 percent of a human
lifetime) and a lifetime. Many chronic RfDs have
been reviewed and verified by an intra-Agency
RfD Workgroup and entered into the Agency's
Integrated Risk Information System (IRIS).
FORMER TERMINOLOGY
Prior to the development of RfDs, noncarcinogenic
effects of chronic exposures were evaluated using values
called acceptable daily intakes (APIs') or acceptable
intakes for chronic exposure (AICsV While ADIs and
AICs are similar in concept to RfDs, RfDs have been
derived using a more strictly defined methodology and
represent the Agency's preferred toxicity values.
Furthermore, many chronic RfDs have been reviewed
and verified by an intra-Agency RfD Workgroup; these
verified RfDs represent an Agency consensus and are
preferred over other RfDs that have not undergone such
review (see Section 7.2.7, Verification of RfDs).
Similarly, acceptable intakes for subchronic exposures
(AISs) have been superseded by the more strictly
defined subchronic RfD values. Therefore, the former
terminology (ADI, AIC, AIS) should no longer be used
in Superfund program risk assessments.
More recently, EPA has begun developing
subchronic RfDs (RfD^s'), which are useful for
characterizing potential noncarcinogenic effects
associated with shorter-term exposures, and
developmental RfDs (RfD^/s). which are useful
specifically for assessing potential developmental
effects resulting from exposure to a compound.
As a guideline for Superfund program risk
assessments, subchronic RfDs should be used to
evaluate the potential noncarcinogenic effects of
exposure periods between two weeks and seven
years. Such short-term exposures can result when
a particular activity is performed for a limited
number of years or when a chemical with a short
half-life degrades to negligible concentrations
within several months. Developmental RfDs are
used to evaluate the potential effects on a
developing organism following a single exposure
event.
7.2.1 CONCEPT OF THRESHOLD
For many noncarcinogenic effects, protective
mechanisms are believed to exist that must be
overcome before the adverse effect is manifested.
For example, where a large number of cells
perform the same or similar function, the cell
population may have to be significantly depleted
before the effect is seen. As a result, a range of
exposures exists from zero to some finite value
that can be tolerated by the organism with
essentially no chance of expression of adverse
effects. In developing a toxicity value for
evaluating noncarcinogenic effects (i.e., an RfD),
the approach is to identify the upper bound of
this tolerance range (i.e., the maximum
subthreshold level). Because variability exists in
the human population, attempts are made to
identify a subthreshold level protective of sensitive
individuals in the population. For most chemicals,
this level can only be estimated; the RfD
incorporates uncertainty factors indicating the
degree or extrapolation used to derive the
estimated value. RfD summaries in IRIS also
contain a statement expressing the overall
confidence that the evaluators have in the RfD
(high, medium, or low). The RfD is generally
considered to have uncertainty spanning an order
of magnitude or more, and therefore the RfD
should not be viewed as a strict scientific
demarcation between what level is toxic and
nontoxic.
7.2.2 DERIVATION OF AN ORAL RfD (RfD0)
Identifying the critical study and determining
the NOAEL. In the development of oral RfDs, all
available studies examining the toxicity of a
chemical following exposure by the oral route are
gathered and judged for scientific merit.
Occasionally, studies based on other exposure
routes (e.g., inhalation) are considered, and the
data are adjusted for application to the oral route.
Any differences between studies are reconciled and
an overall evaluation is reached. If adequate
human data are available, this information is used
as the basis of the RfD. Otherwise, animal study
data are used; in these cases, a series of
professional judgments are made that involve,
among other considerations, an assessment of the
relevance and scientific quality of the experimental
studies. If data from several animal studies are
being evaluated, EPA first seeks to identify the
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Page 7-7
animal model that is most relevant to humans
based on a defensible biological rationale, for
instance, using comparative metabolic and
pharmacokinetic data. In the absence of a species
that is clearly the most relevant, EPA assumes
that humans are at least as sensitive to the
substance as the most sensitive animal species
tested. Therefore, as a matter of science policy,
the study on the most sensitive species (the
species showing a toxic effect at the lowest
administered dose) is selected as the critical study
for the basis of the RfD. The effect characterized
by the "lowest-observed-adverse-effect-lever
(LOAEL) after dosimetric conversions to adjust
for species differences is referred to as the critical
toxic effect.
After the critical study and toxic effect have
been selected, EPA identifies the experimental
exposure level representing the highest level tested
at which no adverse effects (including the critical
toxic effect) were demonstrated. This highest "no-
observed-adverse-effect level" (NOAEL) is the key
datum obtained from the study of the dose-
response relationship. A NOAEL observed in an
animal study in which the exposure was
intermittent (such as five days per week) is
adjusted to reflect continuous exposure.
The NOAEL is selected based in part on the
assumption that if the critical toxic effect is
prevented, then all toxic effects are prevented.
The NOAEL for the critical toxic effect should
not be confused with the "no-observed-effect level"
(NOEL). The NOEL corresponds to the exposure
level at which no effect at all has been observed;
frequently, effects are observed that are not
considered to be of lexicological significance. In
some studies, only LOAEL rather than a NOAEL
is available. The use of a LOAEL, however,
MULTIPLE TOXIC EFFECTS AND RfDs
The RfD is developed from a NOAEL for the most
sensitive, or critical, toxic effect based in part on the
assumption that if the critical toxic effect is prevented,
then all toxic effects are prevented. It should be
remembered during the risk characterization step of the
risk assessment that if exposure levels exceed the RfD,
then adverse effects in addition to the critical toxic
effect may begin to appear.
requires the use of an additional uncertainty factor
(see below).
Applying uncertainty factors. The RfD is
derived from the NOAEL (or LOAEL) for the
critical toxic effect by consistent application of
uncertainty factors (UFs) and a modifying factor
(MF). The uncertainty factors generally consist of
multiples of 10 (although values less than 10 are
sometimes used), with each factor representing a
specific area of uncertainty inherent in the
extrapolation from the available data. The bases
for application of different uncertainty factors are
explained below.
• A UF of 10 is used to account for
variation in the general population and
is intended to protect sensitive
subpopulations (e.g., elderly, children).
• A UF of 10 is used when extrapolating
from animals to humans. This factor is
intended to account for the interspecies
variability between humans and other
mammals.
• A UF of 10 is used when a NOAEL
derived from a subchronic instead of a
chronic study is used as the basis for a
chronic RfD.
• A UF of 10 is used when a LOAEL is
used instead of a NOAEL. This factor
is intended to account for the
uncertainty associated with extrapolating
from LOAELs to NOAELs.
In addition to the UFs listed above, a modifying
factor (MF) is applied.
• An MF ranging from >0 to 10 is
included to reflect a qualitative
professional assessment of additional
uncertainties in the critical study and in
the entire data base for the chemical not
explicitly addressed by the preceding
uncertainty factors. The default value
for the MF is I.1
To calculate the RfD, the appropriate NOAEL
(or the LOAEL if a suitable NOAEL is not
available) is divided by the product of all of the
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Page 7-8
applicable uncertainty factors and the modifying
factor. That is:
RfD = NOAEL or LOAEL/(UF7 x UF2... x
MF)
Oral RfDs typically are expressed as one
significant figure in units of mg/kg-day. These
concepts are shown graphically in EPA (1989g).
To date, most RfDs developed by EPA and
included in the sources listed in Section 7.4 are
based on administered doses, not absorbed doses
(see box on page 7-10).
7.2.3 DERIVATION OF AN INHALATION
RfD (RfD,)
The methods EPA uses in the derivation of
inhalation RfDs are similar in concept to those
used for oral RfDs; however, the actual analysis
of inhalation exposures is more complex than oral
exposures due to (1) the dynamics of the
respiratory system and its diversity across species
and (2) differences in the physicochemical
properties of contaminants. Additional
information can be found in EPA's Interim
Methods for Development of Inhalation Reference
Doses (EPA 1989d).
Identifying the critical study and determining
the NOAEL. Although in theory the identification
of the critical study and the determination of the
NOAEL is similar for oral and inhalation
exposures, several important differences should be
noted. In selecting the most appropriate study,
EPA considers differences in respiratory anatomy
and physiology, as well as differences in the
physicochemical characteristics of the contaminant.
Differences in respiratory anatomy and physiology
may affect the pattern of contaminant deposition
in the respiratory tract, and the clearance and
redistribution of the agent. Consequently, the
different species may not receive the same dose of
the contaminant at the same locations within the
respiratory tract even though both species were
exposed to the same particle or gas concentration.
Differences in the physicochemical characteristics
of the contaminants, such as the size and shape of
a particle or whether the contaminant is an
aerosol or a gas, also influence deposition,
clearance, and redistribution.
In inhalation exposures, the target tissue may
be a portion of the respiratory tract or, if the
contaminant can be absorbed and distributed
through the body, some extrarespiratory organ.
Because the pattern of deposition may influence
concentrations at the alveolar exchange boundary
or different tissues of the lung, the toxic health
effect observed may be more directly related to
the pattern of deposition than to the exposure
concentration. Consequently, EPA considers the
deposition, clearance mechanisms, and the
physicochemical properties of the inhaled agent in
determining the effective dose delivered to the
target organ.
Doses calculated in animals are converted to
equivalent doses in humans on the basis of
comparative physiological considerations (e.g.,
ventilatory parameters, regional lung surface
areas). Additionally, if the exposure period was
discontinuous, it is adjusted to reflect continuous
exposure.
Applying uncertainty factors. The inhalation
RfD is derived from the NOAEL by applying
uncertainty factors similar to those listed above
for oral RfDs. The UF of 10 is used when
extrapolating from animals to humans, in addition
to calculation of the human equivalent dose, to
account for interspecific variability in sensitivity to
the toxicant. The resulting RfD value for
inhalation exposure is generally reported as a
concentration in air (in mg/m5 for continuous, 24
hour/day exposure), although it may be reported
as a corresponding inhaled intake (in mg/kg-day).
A human body weight of 70 kg and an inhalation
rate of 20 m3/day are used to convert between an
inhaled intake expressed in units of mg/kg-day and
a concentration in air expressed in mg/m5.
7.2.4 DERIVATION OF A SUBCHRONIC RfD
The chronic RfDs described above pertain to
lifetime or other long-term exposures and may be
overly protective if used to evaluate the potential
for adverse health effects resulting from
substantially less-than-lifetime exposures. For
such situations, EPA has begun calculating toxicity
values specifically for subchronic exposure
durations, using a method similar to that outlined
above for chronic RfDs. EPA's Environmental
Criteria and Assessment Office develops
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Page 7-9
subchronic RfDs and, although they have been
peer-reviewed by Agency and outside reviewers,
RfDs values have not undergone verification by an
intra-Agency workgroup (see Section 7.2.7). As
a result, subchronic RfDs are considered interim
rather than verified toxicity values and are not
placed in IRIS.
Development of subchronic reference doses
parallels the development of chronic reference
doses in concept; the distinction is one of
exposure duration. Appropriate studies are
evaluated and a subchronic NOAEL is identified.
The RfDs is derived from the NOAEL by the
application of UFs and MF as outlined above.
When experimental data are available only for
shorter exposure durations than desired, an
additional uncertainty factor is applied. This is
similar to the application of the uncertainty factor
for duration differences when a chronic RfD is
estimated from subchronic animal data. On the
other hand, if subchronic data are missing and a
chronic oral RfD derived from chronic data exists,
the chronic oral RfD is adopted as the subchronic
oral RfD. There is no application of an
uncertainty factor to account for differences in
exposure duration in this instance.
7.2.5 DERIVATION OF A DEVELOPMENTAL
TOXICANT RfD (RfDA)
In developing an RfD^r, evidence is gathered
regarding the potential of a substance to cause
adverse effects in a developing organism as a
result of exposure prior to conception (either
parent), during prenatal development, or
postnatally to the time of sexual maturation.
Adverse effects can include death, structural
abnormality, altered growth, and functional
deficiencies. Maternal toxicity also is considered.
The evidence is assessed, and the substance is
assigned a weight-of-evidence designation
according to the scheme outlined below and
summarized in the box in the opposite column.
In this scheme, three levels are used to indicate
the assessor's degree of confidence in the data:
definitive evidence, adequate evidence, and
inadequate evidence. The definitive and adequate
evidence categories are subdivided as to whether
the evidence demonstrates the occurrence or the
absence of adverse effects.
WEIGHT-OF-EVIDENCE SCHEME FOR
DEVELOPMENTAL TOXICITY
• Definitive Evidence for:
- Human Developmental Toxicity
- No Apparent Human Developmental Toxicity
» Adequate Evidence for:
- Potential Human Developmental Toxicity
- No Apparent Potential Human Developmental
Toxicity
• Inadequate Evidence for Determining Potential
Human Developmental Toxicity
After the weight-of-evidence designation is
assigned, a study is selected for the identification
of a NOAEL. The NOAEL is converted to an
equivalent human dose, if necessary, and divided
by uncertainty factors similar to those used in the
development of an oral RfD. It should be
remembered that the RfD^t is based on a short
duration of exposure because even a single
exposure at a critical time (e.g., during gestation)
may be sufficient to produce adverse
developmental effects and that chronic exposure
is not a prerequisite for developmental toxicity to
be manifested. Therefore, RfD^, values are
appropriate for evaluating single event exposures,
which usually are not adjusted based on the
duration of exposure. Additional information on
the derivation of RfD^ values is available in
EPA's Proposed Amendments to the Guidelines for
the Health Assessment of Suspect Developmental
Toxicants (EPA 1989e).
7.2.6 ONE-DAY AND TEN-DAY HEALTH
ADVISORIES
Reference values that may be useful for
evaluating potential adverse effects associated with
oral exposures of shorter duration have been
developed by the Office of Drinking Water.
These values are known as One-day and Ten-day
Health Advisories, which are issued as
nonregulatory guidance. Health Advisory values
are concentrations of contaminants in drinking
water at which adverse health effects would not be
expected to occur for an exposure of the specified
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Page 7-10
duration. The Health Advisory values are based
on data describing noncarcinogenic effects and are
derived by dividing a NOAEL or LOAEL by the
appropriate uncertainty and modifying factors.
They are based on a 10-kg child assumed to drink
1 liter of water per day, and a margin of safety is
included to protect sensitive members of the
population. One-day and Ten-day Health
Advisories do not consider any carcinogenic risk
associated with the exposure even if the compound
is a potential carcinogen. For additional
information on the derivation of Health Advisory
values, refer to the Agency's guidance document
(EPA 1989c).
7.2.7 VERIFICATION OF RfDs
EPA has formed an RfD Workgroup
composed of members from many EPA offices to
verify existing Agency RfDs and to resolve
conflicting toxicity assessments and toxicity values
within the Agency. The Workgroup reviews the
information regarding the derivation of an RfD
for a substance and summarizes its evaluations,
conclusions, and reservations regarding the RfD
in a standardized summary form from one to
several pages in length. This form contains
information regarding the development of the
RfD, such as the chosen effect levels and
uncertainty factors, as well as a statement on the
confidence that the evaluators have in the RfD
itself, the critical study, and the overall data base
(high, medium, or low). Once verified, these data
ABSORBED VERSUS
ADMINISTERED DOSE
Toxicity values -- for both noncarcinogenic and
carcinogenic effects -- are generally calculated from
critical effect levels based on administered rather than
absorbed doses. It is important, therefore, to compare
such toxicity values to exposure estimates expressed as
intakes (corresponding to administered doses), not as
absorbed doses. For the few toxicity values that have
been based on absorbed doses, either the exposure
estimate or the toxicity value should be adjusted to
make the values comparable (i.e., compare exposures
estimated as absorbed doses to toxicity values expressed
as absorbed doses, and exposures estimated as intakes
to toxicity values expressed as administered doses). See
Appendix A for guidance on making adjustments for
absorption efficiency.
evaluation summaries are entered into IRIS and
are available for public access.
Workgroup-approved RfDs are referred to as
verified RfDs. Those RfDs awaiting workgroup
approval are referred to as interim RfDs. At the
time of this manual's publication, only chronic
RfDs are being verified. No workgroup has been
established to verify subchronic RfDs or
developmental RfDs.
7.3 TOXICITY ASSESSMENT FOR
CARCINOGENIC EFFECTS
This section describes how the types of
toxicity information presented in Section 7.1 are
considered in the toxicity assessment for
carcinogenic effects. A slope factor and the
accompanying weight-of-evidence determination
are the toxicity data most commonly used to
evaluate potential human carcinogenic risks. The
methods EPA uses to derive these values are
outlined below. Additional information can be
obtained by consulting EPA's Guidelines for
Carcinogen Risk Assessment (EPA 1986a) and
Appendix B to IRIS (EPA 1989a).
7.3.1 CONCEPT OF NONTHRESHOLD
EFFECTS
Carcinogenesis, unlike many noncarcinogenic
health effects, is generally thought to be a
phenomenon for which risk evaluation based on
presumption of a threshold is inappropriate. For
carcinogens, EPA assumes that a small number of
molecular events can evoke changes in a single
cell that can lead to uncontrolled cellular
proliferation and eventually to a clinical state of
disease. This hypothesized mechanism for
carcinogenesis is referred to as "nonthreshold"
because there is believed to be essentially no level
of exposure to such a chemical that does not pose
a finite probability, however small, of generating
a carcinogenic response. That is, no dose is
thought to be risk-free. Therefore, in evaluating
cancer risks, an effect threshold cannot be
estimated. For carcinogenic effects, EPA uses a
two-part evaluation in which the substance first is
assigned a weight-of-evidence classification, and
then a slope factor is calculated.
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Page 7-11
7.3.2 ASSIGNING A WEIGHT OF EVIDENCE
In the first step of the evaluation, the
available data are evaluated to determine the
likelihood that the agent is a human carcinogen.
The evidence is characterized separately for human
studies and animal studies as sufficient, limited,
inadequate, no data, or evidence of no effect. The
characterizations of these two types of data are
combined, and based on the extent to which the
agent has been shown to be a carcinogen in
experimental animals or humans, or both, the
agent is given a provisional weight-of-evidence
classification. EPA scientists then adjust the
provisional classification upward or downward,
based on other supporting evidence of
carcinogenicity (see Section 7.1.3). For a further
description of the role of supporting evidence, see
the EPA guidelines (EPA 1986a).
The EPA classification system for weight of
evidence is shown in the box in the opposite
column. This system is adapted from the
approach taken by the International Agency for
Research on Cancer (IARC 1982).
7.3.3 GENERATING A SLOPE FACTOR2
In the second part of the evaluation, based
on the evaluation that the chemical is a known or
probable human carcinogen, a toxicity value that
defines quantitatively the relationship between
dose and response (i.e., the slope factor) is
calculated. Slope factors are typically calculated
for potential carcinogens in classes A, Bl, and B2.
Quantitative estimation of slope factors for the
chemicals in class C proceeds on a case-by-case
basis.
Generally, the slope factor is a plausible
upper-bound estimate of the probability of a
response per unit intake of a chemical over a
lifetime. The slope factor is used in risk
assessments to estimate an upper-bound lifetime
probability of an individual developing cancer as
a result of exposure to a particular level of a
potential carcinogen. Slope factors should always
be accompanied by the weight-of-evidence
classification to indicate the strength of the
evidence that the agent is a human carcinogen.
Identifying the appropriate data set. In
deriving slope factors, the available information
EPA WEIGHT-OF-EVIDENCE
CLASSIFICATION SYSTEM FOR
CARCINOGENICITY
Group
Description
A Human carcinogen
Bl or Probable human carcinogen
B2
Bl indicates that limited human data are
available.
B2 indicates sufficient evidence in
animals and inadequate or no evidence in
humans.
C Possible human carcinogen
D Not classifiable as to human
carcinogenicity
E Evidence of noncarcinogenicity for
humans
about a chemical is evaluated and an appropriate
data set is selected. In choosing appropriate data
sets, human data of high quality are preferable to
animal data. If animal data are used, the species
that responds most similarly to humans (with
respect to factors such as metabolism, physiology,
and pharmacokinetics) is preferred. When no
clear choice is possible, the most sensitive species
is given the greatest emphasis. Occasionally, in
situations where no single study is judged most
appropriate, yet several studies collectively support
the estimate, the geometric mean of estimates
from all studies may be adopted as the slope.
This practice ensures the inclusion of all relevant
data.
Extrapolating to lower doses. Because risk
at low exposure levels is difficult to measure
directly either by animal experiments or by
epidemiologic studies, the development of a slope
factor generally entails applying a model to the
available data set and using the model to
extrapolate from the relatively high doses
administered to experimental animals (or the
exposures noted in epidemiologic studies) to the
lower exposure levels expected for human contact
in the environment.
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Page 7-12
A number of mathematical models and
procedures have been developed to extrapolate
from carcinogenic responses observed at high
doses to responses expected at low doses.
Different extrapolation methods may provide a
reasonable fit to the observed data but may lead
to large differences in the projected risk at low
doses. In keeping with EPA's Guidelines for
Carcinogen Risk Assessment (EPA 1986a) and the
principles outlined in Chemical Carcinogens: A
Review of the Science and Its Associated Principles
(OSTP 1985), the choice of a low-dose
extrapolation model is governed by consistency
with current understanding of the mechanism of
carcinogenesis, and not solely on goodness-of-fit
to the observed tumor data. When data are
limited and when uncertainty exists regarding the
mechanisms of carcinogenic action, the EPA
guidelines and OSTP principles suggest that
models or procedures that incorporate low-dose
linearity are preferred when compatible with the
limited information available. EPA's guidelines
recommend that the linearized multistage model
be employed in the absence of adequate
information to the contrary. Among the other
models available are the Weibull, probit, logit,
one-hit, and gamma multihit models, as well as
various time-to-tumor models. Most of these
models are less conservative (i.e., predict lower
cancer potency) than the linearized multistage
model. These concepts and models are shown
graphically in EPA (1989g) and OTA (1981).
In general, after the data are fit to the
appropriate model, the upper 95th percent
confidence limit of the slope of the resulting dose-
response curve is calculated. This value is known
as the slope factor and represents an upper 95th
percent confidence limit on the probability of a
response per unit intake of a chemical over a
lifetime (i.e., there is only a 5 percent chance that
the probability of a response could be greater than
the estimated value on the basis of the
experimental data and model used). In some
cases, slope factors based on human dose-response
data are based on the "best" estimate instead of
the upper 95th percent confidence limits. Because
the dose-response curve generally is linear only in
the low-dose region, the slope factor estimate only
holds true for low doses. Information concerning
the limitations on use of slope factors can be
found in IRIS.
Determining equivalent human doses. When
animal data are used as a basis for extrapolation,
the human dose that is equivalent to the dose in
the animal study is calculated using the
assumption that different species are equally
sensitive to the effects of a toxicant if they absorb
the same amount of the agent (in milligrams) per
unit of body surface area. This assumption is
made only in the absence of specific information
about the equivalent doses for the chemical in
question. Because surface area is approximately
proportional to the 2/3 power of body weight, the
equivalent human dose (in mg/day, or other units
of mass per unit time) is calculated by multiplying
the animal dose (in identical units) by the ratio of
human to animal body weights raised to the 2/3
power. (For animal doses expressed as mg/kg-day,
the equivalent human dose, in the same units, is
calculated by multiplying the animal dose by the
ratio of animal to human body weights raised to
the 1/3 power.)
When using animal inhalation experiments to
estimate lifetime human risks for partially soluble
vapors or gases, the air concentration (ppm) is
generally considered to be the equivalent dose
between species based on equivalent exposure
times (measured as fractions of a lifetime). For
inhalation of particulates or completely absorbed
gases, the amount absorbed per unit of body
surface area is considered to be the equivalent
dose between species.
Summary of dose-response parameters.
Toxicity values for carcinogenic effects can be
expressed in several ways. The slope factor is
usually, but not always, the upper 95th percent
confidence limit of the slope of the dose-response
curve and is expressed as (mg/kg-day)"^. If the
extrapolation model selected is the linearized
multistage model, this value is also known as the
q/. That is:
Slope factor = risk per unit dose
= risk per mg/kg-day
Where data permit, slope factors listed in IRIS
are based on absorbed doses, although to date
many of them have been based on administered
doses. (The qualifiers related to absorbed versus
administered dose given in the box on page 7-10
apply to assessment of cancer risk as well as to
assessment of potential noncarcinogenic effects.)
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Page 7-13
Toxicity values for carcinogenic effects also
can be expressed in terms of risk per unit
concentration of the substance in the medium
where human contact occurs. These measures,
called unit risks, are calculated by dividing the
slope factor by 70 kg and multiplying by the
inhalation rate (20 m3/day) or the water
consumption rate (2 liters/day), respectively, for
risk associated with unit concentration in air or
water. Where an absorption fraction less than 1.0
has been applied in deriving the slope factor, an
additional conversion factor is necessary in the
calculation of unit risk so that the unit risk will
be on an administered dose basis. The
standardized duration assumption for unit risks is
understood to be continuous lifetime exposure.
Hence, when there is no absorption conversion
required:
air unit risk = risk per ug/m3
= slope factor x 1/70 kg x
20m3/day x 10'3
water unit risk = risk per ug/L
= slope factor x 1/70 kg x
2L/day x 10'3
The multiplication by 10~3 is necessary to convert
from mg (the slope factor, or q/, is given in
(mg/kg-day)";) to ug (the unit risk is given in
-1 or (ug/L)-r).
7.3.4 VERIFICATION OF SLOPE FACTORS
EPA formed the Carcinogen Risk Assessment
Verification Endeavor (CRAVE) Workgroup to
validate Agency carcinogen risk assessments and
resolve conflicting toxicity values developed by
various program offices. Workgroup members
represent many different EPA offices and are
scientists experienced in issues related to both the
qualitative and quantitative risk assessment of
carcinogenic agents. Slope factors verified by
CRAVE have undergone extensive peer review
and represent an Agency consensus. CRAVE-
verified review summaries (similar to RfD
Workgroup summaries) are entered into the IRIS
data base.
7.4 IDENTIFYING APPROPRIATE
TOXICITY VALUES FOR SITE
RISK ASSESSMENT
Using the methods outlined above, EPA has
performed toxicity assessments for many chemicals
found at Superfund sites and has made the results
available for use. This section provides step-by-
step methods for locating appropriate toxicity
information, including numerical toxicity values, to
be used in Superfund risk assessments. Because
one's confidence in toxicity values depends heavily
on the data base and the methods of extrapolation
used in their development, guidance is also
included for identifying the important information
on which these values are based.
7.4.1 GATHER TOXICITY INFORMATION
FOR CHEMICALS BEING EVALUATED
In the first step of the toxicity assessment,
information is collected regarding the toxic effects
that occur following exposure to the chemical
being evaluated. Particular attention should be
paid to the route of exposure, the frequency and
length of exposure, and the doses at which the
adverse effects are expected to occur. Chemicals
having potential reproductive or developmental
effects should be flagged. Later in the evaluation,
special reference doses for developmental effects
can be sought for these chemicals.
Several sources may provide useful toxicity
information and references to primary literature,
although only some of them should be used as
sources for slope factors and reference doses (as
explained below).
Integrated Risk Information System (IRIS).3
IRIS is an EPA data base containing up-to-date
health risk and EPA regulatory information for
numerous chemicals. IRIS contains only those
RfDs and slope factors that have been verified by
the RfD or CRAVE Workgroups and
consequently, is considered to be the preferred
source of toxicity information. Information in
IRIS supersedes all other sources. Only if
information is not available in IRIS for the
chemical being evaluated should the sources below
be consulted. IRIS consists of a collection of
computer files on individual chemicals. Existing
information on the chemicals is updated as new
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Page 7-14
scientific data are reviewed. New files and new
chemicals are added as information becomes
available. These chemical files contain descriptive
and quantitative information in the following
categories:
• oral and inhalation chronic reference
doses;
• oral and inhalation slope factors and
unit risks for chronic exposure to
carcinogens;
• Health Advisories from EPA's Office of
Drinking Water;
• EPA regulatory action summaries; and
• supplemental data on acute health
hazards and physical/chemical properties.
To ensure access to the most up-to-date
chemical information, IRIS is only available on-
line. For information on how to access this data
base, call IRIS User Support at 513-569-7254 or
see the Federal Register notice regarding the
availability of IRIS (EPA 1988a).
Should EPA regional staff have specific
technical or scientific questions about any
verification workgroup's analysis of particular data
cited in IRIS, the Agency contact for a particular
chemical (identified at the end of each IRIS file)
should be consulted. If new data are identified
suggesting that existing IRIS information may be
outdated, or if there is concern or disagreement
about the overall findings of particular files, the
Agency IRIS coordinator should be consulted.
The IRIS coordinator can assist in making
arrangements should discussions with a verification
workgroup be needed.
Health Effects Assessment Summary Tables
(HEAST). Formerly "The Quarterly" and
associated references, HEAST is a tabular
presentation of toxicity information and values for
chemicals for which Health Effects Assessments
(HEAs), Health and Environmental Effects
Documents (HEEDs), Health and Environmental
Effects Profiles (HEEPs), Health Assessment
Documents (HADs), or Ambient Air Quality
Criteria Documents (AAQCDs) have been
prepared. HEAST summarizes interim (and some
verified) RiDs and slope factors as well as other
toxicity information for specific chemicals. In
addition, HEAST directs readers to the most
current sources of supporting toxicity information
through an extensive reference section. Therefore,
HEAST is especially helpful when verified
information for a chemical is not in IRIS.
HEAST, which is updated quarterly, also provides
a valuable pointer system for identifying current
references on chemicals that are not in IRIS.
HEAST can be obtained upon request from
the Superfund Docket (FTS or 202-382-3046).
The Docket will mail copies of HEAST to callers
and place requestors on a mailing list to receive
an updated version quarterly. HEAs, HEEDs,
HEEPs, HADs, and AAQCDs referenced in
HEAST are available through EPA's Center for
Environmental Research Information (CERI) in
Cincinnati, OH (513-569-7562 or FTS 684-7562)
or the National Technical Information Service
(NTIS), 5285 Port Royal Road, Springfield, VA
22161 (703-487-4650 or 800-336-4700).
EPA criteria documents. These documents
include drinking water criteria documents, drinking
water Health Advisory summaries, ambient water
quality criteria documents, and air quality criteria
documents, and contain general toxicity
information that can be used if information for a
chemical is not available through IRIS or the
HEAST references. Criteria documents are
available through NTIS at the address given above.
Information on drinking water criteria documents
can be obtained through the Safe Drinking Water
Hotline (800-426-4791).
Agency for Toxic Substances and Disease
Registry (ATSDR) toxicological profiles. ATSDR
is developing toxicological profiles for 275
hazardous substances found at Superfund sites.
The first 200 substances to be addressed have
been identified in Federal Register notices (EPA
1987, 1988b). These profiles contain general
toxicity information and levels of exposure
associated with lethality, cancer, genotoxicity,
neurotoxicity, developmental and reproductive
toxicity, immunotoxicity, and systemic toxicity (i.e.,
hepatic, renal, respiratory, cardiovascular,
gastrointestinal, hematological, musculoskeletal,
and dermal/ocular effects). Health effects in
humans and animals are discussed by exposure
route (i.e., oral, inhalation, and dermal) and
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Page 7-15
HIERARCHY OF TOXICITY INFORMATION
Because toxicity informatioa may change rapidly and quickly become outdated, care should be taken to find the most recent
information available. IRIS is updated monthly, provides verified RfDs and slope factors, and is the Agency's preferred source
of toxicity information. Only it values are unavailable in IRIS should other information sources be consulted.
HEAST is the second most current source of toxicity information of importance to Superfund. Unlike IRIS, HEAST provides
information regarding interim as well as verified RfDs and slope factors. Readers are directed to supporting toxicity information
for interim and verified values in an extensive reference section of HEAST. HEAST information should only be sought for those
chemicals not listed in IRIS.
Toxicity information, RfDs, and slope factors also can be found in other EPA documents. Although these values were
developed by offices within the Agency, they have not necessarily been verified by the RfD or CRAVE Workgroups. The use
of up-to-date verified information is preferred to the use of interim information and, therefore, toxicity information should be
obtained from other EPA references only if information could not be found in IRIS or HBAST. Before using references other
than those cited in IRIS or HEAST, check with ECAO at 513-569-7300 (FTS 684-7300) to see if more current information is
available.
duration (i.e., acute, intermediate, and chronic).
Also included in the profiles are chapters on
physicochemical properties, environmental fate,
potential for human exposure, analytical methods,
and regulatory and advisory status. Contact NTIS
at the address given on the previous page for
further information on the status or availability of
a particular profile.
EPA's Environmental Criteria and
Assessment Office (ECAO). ECAO may be
contacted at 513-569-7300 (FTS 684-7300) for
general lexicological information as well as for
technical guidance concerning route-to-route
extrapolations, toxicity values for dermal
exposures, and the evaluation of chemicals without
toxicity values. The requestor should identify their
need for a "rapid response request" (within 48
hours) for interim guidance on Superfund health-
related issues. Contractors must give the name
and address of their RPM or regional risk
assessment contact before ECAO will respond.
RPMs and regional contacts will be sent a copy
of ECAO's response to the contractor.
Open literature. A primary literature search
may be valuable for determining whether new data
are available that may affect IRIS information.
7.4.2 DETERMINE TOXICITY VALUES FOR
NONCARCINOGENIC EFFECTS (RfDs)
After general toxicity information for the
chemicals of concern has been located, the next
step is to identify the appropriate toxicity values
to be used in evaluating noncarcinogenic effects
associated with the specific exposures being
assessed. First, by referring to the exposure
information generated in Chapter 6, the exposure
periods for which toxicity values are necessary and
the exposure route for each chemical being
evaluated should be determined. The appropriate
toxicity values for the chemical for each exposure
duration and route of exposure can then be
identified using the sources listed above.
For Superfund risk assessments, chronic RfDs
should be identified for evaluating exposure
periods between seven years and a lifetime,
subchronic RfDs for exposure periods between two
weeks and seven years, and One- or Ten-day
Health Advisories for oral exposure periods of less
than two weeks. According to EPA (1988c), One-
day Health Advisories are applicable to exposure
periods as long as five days and Ten-day Health
Advisories are applicable to exposure periods as
long as two weeks. Developmental RfDs should
be identified for evaluating single exposure events
and other very short exposures (e.g., one day).
Note that for some substances and some exposure
situations, more than one of the toxicity values
listed above may be needed to adequately assess
potential noncarcinogenic effects.
Because carcinogens also commonly evoke
noncarcinogenic effects, RfDs should be sought for
all chemicals being carried through the risk
assessment, including carcinogens. The RfDs
derived for carcinogens, however, are based on
noncancer effects and should not be assumed to
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Page 7-16
be protective against carcinogenicity. A sample
format for summarizing RfDs and other toxicity
values is shown in Exhibit 7-2. This information
will be needed in the risk characterization step
(see Exhibits 8-3 and 8-4).
7.4.3 DETERMINE TOXICITY VALUES FOR
CARCINOGENIC EFFECTS (SLOPE
FACTORS)
In this step of the toxicity assessment,
appropriate toxicity values for evaluating the
carcinogenic risks associated with exposure are
identified. First, by referring to the exposure
information generated in Chapter 6, the route of
exposure for the potential carcinogens being
evaluated should be identified. Slope factors for
these chemicals can then be identified using the
hierarchy of sources listed in the box on page
7-15. Slope factors for all potential carcinogens
having a weight-of-evidence classification of A, B,
or C should be sought. A notation of the EPA
weight-of-evidence classification should always be
included with the slope factor. A sample format
for summarizing the required toxicity values is
shown in Exhibit 7-3. This information will be
needed in the risk characterization step (see
Exhibit 8-2).
7.5 EVALUATING CHEMICALS
FOR WHICH NO TOXICITY
VALUES ARE AVAILABLE
If EPA-derived RfDs and slope factors are
available for the chemicals being examined, these
values should always be used in the risk
assessment. Use of EPA-derived toxicity values
prevents duplication of effort and ensures
consistency among risk assessments. If EPA-
derived toxicity values are not available, the
following measures are recommended.
7.5.1 ROUTE-TO-ROUTE EXTRAPOLATION
For cases in which EPA-derived toxicity
values are not available for the route of exposure
being considered but are available for another
route, EPA recommends contacting ECAO for
guidance on route-to-route extrapolation. If
toxicity information is not available from ECAO,
a qualitative rather than quantitative evaluation of
the chemical is recommended. The implications
of the absence of this chemical from the risk
estimate should be discussed in the uncertainty
section.
7.5.2 DERMAL EXPOSURE
No RfDs or slope factors are available for
the dermal route of exposure. In some cases,
however, noncarcinogenic or carcinogenic risks
associated with dermal exposure can be evaluated
using an oral RfD or oral slope factor,
respectively. EPA recommends contacting ECAO
for guidance on appropriate methods for
evaluating dermal exposure for specific chemicals;
some general guidance for calculating intakes via
the dermal route and making appropriate
comparisons with oral RfD values is given in
Appendix A. In brief, exposures via the dermal
route generally are calculated and expressed as
absorbed doses. These absorbed doses are
compared to an oral toxicity value that has been
adjusted, if necessary, so that it too is expressed
as an absorbed dose.
It is inappropriate to use the oral slope
factor to evaluate the risks associated with dermal
exposure to carcinogens such as benz(a)pyrene,
which cause skin cancer through a direct action at
the point of application. These types of skin
carcinogens and other locally active compounds
must be evaluated separately from the above
method; consult ECAO for guidance. Generally
only a qualitative assessment of risks from dermal
exposure to these chemicals is possible. This does
not apply to carcinogens such as arsenic, which
are believed to cause skin cancer through a
systemic rather than local action.
If information is not available from ECAO,
the assessor should describe the effects of the
chemical qualitatively and discuss the implications
of the absence of the chemical from the risk
estimate in the uncertainty section of the risk
assessment.
7.5.3 GENERATION OF TOXICITY VALUES
If EPA-derived toxicity values are unavailable
but adequate toxicity studies are available, one
may derive toxicity values using Agency
methodology. Any such derivation should be done
-------
Page 7-17
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EXHIBIT 7-3
EXAMPLE OF TABLE FORMAT FOR
TOXICITY VALUES: POTENTIAL CARCINOGENIC EFFECTS
Chemical
Slope Factor (SF) Weight-of-Evidence Type of
(mg/kg-day)'; Classification Cancer"
SF Basis/
SF Source
Oral Route
Benzene
Chlordane
Inhalation Route
0.029*
1.3*
B2*
Leukemia
Water6/
IRIS
Water6/
IRIS
* Values for illustration only.
a Identify type(s) of cancer in this table for Class A carcinogens only.
* Slope factor based on administered dose in drinking water and assumed absorption fraction of 1.0.
-------
Page 7-19
in conjunction with the regional risk assessment
contact, who will submit the derivation to ECAO
for approval. Contact with ECAO should be
established early in the process to eliminate any
duplication of effort because ECAO may have
information on the chemical being evaluated.
7.6 UNCERTAINTIES RELATED
TO TOXICITY INFORMATION
Toxicity information for many of the
chemicals found at Superfund sites is often
limited. Consequently, there are varying degrees
of uncertainty associated with the toxicity values
calculated. Sources of uncertainty associated with
toxicity values may include:
• using dose-response information from
effects observed at high doses to predict
the adverse health effects that may occur
following exposure to the low levels
expected from human contact with the
agent in the environment;
• using dose-response information from
short-term exposure studies to predict
the effects of long-term exposures, and
vice-versa;
• using dose-response information from
animal studies to predict effects in
humans; and
• using dose-response information from
homogeneous animal populations or
healthy human populations to predict the
effects likely to be observed in the
general population consisting of
individuals with a wide range of
sensitivities.
An understanding of the degree of
uncertainty associated with toxicity values is an
important part of interpreting and using those
values. Therefore, as part of the toxicity
assessment for Superfund sites, a discussion of the
strength of the evidence of the entire range of
principal and supporting studies should be
included. The degree of confidence ascribed to
a toxicity value is a function of both the quality
of the individual study from which it was derived
and the completeness of the supporting data
base. EPA-verified RfDs found in IRIS are
accompanied by a statement of the confidence that
the evaluators have in the RfD itself, the critical
study, and the overall data base. All EPA-verified
slope factors are accompanied by a weight-of-
evidence classification, which indicates the
likelihood that the agent is a human carcinogen.
The weight-of-evidence classification is based on
the completeness of the evidence that the agent
causes cancer in experimental animals and
humans. These designations should be used as
one basis for the discussion of uncertainty.
The discussion of uncertainty also should
include an indication of the extent to which an
analysis of the results from different studies give
a consistent, plausible picture of toxicity. The
greater the strength of the evidence, the greater
one's confidence in the conclusions drawn. The
following factors add to the strength of the
evidence that the chemical poses a hazard to
humans and should be considered:
• similar effects across species, strains, sex,
and routes of exposure;
• clear evidence of a dose-response
relationship;
• a plausible relationship among data on
metabolism, postulated mechanism of
action, and the effect of concern (see
Section 7.1.3);
• similar toxicity exhibited by structurally
related compounds (see Section 7.1.3);
and
• some link between the chemical and
evidence of the effect of concern in
humans (see Section 7.1.1).
High uncertainty (low confidence; low
strength of evidence) indicates that the toxicity
value might change if additional chronic toxicity
data become available. Low uncertainty (high
confidence) is an indication that a value is less
likely to change as more data become available,
because there is consistency among the toxic
responses observed in different species, sexes,
study designs, or in dose-response relationships.
The lower the uncertainty about toxicity values,
-------
Page 7-20
the more confidence a decision-maker can have in
the risk assessment results. Often, high
confidence is associated with values that are based
on human data for the exposure route of concern.
7.7 SUMMARIZATION AND
PRESENTATION OF THE
TOXICITY INFORMATION
This section discusses methods for presenting
toxicity information in the risk assessment
document for the chemicals being evaluated.
7.7.1 TOXICITY INFORMATION FOR THE
MAIN BODY OF THE TEXT
A short description of the toxic effects of
each chemical carried through the assessment in
non-technical language should be prepared for
inclusion in the main body of the risk assessment.
Included in this description should be information
on the effects associated with exposure to the
chemical and the concentrations at which the
adverse effects are expected to occur in humans.
Toxicity values should be accompanied by a brief
description of the overall data base and the
particular study from which the value was derived.
In addition, a notation should be made of the
critical effect and any uncertainty factors used in
the calculation. For any RfD value obtained from
IRIS, a notation of the degree of confidence
associated with the determination should also be
included. To aid in the risk characterization, it
should be indicated if absorption efficiency was
considered and also what exposure averaging
periods are appropriate for comparison with the
value.
Summary tables of toxicity values for all
chemicals should be prepared for inclusion in the
main body of the risk assessment report. RfDs in
the table should be accompanied with the
uncertainty factors used in their derivation, the
confidence rating given in IRIS (if applicable), and
a notation of the critical effect. Slope factors
should always be accompanied by EPA's weight-
of-evidence classification.
7.7.2 TOXICITY INFORMATION FOR
INCLUSION IN AN APPENDIX
If toxicity values were derived in conjunction
with the regional risk assessment contact and
ECAO for chemicals lacking EPA-derived values,
a technical documentation/justification of the
method of derivation should be prepared and
included in the appendix of the risk assessment
report. Included in this explanation should be a
description of the toxic effects of the chemical
such as information regarding the noncarcinogenic,
carcinogenic, mutagenic, reproductive, and
developmental effects of the compound. Also
presented should be brief descriptions (species,
route of administration, dosages, frequency of
exposure, length of exposure, and critical effect)
of the studies from which the values were derived
as well as the actual method of derivation.
References for the studies cited in the discussion
should be included.
-------
Page 7-21
ENDNOTES FOR CHAPTER 7
1. The MF is set less than one for a small number of substances to account for nutritional essentiality.
2. The slope factor is occasionally referred to as a cancer potency factor; however, use of this terminology is not recommended.
3. The quantitative risk values and supporting information found in IRIS represent a consensus judgement of EPA's Reference Dose
Workgroup or Carcinogen Risk Assessment Verification Endeavor (CRAVE) Workgroup. These workgroups are composed of scientists
from EPA's program offices and the Office of Research and Development. The concept of Agency-wide consensus is one of the most
valuable aspects of IRIS.
-------
Page 7-22
REFERENCES FOR CHAPTER 7
Environmental Protection Agency (EPA). 1986a. Guidelines for Carcinogen Risk Assessment. 51 Federal Register 33992 (September
24, 1986).
Environmental Protection Agency (EPA). 19865. Guidelines for the Health Assessment of Suspect Developmental Toxicants. 51
Federal Register 34028 (September 24, 1986).
Environmental Protection Agency (EPA). 1987. First Priority List of Hazardous Substances That Will Be the Subject of Toxicological
Profiles. 52 Federal Register 12866 (April 17, 1987).
Environmental Protection Agency (EPA). 1988a. Availability of the Integrated Risk Information System (IRIS). 53 Federal Register
20162 (June 2, 1988).
Environmental Protection Agency (EPA). 1988b. Hazardous Substances Priority List, Toxicological Profiles; Second List. 53 Federal
Register 41280 (October 20, 1988).
Environmental Protection Agency (EPA). 1988c. Office of Drinking Water Health Advisories. Reviews of Environmental
Contamination and Toxicology 104.
Environmental Protection Agency (EPA). 1989a. EPA Approach for Assessing the Risk Associated with Exposure to Environmental
Carcinogens. Appendix B to the Integrated Risk Information System (IRIS).
Environmental Protection Agency (EPA). 1989b. General Quantitative Risk Assessment Guidelines for Noncancer Health Effects.
External Review Draft. Risk Assessment Forum Technical Panel on Risk Assessment Guidelines for Noncancer Health Effects.
ECAO-CIN-538.
Environmental Protection Agency (EPA). 1989c. Guidelines for Authors of EPA Office of Water Health Advisories for Drinking Water
Contaminants. Office of Drinking Water.
Environmental Protection Agency (EPA). 1989d. Interim Methods for Development of Inhalation Reference Doses. Environmental
Criteria and Assessment Office. EPA/600/8-88/066F.
Environmental Protection Agency (EPA). 1989e. Proposed Amendments to the Guidelines for the Health Assessment of Suspect
Developmental Toxicants. 54 Federal Register 9386 (March 6, 1989).
Environmental Protection Agency (EPA). 1989f. Reference Dose (RfDI: Description and Use in Health Risk Assessments. Appendix
A to the Integrated Risk Information System (IRIS).
Environmental Protection Agency (EPA). 1989g. Guidance Manual for Assessing Human Health Risks from Chemically Contaminated
Fish and Shellfish. Office of Marine and Estuarine Protection. EPA/503/8-89/002.
International Agency for Research on Cancer (IARC). 1982. IARC Monographs on the Evaluation of the Carcinogenic Risk of
Chemicals to Humans. Supplement 4. Lyon, France.
National Academy of Sciences (NAS). 1983. Risk Assessment in the Federal Government: Managing the Process. National Academy
Press. Washington, D.C.
Office of Science and Technology Policy (OSTP). 1985. Chemical Carcinogens: A Review of the Science and Its Associated Principles.
50 Federal Register 10372 (March 14, 1985).
Office of Technology Assessment (OTA). 1981. Assessment of Technologies for Determining Cancer Risks from the Environment.
Congress of the United States. Washington, D.C.
-------
CHAPTER 8
RISK CHARACTERIZATION
FROM:
•Site discovery
• Preliminary
assessment
• Site inspection
. listing >
Toxicity
Assessment
Data i Data
Collection , Evaluation
Risk
Characterization
Exposure
Assessment
RISK CHARACTERIZATION
• Review outputs from toxicity and
exposure assessments
• Quantify risks from individual
chemicals
• Quantify risks from multiple
chemicals
• Combine risks across exposure
pathways
• Assess and present uncertainty
• Consider site-specific human
studies
TO:
•Selection of
remedy
• Remedial
design
• Remedial
action
-------
CHAPTERS
RISK CHARACTERIZATION
This chapter describes the final step of the
baseline health risk assessment process, risk
characterization. In this step, the toxicity and
exposure assessments are summarized and
integrated into quantitative and qualitative
expressions of risk. To characterize potential
noncarcinogenic effects, comparisons are made
between projected intakes of substances and
toxicity values; to characterize potential
carcinogenic effects, probabilities that an
individual will develop cancer over a lifetime of
exposure are estimated from projected intakes and
chemical-specific dose-response information.
Major assumptions, scientific judgments, and to
the extent possible, estimates of the uncertainties
embodied in the assessment are also presented.
Risk characterization also serves as the bridge
between risk assessment and risk management and
is therefore a key step in the ultimate site
decision-making process. This step assimilates risk
assessment information for the risk manager
(RPM or regional upper management involved in
site decision-making) to be considered alongside
other factors important for decision-making such
as economics, technical feasibility, and regulatory
context. The risk characterization methods
described in this chapter are consistent with EPA's
published risk assessment guidelines. Exhibit 8-1
is an overview of risk characterization, and
illustrates how it relates to the preceding toxicity
and exposure assessments and to the following
development of preliminary remediation goals.
In the following sections, the risk
characterization methodology is described. There
are separate discussions for carcinogenic and
noncarcinogenic effects because the methodology
differs for these two modes of chemical toxicity.
In addition to giving instructions for calculating
numerical estimates of risk, this chapter provides
guidance for interpreting, presenting, and
qualifying the results. A risk characterization
cannot be considered complete unless the
numerical expressions of risk are accompanied by
explanatory text interpreting and qualifying the
results.
8.1 REVIEW OF OUTPUTS FROM
THE TOXICITY AND
EXPOSURE ASSESSMENTS
Most sites being assessed will involve the
evaluation of more than one chemical of concern
and might include both carcinogenic and
noncarcinogenic substances. The first step in risk
characterization is to gather, review, compare, and
organize the results of the exposure assessment
(e.g., intakes for all exposure pathways and land-
uses and for all relevant substances) and toxicity
assessment (e.g., toxicity values for all exposure
ACRONYMS FOR CHAPTER 8
ARAR - Applicable or Relevant and Appropriate
Requirement
ATSDR« Agency for Toxic Substances and Disease
Registry
COI - Chronic Daily Intake
ECA0 = Environmental Criteria and Assessment
Office
E = Exposure Level
HI " Hazard Index
IRIS = Integrated Risk Information System
LOAEL = Lowest-Observed-Adverse-Effect-Level
NOAEL = No-Observed-Adverse-Effect-Level
NRC = Nuclear Regulatory Commission
RfD = Reference Dose (when used without
other modifiers, RfD generally refers to
chronic reference dose)
RfD
-------
Page 8-2
DEFINITIONS FOR CHAPTER 8
Absorbed Dose. The amount of a substance penetrating the exchange boundaries of an organism after contact. Absorbed dose
is calculated from the intake and the absorption efficiency. It usually is expressed as mass of a substance absorbed into
the body per unit body weight per unit time (e.g., mg/kg-day).
Administered Dose. The mass of substance given to an organism and in contact with aiv exchange boundary (e.g,,
gastrointestinal tract) per unit body weight per unit time (e.g., mg/kg-day).
Chronic Reference Dose (RED). An estimate (with uncertainty spanning perhaps an order Of magnitude or greater) of a daily
exposure level for the Iranian population, including sensitive subpopulations, that is likely to be without an appreciable risk
of deleterious effects during a lifetime. Chronic RfDs are specifically developed to be protective for tong-iertn exposure
to a compound (as a Superfund program guideline, seven years to lifetime).
Developmental Reference Dose (RfD,^). An estimate (with uncertainly spanning perhaps an order of magnitude or greater)
of an exposure level for the human population, including sensitive subpopulations, that is likely to be without an appreciable
risk of development effects. Developmental RfDs are used to evaluate the effects of a single exposure event.
Exposure. Contact of an organism with a chemical or physical agent. Exposure is quantified as the amount of the agent
available at the exchange boundaries of the organism (e.g., skin, lungs, gut) and available for absorption.
Exposure Assessment. The determination or estimation (qualitative or quantitative) of the magnitude, frequency, duration, and
route of exposure.
Exposure Pathway, 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 of
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 is included,
Exposure Route. The way a chemical or physical agent comes in contact with an organism (e,g,, by ingestion, inhalation, dermal
contact).
Hazard Index (HI}. The sum of more than one hazard quotient for multiple substances and/or multiple exposure pathways.
The HI is calculated separately for chronic, subchronic, and shorter-duration exposures.
Hazard Quotient. The ratio of a single substance exposure level over a specified time period (e.g., subchronic) to a reference
dose for that substance derived from a similar exposure period.
Intake. A measure of exposure expressed as the mass of a substance in contact with the exchange boundary per unit body
weight per unit time (e.g., mg chemical/kg body weight-day). Also termed the normalized exposure rate; equivalent to
administered dose,
Integrated Risk Information System flRIS). An EPA data base containing verified RfDs and slope factors and up-to-date health
risk and EPA regulatory information for numerous chemicals. IRIS is EPA's preferred source for toxicity information for
Superfund.
Reference Dose CRiDV The Agency's preferred toxicity value for evaluating noncarcinogenic effects result from exposures at
Superfund sites. See specific entries for chronic RfD, subchronic RfD, and developmental RfD. The acronym RfD, when
used without other modifiers, either refers genetically to all types of RfDs or specifically to chronic RfDs; it never refers
specifically to subchronic or developmental RfDs.
Slope Factor. A plausible upper-bound estimate of the probability of a response per unit intake of a chemical over a lifetime.
The slope factor is used to estimate an upper-bound probability of an individual developing cancer as a result Of a lifetime
of exposure to a particular level of a potential carcinogen.
Subchronic Reference Dose fRfD^. An estimate (with uncertainty spanning perhaps an order of magnitude or greater) of a
daily exposure level for the human population, including sensitive subpopulations, that is likely to be without an appreciable
risk of deleterious effects during a portion of a lifetime (as a Superfund program guideline, two weeks to seven years).
Weight -of-Evidencfe Classification. An EPA classification system for characterizing the extent to which the available data
indicate thai an agent is a human carcinogen. Recently, EPA has developed weight-of-evidence classification systems tor
some other kinds of toxic effects, such as developmental effects.
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Page 8-3
EXHIBIT 8-1
STEPS IN RISK CHARACTERIZATION
Step 1: Organize Outputs of
Exposure and Toxicity Assessments
• Exposure Duration
• Absorption Adjustments
• Consistency Check
Step 2: Quantify Pathway Risks
For Each Substance, Estimate:
• Cancer Risk
• Noncancer Hazard Quotient
For Each Pathway, Calculate:
• Total Cancer Risk
• Noncancer Hazard Index
I 1
. Exposure Assessment .
~" Intake Estimates
| |
J Toxicity Assessment '
| Toxicity Values I
i j
Step 3: Combine Risks Across Pathways
that affect the same individual(s) over
the same time periods
• Sum Cancer Risks
• Sum Hazard Indices
Step 4: Assess and Present
Uncertainty
• Site-specific Factors
• Toxicity Assessment
Factors
Step 5: Consider Site-Specific
Health or Exposure Studies
• Compare Adequate
Studies with Results of
Risk Assessment
Step 6: Summarize Results of the
Baseiine Risk Assessment
I Identify ARARs
i .
I
Develop Preliminary
Remediation Goals
-------
Page 8-4
routes and relevant substances). The following
two subsections describe how to organize the
outputs from the exposure and toxicity assessments
and how to check for the consistency and validity
of the information from the preceding exposure
and toxicity assessments.
8.1.1 GATHER AND ORGANIZE
INFORMATION
For each exposure pathway and land-use
evaluated in the exposure assessment, check that
all information needed to characterize risk is
available. The necessary exposure information is
outlined in the box below.
EXPOSURE INFORMATION NEEDED
FOR RISK CHARACTERIZATION
• Estimated intakes (chronic, subchronic, and
shorter-term, as appropriate) for chemicals.
• Important exposure modeling assumptions,
including:
- chemical concentration at the exposure
points;
- frequency and duration of exposure;
- absorption assumptions; and
- characterization of uncertainties.
• List of which exposure pathways can reasonably
contribute to the exposure of the same individuals
over the same time period.
For each chemical or substance evaluated in
the toxicity assessment, use the checklist provided
in the box below to ensure that all information
needed to characterize risk is available.
8.1.2 MAKE FINAL CONSISTENCY AND
VALIDITY CHECK
Check the consistency and validity of key
assumptions common to the exposure outputs and
the toxicity outputs for each contaminant and
exposure pathway of concern. These assumptions
include the averaging period for exposure, the
exposure route, and the absorption adjustments.
The basic principle is to ensure that the exposure
TOXICITY INFORMATION NEEDED
FOR RISK CHARACTERIZATION
« Slope factors for all carcinogenic chemicals.
• Discussion of weight of evidence and classifications
for all carcinogenic chemicals.
• Type of cancer for Class A carcinogens.
• Chronic and subchronic RfDs and shorter-term
toxicity values (if appropriate) for all chemicals
(including carcinogens and developmental
toxicants).
• Critical effect associated with each RfD.
• Discussion of uncertainties, uncertainty factors,
and modifying factor used in deriving each RfD
and "degree of confidence" in RfD (i.e., high,
medium, low),
• Whether the toxicity values are expressed as
absorbed or administered doses.
• Pharmacokinetic data that may affect the
extrapolation from animals to humans for both
the RfD and slope factor.
• Uncertainties in any route-to-route extrapolations.
estimates correspond as closely as possible with
the assumptions used in developing the toxicity
values.
Averaging period for exposure. If the toxicity
value is based on average lifetime exposure (e.g.,
slope factors), then the exposure duration must
also be expressed in those terms. For estimating
cancer risks, always use average lifetime exposure;
i.e., convert less-than-lifetime exposures to
equivalent lifetime values (see EPA 1986a,
Guidelines for Carcinogen Risk Assessment). On
the other hand, for evaluating potential
noncarcinogenic effects of. less-than-lifetime
exposures, do not compare chronic RfDs to short-
term exposure estimates, and do not convert
short-term exposures to equivalent lifetime values
to compare with the chronic RfDs. Instead, use
subchronic or shorter-term toxicity values to
evaluate short-term exposures. Check that the
estimated exposure duration is sufficiently similar
to the duration of the exposure in the study used
to identify the toxicity value to be protective of
human health (particularly for subchronic and
-------
Page 8-5
shorter-term effects). A lexicologist should review
the comparisons. In the absence of short-term
toxicity values, the chronic RfD may be used as an
initial screening value; i.e., if the ratio of the
short-term exposure value to the chronic RfD is
less than one, concern for potential adverse health
effects is low. If this ratio exceeds unity, however,
more appropriate short-term toxicity values are
needed to confirm the existence of a significant
health threat. ECAO may be consulted for
assistance in finding short-term toxicity values.
EPA ENVIRONMENTAL CRITERIA
AND ASSESSMENT OFFICE (ECAO)
TECHNICAL ASSISTANCE
FTS 684-7300
513-569-7300
Exposure route. Check that all toxicity values
used for each exposure pathway being evaluated
at the site are consistent with the route of
exposure (e.g., oral to oral, inhalation to
inhalation). It is not possible to extrapolate
between exposure routes for some substances that
produce localized effects dependent upon the
route of exposure. For example, a toxicity value
based on localized lung tumors that result only
from inhalation exposure to a substance would not
be appropriate for estimating risks associated with
dermal exposure to the substance. At this time,
EPA considers it appropriate only to extrapolate
dermal toxicity values from values derived for oral
exposure. It is not recommended that oral toxicity
reference values be extrapolated casually from
inhalation toxicity values, although this
extrapolation may be performed on a case-by-case
basis in consultation with ECAO. In general,
inhalation values should not be extrapolated from
oral values. See Section 7.5.1 for additional
information.
Inhalation RfD,- values obtained from IRIS
will usually be expressed as ambient air
concentrations (i.e., mg/m5), instead of as
administered doses (i.e., mg/kg-day). It may be
necessary, therefore, to calculate the RfDi in units
of mg/kg-day for comparison with the intake
estimated in the exposure assessment. The RfD/
expressed in mg/kg-day would be equal to the
RfD,- in mg/m5 multiplied by 20 m3 air inhaled
per person per day divided by 70 kg per person.
Absorption adjustment. Check that the
exposure estimates and the toxicity values are
either both expressed as absorbed doses or both
expressed as intakes (i.e., administered doses).
Except for the dermal route of exposure, the
exposure estimates developed using the methods
provided in Chapter 6 should be in the form of
intakes, with no adjustments made for absorption.
However, there are three types of absorption
adjustments that might be necessary or
appropriate depending on the available toxicity
information. These are described below. Sample
calculations for these absorption adjustments are
provided in Appendix A.
(1) Dermal exposures. The output of the
exposure assessment for dermal exposure
is expressed as the amount of substance
absorbed per kg body weight per day. It
therefore may be necessary to derive an
absorbed-dose toxicity value from an
administered-dose toxicity value to compare
with the exposure estimate. See Appendix
A for sample calculations.
(2) Absorbed-dose toxicitv value. For the
substances for which the toxicity value is
expressed as an absorbed rather than
administered dose (e.g., inhalation slope
factor in IRIS for trichloroethylene and
several other substances), one should
express exposure as an absorbed dose
rather than as an intake. See Appendix A.
(3) Adjustment for medium of exposure.
Adjusting for different absorption
efficiencies based on the medium of
exposure (e.g., food, soil, or water for oral
exposure, water or particulates for
inhalation exposure) is occasionally
appropriate, but not generally
recommended unless there are strong
arguments for doing so. Many oral RfD
and slope factor values assume ingestion in
water even when based on studies that
employed administration in corn oil by
gavage or in feed. Thus, in most cases, the
unadjusted toxicity value will provide a
-------
Page 8-6
reasonable or conservative estimate of risk.
See Appendix A.
8.2 QUANTIFYING RISKS
This section describes steps for quantifying risk
or hazard indices for both carcinogenic and
noncarcinogenic effects to be applied to each
exposure pathway analyzed. The first subsection
covers procedures for individual substances, and
is followed by a subsection on procedures for
quantifying risks associated with simultaneous
exposures to several substances. Sample table
formats for recording the results of these
calculations as well as recording associated
information related to uncertainty and absorption
adjustments are provided in Exhibits 8-2 through
8-4.
8.2.1 CALCULATE RISKS FOR INDIVIDUAL
SUBSTANCES
Carcinogenic effects. For carcinogens, risks
are estimated as the incremental probability of an
individual developing cancer over a lifetime as a
result of exposure to the potential carcinogen
(i.e., incremental or excess individual lifetime
cancer risk). The guidelines provided in this
section are consistent with EPA's (1986a)
Guidelines for Carcinogen Risk Assessment. For
some carcinogens, there may be sufficient
information on mechanism of action that a
modification of the approach outlined below is
warranted. Alternative approaches may be
considered in consultation with ECAO on a case-
by-case basis.
The slope factor (SF) converts estimated daily
intakes averaged over a lifetime of exposure
directly to incremental risk of an individual
developing cancer. Because relatively low intakes
(compared to those experienced by test animals)
are most likely from environmental exposures at
Superfund sites, it generally can be assumed that
the dose-response relationship will be linear in the
low-dose portion of the multistage model dose-
response curve. (See the Background Document
2 of IRIS for a discussion of the multistage
model). Under this assumption, the slope factor
is a constant, and risk will be directly related to
intake. Thus, the linear form of the carcinogenic
risk equation is usually applicable for estimating
Superfund site risks. This linear low-dose
equation is described in the box below.
LINEAR LOW-DOSE CANCER
RISK EQUATION
Risk = CDI x SF
where:
Risk — a unitless probability (e.g., 2 x
1Q~5) of an individual developing
cancer;
CDI = chronic daily intake averaged over
70 years (mg/kg-day); and
SF = slope factor, expressed in (mg/kg-
The CDI is identified in Exhibits 6-11 through 6-19 and
6-22 and the SF is identified in Exhibit 7-3.
However, this linear equation is valid only at
low risk levels (i.e., below estimated risks of 0.01).
For sites where chemical intakes might be high
(i.e., risk above 0.01), an alternate calculation
equation should be used. The one-hit equation,
which is consistent with the linear low-dose model
given above and described in the box on page
8-11, should be used instead.
Because the slope factor is often an upper
95th percentile confidence limit of the probability
of response based on experimental animal data
used in the multistage model, the carcinogenic risk
estimate will generally be an upper-bound
estimate. This means that EPA is reasonably
confident that the "true risk" will not exceed the
risk estimate derived through use of this model
and is likely to be less than that predicted.
Noncarcinogenic effects. The measure used to
describe the potential for noncarcinogenic toxicity
to occur in an individual is not expressed as the
probability of an individual suffering an adverse
effect. EPA does not at the present time use a
probabilistic approach to estimating the potential
for noncarcinogenic health effects. Instead, the
-------
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-------
Page 8-10
EXPLANATION OF SAMPLE TABLE FORMAT
FOR CANCER RISK ESTIMATES
A sample table format for summarizing Cancer risk estimates is provided in Exhibit 8-2. For each baseline risk assessment,
at feast two summary tables generally would be required: one for current land uses and one for future land uses. In the
example provided in Exhibit 8-2, two exposure pathways were determined to contribute to exposure of a nearby residential
population under current land use: ingestion of private well water contaminated with benzene and chlordane and ingestion of
fish contaminated with chlordane. Moreover, a subset of the population in Area Y was exposed to the maximal well water
contamination and consumed more locally caught fish than the remainder of the nearby population.
Values for the chronic daily intake (GDI), averaged over a lifetime, of each contaminant by each exposure pathway would
be obtained from a table such as that shown in Exhibit 6-22. The GDI via well water was not adjusted for absorption efficiency
because the slope factors for these substances assume ingestion in water and an absorption fraction of 1.0. The GDI for
chlordane in fish was not adjusted for vehicle of exposure (i.e., food versus water) because absorption efficiency data were
limited, and an absorption fraction of 1.0 was used as a conservative assumption. If, for example, available data had indicated
that only 10 percent of chlordane ingested with fish is absorbed, the GDI could have been adjusted downward to 0.000008 mg/kg-
day (i.e., 0.00008 mg/kg-day x 0.10 absorption fraction).
Values for the slope factors (SF), weight-of-evidenee classification, type of cancer (for Class A carcinogens), reference
source of the SF, and basis of the SF (vehicle of administration and absorption efficiency) would be obtained from a table such
as that shown in Exhibit 7-3, The chemical-specific risks were calculated from the GDI and SF using the linear low-dose cancer
risk equation (risk = GDI x SF), The total pathway risk for ingestion of private well water is the sum of the two chemical-
specific risks for that pathway. The total risk estimate for the nearby residential population in area Y is the sum of the cancer
risks for the two pathways. Note that it is important to summarize the weight of evidence for the carcinogens contributing most
to the total cancer risk estimate; in this example, chlordane, a Class B2 carcinogen, accounted for most of the risk.
EXPLANATION OF SAMPLE TABLE FORMAT
FOR CHRONIC HAZARD INDEX ESTIMATES
A sample table format for summarizing chronic hazard index estimates is provided in Exhibit 8-3. For each baseline risk
assessment, at least two summary tables generally would be required: one for current land uses and one for future land uses.
In the example provided in Exhibit 8-3, two exposure pathways were determined to contribute to exposure of a nearby residential
population under current land use: ingestion of private well water contaminated with phenol, nitrobenzene, and cyanide and
ingestion of fish contaminated with phenol and methyl ethyl ketone (MBK). Moreover, a subset of the population in Area Y
was exposed to the maximal well water contamination and consumed more locally caught fish than the remainder of the nearby
population.
Values for the chronic daily intake (GDI), averaged over the period of exposure, of each contaminant by each exposure
pathway would be obtained from a table such as that shown in Exhibit 6-22. The GDI via well water was not adjusted for
absorption efficiency because the RfDs for these substances are based on ingestion in water and an absorption fraction of 1.0.
The GDI for phenol and MEK in fish was not adjusted for vehicle of exposure (i.e., food versus water) because absorption
efficiency data were limited, and an absorption fraction of 1.0 was used as a conservative assumption. If, for example, available
data had indicated that only 20 percent of MEK ingested with fish is absorbed, the GDI for MEK could have been adjusted
downward to 0.001 mg/kg-day (i.e., 0.005 mg/kg-day x 0,20 absorption efficiency).
Values for the RfDs, confidence level in the RfD, critical effect, source of the value, and basis of the RfD (vehicle of
administration and absorption efficiency) would be obtained from a table such as that shown in Exhibit 7-2. The chemical-
specific hazard quotients are equal to the GDI divided by the RfD. The total pathway hazard index for ingestion of private well
water is the sum of the three chemical-specific hazard quotients for that pathway. The total hazard index estimate for the nearby
residential population in area Y is the sum of the hazard indices for the two exposure pathways.
Note that it is important to include the noncarcinogenjc effects of carcinogenic substances when appropriate reference doses
are available. For example, in an actual risk assessment of the chemicals summarized in Exhibit 6-22, the potential
noncarcinogenic effects of chlordane should be evaluated and appropriate entries made in tables such as those shown in Exhibits
7-2 and 8-3,
-------
Page 8-11
ONE-HIT EQUATION FOR HIGH
CARCINOGENIC RISK LEVELS
Risk = 1 - exp(-CDI x SF)
where:
Risk = a unitless probability (e.g,, 2 x
10~5) of an individual
developing cancer;
exp = the exponential;
CDI = chronic daily intake averaged
over 70 years (mg/kg-day); and
SF = slope factor, in (mg/kg-day)"7.
potential for noncarcinogenic effects is evaluated
by comparing an exposure level over a specified
time period (e.g., lifetime) with a reference dose
derived for a similar exposure period. This ratio
of exposure to toxicity is called a hazard quotient
and is described in the box in the opposite
column.
The noncancer hazard quotient assumes that
there is a level of exposure (i.e., RfD) below
which it is unlikely for even sensitive populations
to experience adverse health effects. If the
exposure level (E) exceeds this threshold (i.e., if
E/RfD exceeds unity), there may be concern for
potential noncancer effects. As a rule, the greater
the value of E/RfD above unity, the greater the
level of concern. Be sure, however, not to
interpret ratios of E/RfD as statistical
probabilities; a ratio of 0.001 does not mean that
there is a one in one thousand chance of the
effect occurring. Further, it is important to
emphasize that the level of concern does not
increase linearly as the RfD is approached or
exceeded because RfDs do not have equal
accuracy or precision and are not based on the
same severity of toxic effects. Thus, the slopes of
the dose-response curve in excess of the RfD can
range widely depending on the substance.
Three exposure durations that will need
separate consideration for the possibility of
adverse noncarcinogenic health effects are chronic,
NONCANCER HAZARD QUOTIENT
Noncancer Hazard Quotient = E/RfD
where:
E = exposure level (or intake);
RfD= reference dose; and
E and RfD are expressed in the same
units and represent the same exposure
period (i.e., chronic, subchronic, or
shorter-term).
subchronic, and shorter-term exposures. As
guidance for Superfund, chronic exposures for
humans range in duration from seven years to a
lifetime; such long-term exposures are almost
always of concern for Superfund sites (e.g.,
inhabitants of nearby residences, year-round users
of specified drinking water sources). Subchronic
human exposures typically range in duration from
two weeks to seven years and are often of concern
at Superfund sites. For example, children might
attend a junior high school near the site for no
more than two or three years. Exposures less
than two weeks in duration are occasionally of
concern at Superfund sites. For example, if
chemicals known to be developmental toxicants
are present at a site, short-term exposures of only
a day or two can be of concern.
8.2.2 AGGREGATE RISKS FOR MULTIPLE
SUBSTANCES
At most Superfund sites, one must assess
potential health effects of more than one chemical
(both carcinogens and other toxicants).
Estimating risk or hazard potential by considering
one chemical at a time might significantly
underestimate the risks associated with
simultaneous exposures to several substances. To
assess the overall potential for cancer and
noncancer effects posed by multiple chemicals,
EPA (1986b) has developed Guidelines for the
Health Risk Assessment of Chemical Mixtures that
can also be applied to the case of simultaneous
exposures to several chemicals from a variety of
sources by more than one exposure pathway.
-------
Page 8-12
Although the calculation procedures differ for
carcinogenic and noncarcinogenic effects, both sets
of procedures assume dose additivity in the
absence of information on specific mixtures.
Information on specific mixtures found at
Superfund sites is rarely available. Even if such
data exist, they are often difficult to use.
Monitoring for "mixtures" or modeling the
movement of mixtures across space and time
present technical problems given the likelihood
that individual components will behave differently
in the environment (i.e., fate and transport). If
data are available on the mixtures present at the
site, but are not adequate to support a
quantitative evaluation, note the information in
the "assumptions" documentation.
Carcinogenic effects. The cancer risk equation
described in the box below estimates the
incremental individual lifetime cancer risk for
simultaneous exposure to several carcinogens and
is based on EPA's (1986a,b) risk assessment
guidelines. This equation represents an
approximation of the precise equation for
combining risks which accounts for the joint
probabilities of the same individual developing
cancer as a consequence of exposure to two or
more carcinogens/ The difference between the
precise equation and the approximation described
in the box is negligible for total cancer risks less
than 0.1. Thus, the simple additive equation is
appropriate for most Superfund risk assessments.
CANCER RISK EQUATION FOR
MULTIPLE SUBSTANCES
Riskr = S Risk,-
where:
Riskj = the total cancer risk, expressed
as a unitless probability; and
Risk/ = the risk estimate for the ith
substance.
The risk summation techniques described in
the box on this page and in the footnote assume
that intakes of individual substances are small.
They also assume independence of action by the
compounds involved (i.e., that there are no
synergistic or antagonistic chemical interactions
and that all chemicals produce the same effect,
i.e., cancer). If these assumptions are incorrect,
over- or under-estimation of the actual multiple-
substance risk could result.
Calculate a separate total cancer risk for each
exposure pathway by summing the substance-
specific cancer risks. Resulting cancer risk
estimates should be expressed using one significant
figure only. Obviously, the total cancer risk for
each pathway should not exceed 1. Exhibit 8-2
provides a sample table format for presenting
estimated cancer risks for specified exposure
pathways in the "Total Pathway Risk" column.
There are several limitations to this approach
that must be acknowledged. First, because each
slope factor is an upper 95th percentile estimate
of potency, and because upper 95th percentiles of
probability distributions are not strictly additive,
the total cancer risk estimate might become
artificially more conservative as risks from a
number of different carcinogens are summed. If
one or two carcinogens drive the risk, however,
this problem is not of concern. Second, it often
will be the case that substances with different
weights of evidence for human carcinogenicity are
included. The cancer risk equation for multiple
substances sums all carcinogens equally, giving as
much weight to class B or C as to class A
carcinogens. In addition, slope factors derived
from animal data will be given the same weight as
slope factors derived from human data. Finally,
the action of two different carcinogens might not
be independent. New tools for assessing
carcinogen interactions are becoming available,
and should be considered in consultation with the
RPM (e.g., Arcos et al. 1988). The significance
of these concerns given the circumstances at a
particular site should be discussed and presented
with the other information described in Section
8.6.
Noncarcinogenic effects. To assess the overall
potential for noncarcinogenic effects posed by
more than one chemical, a hazard index (HI)
approach has been developed based on EPA's
-------
Page 8-13
(1986b) Guidelines for Health Risk Assessment of
Chemical Mixtures. This approach assumes that
simultaneous subthreshold exposures to several
chemicals could result in an adverse health effect.
It also assumes that the magnitude of the adverse
effect will be proportional to the sum of the ratios
of the subthreshold exposures to acceptable
exposures. The hazard index is equal to the sum
of the hazard quotients, as described in the box
below, where E and the RfD represent the same
exposure period (e.g., subchronic, chronic, or
shorter-term). When the hazard index exceeds
unity, there may be concern for potential health
effects. While any single chemical with an
exposure level greater than the toxicity value will
cause the hazard index to exceed unity, for
multiple chemical exposures, the hazard index can
also exceed unity even if no single chemical
exposure exceeds its RfD.
NONCANCER HAZARD INDEX
Hazard Index = E1fRfD1 + E2/RfD2 + ...
+ E;/RfD;
where:
E, — exposure level (or intake) for
the ith toxicant;
RfD/ = reference diose for the i*
toxicant; and
E and RfD are expressed in the same
units and represent the same exposure
period (i.e., chronic, subchronic, or
shorter-term).
It is important to calculate the hazard index
separately for chronic, subchronic, and shorter-
term exposure periods as described below. It is
also important to remember to include RfDs for
the noncancer effects of carcinogenic substances.
(1) Noncarcinogenic effects
chronic
exposures. For each chronic exposure
pathway (i.e., seven year to lifetime
exposure), calculate a separate chronic
hazard index from the ratios of the chronic
daily intake (GDI) to the chronic reference
dose (RfD) for individual chemicals as
described in the box below. Exhibit 8-3
provides a sample table format for
recording these results in the "Pathway
Hazard Index" column.
CHRONIC NONCANCER HAZARD
INDEX
Chronic
Hazard Index s= CDI;/RfD7 + CDI2/RfD2
4- ... + CDtyRfD;
where;
CDI,- = chronic daily intake for the \th
toxicant in mg/kg-day, and
RfD,- = chronic reference dose for the
f* toxicant in mg/kg-day.
The CDI is identified in Exhibits 6-11 through 6-19
and 6-22 and the RfD is identified in Exhibit 7-2.
(2) Noncarcinogenic effects - subchronic
exposures. For each subchronic exposure
pathway (i.e., two week to seven year
exposure), calculate a separate subchronic
hazard index from the ratios of subchronic
daily intake (SDI) to the subchronic
reference dose (RfDJ for individual
chemicals as described in the box on the
next page. Exhibit 8-4 provides a sample
table format for recording these results in
the "Pathway Hazard Index" column. Add
only those ratios corresponding to
subchronic exposures that will be occurring
simultaneously.
(3) Noncarcinogenic effects — less than two
week exposures. The same procedure may
be applied for simultaneous shorter-term
exposures to several chemicals. For
drinking water exposures, 1- and 10-day
Health Advisories can be used as reference
toxicity values. Depending on available
data, a separate hazard index might also be
calculated for developmental toxicants
(using RfD^s), which might cause adverse
-------
Page 8-14
SUBCHRONIC NONCANCER
HAZARD INDEX
Subchronic
Hazard Index ~
+ ... +
where:
SDI/ ss subchronic daily intake for the
Ith toxicant in mg/kg-day; and
= subchronic reference dose for
the ith toxicant in mg/kg-day.
effects following exposures of only a few
days. See Guidelines for the Health
Assessment of Suspect Developmental
Toxicants (EPA 1986c; EPA 1989) for
further guidance.
There are several limitations to this approach
that must be acknowledged. As mentioned earlier,
the level of concern does not increase linearly as
the reference dose is approached or exceeded
because the RfDs do not have equal accuracy or
precision and are not based on the same severity
of effect. Moreover, hazard quotients are
combined for substances with RfDs based on
critical effects of varying lexicological significance.
Also, it will often be the case that RfDs of
varying levels of confidence that include different
uncertainty adjustments and modifying factors will
be combined (e.g., extrapolation from animals to
humans, from LOAELs to NOAELs, from one
exposure duration to another).
Another limitation with the hazard index
approach is that the assumption of dose additivity
is most properly applied to compounds that
induce the same effect by the same mechanism of
action. Consequently, application of the hazard
index equation to a number of compounds that
are not expected to induce the same type of
effects or that do not act by the same mechanism
could overestimate the potential for effects,
although such an approach is appropriate at a
screening level. This possibility is generally not
of concern if only one or two substances are
responsible for driving the HI above unity. If the
HI is greater than unity as a consequence of
summing several hazard quotients of similar value,
it would be appropriate to segregate the
compounds by effect and by mechanism of action
and to derive separate hazard indices for each
group.
Segregation of hazard indices. Segregation of
hazard indices by effect and mechanism of action
can be complex and time-consuming because it is
necessary to identify all of the major effects and
target organs for each chemical and then to
classify the chemicals according to target organ(s)
or mechanism of action. This analysis is not
simple and should be performed by a toxicologist.
If the segregation is not carefully done, an
underestimate of true hazard could result. Agency
review of particularly complex or controversial
cases can be requested of ECAO through the
regional risk assessment support staff.
The procedure for recalculating the hazard
index by effect and by mechanism of action is
briefly described in the box on the next page. If
one of the effect-specific hazard indices exceeds
unity, consideration of the mechanism of action
might be warranted. A strong case is required,
however, to indicate that two compounds which
produce adverse effects on the same organ system
(e.g., liver), although by different mechanisms,
should not be treated as dose additive. Any such
determination should be reviewed by ECAO.
If there are specific data germane to the
assumption of dose-additivity (e.g., if two
compounds are present at the same site and it is
known that the combination is five times more
toxic than the sum of toxicities for the two
compounds), then modify the development of the
hazard index accordingly. Refer to the EPA
(1986b) mixtures guidelines for discussion of a
hazard index equation that incorporates
quantitative interaction data. If data on chemical
interactions are available, but are not adequate to
support a quantitative assessment, note the
information in the "assumptions" being
documented for the site risk assessment.
-------
Page 8-15
PROCEDURE FOR SEGREGATION OF
HAZARD INDICES BY EFFECT
Segregation of hazard indices requires identification
of the major effects of each chemical, including those
seen at higher doses than the critical effect (e.g., the
chemical may cause liver damage at a dose of 100
mg/kg-day and neurotoxicity at a dose of 250 mg/kg-
day). Major effect categories Include neurotraricity,
developmental toxicity, reproductive toxicity,
immunotoxicity, and adverse effects by target organ (i.e.,
hepatic, renal, respiratory, cardiovascular,
gastrointestinal, hematological, musculoskeletal, and
dermal/ocular effects). Although higher exposure levels
may be required to produce adverse health effects other
than the critical effect, the RfD can be used as the
toxicity value for each effect category as a conservative
and simplifying step.
INFORMATION SOURCES FOR
SEGREGATION OF HAZARD INDICES
Of the available information sources, the ATSDR
Toxicological Profiles are well suited in format and
content to allow a rapid determination of additional
health effects that may occur at exposure levels higher
than those that produce the critical effect. Readers
should be aware that the ATSDR definitions of
exposure durations are somewhat different than EPA's
and are independent of species; acute - up to 14 days;
intermediate ~ more than 14 days to 1 year; chronic
-- greater than one year. IRIS contains only limited
information on health effects beyond the critical effect,
and EPA criteria documents and HEAs, HEEPs, and
HEEDs may not systematically cover all health effects
observed at doses higher those associated with the most
sensitive effects.
8.3 COMBINING RISKS ACROSS
EXPOSURE PATHWAYS
This section gives directions for combining the
multi-chemical risk estimates across exposure
pathways and provides guidance for determining
when such aggregation is appropriate.
In some Superfund site situations, an
individual might be exposed to a substance or
combination of substances through several
pathways. For example, a single individual might
be exposed to substance(s) from a hazardous waste
site by consuming contaminated drinking water
from a well, eating contaminated fish caught near
the site, and through inhalation of dust originating
from the site. The total exposure to various
chemicals will equal the sum of the exposures by
all pathways. One should not automatically sum
risks from all exposure pathways evaluated for a
site, however. The following subsections describe
how to identify exposure pathways that should be
combined and, for these, how to sum cancer risks
and noncancer hazard indices across multiple
exposure pathways.
8.3.1 IDENTIFY REASONABLE EXPOSURE
PATHWAY COMBINATIONS
There are two steps required to determine
whether risks or hazard indices for two or more
pathways should be combined for a single exposed
individual or group of individuals. The first is to
identify reasonable exposure pathway
combinations. The second is to examine whether
it is likely that the same individuals would
consistently face the "reasonable maximum
exposure" (RME) by more than one pathway.
Identify exposure pathways that have the
potential to expose the same individual or
subpopulation at the key exposure areas evaluated
in the exposure assessment, making sure to
consider areas of highest exposure for each
pathway for both current and future land-uses
(e.g., nearest downgradient well, nearest downwind
receptor). For each pathway, the risk estimates
and hazard indices have been developed for a
particular exposure area and time period; they do
not necessarily apply to other locations or time
periods. Hence, if two pathways do not affect the
same individual or subpopulation, neither
pathway's individual risk estimate or hazard index
affects the other, and risks should not be
combined.
Once reasonable exposure pathway
combinations have been identified, it is necessary
to examine whether it is likely that the same
individuals would consistently face the RME as
estimated by the methods described in Chapter 6.
Remember that the RME estimate for each
exposure pathway includes many conservative and
upper-bound parameter values and assumptions
(e.g., upper 95th confidence limit on amount of
water ingested, upper-bound duration of occupancy
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Page 8-16
of a single residence). Also, some of the exposure
parameters are not predictable in either space or
time (e.g., maximum downwind concentration may
shift compass direction, maximum ground-water
plume concentration may move past a well). For
real world situations in which contaminant
concentrations vary over time and space, the same
individual may or may not experience the RME
for more than one pathway over the same period
of time. One individual might face the RME
through one pathway, and a different individual
face the RME through a different pathway. Only
if you can explain why the key RME assumptions
for more than one pathway apply to the same
individual or subpopulation should the RME risks
for more than one pathway be combined.
In some situations, it may be appropriate to
combine one pathway's RME risks with other
pathways' risk estimates that have been derived
from more typical exposure parameter values. In
this way, resulting estimates of combined pathway
risks may better relate to RME conditions.
If it is deemed appropriate to sum risks and
hazard indices across pathways, the risk assessor
should clearly identify those exposure pathway
combinations for which a total risk estimate or
hazard index is being developed. The rationale
supporting such combinations should also be
clearly stated. Then, using the methods described
in Sections 8.3.2 and 8.3.3, total cancer risk
estimates and hazard indices should be developed
for the relevant exposure areas and individuals (or
subpopulations). For example, Exhibits 8-2 and
8-3 illustrate the combination of cancer risk
estimates and chronic noncancer hazard indices,
respectively, for a hypothetical nearby residential
population exposed to contaminants from a site
by two exposure pathways: drinking contaminated
ground water from private wells and ingestion of
contaminated fish caught in the local river. In
this hypothetical example, it is "known" that the
few families living next to the site consume more
locally caught fish than the remaining community
and have the most highly contaminated wells of
the area.
The following two subsections describe how to
sum risks and hazard indices for multiple exposure
pathways for carcinogenic and noncarcinogenic
substances, respectively.
8.3.2 SUM CANCER RISKS
First, sum the cancer risks for each exposure
pathway contributing to exposure of the same
individual or subpopulation. For Superfund risk
assessments, cancer risks from various exposure
pathways are assumed to be additive, as long as
the risks are for the same individuals and time
period (i.e., less-than-lifetime exposures have all
been converted to equivalent lifetime exposures).
This summation is described in the box below.
The sample table format given in Exhibit 8-2
provides a place to record the total cancer risk
estimate.
CANCER RISK EQUATION FOR
MULTIPLE PATHWAYS
Total Exposure Cancer Risk =
Risk(exposure pathway;) +
Risk(exposure pathway2) +
Risk(exposure pathway/)
.... -f
As described in Section 8.2.2, although the
exact equation for combining risk probabilities
includes terms for joint risks, the difference
between the exact equation and the approximation
described above is negligible for total cancer risks
of less than 0.1.
8.3.3 SUM NONCANCER HAZARD INDICES
To assess the overall potential for
noncarcinogenic effects posed by several exposure
pathways, the total hazard index for each exposure
duration (i.e., chronic, subchronic. and shorter-
term) should be calculated separately. This
equation is described in the box on the next page.
The sample table format given in Exhibit 8-3
provides a place to record the total exposure
hazard index for chronic exposure durations.
When the total hazard index for an exposed
individual or group of individuals exceeds unity,
there may be concern for potential noncancer
health effects. For multiple exposure pathways,
the hazard index can exceed unity even if no
single exposure pathway hazard index exceeds
unity. If the total hazard index exceeds unity and
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Page 8-17
HAZARD INDEX EQUATION FOR
MULTIPLE PATHWAYS
Total Exposure Hazard Index =
Hazard Index(exposure pathway;) +
Hazard Index(exposure pathway2) -f
Hazard Index(exposure pathway,-)
where:
Total Exposure Hazard Index is
calculated separately for chronic,
subchronic, and shorter-term exposure
periods.
if combining exposure pathways has resulted in
combining hazard indices based on different
chemicals, one may need to consider segregating
the contributions of the different chemicals
according to major effect (see Section 8.2.2.).
8.4 ASSESSMENT AND
PRESENTATION OF
UNCERTAINTY
This section discusses practical approaches to
assessing uncertainty in Superfund site risk
assessments and describes ways to present key
information bearing on the level of confidence in
quantitative risk estimates for a site. The risk
measures used in Superfund site risk assessments
usually are not fully probabilistic estimates of risk,
but conditional estimates given a considerable
number of assumptions about exposure and
toxicity (e.g., risk given a particular future land-
use). Thus, it is important to fully specify the
assumptions and uncertainties inherent in the risk
assessment to place the risk estimates in proper
perspective. Another use of uncertainty
characterization can be to identify areas where a
moderate amount of additional data collection
might significantly improve the basis for selection
of a remedial alternative.
Highly quantitative statistical uncertainty
analysis is usually not practical or necessary for
Superfund site risk assessments for a number of
reasons, not the least of which are the resource
requirements to collect and analyze site data in
such a way that the results can be presented as
valid probability distributions. As in all
environmental risk assessments, it already is
known that uncertainty about the numerical
results is generally large (i.e., on the range of at
least an order of magnitude or greater).
Consequently, it is more important to identify the
key site-related variables and assumptions that
contribute most to the uncertainty than to
precisely quantify the degree of uncertainty in the
risk assessment. Thus, the focus of this section is
on qualitative/semi-quantitative approaches that
can yield useful information to decision-makers for
a limited resource investment.
There are several categories of uncertainties
associated with site risk assessments. One is the
initial selection of substances used to characterize
exposures and risk on the basis of the sampling
data and available toxicity information. Other
sources of uncertainty are inherent in the toxicity
values for each substance used to characterize risk.
Additional uncertainties are inherent in the
exposure assessment for individual substances and
individual exposures. These uncertainties are
usually driven by uncertainty in the chemical
monitoring data and the models used to estimate
exposure concentrations in the absence of
monitoring data, but can also be driven by
population intake parameters. Finally, additional
uncertainties are incorporated in the risk
assessment when exposures to several substances
across multiple pathways are summed.
The following subsections describe how to
summarize and discuss important site-specific
exposure uncertainties and the more general
toxicity assessment uncertainties.
8.4.1 IDENTIFY AND EVALUATE
IMPORTANT SITE-SPECIFIC
UNCERTAINTY FACTORS
Uncertainties in the exposure assessment
typically include most of the site-specific
uncertainties inherent in risk characterization, and
thus are particularly important to summarize for
each site. In risk assessments in general, and in
the exposure assessment in particular, several
sources of uncertainty need to be addressed: (1)
definition of the physical setting, (2) model
-------
Page 8-18
applicability and assumptions, (3) transport, fate,
and exposure parameter values, and (4) tracking
uncertainty, or how uncertainties are magnified
through the various steps of the assessment.
Some of these sources of uncertainty can be
quantified while others are best addressed
qualitatively.
Definition of the physical setting. The initial
characterization of the physical setting that defines
the risk assessment for a Superfund site involves
many professional judgments and assumptions.
These include definition of the current and future
land uses, identification of possible exposure
pathways now and in the future, and selection of
substances detected at the site to include in the
quantitative risk assessment. In Superfund risk
assessments, particular attention should be given
to the following aspects of the definition of the
physical setting.
• Likelihood of exposure pathways and land
uses actually occurring. A large part of the
risk assessment is the estimation of cancer
risks or hazard indices that are conditional
on the existence of the exposure conditions
analyzed; e.g., if a residential development
is built on the site 10 years from now, the
health risks associated with contaminants
from the site would be X. It is important
to provide the RPM or other risk manager
with information related to the likelihood
that the assumed conditions will occur to
allow interpretation of a conditional risk
estimate in the proper context. For
example, if the probability that a residential
development would be built on the site 10
or 50 years from now is very small,
different risk management decisions might
be made than if the probability is high.
Present the information collected during
scoping and for the exposure assessment
that will help the RPM to identify the
relative likelihood of occurrence of each
exposure pathway and land-uses, at least
qualitatively (e.g., institutional land-use
controls, zoning, regional development
plans).
• The chemicals not included in the
quantitative risk estimate as a consequence
of missing information on health effects or
lack of quantitation in the chemical
analysis may represent a significant source
of uncertainty in the final risk estimates.
If chemicals with known health effects were
eliminated from the risk assessment on the
basis of concentration or frequency of
detection, one should now review and
confirm whether or not any of the
chemicals previously eliminated should
actually be included. For substances
detected at the site, but not included in the
quantitative risk assessment because of data
limitations, discuss possible consequences
of the exclusion on the risk assessment.
A checklist of uncertainty factors related to the
definition of the physical setting is described in
the box below.
LIST PHYSICAL SETTING DEFINITION
UNCERTAINTIES
• For chemicals not included in the quantitative risk
assessment, describe briefly:
reason for exclusion (e.g., quality control), and
possible consequences of exclusion on risk
assessment (e.g., because of widespread
contamination, underestimate of risk).
• For the current land uses describe:
- sources and quality of information, and
- qualitative confidence level.
• For the future land uses describe:
- sources and quality of information, and
information related to the likelihood of
occurrence.
• For each exposure pathway, describe why pathway
was selected or not selected for evaluation (i.e.,
sample table format from Exhibit 6-8).
• For each combination of pathways, describe any
qualifications regarding the selection of exposure
pathways considered to contribute to exposure of
the same individual or group of individuals over
the same period of time.
Model applicability and assumptions. There
is always some doubt as to how well an exposure
model or its mathematical expression (e.g.,
ground-water transport model) approximates the
true relationships between site-specific
environmental conditions. Ideally, one would like
to use a fully validated model that accounts for all
the known complexities in the parameter
-------
Page 8-19
interrelationships for each assessment. At present,
however, only simple, partially validated models
are available and commonly used. As a
consequence, it is important to identify key model
assumptions (e.g., linearity, homogeneity, steady-
state conditions, equilibrium) and their potential
impact on the risk estimates. In the absence of
field data for model validation, one could perform
a limited sensitivity analysis (i.e., vary assumptions
about functional relationships) to indicate the
magnitude of uncertainty that might be associated
with model form. At a minimum, one should list
key model assumptions and indicate potential
impact of each on risk with respect to both
direction and magnitude, as shown in the box
below. A sample table format is presented in
Exhibit 6-21 of Chapter 6.
CHARACTERIZE MODEL
UNCERTAINTIES
List/summarize the key model assumptions.
Indicate the potential impact of each on risk:
- direction (i.e., may over- or underestimate
risk); and
- magnitude (e.g., order of magnitude).
Parameter value uncertainty. During the
course of a risk assessment, numerous parameter
values are included in the calculations of chemical
fate and transport and human intake. A first step
in characterizing parameter value uncertainty in
the baseline risk assessment is to identify the key
parameters influencing risk. This usually can be
accomplished by expert opinion or by an explicit
sensitivity analysis. In a sensitivity analysis, the
values of parameters suspected of driving the risks
are varied and the degree to which changes in the
input variables result in changes in the risk
estimates are summarized and compared (e.g., the
ratio of the change in output to the change in
input). It is important to summarize the
uncertainty associated with key parameters, as
described below.
• Significant site data gaps might have
required that certain parameter values be
assumed for the risk assessment. For
example, no information on the frequency
with which individuals swim in a nearby
stream might be available for a site, and an
assumed frequency and duration of
swimming events based on a national
average could have driven the exposure
estimate for this pathway.
• Significant data uncertainties might exist
for other parameters, for example, whether
or not the available soil concentration
measurements are representative of the
true distribution of soil contaminant
concentrations.
Tracking uncertainty. Ideally, one would like
to carry through the risk assessment the
uncertainty associated with each parameter in
order to characterize the uncertainty associated
with the final risk estimates. A more practical
approach for Superfund risk assessments is to
describe qualitatively how the uncertainties might
be magnified or biased through the risk models
used. General quantitative, semi-quantitative, and
qualitative approaches to uncertainty analysis are
described below.
Quantitative approach. Only on the rare
occasions that an RPM may indicate the need for
a quantitative uncertainty analysis should one be
undertaken. As mentioned earlier, a highly
quantitative statistical uncertainty analysis is
usually not practical or necessary for Superfund
sites.
If a quantitative analysis is undertaken for a
site, it is necessary to involve a statistician in the
design and interpretation of that analysis. A
quantitative approach to characterizing uncertainty
might be appropriate if the exposure models are
simple and the values for the key input
parameters are well known. In this case, the first
step would be to characterize the probability
distributions for key input parameter values
(either using measured or assumed distributions).
The second step would be to propagate parameter
value uncertainties through the analysis using
analytic (e.g., first-order Taylor series
approximation) or numerical (e.g., Monte Carlo
simulation) methods, as appropriate. Analytic
methods might be feasible if there are a few
parameters with known distributions and linear
relationships. Numerical methods (e.g., Monte
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Page 8-20
Carlo simulation) can be suitable for more
complex relationships, but must be done on a
computer and can be resource intensive even with
time-saving techniques (e.g., Latin Hypercube
sampling).
Two common techniques of propagating
uncertainty are first-order analyses and Monte
Carlo simulations. First-order analysis is based on
the assumption that the total variance of a model
output variable is a function of the variances of
the individual model input variables and the
sensitivity of the output variable to changes in
input variables. The sensitivity of the output
variable is defined by the first derivative of the
function or model, which can be generated
analytically or numerically. A Monte Carlo
simulation estimates a distribution of exposures or
risk by repeatedly solving the model equation(s).
The probability distribution for each variable in
the model must be defined. The computer selects
randomly from each distribution every time the
equation is solved. From the resulting output
distribution of exposures or risk, the assessor can
identify the value corresponding to any specified
percentile (e.g., the 95th percentile in the
exposure distribution).
These quantitative techniques require
definition of the distribution of all input
parameters and knowledge of the degree of
dependence (i.e., covariance) among parameters.
The value of first-order analyses or Monte Carlo
simulations in estimating exposure or risk
probability distributions diminishes sharply if one
or more parameter value distributions are poorly
defined or must be assumed. These techniques
also become difficult to document and to review
as the number of model parameters increases.
Moreover, estimating a probability distribution for
exposures and risks can lead one into a false sense
of certainly about the analysis. Even in the most
comprehensive analyses, it will generally be true
that not all of the sources of uncertainty can be
accounted for or all of the parameter
codependencies recognized. Therefore, in addition
to documenting all input distributions and
covariances, it is very important to identify all of
the assumptions and incomplete information that
have not been accounted for in the quantitative
uncertainty analysis (e.g., likelihood that a
particular land use will occur) when presenting the
results.
References describing numerical methods of
propagating uncertainty through a risk analysis
include Burmaster and von Stackelberg (1988),
Hoffman and Gardner (1983), Iman and Helton
(1988), and NRC (1983). References describing
analytic methods of tracking uncertainty include
Hoffman and Gardner (1983), NRC (1983),
Downing et al. (1985), and Benjamin and Cornell
(1970).
Semi-quantitative approach. Often available
data are insufficient to fully describe parameter
distributions, but are sufficient to describe the
potential range of values the parameters might
assume. In this situation, sensitivity analyses can
be used to identify influential model input
variables and to develop bounds on the
distribution of exposure or risk. A sensitivity
analysis can estimate the range of exposures or
risk that result from combinations of minimum
and maximum values for some parameters and
mid-range values for others. The uncertainty for
an assessment of this type could be characterized
by presenting the ranges of exposure or risk
generated by the sensitivity analysis and by
describing the limitations of the data used to
estimate plausible ranges of model input variables
(EPA 1985).
Qualitative approach. Sometimes, a qualitative
approach is the most practical approach to
describing uncertainty in Superfund site risk
assessments given the use of the information (e.g.,
identifying areas where the results may be
misleading). Often the most practical approach
to characterizing parameter uncertainty will be to
develop a quantitative or qualitative description of
the uncertainty for each parameter and to simply
indicate the possible influence of these
uncertainties on the final risk estimates given
knowledge of the models used (e.g., a specific
ground-water transport model). A checklist of
uncertainty factors related to the definition of
parameters is described in the box on page 8-22.
A sample table format is provided in Exhibit
6-21 of Chapter 6.
Consider presentation of information on key
parameter uncertainties in graphic form to
illustrate clearly to the RPM or other risk
managers the significance of various assumptions.
For example, Exhibit 8-5 plots assumptions
regarding contaminated fish ingestion and resulting
-------
Page 8-21
EXHIBIT 8-5
EXAMPLE OF PRESENTATION OF IMPACT OF EXPOSURE ASSUMPTIONS
ON CANCER RISK ESTIMATE
digestion of Fish Contaminated with Chemical X
(30 mg X/Kg Fish Wet Weight)
XL
co
ir
k_
CD
O
c
CO
O
CD
'•^
CD
CO
en
CD
O
X
LLI
O
_Q
i_
CD
Q.
Q.
164'5J
165° J
165'5-J
10
20 30 40
Grams/Person/Day
50
60
Fillet with Skin
Fillet Only
The risk of developing cancer is plotted on a log scale. A risk of 10~4indicates a probability
of 1 chance in 10,000 and a risk of 10'5indicates a probability of 1 chance in 100,000 of an
individual developing cancer.
-------
Page 8-22
impacts on the cancer risk estimate for this
exposure pathway. Exhibit 8-6 illustrates the
significance of these same assumptions for the
hazard index estimates for contaminated fish
consumption. Additionally, maps showing
isopleths of risks resulting from modeled air
exposures such as emissions near the site may
assist the RPM or risk manager in visualizing the
significance of current or future site risks for a
community.
CHARACTERIZE FATE AND
TRANSPORT AND EXPOSURE
PARAMETER UNCERTAINTIES
• List all key exposure assessment parameters (e.g.,
infiltration rate, exposure duration,
bioconcentration factors, body weight).
• List the value used for each parameter and
rationale for its selection.
• Describe the measured or assumed parameter
value distributions, if possible, considering:
- total range;
- shape of distribution, if known (e.g., log-
normal);
- mean (geometric or arithmetic) + standard
deviation; and/or
- specific percentiles (e.g., median, 95th).
• Quantify the uncertainty of statistical values used
in the risk assessment (e.g., standard error of the
mean) or data gaps and qualifiers,
• Describe potential direction and magnitude of bias
in risk estimate resulting from assumptions or data
gaps (see Exhibit 6-21).
8.4.2 IDENTIFY/EVALUATE TOXICITY
ASSESSMENT UNCERTAINTY
FACTORS
For substances that contribute most to the
estimates of cancer risk and noncancer hazard
indices, summarize the uncertainty inherent in the
toxicity values for the durations of exposure
assessed. Some of the information (e.g., weight of
evidence for potential human carcinogens,
uncertainty adjustments for noncancer toxicity
values) has already been recorded in the sample
table formats provided in Exhibits 8-2 through
8-4. Other information will be developed during
the toxicity assessment itself (see Chapter 7).
The box on page 8-24 provides a checklist of
uncertainties that apply to most toxicity
assessments.
Multiple substance exposure uncertainties.
Uncertainties associated with summing risks or
hazard indices for several substances are of
particular concern in the risk characterization step.
The assumption of dose additivity ignores possible
synergisms or antagonisms among chemicals, and
assumes similarity in mechanisms of action and
metabolism. Unfortunately, the data available to
assess interactions quantitatively are generally
lacking. In the absence of adequate information,
EPA guidelines indicate that carcinogenic risks
should be treated as additive and that noncancer
hazard indices should also be treated as additive.
These assumptions are made to help prevent an
underestimation of cancer risk or potential
noncancer health effects at a site.
Be sure to discuss the availability of
information concerning potential antagonistic or
synergistic effects of chemicals for which cancer
risks or hazard indices have been summed for the
same exposed individual or subpopulations. On
the basis of available information concerning
target organ specificity and mechanism of action,
indicate the degree to which treating the cancer
risks as additive may over- or under-estimate risk.
If only qualitative information is available
concerning potential interactions or dose-additivity
for the noncarcinogenic substances, discuss
whether the information indicates that hazard
indices may have been over- or under-estimated.
This discussion is particularly important if the
total hazard index for an exposure point is slightly
below or slightly above unity, or if the total
hazard index exceeds unity and the effect-specific
hazard indices are less than unity, and if the
uncertainty is likely to significantly influence the
risk management decision at the site.
8.5 CONSIDERATION OF SITE-
SPECIFIC HUMAN STUDIES
This section describes how to compare the
results of the risk characterization step with
-------
Page 8-23
EXHIBIT 8-6
EXAMPLE OF PRESENTATION OF IMPACT OF EXPOSURE ASSUMPTIONS
ON HAZARD INDEX ESTIMATE
Ingestion of Fish Contaminated with Chemical Y
(10 mg Y/Kg Fish Wet Weight)
2.0 -
1.5 -
X
0)
_c
•9
I
0.5 -
10 20 30 40
Grams/Person/Day
50
60
Fillet with Skin
Fillet Only
-------
Page 8-24
ATSDR health assessments and other site-specific
human studies that might be available. The first
subsection outlines how to compare an ATSDR
health assessment for the site with the risk results
summarized in the previous sections (Sections 8.2,
8.3, and 8.4). The second subsection discusses
when epidemiological or health studies might
provide useful information for assessing exposures
and health risks associated with contaminants
from a site.
CHARACTERIZE TOXICITY
ASSESSMENT UNCERTAINTIES
For each substance Carried through the quantitative
risk assessment, list uncertainties related to:
• qualitative hazard findings (i.e., potential for
human toxicity);
« derivation of toxicity values, e.g.,
- human or animal data,
- duration of study (e.g., chronic study used to set
subchronic RfD), and
- any special considerations;
• the potential for synergistic or antagonistic
interactions with Other substances affecting the
same individuals; and
• calculation of lifetime cancer risks on the basis of
less-than-lifetime exposures.
For each substance not included in the quantitative
risk assessment because of inadequate toxicity
information, list:
• possible health effects; and
• possible consequences of exclusion on final risk
estimates.
8.5.1 COMPARE WITH ATSDR HEALTH
ASSESSMENT
ATSDR health assessments were defined and
compared to the RI/FS risk assessment in Section
2.2.2. As of 1989, preliminary ATSDR health
assessments should be completed before the RI/FS
risk assessment is initiated and therefore should
be available to the risk assessor as early as
"scoping." The steps for comparing the
preliminary ATSDR health assessment with the
baseline risk assessment are outlined below.
Review again the ATSDR health assessment
findings and conclusions. These will be largely
qualitative in nature. If the ATSDR health
assessment identifies exposure pathways or
chemicals of concern that have not been included
in the RI/FS baseline risk assessment, describe the
information supporting the decision not to include
these parameters. If there are differences in the
qualitative conclusions of the health assessment
and the quantitative conclusions of the baseline
risk assessment, explain the differences, if possible,
and discuss their implications.
8.5.2 COMPARE WITH OTHER AVAILABLE
SITE-SPECIFIC EPIDEMIOLOGICAL
OR HEALTH STUDIES
For most Superfund sites, studies of human
exposure or health effects in the surrounding
population will not be available. However, if
controlled epidemiological or other health studies
have been conducted, perhaps as a consequence
of the preliminary ATSDR health assessment or
other community involvement, it is important to
include this information in the baseline risk
assessment as appropriate. However, not all such
studies provide meaningful information in the
context of Superfund risk assessments.
One can determine the availability of other
epidemiological or health studies for populations
potentially exposed to contaminants from the site
by contacting the ATSDR Regional
Representative, the Centers for Disease Control
in Atlanta, Georgia, and state and local health
agencies as early in the risk assessment process as
possible. It is important to avoid use of anecdotal
information or data from studies that might
include a significant bias or confounding factor,
however. Isolated reports of high body levels of
substances that are known to be present at the
site in a few individuals living near the site are
not sufficient evidence to confirm the hypothesis
that these individuals have received significant
exposures from the site. Nor can isolated reports
of disease or symptoms in a few individuals living
near the site be used to confirm the hypothesis
that the cause of the health effects in these
individuals was exposure to contamination from
the site. A trained epidemiologist should review
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Page 8-25
any available studies in order to identify possible
study limitations and implications for site risk
findings. The small populations and variable
exposures predominating at most Superfund sites
will make it extremely difficult to detect site-
related effects using epidemiological techniques.
If site-specific health or exposure studies have
been identified and evaluated as adequate, one
should incorporate the study findings into the
overall risk characterization to strengthen the
conclusions of the risk assessment (e.g., the risk
assessment predicts elevated blood lead levels and
the human exposure study documented elevated
blood lead levels only among those exposed to
ground water contaminated by the site). Because
of the generally large and different types of
uncertainties associated with the risk assessment
and actual health studies, a qualitative, not
quantitative, comparison between the two types of
studies is generally warranted. Areas of
agreement and disagreement between the health
study(ies) and the risk assessment should be
described and factors that might contribute to any
disagreement discussed.
8.6 SUMMARIZATION AND
PRESENTATION OF THE
BASELINE RISK
CHARACTERIZATION
RESULTS
This section provides guidance on interpreting
and presenting the risk characterization results.
The results of the baseline evaluation should not
be taken as a characterization of absolute risk.
An important use of the risk and hazard index
estimates is to highlight potential sources of risk
at a site so that they may be dealt with effectively
in the remedial process. It is the responsibility of
the risk assessment team to develop conclusions
about the magnitude and kinds of risk at the site
and the major uncertainties affecting the risk
estimates. It is not the responsibility of the risk
assessment team to evaluate the significance of the
risk in a program context, or whether and how
the risk should be addressed, which are risk
management decisions.
The ultimate user of the risk characterization
results will be the RPM or other risk manager for
the site. This section therefore outlines a
presentation of material that is designed to assist
the risk manager in using risk information to
reach site-specific decisions.
8.6.1 SUMMARIZE RISK INFORMATION IN
TEXT
The final discussion of the risk characterization
results is a key component of the risk
characterization. The discussion provides a means
of placing the numerical estimates of risk and
hazard in the context of what is known and what
is not known about the site and in the context of
decisions to be made about selection of remedies.
At a minimum, the discussion should include:
• confidence that the key site-related
contaminants were identified and discussion
of contaminant concentrations relative to
background concentration ranges;
• a description of the various types of cancer
and other health risks present at the site
(e.g., liver toxicity, neurotoxicity),
distinguishing between known effects in
humans and those that are predicted to
occur based on animal experiments;
• level of confidence in the quantitative
toxicity information used to estimate risks
and presentation of qualitative information
on the toxicity of substances not included
in the quantitative assessment;
• level of confidence in the exposure
estimates for key exposure pathways and
related exposure parameter assumptions;
• the magnitude of the cancer risks and
noncancer hazard indices relative to the
Superfund site remediation goals in the
NCP (e.g., the cancer risk range of 10~4 to
10"7 and noncancer hazard index of 1.0);
• the major factors driving the site risks (e.g.,
substances, pathways, and pathway
combinations);
• the major factors reducing the certainty in
the results and the significance of these
uncertainties (e.g., adding risks over several
substances and pathways);
-------
Page 8-26
• exposed population characteristics; and
• comparison with site-specific health studies,
when available.
In addition, if the size of the potentially
exposed population is large, the presentation of
population numbers may be of assistance to the
RPM, especially in evaluating risks in the context
of current land use. Individual risk estimates
based on the reasonable maximum exposure
(RME) should not be presented as representative
of a broadly defined population, however.
8.6.2 SUMMARIZE RISK INFORMATION IN
TABLES
A tabular summary of the cancer risks and
noncancer hazard indices should be prepared for
all exposure pathways and land uses analyzed and
for all substances carried through the risk
assessment. These tables must be accompanied by
explanatory text, as described in the previous
section, and should not be allowed to stand alone
as the entire risk characterization. The sample
table formats presented in Chapter 6 and in
Exhibits 8-2 to 8-6 provide basic summary formats.
Exhibits 8-7 and 8-8 provide examples of optional
presentations that might assist in visualization of
the risk assessment results. These bar graphs
present the baseline cancer risk estimates and
noncancer hazard indices, respectively, by pathway
for an identified subpopulation near the site. The
stacked bars in Exhibit 8-8 allow the reader to
immediately identify the pathway(s) contributing
most to the total hazard index as well as identify
the substances driving the indices in each pathway.
Reference levels are also provided (e.g., hazard
index of 1.0). Exhibits 8-5 and 8-6 introduced in
Section 8.4.1 provide examples of figures that
could help the RPM or other risk manager
visualize the impact of various assumptions and
uncertainties on the final risk or hazard index
estimate. In addition, graphics relating risk level
(or magnitude of hazard index) to concentrations
of substances in environmental media and cost of
"treatment" could allow the RPM or other risk
manager to weigh the benefits of various remedial
alternatives more easily. Examples of the last type
of graphics are presented in Part 'C of this
manual.
In a few succinct concluding paragraphs,
summarize the results of the risk characterization
step. It is the responsibility of the risk assessment
team members, who are familiar with all steps in
the site risk assessment, to highlight the major
conclusions of the risk assessment. The discussion
should summarize both the qualitative and the
quantitative findings of cancer risks and noncancer
hazards, and properly qualify these by mention of
major assumptions and uncertainties in the
assessment.
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Page 8-27
EXHIBIT 8-7
EXAMPLE OF PRESENTATION OF RELATIVE CONTRIBUTION OF INDIVIDUAL
CHEMICALS TO EXPOSURE PATHWAY AND TOTAL CANCER RISK ESTIMATES
_
co
tr
i_
CD
O
rt
O
CD
E
10-H
a 10"°-
CO
CO
CD
O
X
111
T3
10-H
10-H
.
CD
Q.
a.
10-H
10
-7
Nearby Resident Population
Excess Lifetime Cancer Risk < 3 x 10~4
Public Water Supply
< 2x10'
- !•
- >
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Page 8-28
EXHIBIT 8-8
EXAMPLE OF PRESENTATION OF RELATIVE CONTRIBUTION OF INDIVIDUAL
CHEMICALS TO EXPOSURE PATHWAY AND TOTAL HAZARD INDEX ESTIMATES
1.2
Nearby Resident Population
Chronic Hazard Index = 0.6
1.1 -
1 _
0.9 _
0.8 _
x
•D 0.7 _
"S 0.6 _
I 0.5 _
0.4 _
0.3
0.2 _
0.1 _
Phenol
Nitrobenzene
MEK
Well Water
*™5s%8fe *""
Contaminated Fish
Swimming
Exposure Pathway
-------
Page 8-29
ENDNOTE FOR CHAPTER 8
1. The probability of an individual developing cancer following exposure to more than one carcinogen is the probability of developing
cancer from at least one of the carcinogens. For two carcinogens, the precise equation for estimating this probability is risk} + risk2 -
probability (risk}, risk2) where the latter term is the joint probability of the two risks occurring in the same individual. If the risk to
agent 1 is distributed in the population independently of the risk to agent 2, the latter term would equal (riskj)(risk2). This equation
can be expanded to evaluate risks from more than two substances.
-------
Page 8-30
REFERENCES FOR CHAPTER 8
Arcos, J., Woo, Y.T., and Lai, D. 1988. Data Base on Binary Combination Effects of Chemical Carcinogens. Environ. Carcino.
Revs. [J. Environ. Sci. Health Pt. C] 6:1-150.
Benjamin, J.R. and C.A. Cornell. 1970. Probability, Statistics, and Decision-making for Civil Engineers. McGraw Hill. New York.
Burmaster, D.E. and K. von Stackelberg. 1988. A New Method for Uncertainty and Sensitivity Analysis in Public Health Risk
Assessments at Hazardous Waste Sites Using Monte Carlo Techniques in a Spreadsheet. Pages 550-556 in Superfund '88.
Proceedings of the 9th National Conference. Washington, D.C. Sponsored by the Hazardous Materials Control Research Institute.
Downing, D. J., Gardner, R. H., and Hoffman, F. O. 1985. Response Surface Methodologies for Uncertainty Analysis in Assessment
Models. Technometrics 27:151-163.
Environmental Protection Agency (EPA). 1985. Methodology for Characterization of Uncertainty in Exposure Assessments. Prepared
by Research Triangle Institute. NTIS: PB85-240455.
Environmental Protection Agency (EPA). 1986a. Guidelines for Carcinogen Risk Assessment. 51 Federal Register 33992 (September
24, 1986).
Environmental Protection Agency (EPA). 1986b. Guidelines for the Health Risk Assessment of Chemical Mixtures. 51 Federal
Register 34014 (September 24, 1986).
Environmental Protection Agency (EPA). 1986c. Guidelines for the Health Assessment of Suspect Developmental Toxicants. 51
Federal Register 34028 (September 24, 1986).
Environmental Protection Agency (EPA). 1989. Proposed Amendments to the Guidelines for the Health Assessment of Suspect
Developmental Toxicants. 54 Federal Register 9386 (March 6, 1989).
Hoffman, F. O. and R. H. Gardner. 1983. Evaluation of Uncertainties in Radiological Assessment Models. In: Radiological
Assessment. A Textbook on Environmental Dose Analysis. Till, J. E., and H.R. Meyer, (eds.). Prepared for Office of Nuclear
Reactor Regulation, U.S. Nuclear Regulatory Commission. Washington, DC. NRC FIN B0766. NUREG/CR-3332.
Iman, R. L. and J. C. Helton. 1988. An Investigation of Uncertainty and Sensitivity Analysis Techniques for Computer Models.
Risk Analysis 8:71-90.
IRIS. Integrated Risk Information System (data base). 1989. U.S. Environmental Protection Agency, Office of Research and
Development.
Metcalf, D.R. and J.W. Pegram. 1981. Uncertainty Propagation in Probabilistic Risk Assessment: A Comparative Study. Transactions
of the American Nuclear Society 38:483-484.
Nuclear Regulatory Commission (NRC). 1983. PRA Procedures Guide - A Guide to the Performance of Probabilistic Risk
Assessments for Nuclear Power Plants. Office of Nuclear Regulatory Research, Washington, D.C. NUREG/CR-2300. Vol. 2.
Vesely, W. E. and D. M. Rasmuson. Uncertainties in Nuclear Probabilistic Risk Analysis. Risk Analysis 4:313-322.
-------
CHAPTER 9
DOCUMENTATION, REVIEW, AND
MANAGEMENT TOOLS FOR
THE RISK ASSESSOR,
REVIEWER, AND MANAGER
This chapter provides tools for the
documentation, review, and management of the
baseline risk assessment. These tools will help
ensure completeness and consistency throughout
the risk assessment and in the reporting of
assessment results. Section 9.1 provides
documentation tools (for risk assessors), Section
9.2 provides review tools (for risk assessment
reviewers), and Section 9.3 provides management
tools (for remedial project managers [RPMs] and
other decision-makers concerned with the site).
9.1 DOCUMENTATION TOOLS
Throughout Chapters 4 to 8 of this manual,
guidance is provided to the risk assessor on how
to summarize and document many beginning,
intermediate, and final steps of the risk
assessment. The purpose of this section is to
consolidate that guidance, provide a final check to
ensure that all appropriate documentation has
been completed, and provide additional
information that should be helpful. This section
addresses (1) basic principles of documenting a
Superfund site risk assessment (e.g., key "dos" and
don'ts", the rationale for consistency), (2) a
suggested outline and guidance for the risk
assessment report, and (3) guidance for providing
risk assessment summaries in other key reports.
9.1.1 BASIC PRINCIPLES
There are three basic principles
documenting a baseline risk assessment:
for
(1) address the main objectives of the risk
assessment;
(2) communicate using clear, concise, and
relevant text, graphics, and tables; and
(3) use a consistent format.
Addressing the objectives. The objectives of
the baseline risk assessment - to help determine
whether additional response action is necessary at
the site, to provide a basis for determining
residual chemical levels that are adequately
protective of public health, to provide a basis for
comparing potential health impacts of various
remedial alternatives, and to help support
selection of the "no-action" remedial alternative
(where appropriate) ~ should be considered
carefully during the documentation of the risk
assessment. Recognizing these objectives early
and presenting the results of the risk assessment
with them in mind will assist the RPM and other
decision-makers at the site with readily obtaining
and using the necessary information to evaluate
the objectives. Failing to recognize the
importance of the objectives could result in a risk
assessment report that appears misdirected and/or
unnecessary.
Communicating. Clearly and concisely
communicating the relevant results of the risk
assessment can be one of the most important
aspects of the entire RI/FS. If done correctly, a
useful instrument for mitigating public health
threats will have been developed. If done
incorrectly, however, risks could be
underemphasized, possibly leading to the
-------
Page 9-2
occurrence of adverse health effects, or they could
be overemphasized, possibly leading to the
unnecessary expenditure of limited resources. See
the box below for some helpful hints on
communicating the baseline risk assessment.
HELPFUL HINTS; COMMUNICATING
THE BASELINE RISK ASSESSMENT
Try to:
use a mix of well written text, illustrative
graphics, and summary tables;
explain the major steps and the results of the
risk assessment in terms easily understood by
the general public (and especially by members
of exposed or potentially exposed populations);
define highly technical terms early (e.g., IB a
glossary); and
use a standard quantitative system - preferably
the metric system -- throughout and Units that
are the same Mvnere possible (e.g., ugft, for all
water concentrations).
Avoid:
the use of large blocks of text uiibrblcen by
any headings, graphics, tables, lists, or other
'Visual dividers";
the presentation of much quantitative
infonaation within the text (rather than in
tables); and
the drawing of "risk management" conclusions
(e,g., stating that the total or largest risk is
insignificant).
Many skills for communicating the baseline
risk assessment also can be learned by reviewing
the literature on risk communication. The
following box lists just some of the literature that
is available. Courses on the subject also exist.
Using a consistent format. A consistent
format for all Superfund risk assessments is
strongly recommended for four important reasons:
(1) it encourages consistency and
completeness in the assessment itself;
RISK COMMUNICATION GUIDANCE
Explaining Environmental Risk (EPA 1986}
Tools for Environmental Professionals
Involved in Risk Communication At
Hazardous Waste Facilities Undergoing Siting,
Permitting, or Remediation (Bean 1987)
Improving Dialogue with Communities: A
Short Guide for Government Risk
Communication (NJDEP 1987)
Seven Cardinal Rules of Risk Communication
(EPA I988a)
(2) it allows for easier review of the risk
assessments;
(3) it encourages consistent use of the
results by RPMs and other decision-
makers; and
(4) it helps demonstrate to the public and
others that risk assessments are
conducted using the same framework (if
not the same specific procedures).
Using other formats can lead to slower review
times, different interpretations of similar results,
and the charge that risk assessments are
inappropriately being conducted differently from
one site to another. The following subsections
provide guidance on the use of consistent formats.
9.1.2 BASELINE RISK ASSESSMENT
REPORT
The baseline risk assessment report references
and supports the RI/FS report. Depending on the
site, the risk assessment report can range from a
small, simple document with no appendices that
can simply be added to the RI/FS report as a
chapter, to a large, complex document with many
appendices that can "stand alone." This subsection
provides general guidance on how to organize the
baseline risk assessment report and which
information should be included in the report.
More detailed guidance, however, is found by
following the guidance in previous chapters of this
-------
ee9-3
manual. Careful use of that guidance will ensure
a well-documented baseline risk assessment report.
Exhibit 9-1 provides a suggested outline for
the full baseline risk assessment report. This
outline generally follows the flow of the risk
assessment and the organization of this manual.
The "bulleted" items are not necessarily section
headings, but rather are often items that should
be considered when writing the report. Note that,
as with the manual, not all components of the
outline are applicable to all sites. This is
especially true if the risk assessment report will be
a chapter in the RI/FS report. At some sites, and
especially when the risk assessment report will be
a stand-alone document, more site-specific items
could be added to the report.
Examples of tables and graphics that should
be included in the report are presented as exhibits
in previous chapters of this manual. Note,
however, that additional tables and graphics may
be useful.
This suggested outline may be used as a
review guide by risk assessors (and risk assessment
reviewers) to ensure that all appropriate
components of the assessment have been
addressed. Section 9.2 addresses review tools in
greater detail.
9.1.3
OTHER KEY REPORTS
Two important reports that must include
summaries of the baseline risk assessment are (1)
the remedial investigation/feasibility study (RI/FS)
report and (2) the record of decision (ROD)
report.
Summary for the RI/FS report. One of the
chapters of the RI/FS typically is devoted to a
summary of the baseline risk assessment. Part of
this summary should address the human health
evaluation (the other part should address the
environmental evaluation). The human health
summary should follow the same outline as the
full baseline risk assessment report, with almost
each section of the summary being a distillation
of each full report chapter. The risk
characterization chapter is an exception, however,
in that it could be included in the RI/FS report
essentially unchanged. Most tables and graphics
should be included unchanged as well. For more
information, see Guidance for Conducting Remedial
Investigations and Feasibility Studies Under
CERCLA (EPA 1988b).
Summary for the ROD report. The ROD
documents the remedial action selected for a site.
It consists of three basic components: (1) a
Declaration; (2) a Decision Summary; and (3) a
Responsiveness Summary. The second component,
a Decision Summary, provides an overview of the
site-specific factors and analyses that led to the
selection of the remedy. Included in this
component is a summary of site risks. As with
the risk assessment summary for the RI/FS report,
the summary for the ROD report should follow
the same outline as the full risk assessment. This
summary, however, should be much more
abbreviated than the RI/FS summary, although
care must be taken to address all of the relevant
site-specific results. For more information, see
Interim Final Guidance on Preparing Superfund
Decision Documents: The Proposed Plan, the
Record of Decision, Explanation of Significant
Differences, and the Record of Decision Amendment
(EPA 1989).
9.2 REVIEW TOOLS
This section provides guidelines on reviewing
a risk assessment report. A checklist of many
essential criteria that should be adequately
addressed in any good risk assessment is provided
(Exhibit 9-2). The checklist touches upon issues
that are often problematic and lead to difficulty
and delay in the review of risk assessments.
Principal questions are presented in the checklist
with qualifying statements or follow-up questions,
as well as references to appropriate chapters and
sections of this manual. The checklist is intended
as a guide to assist the preliminary reviewer by
ensuring that critical issues concerning the quality
and adequacy of information are not overlooked
at the screening level review of risk assessments.
Experience has shown that reviewers should pay
particular attention to the following concerns.
• Were all appropriate media sampled?
• Were any site-related chemicals (e.g.,
human carcinogens) eliminated from
analysis without appropriate justification?
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Page 9-4
EXHIBIT 9-1
SUGGESTED OUTLINE FOR A BASELINE RISK ASSESSMENT REPORT
1.0 INTRODUCTION
1.1 Overview
• General problem at site
• Site-specific objectives of risk assessment
1.2 Site Background
• Site description
• Map of site
• General history
-- Ownership
-- Operations
-- Contamination
• Significant site reference points
• Geographic location relative to offsite areas of interest
• General sampling locations and media
1.3 Scope of Risk Assessment
• Complexity of assessment and rationale
• Overview of study design
1.4 Organization of Risk Assessment Report
2.0 IDENTIFICATION OF CHEMICALS OF POTENTIAL CONCERN
2.1 General Site-specific Data Collection Considerations
Detailed historical information relevant to data collection
Preliminary identification of potential human exposure
Modeling parameter needs
Background sampling
Sampling locations and media
Sampling methods
QA/QC methods
Special analytical services (SAS)
2.2 General Site-specific Data Evaluation Considerations
• Steps used (including optional screening procedure steps, if used)
• QA/QC methods during evaluation
• General data uncertainty
2.3 Environmental Area or Operable Unit 1 (Complete for All Media)
• Area- and media-specific sample collection strategy (e.g., sample size, sampling locations)
• Data from site investigations
(continued)
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Page 9-5
EXHIBIT 9-1 (continued)
SUGGESTED OUTLINE FOR A BASELINE RISK ASSESSMENT REPORT
Evaluation of analytical methods
Evaluation of quantitation limits
Evaluation of qualified and coded data
Chemicals in blanks
Tentatively identified compounds
Comparison of chemical concentrations with background
Further limitation of number of chemicals
Uncertainties, limitations, gaps in quality of collection or analysis
2.4 Environmental Area or Operable Unit 2 (Repeat for All Areas or Operable Units, As
Appropriate)
2.X Summary of Chemicals of Potential Concern
3.0 EXPOSURE ASSESSMENT
3.1 Characterization of Exposure Setting
• Physical Setting
-- Climate
- Vegetation
-- Soil type
-- Surface hydrology
-- Ground-water hydrology
• Potentially Exposed Populations
-- Relative locations of populations with respect to site
-- Current land use
-- Potential alternate future land uses
-- Subpopulations of potential concern
3.2 Identification of Exposure Pathways
• Sources and receiving media
• Fate and transport in release media
• Exposure points and exposure routes
• Integration of sources, releases, fate and transport mechanisms, exposure points, and exposure
routes into complete exposure pathways
• Summary of exposure pathways to be quantified in this assessment
3.3 Quantification of Exposure
• Exposure concentrations
• Estimation of chemical intakes for individual pathways
(continued)
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Page 9-6
EXHIBIT 9-1 (continued)
SUGGESTED OUTLINE FOR A BASELINE RISK ASSESSMENT REPORT
3.4 Identification of Uncertainties
Current and future land-use
Environmental sampling and analysis
Exposure pathways evaluated
Fate and transport modeling
Parameter values
3.5 Summary of Exposure Assessment
4.0 TOXICITY ASSESSMENT
4.1 Toxicity Information for Noncarcinogenic Effects
• Appropriate exposure periods for toxicity values
• Up-to-date RfDs for all chemicals
• One- and ten-day health advisories for shorter-term oral exposures
• Overall data base and the critical study on which the toxicity value is based (including the
critical effect and the uncertainty and modifying factors used in the calculation)
• Effects that may appear at doses higher than those required to elicit the critical effect
• Absorption efficiency considered
4.2 Toxicity Information for Carcinogenic Effects
• Exposure averaged over a lifetime
• Up-to-date slope factors for all carcinogens
• Weight-of-evidence classification for all carcinogens
• Type of cancer for Class A carcinogens
• Concentration above which the dose-response curve is no longer linear
4.3 Chemicals for Which No EPA Toxicity Values Are Available
• Review by ECAO
• Qualitative evaluation
• Documentation/justification of any new toxicity values developed
4.4 Uncertainties Related to Toxicity Information
• Quality of the individual studies
• Completeness of the overall data base
4.5 Summary of Toxicity Information
5.0 RISK CHARACTERIZATION
5.1 Current Land-use Conditions
• Carcinogenic risk of individual substances
• Chronic hazard quotient calculation (individual substances)
• Subchronic hazard quotient calculation (individual substances)
(continued)
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Page 9-7
EXHIBIT 9-1 (continued)
SUGGESTED OUTLINE FOR A BASELINE RISK ASSESSMENT REPORT
Shorter-term hazard quotient calculation (individual substances)
Carcinogenic risk (multiple substances)
Chronic hazard index (multiple substances)
Subchronic hazard index (multiple substances)
Shorter-term hazard index calculation (multiple substances)
Segregation of hazard indices
Justification for combining risks across pathways
Noncarcinogenic hazard index (multiple pathways)
Carcinogenic risk (multiple pathways)
5.2 Future Land-use Conditions
• Carcinogenic risk of individual substances
• Chronic hazard quotient calculation (individual substances)
• Subchronic hazard quotient calculation (individual substances)
• Carcinogenic risk (multiple substances)
• Chronic hazard index (multiple substances)
• Subchronic hazard index (multiple substances)
• Segregation of hazard indices
• Justification for combining risks across pathways
• Noncarcinogenic hazard index (multiple pathways)
• Carcinogenic risk (multiple pathways)
5.3 Uncertainties
• Site-specific uncertainty factors
-- Definition of physical setting
— Model applicability and assumptions
- Parameter values for fate/transport and exposure calculations
• Summary of toxicity assessment uncertainty
- Identification of potential health effects
-- Derivation of toxicity value
- Potential for synergistic or antagonistic interactions
- Uncertainty in evaluating less-than-lifetime exposures
5.4 Comparison of Risk Characterization Results to Human Studies
• ATSDR health assessment
• Site-specific health studies (pilot studies or epidemiological studies)
• Incorporation of studies into the overall risk characterization
5.5 Summary Discussion and Tabulation of the Risk Characterization
• Key site-related contaminants and key exposure pathways identified
• Types of health risk of concern
• Level of confidence in the quantitative information used to estimate risk
• Presentation of qualitative information on toxicity
(continued)
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Page 9-8
EXHIBIT 9-1 (continued)
SUGGESTED OUTLINE FOR A BASELINE RISK ASSESSMENT REPORT
Confidence in the key exposure estimates for the key exposure pathways
Magnitude of the carcinogenic and noncarcinogenic risk estimates
Major factors driving risk
Major factors contributing to uncertainty
Exposed population characteristics
Comparison with site-specific health studies
6.0 SUMMARY
6.1 Chemicals of Potential Concern
6.2 Exposure Assessment
6.3 Toxicity Assessment
6.4 Risk Characterization
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Page 9-9
EXHIBIT 9-2
REVIEWER CHECKLIST
1.0 GENERAL CONCERNS
• Were the site-specific objectivef's') of the risk assessment stated? (HHEM - 1)
• Was the scope of the assessment described (e.g., in terms of the complexity of the assessment and
rationale, data needs, and overview of the study design)? (HHEM - 1.1.1, 3.5)
• Was an adequate history of site activities provided, including a chronology of land use (e.g.,
specifying agriculture, industry, recreation, waste deposition, and residential development at the
site)? (HHEM - 2.1.4, 9.1)
• Was an initial qualitative overview of the nature of contamination included (e.g., specifying in a
general manner the kinds of contaminants, media potentially contaminated)? (HHEM - 2.1.4, 9.1)
• Was a general map of the site depicting boundaries and surface topography included, which
illustrates site features, such as fences, ponds, structures, as well as geographical relationships
between specific potential receptors and the site? (HHEM - 2.1.4, 9.1)
2.0 CONCERNS IN REVIEWING DATA COLLECTION AND EVALUATION
2.1 Data Collection
• Was an adequate "conceptual model" of the site discussed? (HHEM - 4.2)
-- a qualitative discussion of potential or suspected sources of contamination, types and
concentrations of contaminants detected at the site, potentially contaminated media, as well
as potential exposure pathways and receptors
• Was an adequate Data Quality Objectives (DQO) statement provided? (HHEM - 4.1.4)
- a statement specifying both the qualitative and quantitative nature of the sampling data,
in terms of relative quality and intent for use, issued prior to data collection, which helps
to ensure that the data collected will be appropriate for the intended objectives of the study
• Were key site characteristics documented? (HHEM - 4.3, 4.5)
-- soil/sediment parameters (e.g., particle size, redox potential, mineral class, organic carbon
and clay content, bulk density, and porosity)
-- hydrogeological parameters (e.g., hydraulic gradient, pH/Eh, hydraulic conductivity, location,
saturated thickness, direction, and rate of flow of aquifers, relative location of bedrock layer)
(continued)
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Page 9-10
EXHIBIT 9-2 (continued)
REVIEWER CHECKLIST
-- hydrological parameters (e.g., hardness, pH, dissolved oxygen, salinity, temperature, total
suspended solids, flow rates, and depths of rivers or streams; estuary and embayment
parameters such as tidal cycle, range, and area; as well as lake parameters such as area,
volume, depth, and depth to thermocline)
- meteorological parameters (e.g., direction of prevailing wind, average wind speed,
temperature, humidity, annual average and 24 hour maximum rainfall)
• Were all appropriate media sampled? (HHEM - 4.4, 4.5, 4.6)
-- was there adequate justification for any omissions?
- were literature estimates employed for omissions in background sampling and were they
referenced properly?
• Were all key areas sampled, based on all available information (e.g., preliminary assessment,
field screening)? (HHEM - 4.4, 4.5, 4.6)
• Did sampling include media along potential routes of migration (e.g., between the contaminant
source and potential future exposure points)? (HHEM - 4.5, 4.6)
• Were sampling locations consistent with nature of contamination (e.g., at the appropriate
depth)? (HHEM - 4.5, 4.6)
• Were sampling efforts consistent with field screening and visual observations in locating "hot
spots"? (HHEM - 4.5, 4.6)
• Were detailed sampling maps provided, indicating the location, type (e.g., grab, composite,
duplicate), and numerical code of each sample? (HHEM - 5.10)
• Did sampling include appropriate QA/QC measures (e.g., replicates, split samples, trip and field
blanks)? (HHEM - 4.7, 5.4)
• Were background samples collected from appropriate areas (e.g., areas proximate to the site,
free of potential contamination by site chemicals or anthropogenic sources, and similar to the
site in topography, geology, meteorology, and other physical characteristics)? (HHEM - 4.4,
5.7)
2.2 Data Evaluation
• Were any site-related chemicals fe.g.. human carcinogens^) eliminated from analysis without
appropriate justification? (HHEM - 5.9)
(continued)
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Page 9-11
EXHIBIT 9-2 (continued)
REVIEWER CHECKLIST
-- as infrequently detected chemicals (HHEM - 5.3.3, 5.9.3)
-- as non-detects in a specific medium without employing a "proxy" concentration (HHEM -
5.3)
~ as common laboratory contaminants even though sample concentrations were significantly
higher than that found in blanks? (HHEM - 5.5)
- as present at a "ubiquitous level"? (HHEM - 5.7)
• Were inappropriate "proxy concentrations" assigned to site-related chemicals? (HHEM - 5.3)
- was a value of zero or the instrument detection limit (IDL) assigned?
~ was an erroneous sample-specific quantitation limit employed?
• Were appropriate analytical methods employed for collection of data upon which risk estimates
are based? (HHEM - 5.2)
- were the methods consistent with the requisite level of sensitivity?
- were established procedures with adequate QA/QC measures employed?
• Did the data meet the Data Quality Objectives (DQO)? (HHEM - 4.1.4)
-- were the sampling methods consistent with the intended uses of data?
• Were appropriate data qualifiers employed? (HHEM - 5.4)
• Were special analytical services (SAS) employed when appropriate? (HHEM - 5.3)
- was SAS employed as an adjunct to routine analysis in cases where certain contaminants
were suspected at low levels, as non-TCL chemicals, in non-standard matrices, or in
situations requiring a quick turnaround time?
3.0 CONCERNS IN REVIEWING THE EXPOSURE ASSESSMENT
• Were "reasonable maximum exposures" considered (i.e., the highest exposures that are reasonably
expected to occur)? (HHEM - 6.1.2, 6.4.1, 6.6)
• Were current and future land uses considered? (HHEM - 6.1.2, 6.2)
(continued)
-------
Page 9-12
EXHIBIT 9-2 (continued)
REVIEWER CHECKLIST
Was residential land use considered as an alternative future land use? (HHEM - 6.2.2)
— if not, was a valid rationale provided?
Were all potential sensitive subpopulations considered (e.g., elderly people, pregnant or nursing
women, infants and children, and people with chronic illnesses)? (HHEM - 6.2.2)
Were all significant contaminant sources considered? (HHEM - 6.3.1)
Were all potential contaminant release mechanisms considered, such as volatilization, fugitive dust
emission, surface runoff/overland flow, leaching to ground water, tracking by humans/animals, and
soil gas generation? (HHEM - 6.3.1)
Were all potential contaminant transport pathways considered, such as direct air transport
downwind, diffusion in surface water, surface water flow, ground-water flow, and soil gas migration?
(HHEM - 6.3)
Were all relevant cross-media transfer effects considered, such as volatilization to air, wet
deposition, dry deposition, ground-water discharge to surface, and ground-water recharge from
surface water? (HHEM - 6.3)
Were all media potentially associated with exposure considered? (HHEM - 6.2, 6.3)
Were all relevant site-specific characteristics considered, including topographical, hydrogeological,
hydrological, and meteorological parameters? (HHEM - 6.1, 6.3)
Were all possible exposure pathways considered? (HHEM - 6.3)
-- was a valid rationale offered for exclusion of any potential pathways from quantitative
evaluation?
Were all "spatial relationships" adequately considered as factors that could affect the level of
exposure (e.g., hot spots in an area that is frequented by children, exposure to ground water from
two aquifers that are not hydraulically connected and that differ in the type and extent of
contamination)? (HHEM - 6.2, 6.3)
Were appropriate approaches employed for calculating average exposure concentrations? (HHEM
- 6.4, 6.5)
~ was a valid rationale provided for using geometric or arithmetic means?
Were appropriate or standard default values used in exposure calculations (e.g., age-specific body
weights, appropriate exposure frequency and duration values)? (HHEM - 6.4, 6.5, 6.6)
(continued)
-------
Page 9-13
EXHIBIT 9-2 (continued)
REVIEWER CHECKLIST
4.0 CONCERNS IN REVIEWING THE TOXICITY ASSESSMENT
• Was the exclusion of any carcinogen from analysis adequately justified (e.g., were "weight-of-
evidence" classifications and completeness of exposure pathways considered in this decision)?
(HHEM - 5.9, 7.3)
• Were appropriate "route-to-route" extrapolations performed in cases where a toxicity value was
applied across differing routes of exposure? (HHEM - 7.5.1, 8.1.2)
- were the extrapolations based on appropriate guidance?
• Were appropriate toxicity values employed based on the nature of exposure? (HHEM - 7.4, 7.5)
-- were subchronic vs., chronic RfDs applied correctly based on the duration of exposure?
- were all sensitive subpopulations, such as pregnant or nursing women potentially requiring
developmental RfDs (RfD^), considered in the selection of the toxicity values used?
• Were the toxicity values that were used consistent with the values contained within the Integrated
Risk Information System (IRIS) or other EPA documents? (HHEM - 7.4, 7.5)
5.0 CONCERNS IN REVIEWING THE RISK CHARACTERIZATION
• Were exposure estimates and toxicity values consistently expressed as either intakes or absorbed
doses for each chemical taken through risk characterization? (HHEM - 8.1.2)
-- was a valid rationale given for employing values based on absorbed dose?
• Were all site-related chemicals that were analyzed in the exposure assessment considered in risk
characterization? (HHEM - 8.1.2)
- were inconsistencies explained?
• Were risks appropriately summed only across exposure pathways that affect the same individual
or population subgroup, and in which the same individual or population subgroup faces the
"reasonable maximum exposure," based on the assumptions employed in the exposure assessment?
(HHEM - 8.3)
• Were sources of uncertainty adequately characterized? (HHEM - 8.4)
-------
Page 9-14
• Were current and future land uses
considered?
• Were all significant contaminant sources
considered?
• Were appropriate or standard default
values used in exposure calculations?
• Were the toxicity values that were used
consistent with the values contained
within the Integrated Risk Information
System (IRIS) or other EPA documents?
Although the checklist addresses many pertinent
issues, it is not a complete listing of all potential
concerns, since this objective is beyond the scope
of a preliminary review tool. In addition, some of
the concerns listed are not necessarily appropriate
for all risk assessment reports.
The recommended steps in reviewing a risk
assessment report are as follows:
(1) compare the risk assessment report
outline to the suggested outline in
Section 9.1 of this chapter (i.e., Exhibit
9-1);
(2) use the checklist in this section (i.e.,
Exhibit 9-2); and
(3) conduct a comprehensive review.
The outline (Exhibit 9-1) and the checklist
(Exhibit 9-2) are intended only as tools to assist
in a preliminary review of a risk assessment, and
are not designed to replace the good judgment
needed during the comprehensive review. These
two tools should provide a framework, however,
for the timely screening of risk assessments by
reviewers with a moderate level of experience in
the area. If these steps are followed in order,
then some of the major problems with a risk
assessment report (if any) can be identified before
significant resources are expended during the
comprehensive review.
9.3 MANAGEMENT TOOLS
This section provides a concise checklist for
the RPM to use in carrying out their role in the
risk assessment process (see Exhibit 9-3). Other
decision-makers at the site also may find this
checklist useful. Specific points at which the
managers should be involved, or may be called
upon to become involved, during the risk
assessment are discussed in Chapters 4 through 8
of the manual. This checklist extracts information
from those chapters, and also includes pointers on
planning and involvement for the manager. The
purpose of the checklist is to involve managers in
the direction and development of the risk
assessment and thereby avoid serious mistakes or
costly misdirections in focus or level of effort.
Although the checklist is shaped to suggest
when and how the manager should become
involved in the risk assessment process, it is
assumed that part of the manager's involvement
will require consultation with technical resources
available in the region or state. The checklist
advises consulting the "regional risk assessment
support staff at a number of points in the
process. This contact may not be one person, but
could be a number of different technical people
in the region, such as a toxicologist,
hydrogeologist, or other technical reviewer. The
manager should become aware of the resources
available to him or her, and use them when
appropriate to ensure that the risk assessment
developed is useful and accurate.
-------
Page 9-15
EXHIBIT 9-3
CHECKLIST FOR MANAGER INVOLVEMENT
1. GETTING ORGANIZED
• Ensure that the workplan for the risk assessment contractor support is in place (if needed).
• Identify EPA risk assessment support personnel (to be used throughout the risk assessment
process).
• Gather relevant information, such as appropriate risk assessment guidances and site-
specific data and reports.
• Identify available state, county, and other non-EPA resources.
2. BEFORE THE SCOPING MEETING
• Make initial contact with risk assessor.
• Provide risk assessor with available guidances and site data.
• Determine (or review) data collection needs for risk assessment, considering:
-- modeling parameter needs;
-- type and location of background samples;
-- the preliminary identification of potential human exposure;
-- strategies for sample collection appropriate to site/risk assessment data needs;
-- statistical methods;
-- QA/QC measures of particular importance to risk assessment;
-- special analytical services (SAS) needs;
-- alternate future land use; and
-- location(s) in ground water that will be used to evaluate future ground-water exposures.
3. AT THE SCOPING MEETING
• Present risk assessment data collection needs.
• Ensure that the risk assessment data collection needs will be considered in development
of the sampling and analysis plan.
• Where limited resources require that less-than-optimal sampling be conducted, discuss potential
impacts on risk assessment results.
4. AFTER THE SCOPING MEETING
• Ensure that the risk assessor reviews and approves the sampling and analysis plan.
• Consult with ATSDR if human monitoring is planned.
(continued)
-------
Page 9-16
EXHIBIT 9-3 (continued)
CHECKLIST FOR MANAGER INVOLVEMENT
5. DURING SAMPLING AND ANALYSIS
• Ensure that risk assessment needs are being met during sampling.
• Provide risk assessor with any preliminary sampling results so that he/she can determine
if sampling should be refocused.
• Consult with ATSDR to obtain a status report on any human monitoring that is being conducted.
Provide any results to risk assessor.
6. DURING DEVELOPMENT OF RISK ASSESSMENT
• Meet with risk assessor to discuss basis of excluding chemicals from the risk assessment
(and developing the list of chemicals of potential concern). Confirm appropriateness of
excluding chemicals.
• Confirm determination of alternate future land use.
• Confirm location(s) in ground water that will be used to evaluate future ground-water exposures.
• Understand basis for selection of pathways and potentially exposed populations.
• Facilitate discussions between risk assessor and EPA risk assessment support personnel
on the following points:
— the need for any major exposure, fate, and transport models (e.g., air or ground-water
dispersion models) used;
-- site-specific exposure assumptions;
- non-EPA-derived toxicity values; and
- appropriate level of detail for uncertainty analysis, and the degree to which uncertainties will
be quantified.
• Discuss and approve combination of pathway risks and hazard indices.
• Ensure that end results of risk characterization have been compared with ATSDR health
assessments and other site-specific human studies that might be available.
7. REVIEWING THE RISK ASSESSMENT
• Allow sufficient time for review and incorporation of comments.
• Ensure that reviewers' comments are incorporated.
(continued)
-------
Page 9-17
EXHIBIT 9-3 (continued)
CHECKLIST FOR MANAGER INVOLVEMENT
8. COMMUNICATING THE RISK ASSESSMENT
• Plan a briefing among technical staff to discuss significant findings and uncertainties.
• Discuss development of graphics, tools, and presentations to assist risk management decisions.
• Consult with other groups (e.g., community relations staff), as appropriate.
• Brief upper management.
-------
Page 9-18
REFERENCES FOR CHAPTER 9
Bean, M.C. (CH2M Hill). 1987. Tools for Environmental Professionals Involved in Risk Communication at Hazardous Waste Facilities
Undergoing Siting, Permitting, or Remediation. Presented at the Air Pollution Control Association Annual Meeting. New York.
June 21-26, 1987.
Environmental Protection Agency (EPA). 1986. Explaining Environmental Risk. Office of Toxic Substances.
Environmental Protection Agency (EPA). 1988a. Seven Cardinal Rules of Risk Communication. Office of Policy Analysis.
Environmental Protection Agency (EPA). 19885. Guidance for Conducting Remedial Investigations and Feasibility Studies Under
CERCLA. Office of Emergency and Remedial Response. (OSWER Directive 9355.3-01).
Environmental Protection Agency (EPA). 1989, Interim Final Guidance on Preparing Superfund Decision Documents: The Proposed
Plan, the Record of Decision, Explanation of Significant Differences, and the Record of Decision Amendment. Office of
Emergency and Remedial Response. (OSWER Directive 9355.3-02).
New Jersey Department of Environmental Protection (NJDEP). 1987. Improving Dialogue with Communities: A Short Guide for
Government Risk Communication. Division of Science and Research.
-------
CHAPTER 10
RADIATION RISK ASSESSMENT
GUIDANCE
There are many sites contaminated with
radioactive substances that are included on the
National Priorities List (NPL), and additional sites
are expected in future NPL updates. This chapter
provides supplemental baseline risk assessment
guidance for use at these sites. This guidance is
intended as an overview of key differences in
chemical and radionuclide assessments, and not as
a comprehensive, stand-alone approach for
assessing the risks posed by radiation.
The reader should be familiar with .the
guidance provided in Chapters 2 through 9 before
proceeding further in Chapter 10. Although the
discussions in the previous chapters focus
primarily on chemically contaminated sites, much
of the information presented is also applicable to
the evaluation of radioactively contaminated
Superfund sites. For consistency and completeness,
the topics discussed in each section of this chapter
parallel the topics covered in each of the previous
chapters.
After a brief introduction to some of the
basic principles and concepts of radiation
protection (Section 10.1), seven additional areas
are addressed:
(1) Regulation of Radioactively
Contaminated Sites (Section 10.2);
(2) Data Collection (Section 10.3);
(3) Data Evaluation (Section 10.4);
(4) Exposure and Dose Assessment (Section
10.5);
ACRONYMS, SYMBOLS, AND UNITS
FOR CHAPTER 10
A(t) - Activity at Time t
Bq = Becquerel
Ci » Curie
CLP = Contract Laboratory Program
D « Absorbed Dose
DCF = Dose Conversion Factor Per Unit Intake
HE = Effective Dose Equivalent
HX = Dose Equivalent Averaged Over Tissue or
• Organ T
= Committed Effective Dose Equivalent Per
Unit Intake
HT,50 = Committed Dose Equivalent Averaged
Over Tissue T
LET = Linear Energy Transfer
LLD = Lower Limit of Detection
MeV - Million Electron Volts
N « Modifying Factor in the Definition of
Dose Equivalent
pCi = PicoCurie (10'12 Ci)
Q = Quality Factor in Definition of Dose
Equivalent
RBE = Relative Biological Effectiveness
SI = International System of Units
Sv = Sievert
T = Tissue or Target Organs
Wf = Weighting Factor in the Definition of
Effective Dose Equivalent and Committed
Effective Dose Equivalent
(5) Toxicity Assessment (Section 10.6);
(6) Risk Characterization (Section 10.7); and
(7) Documentation, Review, and
Management Tools for the Risk
Assessor, Reviewer, and Manager
(Section 10.8).
-------
Page 10-2
DEFINITIONS FOR CHAPTER 10
Absorbed Pose fD\ The mean energy imparted by ionizing radiation to matter per unit mass. The special SI unit of
absorbed dose is the gray (Gy); the conventional unit is the rad (1 rad « 0.01 Gy).
Beccmerel CBq.V One nuclear disintegration per second; the name for the SI unit of activity. : 1 Bq ~ 2.7 x 10'H Q.
Committed Dose Equivalent {Hf*n\ The total dose equivalent (averaged over tissue I) deposited over the 50-year
period following the intake of a radionuclide,
Committed Effective Dose Equivalent (Hp *n). The weighted sum of committed dose equivalents to specified organs and
tissues, in analogy to the effective dose equivalent.
Curie (CD. 3.7 x 10-*^ nuclear disintegrations per second, the name for the conventional Unit of activity, 1 Ci = 3.7 X
Decay Produces'). A radiouucHde or a series of radkmuclides formed by the nuclear transformation of another
radionuclide which, in this context, is referred to as the parent.
Dose Conversion Factor fDCFX The dose equivalent per unit intake of radionuclide.
Dose Equivalent CHI. The product of the absorbed dose (D), the quality factor (Q), and any other modifying factors (N).
The SI unit of dose equivalent is the sievett (Sv); the conventional unit is the rem (1 rem = 0.01 Sv).
Effective Dose Equivalent fHgl. The sum over specified tissues of the products of the dose equivalent in a tissue or
organ (T) and the weighting factor for that tissue.
External Radiation. Radiations incident upon the body from an external source.
Gray /Cy). The SI unit of absorbed dose. IGy = I Joule kg'1 = 100 rad,
Half-Life (physical, biological, or effective'). The time for a quantity of radionuclide, i*., its, activity, to diminish by a, .
factor of a half (because of nuclear decay events, biological elimination o£ the material, or both.). :
Internal Radiation. Radiation emitted from radionuclides distributed within the body.
Ionizing Radiation. Any radiation capable of displacing electrons from atoms or molecules, thereby producing ions.
Linear Energy Transfer (LET). A measure of the rate of energy absorption, defined as the average energy imparted to
the absorbing medium by a charged particle per unit distance (KeV per um).
Nuclear Transformation. The spontaneous transformation Of one radionuclide into a different nucjide or into a different
energy State of the same nuclide.
Quality Factor (Q). The principal modifying factor that is employed in deriving dose equivalent, H, from absorbed dose,
D; chosen to account for the relative biological effectiveness (RBE) of the radiation fa question, but to be
independent of the tissue or organ under consideration, and of the biological endpoint. For radiation protection
purposes, the quality factor is determined by the linear energy transfer (LET) of the radiation.
Rad. The conventional unit for absorbed dose of ionizing radiation; the corresponding SI unit is the gray (Gy); 1 rad —
0.01 Gy = 0.01 Joule/kg.
Rem. An acronym of radiation equivalent man, the conventional unit of dose equivalent; the corresponding SI unit is the
Sievert; 1 Sv = 100 rem.
Sievert (Sv). The special name for the SI unit of dose equivalent. 1 Sv = 100 rem.
Slope Factor. The age-averaged lifetime excess cancer incidence rate per unit intake (or unit exposure for external
exposure pathways) of a radionuclide.
Weighting Factor fw-j-V Factor indicating flie relative risk of cancer induction or hereditary defects from irradiation of a
given tissue or organ; used in calculation of effective dose equivalent and committed effective close equivalent.
-------
Page 10-3
There are special hazards associated with
handling radioactive waste and EPA strongly
recommends that a health physicist experienced in
radiation measurement and protection be
consulted prior to initiating any activities at a site
suspected of being contaminated with radioactive
substances. EPA also recommends that the
remedial project manager (RPM) or on-scene
coordinator (OSC) should designate both a
chemical risk assessor and a radiation risk
assessor. These individuals should work closely
with each other and the RPM to coordinate
remedial activities (e.g., site scoping, health and
safety planning, sampling and analysis) and
exchange information common to both chemical
and radionuclide assessments, including data on
the physical characteristics of the site, potentially
impacted populations, pathways of concern, and
fate and transport models used. At the conclusion
of the remedial investigation/feasibility study
(RI/FS) process, the RPM should issue a single
report that summarizes and integrates the results
from both the chemical and the radiation risk
assessments.
A two-phase evaluation is described for the
radiation risk assessment. As discussed in Section
10.5, procedures established by the International
Commission on Radiological Protection (ICRP
1979) and adopted by EPA in Federal Guidance
Report No. 11 (EPA 1988) are used to estimate
the radiation dose equivalent to humans from
potential exposures to radionuclides through all
pertinent exposure pathways at a site. Those
estimates of dose equivalent may be used for
comparison with established radiation protection
standards and criteria. However, this methodology
was developed for regulation of occupational
radiation exposures for adults and is not
completely applicable for estimating health risk to
the general population at a Superfund site.
Therefore, a separate methodology is presented in
Section 10.7.2 for estimating health risk, based on
the age-averaged lifetime excess cancer incidence
per unit intake (and per unit external exposure)
for radionuclides of concern. Radiation risk
assessments for Superfund sites should include
estimates of both the dose equivalent computed
as described in Section 10.5, and the health risk
attributable to radionuclide exposures computed
using the approach described in Section 10.7.
Only summary-level information is presented
in this chapter, and references are provided to a
number of supporting technical documents for
further information. In particular, the reader is
encouraged to consult Volume 1 of the
Background Information Document for the Draft
Environmental Impact Statement for Proposed
NESHAPS for Radionuclides (EPA 1989a) for a
more comprehensive discussion of EPA's current
risk assessment methodology for radionuclides.
For additional radiation risk assessment
information and guidance, RPMs and other
interested individuals can contact the Office of
Radiation Programs (ORP) within EPA
headquarters at 202-475-9630 (FTS 475-9630).
Interested individuals also can contact the
Regional Radiation Program Managers within
each of the EPA regional offices for guidance and
health physics support.
10.1 RADIATION PROTECTION
PRINCIPLES AND
CONCEPTS
Radioactive atoms undergo spontaneous
nuclear transformations and release excess energy
in the form of ionizing radiation. Such
transformations are referred to as radioactive
decay. As a result of the radioactive decay
process, one element is transformed into another;
the newly formed element, called a decay product,
will possess physical and chemical properties
different from those of its parent, and may also be
radioactive. A radioactive species of a particular
element is referred to as a radionuclide or
radioisotope. The exact mode of radioactive
transformation for a particular radionuclide
depends solely upon its nuclear characteristics, and
is independent of the nuclide's chemical
characteristics or physical state. A fundamental
and unique characteristic of each radionuclide is
its radioactive half-life, defined as the time
required for one half of the atoms in a given
quantity of the radionuclide to decay. Over 1,600
different radionuclides have been identified to
date, with half-lives ranging from fractions of a
second to millions of years. Selected radionuclides
-------
Page 10-4
of potential importance at Superfund sites are
listed in Exhibit 10-1.
Radiation emitted by radioactive substances
can transfer sufficient localized energy to atoms
to remove electrons from the electric field of their
nucleus (ionization). In living tissue this energy
transfer can destroy cellular constituents and
produce electrically charged molecules (i.e., free
radicals). Extensive biological damage can lead to
adverse health effects. The type of ionizing
radiation emitted by a particular radionuclide
depends upon the exact nature of the nuclear
transformation, and may include emission of alpha
particles, electrons (beta particles or positrons),
and neutrons; each of these transformations may
be accompanied by emission of photons (gamma
radiation or x-rays). Each type of radiation
differs in its physical characteristics and in its
ability to inflict damage to biological tissue. These
characteristics and effects are summarized in the
box on this page.
Quantities of radionuclides are typically
expressed in terms of activity at a given time t
(A(t)). The SI unit of activity is the becquerel
(Bq), which is defined as the quantity of a given
radionuclide in which one atom is transformed per
second (i.e., one decay per second). The
conventional unit of activity is the curie (Ci),
which is defined as the quantity of a given
radionuclide in which 3.7x10™ atoms undergo
nuclear transformation each second; one curie is
approximately equivalent to the decay rate of one
gram of Ra-226. A more convenient unit of
activity for expressing environmental
concentrations of radionuclides is the picoCurie
(pCi), which is equal to W12 Ci. Occasionally,
activity is expressed incorrectly in terms of counts
per second (cps) or counts per minute (cpm):
these refer to the number of transformations per
unit time measured by a particular radiation
detector and do not represent the true decay rate
of the radionuclide. To derive activity values,
count rate measurements are multiplied by
radioisotope-specific detector calibration factors.
PRINCIPAL TYPES OF IONIZING RADIATION
Alpha particles are doubly charged cations, composed of two protons and two neutrons, which are ejected monoenergeticalty
from the nucleus of an atom when the neutron to proton ratio is too low. Because of their relatively large mass and charge,
alpha particles tend to ionize nearby atoms quite readily, expending their energy in short distances. Alpha particles will usually
not penetrate an ordinary sheet of paper or the outer layer of skin. Consequently, alpha particles represent a significant hazard
only when taken into the body, where their energy is completely absorbed by small volumes of tissues.
Beta particles are electrons ejected at high speeds from the nucleus of an unstable atom when a neutron spontaneously
converts to a proton and an electron. Unlike alpha particles, beta particles are not emitted with discrete energies but are ejected
from the nucleus over a continuous energy spectrum. Beta particles are smaller than alpha particles, cany a single negative
charge, and possess a lower specific ionization potential. Unshielded beta sources can constitute external hazards if the beta
radiation is within a few centimeters of exposed skin surfaces and if the beta energy is greater than 70 keV. Beta sources
shielded with certain metallic materials may produce bremsstrahlung (low energy x-ray) radiation which may also contribute to
the external radiation exposure. Internally, beta panicles have a much greater range than alpha particles in tissue. However,
because they cause fewer ionizations per unit path length, beta particles deposit much less energy to small volumes of tissue and,
consequently, inflict must less damage than alpha particles.
Positrons are identical to beta particles except that they have a positive charge. A positron is emitted from the nucleus of
a neutron-deficient atom when a proton spontaneously transforms into a neutron. Alternatively, in cases where positron emission
is not energetically possible, the neutron deficiency ittay be overcome by electron capture, whereby one of the orbital electrons
is captured by the nucleus and united with a proton to form a neutron, or by annihilation radiation, whereby the combined mass
of a positron and electron is converted into photon energy. The damage inflicted by positrons to small volumes of tissue is
similar to that of beta particles.
Gamma radiations are photons emitted from the nucleus of a radioactive atom. X-rays, which are extra-nuclear in origin, are
identical in form to gamma rays, but have slightly lower energy ranges. There are three main ways in which x- and gamma rays
interact with matter: the photoelectric effect, the Cbmpton effect, and pair production. All three processes yield electrons which
then ionize or excite other atoms of the substance. Because of their high penetration ability, x- and gamma radiations are of
most concern as external hazards.
Neutrons are emitted during nuclear fission reactions, along with two smaller nuclei, called fission fragments, and beta and
gamma radiation. For radionuclides likely to be encountered at Superfund sites, the rate of spontaneous fission is minute and
no significant neutron radiation is expected.
-------
Page 10-5
EXHIBIT 10-1
RADIOLOGICAL CHARACTERISTICS OF SELECTED RADIONUCLIDES
FOUND AT SUPERFUND SITES0
Nuclide
Am-241
Am-243
Ba-137m
C-14
Ce-144
Cm-243
Cm-244
Co-60
Cr-51
Cs-134
Cs-135
Cs-137
Fe-59
H-3
1-129
1-131
K-40
Mn-54
Mo-99
Nb-94
Np-237
P-32
Pb-210
Po-210
Pu-238
Pu-239
Pu-240
Pu-241
Pu-242
Ra-226
Ra-228
Ru-106
S-35
Sr-89
Sr-90
Tc-99
Tc-99m
Th-230
Th-232
U-234
U-235
U-238
Half-lifec
4.32X102 y
7.38X103 y
2.55x10° h
5.73x10* y
2.84X102 d
2.85x10* y
l.SlxlO7 y
5.27x10° y
2.77X107 d
2.06x10° y
2.30xl06 y
S.OOxlO7 y
4.45x10' d
1.23X107 y
1.57xl07 y
8.04x10° d
1.28X109 y
3.13X102 d
6.60X107 h
2.03xl04 y
2.14xl06 y
\A3xlQ1 d
2.23x10' y
1.38X102 d
8.77x10' y
2.41xl04 y
6.54X103 y
1.44x10' y
3.76X105 y
1.60X105 y
5.75x10° y
3.68xl02 d
8.74x10' d
5.05X107 d
2.91x10' y
2.13X105 y
6.02x10° h
7.70x10"* y
lAlKlO10 y
2.44X105 y
7.04X108 y
4.47X109 y
Average
Alpha
5.57x10°
5.36x10°
—
5.89x10°
5.89x10°
_.
_.
—
—
-.
_.
—
„
__
4.85x10°
-.
5.40x10°
5.59x10°
5.24x10°
5.24x10°
1.22X10-4
4.97x10°
4.86x10°
—
..
_^
—
—
4.75x10°
4.07x10°
4.84x10°
4.47x10°
4.26x10°
Radiation Energies (MeV/decav1fc
Beta, Electron
5.21xlO"2
2.17xlO2
6.37xlO'2
4.95xlO2
9.22xlO"2
1.38x10''
8.59xlO"5
9.65X10'2
3.86X10'5
1.64xlO7
6.73xlQ-2
1.87x10-'
1.17x10"'
5.68X10'3
6.38X10'2
1.92x10''
5.23x10''
4.22xlO"3
3.93x10-'
1.68x10-'
7-OlxlO"2
6.95x10''
3.80xlQ-2
8. 19x10-*
1.06xlO-2
6.74X10'5
1.06xlO"2
5.25xlO'5
8.73xlQ-J
3.59X10'5
1.69xlO'2
l.OOxlO'2
4.88X10"2
5.83x10"'
1.96x10''
1.01x10-'
1.62xlO-2
1.42xlO'2
1.25X10'2
1.32xlO-2
4.92xlO-2
l.OOxlO-2
x, Gamm;
3.25xlO-2
5.61xlO2
5.98x10"'
2.07xlQ-2
1.35xlO'
1.70xlO-5
2.50x10°
3.26xlQ-2
1.55x10°
„
—
1.19x10°
„
2.46xlQ-2
3.81x10"'
1.56x10-'
8.36x10-'
1.50x10-'
1.57x10°
3.46X10'2
..
4.81xlQ-3
8.51xlO-6
l.SlxlO"3
8.07xlO'4
1.73xlQ-5
2.55xlO-6
1.44xlO'3
6.75X10'5
4.14xlQ-9
8.45xlO-5
__
_-
1.26xlO'
1.55xlO"5
1.33xlO"3
1.73xlO5
1.56x10''
1.36X10'5
Source: ICRP 1983 (except Ba-137m data from Kocher 1981).
b Computed as the sum of the products of the energies and yields of individual radiations.
c Half-life expressed in years (y), days (d), and hours (h).
-------
Page 10-6
The activity per unit mass of a given
radionuclide is called the specific activity, and is
usually expressed in units of becquerels per gram
(Bq/g) or curies per gram (Ci/g). The shorter the
half-life of the radionuclide, the greater is its
specific activity. For example, Co-60 has a
radioactive half-life of about 5 years and a specific
activity of 4x10^ Bq/g, whereas Np-237 has a
half-life of 2 million years and a specific activity
of 3xl07 Bq/g.
Several terms are used by health physicists to
describe the physical interactions of different types
of radiations with biological tissue, and to define
the effects of these interactions on human health.
One of the first terms developed was radiation
exposure, which refers to the transfer of energy
from a radiation field of x- or gamma rays to a
unit mass of air. The unit for this definition of
exposure is the roentgen (R), expressed as
coulombs of charge per kilogram of air (1 R =
2.58xlQ-4 C/kg).
The term exposure is also defined as the
physical contact of the human body with radiation.
Internal exposure refers to an exposure that occurs
when human tissues are subjected to radiations
from radionuclides that have entered the body via
inhalation, ingestion, injection, or other routes.
External exposure refers to the irradiation of
human tissues by radiations emitted by
radionuclides located outside the body either
dispersed in the air or water, on skin surfaces, or
deposited on ground surfaces. All types of
radiation may contribute to internal exposure,
whereas only photon, beta, and neutron radiations
contribute significantly to external exposure.
Ionizing radiation can cause deleterious
effects on biological tissues only when the energy
released during radioactive decay is absorbed in
tissue. The absorbed dose (D) is defined as the
mean energy imparted by ionizing radiation per
unit mass of tissue. The SI unit of absorbed dose
is the joule per kilogram, also assigned the special
name the gray (1 Gy = 1 joule/kg). The
conventional unit of absorbed dose is the rad (1
rad = 100 ergs per gram = 0.01 Gy).
For radiation protection purposes, it is
desirable to compare doses of different types of
radiation. The absorbed dose of any radiation
divided by the absorbed dose of a reference
radiation (traditionally 250 kVp x-rays) that
produces the same biological endpoint is called
the Relative Biological Effectiveness or RBE. For
regulatory purposes, an arbitrary consensus RBE
estimate called the Quality Factor or Q is often
used. The dose equivalent (H) was developed to
normalize the unequal biological effects produced
from equal absorbed doses of different types of
radiation. The dose equivalent is defined as:
H = DQN
where D is the absorbed dose, Q is a quality
factor that accounts for the RBE of the type of
radiation emitted, and N is the product of any
additional modifying factors. Quality factors
currently assigned by the International
Commission on Radiological Protection (ICRP)
include values of Q=20 for alpha particles, Q=10
for neutrons and protons, and Q=l for beta
particles, positrons, x-rays, and gamma rays (ICRP
1984). These factors may be interpreted as
follows: on average, if an equal amount of energy
is absorbed, an alpha particle will inflict
approximately 20 times more damage to biological
tissue than a beta particle or gamma ray, and
twice as much damage as a neutron. The
modifying factor is currently assigned a value of
unity (N=l) for all radiations. The SI unit of
dose equivalent is the sievert (Sv), and the
conventional unit is the rem (1 rem = 0.01 Sv).
GENERAL HEALTH PHYSICS
REFERENCES
Introduction to Health Physics (Cember
1983)
Atoms, Radiation, and Radiation Protection
(Turner 1986)
Environmental Radioactivity (Eisenbud
1987)
The Health Physics and Radiological Health
Handbook (Shleien and Terpilak 1984)
-------
Page 10-7
EFFECTIVE DOSE EQUIVALENT
The effective dose equivalent, Hg , is a weighted sum of dose equivalents to all organs and tissues (ICRP 1977, ICRP 1979),
defined as:
T
where w-j- is the weighting factor for organ or tissue T and Hj is the mean dose equivalent to organ or tissue T, The factor
w-p, which is normalized so that the summation of all the organ weighting factors is equal to one, corresponds to the fractional
contribution of organ or tissue T to the total risk of stochastic health effects when the body is uniformly irradiated. Similarly,
the committed effective dose equivalent, Hg^Q, is defined as the weighted sum of committed dose equivalents to all irradiated
organs and tissues, as follows:
HE,50 =
HT 50
Kg and Hj5 50 thus reflect both the distribution of dose among the various organs and tissues of the body and their assumed
relative sensitivities to stochastic effects. The organ and tissue weighting factor values wr- are as follows: Gonads, 0.25; Breast,
0.15; Red Marrow, 0.12; Lungs, 0.12; Thyroid, 0.03; Bone Surface, 0.03; and Remainder, 0.30 (i.e., a value of WT = 0.06 is
applicable to each of the five remaining organs or tissues receiving the highest doses).
The dose delivered to tissues from radiations
external to the body occurs only while the
radiation field is present. However, the dose
delivered to body tissues due to radiations from
systemically incorporated radionuclides may
continue long after intake of the nuclide has
ceased. Therefore, internal doses to specific
tissues and organs are typically reported in terms
of the committed dose equivalent (Hj^o), which
is defined as the integral of the dose equivalent in
a particular tissue T for 50 years after intake
(corresponding to a working lifetime).
When subjected to equal doses of radiation,
organs and tissues in the human body will exhibit
different cancer induction rates. To account for
these differences and to normalize radiation doses
and effects on a whole body basis for regulation
of occupational exposure, the ICRP developed the
concept of the effective dose equivalent (H£) and
committed effective dose equivalent (H^ 50), which
are defined as weighted sums of the organ-specific
dose equivalents (i.e., S wyHj-) and organ-specific
committed dose equivalents (i.e., ^wTHT50~),
respectively. Weighting factors, wr, are based on
selected stochastic risk factors specified by the
ICRP and are used to average organ-specific dose
equivalents (ICRP 1977,1979). The effective dose
equivalent is equal to that dose equivalent,
delivered at a uniform whole-body rate, that
corresponds to the same number (but possibly a
dissimilar distribution) of fatal stochastic health
effects as the particular combination of committed
organ dose equivalents (see the box on this page).
A special unit, the working level (WL), is
used to describe exposure to the short-lived
radioactive decay products of radon (Rn-222).
Radon is a naturally occurring radionuclide that
is of particular concern because it is ubiquitous,
it is very mobile in the environment, and it decays
through a series of short-lived decay products that
can deliver a significant dose to the lung when
inhaled. The WL is defined as any combination
of short-lived radon decay products in one liter of
air that will result in the ultimate emission of
l.SxlO5 MeV of alpha energy. The working level
month (WLM) is defined as the exposure to 1
WL for 170 hours (1 working month).
Radiation protection philosophy encourages
the reduction of all radiation exposures as low as
reasonably achievable (ALARA), in consideration
of technical, economic, and social factors.
Further, no practice involving radiation exposure
should be adopted unless it provides a positive net
benefit. In addition to these general guidelines,
specific upper limits on radiation exposures and
doses have been established by regulatory
authorities as described in the following section.
-------
Page 10-8
Additional discussion on the measurement of
radioactivity is provided in Sections 10.3 and 10.4,
and the evaluation of radiation exposure and dose
is discussed further in Section 10.5. Discussion of
potential health impacts from ionizing radiation
is presented in Section 10.6.
10.2 REGULATION OF
RADIOACTIVELY
CONTAMINATED SITES
Chapter 2 briefly describes the statutes,
regulations, guidance, and studies related to the
human health evaluation process for chemical
contaminants. The discussion describes CERCLA,
as amended by SARA, and the RI/FS process.
Since radionuclides are classified as hazardous
substances under CERCLA, this information is
also applicable to radioactively contaminated sites.
Chapter 2 also introduces the concept of
compliance with applicable or relevant and
appropriate requirements (ARARs) in federal and
state environmental laws as required by SARA.
Guidance on potential ARARs for the
remediation of radioactively contaminated sites
under CERCLA is available in the CERCLA
Compliance with Other Laws Manual (EPA 1989c).
Only a brief summary of regulatory authorities is
presented here.
The primary agencies with regulatory
authority for the cleanup of radioactively
contaminated sites include EPA, the Nuclear
Regulatory Commission (NRC), the Department
of Energy (DOE), and state agencies. Other
federal agencies, including the Department of
Transportation (DOT) and Department of Defense
(DOD), also have regulatory programs (but more
limited) for radioactive materials. Also, national
and international scientific advisory organizations
provide recommendations related to radiation
protection and radioactive waste management, but
have no regulatory authority. The following is a
brief description of the main functions and areas
of jurisdiction of these agencies and organizations.
• EPA's authority to protect public health
and the environment from adverse effects
of radiation exposure is derived from
several statutes, including the Atomic
Energy Act, the Clean Air Act, the
Uranium Mill Tailings Radiation Control
Act (UMTRCA), the Nuclear Waste
Policy Act, the Resource Conservation
and Recovery Act (RCRA), and
CERCLA EPA's major responsibilities
with regard to radiation include the
development of federal guidance and
standards, assessment of new
technologies, and surveillance of
radiation in the environment. EPA also
has lead responsibility in the federal
government for advising all federal
agencies on radiation standards. EPA's
radiation standards apply to many
different types of activities involving all
types of radioactive material (i.e., source,
byproduct, special nuclear, and naturally
occurring and accelerator produced
radioactive material [NARMJ). For
some of the EPA standards,
implementation and enforcement
responsibilities are vested in other
agencies, such as NRC and DOE.
• NRC licenses the possession and use of
certain types of radioactive material at
certain types of facilities. Specifically, the
NRC is authorized to license source,
byproduct, and special nuclear material.
The NRC is not authorized to license
NARM, although NARM may be
partially subject to NRC regulation when
it is associated with material licensed by
the NRC. Most of DOE's operations
are exempt from NRC's licensing and
regulatory requirements, as are certain
DOD activities involving nuclear
weapons and the use of nuclear reactors
for military purposes.
• DOE is responsible for conducting or
overseeing radioactive material
operations at numerous government-
owned/contractor-operated facilities.
DOE is also responsible for managing
several inactive sites that contain
radioactive waste, such as sites associated
with the Formerly Utilized Sites
Remedial Action Program (FUSRAP),
the Uranium Mill Tailings Remedial
Action Program (UMTRAP), the Grand
Junction Remedial Action Program
(GJRAP), and the Surplus Facilities
-------
Page 10-9
MAJOR FEDERAL LAWS FOR RADIATION PROTECTION
• Atomic Energy Act of 1954, Public Law 83-703 - established the Atomic Energy Commission as the basic regulatory
authority for ionizing radiation.
• Energy Reorganization Act of 1974, Public Law 93-438 - amended the Atomic Energy Act, and established the Nuclear
Regulatory Commission to regulate nondefense nuclear activities.
« Marine Protection, Research, and Sanctuaries Act of 1972, Public Law 92-532 - established controls for ocean disposal of
radioactive waste.
• Safe Drinking Water Act, Public Law 93-523 - mandated regulation of radionuclides in drinking water.
• Clean Air Act Amendments of 1977, Public Law 95-95 - extended coverage of the Act's provisions to include
radionuclides.
« Uranium Mill Tailings Radiation Control Act of 1978, Public Law 96-415 - required stabilization and control of byproduct
materials (primarily mill tailings) at licensed commercial uranium and thorium processing sites.
« Low-Level Radioactive Waste Policy Act of 1980, Public Law 96-573 - made states responsible for disposal of LLRW
generated within their borders and encouraged formation of inter-state compacts.
• Nuclear Waste Policy Act of 1982, Public Law 97-425 - mandated the development of repositories for the disposal of
high-level radioactive waste and spent nuclear fuel.
• Low-Level Radioactive Waste Policy Act Amendments of 1985, Public Law 99-240 - amended LLRWPA requirements and
schedules for establishment of LLRW disposal capacity.
Management Program (SFMP). DOE is
authorized to control all types of
radioactive materials at sites within its
jurisdiction.
Other federal agencies with regulatory
programs applicable to radioactive waste
include DOT and DOD. DOT has
issued regulations that set forth
packaging, labeling, record keeping, and
reporting requirements for the transport
of radioactive material (see 49 CFR
Parts 171 through 179). Most of DOD's
radioactive waste management activities
are regulated by NRC and/or EPA.
However, DOD has its own program for
controlling wastes generated for certain
nuclear weapon and reactor operations
for military purposes. Other agencies,
such as the Federal Emergency
Management Agency (FEMA) and the
Department of the Interior (DOI), may
also play a role in radioactive waste
cleanups in certain cases.
• States have their own authority and
regulations for managing radioactive
material and waste. In addition, 29
states (Agreement States) have entered
into agreements with the NRC, whereby
the Commission has relinquished to the
states its regulatory authority over
source, byproduct, and small quantities
of special nuclear material. Both
Agreement States and Nonagreement
States can also regulate NARM. Such
state-implemented regulations are
potential ARARs.
• The National Council on Radiation
Protection and Measurements (NCRP)
and the International Commission on
Radiological Protection (ICRP) provide
recommendations on human radiation
protection. The NCRP was chartered
by Congress to collect, analyze, develop,
and disseminate information and
recommendations about radiation
protection and measurements. The
ICRP's function is basically the same,
but on an international level. Although
-------
Page 10-10
neither the NCRP nor the ICRP have
regulatory authority, their
recommendations serve as the basis for
many of the general (i.e., not
source-specific) regulations on radiation
protection developed at state and federal
levels.
The standards, advisories, and guidance of
these various groups are designed primarily to be
consistent with each other, often overlapping in
scope and purpose. Nevertheless, there are
important differences between agencies and
programs in some cases. It is important that
these differences be well understood so that when
more than one set of standards is potentially
applicable to or relevant and appropriate for the
same CERCLA site, RPMs will be able to
evaluate which standards to follow. In general,
determination of an ARAR for a site
contaminated with radioactive materials requires
consideration of the radioactive constituents
present and the functional operations that
generated the site, whose regulatory jurisdiction
the site falls under, and which regulation is most
protective, or if relevant and appropriate, most
appropriate given site conditions.
For further information on radiation
standards, advisories, and guidance, RPMs should
consult the detailed ARARs guidance document
(EPA 1989c), as well as EPA's ORP and/or
Regional Radiation Program Managers.
10.3 DATA COLLECTION
Data collection needs and procedures for sites
contaminated with radioactive substances are very
similar to those described in Chapter 4 for
chemically contaminated sites. There are,
however, some basic differences that simplify data
collection for radionuclides, including the relative"
ease and accuracy with which natural background
radiation and radionuclide contaminants can be
detected in the environment when compared with
chemical contaminants.
The pathways of exposure and the
mathematical models used to evaluate the
potential health risks associated with radionuclides
in the environment are similar to those used for
evaluating chemical contaminants. Many of the
radionuclides found at Superfund sites behave in
the environment like trace metals. Consequently,
the types of data needed for a radiation risk
assessment are very similar to those required for
a chemical contaminant risk assessment. For
example, the environmental, land use, and
demographic data needed and the procedures used
to gather the data required to model fate and
effect are virtually identical. The primary
differences lie in the procedures used to
characterize the radionuclide contaminants. In the
sections that follow, emphasis is placed on the
procedures used to characterize the radionuclide
contaminants and not the environmental setting
that affects their fate and effects, since the latter
has been thoroughly covered in Chapter 4.
10.3.1 RADIATION DETECTION METHODS
Field and laboratory methods used to identify
and quantify concentrations of radionuclides in the
environment are, in many cases, more exact, less
costly, and more easily implemented than those
employed for chemical analyses. Selection of a
radiometric method depends upon the number of
radionuclides of interest, their activities and types
of radiations emitted, as well as on the level of
sensitivity required and the sample size available.
In some cases, the selection process requires prior
knowledge of the nature and extent of radioactive
contamination present onsite. See the references
provided in the box on page 10-12 for detailed
guidance on sample collection and preparation,
radiochemical procedures, and radiation counters
and measurement techniques. The following
discussion provides an overview of a few of the
radiation detection techniques and instruments
currently used to characterize sites contaminated
with radioactive materials.
Field methods utilize instrumental techniques
rather than radiochemical procedures to determine
in-situ identities and concentrations of
radionuclides, contamination profiles, and external
beta/gamma exposure rates. Field instruments
designed for radiation detection (see Exhibit 10-
2) are portable, rugged, and relatively insensitive
to wide fluctuations in temperature and humidity.
At the same time, they are sensitive enough to
discriminate between variable levels of background
radiation from naturally occurring radionuclides
and excess radiation due to radioactive waste.
Because of the harsh conditions in which they are
-------
Page 10-11
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Page 10-12
RADIONUCLIDE MEASUREMENT
PROCEDURES
Environmental Radiation Measurements
(NCRP 1976)
Instrumentation and Monitoring Methods for
Radiation Protection (NCRP 1978)
Radiochemical Analytical Procedures for
Analysis of Environmental Samples (EPA
I979a)
Eastern Environmental Radiation Facility
Radiochemistry Procedures Manual (EPA
1984a)
A Handbook of Radioactivity Measurement
Procedures (NCRP 1985a)
sometimes operated, and because their detection
efficiency varies with photon energy, all field
instruments should be properly calibrated in the
laboratory against National Bureau of Standards
(NBS) radionuclide sources prior to use in the
field. Detector response should also be tested
periodically in the field against NBS check-sources
of known activity.
Commonly used gamma-ray survey meters
include Geiger-Muller (G-M) probes, sodium
iodide (Nal(Tl)) crystals, and solid-state
germanium diodes (Ge(Li)) coupled to ratemeters,
sealers, or multichannel analyzers (MCAs). These
instruments provide measurements of overall
exposure rates in counts per minute, or
microRoentgens or microrem per hour. However,
only Nal and Ge(Li) detectors with MCAs provide
energy spectra of the gamma rays detected and
can therefore verify the identity of specific
radionuclides. Thin window G-M detectors and
Pancake (ionization) probes are used to detect
beta particles. Alpha-particle surface monitors
include portable air proportional, gas proportional,
and zinc sulfide (ZnS) scintillation detectors,
which all have very thin and fragile windows. The
references in the box on this page provide
additional information on several other survey
techniques and instruments, such as aerial gamma
surveillance used to map gamma exposure rate
contours over large areas.
Laboratory methods involve both chemical
and instrumental techniques to quantify low-levels
of radionuclides in sample media. The
preparation of samples prior to counting is an
important consideration, especially for samples
containing alpha- and beta-emitting radionuclides
that either do not emit gamma rays or emit
gamma rays of low abundance. Sample
preparation is a multistep process that achieves
the following three objectives: (1) the destruction
of the sample matrix (primarily organic material)
to reduce alpha- and beta-particle self-absorption;
(2) the separation and concentration of
radionuclides of interest to increase resolution and
sensitivity; and (3) the preparation of the sample
in a suitable form for counting. Appropriate
radioactive tracers (i.e., isotopes of the
radionuclides of interest that are not present in
the sample initially, but are added to the sample
to serve as yield determinants) must be selected
and added to the sample before a radiochemical
procedure is initiated.
For alpha counting, samples are prepared as
thin-layer (low mass) sources on membrane filters
by coprecipitation with stable carriers or on metal
discs by electrodeposition. These sample filters and
discs are then loaded into gas proportional
counters, scintillation detectors, or alpha
spectrometry systems for measurement (see Exhibit
10-3). In a proportional counter, the sample is
immersed in a counting gas, usually methane and
argon, and subjected to a high voltage field: alpha
emissions dissociate the counting gas creating an
ionization current proportional to the source
strength, which is then measured by the system
electronics. In a scintillation detector, the sample
is placed in contact with a ZnS phosphor against
the window of a photomultiplier (PM) tube: alpha
particles induce flashes of light in the phosphor
that are converted to an electrical current in the
PM tube and measured. Using alpha spectrometry,
the sample is placed in a holder in an evacuated
chamber facing a solid-state, surface-barrier
detector: alpha particles strike the detector and
cause electrical impulses, which are sorted by
strength into electronic bins and counted. All
three systems yield results in counts per minute,
which are then converted into activity units using
detector- and radionuclide-specific calibration
-------
Page 10-13
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Page 10-14
values. Alpha spectrometry is the only system,
however, that can be used to identify specific
alpha-emitting radionuclides.
For beta counting, samples are prepared both
as thin-sources and as solutions mixed with
scintillation fluid, similar in function to a
phosphor. Beta-emitting sources are counted in
gas proportional counters at higher voltages than
those applied for alpha counting or in scintillation
detectors using phosphors specifically constructed
for beta-particle detection. Beta-emitters mixed
with scintillation fluid are counted in 20 ml vials
in beta-scintillation counters: beta-particle
interactions with the fluid produce detectable light
flashes. Like alpha detectors, beta detectors
provide measurements in counts per minute, which
are converted to activity units using calibration
factors. It should be noted, however, that few
detection systems are available for determining the
identity of individual beta-emitting radionuclides,
because beta particles are emitted as a continuous
spectrum of energy that is difficult to characterize
and ascribe to any specific nuclide.
It is advisable to count all samples intact in
a known geometry on a Nal or Ge(Li) detector
system prior to radiochemical analysis, because
many radionuclides that emit gamma rays in
sufficient abundance and energy can be detected
and measured by this process. Even complex
gamma-ray spectra emitted by multiple
radionuclide sources can be resolved using Ge(Li)
detectors, MCAs, and software packages, and
specific radionuclide concentrations can be
determined. If the sample activity is low or if
gamma rays are feeble, then more rigorous alpha
or beta analyses are advised.
10.3.2 REVIEWING AVAILABLE SITE
INFORMATION
In Chapter 4, reference is made to reviewing
the site data for chemical contaminants in
accordance with Stage 1 of the Data Quality
Objectives (DQO) process (see box on Page 4-4).
This process also applies to radionuclides. For
further guidance on the applicability of DQOs to
radioactively contaminated sites, consult EPA's
Office of Radiation Programs.
10.3.3 ADDRESSING MODELING
PARAMETER NEEDS
Exhibits 4-1 and 4-2 describe the elements of
a conceptual model and the types of information
that may be obtained during a site sampling
investigation. These exhibits apply to radioactively
contaminated sites with only minor modifications.
For example, additional exposure pathways for
direct external exposure from immersion in
contaminated air or water or from contaminated
ground surfaces may need to be addressed for
certain radionuclides; these exposure pathways are
discussed further in subsequent sections. In
addition, several of the parameters identified in
these exhibits are not as important or necessary
for radiological surveys. For example, the
parameters that are related primarily to the
modeling of organic contaminants, such as the
lipid content of organisms, are typically not
needed for radiological assessments.
10.3.4 DEFINING BACKGROUND
RADIATION SAMPLING NEEDS
As is the case with a chemically contaminated
site, the background characteristics of a
radioactively contaminated site must be defined
reliably in order to distinguish natural background
radiation and fallout from the onsite sources of
radioactive waste. With the possible exception of
indoor sources of Rn-222, it is often possible to
make these distinctions because the radiation
detection equipment and analytical techniques
used are very precise and sensitive. At a
chemically contaminated site, there can be many
potential and difficult-to-pinpoint offsite sources
for the contamination found onsite, confounding
the interpretation of field measurements. With a
radioactively contaminated site, however, this is
not usually a problem because sources of
radionuclides are, in general, easier to isolate and
identify. In fact, some radionuclides are so
specifically associated with particular industries
that the presence of a certain radioactive
contaminant sometimes acts as a "fingerprint" to
identify its source. Additional information on the
sources of natural background and man-made
radiation in the environment may be found in the
references listed in the box on the next page.
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Page 10-15
NATURAL BACKGROUND RADIATION
Tritium in the Environment (NCRP 1979)
Ionizing Radiation: Sources and Effects
(UNSCEAR 1982)
Exposure from the Uranium Series with
Emphasis on Radon and its Daughters
(NCRP I984b)
Carbon-14 in the Environment (NCRP
1985c)
Environmental Radioactivity (Eisenbud
1987)
Population Exposure to External Natural
Radiation Background in the United States
(EPA 1987a)
Ionizing Radiation Exposure of the
Population of the United States (NCRP
1987a)
Exposure of the Population of the United
States and Canada from Natural
Background Radiation (NCRP 1987b)
10.3.5 PRELIMINARY IDENTIFICATION
OF POTENTIAL EXPOSURE
Identification of environmental media of
concern, the types of radionuclides expected at a
site, areas of concern (sampling locations), and
potential routes of radionuclide. transport through
the environment is an important part of the
radiological risk assessment process. Potential
media of concern include soil, ground water,
surface water, air, and biota, as discussed in
Chapter 4. Additional considerations for
radioactively contaminated sites are listed below.
• Usually a very limited number of
radionuclides at a site contribute
significantly to the risk. During the site
scoping meeting, it is appropriate to
consult with a health physicist not only
to develop a conceptual model of the
facility, but also to identify the
anticipated critical radionuclides and
pathways.
• In addition to the environmental media
identified for chemically contaminated
sites, radioactively contaminated sites
should be examined for the potential
presence of external radiation fields.
Many radionuclides emit both beta and
gamma radiation, which can create
significant external exposures.
• There are other components in the
environment that may or may not be
critical exposure pathways for the public,
but that are very useful indicators of the
extent and type of contamination at a
site. These components include
sediment, aquatic plants, and fish, which
may concentrate and integrate the
radionuclide contaminants that may be
(or have been) present in the aquatic
environment at a site. Accordingly,
though some components of the
environment may or may not be
important direct routes of exposure to
man, they can serve as indicators of
contamination.
10.3.6 DEVELOPING A STRATEGY FOR
SAMPLE COLLECTION
The discussions in Chapter 4 regarding
sample location, size, type, and frequency apply as
well to radioactively contaminated sites with the
following additions and qualifications. First, the
resolution and sensitivity of radioanalytical
techniques permit detection in the environment of
most radionuclides at levels that are well below
those that are considered potentially harmful.
Analytical techniques for nonradioactive chemicals
are usually not this sensitive.
For radionuclides, continuous monitoring of
the site environment is important, in addition to
the sampling and monitoring programs described
in Chapter 4. Many field devices that measure
external gamma radiation, such as continuous
radon monitors and high pressure ionization
chambers, provide a real time continuous record
of radiation exposure levels and radionuclide
concentrations. Such devices are useful for
determining the temporal variation of radiation
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Page 10-16
levels at a contaminated site and for comparing
these results to the variability observed at
background locations. Continuous measure-ments
provide an added level of resolution for
quantifying and characterizing radiological risk.
Additional factors that affect the frequency of
sampling for radionuclides, besides those discussed
in Chapter 4, include the half-lives and the decay
products of the radionuclides. Radionuclides with
short half-lives, such as Fe-59 (half-life = 44.5
days), have to be sampled more frequently because
relatively high levels of contamination can be
missed between longer sampling intervals. The
decay products of the radionuclides must also be
considered, because their presence can interfere
with the detection of the parent nuclides of
interest, and because they also may be important
contributors to risks.
10.3.7 QUALITY ASSURANCE AND
QUALITY CONTROL (QA/QC)
MEASURES
The QA/QC concepts described in Chapter
4 also apply to sampling and analysis programs for
radionuclides, although the procedures differ.
Guidance regarding sampling and measurement of
radionuclides and QA/QC protocols for their
analyses are provided in the publications listed in
the box on this page.
The QA/QC protocols used for radionuclide
analysis were not developed to meet the evidential
needs of the Superfund program; however, it is
likely that many of the current radiological
QA/QC guidance would meet the intent of
Superfund requirements. Some areas where
radiological QA/QC guidance may not meet the
intent of Superfund are listed below.
• The degree of standardization for
radiochemical procedures may be less
rigorous in the QA/QC protocols than
that required for chemical labs under
the Contract Laboratory Program (CLP).
In radiochemical laboratories, several
different techniques may be used to
analyze for a specific radionuclide in a
given matrix with comparable results.
The CLP requires all participating
chemical laboratories to use standardized
techniques.
• The required number and type of QC
blanks are fewer for radionuclide
samples. For example, a "trip" blank is
not generally used because radionuclide
samples are less likely to be
contaminated from direct exposure to air
than are samples of volatile organics.
Limited guidance is available that specifies
field QA/QC procedures (see the box on this
page). These and other issues related to QA/QC
guidance for radiological analyses are discussed
further in the Section 10.4.
RADIONUCLIDE MEASUREMENT
QA/QC PROCEDURES
Quality Control for Environmental
Measurements Using Gamma-Ray
Spectrometry (EPA 1977b)
Quality Assurance Monitoring Programs
(Normal Operation) - Effluent Streams and
the Environment (NRC 1979)
Upgrading Environmental Radiation Data
(EPA 1980)
Handbook of Analytical Quality Control in
Radioanafytical Laboratories (EPA 1987b)
QA Procedures for Health Labs
Radiochemistry (American Public Health
Association 1987)
10.4 DATA EVALUATION
Chapter 5 describes the procedures for
organizing and evaluating data collected during a
site sampling investigation for use in risk
assessment. The ten-step process outlined for
chemical data evaluation is generally applicable to
the evaluation of radioactive contaminants,
although many of the details must be modified to
accommodate differences in sampling and
analytical methods.
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Page 10-17
10.4.1 COMBINING DATA FROM
AVAILABLE SITE INVESTIGATIONS
All available data for the site should be
gathered for evaluation and sorted by
environmental medium sampled, analytical
methods, and sampling periods. Decisions should
be made, using the process described in Section
5.1, to combine, evaluate individually, or eliminate
specific data for use in the quantitative risk
assessment.
10.4.2 EVALUATING ANALYTICAL
METHODS
As with chemical data, radiological data
should be grouped according to the types of
analyses performed to determine which data are
appropriate for use in quantitative risk assessment.
Analytical methods for measuring radioactive
contaminants differ from those for measuring
organic and inorganic chemicals. Standard
laboratory procedures for radionuclide analyses are
presented in references, such as those listed in the
box on page 10-12. Analytical methods include
alpha, beta, and gamma spectrometry, liquid
scintillation counting, proportional counting, and
chemical separation followed by spectrometry,
depending on the specific radionuclides of interest.
Laboratory accreditation procedures for the
analysis of radionuclides also differ. Radionuclide
analyses are not currently conducted as part of the
Routine Analytical Services (RAS) under the
Superfund CLP. However, these analyses may be
included under Special Analytical Services (SAS).
The EPA Environmental Radioactivity
Intercomparison Program, coordinated by the
Nuclear Radiation Assessment Division of the
Environmental Monitoring Systems Laboratory in
Las Vegas (EMSL-LV), provides quality assurance
oversight for participating radiation measurement
laboratories (EPA 1989b). Over 300 federal, state,
and private laboratories participate in some phase
of the program, which includes analyses for a
variety of radionuclides in media (e.g., water, air,
milk, and food) with activity concentrations that
approximate levels that may be encountered in the
environment. Similar intercomparison programs
for analysis of thermoluminescent dosimeters
(TLDs) for external radiation exposure rate
measurements are conducted by the DOE
Environmental Measurements Laboratory (EML)
and the DOE Radiological and Environmental
Services Laboratory (RESL).
In both cases, these intercomparison
programs are less comprehensive than the CLP in
terms of facility requirements other than analysis
of performance evaluation samples, such as
laboratory space and procedural requirements,
instrumentation, training, and quality control.
However, until such time as radiation
measurements become fully incorporated in the
CLP, use of laboratories that successfully
participate in these intercomparison studies may
be the best available alternative for ensuring
high-quality analytical data. Regardless of
laboratory accreditation, all analytical results
should be carefully scrutinized and not accepted
at face value.
As discussed in Chapter 5 for chemical
analyses, radioanalytical results that are not
specific for a particular radionuclide (e.g., gross
alpha, gross beta) may have limited usefulness for
quantitative risk assessment. They can be useful
as a screening tool, however. External gamma
exposure rate data, although thought of as a
screening measurement, can be directly applied as
input data for a quantitative risk assessment.
10.4.3 EVALUATING QUANTITATION
LIMITS
Lower limits of detection (LLDs), or
quantitation limits, for standard techniques for
most radionuclide analyses are sufficiently low to
ensure the detection of nuclides at activity
concentrations well below levels of concern.
There are exceptions, however: some
radionuclides with very low specific activities, long
half-lives, and/or low-energy decay emissions (e.g.,
1-129, C-14) are difficult to detect precisely using
standard techniques. To achieve lower LLDs, a
laboratory may: (1) use more sensitive
measurement techniques and/or chemical
extraction procedures; (2) analyze larger sample
sizes; or (3) increase the counting time of the
sample. A laboratory may also choose to apply
all three options to increase detection capabilities.
Exhibit 10-4 presents examples of typical LLDs
using standard analytical techniques.
The same special considerations noted for
chemical analyses would also apply for
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Page 10-18
EXHIBIT 10-4
EXAMPLES OF LOWER LIMITS OF DETECTION (LLD)
FOR SELECTED RADIONUCLIDES USING STANDARD ANALYTICAL METHODS0
Isotope
Co-60
Sr-90
Cs-137
Pb-210
Ra-226
Th-232
U-234
U-235
U-238
Sample Mediab
-Water
-Soil (dry wt.)
-Biota (wet wt.)c
-Air^
-Water
-Water
-Soil (dry wt.)
-Biota (wet wt.)
-Air
-Water
-Soil (dry wt.)
-Biota (wet wt.)
-Air
-Water
-Soil (dry wt.)
-Biota (wet wt.)
-Air
-Water
-Soil (dry wt.)
-Biota (wet wt.)
-Air
-Water
-Soil (dry wt.)
-Biota (wet wt.)
-Air
LLD
pCi
10
0.1
0.1
25
1
10
0.3
1
0.3
1
0.3
30
0.2
0.2
0.2
5
100
0.1
0.1
0.1
0.1
1
0.02
0.2
0.02
0.3
0.02
0.1
0.01
0.2
Bq
0.4
0.004
0.004
0.9
0.04
0.4
0.01
0.04
0.01
0.04
0.01
1
0.007
0.007
0.007
0.2
4
0.004
0.004
0.004
0.004
0.04
0.0007
0.007
0.0007
0.01
0.0007
0.004
0.0004
0.007
Methodology
Gamma Spectrometry
Gamma Spectrometry
Gamma Spectrometry
Gamma Spectrometry
Radiochemistry
Gamma Spectrometry
Radiochemistry
Gamma Spectrometry
Radiochemistry
Gamma Spectrometry
Radiochemistry
Gamma Spectrometry
Radiochemistry
Radiochemistry
Radiochemistry
Radiochemistry
Gamma Spectrometry
Radiochemistry
Radon Daughter Emanation
Radon Daughter Emanation
Radon Daughter Emanation
Alpha Spectrometry
Alpha Spectrometry
Radiochemistry
Alpha Spectrometry
Alpha Proportional Counter
Alpha Spectrometry
Alpha Spectrometry
Alpha Spectrometry
Alpha Spectrometry
(continued)
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Page 10-19
EXHIBIT 10-4 (continued)
EXAMPLES OF LOWER LIMITS OF DETECTION (LLD)
FOR SELECTED RADIONUCLIDES USING STANDARD ANALYTICAL METHODS*
LLD
Isotope
Pu-238
Pu-239
Pu-240
Sample Media*
-Water
-Soil (dry wt.)
-Biota (wet wt.)
-Air
pCi
0.02
0.1
0.01
0.2
Bq
0.0007
0.004
0.0004
0.007
Methodology
Alpha Spectrometry
Alpha Spectrometry
Alpha Spectrometry
Alpha Spectrometry
a Source: U.S. Environmental Protection Agency Eastern Environmental Radiation Facility (EPA-EERF), Department of Energy
Environmental Measurements Laboratory (DOE-EML), and commercial laboratories. Note that LLDs are radionuclide-, media-,
sample size-, and laboratory-specific: higher and lower LLDs than those reported above are possible. The risk assessor should
request and report the LLDs supplied by the laboratory performing the analyses.
b Nominal sample sizes: water (1 liter), soil (1 kg dry wt.), biota (1 kg wet wt.), and air (1 filter sample).
c Biota includes vegetation, fish, and meat.
^ Air refers to a sample of 300 m^ of air collected on a filter, which is analyzed for the radionuclide of interest.
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Page 10-20
radionuclides that are not detected in any samples
from a particular medium, but are suspected to be
present at a site. In these cases, three options may
be applied: (1) re-analyze the sample using more
sensitive methods; (2) use the LLD value as a
"proxy" concentration to evaluate the potential
risks at the detection limit; or (3) evaluate the
possible risk implication of the radionuclide
qualitatively. An experienced health physicist
should decide which of these three options would
be most appropriate.
When multiple radionuclides are present in
a sample, various interferences can occur that may
reduce the analytical sensitivity for a particular
radionuclide. Also, in some areas of high
background radioactivity from naturally occurring
radionuclides, it may be difficult to differentiate
background contributions from incremental site
contamination. It may be possible to eliminate
such interferences by radiochemical separation or
special instrumental techniques.
A sample with activity that is nondetectable
should be reported as less than the appropriate
sample and radionuclide-specific LLD value.
However, particular caution should be exercised
when applying this approach to radionuclides that
are difficult to measure and possess unusually high
detection limits, as discussed previously. In most
cases where a potentially important radionuclide
contaminant is suspected, but not detected, in a
sample, the sample should be reanalyzed using
more rigorous radiochemical procedures and more
sophisticated detection techniques.
If radionuclide sample data for a site are
reported without sample-specific radionuclide
quantitation limits, the laboratory conducting the
analyses should be contacted to determine the
appropriate LLD values for the analytical
techniques and sample media.
10.4.4 EVALUATING QUALIFIED AND
CODED DATA
Various data qualifiers and codes may be
attached to problem data from inorganic and
organic chemical analyses conducted under the
CLP as shown in Exhibits 5-4 and 5-5. These
include laboratory qualifiers assigned by the
laboratory conducting the analysis and data
validation qualifiers assigned by personnel involved
in data validation. These qualifiers pertain to
QA/QC problems and generally indicate questions
concerning chemical identity, chemical
concentration, or both. No corresponding system
of qualifiers has been developed for radioanalytical
data, although certain of the CLP data qualifiers
might be adopted for use in reporting
radioanalytical data. The health physicist should
define and evaluate any qualifiers attached to data
for radionuclide analyses. Based on the discussions
in Chapter 5, the references on methods listed
above, and professional judgment, the health
physicist should eliminate inappropriate data from
use in the risk assessment.
10.4.5 COMPARING CONCENTRATIONS
DETECTED IN BLANKS WITH
CONCENTRATIONS DETECTED IN
SAMPLES
The analysis of blank samples (e.g., laboratory
or reagent blanks, field blanks, calibration blanks)
is an important component of a proper
radioanalytical program. Analysis of blanks
provides a measure of contamination introduced
into a sample during sampling or analysis
activities.
The CLP provides guidance for inorganic and
organic chemicals that are not common laboratory
contaminants. According to this guidance, if a
blank contains detectable levels of any uncommon
laboratory chemical, site sample results should be
considered positive only if the measured
concentration in the sample exceeds five times the
maximum amount detected in any blank. Samples
containing less than five times the blank
concentration should be classified as nondetects,
and the maximum blank-related concentration
should be specified as the quantitation limit for
that chemical in the sample. Though they are
not considered to be common laboratory
contaminants, radionuclides should not be
classified as nondetects using the above CLP
guidance. Instead, the health physicist should
evaluate all active sample preparation and
analytical procedures for possible sources of
contamination.
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Page 10-21
10.4.6 EVALUATING TENTATIVELY
IDENTIFIED RADIONUCLIDES
Because radionuclides are not included on the
Target Compound List (TCL), they may be
classified as tentatively identified compounds
(TICs) under CLP protocols. In reality, however,
radioanalytical techniques are sufficiently sensitive
that the identity and quantity of radionuclides of
potential concern at a site can be determined with
a high degree of confidence. In some cases,
spectral or matrix interferences may introduce
uncertainties, but these problems usually can be
overcome using special radiochemical and/or
instrumental methods. In cases where a
radionuclide's identity is not sufficiently
well-defined by the available data set: (1) further
analyses may be performed using more sensitive
methods, or (2) the tentatively identified
radionuclide may be included in the risk
assessment as a contaminant of potential concern
with notation of the uncertainty in its identity and
concentration.
10.4.7 COMPARING SAMPLES WITH
BACKGROUND
It is imperative to select, collect, and analyze
an appropriate number of background samples to
be able to distinguish between onsite sources of
radionuclide contaminants from radionuclides
expected normally in the environment.
Background measurements of direct radiation and
radionuclide concentrations in all media of
concern should be determined at sampling
locations geologically similar to the site, but
beyond the influence of the site. Screening
measurements (e.g., gross alpha, beta, and gamma)
should be used to determine whether more
sensitive radionuclide-specific analyses are
warranted. Professional judgment should be used
by the health physicist to select appropriate
background sampling locations and analytical
techniques. The health physicist should also
determine which naturally occurring radionuclides
(e.g., uranium, radium, or thorium) detected onsite
should be eliminated from the quantitative risk
assessment. All man-made radionuclides detected
in samples collected should, however, be retained
for further consideration.
10.4.8 DEVELOPING A SET OF
RADIONUCLIDE DATA AND
INFORMATION FOR USE IN A
RISK ASSESSMENT
The process described in Section 5.8 for
selection of chemical data for inclusion in the
quantitative risk assessment generally applies for
radionuclides as well. One exception is the lack
of CLP qualifiers for radionuclides, as discussed
previously. Radionuclides of concern should
include those that are positively detected in at
least one sample in a given medium, at levels
significantly above levels detected in blank samples
and significantly above local background levels.
As discussed previously, the decision to include
radionuclides not detected in samples from any
medium but suspected at the site based on
historical information should be made by a
qualified health physicist.
10.4.9 GROUPING RADIONUCLIDES BY
CLASS
Grouping radionuclides for consideration in
the quantitative risk assessment is generally
unnecessary and inappropriate. Radiation dose
and resulting health risk is highly dependent on
the specific properties of each radionuclide. In
some cases, however, it may be acceptable to
group different radioisotopes of the same element
that have similar radiological characteristics (e.g.,
Pu-238/239/240, U-235/238) or belong to the same
decay series. Such groupings should be determined
very selectively and seldom offer any significant
advantage.
10.4.10 FURTHER REDUCTION IN THE
NUMBER OF RADIONUCLIDES
For sites with a large number of
radionuclides detected in samples from one or
more media, the risk assessment should focus on
a select group of radionuclides that dominate the
radiation dose and health risk to the critical
receptors. For example, when considering
transport through ground water to distant
receptors, transit times may be very long;
consequently, only radionuclides with long
half-lives or radioactive progeny that are formed
during transport may be of concern for that
exposure pathway. For direct external exposures,
high-energy gamma emitters are of principal
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Page 10-22
concern, whereas alpha-emitters may dominate
doses from the inhalation and ingestion pathways.
The important radionuclides may differ for each
exposure pathway and must be determined on
their relative concentrations, half-lives,
environmental mobility, and dose conversion
factors (see Section 10.5 for discussion of dose
conversion factors) for each exposure pathway of
interest.
The total activity inventory and individual
concentrations of radionuclides at a Superfund site
will change with time as some nuclides decay
away and others "grow in" as a result of
radioactive decay processes. Consequently, it may
be important to evaluate different time scales in
the risk assessment. For example, at a site where
Ra-226 (half-life = 1600 years) is the only
contaminant of concern in soil at some initial
time, the Pb-210 (half-life = 22.3 years) and
Po-210 (half-life = 138 days) progeny will also
become dominant contributors to the activity
onsite over a period of several hundred years.
10.4.11 SUMMARIZING AND PRESENTING
DATA
Presentation of results of the data collection
and evaluation process will be generally the same
for radionuclides and chemical contaminants. The
sample table formats presented in Exhibits 5-6 and
5-7 are equally applicable to radionuclide data,
except that direct radiation measurement data
should be added, if appropriate for the
radionuclides and exposure pathways identified at
the site.
10.5 EXPOSURE AND DOSE
ASSESSMENT
This section describes a methodology for
estimating the radiation dose equivalent to
humans from potential exposures to radionuclides
through all pertinent exposure pathways at a
remedial site. These estimates of dose equivalent
may be used for comparison with radiation
protection standards and criteria. However, this
methodology has been developed for regulation of
occupational radiation exposures for adults and is
not completely applicable for estimating health
risk to the general population. Section 10.7.2,
therefore, describes a separate methodology for
estimating health risk.
Chapter 6 describes the procedures for
conducting an exposure assessment for chemical
contaminants as part of the baseline risk
assessment for Superfund sites. Though many
aspects of the discussion apply to radionuclides,
the term "exposure" is used in a fundamentally
different way for radionuclides as compared to
chemicals. For chemicals, exposure generally
refers to the intake (e.g., inhalation, ingestion,
dermal exposure) of the toxic chemical, expressed
in units of mg/kg-day. These units are convenient
because the toxicity values for chemicals are
generally expressed in these terms. For example,
the toxicity value used to assess carcinogenic
effects is the slope factor, expressed in units of
risk of lifetime excess cancers per mg/kg-day. As
a result, the product of the intake estimate with
the slope factor yields the risk of cancer (with
proper adjustments made for absorption, if
necessary).
Intakes by inhalation, ingestion, and
absorption are also potentially important exposure
pathways for radionuclides, although radionuclide
intake is typically expressed in units of activity
(i.e., Bq or Ci) rather than mass. Radionuclides
that enter through these internal exposure
pathways may become systemically incorporated
and emit alpha, beta, or gamma radiation within
tissues or organs. Unlike chemical assessments,
an exposure assessment for radioactive
contaminants can include an explicit estimation of
the radiation dose equivalent. As discussed
previously in Section 10.1, the dose equivalent is
an expression that takes into consideration both
the amount of energy deposited in a unit mass of
a specific organ or tissue as a result of the
radioactive decay of a specific radionuclide, as
well as the relative biological effectiveness of the
radiations emitted by that nuclide. (Note that the
term dose has a different meaning for
radionuclides [dose = energy imparted to a unit
mass of tissue] than that used in Chapter 6 for
chemicals [dose, or absorbed dose = mass
penetrating into an organism].)
Unlike chemicals, radionuclides can have
deleterious effects on humans without being taken
into or brought in contact with the body. This is
because high energy beta particles and photons
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Page 10-23
from radionuclides in contaminated air, water, or
soil can travel long distances with only minimum
attenuation in these media before depositing their
energy in human tissues. External radiation
exposures can result from either exposure to
radionuclides at the site area or to radionuclides
that have been transported from the site to other
locations in the environment. Gamma and x-rays
are the most penetrating of the emitted radiations,
and comprise the primary contribution to the
radiation dose from external exposures. Alpha
particles are not sufficiently energetic to penetrate
the outer layer of skin and do not contribute
significantly to the external dose. External
exposure to beta particles primarily imparts a dose
to the outer layer skin cells, although high-energy
beta radiation can penetrate into the human body.
The quantification of the amount of energy
deposited in living tissue due to internal and
external exposures to radiation is termed radiation
dosimetry. The amount of energy deposited in
living tissue is of concern because the potential
adverse effects of radiation are proportional to
energy deposition. The energy deposited in tissues
is proportional to the decay rate of a radionuclide,
and not its mass. Therefore, radionuclide
quantities and concentrations are expressed in
units of activity (e.g., Bq or Ci), rather than in
units of mass.
Despite the fundamental difference between
the way exposures are expressed for radionuclides
and chemicals, the approach to exposure
assessment presented in Chapter 6 for chemical
contaminants largely applies to radionuclide
contaminants. Specifically, the three steps of an
exposure assessment for chemicals also apply to
radionuclides: (1) characterization of the exposure
setting; (2) identification of the exposure
pathways; and (3) quantification of exposure.
However, some of the methods by which these
three steps are carried out are different for
radionuclides.
10.5.1 CHARACTERIZING THE EXPOSURE
SETTING
Initial characterization of the exposure setting
for radioactively contaminated sites is virtually
identical to that described in Chapter 6. One
additional consideration is that, at sites suspected
of having radionuclide contamination, a survey
should be conducted to determine external
radiation fields using any one of a number of field
survey instruments (preferably, G-M tubes and
Nal(Tl) field detectors) (see Exhibit 10-2). Health
and safety plans should be implemented to reduce
the possibility of radiation exposures that are in
excess of allowable limits.
REFERENCES ON EXPOSURE
ASSESSMENT FOR RADIONUCLIDES
Calculation of Annual Doses to Man from
Routine Releases of Reactor Effluents
(NRC 1977)
Radiological Assessment: A Textbook on
Environmental Dose Analysis (Till and
Meyer 1983)
Models and Parameters for Environmental
Radiological Assessments (Miller 1984)
Radiological Assessment: Predicting the
Transport, Bioaccumulation, and Uptake by
Man of Radionuclides Released to the
Environment (NCRP 1984a)
Background Information Document, Draft
EIS for Proposed NESHAPS for
Radionuclides, Volume I, Risk Assessment
Methodology (EPA 1989a)
Screening Techniques for Determining
Compliance with Environmental Standards
(NCRP 1989)
10.5.2 IDENTIFYING EXPOSURE
PATHWAYS
The identification of exposure pathways for
radioactively contaminated sites is very similar to
that described in Chapter 6 for chemically
contaminated sites, with the following additional
guidance.
• In addition to the various ingestion,
inhalation, and direct contact pathways
described in Chapter 6, external exposure
to penetrating radiation should also be
considered. Potential external exposure
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Page 10-24
pathways to be considered include
immersion in contaminated air,
immersion in contaminated water, and
radiation exposure from ground surfaces
contaminated with beta- and photon-
emitting radionuclides.
• As with nonradioactive chemicals,
environmentally dispersed radionuclides
are subject to the same chemical
processes that may accelerate or retard
their transfer rates and may increase or
decrease their bioaccumulation
potentials. These transformation
processes must be taken into
consideration during the exposure
assessment.
• Radionuclides undergo radioactive decay
that, in some respects, is similar to the
chemical or biological degradation of
organic compounds. Both processes
reduce the quantity of the hazardous
substance in the environment and
produce other substances. (Note,
however, that biological and chemical
transformations can never alter, i.e.,
either increase or decrease, the
radioactivity of a radionuclide.)
Radioactive decay products can also
contribute significantly to the radiation
exposure and must be considered in the
assessment.
• Chapter 6 presents a series of equations
(Exhibits 6-11 through 6-19) for
quantification of chemical exposures.
These equations and suggested default
variable values may be used to estimate
radionuclide intakes as a first
approximation, if the equations are
modified by deleting the body weight and
averaging time from the denominator.
However, depending upon the
characteristics of the radionuclides of
concern, consideration of radioactive
decay and ingrowth of radioactive decay
products may be important additions, as
well as the external exposure pathways.
• Chapter 6 also refers to a number of
computer models that are used to predict
the behavior and fate of chemicals in the
10.5.3
environment. While those models may
be suitable for evaluations of radioactive
contaminants in some cases, numerous
models have been developed specifically
for evaluating the transport of
radionuclides in the environment and
predicting the doses and risks to exposed
individuals. In general, models
developed specifically for radiological
assessments should be used. Such
models include, for example, explicit
consideration of radioactive decay and
ingrowth of radioactive decay products.
(Contact ORP for additional guidance on
the fate and transport models
recommended by EPA.)
QUANTIFYING EXPOSURE:
GENERAL CONSIDERATIONS
One of the primary objectives of an exposure
assessment is to make a reasonable estimate of
the maximum exposure to individuals and critical
population groups. The equation presented in
Exhibit 6-9 to calculate intake for chemicals may
be considered to be applicable to exposure
assessment for radionuclides, except that the body
weight and averaging time terms in the
denominator should be omitted. However, as
discussed previously, exposures to radionuclides
include both internal and external exposure
pathways. In addition, radiation exposure
assessments do not end with the calculation of
intake, but take the calculation an additional step
in order to estimate radiation dose equivalent.
The radiation dose equivalent to specified
organs and the effective dose equivalent due to
intakes of radionuclides by inhalation or ingestion
are estimated by multiplying the amount of each
radionuclide inhaled or ingested times appropriate
dose conversion factors (DCFs), which represent
the dose equivalent per unit intake. As noted
previously, the effective dose equivalent is a
weighted sum of the dose equivalents to all
irradiated organs and tissues, and represents a
measure of the overall detriment. Federal
Guidance Report No. 11 (EPA 1988) provides
DCFs for each of over 700 radionuclides for both
inhalation and ingestion exposures. It is
important to note, however, that these DCFs were
developed for regulation of occupational exposures
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Page 10-25
to radiation and may not be appropriate for the
general population.
Radionuclide intake by inhalation and
ingestion is calculated in the same manner as
chemical intake except that it is not divided by
body weight or averaging time. For radionuclides,
a reference body weight is already incorporated
into the DCFs, and the dose is an expression of
energy deposited per gram of tissue.
If intake of a radionuclide is defined for a
specific time period (e.g., Bq/year), the dose
equivalent will be expressed in corresponding
terms (e.g., Sv/year). Because systemically
incorporated radionuclides can remain within the
body for long periods of time, internal dose is
best expressed in terms of the committed effective
dose equivalent, which is equal to the effective
dose equivalent over the 50-year period following
intake.
External exposures may be determined by
monitoring and sampling of the radionuclide
concentrations in environmental media, direct
measurement of radiation fields using portable
instrumentation, or by mathematical modeling.
Portable survey instruments that have been
properly calibrated can display dose rates (e.g.,
Sv/hr), and dose equivalents can be estimated by
multiplying by the duration of exposure to the
radiation field. Alternatively, measured or
predicted concentrations in environmental media
may be multiplied by DCFs, which relate
radionuclide concentrations on the ground, in air,
or in water to external dose rates (e.g., Sv/hr per
Bq/m2 for ground contamination or Sv/hr per
Bq/m5 for air or water immersion).
The dose equivalents associated with external
and internal exposures are expressed in identical
units (e.g., Sv), so that contributions from all
pathways can be summed to estimate the total
effective dose equivalent value and prioritize risk
from different sources.
In general, radiation exposure assessments
need not consider acute toxicity effects. Acute
exposures are of less concern for radionuclides
than for chemicals because the quantities of
radionuclides required to cause adverse effects
from acute exposure are extremely large and such
levels are not normally encountered at Superfund
sites. Toxic effects from acute radiation exposures
are possible when humans are exposed to the
radiation from large amounts of radioactive
materials released during a major nuclear plant
accident, such as Chernobyl, or during
above-ground weapons detonations. Consequently,
the exposure and risk assessment guidance for
radionuclides presented in this chapter is limited
to situations causing chronic exposures to low
levels of radioactive contaminants.
10.5.4 QUANTIFYING EXPOSURE:
DETERMINING EXPOSURE POINT
CONCENTRATIONS
The preferred method for estimating the
concentration of chemical or radioactive
contaminants at those places where members of
the public may come into contact with them is by
direct measurement. However, this will not be
possible in many circumstances and it may be
necessary, therefore, to use environmental fate and
transport models to predict contaminant
concentrations. Such modeling would be
necessary, for example: (1) when it is not possible
to obtain representative samples for all
radionuclides of concern; (2) when the
contaminant has not yet reached the potential
exposure points; and (3) when the contaminants
are below the limits of detection but, if present,
can still represent a significant risk to the public.
Numerous fate and transport models have
been developed to estimate contaminant
concentrations in ground water, soil, air, surface
water, sediments, and food chains. Models
developed for chemical contaminants, such as
those discussed in Chapter 6, may also be applied
to radionuclides with allowance for radioactive
decay and ingrowth of decay products. There are
also a number of models that have been
developed specifically for radionuclides. These
models are similar to the models used for toxic
chemicals but have features that make them
convenient to use for radionuclide pathway
analysis, such as explicit consideration of
radioactive decay and daughter ingrowth.
Available models for use in radiation risk
assessments range in complexity from a series of
hand calculations to major computer codes. For
example, NRC Regulatory Guide 1.109 presents
a methodology that may be used to manually
estimate dose equivalents from a variety of
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Page 10-26
exposure pathways (NRC 1977). Examples of
computerized radiological assessment models
include the AIRDOS-EPA code and the
EPA-PRESTO family of codes, which are used
extensively by EPA to estimate exposures and
doses to populations following atmospheric
releases of radionuclides and releases from a
low-level waste disposal facility, respectively.
Guidance on selection and use of the various
models can be obtained from the EPA Office of
Radiation Programs.
Exhibit 6-10, Example of Table Format for
Summarizing Exposure Concentrations, may be
used for radionuclide contaminants, except that
radionuclide concentrations are expressed in terms
of activity per unit mass or volume of the
environmental medium (e.g., Bq/kg, Bq/L) rather
than mass.
10.5.5 QUANTIFYING EXPOSURE:
ESTIMATING INTAKE AND DOSE
EQUIVALENT
Section 6.6 presents a description of the
methods used to estimate intake rates of
contaminants from the various exposure pathways.
Exhibits 6-11 to 6-19 present the equations and
input assumptions recommended for use in intake
calculations. In concept, those equations and
assumptions also apply generally to radionuclides,
except that the body weight and averaging time
terms in the denominators should be omitted.
However, as discussed previously, the product of
these calculations for radionuclides is an estimate
of the radionuclide intake, expressed in units of
activity (e.g., Bq), as opposed to mg/kg-day. In
addition, the endpoint of a radiation exposure
assessment is radiation dose, which is calculated
using DCFs as explained below. As explained
previously, dose equivalents calculated in the
following manner should be used to compare with
radiation protection standards and criteria, not to
estimate risk.
Internal Exposure. Exhibits 6-11, 6-12, 6-14,
6-17, 6-18, and 6-19 present simplified models for
the ingestion of water, food, and soil as pathways
for the intake of environmental contaminants.
The recommended assumptions for ingestion rates
and exposure durations are applicable to
radionuclide exposures and may be used to
estimate the intake rates of radionuclides by these
pathways. As noted previously, however, these
intake estimates for radionuclides should not be
divided by the body weight or averaging time.
These intake rates must be multiplied by
appropriate DCF values in order to obtain
committed effective dose equivalent values. The
more rigorous and complex radionuclide pathway
models noted previously typically require much
more extensive input data and may include default
parameter values that differ somewhat from the
values recommended in these exhibits.
Exhibit 6-16 presents the equation and
assumptions used to estimate the contaminant
intake from air. For radionuclides, the dose from
inhalation of contaminated air is determined as
the product of the radionuclide concentration in
air (Bq/m5), the breathing rate (mj per day or
year), exposure duration (day or year), and the
inhalation DCF (Sv per Bq inhaled). The result
of this calculation is the committed effective dose
equivalent, in units of Sv.
Chapter 6 points out that dermal absorption
of airborne chemicals is not an important route
of uptake. This point is also true for most
radionuclides, except airborne tritiated water
vapor, which is efficiently taken into the body
through dermal absorption. In order to account
for this route of uptake, the inhalation DCF for
tritium includes an adjustment factor to account
for dermal absorption.
External Exposure. Immersion in air
containing certain beta-emitting and/or
photon-emitting radioactive contaminants can also
result in external exposures. Effective dose
equivalents from external exposure are calculated
as the product of the airborne radionuclide
concentration (Bq/m5), the external DCF for air
immersion (Sv/hr per Bq/m3), and the duration of
exposure (hours).
Exhibits 6-13 and 6-15 illustrate the dermal
uptake of contaminants resulting from immersion
in water or contact with soil. This route of
uptake can be important for many organic
chemicals; however, dermal uptake is generally not
an important route of uptake for radionuclides,
which have small dermal permeability constants.
External radiation exposure due to submersion in
water contaminated with radionuclides is possible
and is similar to external exposure due to
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Page 10-27
immersion in air. However, because of the
shielding effects of water and the generally short
durations of such exposures, immersion in water
is typically of lesser significance. The product of
the radionuclide concentration in water (Bq/m5),
the relevant DCF (Sv/hr per Bq/m3), and the
duration of exposure (hours) yields effective dose
equivalent.
The third external exposure pathway of
potential significance is irradiation from
radionuclides deposited on the ground surface.
Effective dose equivalents resulting from this
pathway may be estimated as the product of the
soil surface concentration (Bq/m2) of
photon-emitting radionuclides of concern, the
external DCF for ground surface exposure (Sv/hr
per Bq/m2), and the duration of exposure (hours).
10.5.6 COMBINING INTAKES AND DOSES
ACROSS PATHWAYS
The calculations described previously result
in estimates of committed effective dose
equivalents (Sv) from individual radionuclides via
a large number of possible exposure pathways.
Because a given population may be subject to
multiple exposure pathways, the results of the
exposure assessment should be organized by
grouping all applicable exposure pathways for each
exposed population. Risks from various exposure
pathways and contaminants then can be integrated
during the risk characterization step (see Section
10.7).
10.5.7 EVALUATING UNCERTAINTY
The radiation exposure assessment should
include a discussion of uncertainty, that, at a
minimum, should include: (1) a tabular summary
of the values used to estimate exposures and doses
and the range of these values; and (2) a summary
of the major assumptions of the exposure
assessment, including the uncertainty associated
with each assumption and how it might affect the
exposure and dose estimates. Sources of
uncertainty that must be addressed include: (1)
how well the monitoring data represent actual site
conditions; (2) the exposure models, assumptions,
and input variables used to estimate exposure
point concentrations; and (3) the values of the
variables used to estimate intakes and external
exposures. More comprehensive discussions of
uncertainty associated with radiological risk
assessment are provided in the. Background
Information Document for the Draft EIS for
Proposed NESHAPS for Radionuclides (EPA
1989a), Radiological Assessment (Till and Meyer
1983), and NCRP Report No. 76 (NCRP 1984a).
10.5.8 SUMMARIZING AND PRESENTING
EXPOSURE ASSESSMENT RESULTS
Exhibit 6-22 presents a sample format for
summarizing the results of the exposure
assessment. The format may also be used for
radionuclide contaminants except that the entries
should be specified as committed effective dose
equivalents (Sv) and the annual estimated intakes
(Bq) for each radionuclide of concern. The
intakes and dose estimates should be tabulated
for each exposure pathway so that the most
important radionuclides and pathways contributing
to the total health risk may be identified.
The information should be organized by
exposure pathway, population exposed, and current
and future use assumptions. For radionuclides,
however, it may not be necessary to summarize
short-term and long-term exposures separately as
specified for chemical contaminants.
10.6 TOXICITY ASSESSMENT
Chapter 7 describes the two-step process
employed to assess the potential toxicity of a given
chemical contaminant. The first step, hazard
identification, is used to determine whether
exposure to a contaminant can increase the
incidence of an adverse health effect. The second
step, dose-response assessment, is used to
quantitatively evaluate the toxicity information and
characterize the relationship between the dose of
the contaminant administered or received and the
incidence of adverse health effects in the exposed
population.
There are certain fundamental differences
between radionuclides and chemicals that
somewhat simplify toxicity assessment for
radionuclides. As discussed in the previous
sections, the adverse effects of exposure to
radiation are due to the energy deposited in
sensitive tissue, which is referred to as the
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Page 10-28
radiation dose. In theory, any dose of radiation
has the potential to produce an adverse effect.
Accordingly, exposure to any radioactive
substances is, by definition, hazardous.
Dose-response assessment for radionuclides
is also more straightforward. The type of effects
and the likelihood of occurrence of any one of a
number of possible adverse effects from radiation
exposure depends on the radiation dose. The
relationship between dose and effect is relatively
well characterized (at high doses) for most types
of radiations. As a result, the toxicity assessment,
within the context that it is used in this manual,
need not be explicitly addressed in detail for
individual radionuclides at each contaminated site.
The sections that follow provide a brief
summary of the human and experimental animal
studies that establish the hazard and dose-response
relationship for radiation exposure. More detailed
discussions of radiation toxicity are provided in
publications of the National Academy of Sciences
Committee on Biological Effects of Ionizing
Radiation (BEIR), the United Nations Scientific
Committee on Effects of Atomic Radiation
(UNSCEAR), NRC, NCRP, and ICRP listed in
the box on this page.
10.6.1 HAZARD IDENTIFICATION
The principal adverse biological effects
associated with ionizing radiation exposures from
radioactive substances in the environment are
carcinogenicity, mutagenicity, and teratogenicity.
Carcinogenicity is the ability to produce cancer.
Mutagenicity is the property of being able to
induce genetic mutation, which may be in the
nucleus of either somatic (body) or germ
(reproductive) cells. Mutations in germ cells lead
to genetic or inherited defects. Teratogenicity
refers to the ability of an agent to induce or
increase the incidence of congenital malformations
as a result of permanent structural or functional
deviations produced during the growth and
development of an embryo (more commonly
referred to as birth defects). Radiation may
induce other deleterious effects at acute doses
above about 1 Sv, but doses of this magnitude are
not normally associated with radioactive
contamination in the environment.
REFERENCES ON HEALTH EFFECTS
OF RADIATION EXPOSURE
Recommendations of the ICRP (ICRP
1977)
Limits for Intake of Radionuclides by
Workers (ICRP 1979)
Influence of Dose and Its Distribution in
Time on Dose-Response Relationships for
Low-LET Radiations (NCRP 1980)
The Effects on Populations of Exposure to
Low Levels of Ionizing Radiation (NAS
1980)
Induction of Thyroid Cancer by Ionizing
Radiation (NCRP 1985b)
Lung Cancer Risk from Indoor Exposures to
Radon Daughters (ICRP 1987)
Health Risks of Radon and Other Intemalfy
Deposited Alpha-Emitters (National
Academy of Sciences 1988)
Ionizing Radiation; Sources, Effects, and
Risks (UNSCEAR 1988)
Health Effects Models for Nuclear Power
Plant Accident Consequence Analysis.-
Low-LET Radiation (NRC 1989)
As discussed in Section 10.1, ionizing
radiation causes injury by breaking molecules into
electrically charged fragments (i.e., free radicals),
thereby producing chemical rearrangements that
may lead to permanent cellular damage. The
degree of biological damage caused by various
types of radiation varies according to how spatially
close together the ionizations occur. Some
ionizing radiations (e.g., alpha particles) produce
high density regions of ionization. For this
reason, they are called high-LET (linear energy
transfer) particles. Other types of radiation (e.g.,
x-rays, gamma rays, and beta particles) are called
low-LET radiations because of the low density
pattern of ionization they produce. In equal
doses, the carcinogenicity and mutagenicity of
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Page 10-29
high-LET radiations may be an order of
magnitude or more greater than those of low-LET
radiations, depending on the endpoint being
evaluated. The variability in biological
effectiveness is accounted for by the quality factor
used to calculate the dose equivalent (see Section
10.1).
Carcinogenesis. An extensive body of
literature exists on radiation carcinogenesis in man
and animals. This literature has been reviewed
most recently by the United Nations Scientific
Committee on the Effects of Atomic Radiation
(UNSCEAR) and the National Academy of
Sciences Advisory Committee on the Biological
Effects of Ionizing Radiations (NAS-BEIR
Committee) (UNSCEAR 1977, 1982, 1988; NAS
1972, 1980, 1988). Estimates of the average risk
of fatal cancer from low-LET radiation from these
studies range from approximately 0.007 to 0.07
fatal cancers per sievert.
An increase in cancer incidence or mortality
with increasing radiation dose has been
demonstrated for many types of cancer in both
human populations and laboratory animals
(UNSCEAR 1982, 1988; NAS 1980, 1988).
Studies of humans exposed to internal or external
sources of ionizing radiation have shown that the
incidence of cancer increases with increased
radiation exposure. This increased incidence,
however, is usually associated with appreciably
greater doses and exposure frequencies than those
encountered in the environment. Therefore, risk
estimates from small doses obtained over long
periods of time are determined by extrapolating
the effects observed at high, acute doses.
Malignant tumors in various organs most often
appear long after the radiation exposure, usually
10 to 35 years later (NAS 1980, 1988; UNSCEAR
1982, 1988). Radionuclide metabolism can result
in the selective deposition of certain radionuclides
in specific organs or tissues, which, in turn, can
result in larger radiation doses and
higher-than-normal cancer risk in these organs.
Ionizing radiation can be considered
pancarcinogenic, i.e., it acts as a complete
carcinogen in that it serves as both initiator and
promoter, and it can induce cancers in nearly any
tissue or organ. Radiation-induced cancers in
humans have been reported in the thyroid, female
breast, lung, bone marrow (leukemia), stomach,
liver, large intestine, brain, salivary glands, bone,
esophagus, small intestine, urinary bladder,
pancreas, rectum, lymphatic tissues, skin, pharynx,
uterus, ovary, mucosa of cranial sinuses, and
kidney (UNSCEAR 1977, 1982, 1988; NAS 1972,
1980, 1988). These data are taken primarily from
studies of human populations exposed to high
levels of radiation, including atomic bomb
survivors, underground miners, radium dial
painters, patients injected with thorotrast or
radium, and patients who received high x-ray doses
during various treatment programs. Extrapolation
of these data to much lower doses is the major
source of uncertainty in determining low-level
radiation risks (see EPA 1989a). It is assumed
that no lower threshold exists for radiation
carcinogenesis.
On average, approximately 50 percent of all
of the cancers induced by radiation are lethal.
The fraction of fatal cancers is different for each
type of cancer, ranging from about 10 percent in
the case of thyroid cancer to 100 percent in the
case of liver cancer (NAS 1980, 1988). Females
have approximately 2 times as many total cancers
as fatal cancers following radiation exposure, and
males have approximately 1.5 times as many (NAS
1980).
Mutagenesis. Very few quantitative data are
available on radiogenic mutations in humans,
particularly from low-dose exposures. Some
mutations are so mild they are not noticeable,
while other mutagenic effects that do occur are
similar to nonmutagenic effects and are therefore
not necessarily recorded as mutations. The bulk
of data supporting the mutagenic character of
ionizing radiation comes from extensive studies of
experimental animals (UNSCEAR 1977, 1982,
1988; NAS 1972, 1980,1988). These studies have
demonstrated all forms of radiation mutagenesis,
including lethal mutations, translocations,
inversions, nondisjunction, and point mutations.
Mutation rates calculated from these studies are
extrapolated to humans and form the basis for
estimating the genetic impact of ionizing radiation
on humans (NAS 1980, 1988; UNSCEAR 1982,
1988). The vast majority of the demonstrated
mutations in human germ cells contribute to both
increased mortality and illness (NAS 1980;
UNSCEAR 1982). Moreover, the radiation
protection community is generally in agreement
that the probability of inducing genetic changes
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Page 10-30
increases linearly with dose and that no
"threshold" dose is required to initiate heritable
damage to germ cells.
The incidence of serious genetic disease due
to mutations and chromosome aberrations induced
by radiation is referred to as genetic detriment.
Serious genetic disease includes inherited ill
health, handicaps, or disabilities. Genetic disease
may be manifest at birth or may not become
evident until some time in adulthood.
Radiation-induced genetic detriment includes
impairment of life, shortened life span, and
increased hospitalization. The frequency of
radiation-induced genetic impairment is relatively
small in comparison with the magnitude of
detriment associated with spontaneously arising
genetic diseases (UNSCEAR 1982, 1988).
Teratogenesis. Radiation is a well-known
teratogenic agent. The developing fetus is much
more sensitive to radiation than the mother. The
age of the fetus at the time of exposure is the
most important factor in determining the extent
and type of damage from radiation. The
malformations produced in the embryo depend on
which cells, tissues, or organs in the fetus are
most actively differentiating at the time of
radiation exposure. Embryos are relatively
resistant to radiation-induced teratogenic effects
during the later stages of their development and
are most sensitive from just after implantation
until the end of organogenesis (about two weeks
to eight weeks after conception) (UNSCEAR
1986; Brent 1980). Effects on nervous system,
skeletal system, eyes, genitalia, and skin have been
noted (Brent 1980). The brain appears to be
most sensitive during development of the
neuroblast (these cells eventually become the
nerve cells). The greatest risk of brain damage
for the human fetus occurs at 8 to 15 weeks,
which is the time the nervous system is
undergoing the most rapid differentiation and
proliferation of cells (Otake 1984).
10.6.2 DOSE-RESPONSE RELATIONSHIPS
This section describes the relationship of the
risk of fatal cancer, serious genetic effects, and
other detrimental health effects to exposure to low
levels of ionizing radiation. Most important from
the standpoint of the total societal risk from
exposures to low-level ionizing radiation are the
risks of cancer and genetic mutations. Consistent
with our current understanding of their origins in
terms of DNA damage, these effects are believed
to be stochastic; that is, the probability (risk) of
these effects increases with the dose of radiation,
but the severity of the effects is independent of
dose. For neither induction of cancer nor genetic
effects, moreover, is there any convincing evidence
for a "threshold" (i.e., some dose level below
which the risk is zero). Hence, so far as is
known, any dose of ionizing radiation, no matter
how small, might give rise to a cancer or to a
genetic effect in future generations. Conversely,
there is no way to be certain that a given dose of
radiation, no matter how large, has caused an
observed cancer in an individual or will cause one
in the future.
Exhibit 10-5 summarizes EPA's current
estimates of the risk of adverse effects associated
with human exposure to ionizing radiation (EPA
1989a). Important points from this summary table
are provided below.
• Very large doses (>1 Sv) of radiation
are required to induce acute and
irreversible adverse effects. It is unlikely
that such exposures would occur in the
environmental setting associated with a
potential Superfund site.
• The risks of serious noncarcinogenic
effects associated with chronic exposure
to radiation include genetic and
teratogenic effects. Radiation-induced
genetic effects have not been observed
in human populations, and extrapolation
from animal data reveals risks per unit
exposure that are smaller than, or
comparable to, the risk of cancer. In
addition, the genetic risks are spread
over several generations. The risks per
unit exposure of serious teratogenic
effects are greater than the risks of
cancer. However, there is a possibility
of a threshold, and the exposures must
occur over a specific period of time
during gestation to cause the effect.
Teratogenic effects can be induced only
during the nine months of pregnancy.
Genetic effects are induced during the
30-year reproductive generation and
cancer can be induced at any point
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Page 10-31
EXHIBIT 10-5
SUMMARY OF EPA'S RADIATION RISK FACTORS0
Risk
Significant Exposure Period
Risk Factor Range
Low LET (G\*)
Teratogenic:b
Severe mental retardation
Genetic:
Severe hereditary defects,
all generations
Somatic:
Fatal cancers
All cancers
High LET
Genetic:
Severe hereditary defects,
all generations
Somatic:
Fatal cancers
All cancers
Weeks 8 to 15 of gestation
30-year reproductive generation
Lifetime
In utero
Lifetime
30-year reproductive generation
Lifetime
Lifetime
0.25-0.55
0.006-0.11
0.012-0.12
0.029-0.10
0.019-0.19
Radon Decay Products (W6 WLM';)
Fatal lung cancer Lifetime
0.016-0.29
0.096-0.96
0.15-1.5
140-720
a In addition to the stochastic risks indicated, acute toxicity may occur at a mean lethal dose of 3-5 Sv
with a threshold in excess of 1 Sv.
b The range assumes a linear, non-threshold dose-response. However, it is plausible that a threshold
may exist for this effect.
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Page 10-32
during the lifetime. If a radiation source
is not controlled, therefore, the
cumulative risk of cancer may be many
times greater than the risk of genetic or
teratogenic effects due to the potentially
longer period of exposure.
Based on these observations, it appears that
the risk of cancer is limiting and may be used as
the sole basis for assessing the radiation-related
human health risks of a site contaminated with
radionuclides.
For situations where the risk of cancer
induction in a specific target organ is of primary
interest, the committed dose equivalent to that
organ may be multiplied by an organ-specific risk
factor. The relative radiosensitivity of various
organs (i.e., the cancer induction rate per unit
dose) differs markedly for different organs and
varies as a function of the age and sex of the
exposed individual. Tabulations of such risk
factors as a function of age and sex are provided
in the Background Information Document for the
Draft Environmental Impact Statement for Proposed
NESHAPS for Radionuclides (EPA 1989a) for
cancer mortality and cancer incidence.
10.7 RISK CHARACTERIZATION
The final step in the risk assessment process
is risk characterization. This is an integration step
in which the risks from individual radionuclides
and pathways are quantified and combined where
appropriate. Uncertainties also are examined and
discussed in this step.
10.7.1 REVIEWING OUTPUTS FROM THE
TOXICITY AND EXPOSURE
ASSESSMENTS
The exposure assessment results should be
expressed as estimates of radionuclide intakes by
inhalation and ingestion, exposure rates and
duration for external exposure pathways, and
committed effective dose equivalents to individuals
from all relevant radionuclides and pathways. The
risk assessor should compile the supporting
documentation to ensure that it is sufficient to
support the analysis and to allow an independent
duplication of the results. The review should also
confirm that the analysis is reasonably complete
in terms of the radionuclides and pathways
addressed.
In addition, the review should evaluate the
degree to which the assumptions inherent in the
analysis apply to the site and conditions being
addressed. The mathematical models used to
calculate dose use a large number of
environmental transfer factors and dose conversion
factors that may not always be entirely applicable
to the conditions being analyzed. For example,
the standard dose conversion factors are based on
certain generic assumptions regarding the
characteristics of the exposed individual and the
chemical and physical properties of the
radionuclides. Also, as is the case for chemical
contaminants, the environmental transfer factors
used in the models may not apply to all settings.
Though the risk assessment models may
include a large number of radionuclides and
pathways, the important radionuclides and
pathways are usually few in number. As a result,
it is often feasible to check the computer output
using hand calculations. This type of review can
be performed by health physicists familiar with
the models and their limitations. Guidance on
conducting such calculations is provided in
numerous references, including Till and Meyer
(1983) and NCRP Report No. 76 (NCRP 1984a).
10.7.2 QUANTIFYING RISKS
Given that the results of the exposure
assessment are virtually complete, correct, and
applicable to the conditions being considered, the
next step in the process is to calculate and
combine risks. As discussed previously, the risk
assessment for radionuclides is somewhat
simplified because only radiation carcinogenesis
needs to be considered.
Section 10.5 presents a methodology for
estimating committed effective dose equivalents
that may be compared with radiation protection
standards and criteria. Although the product of
these dose equivalents (Sv) and an appropriate
risk factor (risk per Sv) yields an estimate of risk,
the health risk estimate derived in such a manner
is not completely applicable for members of the
general public. A better estimate of risk may be
computed using age- and sex-specific coefficients
for individual organs receiving significant radiation
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Page 10-33
doses. This information may be used along with
organ-specific dose conversion factors to derive
slope factors that represent the age-averaged
lifetime excess cancer incidence per unit intake for
the radionuclides of concern. The Integrated Risk
Information System (IRIS) contains slope factor
values for radionuclides of concern at remedial
sites for each of the four major exposure pathways
(inhalation, ingestion, air immersion, and ground-
surface irradiation), along with supporting
documentation for the derivation of these values
(see Chapter 7 for more detail on IRIS).
The slope factors from the IRIS data base for
the inhalation pathway should be multiplied by the
estimated inhaled activity (derived using the
methods presented in Section 6.6.3 and Exhibit
6-16, without division of the body weight and
averaging time) for each radionuclide of concern
to estimate risks from the inhalation pathway.
Similarly, risks from the ingestion pathway should
be estimated by multiplying the ingestion slope
factors by the activity ingested for each
radionuclide of concern (derived using the
methods presented in Exhibits 6-11, 6-12, 6-14, 6-
17, 6-18, and 6-19, without division by the body
weight and averaging time). Estimates of the risk
from the air immersion pathway should be
computed by multiplying the appropriate slope
factors by the airborne radionuclide concentration
(Bq/m5) and the duration of exposure. Risk from
the ground surface pathway should be computed
as the product of the slope factor, the soil
concentration (Bq/m2), and the duration of
exposure for each radionuclide of concern.
The sum of the risks from all radionuclides
and pathways yields the lifetime risk from the
overall exposure. As discussed in Chapter 8,
professional judgment must be used in combining
the risks from various pathways, as it may not be
physically possible for one person to be exposed
to the maximum radionuclide concentrations for
all pathways.
10.7.3 COMBINING RADIONUCLIDE AND
CHEMICAL CANCER RISKS
Estimates of the lifetime risk of cancer to
exposed individuals resulting from radiological and
chemical risk assessments may be summed in
order to determine the overall potential human
health hazard associated with a site. Certain
precautions should be taken, however, before
summing these risks. First, .the risk assessor
should evaluate whether it is reasonable to assume
that the same individual can receive the maximum
radiological and chemical dose. It is possible for
this to occur in some cases because many of the
environmental transport processes and routes of
exposure are the same for radionuclides and
chemicals.
In cases where different environmental fate
and transport models have been used to predict
chemical and radionuclide exposure, the
mathematical models may incorporate somewhat
different assumptions. These differences can result
in incompatibilities in the two estimates of risk.
One important difference of this nature is how the
cancer toxicity values (i.e., slope factors) were
developed. For both radionuclides and chemicals,
cancer toxicity values are obtained by extrapolation
from experimental and epidemiological data. For
radionuclides, however, human epidemiological
data form the basis of the extrapolation, while for
many chemical carcinogens, laboratory
experiments are the primary basis for the
extrapolation. Another even more fundamental
difference between the two is that slope factors
for chemical carcinogens generally represent an
upper bound or 95th percent confidence limit
value, while radionuclide slope factors are best
estimate values.
In light of these limitations, the two sets of
risk estimates should be tabulated separately in
the final baseline risk assessment.
10.7.4 ASSESSING AND PRESENTING
UNCERTAINTIES
Uncertainties in the risk assessment, must be
evaluated and discussed, including uncertainties in
the physical setting definition for the site, in the
models used, in the exposure parameters, and in
the toxicity assessment. Monte Carlo uncertainty
analyses are frequently performed as part of the
uncertainty and sensitivity analysis for radiological
risk assessments. A summary of the use of
uncertainty analyses in support of radiological risk
assessments is provided in NCRP Report No. 76
(NCRP 1984a), Radiological Assessment (Till and
Meyer 1983), and in the Background Information
Document for the Draft ElSfor Proposed NESHAPs
for Radionuclides (EPA 1989a).
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Page 10-34
10.7.5 SUMMARIZING AND PRESENTING
THE BASELINE RISK
CHARACTERIZATION RESULTS
The results of the baseline risk
characterization should be summarized and
presented in an effective manner to assist in
decision-making. The estimates of risk should be
summarized in the context of the specific site
conditions. Information should include the
identity and concentrations of radionuclides, types
and magnitudes of health risks predicted,
uncertainties in the exposure estimates and toxicity
information, and characteristics of the site and
potentially exposed populations. A summary table
should be provided in a format similar to that
shown in Exhibit 6-22, as well as graphical
presentations of the predicted health risks (see
Exhibit 8-7).
10.8 DOCUMENTATION,
REVIEW, AND
MANAGEMENT TOOLS
FOR THE RISK ASSESSOR,
REVIEWER, AND
MANAGER
The discussion provided in Chapter 9 also
applies to radioactively contaminated sites. The
suggested outline provided in Exhibit 9-1 may also
be used for radioactively contaminated sites with
only minor modifications. For example, the
portions that uniquely pertain to the CLP
program and noncarcinogenic risks are not needed.
In addition, because radionuclide hazard and
toxicity have been addressed adequately on a
generic basis, there is no need for an extensive
discussion of toxicity in the report.
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Page 10-35
REFERENCES FOR CHAPTER 10
American Public Health Association. 1987. QA Procedures for Health Labs Radiochemistry.
Beebe, G.W., Kato, H., and Land, C.E. 1977. Mortality Experience of Atomic Bomb Survivors. 1950-1974, Life Span Study Report
8. RERF TR 1-77. Radiation Effects Research Foundation. Japan.
Brent, R.L. 1980. Radiation Teratogenesis. Teratology 21:281-298.
Cember, H. 1983. Introduction to Health Physics (2nd Ed.) Pergamon Press. New York, NY.
Department of Energy (DOE). 1987. The Environmental Survey Manual. DOE/EH-0053.
Department of Energy (DOE). 1988. External Dose-Rate Conversion Factors for Calculation of Dose to the Public. DOE/EH-0070.
Department of Energy (DOE). 1989. Environmental Monitoring for Low-level Waste Disposal Sites. DOE/LLW-13Tg.
Eisenbud, M. 1987. Environmental Radioactivity (3rd Ed.) Academic Press. Orlando, FL.
Environmental Protection Agency (EPA). 1972. Environmental Monitoring Surveillance Guide.
Environmental Protection Agency (EPA). 1977a. Handbook of Analytical Quality Control in Radioanalvtical Laboratories. Office of
Research and Development. EPA/600/7-77/008.
Environmental Protection Agency (EPA). 1977b. Quality Control for Environmental Measurements Using Gamma-Ray Spectrometry.
EPA/500/7-77/14.
Environmental Protection Agency (EPA). 1979a. Radiochemical Analytical Procedures for Analysis of Environmental Samples.
EMSL-LV-0539-17.
Environmental Protection Agency (EPA). 1980. Upgrading Environmental Radiation Data. Office of Radiation Programs. EPA/520/1-
80/012.
Environmental Protection Agency (EPA). 1984a. Eastern Environmental Radiation Facility Radiochemistrv Procedures Manual. Office
of Radiation Programs. EPA/520/5-84/006.
Environmental Protection Agency (EPA). 1984b. Federal Guidance Report No. 10: The Radioactivity Concentration Guides. Office
of Radiation Programs. EPA/520/1-84/010.
Environmental Protection Agency (EPA). 1987a. Population Exposure to External Natural Radiation Background in the United
States. Office of Radiation Programs. EPA ORP/SEPD-80-12.
Environmental Protection Agency (EPA). 1987b. Handbook of Analytical Quality Control in Radioanalvtical Laboratories. Office of
Research and Development. EPA/600/7-87/008.
Environmental Protection Agency (EPA). 1988. Federal Guidance Report No. 11: Limiting Values of Radionuclide Intake and Air
Concentration and Dose Conversion Factors for Inhalation, Submersion, and Ingestion. Office of Radiation Programs. EPA/520/1-
88/020.
Environmental Protection Agency (EPA). 1989a. Background Information Document. Draft BIS for Proposed NESHAPS for
Radionuclides. Volume I, Risk Assessment Methodology. Office of Radiation Programs. EPA/520/1 -89/005.
Environmental Protection Agency (EPA). 1989b. Annual Report Fiscal Year 1988 Laboratory Intercomparison Studies for
Radionuclides.
Environmental Protection Agency (EPA). 1989c. CERCLA Compliance with Other Laws Manual. Part II. Office of Emergency
and Remedial Response. (OSWER Directive 9234.1-02).
International Commission on Radiological Protection (ICRP). 1977. Recommendations of the ICRP. ICRP Publication 26.
International Commission on Radiological Protection (ICRP). 1979. Limits for Intake of Radionuclides by Workers. ICRP Publication
30.
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Page 10-36
International Commission on Radiological Protection (ICRP). 1983. Principles for Limiting Exposure of the Public to Natural Sources
of Radiation. ICRP Publication 39.
International Commission on Radiological Protection (ICRP). 1984. A Compilation of the Major Concepts and Quantities in Use
by the ICRP. ICRP Publication 42.
International Commission on Radiological Protection (ICRP). 1985. Principles of Monitoring for the Radiation Protection of the
Population. ICRP Publication 43.
International Commission on Radiological Protection (ICRP). 1987. Lung Cancer Risk from Indoor Exposures to Radon Daughters.
ICRP Publication 50.
Kato, H. and Schull, W.J. 1982. Studies of the Mortality of A-Bomb Survivors. Report 7 Part 1, Cancer Mortality Among Atomic
Bomb Survivors, 1950-78. Radiation Research 90:395-432.
Kocher, D. 1981. Radioactive Decay Data Tables: A Handbook of Decay Data for Application to Radiation Dosimetry and
Radiological Assessments. DOE/TIC-11026.
Miller. 1984. Models and Parameters for Environmental Radiological Assessments. DOE/TIC-11468.
National Academy of Sciences - National Research Council. 1972. The Effects on Populations of Exposures to Low Levels of Ionizing
Radiation. (BEIR Report)
National Academy of Sciences - National Research Council. 1980. The Effects on Populations of Exposures to Low Levels of Ionizing
Radiation. (BEIR Report).
National Academy of Sciences - National Research Council. 1988. Health Risks of Radon and Other Internally Deposited Alpha-
Emitters. (BEIR Report).
National Council on Radiation Protection and Measurements (NCRP). 1989. Screening Techniques for Determining Compliance
with Environmental Standards. NCRP Commentary No. 3.
National Council on Radiation Protection and Measurements (NCRP). 1976. Environmental Radiation Measurements. NCRP Report
No. 50.
National Council on Radiation Protection and Measurements (NCRP). 1978. Instrumentation and Monitoring Methods for Radiation
Protection. NCRP Report No. 57.
National Council on Radiation Protection and Measurements (NCRP). 1979. Tritium in the Environment. NCRP Report No. 62.
National Council on Radiation Protection and Measurements (NCRP). 1980. Influence of Dose and Its Distribution in Time on
Dose-response Relationships for Low-LET Radiations. NCRP Report No. 64.
National Council on Radiation Protection and Measurements (NCRP). 1984a. Radiological Assessment: Predicting the
Transport. Bioaccumulation. and Uptake by Man of Radionuclides Released to the Environment. NCRP Report No. 76.
National Council on Radiation Protection and Measurements (NCRP). 1984b. Exposure from the Uranium Series with Emphasis
on Radon and its Daughters. NCRP Report No. 77.
National Council on Radiation Protection and Measurements (NCRP). 1985a. A Handbook of Radioactivity Measurement Procedures.
NCRP Report No. 58.
National Council on Radiation Protection and Measurements (NCRP). 1985b. Induction of Thyroid Cancer by Ionizing Radiation.
NCRP Report No. 80.
National Council on Radiation Protection and Measurements (NCRP). 1985c. Carbon-14 in the Environment. NCRP Report No.
81.
National Council on Radiation Protection and Measurements (NCRP). 1987a. Ionizing Radiation Exposure of the Population of the
United States. NCRP Report No. 93.
National Council on Radiation Protection and Measurements (NCRP). 1987b. Exposure of the Population of the United States and
Canada from Natural Background Radiation. NCRP Report No. 94.
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Page 10-37
National Council on Radiation Protection and Measurements (NCRP). 1989. Screening Techniques for Determining Compliance
with Environmental Standards. NCRP Commentary No. 3.
Nuclear Regulatory Commission (NRC). 1977. Calculation of Annual Doses to Man from Routine Releases of Reactor Effluents for
the Purpose of Evaluating Compliance with 10 CFR 50, Appendix I. Regulatory Guide 1.109.
Nuclear Regulatory Commission (NRC). 1979. Quality Assurance Monitoring Programs (Normal Operation) -- Effluent Streams and
the Environment. NRC Regulatory Guide 4.15.
Nuclear Regulatory Commission (NRC). 1989. Health Effects Models for Nuclear Power Plant Accident Consequence Analysis: Low-
LET Radiation, Part II: Scientific Bases for Health Effects Models. NUREG/CR-4214, Rev. 1. Part II.
Otake, M. and Schull W. 1984. Mental Retardation in Children Exposed in Utero to the Atomic Bombs: A Reassessment. Technical
Report RERF TR 1-83. Radiation Effects Research Foundation. Japan.
Schleien, B. and Terpilak, M., (Eds). 1984. The Health Physics and Radiological Health Handbook. (7th Ed.) Nucleon Lectern
Assoc., Inc. Maryland.
Till, J.E. and Meyer, H.R. 1983. Radiological Assessment: A Textbook on Environmental Dose Analysis. Prepared for Office of
Nuclear Reactor Regulation. U.S. Nuclear Regulatory Commission. Washington, DC. NUREG/CR-3332.
Turner, J.E. 1986. Atoms, Radiation, and Radiation Protection. Pergamon Press. New York, NY.
United Nations Scientific Committee Report on the Effects of Atomic Radiation (UNSCEAR). 1958. Official Records: Thirteenth
Session, Supplement No. 17(A/38381. United Nations. New York, NY.
United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). 1977. Sources and Effects of Ionizing
Radiation. United Nations. New York, NY.
United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). 1982. Ionizing Radiation: Sources and
Effects. United Nations. New York, NY.
United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). 1986. Genetic and Somatic Effects of Ionizing
Radiation. United Nations. New York, NY.
United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). 1988. Sources. Effects, and Risks of Ionizing
Radiation. United Nations. New York, NY.
Wakabayashi, T., et al. 1983. Studies of the Mortality of A-Bomb Survivors, Report 7, Part III, Incidence of Cancer in 1959-1978,
Based on the Tumor Registry, Nagasaki. Radiat. Res. 93: 112-146.
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APPENDICES
-------
APPENDIX A
-------
APPENDIX A
ADJUSTMENTS FOR
ABSORPTION EFFICIENCY
This appendix contains example calculations
for absorption efficiency adjustments that might be
needed for Superfund site risk assessments.
Absorption adjustments might be necessary in the
risk characterization step to ensure that the site
exposure estimate and the toxicitv value for
comparison are both expressed as absorbed doses
or both expressed as intakes.
Information concerning absorption effi-
ciencies might be found in the sections describing
absorption toxicokinetics in HEAs, HEEDs,
HEEPs, HADs, EPA drinking water quality
criteria or ambient water quality criteria
documents, or in ATSDR toxicological profiles.
If there is no information on absorption efficiency
by the oral/inhalation routes, one can attempt to
find absorption efficiencies for chemically related
substances. If no information is available,
conservative default assumptions might be used.
Contact ECAO for further guidance.
Adjustments may be necessary to match the
exposure estimate with the toxicity value if one is
based on an absorbed dose and the other is based
on an intake (i.e., administered dose).
Adjustments may also be necessary for different
vehicles of exposure (e.g., water, food, or soil).
For the dermal route of exposure, the
procedures outlined in Chapter 6 result in an
estimate of the absorbed dose. Toxicity values
that are expressed as administered doses will need
to be adjusted to absorbed doses for comparison.
This adjustment is discussed in Section A.l.
For the other routes of exposure (i.e., oral
and inhalation), the procedures outlined in
Chapter 6 result in an estimate of daily intakes.
If the toxicity value for comparison is expressed
as an administered dose, no adjustment may be
necessary (except, perhaps, for vehicle of
exposure). If the toxicity value is expressed as an
absorbed dose, however, adjustment of the
exposure estimate (i.e., intake) to an absorbed
dose is needed for comparison with the toxicity
value. This adjustment is discussed in Section
A2.
Adjustments also may be necessary for
different absorption efficiencies depending on the
medium of exposure (e.g., contaminants ingested
with food or soil might be less completely
absorbed than contaminants ingested with water).
This adjustment is discussed in Section A3.
A.1 ADJUSTMENTS OF TOXICITY
VALUE FROM ADMINISTERED
TO ABSORBED DOSE
Because there are few, if any, toxicity
reference values for dermal exposure, oral values
are frequently used to assess risks from dermal
ACRONYMS FOR APPENDIX A
ATSDR = Agency for Toxic Substances and
Disease Registry
BCAO = Environmental Criteria and Assessment
Office
HAD = Health Assessment Document
HEA = Health Effects Assessment
HEED = Health and Environmental Effects
Document
HEEP « Health and Environmental Effects
Profile
RfD ~ Reference Dose
SF = Slope Factor
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Page A-2
DEFINITIONS FOR APPENDIX A
Absorbed Dose. The amount of a substance penetrating the exchange boundaries of an organism after contact. Absorbed
dose is calculated from the intake and the absorption efficiency, and it usually is expressed as mass of a substance
absorbed into the body per unit body weight per unit time
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Page A-3
(less than 5 percent) by the gastrointestinal tract.
A relatively conservative assumption for oral
absorption in the absence of appropriate
information would be 5 percent.
EXAMPLE: ADJUSTMENT OF AN
ADMINISTERED TO AN
ABSORBED DOSE SLOPE FACTOR
An oral slope factor, unadjusted for
absorption equals 1.6 (mg/kg-day)^.
Other information (or an assumption)
indicates a 20% absorption efficiency in the
species on which the slope factor is based.
The adjusted slope factor that would
correspond to the absorbed dose would be:
1.6(mg/kg-day)-r/0.20 = 8 (mg/kg-day)^.
The adjusted slope factor of 8 (mg/kg-
day)~; would be used to estimate the cancer
risk associated with the estimated absorbed
dose for the dermal route of exposure.
A.2 ADJUSTMENT OF EXPOSURE
ESTIMATE TO AN ABSORBED
DOSE
If the toxicity value is expressed as an
absorbed rather than an administered dose, it may
be necessary to convert the exposure estimate
from an intake into an absorbed dose for
comparison. An example of estimating an
absorbed dose from an intake using an absorption
efficiency factor is provided in the box in the top
right corner. Do not adjust exposure estimates
for absorption efficiency if the toxicity values are
based on administered doses.
A3 ADJUSTMENT FOR MEDIUM
OF EXPOSURE
If the medium of exposure in the site
exposure assessment differs from the medium of
EXAMPLE: ADJUSTMENT OF
EXPOSURE ESTIMATE TO
AN ABSORBED DOSE
The exposure assessment indicates that an
individual ingests 40 mg/kg-day of the
chemical from locally grown vegetables.
The oral RfD (or slope factor) for the
chemical is based on an absorbed, not
administered, dose.
The human oral absorption efficiency for the
contaminant from food is known or assumed
to be 10 percent.
The adjusted exposure, expressed as an
absorbed dose for comparison with the RfD
(or slope factor), would be:
40 mg/kg-day x 0.10 = 4 mg/kg-day.
exposure assumed by the toxicity value (e.g., RfD
values usually are based on or have been adjusted
to reflect exposure via drinking water, while the
site medium of concern may be soil), an
absorption adjustment may, on occasion, be
appropriate. For example, a substance might be
more completely absorbed following exposure to
contaminated drinking water than following
exposure to contaminated food or soil (e.g., if the
substance does not desorb from soil in the
gastrointestinal tract). Similarly, a substance
might be more completely absorbed following
inhalation of vapors than following inhalation of
particulates. The selection of adjustment method
will depend upon the absorption efficiency
inherent in the RfD or slope factor used for
comparison. To adjust a food or soil ingestion
exposure estimate to match an RfD or slope
factor based on the assumption of drinking water
ingestion, an estimate of the relative absorption
of the substance from food or soil and from water
is needed. A sample calculation is provided in
the box on the next page.
In the absence of a strong argument for
making this adjustment or reliable information
on absorption efficiencies, assume that the relative
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Page A-4
EXAMPLE: ADJUSTMENT FOR
MEDIUM OF EXPOSURE
The expected human daily intake of the
substance in food or soil is estimated to be
10 mg/kg-day.
Absorption of the substance from drinking
water is known or assumed to be 90%, and
absorption of the substance from food or
soil is known or assumed to be 30%.
The relative absorption of the substance in
food or soil/drinking water is 0.33 (i.e.,
30/90).
The oral intake of the substance, adjusted
to be comparable with the oral RfD (based
on an administered dose in drinking water),
would be:
10 mg/kg-day x 0.33 = 3.3 mg/kg-day.
absorption efficiency between food or soil and
water is 1.0.
If the RfD or slope factor is expressed as an
absorbed dose rather than an administered dose,
it is only necessary to identify an absorption
efficiency associated with the medium of concern
in the site exposure estimate. In the example
above, this situation would translate into a relative
absorption of 0.3 (i.e., 30/100).
-------
APPENDIX B
-------
APPENDIX B
INDEX
Absorbed dose
calculation 6-34, 6-39, 7-8, 7-10, 7-12
definition 6-2, 6-4, 6-32, 6-34, 7-10, 10-2
following dermal contact with soil,
sediment, or dust 6-39, 6-41 to 6-43, 7-
16
following dermal contact with water 6-34,
6-39, 7-16
radiation 10-1, 10-2, 10-6
toxicity value 7-10, 7-16, 8-5, A-l, A-2
Absorption adjustment
dermal exposures 8-5, A-l, A-2
medium of exposure 8-5, A-3, A-4
Absorption efficiency
default assumptions 6-34, 6-39, A-2 to A-4
dermal 6-34, 6-39
general 6-2, 7-10, 7-20, 8-5, 8-10
Acceptable daily intakes 7-1, 7-2, 7-6
Activity at time t 10-1
Activity patterns 6-2, 6-6, 6-7, 6-24, 7-3
Acute exposures. See Exposure - short-term
Acute toxicants 6-23, 6-28
ADIs. See Acceptable daily intakes
Administered dose 6-2, 6-4, 7-1, 7-2, 7-10, 8-2,
8-5, A-l to A-4
Agency for Toxic Substances and Disease
Registry 1-8, 2-1, 2-3, 2-4, 2-8 to 2-11, 6-1, 6-
17, 7-14, 8-1, 8-15, 8-24
Air data collection
and soil 4-10
background sampling 4-9
concentration variability 4-9
emission sources 4-15
flow 4-8
meteorological conditions 4-15, 4-20
monitoring 4-8, 4-9, 4-14
radionuclides 10-11
sample type 4-19
sampling locations 4-19
short-term 4-15
spatial considerations 4-15
temporal considerations 4-15, 4-20
time and cost 4-21
Air exposure
dispersion models 6-29
indoor modeling 6-29
outdoor modeling 6-29
volatilization 6-29
Analytes 4-2, 5-2, 5-5, 5-7, 5-10, 5-27
Analytical methods
evaluation 5-5 to 5-7
radionuclides 10-12, 10-13
routine analytical services 4-22
special analytical services 4-3, 4-22
Animal studies 7-12, 10-28, 10-29, 10-33
Applicable or relevant and appropriate
requirement 2-2, 2-7, 2-8, 8-1, 10-8 to 10-10
Applied dose 6-2, 6-4
ARAR. See Applicable or relevant and
appropriate requirement
A(t). See Activity at time t
ATSDR. See Agency for Toxic Substances and
Disease Registry
Averaging time 6-23
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Page B-2
B
Background
anthropogenic 4-2, 4-5
comparison to site related contamination 4-
9, 4-10, 4-18
defining needs 4-5 to 4-10, 6-29, 6-30
information useful for data collection 4-1
localized 4-5
naturally occurring 4-2, 4-5, 8-25, 10-14
sampling 4-5 to 4-10, 10-14
ubiquitous 4-5
BCF. See Bioconcentration factor
Bench scale tests 4-3
Benthic oxygen conditions 4-7
Bioconcentration 4-11, 6-31, 6-32
Bioconcentration factor 6-1, 6-12, 6-31, 6-32
Biota sampling 4-7, 4-10, 4-16
Blanks
evaluation 5-17
field 4-22, 4-23, 5-17, 10-20
laboratory 4-22, 5-13, 5-17
laboratory calibration 5-17
laboratory reagent or method 5-17
trip 4-22, 5-17
Body weight as an intake variable 6-22, 6-23, 6-
39, 7-8, 7-12, 10-26, 10-33
Bulk density 4-7, 4-12
Cancer risks
extrapolating to lower doses 7-11, 7-12
linear low-dose equation 8-6
multiple pathways 8-16
multiple substances 8-12
one-hit equation 8-11
radiation 10-28 to 10-32
summation of 8-12, 8-16
Carcinogenesis 7-10, 10-28 to 10-32
Carcinogen Risk Assessment Verification
Endeavor 7-1, 7-13
Carcinogens 5-8, 5-21, 6-23, 7-10, 8-6, 10-30, 10-
33
CDI. See Chronic daily intake
CEAM. See Center for Exposure Assessment
Modeling
Center for Exposure Assessment Modeling 6-1,
6-25, 6-31
CERCLA. See Comprehensive Environmental
Response, Compensation, and Liability Act of
1980
CERCLA Information System 2-4
CERCLIS. See CERCLA Information System
Checklist for manager involvement 9-14 to 9-17
Chemicals of potential concern
definition 5-2
listing 5-20
preliminary assessment 5-8
radionuclides 10-21
reducing 5-20 to 5-24
summary 5-24 to 5-27
Chronic daily intake 6-1, 6-2, 6-23, 7-1, 8-1, 8-6
to 8-11
CLP. See Contract Laboratory Program
Combustible gas indicator 5-6
Common laboratory contaminants 5-2, 5-3, 5-13,,
5-16, 5-17
Comprehensive Environmental Response,
Compensation, and Liability Act of 1980 1-1,'
1-3, 2-1 to 2-4
Concentration-toxicity screen 5-20, 5-23
Conceptual model 4-5, 4-10
Contact rate 6-2, 6-22
Contract Laboratory Program
applicability to radionuclides 10-16, 10-17,
10-20, 10-21
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Page B-3
definition 4-2
routine analytical services 4-22, 5-5, 5-7, 5-
15, 5-18, 5-20
special analytical services 4-3, 4-22, 5-5, 5-7
to 5-10, 5-18 to 5-20
statements of work 5-5
Contract-required detection limit. See
Detection limit
Contract-required quantitation limit. See
Quantitation limit
CRAVE. See Carcinogen Risk Assessment
Verification Endeavor
CRDL. See Contract-required detection limit
Critical study. See Reference dose
Critical toxicity effect. See Reference dose
CRQL. See Contract-required quantitation
limit
Curie 10-2, 10-4, 10-6
D
D. See Absorbed dose ~ radiation
Data
codes 5-11 to 5-16
positive 5-2
qualifiers 5-11 to 5-16
Data quality objectives 3-4, 4-1 to 4-5, 4-19, 4-
24, 10-14
DCF. See Dose conversion factor
Decay products 10-2, 10-7, 10-21, 10-24
Decision Summary 9-3
Declaration 9-3
Dermal
absorption efficiency 6-34, 6-39
contact with soil, sediment, or dust 6-39, 6-
41 to 6-43, A-2
contact with water 6-34, 6-37 to 6-39, A-2
exposure 4-10, 4-11, 4-14, 6-34, 6-37 to 6-
39, 6-43, 8-5, A-2
external radiation exposure 10-22, 10-23,
10-25, 10-26
toxicity values 7-16
Detection frequency 5-20, 5-22
Detection limits
contract-required 5-1, 5-2, 5-8
definition 5-1, 5-2, 5-8
evaluation 4-3 to 4-5, 5-7 to 5-11, 5-20, 6-
31
instrument 4-1, 5-1, 5-7
limitations to 4-15, 4-22, 5-8
method 4-22, 5-1, 5-7
radionuclides 10-17 to 10-20
Diffusivity 6-12
Dissolved oxygen 4-7
DL. See Detection limit
Documentation. See Preparing and reviewing
the baseline risk assessment
Dose
absorbed vs administered 6-4, 7-10, 8-2, A-
1 to A-3
absorption efficiency A-l to A-3
response curve 7-12
response evaluation 7-1, 7-2, 7-11, 7-12
Dose conversion factor 10-1, 10-2, 10-24, 10-25,
10-26
Dose equivalent
committed 10-1, 10-2, 10-7, 10-24, 10-25,
10-26
effective 10-1, 10-2, 10-7, 10-24, 10-25, 10-
26
DQO. See Data quality objectives
Dry weight 4-7
Dust
exposure 6-39, 6-43
fugitive dust generation 4-3, 4-5, 4-15, 6-29
transport indoors 6-29
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Page B-4
E
E. See Exposure level
ECAO. See Environmental Criteria and
Assessment Office
Emission sampling
rate 4-5, 4-7, 4-14
strength 4-7
Endangerment Assessment Handbook 1-1, 2-9
Endangerment assessments 2-1, 2-8
Environmental Criteria and Assessment Office
7-1, 7-15, 7-16, 7-19, 8-1, 8-5, A-l
Environmental Evaluation Manual 1-1, 1-11, 2-9,
4-16
Environmental Photographic Interpretation
Center 4-4
EPIC. See Environmental Photographic
Interpretation Center
Epidemiology
site-specific studies 2-10, 8-22, 8-24
toxicity assessment 7-3, 7-5
Essential nutrients 5-23
Estuary sampling 4-7, 4-13, 4-14
Exposure
averaging time 6-23
characterization of setting 6-2, 6-5 to 6-8
definition 6-2, 8-2
event 6-2
expressed as absorbed doses 6-34, 6-39, A-l
for dermal route 6-34, 6-39, 6-41 to 6-43
frequency/duration 6-22
general considerations 6-19 to 6-24
level 8-1
long-term 6-23
parameter estimation 6-19 to 6-23
pathway-specific exposures 6-32 to 6-47
point 6-2, 6-11
potentially exposed populations 6-6 to 6-8
radionuclides vs chemicals 10-22
route 6-2, 6-11, 6-17, 6-18, 8-2, A-l
short-term 6-23, 8-11, 10-25, 10-28, 10-30
Exposure assessment
definition 1-6, 1-7, 6-1, 6-2, 8-2
intake calculations 6-32 to 6-47
objective 6-1
output for dermal contact with
contaminated soil 6-39
output for dermal exposure to
contaminated water 6-34
preliminary 4-3, 4-10 to 4-16
radiation 10-22 to 10-27
spatial considerations 6-24 to 6-26
Exposure concentrations
and the reasonable maximum exposure 6-19
in air 6-28, 6-29
in food 6-31, 6-32
in ground water 6-26, 6-27
in sediment 6-30
in soil 6-27, 6-28
in surface water 6-29, 6-30
summarizing 6-32, 6-33, 6-50, 6-52
Exposure pathways
components 6-8, 6-9
definition 6-2, 8-2
external radiation exposure 10-22, 10-23,
10-25, 10-26
identification 6-8 to 6-19
multiple 6-47
summarizing 6-17, 6-20
Fate and transport assessment 6-11, 6-14 to 6-
16. See also Exposure assessment
Field blanks. See Blanks
Field investigation team 4-1, 4-16, 4-20, 4-24, 5-
1, 5-2
Field sampling plan 4-1, 4-2, 4-23, 4-24, 10-15
Field screen 4-11, 4-20, 4-21, 5-5, 5-6, 5-24
First-order analysis 8-20
FIT. See Field investigation team
Five-year review 2-3, 2-5
Food chain 2-3, 4-7, 4-10, 4-16, 6-31, 6-32
Fraction organic content of soil 4-7
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Page B-5
Frequency of detection. See Detection
frequency
FS. See Remedial investigation/feasibility study
FSP. See Field sampling plan
G
Ground-water data collection
and air 4-13
and soil 4-12
filtered vs unfiltered samples 4-12, 6-27
hydrogeologic properties 4-12
sample type 4-19
transport route 4-11
well location and depth 4-12
Grouping chemicals by class 5-21, 10-21
H
HADs. See Health Assessment Documents
HAs. See Health Advisories
Half-life 6-12, 10-2
Hazard identification 1-6, 7-1, 7-2, 10-28 to 10-
30
Hazard index
chronic 8-13
definition 8-1, 8-2
multiple pathways 8-16, 8-17
multiple substances 8-12, 8-13
noncancer 8-12, 8-13
segregation 8-14, 8-15
short-term 8-13, 8-14
subchronic 8-13, 8-14
Hazard quotient 8-2, 8-11
Hazard Ranking System 2-5, 2-6, 4-1, 4-4
H£. See Dose equivalent
HEi50. See Dose equivalent
Head measurements 4-7
Health Advisories 2-10, 7-9, 7-10, 8-13
Health and Environmental Effects Documents
7-1, 7-14, A-l
Health and Environmental Effects Profiles 7-1,
7-14, A-l
Health Assessment Documents 7-1, 7-14, A-l
Health Effects Assessments 7-1, 7-14, A-l
Health Effects Assessment Summary Tables 7-1,
7-14
Health physicist 10-3, 10-21
HEAs. See Health Effects Assessments
HEAST. See Health Effects Assessment
Summary Tables
HEEDs. See Health and Environmental Effects
Documents
HEEPs. See Health and Environmental Effects
Profiles
Henry's law constant 6-12
HI. See Hazard index
HNu organic vapor detector 5-6
Hot spots 4-10 to 4-12, 4-17, 4-19, 5-27, 6-24, 6-
28
HQ. See Hazard quotient
HRS. See Hazard Ranking System
HJ-. See Dose equivalent
HT>50. See Dose equivalent
Hydraulic gradient 4-7
I
LARC. See International Agency for Research
on Cancer
IDL. See Instrument detection limit
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Page B-6
Ingestion
of dairy products 4-16, 6-47, 6-48
of fish and shellfish 4-3, 4-11, 4-14, 4-15, 4-
16, 6-43, 6-45
of ground water 6-34, 6-35
of meat 4-15, 4-16, 6-47, 6-48
of produce 4-16, 6-43, 6-46, 6-47
of soil, sediment, or dust 6-39, 6-40
of surface water 4-14, 6-34, 6-35
while swimming 4-14, 6-34, 6-36
Instrument detection limit. See Detection limit
Inhalation 6-43, 6-44
Intake 6-2, 6-4, 6-19, 6-21, 8-2, 10-26
Integrated Risk Information System 7-1, 7-2, 7-
6, 7-12 to 7-15, 8-1, 8-2, 8-7, 8-8, 10-33
International Agency for Research on Cancer 7-
11
International System of Units 10-1
Ionizing radiation. See Radionuclides, radiation
IRIS. See Integrated Risk Information System
K
IQ6-12
K0C 6-12
KOH, 6-12, 6-31
Kriging 6-19
L
Land use
and risk characterization 8-10, 8-20, 8-26
current 6-6
future 6-7
Lentic waters 4-14
LET. See Linear energy transfer
Level of effort 1-6 to 1-8, 3-3
Life history stage 4-7
Lifetime average daily intake 6-2, 6-23, 8-4
Linear energy transfer 10-1, 10-2, 10-28, 10-29,
10-31
Linearized multistage model 7-12, 8-6
Lipid content 4-7, 10-14
LLD. See Lower limit of detection
LOAEL. See Lowest-observed-adverse-effect-
level
Lotic waters 4-13, 4-14
Lower limit of detection 10-1
Lowest-observed-adverse-effect-level 7-1, 7-2, 7-
7, 8-1
M
Management tools 9-1, 9-14, 10-1, 10-34
Maximum contaminant levels 1-8, 5-8
MCLs. See Maximum contaminant levels
MDL. See Method detection limit
Media of concern
air 4-14
biota 4-15
ground water 4-12
sampling 4-2, 4-3, 4-10 to 4-16
soil 4-11
surface water/sediments 4-13
Metals
absorption by gastrointestinal tract A-2, A-
3
default assumptions for A-2
Method detection limit. See Detection limit
MeV. See Million electron volts
MR See Modifying factor
Million electron volts 10-1, 10-5
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Page B-7
Modeling 4-3 to 4-8, 5-8, 5-22, 5-27, 6-25, 6-26,
8-18 to 8-20
Modifying factor 7-7, 7-21, 8-4, 8-8, 10-1, 10-2,
10-6
Monte Carlo simulation 8-19, 8-20
Multistage model. See Linearized multistage
model
N
N. See Dose equivalent
National Oceanographic and Atmospheric
Administration 6-1, 6-6
National Oil and Hazardous Substances
Pollution Contingency Plan 1-1, 2-2, 2-4, 2-5
National Priorities List 2-3, 2-5, 2-6, 10-1
National Response Center 2-4
National Technical Guidance Studies 6-1
NCP. See National Oil and Hazardous
Substances Pollution Contingency Plan
ND. See Non-detect
NOAA. See National Oceanographic and
Atmospheric Administration
NOAEL. See No-observed-adverse-effect-level
Noncancer hazard indices. See Hazard index
Noncancer hazard quotient. See Hazard
quotient
Noncarcinogenic threshold toxicants 7-6
Non-detects 5-1, 5-2, 5-7, 5-10, 5-11, 5-15, 5-16
No-observed-adverse-effect-level 7-1, 7-2, 7-7, 8-
1
Normalized exposure rate 6-4, 8-2, A-2
NPL. See National Priorities List
NRC. See Nuclear Regulatory Commission
NTGS. See National Technical Guidance
Studies
Nuclear Regulatory Commission 8-1, 10-8
Nuclear transformation 10-2
O
OAQPS. See Office of Air Quality Planning
and Standards
OERR. See Office of Emergency and Remedial
Response
Office of Air Quality Planning and Standards 6-
1
Office of Emergency and Remedial Response 1-
1
Office of Radiation Programs 10-3, 10-10, 10-14,
10-24 to 10-26
Operable units 1-8, 1-9, 3-1, 3-2, 5-24
Oral absorption A-2, A-3
Oral cancer potency factor adjustment A-3
Oral reference dose adjustment A-2
Organic carbon content 4-7, 4-12, 5-5
Organic vapor analyzer 5-6
OVA. See Oxygen vapor analyzer
Oxygen-deficient atmosphere 5-6
P
PA. See Preliminary assessment/site inspection
Partition coefficient 4-7, 6-31, 6-32
PA/SI. See Preliminary assessment/site
inspection
PC. See Permeability constant
PE. See Performance evaluation
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Page B-8
Performance evaluation 5-1, 5-5
Permeability constant 6-34, 10-26
Persistence 4-2, 5-21, 6-4, 6-23, 6-24
pH 4-7
PHE. See Public health evaluation
Porosity 4-7, 4-12
PQL. See Practical quantitation limit
Practical quantitation limit 5-1
Preliminary assessment/site inspection 2-4, 2-5,
2-6, 4-2, 4-4, 6-5
Preliminary remediation goals 1-3 to 1-5, 1-8, 8-
1
Preparing and reviewing the baseline risk
assessment
addressing the objectives 9-1, 9-2
communicating the results 9-1, 9-2
documentation tools 9-1 to 9-8
other key reports 9-3
review tools 9-3, 9-9 to 9-14
scope 9-2, 9-3
PRGs. See Preliminary remediation goals
Primary balancing criteria 1-9
Proxy concentration 5-10
Public health evaluation 1-11
Q
Q. See Dose equivalent
QAPjP. See Quality assurance project plan
QA/QC. See Quality Assurance/Quality Control
QL. See Quantitation limit
Qualifiers. See Data
Quality assurance project plan 4-1, 4-2, 4-23
Quality assurance/quality control 3-4, 4-1, 4-3, 5-
1, 5-29
Quality factor 10-2, 10-6
Quantitation limit
compared to health-based concentrations 5-
2, 5-5, 5-7, 5-8, 5-11
contract-required 5-1, 5-2, 5-8
definitions 5-2, 5-5, 5-8
evaluation 5-1 to 5-9, 10-20
high 5-10
radionuclides 10-17 to 10-20
sample 5-8
strategy 4-21
unavailability 4-3, 5-10
R
RA. See Remedial action
Radiation. See Radionuclides, radiation
Radiation advisory groups
International Commission on Radiation
Protection 10-3, 10-9, 10-28
National Academy of Sciences 10-28, 10-29
National Council on Radiation Protection
and Measurements 10-9, 10-28
United Nations Scientific Committee on
the Effects of Atomic Radiation 10-28,
10-29, 10-30
Radiation detection instruments
gas proportional counters 10-12, 10-13
Geiger-Mueller (G-M) counters 10-11, 10-
12
ionization chambers 10-11 to 10-13
scintillation detectors 10-11 to 10-13
solid-state detectors 10-12, 10-13
Radiation units
becquerel 10-1, 10-2, 10-4, 10-6
curie 10-1, 10-2, 10-4, 10-6
picocurie 10-1
rad 10-2, 10-6
rem 10-2
roentgen 10-2, 10-6
sievert 10-1, 10-2, 10-6
working level 10-7
working level month 10-7
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Page B-9
Radionuclides, radiation
alpha particles 10-4, 10-5, 10-28
beta particles 10-4, 10-5, 10-28
decay products 10-2, 10-7, 10-21, 10-24
definition 10-2
external 10-2
half-life 10-2
internal 10-2
ionizing 10-2
linear energy transfer 10-2, 10-28, 10-29,
10-31
lower limit of detection 10-17, 10-20
neutrons 10-4
photons 10-4, 10-5, 10-28
positrons 10-4
quality factors 10-2, 10-6, 10-29
radioactive decay 10-2, 10-2
radon decay products 10-7
regulatory agencies 10-8, 10-9
relative biological effectiveness 10-1, 10-6,
10-29
risk characterization 10-32 to 10-34
toxicity assessment 10-27 to 10-32
RAS. See Routine analytical services
RBE. See Relative biological effectiveness
RCRA. See Resource Conservation and
Recovery Act
RD. See Remedial design
Reasonable maximum exposure
and body weight 6-22, 6-23
and contact rate 6-22
and exposure concentration 6-19
and exposure frequency and duration 6-22
and risk characterization 8-1, 8-15, 8-16, 8-
26
definition 6-1, 6-4, 6-5
estimation of 6-19 to 6-23, 8-15, 8-16
Record of Decision 2-5, 9-3
Redox potential 4-7
Reference dose
chronic 7-1, 7-2, 7-5, 8-1, 8-2, 8-8, 8-10, 8-
13, A-l, A-2
critical toxic effect 7-7, 8-4, 8-10, 8-15
critical study 7-7
definition 7-1, 7-2, 8-2, A-2
developmental 7-1, 7-6, 7-9, 8-2
inhalation 7-8
oral 7-6, 7-7
subchronic 7-1, 7-2, 7-6, 7-8, 7-9, 8-2, 8-9,
8-14
verified 7-10
Regional Radiation Program Managers 10-3, 10-
10
Relative biological effectiveness 10-1, 10-6, 10-
29
Release sources 6-10
Remedial action 1-3, 1-8 to 1-10, 2-5, 2-7, 2-9,
3-1, 3-2, 6-8, 10-8
Remedial action objectives 1-3, 1-8, 2-7
Remedial design 2-5, 2-6, 2-9
Remedial investigation/feasibility study 1-1 to 1-
5, 1-8 to 1-10, 2-5 to 2-7, 3-1 to 3-3, 4-1 to
4-5, 4-23, 8-1
Remedial project manager
and background sampling 4-8
and elimination of data 5-2, 5-17, 5-20, 5-
21
and ground-water sampling 4-13
and radiation 10-3
and reasonable maximum exposure 6-5
and scoping meeting 4-3
definition 1-2
management tools for 9-14 to 9-17
Remedy selection 1-9, 2-5
Resource Conservation and Recovery Act 2-7,
10-8
Responsiveness Summary 9-3
Reviewing the risk assessment. See Preparing
and reviewing the baseline risk assessment
RfD. See Reference dose
See Reference dose
RfDj. See Reference dose
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Page B-10
RI. See Remedial investigation/feasibility
studies
RI/FS. See Remedial investigation/feasibility
study
Risk assessment reviewer 1-2, 9-1, 9-3, 9-9 to 9-
14
Risk assessor
definition 1-2
tools for documentation 9-1 to 9-8
Risk characterization 1-6, 1-7, 8-1
Risk information in the RI/FS process 1-3 to 1-
10
Risk manager 1-2
RME. See Reasonable maximum exposure
ROD. See Record of Decision
Route-to-route extrapolation 7-16
Routine analytical services. See Contract
Laboratory Program
RPM. See Remedial project manager
s
Salinity 4-7, 4-14, 6-5
Saltwater incursion extent 4-7
Sample Management Office 4-1, 4-2, 5-1, 5-5
Sample quantitation limit 5-1. See also
Quantitation limit
Samples. See Sampling
Sampling
annual/seasonal cycle 4-20
composite 4-11, 4-14, 4-19
cost 4-10, 4-17, 4-18, 4-20, 4-21
depth 4-7, 4-11, 4-12, 4-19
devices 4-21
grab 4-19
purposive 4-9, 4-10, 4-12, 4-18, 4-19
radionuclides 10-10 to 10-16
random 4-9, 4-12, 4-18 to 4-20
routes of contaminant transport 4-10 to 4-
16
strategy 4-16
systematic 4-18, 4-19
Sampling and analysis plan 1-4, 4-1, 4-2, 4-3, 4-
22 to 4-24
SAP. See Sampling and analysis plan
SARA See Superfund Amendments and
Reauthorization Act of 1986
SAS. See Special analytical services
Scoping
meeting 4-3, 4-18, 4-22, 4-23, 9-15, 10-15
of project 1-3 to 1-5, 1-8, 2-7, 3r2, 3-3
SDL See Subchronic daily intake
SEAM. See Superfund Exposure Assessment
Manual
Segregation of hazard indices 8-14, 8-15
Selection of remedy. See Remedy selection
Semi-volatile organic chemical 5-1
SI. See International System of Units,
Preliminary assessment/site inspection
Site discovery or notification 2-4
Site inspection. See Preliminary assessment/site
inspection
Skin 5-29, 7-16, 10-4, 10-6, 10-22, 10-29. See
also Dermal
Slope factor 5-9, 5-21, 7-3, 7-11 to 7-13, 7-16, 8-
1, 8-2 to 8-7, 8-10 to 8-12, 10-2, 10-33, A-l
to A-4
SMO. See Sample management office
Soil data collection 4-11
and ground water 4-12
depth of samples 4-12
heterogeneity 4-11
hot spots 4-11
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Solubility 6-12
Sorption 6-27
SOW. See Statements of work
Special analytical services. See Contract
Laboratory Program
Specific organ 4-7, 10-7, 10-22
SPHEM. See Superfund Public Health
Evaluation Manual
SQL. See Sample quantitation limit
Stability class 4-7
Statements of work. See Contract Laboratory
Program
Statistics
and background 4-8 to 4-10, 5-18
certainty 4-8, 4-17, 4-18
methods 4-8, 4-18
power 4-9, 4-18
sampling strategy 4-16 to 4-20
variability 4-9, 4-18
Structure-activity studies 7-5
Subchronic daily intake 6-1, 6-2, 6-23, 7-1, 8-1
Superfund. See Comprehensive Environmental
Response, Compensation, and Liability Act of
1980
Superfund Amendments and Reauthorization
Act of 1986 1-11, 2-1 to 2-4
Superfund Exposure Assessment Manual 2-1, 2-8,
6-1
Superfund Public Health Evaluation Manual 1-1,
2-8
SVOC. See Semi-volatile organic chemical
T
T. See Tissue
TAL. See Target analyte list
Target analyte list 4-1, 4-2, 5-5, 5-8, 5-17
Target compound list 4-1, 4-2, 4-22, 5-1, 5-5, 5-
8, 5-17, 5-21, 10-20
TCL. See Target compound list
Tentatively identified compound 4-1, 5-1, 5-13,
5-17, 5-18
Thermocline 4-7
TIC. See Tentatively identified compound
Tidal cycle 4-7, 4-14
Tissue 10-1
TOC. See Total organic carbon
Tools
documentation 9-1 to 9-8
management 9-13 to 9-17
review 9-3, 9-9 to 9-14
Topography 4-7
Total organic carbon 5-1
Total organic halogens 5-1
TOX. See Total organic halogens
Toxicity assessment 1-6, 1-7, 7-1, 7-4, 10-27 to
10-32
Toxicity values
absorbed vs administered dose 7-10, A-l
definition 7-3
generation of 7-16
hierarchy of information 7-15
oral 7-16, 10-33, A-2
radiation 10-22, 10-32
reducing number of chemicals 5-21, 5-23
Transfer coefficients 6-32
Transformation 5-20, 6-27, 7-5, 10-2, 10-3, 10-5
Treatability 5-21
Trip blanks. See Blanks
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Page B-12
U
UFs. See Uncertainty factors
Uncertainty analysis
exposure 6-17, 6-34, 6-47, 6-49 to 6-51, 8-
18, 8-22
factors 7-7 to 7-10, 8-4, 8-8, 8-9, 8-17, 8-18,
8-20, 8-22
first-order analysis 8-20
model applicability and assumptions 6-50,
8-18 to 8-22
Monte Carlo simulation 8-20
multiple substance exposure 8-22
parameter value 8-19
qualitative 8-20, 8-21
quantitative 8-19, 8-20
radiation 10-27, 10-33
risk 8-17
semi-quantitative 8-20
toxicity 7-19, 7-20, 8-22
Uncertainty factors. See Uncertainty analysis ~
factors
Unit risk 7-13
U.S. Geological Survey 6-1, 6-6
USGS. See U.S. Geological Survey
V
Vapor pressure 6-12
VOC. See Volatile organic chemical
Volatile organic chemical 4-2, 5-1, 5-17, 6-31
w
Water hardness 4-7
Weighting factor 10-1, 10-2, 10-7
Weight-of-evidence classification 5-20, 7-3, 7-9,
7-11, 8-2, 8-4, 8-7, 8-10
Whole body 4-7, 4-16, 6-31, 10-6, 10-7
Workplan 4-1, 4-4, 4-22 to 4-24, 9-15
Wr. See Weighting factor
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