UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

                                      WASHINGTON, D.C.  20460
                                           JUN  1 3 2014
                                                                                      OFFICE OF
                                                                                   SOLID WASTE AND
                                                                                 EMERGENCY RESPONSE
                                                                                  OSWER 9285.6-20

MEMORANDUM

SUBJECT:   Distribution of the "Radiation Risk Assessment At CERCLA Sites: Q&A"
FROM:  LiN-Robin H. Richardson, Acting Director
          \\   Office of Superfund Remediation and Technology Innovation

TO:          Superfund National Policy Managers, Regions 1-10
Purpose

The purpose of this memorandum is to transmit the final guidance "Radiation Risk Assessment At
CERCLA Sites: Q&A.'1 This new final guidance will replace a previous version of the "Radiation Risk
Assessment At CERCLA Sites: Q&A" issued in 1999.

Role of the Guidance

The Office of Superfund Remediation Technology Innovation (OSRTI) developed this document to
present an overview of current EPA guidance for risk assessment and related topics for radioactively
contaminated Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA)
remedial sites. It provides answers to several commonly asked questions regarding risk assessments at
radioactively contaminated CERCLA remedial sites.1 The purpose of this document is to provide
answers to commonly asked questions regarding risk assessment for radioactive contamination, describe
how to analyze levels of radioactive contamination and explain how to assess the risks from radioactive
 The document transmitted by this memorandum provides guidance on risk assessment under CERCLA and is consistent with the
National Oil and Hazardous Substances Pollution Contingency Plan (NCR). It does not alter the NCR's general expectations for
remedial actions, such as those regarding treatment of principal threat waste and the use of containment and institutional controls for
low-level threat waste. Consistent with CERCLA and the NCR, remedial actions need to attain or waive Applicable or Relevant and
Appropriate Requirements (ARARs); potential ARARs for contaminated ground water al radiation sites typically include Maximum
Contaminant Levels (MCLs) or non-zero Maximum Contaminant Level Goals (MCLGs) established under the Safe Drinking Water
Act,

       This document provides guidance to U.S. Environmental Protection Agency (EPA) staff on how to conduct risk
assessments for radioactively contaminated CERCLA sites. The guidance is designed to be consistent with EPA's national guidance
on these issues. This guidance does not, however, substitute for EPA's statutes or regulations, nor is it a regulation itself. Thus, it
cannot impose legally binding requirements on EPA, states, or the regulated community, and may not apply to a particular situation
based upon the circumstances. EPA may change this guidance in the  future, as appropriate.

                                      Internet Address (URL) • http://www.epa.gov
             Recycled/Recyclable • Printed with Vegetable Oil Based Inks on 100% Postconsumer, Process Chlorine Free Recycled Paper

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contamination as part of a remedy for a radioactively contaminated CERCLA remedial site. This
guidance is intended to help health physicists, risk assessors, remedial project managers, and others
involved with risk assessment and decision making at CERCLA remedial sites with radioactive
contamination.

Background

The EPA issued guidance entitled "Establishment of Cleanup Levels for CERCLA Sites with
Radioactive Contamination" (OSWERNo. 9200.4-18, August 22, 1997). This 1997 guidance provided
clarification on establishing protective cleanup levels for radioactive contamination at CERCLA sites.
The guidance reiterated that cleanups of radionuclides are governed by the risk range for all carcinogens
established in the National Oil and Hazardous Substances Pollution Contingency Plan (NCP) when
Applicable or Relevant and Appropriate Requirements (ARARs) are not available or are not sufficiently
protective. Cleanups generally should achieve a level of risk within the 10"4 to 10"6 carcinogenic risk
range based on the reasonable maximum exposure for an individual. In calculating cleanup levels, one
should include exposures from all potential pathways, and through all media (e.g., soil, ground water,
surface water, sediment, air, structures, etc.)  The guidance also provides a listing of radiation standards
that are likely to be used as ARARs to establish cleanup levels or to conduct remedial actions.

The EPA previously issued "Radiation Risk Assessment At CERCLA Sites: Q&A" (OSWER No.
9200.4-3 IP, December  1999). The 1999 Risk Q&A provided an overview of the then current EPA
guidance for risk assessment and related topics for radioactively contaminated CERCLA sites. This
guidance provided answers to several commonly asked questions regarding risk  assessments at
radioactively contaminated CERCLA sites. In addition, it recommended that dose assessments only be
conducted under CERCLA where necessary to demonstrate compliance with ARARs. Today's Risk
Q&A guidance updates the 1999 version of the Risk Q&A by summarizing and  citing guidance that was
developed after the 1999 version. This new guidance explains how to convert radon measurements to
demonstrate compliance with indoor radon standards that are potential ARARs using a methodology
based on international guidance, and it changes the Superfund recommendation on what is considered a
protective dose-based ARAR from 15 to  12 millirem per year (mrem/yr). The new recommendation of
12 mrem/yr regarding what dose-based ARARs are protective is based on using  an updated risk
assessment to achieve the  same 3 x 10"4 cancer risk as the previous recommendation using 15 mrem/yr.

The Radiation Risk Q&A  guidance is part of a continuing effort by OSRTI to provide updated guidance
for addressing radioactively contaminated remedial Superfund sites consistent with our guidance for
addressing chemically contaminated sites (while accounting for the technical differences between
radionuclides and chemicals). OSRTI intends for this effort to facilitate remedial cleanups that are
consistent with the NCP at radioactively contaminated sites and to incorporate new information based on
improvements to the Superfund program.

Implementation

For questions regarding radiation site policy and guidance for CERCLA cleanup actions, readers are
referred to the Superfund Radiation Webpage at
http://www.epa.gov/superfund/health/contaminants/radiation/index.htm. The subject matter specialist
for this guidance is Stuart Walker of OSRTI. He can be reached by e-mail  at walker.stuart@epa.gov or
by telephone at (703) 603-8748.

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Attachment

cc:    Mathy Stanislaus, OSWER
      NitinNatarajan, OSWER
      Barry Breen, OSWER
      Lawrence Stanton, OSWER/OEM
      Barnes Johnson, OSWER/ORCR
      David Lloyd, OSWER/OBLR
      Reggie Cheatham, OSWER/FFRRO
      Carolyn Hoskinson, OSWER/OUST
      Rafael DeLeon, OECA/OSRE
      David Kling, OECA/FFEO
      John Michaud, OGC/SWERLO
      Mike Flynn, OAR/ORIA
      OSRTI Managers
      Regional Superfund Branch Chiefs, Regions 1-10
      Lisa Price, Superfund Lead Region Coordinator, Region 6
      NARPM Co-Chairs
      OSRTI Document Coordinator

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                                          United States                       Office of Superfund         Directive 9200.4-40
                                          Environmental Protection Agency        Remediation and           EPA540-R-012-13
                                                                             Technology Innovation      May 2014

                                    Radiation  Risk  Assessment
                                   At CERCLA Sites:  Q &  A
          NOTICE: The policies set out in this document are intended solely as guidance to U.S. Environmental Protection Agency (EPA)
          personnel; they are not final EPA actions and do not constitute rulemaking.  These policies are not intended, nor can they be
          relied upon, to create any rights enforceable by any party in litigation with the United  States. EPA officials may decide to follow
          the guidance provided in this document, or to act at variance with the guidance, based on analysis of specific-site
          circumstances. EPA also reserves the right to change the guidance at any time without public notice.


Table of Contents                                                                                                     Page
Introduction                                                                                                                2
Purpose                                                                                                                   4
I. Data Collection and Evaluation                                                                                              4
  Q1. What strategy and key information should be considered during the initial planning stage for radiological data collection ?            4
  Q2. How should a list of radionuclides of concern be developed?                                                                6
  Q3. What criteria should be used to determine areas of radioactive contamination or radioactivity releases?                           8
  Q4. How should the areal extent and depth of contamination be determined?                                                      9
  Q5. What field radiation survey instruments should be used and what are their lower limits of detection ?                              9
  Q6. What sample measurement units for radiation risk assessment are typically used?                                            10
  Q7. What sample measurement units for remedial action evaluation may be used?                                               10
  Q8. Are radionuclides included in EPA's Contract Laboratory Program (CLP)? If not, where should comparable radioanalytical
      services be obtained?                                                                                                11
  Q9. How can I decide if the data collected are complete and of good quality?                                                     12
 II.  Exposure Assessment                                                                                                  12
  Q10. For CERCLA risk assessments, is it appropriate to use guidance developed by other Federal, State or Tribal Agencies or
       by International or National organizations?                                                                             12
  Q11. How does the exposure assessment for radionuclides differ from that for chemicals?                                         12
  Q12. Can exposure pathways be added or deleted based on site-specific conditions?                                             13
  Q13. How should radioactive decay products be addressed?                                                                  16
  Q14. To what extent should generic and site-specific factors and parameter values be used in exposure assessments?                16
  Q15. How should exposure point concentrations be  determined?                                                               16
  Q16. What calculation methods or multimedia radionuclide transport and exposure models are recommended by EPA for
       Superfund risk assessments?                                                                                         17
  Q17. How should Radon-222 (radon) and Radon-220 (thoron) exposures and risks be evaluated?                                  18
  Q18. How long a time period should be considered for possible future exposures?                                                19
  Q19. How should the results of the exposure assessment for radionuclides be presented?                                         19
III. Toxicity Assessment                                                                                                    20
  Q20. What is the mechanism of radiation damage?                                                                           20
  Q21. What are radionuclide slope factors?                                                                                  20
  Q22. What are radionuclide dose conversion factors?                                                                        21
  Q23. What is dose equivalent, effective dose equivalent, and related quantities?                                                 21
  Q24. What is the critical organ approach to dose limitation?                                                                   22
  Q25. How should radionuclide slope factors and dose conversion factors be used?                                               22
  Q26. In addition to cancer, should the potential teratogenic and genetic effects of radiation exposures be considered?                 23
  Q27. Should chemical toxicity of radionuclides be considered?                                                                25
IV. Risk Characterization                                                                                                    25
  Q28. How should radionuclide risks be estimated?                                                                           25
  Q29. Should radionuclide and chemical risks be  combined?                                                                   25
  Q30. How should risk characterization results for radionuclides be presented?                                                   26
  Q31. Should the collective risk to populations be estimated along with that to individual receptors?                                  26
  Q32. How should uncertainty in estimates of radiation risk be addressed in the risk characterization report?                          26
  Q33. When should a dose assessment be performed                                                                        27
  Q34  What is the upper end of the risk range with respect to radionuclides                                                      27
  Q35 Should the ARAR protectiveness criteria evaluation recommendation be changed from 15 mrem/yr to reflect the updates to
       Radiation risk estimates contained in Federal Guidance Report 13?                                                       28
  Q36 Should dose recommendations from other federal be used to assess risk or establish cleanup levels?                          28
  Q37. How and when should exposure rate be used to estimate radionuclide risks?                                                29
  Q38. What radiation standards may be applicable or relevant and appropriate requirements (ARARs) ?                              30
V. Ecological Assessments                                                                                                 30
  Q39. What guidance is available for conducting ecological risk assessments?                                                    30
VI. Background Radiation                                                                                                   31
  Q40. How should background levels of radiation be  addressed?                                                               31
Where to go for Further Information                                                                                           33
References                                                                                                               34
Appendix A: EPA's Recommended Guidance for Radiation Risk Assessment at CERCLA Remedial Sites                              43

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INTRODUCTION

Some sites on the U.S. Environmental Protection Agency's (EPA) National Priorities List (NPL)
are radioactively contaminated. To assist in the evaluation and cleanup of these sites under the
Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA or
Superfund), EPA's Office of Superfund Remediation and Technology Innovation (OSRTI) has
developed guidance for conducting radiation risk assessments during the remedial
investigation/feasibility study (RI/FS) process of the CERCLA remedial program. This guidance
may also be useful for non-time critical removal actions.

This guidance does not address emergency or time-critical removals conducted under CERCLA.
Also, this guidance does not address how other cleanup programs (those not conducted under
CERCLA authority) should be implemented. Persons conducting radiation risk assessments at
sites using these other authorities should consult the regulations and guidance that are appropriate
for that authority.

EPA has developed a number of guidance for the CERCLA remedial program. Users of this
guidance should prior to conducting any CERCLA radiation risk assessments at remedial sites be
familiar with the following guidance specific to radiation risk assessment for the CERCLA
remedial program and how they relate to one another:

 •  The Preliminary Remediation Goals (PRGs)for Radionuclides electronic calculator, known
    as the Rad PRO calculator (U.S. EPA 2002a).

 •  The Building Preliminary Remediation Goals for Radionuclides (BPRG) electronic calculator
    (U.S. EPA 2007).

 •  The Radionuclide Outdoor Surfaces Preliminary Remediation Goals (SPRG) electronic
    calculator (U.S. EPA 2009a).

 •  Soil Screening Guidance for Radionuclides contains both a User's Guide and Technical
    Background Document., (known as the Rad SSG documents) that provide information on soil
    screening for radionuclides at CERCLA sites (U.S. EPA 2000a, 2000b). The risk assessment
    equations and the soil screening levels (SSLs) in this guidance have been superseded by the
    Rad PRO calculator.

 •  ARAR Dose Compliance Concentrations for Radionuclides (DCC) electronic calculator (U.S.
    EPA 2004a).

 •  ARAR Dose Compliance Concentrations for Radionuclides in Buildings (BDCC) electronic
    calculator (U.S. EPA 2010a), known as the BDCC calculator.

 •  ARAR Radionuclide Outdoor Surfaces Dose Compliance Concentrations for Radionuclides
    (SDCC) electronic calculator (U.S. EPA 201 Ob), known as the SDCC calculator.

 •  Chapter 10, "Radiation Risk Assessment Guidance" of RAGS Part A (U.S. EPA 1989a).
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 •  Chapter 4, "Risk-based PRGs for Radioactive Contaminants," of RAGS Part B (U. S. EPA
    199 la).

 •  Appendix D, "Radiation Remediation Technologies," of RAGS Part C (U.S. EPA 1991b).

 •  RAGS Part D, Standardized Planning, Reporting, and Review of Super/and Risk Assessments
    (U.S. EPA 1998a).

 •  Superfund Radiation Risk Assessment and How You Can Help: An Overview (U.S. EPA
    2005a).

Appendix A "EPA's Recommended Guidance for Radiation Risk Assessment at CERCLA
Remedial Sites," which are the last two pages of this guidance, has a short overview of these
guidance for radiation risk assessment at CERCLA remedial sites. In addition to PRG and DCC
calculators, Soil Screening Guidance for Radionuclides (Rad SSG) documents, and RAGS,
EPA has  published several other guidance documents and OSWER directives concerning risk
assessment methods for radioactive and nonradioactive contaminants for  remedial sites. The PRG
and DCC calculators are frequently updated. OSWER directives specific to radioactive
contaminants may be found at the Superfund Radiation website at
http://www.epa.gov/superfund/health/contaminants/radiation/index.htm.

Overall, the process for assessing radionuclide exposures and radiation risks at remedial sites for
humans that is presented in the PRG and DCC calculators, Rad SSG documents, RAGS, and in
supplemental guidance documents parallels the process for assessing risks from chemical
exposures (exposure assessment, toxicity assessment, and risk characterization). Both types of
assessments follow the same evaluation process, consider similar exposure scenarios and
pathways (except the external "direct exposure" pathway, which  is unique to radiation and is
included  in the PRG and DCC calculators [EPA 2002a, 2004a, 2007, 2009a, 2010a, and 201 Ob];
and the dermal exposure pathway, which is not a significant contributor to radiological risk and so
is not included in the current PRG and DCC calculators); determine exposure point
concentrations; and provide estimates of cancer risks to humans.

However, several aspects of risk assessment for radioactive contaminants  differ substantially
from those considered for chemical contaminants. Occasionally these differences—in
measurement units, exposure terms and concepts, field and laboratory procedures and detection
limits, and toxicity criteria,  among others—have  led to questions concerning the Agency's
recommended approach for addressing radionuclide contamination and risk and the remediation
of CERCLA radiation sites.
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PURPOSE
OSRTI has prepared this document to provide answers to questions regarding risk assessments at
radioactively contaminated CERCLA remedial action sites raised by Remedial Project Managers
(RPMs), risk assessors, federal, state and local agencies, potentially responsible parties (PRPs),
and contractors. These questions and answers supplement the Frequently Asked Questions (FAQs)
that accompany the remedial program's on-line calculators (see http://epa-
prgs.ornl.gov/radionuclides/faq.html). This document supersedes an earlier version issued in 1999
(EPA 1999a). Its purpose is to provide an overview of current EPA guidance for risk assessment
and related topics for radioactively contaminated CERCLA remedial sites.

The questions and answers (Q&A) that follow are presented in sections corresponding to the four
basic steps in the CERCLA risk assessment process:

1.  Data Collection and Evaluation
2.  Exposure Assessment
3.  Toxicity Assessment
4.  Risk Characterization
I.      DATA COLLECTION AND EVALUATION

Ql.    What strategy and key information should be considered during the initial
       planning  stage for radiological data collection?

A.     The data quality objectives (DQO) process is an important tool for project managers and
       planners to determine the types, quantity, and quality of data needed to support decisions.
       Detailed guidance on the DQO process can be found in Guidancefor the Data Quality
       Objectives Process (U.S. EPA 1994a), Data Quality Objectives for Superfund (U.S. EPA
       1993 a), and Uniform Federal Policy for Implementing Environmental Quality Systems:
       Evaluating, Assessing, and Documenting Environmental Data Collection/Use and
       Technology Programs (U.S. EPA 2005b). Additional guidance on the application of this
       process at radiation sites can be found in the Soil Screening Guidance for Radionuclides
       (Rad SSG) documents which provide EPA's recommended guidance on site-
       characterization of radioactively contaminated sites and in Multi-Agency Radiation Survey
       and Site Investigation Manual (MARS SIM) (U.S. EPA et al. Rev  1. 2000d), which
       provides technical information on final status surveys of radioactively contaminated sites.
       The DQO process outlined in these documents should be completed during the initial
       planning stage for data collection.
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At a minimum, site characterization should evaluate the following key information and
considerations:

S     Review of the site history and records collected during the preliminary assessment
       and site inspection (PA/SI), considering:

•      Past site operations
•      Types and quantities of radioactive material used or produced
•      Radioactive waste stream characteristics
•      Disposal practices and records
•      Previous radiological characterization data and/or environmental monitoring data
•      Physical site characteristics (hydrology, geology, meteorology, etc.)
•      Demography
•      Current and potential future land use

S     Formulation of a conceptual site model to:

•      Identify radionuclides of concern
•      Identify the time period for assessment
•      Identify potentially contaminated environmental media
•      Identify likely release mechanisms, potential for migration and exposure pathways
•      Identify potential human and ecological receptors
•      Focus initial surveys and sampling and analysis plans

S     Development of comprehensive sampling plans based on the conceptual site model
       and available historical information to:

•      Confirm the identities of radionuclide contaminants
•      Confirm release mechanisms and exposure pathways
•      Measure or model exposure point concentrations and point exposure rate (as
       appropriate for the type of radioactive decay)
•      Confirm human and ecological receptors including sensitive sub-populations
•      Specify cleanup levels or develop preliminary remediation goals
•      Establish DQOs

Figure 1 depicts typical conceptual site models for human health risk assessments at
CERCLA sites with radioactive contamination. The user guides of each of the PRO and
DCC calculators (EPA 2002a, 2004a, 2007, 2009a, 2010a, and 201 Ob) include guidance on
developing conceptual site models for the exposure routes addressed by each model. Also,
each of the illustrations in Figure 1 appears in the PRO and DCC user guides with
additional explanatory text and in a larger size that is more legible.

The Rad SSG documents provide EPA's recommended guidance on planning,
implementing, and evaluating radiological site characterization for surface and subsurface
soil. The Rad SSG documents are consistent with EPA's site characterization guidance for
chemicals.

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       The Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM) (U. S.
       EPA et al. Rev 1. 2000d) provides guidance on planning, implementing, and evaluating
       radiological final status site surveys for surface soil and buildings. Final status surveys
       follow scoping, characterization, and any necessary remedial actions. Although this multi-
       agency technical document is not a recommended guidance for CERCLA remedial sites, it
       may provide useful information on final status surveys to demonstrate compliance with
       dose-based or risk-based criteria.
Q2.    How should a list of radionuclides of concern be developed?

A.     When developing a list of potential contaminants of concern, the list should initially be
       developed to be as inclusive of potential contaminants as possible. As more information
       and data are collected and evaluated, it may be appropriate to reduce the number of
       contaminants on the list to include only those that are of concern based on potential
       exposure pathways and the toxicity of site contaminants. An initial  list of radionuclides of
       potential  concern should be based on a review of previous site operations, including
       disposal,  that contributed to the current levels of contamination as  well as the conceptual
       site model. As a first consideration, all radionuclides potentially  used, produced or
       disposed  at the site should be included on the list.  As appropriate,  the list should also
       include all radioactive decay products that may have formed since disposal or termination
       of operations. Radionuclides with short half-lives  and no parent radionuclide to support
       ingrowth may be considered for exclusion from the list if no slope factor was developed
       for the radionuclide. However, careful consideration should be given to its initial and
       current activity inventories, its radioactive half-life, and the time elapsed since the
       contamination occurred to the present before a short-lived radionuclide is excluded from
       the list.

       Site characterization efforts should be directed to confirming or refuting the presence of
       the radionuclides of concern in on-site sources and in environmental media
       contaminated by releases migrating or being transported and dumped off-site. The
       activity concentrations of radionuclides (and decay products, if appropriate) in each
       medium  should then be compared with site-specific background concentrations of those
       radionuclides (i.e., radionuclide  concentrations in environmental  media not related to
       site operations or releases), Preliminary Remediation Goals (PRGs), screening levels, or
       potential  remediation criteria (see Q3). Caution should be exercised in making these
       comparisons, since radionuclide  concentrations in environmental media may change
       over time due to radioactive decay and ingrowth;  therefore, consideration should be
       given to the radioactive half-life of the radionuclides of concern and any decay products,
       and the time period over which risks will be evaluated.
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                    Figure 1.  Typical Conceptual Site Models for Humans
 -         MuMi.l MI i JLi.it,Ml i>jiJ ExpOHUTH Pathwaysf
 Black lines are direct exposure rautes.
 Hl.-=irl-, d.^-herl lines are rtrrert and indirect expns
 Red lines are imiin-r-t et> Liuiure routes
Conceptual Site Model of Quantified Exposure Pathways for radtonuciide BPRGs
Black lines are direct exposure routes.
                                                                                    External
                                                                                    Exposure
Resiispension
-Wind
- Mechanical


Settled
Dust
                          3-D and2-D Sources
 Conceptual Site Model of Quantified Exposure Pathwaysfor radionuclide SPRGs
 Black lines are direct exposure routes.
                                                             -7-

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Q3.    What criteria should be used to determine areas of radioactive contamination or
       radioactivity releases?

       During the site assessment phase, Section 7 of EPA's revised Hazard Ranking System
       (HRS) (see Appendix A to 40 Code of Federal Regulations [CFR] Part 300) outlines the
       methodology for evaluating radioactive releases and determining whether a radioactive
       release is a high priority for the CERCLA remedial program.

       During risk assessments, guidance for the measurement and evaluation of radiological
       contaminants is provided in the Soil Screening Guidance for Radionuclides (Rad SSG)
       documents (U.S. EPA 2000a, 2000b). The Rad SSG also provides guidance on the
       determination of site-specific background levels for comparison to site measurements. The
       Soil Screening Levels (SSLs) are not cleanup standards, but may be used to inform further
       investigation at sites. The SSL risk assessment equations have been superseded by those in
       the PRGs calculator where applicable or relevant and appropriate requirements (ARARs)
       are not available or sufficiently protective; therefore, the PRG calculator should be used for
       determining SSL risk based concentrations rather than the Rad SSG documents.

       General guidance to inform the evaluation of radiological contamination is provided in the
       following Agency documents:

       •      Methods for Evaluating the Attainment of Cleanup Standards—Volume 1: Soil and
             Soil Media  (U.S. EPA 1989b)
       •      Statistical Methods for Evaluating the A ttainment of Cleanup Standards— Volume
             2: Ground Water (U.S. EPA 1992a)
       •      Statistical Methods for Evaluating the A ttainment of Cleanup Standards— Volume
             3: Reference-Based Standards for Soils and Solid Media (U.S. EPA 1992b)

       Although these documents  do not specifically address radionuclides, most of the
       evaluation methods and tests provided in these documents should be applicable to both
       radioactive and nonradioactive contaminants.

       There are two general sampling approaches for determining what is contaminated for site
       characterization or demonstrating compliance with cleanup levels; a not-to-exceed (NTE)
       or area averaging (AA) approach. In general, the same sampling approach should be used
       for both radionuclide and chemical contaminants in the same medium at the same site (e.g.,
       soil, groundwater, surface water, air, or buildings)  to facilitate a consistent approach for
       addressing radionuclides and chemicals; generally, samples for both should be collocated
       in the media of interest. For groundwater contamination, EPA's Superfund remedial
       program generally  recommends an NTE approach. EPA's Superfund remedial program
       general practice has been to use the NTE approach for soil where residential land use is
       assumed. If using the AA approach, users should ensure that exposure of receptors across
       the exposure unit is random. However, exposure is not expected to be random under
       residential land use because residents often engage in activities (such as gardening or
       child's play) in specific portions of a yard. Under most residential situations and other non-

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       random exposure situations, remediating with the AA approach may not be protective of
       human receptors. When an AA approach is used, software such as Spatial Analysis and
       Decision Assistance (SADA) (Stewart and Purucker 2011) may be useful for providing
       visual representations of surface and subsurface contamination and plotting random
       surface and subsurface sampling locations across a survey area.

Q4.    How should the areal extent and depth of radioactivity contamination be determined?

A.     As noted in Ql, a conceptual site model generally should be developed to identify
       reasonable boundaries for investigating the nature and extent of contamination. General
       guidance for site characterization activities is provided in Guidance for Conducting
       Remedial Investigations and Feasibility Studies under CERCLA (U.S. EPA 1988a).
       Guidance specifically for site characterization of radionuclides in soil is found in the Soil
       Screening Guidance for Radionuclides documents (U.S. EPA 2000a, 2000b).

       The choice of a specific method or methods to characterize remedial sites contaminated
       with radioactive substances depends on several factors,  including the decay characteristics
       of the radionuclides potentially present at the site, suspected contamination patterns,  and
       activity concentrations. Ground-based or aerial radiation surveys are typically conducted
       for gamma-emitting radionuclides in near-surface sources, in addition to surface sampling
       to characterize  the areal extent of contamination. Borehole logging for gamma emitters,
       core sampling programs for radionuclides  that emit alpha, beta or gamma radiation, or a
       combination of all types of methods, may be advisable for subsurface contamination. In
       addition to measurements to determine volumetric contamination in environmental media,
       measurements of surface  contamination on building and equipment surfaces may also be
       needed. Additional discussion of measurement techniques and their limitations for soil and
       buildings is provided in Multi-Agency Radiation Survey and Site Investigation Manual
       (MARSSIM) (U.S. EPA et al. Rev 1. 2000d), and for equipment is provided by Multi-
       Agency Radiation Survey and Assessment  of Materials and Equipment Manual
       (MARSAME) (U.S. EPA et al. 2009b).

Q5.    What field radiation survey instruments should be used and what are their lower
       limits of detection?

A.     Selection of appropriate radiation detection instruments for site characterization depends
       on the decay characteristics of the radionuclides potentially present at the site, suspected
       contamination patterns, and activity concentrations, among other factors. Numerous
       documents have been written on this topic. For a general discussion on radiation survey
       instruments,  readers are directed to Real-Time Measurement of Radionuclides in Soil:
       Technology and Case Studies document (ITRC 2006), Real-Time Measurement of
       Radionuclides in Soil on-line training course (ITRC 2008), Multi-Agency Radiation Survey
       and Site Investigation Manual (MARS SIM) (U.S. EPA et al.  Rev 1. 2000d) and Chapter
       10 of RAGs Part A (U.S. EPA 1989a). For supplemental information regarding the
       usability of analytical data for performing  a baseline risk assessment at radioactively
       contaminated sites, readers should refer to Guidance for Data Usability in Risk
       Assessment, Part B (U.S.  EPA 1992d).
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Q6.    What sample measurement units for radiation risk assessment are typically used?

A.     Concentrations of radionuclides in environmental media are typically expressed in terms of
       "activity" of the radionuclide per unit mass (for soil, sediment, and food-stuffs) or volume
       (for water and air) of the environmental medium. Two different systems of units for
       radioactivity are currently in common usage: the International System (SI) units, and the
       "conventional" or "traditional" units, which were used before the advent of the SI system.
       The principal unit of radioactivity in the SI system is the Becquerel (1 Bq = 1
       disintegration/second), while the basic conventional unit of activity is the Curie (1 Ci = 3.7
       x 1010 Bq). Since most radiation standards in the United States are expressed in
       conventional units, this system is used in this document. Concentrations of radionuclides in
       environmental media at contaminated sites are typically far below Curie quantities, and are
       commonly expressed in units of picoCuries (1 pCi = 10~12 Ci = 3.7 x 10~2 Bq). Typical
       conventional units for reporting environmental measurements are picoCuries per gram
       (pCi/g) for soil (dry-weight),  picoCuries per liter (pCi/L) for groundwater or surface water,
       and picoCuries per cubic meter (pCi/m3) for air. The corresponding SI units, typically used
       in other countries, are Bq/g, Bq/L, Bq per  100 cm2, and Bq/m3.

       Radionuclide concentrations on building or equipment surfaces are specified in units of the
       activity concentrations of the radionuclide of concern in a specified surface area, typically
       disintegration per minute (dpm) per 100 square centimeters (cm2) or pCi per 100 cm2,
       while the SI system,  typically used in other countries, would use Bq per 100 cm2.

       A special unit, the working level (WL), is used as a measure of the concentration of short-
       lived radon decay products in air. WL is any combination of short-lived radon decay
       products in 1 liter of air that will result in the ultimate emission of 1.3 x 105 million
       electron volts (MeV) of alpha energy. The working level month (WLM) is exposure to 1
       WL for 170 hours (1  working month).

       The radiation "exposure" rate is often reported in addition to radionuclide concentrations
       in environmental media. Radiation exposure, in this context, refers to the transfer of energy
       from a gamma radiation field to a unit mass of air. The unit for radiation exposure is the
       roentgen (1 R = 2.58 x 10"4 coulombs of charge per kilogram of air). Exposure rates at
       contaminated sites are typically expressed in units of microroentgens/hour (|iR/hr).

Q7.    During a remedial action evaluation what sample measurement  units may be used?

A.     For remedial action evaluations, it is often useful to express radionuclide concentrations in
       terms of mass concentration. Mass units provide insight and information into treatment
       selection, treatment compatibility, and treatment efficiency, particularly for remedial
       actions involving mixed waste. However since radionuclides are generally measured in
       terms of activity for  health evaluation purposes, except when assessing the non-cancer risk
       posed by uranium, the practice of using activity should continue for response actions at
       CERCLA remedial sites in order to ensure protectiveness of human health. Proposed and
       final site decision documents (e.g., proposed plans, Record of Decisions [RODs]) generally
       should include, in addition to activity measurements, estimates of concentrations in terms
       of mass consistent with those used for non-radiological contaminants. Typical units for
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       expressing mass in environmental media for soil and water are milligrams per kilogram
       (mg/kg) for soil and milligrams per liter (mg/L) for water. These mass units also can be
       expressed as parts per million (ppm) for soil and water, which is equivalent to mg/kg and
       mg/L since the density of water is 1 kilogram per liter (kg/L) under most environmental
       conditions. To estimate the radionuclide concentrations in ppm, the following equations
       can be used:

       mg/kgsoli = (2.8x 10~12) xAx Tm x pCi/g

       mg/lwater = (2.8 x 10~15) xAx 7 7/2 x pCi/L

       ppm soil = (2.8 x 10~12) xAx Ti/2 xpd/g

            ter = (2.8 x 10~15) xAx Ti/2X pCi/L
       where A is the radionuclide atomic weight and Ti/2is the radionuclide half-life in years.
       Most radionuclides have half-lives ranging from a few years to 10,000 years, which means
       that for most radionuclides, an activity of 1 pCi/g would mean the concentration value of
       the radionuclide would be well under 1 x 10"6 ppm. EPA's PRO and DCC calculators
       (EPA 2002a, 2004a, 2007, 2009a, 2010a, and 201 Ob) provide concentrations in media
       corresponding to the target risk and dose in both activity and mass where it is possible to
       convert activity concentrations to mass.

Q8.    Are radionuclides included in EPA's Contract Laboratory Program (CLP)? If not,
       where should comparable radioanalytical  services be obtained?

A.     Radionuclides are not standard analytes in EPA's  CLP program. Contract laboratory
       support for radionuclide analysis may be obtained through the EPA Office of Emergency
       Management (OEM) Environmental Response Laboratory Network (ERLN), which keeps
       an updated list of laboratories or through EPA's radiation laboratories. Generally,
       radioanalytical services may also be obtained through a site-specific or pre-placed EPA
       regional or national contract or Interagency Agreement that provides access to analytical
       services.

       EPA has published information on radionuclide methods in Multi-Agency Radiological
       Laboratory Analytical Protocols Manual (MARLAP) (U.S. EPA et al. 2004b) Inventory of
       Radiological Methodologies for Sites Contaminatedwith Radioactive Materials (U.S. EPA
       2006) and Chapter  10 of RAGSVart A (U.S.  EPA 1989a). MARLAP provides guidance for
       planning, implementing, and assessing projects that are using the laboratory analysis of
       radionuclides. The U.S. EPA 2006 document describes radioanalytical methodologies used
       to characterize environmental samples containing radionuclides, including screening
       methodologies and radionuclide-specific analyses. In addition, EPA'sRadiochemistry
       Procedures Manual (U.S. EPA 1984) provides information for radionuclide-specific
       analytical techniques.
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Q9.    How can I decide if the data collected are complete and of known quality?

A.     All data should be collected under an approved site-specific Quality Assurance Project
       Plan (QAPP), which should include appropriate data validation criteria. Relevant policies
       and guidance pertaining to quality assurance and the development of QAPPs are available
       at http://epa.gov/qualitv/document (e.g., EPA Quality Program Policy CIO 2106.0; EPA
       Requirements for Quality Management Plans (QA/R-2), EPA Requirements for QA
       Project Plans (QA/R-5), and Guidance on Systematic Planning Using the Data Quality
       Objectives Process EPA QA/G-4).

II.     EXPOSURE ASSESSMENT

Q10.   For CERCLA risk assessments  at remedial sites, is it appropriate to use guidance or
       approaches developed by other  Federal, State or Tribal Agencies or by International
       or National Organizations?

A.     EPA has made the policy decision that risks from radionuclide exposures at remedial sites
       should  be estimated in the same manner as chemical contaminants, which is consistent
       with EPA's remedial program implementing guidance (e.g., EPA 1997g, 1999d,
       2000f). Consequently, approaches that do not follow the remedial program's policies and
       guidance should not be used at CERCLA remedial sites. Should regional staff have
       questions, they should consult with the Superfund remedial program's National Radiation
       Expert (Stuart Walker of OSRTI at the time this fact sheet was issued, at (703) 603-8748
       or walker.stuart@epa.gov), before using guidance from other organizations that is not
       already incorporated into this and other EPA Superfund remedial program guidance. The
       current Superfund remedial program's National Radiation Expert will be listed on the
       Superfund Radiation webpage at:
       http://www.epa.gov/superfund/health/contaminants/radiation/index.htm.

Qll.   How does the exposure assessment for radionuclides differ from that for chemicals?

A.     For the Superfund remedial program, exposure assessment for radionuclides is similar to
       that for chemicals. Both nonradioactive chemical assessments and radionuclide
       assessments should follow the same basic steps—characterizing the exposure setting,
       identifying exposure pathways and potential receptors, estimating exposure point
       concentrations, and estimating exposures and intakes. In addition to the exposure
       pathways considered for chemicals (e.g., ingestion of contaminated water, soil, or
       foodstuffs, and inhalation of contaminated air), external exposure to penetrating radiation
       (i.e., gamma radiation and X-rays) may be an important exposure pathway for certain
       radionuclides in near-surface soils. Dermal absorption is considered to be an insignificant
       exposure pathway for radionuclides and generally is not evaluated. However,
       radionuclides that are on the skin  would be appropriate for evaluation under the external
       pathway. Figure 2 depicts typical  exposure pathways for humans to radionuclides;
       additional pathways that may be considered on a site-specific basis, where appropriate,

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       are discussed in Q12. Additional discussion of radiation exposure pathways is provided in
       the user guides for the PRO and DCC calculators (EPA 2002a, 2004a, 2007, 2009a,
       2010a, and 201 Ob); each of these illustrations in Figure 2 appears in these user guides
       with additional explanatory text and in a larger size that is more legible.

Q12.   Should exposure pathways be added or  deleted based on site-specific conditions?

A.     Generally, yes. Inclusion or deletion of exposure pathways should be based on site-
       specific conditions, including but not limited to local hydrology, geology, potential
       receptors, and current and potential future  land use, among other factors. Accordingly,
       some exposure pathways may not be appropriate for a given site and may be deleted; in
       such cases, the Region should explain its justification for doing so and provide specific
       supporting data and information in the administrative record documents that discuss the
       risk assessment (e.g., Baseline Risk Assessment, RI, ROD, etc.). In other cases, exposure
       pathways that are typically not significant may be important under site-specific
       conditions (e.g., ingestion of contaminated fish for recreational scenarios, ingestion of
       contaminated meat or milk from livestock for agricultural scenarios) and should be
       included in the assessment. A well-supported conceptual site model should facilitate
       users making site-specific adjustments when appropriately supported by site-specific
       information, such as deleting the contaminated fish pathway for the agricultural
       scenario when the site is in an area that would not support fish ponds.
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   Figure 2. Typical Radionuclide Exposure Pathways for Humans
                                                 Resident: Soil Exposure
Indoor Worker: Soil Exposure
Agricultural Soil Exposure

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Figure 2. Typical Radionuclide Exposure Pathways for Humans - continued
    Indoor Worker: Settled Dust
External Exposure
  to Radiation
                          Incidental digestion
                             
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Q13.   How should radioactive decay products be addressed in an exposure assessment to
       determine dose or risk?

A.     All radionuclides, by definition, undergo radioactive decay. In this process, one unstable
       nucleus of an element transforms (decays) spontaneously to a nucleus of another element.
       As the unstable nucleus decays, energy is released as particulate or photon radiation, or
       both, and the radionuclide is transformed in atomic number and/or atomic mass. The
       resulting decay products, or progeny, may also be radioactive and undergo further decay.
       Various decay products may have different physical and chemical characteristics that
       affect their fate and transport in the environment as well as their radiotoxicity. In cases
       where decay products have greater radiotoxicity than the original radionuclide, the
       potential radiation dose and health risk may increase over time; in such cases, the exposure
       assessment should consider the change in concentrations of all decay products over time to
       determine the time of maximum potential impact.

       To help ensure protectiveness of human health, consideration of all potential  radioactive
       decay products is a key element of the exposure assessment for radionuclides. Many of the
       computerized mathematical models available for simulating the behavior of radionuclides
       in the environment (see Q16) incorporate the ingrowth and decay of radioactive decay
       products as a function of time; these models  are useful in pinpointing the time of maximum
       dose or risk. Similarly, slope factors (see Q21) and dose conversion factors (see Q22) for
       some radionuclides may include consideration of radioactive decay products, where
       appropriate, to facilitate these considerations in estimating potential radiation dose and
       risk. However, these values typically assume that all decay products are present at the
       same concentration as the primary radionuclide (i.e., secular equilibrium), which may not
       be appropriate for all situations. In those situations  model users may need to calculate risks
       or doses for various radionuclides in the decay chain separately and use a sum of the
       fractions approach for determining total risk or dose. For additional information regarding
       such limitations see the user guides for the PRG and DCC calculators (U.S. EPA 2002a,
       2004a, 2007, 2009a, 2010a, and 201 Ob).

Q14.   To what extent should generic and site-specific factors and parameter values be
       used in exposure assessments?

A.     For  both radionuclide and  chemical assessments in the Superfund remedial program,
       EPA recommends use of empirically-derived, site-specific factors and  parameter values,
       where these values can be justified and documented. For generic assessments, EPA
       recommends use of the default parameter values provided in the PRG and DCC calculators
       (EPA 2002a, 2004a, 2007, 2009a, 2010a, and 201 Ob).

Q15.   How should exposure point concentrations be  determined?

A.     As for chemical contaminants, exposure point concentrations for radionuclides in
       environmental media and radiation exposure rates (e.g., alpha, beta, and gamma) should
       be either measured, modeled,  or both, to help ensure protectiveness of human health. To

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       the extent possible, measurement data should be used to evaluate current exposures.
       When measurements at the exposure locations cannot be made, or when potential
       concentrations and exposures will be predicted at future times, modeling may be needed
       to estimate past or future movement of radionuclides (see Q16).

Q16.   What calculation methods or multimedia radionuclide transport and exposure models
       are recommended by EPA for Superfund risk assessments?

A.     The PRO calculators (U. S. EPA 2002a, 2007, 2009a), which are used to develop risk-based
       PRGs for radionuclides, are recommended by EPA for Superfund remedial radiation risk
       assessments. These risk and dose  assessment models are similar to EPA's methods for
       chemical risk assessment at CERCLA sites. Guidance on how to use each calculator, the
       default input parameters and their sources, is provided in the user guide for each calculator.
       In addition, a tutorial for using the PRO calculator is included in module 3 of the on-line
       training course Radiation Risk Assessment: Update and Tools (ITRC 2007), and a tutorial
       for the BPRG and SPRG calculators is provided in module 3 of the on-line training course
       Decontamination and Decommissioning of Radiologically-Contaminated Facilities (ITRC
       2008b). The PRG calculator superseded the Soil Screening Guidance for Radionuclides
       (Rad SSG) calculator (U.S. EPA 2000e).

       To avoid unnecessary inconsistency between radiological and chemical risk
       assessment at the same site, users should generally use the same model for chemical
       and radionuclide risk assessment. If there is a reason on a site-specific basis for using
       another model justification for doing so should be developed. The justification should
       include specific supporting data and information in the administrative record. The
       justification normally would include the  model runs using both the recommended EPA
       PRG model and the alternative model. Users are cautioned that they should have a
       thorough understanding of both the PRG recommended model and any alternative model
       when evaluating whether a different approach is appropriate. When alternative models are
       used, the user should adjust the default input parameters to be as close as possible to the
       PRG inputs, which may be difficult since models tend to use different definitions for
       parameters. Numerous computerized mathematical models have been developed by EPA
       and other organizations to predict the fate and transport of radionuclides in the
       environment; these models include single-media unsaturated zone models (for example,
       groundwater transport) as well as multi-media models. These models have been designed
       for a variety of goals, objectives, and applications; as such, no single model may be
       appropriate for all site-specific conditions. Generally, even when a different model is used
       to predict fate and transport of radionuclides through different media, EPA recommends
       using the PRG calculators for the remedial program to establish the risk-based
       concentrations to ensure consistency with CERCLA, the NCP and EPA's Superfund
       guidance for remedial sites.

       EPA has evaluated five soil to groundwater models ranging from the simple to the multi-
       dimensional in Simulating Radionuclide  Fate and Transport in the Unsaturated Zone:
       Evaluation and Sensitivity Analyses of Select Computer Models (EPA 2002c). This
       evaluation is also summarized in Part 3 of the Rad SSG Technical Background Document
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       (TBD) (EPA 2000b). For further information on selection of models appropriate to meet
       specific-site characteristics and requirements, readers can refer to Ground-Water Modeling
       Compendium (U.S. EPA 1994c), and^4 Technical Guide to Ground-Water Model Selection
       at Sites Contaminated with Radioactive Substances (U.S. EPA 1994d). While these
       documents specifically address groundwater models, the model selection criteria and logic
       may be useful for other models as well.

Q17.   How should Radon-222 (radon) and Radon-220 (thoron) exposures and risks be
       evaluated?

A.     Radon-222 (Rn-222) and Radon-220 (Rn-220) are radioactive gases that are isotopes of
       the element radon (Rn). Each is produced by the radioactive decay of an isotope of radium
       (Ra). The parent radium  isotope for Rn-222 (also called radon), is Ra-226 and the parent
       radium isotope for Rn-220 (also called thoron) is Ra-224. (Although thoron is produced
       from the radioactive decay of Ra-224, it is often referred to as a decay product of Ra-228,
       which is a longer-lived precursor typically measured in environmental samples.) Each
       radon isotope gives rise to a series or chain of short-lived radioactive decay products that
       emit alpha particles, which can damage lung tissues if inhaled. Of the two decay chains,
       the radon series is longer lived and more hazardous than the thoron series. Both decay
       chains are addressed by the same ARAR discussed below. Risk and dose assessments of
       radon and thoron concentrations at CERCLA remedial sites should be developed using the
       PRO and DCC calculators (U.S. EPA 2002a, 2004a, 2007, 2009a, 2010a, and 201 Ob).

       Structures built on radium-contaminated soil or constructed with radium-bearing materials
       can accumulate elevated concentrations of radon and thoron in indoor air. Some radiation
       protection standards that may be potential ARARs at a site explicitly exclude dose or risk
       from radon and its decay products from consideration. Other potential ARARs directly
       address radon and its decay products (for example, under 40 CFR 192.12(b)(l) a standard
       of 0.03 working levels (WL) and a goal of 0.02 WL for allowable concentrations of radon
       decay products in indoor air).

       Several EPA-approved methods are available for measuring radon and progeny
       concentrations in indoor air (EPA et al., Rev 1. 2000d). Because the indoor radon
       guidelines for homeowners are expressed in terms  of picocuries per liter (pCi/L) of air,
       tools to address pCi/L are more prevalent than those to address WL. For purposes of
       demonstrating compliance with the 0.02 WL Uranium Mill Tailings Radiation
       Control Act (UMTRCA) regulations as an ARAR, users may assume that either 5
       pCi/L of Rn-222, or 7.5 pCi/L of Rn-220, corresponds to 0.02 WL. Therefore 5 pCi/L
       of Rn-222 or 7.5 pCi/L of Rn-220 may be considered to be the concentration for
       complying with the UMTRCA indoor radon standard as an ARAR. These values are
       based on an indoor residential equilibrium fraction of 0.4 (40%) for Rn-222 and 0.02 (2%)
       for Rn-220. For the case of secular equilibrium, where the equilibrium fraction is 100%,
       the corresponding concentrations of Rn-222 and Rn-220 would be 2 pCi/L and 0.15 pCi/L
       respectively. The methodology for making this conversion is discussed on page 11 of the
       International Commission on Radiological Protection's (ICRP) guidance Lung Cancer
       Risk from Radon and Progeny (ICRP 2011). To adjust the indoor radon concentration to
       any given equilibrium fraction, the value for 0.02 WL at secular (100%) equilibrium is

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       divided by the appropriate equilibrium fraction. Thus, 2 pCi/L divided by 0.4 yields 5
       pCi/L forRn-222 and 0.15 pCi/L divided by 0.02 yields 7.5 pCi/L for Rn-220. This 40%
       value for Rn-222 is discussed on page 190 of the NAS Report Health Effects of Exposure
       to Radon: BEIR VI (NAS 1999). For Rn-220, the assumed equilibrium factor of 2% is
       discussed on page 206 of Appendix E: Sources-to-effects assessment for radon in homes
       and workplaces of the United Nations Report Effects of Ionizing Radiation Volume II
       (UNSCEAR 2006).

       Computer codes have been developed to predict radon concentrations in indoor air and
       potential human exposure, based on simplified equations and assumptions; these models
       may yield results that are meaningful  on average (e.g., for a geographical  region) but
       highly imprecise for an individual house or structure. Despite their widespread use, these
       codes should be used with caution and their estimates interpreted carefully. Also, some
       states have their own radon testing and mitigation requirements that may be potential
       ARARs at a site (see Q38).

Q18.   How long a time period should be considered for possible future exposures?

A.     The PRG calculators include assumptions for the appropriate time period  for generic land
       use exposure scenarios. Furthermore,  in some cases, federal or state ARARs may include
       specific time-frame requirements for  a given purpose, which is often a thousand years for
       dose-based standards. Several of the isotopes are listed with a "+E"  designation. This
       designation indicates that the dose conversion factor (DCF) includes the contribution from
       ingrowth of daughter isotopes out to 1,000 years. As a result, the DCC calculators allow
       the selection of radionuclides with the +E designation, which provide a dose assessment
       based on the year of peak dose over 1,000 years since many standards that are potential
       ARARs specify this time-period for dose assessments. If the ARAR does  not specify a
       time-period for assessment, users should use the +D designation for a radionuclide where
       the decay chain is in secular equilibrium. The +D designation indicates the contribution
       from ingrowth of daughter isotopes out to 100 years.

Q19.   How should the results of the exposure assessment  for radionuclides be
       presented?

A.     Results of the exposure assessment for radionuclides should be presented  with intake and
       external exposure estimates for use in risk characterization. If it is determined that there
       are dose-based  standards that are ARARs at a CERCLA remedial site, then the  intake and
       external exposure estimates should also be used for dose assessment.

       Note that intake estimates for radionuclides should not be divided by body weight or
       averaging time  as is done for chemical contaminants, because the radionuclide slope
       factors and dose conversion factors are age averaged, which accounts for  average body
       weight in the United States population over different ages and the risk or dose is
       dependent upon the total exposure not the time period over which it occurs. Intake
       estimates for inhalation or ingestion pathways should include the total activity of each
       radionuclide inhaled or ingested via each pertinent route of exposure (e.g., ingestion of
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       contaminated drinking water, direct ingestion of contaminated soil, ingestion of
       contaminated produce, milk, or meat). Measured or predicted external exposure rates
       should be presented, along with the exposure time, frequency, and duration. The
       concentration of each radionuclide in the medium is needed to estimate the risk from the
       external pathway using slope factors.

111.    TOXICITY ASSESSMENT
Q20.   What is the mechanism of radiation damage?

A.     Radiation emitted by radioactive substances can transfer sufficient localized energy to
       atoms to remove electrons from the electron cloud surrounding the nucleus (ionization). In
       living tissue, this energy transfer can produce chemically reactive ions or free radicals,
       destroy cellular constituents, and damage DNA. Improperly repaired DNA damage is
       thought to be a major factor in carcinogenesis. (While ionizing radiation may also cause
       other detrimental health impacts, only radiogenic cancer risk is normally considered in
       CERCLA risk assessments [see Q26].)

       The type of ionizing radiation emitted by a particular radionuclide depends on the exact
       nature of the nuclear transformation, and may include emission of alpha particles, beta
       particles (electrons or positrons), and neutrons; each of these transformations may be
       accompanied by emission of photons (gamma radiation or X-rays). Each type of radiation
       differs in its physical characteristics and in its ability to inflict damage to biological tissue.
       The various types of radiation are often categorized as low linear energy transfer (LET)
       radiation (photons and electrons) and high-LET radiations (alpha particles and neutrons)
       for radiation risk and dose estimates.

       Ionizing radiation can cause deleterious effects on biological tissues only when the energy
       released during radioactive decay is absorbed in tissue. The average energy imparted by
       ionizing radiation per unit mass of tissue is called the "absorbed dose." The SI unit of
       absorbed  dose is the joule per kilogram,  also assigned the special name the Gray (1 Gy  = 1
       joule/kg); the conventional unit of absorbed dose is the rad (1 rad =100 ergs/g = 0.01 Gy).

Q21.   What are radionuclide  slope factors?

A.     EPA has developed slope factors for estimating incremental cancer risks resulting from
       exposure to radionuclides via inhalation, ingestion, and external exposure pathways.
       Slope factors for radionuclides represent the probability of cancer incidence as a result of
       a unit exposure to a given radionuclide averaged over a lifetime using the linear no-
       threshold model. It is the age-averaged lifetime excess cancer incident rate per unit intake
       (or unit exposure for external exposure pathway)  of a radionuclide (U.S. EPA 1989a).

       EPA recommends the slope factors that are used in the PRG calculators for CERCLA
       remedial radiation risk estimates (U.S. EPA 2002a, 2007, and 2009a). Current
       radionuclide slope factors incorporate the age- and gender-specific radiogenic cancer
       risk models from Federal Guidance Report No. 13: Cancer Risk Coefficients for
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       Environmental Exposure to Radionuclides (U.S. EPA 1999c), which assume a maximum
       lifetime for an individual of 120 years, but incorporate competing causes of death over a
       120 year lifetime.

Q22.   What are radionuclide dose conversion factors?

A.     Dose conversion factors (DCFs), or "dose coefficients", for a given radionuclide
       represent the dose equivalent per unit intake (i.e., ingestion or inhalation) or external
       exposure of that radionuclide. These DCFs are used to convert the amount of
       radionuclide externally exposed, ingested, or inhaled to a radiation dose from an
       environmental sample of modeled estimate of radionuclide concentration in soil, air,
       water, or foodstuffs. DCFs may be specified for specific body organs or tissues of
       interest, or as a weighted sum of individual  organ dose, termed the effective dose
       equivalent.  (These quantities are discussed further in Q23.) These DCFs may be
       multiplied by the total activity of each radionuclide inhaled or ingested per year, or the
       external exposure concentration to which a receptor may be exposed, to estimate the
       dose equivalent to the receptor.

       EPA recommends the DCFs that are used in the DCC calculators for CERCLA remedial
       dose assessments (U.S. EPA 2004a, 2010a,  and 2010b). The most up to date
       radionuclide DCFs in the current DCC calculators, ICRP 60, incorporate age- and
       gender-specific models and are  from the CD supplement to Federal Guidance Report
       No. 13: Cancer Risk Coefficients for Environmental Exposure  to Radionuclides (U.S.
       EPA 1999c).

Q23.   What is dose equivalent, effective dose equivalent, and related quantities?

A.     As discussed in Q20, different types of radiation  have differing  effectiveness in
       transferring their energy to  living tissue. Since  it is often desirable to compare doses
       from different types of radiation, the quantity "dose equivalent," or "equivalent dose," has
       been defined as a measure of the energy absorbed by living tissues, adjusted for the type of
       radiation present. The SI unit for dose equivalent is the Sievert (Sv)  and the conventional
       unit is the rem (1 rem = 0.01 Sv). The absorbed dose is multiplied by Quality Factor (Q) or
       radiation weighting factor (WR)  to compute dose equivalent; these values range from 1 for
       photons and electrons to  10 for neutrons to 20 for alpha particles. For an equal amount of
       energy absorbed, an alpha particle will inflict approximately 20 times more damage to
       biological tissue than that inflicted by a beta particle or gamma ray. Internally deposited
       (inhaled or  ingested) radionuclides may be deposited in various organs and tissues long
       after initial  deposition. The "committed dose equivalent" is defined as the integrated dose
       equivalent that will be received by an individual during a 50-year  period following the
       intake. By contrast, external radiation exposure contributes to dose only as long as the
       receptor is present within the external radiation field.

       When they  are exposed to equal doses of radiation, different organs and tissues in the
       human body will exhibit  different cancer induction rates. The quantity "effective dose
       equivalent," or "effective dose," was developed by the International Commission on
       Radiological Protection (ICRP) to account for these differences and to normalize radiation
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       doses and effects on a whole body basis for regulation of occupational exposure. The
       effective dose equivalent is computed as a weighted sum of organ-specific dose equivalent
       values, with weighting factors specified by the ICRP (ICRP 1977, 1979). The effective
       dose equivalent is equal to that dose equivalent, delivered at a uniform whole-body rate,
       that corresponds to the same number (but possibly dissimilar distribution) of fatal
       stochastic health effects as the particular combination of organ dose equivalents.

Q24.   What is the critical organ approach to dose limitation?

A.     Regulatory standards developed by EPA and the Nuclear Regulatory Commission (NRC)
       that use the critical organ approach usually consist of a combination of whole body and
       critical organ dose limits, such as 25 mrem/yr to the whole body, 75 mrem/yr to the
       thyroid, and 25 mrem/yr to any critical organ other than the thyroid. For example,  EPA's
       uranium fuel cycle rule, 40 CFR 190.10(a); NRC's low level waste rule, 10 CFR 61.41;
       and EPA's management and storage of high level waste by NRC and agreement states rule,
       40 CFR 191.03(a), use this "25/75/25 mrem/yr" dose limit approach.  EPA's management
       and storage of high level waste by U.S. Department of Energy (DOE) rule, 40 CFR
       191.03(b), is expressed as 25 mrem/yr to the whole body and 75 mrem/yr to any critical
       organ (including the thyroid). When these standards were adopted, dose was calculated and
       controlled for each organ in the body and uniform radiation of the "whole body." The
       "critical organ" was the organ that received the most dose for the radionuclide concerned.
       With the adoption of the dose equivalent concept, the dose to each organ  is weighted
       according to the effect of the radiation on the overall system (person). The new dose
       system for the EPA and NRC regulations allows for one value of dose equivalent (see Q
       23) to be assigned as a limit, which is protective of the entire system. The critical organ
       approach required individual limits for each organ based on the effect of radiation on that
       organ.

       It should be noted that although most critical organ standards include 25 mrem/yr or higher
       (for example, 75 mrem/yr to the thyroid) dose limits, these critical organ  standards are not
       comparable to 25 mrem/yr effective dose equivalent standards or guidance. EPA has
       determined that for Superfund remedial sites a 25 mrem/yr effective dose equivalent level
       should not be used for the purposes of establishing cleanup levels at CERCLA remedial
       sites (see 1997a). This determination does not apply to critical organ standards (see 1997a).
       For further discussion of EPA's comparison of critical organ and effective dose  equivalent
       limits see pages 4-5 of Attachment B to EPA 1997a. The DCC, BDCC, and SDCC
       calculators are not intended for demonstrating compliance with ARARs using the critical
       organ dose approach based on ICRP 2.

Q25.   How should radionuclide slope factors and dose conversion factors  be used?

A.     EPA recommends that radionuclide slope factors be used to estimate the excess
       cancer risk resulting from exposure to radionuclides at radiologically
       contaminated sites, consistent with the NCP's risk range (10~4 to  10"6  lifetime
       excess cancer risk) for CERCLA remedial responses. The incremental risk generally
       is calculated by multiplying the estimates of chronic daily intake over a lifetime by a
                                          -22-

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       slope factor that is appropriate for the exposure route (ingestion, inhalation and external
       exposure) and media (e.g., soil, food and water) of concern.

       Cancer risk from radionuclide exposures may also be estimated by multiplying the
       effective dose equivalent computed using the dose conversion factors (DCFs) by a risk-
       per-dose factor. Some key differences in the two cancer risk methods are summarized in
       Table 2.

       The primary use of DCFs by the Superfund remedial program generally should be to
       compute doses resulting from site-related  exposures for comparison with radiation
       protection standards  (see Q32 and 33) that are determined to be ARARs. This can be
       accurately accomplished by multiplying the estimates of annual chronic daily intake by a dose
       conversion factor that is appropriate for the exposure route (ingestion, inhalation and external
       exposure) and media (e.g., soil, food and water) of concern.

       At Superfund remedial responses, excess cancer risk generally represents cumulative
       lifetime cancer morbidity risk from a multi-year exposure period (e.g., 30 years of
       exposure for residential scenario). In contrast, when complying with most dose-based
       standards that are considered to be ARARs at CERCLA remedial responses, the dose
       limits are typically expressed in terms of annual exposure (for example, the effective dose
       equivalent resulting from exposure during a  1-year period, mrem/year).

       DCFs from the default settings in the latest versions of the DCC, BDCC, and SDCC
       calculators  (U.S. EPA 2004a, 2010a, and 201 Ob) should be used for complying with
       ARARs based on effective dose equivalent,  while DCFs from ICRP 2 should  be used
       when complying with ARARs based on the critical organ approach. There are some
       potential ARARs (for example, the maximum contaminant levels [MCLs] for beta and
       photon emitters) that specify in the text  of the regulation  itself which DCFs should be
       used.

Q26.   In addition to cancer, should the potential teratogenic and genetic effects of
       radiation  exposures be considered?

A.     Biological effects associated with exposure to ionizing radiation in the environment may
       include carcinogenicity (induction of cancer), mutagenicity (induction of mutations  in
       somatic  or reproductive cells, including  genetic effects), and teratogenicity  (effects on
       the growth  and development of an embryo or fetus). Agency guidance (U.S.  EPA  1989a,
       1994b) indicates that the radiogenic cancer  risk is normally  assumed to be limiting for
       risk assessments at Superfund remedial sites, and evaluation of teratogenic and genetic
       effects is not required. Similarly, consideration of acute effects at CERCLA  remedial
       sites generally is not required, since these effects occur only at  doses much higher than
       those normally associated with environmental exposures.
                                          -23-

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Table  2. Comparison  of Radiation Risk Estimation  Methodologies:  Slope Factors  vs.
Effective  Dose Equivalent
  Parameter
  Competing
  Risks
  Risk
  Models
                                             Slope Factor Approach
Persons dying from  competing causes of death
(such as disease, accidents) are not considered
susceptible to radiogenic cancer.
Probability of dying at a  particular age from
competing risks is considered based on the mortality
rate from all causes at that age in the 1989 to 1991
(previously 1979 to 1981) U.S. population.

Age-dependent and gender-dependent risk models
for 14  cancer sites are considered individually and
integrated into the slope factor estimate.
                                                      Effective Dose Equivalent (EDE) x
                                                      Risk Factor Approach

                                                        Competing risks not considered.
Risk estimate averaged over all
ages, sexes, and cancer sites.
  Genetic
  Risk
  Dose
  Estimates
  RBE for high- LET
  (alpha) radiation
Genetic risk is not considered in the slope factor
estimates; however, ovary is considered as a potential
cancer site.

Low-LET  and high-LET dose estimates considered
separately  for each target organ.
20 for most sites (8 prior to 1994)
10 for breast (8 prior to 1994)
1 for leukemia (1.117 prior to 1994)
EDE value includes genetic risk
component.
Dose-equivalent includes both low-
LET and high-LET radiation,
multiplied by appropriate Quality
Factors.

20 (all sites)
  Organs
  Considered
  Lung Dose
  Definition
  Integration
  Period
  Dosimetric /
  Metabolic
  Models
Estimates of absorbed dose to 16 target organs/tissues
considered for 13 specific cancer sites plus residual
Absorbed  dose used to estimate lung cancer risk
computed  as weighted sum of dose to
tracheobronchial region (80%) and pulmonary lung
(20%).
Variable length (depending on organ-specific risk
models and
consideration of competing risks) not to exceed 110
years.

Metabolic models and parameters for dose estimates
follow recent recommendations of the ICRP series of
documents on age-specific dosimetry (ICRP, 1989,
1993, 1995a, 1995b), where available; previous
estimates based primarily on ICRP 30 (ICRP, 1979).
EDE (ICRP, 1979) considers dose
estimates to six specific target
organs plus remainder (weighted
average of five other organs).

Average dose to total lung (mass
weighted sum of doses to the
tracheobronchial region,
pulmonary region, and pulmonary
lymph nodes).

Fixed integration period of 50 years
typically considered.
Typically employ ICRP
Publication 30 (ICRP 1979)
models and parameter for
radionuclide uptake, distribution,
and retention.
                                                        -24-

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Q27.   Should chemical toxicity of radionuclides be considered?

A.     At Superfund remedial program radiation sites, EPA generally evaluates potential human
       health risks based on the radiotoxicity (the adverse health effects caused by ionizing
       radiation), rather than on the chemical toxicity, of each radionuclide present. Uranium, in
       soluble form, is a kidney toxin at mass concentrations slightly above background levels. It
       is the only radionuclide for which the chemical toxicity has been identified to be
       comparable to or greater than the radiotoxicity and for which an oral reference dose (RfD)
       has been established to evaluate chemical toxicity. To properly evaluate human health
       risks, both effects (radiogenic cancer risk and chemical toxicity) should be considered for
       radioisotopes of uranium. When risk estimates will be made of the chemical toxicity of
       uranium, EPA recommends using the Regional Screening Levels for Chemical
       Contaminants at Superfund Sites (RSL) calculator (U.S. EPA 2008) for uranium in soil,
       water and air and the equations in (U.S. EPA 2003) for uranium in dust inside of buildings.
       The RSL calculator is frequently updated.


IV.    RISK CHARACTERIZATION

Q28.   How should radionuclide risks be estimated?

A.     At Superfund remedial sites, risks from radionuclide exposures should be estimated in
       a manner analogous to that used for chemical contaminants. The estimates of intake by
       inhalation  and ingestion and the external exposure over the period of exposure
       estimated for the land use (e.g., 30 years residential, 25 years commercial/industrial)
       from the exposure assessment should be coupled with the appropriate slope factors for
       each radionuclide and exposure pathway. Only excess cancer risk should be considered
       for most radionuclides (except for uranium, as discussed in Q27).  The total
       incremental lifetime cancer risk attributed to radiation exposure  is estimated as the
       sum of the risks from all radionuclides in all exposure pathways.

Q29.   Should radionuclide and chemical risks be combined?

A.     Generally, yes. At CERCLA remedial sites, excess cancer risk from both radionuclides and
       chemical carcinogens should be summed to provide an estimate of the combined risk
       presented by all  carcinogenic contaminants as specified in OSWER  directive 9200.4-18
       (U.S. EPA 1997a). An exception would be cases in which a person reasonably cannot be
       exposed to both  chemical and radiological carcinogens; Regions should include specific
       supporting data and information in the administrative record to document this conclusion.
       Similarly, the chemical toxicity from uranium should be combined as appropriate with that
       of other site-related contaminants. As recommended in RAGSVart A (U.S. EPA 1989a),
       risk estimates for radionuclides and chemical contaminants also should be tabulated and
       presented separately in the risk characterization report.

       There  are generally several differences between slope factors for radionuclides and
       chemicals. However,  similar differences also occur between different chemical slope
       factors In the absence of additional  information, it is reasonable to assume that

                                           -25-

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       excess  cancer risks are additive for evaluating the total incremental cancer risk
       associated with a contaminated site.

Q30.   How should risk characterization results for radionuclides be presented?

A.     Results should be presented according to the standardized reporting format presented in
       RAGS Part D (U.S. EPA 1998a). EPA guidance for risk characterization (U.S. EPA 1995a,
       1995b) indicates that four descriptors of risk are generally needed for a full
       characterization of risk: (1) central tendency (such as median, mean) estimate of individual
       risk; (2) high-end estimate (for example, the 95th percentile) of individual risk; (3) risk to
       important subgroups of the population, such as highly exposed or highly susceptible groups
       (such as children) or individuals, if known; and (4) population risk. The reasonable
       maximum exposure (RME) estimate of individual risk typically presented in Superfund risk
       assessments represents a measure of the high-end individual exposure and risk. While the
       RME estimate remains the primary scenario for Superfund risk management decisions,
       additional risk descriptors may be included to describe site risks more thoroughly (e.g.,
       central tendency, sensitive subpopulations). Population risk is generally not used as part of
       Superfund risk assessments.

Q31.   Is it necessary to present the collective risk to populations estimated along with  that
       to individual receptors?

A.     Generally, no. Risk to potential RME individual receptors generally is the primary measure
       of protectiveness under the CERCLA remedial  process (thetarget range of 10~6 to 10~4
       lifetime excess cancer risk to the RME receptor). As noted in Q30, however, Agency
       guidance  (U.S. EPA 1995a, 1995b)also indicates that the central tendency risk to the
       potentially exposed population may be evaluated where possible. Consideration of central
       tendency  risk may provide additional input to risk management decisions; such
       considerations may be either qualitative or quantitative, depending on the availability of
       data.

Q32.   How should uncertainty in estimates of radiation  risk be addressed in the risk
       characterization report?

A.     Consideration of uncertainty in estimates of risks from potential exposure to radioactive
       materials  at CERCLA sites typically is an essential element of informed risk management
       decisions. RAGS and subsequent guidance (U.S. EPA 1995a,  1995b) stress the importance
       of a thorough presentation of the uncertainties, limitations, and assumptions that underlie
       estimates of risk. Either qualitative or quantitative evaluation  may be appropriate,
       depending on the availability of data and the magnitude of predicted risk. In either case,
       the evaluation should address both uncertainty ("the  lack of knowledge about specific
       factors, parameters, or models") and variability ("observed differences attributable to true
       heterogeneity or diversity in a  population or exposure parameter"). Estimates of potential
       risk should include both central tendency estimates (median, mean) and high-end
       estimates (such as RME or 95th percentile).
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       Extrapolation from high dose and dose rate exposure is generally done to estimate risks
       of low-level exposures for both chemical carcinogens and radionuclides.  This extrapolation
       typically constitutes the greatest source of uncertainty. Additional uncertainty  may be
       introduced due to extrapolation  of animal data to humans for chemical carcinogens.
       Slope factors for both radionuclides and chemicals are used to estimate incremental cancer
       risk, which typically represents a small increment over a relatively high baseline incidence.
       It should be noted that there is less uncertainty associated with the slope factors for
       radionuclides than any, or almost any, chemical slope factors since the radionuclide slope
       factors are based primarily on human rather than animal data. Other sources of uncertainty
       may be associated with instrumentation and measurements used to characterize the nature
       and extent of radionuclides of concern,  and the parameters used to characterize
       potential  exposures of current and future receptors (such as intake rates and frequency of
       exposure).

       Probabilistic Risk Assessment (PRA) may be used to provide quantitative estimates of the
       uncertainties in the risk assessment. However, probabilistic estimates of risk should be
       presented as a supplement to, not instead of, the deterministic (point estimate) methods
       outlined in RAGS Part A. A tiered approach is  often useful, with the  rigor of the
       analysis depending  on the magnitude of predicted risk. Factors to be considered in
       conducting a probabilistic analysis typically should include the sensitivity of parameters,
       the correlation or dependencies between parameters, and the distributions of parameter values
       and model estimates. Detailed guidance on this topic is provided in Use of Probabilistic
       Techniques (Including Monte Carlo Analysis) in Risk Assessment (U.S. EPA  1997c) and
       Guiding Principles for Monte Carlo Analysis (U.S. EPA 1997d).

Q33.   When should a dose assessment be performed?

A.     Dose assessments should be conducted during CERCLA remedial responses only when
       considering compliance of clean up plans with dose-based ARARs. As discussed in
       OSWER Directive 9200.4-18 (U.S. EPA 1997a), cleanup levels for radioactive
       contamination at remedial sites should be established as they would for any chemical that
       poses an unacceptable risk and the risks should be characterized in standard Agency risk
       language consistent with CERCLA guidance for remedial sites. Thus, cleanup levels not
       based on an ARAR should be based on the carcinogenic risk range (generally 10'4 to
       10'6, with 10'6 as the point of departure and 1 x 10'6 used for PRGs) and expressed in
       terms of risk (# x 10~#).

Q34.   What is the upper end of the risk range with respect to radionuclides?

A.     Consistent with existing Agency guidance for the CERCLA remedial program, while the
       upper end of the risk range is not a discrete line at 1  x 10"4, EPA generally uses 1 x 10"4 in
       making risk management decisions. A specific risk estimate around  10"4 may be considered
       acceptable based on site-specific circumstances. For further discussion of these points and
       how EPA uses the risk range, see OSWER Directive 9355.0-30, Role of the Baseline Risk
       Assessment in SuperfundRemedy Selection Decisions (U.S. EPA  1991d). In general, dose
       assessment used as a method to assess risk is not recommended as a way of ensuring
       protectiveness of human health at CERCLA remedial sites.


                                          -27-

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Q35.   Should the ARAR protectiveness criteria evaluation recommendation be changed
       from 15 mrem/yr to reflect the updates to radiation risk estimates contained in
       Federal Guidance Report 13?

A.    Yes, ARAR protectiveness criteria evaluation recommendation of 15 mrem/yr should
      be changed to 12 mrem/yr to reflect the current federal government position on the
      risks posed by radiation, which is contained in EPA's Federal Guidance Report 13
      (U.S. EPA 1999c).  More recent scientific information reflected in EPA's Federal
      Guidance Report 13 risk estimates show that 12 mrem/yr is now considered to correspond
      approximately to 3 x 10~4 excess lifetime cancer risk. This updated approach is based on
      FGR 13 's assumption of a risk of cancer incidence of 8.46 x 10~4 per rem of exposure
      (while still using the EPA CERCLA standard period of exposure of 30 years for residential
      land use, which also  was the basis of the 15 mrem/yr determination in OSWER Directive
      9200.4-18). Therefore, the ARAR evaluation guidance first discussed in OSWER Directive
      9200.4-18 is being updated to 12 mrem/yr so that ARARs that are greater than 12 mrem/yr
      effective dose equivalent (EDE) are generally not considered sufficiently protective for
      developing cleanup levels under CERCLA at remedial sites. As before, this ARAR
      evaluation tool should not be used as a to be considered (TBC) as a basis for establishing
       12 mrem/yr cleanup levels at CERCLA remedial sites.

       Please note that the prior references to 15 mrem/yr in OSWER Directive 9200.4-18 were
       intended as guidance for the evaluation of potential ARARs and TBCs factors and should
       not be used as a TBC for establishing 15 mrem/yr cleanup levels at CERCLA sites
       Consistent with  that guidance, using  15 mrem/yr as an ARAR evaluation tool originally
       was based on  three factors:

                 1. The CERCLA risk range for remedial sites. In 1997, 15 mrem/yr was
                   estimated to correspond to approximately 3 x 10"4 under the then EPA
                   practice of using the dose to risk estimate conversions assumption of a risk
                   of cancer incidence of 7.6 x 10"4 per rem of exposure, found in ICRP 1991
                   and NAS  1990. This dose to risk estimate has been superseded by the
                   assumption of a risk of cancer incidence of 8.46 x 10"4 per rem of exposure
                   in FGR 13 (U.S. EPA 1999c).
                2. Prior EPA radiation rulemakings, and
                3. Prior EPA CERCLA site-specific decisions.

Q36.   Should dose recommendations from other federal agencies be used to assess risk or
       establish cleanup levels?

A      Generally, no Dose assessments generally should only be performed to assess risks or
       to establish cleanup levels at CERCLA remedial sites to show compliance with an
       ARAR that requires a dose assessment (for example 40 CFR 61 Subparts H and I, and 10
       CFR 61.41). Dose level recommendations from international and other non-EPA
       organizations are not enforceable and therefore cannot be ARARs. The selection of
       cleanup levels for carcinogens for CERCLA remedy selection purposes should be
       consistent with  the NCP and CERCLA guidance - i.e., based on the risk range when
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       ARARs are not available or are not sufficiently protective. EPA has made the policy
       decision to use the NCP's risk range in developing cleanup levels for radionuclides at
       CERCLA remedial sites rather than using dose-based guidance since the use of dose-
       based guidance.  See Q10 for more information on this determination.

       EPA recommends using the DCC, BDCC, and SDCC calculators (U.S. EPA 2004a,
       2010a, and 2010b) to develop dose assessments for ARAR compliance purposes at
       Superfund  remedial sites. As indicated on page 2 of the memorandum transmitting the
       DCC calculator (U.S. EPA  2004c), that guidance superseded the dose assessment
       equations in Chapter 10 of RAGs Part A (U.S. EPA 1989a).

Q37.   How and when should exposure  rate be used to estimate radionuclide risks?

A     As discussed previously (see Q25 and Q28), EPA recommends that estimates  of
       radiation risk should  be derived using slope factors, in a manner analogous to that
       used for chemical contaminants. However, to ensure protectiveness of human health
       consistent with CERCLA and the NCP requirements for the remedial program, there
       may be circumstances where it is desirable at CERCLA remedial sites to also consider
       estimates of risk based on direct exposure rate measurements of penetrating radiation in
       addition to risk estimates based on slope factors. Examples of such circumstances where
       it may be appropriate to also use direct measurements for assessing risk from external
       exposure to  penetrating radiation include:

          •  During early site assessment efforts when the site manager is attempting to
             communicate the relative risk posed by areas containing elevated levels of
             radiation,

          •  As a real-time method for indicating that remedial objectives are being met
             during the conduct of the response action. The use of exposure rate measurements
             during the conduct of the response actions should not decrease the need for a
             final status survey.

       To facilitate developing risk estimates under any of these situations, EPA is developing a
       Counts Per Minute (CPM) calculator (U.S. EPA 2014a) to model correlations in exposure
       rate measurements back to modeled estimates of cancer risk. Direct radiation exposure rate
       measurements may provide important indications of radiation risks at a site, particularly
       during early investigations, when these may be the first data available. However, these data
       may reflect only a subset of the radionuclides and exposure pathways of potential concern
       (for example, only external exposure from gamma-emitting radionuclides in near-surface
       soil), and may present an incomplete picture of site risks (such as risk from internal
       exposures, or potential increased future risks from radionuclides in subsurface soils). In
       most cases, more accurate estimation of radiation risks will require additional site
       characterization data, including concentrations of all radionuclides of concern in all
       pertinent environmental media.  The principal benefit of using direct exposure rate
       measurements is the speed and convenience of analysis, and reducing the potential for
       missing areas of contamination. However, exposure rate data generally should
       be used in conjunction with characterization  data of radionuclides concentrations

                                          -29-

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      in environmental media to obtain a complete picture of potential site-related risks.
      Exposure rate measurements scanned in the field should be correlated with samples
      analyzed in a laboratory by collocating them to ensure that modeled assumptions
      about the correlation between exposure rate and sample concentrations are
      accurate. For a general discussion on radiation survey instruments, readers are directed to
      Real-Time Measurement of Radionuclides in Soil: Technology and Case Studies document
      (ITRC 2006), Real-Time Measurement of Radionuclides in Soil on-line training course
      (ITRC 2008), Multi-Agency Radiation Survey and Site Investigation Manual (MARS SIM)
      (U.S. EPA et al. Rev 1. 2000d) and Chapter 10 of RAGs Part A (U.S. EPA 1989a).

Q38.  What radiation standards may be applicable or relevant and appropriate
      requirements (ARARs)?

A.     In  some cases, cleanup levels may  be derived based on site-specific risk assessments,
      ARARs, and/or to-be-considered materials (TBCs). TBCs are non-promulgated
      advisories or guidance issued by Federal or State governments that are not legally
      binding and do not have the status of potential ARARs. However, TBCs will be
      considered along with ARARs as part of the site risk assessment and may be used in
      determining the necessary level of cleanup for protection of health and the environment.
      Attachment A, "Likely Federal Radiation Applicable or Relevant and Appropriate
      Requirements (ARARs)," of OSWERDirective 9200.4-18 (U.S. EPA 1997a) provides
      information regarding the circumstances in which federal  standards that have often been
      selected as ARARs may be either applicable or relevant and appropriate for particular
      site-specific conditions. The 1997 guidance (U.S. EPA  1997a) should be consulted
      for further direction. For more general information ARARs and TBCs  see the
      CERCLA Compliance with Other Laws Manual (U.S. EPA 1989d).

      OSWER Directive 9200.4-25, Use of Soil Cleanup Criteria in 40 CFR Part 192 as
      Remediation Goals for CERCLA Sites (U.S. EPA 1998c), provides more detailed
      discussion on the use of the concentration limits for radium and/or thorium in subsurface
      soils.

V.    ECOLOGICAL ASSESSMENTS

Q39.  What guidance is available for conducting ecological risk assessments?

A.    EPA is developing a Radiological Ecological Benchmark (REB) (U.S. EPA 2014b)
      calculator that will be designed to develop concentrations protective of biota from
      radioactivity at CERCLA sites. In addition, existing EPA guidance (OSWER Directive
      9285.7-25,  Ecological Risk Assessment Guidance for Superfund: Process for Designing
      and Conducting Ecological Risk Assessments, U.S. EPA 1997e) is intended  to facilitate
      defensible and appropriately scaled site-specific ecological risk assessments at CERCLA
      sites. This guidance is not intended to dictate the scale, complexity, protocols, data needs,
      or investigation methods for such assessments. Professional judgment is required to
      apply the process outlined in this guidance to ecological  risk assessments at specific
      sites. This guidance is supplemented by the guidance Ecological Risk Assessment and
      Risk Management Principle for Superfund Sites (U.S. EPA 1999b). Typical exposure
                                         -30-

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      pathways for ecological risk assessments are in Figure 3. Each of the illustrations in
      Figure 3  is expected to appear in the forthcoming guidance, together with explanatory
      text in the user guide for the ecological calculator (U.S. EPA 2014b).

VI.   BACKGROUND RADIATION

Q40.  How should background levels of radiation be addressed?

A.    Background radiation levels at a specific site generally should be determined the same way
      background levels are determined for other contaminants: on a radionuclide and
      site-specific basis when the same constituents  are found in on-site samples as well as in
      background  samples. The  levels of each constituent of potential concern at a site
      typically are compared with background levels of those constituents to determine whether
      site activities have resulted in elevated levels. For example, background levels for radium-
      226 and  radon-222 would generally not be relevant at a site if these radionuclides were
      not site-related contaminants. Remedial site risk-based cleanup levels for individual
      radionuclides generally are not set below site-specific background levels. When
      background levels exceed the remedial risk range, background levels may be selected
      as the cleanup levels. It should be noted that some ARARs specifically address how
      to factor background into cleanup levels. For example, many radiation standards are
      increments above background levels, while the indoor radon standards under 40 CFR
      192.12(b)(l) are inclusive of background.

      For further information regarding background, see the Role of Background in  the
      CERCLA Cleanup Program (U.S. EPA 2002b) and the section "Background
      Contamination"in OSWER Directive 9200.4-18 (U.S. EPA  1997a).
                                         -31-

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      Figure 3.  Typical  Radionuclide Exposure Pathways  for Biota
                     Aquatic Animals
                                                                                                         Aquatic Plants
                        in sediments
                       = Exposure to radionuclides -
                         iwatei
Internal Dose Pathways
c = Exposure to radionuclides via
         of contaminated
   vegetation including water content
   with dissolved nutrients and minerals
d - Exposure to radionuclides
   homagnified through the food web
                     Riparian Animals
Internal Dose Path1
   Exposure to radiormelides
   ingestion of contaminated
   vegetation including water content
   with dissolved nutrients and minerals
   Exposure to fadionuclldes
   bJomagnlfied through the food web
                   Terrestrial  Animals
                    Internal DOM Pathways
                    c — Exposure lo (Bdwiyd^ws via
                       vegetation including wate' content witti dissolved nutrients
                       and rnrwais
                    ti « Evrosurp to nudioriiciioe* <"» «ripMtir»ri nl cwilsnwidtwJ 'rod
                       and soi. and via Anaiatton of soil
                    e = Exposure to radioruclia.es via tngestwi of
                     External Dose Pathways
                     a - Expoiuie to r..i _i HJ- n.'.j n.ii. L- irt soil
                     b  Exposure to rodionuctides in
                                                                                                                 External Dose Pathways
                                                                                                                 a = Exposure to radionuclides
                                                                                                                    in sediments
                                                                                                                 b = Exposure to radionuclides
                                                                                                                    in water
                                                                                Internal Dose Pathways
                                                                                c ~ Exposure to radionuclides taken up
                                                                                   n water including dissolved
                                                                                   nutrients and minerals
                                                                                                                                  External Dose Pathways
                                                                                      Internal Dose Pathways

                                                                                      bs= Exposure to radionuclides taken
                                                                                         up in pore water including
                                                                                                                                    Exposure to radionuclides
                                                                                            . yen -ntnenisand mineral
                                                                      -32-

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WHERE TO GO FOR FURTHER INFORMATION

Readers should periodically consult the EPA Superfund Radiation webpage for updates
on current guidance and for copies of new documents at this address:
http://www.epa.gov/superfund/health/contaminants/radiation/index.htm.

Radiation and radioactive materials pose special hazards and require specialized detection
instrumentation, techniques and safety  precautions. EPA strongly encourages RPMs and
risk assessors to consult with individuals trained and experienced in radiation
measurements and protection. These  individuals  include health physicists and
radiochemists who can provide additional assistance in designing and executing
radionuclide sampling and analysis plans and interpreting radioanalytical results.

The subject matter specialist for this fact sheet is Stuart Walker of OSRTI. He can be reached
by e-mail at walker.stuart@epa.gov or by telephone at (703) 603-8748.
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REFERENCES

International Atomic Energy Agency (IAEA). 1992. Effects of Ionizing Radiation on Plants and
   Animals at Levels Implied by Current Radiation Protection Standards. IAEA Technical
   Report Series No. 332.

International Commission on Radiological Protection (ICRP). 1977. Recommendations of the
   ICRP. ICRP Publication 26. Pergamon Press, Oxford, UK.

International Commission on Radiological  Protection (ICRP). 1979. Limits for Intakes of
   Radionuclides by Workers.  ICRP Publication 30. Pergamon Press, Oxford, UK.

International Commission on Radiological Protection (ICRP). 1989. Age-Dependent Doses to
   Members of the Public from Intake of Radionuclides, Part 1. ICRP Publication 56. Pergamon
   Press, Oxford, UK.

International Commission on Radiological Protection (ICRP). 1991.  1990 Recommendations of
   the International Commission on Radiological Protection. ICRP Publication 60. Pergamon
   Press, Oxford, UK.

International Commission on Radiological Protection (ICRP). 1993.  Age-Dependent Doses to
   Members of the Public from Intake of Radionuclides, Part 2. ICRP Publication 67. Pergamon
   Press, Oxford, UK.

International Commission on Radiological Protection (ICRP). 1995a. Age-Dependent Doses to
   Members of the Public from Intake of Radionuclides, Part 3. ICRP Publication 69. Pergamon
   Press, Oxford, UK.

International Commission on Radiological Protection (ICRP). 1995b. Age-Dependent Doses to
   Members of the Public from  Intake of Radionuclides, Part 4. ICRP Publication 71. Pergamon
   Press, Oxford, UK.

International Commission on Radiological Protection (ICRP). 2011. Lung Cancer Risk from
   Radon and Progeny. ICRP Publication 115.
   http://www.elsevier.com/wps/fmd/bookdescription.cws  home/726672/description#description

Interstate Technology Regulatory Council (ITRC) 2006. Real-Time Measurement of Radionuclides
   in Soil: Technology and Case Studies
    http://www.itrcweb.org/Documents/RAD 4Web.pdf

Interstate Technology Regulatory Council (ITRC) 2007. Radiation Risk Assessment: Update and
   Tools
   http://www.clu-in.org/conf/itrc/rads  0515077
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Interstate Technology Regulatory Council (ITRC) 2008a. Real-Time Measurement of
   Radionuclides in Soil
   http ://www. clu-in. org/conf/itrc/radsreal time 102808/

Interstate Technology Regulatory Council (ITRC) 2008b. Decontamination and Decommissioning
   of Radiologically-Contaminated Facilities
   http://www.clu-in.org/conf/itrc/radsdd 040308/

 National Academy of Sciences (NAS). 1980. The Effects on Populations of Exposure to Low
    Levels of Ionizing Radiation: 1980. National Research Council, Committee on the Biological
    Effects of Ionizing Radiation (BEIR III). National Academy Press, Washington, DC.

 National Academy of Sciences (NAS). 1988. Health Effects of Radon and Other Internally
    Deposited Alpha-Emitters National Research Council, Committee on the Biological Effects
    of Ionizing Radiation (BEIR IV). National Academy Press., Washington, DC.

 National Academy of Sciences (NAS). 1990. Health Effects of Exposure to Low Levels of
    Ionizing Radiation. National Research Council, Committee on the Biological Effects of
    Ionizing Radiation (BEIR V). National Academy Press., Washington, DC.

 National Academy of Sciences (NAS). 1999. Health Effects of Exposure to Radon.  National
    Research Council, Committee on the Health Effects of Exposure to Radon (BEIR VI).
    National Academy Press., Washington. DC.
    http://books.nap.edu/openbook.php?isbn=0309056454

 National Council on Radiation Protection and Measurements (NCRP). 1976.  Environmental
    Radiation Measurements. NCRP Report No. 50. Bethesda, MD.

 National Council on Radiation Protection and Measurements (NCRP). 1978.  Instrumentation
    andMonitoringMethodsfor Radiation Protection.  NCRP Report No. 57. Bethesda, MD.

 National Council on Radiation Protection and Measurements (NCRP). 1987.  Exposure of the
    Population in the United States and Canada from Natural Background  Radiation. NCRP
    Report No. 94. Bethesda, MD.

 Stewart, R, N. and S. T. Purucker. 2011. "An Environmental Decision Support System for
    Spatial Assessment and Selective Remediation," Environmental Modeling & Software
    26(6): 751-760.
    http://www.sadaproject.net/

United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). 1988.
   Sources, Effects and Risks of Ionizing Radiation. United Nations, NY.

United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). 2006.
   Effects of Ionizing Radiation. Volume II: Scientific Annexes C, D, andE. United Nations, NY.
   http://www.unscear.org/unscear/en/publications/2006 2.html
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U.S. EPA. 1980. Upgrading Environmental Data: Health Physics Society Committee Report
   HPSR-1 (1980). Office of Radiation Programs, Washington, DC.

U.S. EPA. 1984. EERF Radiochemistry Procedures Manual. EPA 520/5-84-006. Office of
   Radiation Programs, Eastern Environmental Radiation Facility, Montgomery, AL.

U.S. EPA. 1988a. Guidance for Conducting Remedial Investigations and Feasibility Studies
   under CERCLA. EPA/540/G-89/004. Office of Radiation Programs, Washington, DC.
   http://rais.ornl.gov/documents/GUIDANCE.PDF

U.S. EPA.  1988b. Limiting Values of Radionuclide Intake and Air Concentration and Dose
   Conversion Factors for Inhalation, Submersion, and Ingestion: Federal Guidance Report
   No. 11. EPA-520/1-88/020. Office of Radiation Programs, Washington, DC.
   http://www.epa.gov/rpdwebOO/docs/federal/520-l-88-020.pdf

U.S. EPA. 1989a. Risk Assessment Guidance for Superfund, Volume 1: HumanHealth
   Evaluation Manual, Part A, Interim Final. EPA/540/1-89/002. Office of Emergency and
   Remedial Response, Washington, DC.  NTIS PB90-155581/ CCE.
   http://www.epa.gov/oswer/riskassessment/ragsa/pdf/rags-vol l-pta_complete.pdf

U.S. EPA. 1989b. Methods for Evaluating the Attainment of Soil Cleanup Standards. Volume 1:
   Soils and Solids. EPA/540/1-89/003. Statistical Policy Branch, Office of Policy, Planning, and
   Evaluation, Washington, DC.
   http://www.clu-in.org/download/stats/vol 1 soils.pdf

U.S. EPA. 1989c. Risk Assessment Methodology: Environmental Impact Statement-NESHAPs
   for Radionuclide s, Background Information Document-Volume 1. EPA-520/1-89-006-1.
   Office of Radiation Programs, Washington, DC.
   http://www.epa.gov/rpdwebOO/docs/neshaps/subpart-w/historical-rulemakings/risk-
   assessments-methodology-eis-neshaps-for-radionuclides.pdf

U.S. EPA. 1989d. Exposure Factors Handbook.  EPA/600/8-89/043. Office of Health and
   Environmental Assessment, Washington, DC.
   http://rais.ornl.gov/documents/EFH 1989 EPA600889043.pdf

U.S. EPA. 1989e. CERCLA Compliance with Other Laws Manual: Interim Final. EPA/540/G-
   89/006. Office of Emergency and Remedial Response, Washington, DC.
   http://www.epa.gov/superfund/policv/remedy/pdfs/540g-89006-s.pdf
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U.S. EPA. 199 la. Risk Assessment Guidance for Super fund, Volume 1: Human Health
   Evaluation Manual (Part B, Development of Risk-Based Preliminary Remediation Goals).
   Publication 9285.7-OIB. Office of Emergency and Remedial Response, Washington, DC.
   NTISPB92-963333.
   http://www.epa.gov/oswer/riskassessment/ragsb/index.htm

U.S. EPA. 1991b. Risk Assessment Guidance for Superfund, Volume 1: Human Health
   Evaluation Manual (Part C, Risk Evaluation of Remedial Alternatives). Interim. OSWER
   Directive 9285.7-01C. Office of Emergency and Remedial Response, Washington, DC.
   http://www.epa.gov/oswer/riskassessment/ragsc/index.htm

U.S. EPA. 1991c. Human Health Evaluation Manual, Supplemental Guidance: Standard Default
   Exposure Factors. OSWER 9285.6-03. Office of Emergency and Remedial Response,
   Washington, DC. NTIS PB91-921314.
   http://epa-prgs.ornl.gov/chemicals/help/documents/OSWERdirective9285.6-03.pdf

U.S. EPA. 199 Id. Role of the Baseline Risk Assessment in Superfund Remedy Selection
   Decisions. OSWER Directive 9355.0-30. Office of Solid Waste and Emergency Response.
   http://www.epa.gov/oswer/riskassessment/pdf/baseline.pdf

U.S. EPA. 1992a. Statistical Methods for Evaluating the Attainment of Cleanup Standards-
   Volume 2: Ground Water. Draft.  Statistical Policy Branch, Office of Policy, Planning, and
   Evaluation, Washington, DC.
   http ://www. clu-in. org/download/stats/vol2gw.pdf

U.S. EPA. 1992b. Statistical Methods for Evaluating the Attainment of Cleanup Standards-
   Volume 3: Reference-Based Standards for Soils and Solid Media. PB94 176831. Statistical
   Policy Branch, Office of Policy, Planning, and Evaluation, Washington, DC.
   http://www.epa.gov/tio/download/stats/vol3-refbased.pdf

U.S. EPA. 1992c. Guidance for Data Usability in Risk Assessment (Part A). Publication
   9285.7A. Office of Emergency and Remedial Response, Washington, DC.
   http://www.epa.gov/oswer/riskassessment/datause/pdf/datause-parta.pdf

U.S. EPA. 1992d. Guidance for Data Usability in Risk Assessment (Part B). Publication
   9285.78. Office of Emergency and Remedial Response, Washington, DC.
   http://www.epa.gov/oswer/riskassessment/datause/pdf/datause-partb.pdf

U. S. EPA. Implementing the Deputy Administrator's Risk Characterization Memorandum.
   Memorandum from H.L. Longest, Director of Office  of Emergency and Remedial
   Response, Washington, DC, 5/26/92.
   http://www.epa.gOv/oswer/riskassessment/pdf/l 992_0526_risk_characterization_memo.pdf

 U.S. EPA. 1993a. Data  Quality Objectives for Superfund, Interim Final Guidance. EPA 504-R-
     93/071. Office of Emergency and Remedial Response, Washington, DC.NTIS PB94-963203.
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 U.S. EPA.  1993b. External Exposure to Radionuclides in Air, Water, and Soil: Federal
     Guidance Report No. 12. EPA-402-R-93-081. Office of Air and Radiation, Washington, DC.
     http://www.epa.gov/rpdwebOO/docs/federal/402-r-93-081.pdf

 U.S. EPA. 1994a. Guidance for the Data Quality Objectives Process. EPA QA/G4. Office of
     Research and Development.
     http://www.epa.gov/osw/hazard/correctiveaction/resources/guidance/qa/epaqag4.pdf

U.S. EPA. 1994b. Estimating Radiogenic Cancer Risks. EPA 402-R-93-076. Office of Radiation
     and Indoor Air, Washington, DC.
     http://www.epa.gov/rpdwebOO/docs/assessment/402-r-93-076.pdf

U.S. EPA. 1995a. EPA Risk Characterization Program. Memorandum from CarolBrowner, Office
     of the Administrator, Washington, DC, 3/21/95.
     http://www.epa.gov/oswer/riskassessment/pdf/1995  0521 risk  characterization_program.pd
     f

U.S. EPA. 1995b. Guidance for Risk Characterization. Science Policy Council, February 1995.
     http://www.epa.gov/spc/pdfs/rcguide.pdf

U.S. EPA. 1996. Radiation Exposure and Risk Assessment Manual: Risk Assessment Using
     Radionuclide Slope Factors. EPA 402-R-96-016, Office of Radiation and Indoor Air,
     Washington, DC, June 1996.

U.S. EPA. 1991 &. Establishment of Cleanup Levels for CERCLA Sites with Radioactive
     Contamination, OSWERNo. 9200.4-18, August 22, 1997.
     http://www.epa.gov/superfund/health/contaminants/radiation/pdfs/radguide.pdf

U.S. EPA. 1997b. Exposure Factors Handbook  (Update). EPA/600/P-95/002F. Office of
     Research and Development, Washington, DC, August  1997.

U.S. EPA. 1997c. Use of Probabilistic Techniques (Including Monte Carlo Analysis) in Risk
     Assessment, Memorandum from Deputy Administrator Hansen, August 1997.
     http ://www. epa. gov/spc/pdfs/probcovr. pdf

U.S. EPA. 1997d. Guiding Principles for Monte Carlo Analysis, EPA/630/R-97-001.
     http ://www. epa. gov/ncea/pdfs/montcarl .pdf

U.S. EPA. 1997e. Ecological Risk Assessment Guidance for Superfund: Process for Designing
     and Conducting Ecological Risk, OSWER Directive 9285.7-25,
     http://www.epa.gov/oswer/riskassessment/ecorisk/pdf/intro.pdf
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U.S. EPA. 1997 f. Clarification of the Role of Applicable, or Relevant and Appropriate
     Requirements in Establishing Preliminary Remediation Goals under CERCLA, OSWERNo.
     9200.4-23, August 22, 1997.
     http://www.epa.gov/superfund/health/contatninants/radiation/pdfs/aras.pdf

U.S. EPA. 1997'g. Memorandum from James E. Woolford, Office of Restoration and Reuse, and
     Stephen D. Luftig, Office of Emergency and Remedial Response, Washington, DC. to
     Raymond P. Berube, U.S. Department of Energy.  12/12/1997.
     http://www.epa.gov/superfund/health/contaminants/radiation/pdfs/EPA1997g.pdf
U.S. EPA. 1998a. Risk Assessment Guidance for Superfund, Volume 1: Human Health
     Evaluation Manual, Part D, Standardized Planning, Reporting, and Review of Superfund
     Risk Assessments. Publication 9285.7-01D. NTIS PB97-963305. Office of Emergency and
     Remedial Response, Washington, DC.
     http://www.epa.gov/oswer/riskassessment/ragsd/index.htm

U.S. EPA. 1998b. Risk Assessment Guidance for Superfund, Volume 1: Human Health
     Evaluation Manual, Part E, Supplemental Guidance to RAGS: The  Use of Probabilistic
     Analysis in Risk Assessment. (Working Draft). Office of Emergency and Remedial
     Response, Washington, DC.
     http://www.epa.gov/oswer/riskassessment/ragse/index.htm

U.S. EPA. 1998c. Use of Soil Cleanup Criteria in 40 CFR Part 192 as Remediation Goals for
     CERCLA Sites, OSWER Directive No. 9200.4-25, February 1998.
     http://www.epa.gov/superfund/health/contaminants/radiation/pdfs/umtrcagu.pdf

U.S. EPA. 1998e. Integrated Risk Information System (IRIS). Cincinnati, OH.
     http ://www. epa.gov/IRIS/
     http ://www. epa. gov/rpdwebOO/heast/index.html

U.S. EPA. 1998f. Health Effects Summary Tables (HEAST); Annual Update, FY1998.
     Environmental Criteria and Assessment Office, Office of Health and Environmental
     Assessment, Office of Research and Development, Cincinnati, OH.
     http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=2877

U.S. EPA. 1999a. Radiation Risk Assessment at CERCLA Sites: Q&A, Office of Emergency and
     Remedial Response and Office of Radiation and Indoor Air. Washington, DC. OSWER
     Directive 9200.4-3 IP,
     http://www.epa.gov/superfund/health/contaminants/radiation/pdfs/riskqa.pdf

U.S. EPA. 1999b. Ecological Risk Assessment and Risk Management Principle for Superfund
     Sites, OSWER Directive 9285.7-28P,
     http://www.epa.gov/oswer/riskassessment/ecorisk/pdf/fmal99.pdf
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U.S. EPA. 1999c. Cancer Risk Coefficients for Environmental Exposure to Radionuclides:
     Federal Guidance Report No. 13. EPA 402-R-99-001. Office of Air and Radiation,
     Washington, DC.
     http ://www. epa. gov/radiation/federal/techdocs.html#report 13

U.S. EPA. 1999d. Distribution of OSWER Radiation Risk Assessment at CERCLA Sites Q&A
     Final Guidance, Memorandum from Stephen D. Luftig, Office of Emergency and
     Remedial Response and Stephen D. Page, Office of Radiation and Indoor Air.
     Washington, DC. 127 17/1999
     http://www.epa.gov/superfund/health/contaminants/radiation/pdfs/EPA1999d.pdf

U.S. EPA. 2000a.  Soil Screening Guidance for Radionuclides: User's Guide. Office of
     Emergency and Remedial Response and Office of Radiation and Indoor Air. Washington,
     DC. OSWER No. 9355.4-16A
     http://www.epa.gov/superfund/health/contaminants/radiation/pdfs/ssuserguide.pdf

U.S. EPA. 2000b.  Soil Screening Guidance for Radionuclides: Technical Background
     Document. Office of Emergency and Remedial Response and Office of Radiation and
     Indoor Air. Washington, DC. OSWER No. 9355.4-16
     http://www.epa.gov/superfund/health/contaminants/radiation/pdfs/sstbd.pdf

U.S. EPA. 2000c. Guidance for Data Quality Assessment. EPA QA/G9. Quality Assurance
     Management Staff, Office of Research and Development, Washington, DC. EPA/600/R-
     96/084
     http://www.clu-in.org/conf/tio/pasi  121603/g9-fmal.pdf

U.S. EPA, NRC, U.S. DOE, and U.S. Department of Defense. 2000d. Multi-Agency Radiation
     Survey and Site Investigation Manual (MARSSIM). NUREG-1575, EPA 402-R-97-016,
     Rev.l Washington, DC.
     http://www.epa.gov/radiation/marssim/obtain.html

U.S. EPA. 2000e.  Soil Screening Guidance for Radionuclides electronic calculator.
     http ://rais. ornl. gov/rad_start. shtml

U.S. EPA. 2000f Memorandum from Robert Perciasepe, Office of Air and Radiation and
     Timothy Fields, Jr. Office of Solid Waste and Emergency Response, Washington, DC. to
     Charles M. Hardin, Conference of Radiation Control Program Directors. 7/7/2000
     http://www.epa.gov/superfund/health/contaminants/radiation/pdfs/EPA2000f.pdf

U.S. EPA. 2002a Radionuclide Preliminary Remediation Goals (PRGs) for Superfund
     electronic calculator.
     http://epa-prgs.ornl.gov/radionuclides/

U.S. EPA. 2002b Role of Background in the CERCLA Cleanup Program.  Office of Emergency
     and Remedial Response. OSWER 9285.6-07P
     http://www.epa.gov/oswer/riskassessment/pdf/bkgpol janOl.pdf
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U.S. EPA. 2002c SimulatingRadionuclide Fate and Transport in the UnsaturatedZone:
     Evaluation and Sensitivity Analyses of Select Computer Models
     http://www.epa.gov/nrmrl/pubs/600r02082/600R02082-full.pdf

U.S. EPA 2003. World Trade Center Indoor Environmental Assessment: Selecting
     Contaminants of Potential Concern and Setting Health-Based Benchmarks. Prepared by
     the Contaminants of Potential Concern (COPC) Committee of the World Trade Center
     Indoor Air Task Force Working Group.
     http ://www. epa. gov/wtc/copc_benchmark. pdf

U.S. EPA. 2004a Radionuclide ARARDose Compliance Concentrations (DCCs) for Superfund
     electronic calculator.
     http://epa-dccs.ornl.gov/

U.S. EPA, NRC, U.S. DOE, and U.S. Department of Defense. 2004b. Multi-Agency Radiation
     Laboratory Analytical Protocols (MARLAP). Washington, DC.
     http ://www. epa. gov/rpdwebOO/marlap/manual. html#voli_chaps

U.S. EPA. 2004c. Distribution ofOSWER Radionuclide ARAR Dose Compliance Concentrations
     (DCCs) for Superfund Electronic Calculator. OSWER 9355.0-86A, January 28, 2004.
     http://www.epa.gov/superfund/health/contaminants/radiation/pdfs/dccmemo.pdf

U.S. EPA. 2005a. Superfund Radiation Risk Assessment and How You Can Help: An Overview.
     http://www.epa.gov/superfund/health/contaminants/radiation/radvideo.htm

U.S. EPA. 2005b. Uniform Federal Policy for Implementing Environmental Quality Systems:
     Evaluating, Assessing, and Documenting Environmental Data Collection/Use and
     Technology Programs. EPA: EPA-505-F-03-001, DoD: DTIC ADA 395303, DOE:
     DOE/EH-0667, Version 2 Washington, DC.
     http://www.epa.gov/superfund/health/contaminants/radiation/radvideo.htm

U.S. EPA. 2006. Inventory of Radiological Methodologies for Sites Contaminated with Radioactive
     Materials. EPA 402-R-06-007 October 2006
     http ://www. epa.gov/narel/IRM Final.pdf

U.S. EPA 2007. Preliminary Remediation Goals for Radionuclides in Buildings (BPRG)
     electronic calculator.
     http ://epa-bprg. ornl. gov/

U. S. EPA 2008. Regional Screening Levels for Chemical Contaminants at Superfund Sites
     (RSL) electronic calculator.
     http://www. epa.gov/reg3hwm d/risk/human/rb-concentration_table/index. htm

U.S. EPA 2009a. Preliminary Remediation Goals for Radionuclides in Outdoor Surfaces
     (SPRG) electronic calculator.
     http://epa-sprg.ornl.gov/
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U.S. EPA, NRC, U.S. DOE, and U.S. Department of Defense. 2009b. Multi-Agency Radiation
     Survey and Assessment of Materials and Equipment Manual (MARSAME). NUREG-
     1575, Supp. 1, EPA 402-R-09-001, Washington, DC.
     http://www.epa.gov/rpdwebOO/marssim/marsame.html

U.S. EPA 2010a. ARAR Dose Compliance Concentrations Goals for Radionuclides in
     Buildings (BDCC) electronic calculator.
     http://epa-bdcc.ornl.gov/

U.S. EPA 2010b. ARAR Dose Compliance Concentrations Goals for Radionuclides in
     Buildings (SDCC) electronic calculator.
     http://epa-sdcc.ornl.gov/

U.S. EPA 2014a. Draft Counts Per Minute (CPM) electronic calculator.

U.S. EPA 2014b. Draft Ecological Benchmarks for Radionuclides electronic calculator.
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                                  APPENDIX A:
                      EPA's Recommended Guidance for
           Radiation Risk Assessment at CERCLA Remedial Sites
•  The Preliminary Remediation Goals (PRGs)for Radionuclides electronic calculator, known
   as the Rad PRG calculator (U.S. EPA 2002a). This electronic calculator presents risk-based
   standardized exposure parameters and equations that should be used for calculating
   radionuclide PRGs for residential, commercial/industrial, agricultural, tap water, and fish
   ingestion exposures. The calculator also presents soil PRGs that protect groundwater, which
   are determined by calculating the concentration of radioactively contaminated soil subject to
   leaching to groundwater that will meet maximum contaminant levels (MCLs) or risk-based
   concentrations.

•  The Building Preliminary Remediation Goals for Radionuclides (BPRG) electronic calculator
   (U.S. EPA 2007).  The BPRG calculator helps standardize the evaluation and cleanup of the
   interiors of radiologically contaminated buildings where risk is being assessed for occupancy.
   BPRGs are radionuclide concentrations in dust, air, and building materials that correspond to
   a specified level of human cancer risk.

•  The Radionuclide Outdoor Surfaces Preliminary Remediation Goals (SPRG)  electronic
   calculator (U.S. EPA 2009a). The SPRG calculator was developed to address radionuclide
   concentrations in dust on and within hard outside surfaces such as building slabs, outside
   building walls, sidewalks, and roads.

•  Soil Screening Guidance for Radionuclides contains both a User's Guide and Technical
   Background Document, (known as the Rad SSG documents) that provide information on soil
   screening for radionuclides at CERCLA sites (U.S. EPA 2000a, 2000b). The risk assessment
   equations and the  soil screening levels (SSLs) in this guidance have been superseded by the
   Rad PRG calculator;

•  ARAR Dose Compliance Concentrations for Radionuclides (DCC) electronic  calculator (U.S.
   EPA 2004a). The DCC calculator equations are identical to those in the PRG  for
   Radionuclides, except that the applicable or relevant and appropriate requirement (ARAR)
   based target dose rate (in millirems per year or mrem/yr) is substituted for the target cancer
   risk (1  x 10"6), the period of exposure is 1 year to indicate year of peak dose, and a Dose
   Conversion Factor (DCF) is used in place of the slope factor. The  DCC calculator presents
   standardized exposure parameters and equations that should be used for calculating
   radionuclide DCCs for residential, commercial/industrial, agricultural, tap water, and fish
   ingestion exposures.

•  ARAR Dose Compliance Concentrations for Radionuclides in Buildings (BDCC) electronic
   calculator (U.S. EPA 2010a), known as the BDCC calculator, was developed  to present
   standardized exposure parameters and equations that should generally be used for calculating
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   radionuclide BDCCs for interiors of contaminated buildings with either a residential or a
   commercial/industrial use.

•  ARAR Radionuclide Outdoor Surfaces Dose Compliance Concentrations for Radionuclides
   (SDCC) electronic calculator (U.S. EPA 201 Ob), known as the SDCC calculator, was
   developed to present standardized exposure parameters and equations that should generally be
   used for calculating radionuclide SDCCs for outside hard surfaces (such as building slabs,
   outside building walls, sidewalks, and roads) with either a residential or a
   commercial/industrial use.

•  Chapter 10, "Radiation Risk Assessment Guidance" of RAGS Part A (U.S. EPA 1989a)
   which covers data collection and evaluation, exposure and dose assessment, toxicity
   assessment, and risk characterization for sites contaminated with radioactive substances.

•  Chapter 4, "Risk-based PRGs for Radioactive Contaminants," of RAGS Part B (U. S. EPA,
   199la) which presents standardized exposure parameters and equations that should generally
   be used for calculating PRGs for radionuclides under residential and commercial/industrial
   land use exposure scenarios. This guidance has been superseded by the PRG, BPRG, and
   SPRG calculators.

•  Appendix D, "Radiation Remediation Technologies," of RAGS Part C (U.S. EPA 1991b),
   which provides guidance on using risk information to evaluate and select remediation
   technologies for sites with radioactive substances.

•  RAGS Part D, Standardized Planning, Reporting, and Review  of Superfund Risk Assessments
   (U.S. EPA, 1998a), which provides guidance on standardized  risk assessment planning,
   reporting, and review throughout the  CERCLA process.

•  Superfund Radiation Risk Assessment and How You Can Help: An Overview (U.S. EPA,
   2005a) is a video that explains to the  public the Superfund risk assessment process and how
   the public can help inform the risk assessment process.
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