EPA/540/1-89/002 

December 1989 

Risk Assessment 

 Guidance for Superfund 

 Volume I 

 Human Health Evaluation Manual 

 (Part A) 

Interim Final 

Office of Emergency and Remedial Response 

U.S. Environmental Protection Agency
 

Washington, D.C. 20450 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page ii 

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. 

Comment [A1]: The latest revisions to the 

NCP were finalized in 1994. An overview of the 

final NCP and a link to the full text are available 

at: 

http://www.epa.gov/oem/content/lawsregs/ncp 

over.htm 

This document represents an annotated version of the Risk Assessment Guidance for Superfund (RAGS) 

Part A. Since the original publication of this guidance in 1988, EPA has issued a number of guidance 

documents, directives and other policy documents that update, supplement, supersede or otherwise affect 

RAGS Part A, or contain new information about one or more topics that are substantially addressed in 

RAGS Part A. There may be additional supplemental guidance available on EPA's Superfund risk 

assessment website 

(see http://www.epa.gov/swerrims/riskassessment/risk_superfund.html) 

 The underlying text of RAGS Part A remains unchanged; any typographical errors or missing text 

reflects the PDF original. Annotations have been added to this document as electronic `sticky notes.' To 

view the information contained in a sticky note, simply place your cursor over it or click it and the text 

will expand. To close the note, press the escape key or click on the `X' in the upper righthand corner of 

the note header. In addition, the word `link' appears in parentheses near each sticky note. This text is a 

hyperlink that users can click to open the relevant document that serves as the source of the information 

provided in the note. 

 All sections of RAGS Part A that have at least one annotation are marked in the Table of Contents 

with a blue arrow and highlighted in yellow. Click on the highlighted text in the Table of Contents to 

jump to the annotated section of the guidance. 

Annotations added: April 2010 
 

 

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ABOUT THE REVISION . . . 

 

 

 

 

 

 

 

 

 

 

 

WHAT IT IS EPA's Human Health Evaluation Manual is a revision of the Superfund Public 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 

NEW detailed 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 

TION PLAN is 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 TO Toxics Integration Branch 

SEND Office of Emergency and Remedial Response 

COMMENTS 401 M Street, SW (OS-230) 

Washington, DC 20460 Phone: 202-475-9486 

 

 

 

Comment [A2]: The latest revisions to the 

NCP were finalized in 1994. An overview of the 

final NCP and a link to the full text are available 

at: 

http://www.epa.gov/oem/content/lawsregs/ncp 

over.htm 
Page iv 

WORKGROUP 

EPA HEADQUARTERS 

Marlene Berg Office of Emergency and Remedial Response: David Cooper 

Linda Cullen 

Carla Dempsey 

Steve Golian 

Bruce Means 

Pat Mundy 

Sandra Panetta 

Stephanie Irene Office of Solid Waste: 

Georgia Valaoras Office of Waste Programs Enforcement: 

Larry Zaragoza Office of Solid Waste and Emergency Response: 

Charlotte White 

Office of Policy, Planning, and Evaluation: Craig Zamuda 

Joe Freedman Office of General Counsel: 

Rebecca Madison 

Office of Research and Development: Sue Norton 

Frank Gostomski 

Office of Water: Robert Zeller 

EPA REGIONAL OFFICES 

Sarah Levinson Region I: 

Dan Bicknell Region V: Pamela Blakley 

Fred Reitman Region VI: 

Dana Davoli 

Region X: David Tetta 

OTHER EPA OFFICES 

Cynthia Fuller Great Lakes National Program Office, IL: 

Office of Health and Environmental Assessment, OH: Chris DeRosa 

Office of Air Quality Planning and Standards, NC: Fred Hauchman 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page v 

TABLE OF CONTENTS 

Page 

INTRODUCTION 

CHAPTER 1 INTRODUCTION ............................................................................................................ 1-1
 

1.1 OVERVIEW OF THE HUMAN HEALTH EVALUATION PROCESS 

IN THE RI/FS ................................................................................................................... 1-2 

1.1.1 Project Scoping...................................................................................................1-3 

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 Guidance..........................................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 .............................................................2-9 

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 
 

 

 

 

 

 

 

 

 

 

 

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4.1.1 TYPES OF DATA ..............................................................................................4-1 

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 .............4-3 

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..................................................................................................................4-16 

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............................................... 4-20 

4.6.5 Use Field Screening Analyses .......................................................................... 4-21 

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............................................................................................. 4-22 

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 ....................... 4-23 

4.9.2 Contribute to Workplan and Review Sampling and Analysis Plan .................. 4-23 
 

 

 

 

 

 

 

 

 

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4.9.3	 Conduct Interim Reviews of Field Investigation Outputs ................................ 4-24 

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 ....................................................................................................5-8 

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 
 

 

 

 

 

 

 

 

 

 

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5.10.2 Summarize Data Collection and Evaluation Results in
 

Tables and Graphics.......................................................................................... 5-27 

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 ........................................................................6-5 

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...................................................... 6-30 

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 
 

 

 

 

 

 

 

 

 

 

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6.8 EVALUATING UNCERTAINTY .................................................................................. 6-47 

6.9	 SUMMARIZING AND PRESENTING THE 

EXPOSURE ASSESSMENT RESULTS ....................................................................... 6-50 

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 (RfDo) ......................................................................7-6 

7.2.3 Derivation of an Inhalation RfD (RfDI)..............................................................7-8 

7.2.4 Derivation of a Subchronic RfD (RfDS) .............................................................7-8 

7.2.5 Derivation of Developmental Toxicant RfD (RfDdt) ..........................................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.......................................................................... 7-17 

7.6	 UNCERTAINTIES RELATED TO TOXICITY INFORMATION ............................... 7-17 

7.7	 SUMMARIZATION AND PRESENTATION OF THE 

TOXICITY INFORMATION ......................................................................................... 7-20 
 

 

 

 

 

 

 

 

 

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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 

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 SITESPECIFIC HUMAN STUDIES....................................... 8-22 

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
 

ASSESOR, 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 

10.7 RISK CHARACTERIZATION .....................................................................................10-32 
 

 

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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, REVIEWER, 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-1 

A.1	 ADJUSTMENTS OF TOXICITY VALUE FROM ADMINISTERED TO ABSORBED 

DOSE ............................................................................................................................... A-1 

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-1 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page xiii 

LIST OF EXHIBITS 

Exhibit Page 

1-1 Risk Information Activities in the RI/FS Process .........................................................................1-5
 

1-2 Part A: Baseeline 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 QAssessment ....5-6
 

5-4 CLP Laboratory Data Qualifiers and Their Potential Use In Quantitative Risk Assessment .....5-12
 

5-5 Validation Data Qualifiers and Their Potential Use in Quantitative Risk Assessment .............. 5-13
 

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 Watera
 

(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 .......6-44
 

6-19 Residential Exposure: Food Pathway – Ingestion of contaminated meat, 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 an 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 .................. 7-18
 

7-3 Example of Table Format for Toxicity Values: Potential Carcinogenic Effects ........................ 7-19
 

8-1 Steps in Risk Characterization ...................................................................................................... 8-3
 
 

 

 

Page xiv 

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 Example 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
 
 

 

 

 

 

Page xv 

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 Superfund. 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 

 

 

 

Comment [A3]: The latest revisions to the 

NCP were finalized in 1994. An overview of the 

final NCP and a link to the full text are available 

at: 

http://www.epa.gov/oem/content/lawsregs/ncp 

over.htm 

 

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 h uman 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 

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 
 

 

 

 

 

Page xvi 

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. 
 

 

 

 

 

 

 

 

 

Page xvii 

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. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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.1

 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 wellestablished 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).3 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 risks 4 

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 Investigations and 

Feasibility Studies Under CERCLA (EPA 

1988b) also was revised in 1988 to incorporate 

Comment [A4]: The latest revisions to the 

NCP were finalized in 1994. An overview of the 

final NCP and a link to the full text are available 

at: 

http://www.epa.gov/oem/content/lawsregs/ncp 

over.htm 
Page 1-2 

 

 

 

 

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 Superfund, 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 nontechnical personnel how to perform technical 

evaluations, nor to allow professionals trained in 

one discipline to perform the work of another. 

 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 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 

 

 

 

Comment [A5]: The latest revisions to the 

NCP were finalized in 1994. An overview of the 

final NCP and a link to the full text are available 

at: 

http://www.epa.gov/oem/content/lawsregs/ncp

over.htm 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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: 

	 baseline risk assessment (described in 

Part A of this manual); 

	 refinement of preliminary remediation 

goals (Part B); and 

	 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 

Page 1-3 

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 

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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 1-4 

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.) 

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; 

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 Chapter 3 for information 

on planning the human health evaluation.) 

	 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: 
 Page 1-5 

EXHIBIT 1-1 

RISK INFORMATION ACTIVITIES IN THE RI/FS PROCESS
 
 

 

 

 

 

 

 

 

 

 

 

 

 

Page 1-6 

	 help determine whether additional 

response action is necessary at the site; 

	 modify preliminary remediation goals; 

	 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, doseresponse 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.) 
Page 1-7 

E XHIBIT 1-2

PARTA: BASEELINE RISK ASSESSMENT 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 1-8 

 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 

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 chemicalspecific 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 

Comment [A6]: The latest revisions to the 

NCP were finalized in 1994. An overview of the 

final NCP and a link to the full text are available 

at: 

http://www.epa.gov/oem/content/lawsregs/ncp 

over.htm 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 1-9 

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 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 groundwater 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 tradeoffs 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. 
Page 1-10 

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 longterm 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 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

is an index. 

making absorption adjustments and Appendix B Comment [A7]: The index in Appendix B may 

not reflect the true page numbers of this annotated 

version. 
 

 

 

 

 

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. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 Mutagenicity Risk Assessment. 51 Federal Register 34006 (September 

24, 1986). 

Environmental Protection Agency (EPA). 1986d. Guidelines for 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/540/1-89/001A. (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). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 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. 
 

 

Comprehensive Environmental Response,

Compensation, and Liability Act of 1980. 

(CERCLA or Superfund) 

Superfund Amendments and 

Reauthorization Act of 1986 (SARA) 

Regulation ("Blueprint" for 

Implementing the Statutes) 

Statutes

Guidance

RI/FS Guidance 

Risk Assessment Guidance for Superfund (RAGS) 

• Human Health Evaluation Manual (HHEM) 

• Environmental Evaluation Manual (REM) 

ARARs Guidance 

Superfund Exposure Assessment Manual (SEAM)

National Oil and Hazardous Substances 

Pollution Contingency Plan (NCP) 

Page 2-2 

EXHIBIT 2-1 

RELATIONSHIP OF DOCUMENTS GOVERNING
 

HUMAN HEALTH EVALUATION 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 costeffective, 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 

Page 2-3 

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 diseases that may be 

associated with the observed levels of 

exposure. The Administrator of ATSDR 

shall use appropriate data, risk assessments, 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 2-4 

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 toxicological data are 

unavailable, rely on the results of animal 

toxicology studies. 

2.1.2 NATIONAL CONTINGENCY PLAN 

(NCP) Comment [A8]: The latest revisions to the 

NCP were finalized in 1994. An overview of the 

final NCP and a link to the full text are available 

at: 

http://www.epa.gov/oem/content/lawsregs/ncp 

over.htm 

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 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 Superfundfinanced 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 

Page 2-5 

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 
 

Page 2-6 

EXHIBIT 2-2 

ROLE OF THE HUMAN HEALTH EVALUATION IN 

THE SUPERFUND REMEDIAL PROCESS 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

conducting field studies to support remedial 

decisions and for identifying, evaluating, 

and selecting remedial action alternatives 

under CERCLA. This 1988 guidance 

document is a 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 1988d; EPA 

Page 2-7 

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, locationspecific, and action-specific requirements 

from RCRA, CWA, and SDWA, and 

provides general procedures for identifying 

and analyzing requirements; 

	 discusses special issues of interpretation and 

analysis involving RCRA requirements, and 

provides guidance on when RCRA 

requirements will be ARARs for CERCLA 

remedial actions; 

	 provides guidance for compliance with 

CWA substantive (for onsite and offsite 

actions) and administrative (for offsite 

actions) requirements for direct discharges, 

indirect discharges, and dredge and fill 

activities; 

	 provides guidance for compliance with 

requirements of the SDWA that may be 

applicable or relevant and appropriate to 

CERCLA sites; and 

	 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: 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 2-8 

	 Chapter 1 provides an introduction to 

Part II of the guidance, and also includes 

extensive summary tables; 

	 describes Clean Air Act requirements 

and related RCRA and state 

requirements; 

	 Chapters 3 and 4 provide guidance for 

compliance with several other federal 

statutes; 

	 discusses potential ARARs for sites 

contaminated with radioactive 

substances; 

	 addresses requirements specific to 

mining, milling, or smelting sites; and 

	 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 

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 

Page 2-9 

	 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 

CERCLA section 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); 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 2-10 

(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 

recommendations regarding further public 

health activities. 

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 healthrelated 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, substancespecific 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 

Superfund 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 

Page 2-11 

exposed to hazardous substances and persons 

with serious diseases or 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. 
 

 

 

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/540/1-86/060. (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/540/188/001. (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. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 health evaluation easier to 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 3-2 

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, 

nonstandard 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 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 

. 

Page 3-3 

	 quality and quantity of available 

monitoring data.1 

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 assessment 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. 
 

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). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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.1 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; 

	 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: 

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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 (DQOs). 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 (QAPjP). 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. 

	 characteristics of sources, especially 

preliminary assessment/site inspection 

(PA/SI) information related to release 

potential; reports, also may be available. 

and 

	 characteristics of the environmental 

setting that may affect the fate, transport 

and persistence of the contaminants. 

4.1.2 DATA NEEDS AND THE RI/FS 

The RI/FS has four primary data collection 

components: 

(1) characterization of site conditions; 

(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" benchscale 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 

Page 4-3 

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 nonroutine (i.e., lower) quantitation limits are 

needed to adequately characterize risks at a site. 

Special Analytical Services (SAS) of the EPA 

Contract Laboratory Program (CLP) may be 

needed to achieve such lower quantitation limits. 

(See Section 4.8 for additional information 

concerning quantitation limits.) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 4-4 

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). 

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 

Page 4-5

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., 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). 

 

Comment [A9]: The information on 

background sampling presented in this 

document is supplemented by EPA's Guidance 

for Comparing Background and Chemical 

Concentrations in Soil for CERCLA Sites. This 

guidance presents information on determining 

whether collecting background samples is 

necessary; when, where, and how to collect 

background samples; and how to evaluate 

background data. 

The Guidance for Comparing Background and 

Chemical Concentrations in Soil for CERCLA 

Sites may be found at: 

http://www.epa.gov/oswer/riskassessment/pdf/

background.pdf 
Page 4-6 

EXHIBIT 4-1 

ELEMENTS OF A CONCEPTUAL EVALUATION MODEL 

SOURCES 

Variables 

CONTAMINANTS 

CONCENTRATIONS 

TIME 

LOCATIONS 

Hypotheses to be Tested 

  SOURCE EXISTS 

  SOURCE CAN BE 

 CONTAINED 

  SOURCE CAN BE 

REMOVED AND 

DISPOSED 

 SOURCE CAN BE 

TREATED 

P 

A 

T 

H 

W 

A 

Y 

 MEDIA  PATHWAY EXISTS 

 RATES OF MIGRATION  PATHWAY CAN BE
 

 TIME INTERRUPTED 

 LOSS AND GAIN  PATHWAY CAN BE
 

FUNCTIONS ELIMINATED 

RECEPTORS 

	 RECEPTOR IS NOT 

IMPACTED BE 

MIGRATION OF 

 TYPES CONTAMINANTS 

 SENSITIVITIES 	 RECEPTOR CAN BE 

 TIME RELOCATED 

 CONCENTRATION  INSTITUTIONAL 

 NUMBRS CONTROLS CAN BE 

APPLIED 

	 RECEPTOR CAN BE 

PROTECTED 
 

 

Page 4-7 

EXHIBIT 4-2 

EXAMPLES OF MODELING PARAMETERS FOR WHICH
 

INFORMATION MAY NEED TO BE OBTAINED DURING 

A SITE SAMPLING INVESTIGATION 

Type of Modeling Modeling Parameters 

Source Characteristics Geometry, physical/chemical conditions, emission rate, emission 

strength, geography 

Soil Particle size, dry weight, pH, redox potential, mineral class, 

organic carbon and clay content, bulk density, soil porosity 

Ground-water Head measurements, hydraulic conductivity (pump and slug test 

results), saturated thickness of aquifer, hydraulic gradient, pH, 

redox potential, soil-water partitioning 

Air 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 

Surface Water 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 

Sediment Particle size distribution, organic content, pH, benthic oxygen 

conditions, water content 

Biota Dry weight, whole body, specific organ, and/or edible portion 

chemical concentrations, percent moisture, lipid content, 

size/age, life history stage 

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. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 4-8 

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.) 

Comment [A10]: Supplemental information 

on the use of statistical tests to evaluate 

background sample data may be found in EPA’s 

Guidance for Comparing Background and 

Chemical Concentrations in Soil for CERCLA 

Sites. 

http://www.epa.gov/oswer/riskassessment/pdf/ 

background.pdf 

Comment [A11]: The statistical software 

package ProUCL includes statistical methods 

that can be used to estimate exposure point 

concentration (EPC) terms, not-to-exceed, and 

background threshold values (BTVs). ProUCL 

4.0 addresses various statistical issues arising 

in: exposure and risk assessment studies, in 

background evaluations, and in background 

versus site comparison applications. It also has 

statistical methods that can be used to verify 

the attainment of cleanup standards and to 

estimate screening levels. ProUCL may be found 

on EPA’s website at: 

http://www.epa.gov/osp/hstl/tsc/software.htm 

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. 

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 Sampling Quality Assurance Guide 

(EPA 1989b) 

error could result in a failure to clean up a site 

when such an action is necessary. 

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 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 4-9 

In customary notations, α (alpha) denotes 

the probability that a Type I error will occur, and 

β (beta) denotes the probability that a Type II 

error will occur. Most statistical comparisons 

refer to α, also known as the level of 

significance of the test. If α = 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 β and a concept called "power." The power 

of a statistical test has the value 1 - β 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 α (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., β = 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 siterelated, 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 α = 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 siterelated 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. 

Comment [A12]: Supplemental information 

on considerations in comparing site and 

background data may be found in EPA’s 

Guidance for Comparing Background and 

Chemical Concentrations in Soil for CERCLA 

Sites. 

http://www.epa.gov/oswer/riskassessment/pdf/ 

background.pdf 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 4-10 

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 toxicological --

rather than simply the statistical -- significance 

of the contamination can be ascertained. 

4.5 PRELIMINARY IDENTIFICATION 

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 (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 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+3 versus Cr+6), 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 

Page 4-11 

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 

(SW846): Physical/Chemical Methods (EPA 

1986a) 

Field Manual for Grid Sampling of PCB 

Spill Sites to Verify Cleanups (EPA 1986b) 

A Compendium of Superfund 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. 
Page 4-12 

 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 

groundwater 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 Superfund Field 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 concentrations in unfiltered versus 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 4-13

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 particulate matter and not dissolved 

in the ground water. This information on the 

form of chemical (i.e., dissolved or suspended 

on particulate 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 references given in the 

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 of Superfund 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 4-14 

box below. 

 Lotic waters. Lotic waters are fastmoving 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 slowmoving 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 salinitystratification, 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 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 procedures, 

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. 

Page 4-15 

 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 modeling. When 

evaluating long-term inhalation exposures, 

sample results should be representative of the 

long-term average air concentrations at the longterm exposure points. This requires an air 

sampling plan of sufficient temporal scale to 

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. 

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 1988f) 

 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 4-16 

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 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 of Superfund 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, 

Comment [A13]: The information on 

developing a strategy for sample collection 

presented in this document is complemented by 

EPA's Guidance for Data Useability in Risk 

Assessment (Part A). This guidance is designed 

to provide data users with a nationally 

consistent basis for making decisions about the 

minimum quality and quantity of environmental 

analytical data that are sufficient to support 

Superfund risk assessment decisions. It 

includes information on determining the number 

of samples collected and applicability of 

alternative sampling designs, and a sampling 

design worksheet. 

EPA’s Guidance for Data Useability in Risk 

Assessment (Part A) may be found at: 

http://www.epa.gov/oswer/riskassessment/data 

use/parta.htm 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 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 

Page 4-17 

SAMPLING STRATEGY GUIDANCE 

Test Methods for Evaluating Solid Waste 

(SW846): 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: RI/FS 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 Superfund Cleanup Standards: Volume 1, Soils 

and Solid Media (EPA 1988f) 

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 

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 

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 

Comment [A14]: Additional statistical 

methods guidance is provided in EPA’s Guidance 

for Data Useability in Risk Assessment (Part A), 

published in 1992. 

http://www.epa.gov/oswer/riskassessment/data 

use/parta.htm 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 4-18 

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 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., α), 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., α

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 

Comment [A15]: For additional information 

on the applicability of different sampling 

designs, see Section 4.1 of EPA’s Guidance for 

Data Useability in Risk Assessment (Part A). 

This guidance may be found at: 

http://www.epa.gov/oswer/riskassessment/data 

use/parta.htm 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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, 

groundwater monitoring well locations, 

continuous air monitor locations, and soil 

sample 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 

Page 4-19 

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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 4-20 

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 

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 groundwater wells or air monitors) actually are time 

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. 

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 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 4-21 

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 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 

groundwater 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. 

 

 

Comment [A16]: For additional information 

on the use of field analyses versus fixed 

laboratory analyses, see the following 

resources: 

- Section 3.2.9 of EPA’s Guidance for Data 

Useability in Risk Assessment (Part A). This 

guidance may be found at: 

http://www.epa.gov/oswer/riskassessment/dat 

ause/parta.htm 

- EPA's website for Field-based Analytical 

Methods at: 

http://www.epa.gov/superfund/programs/dfa/fl 

dmeth.htm#hand 

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, 

(EMSLLV) 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 4-22 

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 groundwater samples, organic chemicals may be 

adsorbed to the well materials and not be present 

in the collected sample. 

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. 

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 

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 1988i). 

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 ole involves three main 

steps: 

Comment [A17]: For additional information 

on selecting analytical methods, including the 

use of routine and non-routine methods and a 

method selection worksheet, see Section 4.2 of 

EPA’s Guidance for Data Useability in Risk 

Assessment (Part A). This guidance may be 

found at: 

http://www.epa.gov/oswer/riskassessment/data 

use/parta.htm 

Comment [A18]: For additional information 

about the role of the risk assessor during 

workplan development, including the 

development of the Sampling and Analysis Plan 

(SAP) and Quality Assurance Project Plan 

(QAPP), see Section 2.2 of EPA’s Risk 

Assessment Guidance for Superfund Volume I: 

Human Health Evaluation Manual (Part D, 

Standardized Planning, Reporting, and Review 

of Superfund Risk Assessments.) RAGS, Part D 

may be found at: 

http://www.epa.gov/oswer/riskassessment/rags 

d/index.htm 

(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. 

4.9.1 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 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 

Page 4-23 

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 

o	 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, 

o	 data needs for statistical analysis of 

the above, and 

o	 data needs for fate and transport 

models; 

	 sample analysis/validation, especially 

with respect to 

o chemicals of concern, and 

o 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 4-24 

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. 

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. 
 

 

 

 

 

 

 

 

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. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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. 

Environmental Protection Agency (EPA). 1986c. Resource Conservation and Recovery Act (RCRA) Ground-water Monitoring 

Technical Enforcement Guidance Document. Office of Waste Programs Enforcement. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 4-27 

	 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 RI/FS-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. 

Environmental Protection Agency (EPA). 1988b. Statistical Methods for Evaluating Ground Water from Hazardous Waste Facilities. 

Office of Solid Waste. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 4-28 

 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 Habitability 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. 

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/450/189/001. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 4-29 

	 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). 1989i. 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 Comment [A19]: For additional information on 

assessing and interpreting data for use in baseline 

human health risk assessments, see Chapter 5 of 

EPA’s Guidance for Data Useability in Risk 

Assessment (Part A). This guidance may be found at: 

http://www.epa.gov/oswer/riskassessment/datause/pa 

rta.htm 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 espect 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 sitespecific 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 

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. 

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 (DL). The lowest amount that can be distinguished from the normal "noise" of an analytical instrument or method. 

Non-detects (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. 

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." 

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. 
 Page 5-3

 

 

 

 

 

 

 

 

 

 

 

 

Is 

quantitation limit (QL) 

> health-based reference 

concentration? 

No 

Yes 

Eliminate data associated with 

inappropriate methods. Possibly use 

qualitatively in other risk 

assessment sections. 

Sampling data from each 

medium of concern 

(Sec. 5.1) 

If QL cannot be reduced, use QL 

or 1⁄2 QL as proxy concentration, 

or eliminate chemical in sample, 

as appropriate. 

Analytical 

method appropriate 

for quantitative 

risk assessment 

(Sec. 5.1)? 

Yes 

Yes 

Is a 

chemical not detected No 

in a sample 

(Sec. 5.1)? 

Is QL unusually high? 

Do other 

samples in same 

medium test 

positive? 

No 

Yes 

No 

Use QL or 1⁄2 QL as 

proxy concentration. 

Generally eliminate 

chemical. 

Yes 

Reanalyze or address 

qualitatively, as appropriate. 

NOTE: See text for details 

concerning specific 

steps in this flowchart. 

Qualifiers Evaluate qualified data, and and codes eliminate, modify, or leave data as attached to data? they are, as appropriate. (Sec.5.4) 

No 

Blank Sample Yes Yes contamination Common lab No concentration ≥ 10x 

(Sec. 5.5)? Contaminants? blank concentration? 

No 

Sample 

concentration ≥ 5x No Eliminate blank 

blank concentration contaminants. 

? 

Yes 

Expected Many to be present tentatively identified Yes Yes and are primary compounds (TICs; contaminants Sec. 5.6)? at site 

? 

No No 

Eliminate TICs (as appropriate).. 

Use SAS, if possible, to confirm identity and concentration; 

otherwise, use TICs as they are (as appropriate). 

Site Chemicals of potential No chemicals equal to Yes Calculate risk of background chemicals Concern for quantitative background Separately from site-related chemicals. risk assessment. (Sec. 5.7)? 

EXHIBIT 5-1 

DATA EVALUATION 
 

 

Area X 

Sample Medium Soil Soil Soil 

Sample ID SRB-3-1 SRB-3-1DU SRB-3-2 

Sample or Screen 0-1’ 0-1’ 2-4’ 

Depth 

Date Collected 12/14/87 12/14/87 12/10/87 

Units μg/kg μg/kg μg/kg 

Blanks or Duplicates Duplicate 

 

 

 

Q Chemical CRQLa

 Concentration Qualifierb CRQLa ualifier Concentration Qualifierb CRQLa Concentration b 

Aroclor-1016 80 80 U 80 80 U 2000c 2000 UJ 

Aroclor-1221 80 80 U 80 80 U 2000c 2000 UJ 

Aroclor-1232 80 80 U 80 80 U 2000c 2000 UJ 

Aroclor-1242 80 40 J 80 42 J 2000c 2000 UJ 

Aroclor-1248 80 30 J 80 36 J 2000c 2000 UJ 

Aroclor-1254 160 120 J 160 110 J 2000c 1800 J 

Aroclor-1260 160 210 160 220 2000c 2100 

 

 

 

c 

Page 5-4 

EXHIBIT 5-2 

EXAMPLE OF OUTPUT FORMAT FOR VALIDATED DATA
 

Note: All values other than qualifiers must be entered as numbers, not as labels. a Contract-required quantitation limit (unless otherwise noted). Values for illustration only. b Refer to Section 5.4 for an explanation of qualifiers. 

Sample quantitation unit. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 

Page 5-5 

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 organics), 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. 
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, Field Screen Total Organic Vapor 

Organic Vapor Analyzer Health and Safety, Field Screen Total Organic Vapor 

Combustible Gas Indicator Health and Safety Combustible Vapors, 

Oxygen-deficient 

Atmosphere 

Field Gas Chromatography a Field Screen/Analytical Method Specific Volatile and Semivolatile Organic Chemicals 

 

a Depending on the detector used, this instrument can be sufficiently sensitive to yield adequate data 

for use in 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. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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., SW846 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 

Page 5-7 

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. 

Comment [A20]: For additional information 

on assessing data quality indicators and 

interpretation of qualified and coded data, see 

Section 5.6 of EPA’s Guidance for Data 

Useability in Risk Assessment (Part A). This 

guidance may be found at: 

http://www.epa.gov/oswer/riskassessment/data 

use/parta.htm 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 5-8 

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 

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 contractrequired quantitation limits (CRQLs) exceed the 

corresponding reference concentrations for 

noncarcinogenic effects, based on the EPAverified reference dose and a 2-liter per day 

ingestion by a 70-kilogram person.1 Estimation 

of cancer risks for several other chemicals (e.g., 

arsenic, styrene) at their CRQLs yields cancer 

risks exceeding 10-4, 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 EPAderived 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 

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 IDL 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. 
 Page 5-9

and TAL, and to develop an analytical 

service for chemicals with special 

standards (e.g., MCLs). 

(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 reanalyze selected samples 

using SAS, if time allows, or address the

chemical qualitatively. In determining which

option is most appropriate for a site, a screeninglevel 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 5-10 

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 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 exceed health-based standards or criteria, 

they may still present problems. If the SQLs 

EXAMPLE OF UNUSUALLY HIGH
 

QUANTIFICATION 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 

μg/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. 

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 concentration 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 nondetected results from the risk assessment. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 

Page 5-11 

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. 

Comment [A21]: For additional information 

on assessing data quality indicators and 

interpretation of qualified and coded data, see 

Section 5.6 of EPA’s Guidance for Data 

Useability in Risk Assessment (Part A). This 

guidance may be found at: 

http://www.epa.gov/oswer/riskassessment/data 

use/parta.htm 
Page 5-12 

EXHIBIT 5-4 

CLP LABORATORY DATA QUALIFIERS AND THEIR POTENTIAL USE 

IN QUANTITATIVE RISK ASSESSMENT
 

Indicates: Include Data in 

Uncertain Uncertain Quantitative Risk 

Qualifier Definition Identity Concentration? Assessment? 

 

 

 

 

 

 

Inorganic Chemical Data:

a 

B Reported value is <CRDL, but No No Yes

>IDL. 

U Compound was analyzed for, Yes Yes ? 

but not detected. 

E Value is estimated due to No Yes Yes

matrix interferences. 

M Duplicate injection precision No Yes Yes

criteria not met. 

N Spiked sample recovery not No Yes Yes

within control limits. 

S Reported value was determined No No Yes

by the Method of Standard

 Additions (MSA). 

W Post-digestion spike for furnace No Yes Yes

AA analysis is out of control 

limits, while sample absorbance 

is <50% of spike absorbance. 

* Duplicate analysis was not No Yes Yes

within control limits. 

+ Correlation coefficient for MSA Yes Yes ? 

was <0.995. 

Organic Chemical Data:

b 

U Compound was analyzed for, Yes Yes ? 

but not detected. 

(continued) 
 

 

 

 

 

Page 5-13 

EXHIBIT 5-4 (CONTINUED)
 

CLP LABORATORY DATA QUALIFIERS AND THEIR POTENTIAL USE
 

IN QUANTITATIVE RISK ASSESSMENT
 

Indicates: Include Data in 

Uncertain Uncertain Quantitative Risk 

Qualifier Definition Identity Concentration? Assessment? 

J Value is estimated, either for a No, for TCL No Yes 

tentatively identified chemicals; 

compound (TIC) or when a 

compound is present (spectral 

identification criteria are met, 

but the value is <CRQL). 

C Pesticide results were Yes, for TICs Yes ? 

confirmed by GC/MS. 

B Analyte found in associated No No Yes 

blank as well as in sample.c 

E Concentration exceeds No Yes Yes 

calibration range of GC/MS 

instrument. 

D Compound identified in an No No Yes 

analysis at a secondary 

dilution factor. 

A The TIC is a suspected aldol­ Yes No Yes 

condensation product. 

X Additional flags defined — — — 

separately. 

— = Data will vary with laboratory conducting analyses. 

a

 Source: EPA 1988b. 

b

 Source: EPA 1988c. See Section 5.5 for guidance concerning blank contamination. Exhibit 5-5 

Validation Data Qualifiers and Their 

Potential Use in Quantitative Risk Assessment 
 

Page 5-14 

EXHIBIT 5-5 

VALIDATION DATA QUALIFIERS AND THEIR 

POTENTIAL USE IN QUANTITATIVE RISK ASSESSMENT
 

Indicates: Include Data in 

Uncertain Uncertain Quantitative Risk 

Qualifier Definition Identity Concentration? Assessment? 

Inorganic and Organic Chemical Data:

a 

U The material was analyzed Yes Yes ? 

for, but not detected. The 

associated numerical value 

is the SQL. 

J The associated numerical No Yes Yes

value is an estimated 

quantity. 

R Quality control indicates No Yes Yes

that 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 No Yes Yes

(inorganic data only). 

Q No analytical result No No Yes

(organic data only). 

N Presumptive evidence of No Yes Yes

presence of material 

(tentative identification).b 

– = Not applicable 

a Source: EPA 1988d,e. 

b Organic chemical data only 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 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 sitespecific factors determine how qualified data are 

to be used in a risk assessment. As seen in 

Exhibits 54 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 

EXAMPLE OF J QUALIFIERS 

In this example, concentrations of volatile organic 

chemicals in ground water have been determined using 

the CLP's RAS. 

Concentration (μg/L) 

Chemical Sample 1 Sample 2 Sample 3 Sample 4 

Tetrachloroethene 14,000 Ja 40 30 Ub 20 J 

a

 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 μg/1, 40 μg/1, and 20 μg/1; 

therefore, these concentrations – as well as the nondetect – should be used in determining representative 

concentrations. 

Page 5-15 

concentrations the same way as 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. 

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 not by the validator), then use the Rqualified data in a manner similar to the use of Jqualified 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 

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 (μg/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 
 

 

 

 

 

 

 

 

 

 

 

 

Page 5-16 

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, 

2butanone (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 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 the 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). 

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. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 byproduct 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 risk 

assessment, and document reasons for excluding 

TICs in the risk assessment report. 

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 SVOCs 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. 

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] reports). As discussed in 

Comment [A22]: Supplemental information on 

use of statistical methods in comparing site and 

background data may be found in EPA’s Guidance 

for Comparing Background and Chemical 

Concentrations in Soil for CERCLA Sites at: 

http://www.epa.gov/oswer/riskassessment/pdf/backg 

round.pdf 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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, 

Page 5-19 

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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 5-20 

background chemicals from the risk assessment 

could result in the loss of important information 

for those potentially exposed. 

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 siterelated 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 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 weightof-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, 

Page 5-21 

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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 5-22 

to implementing any of these optional screening 

procedures at a particular site. 

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 underestimates 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 

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]). 

Page 5-23 

 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 CONCENTRATIONTOXICITY 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 

INDIVIDUAL CHEMICAL SCORES

 Rij = (Cij)(Tij) 

where: 

Rij = risk factor for chemical i in medium j; 

Cij = concentration of chemical i in medium j; 

and 

Tij = toxicity value for chemical i in medium j 

(i.e., either the slope factor or 1/RfD). 

concentrations at the site and its toxicity. 

Therefore, in this screening procedure, each 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 5-24 

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. 

The units for the risk factor Rij 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 Rj will be 

calculated for carcinogenic and noncarcinogenic 

effects. The ratio of the risk factor for each 

chemical to the total risk factor (i.e., Rij/Rj) 

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 Rij/Rj ratios that are 

very low compared with the ratios of other 

chemicals in the medium. The RPM may wish to 

TOTAL CHEMICAL SCORES 

R = R1j + R2j + R3j + . . . + Rij 

where 

Rj = total risk factor for medium j; and 

R1j + . . . + Rij = risk factors for chemicals 1 through i 

in medium j. 

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 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. 

Comment [A23]: EPA’s Risk Assessment 

Guidance for Superfund Volume I: Human Health 

Evaluation Manual (Part D, Standardized Planning, 

Reporting, and Review of Superfund Risk 

Assessments) provides planning tables for use during 

the risk assessment process, including the data 

evaluation stages. See Part D, Section 3.1.1 (page 3­

4) for an overview of using Planning Table 2: 

Occurrence, Distribution, and Selection of COPCs. 

Also see Appendix A for the downloadable Planning 

Table 2 template and instructions for completing 

Table 2. RAGS, Part D may be found at: 

http://www.epa.gov/oswer/riskassessment/ragsd/inde 

x.htm. 
 

 

 

 

 

 

 

Page 5-25 

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 

 

Range of Sample Range of Detected 

Frequency of Quantitation Concentrations Background 

Chemical Detectiona Limits (units) (units) Levels 

Chemical A 3/25 5 – 50 320 – 4600 100 – 140 

* Chemical B 25/25 1 – 32 16 – 72 – 

– = 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. 
 

 

 

 

 

 

 

 

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 

Soils Ground Water Surface Water Sediments Air 

Chemical (mg/kg) (μg/L) (μg/L) (μg/kg) (μg/m3

) 

Chemical A 5 – 1,100 – 2 – 30 – – 

Chemical B 0.5 – 64 5 – 92 – 100 – 45,000 – 

Chemical C – 15 – 890 50 – 11,000 – – 

Chemical D 2 – 12 – – – 0.1 – 940 

– = Not available. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 

Page 5-27 

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 
 

 

 

 

 

 

 

 

 

 

 

 

 

Page 5-28 

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 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. 
 

 

 

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-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 

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, Multiconcentration. 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, Multiconcentration. 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 doseresponse 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. 
 Page 5-31

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CHAPTER 6
 

EXPOSURE ASSESSMENT 

Comment [A24]: EPA has developed additional 

information concerning exposure and risk 

assessment for lead and asbestos to supplement the 

information presented in RAGS Part A. This 

information is needed because there are a number of 

unique scientific and technical issues associated with 

the investigation of human exposure and risk from 

these contaminants. This information on lead and 

asbestos at Superfund sites may be found at: 

http://www.epa.gov/superfund/health/contaminants/a 

sbestos/ 

http://www.epa.gov/superfund/health/contaminants/l 

ead/ 

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 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. 

ACRONYMS FOR CHAPTER 6 

ATSDR = Agency for Toxic Substances and Disease 

Registry 

BCF = Bioconcentration Factor 

CDI = 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 = Subchronic Daily Intake 

SEAM = Superfund Exposure Assessment Manual 

USGS = U.S. Geological Survey 
Page 6-2 

Absorbed Dose. The amount of a substance penetrating the exchange boundaries of a

is calculated from the intake and the absorption efficiency. It usually is exp

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 wit

gastrointestinal tract) per unit body weight per unit time (e.g., mg/kg-day). 

 

n organism after contact. Absorbed dose 

ressed as mass of a substance absorbed 

h an exchange boundary (e.g., 

Applied Dose. The amount of a substance given to an organism, especially through d

Chronic Daily Intake (CDI). Exposure expressed as mass of a substance contacted pe

averaged over a long period of time (as aSuperfund program guideline, sev

Contact Rate. Amount of medium (e.g., ground water, soil) contacted per unit time or

day). 

Exposure. Contact of an organism with a chemical or physical agent. Exposure is qua

available at the exchange boundaries of the organism (e.g., skin, lungs, gut) 

Exposure Assessment. The determination or estimation (qualitative or quantitative) o

and route of exposure. 

 

 

 

 

 

 

 

 

 

ermal contact. 

r unit body weight per unit time, 

en years to a lifetime). 

 event (e.g. liters of water ingested per 

ntified as the amount of the agent 

 and available for absorption. 

f the magnitude, frequency, duration, 

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 (SDI). Exposure expressed as mass of a substance contacted per unit body weight per unit time, 

averaged over a portion of a lifetime (as aSuperfund program guideline, two weeks to seven years). 

DEFINITIONS FOR CHAPTER 6 

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 potential future populations that

may differ under an alternate land use. 
 

 

EXHIBIT 6-1 

THE EXPOSURE ASSESSMENT PROCESS
 
 

 

 

 

 

 

 

 

 

 

 

 

Page 6-4 

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. 

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 

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 

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 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 also 

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 upperbound 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 

Page 6-5 

uncertainty in the exposure estimate are more 

easily identified. 

6.2 STEP 1: CHARACTERIZATION 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 6-6 

maps, aerial 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 RI; 

	 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 userelated 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, 

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 example, 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. 

Page 6-7 

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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 6-8 

that may be 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. 
 Page 6-9 

EXHIBIT 6-2 

ILLUSTRATION OF EXPOSURE PATHWAYS
 
 

Page 6-10 

EXHIBIT 6-3 

COMMON CHEMICAL RELEASE SOURCES AT
 

SITES IN THE ABSENCE OF REMEDIAL ACTION 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 mediaspecific 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 

Page 6-11 

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 sitespecific 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 sailor 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, nnadjnsted for dependence upon organic carbon. To adjust for 

the fracti(m of organic carh(m present in soil or sediment (foc), use Kd = Koc x foc. The 

higher the Kd, the more likely a chemical is to bind to soil or sediment than to remain in 

water. 

Kow	 provides a measure of the extent of chemical partitioning between water and octanol at 

equilibrinm. The greater the Kow 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 nonaqueous phase liquid. 

Henry's Law Constant provides a measure of the cxtent of chemical partitioning between aIr and 

water at equilibrinm. The higher the Henry's Law constant, the more likely a chemical is to 

volatize than to remain in 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 ReF, 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 

(continued) 
 Page 6-15 
Page 6-16 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 

Page 6-17 

	 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) and also is useful as documentation of 

the exposure pathway analysis. Exhibit 6-8 

provides a sample format for presenting this 

information. 
 

 

EXHIBIT 6-7 

MATRIX OF POTENTIAL EXPOSURE ROUTES
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 pathwayspecific 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 

assessment-determined variable -­

averaging time. 

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 

Page 6-19 

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 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. 
 

 

 

 EXHIBIT 6-8 

EXAMPLE OF TABLE FORMAT FOR SUMMARIZING
 

COMPLETE EXPOSURE PATHWAYS AT A SITE
 
 

 

 

Page 6-21 

EXHIBIT 6-9 

GENERIC EQUATION FOR CALCULATING CHEMICAL INTAKES
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 6-22 

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 constant, error from this 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 6-23 

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 doserate 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

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: 

DETERMINATION 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) 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 

Page 6-25 

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 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 6-26 

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-steadystate 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 groundwater 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 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, groundwater 

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, 

Page 6-27 

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 

groundwater 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 groundwater 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 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 6-28 

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 shortterm 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. 

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 
 Page 6-29

 

 

 

 

 

 

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 outdoorgenerated 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 shortterm 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 

should be examined relative to surface water 

mixing zones. Concentrations within the 

mixing zone may be significantly higher 

 

 

Comment [A25]: For more information on 

conducting screening evaluations of the 

transport of vapors indoors see EPA’s Draft 

Guidance for Evaluating the Vapor Intrusion 

Pathway form Groundwater and Soils 

(Subsurface Vapor Intrusion Guidance). This 

guidance may be found at: 

http://www.epa.gov/osw/hazard/correctiveaction/

eis/vapor/complete.pdf
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 6-30 

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 

groundwater 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 siterelated 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 nonpoint 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. 

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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 6-31 

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 (Kow). 

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 Kow 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 

Kow 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 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 6-32 

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 cropspecific (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 Kow 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 Kow 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 

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. 
 

 

Page 6-33 

EXHIBIT 6-10
 

EXAMPLE OF TABLE FORMAT FOR SUMMARIZING EXPOSURE CONCENTRATIONS
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 6-34 

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 chemicalspecific 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., 8.4x10 ­

4

cm/hr].) Note that this approach may 

underestimate dermal permeability for some 

organic chemicals. 

Comment [A26]: EPA has supplemented the 

general guidance for evaluating dermal exposure 

provided in RAGS Part A with procedures for 

estimating permeability coefficients of toxic 

chemicals and for evaluating the dermal absorbed 

dose. These procedures may be found in Risk 

Assessment Guide for Superfund Part E, 

Supplemental Guidance for dermal Risk Assessment. 

Please consult Section 3.1 for a description of these 

procedures and specific equations for estimating 

dermal exposures to chemicals in water. RAGS Part 

E may be found at: 

http://epa.gov/oswer/riskassessment/ragse/index.htm 
 

 

 

 

Page 6-35 

EXHIBIT 6-11 

RESIDENTIAL EXPOSURE: INGESTION OF
 

CHEMICALS IN DRINKING WATERA
 

(AND BEVERAGES MADE USING DRINKING WATER)
 
Page 6-36 

EXHIBIT 6-12
 

RESIDENTIAL EXPOSURE:
 

INGESTION OF CHEMICALS IN SURFACE WATER 

WHILE SWIMMINGA
 
 Page 6-37

EXHIBIT 6-13 Comment [A27]: EPA’s Risk Assessment 

Guidance for Superfund Volume I: Human 

Health Evaluation Manual (Part B, Development 

of Risk-based Preliminary Remediation Goals) 

provides instructions for evaluating the 

inhalation of volatiles from a range of 

household water uses (e.g., s howering, 

laundering, dish washing) -- see Section 3.1.1. 

RAGS Part B may be found at: 

http://www.epa.gov/oswer/riskassessment/ragsb 

Comment [A28]: EPA has supplemented the 

general guidance for evaluating dermal 

exposure provided in RAGS Part A. Updated 

procedures and equations for evaluating the 

dermal absorbed dose for chemicals in water 

may be found in found in Risk Assessment 

Guide for Superfund Part E, Supplemental 

Guidance for Dermal Risk Assessment. Please 

consult Section 3.1, Equation 3.1 for a 

description of these procedures and the specific 

equation for estimating dermal exposures to 

chemicals in water. RAGS Part E may be found 

at: http://epa.gov/oswer/riskassessment/ragse/in

dex.htm

RESIDENTIAL EXPOSURE:
 

DERMAL CONTACT WITH CHEMICALS IN WATERA
 
 

Page 6-38 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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. Comment [A29]: EPA has supplemented the 

general guidance for evaluating dermal 

exposure provided in RAGS Part A with 

procedures for estimating permeability 

coefficients of toxic chemicals and for 

evaluating the dermal absorbed dose. These 

procedures can be found in Risk Assessment 

Guide for Superfund (Part E, Supplemental 

Guidance for Dermal Risk Assessment). Please 

consult Section 3.2 for a description of these 

procedures and specific equations for 

estimating dermal exposures to chemicals in 

soil. RAGS Part E may be found at: 

http://epa.gov/oswer/riskassessment/ragse/ind 

ex.htm 

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 

Page 6-39 

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. 
 

 

 

Page 6-40 

EXHIBIT 6-14
 

RESIDENTIAL EXPOSURE:
 

INGESTION OF CHEMICALS IN SOILA
 

Comment [A30]: EPA’s Supplemental 

Guidance for Developing Soil Screening Levels 

for Superfund Sites provides updated equations 

for residential exposure that combine ingestion 

and dermal absorption. It also presents new 

methods for evaluating non-residential 

exposure. This guidance may be found at: 

http://www.epa.gov/superfund/health/conmedi 

a/soil/index.htm 

 

Comment [A31]: EPA’s Supplemental 

Guidance for Developing Soil Screening Levels 

for Superfund Sites provides equations for 

exposure through dermal contact in a nonresidential scenario. This guidance may be 

found at: 

http://www.epa.gov/superfund/health/conmedi 

a/soil/index.htm 
 Page 6-41 

EXHIBIT 6-15
 

RESIDENTIAL EXPOSURE:
 

DERMAL CONTACT WITH CHEMICALS IN SOILA
 

 

Comment [A32]: EPA has supplemented the 

general guidance for evaluating dermal 

exposure provided in RAGS Part A. Updated 

procedures and equations for evaluating the 

dermal absorbed dose for chemicals in soil may 

be found in found in Risk Assessment Guide for 

Superfund Part E, Supplemental Guidance for 

Dermal Risk Assessment. Please consult 

Sections 3.2 and Equation 3.12 for a description 

of these procedures and the specific equation 

for estimating dermal exposures to chemicals in 

soil. RAGS Part E may be found at: 

http://epa.gov/oswer/riskassessment/ragse/ind 

ex.htm 
 

Page 6-42 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

"Best guess" values for children potentially 

useful in risk assessments are 3 times/week for 

fall and spring days (>32o

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 Comment [A33]: The Superfund Program has 

updated its inhalation risk paradigm and no 

longer recommends the approach described in 

this section. Please consult Chapter 3 of EPA’s 

Risk Assessment Guidance for Superfund 

Volume I: Human Health Evaluation Manual 

(Part F, Supplemental Guidance for Inhalation 

Risk Assessment) for current recommendations 

regarding exposure assessments for inhaled 

contaminants. RAGS, Part F may be found at: 

http://www.epa.gov/oswer/riskassessment/rags 

f/index.htm. 

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/m3

) 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. 

Page 6-43 

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). 

Comment [A34]: EPA has developed guidance 

for assessing health risks associated with the 

consumption of chemically contaminated noncommercial fish. This document, Guidance for 

Assessing Chemical Contaminant Data for Use 

in Fish Advisories, includes volumes on "Fish 

Sampling and Analysis" and "Risk Assessment 

and Fish Consumption Limits". It may be found 

at: 

http://www.epa.gov/fishadvisories/technical/gui 

dance.html 

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. 
EXHIBIT 6-16
 

RESIDENTIAL EXPOSURE:
 

INHALATION OF AIRBORNE (VAPOR PHASE) CHEMICALS A B Comment [A35]: The Superfund Program has 

updated its inhalation risk paradigm and no longer 

recommends use of the equation described in Exhibit 

6-16. Please consult Chapter 3 of EPA’s Risk 

Assessment Guidance for Superfund Volume I: 

Human Health Evaluation Manual (Part F, 

Supplemental Guidance for Inhalation Risk 

Assessment) for current recommendations regarding 

exposure assessments for inhaled contaminants. 

RAGS, Part F may be found at: 

http://www.epa.gov/oswer/riskassessment/ragsf/inde

x.htm 

Page 6-44 
 Page 6-45

EXHIBIT 6-17
 

RESIDENTIAL EXPOSURE: FOOD PATHWAY – INGESTION 

OF CONTAMINATED FISH AND SHELLFISH α
 

 

 

Comment [A36]: EPA has developed guidance 

for assessing health risks associated with the 

consumption of chemically contaminated noncommercial fish. Guidance for Assessing 

Chemical Contaminant Data for Use in Fish 

Advisories, includes volumes on "Fish Sampling 

and Analysis" and "Risk Assessment and Fish 

Consumption Limits". It may be found at: 

http://www.epa.gov/fishadvisories/technical/gui

dance.html 
 

 

Page 6-46 

EXHIBIT 6-18 

RESIDENTIAL EXPOSURE: FOOD PATHWAY – INGESTION 

OF CONTAMINATE FRUITS AND VEGETABLES a
 

D 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This pathway will be most significant for 

farmers and for rural and urban residents 

consuming homegrown fruits and vegetables. 

For 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 (worstcase). (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 

Page 6-47 

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 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. 
 

Page 6-48 

EXHIBIT 6-19 

RESIDENTIAL EXPOSURE: FOOD PATHWAY – 

INGESTION OF CONTAMINATED MEAT, EGGS,
 

AND DAIRY PRODUCTS a
 
 

 

Page 6-49 

EXHIBIT 6-20
 

EXAMPLE OF TABLE FORMAT FOR SUMMARIZING

 VALUES USED TO ESTIMATE EXPOSURE 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 6-50 

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., firstorder 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. 

Comment [A37]: EPA’s Risk Assessment 

Guidance for Superfund Volume I: Human 

Health Evaluation Manual (Part D, Standardized 

Planning, Reporting, and Review of Superfund 

Risk Assessments) provides planning tables for 

use during the risk assessment process, 

including the exposure assessment. See Part D, 

Section 3.1.1, page 3-5, for an overview of 

using Planning Table 3: Exposure Point 

Concentration Summary. See page 3-6 for an 

overview of using Planning Table 4: Values 

Used for Daily Intake Calculations. Also see 

Appendix 1 for the downloadable Planning 

Table templates and instructions for completing 

the tables. RAGS Part D may be found at: 

http://www.epa.gov/oswer/riskassessment/rags 

d/index.htm 
 

 

 

Page 6-51 

EXHIBIT 6-21
 

EXAMPLE OF AN UNCERTAINTY TABLE FOR
 

EXPOSURE ASSESSMENT
 
 

Page 6-52 

EXHIBIT 6-22
 

EXAMPLE OF TABLE FORMAT FOR SUMMARIZING
 

THE RESULTS OF THE EXPOSURE ASSESSMENT –
 

CURRENT LAND USEΑ
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 6-53 

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 SludgeOffice 

of Water.. (Individual documents are available for a number of substances). 

Environmental Protection Agency (EPA). 1986a.Guidelines for Exposure Assessmen.t51 Federal Register34042 (September 24, 1986). 

Environmental Protection Agency (EPA). 1986b.Guidelines for Carcinogen Risk Assessmen.t 51 Federal Register33992 (September 24, 

1986). 

Environmental Protection Agency (EPA). 1987a.Industrial Source Complex (ISC) Dispersion Model User's Guide. Volume. IOffice 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 Register48830 

(December 2, 1988). 

Environmental Protection Agency (EPA). 1988b.Superfund Exposure Assessment Manua.lOffice of Emergency and Remedial 

Response.EPA/540/188/001. (OSWER Directive 9285.5-1). 

Environmental Protection Agency (EPA). 1988c.Selection Criteria for Mathematical Models Used in Exposure Assessments: Groundwater 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 Register9386 (March 6, 1989). 

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 Rate.sOffice 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. 
 

 

 

 

 

 

 

 

 

 

 

Page 6-54 

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 Monitorin.gVan 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 Industrie.sVienna. 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, S.J. 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. 

51 54 59 60 

Van Bruwaene, R., Gerber, G.B., Kerchmann, R., Colard, J. and Van Kerkom, J. 1984. Metabolism of Cr, Mn, Fe and Co in 

Lactating Dairy Cows. Health Physics46:1069-1082. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CHAPTER 7
 

TOXICITY ASSESSMENT 

The purpose of the toxicity 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 doseresponse 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 toxicological 

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 

toxicologist. This chapter provides step-by-step 

guidance for locating EPA toxicity assessments 

and accompanying values, and advises how to 

determine which values are most appropriate 

when multiple values exist. Prior to this 

procedural discussion, background 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. 

ACRONYMS FOR CHAPTER 7 

ADI = Acceptable Daily Intake 

AIC = Acceptable Intake for Chronic Exposure 

AIS = Acceptable Intake for Subchronic Exposure 

CRAVE = Carcinogen Risk Assessment 

Verification Endeavor 

ECAO = Environmental Criteria and Assessment 

Office 

HAD = Health Assessment Document 

HEA = Health Effects Assessment 

HEAST = Health Effects Assessment Summary 

Tables 

HEED = Health and Environmental Effects 

Document 

HEEP = Health and Environmental Effects 

Profile 

IRIS = Integrated Risk Information System 

LOAEL = Lowest-Observed-Adverse-Effect-Level 

NOAEL = No-Observed-Adverse-Effect-Level 

NOEL = No-Observed-Effect-Level 

RfD = Reference Dose (when used without other 

modifiers, RfD generally refers to chronic 

reference dose) 

RfDdt = Developmental Reference Dose 

RfD = Subchronic Reference Dose 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 7-2 

DEFINITIONS FOR CHAPTER 7 

Acceptable Daily Intake (ADI). 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 (AIC). An estimate similar in concept to the RfD, but derived using a less 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 (AIS). An estimate similar in concept to the subchronic RfD, but derived 

using a less strictly defined methodology. Subchronic 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 (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 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 (RfD dt). 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 (IRIS). 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 (LOAEL). 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 (NOAEL). 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 (NOEL). 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. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 (RfDs). 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). 

Toxicity 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. 

Derivation and interpretation of toxicity 

values requires toxicological 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 doseresponse assessment, and animal toxicity studies 

are used as supportive evidence. 
Page 7-4 

EXHIBIT 7-1 

STEPS IN TOXICITY ASSESSMENT
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 nonhuman 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). 

Comment [A38]: The Superfund Program has 

updated its inhalation risk paradigm to be 

compatible with the Agency's current 

methodology for inhalation dosimetry and 

derivation of inhalation toxicity values. EPA no 

longer recommends the use of inhalation RfDs. 

Please consult Chapter 2 of EPA’s Risk 

Assessment Guidance for Superfund Volume I: 

Human Health Evaluation Manual Part F, 

Supplemental Guidance for Inhalation Risk 

Assessment for current background on 

derivation of the inhalation toxicity values used 

in risk assessments of inhaled contaminants. 

RAGS Part F may be found at: 

http://www.epa.gov/oswer/riskassessment/rags 

f/index.htm. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 7-6 

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 

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 

(ADIs) or acceptable intakes for chronic exposure 

(AICs). 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 intraAgency 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 ss), which are useful for 

characterizing potential noncarcinogenic effects 

associated with shorter-term exposures, and 

developmental RfDs (RfD dts), 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 shortterm 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 

(RFDO) 

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 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 "lowestobserved- adverse-effect-level" (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-observedadverse-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 

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. 

Page 7-7 

are not considered to be of toxicological 

significance. In some studies, only LOAEL 

rather than a NOAEL is available. The use of a 

LOAEL, however, 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 1.1 

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 applicable uncertainty factors and the 

modifying factor. That is: 

RfD = NOAEL or LOAEL/(UF1 x UF2... x MF) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 7-8 

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 (RFDI) 

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/m3 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/m3

. 

7.2.4 DERIVATION OF A SUBCHRONIC RFD 

(RFDS) 

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 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 

Comment [A39]: The Superfund Program has 

updated its inhalation risk paradigm to be 

compatible with the Agency's current 

methodology for inhalation dosimetry and 

derivation of inhalation toxicity values. EPA no 

longer recommends the use of inhalation RfDs. 

Please consult Chapter 2, Section 2.3 of EPA’s 

Risk Assessment Guidance for Superfund 

Volume I: Human Health Evaluation Manual 

Part F, Supplemental Guidance for Inhalation 

Risk Assessment for current background on 

derivation of the non-cancer inhalation toxicity 

values used in risk assessments of inhaled 

contaminants. RAGS Part F may be found at: 

http://www.epa.gov/oswer/riskassessment/rags 

f/index.htm. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 7-9 

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 DEVELOPMENTAL 

TOXICANT RFD (RFDDT) 

In developing an RfDdt, 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 

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 

RfDdt 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, RfDdt 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 RfDdt 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 7-10 

be expected to occur for an exposure of the 

specified 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 

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. 

have in the RfD itself, the critical study, and the 

overall data base (high, medium, or low). Once 

verified, these data 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 

isinappropriate. 

 

 

 

 

Comment [A40]: 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. 
 Page 7-11

 

 

 

 

 

 

 

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. 

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 weightof-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 FACTOR 2 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Comment [A41]: THE SUPERFUND PROGRAM 

HAS UPDATED ITS INHALATION RISK 

PARADIGM TO BE COMPATIBLE WITH THE 

AGENCY'S CURRENT METHODOLOGY FOR 

INHALATION DOSIMETRY AND DERIVATION OF 

INHALATION TOXICITY VALUES. FOR 

UPDATED INFORMATION ON THE DERIVATION 

OF INHALATION UNIT RISKS, PLEASE 

CONSULT CHAPTER 2 OF EPA’S Risk 

Assessment Guidance for Superfund Volume I: 

Human Health Evaluation Manual (Part F, 

Supplemental Guidance for Inhalation Risk 

Assessment) for current background on 

derivation of the inhalation toxicity values used 

in risk assessments of inhaled contaminants. 

RAGS, Part F may be found at: 

http://www.epa.gov/oswer/riskassessment/rags 

f/index.htm. 

Comment [A42]: EPA has developed 

additional information to consider in selecting 

cancer toxicity factors addressing a number of 

issues pertaining to cancer risks associated with 

early-life exposures, including specific guidance 

on potency adjustments for carcinogens acting 

through a mutagenic mode of action. This 

Information is available in EPA’s Handbook for 

Implementing the Supplemental Guidance at 

Waste and Cleanup Sites: 

http://epa.gov/oswer/riskassessment/sghandbo 

ok/chemicals.htm 

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, 

B1, 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-ofevidence 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 

about a chemical is evaluated and an appropriate 

EPA WEIGHT-OF-EVIDENCE 

CLASSIFICATION SYSTEM FOR 

CARCINOGENICITY 

Group Description 

A Human carcinogen 

B1 or Probable human carcinogen 

B2

B1 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 

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. 

 

 

Comment [A43]: In its 2005 Guidelines for 

Carcinogen Risk Assessment, EPA has replaced 

the Alphanumeric Classification shown in this 

text box with a weight of evidence that lays out 

a summary of the key evidence, describes the 

agent's mode of action, characterizes the 

conditions of hazard expression, and 

recommends appropriate dose response 

approach(es). The overall conclusion as to the 

likelihood of human carcinogenicity is presented 

according to the following five recommended 

standard hazard descriptors: “Carcinogenic to 

Humans,” “Likely to Be Carcinogenic to 

Humans,” “Suggestive Evidence of Carcinogenic 

Potential,” “Inadequate Information to Assess 

Carcinogenic Potential,” and “Not Likely to Be 

Carcinogenic to Humans.” The Guidelines for 

Carcinogen Risk Assessment may be found at: 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm 

?deid=116283 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 7-12 

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. 

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-totumor 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/kgday, 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 

 

 

 

 

 

Comment [A44]: The Superfund Program has 

updated its inhalation risk paradigm to be 

compatible with the Agency's current 

methodology for inhalation dosimetry and 

derivation of inhalation toxicity values. For 

updated information on the derivation of 

inhalation unit risks, please consult Chapter 2, 

Section 2.1 of EPA’s Risk Assessment Guidance 

for Superfund Volume I: Human Health 

Evaluation Manual Part F, Supplemental 

Guidance for Inhalation Risk Assessment for 

current background on determining equivalent 

human doses for use in deriving toxicity values 

used in risk assessments of inhaled 

contaminants. RAGS, Part F may be found at: 

http://www.epa.gov/oswer/riskassessment/rags 

f/index.htm. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 7-13 

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 doseresponse curve and is expressed as (mg/kg-day)­

1

. If the extrapolation model selected is the 

linearized multistage model, this value is also 

known as the q1*

. 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.) 

 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 μg/m3 

= slope factor x 1/70 kg x 

20m3

/day x 10–3 

water unit risk = risk per μg/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 q1*

, is 

given in (mg/kg day)–1) to μg (the unit risk is 

given in (μg/m3

)

–1 or (μg/L)–1). 

 

 

 

 

 

 

Comment [A45]: The Superfund Program has 

updated its inhalation risk paradigm to be 

compatible with the Agency's current 

methodology for inhalation dosimetry and 

derivation of inhalation toxicity values. For 

updated information on the derivation of 

inhalation unit risks, please consult Chapter 2, 

Section 2.2 of EPA’s Risk Assessment Guidance 

for Superfund Volume I: Human Health 

Evaluation Manual Part F, Supplemental 

Guidance for Inhalation Risk Assessment for 

current background on derivation of the 

inhalation unit risk values used in risk 

assessments of inhaled contaminants. RAGS, 

Part F may be found at 

http://www.epa.gov/oswer/riskassessment/rags 

f/index.htm. 

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 

 

 

 

 

 

 

 

 

 

Toxicity values for carcinogenic effects

Comment [A46]: The Superfund Program has 

updated the toxicity value source hierarchy 

presented in Section 7.4 of RAGS Part A. The 

current recommended hierarchy is described in 

a December 5, 2003 policy memorandum titled 

“Human Health Toxicity Values in Superfund 

Risk Assessments,” (OSWER Directive 9285.7-

53). For additional details, please consult the 

memorandum at: 

http://www.epa.gov/oswer/riskassessment/pdf/ 

hhmemo.pdf 

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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 7-14 

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 upto-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 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 online. 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) RfDs 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 (513569-7562 or FTS 684-7562) 

or the National Technical Information Service 

(NTIS), 5285 Port Royal Road, Springfield, VA 

22161 (703-487-4650 or 800-3364700). 

EPA criteria documents. These documents 

include drinking water criteria documents, 

Comment [A47]: The Superfund Program has 

updated the toxicity value source hierarchy 

presented in Section 7.4 of RAGS Part A. The 

current recommended hierarchy is described in 

a December 5, 2003 policy memorandum titled 

“Human Health Toxicity Values in Superfund 

Risk Assessments,” (OSWER Directive 9285.7-

53). For additional details, please consult the 

memorandum at: 

http://www.epa.gov/oswer/riskassessment/pdf/ 

hhmemo.pdf 

Comment [A48]: The Superfund Program has 

updated the toxicity value source hierarchy 

presented in RAGS Part A. The current 

recommended hierarchy is described in a 

December 5, 2003 policy memorandum titled 

“Human Health Toxicity Values in Superfund 

Risk Assessments,” (OSWER Directive 9285.7-

53). For additional details, please consult the 

memorandum at: 

http://www.epa.gov/oswer/riskassessment/pdf/ 

hhmemo.pdf 
 Page 7-15

Because toxicity information 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 if 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 HEAST. 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. 

HIERARCHY OF TOXICITY INFORMATION 

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 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 

 

Comment [A49]: The Superfund Program has 

updated the toxicity value source hierarchy 

presented in Section 7.4 of RAGS Part A. The 

current recommended hierarchy is described in 

a December 5, 2003 policy memorandum titled 

“Human Health Toxicity Values in Superfund 

Risk Assessments,” (OSWER Directive 9285.7-

53). For additional details, please consult the 

memorandum at: 

http://www.epa.gov/oswer/riskassessment/pdf/

hhmemo.pdf 

For further assistance in selecting appropriate 

toxicity values, contact the Superfund Health 

Risk Technical Support Center. 

further information on the status or availability 

of a particular profile. 

EPA's Environmental Criteria and

Assessment Office (ECAO). ECAO may be 

contacted at 513569-7300 (FTS 684-7300) for 

general toxicological 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 
Page 7-16 

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 Oneor 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 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 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) 

Comment [A50]: The Superfund Program has 

updated the toxicity value source hierarchy presented 

in Section 7.4 of RAGS Part A. The current 

recommended hierarchy is described in a December 

5, 2003 policy memorandum titled “Human Health 

Toxicity Values in Superfund Risk Assessments,” 

(OSWER Directive 9285.7-53). For additional 

details, please consult the memorandum at: 

http://www.epa.gov/oswer/riskassessment/pdf/hhme

mo.pdf 

For further assistance in selecting appropriate 

toxicity values, contact the Superfund Health Risk 

Technical Support Center. 

 

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 EPAderived toxicity values are not available, the 

following measures are recommended. 

7.5.1	 ROUTE-TO-ROUTE EXTRAPOLATION 

Comment [A51]: The Superfund Program has 

updated its inhalation risk paradigm and 

provides revised information concerning how to 

address inhaled contaminants that lack 

inhalation-based toxicity values. Please consult 

Chapter 4, Section 4.2 of EPA’s Risk Assessment 

Guidance for Superfund Volume I: Human 

Health Evaluation Manual Part F, Supplemental 

Guidance for Inhalation Risk Assessment for 

current recommendations regarding exposure 

assessments for inhaled contaminants. RAGS, 

Part F may be found at: 

http://www.epa.gov/oswer/riskassessment/rags 

f/index.htm 

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 

 

 

 

Comment [A52]: EPA has supplemented the 

general guidance for evaluating dermal 

exposure provided in RAGS Part A . Updated 

procedures for deriving toxicity factors to 

characterize risk from the dermal exposure 

pathway may be found in found in Risk 

Assessment Guide for Superfund, Part E 

Supplemental Guidance for Dermal Risk 

Assessment. Please consult Sections 4.2 and 

4.3 for a description of these procedures for 

adjusting oral toxicity factors by calculating 

absorbed toxicity values that can be used to 

characterize risk from the dermal exposure 

pathway. RAGS Part E may be found at: 

http://epa.gov/oswer/riskassessment/ragse/ind

ex.htm 

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 
 

 

 

 

Page 7-17

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 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Comment [A53]: The Superfund Program has 

updated the toxicity value source hierarchy 

presented in Section 7.4 of RAGS Part A. The 

current recommended hierarchy is described in 

a December 5, 2003 policy memorandum titled 

“Human Health Toxicity Values in Superfund 

Risk Assessments,” (OSWER Directive 9285.7-

53). For additional details, please consult the 

memorandum at: 

http://www.epa.gov/oswer/riskassessment/pdf/ 

hhmemo.pdf 

For further assistance in selecting appropriate 

toxicity values, contact the Superfund Health 

Risk Technical Support Center. 

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 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 viceversa; 

	 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-ofevidence 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. 
Page 7-18 

EXHIBIT 7-2 

EXAMPLE OF TABLE FORMAT FOR 

TOXICITY VALUES: POTENTIAL NONCARCINOGENIC EFFECTS
 

 

 

Comment [A54]: EPA’s Risk Assessment 

Guidance for Superfund Volume I: Human 

Health Evaluation Manual (Part D, Standardized 

Planning, Reporting, and Review of Superfund 

Risk Assessments) provides planning tables for 

use during the risk assessment process. See 

Part D, Section 3.1.1 (page 3-8) for an overview 

of using Planning Tables 5: Non-cancer Toxicity 

Values. Also see Appendix A for the 

downloadable Planning Table 5 templates and 

instructions for completing these templates. 

RAGS, Part D may be found at: 

http://www.epa.gov/oswer/riskassessment/rags 

d/index.htm 
 Page 7-19 

EXHIBIT 7-3 

EXAMPLE OF TABLE FORMAT FOR 

TOXICITY VALUES: POTENTIAL CARCINOGENIC EFFECTS
 

 

 

 

 

 

 

Comment [A55]: EPA’s Risk Assessment 

Guidance for Superfund Volume I: Human 

Health Evaluation Manual (Part D, Standardized 

Planning, Reporting, and Review of Superfund 

Risk Assessments) provides planning tables for 

use during the risk assessment process. See 

Part D, Section 3.1.1 (page 3-8) for an overview 

of using Planning Table 6: Cancer Toxicity 

Values. Also see Appendix A for the 

downloadable Planning Table 6 templates and 

instructions for completing these templates. 

RAGS, Part D may be found at: 

http://www.epa.gov/oswer/riskassessment/rags 

d/index.htm 
Page 7-20 

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, 

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 

 

 

 

 

Comment [A56]: EPA’s Risk Assessment 

Guidance for Superfund Volume I: Human 

Health Evaluation Manual (Part D, Standardized 

Planning, Reporting, and Review of Superfund 

Risk Assessments) provides planning tables for 

use during the risk assessment process, 

including the toxicity assessment. See Part D, 

Section 3.1.1 (page 3-7) for an overview of 

using Planning Tables 5 and 6: Non-Cancer and 

Cancer Toxicity Data. Also see Appendix 1 for 

the downloadable Planning Table templates and 

instructions for completing the tables. RAGS, 

Part D may be found at: 

http://www.epa.gov/oswer/riskassessment/rags

d/index.htm

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 

nontechnical 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 EPAderived 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 

Page 7-21 

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 7-22 

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 7-23 

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). 1986b. 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 (RfD): 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 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Comment [A57]: EPA has developed 

additional information concerning exposure and 

risk assessment for lead and asbestos to 

supplement the information presented in RAGS 

Part A. This information is needed because 

there are a number of unique scientific and 

technical issues associated with the 

investigation of human exposure and risk from 

these contaminants. This information on lead 

and asbestos at Superfund sites may be found 

at: 

http://www.epa.gov/superfund/health/contamin 

ants/asbestos/ 

http://www.epa.gov/superfund/health/contamin 

ants/lead/ 

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 routes and 

relevant substances). 

ACRONYMS FOR CHAPTER 8 

ARAR =	 Applicable or Relevant and Appropriate 

Requirement 

ATSDR= Agency for Toxic Substances and 

Disease Registry 

CDI = Chronic Daily Intake 

ECAO = 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) 

RfDdt = Developmental Reference Dose 

RfDs = Subchronic Reference Dose 

RI/FS = Remedial Investigation/Feasibility Study 

RME = Reasonable Maximum Exposure 

SDI = Subchronic Daily Intake 

SF = Slope Factor 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 an exchange boundary (e.g., gastrointestinal 

tract) per unit body weight per unit time (e.g., mg/kg-day). 

Chronic 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 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 (RfD dt). 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 

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 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 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 (IRIS). 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 (RfD). 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 generically 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 (RfD s). 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-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. 
 

 

Page 8-3 

EXHIBIT 8-1 

STEPS IN RISK CHARACTERIZATION
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 8-4 

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: 

o chemical concentration at the exposure points; 

o frequency and duration of exposure; 

o absorption assumptions; and 

o 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 estimates correspond as closely as 

possible with the assumptions used in developing 

the toxicity values. 

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 shorterterm 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. 

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-thanlifetime 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 shorter-term 
 Page 8-5 

 

 

 

 

 

 

effects). A toxicologist 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. 

 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-bycase basis in 

consultation with ECAO. In general, inhalation 

values should not be extrapolated from oral 

values. See Section 7.5.1 for additional 

information. 

EPA ENVIRONMENTAL CRITERIA
 

AND ASSESSMENT OFFICE (ECAO)
 

TECHNICAL ASSISTANCE 

FTS 684-7300 

513-569-7300 

Inhalation RfD values obtained from IRIS 

will usually be expressed as ambient air 

concentrations (i.e., mg/m3

), 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/m3 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 toxicity 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 
Page 8-6 

will provide a 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., 2×10-5) of an 

individual developing cancer; 

CDI = chronic daily intake averaged over 70 years 

(mg/kg-day); and 

SF = slope factor, expressed in (mg/kg-day) -1. 

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. 

 

 

 

Comment [A58]: The Superfund Program has 

updated its inhalation risk paradigm and 

provides updated information concerning how 

to quantify risk or hazard indices for both 

carcinogenic and non-carcinogenic effects of 

inhaled contaminants. Please consult Chapter 5 

of EPA’s Risk Assessment Guidance for 

Superfund Volume I: Human Health Evaluation 

Manual Part F, Supplemental Guidance for 

Inhalation Risk Assessment for current 

recommendations regarding exposure 

assessments for inhaled contaminants. RAGS, 

Part F may be found at: 

http://www.epa.gov/oswer/riskassessment/rags

f/index.htm 
 

 

 

 

 

 

Page 8-7 

EXHIBIT 8-2 

EXAMPLE OF TABLE FORMAT FOR CANCER RISK ESTIMATES
 Comment [A59]: EPA’s Risk Assessment 

Guidance for Superfund Volume I: Human 

Health Evaluation Manual (Part D, Standardized 

Planning, Reporting, and Review of Superfund 

Risk Assessments) provides planning tables for 

use during the risk assessment process. See 

Part D, Section 3.1.1 (page 3-10) for an 

overview of using Planning Table 7: Calculation 

of Chemical Cancer and Non-cancer Hazards 

Risk. Also see Appendix A for the downloadable 

Planning Table 7 templates and instructions for 

completing these templates. RAGS, Part D may 

be found at: 

http://www.epa.gov/oswer/riskassessment/rags 

d/index.htm 
 

 

 

 

Page 8-8 

EXHIBIT 8-3 

EXAMPLE OF TABLE FORMAT FOR CHRONIC HAZARD INDEX ESTIMATES Comment [A60]: EPA’s Risk Assessment 

Guidance for Superfund Volume I: Human 

Health Evaluation Manual (Part D, Standardized 

Planning, Reporting, and Review of Superfund 

Risk Assessments) provides planning tables for 

use during the risk assessment process. See 

Part D, Section 3.1.1 (page 3-10) for an 

overview of using Planning Table 7: Calculation 

of Chemical Cancer and Non-cancer Hazards 

Risk. Also see Appendix A for the downloadable 

Planning Table 7 templates and instructions for 

completing these templates. RAGS, Part D may 

be found at: 

http://www.epa.gov/oswer/riskassessment/rags 

d/index.htm 
 

 

 

 

 

 

 

 

Page 8-9 

EXHIBIT 8-4 

EXAMPLE OF TABLE FORMAT FOR SUBCHRONIC HAZARD INDEX ESTIMATES Comment [A61]: EPA’s Risk Assessment 

Guidance for Superfund Volume I: Human 

Health Evaluation Manual (Part D, Standardized 

Planning, Reporting, and Review of Superfund 

Risk Assessments) provides planning tables for 

use during the risk assessment process. See 

Part D, Section 3.1.1 (page 3-10) for an 

overview of using Planning Table 7: Calculation 

of Chemical Cancer and Non-cancer Hazards 

Risk. Also see Appendix A for the downloadable 

Planning Table 7 templates and instructions for 

completing these templates. RAGS, Part D may 

be found at: 

http://www.epa.gov/oswer/riskassessment/rags 

d/index.htm 
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 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 8-2, 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 (CDI), 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 CDI 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 CDI 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 CDI could have been adjusted downward to 0.000008 mg/kg-day (i.e., 

0.00008 mg/kg-day × 0.10 absorption fraction). 

Values for the slope factors (SF), weight-of-evidence 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 CDI and SF using the linear low-dose cancer risk 

equation (risk = CDI × 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. 

 

Comment [A62]: The Superfund Program has 

updated its inhalation risk paradigm and no 

longer uses the chronic daily intake to assess 

inhalation exposures. Please consult Chapter 3 

of EPA’s Risk Assessment Guidance for 

Superfund Volume I: Human Health Evaluation 

Manual (Part F, Supplemental Guidance for 

Inhalation Risk Assessment) for current 

recommendations regarding exposure 

assessments for inhaled contaminants. RAGS, 

Part F may be found at: 

http://www.epa.gov/oswer/riskassessment/rags

f/index.htm 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 (MEK). 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 (CDI), 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 CDI 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 

CDI 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 CDI 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 chemicalspecific hazard quotients are equal to the CDI 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 noncarcinogenic 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. 

 

Comment [A63]: The Superfund Program has 

updated its inhalation risk paradigm and no 

longer uses the chronic daily intake to assess 

inhalation exposures. Please consult Chapter 3 

of EPA’s Risk Assessment Guidance for 

Superfund Volume I: Human Health Evaluation 

Manual (Part F, Supplemental Guidance for 

Inhalation Risk Assessment) for current 

recommendations regarding exposure 

assessments for inhaled contaminants. RAGS, 

Part F may be found at: 

http://www.epa.gov/oswer/riskassessment/rags

f/index.htm 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 ×10-5) of an 

individual developing cancer; 

exp = the exponential; 

CDI = chronic daily intake averaged over 70 years 

(mg/kg-day); and 

EPA does not at the present time use a 

probabilistic approach to estimating the potential 

for noncarcinogenic health effects. Instead, the 

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, subchronic, and shorter-term exposures. 

As guidance for Superfund, chronic exposures 

for humans range in duration from seven years 

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 

to a lifetime; such long-term exposures are 

almost always of concern for Superfund sites 

(e.g., inhabitants of nearby residences, yearround 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. 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. 

Comment [A64]: EPA has developed guidance 

for assessing health risks form exposures to multiple 

chemical or mixtures that supplements the 

information presented in RAGS Part A. In August 

2000, EPA published Supplementary Guidance for 

Conducting Health Risk Assessment of Chemical 

Mixtures, which describes details for several 

procedures for chemical mixture assessment, 

including methods for using whole-mixture data on a 

toxicologically similar mixture, methods for 

incorporating information on toxicologic interactions 

to modify a Hazard Index (HI), and generalized 

procedures for mixtures involving classes of similar 

chemicals. This guidance document may be found at: 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid 

=20533 
 

 

 

 

 

 

 

 

 

 

 

Page 8-12 

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.1 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
 

RiskT = ∑ Riski 

where: 

RiskT = the total cancer risk, 

 expressed as a unitless 

 probability; and 

 Riski = 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 underestimation 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 (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 = E1/RfD1 + E2/RfD2+ ... 

+ Ei/RfDi 

where: 

th 

Ei = exposure level (or intake) for the i 

toxicant; 

th

RfDi = reference dose 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 (CDI) to the chronic reference 

Page 8-13 

CHRONIC NONCANCER HAZARD INDEX 

Chronic 

Hazard Index = CDI 1/RfD1 + CDI 2 /RfD2 

+ ... 

+ CDI /RfDi i 

where: 

CDIi = chronic daily intake for the ith 

toxicant in mg/kg-day, and 

RfDi = chronic reference dose for 

the ith 

toxicant in mg/kg-day. 

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. 

(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 (RfDs) 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 RfDdts), which might cause adverse 

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. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 8-14 

SUBCHRONIC NONCANCER
 

HAZARD INDEX
 

Subchronic 

Hazard Index = SDI1 /RfDs1 +SDI 2/RfDs2

 + ... + SDIi /RfDsi 

where: 

th

SDIi = subchronic daily intake for the i 

 toxicant in mg/kg-day; and

th

 RfDsi = subchronic reference dose for the i 

 toxicant in mg/kg-day. 

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 

toxicological 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 timeconsuming 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. 

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 neurotoxicity, 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, 

Page 8-15 

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 landuses (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 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 8-16 

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-thanlifetime 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 pathway1) + 

Risk(exposure pathway2) + ...... + 

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 if combining exposure 

pathways has resulted in combining hazard 

indices based on different chemicals, one may 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

HAZARD INDEX EQUATION FOR 

MULTIPLE PATHWAYS
 

Total Exposure Hazard Index = 

Hazard Index(exposure pathway1) + 

Hazard Index(exposure pathway2) + ...... + 

Hazard Index(exposure pathwayi) 

where: 

Total Exposure Hazard Index is calculated separately 

for chronic, subchronic, and shorter-term exposure 

periods. 

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 

Page 8-17 

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/semiquantitative 

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 

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. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 8-18 

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 sitespecific environmental conditions. Ideally, one 

would like to use a fully validated model that 

accounts for all the known complexities in the 

parameter 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: 

o	 direction (i.e., may over- or underestimate 

risk); and 

o	 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 

Page 8-19 

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, semiquantitative, 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 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 8-20 

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 certainty 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 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. 
 

 

 

Page 8-21 

EXHIBIT 8-5 

EXAMPLE OF PRESENTATION OF IMPACT OF EXPOSURE ASSUMPTIONS 

ON CANCER RISK ESTIMATE 

a

The risk of developing cancer is plotted on a log scale, A risk of 10-4 indicates a probability of 1 

chance In 10,000 and a risk of 10-5 Indicates a probability of 1 chance In 100,000 of an individual 

developing cancer. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 8-22 

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: 

o	 total range; 

o	 shape of distribution, if known (e.g., 

lognormal); 

o	 mean (geometric or arithmetic) + standard 

deviation; and/or 

o	 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 underestimate 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 

SITESPECIFIC HUMAN STUDIES 

This section describes how to compare the 

results of the risk characterization step with 

ATSDR health assessments and other sitespecific 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. 
 

 

 

Page 8-23 

EXHIBIT 8-6 

EXAMPLE OF PRESENTATION OF IMPACT OF EXPOSURE ASSUMPTIONS 

ON HAZARD INDEX ESTIMATE
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 8-24 

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 any available 

studies in order to identify possible study 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 8-25 

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 population 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); 

Comment [A65]: EPA’s Risk Assessment 

Guidance for Superfund Volume I: Human 

Health Evaluation Manual (Part D, Standardized 

Planning, Reporting, and Review of Superfund 

Risk Assessments) provides planning tables for 

use during the risk assessment process, 

including risk characterization. See Part D, 

Section 3.1.1 (page 3-9) for an overview of 

using Planning Tables 7, 9 and 10: Calculation 

of Chemical Cancer Risks and Non-Cancer 

Hazards, Summary of Receptor Risk and 

Hazards for COPCs, and Risk Summary, 

respectively. Also See Appendix 1 for the 

downloadable Planning Tables and instructions 

for completing the tables. RAGS, Part D may be 

found at: 

http://www.epa.gov/oswer/riskassessment/rags 

d/index.htm 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 8-26 

	 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); 

	 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 results may be of assistance to the 

RPM, especially characterization. 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. 
 

 

 

 

 

Page 8-27 

EXHIBIT 8-7 

EXAMPLE OF PRESENTATION OF RELATIVE CONTRIBUTION OF INDIVIDUAL
 

CHEMICALS TO EXPOSURE PATHWAY AND TOTAL CANCER RISK ESTIMATES 

a

The risk of developing cancer is plotted on a log scale. A risk of 10-4 indicates a probability of 1 

chance in 10,000 of an individual developing cancar. Risks of 10-5 and 10-6 corre.pond to 

probabilities of 1 chance in 100,000 and 1 chance in 1,000,000 respectively. Values in 

parentheses represent EPA’s weight-of-evidence classification of the agent as a potential human 

carcinogen: A = human carcinogen; and 82 = probable human carcinogen (with sufficient 

evidence in animals and inadequate or no evidence in humans). 
 

 

 

 

Page 8-28 

EXHIBIT 8-8 

EXAMPLE OF PRESENTATION OF RELATIVE CONTRIBUTION OF INDIVIDUAL
 

CHEMICALS TO EXPOSURE PATHWAY AND TOTAL HAZARD INDEX ESTIMATES
 

a The hazard index is equal to the sum of the hazard quotients (i.e., exposure 

leve/RfD for each chemical. It is not a probability; a hazard index or quotient of ~ 

1.0 indicates that it is unlikely for even sensitive populations to experience adverse 

health effects. 
 

 

 

 

 

 

 

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 risk1 + risk 2 ­

probability (risk1, 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 (risk1)(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 ASSESOR, 

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 for 

documenting a baseline risk assessment: 

(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 

occurrence of adverse health effects, or they 

could be overemphasized, possibly leading to 

the unnecessary expenditure of limited 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 9-2 

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., in a
 

glossary); and
 

	 use a standard quantitative system -- preferably 

the metric system -- throughout and units that are 

the same where possible (e.g., ug/L for all water 

concentrations). 

Avoid: 

	 the use of large blocks of text unbroken by any 

headings, graphics, tables, lists, or other "visual 

dividers"; 

	 the presentation of much quantitative information 

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). 

resources. See the box below for some helpful 

hints on communicating the baseline risk 

assessment. 

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; 

(2)	 it allows for easier review of the risk 

assessments; 

(3)	 it encourages consistent use of the 

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 1988a) 

results by RPMs and other decisionmakers; 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 manual. 

Careful use of that guidance will ensure a welldocumented baseline risk assessment report. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 9-3 

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 sitespecific 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? 
 

 

 

 

 

 

 

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) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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) 
 

 

 

 

 

 

 

 

 

 

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) 
 

 

 

 

 

 

 

 

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 6.2 Exposure Assessment 

6.3 6.3 Toxicity Assessment 

6.4 6.4 Risk Characterization 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 9-9 

EXHIBIT 9-2 

REVIEWER CHECKLIST 

1.0 GENERAL CONCERNS 

	 Were the site-specific objective(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) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 (e.g., human carcinogens) eliminated from analysis without 

appropriate justification? (HHEM - 5.9) 

(continued) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 "weightofevidence" 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 (RfDdt s), 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. C 

 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). 1988b. 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, standalone 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 

HT = Dose Equivalent Averaged Over Tissue or Organ 

T 

HE,50 = Committed Effective Dose Equivalent Per 

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 

wT = 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 and Tools for the Risk 

Assessor, Reviewer, and Manager 

(Section 10.8). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 10-2 

DEFINITIONS FOR CHAPTER 10 

Absorbed Dose (D). 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). 

Becquerel (Bq). One nuclear disintegration per second; the name for the SI unit of activity. 1 Bq = 2.7 x 10-11 Ci. 

Committed Dose Equivalent (H T,50 ). The total dose equivalent (averaged over tissue T) deposited over the 50-year period following the
 

intake of a radionuclide. 

Committed Effective Dose Equivalent (H E,50 ). The weighted sum of committed dose equivalents to specified organs and tissues, in
 

analogy to the effective dose equivalent.
 

Curie (Ci). 3.7 x 1010 nuclear disintegrations per second, the name for the conventional unit of activity. 1 Ci = 3.7 x 10 10Bq.
 

Decay Product(s). A radionuclide or a series of radionuclides formed by the nuclear transformation of another radionuclide which, in this
 

context, is referred to as the parent.
 

Dose Conversion Factor (DCF). The dose equivalent per unit intake of radionuclide. 

Dose Equivalent (H). 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 sievert (Sv); the conventional unit is the rem (1 rem = 0.01 Sv). 

Effective Dose Equivalent (H E). 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 (Gy). The SI unit of absorbed dose. 1Gy = 1 Joule kg-1 = 100 rad.
 

Half-Life (physical, biological, or effective). The time for a quantity of radionuclide, i.e., its activity, to diminish by a factor of a half
 

(because of nuclear decay events, biological elimination of 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 nuclide 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 in 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 (w T). Factor indicating the 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 dose equivalent. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 onscene 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 

Page 10-3 

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 of potential importance at 

Superfund sites are listed in Exhibit 10-1. 

Comment [A66]: The Superfund program has 

updated its approach for assessing radiation 

risks at sites. For current information, consult 

EPA’s Radiation Risk Assessment Guidance for 

CERCLA Sites posted on the Agency’s website: 

http://www.epa.gov/superfund/health/contamin 

ants/radiation/radrisk.htm 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 10-4 

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 xrays). 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 3.7x1010 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 10-12 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 adioisotope-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 

monoenergetically 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, 

carry 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 particles 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 may 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 xand gamma rays interact with matter: the photoelectric effect, the Compton 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. 
 

 

EXHIBIT 10-1 

RADIOLOGICAL CHARACTERISTICS OF SELECTED RADIONUCLIDES a FOUND AT SUPERFUND SITES 

a	 

 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, Co60 has a radioactive half-life of about 5 years 

and a specific activity of 4x10 13 Bq/g, whereas 

Np-237 has a half-life of 2 million years and a 

specific activity of 3×107

 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 = 2.58×10-4C/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=1 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=1) 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, HE , is a weighted sum of dose equivalents to all organs and tissues (ICRP 1977, ICRP 

1979), defined as: 

HE = Σ wT HT
 

T 

where w is the weighting factor for organ or tissue T and HT is the mean dose equivalent to organ or tissue T. The factor 

wT, 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, HE,50, is defined as the weighted sum of committed dose 

equivalents to all irradiated organs and tissues, as follows: 

HE,50 = Σ wT HT,50
 

T 

HE and HE,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 wT 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 (HT,50 ),

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 (HE,50), which are defined as 

weighted sums of the organ-specific dose 

equivalents (i.e., wTHT ) and organ-specific 

committed dose equivalents (i.e., wTHT,50), 

respectively. Weighting factors, wT, 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 1.3×105 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. 
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, 

Page 10-8 

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 

[NARM]). 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 governmentowned/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 
 

 

 

 

 

 

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 

Program (GJRAP), and the Surplus 

Facilities 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 sourcespecific) 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. 
 

 

Page 10-11 

EXHIBIT 10-2 

TYPES OF FIELD RADIATION DETECTION INSTRUMENTS
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 

1979a) 

Eastern Environmental Radiation Facility 

Radiochemistry Procedures Manual (EPA 

1984a) 

A Handbook of Radioactivity Measurement 

Procedures (NCRP 1985a) 

Because of the harsh conditions in which they 

are 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 (NaI(Tl)) crystals, and solid-state 

germanium diodes (Ge(Li)) coupled to 

ratemeters, scalers, or multichannel analyzers 

(MCAs). These instruments provide 

measurements of overall exposure rates in 

counts per minute, or microRoentgens or 

microrem per hour. However, only NaI 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 
 

 

 

Page 10-13 

using detector-and radionuclide-specific calibration 

EXHIBIT 10-3 

TYPES OF LABORATORY RADIATION DETECTION INSTRUMENTSα
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 betascintillation 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 NaI 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 1984b) 

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 in the environment may be found in the 

references listed in the box on the next page. 

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 levels at a contaminated site and for 
 

 

 

 

 

 

 

 

 

 

 

 

 

Page 10-16 

comparing these results to the variability 

observed at background locations. Continuous 

measurements 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 halflives and the decay products of the 

radionuclides. Radionuclides with short halflives, 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 

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 

Radioanalytical Laboratories (EPA 1987b) 

QA Procedures for Health Labs 

Radiochemistry (American Public Health 

Association 1987) 

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. 

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. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 

Page 10-17 

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., I-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. 
Page 10-18 

EXHIBIT 10-4 

EXAMPLE OF LOWER LIMITS OF DETECTION (LLD) 

FOR SELECTED RADIONUCLIDES USING STANDARD ANALYTICAL METHODSa 

 LLD 

Isotope Sample Mediab 

 pCi Bq Methodology 

Co-60 -Water 10 0.4 Gamma Spectrometry 

 -Soil (dry wt.) 0.1 0.004 Gamma Spectrometry 

 -Biota (wet wt.)c

 0.1 0.004 Gamma Spectrometry 

 -Aird 25 0.9 Gamma Spectrometry 

Sr-90 -Water 1 0.04 Radiochemistry 

Cs-137	 -Water 10 0.4 Gamma Spectrometry 

 0.3 0.01 Radiochemistry 

 -Soil (dry wt.) 1 0.04 Gamma Spectrometry 

 0.3 0.01 Radiochemistry 

 -Biota (wet wt.) 1 0.04 Gamma Spectrometry 

 0.3 0.01 Radiochemistry

 -Air 30 1 Gamma Spectrometry 

Pb-210 -Water 0.2 0.007 Radiochemistry 

 -Soil (dry wt.) 0.2 0.007 Radiochemistry 

 -Biota (wet wt.) 0.2 0.007 Radiochemistry 

 -Air 5 0.2 Radiochemistry 

Ra-226 -Water 100 4 Gamma Spectrometry 

 0.1 0.004 Radiochemistry 

0.1 0.004 Radon Daughter Emanation 

 -Soil (dry wt.) 0.1 0.004 Radon Daughter Emanation 

 -Biota (wet wt.) 0.1 0.004 Radon Daughter Emanation

 -Air 1 0.04 Alpha Spectrometry 

 

Th-232 -Water 0.02 0.0007 Alpha Spectrometry 

 -Soil (dry wt.) 0.2 0.007 Radiochemistry 

 -Biota (wet wt.) 0.02 0.0007 Alpha Spectrometry

 -Air 0.3 0.01 Alpha Proportional Counter 

 

U-234 -Water 0.02 0.0007 Alpha Spectrometry 

U-235 -Soil (dry wt.) 0.1 0.004 Alpha Spectrometry 

U-238 -Biota (wet wt.) 0.02 0.0004 Alpha Spectrometry

 -Air 0.2 0.007 Alpha Spectrometry 

(continued) 
 

 

Page 10-19 

EXHIBIT 10-4 (CONTINUED)
 

EXAMPLES OF LOWER LIMITS OF DETECTION (LLD)
 

FOR SELECTED RADIONUCLIDES USING STANDARD ANALYTICAL METHODS3 

 LLD 

Isotope Sample Mediab pCi Bq Methodology 

Pu-238 -Water 0.02 0 .0007 Alpha Spectrometry 

Pu-239 -Soil (dry wt.) 0.1 0.004 Alpha Spectrometry 

Pu-240 -Biota (wet wt.) 0.01 0.0004 Alpha Spectrometry 

 -Air 0.2 0.007 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. 

d Air refers to a sample of 300 m3

 of air collected on a filter, which is analyzed for the radionuclide of interest. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 10-20 

Exhibit 10-4 presents examples of typical LLDs 

using standard analytical techniques. The same 

special considerations noted for chemical 

analyses would also apply for 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. 

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 

Page 10-21 

thorium) detected onsite should be eliminated 

from the quantitative risk assessment. All manmade 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, U235/238) 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 10-22 

transport through ground water to distant 

receptors, transit times may be very long; 

consequently, only radionuclides with long halflives 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 

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, halflives, 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 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 

Page 10-23 

the methods by which these three steps are 

carried out are different for radionuclides. 

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) 

10.5.1 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 NaI(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. 

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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 10-24 

considered. Potential external exposure 

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 

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.) 

10.5.3 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 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 2 

per Bq/m for ground contamination or Sv/hr 

per Bq/m3 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 

Page 10-25 

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 exposure pathways (NRC 1977). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 10-26 

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/m3

), the breathing rate (m3 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 photonemitting 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/m3

), 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 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/m3

), 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 photonemitting 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 

Page 10-27 

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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 doseresponse 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 Internally 

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 lowLET radiations because of the low density 

pattern of ionization they produce. In equal 

doses, the carcinogenicity and mutagenicity of 

high-LET radiations may be an order of 

magnitude or more greater than those of lowLET 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-thannormal 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 

Page 10-29 

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 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 10-30 

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 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. 
 

 

 

 

Page 10-31 

EXHIBIT 10-5 

SUMMARY OF EPA'S RADIATION RISK FACTORSa
 

Risk Significant Exposure Period Risk Factor Range 

 

 

 

 

 

 

 

 

 

 

 

Low LET (Gy-1) 

Teratogenic:

b

 Severe mental retardation Weeks 8 to 15 of gestation 0.25-0.55 

Genetic: 

 Severe hereditary defects, 30-year reproductive generation 0.006-0.11 

 all generations 

Somatic: 

 Fatal cancers Lifetime 0.012-0.12 

In utero 0.029-0.10 All cancers Lifetime 0.019-0.19 

High LET (Gy-1) 

Genetic: 

 Severe hereditary defects, 30-year reproductive generation 0.016-0.29 

 all generations 

Somatic:

 Fatal cancers Lifetime 0.096-0.96 

 All cancers Lifetime 0.15-1.5 

Radon Decay Products (10–6 LM–1) 

 Fatal lung cancer Lifetime 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. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 10-32 

Based on these observations, it appears 

that the risk of cancer is limiting and may be 

used as the sole basis for assessing the radiationrelated 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 Comment [A67]: EPA’s Risk Assessment 

Guidance for Superfund Volume I: Human 

Health Evaluation Manual (Part D, Standardized 

Planning, Reporting, and Review of Superfund 

Risk Assessments) provides planning tables and 

worksheets for use during the risk assessment 

process, radiation risk characterization. See Part 

D, Section 3.1.1, page 3-10 for an overview of 

using Planning Table 8: Calculation of Radiation 

Cancer Risks and page 3-11 for an overview of 

the radiation dose assessment worksheet. Also 

see Appendix 1 for the downloadable Planning 

Tables and instructions for completing the 

tables. See Appendix C for the planning 

worksheets. RAGS, Part D may be found at: 

http://www.epa.gov/oswer/riskassessment/rags 

d/index.htm 

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 doses. This 

information may be used along with organspecific dose conversion factors to derive slope 

factors that represent the age-averaged lifetime 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 10-33 

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/m3

) 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 

Comment [A68]: EPA has updated its 

recommendation concerning the summing of 

radiation cancer risks and chemical cancer risks. 

As stated in its December 1999 document 

Radiation Risk Assessment at CERCLA Sites: 

Q&A (see Q28, page 11), “[e]xcess cancer risk 

from both radionuclides and chemical 

carcinogens should be summed to provide an 

estimate of the combined risk presented by all 

carcinogenic contaminants. An exception would 

be cases in which a person reasonably cannot 

be exposed to both chemical and radiological 

carcinogens. Similarly, the chemical toxicity 

from uranium should be combined with that of 

other site-related contaminants.” While there 

are differences between slope factors for 

radionuclides and chemicals, similar differences 

also occur between different chemical slope 

factors. In the absence of additional 

information, it is reasonable to assume that 

excess cancer risks are additive when 

evaluating the total incremental cancer risk 

associated with contaminated sites. 

EPA continues to recommend that risk 

estimates for radionuclides and chemical 

contaminants also be tabulated and presented 

separately in the risk characterization report. 

The Radiation Risk Assessment Q&A may be 

found at: 

http://www.epa.gov/superfund/health/contamin 

ants/radiation/pdfs/riskqa.pdf 

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 EIS for 
 

 

 

 

 

 

Page 10-34 

Proposed NESHAPs for Radionuclides (EPA 

1989a). 

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. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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. 

RERFTR 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 Radioanalytical 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. EMSLLV 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 Radiochemistry 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 Radioanalytical 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 EIS 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. 

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. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 10-36 

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 AlphaEmitters. (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 Doseresponse 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. 

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: LowLET Radiation, Part II: Scientific Bases for Health Effects Models. NUREG/CR-4214, Rev. 1. Part II. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 10-37 

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/3838). 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. 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 toxicity value for comparison are both 

expressed as absorbed doses or both expressed 

as intakes. 

 Information concerning absorption 

efficiencies 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.1. 

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 

A.2. 

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 A.3. 

 

A.1 ADJUSTMENTS OF TOXICITY 

VALUE FROM ADMINISTERED TO 

ABSORBED DOSE 

 

 

 

 

 

Comment [A69]: EPA has supplemented the 

guidance presented in this document on the 

adjustment of toxicity values from administered 

to absorbed dose. This supplemental 

information can be found in Risk Assessment 

Guide for Superfund (Part E, Supplemental 

Guidance for Dermal Risk Assessment). Please 

consult Sections 4.2 and 4.3 for a description of 

the approach for adjusting toxicity factors and 

calculating absorbed toxicity values. RAGS Part 

E may be found at: 

http://epa.gov/oswer/riskassessment/ragse/ind 

ex.htm 

Because there are few, if any, toxicity 

ACRONYMS FOR APPENDIX A 

ATSDR = Agency for Toxic Substances and 

Disease Registry 

ECAO = 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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 (e.g., mg/kg-day). 

Administered Dose. The mass of substance administered 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). 

Exposure Route. The way a chemical or physical agent comes in contact with an organism (i.e., by 

ingestion, inhalation, or dermal contact). 

Intake. A measure of exposure expressed as the mass of substance in contact with the exchange 

boundary per unit body weight per unit time (e.g., mg/kg-day). Also termed the normalized 

exposure rate, equivalent to administered dose. 

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. 

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 

reference values for dermal exposure, oral 

values are frequently used to assess risks from 

dermal exposure. Most RfDs and some slope 

factors are expressed as the amount of substance 

administered per unit time and unit body weight, 

whereas exposure estimates for the dermal route 

of exposure are eventually expressed as 

absorbed doses. Thus, for dermal exposure to 

contaminants in water or in soil, it may be 

necessary to adjust an oral toxicity value from 

an administered to an absorbed dose. In the 

boxes to the right and on the next page are 

samples of adjustments for an oral RfD and an 

oral slope factor, respectively. If the oral toxicity 

value is already expressed as an absorbed dose 

(e.g., trichloroethylene), it is not necessary to 

adjust the toxicity value. 

In the absence of any information on 

absorption for the substance or chemically 

related substances, one must assume an oral 

absorption efficiency. Assuming 100 percent 

absorption in an oral administration study that 

serves as the basis for an RfD or slope factor 

EXAMPLE: ADJUSTMENT OF AN 

ADMINISTERED TO AN ABSORBED DOSE RfD 

An oral RfD, unadjusted for absorption, equals 10 

mg/kg-day. 

Other information (or an assumption) indicates a 20% 

oral absorption efficiency in the species on which the 

RfD is based. 

The adjusted RfD that would correspond to the 

absorbed dose would be: 

10 mg/kg-day x 0.20 = 2 mg/kg-day. 

The adjusted RfD of 2 mg/kg-day would be compared 

with the amount estimated to be absorbed dermally 

each day. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page A-3 

would be a non-conservative approach for 

estimating the dermal RfD or slope factor (i.e., 

depending on the type of chemical, the true 

absorbed dose might have been much lower than 

100 percent, and hence an absorbed-dose RfD 

should similarly be much lower or the slope 

factor should be much higher). For example, 

some metals tend to be poorly absorbed (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)-1. 

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) –1/0.20 = 8 (mg/kg-day) –1. 

The adjusted slope factor of 8 (mg/kgday)-1 

would be used to estimate the cancer risk 

associated with the estimated absorbed 

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. 

A.3 ADJUSTMENT FOR MEDIUM OF 

EXPOSURE 

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. 

If the medium of exposure in the site 

exposure assessment differs from the medium of 

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. 
 

 

 

 

 

 

 

 

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: 

In the absence of a strong argument for 

making this adjustment or reliable information 

on relative absorption efficiencies, assume that 

the relative 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
 

INDEX 

Comment [A70]: The index in Appendix B may 

not reflect the true page numbers of this annotated 

version. 

A 

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, sedim

or dust 6-39, 6-41 to 6-43, 7-16
 

following dermal contact with water 6-34

39, 7-16 

radiation 10-1, 10-2, 10-6
 

toxicity value 7-10, 7-16, 8-5, A-1, A-2 

 

Absorption adjustment
 

dermal exposures 8-5, A-1, A-2

 medium of exposure 8-5, A-3, A-4
 

 

Absorption efficiency

 default assumptions 6-34, 6-39, A-2 to A

 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-ter

Acute toxicants 6-23, 6-28
 

 

ADIs. See Acceptable daily intakes 

Administered dose 6-2, 6-4, 7-1, 7-2, 7-10, 

8-5, A-1 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

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
 

B 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page B-2 

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 

C 

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 

definition 4-2 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page B-3 

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 

 absorption efficiency A-1 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 

E 

E. See Exposure level 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page B-4 

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-1 

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-1 

 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-1

 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 

F 

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
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page B-5 

Fraction organic content of soil 4-7
 

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 

HE. See Dose equivalent 

HEE,50. 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-1
 

Health and Environmental Effects Profiles 7-1,
 

7-14, 

Health Assessment Documents 7-1, 7-14, A-1 

Health Effects Assessments 7-1, 7-14, A-1
 

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
 

Ht. See Dose equivalent
 

HTT,50. See Dose equivalent
 

Hydraulic gradient 4-7
 

I 

IARC. See International Agency for Research on 

 Cancer
 
 

 

 

 

 

 

 

 

 

 

 

 

 

Page B-6 

IDL. See Instrument detection limit 

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 

Kd 6-12 

Koc 6-12 

Kow 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-effectlevel 

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 

MF. See Modifying factor
 
 

 

 

 

 

 

 

 

 

 

 

 

Million electron volts 10-1, 10-5
 

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
 

Page B-7 

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 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page B-8 

PC. See Permeability constant
 

PE. See Performance evaluation 

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 

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, 

1029
 

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 

Page B-9

chronic 7-1, 7-2, 7-5, 8-1, 8-2, 8-8, 8-10, 8­

13, A-1, 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, 423, 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 

RfDdt. See Reference dose 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page B-10 

RfDs See Reference dose 

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, 3-2, 3-3 

SDI. 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-1 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
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 

Page B-11 

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, 517, 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-1 

 definition 7-3

 generation of 7-16

 hierarchy of information 7-15 

 oral 7-16, 10-33, A-2

 radiation 10-22, 10-32 

educing 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 
 

 

 

 

 

Page B-12 

Trip blanks. See Blanks 

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
 

WT. See Weighting factors