United States Science Advisory EPA-SAB-RAC-ADV-M-OO*
Environmental Board February 1091
Protection Agency Washington. DC Mww.epa.gov/iMfe
•&EPA AN SAB ADVISORY:
Modeling of Radionuclide
Releases from Disposal of
Low Activity Mixed Waste
us EPA Headquarters Ubrary
ADVISORY ON THE OFFICE OF
RADIATION AND INDOOR AIR'S
DRAFT PROPOSALS ON
MODELING OF RADIONUCLIDE
RELEASES FROM DISPOSAL OF
LOW ACTIVITY MIXED WASTE BY
THE RADIATION ADVISORY
COMMITTEE
-------
-------
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
February 22,1999
EPA-SAB-RAC-ADV-99-006
OFFICE OF THE ADMINISTRATOR
Honorable Carol M. Browner • SCIENCE ADVISORY BOARD
Administrator
U.S. Environmental Protection Agency
401 M. Street, S.W.
Washington, DC 20460
Re: Advisory on Modeling of Radionuclide Releases from Disposal of Low Activity
Mixed Waste (LAMW)
Dear Ms. Browner:
The enclosed Advisory was developed by the Radiation Advisory Committee (RAC) of
the Science Advisory Board (SAB) in response to a request from the Office of Radiation and
Indoor Air (ORIA) to provide advice on the modeling of low activity mixed radioactive waste
(LAMRW) and specifically to respond to a three element Charge, summarized below (the detailed
Charge may be found in Section 2.2 of the enclosed report:
a) Does the EPA dose assessment reasonably cover the range of hydrogeologic and
climatic settings that might be used for disposal of low-activity mixed waste?
b) What modeling time frame does the Committee recommend be used to project
potential doses from disposal of low-activity mixed waste? Does a 1000-year time
frame provide an adequate technical basis for setting regulatory limits?
c) Is it reasonable to assign a "high" release rate for the duration of the simulation?
Does the SAB advise an alternative approach?
The RAC held a public meeting on November 17, 18, and 19,1998 at which it was briefed
by, and had technical discussions, with ORIA staff, as well as a writing session by the Committee.
A public teleconference was also held on December 15, 1998. The advisory generated by this
meeting responds both to the three Charge questions, as well as addressing other issues identified
during the public meeting.
ORIA conducted analyses for three sites, based on the hydrogeologic and climatic
characteristics of well-characterized Department of Energy (DOE) sites selected from a group of
ten such sites analyzed in a screening study. The Committee concluded that these sites do not
necessarily cover the range of conditions that might be encountered at current or future RCRA-C
facilities. For example, they include no sites outside the conterminous United States, and
probably do not cover the range of possibilities for depth to groundwater, existence of snowpack
PriflMd en P9trtlul eamm
« httt 75% ncyctod flxr
-------
and freeze-thaw cycles, or soil composition in which RCRA-C facilities are or could be sited.
Moreover, the modeling as conducted does not consider such other site characteristics as soil and
waste pH, redox conditions, the presence of reactive organic matter, and biological activity. The
Committee recommends that ORIA conduct at least screening analyses of the extent to which
these factors could affect radionuclide migration rates. Furthermore, Charge a), as framed by
ORIA seems overly narrow. Although it is desirable to select sites to bound important potential
site conditions and characteristics, the ultimate goal should be to bound probable site
performance. ORIA should consider enhancing its approach to include additional site
characteristics.
The Committee concluded that a sensitivity analysis of the modeling time frame could
provide potentially useful information on the variation of peak dose with time horizon, especially
for less mobile radionuclides with long half-lives. The Committee did not reach consensus,
however, on how ORIA should weigh projections for the longer periods against the more reliable
projections for shorter periods. All members agreed that under the modeling assumptions used by
ORIA, peak doses for some radionuclides might occur after 1,000 years and be significantly
higher than at 1,000 years. While some members stated that this scientific conclusion was
sufficient to extend the modeling time frame to 10,000 years or beyond, others emphasized that
uncertainties inherent not only in the modeling assumptions but also about future scientific and
social changes could make the results irrelevant. Consequently, the Committee's advice is limited
to suggesting issues that should be considered in ORIA's eventual decisions about LAMW.
Among them are:
a) Characterization of the candidate wastes with respect to concentrations and total
inventories of long-lived radionuclides,
b) Harmonization of the modeling time frame between-radioactive and hazardous
wastes,
c) Consideration of uncertainties about not only the validity of the technical
assumptions but also in the relevant medical and social conditions far in the future,
d) Consideration of issues about site ownership, and
e) Appropriate degree of conservatism given the policy intent of the proposed
LAMW disposal option.
The Committee believes that changes in assumptions about the time course of concrete
degradation might significantly affect predictions of the time to peak dose or its magnitude. The
assumption of a constant rate of release relative to the remaining inventory of a radionuclide could
either overestimate or underestimate peak dose, depending on the half life of the parent
radionuclide and the characteristics of its progeny. The Committee recommends that a simulation
-------
be performed to verify, at least qualitatively, that the constant loss rate assumption is reasonably—
but not excessively-conservative. Other assumptions, such as an exponential deterioration
model, could also be considered, although selection of a technically defensible deterioration rate
could be problematic because it could be a complicated function of physical, geochemical, and
thermal factors.
The Committee's major findings and recommendations concerning those issues not
included in the Charge include:
a) ORIA should better justify the choice of the PRESTO model as the principal tool
for the analysis. Benchmarking of the model through comparison with other
models of similar intent would be useful, as would demonstration that its scope of
applicability is appropriate.
b) ORIA should consider using a classification of radionuclides according to half-life
as a refinement of the "unity rule" for determining the acceptability of wastes with
more than one important radionuclide.
c) ORIA should consider whether the total quantity of waste to be emplaced in a
RCRA-C facilities, not just its radionuclide concentrations, should be part of the
decision process. Moreover, the potential presence of non-stabilized hazardous
wastes in a solid waste management unit (SWMU) near to LAMW RCRA-C
SWMUs should be considered.
d) Various modeling assumptions should be re-examined, including ones about
segregated vs. random emplacement, the amount of waste potentially subject to
disposal as LAMW, the composition of such wastes, and the classification of
radionuclides as mobile or immobile.
e) Given the wide range of environments that might be found at current or future
RCRA-C sites, ORIA might be well advised to propose two sets of concentration
criteria, one valid for relatively dry sites with deep groundwater and another for
wet sites. The latter might be able to accept only wastes with short-lived
radionuclides.
f) The modeling effort may be an opportunity for EPA to examine the similarities and
differences in radioactive waste and hazardous waste control systems and waste
acceptance criteria and to harmonize them to the extent feasible. Additional
classes of waste could also be analyzed within the modeling structure.
g) ORIA should take care not to create an incentive for a generator to produce a
waste classifiable as LAMW that would otherwise be simply Low-Level
Radioactive Waste (LLRW). It should also examine whether redefining the waste
-------
would change the liability distribution between waste generators and disposal
facility operators.
The RAC appreciates the opportunity to provide this advisory to you and we hope that it
will be helpful. We look forward to the response of the Assistant Administrator for Air and
Radiation to the advisory in general and to the specific comments and recommendations in this
letter in particular.
Sincerely,
Dr. Joan M. Daisey, Chair
Science Advisory Board
Dr. Stephen L. Brown, Chair
Radiation Advisory Committee
-------
NOTICE
This report has been written as part of the activities of the Science Advisory Board, a
public advisory group providing extramural scientific information and advice to the Administrator
and other officials of the Environmental Protection Agency. The Board is structured to provide
balanced, expert assessment of scientific matters related to problems facing the Agency. This
report has not been reviewed for approval by the Agency and, hence, the contents of this report
do not necessarily represent the views and policies of the Environmental Protection Agency, nor
of other agencies in the Executive Branch of the Federal government, nor does mention of trade
names or commercial products constitute a recommendation for use.
-------
ABSTRACT
On November 17-19, 1998, the Science Advisory Board's Radiation Advisory Committee
conducted an advisory of the Office of Radiation and Indoor Air's (ORIA) modeling of low
activity mixed waste, including: dose assessment over a wide range x>f disposal site-specific
hydrogeologic and climatic settings; the 1000 year modeling time frame; and using a "high"
release rate from concrete for the modeling.
The Committee found that the sites modeled do not necessarily cover the range of
conditions that might be encountered at RCRA-C facilities. It recommends that ORIA should
further assess the impact of site-specific conditions to bound probable site performance better.
While the Committee did not reach consensus on the modeling time frame, it recommends that
ORIA consider: conducting a sensitivity analysis to address the variation of peak dose with time;
improving its waste characterization; the relationship between radioactive and hazardous waste
modeling time frames; uncertainties in its technical assumptions and future medical and social
conditions; site ownership; and its degree of conservatism given the intent of the proposal. The
Committee recommends that ORIA perform a simulation to verify that its assumptions about the
releases from concrete are reasonably conservative.
Beyond the Charge, the Committee recommends that ORIA: better justify choosing the
PRESTO model; consider classifying radionuclides according to half-life; consider whether the
total quantity of waste as well as its radionuclide concentrations should be part of the decision
process; re-examine certain modeling assumptions; propose concentration criteria addressing
"dry" and "wet" sites; and compare control systems and acceptance criteria for radioactive and
hazardous wastes.
KEY WORDS:
low activity mixed wastes; hazardous waste facilities; Resource
Conservation and Recovery Act, Subtitle C (RCRA-C); low level
radioactive waste; modeling of potential releases of radionuclides.
-------
U.S. ENVIRONMENTAL PROTECTION AGENCY
SCIENCE ADVISORY BOARD
RADIATION ADVISORY COMMITTEE
November 17-19,1998, and December IS, 1998
CHAIR
Dr. Stephen L. Brown, Director, Risks of Radiation and Chemical Compounds, Oakland, CA
MEMBERS AND CONSULTANTS
Dr. William J. Bair, Retired, Richland, WA
Dr. Vicki M. Bier, Associate Professor of Industrial Engineering and Engineering Physics,
University of Wisconsin, Dept. of Industrial Engineering, Madison, WI
Dr. June Fabryka-Martin,1 Staff Scientist, Los Alamos National Laboratory, Los Alamos
National Laboratory, Los Alamos, NM
Dr. Thomas F. Gesell, Professor of Health Physics and Director, Technical Safety Office, Idaho
State University, Pocatello, ID
Dr. F. Owen Hoffman, President and Director, SENES Oak Ridge, Inc., Center for Risk
Analysis, Oak Ridge, TN
Dr. Janet Johnson, Senior Radiation Scientist, Shepherd Miller, Inc., Ft. Collins, CO
Dr. Donald Langmuir,1 President, Hydrocfiem Systems Corp., Golden, CO
Dr. Jill Lipoti, Assistant Director for Radiation Protection Programs, Div. of Environmental
Safety, Health and Analytical Programs, New Jersey Dept. of Environmental Protection,
Trenton, NJ
Dr. Ellen Mangione, M.D., M.P.H.,' Director, Disease Control & Environmental Epidemiology
Division, Colorado Department of Public Health and Environment, Denver, CO
Dr. Paul J. Merges, Director, Bureau of Radiation and Hazardous Site Management, Division of
Solid & Hazardous Materials, New York State Department of Environmental
Conservation, Albany, NY
Dr. John W. Poston, Sr.,l Professor and Head, Dept. of Nuclear Engineering, Texas A&M
University, College Station, TX
Did not attend meetings, but provided comments in the review.
Ill
-------
Dr. Genevieve S. Roessler, Radiation Consultant, Elysian, MN
EHC Liaison
Dr. David G. Hoel, Distinguished University Professor, Department of Biometry &
Epidemiology, Medical University of South Carolina, Charleston, SC
EEC Liaisons
Dr. Hilary L Inyang,1 Director, Center for Environmental Engineering and Science
Technologies (CEEST), University of Massachusetts, Lowell, MA
Dr. Calvin C. Chien, Senior Environmental Fellow, E.I. DuPont Company, Wilmington, DE
Former Chair
Dr. James E. Watson, Jr.,2 Professor, Department of Environmental Sciences and Engineering,
University of North Carolina at Chapel Hill, Chapel Hill, NC
Science Advisory Board Staff
Dr. K. Jack Kooyoomjian, Designated Federal Officer, Science Advisory Board, U.S. EPA,
Washington, DC
Mr. Samuel Rondberg^Designated Federal Officer, Science Advisory Board, U.S. EPA,
Washington, DC
Ms. Diana L. Fozun, Management Assistant, Science Advisory Board, U.S. EPA, Washington,
DC
Did not participate in this review.
Provided editorial support in the preparation of this report, but did not participate in die review.
iv
-------
TABLE OF CONTENTS
1. EXECUTIVE SUMMARY 1
2. INTRODUCTION , 6
2.1 Background 6
2.2 Charge to the SAB 7
3. DETAILED FINDINGS AND RECOMMENDATIONS 8
3.1 Extent of the EPA Dose Assessment (Question a) ... ., 8
3.2 Suitability of the 1000-year Time Frame (Question b) 11
3.2.1 Scientific Issues 12
3.2.2 Future Health Risk and Land Ownership Considerations 14
3.2.3 Public Acceptance 14
3.2.4 Economic Considerations 15
3.3 Modeling Release Rates (Question c) 15
3.3.1 Technical Issues 16
3.3.2 Science Policy Issues 18
3.4 Additional Issues 19
3.4.1 Modeling Structure 19
3.4.2 Science Policy Issues 21
3.4.3 Other Policy Issues 23
APPENDIX A-DETAILED COMMENTS A-l
APPENDDC B - TOTAL SYSTEM PERFORMANCE ASSESSMENT APPROACH B-l
REFERENCES R-l
-------
-------
1. EXECUTIVE SUMMARY
The Office of Radiation and Indoor Air (ORIA) is considering a proposal to allow certain
commercial low activity mixed wastes (LAMW) to be disposed of in facilities permitted as
hazardous waste facilities under the Resource Conservation and Recovery Act, Subtitle C
(RCRA-C). LAMW is waste that is currently classified as hazardous under RCRA and as
radioactive waste under the Atomic Energy Act (AEA). Only a subset of the waste classified as
Class A low level radioactive waste (LLRW) would qualify, and the RCRA-C facility would have •
to obtain a (presumably simplified) license for radioactive waste from the Nuclear Regulatory
Commission or an Agreement State.
In support of its decision, ORIA is conducting modeling of potential releases of
radionuclides from such wastes to establish radionuclide concentration criteria for waste
acceptance. Before proceeding further, ORIA sought advice from the Science Advisory Board's
(SAB) Radiation Advisory Committee (RAC) on three questions regarding modeling procedures
and assumptions. The Committee's advice on these questions and on some related broader issues
is summarized below.
Charge question (a) asked:
Having relied on extensive site characterization data from existing and potential low-
level radioactive -waste disposal landfills, does the EPA dose assessment reasonably
cover the range of hydrogeologic and climatic settings that might be used for disposal of
low-activity mixed-waste?
ORIA conducted analyses for three sites based on the hydrogeologic and climatic
characteristics of well-characterized Department of Energy (DOE) sites selected from a group of
ten such sites analyzed in a screening study. The Committee concluded that these sites do not
necessarily cover the range of conditions that might be encountered at current or future RCRA-C
facilities. For example, they include no sites outside the conterminous United States, and
probably do not cover the range of possibilities for depth to groundwater, existence of snowpack
and freeze-thaw cycles, or soil composition in which RCRA-C facilities are or could be sited.
Moreover, the modeling as conducted does not consider the effects of such other site
characteristics, such as soil and waste pH, redox conditions, the presence of reactive organic
matter, and biological activity. The Committee recommends that ORIA take a broader look at the
range of radionuclide leaching and transport behaviors that might occur at real RCRA-C sites.
Furthermore, Question a), as framed by ORIA, seems overly narrow. While it is desirable to
select sites to bound important potential site conditions and characteristics, the ultimate goal
should be to bound probable site performance. Based on the approach being taken, it may be
difficult to develop predictions of the long-term performance of a mixed waste disposal site.
ORIA should also consider using more comprehensive decision schemes such as Total Systems
Performance Assessment. However, the Committee is not recommending that the modeling
-------
exercise include site characteristics that would clearly be found unacceptable for future RCRA-C
facilities.
Charge question (b) asked:
What modeling time frame does the Committee recommend be used to project potential
doses from disposal of low-activity mixed waste? Does a J 000-year time frame provide
an adequate technical basis for setting regulatory limits?
The Committee concluded that a sensitivity analysis of the modeling time frame could
provide potentially useful information on the variation of peak dose with time horizon, especially
for less mobile radionuclides with long half-lives. The Committee did not reach consensus,
however, on how ORIA should weigh projections for the longer periods against the more reliable
projections for shorter periods. All members agreed that under the modeling assumptions used by
ORIA, peak doses for some radionuclides might occur after 1,000 years and be significantly
higher than at 1,000 years. While some members stated that this scientific conclusion was
sufficient to extend the modeling time frame to 10,000 years or beyond, others emphasized that
there are uncertainties not only in the modeling assumptions but also about future scientific and
social changes that could make the modeling results irrelevant. Consequently, the Committee's
advice is limited to suggesting issues that should be considered in ORIA's eventual decision. The
issues fall into four categories: scientific, future land use, public acceptance, and economic
viability, and are explained in detail in Section 3. Major considerations include the following
items:
a) ORIA should attempt to characterize the wastes that might fall under the proposed
disposal option. If these wastes rarely contain long-lived radionuclides, then a
shorter modeling time frame is more easily supported, while a substantial
complement of long-lived radionuclides would argue for a longer time frame or a
constraint on the waste to prevent disposal of such radionuclides.
b) ORIA and other offices of EPA should consider the issue of harmonizing the time
horizons used in analyzing the risks of radionuclides and hazardous wastes. For
instance, lead has an infinite half life and has many other characteristics in common
with long-lived radionuclides.
c) Uncertainties about not only radipnuclide releases and pathways of exposure but
also medical and social conditions grow greatly as the modeling time frame is
extended. Does modeling to 1,000 or 10,000 years help or hinder public
acceptance of the results?
d) The requirements for site ownership differ between radioactive waste disposal and
hazardous waste disposal, with radioactive wastes being more likely to remain
under government control. Should this difference argue for a longer modeling
time frame, consistent with other analyses of radioactive waste?
-------
e) The proposed alternative for LAMW disposal will be useful to waste generators
only to the extent that they can dispose of waste less expensively and/or more
easily than under current regulations. Excessive conservatism in modeling
assumptions, including the time frame, may exclude most waste from the proposed
disposal option. On the other hand, if modeling to 1,000 years or less does not
convince the public to accept radioactive wastes into RCRA-C facilities, the
contemplated rulemaking will also be in vain.
Charge question (c) asked:
Given the modeling approach described [in the Agency's presentation], and the available
knowledge regarding concrete durability and modes of degradation, is it reasonable to
assign a "high" release rate for the duration of the simulation? Does the SAB advise an
alternative approach, such as assuming a lower release at the start and increasing it
incrementally over the modeling period, thereby mimicking the gradual deterioration of
the concrete?
The Committee believes that changes in assumptions about the time course of concrete
degradation might significantly affect predictions of the time to peak dose or its magnitude. The
assumption of a constant rate of release relative to the remaining inventory of a Radionuclide,
even when its quantity and half-life are taken into consideration, could either overestimate or
underestimate peak dose, depending on the half life of the parent radionuclide and the
characteristics of its progeny. The Committee recommends that a simulation be performed to
verify, at least qualitatively, that the constant loss rate assumption is reasonably—but not
excessively—conservative. Other assumptions, such as an exponential deterioration model, could
also be considered. The Committee recognizes that selection of a technically defensible
deterioration rate could be problematic because it could be a complicated function of physical,
geochemical, and thermal factors. The Committee also notes that the concrete deterioration
assumptions interact with the containment failure assumptions; the timing of water infiltration
through the cap and leakage through the liners could affect the rate of concrete deterioration as
well as its significance. Finally, ORIA should consider how to deal with wastes that are not
ordinarily disposed of in concrete containment. Will such wastes simply be excluded from
consideration under the contemplated rule? If not, are the assumptions about concrete
degradation conservative in comparison with the expected behavior of the actual containment?
During the public meetings, the Committee identified and discussed several issues not
incorporated in the Charge; these issues are discussed below.
The Committee reached some conclusions and related recommendations about the LAMW
modeling approach that go beyond the original three questions of the Charge. They include
comments on the overall modeling structure as well as science policy and environmental policy
questions.
-------
The Committee believes that ORIA should better justify the choice of the PRESTO model
as the principal tool for the analysis. Benchmarking of the model through comparison with other
models of similar intent would be useful, as would demonstration that its scope of applicability is
appropriate.
ORIA should consider using a classification of radionuclides according to half-life as a
refinement of the "unity rule" for determining the acceptability of wastes with more than one
important radionuclide. Otherwise, radionuclides with vastly different times of peak dose may be
inappropriately combined.
As currently structured, the decision criteria for waste acceptance appear to be based only
on concentration. ORIA should consider whether the total quantity of waste to be emplaced in
RCRA-C facilities should also be part of the decision process. Moreover, the potential presence
of lion-stabilized hazardous wastes in a solid waste management unit (SWMU) near-to the
RCRA-C facilities should be considered, as they may affect the stability of the concrete
containment or the mobility of some radionuclides.
Various modeling assumptions should be re-examined, including ones about segregated
vs. random4 emplacement, the amount of waste potentially subject to disposal as LAMW, the
composition of such wastes, and the classification of radionuclides as mobile or immobile. In
addition, the time-step modeling must be based on rigorously random, stratified sampling, with
attention devoted to choosing modeling time steps that are appropriate to the dynamics of
radionuclide decay, concrete degradation, and waste movement.
Given the wide range of environments that might be found at current or future RCRA-C
sites, ORIA might be well advised to propose two sets of concentration criteria, addressing the
interaction of waste and site. One set could be designed to be valid for relatively dry sites with
deep groundwater and the other for wet sites. The latter sites might be able to accept only wastes
with short-lived radionuclides.
The Committee sees this modeling effort as an opportunity for EPA to examine the
similarities and differences in radioactive waste and hazardous waste control systems and to
harmonize them to the extent feasible. At the same time, ORIA could study, within the same
modeling framework, a range of waste types beyond that currently being considered, for example
wastes containing RCRA hazardous and technologically enhanced naturally occurring radioactive
material (TENORM) radioactive constituents. ORIA could also study harmonization of the still-
to-be-determined "reference doses" with risk criteria used for hazardous chemical wastes.
Because a waste that contains both chemical and radioactive constituents is potentially
more hazardous than one that contains only one or the other (at the same concentrations), and
By "random." ORIA means emplacement that is not limited to a particular portion of the RCRA-C cell. No formal randomization
process is implied.
-------
because the cost of disposal for hazardous wastes is usually less than for radioactive wastes,
ORIA should take care not to create an incentive for a generator to classify improperly a waste as
LAMW that would otherwise be simply LLRW. It should also examine whether redefining the
waste would change the liability distribution between waste generators and disposal facility
operators.
-------
2. INTRODUCTION
2.1 Background
When a waste is designated as both "hazardous" because of its chemical or physical
properties and "radioactive" because of the presence of radionuclides—a "mixed waste"— the
options for its disposal are limited under current regulatory requirements promulgated by the U.S.
Environmental Protection Agency (EPA or "the Agency") under the Resource Conservation and
Recovery Act (RCRA) and by the U.S. Nuclear Regulatory Commission (NRC) under the Atomic
Energy Act (AEA), respectively. Although certain mixed wastes can be disposed at a commercial
facility in Utah, and although Federal or State regulatory agencies may allow disposal of certain
types of mixed wastes elsewhere under special circumstances; finding a disposal alternative at a
tolerable cost is often difficult, particularly for small-volume generators such as universities,
medical facilities, and other research laboratories. The EPA is therefore seeking alternatives that
would facilitate the safe disposal of these wastes.
As a start, the Agency is investigating the merits of a regulation that would permit certain
low-activity radioactive mixed wastes (LAMW) to be disposed of in facilities permitted as
hazardous waste facilities under RCRA Subtitle C (RCRA-C). Such a site would be required to
obtain a radioactive waste license under NRC (or agreement state) jurisdiction. The intent of the
initiative is to encourage simplification of the radioactive materials license requirements for
RCRA-C sites willing to accept LAMW that meet specific dose criteria considered protective of
human health and the environment. The contemplated regulation would establish acceptance
criteria, generally stated as concentrations of specific radionuclides in the waste, that if met would
allow the disposal of the mixed waste in a RCRA-C facility.
EPA's Office of Radiation and Indoor Air (ORIA) is currently conducting a modeling
exercise to determine what those criteria might be in order to meet radiation dose limits yet to be
finalized. To conduct that modeling, ORIA needs to make a number of assumptions about how
the radionuclides might be released and how people living near or even on the site might become
exposed to them. It also needs to set limits on the range of possible conditions that it will include
in the modeling of human health risks. Using overly conservative assumptions and procedures or
an extremely low reference dose might vastly overstate risks and prevent most or all mixed wastes
generators from realizing the benefits of disposal under the new regulation even if such disposal
were truly of little concern; using less conservative assumptions, however, might allow disposal of
some wastes under conditions that do not provide sufficient protection. The criteria are intended
to prevent any person from receiving an unacceptable radiation dose during any year following
emplacement. The highest estimated annual dose after emplacement, or "peak dose," is therefore
the limiting variable.
-------
2.2 Charge to the SAB
Given the issues noted above, the ORIA requested that the Science Advisory Board's
(SAB) Radiation Advisory Committee (RAC) provide advice on its modeling efforts by
responding to the following three Charge questions:
Question a) Having relied on extensive site characterization data from existing and
potential low-level radioactive waste disposal facilities, does the EPA dose
assessment reasonably cover the range of hydrogeologic and climatic
settings that might be used for disposal of low-activity mixed waste?
Question b) What modeling time frame does the Committee recommend be used to
project potential doses from disposal of low-activity mixed waste? Does a
1000-year time frame provide an adequate technical basis for setting
regulatory limits?
Question c) Given the modeling approach described [in the Agency's presentation], and
the available knowledge regarding concrete durability and modes of
degradation, is it reasonable to assign a "high" release rate for the duration
of the simulation? Does the SAB advise an alternative approach, such as
assuming a lower release at the start and increasing it incrementally over
the modeling period, thereby mimicking the gradual deterioration of the
concrete?
2- \:jj £0430
"
-------
3. DETAILED FINDINGS AND RECOMMENDATIONS
In general, the Agency has provided a modeling approach that is consistent with its
previous analyses of radioactive waste issues and that may be reasonable for establishing
acceptance criteria for the disposal of mixed wastes in RCRA-C disposal cells. The proposal is,
for the most part, clearly described in the materials presented to the Committee, which struck a
good compromise between being comprehensive and being brief (See U.S. EPA/ORIA 1998a
through 1998m). The Committee provides below some suggestions that may help improve the
modeling effort for the task of managing LAMW.
The Committee is supportive of the Agency's intent to find a partial solution to the vexing
problem of disposing of wastes that contain both RCRA-regulated hazardous constituents and
AEA-regulated radioactive constituents. It is entirely reasonable that some level of radionuclide
concentrations should be acceptable for disposal in RCRA-C waste management units. The
challenge is to define criteria that provide sufficient protection from long-term risks yet qualify a
substantial portion of mixed wastes for disposal under less onerous requirements than currently
used for low-level radioactive waste (LLRW) disposal.
The Committee's responses to the three Charge questions appear below. However, the
Committee believes that those responses are to some extent conditioned on choices about
broader—and probably more important—issues in the modeling and regulation of LAMW disposal.
Therefore, we offer in Section 3.4 comments beyond the Charge. We also provide, in Appendix
A, some detailed comments designed to improve any Technical Support Document that is
eventually issued in conjunction with a proposed regulation.
3.1 Extent of the EPA Dose Assessment (Question a)
Charge question (a) asked for comment on EPA's proposed dose assessment, focusing on
its adequacy across the wide range of climatic and hydrogeological settings which might be
encountered in disposing of low-level wastes.
The site characterization does not entirely cover the range of settings for disposal sites.
The Committee believes that some existing RCRA-C sites and possible future RCRA-C sites in
the states of Alaska and Hawaii, as well as the territories of Puerto Rico, Guam, and trusteeships
are not adequately bounded by ORIA's use of three existing DOE sites to cover the range of
hydrogeologic and climatic settings. In order to use the ten selected DOE sites as a point of
departure, EPA must demonstrate that they are similar to the 22 currently operating RCRA-C
disposal facilities, as well as possible future facilities outside the conterminous USA. The
similarity must not only include hydrogeologic and climatic characteristics, but other siting and
design issues such as
-------
a) Are any of the existing and potential future RCRA-C sites in the 100-year or 500-
year flood plain? How should ORIA deal with potential future changes in the
flood plain area due to upstream development, etc.?
b) Do the sites have similar depths below the waste to the groundwater table? What
is the thickness, nature, and extent of infiltration in the unsaturated zone?
c) Are the sites similar with respect to the hydraulic conductivity of their unsaturated
zones? Are other geochemical processes important to the movement of
radioactive materials?
d) Are the sites similar with respect to fracturing of the underlying strata?
e) Are seismic characteristics that might influence the stability of containment similar
between the RCRA-C and DOE sites?
f) Are the ecological systems of the two sets of sites similar? These systems can
influence the probability of cap degradation.
g) Are the containment designs of the RCRA-C facilities similar to the DOE facilities?
h) Do the DOE sites experience similar freeze-thaw and snow pack buildup, as the
RCRA-C facilities?
i) Are dry sites with shallow ground water depth represented by the DOE sites? If
ORIA believes that such sites are not relevant, it should explain why not.
j) Conditions in, and properties of, the waste and surrounding geological materials
control the rate of release and transport of chemical and radioactive contaminants
from the waste to the accessible environment. Important site considerations are
the compositions, proportions and distribution of radioactive and hazardous wastes
at a site, waste and soil redox and pH conditions, the presence of reactive materials
(i.e., highly sorptive), and biological activity. Do the ten DOE sites take into
account the expected variability of these wastes, site conditions and properties?
Without this information, ORIA cannot assume that its "bounding analyses" truly bounds
_ the RCRA-C sites. However, the Committee is not recommending inclusion of site characteristics
that would clearly be found unacceptable for future RCRA-C facilities.
Furthermore, Question (a) (See Section 2.2) as framed by ORIA seems overly narrow.
While it is desirable to select sites to bound important potential site conditions and characteristics,
the ultimate goal should be to bound probable site performance. ORIA should consider
enhancing its approach to include additional site characteristics (See discussion of the Total
-------
Systems Performance Analysis approach in Appendix B). Model predictions of the long-term
performance of potential LAMW sites should be validated as much as possible against the actual
performance of existing waste sites. In some cases, there are sufficient historic data to validate
30-year predictions of hazardous waste site performance, and a few decades of performance data
for several radioactive waste sites are available. However, ORIA is proposing to make
predictions of radionuclide releases for 1,000 yrs or more. Should it be using performance data
for existing waste sites as a basis for modeling predictions for proposed LAMW sites?
In the overview document (U.S. EPA/ORIA 1998a, 1998b), the EPA presents model
calculations to predict the concentrations of different radionuclides assumed to be mobile or
immobile in the typical site. All waste sites are apparently considered oxidizing, based on the
radionuclides that ORIA classifies as mobile (e.g., U, Np, Se, Tc). This assumption will probably
be true in cold and/or dry settings. However, in wet (high rainfall), warm climates in the presence
of reactive organic wastes or organic-rich soils, (near-field) subsurface conditions are more likely
to be reducing, which could make these radionuclides immobile. For other radionuclides,
reducing conditions might enhance mobility.
In the generic characterization document (U.S. EPA/ORIA, 1998f), it appears that ORIA
has considered an extensive list of site-specific physical and hydroponic parameters in the
PRESTO modeling calculations to predict performance of the ten DOE sites in the screening step.
It has assumed single values for all parameters in the calculations, whereas a probability
distribution of values using a Monte Carlo approach, for example, would give more realistic
results and provide an estimate of the uncertainty.
Apparently the only geochemical inputs to predictive modeling are the radionuclide-
specific distribution coefficients (K^ (U.S. EPA,/ORIA, 1998i, p. 2), which the document states
will vary with soil type. Values of Kd for individual actinide elements in particular can vary by up
to five orders of magnitude depending not only on soil type (i.e., soil mineralogy and particle
size), but also on soil and waste pH,s redox conditions, the presence of reactive organic matter,
and biological activity (Langmuir, 1997). The chemical and biological reactivity of the mixed
waste (of its organic, inorganic and radioactive substances) and its interaction with surrounding
soils will control the release rate of the radionuclides. The climatic and general hydrogeologic
conditions at two sites could be identical. However, differences in the composition, reactivity and
relative amounts of chemical and radioactive materials in different wastes, and differences in the
behavior of reactive minerals present in the soil and underlying groundwater systems, could result
in vast differences among sites in the timing and amounts of specific radionuclides that arrive at
adjacent wells.
As or more important than depth to bedrock and thickness of the unsaturated zone (UZ),
is the nature and extent of infiltration through the UZ, which will reflect the structure and
stratigraphy of'soils' in the UZ. For example, does flow at and under the waste site occur in
Ccmenthious materials in the waste, if fresh, will buffer the (near-field) pH near iO.
10
-------
coarse-grained materials (permeable sands and gravels, for example), or in less permeable silts and
clays? At sites with poorly developed or thin soils as on hill slopes or ip mountainous areas,
waste sites may be emplaced in partially weathered bedrock, in which case infiltration of leachates
carrying radionuclides may move easily down fractures in the bedrock (o groundwater. A dual
permeability modeling approach is needed in sites with fractures; an "equivalent continuum"
model is not reliable for travel-time calculations.
The only geochemical process mentioned is the ion exchange behavior of soils, which is
only one of the geochemical processes or conditions of importance to radionuclide releases.
Other processes include specific adsorption by solids in the waste or soil (for trace radionuclides,
generally more important than ion exchange), precipitation or co-precipitation of radionuclides
with solids, waste and soil redox conditions, the presence of substances that can form strong
complexes with radionuclides, increasing their mobilities, among others. Important soil and waste
characteristics that control radionuclide mobilities include: (1) reactive organic matter content6
and its amount relative to that of the radionuclides (as noted above); (2) temperature7; (3) oxygen
flux rate; (4) moisture content and infiltration rate, and (5) the presence of solids in the soil that
are sorptive for actinides (e.g., Fe and Mn oxides, phosphates). All of these characteristics can
change along the flow path from source to well.
Although the Committee recognizes that ORIA is attempting a generic analysis that
cannot take into account all the site-specific characteristics of real sites or the properties of real
combinations of wastes, we recommend that ORIA take a broader look'at the range of
radionuclide leaching and transport behaviors that might occur at real RCRA-C sites. Discussions
with modelers in the RCRA or Superfund programs could be helpful in this regard, as would a
perusal of the EPA Environmental Sciences Division's web page on databases and software.8
This source contains several modeling structures that might help in exploring this issue. At a
minimum, ORIA should discuss what steps it has taken to determine the effect of the variables
mentioned above on model results and why it believes that using a short list of DOE site
characteristics in the PRESTO model will be sufficient.
3.2 Suitability of the 1000-year Time Frame (Question b)
The Committee concluded that a sensitivity analysis of the modeling time frame could
provide potentially useful information on the variation of peak dose with time horizon, especially
for less mobile radionuclides with long half-lives. The Committee did not reach consensus,
however, on how ORIA should weigh projections for the longer periods against the more reliable
projections for shorter periods. The factors that contributed to the Committee's lack of
consensus centered on the consideration of four issues - scientific, future land use, public
6
The decay of cellulosic materials to form ligands that can complex the actinides, for example.
Temperature accelerates biological activity and waste material breakdown.
see http://www.epa.gov/crdlvweb /databases/datahome.htm
11
-------
acceptance, and economic viability. The comments below reflect considerations that should
influence ORIA's ultimate choices about time frame. Because these comments represent the
different perspectives of individual Committee Members, they do not signify a Committee
consensus.
3.2.1 Scientific Issues
The Committee addressed seven major scientific issues, outlined below
a) Capturing the time of peak dose: Clearly, some radionuclides with long half-
lives and low mobility will not attain maximum concentrations in groundwater
within 1,000 years, especially for the "dry" scenario with a very thick unsaturated
zone . The New York State Department of Environmental Conservation
performance assessment modeling in support of a LLRW disposal facility used a
10,000-year time frame. The results of this modeling showed the peak off-site
dose to the public occurred 1,200-2,000 years after closure for most near surface
disposal scenarios modeled. Whether or not a failure to capture the time of peak
dose will be significant from a scientific standpoint depends on the scenario and
policy assumptions that accompany the model (See land use and concrete
containment discussions). If the model time frame were extended to 10,000 years,
it would capture the peak dose for most if not all radionuclides, and it should also
account for the peak dose from in-growth of decay products.
b) Limited life of controls: On the basis of design conservatism of facilities and the
stress system in the near-surface environment in which they are operated, the
controls that may be exerted on radionuclide doses by RCRA-C facilities layers can
be assumed to be zero after a few hundred years. Maintenance activities under a
"perpetual care" commitment by the facility managers and natural hazards can
influence the specific time range. By the time the service life is attained, the
fatigue-type stresses that are common in the near-surface environment (freeze-
thaw, dry-wet cycles, expansion-contraction, weathering, burrowing by animals,
possible physical erosion of covering soils, etc.) would have created and/or
extended flaws in the system to change the fluid entry and release mode from
permeation to pipe-flow. If the analysis is extended to 1,000 years or more, the
influence of containment would then be entirely ignored in the analysis of releases
after 300-400 years.
c) Definitions of failure: One of the most difficult questions to answer on
containment system performance is, "What is failure?" The failure of a component
(cover or liner) may not necessarily mean the failure of the system that contains
many components. Are the components connected structurally or functionally in
parallel or in series? Structural failure may not always mean functional failure.
For the purposes of this project, ORIA should focus on a definition of system
12
-------
functional failure that considers failure as the release of radionuclides sufficient to
cause a dose above the dose criterion in a person residing at a specified location
adjacent to the site.
d) Variable time frame as a function of LAMW composition: The range of the
possible radiological compositions of candidate wastes is not well defined. It
appears that there is greater uncertainty about which of the long-lived
radionuclides may be present in commercial mixed waste than about the short-lived
radionuclides. If there were no long-lived radionuclides, there would be no need
for modeling beyond 500 years. However, if long-lived radionuclides are present,
and the modeling out to 10,000 years demonstrates that the dose standard would
be exceeded at the time of the peak dose, the radionuclide con Therefore, one way
for ORIA to limit the modeling time frame is to verify that certain long-lived
radionuclides would not be present in commercial mixed waste, or alternatively
specify that they must not be present in wastes destined for RCRA-C disposal.
Which radionuclides may be subject to such consideration could be identified by
conducting runs at several time scales (e.g., 100, 300, 1,000, 3,000, and 10,000
years) and comparing peak doses for the various runs.
e) Conservatism of modeling assumptions: Modeling beyond 1,000 years may be
unrealistically conservative and unrealistically uncertain. Among the conservative
assumptions are a) that all waste sites are always oxidizing, which ensures that
certain radionuclides are always modeled as mobile regardless of the waste form or
waste composition, and b) that no reactions or processes within the waste, in the
unsaturated zone, or in the groundwater system other than radioactive decay and
simple adsorption by soil will prevent the release of radionuclides to the
environment. In the presence of concrete, many of the so-called "mobile"
radionuclides in the waste would become less mobile, at least for short times.
f) Effect of climate on long-term predictions: A more comprehensive performance
assessment analysis might show that for some sites, radionuclide releases can be
predicted to be low and not an issue for times up to 1,000 years. Such sites are
likely to be in arid climates with thick, well drained unsaturated zones. It might be
necessary to limit LAMW disposal to such sites. In wet, humid climates, the
performance of sites for near-surface disposal of LAMW cannot be predicted
reliably for time spans beyond a few hundred years. Thus, radionuclides with
longer half lives, such as Np, would still be a problem.
g) Consistency with other waste regulations: The Agency should also consider
what time frame it would use if it regulated hazardous waste disposal with risk-
based rather than technology-based rules. An illustrative example would be lead,
which has an infinite half-life, physical-chemical properties similar to many of the
naturally occurring radionuclides, and a dose-response relationship without an
13
-------
established threshold. Certain carcinogenic heavy metals also could be considered.
While NRC regulations require site characteristics be considered for a minimum of
500 years, most performance assessments for LLRW sites are run to 10,000 years.
Should hazardous waste environmental fate analyses be modeled to 10,000 years?
3.2.2 Future Health Risk and Land Ownership Considerations
The Committee discussed two primary issues:
a) Long-term societal changes: One thousand years may be unrealistically long
given the likelihood of substantial changes in public health and social conditions.
Currently, cancer is the endpoint for health risk from radionuclides. It is certainly
possible that within a 1,000-year time frame, cancer will become a disease of less
concern because of advances in prevention or treatment; cancer as an endpoint
could become largely irrelevant. Likewise, society may view radiation risk in a
much different way. By suggesting modeling out to 10,000 years, we may not
even comprehend what forces will dominate the pathways for exposure. It is when
we consider future societal decision-making that the 10,000-year modeling
scenario appears speculative indeed.
b) Land ownership issues: Part 61 licensed LLRW sites must be owned by Federal
or State government following closure and a post-closure observation period. All
DOE facilities are on Federal government owned sites. It is very important to
consider site ownership by the Federal and State government when discussing
modeling time frames. While no government has lasted 10,000 years and
government agencies do not always meet their obligations as environmental
stewards, government ownership of a site is a clear commitment by a civilization to
maintaining the integrity of a LLRW disposal site over time.
RCRA-C facilities have no such requirement. Profit-making corporations own RCRA-C
facilities. They have different responsibilities to their shareholders, and any post-closure land use
scenario is possible, constrained only by local planning and zoning boards' interpretation of
RCRA guidance.
3.2.3 Public Acceptance
Although the Charge to the SAB is specific to providing an adequate technical basis for
setting regulatory limits, the Committee members have enough experience with public acceptance
of LLRW disposal facilities to comment on this aspect of deciding on appropriate modeling time
frames. It appears that modeling can be a useful tool for describing the behavior of radionuclides
at an RCRA-C site. Particularly important is the fact that the site is already in operation accepting
hazardous waste, and was not sited using Part 61 characteristics. Therefore it must be made
crystal clear to the public that the site will operate within radiation standards. If the site cannot be
14
-------
shown to be "safe" at the time of the peak dose, it is likely not to win public acceptance. So if the
site is modeled to 1,000 years, the public may not be convinced that it should approve the disposal
of radioactive material there. However, if conservative assumptions show that, at the time of
peak dose, the site will still be adequate to protect public health, public acceptance is more likely.
If the RCRA-C sites that are permitted to accept LAMW commit to "perpetual care," acceptance
would be further enhanced.
Table 2 on pages 6 through 8 of the Modeling Time Frame document (U.S. EPA/ORIA,
1998g) has 30 of 48 radionuclides peaking at 1,000 years in the 1,000-year modeling period,
demonstrating that the peak dose was not captured during the 1,000-year time frame. Attachment
3 on page 3.1 of the same document has 129I and "Tc peaks that are much higher at 10,000 years
than at 1,000 years. The public will surely notice that modeling to 1,000 years does not show
peak dose for all radionuclides. Therefore, modeling to 10,000 years would be useful.
On the other hand, the public may be accepting of model predictions of fate and transport
for a time frame of 100 years. The use of 10,000 years could raise serious questions concerning
the degree of uncertainty and possibly the credibility of the entire approach for estimating future
health risks.
3.2.4 Economic Considerations
The entire premise of the EPA's proposed LAMW disposal rule is to provide a lower cost
option for RCRA-C facilities to apply for Part 61 licenses so that they could also accept mixed
waste. This proposed rule will assist some research facilities, medical facilities, and utilities by
providing additional disposal options for mixed wastes. These facilities currently store this waste
and are waiting for a place to dispose of it in a cost-effective manner.
If the modeling to 10,000 years puts such constraints on the radionuclide concentrations
that no RCRA-C facility applies for the Part 61 license, the purpose for the proposed rule is lost.
RCRA-C facilities have to be able to make a profit on the waste or they will not accept it.
However, if modeling to 1,000 years does not convince the public to accept radioactive
wastes into RCRA-C facilities, the rulemaking will also be in vain. Currently, the most expensive
item in siting a new disposal facility is winning public acceptance.
3.3 Modeling Release Rates (Question c)
The last Charge question asked the RAC to comment on EPA's approach to modeling
release rates over time, taking into consideration the available knowledge regarding concrete
durability and modes of degradation.
The Committee concluded that the key issue in this third question was the impact of the
deterioration assumption on the calculation of the peak annual dose.
15
-------
3.3.1 Technical Issues
In order to determine the limits for radionuclides in mixed waste to be disposed in RCRA-
C facilities, doses were calculated for unit concentrations of specific nuclides in the wastes.
Doses were modeled assuming that the waste was solidified in concrete, using an inexpensive,
normal Portland cement. This assumption could be conservative as long as this type of treatment
is the minimum RCRA requirement. Use of special types of cement/concrete mixtures that would
minimize the potential for degradation, i.e., sulfate resistant cement (U.S. EPA/ORIA, 19981,
citing SMI, 1998) or specific construction and reinforcement as described in the New York State
Final Generic Environmental Impact Statement for Low-Level Waste Landfills (NY, 1993) could
be addressed in site-specific radioactive materials license conditions.
The release rates from concrete used in developing the dose estimates are based on the
assumption that the concrete degrades over time, releasing all radionuclides at a constant
(relative) rate. This rate was assumed to be 0.001 per year, based on the diffusion coefficient for
tritium in concrete. The release rate assumes a first-order reaction; that is, the rate of release is
proportional to the inventory remaining in the waste form. Values of 0.0005 per year and 0.005
per year for the relative release rate were also used in the dose calculations. The initial
concentrations in groundwater were determined using radionuclide-specific distribution
coefficients (Kj) for the concrete/water partitioning, and were derived from the literature. The
retardation factor in the concrete was applied in the calculation in the same manner as it is in the
calculation of retardation in soils.
The rate of release has a significant effect on the calculation of a peak dose via the
groundwater pathway. For 3H, the fractional increase in dose is approximately equal to the
fractional increase in release rate for tritium. For 129I, however, the dose increased by a factor less
than 2 when the release rate was increased by a factor of 5, indicating a non-linear response for
this radionuclide. ORIA states, however, that changing the release rate does not affect the year in
which the peak dose occurs for this radionuclide.
ORIA also states that the constant release rate assumption results in peak doses not
significantly different from the doses that would be calculated using a variable release rate, i.e., a
slow initial rate increasing over time as the concrete degrades. While degradation rates for
concrete could not be quantitatively determined from the available literature, progressive
degradation is a more reasonable scenario (U.S. EPA/ORIA, citing SMI, 1998). The Committee
recommends that a simulation be performed to verify, at least qualitatively, that the constant loss
rate assumption is reasonably—but not excessively—conservative, for all radionuclides.
For example, an exponential deterioration model can be used to scale its structural
properties with respect to time (e.g., porosity).. Then for each time segment within the modeling
time frame, the relevant magnitude of the structural parameters can be fed into the selected
leaching model to estimate release rates. Monolith leaching models such as those that relate to
16
-------
the American Nuclear Society's American National Standards Institute (ANSI) 6.1 test can be
adapted for use.
The concrete deterioration model also interacts with the containment failure models.
There is no scientific basis for ORIA's assumption that at the time the liner fails completely
(100% failure), the cover would have failed only by 10%. Actually, one could argue that the
cover is likely to fail before the liner because it is subject to extremes and reversals in temperature
and moisture conditions and access by burrowing animals and plant roots. A deterioration pattern
could be analyzed based on the transport-related characteristics of the containment system. Then,
depending on the time frame of concern, the relevant magnitude of the parameter could be fed
into the model instead of specifying an arbitrary failure rate or ratio (See Figure 1).
Although RCRA-C facilities incorporate polymeric membranes in both the cover (cap) and
lining systems, ORIA's analysis focuses only on soil layers. Significant decreases in radionuclide
release rates would be obtained if engineering barriers were included in the analysis. Essentially,
the barrier system is the second line of defense for the radionuclides, after the concrete
encapsulation itself. Error in the release rates would propagate throughout the entire analysis,
including the calculation of dose rates.
For radionuclides with short half-lives, the doses could be significantly overestimated by
assuming a high constant loss rate. In the initial phases, when the concrete remains intact and the
loss rate is, in fact, very low, the short-lived radionuclides would decay before release, thus
producing very little, if any, dose. On the other hand, for longer-lived radionuclides that decay to
progeny with higher bioaccumulation potential and dose coefficients (e.g., ^"Th to ^Ra), the
assumption that the loss rate is constant may not be conservative, depending on the effect of
retardation (Kj) as the radionuclides move through the concrete and soil matrices.
The emphasis on concrete degradation assumes that the treatment option for all of the
mixed waste potential candidates for disposal at RCRA sites would be solidification in concrete.
For some wastes, such as contaminated soils, lead bricks or lab trash, solidification may not be the
optimal treatment. Under the Land Disposal Restrictions (LDR), moreover, some hazardous
wastes require treatments other than solidification in concrete. The Agency should either exclude
such wastes from the rulemaking on LAMW or assure the required LDR treatment is more
restrictive than solidification in concrete. For example, is the requirement for amalgamation of
mercury more restrictive over 1,000 or 10,000 years than solidification in concrete? The concrete
waste form may not be the most conservative assumption. Even for concrete, the possible
influence of the hazardous waste constituents on concrete stability should be considered.
17
-------
Deteriorating Umr
. Monitoring
/ vwll
Direction of groun^
water movormnt
Figure 1 Barrier Performance Assessment through Mathematical Modeling and
Monitoring (Provided courtesy of Dr. Hillary Inyang, Chair, SAB/EEC).
3.3.2 Science Policy Issues
The question of whether the most conservative assumptions for the disposal options are
the most effective in reducing overall risk should be addressed in the background considerations
for the RCRA mixed waste standards. Unduly restrictive limits for disposal at RCRA-C facilities
may significantly reduce the effectiveness of this option. Wastes that currently cannot or should
not be disposed at licensed LLW sites or conventional mixed waste facilities are generally stored
at or near the site of generation. Although such wastes are subject to inspections and other
requirements designed to ensure their safety during storage, indefinite accumulation and storage
of mixed waste at the site of generation clearly runs counter to current waste management
philosophy. Waste stored at the generator site is usually closer to workers and the public than
would be the situation with disposed waste. This proximity increases the probability of human
contact with the waste as a consequence of normal handling, accidents and natural disasters and
thus may increase the health risks over what they would be if the wastes were disposed of at
RCRA-C facilities. The goal of this effort should be to reduce overall risk. Therefore,
unnecessary conservatism in setting disposal limits may be counter-productive.
18
-------
The Committee recommends that ORIA investigate the types of waste that might fall
under the provisions of the proposed rule and the conditions under which they are currently stored
and, to the extent possible, characterize the health risks of plausible failure scenarios. The risk
assessment principles should be similar to those used in the present modeling exercise, in the sense
of using similar degrees of conservatism. Ideally, both analyses would have elements of a
quantitative uncertainty analysis. Then, the probability of improving the overall risk balance for
different sets of waste acceptance criteria could be studied. (Note: this comment applies to any
assumption posited on the grounds of conservatism.)
3.4 Additional Issues
3.4.1 Modeling Structure
ORIA has selected the PRESTO model to conduct the acceptance criteria modeling.
Although the Committee understands that PRESTO has a long history of use in the Agency and
that ORIA has considerable confidence in the applicability of its results for the intended purpose,
we advise that ORIA be prepared to justify its use in the Technical Support Document that will
eventually be produced to support any rulemaking. Such justification might include answers to
the following questions:
a) Has it been benchmarked (e.g., through BIOMASS or another effort for cross-
comparison of models)?
b) Can it adequately simulate the role of geochemical processes in enhancing or
retarding radionuclide transport (not just Kd and radioactive decay)?
c) Can it consider the effects of variations in the composition and form of mixed
waste as emplaced on radionuclide releases?
d) Does it account for the ingrowth of decay products after disposal of the parent
radionuclide for which the criteria are calculated? (Decay products are not
included in dose tabulations in some EPA publications.)
e) Is it particularly suited for the spatial scale of the analysis (e.g., a potable water
well 50 m from the edge of the RCRA cell)?
f) Has it been updated and enhanced to be consistent with the current state-of-the-art
of multimedia health risk models? With RCRA modeling assumptions?
Any other assurances of its applicability and reliability would also be welcome. For
example, ORIA might consider using a second relevant model as a check on the doses predicted
for unit concentration of each radionuclide. Reasonable agreement would support the choice of
19
-------
PRESTO. Disagreement, however, would require ORIA to investigate the causes of the
disagreement and make informed choices about any needed adjustments to its modeling.
ORIA stated that it would use the "unity rule" for judging the acceptability of LAMW
containing more than one relevant radionuclide. Under the unity rule, the concentration of each
radionuclide in a candidate waste would be divided by the corresponding criterion concentration
and these fractions would be summed over all radionuclides. If the sum of fractions is less than
1.0, the waste would be found acceptable for disposal. This rule may be unnecessarily restrictive
for certain combinations of radionuclides. For example, if a waste contained both 3H and 14C at
their respective concentration limits based on the reference dose, application of the unity rule
would prohibit its disposal at a wet RCRA-C facility (e.g., one with characteristics similar to
Fernald). However, the peak dose for 3H is reached in about 100 years but the peak dose for UC
is not reached until 1,000 years or more after the liner is breached. Therefore, the dose to an
exposed individual could not exceed the reference dose in any year. To overcome this unintended
consequence, radionuclides could be classified according to similar peak dose time frames and the
unity rule applied only within those time classes. The Committee recognizes that such a
procedure would increase the complexity of the contemplated rule and might appear to be in
conflict with similar NRC procedures.
Presumably, the eventual Technical Support Document will describe more clearly the
process of determining acceptance criteria in concentration units starting with a policy choice
about the acceptable reference dose. If the Committee understands ORIA's intent correctly,
concentration would be the principal if not the only determining criterion for waste acceptance.
However, it seems likely that the potential peak dose for a given concentration in waste would
also depend on the total quantity of wastes of that concentration deposited in the modeled site.
ORIA appears to be currently assuming that only a small fraction of the total waste in the RCRA-
C cell would be LAMW at the criterion concentration. But there appears to be no restriction
against a larger fraction nor any credit given for a smaller fraction. ORIA might consider
additional limitations on the total quantity of any one long-lived Radionuclide allowable at a
RCRA-C facility of given capacity. If it does so, it should also consider the implications of such a
limitation on the unity rule.
Some pathways of exposure seem to have been excluded from the modeling. For
example, it is not clear that evolution of radon or other volatiles from potable water use in the
home has been treated, and it is clear that soil ingestion and dermal contact with soil have not
been included, even though the on-site residential ("immobile1') scenario postulates excavation of
soil from the disposal cell during construction. While dermal absorption of inorganic hazardous
chemicals is usually unimportant, the same is not always true for soil ingestion, which is frequently
more important than soil re-suspension, a modeled pathway
Many of the existing RCRA-C disposal facilities have SWMUs that contain non-stabilized
hazardous wastes. EPA should consider whether or not these wastes could enhance the
degradation of LAMW containment or the mobility of radionuclides after release. Even for the
20
-------
licensing of new facilities with stabilized wastes, the potential for enhanced mobility from the co-
disposal of hazardous and radioactive wastes should be considered.
For the mobile (groundwater) scenario, there are different results for the assumption of
segregated vs. random emplacement. However for the immobile (intruder) scenario, separate
calculations are not made for assumptions of segregated vs. random emplacement. Because the
immobile scenario postulates an intruder, exposure would seem to be strongly dependent upon
whether the waste was segregated or placed randomly, suggesting that separate calculations are
appropriate. The detailed assumptions for the segregated vs. random emplacement should be
better described.
On p.2 of the Overview (U.S. EPA/ORIA, 1998b), EPA apparently is using a 1990 NRC
survey published in 1992 as NUREG/CR-5938 (U.S. NRC, 1992) to estimate the volume of
commercial mixed waste generated in the U.S.. Pollution prevention and waste minimization
efforts have significantly reduced annual mixed waste volumes since then. On the other hand, the
decontamination and decommissioning of nuclear power plants and naval reactors in the next ten
years may result in a significant increase in commercial mixed waste volumes.
On p.l 1 of the Overview (U.S. EPA/ORIA, 1998b), 3H and UC in waste gases are
assumed to be negligible due to prior treatment by incineration. Based on the large volumes of
wastes containing these radionuclides being generated at commercial sites, this assumption needs
to be justified. Also, EPA should consider modeling root uptake of these radionuclides in cover
vegetation.
On p. 13 of the Overview (U.S. EPA/ORIA, 1998b), it is stated that a subset of
radionuclides from Table 4 were included in the mobile modeling scenario. *°Sr was not included
in the list of the mobile radionuclides, and was listed in Table 7 as a Radionuclide that resulted in
no doses from mobile or immobile scenarios. EPA should reexamine the scenarios in view of
'"Sr's historic problems at LLRW sites.
i
3.4.2 Science Policy Issues
Given the large range in the results for the different environments modeled, one has to
question the utility of a single set of Radionuclide concentration limits, which would, of necessity,
have to apply to the worst possible environment. The large differences for the "dry" and "wet"
sites suggest an approach of developing at least two sets of concentration limits. For example,
Type 1 sites could include sites in arid climates with deep, well drained unsaturated zones and
sites in semi-arid climates in groundwater recharge zones with deep, well drained soils if the latter
were capped with compacted clay, contoured to export runoff, and vegetated to minimize
infiltration. It would be easier to predict the long-term performance of such sites than sites in
wetter settings. Type 1 sites could perhaps accept long-lived radionuclides. Type 2 sites would
be those in wetter settings with a shallower groundwater table. Because of the difficulty of
defensibly predicting their performance for long times, and the greater risk of radionuclide
21
-------
releases, Type 2 sites might be limited to the disposal of LAMW containing only short-lived
radionuclides. In addition, it should be made possible for an applicant to demonstrate, through
site-specific modeling, that the dose limit could be met with alternative concentrations. Again, the
Committee recognizes the additional complexity of such a procedure and that it might appear to
be in conflict with similar NRC procedures.
In its eventual technical product, ORIA should attempt to tie together the modeling
assumptions and health risk criteria between the hazardous chemical constituents and the
radioactive constituents of the mixed waste. The proposal must be seen to be consistent with the
objectives of the current RCRA protection system even if not with its specific requirements. The
Technical Support Document should provide background on the similarities and differences
between chemical and radiation risk management and how the modeling dealt with them.
As described to the Committee, the LAMW proposal would apply to a rather limited
range of wastes generated by "commercial" activities and classified as both RCRA hazardous
waste and AEA Class A LLRW, and the only new disposal alternative would be in a RCRA-C
facility. However, the modeling effort has many additional potential uses, including decisions
about:
a) disposal of wastes containing RCRA hazardous and TENORM, which are not
regulated under the AEA,
b) disposal of wastes containing Toxic Substances Control Act (TSCA) substances
and either AEA or TENORM radioactive constituents,
c) disposal of qualifying Class A radioactive wastes that do not contain RCRA
hazardous components at RCRA-C facilities, and
d) defining "de-minimis" concentrations for radionuclides that would enable non-
hazardous very low level radioactive wastes to be disposed in RCRA-D (sanitary)
landfills.
The Committee recommends that these potential uses be kept in mind when making
modeling choices for the current proposal. ORIA should also examine the forthcoming NCRP
report on waste classification for other possible uses. Having a wider range of modeling uses will
better justify the time and effort spent, which may otherwise seem excessive for the limited
quantities of waste currently thought to fall under the proposed rule. In making this suggestion,
the Committee is well aware that there may be legal, economic, or political reasons for EPA to
disallow disposal of some of these wastes in RCRA facilities even if they meet the dose criterion.
The Committee recommends that the eventual Technical Support Document discuss how
the Agency has responded not only to these comments but also to the RAC's 1985 recommend-
ations (SAB, 1985).
22
-------
3.4.3 Other Policy Issues
The EPA overview document notes that "reference doses" — presumably the doses that
will limit the allowable concentrations of radionuclides in the qualifying waste—are still to be
determined. The Committee notes that the goal of risk harmonization would be furthered if such
doses corresponded to risk levels consistent with those that would be used as guidelines for the
regulation of hazardous chemical waste (SAB, 1992).
A waste that contains radioactive materials AND hazardous constituents is clearly more
hazardous than a waste that contains the same levels of only the radioactive or only the hazardous
components. On purely scientific grounds, it is not logical to allow a mixed waste to be deposited
in a RCRA-C facility when a purely radioactive waste of identical radionuclide content would not
be permitted. The Committee recognizes that EPA may wish to discourage disposal of purely
radioactive waste that would otherwise meet the acceptance criteria for LAMW because it might
disturb established low-level radioactive waste policies or Compact relationships. Such a policy,
however, might encourage waste generators to manage wastes so that they could be disposed of
as LAMW instead of LLRW.
The cost of disposal of LLRW at a Part 61 licensed site is much higher than that for
hazardous wastes at RCRA-C facilities. In addition, access to the nation's LLRW disposal sites
for many states is very tenuous. Thus, LLRW generators may find disposal of LLRW as LAMW
in a RCRA-C facility is cheaper and possibly their only disposal option. Avoiding this perverse
incentive may prove difficult under the LAMW rule as currently contemplated.
It is not clear to the Committee that EPA has considered whether the LAMW rule would
cover mixed radioactive and TSCA wastes (PCBs, asbestos) or mixed wastes containing uranium
mill tailings.
The Agency should consider whether accepting radioactive wastes at a RCRA-C facility
changes the liability between radioactive waste generators and disposal facility operators. The
issue of "taking possession of the radioactive materials" in the LAMW needs to be resolved.
Since RCRA-C facilities currently accept foreign hazardous wastes, will mixed wastes
from other nations be allowed to be disposed of under the LAMW rule? In particular, can
LAMW from Canada and Mexico be excluded under NAFTA? How does this affect EPA's
estimate of the quantity of waste that might fall under the proposed rule?
Part 61.56(a)(7) allows gaseous LLRW disposal under 1.5 atmospheres at 20 degrees
Celsius. Will the LAMW rule allow for the disposal of mixed gaseous wastes?
23
-------
-------
APPENDIX A - DETAILED COMMENTS
a) In any final documentation of the modeling, SI units should be used with the traditional
units in parentheses.
b) In the final work product, the Agency should be sure that undue certainty is not implied by
the use of too many significant figures.
c) Clarify what is meant by dose. Several different wordings appeared in the Committee's
briefing materials, most of which appeared to be synonymous. If differences are intended,
the nomenclature should be clearly defined. If not, uniformity is desirable.
d) The meaning of commercial is not obvious. It seems to be used in one sense to qualify the
facility and in another to qualify the waste. The use of this term should be defined.
e) If the principal focus remains on wastes that are regulated under the ABA, consider
eliminating from the lists radionuclides such as '"K that probably are never considered
germane to AEA control.
f) Only cancer is considered a relevant endpoint for risk assessment. ORIA should be careful
to justify why it believes that other potential effects of radiation, such as birth defects, are
not relevant at the dose criterion eventually selected.
g) Some of the data in Attachment 1 for the Idaho National Engineering Environmental
Laboratory (INEEL) appear to be in error, unless a great deal of conservatism is intended.
The thickness of the vadose zone at INEEL is much greater that 41m, unless perched
water bodies are meant, or basalt is excluded. At the current radioactive facility at
INEEL, the depth to the aquifer is nearly 200 meters. The thickness of the aquifer is much
greater than 12m, and in fact is so thick that its thickness is unknown. The depth of the
aquifer is much greater than 12 m, in fact it is so deep that it is unknown. Is 12 m an
artificial thickness? Although the INEEL was not chosen as one of the three sites used to
bound the various scenarios, these possible discrepancies suggest that the data used for the
model parameters at the other sites should be examined critically, or at least explained.
Similarly, the climatic description for Rocky Flats appears questionable. Note also
inconsistencies between Attachment 1 and Table 2 of the Overview regarding depth of
vadose zone (U.S. EPA/ORIA, 1998b).
h) In Table 2 on page 9 of the overview, the meaning of 31/300 for "end of events" is unclear
(U.S. EPA/ORIA, 1998b).
i) In Table 2 on page 5 of the generic characterization document, the qualitative descriptions
should be accompanied by numeric ranges to avoid confusion (U.S. EPA/ORIA, 1998f).
A-l
-------
APPENDIX B - TOTAL SYSTEM PERFORMANCE ASSESSMENT
APPROACH
The proposed high level waste repository for commercial spent fuel at Yucca Mountain
would be emplaced hundreds of meters below the land surface above the water table in a relatively
dry and geologically stable setting. Even so, predicting the fate of radionuclides to be buried in
the repository for times of 1,000 yrs or longer has been highly contentious. After many years of
being criticized because their predictive approach did not properly consider and weigh the relative
importance of all important site variables and processes, the DOE adapted a comprehensive Total
System Performance Assessment (TSPA) modeling approach. This approach has led to
predictions of site performance including radionuclide release rates in terms of their probability.
ORIA might consider using a similar approach, being careful to select the important
variables that will influence future radionuclide release rates from mixed waste sites. The
importance to radionuclide release rates of the detailed composition and behavior of the wastes
themselves or of waste and waste product interactions with surrounding geological materials
cannot be overemphasized. Predicting the performance of waste sites that contain organics,
metals, metalloids and radionuclides for times of 100 to 1,000 yrs or longer must be based on a
probability analysis which will reflect increasing uncertainty of performance for longer times. A
TSPA modeling approach provides the formal structure on which to hang such a predictive
analysis. TSPA calculations also direct the user towards the most important properties of a
possible disposal site and the most important reactions, for example that control radionuclide
release rates. The public may also be more accepting of performance predictions developed and
defended through TSPA (TRW, 1995). The DOE TSPA model is relatively complex. The
Electric Power Research Institute (EPRI) has developed a simpler TSPA model which may be
adequate for ORIA's purposes (EPRI, 1990).
B-l
-------
APPENDIX C - GLOSSARY OF TERMS AND ACRONYMS
AE A Atomic Energy Act
ANS American Nuclear Society
ANSI American Rational Standards Institute
BIOMASS Bjomass Modeling and Assessment Program, sponsored by the International
Atomic Energy Agency and others. It addressees radiological issues associated
with accidental and routine releases of radionuclides into the environment, and
solid waste management. It covers three themes related to environmental
modeling and safety assessment, which are radioactive waste disposal,
environmental releases, and biosphere processes.
UC £arbon-14, an isotope of carbon with an atomic mass of 14 and a half-life of 5715
years
DOE U. S. Department of Energy (U. S, DOE)
EEC Environmental Engineering Committee (of the U. S. EPA/SAB/EEC)
EHC Environmental Health Committee (of the U.S. EPA/SAB/EHC)
EPA U.S. Environmental Erotection Agency (U.S. EPA, EPA, or "the Agency")
EPRI Electric Rower Research Institute
Fe Iron (Efirric, Esrrous Oxides)
3H Tritium (A radioactive isotope of Hydrogen with an atomic mass of 1 and a half-
life of 12.5 years)
129I Iodine-129, an isotope of iodine with an atomic mass of 129 and a half-life of 16
million years
INEEL Idaho National Engineering Environmental Laboratory
Kd Distribution/Retardation Coefficient
*°K Potassium, an isotope of potassium with an atomic mass of 40
LAMW LOW Activity Mixed Waste
LAMRW LOW Activity Mixed Radioactive W_aste
LDR Land Disposal Restrictions
LLRW Low Level Radioactive W.aste
LLW Low Level Waste
m Meter
Mn Manganese
NAFTA National Eree Trade Agreement
NCRP National Council on Radiation Erotection and Measurements
NORM Naturally-Qccurring Radioactive Material
Np Neptunium (A naturally radioactive element with an atomic number of 93. The
longest-lived isotope is M7Np)
NRC U.S. Nuclear Regulatory Commission (U.S: NRC)
NUREG/CR U.S. Nuclear Regulatory Commission/ Commission Report
ORIA O_ffice of Radiation and Indoor Air (U. S. EPA)
C-l
-------
PATHRAE Computer code used to assess the maximum annual dose to a critical population
group resulting from waste disposal. It is a member of the PRESTO-EPA family
of codes and emphasizes two areas: (1) the addition of exposure pathways
pertaining to on-site workers during disposal operations, off-site personnel after
site closure, and reclaimers and inadvertent intruders after site closure; and (2) the
simplification of the sophisticated dynamic submodels to quasi-steady state
submodels.
Peak Dose Highest annual committed effective dose projected to be received by an off-she
receptor at a specified location.
PCB Eolycjilorinatedbjphenyl
pH Negative log of hydrogen ion concentration
PRESTO A family of codes developed to evaluate doses resulting from the disposal of low-
activity radioactive waste. These codes include PRESTO-EPA-CPG (assesses
annual effective dose equivalents to a critical population group), PRESTO-EPA-
DEEP (assesses cumulative population health effects resulting from the disposal of
low-activity waste using deep geologic repositories), PRESTO-EPA-BRC
(assesses cumulative population health effects to the general population residing in
the downstream regional basin as a result of the disposal of low-activity waste in
an unregulated sanitary landfill), PRESTO-EPA-POP (assesses cumulative
population health effects to the general population residing in the downstream
regional basin on a low-level waste site), and PATHRAE (see above).
Ra Radium-226, an isotope of radium with an atomic mass of 226 and a half-life of
1,599 years, produced from alpha-decay of thorium-230
RAC Eadiation Advisory Committee (of the U.S. EPA/SAB/RAC)
RCRA Resource Conservation and Recovery Act, including its various subtitles
SAB Science Advisory Board (of the U.S. EPA/SAB)
Se Selinium
SI International System of Units (System Internationale)
SMI Shepherd-Miller, Inc.
SWMU Solid \£aste Management Unit
^Sr Strontium, the strontium isotope with a mass of 90, having a half-life of 28 years
TENORM Technologically Enhanced Naturally Qccurring Radioactive Material
"Tc Technetium (Tc) as an element, or Technetium-99, an isotope of technetium with
an atomic mass of 99 and a half-life of 213,000 years
23*Th Ihorium, as an element or isotope (e.g., MITh, ^Th, ™Th,wTh)
TSCA Joxic Substances Control Act
TSPA lotal System Eerformance Assessment
U Uranium, including the isotopes B!U with an atomic mass of 235 and a half-life of
7.13x10* years, and the most common asU with an atomic mass of 238 and a half-
life of 4.51x109 years.
U.S. United States
UZ Unsaturated Zone
226
C-2
-------
REFERENCES
HPRI (Electric Power Research Institute). 1990. "Demonstration of a Risk-Based Approach to
Kgh-Level Waste Repository Evaluation," EPRINP-7057 Project 3055-2 Final Report,
Prepared by Risk Engineering, Inc. Golden, CO for EEI/UWASTE and EPRI's High
Level Waste Program, Nuclear Power Division, Palo Alto, CA, (October)
Langmuir, D., 1997, Aqueous Environmental Geochemistry. Prentice Hall Publ.
NY (New York Department of Environmental Conservation). 1993. Final Generic
Environmental Impact Statement for Promulgation of the 6 NYCRR Part 383:
Regulations for Low-level Radioactive Waste Disposal Facilities (Design, Construction,
Operations, Closure, Post-closure, and Institutional Control. New York Department of
Environmental Conservation)
Rumer, Ralph R. and James K. Mitchell, editors, "Assessment of Barrier Containment
Technologies: A Comprehensive Treatment for Environmental Remediation Applications,"
International Containment Technology Workshop, Baltimore, MD, August 29-31,1995,
Prepared under the auspices of the U.S. Department of Energy, the U.S. Environmental
Protection Agency and the DuPont Company, National Technical Information Service,
US. Department of Commerce, 5288 Port Royal Road, Springfield, VA 22161 [#PB96-
180583], 1995
SAB. 1992. Commentary on Harmonizing Chemical and Radiation Risk-Reduction Strategies,
Radiation Advisory Committee (EPA-SAB-RAC-COM-92-007) (May 18)
SAB. 1985. Review of the March 13, 1985 Draft Background Information Document on Low-
Level Radioactive Waste Disposal, Radiation Advisory Committee (EPA-SAB-RAC-86-
002) (October 28)
Shepard-MiUer Inc. (SMI) 1998 (See U.S. EPA/ORIA, 19981)
TRW (TRW Environmental Safety Systems, Inc., Management & Operating (M&O) Contractor
for Civilian Radioactive Waste Management System). 1995. Total-System Performance
Assessment - 1995: An Evaluation of the Potential Yucca Mountain Repository.
BOOOOOOOO-0717-2200-00099-Rev. 01. Las Vegas, NV: TRW Environmental Safety
Systems, Inc.
U.S. EPA/ORIA. 1998a. SAB Advisory: Low Activity Mixed Waste Disposal Project: Overview
of the Modeling Approach, (October), 17 pages
R-l
-------
U.S. EPA/ORIA. 1998b. SAB Advisory: Low Activity Mixed Waste Disposal Project: Overview
of the Modeling Approach, Attachment 1: 10CFR61.55 Class A Requirements (October),
4 pages
U.S. EPA/ORIA. 1998c. SAB Advisory: Low Activity Mixed Waste Disposal Project: Overview
of the Modeling Approach, Attachment 2: RCRA Subtitle C Hazardous Waste Disposal
Facility Requirements Excerpted from 'Alternative Disposal Options for Very Low-Level
Waste, September 30,1996,' 9 pages
U.S. EPA/ORIA. 1998d. SAB Advisory: Low Activity Mixed Waste Disposal Project: Overview
of the Modeling Approach, Attachment 3: RCRA Orientation Manual (EPA 530-R-98-
004) (May)
U.S. EPA/ORIA. 1998e. SAB Advisory: Low Activity Mixed Waste Disposal Project: Overview
of the Modeling Approach, Attachment 4: Mixed Waste Disposal Regulatory
Requirements (Presentation materials from October 8-9, 1998 EPA/States Workshop), 24
pages
U.S. EPA/ORIA. 1998f. SAB Advisory - Low Activity Mixed Waste Disposal Project: Generic
Characterization of Disposal Sites (October), -9 pages
U.S. EPA/ORIA. 1998g. SAB Advisory - Low Activity Mixed Waste Disposal Project: Modeling
Time Frame (October), 25 pages
U.S. EPA/ORIA- 1998h. SAB Advisory - Low Activity Mixed Waste Disposal Project: Concrete
Degradation (October), 6 pages
U.S. EPA/ORIA. 1998i. SAB Advisory - Low Activity Mixed Waste Disposal Project: Concrete
Degradation, Attachment 1: Distribution Coefficients (Kd) for Selected Radionuclides on
Cementitious Materials (Excerpted from NUREG/CR-6377) (October),pp. 51-59 and pp.
510-552
U.S. EPA/ORIA. 1998J. SAB Advisory - Low Activity Mixed Waste Disposal Project. Concrete
Degradation, Attachment 2: Time Dependent Fractional Release from a 55-gallon Drum
for Different Diffusion Coefficients and Different Hydrodynamic Release Factors
(October), 1 page
U.S. EPA/ORIA. 1998k. SAB Advisory - Low Activity Mixed Waste Disposal Project: Concrete
Degradation, Attachment 3: Diffusion Coefficients for Selected Radionuclides (October),
1 page
R-2
-------
U.S. EPA/ORIA. 19981. SAB Advisory - Low Activity Mixed Waste Disposal Project: Concrete
Degradation, Attachment 4: Review of Cement Chemistry and Stability for Low-Level
Radioactive Waste Disposal Environments, Prepared by Sheperd Miller, Inc. for Tech
Law, Inc. "Review of Cement Chemistry and Stability for Low Level Radioactive Waste
Disposal Environments," (August 15), 44 pages
U.S. EPA/ORIA. 1998m. SAB Advisory - Low Activity Mixed Waste Disposal Project: Concrete
Degradation, Attachment 5: Natural Analogues for Cementitious Systems (Excerpted
fromNUREG-6377, Appendix C, pp. cl - ell)
U.S. NRC. 1992. National Profile on Commercially Generated Low-Level Radioactive Mixed
.Waste, U.S. Nuclear Regulatory Commission, Washington, D.C., NUREG/CR-5938
(December)
R-3
-------
DISTRIBUTION LIST
Deputy Administrator j
Assistant Administrators I
EPA Regional Administrators
EPA Laboratory Directors
Deputy Assistant Administrator for Air and Radiation
Director, Office of Radiation and Indoor Air
Director, Office of Radiation Programs
Deputy Assistant Administrator for Office of Policy, Planing and Evaluation
Director, Office of Strategic Planning and Environmental Data
Director, Office of Policy Analysis
Director, Office of Regulatory Management and Evaluation
EPA Headquarter Libraries
EPA Regional Libraries
EPA Laboratory Libraries
Library of Congress
National Technical Information Center
------- |