United States
         Environmental Protection
         Agency
Great Lakes
National Program Office
77 West Jackson Boulevard
Chicago, Illinois 60604
EPA 905-R93-007
December 1993
&EPA   Assessment and
         Remediation
         Of Contaminated Sediments
         (ARCS) Program
         RISK ASSESSMENT AND
         MODELING OVERVIEW
         DOCUMENT
                             United States Areas of Concern

                             ARCS Priority Areas of Concern

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ASSESSMENT AND REMEDIATION OF CONTAMINATED SEDIMENTS
                     (ARCS) PROGRAM
                RISK ASSESSMENT AND
          MODELING OVERVIEW DOCUMENT
            Great Lakes National Program Office
           U.S. Environmental Protection Agency
                77 West Jackson Boulevard
                Chicago, Illinois 60604-3590
                                   U.S. Environmental Protection Agency
                                   Region 5, Library (PL-12J)
                                   77 West Jackson Boulevard, 12th Floor
                                   Chicago, IL  60604-3590

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             DISCLAIMER
The information in this document has been funded wholly
or in part by the  U.S. Environmental Protection Agency
(USEPA) under USEPA Contract Numbers 68-C1-0012 and
68-CO-0054 to AScI Corporation and under USEPA Con-
tract Number 68-C2-0134 to Battelle  Ocean Sciences.
Mention of trade names or commercial products does not
constitute endorsement  or recommendation  for use  by
USEPA.

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A CKNO WLEDGMENTS
      The initial draft of this report was prepared through support from U.S. Environmental
      Protection Agency (USEPA) to AScI Corporation of Athens,  Georgia, under USEPA
      Contract Numbers 68-C1-0012 and 68-CO-0054, and administered by USEPA's Environ-
      mental Research Laboratory of Athens, Georgia. The primary authors of the initial draft
      report were Dr. James Martin of AScI and Dr. Judy Crane, formerly of AScI, now of
      E.V.S. Consultants of Vancouver, Canada.

      This report was edited and produced by PTI Environmental Services (PTI) of Bellevue,
      Washington, for Battelle  Ocean  Sciences of Duxbury, Massachusetts, under USEPA
      Contract Number 68-C2-0134.  Additions to the text of the initial draft were made by
      Dr. Robert Pastorok and Ms. Lisa Yost of PTI.

      This report was prepared for the Risk Assessment/Modeling Work Group as part of the
      Assessment and Remediation of Contaminated Sediments (ARCS) Program administered
      by USEPA's Great Lakes National  Program  Office (GLNPO) in Chicago, Illinois.
      Dr. Marc  Tuchman of GLNPO served as chairman of the Risk Assessment/Modeling
      Work Group.  Mr. David Cowgill of GLNPO and Dr. Tuchman  served as  the ARCS
      Program managers.

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ABSTRACT
       This document provides an overview of risk assessment and modeling methods as applied
       to areas with  contaminated sediments in the Great Lakes region.  The document was
       prepared under the Assessment and Remediation of  Contaminated Sediments  (ARCS)
       Program, administered by the U.S. Environmental Protection Agency's (USEPA) Great
       Lakes National Program Office (GLNPO), in Chicago, Illinois.

       The goal of the risk assessment and modeling studies  was to develop and demonstrate a
       comprehensive human health and  ecological risk assessment framework for use  in the
       evaluation of alternative remedial  actions for contaminated sediments.   As part of that
       effort, risk assessment and modeling studies were performed at selected Areas of Con-
       cern in the Great Lakes region. The goal of those studies was to  provide estimates of
       potential changes in exposure and risk that may occur either under a no-action alternative
       or following implementation of various remedial alternatives for contaminated sediments.
       The risk estimates may then be used to aid in the selection  of an appropriate remedial
       action. This document does not provide detailed guidance on risk assessment and model-
       ing methods, but refers the reader to pertinent source documents for further information.
                                             IV

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CONTENTS
                                                                  Page

     DISCLAIMER                                                     ii

     ACKNOWLEDGMENTS                                            iii

     ABSTRACT                                                      iv

     LIST OF FIGURES                                                vii

     LIST OF TABLES                                                viii

     ACRONYMS AND ABBREVIATIONS                                 ix

     1.  INTRODUCTION                                               1

         BACKGROUND                                                1

         RISK MANAGEMENT FRAMEWORK                              2

     2.  HUMAN HEALTH AND ECOLOGICAL RISK ASSESSMENTS FOR
         CONTAMINATED SEDIMENTS                                   8

         HUMAN HEALTH RISK ASSESSMENT                             8

             Data Review                                              10
             Identifying Contaminants of Concern                            11
             Exposure Assessment                                        11
             Toxicity Assessment                                         15
             Risk Characterization                                        16
             Uncertainty Analysis                                         18
             Applications                                              19

         ECOLOGICAL RISK ASSESSMENT                               20

             General Framework                                         21
             Problem Formulation                                        24
             Exposure Assessment                                        29

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                                                              Page

       Ecological Effects Assessment                                  32
       Risk Characterization                                         35

3.   MASS BALANCE MODELING APPROACH FOR ASSESSING
    REMEDIAL ALTERNATIVES AT CONTAMINATED SEDIMENT SITES   38

    OVERVIEW                                                   38

    COMPLEXITY OF THE MASS BALANCE MODELING STUDY         40

    COMPONENTS OF THE MASS BALANCE MODELING STUDY         42

       Water Transport Models                                      42
       Sediment Transport Models                                    44
       Contaminant Exposure Model                                  45
       Food Chain Model                                           46

    REQUIRED FIELD DATA                                       47

       Water Transport Data                                         48
       Sediment Transport Data                                      48
       Contaminant Exposure Data                                    49
       Food Chain Data                                            52

    MODEL APPLICATION                                         53

4.   COMPARATIVE RISK  ASSESSMENT                              55

5.   SUMMARY                                                   58

6.   GLOSSARY                                                   60

7.   REFERENCES                                                 69
                                 VI

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LIST OF FIGURES
                                                                           Page

      Figure 1-1.   Overview of the comprehensive risk management process            4

      Figure 2-1.   Components of a human health risk assessment                     9

      Figure 2-2.   Ecological risk assessment framework                           22

      Figure 2-3.   Ecological assessment tools for contaminated sediments             28

      Figure 3-1.   Components of the mass balance modeling study                   43

      Figure 4-1.   Comparative risk assessment in the risk management
                  process                                                     56
                                         VII

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LIST OF TABLES
                                                                           Page

      Table 2-1.   Generic equation for calculating chemical intake levels             14

      Table 2-2.   Estimated carcinogenic and noncarcinogenic risks to
                  individuals residing in the lower Saginaw River Area of
                  Concern                                                    17

      Table 3-1.   Examples of parameters measured for the ARCS RAM
                  mass balance modeling studies                                  51
                                         VIII

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ACRONYMS AND ABBREVIATIONS
      AOC
      ARCS
      Corps
      CSF
      CSO
      GLNPO
      IRIS
      LOAEL
      NOAEL
      PCB
      QA/QC
      RAM
      RAP
      RfC
      RfD
      STORET
      USEPA
      USGS
Area of Concern
Assessment and Remediation of Contaminated Sediments
U.S. Army Corps of Engineers
cancer slope factor
combined sewer overflow
Great Lakes National Program Office
Integrated Risk Information System
lowest-observed-adverse-effect level
no-observed-adverse-effect level
polychlorinated biphenyl
quality assurance and quality control
Risk Assessment/Modeling
Remedial Action Plan
reference concentration
reference dose
storage and retrieval
U.S. Environmental Protection Agency
U.S. Geological Survey
                                         IX

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 1.   INTRODUCTION
      This document provides an overview of risk assessment and modeling methods as applied
      to areas with contaminated sediments in the Great Lakes region. It was prepared under
      the Assessment and Remediation of Contaminated Sediments (ARCS) Program, admini-
      stered by the U.S. Environmental Protection Agency's (USEPA) Great Lakes National
      Program Office (GLNPO) in Chicago, Illinois.
BACKGROUND

       Although toxic discharges in the Great Lakes and elsewhere have been reduced in the last
       20 years, persistent contaminants in sediments continue to pose a potential risk to human
       health and the environment.  High concentrations of contaminants in bottom sediments
       and associated adverse effects have been well  documented throughout the Great  Lakes
       and associated connecting channels. The extent of sediment contamination and its associ-
       ated adverse effects have been the subject of considerable concern and study in the Great
       Lakes community and elsewhere.  Contaminated sediments can have direct toxic effects
       on aquatic life, such as the development of cancerous tumors in fish exposed to polycyc-
       lic aromatic hydrocarbons in sediments.  The bioaccumulation of toxic contaminants in
       the food chain can also pose a risk to humans, wildlife, and aquatic organisms.  As a
       result, advisories against consumption of fish  are in place in many areas of the Great
       Lakes.  These advisories have also had a negative economic impact on the affected areas.

       To address concerns about the deleterious effects of contaminated sediments in the Great
       Lakes, Annex 14 of the Great Lakes Water Quality Agreement between the United States
       and Canada  stipulates that the cooperating parties will identify the nature and extent of
       sediment contamination in the Great Lakes, develop methods to assess impacts, and eval-
       uate the technological capability of programs to remedy such contamination. The 1987
       amendments to the Clear Water Act, in § 118(c)(3), authorized GLNPO to coordinate
       and conduct a 5-year study and demonstration projects relating to the appropriate treat-
       ment of toxic contaminants in bottom sediments.  Five areas were specified in the  Act
       as requiring  priority consideration in conducting demonstration projects:  Saginaw Bay,
       Michigan; Sheboygan Harbor, Wisconsin; Grand  Calumet River, Indiana; Ashtabula
       River, Ohio; and Buffalo  River, New York.  To  fulfill the requirements of the Act,
       GLNPO initiated the ARCS Program.  In addition, the Great Lakes  Critical Programs
       Act of 1990  amended the section, now § 118(c)(7), by extending the program by 1 year
       and specifying completion dates  for certain interim activities.  ARCS  is an integrated
       program for the development and testing of assessment techniques and remedial action
       alternatives for contaminated sediments. Information from ARCS Program activities will
       help address contaminated sediment concerns  in the development of Remedial Action

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                                                                   Chapter 1. Introduction
      Plans (RAPs) for all 43 Great Lakes Areas of Concern (AOCs),  as  identified by the
      United States and Canadian governments, as well as lakewide management plans.

      To accomplish the ARCS  Program objectives, the following work groups were estab-
      lished:

           •   The  Toxicity/Chemistry Work Group was responsible for assessing the
               current nature and extent of contaminated sediment problems in the five
               priority AOCs by studying the chemical, physical, and biological charac-
               teristics of contaminated sediments and their biotic communities, and for
               demonstrating cost-effective assessment  techniques that can be used at
               other Great Lakes AOCs.

           •   The  Risk Assessment/Modeling  (RAM) Work Group was responsible for
               assessing the current and future risks presented by contaminated sediments
               to human and ecological receptors under various remedial alternatives
               (including the no-action alternative) at the five priority AOCs,

           •   The  Engineering/Technology Work Group was responsible for evaluating
               and testing available removal and remedial technologies for contaminated
               sediments, for selecting promising technologies for further testing, and for
               performing field demonstrations at each of the five priority AOCs.

           •   The Communication/Liaison Work Group was responsible for facilitating
               the flow  of information from the technical work groups and the overall
               ARCS Program to the interested public and for providing feedback from
               the public to the  ARCS Program on needs, expectations, and perceived
               problems.

      This document is intended to provide an overview of the risk assessment and modeling
      methods developed by the ARCS RAM Work Group and to provide general guidance on
      their application to other Great Lakes AOCs.
RISK MANAGEMENT FRAMEWORK

       Sediment contamination is of concern primarily because of the potential risks it poses to
       humans, wildlife, and aquatic organisms.  Therefore, the management of contaminated
       sediments includes the overall process of risk management.  For this project,  risk man-
       agement is  defined as the process of integrating findings from a risk assessment with
       engineering, policy, and nontechnical concerns to make decisions about sediment reme-
       diation at a specific site or to set remediation priorities among sites.  Risk management
       should be distinguished from risk assessment, which is the process of producing qualita-
       tive or quantitative estimates of the potential risks  associated with exposure to specific
       concentrations of contaminants under specific current or future exposure conditions at a
       site.

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                                                              Chapter 1. Introduction
The general objective of the ARCS RAM Work Group was to develop and demonstrate
a comprehensive risk management framework for:  1) identifying existing risks to human
health and  ecological receptors at sites with contaminated sediments, 2) estimating the
potential impact of various sediment remedial alternatives on contaminant concentrations
in various  media and their associated risks, and 3) comparing existing  and potential
future risks to aid in the selection of sediment remedial alternatives.

Steps in the overall risk management process are illustrated in Figure 1-1.  A general
discussion of each of the steps is provided below, followed by a more detailed descrip-
tion of the  use of risk assessment and modeling in the ARCS RAM studies.

    Step 1.  Initial Screening of Potential AOCs: The first step in the risk man-
             agement process  involves the use of screening-level assessments  to
             identify sites  that may pose a potential  threat to human health  or
             ecological receptors based, in part, on sediment contamination.  The
             Great  Lakes states,  the U.S. and Canadian governments,  and the
             International Joint Commission have designated 43 AOCs around the
             Great Lakes  on the basis of impairment of beneficial uses.  All but
             one of these AOCs have been identified as having sufficient sediment
             contamination to pose potential threats to human health  or ecological
             receptors.

    Step 2.  Risk Assessment Planning:  In this step, existing information is first
             compiled to describe the physical features of the AOC, the general
             distribution of sediment contaminants and their potential sources, and
             the human and ecological receptor populations likely to be present.
             Contaminants of concern, biological species, endpoints (measured bio-
             logical or ecological qualities), and primary exposure pathways for
             human and ecological receptors are then identified for use in the risk
             assessment. This information is used to develop preliminary remedial
             action objectives, which are general descriptions of what  remedial
             actions should accomplish,  including the reduction of risks associated
             with exposure to contaminated sediments.  Potential remedial actions
             may then be identified.  As part of risk assessment planning, deficien-
             cies in the available data that might preclude an adequate baseline risk
             assessment  should  be  identified.   Supplementary  field  sampling
             (Step 3) may then be conducted if necessary.   The risk assessment
             planning step provides  the organizational framework for the subse-
             quent steps in the risk management process.

    Step 3.  Supplementary Field Sampling:  If data gaps were identified as part
             of the previous step, supplementary field  sampling  efforts may  be
             required to  collect  the information necessary for  a  detailed site
             assessment.  Additional information may need to be gathered on the
             physical, biological, and chemical conditions of the system to further

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                    Modeling of Contaminant
                       Transport and Fate
 f
                                                         Initial Screening of
                                                     Potential Areas of Concern
                                                             (AOCs)
                                                f
         Risk Assessment
             Planning
t
                                                     Baseline Risk Assessment
f
                                                        Ranking of Subareas
                                                          within the AOC
                                                ••
                                                  I
         Initial Screening of
       Remedial Alternatives
                                               -r
         Comparative Risk
           Assessment
f
F
Supplementary Field
     Sampling
                                                     Selection and Implementation
                                                     of Final Remedial Action Plan

                                                     Post-Remediation Monitoring
                         Figure 1-1. Overview of the comprehensive risk management process.

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                                                         Chapter 1.  Introduction
         characterize the nature and extent of the sediment contamination prob-
         lem. The data are also used to develop appropriate sediment remedial
         alternatives, to support mass balance modeling, and to conduct the
         comparative risk assessment of the remedial alternatives.  A separate
         ARCS Assessment Guidance Document (USEPA 1993) describing field
         sampling methods is being prepared as part of the ARCS Program.

Step 4.   Baseline Risk Assessment:  A baseline  risk assessment  estimates
         current  risks to  humans, wildlife,  and aquatic organisms resulting
         from direct and  indirect exposure to contaminated sediments in the
         absence of any sediment remediation.  The baseline risk estimates,
         developed using  conservative, or health protective, assumptions are
         used to  determine which contaminants and exposure pathways pose
         the greatest risk, to determine  whether remediation is likely to be
         required, and to provide a baseline against which any future remedial
         action can be evaluated.

Step 5.   Ranking of Subareas Within the AOC:   Within a particular AOC,
         there will be spatial variations in  the  concentrations  and types of
         sediment contaminants; variations in the risks the sediment contami-
         nants pose to humans and ecological receptors resulting from varying
         exposure potential, bioavailability,  or toxicity; and variations in the
         costs associated with sediment remediation. Available information on
         sediment chemistry, toxicity tests, and benthic community structure
         may be  combined in a numerically based ranking system to prioritize
         specific subareas within  an AOC for remedial action.  Additional
         detail on sediment ranking procedures developed under the ARCS
         Program is provided in the ARCS Assessment Guidance Document
         (USEPA 1993).  The results of the human health and ecological risk
         assessments may be qualitatively considered along with  the numerical
         sediment ranking in this prioritization process.

Step 6.   Initial Screening of Remedial Alternatives: There  is a wide variety
         of possible sediment remedial alternatives, only a few of which may
         be practical at a particular site. This step in the risk management
         process  involves the selection of a limited  number of possible reme-
         dial alternatives  (e.g., no action, in situ treatment, or removal alter-
         natives) for further evaluation.  Additional  field  sampling may be
         required following the selection of the sediment remedial alternatives
         to be evaluated.   The selection of candidate subareas for sediment
         remediation and  possible remedial alternatives is based on a detailed
         site assessment,  which delineates the nature and extent of sediment
         contamination within subareas of the AOC.

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                                                         Chapter 1. Introduction
Step 7.   Modeling of Contaminant Transport and Fate:  To assess the human
         health and ecological  risks posed by various sediment remediation
         scenarios,  contaminant releases must be  estimated for each of the
         remedial alternatives.  Previous steps of the risk management process
         provide information concerning  the nature  and extent of  existing
         sediment contamination and estimates of baseline human health and
         ecological risks.  However, those steps provide little information that
         can be used directly to estimate changes that may occur as a result of
         remediation.  In this step, transport and  fate models are  used with
         physical, chemical, and biological data for the AOC to evaluate the
         effectiveness of the various remedial alternatives in reducing contam-
         inant concentrations in environmental media of concern.   Outputs
         from these models may include predictions of contaminant concentra-
         tions in air, water,  soil,  sediments, and  biota based on present  or
         projected contaminant loadings or expected changes in contaminant
         concentrations over time following remediation.

Step 8.   Comparative Risk Assessment:  The objective of this step is to esti-
         mate changes in risks, relative to the baseline risk, that would result
         from implementation of the various remedial alternatives evaluated.
         For example, the comparative risk assessment can be used to estimate
         the impacts of various remedial  alternatives on human health risks
         from consumption of contaminated fish over time.  This assessment
         integrates data from all previous  steps into a risk assessment frame-
         work.  Ideally, this comparative risk assessment should include  an
         estimation of both the changes in risks at the AOC following sediment
         remediation  and the changes  in  risks  at the site of disposal of the
         contaminated sediments. The remedial action objectives that had been
         developed under Step  2 are then  refined during this step.

Step 9.   Selection and Implementation of Final Remedial Action Plan: In this
         step, information from the comparative risk assessment is  used in
         conjunction with other factors (e.g., economic, political) to select the
         most appropriate remedial alternative(s) to implement.

Step 10. Post-Remediation Monitoring: The last step in the risk management
         process is to monitor the AOC  following sediment remediation to
         demonstrate successful reductions in sediment contamination and
         associated risks to human health and ecological receptors. Monitoring
         should focus on parameters that  have  the greatest influence on risk
         estimates and remedy selection.  For example, if the human health
         risk estimates are predominantly based on concentrations of polychlor-
         inated biphenyls (PCBs) in fish, this parameter should be used as the
         indicator of remedial effectiveness.

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                                                             Chapter 1. Introduction
The studies of the ARCS RAM Work Group have provided support for Steps 4-8 of the
risk management process. Other ARCS studies deal specifically with other aspects of the
decision-making process.  The final results of the ARCS RAM studies are estimates of
contaminant concentrations and potential risks associated with various sediment remedial
alternatives that may then be used, along with other information collected at a site, to
select the appropriate remedial  action  from among  the various alternatives.   The
following sections of this document provide an overview of the use of risk assessment
and modeling in the ARCS RAM studies.

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2.   HUMAN HEAL TH AND ECOL OGICAL  RISK
      ASSESSMENTS FOR CONTAMINATED
      SEDIMENTS
      As part of the ARCS RAM studies, baseline risk assessments were performed to estimate
      the current health risks to humans and wildlife exposed to sediment-derived contaminants
      in the absence of any remediation.   The results of these assessments can be used by
      ARCS risk managers in prioritizing sites and making decisions concerning the need for
      sediment remediation. The risk assessment approach developed and used in the ARCS
      Program is intended to produce conservative estimates of risk in order to ensure adequate
      protection of human  health and the environment.  This approach to risk assessment is
      specifically designed  not to underestimate risks and, therefore, is likely to overestimate
      risks at many sites.  The following sections provide an overview  of the risk assessment
      approach used under the ARCS Program.  This approach may be used to assess potential
      human and ecological risks at other sites with contaminated sediments.
HUMAN HEAL TH RISK ASSESSMENT

      Individuals in the Great Lakes region may be exposed to sediment contaminants through
      various activities that result in intake of contaminants through dermal, ingestion, and/or
      inhalation pathways.  For the ARCS risk assessments, human health risk estimates were
      determined  for both  carcinogenic effects (i.e., increased probability of an individual
      developing  cancer over  a lifetime)  and noncarcinogenic effects (i.e.,  chronic or
      subchronic effects other than cancer)  over a range of exposure scenarios.  The risk
      estimates were calculated by using conservative exposure assumptions and USEPA-
      verified toxicity values called cancer slope factors (CSFs) and reference doses (RfDs)
      (for  noncarcinogenic  effects).   The  primary  guidance used to  conduct these  risk
      assessments was obtained from USEPA's Risk Assessment Guidance for Superjund—
      Volume I: Human Health Evaluation Manual (Part A) (USEPA 1989c), although the use
      of additional USEPA guidance for risk assessment (USEPA 1988b, 1989a,b, 1991) is
      also  described herein.  The following sections  describe the main components used  in
      performing  the ARCS human health risk assessments (Figure 2-1), including specific
      examples and recommendations. Baseline human health risk assessments were conducted
      under the ARCS Program for the five priority AOCs: Saginaw River, Michigan (Crane
      1992b); Sheboygan River, Wisconsin (Crane 1993a); Grand Calumet  River, Indiana
      (Crane 1993b); Ashtabula River,  Ohio (Crane  1992a); and Buffalo River, New York
      (Crane 1993c).  The same human health risk assessment framework can be applied to any
      site with contaminated sediments.
                                           8

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                                               Example of an Exposure Pathway for
                                                      Recreational Fishing
                                              Sediments
        Basis for Selection of
      Contaminants of Concern
Frequency of detections

Comparison with background
concentrations

Consideration of potential
laboratory contamination
                     Exposure Assessment
                      • Populations
                      • Pathways
                      • Exposure point
                        Concentrations
                      • Intake rates
  Data Review
and Identification
of Contaminants
  of Concern
Toxicity, persistence, and mobility
                           Carcinogens
Risk Characterization
 • Carcinogenic and
  noncarcinogenic risks
 • Uncertainty assessment
                                                       Toxicity Assessment
                                                                      Risk =
                                                                      Intake x Cancer Slope Factor
Noncarcinogens
Hazard Index =
Site-specific Intake
 Reference Dose
                                                |  Carcinogenic Effects

                                                 Use cancer slope factors
                                                I  Noncarcinogenic Effects

                                                 Use reference doses
    Figure 2-1.  Components of a human health risk assessment.

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                                          Chapter 2. Human Health and Ecological Risk Assessment
Data Review
       Prior  to beginning the human health risk assessment,  site data must be collected and
       analyzed to determine contaminant concentrations in the media of interest (e.g., air,
       water, sediments, biota) and potential routes of exposure to contaminated media.  Avail-
       able historical data, including information on site use and possible contaminant sources,
       should be reviewed to focus sampling efforts on contaminants known or likely to be pres-
       ent.  Such data may include analytical data  from previous sampling efforts, descriptions
       of the past uses of the site or other site records, and  interviews with  site personnel that
       may suggest what contaminants may be present.  For example, RAPs contain information
       about monitoring and scientific studies that have been conducted at Great Lakes sites.
       USEPA's storage and retrieval (STORET) database is also a good source of water quality
       data that are routinely collected at U.S. Geological  Survey (USGS) and statewide gaging
       stations.  In addition, to determine current or future uses of the site, personnel at various
       local, State, and Federal agencies that deal with public health, natural resource, and fish
       and wildlife issues should also be contacted  for information about the site.  In particular,
       applicable zoning regulations, land use plans, and restrictions on site uses  (e.g., fishing
       or hunting bans) should be described in the risk assessment.  The risk assessor  should
       visit the site, preferably during the period of greatest activity or during several seasons,
       to observe recreational and business uses of the AOC.  It may also be helpful to inter-
       view  game wardens, lifeguards,  and local officials regarding site use.

       A thorough sampling program for sediments,  water, fish, and other important media
       should be conducted using appropriate quality  assurance and quality control (QA/QC)
       procedures, such as those identified in Guidance for Data Usability in Risk Assessment
       (USEPA 1990). Water, sediment, and fish  samples should be collected preferentially in
       areas  where people are known to be using the site, such as public beaches, or are likely
       to use the site in the future, such  as areas near shorelines or along access roads.  Samples
       should also be collected at one or more reference sites (i.e., areas that are unlikely to be
       influenced by sediment contaminants within  the AOC or by other anthropogenic  sources).
       In addition, several species of fish should be sampled, including species that feed on the
       bottom, such as carp and catfish, and species  that feed in  the water column, such as
       walleye. Both whole body and skin-on or skin-off fillets should be analyzed for various
       organic and inorganic chemicals, especially  those chemicals detected in the sediments and
       known to bioaccumulate in fish  tissue.

       The need for air sampling should be evaluated on a case-by-case basis.   Exposures to
       contaminants in air are likely to contribute much less to overall site risks than exposures
       via other pathways such as consumption of fish.  Thus,  air sampling is  not  generally
       required for screening-level evaluations and was not conducted as part of the ARCS risk
       assessments.   However,  the air pathway may   be important  at sites  with volatile
       contaminants of concern, where upland soils  are exposed, or where  areas of sediments
       are dry for a substantial proportion of the time and thus may be a  source of airborne
       particulates.  At some such sites, simple models may be used to estimate exposures to
       contaminants via the air pathway.
                                               10

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                                         Chapter 2.  Human Health and Ecological Risk Assessment
       Once data from current and historical sources have been reviewed, the most appropriate
       data available for the media of interest should be selected for use in the risk assessment.
       The adequacy of QA/QC procedures followed in generating the analytical data should be
       a key criterion in  selecting  data.  However,  a complete QA/QC review  may  not be
       possible, particularly when analyses are conducted using historical data.  For example,
       the ARCS risk assessments relied primarily on historical data, and in many cases, little
       QA/QC information was supplied with the data. Thus, risk assessment staff should work
       with  the regulatory agency's project manager in  determining  whether a data set is
       adequate for a specific risk assessment application.  In addition, the implications of any
       limitations in available data should be discussed in  the risk assessment document.  For
       example, unsuitable detection and quantification limits are often a major limitation in the
       use of historical data sets.
Identifying Contaminants of Concern

       A list of all the contaminants detected in the media of interest at the site should be made.
       Inorganic chemicals present at concentrations near background levels and chemicals that
       are  infrequently detected or that may be  present as laboratory contaminants may be
       excluded.  Where the list of contaminants of concern is extensive, a screening step can
       be conducted to exclude contaminants that only contribute  a minimal amount to  the
       overall site risk.  For example, risks associated with the maximum detected concentration
       can  be calculated using toxicity data available in USEPA's Integrated Risk Information
       System  (IRIS)  database and exposure assumptions  that assume a higher degree of
       exposure than is likely  to occur at the site.  Such  an approach is considered  to be
       conservative because it incorporates assumptions that may overestimate risks in order to
       ensure that risks are not underestimated.  Using this approach, contaminants can then be
       excluded when they contribute an individual risk of less than  1 x 10~7 (for carcinogens)
       or a hazard quotient of less than 0.1 (for noncarcinogens).  A  carcinogenic risk of
       1 x 10~7 corresponds to  a one-in-ten-million chance of an individual developing cancer
       during their lifetime.   Use of these conservative  target risk  levels  and worst-case
       exposure assumptions (e.g., use  of the maximum detected concentration) generally
       ensures that chemicals with  significant risks due to the cumulative  effects of multiple
       contaminants and multiple exposure pathways are not prematurely excluded from the risk
       assessment.
Exposure Assessment

       In the exposure assessment, the magnitude, frequency, duration, and route of direct and
       indirect exposures of individuals to sediment-derived contaminants from an AOC are
       determined.  Populations that may be exposed (i.e., receptor populations) should first be
       identified by considering the site's  proximity to population centers, the accessibility of
       the site, and any features such as beaches or fishing piers that would attract visitors. The
       predominant types of receptor populations to consider are residents, workers, and recrea-
       tional visitors.  Recreational uses of AOCs may include fishing, swimming, boating, or
                                              11

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                                   Chapter 2. Human Health and Ecological Risk Assessment
beach activities. Current and potential future exposures should be evaluated. In particu-
lar,  future exposures should  be evaluated when  future uses of a site may increase the
potential for exposure to site contaminants. For example, if a site may be used for resi-
dential  purposes  in  the future, exposure to  site soils and  sediment could be  greatly
increased in comparison with a current recreational scenario.

Exposures to contaminants can potentially occur via three exposure routes:  ingestion,
dermal  contact, and inhalation, each of which is in turn  part of numerous  exposure
pathways.   Ingestion  of contaminants can  result from  inadvertent consumption of
contaminated soils or sediment, or through consumption of drinking water, surface water,
or wildlife. Dermal contact involves direct contact of the skin with either contaminated
sediments, riverplain soils, or overlying water.  Inhalation of airborne vapors  or dust
may  introduce contaminants of concern  into the respiratory  system.   The  ingestion
exposure pathways often result in higher exposure estimates than the dermal or inhalation
pathways because  of the greater absorption of contaminants through the gastrointestinal
tract  as compared with absorption through the skin, and  the relatively high  levels of
intake of contaminants in soil, water, and  food as compared with inhalation of contami-
nants.

The potential pathways by which people may be exposed to contaminants from an AOC
are then examined to determine whether they are complete or incomplete. An exposure
pathway is complete if there is:  1) a source and mechanism of chemical release, 2) a
retention or transport medium  (or media) whereby chemicals are  transferred between
media, 3) an exposure point where contact occurs, and 4) an exposure route by which
contact  occurs  (USEPA 1989c).  An exposure pathway is incomplete if any of these
conditions is not met.  The exposure pathways that were complete for most of the five
priority ARCS  sites  included: 1)  consumption of contaminated  fish, 2) dermal  contact
with contaminated water,  3)  limited  dermal contact  with contaminated sediments, and
4) limited ingestion of surface water while swimming.  Incidental ingestion of sediment
may also be of concern at some sites.

All complete exposure pathways should be evaluated in the exposure assessment unless
certain criteria  apply.  These criteria include:  1) the potential  magnitude of exposure
from a pathway is low, or 2) the probability of the exposure occurring is very low and
the risks associated with the occurrence are not high  (USEPA 1989c).  For example, at
the Saginaw River AOC, there are no beaches along the river and swimming may occur
only infrequently when people jump off recreational boats into the water. In addition to
contacting  the water, these people could ingest some water while swimming.  In this
case, the risk from ingesting surface water was considered insignificant, and an assump-
tion  was made  that the health risk from dermal contact would be even lower than the
health risk associated with ingestion (Crane 1992b).  At some sites, it may be reasonable
to assume that no  fishing takes place because of the  absence of edible fish or shellfish
or because sites are physically inaccessible or remote.

Once the exposure  pathways to  be  quantitatively  evaluated are selected for  a  site,
contaminant concentrations and exposure parameters are used to calculate the chronic or
                                       12

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                                  Chapter 2.  Human Health and Ecological Risk Assessment
subchronic intake level of each contaminant (in mg of chemical per kg body weight per
day) (Table 2-1).  For each current and potential future exposure  scenario,  exposure
parameters may be selected to represent typical, reasonable maximum,  and,  in some
instances, worst-case exposure conditions. Typical, or average, exposures  and reason-
able maximum exposures (i.e.,  the maximum exposure that is reasonably  expected to
occur at a site) are usually evaluated for each complete pathway.  In general, an average
exposure case is calculated  using site concentrations and exposure parameters that best
represent the central tendency of the data.  Under the  reasonable maximum exposure
case, 95th or 90th percentile values are used for contact rates, intake rates, and exposure
frequency and  duration variables, and the upper 95  percent  confidence limit on the
average concentration is used for the exposure point concentration in the contaminated
media.  (See also  US EPA  [1992c] for further clarification of calculation of exposure
point concentrations.)

Site-specific information is often not available for many exposure parameters; thus,
assumptions about the types and frequencies of exposure may be made based on recom-
mended USEPA values or on professional judgment. The following documents provide
useful  information  on  estimating exposure parameters  and  conducting  the  exposure
assessment:  Superfund Exposure Assessment Manual (USEPA 1988b); Exposure Factors
Handbook (USEPA 1989b); Assessing Human Health Risks from Chemically  Contami-
nated Fish and Shellfish: A Guidance Manual (USEPA 1989a); and Standard Default
Exposure Factors: Interim Final (USEPA 1991), which is a supplement to  the Superfund
risk assessment manual (USEPA 1989c); and Dermal Exposure Assessment: Principles
and Applications (USEPA 1992a).

In some cases,  it may be appropriate to determine the fractional intake of exposure that
occurs at a site.  The fractional intake, which is the proportion of all exposure of a given
type (e.g., the fraction of all fish consumed) that comes from the site, is generally esti-
mated based on best professional judgment of factors such as the site size and accessibil-
ity and any restrictions on site use (e.g., warning signs, fishing bans, or barriers to the
site). In calculating fractional intake for fish consumption, the abundance of edible fish
and shellfish at a site should be considered.  Some sites may not have any  fish or may
not have edible aquatic species.   However, although it is important to consider these
limits on site use, they may not be sufficient to prevent access at a site, and thus the risk
assessment should not assume that exposure will not occur.  For example,  although all
of the five priority AOCs examined for the ARCS Program had fish advisories in effect,
some people continued to fish from the river.

Because recreational fishing is very popular in the Great Lakes region and consumption
of contaminated fish is an important exposure pathway, several researchers have gathered
data on consumption rates of fish by Great Lakes populations. A survey of the angler
population in  the AOC should be made to obtain a better estimate of local fish con-
sumption rates and  patterns. If these data cannot be obtained,  the results  of a survey of
Michigan anglers and their families by researchers at the University of Michigan (West
et al. 1989) may be used to estimate more "localized" consumption patterns.  The survey
results can be obtained from Patrick West at the University of Michigan.  An  important
                                       13

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         TABLE 2-1. GENERIC EQUATION FOR CALCULATING
                      CHEMICAL INTAKE LEVELS
                              C x CR x EFD
                                BW  x  AT
where:

   I
       Intake =
                           the amount of chemical at the exchange
                           boundary (mg chemical/kg body weight-day)
 Chemical-Related Variables
   C     Chemical
         concentration =    the average concentration contacted over the
                           exposure period (e.g., mg/L)

Variables that Describe the Exposed Population

         Contact rate =
CR


EFD
                           the amount of contaminated medium contacted
                           per unit time or event (e.g., L/day)

          Exposure frequency
          and duration =    how long and how often exposure occurs;
                           often calculated using two terms, EF and ED,
                           where:
  BW
       Body weight =
                               EF =  exposure frequency (days/year)
                               ED = exposure duration (years)

                            the average body weight (kg) over the
                            exposure period
 Assessment-Determined Variables

   AT    Averaging time =   period over which exposure is averaged (days)

Source:  U.S. EPA (1989c).
                                  14

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                                         Chapter 2.  Human Health and Ecological Risk Assessment
      result of this survey was that Michigan anglers and their families had an average fish
      consumption rate of 19.2 g/person-day (West et al. 1989), nearly 3 times the average fish
      consumption rate of people in the United States as a whole (USEPA 1989c).  Anglers in
      other Great Lakes states may be consuming fish  at  a comparable rate to Michigan
      anglers.  Additional data on fish consumption rates  for sport anglers on Lake Michigan
      are provided as part of a nationwide survey reported in Rupp et al. (1980).

      In selecting appropriate consumption rates,  subsistence fishing or  hunting should be
      considered (in addition to the average and reasonable maximum exposure cases) at sites
      with special subgroups of people who rely on locally  caught fish, waterfowl, or other
      aquatic-related wildlife as their main source of protein.  Examples may include members
      of a particular ethnic community who traditionally rely on fish as  an important part of
      their diet (e.g., the southeast Asian community of Hmong in Sheboygan,  Wisconsin) or
      indigent people who spend time in the area and may rely on locally caught fish for their
      main source of protein.
Toxicity Assessment

      In a toxicity  assessment, available  data are reviewed to  determine and quantify the
      relationship between the level of exposure to a contaminant (dose or intake level) and the
      increased likelihood and/or severity  of adverse effects.  This relationship is termed the
      dose-response relationship and provides the basis for deriving quantitative toxicity values
      used in the risk assessment.  For carcinogenic health effects,  CSFs are used to estimate
      the  risk of developing cancer  that corresponds to estimated  exposure concentrations.
      This risk is in addition to the risk of developing cancer due to other causes and thus is
      often termed excess cancer  risk.

      The potential for noncarcinogenic health effects from oral exposures is typically evaluated
      by comparing estimated daily intake levels with RfDs, which represent daily intake levels
      at which no  adverse effects are expected  to occur.   For  assessment of inhalation
      exposures,  USEPA has recently begun issuing  reference concentrations  (RfCs) that
      represent exposure concentrations at which no adverse effects are expected to occur.

      Carcinogens and systemic toxicants are treated differently, because according to current
      scientific theory it is plausible that  for any dose of a carcinogen there could be some
      finite increase in cancer risk.  Systemic toxicants are considered to  act via a threshold
      mechanism, which allows for the identification of a safe dose.  Hazard identification and
      dose-response evaluations for more than 600 chemicals have been conducted and verified
      by USEPA work groups; additional chemicals are awaiting  review.  USEPA-verified
      toxicity values can be obtained by accessing USEPA's IRIS  database.  The IRIS User
      Support group can provide technical assistance and information on  how to access  IRIS
      and can be reached at (513) 569-7254.

      Brief toxicity profiles on contaminants of concern should be prepared as  part of the
      toxicity assessment.  At a  minimum, such profiles should contain information on the
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                                          Chapter 2. Human Health and Ecological Risk Assessment
       derivation of toxicity values for the contaminants of concern  and should describe any
       uncertainties associated with the toxicity values. The following data should be gathered,
       to the extent available, for all contaminants of concern that have been shown to be carci-
       nogenic in experimental animals or in human populations:

           •    Current CSFs from IRIS

           •    Weight-of-evidence classifications, which characterize the degree to which
                the available evidence indicates that an agent is a human carcinogen

           •    Type of cancer for Class A carcinogens (i.e., contaminants that have been
                shown to cause cancer  in humans).

       Pertinent data to be identified and discussed in the baseline risk assessment for contami-
       nants associated with noncarcinogenic effects include the following:

           •    Current RfDs (and RfCs, if applicable) from IRIS

           •    Confidence level in the overall database and the critical study on  which the
                toxicity  value is based, including identification of the critical effects

           •    Effects that occur at doses higher than those required to elicit the critical
                effect

           •    Uncertainty factors used by USEPA in deriving the toxicity value

           •    1- and  10-day health advisories for shorter-term  oral exposures.

       Inclusion of these background data in  the toxicity assessment assists risk managers in
       interpreting the findings of the risk assessment.
Risk Characterization

       The purpose  of the risk characterization step is to combine the exposure and toxicity
       estimates into an integrated expression of human health risk.  Three means of expressing
       carcinogenic  and noncarcinogenic risks are  presented in the risk  assessment.   First,
       chemical-specific risks are estimated for each  exposure  pathway.   Second,  these
       chemical-specific risks are added to estimate a cumulative path way-specific risk.  Finally,
       risks are added across all chemicals and relevant pathways to estimate the total human
       health risks to individuals exposed to contaminants from the AOC.  Table  2-2 illustrates
       how  a summary table of risk  estimates may be  arranged.   The approaches  used to
       quantify carcinogenic and noncarcinogenic health risks are described below.

       Carcinogenic risk is expressed  as the upper-bound excess probability of an  individual
       developing cancer over their lifetime following exposure to a given chemical concentra-
       tion for a specified period of time. Carcinogenic risk estimates are  computed by multi-
       plying the chronic daily intake prorated over a lifetime of exposure by the CSF for each
       carcinogen of interest.  Carcinogenic effects are summed for all chemicals in an exposure
                                               16

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    TABLE 2-2.  ESTIMATED CARCINOGENIC AND NONCARCINOGENIC RISKS TO
    INDIVIDUALS RESIDING IN THE LOWER SAGINAW RIVER AREA OF CONCERN
        Type of
   Risk and Exposure3
                                Individual Risks
Walleye
            Carp
Waterfowl
                                        Additive Risks
Walleye +     Carp +
Waterfowl   Waterfowl
 Carcinogenic

   Typical

   Reasonable Maximum

   Subsistence
1x10~5    1x10~4    6x10~6

2x10~4    3x10~3    2x10~4

2x10~3    2x10~2    1x10"3
                                     2xicr5    ixicr4
                                     4x10"4    3x10~3
 Noncarcinogenic
 (hazard index)
Typical
Reasonable Maximum
Subsistence
0.02
0.2
1
0.08
0.5
4
0.001
0.02
0.08
0.02
0.2

0.08
0.5

Source: Crane (1992b)

a Noncarcinogenic risks were averaged over the same period as the exposure duration, while
carcinogenic risks were averaged over a period of 70 years (i.e., average lifetime of an individual).
                                        17

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                                         Chapter 2. Human Health and Ecological Risk Assessment
       pathway (e.g., consumption of fish, incidental ingestion of sediments). This summation
       of carcinogenic risks assumes that there are no synergistic or antagonistic chemical inter-
       actions and that all chemicals produce the same effect.   USEPA believes it is prudent
       public health policy to consider actions to mitigate or minimize exposures to contami-
       nants  when estimated excess lifetime cancer  risks exceed the 10~5 to 10~6 range
       (USEPA 1988a).

       Noncarcinogenic effects are evaluated by  calculating the ratio, otherwise known as the
       hazard quotient, of a site-specific exposure level for a specified time period to an RfD
       derived from a similar exposure period. Unlike cancer risk estimates, hazard quotients
       are not  expressed as a probability.  A hazard quotient of less than  1  indicates that
       exposures are not likely to be associated with adverse noncarcinogenic effects.  As the
       hazard quotient approaches or exceeds  10, the likelihood of adverse effects is increased
       to the point where action to reduce human exposure should be considered (although the
       magnitude of the uncertainty factors used  to derive the RfD should  also be considered).
       Because of the uncertainties involved with  these estimates, values between 1 and  10 may
       be of concern, particularly when additional significant risk factors are present.  However,
       because RfDs do not have equal accuracy or precision  and they are not based on the
       same severity of toxic effects, evaluation of hazard indices (the sum of two or more
       hazard quotient values for multiple substances and/or multiple exposure pathways) should
       take into account the uncertainties associated with specific RfDs.

       The consumption of contaminated fish resulted  in the greatest human health risk at the
       five priority AOCs examined in the ARCS Program: Saginaw River, Michigan (Crane
       1992b);  Sheboygan  River,  Wisconsin  (Crane  1993a);  Grand  Calumet River, Indiana
       (Crane 1993b);  Ashtabula  River, Ohio (Crane  1992a);  and Buffalo River, New York
       (Crane 1993c). Locally caught fish were assumed to accumulate contaminants primarily
       through  the food chain,  and in-place contaminated sediments  were assumed to be the
       major source of contaminants to the food chain  and water column.  In most cases, PCB
       contamination contributed the greatest degree of carcinogenic risk. Noncarcinogenic risk
       levels were usually not of  concern  except for the subsistence exposure case; however,
       some chemicals (e.g., PCBs) lacked a verified RfD, and thus the noncarcinogenic effects
       of these contaminants could not be evaluated in the risk assessments.  In addition, the
       consumption of bottom-feeding fish species,  like carp,  usually resulted in carcinogenic
       risks greater than 10~6, whereas the consumption of water column-feeding fish species,
       like walleye, did not always result in significant carcinogenic risks.
Uncertainty Analysis

       A number of assumptions and estimated values are used in baseline risk assessments that
       contribute to the level of uncertainty about possible human health risks.  As with most
       environmental risk assessments, the uncertainty about the risk estimate is generally at
       least an order of magnitude or greater (USEPA  1989c).  Thus, at a minimum, the risk
       assessment  should include  a qualitative  uncertainty analysis that identifies  the key
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                                          Chapter 2.  Human Health and Ecological Risk Assessment
       site-related variables and assumptions that contribute most to the uncertainty inherent in
       the risk estimates.

       Some of the major uncertainties in the ARCS risk assessments arose from the following
       factors:

            •   Use of contaminant burdens in fish based on uncooked fish, and in some
                instances, whole fish

            •   Exclusion of some complete exposure pathways (e.g., dermal exposure to
                water and sediments)

            •   Use of default exposure frequency and duration variables, body weight,
                life expectancy, and population characteristics

            •   Use of RfDs and CSFs that are usually based  on animal studies and that
                may be based on only one form of a chemical (e.g., Aroclor®  1260 was
                used to  derive the CSF for PCBs)

            •   Assuming additive health risks for  both carcinogenic and noncarcinogenic
                effects

            •   Natural variability  (e.g.,  small-scale spatial and temporal variability in
                sediment and hydrological conditions)

            •   Inherent approximations of physical, chemical,  and biological processes in
                the models.

       For each of these assumptions,  the level of uncertainty associated with the final risk
       estimates was estimated as low,  moderate, or high.  Additional site-specific sources of
       uncertainty are likely to  be important for  risk assessments conducted  at  other con-
       taminated sediment sites.  Calibration and fine-tuning of model results after field testing
       can greatly reduce uncertainties associated with risk estimates at specific sites.
Applications

       The results of the baseline risk assessment can be used by risk managers for several
       purposes. First, the baseline risk assessment provides a quantitative way to identify the
       exposure pathways and contaminants that contribute to carcinogenic and noncarcinogenic
       human health risks at a site.  However,  the calculated human health risks are not actual
       values,  but  are  instead estimates that  must be interpreted  in  the context  of all the
       uncertainties  associated with each  step in the risk assessment  process.  Second, the
       baseline risk assessment can be used to identify sensitive  subgroup populations (e.g.,
       children, subsistence anglers) within the AOC.  Third, the results of the baseline risk
       assessment can be used to compare the estimated  risks of different sediment remedial
       alternatives with the impact of the no-action alternative during the  comparative risk
       assessment.   Additional applications of the baseline  risk assessment are discussed in
       subsequent chapters.


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                                         Chapter 2. Human Health and Ecological Risk Assessment
ECOLOGICAL RISK ASSESSMENT

       The wildlife and aquatic organisms of the Great Lakes region may be exposed to sedi-
       ment contaminants through various mechanisms, resulting in ingestion, inhalation, or
       dermal uptake of potentially toxic chemicals. For the Great Lakes AOCs, ecological risk
       assessments  may be conducted to evaluate the likelihood of acute and chronic adverse
       effects of sediment contaminants on wildlife, aquatic plants, benthic invertebrates, and
       fish that rely on lakes and streams for habitat,  food, and  drinking water.   Under the
       ARCS Program, wildlife risk assessments were conducted for two of the priority AOCs,
       Buffalo River and Saginaw River.

       Ecological assessments may involve empirical measurements of realized effects using the
       retrospective approach and theoretical modeling to estimate the probability of effects
       using the predictive approach.   The balance of empirical and modeling  approaches
       depends on the objectives of the assessment, the practicality  of measurement methods for
       the receptors of concern, and data availability.  For example, empirical approaches are
       commonly used to evaluate the effects of existing contamination on species  populations
       and communities that are easily sampled, and on endpoints such as population abundances
       that can be easily quantified and interpreted.  Theoretical  models  are used to estimate
       exposure of large-bodied wildlife species and rare species for which direct measurement
       of population or community endpoints is impractical, and to predict the effects of future
       conditions.

       USEPA is currently developing  guidelines for conducting ecological risk  assessments
       (Norton et al. 1992) and recently issued their Framework for Ecological Risk Assessment
       (USEPA 1992b). This  framework report  describes the elements of an ecological risk
       assessment and  provides the basis for conducting ecological risk assessments  within
       USEPA.  Development  of specific  guidelines  for ecological risk assessment is  in
       progress, but will require considerable time (Norton et al. 1992). USEPA Region V has
       issued its  own framework  document  entitled Regional  Guidance for  Conducting
       Ecological  Assessments.    In addition,  the  State of Wisconsin  recently issued  their
       Guidance for Assessing Ecological Impacts and  Threats from Contaminated Sediments
       (WDNR 1992a,b).   In addition to the guidance offered herein, these  other guidance
       documents  should be consulted  in planning an ecological  risk assessment for  con-
       taminated sediments.  Past ecological risk assessments  that have been performed for
       contaminated sediment sites in Region V are available from USEPA Region V.

       Because of the variety of habitats and species associated with sediments and interactions
       between  biota  and  physical-chemical conditions, diverse  techniques may be used  in
       ecological risk assessments.   The physical and chemical structure of an ecosystem
       influences the bioavailability and toxicity of contaminants to resident species. Biological
       interactions  may determine the transport and fate of contaminants in the environment as
       well as species exposure patterns. Thus,  the risk assessment process cannot be easily
       standardized to a "cookbook" approach.
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                                         Chapter 2. Human Health and Ecological Risk Assessment
      The remainder of this chapter presents an overview of ecological risk assessment methods
      as they might be applied to contaminated sediments.    The elements of the approach
      described below are consistent with USEPA's framework report and  other USEPA
      reports (USEPA 1989d,e; Warren-Hicks et al. 1989).  Other related activities in the
      development of ecological risk assessment  guidance for aquatic  habitats include:
      1) formation of an Ecorisk Group within the  USEPA Office of Water to develop  a
      paradigm for ecological risk assessment, 2) development of sediment quality criteria by
      USEPA based on the equilibrium partitioning model (DiToro et al. 1991), 3) issuance
      of a review of aquatic risk assessment methods by Parkhurst et al. (1990) for the Water
      Environment  Federation (formerly the Water  Pollution  Control  Federation),  and
      4) USEPA's development of proposed methods for the derivation of ambient water qual-
      ity criteria that  would be protective of human health,  wildlife, and aquatic organisms
      under the Great Lakes  Initiative  (40 CFR  Parts  122, 123, 131, and  132;  58 Fed.
      Reg. 20802).

      Because of the varied nature  of  contaminated sediment sites and  the  objectives of
      individual ecological risk assessments, only general guidance is offered here. Ecological
      risk assessors must still rely on their own judgment and expertise when evaluating poten-
      tial  risks  to wildlife and/or aquatic organisms.  Thus, any  ecological risk assessment
      should include a clear  statement of assumptions and an uncertainty analysis.
General Framework

       The risk assessment process  developed for estimating human health risks generally
       applies to determination of ecological risks.  However, the complexity of ecological
       systems requires consideration of multiple species and other physical-chemical stressors
       in addition to toxic chemicals.  Ecological endpoints may also differ from those used in
       human health risk assessment.  For example, survival, growth, and reproduction may be
       emphasized as ecological endpoints, instead of cancer or more subtle sublethal effects.
       In ecological risk assessment,  risks to  populations,  communities,  and ecosystems are
       often  considered  more  relevant  than  individual risk.   Except in the case of rare,
       threatened, and endangered species, individual plants and animals are not highly valued
       because compensatory  mechanisms in  ecological systems may preclude higher-level
       effects even  if individuals are eliminated from a population.  In ecological  risk assess-
       ment, the ability of the ecosystem to recover from the stress may also be considered.

       USEPA (1992b) defines ecological risk assessment  as  "a  process that evaluates the
       likelihood that  adverse  ecological effects may occur or are occurring as  a result of
       exposure to one or more stressors."  In general, both wildlife and aquatic  risk assess-
       ments follow the basic framework shown in Figure 2-2 (USEPA 1992b):

           •   Problem Formulation: This planning and scoping step defines the objec-
                tives,  approach,  and data needs  for the assessment.   It includes:  1)  a
                qualitative evaluation  of  contaminant release,  transport, and fate;  2)
                identification of contaminants  of concern, receptors, exposure pathways,
                                              21

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IV)
                                                  Problem Formulation
                             Exposure Assessment
Ecological Effects Assessment
Sediment/Water Analysis
Bioaccumulation


Toxicity Tests
Community Analysis
Food Web Models

                                                 Risk Characterization
               Figure 2-2.  Ecological risk assessment framework.

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                                   Chapter 2. Human Health and Ecological Risk Assessment
        and known ecological effects of the contaminants; 3) selection of endpoints
        for further study; and 4) integration of the preceding information into a
        conceptual model.  Assessment  endpoints  should  represent  ecological
        "values"  to be protected.  Measurement endpoints are the observed or
        measured variables related to assessment endpoints. The lack of standard-
        ized ecological risk assessment procedures and the complexity of ecosys-
        tems make the initial planning of the assessment extremely important.

    •   Exposure Assessment:  The exposure assessment uses chemical measure-
        ments and chemical transport and fate models to estimate  the magnitude,
        duration, and frequency of exposure to the contaminants  of concern.  It
        involves the following steps:  1)  quantification  of contaminant release,
        transport, and fate including information on temporal and spatial variabil-
        ity; 2) characterization of exposure pathways and receptors; 3) measure-
        ment or estimation of exposure point concentrations (or chemical intake
        rates);  and 4) evaluation of  the quality  of the data available for  the
        exposure assessment.

    •   Ecological Effects Assessment: The ecological effects assessment deter-
        mines the relationship between the levels of exposure and the levels and
        types of effects.   It involves an evaluation  of literature  reviews, field
        studies, and toxicity tests that link contaminant concentrations to effects on
        ecological receptors.  The effects assessment often uses models to extrapo-
        late toxicity test  data to different  species, life stages, levels of biological
        organization,  and exposure conditions.

    •   Risk Characterization:   The risk characterization  documents existing
        chemical effects  and estimates the likelihood of adverse ecological effects
        by integrating the exposure and  ecological effects assessments.   It also
        provides narrative explanations of underlying assumptions, the nature  and
         magnitude of uncertainties, and the quality of the data.

In ecological risk  approaches, assessment  endpoints are defined as environmental
characteristics or values that are to be protected, such as wildlife population abundance,
species diversity, or ecosystem productivity (Suter 1989).  For example, maintenance or
restoration of valuable natural resources is typically a goal of the remediation  process.
If protection of a valuable  commercial fish stock is the goal, the assessment endpoint may
be recruitment rate for the species population.  Measurement endpoints are quantitative
expressions of  an  observed or  measured biological response related to the valued
environmental characteristic chosen as the assessment endpoint.  In some cases, the
measurement  endpoint is  the same as  the assessment endpoint.   When these endpoints
differ, a model must be used to express their relationship.

The process of estimating ecological risk based on chemical, lexicological, and ecological
data is called a forward-mode assessment.   Risk assessment procedures may also be used
to back-calculate exposure guidelines  from  an  allowable risk level or a no-observed-
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                                          Chapter 2. Human Health and Ecological Risk Assessment
       adverse-effect level (NOAEL).  A reverse-mode assessment may be used  to derive
       cleanup levels (e.g., maximum allowable concentrations of contaminants in sediment).

       The level of detail required  for a given risk assessment depends on remedial  action
       objectives, the complexity of  the  site, and  the difficulty  in  adequately  describing
       exposure, toxicity, and other  properties  of the contaminants of concern. An ecological
       risk assessment can be conducted in tiers with the most basic analyses conducted first.
       For example, an initial screening-level risk assessment is conducted that uses available
       data and conservative assumptions about exposure and toxicity.  From  the results of this
       screening-level assessment, areas, contaminants, and species of concern are identified and
       decisions  are made about additional data collection.   In  the next tier, more realistic
       models are  used and  additional  data  may be collected  that will  better define the
       relationship between chemical concentrations and adverse effects at the site.
Problem Formulation

       The  conceptual  model  developed during  the  planning phase of an ecological  risk
       assessment illustrates how exposure to sediment  contaminants may cause ecological
       effects.  The results of the problem formulation stage clarify the scope of an ecological
       risk assessment and  how  the results will be  used  in developing RAPs for the AOCs.
       Based on the results of a screening-level assessment, chemicals, species,  and endpoints
       are selected  for a detailed assessment that may involve collection of additional field data
       and risk modeling.
       Selection of Contaminants of Concern

       Contaminants of concern are selected for the risk assessment based on available data and
       the preliminary evaluation of releases, transport, and  fate of sediment contaminants
       relative to their potential toxicity.  Sequential criteria for selection of contaminants of
       concern for an ecological risk assessment may include:

           1.    Detection in sediments within the AOC

           2.    Presence in sediments or  tissues at  concentrations significantly  above
                reference concentrations

           3.    Relationship to human activities

           4.    Presence at concentrations above screening toxicity criteria.

       The last step in the selection process is to compare measured or estimated environmental
       concentrations with threshold concentrations such as NOAELs.  This analysis should be
       conservative by incorporating plausible worst-case assumptions regarding bioavailability,
       exposure, and sensitivity of ecological receptors.
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                                   Chapter 2.  Human Health and Ecological Risk Assessment
The list of contaminants of concern for an ecological risk assessment may differ from
that used for  a human health risk assessment because of differences  in  exposure
pathways, uptake, and sensitivities between humans and ecological receptors. Therefore,
the initial list of contaminants considered for evaluation in the selection process described
above should be comprehensive rather than simply the list selected for evaluation in the
human health risk assessment.
Selection of Species

Because  of the complexity of the food web in the Great Lakes basin, not all of the
trophic levels and species can be evaluated.  Thus, a few species or species groups may
be selected as ecosystem indicators of environmental conditions.  The Ecosystem Objec-
tives Committee of the International Joint Commission developed the following criteria
(as cited in Kubiak and Best [1991]) for selecting indicator species:

     •   Displays a broad distribution within the AOC

     •   Maintains itself through natural reproduction and is indigenous

     •   Interacts directly with many components of its ecosystem

     •   Maintains well-documented and quantifiable niche dimensions

     •   Exhibits a gradual response to a variety of human-induced stresses

     •   Responds to stresses in a manner that is both identifiable and quantifiable

     •   Represents an important species  to humans.

These  criteria for selection  of indicator  species were  adopted for use in the ARCS
Program.  In addition, species selected for the assessment should be sensitive to effects
of the  contaminants of concern and, if possible, should  be representative of a group of
valuable species.

The U.S. Fish and Wildlife  Service is evaluating  the bald eagle, mink, otter,  colonial
waterbird group, and lake trout (salmonids) as possible indicator species for Great Lakes
water quality  (Kubiak and Best 1991).  These species can also be used to evaluate the
effects of contaminated sediments.   In addition,  other  aquatic biota that should  be
considered in most risk assessments include  benthic macroinvertebrates and  bottom-
feeding fish.

Any of the species or  groups just discussed  could be considered in a predictive as-
sessment.  For empirical assessments  of  existing  conditions, the following ecosystem
indicators are recommended:

     •   Bottom-feeding fish populations

     •   Higher tropic level fish (if AOC is very large)
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                                   Chapter 2. Human Health and Ecological Risk Assessment
     •   Benthic macroinvertebrate communities

     •   Locally important species of amphipods and chironomids.

For a specific risk assessment, the selection of species to be evaluated also depends on
the contaminants of concern and the scale of resolution needed to define problem areas
within AOCs. For example, assessment of bioconcentratable contaminants such as PCBs
and dioxins over a wide portion of Lake Michigan might consider wide-ranging fish and
wildlife species that feed at high trophic levels.  Relatively fine-scale resolution of
problem areas within a tributary might consider benthic macroinvertebrates and localized
bottom-feeding fish species like bullhead.  The selection of species and endpoints for an
assessment should consider whether the contaminants biomagnify and whether they cause
direct toxicity to receptors at lower trophic levels.

Practical  methods for  field  and/or laboratory  measurements must  be available  for
retrospective assessments. Predictive and retrospective assessments both require adequate
data on contaminant distributions or appropriate  transport and fate models to estimate
exposure.  Limitations in data or models may influence the final selection of species for
the assessment.
Selection of Endpoints

Both  assessment endpoints  and measurement  endpoints are used  as indicators  of
ecological risk.  When the measurement endpoint differs from the assessment endpoint,
a model must be used to express their  interrelationship.  The primary measurement
endpoints for an ecological risk assessment should be related to the survival, growth, and
reproduction of exposed  organisms.  These endpoints are used  in  most standardized
toxicity tests and in the development of USEPA ambient water quality criteria, wildlife
criteria, and sediment quality criteria.  Moreover, such endpoints can be quantitatively
related to changes in population numbers and structure. For example, PCBs are known
to be accumulated in gull eggs in the Great Lakes region and have been linked to repro-
ductive failure.  Here, the measurement  endpoint might be the proportion of nonviable
gull eggs, as a predictor  of effects at the population level.  Although other endpoints,
such  as  enzymatic responses  and  histological  lesions in individual organisms,  may
indicate chemical exposure and response, they do not necessarily indicate adverse effects
on populations,  communities, or ecosystems.

Various endpoints may be used for predictive assessments, but their final selection is
often affected by the  availability of toxicity data in the literature and the quality of the
data.  Because  prediction of community-level  responses  from survival, growth, and
reproductive endpoints involves substantial uncertainties, wherever practical, effects  on
selected communities should  be directly observed in the field.  For example, population
and community analyses of benthic  macroinvertebrate communities may be used  to
evaluate toxic effects of sediment contamination.
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                                   Chapter 2. Human Health and Ecological Risk Assessment
Ecological Risk Assessment Objectives

The objectives of an ecological risk assessment are developed from conceptual models
of chemical transport and fate, exposure pathways for selected receptors, and potential
mechanisms for adverse  ecological effects.  The objectives should specify the selected
contaminants, receptors,  and endpoints to be included in the assessment.  An  example
conceptual model of a site near a tributary might show the transport of contaminants of
concern  from  soil to groundwater,  which  is then discharged  to  the river,  where
contaminants are absorbed or ingested by fish.  Contaminants may be transferred to the
terrestrial environment  when a waterbird eats  fish from  an affected portion  of the
tributary.

Assessment techniques appropriate for the receptors and contaminants of concern and the
level of complexity of the risk assessment  are determined on a site-by-site basis.  The
selection of ecological assessment techniques to be applied at a site  depends on the
objectives of the risk assessment, site-specific receptor species  and contaminants of
concern, and the extent of available data.  The primary techniques are:

    •   Chemical analysis  of samples  of sediment, surface water, and organism
         tissues from the site

    •   Toxicity  testing of sediments

    •   Community analysis based on  measurements of the types and number of
         benthic macroinvertebrates at the site

    •   Exposure models to predict chemical concentrations and  bioavailability in
         environmental media and to  estimate uptake by key receptors

    •   Ecological  models to extrapolate from measurement endpoints to assess-
         ment endpoints in receptor groups for which community analysis is not a
         primary tool.

Each  combination of tools selected for  an AOC  should provide  adequate data for the
assessment and facilitate  risk predictions. Figure 2-3 summarizes  some of the candidate
tools for ecological risk assessments according to habitat, media,  and receptors.

The problem formulation stage should include development of a strategy for integrating
the results of  individual assessment  tools into the overall  approach  to  risk charac-
terization.  Moreover, the risk assessment objectives should be clearly related to remedial
action objectives and the  decision-making process.  The overall assessment  strategy may
involve both empirical and theoretical approaches.

Empirical approaches involve direct measurement of biological effects  or  derivation of
relationships between chemical and biological variables from field data, or toxicity testing
of field-collected samples. Empirical  approaches  rely heavily on observed relationships
without attempting to describe theoretical cause-effect relationships. Warren-Hicks et al.
(1989) describe empirical assessment approaches  used to quantify the ecological  effects
                                        27

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                                                                                                  Riparian and Upland
           Chemical Analyses

              Sediment/Water

              Tissue
                                                                             Plants
                                                                                               Birds
                                                                                                    Small Animals
Large Animals
           Toxicity Tests
                                                               O
IV)
00
Community Analysis
              Models
           Exposure Models'
           Ecological Models
          a  Includes transport and fate models and food web
             models to estimate exposure.

          b  Includes models to extrapolate measurement
             endpoints (e.g., organism-level effects) to
             assessment endpoints (e.g., population- or
             community-level effects).
                                                   •   Primary tool - used at most sites

                                                   O   Secondary tool - used at selected
                                                       sites based on specific conditions
                      Figure 2-3.  Ecological assessment tools for contaminated sediments.

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                                         Chapter 2.  Human Health and Ecological Risk Assessment
       of contaminants at hazardous waste sites, including:  1) toxicity testing, 2) use of bio-
       markers, including analysis of tissue contaminants, and 3) community analysis based on
       field surveys.

       Theoretical models are mainly derived from theoretical principles and include explicit
       mechanistic (cause-effect) relationships. Modeling may be used to support empirical risk
       assessments and to make risk predictions.  Mathematical exposure models are used for
       dynamic systems (such as river water), for long-term predictions in more stable systems
       (such as sediment), and for transfer of chemicals  through the  food web to receptors
       higher up the  food chain.  Ecological models are  used primarily to extrapolate from
       measurement endpoints to assessment endpoints in receptor groups such as amphibians,
       birds, and large mammals.  Both exposure models and ecological models may vary from
       relatively simple extrapolation models with few data requirements to complex mechanistic
       models with substantial data requirements.  Whenever practical, models should be based
       on site-specific data and validated.
Exposure Assessment

       In the exposure assessment phase, measurements or estimates are made of the concentra-
       tions of contaminants of concern in the environment or the rate of chemical intake by
       organisms. Analysis of the magnitude, duration, and frequency of exposure is based on
       information or assumptions about:

           •   Chemical sources and pathways

           •   Chemical distributions in  water, sediment,  and organisms

           •   Spatial/temporal distributions of key receptors.

       For empirical assessments,  tissue concentrations of contaminants in key species may be
       measured as indicators of exposure.   To develop  estimates of exposure using models,
       exposure  scenarios are developed from the  conceptual  site model to describe the
       pathways a  chemical  may take through various environmental media to reach an
       organism. For each site, the analysis of several exposure scenarios helps to identify data
       gaps for transport pathways and  key exposure processes, such as chemical transforma-
       tions or biological uptake.  Data gaps for specific chemical forms or processes related
       to important pathways are filled through estimations from predictive chemical models or
       the collection of additional site-specific data.

       The distributions and seasonal activity  patterns of receptors  are  described relative to
       contaminant distributions  in various  habitats  at  a  site.  Habitats,  concentrations of
       contaminants of concern, species distributions, and exposure variables related to species
       activities  may be mapped  and spatial patterns investigated using a  mapping/database
       system such as a geographic information system.
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                                   Chapter 2.  Human Health and Ecological Risk Assessment
Information from the transport and fate analysis for each exposure scenario is used to
develop quantitative estimates of exposure that serve as inputs to the risk characteriza-
tion.  Summaries of data for the exposure assessment may include:

     •   Contaminant sources

              Mapping of source locations

              Contaminant release data for outfalls, landfills, combined sewer
              overflows (CSOs), and other sources

     •   Sediment

              Mapping of contaminant distributions

              Comparison of contaminant concentrations in sediments at the
              site with reference area values

              Comparison of contaminant concentrations in sediments  with
              levels associated  with  biological  effects (based  on available
              toxicological literature  and field surveys)

              Pattern analysis of contaminant data to evaluate potential sources
              of contamination

              Evaluation of the suitability of the reference area

     •   Surface water

              Comparison of concentrations  of contaminants in water  with
              USEPA ambient water quality criteria

              Pattern analysis of contaminant data to evaluate potential sources
              of the contamination

              Evaluation  of the  degree of chemical contamination in water
              collected from stations near the site relative to reference values

              Evaluation of the suitability of the reference area

     •   Bioaccumulation

              Evaluation of the degree of chemical contamination in fish tissue
              collected from the site  relative to reference values

              Evaluation  of contaminant concentration  gradients in tissue
              collected from the site

              Evaluation of the suitability of the reference area.

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                                   Chapter 2, Human Health and Ecological Risk Assessment
Wildlife

The principal routes of chemical uptake for terrestrial wildlife are ingestion, inhalation,
and dermal absorption.  For riparian or terrestrial wildlife species,  some routes of
exposure, particularly ingestion,  may involve many different media.  Scientists from the
U.S. Fish and Wildlife Service  have conducted risk assessments for wildlife indicator
species (e.g., bald eagle, other fish-eating birds,  mink) for the ARCS Program at the
Buffalo and Saginaw River  AOCs.   The approaches  used by these researchers  can
generally be applied to other areas with sediments contaminated by bioconcentratable
chemicals.  Such chemicals are typically the primary contaminants  of concern for
assessment of sediment-associated risk to wildlife.

The exposure assessment for indicator species can be approached in two different ways
(Kubiak and Best  1991).   The first  approach  requires  site-specific information or
estimates of the types of forage items  commonly eaten, contaminant concentrations in
forage items, and grams of food eaten per kilogram of wildlife predator body weight.
This information is used to  calculate an ingested dose for contaminants of concern in the
indicator species, similar  to food web  model  approaches currently  being  used for
sediments and other media at hazardous waste sites (e.g., Fordham and Reagan 1991;
Menzie et al. 1992).  The calculated ingested  dose  is then compared to a NOAEL
developed from a model feeding study where known adverse toxicological endpoints were
measured.  There is considered to be a significant risk to the indicator species if the
calculated ingested dose exceeds  the NOAEL. Unfortunately, the database necessary for
applying this approach is not sufficiently developed for Great Lakes species.

The second approach can be conducted for contaminants that bioaccumulate through the
food chain  (e.g., DDE, PCBs, dieldrin).  In this approach, the  concentration of a
contaminant of interest is measured in a specific tissue of the indicator species.  Because
the exposure estimate is expressed as a contaminant concentration in tissue, the ecological
effects assessment  includes  an  estimate of the NOAEL  expressed as a contaminant
concentration  in the tissue  rather than  as  an ingested dose.   The measured tissue
contaminant concentration is compared with the NOAEL to evaluate existing risk.  Based
on the NOAEL and on biomagnification factors calculated from actual field data, Kubiak
and Best (1991) also applied this approach to backcalculate the contaminant concentra-
tions in forage fish that would be necessary to result in a contaminant concentration equal
to the  NOAEL in the tissue of the indicator species.

Either  approach,  appropriately  used, could be applied  to  the calculation of "safe
concentrations"  or remedial action goals for sediments.  The goal would be to determine
the contaminant concentrations in sediments that would not result in exceedances of the
NOAELs, expressed as an  ingested dose to the indicator species in  the first approach or
as a tissue contaminant concentration in the second approach. For the ARCS Program,
the second approach was applied for bald  eagle, other fish-eating birds, and mink in the
wildlife risk assessments conducted for the Buffalo River AOC (Mann-Klager, in prep.)
and the Saginaw River AOC (Kubiak, in prep.).
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                                          Chapter 2. Human Health and Ecological Risk Assessment
       Aquatic Life

       The principal routes of chemical uptake for aquatic organisms are gill and body-surface
       absorption of chemicals in surface water or sediment pore water, and ingestion of water,
       sediments, and food.  Exposure estimates for aquatic life may be based on one or more
       of the following:

           •    Contaminant concentration in bulk sediment

           •    Contaminant concentration in sediment pore water

           •    Contaminant concentration in the water column

           •    Contaminant concentration in organism tissue.

       In most cases, the exposure estimate will be expressed as the contaminant concentration
       in the bulk sediment, pore water,  or  water column, which  is obtained from empirical
       measurements.  Few toxicity data are available to interpret exposure estimates expressed
       as contaminant concentrations in tissue (e.g., Dillon  1984).
Ecological Effects Assessment

       Ecological effects assessment includes a hazard identification step to identify the potential
       effects of chemicals and an exposure-response assessment to characterize the relationship
       between each stressor and the biological or ecological endpoints.   Confounding effects
       of physical stressors such as currents or sediment grain size must be addressed by using
       models, reference-area measurements, or experimental designs to separate the effects of
       physical factors from those of chemicals.

       Techniques for ecological effects assessment may include the following:

           •   Laboratory/field toxicity tests

           •   Observational field studies

           •   Interspecies extrapolation of effects

           •   Interchemical extrapolation based on knowledge of their modes of action,
               such as quantitative structure-activity relationships

           •   Biological or  ecological  modeling  to  extrapolate  from  measurement
               endpoints to assessment endpoints.

       Data from direct field measurements or from laboratory analyses of field samples should
       be used whenever possible to derive exposure-response relationships.  Site-specific prop-
       erties of sediment and water may modify the bioavailability of chemicals, and literature
       data may not be appropriate for ecological effects assessment.
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                                   Chapter 2. Human Health and Ecological Risk Assessment
Wildlife

Although site-specific toxicity data are preferred for exposure-response assessment, use
of available data from the general literature may be appropriate in certain cases.  For
example, literature estimates of stress thresholds such as NOAELs for wildlife species
might be used with conservative assumptions about bioavailability in  a screening-level
assessment.

An estimate of the NOAEL for each contaminant of concern can  be  derived from the
literature or from a model feeding study on a surrogate laboratory species.  NOAELs can
be expressed as chemical intake rates, which typically result from ingestion of chemicals,
or chemical concentrations in tissue. The units for the NOAEL must correspond to the
units  used for the exposure estimate.   When developing  NOAELs, the following
guidelines developed by PTI (1992) are relevant:

    •   Data from the receptor  species of concern or  a representative surrogate
         species that is  closely related to the  receptor  should be  used to derive
         NOAELs

    •   Ecologically relevant endpoints should be selected or a quantitative uncer-
         tainty analysis,  which delimits  the probable range of the NOAELs, should
         be performed when endpoint extrapolations are required

    •   The mode of administration of chemicals in laboratory exposures must be
         evaluated, and inter-route extrapolations should be  avoided if possible.

An endpoint for a relatively sensitive tissue, organ, or life stage should be determined
to derive a conservative estimate of a NOAEL.  Adverse effects on reproductive organs
and early life stages are  typically good  endpoints for risk assessment  because they are
likely relevant to changes at the population level.  For birds, the most sensitive stages
are the egg and the developing embryo, at least for chlorinated organic compounds and
methylmercury.  In contrast, the liver is the  most sensitive tissue  known  for  mink
(Kubiakand Best 1991).
Aquatic Life

Ecological effects assessments for aquatic life may be based on theoretical approaches
such as the use of sediment criteria developed from equilibrium partitioning models (e.g.,
DiToro et al. 1991) and bioaccumulation models (e.g., Thomann et al.  1992).   An
ecological epidemiological approach is recommended to enhance sediment risk assess-
ments by taking into account factors other than source information.  In this empirical
approach, summaries of data for the aquatic ecological effects  assessment may include:

     •   Sediment toxicity

             Estimation of mean and variance of percent response for each
             toxicity test endpoint at each station


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                                   Chapter 2.  Human Health and Ecological Risk Assessment
             Mapping of bioassay response data

             Correlations of bioassay response with contaminant concentra-
             tions  and ancillary variables to  evaluate potential  cause-effect
             relationships

             Evaluation of the suitability of the reference area (if available)
             and negative controls

             Pairwise statistical comparison of mean percent response at each
             potentially contaminated site with the reference area (if available)
             or negative control responses

    •    Benthic macroinvertebrate communities

             Estimation of mean and variance of taxon abundances or commu-
             nity indices at  each  station

             Mapping of benthic invertebrate data

             Correlations of community parameters with contaminant concen-
             trations and ancillary variables to evaluate potential cause-effect
             relationships

             Evaluation of the suitability of the reference area (if available)

             Pairwise statistical comparison of community parameters at each
             potentially contaminated  site with the reference area value (if
             available)

    •    Fish histopathology

             Correlations of the prevalence of tumors and other abnormalities
             with  contaminant concentrations   and ancillary variables to
             evaluate potential cause-effect relationships

             Evaluation of the suitability of the reference area (if available)

             Pairwise statistical comparison of the prevalence of tumors and
             other abnormalities at each potentially contaminated site with the
             reference area value (if available).

Guidance on the use of toxicity tests, benthic macroinvertebrate community surveys, and
fish histopathology investigations  in support of ecological risk assessments is provided
in the ARCS Assessment Guidance Document (USEPA 1993).
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                                          Chapter 2.  Human Health and Ecological Risk Assessment
Risk Characterization

       In risk characterization, the exposure and ecological effects assessments are combined
       to estimate the probability of adverse ecological effects.  Final risk estimates may be
       expressed in simple narrative terms or as quantitative values. The risk characterization
       should summarize:

           •   Results of the exposure and ecological effects assessments

           •   Risk estimates for aquatic and wildlife receptors of concern

           •   Potential ecological consequences

           •   Major sources of uncertainty.

       Mitigating factors,  such as reduced bioavailability of contaminants incorporated into
       sediment particles and mechanisms for possible wildlife avoidance of hot spots, should
       be discussed.   The importance of mitigating factors  should  be confirmed by field
       measurements or laboratory experiments on samples from the site.  Also, compensatory
       mechanisms that  preclude population-  or community-level effects should be acknowl-
       edged, even though effects on individuals may  be predicted.

       Approaches to develop quantitative risk estimates (or hazard indices) include the quotient
       method, joint probability analysis, model uncertainty analysis, and integrated analysis of
       site-specific empirical data (Barnthouse et al. 1986; Suter et al. 1992; Ginn and Pastorok
       1992; Chapman et al.  1992).  The quotient method uses  a ratio of the value of an end-
       point  at the site to a toxicity  reference  value such as a NOAEL as an approximate risk
       index. The quotient method is useful mainly for screening-level analyses because it does
       not provide a  complete  characterization  of the magnitude of risk and uncertainties
       (Bascietto et al. 1990). Joint  probability analysis (Barnthouse et al. 1986) can be applied
       to estimate the risk that exposure exceeds toxicity thresholds or criteria where probability
       distributions are available for the variables being compared.  Model uncertainty analysis
       (Barnthouse et al. 1986; Suter et al. 1992) may be used  to develop risk estimates for a
       species based on statistical analysis of growth, survival, and reproduction of individuals.
       Approximate risk estimates may be derived for an  ecological system  associated with
       sediments  by combining  site-specific  data for chemicals, toxicity tests,  community
       indices, and possibly other risk indicators (Chapman et al. 1992).
       Wildlife

       The quotient method and joint probability analysis will likely continue to be the primary
       methods for expressing estimates of risk to wildlife receptors.  An estimated chemical
       intake by a wildlife receptor may be compared with a NOAEL.  In interpreting hazard
       quotients, Kubiak and Best (1991) propose that to be ecologically protective, the ratio of
       the exposure to the NOAEL should be less than 1,  because this provides a reasonable

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                                   Chapter 2. Human Health and Ecological Risk Assessment
level of assurance that adverse effects would not occur as a result of excessive contami-
nant exposures.  However, hazard quotients must be interpreted relative to the assump-
tions on which the assessment is based, the assessment endpoints, and the degree of con-
fidence in the relationship between the assessment endpoints and the  measurement end-
point used in the hazard quotient.  For example, for reasonable maximum exposure scen-
arios, hazard quotient values between 1 and 10 do not necessarily indicate a significant
risk. For most exposure scenarios, hazard quotients of greater than 10 are generally con-
sidered to  represent  a  significant ecological  risk.  Prior to interpreting any hazard
quotient, agreement must be reached  on the  toxicity value analyzed (e.g.,  dose of a
substance that results in 50-percent mortality in a population of test  organisms  [LD50],
lowest-observed-adverse-effect  level [LOAEL], NOAEL, reference dose).

The joint action of contaminants should also be considered.  Hazard  quotients  for
individual contaminants with similar modes of action may be summed to yield a hazard
index.
Aquatic Life

The quotient method, joint probability analysis, and site-specific integrated data analysis
will likely be the approaches  that are commonly applied to assess risks to aquatic life
associated with contaminated sediments.   Use of the quotient method may involve
comparison of a measured assessment endpoint to a threshold value considered indicative
of toxicity or to a value indicative of reference area conditions.
Uncertainty Analysis

Possible sources of uncertainty include natural variation, missing information, and errors
associated with measurements, extrapolations of data, or models.  Uncertainties may be
related  to  selection of  contaminants of concern, selection of  species, estimates of
exposure concentrations or doses, the quality of the toxicological data used for NOAELs
or LOAELs, or differences  in exposure-response relationships or bioaccumulation of
chemicals among species.  The  most important sources of uncertainty identified in the
exposure and ecological effects  assessments should be evaluated and quantified to the
extent possible.  Model uncertainty analysis may include sensitivity analysis and Monte
Carlo simulation.

The baseline aquatic risk assessments for the ARCS Program were designed to comple-
ment the baseline  human  health  and wildlife risk  assessments  so that the  exposure
pathways leading from sediments to fish to humans  and wildlife could be quantified.
However, these aquatic risk  assessments were difficult to perform for different  trophic
levels of the aquatic food  chain because of data gaps.  Conservative assumptions and
published data from other  studies were used to fill missing information.  The problem
of data gaps affects most aquatic and wildlife risk assessments and constitutes a major
source of uncertainty in  the risk estimates.
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                                    Chapter 2. Human Health and Ecological Risk Assessment
Uncertainty  analysis  should be conducted during  the problem formulation  stage  to
identify data gaps and plan the approach for the ecological  risk assessment.  When
significant data gaps exist, the assessment  should typically  include several tiers  of
analysis, with use of available data in the early screening tier to help define critical data
needs to be  addressed in further field  sampling or laboratory studies  and subsequent
analyses in the next tier.
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3.   MA SS BALANCE MODELING APPRO A CH
      FOR ASSESSING REMEDIAL AL TERN A TIVES
      A T CONTAMINA TED SEDIMENT SITES
      Mass balance modeling studies were conducted at the Buffalo and Saginaw River AOCs
      to demonstrate the use of this approach in evaluating  remedial alternatives for con-
      taminated sediments.  Mass balance modeling studies were  applied at these AOCs to
      estimate changes in contaminant concentrations in water, sediments, and biota that may
      occur following sediment remediation.  The estimated concentrations can then be used
      to compute changes in human health and ecological risks and to aid in the selection of
      remedial alternatives. The mass balance modeling studies, as described below, are based
      on established  models and methods and are considered applicable to other sites with
      contaminated sediments.
OVERVIEW

      While there are many possible remedial alternatives for contaminated sediments, only a
      few may be feasible at a particular site.  After the range of feasible remedial alternatives
      is identified for a site, the potential for reduction of contaminant concentrations in water,
      sediments, and biota must be considered when selecting a remedial alternative.  This
      selection process requires some method to estimate changes in contaminant concentrations
      that would result from each remedial alternative.  The preferred approach for estimating
      these changes, and the approach used in  the ARCS  RAM  studies, is based on the
      application of mass balance models.

      Mass balance models attempt to describe each of the underlying mechanisms  causing
      change in the  system,  and are  termed mechanistic.  In the mass balance modeling
      approach, the law of conservation of mass is applied in the evaluation of the sources,
      transport, and  fate of  contaminants.   This  approach requires  that the  quantities of
      contaminants entering the system (i.e., contaminant loading) equal the quantities leaving
      the system,  less the quantities stored, transformed, or degraded. Thus, the mass balance
      is simply a  bookkeeping of all of the processes affecting the mass of contaminants in a
      system.  After the mass balance  has been established for each contaminant of concern,
      quantitative changes in  contaminant concentrations can be estimated. For example, the
      mass balance can be used to estimate the change that may be expected following removal
      of some portion of the  contaminant mass.

      Mass balance models have been  successfully applied to the Great Lakes and elsewhere
      in the regulation of toxic and conventional pollutants. Properly applied, a mass balance
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                                             Chapter 3. Mass Balance Modeling Approach
model can serve as a surrogate for the natural system  that is  easily manipulated to
estimate the system's response to change.

Management questions that can be  addressed with a mass balance model include:

     1.   What are the consequences of leaving the contaminated sediments in place
         (the no-action alternative) under present conditions or where contaminant
         loadings are reduced?

         a.   Is the system in equilibrium with present loadings? For exam-
             ple,   will  sediment  contaminant  concentrations  increase  or
             decrease over time or remain the same under present  loading
             conditions?

         b.   What are the relative contributions  of loadings from point and
             nonpoint sources? What are the major loss mechanisms (e.g.,
             outflow, burial)?

         c.   What  is the effect of changes in loadings?   For example,  if
             loadings are reduced  or eliminated, what is the effect on contam-
             inant concentrations in the water, sediments,  and biota?

         d.   How long  does it take for the system to respond  to changes in
             loadings?  For  example, if the loads are reduced, how long
             would it take for the  concentrations to reach acceptable levels in
             water, sediments, and biota?

         e.   If left in  place, will contaminated  sediments pose a threat to
             downstream areas or will they become more widely dispersed?

     2.   What are the consequences of alternative remedial/mitigative actions, such
         as  removing, immobilizing, or treating the contaminated sediments?

         a.   What are the expected benefits of alternative remedial/mitigative
             actions in  terms of contaminant reductions in water, sediment,
             and biota?

         b.   What is the probability of recontamination following remedial/
             mitigative  actions under  present loading conditions?  How long
             would recontamination take?

         c.   What  risks are associated with implementation of alternative
             remedial/mitigative actions?
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                                                   Chapter 3. Mass Balance Modeling Approach
           3.   What are the estimated  loadings from the AOC  to  downstream  water
               bodies? For example, the Buffalo River may serve as a source of contami-
               nants to Lake Ontario, whereas contaminants from the Saginaw River may
               be transported to Saginaw Bay.  What changes can be expected in these
               loadings following the implementation of selected remedial/mitigative
               actions?
COMPLEXITY OF THE MASS BALANCE MODELING STUDY

      Mass balance modeling studies vary widely in their complexity. The modeling approach
      can  vary from  simple screening calculations to applications of  complex  computer
      programs.   Modeling  studies also vary in the complexity of the field studies used to
      support the mass balance calculations, from studies relying solely on historical data to
      large and expensive field efforts.  The degree of complexity required  depends on the
      physics of the system,  factors affecting the transport and transformations specific to the
      contaminants of concern, and the management questions the mass balance modeling study
      will address. The degree of complexity used in particular studies is often dictated  by the
      time and funding available.

      Modeling studies of contaminants in the Great Lakes have typically  been cataloged into
      groups or study levels depending on the level  of effort and complexity  in the modeling
      and  supporting field studies.  Studies have  been categorized as either "screening"  or
      "detailed"  studies, as well as "Level 0" through "Level III" studies. The study levels
      can  generally be described as:

           •   Level 0—Application  of simple manual or graphical methods based on
               statistical or deterministic equations to obtain rough estimates of contami-
               nant concentrations over extensive areas or to identify trouble  spots for
               more detailed analyses.  These analyses rely solely on available data to
               obtain  a preliminary assessment of management options and  to identify
               deficiencies in the  database when planning more detailed evaluations.

           •   Level I—Application of simple computerized models to obtain  rough esti-
               mates  of  contaminant concentrations  over  extended periods  of  time.
               Model equations are generally mechanistic in nature but only approximate
               the basic processes.  As a result, model projections used  to address the
               management questions  involve considerable uncertainty.  Data collection
               is  usually limited to one preliminary data collection study.   Qualitative
               estimates are usually based  on experience in  interpreting the  results.  A
               formal uncertainty  analysis is generally not included.

           •   Level n—Application of a computerized model of intermediate  complexity
               as a planning model, or as a rough engineering design or resource manage-
               ment model.  Extensive areas and periods of time can be simulated but at
               significant cost in data collection and preparation.  Data collection involves
               acquisition of at least two  independent data sets  to  bracket important
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                                             Chapter 3. Mass Balance Modeling Approach
         environmental conditions (e.g., high-flow vs. low-flow). All contaminant
         loadings to the system must be well characterized.  Some simplifications
         and approximations limit the applicability of the model for remedial design
         and management.  Thus, uncertainty analyses are  generally included as
         part of the model application.

     •   Level in—Application of advanced mechanistic computerized models for
         detailed remedial design and management.  The modeling approach would
         typically include descriptions of the hydrodynamics and sediment transport
         in the system, as well as detailed computerized models of water quality
         processes.  Data collection  involves at least two surveys to provide input
         for both model calibration  and model evaluation.  The surveys may be
         coupled with data collection over longer periods  to establish trends and the
         range of environmental conditions.

Generally,  the level of uncertainty is  reduced as the studies increase in complexity from
Level 0 to Level III, while the time and costs associated with each study level increase.

Increases in modeling  complexity need  not always correspond to  increases  in data
collection,  so various combinations  of the levels mentioned above  are possible.  For
example, simple models usually predict average conditions,  so  sufficient data must be
collected to provide an accurate estimate of the average condition for comparison with
predictions.  However, more complex models may  predict conditions at a specific point
(in time and space),  thus reducing the need for averaging.

In the ARCS RAM studies, both near-field and far-field modeling  studies  were con-
ducted.  The near-field modeling studies  concentrated  on  the  lower portions  of the
Buffalo and Saginaw Rivers where sediment contamination was the greatest and where
remedial actions will likely be implemented.  The far-field modeling studies were used
to estimate the  impact of remediation of the  Buffalo and Saginaw Rivers  on their
receiving waters—Lake Ontario and Saginaw  Bay,  respectively.

While the general mass balance modeling approaches used in the near-field and far-field
studies were similar, they differed in the resolution of the models applied and in the level
of supporting field studies.  The ARCS near-field studies were categorized as Level I or
a "Mini-Mass Balance" modeling effort.  The primary criterion restricting the modeling
studies to Level I was the limited level of supporting field studies.

The  far-field modeling  was more typical of Level 0, in terms  of data collection, and
Level I, in terms of modeling.  These studies were designed to estimate the long-term
impact of changes in loadings from the rivers on their respective receiving water bodies.
As such, hydrodynamics and sediment transport were described rather than predicted,
and the resolution was not as precise  as in the near-field studies.   The far-field modeling
studies of Lake Ontario and Saginaw Bay relied exclusively  on historical data.
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                                                  Chapter 3.  Mass Balance Modeling Approach
COMPONENTS OF THE MASS BALANCE MODELING STUDY

       The application of the mass balance modeling approach involves the quantification of the
       sources, transport, and fate of contaminants. The components of the modeling approach
       are illustrated in Figure 3-1.  The typical steps in a mass balance modeling study are:
       1) predict water and sediment transport, 2) use the predicted water and sediment trans-
       port, along with estimates of contaminant loadings  from point and nonpoint sources, to
       estimate the changes in chemical concentrations in water and sediments, and 3) use the
       predicted contaminant concentrations in water and sediments to estimate the transfer of
       contaminants through the food chain and their accumulation in fish.  The models used
       for each step of this process are described below.
Water Transport Models

       The first step in characterizing the transport of dissolved contaminants is to characterize
       the transport of the water, or its motion.  Often, much of the variability of contaminant
       concentrations  in the water  column can be explained by water transport alone.  Water
       transport  models may be descriptive (i.e., based on a balance of the water's mass) or
       hydrodynamic  (i.e., based on a balance of the water's momentum).

       Characterization of water transport may be qualitative or quantitative, depending on the
       study  level.  In a qualitative approach, flow  patterns are either  measured directly or
       inferred from  measurements of related parameters.  The qualitative approach is often
       adequate  where the system is very simple (hydraulically) or where only long-term,
       relatively rough estimates of water transport are required. A qualitative approach is most
       often used in Level 0 and Level I studies and is occasionally used in Level II studies.

       Hydrodynamic models are used to quantitatively predict changes in volumes, depths,  and
       velocities in response to changes in flow or water surface elevations.  Hydrodynamic
       models require data on boundary conditions (i.e., flows or water surface elevations, wind
       speed and direction), which  are applied to predict the resulting flows within the modeled
       system.  Flows are often measured at gaging stations on many Great Lakes tributaries,
       and water surface elevations are routinely measured at many locations within the Great
       Lakes. Where such direct measurements of flows in the tributaries of the Great  Lakes
       are problematical because of the complex interactions and relationships between upstream
       inflows and lake effects, hydrodynamic models can be used to  quantitatively predict
       flows.  Hydrodynamic models can  also be used to estimate changes in flows that may
       occur under future conditions,  such as in evaluating the effects of changes in dredging
       patterns.

       The  hydrodynamic  models used  in  the  ARCS  RAM  modeling studies included
       HYDRO-3D,  a 3-dimensional hydrodynamic and transport model, and RIVMOD, a
       1-dimensional  model.  Both models are maintained  and distributed by  the Center for
       Exposure Assessment Modeling at Athens, Georgia.  Multidimensional models were
       required where it was  necessary to resolve variations in water transport and chemical


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                         Hydrodynamic Model
Sediment Transport
00
                                          Contaminant Transport
                Loading Study
                                            Food Chain Model
                Figure 3-1.  Components of the mass balance modeling study.

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                                                  Chapter 3.  Mass Balance Modeling Approach
       characteristics along  the longitudinal, vertical, and lateral  axes  of the  rivers.   For
       example, a model that was capable of estimating variations in transport with depth was
       required in  the Buffalo River because of water column stratification during low-flow
       periods.

       A qualitative approach was taken for the far-field studies. For Lake Ontario, historical
       measurements of inflows and outflows were used to compute water transport, while for
       Saginaw Bay, water transport was computed from measured  flows and chemical data.
Sediment Transport Models

      Because contaminant concentrations in surface sediments are a primary concern in the
      AOCs, adequate characterization of the movement of surface sediments is a critical step
      in the mass balance modeling process.  There are two primary goals of the sediment
      transport model:  1) to predict the movement of the sediments to estimate changes that
      may occur  in patterns  of erosion, deposition, and transport, and  2) to estimate the
      transport of the paniculate contaminant mass.

      Sediment transport models are based on a sediment mass balance.   As with water
      transport, sediment transport may be  described either qualitatively or quantitatively in
      mass balance modeling studies.

      Qualitative approaches have commonly been used in Level 0 and Level I studies.  In
      studies of this type, measured or estimated settling, resuspension, and sedimentation rates
      are used to  compute the  transport of sediments and their associated  contaminants.
      Although it is generally assumed that there is no net  sedimentation or erosion,  the
      different contaminant concentrations on suspended and settled paniculate matter make the
      quantification of these processes important. The qualitative approach has proven useful
      in providing rough estimates  of the effects of sediment transport on contaminant
      distributions. However, sediment transport is a very dynamic process and the assumption
      of no net sedimentation or erosion is a gross simplification.

      In more quantitative sediment transport models, resuspension and transport are computed
      using  the output of a hydrodynamic model and the measured  characteristics  of the
      sediments.  The sediment types of primary importance are silts and clays, rather  than
      sands.  Silts and clays are classified as cohesive sediments, while sand is classified as a
      noncohesive  sediment.  The sediment transport model  is used to predict changes in
      sediment resuspension, deposition, and transport  and  the effect of these processes on
      particulate concentrations  in the water column.  The sediment transport model  is also
      used to estimate  changes  in the structure of the sediment bed, such as the impact of
      erosion or deposition on the channel shape and sediment composition.

      As with hydrodynamic models,  sediment transport  models can be used to interpolate
      between existing  measurements or estimate sediment transport for conditions for which
      data are not available.  The majority of sediment transport occurs during extreme (rare)
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                                                  Chapter 3.  Mass Balance Modeling Approach
      events, such as storms on lakes and large runoff events in rivers. Because data are rarely
      available for these events, sediment transport models must be used to estimate transport
      under these conditions. For example, these models may be used to estimate whether con-
      taminated sediments may be buried or exposed by a  10-year  or  100-year flood.  This
      information can be used in the evaluation of remedial alternatives as well as the no-action
      alternative.  Sediment transport models  may also be used to evaluate the impact of
      removing or immobilizing sediments on subsequent erosion and deposition patterns. For
      example, if sediments  are removed from a particular area, sediment transport models
      may be used to estimate how long it may take for the area to fill in, as well as changes
      that may occur in deposition and erosion areas.

      In the ARCS RAM modeling studies, a model of the transport of cohesive sediments was
      applied to both of the near-field study sites (i.e., Buffalo and Saginaw Rivers) to predict
      the interactions between the transport, deposition, and resuspension of sediments under
      various meteorological  and  hydrological  conditions.    The model  applied  was  a
      2-dimensional (longitudinal and lateral),  time-variable, hydrodynamic and  sediment
      transport model developed  by Wilbert Lick at  the University of California,  Santa
      Barbara.  This model  has been applied at various locations  around the Great Lakes,
      including the  Detroit River, Fox  River,  Green Bay,  Lake Erie, and elsewhere.   The
      sediment transport model was coupled with a 3-dimensional, time-variable model of the
      sediment bed and its properties, the Water Quality Analysis Program, WASP4 (Ambrose
      et al. 1990).  WASP4 integrates predictions from the hydrodynamic and sediment trans-
      port model to estimate contaminant concentrations in  the water and  sediment.   The
      WASP4  model, maintained and distributed by the Center for Exposure  Assessment
      Modeling at Athens, Georgia,  has been  widely distributed.   WASP4 is currently the
      framework used for modeling studies in Green Bay, Lake Michigan, Lake Ontario, and
      elsewhere around  the Great Lakes.  It is generally assumed  that the water column  is
      completely mixed vertically because  sediment resuspension  typically occurs at  flows
      where this  would be the case.   This model was used to predict variations in suspended
      solids concentrations, resuspension and deposition rates, and variations in  the sediment
      bed as a function  of flows and loadings.   The model  provided predictions for use in
      determining the transport of sorbed contaminants  and resuspension of toxic sediments.
      Application of the sediment transport model was of particular importance in these studies
      because of the lack of  historical sediment data.  Therefore, these studies relied heavily
      on the sediment transport model to supply estimates of sediment transport, resuspension,
      and deposition.
Contaminant Exposure Model

      The contaminant exposure model is the mass balance model for contaminants.   The
      contaminant exposure model used as  a  framework for the ARCS RAM mass balance
      modeling studies was WASP4. In the application of the contaminant exposure model,
      the rate of change in contaminant mass  (accumulation) is a function of the transport of
      a  contaminant into, out of,  and within the  system  via water  transport or sediment
      transport  for those materials  that sorb to sediments; the mass added to the system via
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                                                   Chapter 3.  Mass Balance Modeling Approach
       point  and nonpoint loadings minus the outputs;  and the quantities transformed and
       degraded within the system via processes such as volatilization, biodegradation, and
       photodegradation.  The output expected from the contaminant exposure model includes
       estimated contaminant concentrations of both paniculate and dissolved forms in water and
       sediments,  as well as estimated changes in  mass fluxes due to inflows and loadings,
       outflows, and degradation and  transformation processes.  Depending on the level  of
       complexity, the transport via water and sediments may be described or predicted using
       hydrodynamic  and sediment transport models, which are then coupled with the con-
       taminant exposure model.

       In the ARCS RAM near-field studies, WASP4 was applied to predict the effects of water
       transport,  sediment transport,  sorption,  and transformation  processes on the concen-
       trations of selected contaminants of concern.  The WASP4 model was linked to the out-
       put of the hydrodynamic and sediment transport models, which together provided the
       necessary transport information, using data collected during  ARCS field studies.  The
       output of the contaminant exposure model included temporally and spatially varying
       estimates of contaminant concentrations in water  (both particulate and dissolved) and
       sediments for comparison to field data and for projections of the effectiveness of various
       remedial alternatives.  In addition, the output included estimates of the magnitude of all
       processes that result in gains or losses of contaminants, so that their relative importance
       could be evaluated.  The contaminant exposure model also  provided  information that
       could be incorporated  into  the food chain  model to estimate the contaminant body
       burdens in  fish due to varying contaminant concentrations in  water  and sediment.

       The same contaminant exposure model used in the near-field studies (WASP4) was
       applied in the far-field studies.  However, in the far-field studies the resolution was not
       as precise  as in the near-field studies.   Therefore,  there was no need to  apply the
       hydrodynamic  and sediment transport models in  the far-field  studies.  WASP4 was
       applied to predict steady-state (long-term average) conditions over  large spatial  scales.
       The output of the model included load-response relationships.  For example, given a
       particular  contaminant loading, the  model  predicted the average contaminant  con-
       centrations in water [both particulate and dissolved] and sediments. This relationship was
       then used to evaluate the impact of changes in loadings from the two AOCs on Lake
       Ontario and Saginaw Bay.
Food Chain Model

      The food chain model is a mass balance model for contaminants where the rate of change
      in contaminant mass in each component of the food chain is a function of the transport
      of a contaminant into and out of that component (e.g.,  via ingestion, gill exchange,
      excretion), as well as  internal changes that may occur due to growth.  The food chain
      model supports evaluation of the impact of various remedial alternatives including the no-
      action alternative on contaminant concentrations  within the food chain,  given  variations
      in contaminant concentrations  in water  and sediments derived  from  the contaminant
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                                                   Chapter 3.  Mass Balance Modeling Approach
       exposure model.  Outputs from the food chain model include time-variable estimates of
       contaminant concentrations in each component of the food chain.

       The food chain model applied to both the Buffalo and Saginaw Rivers as part of the
       ARCS RAM studies was the Water Quality Analysis Simulation for Toxics, WASTOX
       (USEPA 1985), a predecessor of WASP4 that includes a food chain component. In the
       Buffalo  River, the only fish species simulated was carp,  because it is a bottom-feeder
       with a high fat content and would be expected to have an  appreciable contaminant body
       burden.  In the Saginaw River, the food chain model included forage fish and walleye,
       the latter due to its high importance to recreational anglers. Data collected as part of the
       ARCS RAM studies were used to construct a simple food chain model.
REQUIRED FIELD DATA

       Field data are required to apply any mass balance model.  For model application, field
       data are required to define the characteristics of the site and the mass fluxes of water,
       sediment, and the associated contaminants into and out of the site. In addition, data are
       often required to estimate the site-specific values of model parameters and to assess the
       uncertainty associated with model projections.  The confidence that can be placed  on
       those projections is dependent upon both the integrity  of the model and how  well the
       model is calibrated to that particular water body.

       While models can be run with minimal data, the resulting predictions are subject to large
       uncertainty. Models are best used to interpolate between existing conditions but may be
       used to  extrapolate from existing to future conditions,  such as in the evaluation  of the
       effects of remedial or mitigative alternatives.

       The types of data required and the necessary frequency of measurement vary  with the
       level of model  complexity, the characteristics of the system, and the contaminants of
       concern. Generally, three kinds of data are required: 1) boundary conditions,  2) initial
       conditions, and 3) data  for calibration/evaluation. Boundary conditions are external to
       the model (i.e., the model does not predict them). Instead, they are used to "drive" the
       model.  Initial conditions are used to aid in the design of the model application (e.g., to
       determine segmentation) and to provide a starting  point for model predictions. For
       example, the initial, or existing, sediment  contaminant concentrations are required to
       provide a  starting point for model predictions.   Temperature data  may  be used to
       determine the need for predicting water-column stratification and its effects on  contami-
       nant transport.  Model calibration/evaluation data include the parameters that the model
       is designed to predict (e.g., contaminant concentrations and fluxes).  These  data are
       compared to the model's predictions  to aid in determining the values  of site-specific
       parameters and in estimating the uncertainty associated with those predictions. The types
       of data  required  for each component  of a mass balance modeling study are described
       below.
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                                                   Chapter 3. Mass Balance Modeling Approach
Water Transport Data

       Boundary condition data for the water transport models include the system's bathymetry,
       point source and nonpoint source flows and loadings, upstream and downstream flows
       and/or  water surface elevations, and  weather data (e.g., wind  speed and direction,
       temperature). These data can often be obtained from the National Oceanic and Atmos-
       pheric Administration,  U.S. Army Corps of Engineers (Corps),  USEPA, USGS,  and
       local government agencies.  Both historical data and data collected during the course of
       field studies of the AOC are required.  Model calibration/evaluation data may include
       measurements of flows, velocities, or water surface elevations within the system under
       investigation for comparison to model predictions.

       The frequency of measurement of hydrodynamic parameters varies with the complexity
       of the system under investigation. However, for most  Great Lakes rivers and harbors,
       their dynamic nature requires that data be available on an hourly basis for major tributary
       flows, water surface elevations, and weather data.  Water surface elevation and weather
       data are usually readily available at this frequency.

       In the ARCS RAM modeling studies, historical data were available on flows, water  sur-
       face elevations at the mouths of the Buffalo and Saginaw Rivers, meteorological condi-
       tions, and the values of some conventional parameters, such as temperature and conduc-
       tivity.  Additional measurements of water  surface elevations, water velocities and  dis-
       charges, and wind velocities and directions were also obtained concurrently with the
       ARCS field studies.
Sediment  Transport Data

       Because sediment transport models are driven by hydrodynamic models, their application
       requires the same data described above.  The data for the system's bathymetry should be
       the same as that used for the hydrodynamic model.  However, because a sediment trans-
       port model may  be used to predict changes in the bathymetry in response to storm or
       flow  events,  additional bathymetric information  collected periodically (e.g.,  every
       3 months or after large storm events) is highly desirable for evaluating the  model's
       performance.

       Data  on the initial conditions of sediment properties include particle size distributions,
       bulk densities, porosity (water content), and resuspension  potential.  Because sediment
       properties  may vary spatially, characterization or mapping of these properties over the
       study  area is usually necessary.   This  mapping  may  be quantitative or qualitative,
       depending  on the objectives of the particular study.

       Suspended solids concentrations at the boundaries over time are required to drive the
       model, and suspended  solids data within the modeled system are required  for model
       calibration/evaluation.  Because sediment transport  is nonlinear and highly dynamic,
       these data  are required  as frequently as possible (i.e., continuously if feasible) at least
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                                                   Chapter 3. Mass Balance Modeling Approach
      during the course of high-flow events.  Collection of these data may often be readily
      accomplished using automated sampling techniques or using some surrogate measurement
      (e.g., water transparency) to estimate suspended solids concentrations where a relation-
      ship can be established between the surrogate  measurement and the suspended solids
      concentration.

      Data used in the ARCS RAM studies of the Buffalo and Saginaw Rivers included histori-
      cal data, such as Corps dredging records.  In addition:  1) data on sediment characteris-
      tics (e.g., grain size, water content) were collected during the ARCS sediment surveys,
      2) periodic bathymetric surveys were conducted to  estimate changes in the system's
      morphometry,  3) suspended solids concentrations were measured concurrently  with the
      river sampling, 4) suspended solids concentrations were measured either during high-flow
      events (Buffalo River) or hourly during periods of the year (Saginaw River) to support
      the sediment transport model, and 5) studies were conducted to estimate the resuspension
      characteristics  of the sediments.
Contaminant Exposure Data

       The computation of contaminant exposure also requires information on water and sedi-
       ment transport from the hydrodynamic and sediment transport models. When not avail-
       able from models, these data must be derived from field measurements, similar sites, or
       general guidelines.

       Data on boundary conditions include measured concentrations of the contaminant(s) of
       concern or loadings (mass per unit time) from all significant sources (e.g., tributaries,
       point and nonpoint sources).  Data on initial conditions include existing contaminant
       concentrations in the water and surface sediments.  Contaminant concentration profiles
       of sediments are required if the impact of exposing deep sediments is to be evaluated.
       For example, if dredging to a certain depth is proposed, then measurements of contami-
       nant concentrations in the sediment layer expected to be exposed are required.  Data
       should be collected during both high-  and low-flow events because the relative impor-
       tance of processes affecting  contaminant  transport and  fate vary under different flow
       conditions.

       The analytical approach used to support mass balance modeling may differ from that used
       to support other studies.  For example, for regulatory purposes it may be sufficient to
       know that contaminant concentrations are below some criterion. However, to compute
       contaminant mass the contaminant concentrations must be accurately known. Appreciable
       numbers of concentrations below analytical detection limits,  "non-detects," may  make
       the data unsuitable for use in mass balance modeling studies.  In addition, excessive
       "noise" in  the data  (random high or low detections due to sampling or  analytical
       variability)  may make it  difficult  to distinguish trends.   Specialized  sampling and
       analytical methods for trace metal and organic analyses  are often required  to reduce
       analytical noise and obtain sufficiently low analytical  detection  limits.
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                                            Chapter 3.  Mass Balance Modeling Approach
Data are also required for materials that may affect the transport and transformation of
contaminants.  For example, sorption onto solids affects the transport and transformation
of some organic and inorganic chemicals.  The prediction of sorption requires that data
be available on the fraction of organic carbon  in  sediments and suspended  solids,
dissolved organic carbon concentrations, and phytoplankton concentrations. Data on pH
are required to predict the speciation of metals and ionization of some organic chemicals.
Data on sulfides are required to predict metal precipitation.  If data are not available for
constituents that affect contaminant transport and transformations, large uncertainties may
be introduced in the modeling study.  Knowledge of the geochemistry of the contami-
nant(s) of concern and of the site to be modeled is essential.

In the ARCS RAM near-field studies, both historical and field data collected as part of
the ARCS  Program for  ambient water, sediment, contaminant loading, and food chain
relationships were used  for the calibration of the contaminant exposure model. For the
far-field  studies, only historical data were used.

The  ARCS RAM near-field studies concentrated on the lower Buffalo and Saginaw
Rivers.  Although there  were some differences, the field sampling plans for the two sites
were similar in design.  Synoptic surveys were conducted at the Buffalo and Saginaw
Rivers to identify spatial variability in the systems during certain low- and  high-flow
periods.  Synoptic surveys provide a "snapshot"  of the system,  or data at a particular
point in  time.  Six sampling stations were  selected  to allow estimates to be made of
contaminant fluxes into, and out of, the AOCs.  Samples were integrated over the width
of the system  and,  in  some cases,  over  depth.  Where significant stratification was
encountered, samples were collected at several depths.  Ambient data for particulate and
dissolved contaminants, as  well as conventional parameters,  were obtained over six
sampling days during 1990 and 1991. Selected conventional parameters were measured
at a greater frequency to aid in calibration of the  hydrodynamic and sediment transport
models and to aid in estimating yearly loadings.  Examples of the parameters measured
for the ARCS  RAM mass balance modeling studies are listed in Table 3-1.  Sediment
contaminant concentrations were measured during separate field  sampling studies.

ARCS studies were also conducted to identify contaminant loadings and concentrations
in water, sediments, and biota.  Contaminant loadings were  estimated and/or measured
from both  point and nonpoint sources.  Historical data were used to estimate loadings
from point sources.  Loading measurements were also acquired concurrently with the
ambient water quality studies.  Loadings from CSOs in the Buffalo River were estimated
based on a limited field sampling program  (24 samples at 10 CSOs) and storm water
modeling.  For the Saginaw River study, CSOs were not identified as a significant source
of contaminant loadings and were, therefore, not sampled. Loadings of contaminants and
suspended solids from upstream tributaries were based on six daily measurements during
the fall of 1990 and the spring of 1991.  Historical contaminant, suspended solids, and
flow data,  as well as data from a suspended solids survey, were collected to extrapolate
these measurements to annual loading rates.
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TABLE 3-1. EXAMPLES OF PARAMETERS MEASURED FOR THE ARCS RAM
               MASS BALANCE MODELING STUDIES

Parameter
Dissolved PCBs
Participate PCBs
Total PCBs
Dissolved PAHs
Paniculate PAHs
Total PAHs
(benz[a]anthracene, benzo[b]fluoranthene,
benzo[k]fluoranthene, benzo[a]pyrene.
chrysene)
Dissolved metals
Paniculate metals
Total metals
(lead, copper, zinc3)
Paniculate iron
Sulfides8
Dissolved oxygen
Conductivity
Temperature
PH
Alkalinity
Suspended solids
Dissolved organic carbon
Paniculate organic carbon
Chlorophyll a and phaeophytin
Hardness
Total incident radiation
Light extinction
Wind velocity and direction
Water surface and elevation
Flow
Lipid content

River
X
X
S
X
X
S



X
X
S

X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X

Tributaries,
Point Sources


X
X
X
S



X
X
S


X
X
X
X
X
X
X
X
X







X

Biota


X








X










X







X
Note: PAH - polycyclic aromatic hydrocarbon
PCB - polychlorinated biphenyl
S - total computed from sum of

paniculate


and dissolved concentrations
Saginaw River study only.
                              51

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                                                    Chapter 3.  Mass Balance Modeling Approach
Food Chain Data
       The predictions of the food chain model are based on the contaminant concentration data
       obtained from the contaminant exposure model.  That is, the food chain model is the
       final link in the chain of models relating transport  and contaminant transformations to
       concentrations of contaminants in biota.  The exposure concentrations of chemicals are
       used along with information on the bioenergetics of organisms to estimate concentrations
       in the biota.

       Generally, the species that are of interest in food chain modeling are the higher preda-
       tors, such as walleye. However, to estimate the variation of contaminant concentrations
       in these higher predators, and the effects of changing conditions on them, it is necessary
       to estimate the contaminant concentrations in the components of the food chain leading
       up to the higher predators.  Therefore, one of the initial steps in the food chain modeling
       is the determination of the components of the food chain for  the species of interest. The
       food chain may not only include different species of fish and forage but may be further
       subdivided into different life stages because of variations in food or feeding patterns.  In
       addition, many higher predators may migrate into and out of the study area.  The prefer-
       ence for a particular forage species may also change seasonally. It is often desirable to
       select target organisms that have limited and well-defined food chains and migration pat-
       terns to minimize the complexity of the food chain model and the extent of the supporting
       field data that will be required.

       In addition  to  food chain relationships,  it is necessary to have  information on the
       bioenergetics of the components of the food chain. This information may include growth
       rates, reproduction rates,  gill characteristics,  ingestion  rates and  uptake efficiencies,
       swimming rates, and excretion rates.  Although site-specific information is preferred,
       much of these data can be obtained from available  literature and databases.

       Contaminant concentrations in the various components of the food chain are required to
       provide a starting point for the model (the initial conditions) as well  as to provide for
       model calibration/evaluation.  In addition to contaminant concentrations, data should be
       collected on other characteristics affecting uptake.  For example,  data on  lipid content
       are required because it affects the uptake of many hydrophobic contaminants. One diffi-
       culty with obtaining data for calibration/evaluation  of  food chain  models,  as with
       contaminant exposure models, is that changes in contaminant concentrations may occur
       slowly.  Particularly in higher predators, changes may occur over seasons and over years
       so that, ideally, data should  be available on those  time scales.  Therefore, a complete
       characterization requires either an adequate historical database or long-term field studies.
       The lack of these data may result  in greater uncertainty in model predictions.

       Data were collected in ARCS studies to support food chain modeling studies.  In the
       Buffalo River,  contaminant concentrations in carp  and in their stomach contents were
       analyzed to establish a relationship between contaminant concentrations in carp tissue and
       contaminant concentrations in their benthic forage.  Carp were selected because  there are
       currently advisories in effect against consumption of carp from the Buffalo River.  Data
                                               52

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                                                    Chapter 3.  Mass Balance Modeling Approach
       were collected for nine carp composited into three age classes for analysis.  Sampling in
       the Saginaw River concentrated on walleye and its food chain, because of the importance
       of the walleye fishery in this area.
MODEL APPLICATION

       A  typical model application involves characterization of the system followed  by an
       evaluation of model predictions.  Upon completion of the evaluation, the model is then
       used to address management questions.

       The characterization step involves establishing the boundary  conditions for the  model
       (those things  outside of the model  that affect  its predictions, such as inflows  and
       bathymetry), determining the initial conditions of the system (such as initial sediment
       contaminant concentrations), and determining site-specific parameter values.  Some site-
       specific parameters may be known from previous  studies or  may be easily measured.
       Some parameters may be unknown or difficult to measure.  Unknown parameters can be
       estimated by calibrating the model  to field data,  by applying values that  have been
       established as representative of similar sites, or by  using general guidelines to establish
       values.

       Model calibration using  site-specific field data is likely to yield the most accurate esti-
       mates for unknown parameters, but can only be applied when existing data (e.g., particle
       distributions, contaminant distributions in water and solids, or contaminant distributions
       in species) are available.  In addition, as the number of unknown parameters increases,
       so does the difficulty of estimating them by calibrating the model  to a single data set.
       With  even two unknown parameters, it is possible  that values could be selected so that
       the model prediction matches a data set used for calibration, but these values may  not be
       intrinsically accurate. Therefore, the values may lead to biased predictions under other
       conditions, such as a change in contaminant loading.

       Parameter values that have been established as representative of a site similar to the one
       being modeled may be used if those values are the  result of direct observation, calibra-
       tion of the model at that other site, or the prediction of a different model  that in turn has
       been  calibrated and verified. Two  sites need not be similar in all respects for some
       parameters to apply equally well to both.   For example, similarity of particle settling
       rates might be established on the basis of bottom type, particle type, particle supply rate,
       and current velocities; other site characteristics such as size and boundary configuration
       could be very different.

       General guidelines for establishing parameter values may consist of published tables of
       values, statistical distributions or regressions, or rule-of-thumb calculations.  A literature
       search may be needed to locate such general guidelines, if they exist.  One potentially
       useful compendium of guidelines is  Bowie et al.  (1985).  General guidelines usually
       suggest a range of parameter values that may be appropriate for a given situation.  Such

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                                             Chapter 3.  Mass Balance Modeling Approach
ranges may be used to estimate the potential error of the model's prediction, or they can
be used to select an environmentally protective value.

The evaluation step involves comparisons of model predictions to field data.  These data
are separate from those used in the calibration step. The comparison of predictions to
field data in the evaluation step allows an estimation of model uncertainty.

The final step of model application is the use of the model for its intended purpose, that
is  to address management questions concerning  an AOC.  Some of the management
questions a model may be used to address were listed at the beginning of this chapter.

The model applications at the Buffalo and Saginaw River AOCs resulted in estimated
concentrations of selected contaminants in sediment, water, and biota as a function of
contaminant loadings. In addition,  these models provided a means of estimating the
consequences of various remedial or mitigative alternatives. Specific model outputs for
each AOC included:

    •   Loading/response curves for each selected contaminant, relating external
         loadings to  contaminant concentrations  in water, sediment, and specific
         fish species by age group, for each river reach.  Uncertainty estimates
         were provided for loading/response relationships.

    •   For each selected contaminant, estimated loadings from the AOC to  the
         receiving water body for a variety of flow conditions and  as affected by
         selected remedial or mitigative alternatives.

    •   Estimated time to recovery in order to assess the no-action alternative as
         well as the relative benefits of selected remedial or mitigative alternatives.

    •   Estimates  of the  relative importance of various processes affecting  the
         transport and transformations of contaminants,  such as  losses due to
         volatilization, burial, and outflows.
                                        54

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4.    COMPARA TIVE RISK ASSESSMENT
       The comparative risk assessment is the final step in the comprehensive risk management
       process (Figure 1-1) that was addressed in the ARCS RAM studies. The comparative
       risk assessment integrates information from all previous steps in the process to estimate
       changes in risk, relative to the baseline risk, that would result from implementation of
       the various sediment remedial alternatives evaluated.  Thus, the comparative risk assess-
       ment provides a prognostic  framework that can aid in addressing management questions.
       Management questions that may be addressed by the comparative risk assessment, such
       as the potential impacts of proposed remedial alternatives, generally coincide  with those
       addressed by mass balance  models.  However, in the comparative risk assessment, con-
       taminant concentration estimates  generated  by mass  balance modeling (Step 7  of
       Figure 1-1) are used to derive risk estimates for various remedial alternatives being
       considered within an  AOC.  The  remedial  action  objectives  that had  initially been
       developed during risk assessment planning (Step 2 of Figure 1-1) are then refined during
       the comparative risk assessment.

       The approach used in the comparative risk assessment integrates  the results from the
       baseline risk assessment, field studies, and mass balance modeling studies  to provide
       estimates of the potential impact of remedial actions on human health, wildlife, and
       aquatic organisms.   The output of the baseline risk assessment and modeling  studies
       serves as input to the  comparative risk assessment (Figure 4-1).  For example, output
       from the baseline risk assessment includes algorithms, exposure parameters, and toxicity
       values used for deriving conservative estimates of risks based on current site conditions.
       Output from the field studies includes  measured contaminant concentrations in water,
       sediments, and biota. Output from the mass balance modeling studies includes estimated
       contaminant concentrations in water, sediments, and selected fish species following the
       implementation of proposed remedial  alternatives.  The  comparative risk assessment
       integrates these outputs to produce estimates of risks for all remedial alternatives under
       consideration.  Thus, the risks associated with each remedial alternative can be compared
       with the risks associated with the other remedial alternatives, as well as with the baseline
       risks.

       Comparative risk assessment studies were conducted for the Buffalo and Saginaw River
       AOCs to demonstrate methods for estimating potential changes in risks to humans, wild-
       life,  and aquatic organisms exposed to sediment-derived contaminants  under selected
       remedial alternatives. The comparative  risk assessments  resulted in estimates of potential
       risks that may  be used in the selection of the most appropriate remedial  alternatives.

       In the ARCS RAM studies, potential remedial alternatives considered included no action
       and several dredging and capping scenarios.   No action was defined as no change in
       existing sediment  management  practices  (e.g., continued  maintenance  dredging).

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                                                            Site Characterization
                                                                Evaluation
                                                              of Available Data
                                     Mass Balance
                                    Modeling Studies
                      Field Studies
                      Baseline Risk Assessment
                       (human health, wildlife,
                        aquatic organisms)
                             Human Health
                                                  COMPARATIVE RISK ASSESSMENT
                         Wildlife
CJl
                       t
                t
                                 B
 No
Action
                               REMEDIAL
                             ALTERNATIVE
    B    C    No
            Action
  REMEDIAL
ALTERNATIVE
                                                               Selection and
                                                              Implementation of
                                                             Remedial Alternative
                                 Aquatic Organisms
                             t
    B    C    No
            Action
  REMEDIAL
ALTERNATIVE
                  Figure 4-1. Comparative risk assessment in the risk management process.

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                                                 Chapter 4.  Comparative Risk Assessment
Dredging options  that were considered included complete dredging  of contaminated
sediments, dredging of hot spots, dredging to a selected depth, and cessation of dredging
in part or all of a channel.  The comparative risk assessment produced estimates of the
potential changes in risk that may result from each of these remedial alternatives.  These
estimates may then be compared to the existing (baseline) risk to evaluate the relative
benefits of remediation and aid in the selection of the most appropriate  remedial alterna-
tive.
                                       57

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5.    SUMMARY
       There are currently large numbers of sites in the Great Lakes and elsewhere where con-
       taminant concentrations in sediments are at levels that are of concern to environmental
       scientists, regulatory agencies, and the general public.  Many of these contaminants, such
       as heavy metals and chlorinated organic compounds, are resistant to  degradation by
       physical,  chemical,  or biological processes.  Therefore, the impact of contaminated
       sediments may continue well into the future.

       Among the primary concerns associated with contaminated sediments are the risks they
       pose to humans, wildlife, and aquatic organisms.  To protect human health, local authori-
       ties  in many areas have posted fishing and swimming bans,  issued fisheries advisories,
       or ceased drawing drinking water from areas  with contaminated sediments.  Sediment
       contamination has made many areas uninhabitable for benthic organisms or has resulted
       in bioaccumulation through the food chain,  adversely affecting both fish and  wildlife.

       The risks posed by contaminated sediments result from the exposure of organisms to the
       chemicals through a number of pathways, including direct adsorption from water or sedi-
       ments or through feeding.   However, myriad processes  are known  to  affect that
       exposure.  For example, factors affecting the degree of contamination and exposure may
       include the degree of ongoing contaminant loading, hydraulic and sedimentation patterns,
       the physical characteristics of the sediments, the degree of  sediment/water interaction,
       and  the characteristics of the chemicals.

       As part of  the ARCS Program, studies were  conducted by the RAM Work Group to
       demonstrate an integrated approach to evaluating the processes that affect exposure and
       risks resulting from sediment contamination. This approach is potentially applicable to
       other areas  with contaminated sediments, both  in the Great Lakes region and elsewhere.
       The first step in the  approach is the identification of the degree  of existing sediment
       contamination, potential exposure pathways, chemical toxicity, and the resulting potential
       risks posed to humans, wildlife, and aquatic organisms.  The second step, if required,
       is to conduct field studies to further characterize the distributions and concentrations of
       contaminants of concern and to aid in identifying factors affecting their transport and
       transformations.  Based  on those field  studies and risk  assessments, priorities can be
       established  for areas  that need remediation and potential remedial alternatives can be
       identified.   Next, mass balance models can be used to evaluate  the processes affecting
       exposures and risks and to predict potential changes in conditions that may occur follow-
       ing  implementation of the  selected remedial  alternative(s).   Finally, these predicted
       changes in conditions can be used to estimate potential changes in risks  that may occur
       following remediation.
                                              58

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                                                                Chapter 5.  Summary
The integrated approach used in the ARCS RAM studies and described  in this report
provides a means of evaluating the potential consequences of remediation, in terms of
both exposure and risks.  The approach can be used to aid in addressing management
questions, such as "How long will it take for the problem to go away through natural
processes in the absence of active remediation?,"  "What happens if the  sediments are
dredged to a particular depth?," or "Will the sediments become recontaminated following
remediation?" Like all such approaches, there are various limitations that result from
deficiencies in the current understanding of factors affecting the transport and transfor-
mations of contaminants, chemical characteristics, or chemical  toxicity. However, prop-
erly used, the approach may provide a viable means of assessing the nature and extent
of sediment contamination and aid in the evaluation and selection of appropriate remedial
alternatives.

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6.    GLOSSARY
      Acute—Characterized by a time period that is relatively short in comparison to the life
      span of an organism.  Acute toxicity is the characteristic of a chemical to cause a toxic
      response in organisms immediately or shortly after exposure to  the chemical.

      Adverse effect—An impairment  of biological functions  or  description  of ecological
      processes that results in unfavorable changes in an ecological system.

      Ambient water quality criterion (plural: criteria)—An estimate of how much of a
      chemical could be present in the water without harming human  health or aquatic life.

      Aquatic—Living or growing in water.

      Area of Concern (AOC)—A waterbody (e.g., river, harbor, bay) within the Great Lakes
      basin that  has been identified as  having  impairment of beneficial uses attributable to
      chemical contamination.  In most  of the Great Lakes AOCs, sediment contamination is
      a significant contributor to the impairment of beneficial uses.

      Assessment endpoint—An ecological value to  be protected  (e.g.,  trout population
      abundance or community structure that indicates a "healthy" biological community).

      Baseline risk  assessment—An  assessment that estimates risks associated with existing
      environmental conditions.

      Benthic—Pertaining to, or associated with, the bottom of a body of water.

      Bioaccumulation—Net uptake of  a chemical into the tissues of an organism as a result
      of direct contact with a  medium, such as  water or soil, or through the diet.

      Biodegradation—The decomposition  of  a chemical substance by natural biological
      processes.

      Biomagnification factor—A measure of the degree of increase in the tissue concentration
      of a chemical  with each trophic step in a  food chain.  For example, a biomagnification
      factor of 5.0  indicates that the concentration of a  given  chemical  in the tissues of a
      predator is 5 times the concentration of that chemical in the tissues of its primary prey
      species.

      Bioavailability—The degree to which  a  chemical can be taken into  the tissues  of an
      exposed organism.
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                                                                Chapter 6. Glossary
Biomass—The total weight of live organisms in a sampled population or community.

Cancer slope factor (CSF)—Plausible  upper-bound estimate of the probability of a
response per unit of intake of a chemical over a lifetime. The cancer 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 particular carcinogen.

Carcinogenic—Capable of causing cancer in an organism.

Chronic—Characterized by a time period that represents a substantial portion of the life
span of an organism (e.g., chronic toxicity is the characteristic of a chemical to produce
a toxic response when an organism is exposed over a long  period of time).

Chronic intake level—Exposure expressed as the mass of a substance contacted per unit
body weight  over a long-term exposure period,  often expressed as  mg/kg-day over a
lifetime.

Community—Interacting populations of species  (plants or animals) living  in the same
habitat.

Comparative risk assessment—An evaluation of the changes in human health and/or
ecological risks resulting from a range of candidate  remedial alternatives.  Ideally,  the
comparative risk assessment should include evaluation of the risks associated with all
components  (e.g.,  removal,  pretreatment,  treatment,  disposal)  of  each   remedial
alternative under consideration.

Compensatory mechanism—A biological process that offsets or counteracts an adverse
effect (e.g., increased survival of young fish related to reduced competition  because egg
hatching success was reduced).

Concentration—The amount of a chemical substance expressed relative to the amount
of environmental  medium (e.g., jug/L [micrograms  of chemical per liter of water] or
/ug/g [micrograms of chemical per gram of soil]).

Conceptual  model—A simplified  description  of important functional or  structural
relationships  in an ecosystem, including  working hypotheses of how chemicals might
affect populations or communities.

Contaminant exposure model—A mass balance model for contaminants, in which  the
rate of change in contaminant mass (accumulation)  is a function of the transport of a
contaminant into, out of, and within the system (via water transport or sediment transport
for those materials that sorb to sediments);  the mass added to the system (via point and
nonpoint loadings) minus the outputs; and the quantities transformed and degraded within
the system (via processes such as  volatilization, biodegradation,  and photodegradation).
                                       61

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                                                               Chapter 6.  Glossary
Contaminant of concern—A chemical or specific form of a chemical suspected of being
present in concentrations in the environment that may cause adverse effects to humans
or ecological receptors.

Dose—The amount of chemical taken into an organism per unit of time.

Dose-response  relationship—The relationship  between  the  dose  of a  contaminant
administered or received and the incidence of adverse 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.

Ecological effects assessment—An assessment conducted  to determine the relationship
between the levels of contaminant exposure (or other stressors) and the levels and types
of ecological effects.

Ecological epidemiological approach—An empirical assessment approach based on an
evaluation of existing ecological effects, especially the establishment  of the causes of
reduced population abundances and alterations of community structure.

Ecological risk assessment—Evaluation of the likelihood  of adverse effects on organ-
isms, populations, and communities from chemicals present in the environment.

Ecosystem—An  ecological community of plants and animals together  with its physical
environment, regarded as a unit.

Endpoint—The biological or ecological unit or variable being measured or assessed (see
measurement endpoint and assessment endpoint).

Equilibrium partitioning model—A  mathematical  expression  that  describes  the
distribution  of a  chemical between sedimentary  organic carbon  and  interstitial water
based on the assumption of thermodynamic equilibrium.

Exposure—Contact  between a  human  or ecological  receptor and a  chemical in  the
environment.

Exposure assessment—The portion of the risk assessment that describes the frequency,
magnitude, and duration of exposure  of human or ecological receptors to contaminants
of concern.

Exposure duration—In human health risk assessment, the estimated number of years
over which exposure to contaminated media may  occur.

Exposure frequency—In human health risk assessment, the number of days per year that
a person may contact contaminated media.
                                       62

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                                                               Chapter 6.  Glossary
Exposure parameters—Values used to estimate exposure in a risk assessment, such as
the number of days per  week that exposure  is expected to occur, or the amount of
contaminated media that a person might incidentally ingest per day.

Exposure pathway—The path a chemical takes or could take from a source to exposed
organisms.  Exposure pathways include the source,  the  mechanism of release  and
transport, a point of contact, and the means of contact  (e.g., ingestion or inhalation).

Exposure point concentration—The concentration of a  chemical at the point of exposure
to an organism.  For example, the concentration in the  soil in which a plant is growing.

Exposure-response assessment—A description of the relationship between the concentra-
tion (or  dose) of the chemical  that causes adverse  effects and the magnitude of the
response of the receptor.

Exposure route—The means of contact between an organism and a toxic chemical (e.g.,
eating [ingestion], breathing [inhalation], or touching [dermal contact]).

Exposure scenario—A conceptual model of how exposure takes place, including specific
combinations of exposure media, pathways, and receptors and organism  activities  that
may lead to exposure.

Food chain—A sequence of species at different trophic (feeding) levels that represent a
single path of energy within a food web.  For example, grasses and seeds are eaten by
a mouse which is then eaten by an owl.  The owl is higher up the food chain (at a higher
trophic level) than the mouse.

Food web—Interconnected food chains that describe the pathways of energy and matter
flow in  nature.

Forward-mode assessment—The use of ecological risk  assessment techniques to estimate
risk (see reverse-mode assessment).

Fractional intake—The fraction of total contaminant intake that occurs at an AOC.  For
example, an exposure assessment might estimate that an individual ingests 56 g of fish
per day from all sources, but that the fractional intake of fish consumed from the specific
AOC is only 0.1, indicating that only  one-tenth of the  total fish consumption (or 5.6 g
per day) is from the AOC in question.

Habitat—The place where animals and plants normally live, often characterized by a
dominant plant form or physical characteristic.

Hazard—The ability of a physical, chemical, or biological agent to harm plants, animals,
or humans under a particular set of circumstances.
                                       63

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                                                                Chapter 6.  Glossary
Hazard identification—The stage of the toxicity assessment that defines the qualitative
relationship between chemicals and adverse effects to receptors.

Hazard index (plural: indices)—The sum of more than one hazard quotient for multiple
substances and/or multiple pathways.   The hazard index 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.

Human health risk assessment—Prediction of the likelihood of adverse effects in human
populations through calculations combining quantitative estimates  of the toxicity  of
chemical contaminants in the environment with quantitative estimates of the potential for
human populations to be exposed to those contaminants.

Hydrodynamic model—A description of the transport of water,  or its motion, based on
a balance  of the water's momentum.

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)

Joint probability analysis—A statistical technique used  to estimate the likelihood  of
chemical concentrations exceeding toxicity criteria.

LD50—Dose of a substance that results in 50-percent mortality in a population of test
organisms.

Life stage—A developmental  stage of an organism (e.g., juvenile, adult, egg,  pupa,
larva).

LOAEL (lowest-observed-adverse-effect level)—The lowest concentration or  dose at
which significant  adverse effects were observed in experimental trials.

Macroinvertebrate—An invertebrate organism visible to the naked eye. Often refers to
animals such as insects, worms,  and snails.

Mass balance model—A quantitative  description of the sources, transport, and fate of
the mass of a substance (e.g., water, sediment, or chemical contaminants), such  that the
mass  entering the system equals the  mass  leaving the system, less the mass stored,
transformed, or degraded.

Measurement endpoint—An  ecological variable that  is  measured  to quantify  the
response of an organism, population,  community, or ecosystem to chemicals.   Each
measurement endpoint is related  to an assessment endpoint.
                                       64

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                                                                Chapter 6.  Glossary
Medium (plural: media)—The substance in which a chemical may exist, such as air,
soil, sediments, and water.

No-action alternative—The alternative in which no remedial action is taken.

Noncarcinogenic—Capable of causing chronic or subchronic  effects other than cancer
in an organism.

NOAEL (no-observed-adverse-effect level)—The highest concentration or dose at which
no significant adverse effects were observed in experimental trials.

Organism—An individual plant or animal.

Photodegradation—The decomposition of a chemical  substance by radiant  energy,
generally natural sunlight.

Population—A group  of individuals  of the same species interacting  within  a given
habitat.

Predictive approach—Any assessment approach that estimates risks based on assumed
scenarios (e.g., future conditions),  extrapolation models,  or theory rather than direct
measurement.

Probability—The likelihood  of an  event occurring,  expressed as a numerical ratio,
frequency, or percent.

Quotient method—The process of comparing  a concentration or dose (estimated or
measured) with a concentration or dose known to have adverse effects on organisms.

Receptor—The organism, population,  or community that might be affected by exposure
to a contaminant of concern.

Reference  area—An area that  has  similar physical characteristics  to  a  site being
evaluated, but is unaffected by contaminants of concern.  The reference area is compared
to the site to assess  the effects of contaminants of concern.

Reference  concentration  (RfC)—For assessment of inhalation  exposures, the con-
taminant concentrations in the air at which no adverse effects are expected to occur.

Reference dose (RfD)—For an individual chemical, an estimate of an exposure level for
the human population, including sensitive subpopulations, that is likely to be without an
appreciable  risk  of noncarcinogenic  effects.    There  are chronic,  subchronic, and
developmental reference doses, but when used without a  modifier, reference  dose  is
generally understood to mean the  chronic reference  dose,  or the acceptable daily
exposure level that is likely to be without an appreciable risk of noncarcinogenic effects
during a lifetime.
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                                                                Chapter 6.  Glossary
Remedial action objectives—The general descriptions of what remedial actions should
accomplish (e.g., to reduce risks to particular species of plants and animals at a site).

Remedial action goals—A subset of remedial action objectives consisting of medium-
specific chemical concentrations that are protective of human health and the environment.

Remedial Action Plan—A detailed description of the activities selected for the remedia-
tion of contamination (especially sediments) within a given  AOC.

Remedial action alternative  (or remedial alternative)—A combination of technologies
used in series and/or parallel to isolate contaminated sediments or to alter the con-
centrations of sediment contaminants in order to achieve specific project objectives.  In
the simplest case, a remedial alternative may employ a single technology, such as in situ
capping.  In more complex  cases, a remedial  alternative may involve several tech-
nologies, such as dredging, pretreatment, treatment, and confined disposal.

Remediation—Action taken to control the sources of contamination and/or to clean  up
contaminated media (e.g., sediments).

Retrospective approach—Any empirical assessment approach based on evaluation of
existing ecological effects and stressors.

Reverse-mode assessment—The use of ecological risk assessment techniques to derive
criteria or cleanup levels corresponding to a specified risk level (e.g., acceptable risk
level set by policy) (see forward-mode assessment).

Riparian—The land and  habitat along the bank of a stream,  river, or lake. The riparian
area of a river or stream includes the active flood plain (contrasted with upland).

Risk  assessment planning—A step in an ecological risk assessment that evaluates
physical, chemical, and biological characteristics of a site to provide a preliminary risk
characterization, to determine whether an ecological risk assessment is warranted, and,
if so,  to develop risk assessment objectives.

Risk characterization—The step in an ecological risk assessment in which information
on exposure and toxicity are combined to estimate the probability of adverse effects  on
organisms, populations, or communities.

Risk index—An expression of the potential for adverse effects to the biological com-
munity derived from endpoints.  For example, the quotient of exposure concentrations
to species toxicity values.

Risk management—The process of integrating findings from a risk assessment with
engineering, policy, and nontechnical concerns  to make decisions about the need for
remediation at a specific  site or to set remediation priorities among sites.
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                                                                Chapter 6.  Glossary
Screening level—A process or criterion that separates  sites that pose no apparent risk
from those for which further analysis is necessary.

Sediment transport model—A description of the physical transport of sediments in
natural systems, in either bed-load or suspended forms.

Speciation—Refers to the various forms in which metals occur.

Stressor—A physical, chemical, or biological agent that can induce an adverse response
in organisms or other components of ecosystems.

Subchronic intake level—Exposure expressed as the mass of a substance contacted per
unit body weight over an exposure period of less than a lifetime, often expressed as
mg/kg-day over 1-10 years.

Terrestrial—Living or growing on land.

Threatened or endangered species—Species that are at risk of becoming extinct.

Threshold—The chemical concentration (or dose) at which physical or biological effects
begin to be produced.

Toxicity—The property of a chemical substance manifested as its ability to cause a
harmful effect (e.g., death, disease, reduced growth, modified behavior) on an organism.

Toxicity assessment—The stage of a risk assessment that describes the potential effects
of a chemical  on organisms and the quantitative exposure-response relationship.

Toxicity test—A test in which organisms are exposed to chemicals  in a test medium
(e.g., waste, sediment, soil) to  determine the effects of exposure.

Transport and fate—A description of how a chemical is  carried through the environ-
ment.  This may include transport through  biological as well as physical parts of the
environment.

Uncertainty  analysis—An evaluation,  qualitative or  quantitative,  of parameters  or
assumptions used in a  risk assessment that are not completely  known  or  cannot  be
precisely estimated, which is used to help place quantitative risk estimates in perspective.

Upland—Land usually  above  the floodplain of  a river  or stream (contrasted with
riparian).

Volatilization—The conversion of a chemical substance from a liquid or solid state to
a gaseous  or  vapor  state  by the application of heat,  by reducing  pressure, or by a
combination of these processes.
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                                                               Chapter 6.  Glossary
Water transport model—A description of the transport of water,  or  its motion,  in
natural systems that may be descriptive (i.e., based on a balance of the water's mass) or
hydrodynamic (i.e., based on a balance of the water's momentum).
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7.   REFERENCES
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      Barnthouse, L.W., G.W. Suter, S.M. Bartell, J.J. Beauchamp, R.H. Gardner, E. Under,
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      Bascietto, J.D. Hinckley, J. Plafkin, and M. Slimak. 1990. Ecotoxicity and ecological
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      Chapman, P.M., E.A. Power, and G.A. Burton, Jr. 1992. Integrative assessments in
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      Crane,  J.L.  1992a.  Baseline human health risk assessment:   Ashtabula River, Ohio,
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      Crane,  J.L.  1992b. Baseline human health risk assessment: Saginaw River, Michigan,
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      Crane,  J.L.  1993a. Baseline assessment of human health risks resulting from PCB con-
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      Crane,  J.L.  1993b. Baseline human health  risk assessment:  Grand  Calumet River/
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                                                             Chapter 7. References
Crane, J.L.  1993c.  Baseline human health risk assessment:  Buffalo River, New York,
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Kubiak, T.J.   In Preparation.  Baseline wildlife risk assessment for  Saginaw Bay and
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Parkhurst, B., H. Bergman, M. Marcus, C. Creager, W. Warren-Hicks, A. Boelter, and
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                                                            Chapter 7. References
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                                                            Chapter 7. References
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